Abstract:
A linear actuator is driven by an internal motor and delivers force to an output shaft. Advantageously, the technique provides speed/force tradeoffs via a simple, high-efficiency mechanism; continuous output force is provided by alternating the load between two belts deflected by, by way of example but not limitation, cam devices. The technique provides high force, allows the force to be traded for speed at a given power level, and provides continuous output force when operated as an actuator or continuous braking force when operated as a generator. Sensors may provide a low power tracking mode to allow the output to move freely.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This Application claims the benefit of U.S. Provisional Application No. 60/755,466 filed Dec. 30, 2005, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     Motors and actuators are used in a wide variety of applications. Many applications, including robotics and active orthotics, require characteristics similar to human muscles. The characteristics include the ability to deliver high force at a relatively low speed and to allow free-movement when power is removed, thereby allowing a limb to swing freely during portions of the movement cycle. This may call for an actuator that can supply large forces at slow speeds and smaller forces at higher speeds, or a variable ratio transmission (VRT) between the primary driver input and the output of an actuator.  
         [0003]     In the past, several different techniques have been used to construct a VRT. Some examples of implementations of VRTs include Continuously Variable Transmissions (CVTs) and Infinitely Variable Transmissions (IVTs). The underlying principle of most previous CVTs is to change the ratio of one or more gears by changing the diameter of the gear, changing the place where a belt rides on a conical pulley, or by coupling forces between rotating disks with the radius of the intersection point varying based on the desired ratio. Prior art CVTs have drawbacks in efficiency, complexity, maximum torque, and range of possible ratios.  
         [0004]     The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.  
       SUMMARY  
       [0005]     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools, and methods that are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.  
         [0006]     A linear actuator is driven by an internal motor and delivers force to an output shaft. Advantageously, the technique provides speed/force tradeoffs via a simple, high-efficiency mechanism; continuous output force is provided by alternating the load between two belts deflected by, by way of example but not limitation, cam devices. The technique provides high force, allows the force to be traded for speed at a given power level, and provides continuous output force when operated as an actuator or continuous braking force when operated as a generator. Sensors may provide a low power tracking mode to allow the output to move freely.  
         [0007]     The technique may be used to construct actuators for active orthotics, robotics or other applications. Versions with passive clutches may also be used to construct variable-ratio motor gearheads, or may be scaled up to build continuously variable transmissions for automobiles, bicycles, or other vehicles.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Embodiments of the invention are illustrated in the figures. However, the embodiments and figures are illustrative rather than limiting; they provide examples of the invention.  
         [0009]      FIGS. 1A and 1B  are diagrams illustrating a principle of operation.  
         [0010]      FIG. 2  depicts an example of a variable ratio linear actuator system.  
         [0011]      FIG. 3A, 3B , and  3 C are flowcharts of methods for actuator-mode operation of a lead screw-braked actuator.  
         [0012]      FIG. 4  is a graph illustrating continuous force as tension is passed from one belt to another belt.  
         [0013]      FIG. 5  depicts another example of a variable ratio linear actuator system.  
         [0014]      FIGS. 6A and 6B  depict another example of a linear actuator system.  
         [0015]      FIGS. 7A and 7B  depict an example of linear actuator system with an output piston that is pushed or pulled depending on the position of a lead-screw driven carriage.  
         [0016]      FIGS. 8A and 8B  depict drawings of a specific implementation of a linear actuator system.  
     
    
     DETAILED DESCRIPTION  
       [0017]     In the following description, several specific details are presented to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or in combination with other components, etc. In other instances, well-known implementations or operations are not shown or described in detail to avoid obscuring aspects of various embodiments, of the invention.  
         [0018]      FIGS. 1A and 1B  illustrate a principle of operation useful for an understanding of the teachings provided herein.  FIGS. 1A and 1B  show how a force can be used to deflect a belt and exert a strong force over a short distance or a weak force over a longer distance.  FIG. 1A  shows weight W 1  attached to a rope that is anchored at one end and supported by a pulley. A force F deflects the rope near the middle and force F causes weight W 1  to be lifted a distance M 1 .  FIG. 1   b  shows that when the weight is replaced by a heavier weight W 2 , the same driving force F causes it to be lifted a smaller distance M 2 . Hence the rope has provided a variable transmission between the driving force F and the resisting force applied by the weight. By constructing a device that allows for multiple sequential deflections of a flexible belt, this principle can be used to construct a variety of actuators and transmissions.  
         [0019]     U.S. patent application Ser. No. 11/033,368, which was filed on Jan. 13, 2005, and which is incorporated by reference, describes a high torque “pinch” motor with a variable ratio coupling between a driver and output. The motor includes a flexible disk or belt that couples a braking pulley and an output pulley. The output is alternately advanced or held in place while the driver returns to the position where it can again deflect the belt or disk to advance the output. However, the design does not allow for continuous output torque.  
