Patent Grant
9526977
The present inventions relate to personal transportation devices including powered skating devices.
The motorized skates known to the art are largely operated manually by means of a throttle, joystick, foot switch or other manual controls. U.S. Pat. Publ. No. 2003/0141124 to Mullet, U.S. Pat. No. 7,204,330 to Lauren and U.S. Pat. No. 5,829,543 to Diaz and many others disclose a motor mechanically connected to a wheel of the skate by gears, belts, cables or other indirect mechanical couplings, where the motor is controlled by the rider by means of a hand throttle or other manual speed control means. The skating devices known to the art, both without motors or with motors with manual speed control, have the disadvantage of requiring considerable skill and practice to utilize effectively and are not stable and controllable enough to be widely used with safety in a environment where significant other foot or vehicle traffic is present.
U.S. Pat. No. 6,059,062 to Staelin and U.S. Pat. No. 7,481,291 to Nishikawa teach a skate with motors and a means to modify the operation in response to weight transfer. Directly controlling the motor on each skate by weight transfer commonly causes motor action in response to normal skating or stepping actions where weight shifts forward and back on each foot. So when this approach to motor control is used, the skates often work against each other or work inappropriately if the rider does not keep their feet close together or if the rider attempts to step or skate.
U.S. Pat. Publ. No. 2006/0170174 to Hiramatsu and U.S. Pat. Publ. No. 2006/0213711 to Hara and U.S. Pat. No. 6,050,357 to Staelin et al. and U.S. Pat. No. 7,138,774 to Negoro et al. and U.S. Pat. No. 5,487,441 to Endo et al and other similar references all disclose skateboards with load sensors. These methods allow a rider to control a skateboard by leaning, or by shifting weight forward or backwards. However, these techniques are not suitable for use in skates for the same reasons as described above.
A further disadvantage of motorized skates known to the art is the presence of gears, cogs, belts, chains or other indirect torque transfer methods that introduce friction and sufficient energy loss such that the wheels to which the motors are coupled are not capable of freewheeling in a practical manner. This means that skating without assistance from the motor is not practically possible due to the drag effect from the motor. U.S. Pat. No. 6,428,050 to Brandley discloses a skate with a motor consisting of a rotor that is also the wheel of the skate and a stator that is located outside. However, the small amount of magnetic coupling provided between rotor and stator will severely limit the torque possible from such a motor.
Aspects of the invention relate to a powered skate with automatic motor control. In one embodiment, the invention relates to a system for controlling powered skates, the system including a pair of powered skates, each including a foot platform configured to receive a foot of a rider, a plurality of wheels coupled to the foot platform, a motor coupled to at least one of the plurality of wheels, the motor configured to rotate the at least one wheel, and a load sensor coupled to the foot platform and configured to sense an applied force, and a controller coupled to each of the motors and to each of the load sensors, the controller configured to control each of the motors, using a single algorithm, based on signals received from each of the load sensors.
In another embodiment, the invention relates to a system for controlling powered skates, the system including a powered skate including a foot platform configured to receive a foot of a rider, a front wheel coupled to the foot platform, a rear wheel coupled to the foot platform and positioned closer to an area of the foot platform for receiving a heel of the rider than the front wheel, a hub motor coupled to at least one of the front wheel and the rear wheel, the hub motor configured to rotate the at least one of the front wheel and the rear wheel, and a load sensor coupled to the foot platform and configured to sense an applied force, and a controller coupled to the hub motor and to the load sensor, the controller configured to control the hub motor based on a signal received from the load sensor.
In yet another embodiment, the invention relates to a system for controlling powered skates, the system including a powered skate including a foot platform configured to receive a foot of a rider, a plurality of wheels coupled to the foot platform, and a motor coupled to at least one of the plurality of wheels, the motor configured to rotate the at least one wheel, a motion sensor coupled to a body of the rider and configured to sense motion, and a controller coupled to the motor and to the motion sensor, the controller configured to control the motor based on a signal received from the motion sensor.
In still yet another embodiment, the invention relates to a method for controlling powered skates, the method including providing a pair of powered skates, each including a foot platform configured to receive a foot of a rider, a plurality of wheels coupled to the foot platform, a motor coupled to at least one of the plurality of wheels, the motor configured to rotate the at least one wheel, and a load sensor coupled to the foot platform and configured to sense an applied force, and controlling, using a controller coupled to each of the motors and to each of the load sensors, each of the motors, using a single algorithm, based on signals received from each of the load sensors.
