Source: http://www.freepatentsonline.com/7365463.html
Timestamp: 2019-10-19 22:11:14
Document Index: 357822533

Matched Legal Cases: ['art 1300', 'art 1300', 'art 1300', 'art 1300', 'art 1300', 'art 1300', 'art 1300']

United States Patent 7365463
A motor that delivers high force linear motion or high torque rotary motion to a moving element. The motor may include a driving brake, a driver, a holding brake and a flexible moving element. Operation of the motor may involve activating the holding brake, activating the driver to flex the moving element, activating the holding brake to maintain the position of a portion of the moving element, releasing the driving brake, and restoring the moving element to an unflexed position. The elements are arranged to provide linear motion, belt-driven rotary motion, or directly-coupled rotary motion using brakes and drivers arranged in linear or circular fashion. Drivers may be linear or rotary actuators or motors based on electrostatic, piezoelectric, magnetic, or electrostrictive properties. The brakes may be applied through electrostatic forces, magnetic forces, or mechanical gears engaged with a linear or rotary driving mechanism.
11/033368
242/410, 310/120
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1. A belted motor, comprising: a driven flexor belt under tension from a first direction and connected to a load; a stator, including: a driver mounted to repetitively reciprocatively deflect the flexor belt by a certain amount in a second direction transverse to the first direction; a first brake and a second brake acting directly on the flexor belt with the driver therebetween, the first brake that, when operationally configured, is positioned to clamp the flexor belt at a first point and with the second brake being released permits motion of the flexor belt when the driver deflects the flexor belt and wherein; the second brake when operationally configured, is positioned to clamp the flexor belt at a second point when the first brake is released permits motion of the flexor belt in the first direction when the driver no longer deflects the flexor belt, the first and second brakes having means for operating alternately to provide repetitive incremental motion to the driven flexor belt and to the load corresponding to the certain amount of repetitive reciprocative deflection of the flexor belt.
2. The motor of claim 1, further comprising an extremity operationally connected to the load, wherein the extremity is mobile when the belt moves in the first direction.
3. The motor of claim 1, wherein the stator further comprises: a tension gear that, when operationally configured, is coupled to the flexor belt applying tension thereto when the first brake is not clamping the flexor belt; and an output gear that, when operationally configured, is coupled to the flexor belt and to the load, wherein when the flexor belt moves in the first direction, the flexor belt rotates the output gear and the output gear pulls the load.
4. The motor of claim 3, wherein the second brake, when engaged, substantially halts movement of the output gear.
5. The motor of claim 3, wherein the belt includes first teeth and the tension gear includes second teeth, and wherein the first teeth engage the second teeth such that the tension gear is pulled by the movement of the belt.
6. The motor of claim 3, wherein the belt includes first teeth and the output gear includes second teeth, and wherein the first teeth engage the second teeth such that the output gear is pulled by the movement of the belt.
7. A motor comprising: a moveable flexor belt under tension in a first direction from a tension gear or roller and connected to rotate a rotatable output gear or roller, the moveable linear flexor belt communicating with first and second brakes that act directly on the flexor belt and are operable to apply braking force by a timing means for operating the first brake and releasing the second brake, then operating the second brake and releasing the first brake, then repeating the sequence; and a driver applying repetitive flexing to the flexor in a second direction transverse to the first direction only when one of the brakes is released in a manner that repetitively incrementably rotates the rotatable output gear or roller corresponding to repetitive flexing of the flexor.
8. The motor of claim 7 further comprising an extremity operationally connected to the output gear or roller wherein the extremity is rotationally mobile when the flexor moves in the first direction.
9. The motor of claim 7 wherein the driver is a linear actuator.
10. A motor driven extremity comprising: a flexor belt under tension from a drive gear or roller toward an output gear or roller in a first direction, the output gear or roller carrying an extremity; first and second braking means between the drive gear or roller and the output gear or roller, with each of the braking means alternately clamping and releasing the flexor belt; and a driver means coupled between said first and second braking means for repetitively moving a portion of the flexor belt that is not held by one of the braking means by a certain amount in a second direction transverse to the first direction, the tension from the drive gear or roller advancing the flexor belt toward the drive gear or roller in the first direction as the output gear or roller rotates an amount corresponding to the certain amount of movement of the driver means in the second direction.
11. The system of claim 10, wherein said driver means includes a linear actuator.
12. The system of claim 11, wherein said linear actuator is electrostatic.
13. The system of claim 11, wherein said linear actuator is electromagnetic.
14. The system of claim 10 wherein said driver means includes a cam actuator.
15. The system of claim 10, wherein said driver means includes an offset roller actuator.
16. The system of claim 10, wherein said driver means includes a bender actuator.
17. The system of claim 10, wherein said braking means includes a linear actuator.
18. The system of claim 17, wherein said linear actuator is electrostatic.
19. The system of claim 10, wherein said braking means includes a plurality of electrodes coupled to a conductive shaft.
20. The system of claim 10, wherein said braking means includes an actuator with gear teeth for engaging a pinch plate with gear teeth.
21. A motor driven extremity comprising: a flexor belt under tension fed from an output gear or roller carrying an extremity toward a drive gear or roller in a first direction and receiving impulsive force in a second direction transverse to the first direction; a first brake means for clamping and releasing the flexor belt at a first point and a second brake means for clamping and releasing the flexor belt at a second point, the clamping of one brake means for at least some time when the flexor belt is released by the other brake means; and a driver means for applying a certain amount of repetitive impulsive force to the flexor belt at a third point between the first point and the second point, the timing of impulsive force corresponding to the clamping by one of the brake means wherein impulsive force causes rotation of the output gear or roller carrying the extremity by an incremental amount.