         [0020]     U.S. patent application Ser. No. ______ (Attorney Docket No. 57162-8002.US01) entitled “Rotary Actuator” by Horst et al. filed concurrently herewith is incorporated by reference. U.S. patent application Ser. No. ______ (Attorney Docket No. 57162-8010.US01) entitled “Continuously Variable Transmission” by Horst et al. filed concurrently herewith is incorporated by reference. U.S. patent application Ser. No. ______ (Attorney Docket No. 57162-8011.US01) entitled “Deflector Assembly” by Horst et al. filed concurrently herewith is incorporated by reference.  
         [0021]      FIG. 2  depicts an example of a variable ratio linear actuator system  200 . The system  200  includes two brakes  202 , two cables  204 , an output tendon  206 , an optional output lever  208 , two tensioners  210 , two actuators  212 , and an optional pulley  214 . In an illustrative embodiment, the brakes  202  are implemented as lead screw/nuts with a lead angle steep enough to prevent backdriving the screw when a load is applied to the nut. However, any applicable known or convenient device capable of acting as a brake could be used. In the example of  FIG. 2 , the brake  202  is coupled to the cables  204 . In the illustrative embodiment, each cable  204  is attached to each nut of the lead screw/nuts.  
         [0022]     In the example of  FIG. 2 , the cables  204  are coupled to approximately the same point of a lever which is coupled to an output tendon  206  and/or an output lever  208 .  
         [0023]     In an illustrative embodiment, the cables  204  have tensioners  210  at the top and bottom of each of the cables  204 . Advantageously, the tensioners  210  may facilitate forward and reverse operation. The tensioners  210  may have magnets attached to change the magnetic field at linear hall-effect sensors mounted to a housing (not shown). The hall-effect sensors may be read by controlling electronics and used to determine belt tension at the top and bottom of each cable  204 . The belt tension can be used to determine the force being supplied to or from the output. The force sensors may be used, by way of example but not limitation, to control the operation of lead screw motors or to sense movement of motor output from external forces.  
         [0024]     Each of the cables  204  has an actuator  212  that applies driving force to deflect the belt. In an illustrative embodiment, the ratio is determined by the displacement of each actuator  212 . When a low ratio is desired, the controlling electronics drives each actuator  212  for a short time before switching to the other. Thus the controlling electronics or computer can set the ratio as desired. In other illustrative embodiments, there are at least three different ways of running, for example, ball screw deflectors: 1) Use electronics to drive to a fixed deflection amount to set a fixed ratio, 2) Drive each actuator for a fixed time, and 3) Drive each actuator until a fixed current is reached. These different ways will likely be associated with slightly different behavior, but those of skill in the relevant art with this reference before them will have little difficulty understanding the repercussions of choosing one way over another.  
         [0025]     In an illustrative embodiment, the actuators  212  are implemented as ball screw/nuts, which are backdrivable. However, any applicable known or convenient actuator could be used. If a regenerative braking mode is desired, the drivers should be back drivable. Ball screw actuators are a type of lead screw with recirculating ball bearings and that allows them to be back driven from the load. Hence in this illustrative embodiment, tension on the cables  204  can force the ball screw actuators  212  to rotate to allow driver motors to be run as generators.  
         [0026]     The system  200  may or may not apply force in only one direction. For example, the system  200  can pull the tendon  206 , or rotate the lever arm  208  clockwise, but may be unable to drive significant force in the counter clockwise direction. A second pair of cables can be added to pull a second tendon or lever for the opposite direction. The added cables do not require adding more motors or lead screws. The pulleys  214  (only one of which is illustrated in the example of  FIG. 2  to avoid cluttering the figure) can be used to engage the second pair of cables.  
         [0027]      FIG. 3A  is a flowchart  300 A showing operation of a lead screw-braked device in actuator mode. This method and other methods are depicted as modules arranged serially or in parallel. However, modules of the methods may be reordered, or arranged for parallel or serial execution as appropriate.  FIG. 3A  is intended to illustrate an actuator mode of a continuous variable ratio actuator.  
         [0028]     In the example of  FIG. 3A , the flowchart  300 A starts at module  302  with selecting actuator mode. The flowchart  300 A continues at module  304  with advancing lead screw motor A. Lead screw motor A may be either of dual (or more) lead screw motors that are part of a lead screw brake assembly of a continuously variable ratio actuator. The result of advancing lead screw motor A is that belt A is tightened. Belt A may be either of dual (or more) belts that are part of a continuous variable ratio motor. It may be noted that the module  304  is optional in that if belt A is already tightened, the module  304  is not necessary to tighten belt A. The necessity of module  304 , therefore, is dependent upon implementation and/or circumstances.  