Various embodiments of the invention are described herein. Some embodiments of the invention include a pair of skates where each skate has sensors and a motor that turns at least one of its wheels; and at least one controller which changes the signals applied to both motors in response to input from the sensors.
In some other embodiments of the invention, the controller receives signals from the load sensors on skate 1, the load sensors on skate 2 and motion sensors on the rider's body 22, determines the desired torque for each motor, and sends signals to the motors on skate 1 and skate 2. In some other embodiments, the controller may also use signals from other sensors 23 to determine the desired torque for each motor.
In the embodiment illustrated in
In the embodiment illustrated in
1. Stopped mode to Skating mode (S7): if a skating action is detected making the speed of either of the skates above a certain speed threshold Sth1 (S8);
2. Skating or Braking to Stopped mode (S13): if the speed of both skates is below a threshold, Sth3 (S15);
3. Skating or Speed Control to Braking mode (S16): if the position of the rider's Zero Moment Point is behind a threshold ZMPth (S9); and
4. Skating to Speed Control mode (S10): if the absolute value of the difference between the measured speed of the two skates is less than a speed threshold Sth2 (S11).
The initial operating mode of the controller when it is first powered up can be a Stopped mode (S1).
In other embodiments the controller has the following four modes of operation: Stopped, Skating, Braking, and Balancing. The controller can transition between operating modes when certain conditions are met, including, for example:
1. Stopped mode to Skating mode: if a skating action is detected;
2. Skating to Stopped mode: if the speed of both skates is below a threshold;
3. Skating to Braking mode: if the rider's weight is behind a threshold;
4. Skating to Balancing mode: if the rider is in, or is close to being in, an unstable position;
5. Braking to Balancing mode: if the rider is in, or is close to being in, an unstable position; and
6. Balancing mode to Skating mode: the rider is in a sufficiently stable position.
In certain embodiments the controller has the following three modes of operation: Stopped, Skating, and Braking. The controller can transition between operating modes when certain conditions are met, including, for example:
1. Stopped mode to Skating mode: if a skating action is detected;
2. Skating or Braking to Stopped mode: if the speed of both skates is below a threshold; and
3. Skating to Braking mode: if the rider's weight is behind a threshold.
It is to be understood that the term controller refers to the means of generating outputs such as current in the motor windings or torque from sensor inputs such as motion or force. There are many means known to the art to implement such a controller, and any of them may be used with this invention. Examples include software executing a microprocessor or Digital Signal Processor (DSP) or functions programmed into a Field Programmable Gate Array (FPGA) or in hardware such as analog circuitry or an Application Specific Integrated Circuit (ASIC) or a combination of more than one of these connected together.
In certain embodiments the controller includes three digital signal controllers (DSCs), one on each powered skate and one on the battery enclosure on the rider, that all communicate with each other using a Controller Area Network (CAN). The controller is distributed among software executing on the different DSCs.
In certain embodiments, a controller on the battery enclosure operates as a master controller and controllers on each of the skates operate as slave controllers. Each slave controller receives signals from the sensors on that skate and can perform some processing such as digital filtering before passing the resulting sensor information to the master controller. Each slave controller further receives signals from the master controller that causes said slave controller to send signals to the motor to cause it to generate torque as commanded by the master controller. The master controller uses a single algorithm to determine the torque for both skates.
In certain embodiments, the controller has a Skating mode of operation in which the controller causes the motors to freewheel, producing (S30, S31) zero torque on both skates, and therefore not resist motion of the skates. This allows the rider to skate in the same manner as conventional skates without motors.
In certain embodiments, the controller causes the motor to freewheel by causing no current to flow in the motor windings. If the motor is a hub motor, in many cases, the friction resulting from the motor freewheeling may be negligible.
In certain embodiments, where motor friction is not negligible, the controller causes each skate's motor to generate torque in the direction of motion that simulates freewheeling by overcoming friction so that the rider's foot experiences closer to zero net force from the skate in the direction of rolling. In such case, no acceleration is caused by this freewheeling torque and the rider perceives the result as frictionless skating.
In certain embodiments, the controller has a Skating mode of operation in which the controller causes the motors to freewheel except when a certain stage of the skating action is detected, during which it causes one or both of the motors on the skates to generate forward torque.
A skate forward push is part of the normal skating action and is typified by the rider transferring weight from the rear foot to the front foot while pushing backwards and outwards on the rear foot.