22. The motor of claim 21 wherein the drive gear and the output gear or roller are reversible in roles wherein the first direction is reversed and the rotation of the output gear or roller is reversed.
This application claims priority to U.S. Provisional Application 60/642,398, entitled HIGH-TORQUE MOTOR, filed Jan. 7, 2005, which is hereby incorporated by reference.
With a standard DC motor, torque varies directly in proportion to the motor current. This relationship is expressed as a torque constant, KT, which may be in N-m per amp. The same constant relates voltage to rotation speed. In SI units, KV=KT, which may be in Volts/rad/s. A DC motor is normally designed with a single torque constant. This means the motor operating at a fixed power input cannot dynamically trade off speed for torque. Accordingly, manufacturers typically sell families of motors with different motor constants depending on whether the application needs high torque (high KT) or high speed (low KV). This is a significant drawback for applications that require relatively fast, low torque operations as well as slower, high torque example, imitate the modes of operation of human muscles, which allow the same arm to swat a fly (fast, low torque) and to lift a heavy weight (slow, high torque).
Standard electric motors typically operate at thousands of RPMs, and the range of typical motor constants does not extend down to the point where standard motors can deliver extremely high torque at low speed. In order to provide this capability, a reduction gear must be added to convert the motor's high speed and low torque into the desired low speed and high torque. Current reduction gearing techniques include spur gears, worm gears, pulleys and harmonic drive gears. All of these techniques decrease efficiency and have other undesirable characteristics including the addition of cost, weight, volume, and noise. Also, when an output shaft is driven through a high gear ratio, it is difficult to turn the output shaft when the motor is not powered. The absence of an unpowered free-movement mode is a significant disadvantage in some applications.
Between each pair of brakes (“Brake 1” and “Brake 2”) is a driver which, in an embodiment, acts primarily at right angles to the flexor to cause the flexor to bend or otherwise deflect. The driver may include a linear actuator, a motor with cam, a motor with offset rollers, a piezoelectric bender, or other technology that delivers a force to bend the flexor. A first step of operation involves activating both Brake 1 and the driver. The activation of the driver then bends the flexor and causes the part of the flexor near Brake 2 to move a small distance toward Brake 1. A second step involves activating Brake 2, and a third step involves releasing Brake 1 and deactivating the driver. During the third step, the flexor may be restored to its unbent position. The cycle then repeats with the first step to impart a repetitive linear or rotary motion to the flexor.
The amount of movement of load during each activation of the driver may be associated with the distance between the brakes and the amount of deflection of the flexor. When the deflection imparted by the driver is small compared to the distance between the brakes, the mechanical advantage is large, and a relatively weak driver force can move the free portion of the flexor a small distance against a strong load force resisting the movement. In this situation, the driver has a mechanical advantage against the load because the load is pulling at nearly right angles to the driving force. As the driver deflection distance increases, the driving force vector rotates and the component of the driving force vector opposing the load force increases, thereby decreasing the mechanical advantage. The mechanical advantage is approximately determined by the formula:
Mechanical_Advantage=11-cos⁡(θ),
When drivers or brakes are engaged, a force acts on the flexor. However, in an embodiment, when the drivers or brakes are disengaged, the force does not act on the flexor and the flexor is free to move, thus providing a “free movement mode.” Brakes may be implemented through electrostatics, magnetics, actuators with gears or brake pads, or other means. If the brakes are implemented using electrostatics, very little power is dissipated when holding in the active position, providing a low power locked mode as well as an “unpowered free movement mode.” Very little power is dissipated when moving slowly, because the flexor is held by the electrostatic brakes between driver activations.
Many driver technologies, including motors and piezoelectric benders, can operate in either an actuator (motor) mode or a generator mode. A motor constructed according to the technique described herein can sequence the brakes and motor phases in such a way as to extract energy from the movement of the load instead of supplying energy to move the load. The “generator mode” can be used in applications calling for regenerative braking to extend battery life or make the operation of the motor more efficient.
Thus, a motor may be constructed that provides high torque and allows the torque to be traded for speed at a given power level. In various embodiments, the motor may have low-power or unpowered modes to hold the current position, or to allow free movement.
FIGS. 3A to 3F depict conceptual diagrams of various driver technologies for use in various embodiments.
FIGS. 8A and 8B depict conceptual diagrams of forces on a motor according to respective embodiments.
FIGS. 9A and 9B depict conceptual diagrams of a motor according to an embodiment.
FIGS. 10A and 10B depict drawings of a rotary motor according to an embodiment.
FIGS. 11A to 11D depict conceptual drawings of a rotary motor in multiple states of operation according to embodiments.
In an embodiment, the input buffers 124 and output buffers 126 are used for receiving and sending signals or messages in a manner that is known in the art of computer engineering. In another embodiment, the analog-to-digital converter 128 may be logic that converts analog signals to digital signals in a manner that is well-known in the art of electronics.
In an embodiment, the memory 122 may include random access memory (RAM) and/or flash memory. In another embodiment, the memory 122 may include dynamic RAM (DRAM), static RAM (SRAM), flash memory, and/or non-volatile storage. The non-volatile storage is often a magnetic hard disk, an optical disk, or another form of storage for large amounts of data. Some of this data is often written, by a direct memory access process, into the memory 122 during execution of applications in, for example, RAM. One of skill in the art will immediately recognize that the terms “machine-readable medium” or “computer-readable medium” includes any type of storage device that is accessible by the processor 120 and also encompasses a carrier wave that encodes a data signal.
The system 100 is one example of many possible systems which have different architectures. A typical computer system will usually include at least a processor, memory, and a bus coupling the memory to the processor. In addition, the system 100 may be controlled by operating system software. One example of an operating system software is the family of operating systems known as Windows® from Microsoft Corporation of Redmond, Wash. Another example of operating system software is the Linux operating system. The file management system associated with an operating system is typically stored in the non-volatile storage and causes the processor 120 to execute the various acts required by the operating system to input and output data and to store data in memory 122, including storing files in non-volatile storage (if applicable).
