Patent Application
20240316391
The present invention relates generally to an apparatus for exercise. More specifically, the present invention is an apparatus for exercise, it is a platform that provides controlled and adjustable resistance to the user for the purposes of strength training, physical therapy, and the like.
There exist many methods and systems for resistance training and exercise. The present invention seeks to improve upon the prior art by providing an exercise system with easily controllable and adjustable resistance as well as safety features to protect both the user and the invention. The present invention further seeks to provide a low-profile portable device that can be easily carried, mounted, and stored. The present invention allows the user to perform a variety of versatile exercises. The present invention seeks to drive down production and unit costs and provide a user experience that is pleasant and informative.
All illustrations of the drawings are for the purpose of describing selected versions of the present invention and are not intended to limit the scope of the present invention.
The Electronically Controlled Resistance Device (ECORD) is an exercise platform that provides controlled and adjustable resistance to the user for the purposes of strength training, physical therapy, and the like. The platform provides a cabled connection to a brushless motor that spools the rope in and out as the user exercises through a range of motion. The motor-control electronics and tension-sensor work to maintain the resistance that is set by the user. A simple user-interface (UI) on the platform allows the user to adjust the rope tension based on an equivalent weight. A separate wireless remote can be attached to the handle to allow the user to adjust the weight during an exercise. A wireless connection to a smartphone running the associated app presents the user with additional settings, control, rich exercise-related information as well as various resistance profiles. The platform is powered with an onboard AC/DC converter that is plugged into a wall socket.
The primary objectives for the development of the ECORD are as follows:
The following sections provide detailed information about the ECORD.
The heart of the ECORD is the motor. There are many different types of rotational motors in commercial use today, such as DC brush motors, brushless motors, and induction motors to name just a few, with some branching into sub types. There are advantages and disadvantages for each, therefore the motor type that is the best fit for the intended application is selected for use.
Common to all motors are the stator and rotor. The stator (13) is fixed relative to the device the motor is embedded in and the rotor is the part that rotates. Because the ECORD makes use of a brushless motor, the remainder of the motor discussion will focus on this type.
There are two general configurations for brushless motors: Radial-flux type and axial-flux type. By far, the radial-flux is the most common. In this configuration, the magnets are fixed to the rotor such that the magnetic field lines (5) flow in the radial direction. A highly simplified diagram of a radial-flux brushless motor is shown in
The stator windings (1) are copper coils wrapped around stator teeth (3). These “slotted” motors are by far the most common type in use. The magnets are fixed to the rotor. There are many different approaches to affixing the magnets to the rotor, but generally they are mounted to the surface or embedded inside the rotor. This arrangement causes the magnetic field produced by the magnets to flow in the general direction shown by the dashed lines. Brushless motors require the winding to be electronically commutated in order to produce torque and cause the rotor to rotate in the desired direction. The torque of a radial-flux motor is proportional to the square of the radius. The axial dimension (into the page) of the motor also affects the torque, but linearly.
In contrast, axial-flux motors are arranged in such a way that the magnetic field flows in the axial direction. A highly simplified diagram is shown in
Axial flux motors follow the same square law where the torque produced is proportional to the square of the radius. The axial dimension is mostly dictated by the thickness of the magnets, coils, and yoke (8 and 9); therefore, it is much more restrictive than radial-flux motors. However, additional stages of a stator-rotor combination can be added to increase the length (in the axial direction), which will increase the torque linearly.
2. 2 Yoke Vs. Yokeless Design:
The yoke (7) of the motor is an important part of the stator design. As shown by the dashed lines in
The magnetic field lines (5)—produced by the magnets (see section 2.1)—rotate with the magnets when the motor spins, producing a time-varying magnetic field at any given point in the yoke (7). When a piece of metal is subjected to a time-varying magnetic field, eddy currents are produced that work to counter that field. Also, the non-zero resistance of the metal causes it to heat up due to this current.
If the yoke (7) of the radial-flux motor is constructed with a continuous piece of iron, the motor will experience significant power loss with increasing motor speed. As the motor spins faster, the rate of change of the magnetic field, as experienced by the yoke (7), will increase, which in turn will produce greater eddy currents that counter the magnetic field of the magnets, working to reduce the torque while heating up the yoke (7). This is undesirable. Therefore, the yokes (7) are never constructed with continuous pieces of iron, but rather with laminated stacks of iron that when stacked together form the complete yoke (7). Since these laminated stacks break up the continuity of the metal of the yoke (7), significant reduction in eddy-current production takes place.
The yoke (8 and 9) of the radial-flux motor will similarly experience eddy-current losses if it is made with a continuous piece of iron. Therefore, it also utilizes lamination to introduce interruptions in the metal structure, but instead of stamped stacks it may be constructed with a thin, insulated “ribbon” that is wound around in a spiral fashion to form the yoke (8 and 9).
An alternative approach that can be applied to both types of motors is to produce a yoke made from soft magnetic composite (SMC) material. SMC material uses iron powder particles that are insulated from each other, which significantly reduces eddy-current losses.
The axial-flux configuration shown in
In this arrangement, the rotor supports two sets of magnets, one above and another below the stator (25), which comprises copper windings (1) coiled around individual teeth (3) comprising the yoke (7). The stator (25) is sandwiched between the two sets of magnets. The magnetic field lines (5) still flow in the same fashion as before, but the number of magnets has doubled. Notice that the magnets need to be arranged such that the north pole (“N”) of the top magnet (6) faces the south pole (“S”) of the bottom magnet (6) to allow the magnetic field to flow in the loop shown by the dashed lines.
With this arrangement, the top and bottom magnets are adhered to their respective backirons (11 and 12) and the backirons (11 and 12) mechanically coupled so that they rotate together, while the stator (25) is fixed in place (much like the previously mentioned motor structures). As a result, the magnetic field lines (5) rotate with the magnets as the motor spins, therefore the metallic yoke (7) of the stators (25) must be manufactured in a way that breaks up the metal continuity, using the ribbon method or SMC.
The configuration shown in
2. 3 Slotted Vs. Slotless Stator:
As mentioned previously, slotted stators allow the winding (1) to coil around the stator teeth (3). This is a widely common form of winding the coils. The advantage is that the stator teeth (3) can be very close to the magnets, which helps to increase the output torque. The disadvantage is that they produce a varying magnetic field reluctance as experienced by the magnets, that is, the rotor has preferential positions as it is spun around. This “cogging” torque is easily felt by the pulsations produced when manually rotating the shaft (4) of an unpowered motor. During normal operation, this cogging torque exists, which may be undesirable for certain applications.
To eliminate the cogging torque produced by the stator slots, some motors are designed without stator teeth (3). These slotless motors experience no cogging torque and produce a smoother motion, which is required by some applications, such as those requiring precision positioning. Slotless motors, on the other hand, generally have less torque output than their slotted counterparts and are significantly more expensive.
One of the primary objectives of the ECORD is to provide a pleasant user experience (UX). Part of the UX includes what the user physically feels when pulling on the rope. In the presence of cogging torque, the user will experience vibrations as the rope is pulled. This is not desirable, therefore cogging torque must be eliminated, which points to the use of a slotless motor.
Another primary objective is to produce a very low-profile device. As discussed previously, axial-flux motors are much lower in profile than radial-flux types, although larger in diameter. For the ECORD, the height of the motor is a far more critical dimension to minimize rather than its diameter, therefore the ECORD makes use of an axial-flux type motor.
In order to produce a low-cost motor, the configuration shown in
This is because the yoke (8 and 9) required for the configuration of
To maintain a low production cost for the motor, the stator (13) of the ECORD motor is designed using PCB technology. Given the proliferation of electronics in today's modern life, there are countless PCB fabrication and assembly facilities throughout the US and around the world. PCB manufacturing and assembly is a highly mature industry capable of producing exceedingly reliable PCBs.
Unlike the coil examples shown in
In a motor that makes use of magnets (unlike induction motors that have none), torque is produced with the interaction of current flowing in the stator winding and the magnets. The direction of current flow and the magnetic field determine the direction of torque production.
To help visualize the direction of torque, consider the diagram of the “right-hand-rule,” shown in
With the general principle of force-production in mind, consider the illustration shown in
Since the stator (13) is fixed in position and the magnets are allowed to spin, the overall force produced by the stator (13) acts to spin the magnets. Since the magnets are adhered to their respective backiron (11 and 12), and the backirons (11 and 12) are coupled to the shaft (4), the torque applied to the shaft (4) is in the opposite direction as that of the force (as indicated by the black arrow).
The torque τ produced by a group of traces (14) can be approximated as:
Here, ri and ro represent the inner and outer radii of the magnets, respectively, as shown in
As shown by Eq. 1, there are a plurality of levers that can be adjusted in order to maximize torque, however, there is a tradeoff for each.