In certain embodiments, the controller detects the stage of the skating action where the rider performs a normal roller skating forward push and causes the motors to generate additional torque in response.
In certain embodiments, the controller detects the stage of the skating action where the rider performs a normal roller skating forward push and changes parameters used to generate torque while the push is in progress.
In certain embodiments, the controller detects a skate push by comparing several measured values to thresholds. In certain embodiments, the controller detects a skate push by comparing relative speed of the two skates, weight on a skate and rate of change of weight on a skate to thresholds, for example:
IF (S1−S2>St) AND (dW1>dWt) AND (W1>Wt) THEN SkatePush=1
ELSE IF (S2−S1>St) AND (dW2>dWt) AND (W2>Wt) THEN SkatePush=2
ELSE SkatePush=0
where S1 is the speed of skate 1, S2 is the speed of skate 2, W1 is the weight on skate 1, W1 is the weight on skate 2, dW1 is the rate of change of the weight on skate 1, dW1 is the rate of change of the weight on skate 2, and St, Wt and dWt are threshold values for the respective parameters. In such case, SkatePush=1 indicates that a push action is detected with skate 1 being the receiving skate and SkatePush=2 indicates that a push action is detected with skate 2 being the receiving skate and SkatePush=0 indicates that no push action is detected.
In certain embodiments, the controller has a Stopped mode of operation in which the controller causes the motors to generate torque to resist motion of the skates. This Stopped mode of operation can allow the rider the stand or take steps without unintentionally causing a skate to roll away from a stable position. It is not necessary to completely prevent the skates from moving to provide this benefit, but enough resistance can be created to allow the rider to balance themselves.
In certain embodiments, the motor torque that generates this motion resistance is calculated for each skate independently based on wheel position relative to a fixed position reference. The fixed position reference may be the recorded position of the wheel when the Stopped mode was entered. The wheel position may be determined from a wheel position sensor such as the magnetic encoder on the hub motor. In such case, it can be necessary to take into account full turns of the wheel when using such an encoder.
In some embodiments, when in stopped mode (S24), the torque that the controller causes the skate to generate to cause the motion resistance for that skate is calculated (S25, S26) proportionally to the measured speed of said skate:
T=−K·S
where T is the torque for the skate, S is the measured speed of the skate, and K is a constant chosen to produce the desired level of resistance.
In certain embodiments, the torque used to cause the motion resistance is calculated using a Proportional plus Derivative (PD) rule based on the position and speed of the wheel. For example:
T=K1·(X−Xs)+K2·dX/dt
where T is motor torque, X is wheel position and Xs is the position reference and K1 and K2 are constants that depend on the implementation. In certain embodiments, K1 may equal zero such the skate only resists movements while it is in motion. In certain embodiments, the position used to determine torque has a Dead Zone, where K1 is 0 for small values of (X−Xs). In certain embodiments, the position reference Xs is altered to limit the maximum torque requested.
It is to be understood that the torque required to cause the disclosed motion resistance effect can be calculated using a variety of methods known to the art, of which the above are simply examples of some of those methods.
In some embodiments, the controller passively generates the motion resistance torque by the causing the motor driver to connect both ends of a winding together such that whatever current is generated by the motor turning continues to circulate in the winding and therefore generates torque to oppose the motion. This method has the advantage of not requiring power to be drawn from the battery.
In some embodiments, the controller switches between actively and passively resisting motion, for example, the motion resistance becomes passive after being in Stopped mode for a certain amount of time.
In certain embodiments, the controller also causes the motor to apply torque to resist motion of the skate in the reverse direction regardless of the operating mode.
A system that tilts can be actively balanced by regulating the tilt to near the vertical position, which is well known to be achieved by a control law with a proportional plus derivative action. However, a system that does not tilt, for example a rider on platform such as a skateboard or roller-skate, generally must be treated more like a rigid body. An appropriate concept to the balancing of rigid bodies is that of Zero Moment Point. It is to be understood that the term ‘Zero Moment Point’ and its abbreviation ‘ZMP’ are taken to mean the point on the surface of the Foot Platform where the effect of all the forces acting on the rider from the platform can be replaced by a single force. This is consistent with the industry use of the term ZMP as defined by Vukobratovic and Borovac (‘Zero-Moment Point’ in international journal of humanoid robotics. Vol. 1, No. 1 (2004) 157-173), which is incorporated herein by reference in its entirety.