Referring once again to FIG. 1, in operation, the controller 102 programmatically controls one or more of the other components based on inputs from the control panel 104. The power regulator 106 supplies power for the circuit from the power source 108. The controller 102 activates the motor 110 with the phase drivers 112. Output phases may be buffered by the phase drivers 112 and the buffered phases are sent to the motor 110. The phase drivers 112 outputs may be fed back to the controller 102 through the V/I sense circuit 114 to provide feedback. The feedback enables the controller 102 to determine when voltage or current have reached a threshold. In this way, the controller 102 may be able, for example, to limit the voltage or current to set a maximum torque of the motor 110. The feedback can also be used, for example, to determine the back-EMF of motor-based drivers to aid in the control of the motor 110.
The flexor 208 is a flexible “muscle” that, when flexed, acts to bend a limb, a flipper, or some other appendage at a joint. In the example of FIG. 2, the extremity 212 represents the appendage and the pivot point 214 represents the joint. The flexor 208 may be constructed from polymer film, such as polyester or polycarbonate, or some other material that can be bent by the force of the driver 202.
The driver 202, driving brake 204, and holding brake 206 may be referred to collectively as a stator 210. Thus, the motor 200 comprises the flexor 208 and the stator 210. The stator 210 may be thought of as the stationary part of the motor 200. The flexor 208 and stator 210 may be constructed from plastic films with conductive elements such as, for example, polyamide (e.g., Dupont Pyralux AP Kapton™ film) or polyester (Mylar™).
The performance of the motor 200 is related to the performance of the brakes. The maximum torque of the motor 200 should not be greater than the torque applied by either the driving brake 204 or the holding brake 206. Also, a maximum “pinch ratio” is determined partially by the amount of slip in the brakes which may become one of the limiting factors in high torque operations. As used herein, the pinch ratio (PRatio) is defined as the average rotational speed of the driver 202 divided by the average rotational speed of the output (at the pivot point 214).
The maximum speed of the motor 200 may be governed by the slower of the speeds at which the driving or braking forces can be applied. Hence, small improvements in the brakes can have a large impact on performance. Brakes generate braking forces in proportion to the coefficient of friction (COF) between the moving and stationary parts of the brake. Various materials and surface treatments can be used to increase the COF, thereby improving the performance of the brakes without increasing the force normal to the surface of the brakes.
At some point in time, the holding brake 206 may be activated to keep the flexor 208 in place while the driver 202 is retracted and the driving brake 204 released (to, for example, take out the “slack” in the flexor 208). When the driving brake 204 is released, the flexor 208 is restored to an unbent (e.g., unflexed) position. The restoring force may be supplied by the spring force in the flexor 208 material, by a mechanical linkage from the driver 202 that forces the slider to flatten as the driver 202 is deactivated, or by a second driver used to provide the restoring force.
It should be noted that the flexor 208 may be moved toward the left (in the direction of the arrow) or toward the right (in the opposite direction of the arrow). In the latter case, it may be necessary to swap the activation order of the brakes, effectively turning the driving brake 204 into a holding brake and the holding brake 206 into a driving brake. However, when moving towards the right, it is difficult to couple a large force to an output load because the force pushing to the right may exceed the force needed to buckle the flexor 208. In general, larger forces can be coupled when pulling on a flexible material than when pushing on the material. At an extreme, when the material is as flexible as, for example, a rope, the force that can be applied when pushing on a flexor of this material is inadequate for most applications.
FIGS. 3A to 3F depict conceptual diagrams of various driver technologies for use in various embodiments. While the driver technologies are offered as examples, the motor 200 is not restricted to using one of these technologies for the driver. An exhaustive list of every potential driver technology that could be used has not been attempted herein. In general, a technology that can impart a force to deflect the flexor 208 can probably be used, though some technologies may be more applicable and advantageous than others.
FIG. 3B depicts an electrostatic motor 300B that includes a stator 310, a driver HV electrode 314, a braking HV electrode 316, and a conductive flexor 318. Electrostatic driver technology operates by applying a high voltage between the conductive flexor 318 and the driver HV electrode 314 embedded in the stator 310. In the example of FIG. 3B, the stator 310 is formed into a wave with a wave gap between the driver HV electrode 314 and the conductive flexor 318.
When both the driver and brakes are electrostatic, as in the example of FIG. 3B, both the brake and driver electrodes may be formed as part of the stator 310. It is also possible to electrically connect the braking HV electrode 316 to the driver HV electrode 314, because they may be activated at the same time. In this case, the electrode formed as the combination of the braking HV electrode 316 and the driver HV electrode 314, will be called, for the purposes of example, the “Left Electrode.” The Left Electrode performs the braking function at the top of each hill, and performs the driver function at the down slope of the hill to move the conductive flexor 318 towards the left. The Right Electrode (not shown) slopes the opposite direction, and is used to move the conductive flexor 318 towards the right. When moving the conductive flexor 318 one direction, say to the left, the Left Electrode is used as the driving brake and the driver, and the Right Electrode is used as the holding brake.
FIG. 3C depicts a magnetic motor 300C that includes an electromagnet 320 and a ferromagnetic flexor 328. In the example of FIG. 3C, the ferromagnetic flexor 328 should be made out of a ferromagnetic material in order to be attracted to the electromagnet 320. Possible materials include, for example, a flexible steel or iron alloy, or a polymer filled with a ferromagnetic material such as the type used to construct flexible magnets.