Starting with the current, the greater it is, the greater will be the output torque. However, current cannot be injected into the motor without limit. The traces (14) forming the winding have a non-zero resistance that generate heat in the presence of current. This is a form of power loss, with its instantaneous value quantified as:
As can be seen, the power loss is a function of the square of the current I, but linearly proportional to the total winding resistance R. So, if the current is doubled, the torque is doubled, but the power loss is quadrupled. If this heat is not dissipated properly it can lead to critical damage of the traces (14) on the PCB. Therefore, the goal is to keep the resistance low and also to dissipate the heat so that the motor can operate safely. There are a number of ways to achieve this:
There are of course, tradeoffs to all the above:
The next factor that can be adjusted in Eq. 1 is N. The greater the number of traces (14) the greater the torque. However, as discussed above, there are manufacturing limitations. Consider the parallel traces (14) illustrated in
In order to increase N, either or both w and g must be minimized. From a manufacturing standpoint, there is a limit to how small w and g can become. From a thermal-design point of view, the smaller w gets the greater the temperature-rise due to the current flow. Temperature rises exponentially as w is decreased. As for the gap, g, there is no reason to increase this value beyond the minimum that is manufacturable. The gap, however, is a function of the trace thickness. The greater the thickness the greater must be the gap, again due to manufacturing limits.
The next lever that can be adjusted in Eq. 1 is the magnetic field strength, which is entirely dependent upon the magnet (6) used. Neodymium Iron-Boron (NdFeB) magnets are the strongest rear-Earth magnets available, and they come in several grades. The higher the grade value the stronger the magnet. The magnetic field strength also increases with increasing magnet thickness. The tradeoffs are as follows:
The last parameters that can be adjusted in Eq. 1 are the inner and outer radii of the magnets. In order to increase the torque, the difference between the squares of these values must be increased. At first glance, it appears that reducing the inner radius and increasing the outer radius are good ways to go, but of course, there are tradeoffs. They are as follows:
There is a delicate dance in optimizing the various parameters of Eq. 1 given their tradeoffs, and it is up to the designer to determine which parameters are more important to prioritize over others based on the requirements of the application.
The ECORD rotors (26) are designed using NdFeB magnets with the following specifications:
The purpose for selecting these parameters was market availability at a reasonable price and estimated torque-production that met the design requirements. The size of the magnets then drove most of the design of the stator (13).
Let NMAG be the number of magnets used on each backiron (11 and 12). Given the design choices discussed in section 2.4 and the size of the magnets, the ECORD motor makes use of two sets of NMAG=16 magnets, one set for the top-backiron (11) and the other for the bottom-backiron (12). The illustration of
The stator (13) is designed on a circular 2-sided PCB (part of which is shown). There is also a circular cutout (partially visible in the illustration) at the center of the PCB to allow the shaft (4) of the motor to pass through. A double-sided PCB allows copper traces (14) to be etched on the top and bottom sides of the board. The dashed outlines represent the magnets (only 3 shown for clarity). Keep in mind that there are magnets above and below the PCB stator (13) and that they are lined up with one another (see
Starting from the trace on the far left, the trace approaches the left magnet (6) at an angle, then travels down radially towards the center of the PCB, but just after passing the inner radius of the left magnet, it makes another slight turn and travels down at an angle. Before reaching the inner circular cutout of the PCB the trace transitions layers with the use of a via (outlined with a circle). A via is a plated hole that allows a trace to transition from one layer to another. The trace now continues on the bottom layer of the PCB. Once on the bottom layer, the segment travels back up towards the middle magnet (6) at an angle (same angle as the top trace), then when it reaches the inner radius of the middle magnet, it travels radially upward until it reaches its outer radius. It then makes another slight turn and travels further out, until it makes another layer transition back onto the top layer. The trace segment on the bottom of the PCB is a mirror image of the trace segment on the top layer. The segment of the trace starting from the left and ending at the second via constitutes one turn of the winding (27) of a phase for the stator (13). This pattern continues all the way around the PCB.
The direction of the flow of current I and magnetic field B is shown, as well as the direction of the force F applied to the traces (14). The · represents a magnetic field that points into the page, whereas the x represents a field that points out of the page. Using the right-hand-rule, it is clear that the force F is in the same direction for all trace segments, therefore the forces add up to produce the desired torque. As the magnets rotate over the stator (13), the control electronics varies the current magnitude and direction to keep the motor spinning in the design direction with the desired torque.
According to the illustration of
The number of segments under each magnet, NSEG_PER_MAG is a design parameter. The larger NSEG_PER_MAG is the narrower the segments must be, which according to the discussion of section 2.4.1.2, results in increased power loss. Therefore, a balance must be struck between NSEG_PER_MAG and power loss. There are also practical manufacturing matters to consider since the traces (14) cannot be too narrow given the trace thickness.
Once NSEG_PER_MAG is selected, the trace geometry can be optimized to achieve a maximum width given a minimum trace-to-trace separation, or gap (see section 2.4.1.2). Maximizing width while minimizing the gap is desirable to reduce the resistance of a segment. Lower resistance equals lower power loss.
The details of a “standard” segment geometry are shown in
Two angles, ϕ and θ, are shown with respect to a line that is orthogonal with the segment's centerline (vertical dashed line). Detail A shows the dimensions of the transitioning via, with the hole diameter indicated as v. The width of the trace, w, is indicated, which is the dimension that is to be maximized. The gap, g, between two adjacent segments is also indicated, which is the dimension that is to be minimized. The minimum gap, g, between two adjacent copper features on a PCB is determined by the copper thickness (t in
The dimension w is a function of ri, α, g, NSEG_PER_MAG and θ. The parameters ri and α are determined by the selected magnets (see
Notice that w is specified as the width of the segment right at the via. Travelling radially upward allows w to increase, this is because the separation between adjacent traces (14) is maintained at a constant, determined by the parameter g. This widening of the segment helps to reduce its overall resistance.
As for the outer end-turn (15), the angle 4 must be minimized. The angle 4 is a function of NSEG_PER_MAG, w, α, ro, and g. The angle 4 is selected as the minimum angle that ensures the gap, g, is at its minimum.
In order to add additional segments under each magnet (6) (to increase N), the stator design requires a variety of segment geometries other than the standard segment. Consider the simplified illustration of
Beginning at “start,” the pattern travels radially inward then transitions to the bottom layer. There, it travels radially upward, where it transitions again to the top layer. This pattern repeats all the way around until it reaches the starting point. If the pattern only uses standard segments, then the pattern will essentially terminate where it started from, preventing additional turns from being added. Therefore, the last segment of the pattern changes its geometry to the “extended” variant (shown as small-dash lines). Prior to transitioning to the top layer, this extended variant extends its upper end-turn (18) beyond the upper end-turn of the trace of top-layer starting-segment. At this point, the pattern has made one full revolution around the PCB, therefore N=1. This constitutes one full revolution of a winding of a phase, comprising 8 winding (27) turns.
Once at the top layer, the next segment must also be of the extended variant, where it travels inward radially until it transitions to the bottom layer. From this point forward, standard segments are once again used and the pattern repeats. When the pattern makes another full revolution, extended segments are required to allow for additional turns. With each full revolution, the value of N for the overall winding of the phase increases by 1.
As discussed in the previous section, additional turns can be added to increase N. Consider the illustration shown in
As can be seen in
Consider
The illustration of
The example phase winding discussed so far and illustrated in
A pole-pair pitch is the mechanical angle that spans the angle covered by a pair of North-South magnets. As an example, the number of pole-pairs (NPP) of the ECORD motor is NPP=NMAG/2=8, where NMAG is the total number of magnets used per rotor. As a result, a pole-pair pitch spans 360/NPP=360/8=45 mechanical degrees. A pole-pair pitch, however, is equivalent to 360 electrical degrees. Therefore, the requirement to separate the phases by 120 electrical degrees translates to separating them by 15 mechanical degrees, which is the offset by which the other phases are laid out.
There are a few additional segment geometries that are used to construct the full three-phase winding on the PCB stator (13). Their shape is very similar to the other shapes discussed so far, except tailored to fit between adjacent segments as necessary in order to allow all three phases to be wound on the board.
This approach produces a very high fill ratio, that is, the ratio of the total copper area to that of the PCB area underneath the magnets. Only the area underneath the magnets is considered since this is the only active area responsible for torque production, therefore it must be used maximally for greater efficiency. For example, the ECORD prototype stator (13) has a fill ratio is 85.74%. This means 14.26% of the total area is taken up by the area between adjacent segments, as defined by the gap, g.
A partial view of the top layer of a fully routed PCB stator (13) is shown in
The start and end of a phase (as illustrated in
Notice that there are rectangular solder pads (35) emerging from the traces (14) that lead to the start and end castellations. The purpose of these pads is to allow the motor phase wires to be soldered directly to the PCB stator (13). Since both ends of a phase are exposed, the motor phases can be configured in one of two ways; star or delta formation, as shown in
In the star formation, the end points X2 are soldered together, and the start points X1 are driven by the motor-driver electronics. In the delta configuration, U1-V2 are soldered, W1-U2 are soldered, and V1-W2 are soldered through wires, and then from each of the three points additional wires are soldered and fed into the motor-driver electronics. By far, the star formation is the most popular, and it is the configuration used in the ECORD.
Notice that in
As mentioned previously, one way to increase torque is to increase N. With the 2-layer stator (13) design, it is not possible to add any more segments; the PCB is maximally filled. However, N can still increase by using additional PCB stators (13). As an example, suppose a second PCB stator (13) is added to the bottom side of a first PCB stator (13) (like that shown in
Adding additional PCB stators (13) to the bottom of the stack and rotating them accordingly will continue to increase N. There is a limit, however, to the number of stators (13) that can be added in this “series-connected” fashion. That number is NSERIES_MAX_STATORS=NPP−1. Anything greater than this value will ultimately result in shorting all phases together.