For example, when the platform is at rest, the ZMP on the platform's surface is the point vertically below the rider's center of mass, meaning that the moment about that point on the platform's surface is zero. If the rider's foot is secured to the platform and the ZMP is outside of the ground contacting elements of the platform, for example, in front of the front-most wheel, then the platform will tip over. The control problem of balancing a rider on a platform is therefore the problem of maintaining the ZMP within the zone of stability within the ground contacting elements.
In some embodiments, controller sends signals to the motor on a skate to generate torque to resist acceleration when the direction of the acceleration of that skate is currently towards a position that will make the rider unstable.
For example, when the ZMP on a skate is in a forward end of the skate, and the skate is accelerating in the reverse direction, the rider would perceive this as having the foot slip backwards in an unintended way. In this example, if the skate moves far enough in the reverse direction, then the rider's leg will pivot forwards and be unable to support weight, lifting the rear of the skate off the ground. The controller can determine whether acceleration is in the direction that will make the rider unstable by comparing the acceleration and ZMP of each skate to certain thresholds.
In some embodiments, the additional torque T that the controller causes to be generated at one of the skates is determined as a predetermined function M of both acceleration and the location of the rider's ZMP on that skate:
T=M(A,Z)
where Z is the ZMP of the skate with acceleration A. An example for the function M may be represented in pseudo code as follows:
IF A1>th1 AND ZMP1<th2 THEN
T=k·(A−Ath1)
IF A1<th3 AND ZMP1>th4 THEN
T=k·(A−Ath3)
where Ath1 is a forward acceleration threshold and Ath3 is a negative acceleration threshold and th2 is a ZMP threshold near the rear of the skate and th4 is a ZMP threshold near the front of the skate and k is a scaling factor that depends on the specific embodiment.
In some embodiments, the controller calculates the measured values of acceleration by means such as differentiation or Kalman filtering. In other embodiments, the values used for A-th1 and A-th3 may be estimated as the difference between the skate's measured or calculated speed and a rate limited version of that same speed.
In certain embodiments, the main controller sums one torque value for each skate, which it may have calculated by function M to resist acceleration when the direction of the acceleration of that skate is currently towards a position that will make the rider unstable, with another torque value which the main controller has calculated using other algorithms, such as from the process illustrated in
In some embodiments, the skate system includes a sensor system for measuring the motion of the rider's upper body. The controller receives signals from the motion sensor system and in response sends signals that cause torque in the motors.
In some embodiments, the skate system includes a sensor system for measuring the angle or angular rate of change of the rider's upper body. The sensor system can be affixed to the rider's body in a location where the angle or angular rate of the sensors will substantially match that of the rider's torso.
In one embodiment, the sensor system is fixed within an enclosure (e.g., component 6 in
In some embodiments, the sensors are configured to measure angle in the forward-reverse direction, and in other embodiments, the sensors are further configured to also measure angle in the side to side direction. In some embodiments the angle sensor is a micro electro-mechanical (MEMS) gyroscope that measures angular rate. In some embodiments the motion sensor is a accelerometer that measures force due to gravity in at least one axis to determine how far the rider's upper body has tilted in the forward-reverse direction from the vertical position or some reference position.
In some embodiments the motion sensor system is a combination of a gyroscope and an incline sensor or acceleration sensor. Multiple sensor readings may be combined into a single measurement of tilt, and also possibly a measurement of tilt rate of change. Many means of combining multiple angular sensors into a single measurement are well known to the art, including a Kalman filter. It is to be understood that other equivalent means of measuring angle or angular rate or tilt may be used.
It is to be understood that motor torque, motor current and motive force are closely related by the physics of the structure of the vehicle, and therefore disclosure of control methods that use motor torque should also be understood to also disclose the same methods using motor current or motive force.
In some embodiments and as discussed above, the controller has a Braking Mode, in which the controller causes reverse torque to be generated by the motors to slow the rider's forward motion.
In some embodiments, the controller enters Braking mode when the rider's ZMP across both skates in the forward-reverse direction passes behind a threshold ZMPth (S9). The ZMP can be filtered by a low pass filter such that fluctuations or short movements in the rider's ZMP do not cause the controller to enter Braking mode. In some embodiments, this ZMP filter has a corner frequency of 1 Hz.
