Strength training, also referred to as resistance training or weight lifting, is an important part of any exercise routine. It promotes the building of muscle, the burning of fat, and improvement of a number of metabolic factors including insulin sensitivity and lipid levels. Many users seek a more efficient and safe method of strength training.
Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.
The invention can be implemented in numerous ways, including as a process; an apparatus; a system; a composition of matter; a computer program product embodied on a computer readable storage medium; and/or a processor, such as a processor configured to execute instructions stored on and/or provided by a memory coupled to the processor. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. Unless stated otherwise, a component such as a processor or a memory described as being configured to perform a task may be implemented as a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. As used herein, the term ‘processor’ refers to one or more devices, circuits, and/or processing cores configured to process data, such as computer program instructions.
A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.
Traditionally, the majority of strength training methods and/or apparatuses fall into the following categories:
While gravity is the primary source of tension and/or resistance in all of the above, tension has also been achieved using springs and/or flexing nylon rods as with Bowflex, elastics comprising rubber bands/resistance bands as with TheraBand, pneumatics, and hydraulics. These systems have various characteristics with their own applied tension curve.
Electronic Resistance.
Using electricity to generate tension/resistance may also be used, for example, as described in co-pending U.S. patent application Ser. No. 15/655,682 (Attorney Docket No. RIPTP001) entitled DIGITAL STRENGTH TRAINING filed Jul. 20, 2017, which is incorporated herein by reference for all purposes. Examples of electronic resistance include using an electromagnetic field to generate tension/resistance, using an electronic motor to generate tension/resistance, and using a three-phase brushless direct-current (BLDC) motor to generate tension/resistance. The techniques discussed within the instant application are applicable to other traditional exercise machines without limitation, for example exercise machines based on pneumatic cylinders, springs, weights, flexing nylon rods, elastics, pneumatics, hydraulics, and/or friction.
Low Profile.
A strength trainer using electricity to generate tension/resistance may be smaller and lighter than traditional strength training systems such as a weight stack, and thus may be placed, installed, or mounted in more places for example the wall of a small room of a residential home. Thus, low profile systems and components are preferred for such a strength trainer. A strength trainer using electricity to generate tension/resistance may also be versatile by way of electronic and/or digital control. Electronic control enables the use of software to control and direct tension. By contrast, traditional systems require tension to be changed physically/manually; in the case of a weight stack, a pin has to be moved by a user from one metal plate to another.
Such a digital strength trainer using electricity to generate tension/resistance is also versatile by way of using dynamic resistance, such that tension/resistance may be changed nearly instantaneously. When tension is coupled to position of a user against their range of motion, the digital strength trainer may apply arbitrary applied tension curves, both in terms of position and in terms of phase of the movement: concentric, eccentric, and/or isometric. Furthermore, the shape of these curves may be changed continuously and/or in response to events; the tension may be controlled continuously as a function of a number of internal and external variables including position and phase, and the resulting applied tension curve may be pre-determined and/or adjusted continuously in real time.
a controller circuit (1004), which may include a processor, inverter, pulse-width-modulator, and/or a Variable Frequency Drive (VFD);
a motor (1006), for example a three-phase brushless DC driven by the controller circuit;
a spool with a cable (1008) wrapped around the spool and coupled to the spool. On the other end of the cable an actuator/handle (1010) is coupled in order for a user to grip and pull on. The spool is coupled to the motor (1006) either directly or via a shaft/belt/chain/gear mechanism. Throughout this specification, a spool may be also referred to as a “hub”;
a filter (1002), to digitally control the controller circuit (1004) based on receiving information from the cable (1008) and/or actuator (1010);
optionally (not shown in
one or more of the following sensors (not shown in
a position encoder; a sensor to measure position of the actuator (1010) or motor (100). Examples of position encoders include a hall effect shaft encoder, grey-code encoder on the motor/spool/cable (1008), an accelerometer in the actuator/handle (1010), optical sensors, position measurement sensors/methods built directly into the motor (1006), and/or optical encoders. In one embodiment, an optical encoder is used with an encoding pattern that uses phase to determine direction associated with the low resolution encoder. Other options that measure back-EMF (back electromagnetic force) from the motor (1006) in order to calculate position also exist;
a motor power sensor; a sensor to measure voltage and/or current being consumed by the motor (1006);
a user tension sensor; a torque/tension/strain sensor and/or gauge to measure how much tension/force is being applied to the actuator (1010) by the user. In one embodiment, a tension sensor is built into the cable (1008). Alternatively, a strain gauge is built into the motor mount holding the motor (1006). As the user pulls on the actuator (1010), this translates into strain on the motor mount which is measured using a strain gauge in a Wheatstone bridge configuration. In another embodiment, the cable (1008) is guided through a pulley coupled to a load cell. In another embodiment, a belt coupling the motor (1006) and cable spool or gearbox (1008) is guided through a pulley coupled to a load cell. In another embodiment, the resistance generated by the motor (1006) is characterized based on the voltage, current, or frequency input to the motor.