The key to connecting additional PCB stators (13) in series is the placement of the outer castellations (20), which are driven by the symmetry of the stator winding design that in turn are driven by the inherent symmetry of the magnets. As discussed previously, the magnets are arranged around the backiron (11 and 12) in alternating magnetic-field polarities. From the perspective of the PCB stator (13) the magnetic field repeats itself every λ=360/NPP °M, where °M indicates mechanical degrees around the motor. For the ECORD, NPP=8, therefore λ=45 °M. Since λ spans a pair of magnets and each magnet (6) spans α degrees, then by definition λ=2α. For the ECORD, α=22.5° (see
Like the magnet pole-pairs, a single turn of the winding (27) for any phase also repeats itself every λ °M. Therefore, the magnitude and phase of the currents within a single turn of a winding (27) also repeat themselves under each pole pair. As a result, there are 360 °E under each pole pair, where ° E is degrees electrical. This is equivalent to λ=45 °M=360 °E, or more generally, λ=2α=360 °E. This implies that rotating one PCB stator (13) by 45 °M with respect to another will result in rotating that same PCB stator (13) by 360 °E. In other words, mechanically and electrically all phase windings between the two PCB stators (13) will be perfectly lined up.
To solder two or more PCB stators (13) together in order to form a series-connected PCB stack, their respective castellations must also line up when the PCBs are rotated by λ=2α with respect to each other. The easiest way to do this is to space them according to the following equation.
The angle γo is shown in
The purpose of the inner castellations (21) is strictly for adding rigidity to the PCB stator (13) stack. They must also line up when individual PCB stators (13) are rotated, however, their spacing does not depend on the number of motor phases. For the inner castellations (21), γi=2α/n (see
The mounting holes (19) of the PCB stator (13) shown in
As discussed previously, torque may also be increased by increasing the current I (see Eq. 1). However, this comes with increasing power loss PL (see Eq. 2). To reduce PL the winding resistance R must be reduced. This can be achieved by parallel connecting the PCB stators (13). The total resistance RT for resistors connected in parallel is given by the following:
If there are 4 resistors of equal value, that is R1=R2= . . . =R4=R then RT=R/4. The same goes for the phase winding of the PCB stator (13). Parallel connecting them reduces the overall resistance of the phases. In order to connect the PCB stators (13) in parallel, they are simply stacked without any rotation (i.e., all W1's, V1's, etc. are in line) and soldered along the castellations. The equivalent schematic representation for two parallel-connected stators (13) is shown in
Unlike its series-connected counterpart, there is no limit similar to NSERIES_MAX_STATORS with the parallel-connected scheme. There is, however, a diminishing return in continuing to add stators (13). This is because each PCB stator (13) has a thickness associated to it. For example, in the ECORD prototype, the PCB stator (13) is fabricated using 4 oz. copper with dielectric material between the two layers. The PCB stackup is shown in
With each additional stator (13), the total thickness of the stack grows, and as the stack grows, the rotor magnets (6) must be moved farther apart. The distance between the magnets (6) of the top and bottom rotors is dMAGNETS=2dAIR_GAP+tPCB_STACK (see
With greater mechanical precision, dAIR_GAP can be reduced in order to decrease dMAGNETS, however, with increasing precision comes increasing fabrication cost for the mechanical components. Also, dAIR_GAP is already a fraction of tPCB_STACK, therefore minimizing it as much as possible does not offer significant increases in the magnetic field strength.
It is important to note that the diminishing return in adding more stators (13) also holds true for the series-connected scheme. With each addition, N increases, but so does dMAGNETS, therefore a careful analysis is required to justify the added stators (13).
An additional way of configuring the stators (13) is through a combination of series- and parallel-connected schemes. In a combo-connected scheme, several stators (13) would be connected in parallel. A second group of parallel-connected stators (13) would then be rotated and soldered to the first group of parallel-connector stators (13), forming a combination of two parallel-connected groups connected in series. The schematic of this connection is shown in
The same NPP−1 limit that applies to the series-connected scheme applies to the combo-connected scheme. Similarly, the number of parallel-connected groups cannot increase without limit, since they work to grow the stack thickness, necessitating the magnets (6) to be placed farther apart, weakening the magnetic field between them.
The decision to use series-, parallel-, or combo-connected stators (13) is highly application dependent, part of which is the design of the motor driving electronics. A three-phase motor is typically driven by the motor-driver electronics, which is powered by the bus voltage VBUS. Depending on the application, at any given point in time the motor is driven in either velocity mode (where the velocity is controlled irrespective of the torque) or in torque mode (where the torque is controlled irrespective of the velocity). In either case, when the motor spins, it generates a back electromotive force (back EMF). The back EMF works in opposition to VBUS and is proportional to velocity. In other words, the faster the motor spins, the greater the magnitude of the back EMF, and the lower the difference between VBUS and back EMF. Since the phase windings have resistance, the amount of current that can be drawn from VBUS decreases with increasing back EMF, therefore the amount of torque that the motor is capable of generating, decreases with increasing velocity. At the point where the back EMF is approximately equal to VBUS, the motor has almost zero torque. With this in mind, the following table compares properties of motors using all three stator combinations.
Once the PCB stator (13) is designed and fabricated, they can be stacked together to form the selected connection scheme. The first step is to ensure that the PCB stators (13) are aligned vertically such that there is no angular offset between them. Any offset would result in the “closing” of the mounting hole (19) when looking through the stack of mounting holes (19) in the axial direction. This offset would prevent the mounting screw from fitting through the stack of mounting holes (19). An apparatus may be required in assisting with the alignment. An example is shown
As can be seen, the alignment apparatus has several pegs that are placed at the exact position of the mounting holes (19). There is no need to have a peg for each mounting hole (19). In the example above, there is a peg for every other mounting hole (19). This allows the PCB stators (13) to be inserted into the apparatus during the bonding process. Any rotation required to place the PCB stators (13) into a series-connected scheme (see section 2.4.1.7.1) would take place in this process.
The PCB stators (13) can be bonded together in one of two ways. 1) Once all the PCB stators (13) are placed in the stack using the alignment apparatus, the inner and outer castellations (20) are to be soldered together. Some modest level of pressure is to be applied to the PCB stack during the soldering process to eliminate any gaps between adjacent PCBs that can add to the overall height of the stack. Once soldered, the stack can be removed from the alignment apparatus. 2) When the first PCB stator (13) is placed into the alignment apparatus, a thermally conductive adhesive is applied to the top surface of the first PCB stator (13). Then, the second PCB stator (13) is added to the top of the first PCB stator (13) and the thermally conductive adhesive applied to the top surface of the second PCB stator (13). This process continues until the last PCB stator (13) has been added. At this point, the inner (21) and outer castellations (20) are to be soldered together as before, by applying some pressure to eliminate any gaps between adjacent PCBs and to ensure the adhesive spreads out. After soldering, the PCB stator stack can be removed from the alignment apparatus and may be required to be placed under some uniform pressure application to ensure the adhesives cures in such a way that does not cause any warping of the PCB stator stack.
Bonding process #1 is faster but does not offer as good of a thermal performance as bonding process #2. This may or may not be a factor, depending on the expected worse-case power dissipation. Bonding process #2 takes longer and it may result in a slightly thicker stack compared to bonding process #1 due to the addition of the thermally conductive adhesive. However, it performs much better thermally, and the PCB stator stack has much greater rigidity.
The PCB stator design discussed in the previous section uses a 2-layer board and requires bonding several of them depending on the application. This bonding is an additional step in the overall assembly of the system that incurs a cost. To eliminate this bonding step, an alternative way in designing the stator (13) is to fabricate all phase windings onto a single PCB. This requires determining the connection scheme ahead of time, then designing a multi-layer PCB to accommodate all the windings.
For example, suppose three series-connected stators (13) are to be integrated onto a single board. Since each stator (13) comprises two layers, this will require the board to have 6 copper layers. An example stackup for such a multi-layer board is shown in
The phase winding of the series-connected stator has its “start” point (see
The 2-layer stator (13) discussed in the previous sections uses through-hole vias (22), which are drilled all the way through the board, connecting the top and bottom layers. The multi-layer series-connected design cannot use through-hole vias (22) to transition between layers as shown by the dashed circles of
For a multi-layer design, looking down into the dashed circles of
In order to transition the winding from the “end” point of Layer 2 to the “start” point of Layer 3 (see
This approach allows the winding to start on Layer 1 and finish on Layer 6. The end of the winding on Layer 6 may make one final transition up to Layer 1, where pads may be added to the start and end of the winding to allow soldering of phase wires. Alternatively, one or more connectors may be added to allow phase wires to plug into the multi-layer stator (13).
Just like the multi-layer series-connected stator (13), a multi-layer parallel-connected stator (13) may also be designed, except there would not be a need for blind vias (23) and buried vias (24). Since all the individual groups of windings within a phase are in parallel, a through-hole via (22) can now be used where dashed circles are shown in
For the parallel-connected stator, the phase winding is exactly the same as that for the 2-layer design, except the phase winding would repeat on layer pairs 1/2, 3/4, and 5/6. And the vias (shown in
Finally, for the combo-connected stator, there would be several groups of parallel-connected layers, which are connected in series. This sort of PCB design would once again use blind vias (23) and buried vias (24), an example of which is shown
The advantages and disadvantages of the multi-layer stator compared to the 2-layer stator (13) is provided in the table below.