In some embodiments, the overall ZMP across both skates is determined as follows (S6):
Zboth=(ZMP1·W1+ZMP2·W2)/(W1+W2)
where Zboth is the combined ZMP, ZMP1 is the ZMP of the rider on skate 1, ZMP2 is the ZMP of the rider on skate 2, W1 is the weight on skate 1 and W2 is the weight on skate 2. In some embodiments, the controller only needs to calculate Zboth if it is in skating the speed control modes (S5). In some embodiments, the controller may enter Braking mode in response to the rider's torso lean passing behind a threshold.
In some embodiments, the controller enters braking mode in response to detecting that the rider is lifting the front wheel on one skate while still having weight on it and is also leaning back (S12). This may be implemented using the following comparisons:
((ZMP1<ZMPth AND W1>Wth) OR (ZMP2<ZMPth AND W2>Wth)) AND Ang<AngTh
where ZMP1 is the ZMP of the rider on skate 1, ZMP2 is the ZMP of the rider on skate 2, W1 is the weight on skate 1 and W2 is the weight on skate 2, Wth is a threshold indicating that at least some weight is on that foot, Ang is the torso angle of the rider, and AngTh is a torso angle threshold that indicates a backward lean. The thresholds used in this comparison may be set so that the detected posture is similar to the one adopted by a rider attempting to use the heel brake of a conventional inline skate.
In some embodiments, once braking mode has been entered, the controller can return to skating mode in response to measurements including the lean angle of the rider exceeding a certain threshold in the forward direction, or the rider's ZMP passing in front of a threshold, or the rider's lateral weight distribution passing outside certain thresholds. In other embodiments, such as that represented by
In some embodiments, when in braking mode (S20), the controller calculates the total required torque using a function of rider angle and rider angle threshold (S21), as follows:
Tboth=F(Ang,Angth)
where Ang reflects rider body angle, Angth is a rider body angle threshold reflecting the rider's body angle in an approximately upright position and F is a function. Function F may be a linear factor of distance from the threshold as follows:
F(Ang,Angth)=K·(Ang−Angth)
where K is a predetermined constant.
In some other embodiments, the function F may have other parameters, such as the time derivative of the rider body angle and may implement a PD control system. The control problem of balancing a rider on a mobile platform by applying force at the ground and measuring angle is well known to those skilled in the art of control systems, and is often called the inverted pendulum, and numerous control systems can be applied, including Proportional+Derivate (PD), optimal Linear Quadratic Regulator (LQR) and Model Predictive Control (MPC).
In some embodiments, when the controller is causing the motors to provide torque, the controller changes the distribution of torque across the two skates in response to certain measured parameters. Examples of when this might be beneficial is if most of the rider's weight was substantially on one foot during a stepping or skating action.
In certain embodiments, the torque between the two skates is allocated such that the total torque produced is a value that the controller has previously determined by one or a combination of methods, such as those disclosed herein.
In some embodiments, the controller changes the distribution of torque across the two skates in response to weight distribution across the two skates. For example, the torque distribution may be determined as follows (S27):
P=W1/(W1+W2)
where P is a proportion of torque allocated to skate 1 and W1,W2 reflect a weight on skates 1 and 2, respectively. The P value may then be used as follows (S28, S29):
T1=P·Tboth
T2=(1−P)·Tboth
where T1,T2 reflect the torque allocated to skate 1 and skate 2, respectively, and Tboth represents a total torque calculated by the controller.
The torque distribution may also be determined from a non-linear function of weight distribution, H, for example:
P=H(W1,W2)
The function H used can also depend on the mode of operation of the controller or on other measured inputs.
In some embodiments, the controller changes the distribution of torque across the two skates in response to the speeds of the two skates. For example, the allocation may depend on the difference in speed between the two skates such that more torque is applied to the slower skate causing them to be driven towards each other.
In some embodiments, the controller changes the distribution of torque across the two skates in response to changes in the relative position of the two skates. For example, the allocation may depend on the difference in position between the two skates such that more torque is applied to the rearward skate causing them to be driven towards each other. The controller may determine the relative position of the skates by using the rotation sensors to determine how far each skate has moved from a reference position.
In some embodiments, the controller allocates a total torque across the two skates in response to what stage the rider is at of the skating action.
The total torque that the controller causes the two motors to apply may be determined by a variety of means, such as a combination of those described previously, and may also depend on the mode of operation of the controller.
In some embodiments, the controller has a speed control mode of operation where it causes at least one motor to generate torque to control the speed of the rider to a certain speed. The speed of each skate may be measured directly by means of a speed sensor, or it may be calculated from other measurements, using methods well known to the art, which may include the motor's rotor position, the motor's rotor's magnetic field, or voltages generated in the motor windings.