In one embodiment, a three-phase brushless DC motor (1006) is used with the following:
In some embodiments, the controller circuit (1002, 1004) is programmed to drive the motor in a direction such that it draws the cable (1008) towards the motor (1006). The user pulls on the actuator (1010) coupled to cable (1008) against the direction of pull of the motor (1006).
One purpose of this setup is to provide an experience to a user similar to using a traditional cable-based strength training machine, where the cable is attached to a weight stack being acted on by gravity. Rather than the user resisting the pull of gravity, they are instead resisting the pull of the motor (1006).
Note that with a traditional cable-based strength training machine, a weight stack may be moving in two directions: away from the ground or towards the ground. When a user pulls with sufficient tension, the weight stack rises, and as that user reduces tension, gravity overpowers the user and the weight stack returns to the ground.
By contrast in a digital strength trainer, there is no actual weight stack. The notion of the weight stack is one modeled by the system. The physical embodiment is an actuator (1010) coupled to a cable (1008) coupled to a motor (1006). A “weight moving” is instead translated into a motor rotating. As the circumference of the spool is known and how fast it is rotating is known, the linear motion of the cable may be calculated to provide an equivalency to the linear motion of a weight stack. Each rotation of the spool equals a linear motion of one circumference or 2πr for radius r. Likewise, torque of the motor (1006) may be converted into linear force by multiplying it by radius r.
If the virtual/perceived “weight stack” is moving away from the ground, motor (1006) rotates in one direction. If the “weight stack” is moving towards the ground, motor (1006) rotates in the opposite direction. Note that the motor (1006) is pulling towards the cable (1008) onto the spool. If the cable (1008) is unspooling, it is because a user has overpowered the motor (1006). Thus, note a distinction between the direction the motor (1006) is pulling, and the direction the motor (1006) is actually turning.
If the controller circuit (1002, 1004) is set to drive the motor (1006) with, for example, a constant torque in the direction that spools the cable, corresponding to the same direction as a weight stack being pulled towards the ground, then this translates to a specific force/tension on the cable (1008) and actuator (1010). Calling this force “Target Tension”, this force may be calculated as a function of torque multiplied by the radius of the spool that the cable (1008) is wrapped around, accounting for any additional stages such as gear boxes or belts that may affect the relationship between cable tension and torque. If a user pulls on the actuator (1010) with more force than the Target Tension, then that user overcomes the motor (1006) and the cable (1008) unspools moving towards that user, being the virtual equivalent of the weight stack rising. However, if that user applies less tension than the Target Tension, then the motor (1006) overcomes the user and the cable (1008) spools onto and moves towards the motor (1006), being the virtual equivalent of the weight stack returning.
BLDC Motor.
While many motors exist that run in thousands of revolutions per second, an application such as fitness equipment designed for strength training has different requirements and is by comparison a low speed, high torque type application suitable for certain kinds of BLDC motors configured for lower speed and higher torque.
In one embodiment, a requirement of such a motor (1006) is that a cable (1008) wrapped around a spool of a given diameter, directly coupled to a motor (1006), behaves like a 200 lbs weight stack, with the user pulling the cable at a maximum linear speed of 62 inches per second. A number of motor parameters may be calculated based on the diameter of the spool.