The ECORD Motor makes use of the dual-rotor design, shown in
The thickness of the backiron (11 and 12), tBACKIRON (see
Because of the dual-rotor design, there is a tremendous force of attraction between the two half rotors, due to the proximity of the magnets (6) to one another. The magnets (6) are adhered to the backirons (11 and 12) through the use of epoxy or similar strong adhesives; therefore, this force is transferred to the backirons (11 and 12). Thin backirons (11 and 12) can deform in the presence of such a force. If the air gap is sufficiently small and the backirons (11 and 12) sufficiently thin, it is possible for the backirons (11 and 12) to deform enough such that the outer edge of the magnets (6) come in contact with the PCB stator stack, scraping against it as the rotor spins.
Thicker backirons (11 and 12) resolves these issues but add weight. Therefore, tBACKIRON should be made as thick as necessary to eliminate the saturation and deformation, but no thicker. One alternative is to make the backirons (11 and 12) thick but remove small sections throughout the volume, for example, small diameter holes can be drilled throughout the material to make it lighter. Computer simulations can be performed to optimize the weight and performance in terms of magnetic-field saturation to strike a balance between the two. A partial view of a backiron with example cutouts is shown in
The illustration shown in
The ring of magnets (6) shown in (b) are arranged in an alternating polarity, indicated by two shades of gray. They are individually adhered to the opposite side of the backiron (11 or 12) (using a strong adhesive) forming half of the rotor (26)(c). In (c), the backiron is made transparent to indicate the magnets (6) are on the bottom side, opposite to the countersink holes. It is important to note that the rotor (26) is designed to be symmetrical along the lines of symmetry, as shown in
It is important to note that the example shown in
Once both rotor halves (26) are assembled and the PCB stator stack soldered in the desired configuration, they can all be assembled onto the shaft (4), as shown in
The force between the two half rotors is shown as FATTRACTION. Although the arrows are to one side of the diagram, the force is uniformly distributed across the top and bottom rotors, such that the rotor support structure (2) experiences a uniform compression force.
In a typical motor, the shaft (4) has a cutout for a key, however, in the ECORD design this is eliminated, per the discussion in section 2.5.2. Finally, the ends of the shaft (4) are designed to be inserted into bearings as discussed in section 3.
To operate a brushless motor, the three phases must be commutated properly. This requires knowledge of where the rotor angle or position is with respect to the stationary stator (13). Rotor position can be obtained with the aid of Hall Effect sensors, which are positioned with respect to the stator (13). Hall Effect sensors sense the presence of the magnetic field of the rotor magnets (6) and provide a logic-level signal that represents the sensed polarity of the magnetic field. They are positioned 120 °E apart from each other. This translates to 15 °M in the case of the ECORD motor design (see section 2.4.1.7.1). Hall Effect sensors provide a rotor position resolution of 60 °E. In the case of the ECORD motor design, this translates to 7.5 °M. For trapezoidal commutation—where the waveform of the phase currents resembles the shape of a trapezoid—Hall Effect sensors are sufficient for motor commutation. There are also sensorless control methods that do not require any Hall sensors at all, only the zero-crossing of the back EMF of the floating phase is required to be sensed to commutate the motor.
In sinusoidal commutation—where the waveform of the phase currents is modulated in a sinusoidal fashion—an encoder is required to provide a high-resolution position of the rotor. Sinusoidal commutation produces a much lower torque ripple at the cost of somewhat lower maximum output torque compared to trapezoidal commutation. Encoders produce at least two quadrature signals, called A and B, where A and B are square-wave signals that are out of phase by 90°. Quadrature encoder signals can provide a very high-resolution angular position—on the order of an arcminute or less—to the motor controller. A subset of commercial encoders also provides an index signal, called Z, which triggers a pulse once per mechanical revolution. A much smaller subset yet, provides the commutation signals, eliminating the need for the Hall sensors. Encoders that provide the commutation signals are programmable, to allow the factory to set the number of poles (number of motor magnets) and alignment of the commutation signals with the back EMF signal of the motor. The number of poles is limited by the encoder and there is an even smaller subset that allow for high poles counts. The 16 poles used in the ECORD motor is considered a high number.
The vast majority of the available encoders in the market today are mounted on the opposite end of the shaft (4), as illustrated in the
The encoder (31) shown in
An alternative method of generating the encoder signals is to use a commercial optical encoder IC and replace the magnetic encoder wheel with an optical encoder wheel. The optical encoder wheel is comprised of a reflective surface with small, equally spaces cutouts. The optical encoder IC shines a light onto the surface of the optical encoder wheel and detects a signal where the light reflects off the surface and no signal when it doesn't. As the motor spins, these alternating signals are processed and converted into the quadrature signals by the IC. The optical encoder wheel may additionally possess cutouts for the index and commutation signals assuming the encoder IC supports detecting them.
The rope that provides the tension during an exercise is spooled onto the spooler. When the rope is retracted by the motor, the rope is spooled in. When the user pulls on the rope, it is spooled out. The spooler is designed to have a very low height to meet the ECORD's low-profile objective. An embodiment of the spooler is shown in
The spooler (59) is made from three parts, two of which are identical: the top rope retainer (50) and bottom rope retainer (50). Sandwiched between them is the spooling structure (54). The spooler assembly begins by first mounting the bottom retainer to the spooling structure via screws (58). This requires the spooling structure (54) to have threaded screw holes (55) but the top- and bottom-retainers (50) to have unthreaded screw-clearance holes. Next, the rope is anchored by first routing it through the anchor path (53) then making a knot (57) at the end such that once the knot is placed within the rope anchor point (52) it will be too large to slide out of the path. The rope may be further reinforced by potting the anchor point (52) and/or anchor path (53). Once the rope is secured (and possibly potted), the top retainer (50) is mounted via screws (58), completing the assembly. For the lowest profile, flathead screws (58) can be used, requiring countersink mounting holes (60) to be drilled into the top- and bottom-retainers. Although only four screws (58) are shown in the figure, more may be added as necessary for greater support.
The top illustration of
All three pieces of the spooler have an identical cutout (51) for the shaft hole, including the key (rectangular shape in the cutout). The three-piece approach helps reduce the overall manufacturing cost due to 1) all pieces are essentially two-dimensional structures (not including the countersink holes). This means a flat piece of aluminum (or other metal) of the required thickness is simply cut and drilled. It does not undergo any three-dimensional manipulation during fabrication. 2) the top (50) and bottom retainers (50) are identical, which reduces cost due to economy of scale. It is possible to make the bottom retainer and the spooling structure out of a single piece of metal. This will increase the cost but there will be less assembly work to put the spooler pieces together. A consequence of using a low-profile spooler is that the rope must spool over itself, which means that the radius of the spooled rope changes depending on how much of the rope is paid out. This is illustrated in
As can be seen, the more rope that is spooled in, the greater the radius, such that r1>r2. The force, Fi (where i=1 or 2), is what the user feels when performing an exercise. For a given motor torque, this force is Fi=τ/ri, where τ is the motor torque. For a fixed torque, F1<F2, which means the user will feel the least force at the beginning of a rep than at the end. This essentially mimics a resistance band. This may or may not be desirable. If this is undesired, user may set the system to “constant force” in the App. In this case, the motor torque will vary in such a way to maintain a constant force. In other words, more torque will be applied when ri is large and proportionally less torque will be applied as ri decreases. This variation in the torque is taken care of via the feedback system of the ECORD, which will be discussed in section 3.2.
The spooler fits over the shaft (4) and positioned such that its key-notch slides over the key of the shaft (4). There may or may not be a gap between the spooler and the bottom backiron (12). Various mounting schemes are illustrated in
As discussed in the previous section, the spooler may sit flush against the bottom backiron (12) (
As can be seen, the bottom backiron (12) now has two roles: bottom backiron (12) and bottom rope-retainer (50). The spooler has also been reduced to only two parts: the bottom rope retainer (50) and the spooling structure (54). The bottom backiron (12) will require matching threaded screw holes as those found on the spooler parts (see
This approach has several advantages: 1) Reduced number of parts due to the spooler requiring only two parts rather than three, saving on cost. 2) No key required on the shaft (4). This is due to the spooling structure being mounted to the bottom backiron (12) via screws (58) to hold it in place, eliminating the need for a key on the shaft (4). This saves cost on shaft (4) manufacturing by not needing to call out a key cutout as well as not needing a tight tolerance for that cutout. There are also some minor cost savings for not needing a key. 3) No twisting force on the narrower parts of the shaft (4). Since the rope spooling structure is mounted to the bottom backiron (12) and the bottom backiron (12) is mounted to the rotor support structure (2) (see
In the ECORD prototype, the spooler used follows the simplified spooler assembly discussed in section 2.5.2 and is made from a single piece of aluminum. In addition, the shaft (4) used in the ECORD prototype does not use a shaft key, therefore the spooler does not require a key cutout.
The general structure of the ECORD is relatively simple. The ECORD motor, associated electronics, UI, and feedback system are all sandwiched between two plates: Top Plate (61) and Bottom Plate (62). This section provides details of this structure.