In embodiments where there are two skates, the rider speed is determined by a combination of the speeds of the two skates. In some embodiments, this combination is the mean value (S14). In other embodiments, this combination is a weighted average weighted by the load (e.g., weight) measured on each skate. In some conditions, this combined speed may just be the speed of one of the skates, for example if the other is lifted off the ground.
In the embodiment illustrated in
Tboth=G(S1,S2,Ssp)
The relationship represented above as G that the controller applies between the combined motor torque and the speed set point and the measured or calculated speed can have other inputs or other state and can reflect any of a number of control systems for speed control well known to the art, including methods such as Proportional+Integral+Derivative control or Model Predictive Control. The rate at which the controller permits the speed to change may be limited using ramp-up and ramp-down methods well known to the art.
In some embodiments, where the combined speed of the skates exceeds the speed set point (e.g., such as when descending a hill), the controller causes reverse torque to be applied by the skate motors resulting in a braking action. In some embodiments, the braking action is regenerative resulting in power being stored into the battery.
In some embodiments, the controller sets the speed set point, and enters and exits the speed control mode when it detects certain phases of the skating action. For example, the controller may enter speed control mode when the difference between the weights measured in each skate is less than a threshold; and, upon entering speed control mode, also set the speed set point to the current rider speed (S19). For example, the controller may enter speed control mode when the following condition is met (S11):
ABS(S1−S2)<Sth2
where S1 and S2 reflect the speeds of each skate, and Sth2 is a speed threshold. In some embodiments, this speed threshold is a value in the range of about 0.05 to about 0.5 meters/second or m/s. In some embodiments this speed threshold is about 0.1 m/s.
In some embodiments, he controller can leave speed control mode when the difference between the weights measured in each skate is greater than another threshold. The controller may calculate the thresholds for entering and leaving speed mode as a proportion of the total rider weight.
In some embodiments, the speed set point may be set or adjusted by means of user input, such as from a remote control, a knob, a wireless signal from a hand-held computing device or other form of user interface known to the art. For example, a hand held control box with two buttons may be used by the rider to adjust the speed set point, where pressing one button causes an increase in speed set point, while pressing the other button causes a decrease. The hand held control box may be wired to the controller or it may use wireless communications.
The controller may also enter or leave speed control mode in response to an external signal, such as from a button, a remote control, a hand switch, a wireless signal from a hand-held computing device or other form of user interface known to the art.
This manual control of the speed control mode and set point may be employed in situations where constant speed is desired, such as when making a motion picture or other video recording.
In some embodiments, the controller increases the speed set point while in speed control mode upon detecting specific rider actions. For example, the rider leaning forward with both feet on the ground causes the controller to increase the speed set-point.
In some embodiments, when the controller is in Speed Control mode (S17), the speed set point may be adjusted as follows (S18, S19):
IF W1>Wth AND W2>Wth AND Ang<AngTh THEN
Ssp=Ssp+Sdelta
where W1,W2 reflect the weight on skates 1 and 2 respectively, Wth is a threshold indicating that at least some weight is on that foot, Ang reflects the body angle of the rider, AngTh is a body angle threshold that indicates a forward lean, Ssp is the speed set point, and Sdelta is a preselected change in Ssp over a preselected sampling interval.
In some embodiments, each skate's ZMP is compared to a threshold to determine if the speed set point should be adjusted. The ZMP comparison may be done in addition to the weight and angle comparisons, or may replace the weight comparison as follows:
IF ZMP1<ZMPth1 AND ZMP2<ZMPth1 AND ZMP1>ZMPth2 AND ZMP2>ZMPth2 AND Ang<AngTh THEN
Ssp=Ssp+Sdelta
where ZMP1 reflects the ZMP of the rider on skate 1, ZMP2 reflects the ZMP of the rider on skate 2, ZMPth1 and ZMPth2 are ZMP thresholds that can be set such that they reflect a condition where the rider is in a stable and centered position, Ang is the torso angle of the rider, AngTh is a torso angle threshold that indicates a forward lean, Ssp is the speed set point, and Sdelta is the change in Ssp over the preselected sampling interval.
In most embodiments, the coupling between the upper and lower platforms does not distort under load substantially so that the two platforms do not tilt appreciably relative to each other. In some embodiments, the load sensors are of a type such that each is substantially sensitive to only vertically oriented loads. In other embodiments, the load sensors are disposed such that they are only substantially subject to vertically oriented loads, while loads in the lateral or forward/reverse directions being carried by other support members (not shown).