Thus, a motor with 67.79 Nm of force and a top speed of 395 RPM, coupled to a spool with a 3 inch diameter meets these requirements. 395 RPM is slower than most motors available, and 68 Nm is more torque than most motors on the market as well.
Hub motors are three-phase permanent magnet BLDC direct drive motors in an “out-runner” configuration: throughout this specification out-runner means that the permanent magnets are placed outside the stator rather than inside, as opposed to many motors which have a permanent magnet rotor placed on the inside of the stator as they are designed more for speed than for torque. Out-runners have the magnets on the outside, allowing for a larger magnet and pole count and are designed for torque over speed. Another way to describe an out-runner configuration is when the shaft is fixed and the body of the motor rotates.
Hub motors also tend to be “pancake style”. As described herein, pancake motors are higher in diameter and lower in depth than most motors. Pancake style motors are advantageous for a wall mount, subfloor mount, and/or floor mount application where maintaining a low depth is desirable, such as a piece of fitness equipment to be mounted in a consumer's home or in an exercise facility/area. As described herein, a pancake motor is a motor that has a diameter higher than twice its depth. As described herein, a pancake motor is between 15 and 60 centimeters in diameter, for example 22 centimeters in diameter, with a depth between 6 and 15 centimeters, for example a depth of 6.7 centimeters.
Motors may also be “direct drive”, meaning that the motor does not incorporate or require a gear box stage. Many motors are inherently high speed low torque but incorporate an internal gearbox to gear down the motor to a lower speed with higher torque and may be called gear motors. Direct drive motors may be explicitly called as such to indicate that they are not gear motors.
If a motor does not exactly meet the requirements illustrated in the table above, the ratio between speed and torque may be adjusted by using gears or belts to adjust. A motor coupled to a 9″ sprocket, coupled via a belt to a spool coupled to a 4.5″ sprocket doubles the speed and halves the torque of the motor. Alternately, a 2:1 gear ratio may be used to accomplish the same thing. Likewise, the diameter of the spool may be adjusted to accomplish the same.
Alternately, a motor with 100× the speed and 100th the torque may also be used with a 100:1 gearbox. As such a gearbox also multiplies the friction and/or motor inertia by 100×, torque control schemes become challenging to design for fitness equipment/strength training applications. Friction may then dominate what a user experiences. In other applications friction may be present, but is low enough that it is compensated for, but when it becomes dominant, it is difficult to control for. For these reasons, direct control of motor torque is more appropriate for fitness equipment/strength training systems. This would normally lead to the selection of an induction type motor for which direct control of torque is simple. Although BLDC motors are more directly able to control speed and/or motor position rather than torque, torque control of BLDC motors can be made possible with the appropriate methods when used in combination with an appropriate encoder.
Reference Design.
Sliders (401) and (403) may be respectively used to guide the cable (500) and (501) respectively along rails (400) and (402). The exercise machine in
In one embodiment, electronics bay (600) is included and has the necessary electronics to drive the system. In one embodiment, fan tray (500) is included and has fans that cool the electronics bay (600) and/or motor (100).
Motor (100) is coupled by belt (104) to an encoder (102), an optional belt tensioner (103), and a spool assembly (200). Motor (100) is preferably an out-runner, such that the shaft is fixed and the motor body rotates around that shaft. In one embodiment, motor (100) generates torque in the counter-clockwise direction facing the machine, as in the example in
Spool assembly (200) comprises a front spool (203), rear spool (202), and belt sprocket (201). The spool assembly (200) couples the belt (104) to the belt sprocket (201), and couples the two cables (500) and (501) respectively with front spool (203) and rear spool (202). Each of these components is part of a low profile design. In one embodiment, a dual motor configuration not shown in
As shown in
In one embodiment, motor (100) should provide constant tension on cables (500) and (501) despite the fact that each of cables (500) and (501) may move at different speeds. For example, some physical exercises may require use of only one cable at a time. For another example, a user may be stronger on one side of their body than another side, causing differential speed of movement between cables (500) and (501). In one embodiment, a device combining dual cables (500) and (501) for single belt (104) and sprocket (201), should retain a low profile, in order to maintain the compact nature of the machine, which can be mounted on a wall.