It may be noted that, in an embodiment, the rotation direction of driver 332 does not determine the direction of movement of the flexor 338. Rather, the direction of movement is determined by whether the brake (not shown) to the right or the left of the driver 332 is activated. Hence the driver 332 can be run in a single direction and does not need to be reversed when the flexor 338 movement is reversed.
The offset roller 346 functions similar to a cam (see, e.g., FIG. 3D), but rolls instead of slides against the flexor 348, possibly reducing wear. The diameter of the offset roller 346 can be changed as desired to change the duty cycle during which the offset roller 346 deflects the flexor 348. Vibrations can be avoided through counterweights or with multiple rollers arranged to make the center of mass coincident with the motor shaft axis (not shown).
Bender actuators are well known in the art and operate by laminating two materials together, one of which expands or contracts when powered. One type of piezoelectric bender is the FACE Thunder series of actuators. These actuators have a steel backing plate bonded to a piezoelectric material that expands or contracts upon application of an external voltage. The Thunder actuator is curved in its unpowered position. Applying one polarity of voltage causes is to flatten, and applying the opposite polarity causes it to bend further. Other benders include thermocouples and benders based on the electrostrictive and electrostatic properties of electro-active polymers.
FIG. 4A depicts a motor 400A that includes a linear actuator 402, a brake pad 404, a pinch plate 406, and a flexor 408. In the example of FIG. 4A, the linear actuator 402 pushes the brake pad 404 against the flexor 408 to pinch the flexor 408 against the pinch plate 406. The example of FIG. 4A can serve to represent any number of mechanical friction brakes. The linear actuator 402 may be replaced with any applicable driver technology, such as, for example, the technologies described with reference to FIGS. 3A to 3F. Advantageously, the mechanical friction brake may be operated such that the flexor 408 need not move in discrete steps. However, a strong linear actuator 402 may be required to apply the desired braking force.
BrakingForce=COF·Areab·ɛ0·ɛd·V22·gapd2,
where COF is the coefficient of friction between the moving elements, Areab is the effective area of the braking electrode, ∈0 is the permittivity of free space (8.854×10−12 coulomb per volt-m), ∈d is the relative dielectric constant of the material in the dielectric gap, V is the voltage between the plates, and gapd is the distance between the plates.
Another type of electrostatic brake can be made by replacing the insulating dielectric with a semiconducting layer. This technique makes use of the Johnson-Rahbeck effect and uses the types of materials that have been developed for electrostatic clutches (see U.S. Pat. Nos. 5,463,526 and 5,525,642, which are incorporated herein by reference). The Johnson-Rahbeck effect allows a small current to flow where the moving plate touches the semiconductor, but the current flows only through the high points in the surface irregularities, while a large electric field develops in the low points of the surface irregularities. Because the gap is very small at the low points, a small voltage can develop a very large force. Brakes making use of the Johnson-Rahbeck effect can be quite durable, because the semiconducting layer can be made quite thick. The thick layer does not affect the force developed because the electric field is not strongly dependent on the thickness of the semiconducting layer. However, these brakes are generally slower than electrostatic brakes with insulating layers, because the high resistance of the semiconducting layer introduces a long RC time constant for charging or discharging the electrodes when the brake is switched on or off.
In the example of FIG. 4C, in operation, the HV electrodes 424 and 426 are electrostatically attracted to the conductive rotors 428. The multiple layers of the brakes 1 and 2 (respectively including the HV electrodes 424 and 426) each provide braking forces. Brake 1 and Brake 2 are rectangular or wedge-shaped brakes arranged around the circumference of the conductive rotors 428. Each brake is constructed as a strip with an electrode sandwiched between a thin dielectric and thick dielectric. The strip is folded into multiple layers and, when operationally configured, the thin side faces the conductive rotors 428. The thin dielectric is selected for its electrical properties for applying braking forces, and the thick dielectric is selected for its mechanical properties for delivering the braking force to the motor housing. The braking force can be increased by increasing the number of layers or by making use of more of the surface area of each rotor.
When the worm motor 442 is running and there is little blocking force, the worm gear 446 rotates clockwise or counter clockwise based on the rotation direction of the worm 444. If the worm gear 446 has an external load force blocking the movement, the worm motor 442 may not have sufficient torque to drive the load and the worm motor 442 may stall when driving the flexor 448 against the load, leaving worm gear 446 stopped (braked). Then, when a driver (see, e.g., FIGS. 3A to 3F) flexes the flexor 448, the pressure on the worm gear 446 is released, allowing the worm motor 442 to advance the worm gear 446 by a (typically) small amount. In this way, the worm motor 442 and the worm gear 446 can be used to advance the braking point a small amount each time the driver is activated.
The maximum torque of the motor 400E is largely determined by the braking force of the worm brake 450, which depends more on the material strength of the worm gear 446 than the power of the worm motor 442. An advantage of the worm brake 450 is that no timing is required to activate the worm brake 450 at a particular time relative to the activation of the driver. In an embodiment, the worm brake 450 may be constantly driven by a low current to apply a small torque in the desired direction of movement. The worm motor 442 stalls while waiting for slack in the flexor 448, at which time it is allowed to advance. The no-load speed of the worm motor 442 divided by the gear ratio of the worm drive is typically set high enough that it does not limit the speed of the motor 400E. The worm brake 450 does not, by itself, provide free movement mode. It is ideal for applications of motors needing an unpowered mode to be locked instead of free-moving.
It may be noted that the description of this and subsequent figures is for counter-clockwise motion of the output gear 526. Clockwise motion is performed in a complementary fashion by reversing the functions of the brakes, making the right brake the driving brake and the left brake the holding brake.