The Top Plate (61) and Bottom Plate (62) are part of the ECORD enclosure, and the motor is fitted internally between the two. The ECORD motor assembly comprises the motor (see section 2.4.3), the spooler (59) mounted to the bottom backiron (12) (see section 2.5) and encoder magnetic wheel (34) (see section 2.4.4.1). The Top Plate (61) and Bottom Plate (62) each support a bearing hole that a bearing fits through. The motor shaft (4), in turn, fits inside these bearings, supported by the bearing support surfaces (40) on the shaft (4). The PCB stator (13) stack has several mounting holes (19) located around the perimeter of the PCB (see
The assembly is straightforward. First the top bearing (66) and bottom bearing (67) are fitted onto their respective plates using transition or interference fitting. (“Transition,” “interference,” and “clearance” are industry standard terminology with specific definitions based on the bearing size, the housing size that supports the bearing and the requirements for the specific application.) Next, the threaded standoffs (63) are mounted to the Bottom Plate (62) via flat-head screws (64). The Bottom Plate (62) has countersink holes so that these screws (64), when mounted, are flush with the surface. This is necessary to keep the total height, hECORD, to a minimum. Next, the ECORD motor assembly is placed such that the shaft (4) fits through the bottom bearing (67) using clearance fitting. Clearance fitting does not require pressing the bearing onto the shaft (4), but the tolerance can still be tight to ensure the motor does not wobble during operation. Once in place, the PCB stator stack is mounted to the threaded standoffs (63) using the top screws (65). Finally, the Top Plate (61) is placed such that the top of the shaft (4) fits through the top bearing (66) using a clearance fit.
The various gaps and heights are called out in
Notice that the bearings are thinner than the thickness of their respective plates, which have a thickness of hPLATE=6.35 mm or ¼.″ Although the bearings could have been selected to have the same thickness as the plates, this would have required a complete through-hole to be drilled for the bearing. This would have exposed the bearings to dirt and dust from the environment and would require a bearing to be shielded or sealed, which cost more than open bearings. The bearing would also have been visible from the outside, which would not be esthetically pleasing. As a result, a bearing slightly thinner than the thickness of the plate was selected so that the bearing hole can be cut “blind” and not visible from the outside. Also, the bearing sits flush with respect to the inner surface of its respective plate. Notice that the gap between the motor and the Top Plate (gMOTOR_TOP_PLATE) is only 1 mm. If the bearing does not sit flush and protrudes a bit (say, if a thicker bearing was used), it runs the risk of scraping against the top backiron (11) due to the small gap, gMOTOR_TOP_PLATE.
Also notice the small gap available for the encoder (34), gSPOOLER_TO_PLATE, is only 5.6 mm. There are no commercial encoders available that can fit within this small a gap and provide all of the quadrature, index, and commutations signals, and support a high number of poles, necessitating the design of a custom encoder board using the methods discussed in section 2.4.4.
This section provides details of the ECORD Rope Management System, which comprises several rollers, internal rope tensioning, and the feedback system that continuously measures the rope tension and provides this data to the main controller.
The Rope Management System has two main functions: 1) It ensures that during normal operation the rope spools in-and-out properly from the spooler and that the rope does not mis-spool due to too much rope slack, and 2) the tension of the rope is continuously measured as part of the main feedback system. This is illustrated in the
As indicated, the rope (79) is fed between the Inner (71) and Outer (73) rollers, going over the Center (72) roller. The Center roller (72) is mechanically coupled to a cantilevered Beam (78). Any tension on the rope (79) causes a downward force on the Center roller (72), which in turn causes the Beam (78) to deflect. An electronics board continuously monitors this deflection, which is mapped to the amount of tension on the rope (79). As a result, the ECORD directly measures the tension of the rope (79). The forces acting upon the Center roller (72) (CR) are illustrated in
As the rope (79) is fed between the Inner roller (71) (IR) and Outer roller (73) (OR), it generates angles with respect to the horizontal, specified as θIR and θOR, respectively. These angles, together with the rope, under tension T, produce horizontal and vertical force components, THx and TVx, respectively, where x is IR or OR. These forces all act upon the Center roller (72). For simplicity, assume the Inner and Outer rollers are horizontally centered and of equal distance from the Center roller. As a result, the horizontal components, THIR, and THOR will be of equal magnitude but opposite in direction. Therefore, they will cancel out. The vertical components, TVIR and TVOR, however, are in the same direction, therefore they will add up to a total vertical force of FCR=TVIR+TVOR that is proportional to T.
The rollers are designed to be straight forward and simple. They comprise bearing retainers (supports roller bearings), bearings, and rollers. Two categories of rollers are used in the ECORD: single and parallel. Within the single roller category, there are two sub types; the Egress Roller and those used as part of the feedback mechanism called Feedback Rollers. These are the rollers indicated as Inner (71), Center (72), and Outer (73) in
Detailed views of the Feedback Roller are shown in
Notice that in
The Parallel Roller assembly is shown in
The Parallel Rollers are yet one other way to keep some amount of pressure on the rope by setting a specific gap for gROPE shown in
The Egress Roller (75) is shown in
The area marked with a dashed line (102) is completely open when viewing the ECORD from the top. This opening allows the user to pass their fingers through and grip the roller (103)—as if gripping the handle of a suitcase—to facilitate moving the ECORD. This opening has a width wGO of 25.4 mm (1″) and length lGO of 101.6 mm (4″). The wide 25 mm diameter of the Egress Roller (103) along with the large opening (102) make gripping and moving the ECORD around comfortable.
When the rope (79) exits the ECORD, it can span wide angles to allow the user the most amount of versatility in the types of exercises that can be performed. Consider the perspective views shown in
In figure (a), the rope (79) is shown as a dashed line, indicating that it can exit horizontally and be pulled out by the user towards the front of the ECORD or wrap around the Egress Roller (75) as the user pulls the rope in the direction towards the back of the ECORD, spanning a total front-to-back angle of φFB of approximately 180°. In figure (b), the rope (79) is once again shown as a dashed line exiting the ECORD between the Outer Parallel Rollers (74) and through the gap gROPE_STOP and able to span left-to-right at an angle of φLR of approximately 120°. Figure (c) simply shows a perspective view of the various rollers. Note that the combination of the Egress Roller (75) and the Outer Parallel Rollers (74) act as a sort of fairlead.
As discussed previously, the tension of the rope (79) generates a force FCR acting on the Center Feedback Roller (72), which is mounted to a cantilevered Beam (78) (made from aluminum or other metal) that flexes as a function of FCR. This is shown in
The constant spooling in/out of the rope (79) causes variations in the force FCR and hence, the flexing of the Beam (78). If the Beam (78) is not designed carefully, over time its performance can degrade due to reaching the Beam material's fatigue strength, which can result in plastic deformation, significantly worsening the performance of the ECORD feedback system. The geometric dimensions and metal material used for the ECORD Beam (78) (Aluminum 7075-T6) were selected based on results obtained from computer stress-simulations. Even though gSENSOR is a linear function of T, the measured data of the LDC IC is not. It relates to gSENSOR in a polynomial fashion. An example is shown in
As can be seen, the output data is not a straight line and changes like a polynomial. The best curve-fit equation shows this data to be a polynomial of 4th power. Turns out the LDC IC is most sensitive to metal objects at close distances, as can be seen by the steeper slope at smaller distances. This works to the advantage of the ECORD. The larger output data values correspond to smaller distances, producing more sensitivity at lower tensions where it is needed the most. The ECORD is not a 100% efficient system and possesses some level of mechanical losses due to friction. This friction is a greater source of error when the rope tension is low due to being a larger fraction of that tension, which the ECORD is to maintain throughout an exercise routine. The polynomial nature of the output data in conjunction with the higher SNR of the high-resolution output data produces a greater level of sensitivity that will help improve the performance of the ECORD at low tension settings. As the tension is increased the output data sensitivity is somewhat decreased, however, at greater tensions the frictional forces become a much smaller fraction of that tension, hence a much smaller source of error that the feedback system is to overcome to maintain the desired tension.
There are several advantages to this method of approach in measuring the rope tension. 1) This is an extremely low-cost solution. Usually, load cells are used to measure force, but they can be expensive and require the design of a low-noise analog circuit to amplify the signal. Additional circuitry is required to convert this signal to a digital form for processing. With the approach used here, the analog front-end and digital conversion is done on the IC. The beam itself can be as simple as an aluminum rectangle with two threaded holes for mounting to a spacer that is mounted to the Bottom Plate (62). The ISB is also a low-cost board since it requires very few components and does not need to be more than 4 layers. It may be possible to design a 2-layer version for additional cost reduction. All other fastening components are readily available and very low cost. 2) The rope tension is measured without the need for the user to stand on the ECORD. In other words, there is no requirement to apply a downward force to the ECORD in order to measure the tension as some other inventions require.
In order to map the measured displacement to the physical tension or weight, this mapping needs to be generated. This can be done experimentally with the aid of discrete known weights that span the weight range of the ECORD. For example, weights in 5 lb. increments, can be attached and hung from the ECORD one at a time while the displacement is measured. The results are then plotted and curve-fitted to generate an equation for the curve. This “calibration” equation is used by the Controller Board to determine the weight based on the measured displacement. If the ECORD is mass-produced, each device will require its own calibration equation. If the same equation is used across all ECORDs, there will be some amount of error due to variations in manufacturing and assembly. However, this error may still be acceptable. One way to reduce this error is by specifying tighter manufacturing and assembly tolerances. Although this slightly adds to the overall cost, there will be savings in not having to generate the calibration equation for each individual ECORD.