In one embodiment, pancake style motor(s) (100), sprocket(s) (201) and spools (202, 203) are manufactured and arranged in such a way that they physically fit together within the same space, thereby maximizing functionality while maintaining a low profile.
As shown in
The cables (500) and (501) are respectively positioned in part by the use of “arms” (700) and (702). The arms (700) and (702) provide a framework for which pulleys and/or pivot points may be positioned. The base of arm (700) is at arm slider (401) and the base of arm (702) is at arm slider (403).
The cable (500) for a left arm (700) is attached at one end to actuator (800). The cable routes via arm slider (401) where it engages a pulley as it changes direction, then routes along the axis of rotation of track (400). At the top of track (400), fixed to the frame rather than the track is pulley (303) that orients the cable in the direction of pulley (300), that further orients the cable (500) in the direction of spool (202), wherein the cable (500) is wound around spool (202) and attached to spool (202) at the other end.
Similarly, the cable (501) for a right arm (702) is attached at one end to actuator (601). The cable (501) routes via slider (403) where it engages a pulley as it changes direction, then routes along the axis of rotation of track (402). At the top of the track (402), fixed to the frame rather than the track is pulley (302) that orients the cable in the direction of pulley (301), that further orients the cable in the direction of spool (203), wherein the cable (501) is wound around spool (203) and attached to spool (203) at the other end.
One important use of pulleys (300, 301) is that they permit the respective cables (500, 501) to engage respective spools (202, 203) “straight on” rather than at an angle, wherein “straight on” references being within the plane perpendicular to the axis of rotation of the given spool. If the given cable were engaged at an angle, that cable may bunch up on one side of the given spool rather than being distributed evenly along the given spool.
In the example shown in
When the motor is being back-driven by the user, that is when the user is retracting the cable, but the motor is resisting, and the motor is generating power. This additional power may cause the internal voltage of the system to rise. The voltage is stabilized to prevent the voltage rising indefinitely causing the system to fail or enter an unsafe state. In one embodiment, power dissipation is used to stabilize voltage, for example to burn additional power as heat.
Voltage Stabilization.
Controller (604) may be implemented using a micro-controller, micro-processor, discrete digital logic, any programmable gate array, and/or analog logic, for example analog comparators and triangle wave generators. In one embodiment, the same microcontroller that is used to implement the motor controller (601) is also used to implement voltage stabilization controller (604).
In one embodiment, a 48 Volt power supply (603) is used. The system may be thus designed to operate up to a maximum voltage of 60 Volts. In one embodiment, the Controller (604) measures system voltage, and if voltage is below a minimum threshold of 49 Volts, then the PWM has a duty cycle of 0%, meaning that the FET (610) is switched off. If the motor controller (601) generates power, and the capacitance (612) charges, causing system voltage (611) to rise above 49 Volts, then the controller (601) will increase the duty cycle of the PWM. If the maximum operating voltage of the system is 60 Volts, then a simple relationship to use is to pick a maximum target voltage below the 60 Volts, such as 59 Volts, so that at 59 Volts, the PWM is set to a 100% duty cycle. Hence, a linear relationship of PWM duty cycle is used such that the duty cycle is 0% at 49 Volts, and 100% at 59 Volts. Other examples of relationships include: a non-linear relationship; a relationship based on coefficients such as one representing the slope of a linear line adjusted by a PID loop; and/or a PID loop directly in control of the duty cycle of the PWM.
In one embodiment, controller (604) is a micro-controller such that 15,000 times per second an analog to digital converter (ADC) measures the system voltage, invokes a calculation to calculate the PWM duty cycle, then outputs a pulse with a period corresponding to that duty cycle.
Safety.
Safety of the user and safety of the equipment is important for an exercise machine. In one embodiment, a safety controller uses one or more models to check system behavior, and place the system into a safe-stop, also known as an error-stop mode or ESTOP state to prevent or minimize harm to the user and/or the equipment. A safety controller may be a part of controller (604) or a separate controller (not shown in
Depending on the severity of the error, recovery from ESTOP may be quick and automatic, or require user intervention or system service.