In addition, for the output gear 526 to rotate once, the belt must move a distance of 2πr. With each rotation of the driver 502, the flexor 508 moves by the difference in the arc length in the deflected position and the flat position. The deflected position approximately forms two right triangles with short side h, and long side l, where l is half the difference between the axis of the rollers 516 (or the distance between the axis of the tension gear 524 and the output gear 526 in the case where the optional rollers 516 are omitted). Accordingly, the distance traveled by the belt on each revolution is twice the difference between the hypotenuse and the long side of the triangle. The PRatio is computed as the ratio of the circumference of output gear 526 and the movement caused by each revolution of the driver 502. Hence, the equation for the PRatio is:
PRatio=2⁢π·r2·(h2+l2-1)=π·rh2+l2-l
Pinch ratio vs. h for one value of r and l
h PRatio
0.1 945
0.3 107
Table 1 shows how the PRatio varies for some values of r, l and h when each variable is measured in the same units of distance (e.g. inches or cm). For very small deflections of the flexor 508, the PRatio grows relatively large. In the example of Table 1, where r=1.5 and l=1, the PRatio can vary from 945 to 28 by changing l, the displacement of the driver 502, from 0.1 to 0.6. Thus, it is possible to achieve a wide range of mechanical advantage by varying the displacement of the driver 502. Changing the time when the driving brake 504 is applied may have a similar effect to changing the driver displacement. Hence the mechanical advantage can be controlled through a change in the timing of the phases that control the timing of the driver 502 and brakes 504, 506.
The PRatio equation above assumes that the brakes, belt, and motor housing are all ideal. In an ideal belt motor, the brakes do not slip, the belt does not stretch, the housing is perfectly rigid, and the restoring phase completely flattens out the belt to prepare for each subsequent driver activation. In any real implementation, as the displacement l approaches zero, one of these effects will probably limit the maximum PRatio. These terms together can be modeled with a new slip variable, s, that sums all potential backwards motion on each revolution of the driver 502. With this new term added, the PRatio equation becomes:
PRatio=π·rh2+l2-l-s
The effect of slip on PRatio for several values of h.
h 0 0.001 0.002 0.004 0.008 0.016
0.1 1886 3145 9454 −3138 −857 −349
0.2 472 525 591 789 2386 −782
0.3 211 220 231 256 328 739
0.4 119 122 125 132 149 200
0.5 77 78 79 82 88 103
0.6 54 54 55 56 59 65
In the example of Table 2, where r=1.5 and l=1, when slip, s, increases to 0.004 and beyond, PRatio becomes negative for small values of h, indicating that the forward movement made by pinching the flexor is less than the reverse movement due to slip. Hence, the maximum PRatio and maximum torque of the belted motor 500 is determined largely by the quality of the brakes and stiffness of the housing. When using brakes with gear teeth, the pitch of the teeth is part of the slip, and very fine teeth are desirable to have a large PRatio.
FIGS. 6A to 6D depict conceptual diagrams of the belted motor 500 (FIG. 5) in multiple operation states according to an embodiment. FIG. 6A is intended to illustrate a “pinch phase” in which the driving brake 504 is engaged and the driver 502 rotates to pinch the flexor 508 and move the output gear 526 counter-clockwise.
FIG. 6B is intended to illustrate a “hold phase” at a point in time just after the maximum deflection of the flexor 508 has been reached. At this point, in an embodiment, both the driving brake 504 and the holding brake 506 are on. Both brakes are on briefly in order to make sure there is no point in time when the load could pull holding gear 526 backwards. In an alternative, the brakes are not simultaneously engaged if the load would not pull the holding gear 526 backwards.
FIG. 6C is intended to illustrate a “restore phase” in which the holding brake 506 is active, the drive brake 504 is inactive, and the driver 502 is rotating to pull the slack out of the top part of the belt and restore it to its flattened position. In an embodiment, during the restore phase, the tension gear 524 rotates counter-clockwise.
FIG. 6D is intended to illustrate a “hold phase” that follows the restore phase. In this hold phase, both brakes are briefly engaged to hold the flexor in position in preparation for the next cycle. In an embodiment, each cycle includes the pinch phase (see, e.g., FIG. 6A) and a restore phase (see, e.g., FIG. 6C), with, in an embodiment, intervening hold phases (see, e.g., FIGS. 6B and 6D).
FIGS. 7A to 7F depict conceptual diagrams of the motor 500 (FIG. 5) operating at high torque in multiple operation states according to an embodiment. FIG. 7A is intended to illustrate a position where the maximum torque setting is reached (at less than maximum pinch). The maximum torque can be determined based on the back-EMF of the motor, the total current draw, a position sensor, or some other feedback system.
FIG. 7C is intended to illustrate a first part of a “free belt phase” in which, once the holding brake 506 is fully engaged, the driving brake 504 is released to free the belt. During the free belt phase, the driving brake 504 is off when the holding brake 506 is on and the tension gear 524 may move clockwise (e.g., backwards from its normal direction), allowing slack in the flexor 508. Because there is slack in the flexor 508, the driver 502 should not be prevented from reaching its maximum deflection position.
FIG. 7F is intended to illustrate a hold phase, in which both brakes are engaged, in preparation for a next pinch phase. In an embodiment, each cycle includes the pinch phase (see, e.g., FIG. 7A) and the free belt phase (see, e.g., FIGS. 7C, 7D, and 7E), with, in an embodiment, intervening hold phases (see, e.g., FIGS. 7B and 7F). By controlling the timing of the brakes, in an embodiment, the driver 502 can be prevented from stalling and the motor torque can be limited to a desired value.
FIGS. 8A and 8B depict conceptual diagrams of motors according to respective embodiments. FIG. 8A is intended to illustrate forces for a driver and brake in a conical motor 800A, which includes a flexor 808 and a stator 810. The flexor 808 has a longer circumference than the stator 810, and when they are clamped together at two places, the flexor 808 forms a hill with wave gap separating the flexor 808 from stator 810. When the driver, which in the example of FIG. 8A is an electrostatic force, pushes the flexor 808 towards stator 810 with one portion clamped by a driving brake, which in the example of FIG. 8A is also an electrostatic force, the free portion of the flexor 808 is pushed away from driving brake.