The main Controller Board uses the measured data and the user-specified weight to command the motor torque required to maintain the specified tension on the rope. This is done through a simple Proportional-Integral-Derivative or PID algorithm. The PID algorithm takes the error signal, which is the difference between the measured tension and the user-specified tension (or weight) and applies a correction to the commanded motor current based on the PID gains. The current of a motor is proportional to the torque, therefore controlling the current allows the torque to be controlled.
This feedback system is necessary in order to compensate for various system dynamics during operation. One of them is the variation in the rope exit radius from the spooler (see section 2.5). Another would be the various sources of friction in the system. Another dynamic would be during operation as the user is pulling on the rope, say during a concentric phase of an exercise like a bicep curl then letting it down during the eccentric phase. During the eccentric phase, the user is allowing the motor to spool the rope (79) back, therefore there will be less tension on the rope. The PID algorithm compensates to allow the tension to be maintained during both phases of the exercise.
The external assembly of the ECORD is shown in
A representation of the rope and the rope clamp are also shown. In this particular case the Outer Parallel Rollers (74) are not fully installed since only one roller is needed (see
The outer dimensions of the ECORD are 18″×14″×2″, as shown in
As shown, there are two 0.5″ diameter through holes (126), 16″ apart, that allow the ECORD to be mounted to a wall. See section 6.1 for the various anchoring schemes. Note that the back wall of the ECORD is flat, allowing it to be stood up vertically without tipping over. This allows it to be easily stored away in the vertical position when not in use. A second function is to stand it up against a wall for certain types of exercises (see section 7) without the need to install it on that wall using the anchor bolts. For the vast majority of the exercises, however, the user must stand or apply a downward pressure on the Top Plate (61) of the ECORD. To prevent accidental pressing of any of the buttons or applying pressure to the display glass, all buttons and the display glass are recessed from the top surface of the Top Plate (61).
The internal layout of the ECORD is shown in
Note that the walls do not bear any load and are simply screwed onto the square standoffs (128). They can be fabricated using sheet metal or 3D printed for a low-cost, albeit not as aesthetically pleasing solution. Alternatively, the walls and the standoffs (128) can be combined with the Bottom Plate (62) and fabricated out of a single aluminum block. This would eliminate many screws and simplify the assembly process, but the fabrication cost would be significant.
In a typical application where bearings are used, they are sized to withstand a certain amount of static and dynamic radial load. This is usually the case with motors. Any load applied to a bearing in the axial direction must be significantly less than its radial limit, otherwise the bearing will be damaged. There are “thrust” type bearings that can withstand a strong force in the axial direction, however, these types of bearings are more expensive and not as prevalent. For this reason, the ECORD does not use thrust bearings. As described in the previous paragraph, a large amount of load applied to the Top Plate (61) will transfer a significant amount of axial force to the motor bearings as the Top Plate (61) deforms. Two steps are taken in the ECORD design to alleviate this axial load from the bearings: 1) A certain amount of headroom is made available to the top bearing (66) of the motor, and 2) the motor is fixed to the Bottom Plate (62). The latter is achieved by pressing the bottom bearing (67) into the Bottom Plate (62) via an interference fit and the shaft (4) inserted into that bearing (67) with a clearance fit but adhered to it via a strong adhesive (or the opposite, that is, the bearing (67) is inserted into the shaft (4) via an interference fit and then fitted into the Bottom Plate (62) via a clearance fit but adhered to it).
These steps perform two functions. If the ECORD is placed onto the floor and a large compressive force is applied to the Top Plate (61), the headroom made available to the top bearing (66) of the motor will decrease as the Top Plate (61) deforms, but it will not make contact with the top bearing (66), therefore it will not transfer any axial force to it. This is shown in
The interference fit and the adhesive used, fix the motor to the Bottom Plate (61) to prevent any axial play given that there is a bit of headroom made available to the top bearing (66). This is important because any amount of axial play may cause the motor to come into contact with the PCB stator stack, which is fixed to the Bottom Plate (62).
One example of the internal assembly of the ECORD, comprising the motor and the Rope Management System is shown in the
As discussed, the Inner (70) and Outer (74) Parallel Rollers help to set the rope (79) centered along the Inner-(71), Center-(72), and Outer-(73) Feedback Rollers regardless of the angle of the rope (79) coming off the Spooler (59) and leaving the Egress Roller (75) (see
In example (a) the entire Rope Management System has been rotate by 90 degrees, reducing dME and eliminating one of the rollers of the Inner Parallel Rollers (70) but positioning the Egress roller (75) down. In example (b), the same orientation as (a) is used, except, the assembly has been shifted up and the Egress Roller (75) rotated by 90 degrees so that it is facing in the same direction as in
If the Rope Management System is off-center from the motor, as illustrated in
The ECORD is designed to provide up to 100 lb. of tension. As such, the bearings and the roller support structures are designed to support forces greater than 3× this maximum amount. The rope itself is rated just north of 1000 lb.
The ECORD is an electromechanical device, therefore it requires electronics to power and drive it. There are several electronic components within the ECORD: The power supply (133), the Controller Board (129), the ISB (110), a couple of wireless modules (RF transceiver (131) and Bluetooth Module (132)) and several fans (134). These will be discussed in this section.
The ECORD uses an internal AC/DC power supply (133) to provide the main power to the system. The AC/DC module accepts AC as the input power, as supplied through a standard wall plug (125), and converts it to DC power for distribution to the various electronics. The AC/DC module is appropriately sized to deliver the maximum amount of power required by the ECORD, which occurs at the highest weight setting that the ECORD can support. The AC/DC power supply may be framed or frameless. The frame primarily protects the user from accidental shocks but can also be water resistant in case of accidental spillage. If a frameless AC/DC power supply is to be used, it will be placed within a custom water-resistant frame between the Top (61) and Bottom (62) Plates. A standard 3-contact power cord is used to attach the ECORD to the wall socket.
There are several similar inventions that use batteries as the main power source. Exercise machines, such as the ECORD, demand a lot of current from the power source, which is highly dependent upon the resistance setting. The higher the resistance setting, the greater the power demand. An exercise device would size its batteries as large as needed and no larger because batteries are expensive and heavy. This means that when the device is used throughout an exercise session, there is a very good chance that the battery would be almost completely depleted, therefore requiring a full charge. If the device is used several times a week, then the battery will have undergone several deep charge/discharge cycles, which is exactly the kind of charging cycle that diminishes the battery capacity more rapidly over time. In addition, as the user maintains a consistent exercise regiment, then he/she should get stronger over time, therefore demanding greater resistance from the device. So, as the battery capacity is diminishing over time, the resistance setting from the user is increasing over time, demanding greater power from a diminishing battery capacity. These are conflicting properties, resulting in the device not being able to last the required amount of time for a given session, cutting the workout very short. The remedy is to change the battery, which may or may not be possible depending on the design of the device. If the battery can be replaced, each time it is, there would be an associated cost to the user.
This is not an issue for the ECORD since it is powered from the grid. There is no diminishing power source, and the power supply can be sized well over what is needed without much additional weight or size.
The general electronics system of the ECORD is illustrated in the
As mentioned in section 4.1, the ECORD is powered via an AC/DC converter (133), which supplies DC power to the mid-level voltage regulator as well as the bridge. The output voltage of the AC/DC converter, which can be in the range of 30V-100V, is the motor voltage, indicated as bus voltage in
The mid-level voltage regulator supplies power to downstream low-voltage regulators as well as the fans (134). Depending on the fan, however, it may instead be powered via one of the low-voltage regulators. All other electronics are powered by one of the two low-voltage regulators. Typically, these regulators supply 5V and 3.3V to the system, but they can be configured to supply other voltage levels as well, depending on the requirements.
The bridge is the interface between the Controller Board (129) and the 3-phase ECORD motor. The term bridge is used as a general description. Typically, they are called 3-phase bridge inverters since they transform DC (from AC/DC supply) into three-phase trapezoidal or three-phase AC power used by a three-phase motor. The Bridge is constructed from 6 transistors, using either MOSFETs, IGBTs, SiCs or GaN technology. The selection depends on voltage, efficiency, and switching speed requirements. It is possible for the transistors to get very hot, which is why they are heatsinked to the Top Plate (61) by using a standard thermal compound.
The Bridge is driven by the Motor Driver IC, which drives the gate of the 6 transistors via pulse-width modulated (PWM) signaling. The Motor Driver IC may receive some feedback signals from the Current and Voltage feedback circuitry so that it can act very quickly in case of catastrophic failures.
The Current and Voltage feedback circuitry senses the Bridge voltage and the currents in two or all three of the phases. This is typically done in the analog domain and the analog signals are fed back to the Motor Controller IC. These signals are optionally provided to the Motor Driver IC and the Main processor.
The Motor Controller IC supplies the PWM signals that drive the Motor Driver IC. These PWM signals are generated based on the feedback signals (discussed above), the selected control scheme (e.g., velocity or torque control), and the commanded velocity or torque as supplied by the Main Processor. The Motor Controller IC contains the actual motor-controller algorithm and provides a configuration interface that allows it to be configured based upon the application needs. The ECORD uses torque (current) control with sinusoidal motor commutation for the smoothest operation.
The Main Processor (MP) executes the general code of the system. This will be discussed in detail in 5.1. It is in charge of communicating with all of the peripheral modules, like the two wireless modules (131 and 132), ISB (110), Accelerometer, Motor Controller IC, and to the Secondary Processor if it exists.