In step 3002, data is collected from one or more sensors, examples including:
In step 3004, a model analyzes sensor data to determine if it is within spec or out of spec, including but not limited to:
In step 3006, if a model has been determined to be violated, the system may enter an error stop mode. In such an ESTOP mode, depending on the severity, it may respond with one or more of:
Arms.
Traditionally, exercise machines utilize one or more arms pivoting in the vertical direction to offer adjustability in the vertical direction. However, to achieve the full range of adjustability requires long arms. If a user wishes to have 8 feet of adjustment such that the tip of the arm may be above the user 8 feet off the ground, or at a ground position, then a 5 foot arm may be required to be practical. This is inconvenient because it requires more space to pivot the arm, and limits the number of places where such a machine can be placed. Furthermore, a longer arm undergoes higher lever-arm forces and increases the size and complexity of the joint in order to handle those larger forces. If arms could be kept under three feet in length, a machine may be more conveniently placed and lever-arm forces may be more reasonable.
An arm (702) of an exercise machine capable of moving in different directions and ways is disclosed. Three directions and ways include: 1) translation; 2) vertical pivot; and 3) horizontal pivot.
Translation.
In one embodiment, as shown in
As shown in
Sliding the slider (403) up and down track (402) physically includes the weight of the arm (702). The arm (702), being between 2 and 5 feet long, for example 3 feet long, and for example made of steel, may weigh between 6 and 25 lbs, for example 10 lbs. This may be considered heavy by some users to carry directly. In one embodiment, motor (100) is configured to operate in an ‘arm cable assist’ mode by generating a tension matching the weight of the arm (702) on the slider (403), for example 10 lbs on cable (501), and the user may easily slide the slider (403) up and down the track without perceiving the weight of the arms.
The exercise machine is calibrated such that the tension on the cable matches the weight of the slider, so the user perceives none of the weight of the arm. Calibration may be achieved by adjusting cable tension to a level such that the slider (403) neither rises under the tension of the cable (501), or falls under the force of gravity. By increasing or reducing motor torque as it compares to that used to balance gravity, the slider may be made to fall lower, or raise higher.
Placing the motor (100) and dual-spool assembly (200) near the top of the machine as shown in
Vertical Pivot.
In addition to translating up and down, the arms may pivot up and down, with their bases in fixed position, to provide a great range of flexibility in positioning the user origination point of a given arm. Keeping arm (702) in a fixed vertically pivoted position may require locking arm (702) with slider (403).
Using trapezoidal teeth for locking is disclosed. The teeth (422) and matching female locking member (722) use a trapezoidal shape instead of a rectangular shape because a rectangular fitting should leave room for the teeth to enter the female locking member. Using a rectangular tooth causes “wiggle” in the locking joint, and this wiggle is leveraged at the end of arm (702). A trapezoidal set of teeth (422) to enter female locking mechanism (722) makes it simpler for the two members to be tightly coupled, minimizing joint wiggle.
Using a trapezoidal set of teeth increases the risk of the joint slipping/back-drive while under the stress of high loads. Empirically a slope of between 1 and 15 degrees, for example 5 degrees, minimizes joint slippage while maximizing ease of entry and tightening. The slope of the trapezoid is set such that the amount of back-drive force is lower than the amount of friction of the trapezoidal surfaces on one another.
In
Horizontal Pivot.
The arms may pivot horizontally around the sliders to provide user origination points for actuators (800,802) closer or further apart from each other for different exercises. In one embodiment, track (402) pivots, thus allowing arm (702) to pivot.
Concentric Path.
In order for cable (501) to operate properly, bearing high loads of weight, and allow the track to rotate, it should always remain and travel in the center of track (402), no matter which direction arm (702) is pointed or track (402) is rotated.
Arm Mechanical Drawings.
In one embodiment, the user origination point (704) is a configurable “wrist” to allow local rotation for guiding the cable (500, 501).
Stowing.
Stowing arms (700, 702) to provide a most compact form is disclosed. When arm (702) is moved down toward the top of the machine as described above, and pivoted vertically until is flush with the machine as described above, the machine is in its stowed configuration which is its most compact form.