FIG. 8B illustrates the forces for one driver in the wavy motor 800B. The flexor 858 has a shorter circumference than the stator 860, and a wave gap is formed in the valley of the stator 860 underneath the flat flexor 858. When the driver pulls the flexor 858 towards the stator 860 with one portion clamped by a driving brake, the free portion of the flexor 858 is pulled toward the driving brake. A sequence of hills and valleys is repeated around the circumference of the stator 860. When the flat flexor 858 is pinched to the wavy stator 860 and the pinch point is moved around the stator 860 once, the rotor moves in the opposite direction as the pinch point.
F=ɛ0⁢ɛr⁢AV22⁢h2,
where ∈0 is the permittivity of free space (8.854×10−12 coulomb per volt-m), ∈r is the relative dielectric constant of the insulating material (e.g., 1 for air and 3.4 for a typical insulating material such as polyimide), A is the area of the plates, V is the voltage between the conductive plates (typically in the range of 1 KV to 4 KV), and h is the spacing between the plates.
This equation shows the importance of decreasing the spacing between the plates, because the force goes up by a factor of 4 each time the distance is halved. In an embodiment, the design does not require any extra spacing for lubrication. When the plates have both an air gap and an insulator, the force depends on the height of the air gap, the height of the insulator, and the dielectric constant of the insulator.
FIGS. 9A and 9B depict conceptual diagrams of a rotary motor according to an embodiment. FIG. 9A depicts a stator 910 with four drivers 902-1 to 902-4 (collectively referred to hereinafter as the drivers 902) and four brakes 904-1 to 904-4 (collectively referred to hereinafter as the brakes 904). The drivers 902 and brakes 904 may be of any type.
FIG. 9B depicts a flexor 908, which may include a disk made of a flexible conductive material such as, for example, conductive Kapton film, carbon-filled polycarbonate, or a polymer coated with a conductive ink. The flexor 908 may be connected to ground or common voltage. In an embodiment, the path for this connection is from the motor housing through a conductive bearing and shaft and finally to the flexor 908. High voltage phases are applied to the brakes 904 of the stator 910, and they attract the flexor 908 through a thin dielectric layer between the high voltage brake electrodes (not shown) and the flexor 908.
A way to understand a principle of operation of the rotary motor depicted in the example of FIGS. 9A and 9B, is to imagine two disks cut out of a thin sheet plastic or paper. One disk, the stator, has a small wedge cut from it and the ends are joined together to form a cone. A pin connects the center of the stator cone to the center of the flexor disk. The disk and cone are pinched together at one point around the outer diameter and a mark is made on both the cone and disk near the points where they touch. If the disk and cone are pinched together at successive pinch points around the circumference, when the pinch point has traveled all the way around once, the marks on the cone and disk will be displaced by a distance equal to the amount of wedge that was previously cut from the cone. Hence the (flexor) disk has advanced a distance relative to the (stator) cone, and the amount of advancement depends on the arc length difference at the radius of the circle formed by the sequence of pinch points. The difference in arc length divided by the total circumference is the mechanical advantage, or PRatio. If the diameter of the disk is about 3.2 inches, then the circumference at the outer diameter is 10 inches. If the pie-shaped cutout was 0.1 inch at the outer diameter, then the pinch point needs to travel around 100 times (10/0.1) in order for the rotor to rotate back to its original position. This design has a PRatio of 100:1 with the rotor advancing in the same direction as the pinch point.
FIGS. 10A and 10B depict drawings of a rotary motor 1000 according to an embodiment. As depicted in the example of FIG. 10A, the rotary motor 1000 includes driver motors 1002-1 to 1002-4 (collectively referred to hereinafter as the drivers 1002) with respective offset rollers 1016-1 to 1016-4 (collectively referred to hereinafter as the offset rollers 1016) and counterweights 1018-1 to 1018-4 (collectively referred to hereinafter as the counterweights 1018), electrostatic brakes 1004-1 to 1004-4 (collectively referred to hereinafter as the brakes 1004), a pinch plate 1006, a bottom plate 1012, and top and bottom bearings 1014-1 and 1014-2 (collectively referred to hereinafter as the bearings 1014).
The components depicted in the example of FIG. 10A may be referred to collectively as the stator assembly 1010. The drivers 1002 are mounted to the bottom plate 1012 via respective mounting brackets 1020-1 to 1020-4 (collectively referred to hereinafter as the mounting brackets 1020). In an embodiment, a motor shaft (not shown) may pass through the bearings 1014, and a flexor disk (not shown) may be coupled to the shaft between the offset rollers 1006 and the pinch plate 1016. In the example of FIG. 10A, the brakes 1004 are electrostatic and the drivers 1002 are motors with offset rollers 1016.
FIG. 10B depicts a pinch plate 1006 for use with the rotary motor 1000 (FIG. 10A). In the example of FIG. 10B, the pinch plate 1006 includes wave gaps 1032-1 to 1032-4 (collectively referred to hereinafter as the wave gaps 1032), brake areas 1034-1 to 1034-4 (collectively referred to hereinafter as the brake areas 1034), and a hole for bearing 1036.
In operation, one of the drivers 1002 pinches the flexor into one of the corresponding wave gaps 1032. The wave gaps 1032 should be deep enough that the drivers 1002 can fully extend when pinching the flexor and do not bottom out. It may be noted that in the drawing of FIG. 10B, the bottom of the wave gaps 1032 appear to have concentric rings, but these are just tooling marks and do not necessarily serve a function.