The Secondary Processor (SP) can be used to interface and manage the UI in order to offload that code from the MP. Depending on the type of UI used, this code may be simple or complex. In either case, the MP and the SP communicate with each other over a simple interface, like logic-level serial. The MP, for example, can communicate the user-selected weight to the SP, which displays this information over the UI.
If the MP has sufficient processing capabilities after all main functions are considered, then it can handle the UI without a requirement for an SP.
The UI is designed to provide basic level information to the user, indicating:
The display (123) can be as simple as three 7-segment LED units, arranged to indicate the user-selected weight in xx.y format, where xx is between 0 to 99 and γ is between 0 to 9. Together, the weight can be displayed in pounds, with a resolution of 0.1 pound. Two or more pushbuttons are required to allow the user to increase and decrease weight. Alternatively, a toggle switch can be used to increase the weight if pressed one way and decrease the weight if pressed the other. A third pushbutton can be used to change the increment/decrement resolution, say from 0.1 pound to 1 pound to help speed up the incrementing and decrementing of the weight. Additional LEDs may be added to the UI to indicate information such as what increment/decrement resolution is currently in use. For example, if the LED is on, then the resolution is 1 pound, and if off, it is 0.1 pound.
The 7-segment displays can be used to display a specific pattern of lights that convey a message to the user. For example, the individual LEDs can be lit in a circular pattern to indicate the system is busy.
On the other end of the spectrum of possibilities for the UI lies a high-resolution touchscreen display. Such a display can convey rich information to the user and would eliminate the requirement for discrete pushbuttons or switches but adds to the complexity of the code required to interface to the UI. It is also more expensive as compared to the 7-segment displays and pushbuttons.
A 3-axis accelerometer is integrated onto the Controller Board (129) and its primary role is for the safety of the ECORD operation. The ECORD is required to be anchored in order for the user to be able to pull out the rope. The various anchoring schemes are discussed in 6.1. If during operation the anchoring is compromised (e.g., the user steps off the ECORD by accident) while the user is actively pulling on the rope and depending on the selected weight, it can cause the ECORD to fly off towards the user. This can potentially lead to injury. Under this condition, the ECORD will undergo a sudden acceleration. The MP obtains the accelerometer data at the loop rate (discussed in 5.1) and if the acceleration is above a normal acceptable limit, the MP will immediately set the resistance to zero. It will also turn off the Motor Controller and Motor Driver, thereby preventing the ECORD from accelerating towards the user.
The secondary role of the accelerometer is to invert the UI display if necessary. The ECORD can be placed on the floor or mounted to the wall. Depending on how it is oriented, the information on the display will need to be displayed right-side up. The orientation of the ECORD is sensed and the information of the display inverted, if necessary, in order to show it right-side up to the user.
The ECORD monitors the temperature of various sections of the circuitry, in particular, the Bridge transistors. These transistors increase in temperature with greater power demand from the user. If they reach a critically high temperature level an overtemperature condition will be triggered. This is discussed in detail in section 5.1.
It is well known that motors can also operate as generators when external mechanical input is provided to the motor. In the ECORD this occurs when the user's movement results in the rope being spooled out, for example, during the concentric phase of a bicep curl. During this phase, the motor is attempting to spool the rope in, but the user is forcing the motor to spin in the opposite direction, thereby providing mechanical input energy to the ECORD. This mechanical energy is converted into electrical energy by the motor, which must be used or stored. If no provisions are made to store it or use it, then it will be stored into the output capacitor of the AC/DC converter, which typically is not very large. Given this minimal amount of capacitance, the energy will cause its voltage to increase. If this voltage is left unchecked, it can continue to rise, ultimately resulting in catastrophic failure of the electronics system. The purpose of the Regenerated-Power Mitigation circuitry is to ensure the generated energy is utilized in order to keep the bus voltage at a safe level. Several mitigation methods may be used, each of which are illustrated in
During an exercise routine, the motor is in one of three states: motoring (spools rope in when user force is less than motor force), generating (when user force is greater than motor force), or stalling (user force is equal to motor force). When stalling, the motor winding resistance consumes all the energy, generating heat and no motion. Stalling does not result in an increase in bus voltage but can be damaging to the motor depending on the amount of heat generated. When motoring, energy flows from the AC/DC converter to the Controller Board and to the motor, which is consuming electrical energy, part of which turns into heat due to the winding resistance and the remainder producing motion. When generating, electrical energy flows from the motor back to the electronics but part of that energy turns into heat due to the motor winding resistance. Electrical current flow is indicated by arrows in
Method 1 is the simplest mitigation approach and the method used in the ECORD prototype, indicated as the Power Dissipation Board (130) in
Note that R may be composed of several power resistors in parallel. Furthermore, when the switch must be in the closed position, it may be rapidly opening and closing based on a PWM signal. PWMing the switch allows modulating the amount of current the resistor is to dissipate.
It is important to ensure that no power flows into the AC/DC converter during the generating phase. This is accomplished with the aid of a diode, D. The diode is reverse biased during the generating phase, preventing any current from flowing into the AC/DC converter. An alternative to using a diode, which is not very efficient, is to use a transistor, like a MOSFET. A MOSFET can be used as a very efficient sold-state switch. It opens during the generating phase to prevent current from flowing into the AC/DC converter and closes during the motoring phase to allow the AC/DC converter to supply power.
Although method 1 is simple, all the generated energy turns into heat. There are other, more efficient ways to make use of the generated energy, as in Method 2. In this method, a bi-directional DC-DC converter is used to charge a bank of capacitors or a large supercapacitor, C. A bi-directional DC-DC converter allows power to flow in either direction. For example, power from a high-voltage source can be stepped down into a low-voltage source. If something on the low-voltage side can produce power, then power can be made to flow in the opposite direction. A bi-directional DC-DC converter may also provide regulated current as opposed to regulated voltage. This is what is used in method 2. When VBUS increases due to generated power, the DC-DC converter turns on and supplies regulated, constant current to C. Charging a capacitor with a constant-current results in a linear increase in the capacitor voltage. Consequently, during the charging phase of the capacitor a load is presented to VBUS, causing its voltage to drop. When it drops below the lower hysteresis threshold, charging ceases. Charging may begin again if the motor is still generating. This cycle will continue until the generating phase ends.
A minimum capacitor voltage is required in order for the bi-directional DC-DC converter to be able to transfer power from the capacitor to VBUS. When this condition is met and the system is in the motoring phase, the capacitor is discharged, and its power transferred to VBUS. This will allow the system to be fully or partially powered by the power transferred from C. The AC/DC will supply any residual power required in order to keep the system running. When C is fully depleted, the AC/DC will take over and fully supply the required power. Just as in method 1, no current may flow into the AC/DC converter, necessitating the use of a current-blocking diode or MOSFET.
In method 3, the energy produced during the generating phase is transferred to a removable battery pack. This is accomplished by sensing VBUS as in methods 1 and 2 and closing the switch SW to allow power to flow into the battery charger, which in turn will charge the battery pack. When the battery is being charged, it presents a load to VBUS, dropping its voltage similar to that described for methods 1 and 2. The charging ceases when VBUS drops below the lower hysteresis threshold level. During the motoring phase the switch is open to prevent the AC/DC converter from charging the battery pack. As before, a current-blocking diode or MOSFET is required.
Instead of a battery pack, a USB port may be made available to allow a smartphone or tablet to be plugged into the ECORD to be charged in this manner. One disadvantage of this system is that when the battery pack or device is fully charged, it can no longer be presented as a load for the generated power. As a result, VBUS can rise to dangerous levels. To mitigate this, method 3 can be combined with method 1 so that when a battery is fully charged, the system will switch to using method 1 to mitigate the generated energy.
The fourth and the most elegant method is to use a bi-directional AC/DC converter, which supplies power to the motor during motoring and sources power to the grid during generation. The bi-directional AC/DC block of
The ISB (110) has already been discussed in section 3.2.3. It contains an inductance-to-digital converter IC that communicates with the MP. The IC used in the ECORD prototype makes use of the popular SPI interface. Other sensors may use a different interface. The MP supports a wide-variety of interfaces, like logic-level serial, I2C, CAN bus, and of course SPI.
The ECORD supports two wireless modules. One is a Bluetooth module (132) used to communicate with a smartphone or tablet, which supports the ECORD app (see section 5.2). The other RF transceiver (131) communicates with a small Remote Control (140) (see section 6.2) that the user can attach to a handle, bar, or similar, that in turn hooks onto the loop on the rope. The Remote Control (140) can be used to command an increase in resistance, decrease in resistance, an emergency stop, or resistance activation during an exercise routine. Both of these modules are low-cost commercial products that meet the FCC requirements and are certified for use.
Like all motors, the ECORD motor generates heat during operation. This heat is actively removed with the aid of fans (134). As discussed in section 3.3, there are many slits and cutouts (127) along the perimeter walls to facilitate good airflow.
The main code of the ECORD is executed on the MP. The code of the UI system may be executed on the SP or the MP, as discussed previously. There is also an ECORD app that is executed on a smartphone or tablet. These are discussed in this section.