Range of Motion.
An exercise machine such as a strength training machine is more useful when it can facilitate a full body workout. An exercise machine designed to be configurable such that it can be deployed in a number of positions and orientation to allow the user to access a full body workout is disclosed. In one embodiment, the exercise machine (1000) is adjustable in three degrees of freedom on the left side, and three degrees of freedom on the right side, for a total of six degrees of freedom.
As described above, each arm (700, 702) may be translated/moved up or down, pivoted up or down, or pivoted left and right. Collectively, this wide range of motion provides a substantial footprint of workout area relative to the compact size of machine (1000).
Arm Sensor.
Wiring electrical/data connectivity through a movable arm (700, 702) is not trivial as the joint is complex, while sensors to measure angle of an arm are useful. In one embodiment, an accelerometer is placed in the arm coupled to a wireless transmitter, both powered by a battery. The accelerometer measures the angle of gravity, of which gravity is a constant acceleration. The wireless transmitter sends this information back to the controller, and in one embodiment, the wireless protocol used is Bluetooth.
For manufacturing efficiency, one arm is mounted upside down from the other arm, so control levers (732) in either case are oriented inwards. As the two arms are thus mirror images of one another, the signals from the accelerometer may be distinguished based at least in part because the accelerometer is upside down/mirrored on one opposing arm.
Differential.
This configuration of sun gears (204, 206) and planet gear (205) operates as a differential. That is, sun gears (204, 206) rotate in a single vertical plane around shaft (210), whereas planet gear (205) rotates both in that vertical plane, but also horizontally. As described herein, a differential is a gear box with three shafts such that the angular velocity of one shaft is the average of the angular velocities of the others, or a fixed multiple of that average. In one embodiment, bevel style gears are used rather than spur gears in order to promote a more compact configuration.
The disclosed use of sun gears (204, 206) and planet gear (205) and/or embedding the gears within other components such as sprocket (201) permit a smaller size differential for dividing motor tension between cables (500) and (501) for the purposes of strength training.
As shown in
In one embodiment, each planet and sun gear in the system has at least two bearings installed within to aid in smooth rotation over a shaft, and the sprocket (201) has at least two bearings installed within its center hole to aid in smooth rotation over shaft (210). Shaft (210) may have retaining rings to aid in the positioning of the two sun gears (204, 206) on shaft (210).
In one embodiment, spacers may be installed between the sun gears (204, 206) and the sprocket (201) on shaft (210) to maintain the position of the sun gears (204, 206). The position of the planet gears (205, 207) may be indexed by the reference surfaces on the cage (200) holding the particular planet gear (205, 207), with the use of either spacers or a built in feature.
Differential Mechanical Drawings.
Together, the components shown in
The use of a differential in a fitness application is not trivial as users are sensitive to the feel of cables. Many traditional fitness solutions use simple pulleys to divide tension from one cable to two cables. Using a differential (200) with spools may yield a number of benefits and challenges. An alternative to using a differential is to utilize two motor or tension generating methods. This achieves two cables, but may be less desirable depending on the requirements of the application.
One benefit is the ability to spool significantly larger amounts of cables. A simple pulley system limits the distance that the cable may be pulled by the user. With a spool based configuration, the only limitation on the length of the pull is the amount of the cable that may be physically stored on a spool—which may be increased by using a thinner cable or a larger spool.
One challenge is the feel of the cable. If a user pulls a cable and detects the teeth of the gears passing over one another, it may be an unpleasant experience for the user. Using spherical gears rather than traditional straight teeth bevel gears is disclosed, which provides smoother operation. Metal gears may be used, or plastic gears may be used to reduce noise and/or reduce the user feeling of teeth.
Cable Zero Point.
With configurable arms (700, 702), the machine (1000) must remember the position of each cable (500, 501) corresponding to a respective actuator (800, 801) being fully retracted. As described herein, this point of full retraction is the “zero point”. When a cable is at the zero point, the motor (100) should not pull further on that cable with full force. For example, if the weight is set to 50 lbs, the motor (100) should not pull the fully retracted cable with 50 lbs as that wastes power and generates heat.