The load sensors 45 and 46 are illustrated as disposed above the chassis 42, but they may also be disposed within or below the chassis and attached to the foot platform 43 by vertical members that are not themselves supported by the chassis.
In some embodiments, a brake 47 is attached to the chassis. The brake can operate in the manner of rear skate brakes known to the art. The brake 47 is disposed along the chassis 42 such that if the entire skate is tilted backwards, the bottom of the brake will contact the ground surface and the resulting friction resists motion. It is understood that structures implementing any of the braking methods for skates known to the art can be used here.
The coupling between the wheels and the platform may use a vertical force sensing coupling. The vertical force sensing coupling is an assembly of parts that is substantially rigid in all directions and provides a measurement of force in substantially only the vertical direction. In some embodiments, the vertical force sensing coupling consists of a plurality of linear guides and a load cell that are all coupled between the front wheel and the platform. The linear guides can be constructed such that they do not transfer any substantial force in the vertical direction, while not allowing any rotation or any substantial movement in the horizontal plane. The load cells are therefore subject to substantially all of the vertical force supporting the platform.
In other embodiments, the vertical force sensing coupling has a hinge or other mechanical structure that provides support in the forward/reverse and lateral directions, and transfers substantially all of the vertical forces to a load cell or other force sensor.
It is to be understood that the term ‘load sensor’ can refer to any sensor assembly that gives a measurement the amount of force applied to it, a wide variety of which are known to the art. In some embodiments, the load sensor can include, without limitation: a strain gauge affixed to a structural member, pressure sensitive resistive material, a membrane switch with resistance that depends on pressure, piezoelectric material, and/or combinations thereof.
A variety of different foot restraining mechanisms can be employed to serve as the foot retention mechanism, including straps in a variety of configurations, with and without fasteners such as clasps, buckles, laces or hook-and-loop material; or a flexible material can partially envelope the foot in the manner of a shoe and be secured by straps or laces.
The foot platform 62 is a largely flat structure that is configured to fully support the rider's foot. The individual skates intended for the left and right foot of the rider may have the foot platform and straps disposed in the mirror image of each other to match the configuration of human feet.
In the illustrated embodiment the ankle straps may be fastened to the foot platform at different locations to allow fitting of various sized feet. In some embodiments, the rearward portion of the foot platform 62 and the ankle straps (60, 61) may be slidably disposed relative to the forward part of the Foot Platform and the Foot Straps to allow appropriate securing of feet of different sizes. In some embodiments, further ankle support members and a strap are attached to the foot platform.
The Chassis 63 is a supporting structure to which other elements are attached.
In the illustrated embodiment, the load sensors are implemented with four load cells 64 that are each fixed to the chassis at one end and the foot platform at the other end, such that in combination they provide the entire support for the foot platform, and such that in combination measure the entire weight applied to the foot platform. In some embodiments, the foot platform is rigid enough so that intended loads do not cause its shape to distort which may adversely affect the load sensor measurements.
In the illustrated embodiment, wheel 66 is rotationally coupled to the chassis in a position substantially to the right and rear of the rider's center of gravity and another wheel 68 is rotationally coupled to a platform in a position substantially to the left and rear of the rider's center of gravity. The rear wheels (66, 68) are rotationally coupled to the steerable truck 69. The steerable truck 69 is of a design well known to the art and widely used in roller-skates and skateboards; it is fixed to the chassis by two offset couplings, one permits rotation and one permits both lateral tilting and rotation, such that lateral tilting induced by lateral weight distribution causes a steering effect from the truck.
In the illustrated embodiment, the front wheel 65 is driven by a hub motor 67 that is coupled to the chassis 63 in a position in front rider's center of gravity and laterally substantially in the center of the platform. The hub motor 67 and the sensors are electrically connected to control electronics which are located within an electronics enclosure 70.
In other embodiments, the control electronics can be located at any of several suitable locations attached to the chassis. The control electronics can also be connected to a battery or batteries; the battery or batteries may be located at any of several locations attached to the chassis, or may be located remotely from the powered skate, for example, attached to the rider's back or belt.
The wheel configuration used in the illustrated embodiment of a powered frontward wheel with two laterally place rearward wheels has an advantage as compared to conventional skates which have the rear wheel powered. For the conventional skates, forward stepping or skate push action lifts the powered wheel off the ground after the un-powered wheels, such that there is normally no time during which the rider is pushing against an un-powered wheel. As a result of being un-powered, such a wheel on a conventional skate cannot provide speed control or resist destabilizing motion.