The Operation Code is the main firmware running on the MP. It is responsible for controlling the motor, including any safety features, as well as communicating with the various modules and peripherals (shown in
When the system is powered on, the MP steps through an initialization routine, where it configures the various wireless modules for proper wireless communication, checks the functionality of the accelerometer, checks the functionality of the temperature sensor(s), configures the Motor Controller IC with the various parameters required to operate the motor, and configures the inductance-to-digital converter on the ISB (110). Once completed, the code enters the main loop. The first step is to obtain the measurements from the various sensors, which include:
Once the data is obtained, it is filtered to smooth out any noise. This filtering is in the form of a moving average, where the last NSAMPLES is used to calculate the average of the data. NSAMPLES can be adjusted to suit the needs of the application. For ECORD, it is set somewhere between 5-10, depending on the data type, need for smoothing, and amount of acceptable filter delay (the larger NSAMPLES is the greater the filter delay). Additionally, the data is filtered using a median filter to get rid of noise. This is also performed over NSAMPLES, with the same tradeoffs.
After filtering, the code enters the Master Operation block. Here, the code is organized as a state machine. On initial power-up, the system does not know what the state of the rope is. It may have been pulled out to some extent when the ECORD was off. Therefore, it will initially spool the rope in until it detects that the motor has stopped moving, indicating that the rope has been fully spooled and it has reached the stop point (see section 3.3). At this point, the system marks the zero position of the rope and moves onto the Idle state assuming there are no overtemperature conditions.
In the Idle state, the system is ready and waiting for the user to select a weight, either via the UI, the app, or the Remote Control on the handle. Once the weight is selected, the resistance is applied, and the system consumes power proportional to the selected weight. There is no reason to continue wasting power and heating up the motor and electronics while waiting indefinitely for the user to begin exercising. Therefore, if the user does not begin the exercise within a predetermined timeout period (set within the app), the weight is set back to zero and the system enters the Idle state.
There are two ways to apply the resistance after weight-selection has been made. It may be applied at once or it can ramp linearly over time up to the selected weight. This choice can be made within the app. Applying the weight linearly may be beneficial depending on how the user is situated for the specific exercise to be performed.
Once the user begins the exercise the system enters the operation state where the following safety features are checked:
Three of the four safety features (over-velocity, over-acceleration, and overtemperature) will trigger the entry into the Initialize state. The overtemperature condition will keep the system in the Initialize state until the temperature level(s) return to acceptable limits. Hysteresis is added to ensure the downward trending temperature is well below the upward safety-triggering level.
The MP uses a main timer that triggers an interruption every TLOOP period. Usually, the MP executes all the required code well within this period. Before TLOOP is reached, the MP checks for additional information received asynchronously from the wireless modules, the SP, or any touchscreen and handles them in such a way that does not interfere with the main operating loop. Since TLOOP is on the order of a few milliseconds, the code polls the UI button presses instead of using interrupts. This makes the code easier to handle, however, interrupts may also be used to determine the state of the pushbuttons.
Although the ECORD may be operated as a standalone device, allowing the user to select the desired weight and perform exercises, it may also be paired with a smartphone or a tablet via the Bluetooth wireless module (132) in order to provide the user with additional capabilities and information. These are:
In a gym setting, where several ECORD stations may be in close proximity to one another, a user can pair to a specific ECORD without interfering with another. This is taken care of by the pairing mechanism provided via Bluetooth.
Operating the ECORD is straightforward. It is simply plugged into an outlet and the power-on button pressed. After initialization has taken place (see section 5.1), the user selects a desired weight with the onboard UI and performs an exercise. When the set is complete, the user lowers the handle back down until it is spooled back by the motor into the stop position. At this point, the user may change the weight if desired or set it to zero if rest is required. The process repeats until the exercise session is over, at which point the ECORD can be turned off (using the power switch), unplugged, and put away.
The above scenario describes the standalone operation of the ECORD, where it is not paired with a smartphone or tablet. When the ECORD is turned on, it broadcasts its availability over Bluetooth. There is no requirement to connect with a smartphone or tablet and the unit can be operated as described above. If pairing is required, it is done so using the smartphone or tablet. Once paired, the user may control the ECORD either from the onboard UI or via the smartphone or tablet. When connected, the ECORD will provide exercise related information to the connected device during a set. This information includes the reps, the weight (even if the weight changes during the set), velocity, and any status or failure messages. The app then integrates this information with the user-specified exercise that is currently underway. The user-specified exercise may have been selected ahead of time or on the fly. This integrated information then resides in the exercise history in order to help the user track his/her performance over time. This history is especially helpful to fitness trainers that may choose to have their clients train with an ECORD.
The ECORD is designed to be versatile to accommodate as many different types of exercises as possible. Although its main application is to simply be placed on the floor and have the user anchor it with their own weight, there are other ways to anchor the ECORD that facilitate additional types of exercises.
During operation, the user anchors the ECORD in one of four ways (examples are shown in section 7):
The ECORD offers two mounting holes (126) spaced 16″ apart, which is the most popular separation between two studs in a wall. It is important to mount the ECORD to the studs for maximum support. (The ECORD should never be mounted to drywall only.) The user can install two threaded anchor bolts to the wall at the appropriate height, insert the ECORD through those bolts, and fasten it with butterfly nuts. This allows the ECORD to easily and quickly be mounted to a wall for certain types of exercises (see section 7). Note that there is no need for any additional mounting holes (126) elsewhere on the device since the rope (79) coming off the Egress Roller (75) is nearly in line with the bolts, just slightly above them. The force of that rope (79) produces a very small amount of torque moment on the bolts, and the little that is produced works to further push the opposite end of the ECORD (near the rear) into the wall, not away from it.
The Remote Control (140) discussed in section 4.4 is a small form-factor device that can be attached to a handle or bar or held by the user's other hand during an exercise routine in order to wirelessly command weight increase, weight decrease, emergency stop, or resistance activation. The ECORD does not require the design of a custom handle, bar, or similar since there are countless commercial products available to choose from. The user may also have their own preference for a specific type of handle. Therefore, the mounting mechanism of the Remote Control (140) is such that it can be mounted to just about any type of handle or bar. This concept is illustrated in
The Remote Control (140) comprises a pushbutton (141) for initiating commands, an enclosure (142) for the electronics and battery, and an adjustable strap (143). In order to keep the size of the Remote Control (140) small and its operation simple, only a single button (141) is made available, with the commands as follows:
The most likely command used during an exercise routine would be to decrease the weight, which is why it is assigned as the simplest action; single-click. Decrementing the weight is useful in performing drop-sets, where the user begins with one weight, then after maxing out the number of reps performed at that weight, the weight is lowered, and the exercise continues. Additional drop-sets may follow as desired. Decrementing the weight can also be used to help the user finish a set, very similar to what a spotter does. In a sense, the Remote Control (140) offers a form of self-spotting.
There may be conditions where the user will need to turn off the weight rapidly, say to avoid injury. This is easily accomplished by pressing and holding the button for at least 0.5 seconds. When the weight has already been applied, this action would turn it off immediately. However, if the weight has not yet been applied, the same action will apply the weight depending on how its application is configured in the app; all at once or smoothly over time. This is beneficial if the user needs to get situated first before any weight is applied. This requires the ECORD to be configured via the app, since the default condition is to apply the weight at once as soon as it is selected. As an example, when the ECORD is initially powered and operating without a connection to a smartphone or tablet, as soon as the increment button is pressed on the onboard UI, the weight is applied. With additional weight increments, the tension of the rope increases. The ECORD will start a timeout period as soon as a new weight is selected, waiting for the user to begin exercising. See section 5.1.
The enclosure (142) of the Remote Control (140) contains an FCC certified wireless module, a microcontroller, power regulation circuitry, and a battery (e.g., coin type). The unit is designed to draw minimal power during transmission and goes into sleep when there is no action from the button. In sleep mode it draws very little power, allowing the battery to last well over a year. Whenever the button (141) is pressed, an LED indicator shows that the command has been transmitted. This provides the user with a visual indicator that the unit is operating.
In a gym setting, where there may be several ECORD stations in near proximity, each Remote Control (140) will be paired with its associated ECORD so that commands sent from one Remote Control do not affect another. The pairing is made possible via the messaging protocol used by the wireless module within the Remote Control.
The strap (143) of the Remote Control is adjustable, like a watch strap or stretch Velcro material, to accommodate varying handle thicknesses. It can be mounted onto a handle as shown in
This section illustrates a small selection of exercises shown in
The versatility of the ECORD design allows it to be mounted to additional equipment for even more exercise possibilities. For instance, the ECORD can be mounted to a rack that allows its position to be adjusted depending on the exercise to be performed. Some examples are shown in
In (a) the user is performing a face-pull exercise, where the ECORD must be mounted head high. For bicep curls (c), the ECORD must be lowered. For lat pulls (b), the ECORD may be positioned high or low. In example (d), the user is performing flys. This requires the use of two ECORDs, both of which are mounted to adjustable racks that are oriented horizontally. A bench is placed in the middle. In this case the user must get situated before turning on the weight, which can be done with the Remote Controls (140), one for each ECORD. For a bench-press exercise, the ECORDs would be moved closer to the bench.
For some of the exercises shown, the starting position of the handle is far from the Egress roller (75). For example, the single-arm bicep curl requires the user to start with the handle right by their thigh, leaving less rope within the ECORD to perform the full range of motion. In such cases, a simple extension rope (e.g., 2 feet long) may be added to offset the starting position, leaving more rope within the ECORD to perform the full range of motion. The extension rope can have carabiners on both ends, one to hook onto the handle and the other to connect to the rope-loop of the ECORD.
Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63491105 | Mar 2023 | US |