In one embodiment, the motor (100) is driven to reduce cable tension instead to a lower amount, for example 5 lbs, whenever the end of the cable is within a range of length from the zero point, for example 3 cm. Thus when a user pulls on the actuator/cable that is at the zero point, they will sense 5 lbs of nominal tension of resistance for the beginning 3 cm, after which the intended full tension will begin, for example at 50 lbs.
In one embodiment, to determine the zero point upon system power-up the cables are retracted until they stop. In addition, if the system is idle with no cable motion for a pre-determined certain amount of time, for example 60 seconds, the system will recalibrate its zero point. In one embodiment, the zero point will be determined after each arm reconfiguration, for example an arm translation as described in
Cable Length Change.
In order to determine when a cable is at the zero point, the machine may need to know whether and how much that cable has moved. Keeping track of cable length change is also important for determining how much of the cable the user is pulling. For example, in the process demonstrated in
In a preferred embodiment, to keep track of cable length change the machine has a sensor in each of the column holes (405) of
In practice, a user retracts and replaces pin (404) only when the cable is fully retracted since any cable resistance above the slider and arm weight matching resistance as described above makes it quite physically difficult to remove the pin. As the machine (1000) is always maintaining tension on the cable in order to offset the weight of the slider plus arm, as the slider moves up and down, the cable automatically adjusts its own length. After the pin is re-inserted, the machine re-zeroes the cable length and/or learns where the zero point of the cable is.
In an alternate embodiment, the sensor is in pin (404) instead of holes (405). In comparison to the preferred embodiment, the physical connections between holes (405) and electronics bay (600) still exist and signals are still generated to be sent to electronics bay (600) once pin (404) is removed or reset. One difference is that the signal is initiated by pin (404) instead of by the relevant hole (405). This may not be as efficient as the preferred embodiment because holes (405) still need to transmit their location to electronics bay (600) because of system startup, as if the hole (405) were not capable of transmitting their location, the machine would have no way of knowing where on track (402) slide (403) is located.
In one embodiment, using hole sensors (405) is used by the electronics (600) to determine arm position and adjust torque on the motor (100) accordingly. The arm position may also be used by electronics (600) to check proper exercise, for example that the arm is low for bicep curl and high for a lat pulldown.
Cable Safety.
When a user has retracted cable (501), there is typically a significant force being applied on slider (403) of
Without a safety protocol, if a user were able to begin removing pin (404) while, for example, 50 lbs of force is being applied to cable (501), a race would ensue between the user fully removing pin (404) and the machine reducing tension weight to 5 lbs. As the outcome of the race is indeterminate, there is a potentially unsafe condition that the pin being removed first would jerk the slider and arm suddenly upwards with 50 lbs of force. In one embodiment, a safety protocol is configured so that every sensor in holes (405) includes a safety switch that informs the electronics bay (600) to reduce motor tension to a safe level such as 5 or 10 lbs. The electrical speed of such a switch being triggered and motor tension being reduced is much greater than the speed at which the slider would be pulled upward against gravity.
In a preferred embodiment, the removal of the locking pin (404) causes the system to reduce cable tension to the amount of tension that offsets the weight of the slider and arm. This allows the slider and arm to feel weightless.
Wall Bracket.
To make an exercise machine easier to install at home, in one embodiment the frame is not mounted directly to the wall. Instead, a wall bracket is first mounted to the wall, and the frame as shown in
Compactness.
An advantage of using digital strength training is compactness. The system disclosed includes the design of joints and locking mechanisms to keep the overall system small, for example the use of a pancake motor (100) and differential (200) to keep the system small, and tracks (400) and sliders (401) to keep arms (700) short.
The compact system also allows the use of smaller pulleys. As the cable traverses the system, it must flow over several pulleys. Traditionally fitness equipment uses large pulleys, often 3 inches to 5 inches in diameter, because the large diameter pulleys have a lower friction. The disclosed system uses many 1 inch pulleys because of the friction compensation abilities of the motor control filters in electronics box (600); the friction is not perceived by the user because the system compensates for it. This additional friction also dampens the feeling of gear teeth in the differential (200).
Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.