The shape of pinch plate 1006 may be relatively complex. The brake areas 1034 are not flat, but instead slope downward. In an embodiment, this shape is cut by first machining the pinch plate 1006 into a cone, then cutting the deep wave gaps 1032. The angle of the cone is determined by the number of drivers 1002 that will be simultaneously active, two in the case of the rotary motor 1000, and by the maximum travel of each driver 1002. When the active drivers are in their fully extended position, the flexor may be pinched into the corresponding wave gaps but pulled tightly across the wave gaps of the inactive drivers, and pulled tightly across the brakes 1004. If the cone angle is too shallow or flat, the circumference of the flexor may not be large enough to be pushed into the wave gaps of the active drivers. If the cone angle is too steep, then when the drivers 1002 are active, the rest of the flexor is too loose and there is no restoring force to pull the flexor out of the wave gaps of the previously active drivers. When the cone angle is too steep, the flexor can completely follow the contours of the pinch plate 1006 and the drivers 1002 are free to rotate without imparting any force to the flexor.
FIGS. 10A and 10B depict a rotary motor with four drivers and four brakes; however, in alternative embodiments, rotary motors may be constructed with different numbers. A rotary motor constructed according to techniques described herein has at least two drivers and two brakes because each driver activation pinches the flexor under one driver and restores it under the other driver. The number of drivers can be increased without bound within the physical constraints of the other components. In the rotary design, the number of brakes may be the same as the number of drivers.
FIGS. 11A to 11D depict conceptual drawings of a rotary motor in multiple states of operation according to embodiments. FIG. 11A depicts a rotary motor 1100 with drivers denoted D1 to D4, arranged clockwise around the circumference of a rotor 1110. Brakes are denoted B12, B23, B34, and B41, where the numeric portion represents the nearest drivers; for instance, B12 is between D1 and D2. Each driver and each brake has an associated circle 1102. Beneath the circle of each driver, on the rotor 1110, is a rotor portion 1112. Beneath each circle of each brake, on the rotor 1110, is a rotor portion 1114.
In the FIGS. 11B to 11D, when a brake is active, one of the circles 1102 (i.e., the circle associated with the brake) is darkened. If a brake is active, then the associated rotor portion 1114 is also darkened. Similarly, when a driver active, one of the circles 1102 (i.e., the circle associated with the driver) is darkened. If a driver is active, then the associated rotor portion 1112 is pinched. In addition, the rotor portion associated with the driver remains pinched during a next state. The circles 1102 and rotor portions 1112, 1114 are intended to be conceptual only; they may or may not correspond to actual components of a rotary motor.
FIG. 11B is intended to illustrate a free movement state for the rotary motor 1100. As shown in the example of FIG. 11B, none of the circles are darkened (indicating that none of the drivers or brakes are active). A free movement state is advantageous for certain applications, as described previously.
FIG. 11C is intended to illustrate a sequence of rotary motor states (in low gear). The first state is a pinch state 1122, in which drivers D1 and D3 are active and brakes B41 and B23 are active to cause the free portions of the flexor to move in the reverse (counter-clockwise) direction. The next state is a hold state 1124 in which all brakes are active and in which the previously pinched portions of the flexor remain as they were when the driver moved them to that position. The next state is a pinch state 1126 in which drivers D2 and D4 are active and brakes B12 and B34 are active to cause the free portions of the flexor to move in the reverse direction. The next state is a hold state 1128, in which the previously pinched flexor position is held by activating all four of the brakes. In an embodiment, the sequence of states may repeat from state 1122 to 1128 and back to 1122.
FIG. 11D is intended to illustrate another sequence of rotary motor states (in high gear). The motor of FIG. 11D may be the same as the motor of FIG. 11C. As with the example of FIG. 11C, the sequence of states may start with a free movement state (see, e.g., FIG. 11B). In FIG. 11D, the first state is a pinch state 1132 in which drivers D1 and D4 are active and brake B34 is active. It should be noted that in the pinch state 1132, the active drivers are not opposite each other. Rather, the active drivers are adjacent to one another. The next state is a hold state 1134 in which brakes B12 and B34 are active and in which the previously pinched portions of the flexor remain as they were when the driver moved them to that position. The next state is a pinch state 1136 in which drivers D2 and D3 are active and brake B12 is active, allowing the free portions of the flexor to move in the reverse direction. The next state is a hold state 1138 with brakes B12 and B34 active. In an embodiment, the sequence of states may repeat from state 1132 to 1138 and back to 1132.
It may be noted that, in the example of FIG. 11D, each successive pinch state moves the pinch point by +180 degrees in a clockwise direction (while the rotor moves counter-clockwise). In this example, moving the pinch point around once requires two pinch states, and each pinch state activates two drivers. Hence each driver is activated once per revolution of the pinch point. It may be further noted that, in the example of FIG. 11D, some states have only a single brake active. It may be further noted that, in the example of FIG. 11D, some states have two drivers active, but those drivers are pulling against the same brake, not independently pulling against different brakes. Thus, the force is that of just one driver, but with twice the displacement.
If a rotary motor is driven according to the sequence of states described with reference to FIG. 11C and then driven with the same state transition speed according to the sequence of states described with reference to FIG. 11D, the movement in FIG. 11D is twice as fast but with half of the torque of FIG. 11C. In this way, these sequences are analogous to a two-speed transmission, with FIG. 11C corresponding to low gear and FIG. 11D corresponding to high gear. With six drivers and six brakes, three different sequences could be defined corresponding to three different gears, with the third gear having three times the speed and ⅓ the torque of low gear.