In some embodiments, a brake is attached to the rear of the skate such that it will contact the ground if the rider is sufficiently out of balance to lift the powered front wheel off the ground and cause a significant tilt of the skate. In some embodiments, the brake is attached to the rear of the steerable truck. In the embodiment illustrated in
The brake 71 can function to help prevent loss of balance of the rider when the motorized front wheel has lifted off of the ground. If this occurs while in forward motion, the friction of the brake on the ground will cause deceleration resulting in a forward shift of the rider's weight causing the motorized front wheel to resume contact with the ground.
In the embodiment of
In some embodiments there are four load sensors, each disposed substantially in one corner of the foot platform 87. In other embodiments there are three load sensors, one of which is in the lateral center at the front or rear. In other embodiments there are two load sensors, one to the front and one to the rear.
In some embodiments, the powered skate has two front wheels. In such case, either one or both of the front wheels is driven by a motor, either a directly coupled motor such as a hub motor or a motor indirectly coupled by means of a belt, chain or gears. The two front wheels and at least one rear wheel are rotationally coupled to a chassis. In some embodiments, the two front wheels are rotationally coupled to a steerable truck, which is coupled to the chassis.
It is to be understood that in some embodiments of this invention, the shape of the physical structures will vary, and that additional structures may be present to improve the cosmetic appearance beyond that represented herein or to provide additional functionality not discussed herein.
In some embodiments, the powered skate includes a hub motor. In such case, the hub motor has a stator that is fixed to the skate and a rotating part that is fixed to a ground contacting element and the rotating part is rotationally fixed to rotate around the outside of the stator. A hub motor is different from a conventional motor, in which the rotating part rotates inside the stator and transfers torque through a shaft.
In certain embodiments, a controller sends signals to the motor driver electronics, which cause current to flow in one or more of the windings to create torque in the direction required. The controller controls how current is applied to the windings by means of a sensor that measures voltages on the windings, or by a sensor that measures the rotational position of the rotor, or both.
In certain embodiments, the skate contains a sensor that measures the rotational position of the rotor which consists of a plurality of magnetic field sensors that are positioned near the motor's rotor in such a manner as to each sense a different portion of the magnetic fields created by the magnets. The magnetic field sensors may be located either inside or outside of the rotor.
In certain embodiments, the stator of the hub motor has a temperature sensor incorporated into it. The control system may alter the amount of current permitted to flow in the windings in response to temperature measurements.
The absence of any gears, belts, electrical brushes or other points of physical contact between the stationary and rotating parts except for the bearing can allow the wheel and motor to rotate during normal skating without absorbing significant amount of energy when it is not generating torque.
It is to be understood that a practical controller, for example one implemented within the software of one or more microcontrollers, will also contain a number of other elements, including but not limited to: communications, timing, data logging, user interface, power management and fault detection.
The digital communication link may be a wired multiple device network such as Controller Area Network (CAN), Inter-Integrated Circuit (I2C), differential serial communications of specification RS485, the digital communication link may be a direct logic level digital connection between the skates, the digital communication link may be a wireless digital connection between the skates such as Zigbee, Bluetooth or PSK modulated FM, or the digital communication link may be any of the other digital communications systems known to the art.
In certain embodiments, parts of the system including the battery or energy storage device are located remotely from the skate and attached to a different part of the body of the rider and transfers energy to and from the skate by means of at least a pair of wires.
In certain embodiments, the system includes a user input device such as a button or trigger that the user may use to provide signals to the controller. The controller may modify its operating state based on the user input.
In certain embodiments, the pair of skates contain at least one sensor to determine the position of the skates relative to each other. This sensor may be any of the distance or direction sensors known to the art including ultrasonic distance sensors, Radio Frequency direction sensors, optical or infrared imaging or detection sensors or magnetic sensors. The controller modifies the distribution of torque between the two skates based on their relative position.
It is to be understood that the embodiments described herein are merely exemplary and numerous modifications and variations will be apparent to those skilled in the art. All such modifications and variations are intended to be within the scope of the present inventions.
The present application claims priority to and the benefit of Provisional Application No. 61/617,635, filed Mar. 29, 2012, entitled “SKATING DEVICE WITH AUTOMATIC MOTOR CONTROL”, the entire content of which is incorporated herein by reference.
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