By controlling the sequencing of drivers and brakes as described with reference to FIGS. 11A to 11D, a multiple speed transmission can be implemented with the shifting between gears determined by the timing of a motor controller. Advantageously, in an embodiment, no mechanical linkages are required to change the drive ratio in this way, providing a significant benefit over prior art transmissions. The automatic transmission properties described previously with reference to Table 1 are also present in a rotary motor embodiment, but the existence of high and low gears further extends the range. In a four-driver rotary motor embodiment, for example, the PRatios in low gear are half of the PRatios in high gear.
FIG. 12B shows a timing diagram 1204 corresponding to a high gear rotary motor operation, such as described with reference to FIG. 11D. For illustrative purposes, the timings are the same as in the example of FIG. 12A, but each waveform drives the activation of a different set of drivers or brakes.
FIG. 12C shows a timing diagram 1206 of ultra low gear rotary motor operation in which pairs of opposing drivers are driven as in low gear, but in which the driver stops delivering torque before it reaches its maximum displacement. By terminating early, the driver never reaches the lower PRatios, and, accordingly, drives at higher torque and lower displacement. In this diagram, shaded areas 1210 show the times during which a driver is applying torque to the output. The portion of the driver cycle after the shaded area is the time the driver is finishing its travel, but the brakes have been set to allow the diver to move without applying force against the output load. Using this technique, when the motor current hits a trip point, the brakes can switch to shed the load. In an embodiment, torque is applied to the load only during the shaded portions of the motor rotation.
FIG. 13 depicts a flowchart 1300 of a brake and driver activation method according to an embodiment. The flowchart 1300 is sufficiently general that it may be used to describe a method applicable to, for example, a linear embodiment, a belted embodiment, a rotary embodiment, or some other embodiment of a “pinch” motor according to techniques described herein. For the purposes of example, it is assumed that a “pinch” motor includes a flexor and a stator assembly. The stator assembly includes brakes (including holding brakes and driving brakes, which may or may not be interchangeable) and drivers. This method and other methods are depicted as serially arranged modules. However, modules of the methods may be reordered, or arranged for parallel execution as appropriate.
In the example of FIG. 13, the flowchart 1300 continues at module 1304 where previously active holding brakes (if any) are deactivated. In an embodiment, the module 1302 occurs before the module 1304 to allow for some overlap time with multiple brakes active. This may be desirable to reduce the probability of slipping when switching from one brake to another. If the example of FIG. 13, the flowchart 1300 continues at module 1306 where a driver is activated to pinch the flexor. This facilitates movement of a part of the flexor that is not held by a brake. The modules 1304 and 1306 may be associated with a “pinch state” of operation.
In the example of FIG. 13, the flowchart 1300 continues at module 1308 where a holding brake is activated to capture the movement just made in module 1306. In an embodiment, the holding brake also prevents a load force from moving the flexor opposite to the intended movement direction. In the example of FIG. 13, the flowchart 1300 continues at module 1310 where the driving brake is released. When the driving brake is released, some or all of the holding force is transferred to the holding brake. In the example of FIG. 13, the flowchart 1300 continues at module 1312 where the driver is retracted to its initial position. This facilitates the restoration of the flexor to an unflexed position. The modules 1308, 1310, and 1312 may be associated with a “hold state” of operation.
Motors and actuators according to various embodiments may have the ability to work in reverse as generators. Generator mode may be used in portable power generating equipment, and may be used intermittently for regenerative braking to extend the life of batteries in battery-powered applications. DC motors may generate current when a shaft is driven by an external force. Piezoelectric elements generate a high voltage when a force is applied, and electrostatic (capacitive) actuators generate an increased voltage when an external force separates the plates. In an embodiment, a motor using such a reversible technology for its drivers can also become a generator by proper sequencing of the brakes and proper control of the phases connected to the drivers.
The motor 110 may be of any compatible type. However, generator mode is slightly different for linear and rotary drivers. With a linear driver, the driver electronics is first put into a mode where driver power from the phase drivers 112 is fed back to the power source 108 through the regenerative braking circuit 116. Once the electronics are in this mode, brakes associated with the motor 110 are sequenced in such a way that a flexor is alternately pulled tight and then relaxed against one or more drivers. Before each cycle, the driver must be extended into the wave gap, either by the inherent spring action of the driver or by activating the driver to move to that position. Then a brake is activated to stretch the flexor against the extended driver to force it to its non-extended position. The sequence is repeated at the next driver. With drivers that have a natural oscillation frequency of their own, such as piezoelectric drivers, it may be advantageous to cycle at a rate that causes the driver to oscillate near its resonant frequency. In generator mode, the mechanical advantage works in reverse to extract work from a slow moving, strong external force, delivering it as a fast sequence of small power bursts.
In the example of FIG. 15, the motor 1500 includes brakes 1504-1 to 1504-4 (collectively referred to hereinafter as the brakes 1504) and pinch and bottom plates 1510. In an embodiment, the brakes 1504 are electrostatic brakes, but other braking technologies could be used in other embodiments. The pinch and bottom plates 1510 are attached to a motor housing (not shown) through extenders 1520-1 to 1520-4 (collectively referred to hereinafter as the piezoelectric extenders 1520). Each time the brakes 1504 are pulsed, the piezoelectric extenders 1520 are pushed or pulled by a momentary force. If the brakes 1504 are pulsed at the resonant frequency of the piezoelectric extenders 1520, each pulse tends to increase the amplitude of the oscillations. The piezoelectric extenders 1520 generate an AC voltage when oscillating, and their output can be used to drive a load or can be rectified and used to recharge a battery.
As used herein, a motor associated with mechanical work that is delivered by drivers with force or torque multiplied by the pinch ratio may be referred to as a “pinch motor.” The pinch motor can be used as a generator or for regenerative braking by timing the braking to drive energy back into the drivers, or through added piezoelectric elements. The pinch motor may include a stator and a flexor. As used herein, a flexor is a flexible element that is mobile with respect to the stator.
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