         [0029]     In the example of  FIG. 3A , the flowchart  300 A continues at modules  306 - 1  and  306 - 2 , which are executed simultaneously. It may be noted that precise simultaneous execution may be impossible to achieve. Accordingly, “simultaneous” is intended to mean substantially simultaneous, or approximately simultaneous. Moreover, certain applications may require more or less accurate approximations of simultaneity. At module  306 - 1 , a cam is rotated to deflect belt A. This has the result of moving a load in response to the deflection of belt A. At module  306 - 2 , lead screw motor B is advanced to tighten belt B. Thus, the cam is rotated to deflect belt A while simultaneously tightening belt B.  
         [0030]     In the example of  FIG. 3A , the flowchart  300 A continues at modules  308 - 1  and  308 - 2 , which are executed simultaneously. At module  308 - 1 , lead screw motor A is advanced to tighten belt A. At module  308 - 2 , the cam is rotated to deflect belt B, and the load may be moved thereby. Thus, the cam is rotated to deflect belt B while simultaneously tightening belt A.  
         [0031]     In the example of  FIG. 3A , the flowchart  300 A continues at the modules  306 - 1 ,  306 - 2 , as described previously. In this way, continuous motion of the output is sustained. It should be noted that the flowchart  300 A makes reference to a single cam, but that two cams could be used in alternative embodiments (e.g., a cam A and a cam B).  
         [0032]      FIG. 3B  is a flowchart  300 B showing operation of a lead screw-braked device in tracking mode.  FIG. 3B  is intended to illustrate a tracking mode of a continuously variable ratio actuator. In the example of  FIG. 3B , the flowchart  300 B starts at module  312  with selecting tracking mode.  
         [0033]     In the example of  FIG. 3B , the flowchart  300 B continues at module  314  with determining output shaft position and passive carriage positions. Passive carriages are described later with reference to  FIGS. 6, 7 , and  8 . The flowchart  300 B continues at modules  316 - 1  and  316 - 2 , which may or may not be executed simultaneously. At the module  316 - 1 , a gap between brake A and both passive carriages A is determined. At the module  316 - 2 , a gap between brake B and both passive carriages B is determined.  
         [0034]     In the example of  FIG. 3B , the flowchart  300 B continues at modules  318 - 1  and  318 - 2 , which may or may not be executed simultaneously. At the module  318 - 1 , the lead screw motor A is moved in a direction to reduce the larger gap and increase the smaller gap. At the module  318 - 2 , the lead screw motor B is moved in a direction to reduce the larger gap and increase the smaller gap.  
         [0035]     The flowchart  300 B continues at module  314  as described previously. In this way, the tracking mode can continue until the tracking mode is exited. It should be noted that it may be impossible to entirely equalize the larger and smaller gaps, and different applications may demand different degrees of success in equalizing the gaps.  
         [0036]      FIG. 3C  is a flowchart  300 C showing operation of a lead screw-braked device in braking mode.  FIG. 3C  is intended to illustrate a braking mode of a continuous variable ratio actuator. It may be noted that in braking mode, the cam moves in the opposite direction to its motion in actuator mode. In the example of  FIG. 3C , the flowchart  300 C starts at module  322  with selecting braking mode.  
         [0037]     In the example of  FIG. 3C , the flowchart  300 C continues at modules  326 - 1  and  326 - 2 , which may be executed simultaneously. At the module  326 - 1 , tension on belt A rotates a cam until a load moves to belt B. At the module  326 - 2 , lead screw motor B is moved to loosen belt B. When an external force is applied, one of the belts becomes tight at the top or bottom, and that tension pulls against the cam to cause it to rotate. While that belt is supporting the load, the other lead screw motor loosens the other belt. The amount of loosening is chosen such that the load is passed from the first to the second belt before the first cam is rotated to its minimum displacement position.  
         [0038]     In an embodiment, when the cam is being moved by the belt, energy can be recaptured by using the driver motor as a generator. Hence this mode can be used for regenerative braking or as a generator. In another embodiment, where the braking force is insufficient to rotate the cam, the cam motor can be controlled to force the appropriate rotation of the cam.  
         [0039]     In the example of  FIG. 3C , the flowchart  300 C continues at modules  328 - 1  and  328 - 2 , which may be executed simultaneously. At the module  328 - 1 , lead screw motor A is moved to loosen belt A. At the module  328 - 2 , tension on belt B rotates the cam until the load moves to belt A. The flowchart  300 C then returns to the modules  326 - 1  and  326 - 2  to repeat the modules while in braking mode.  
         [0040]      FIG. 4  shows a plot of the rotation angle of the two cams versus the change in belt length caused by the deflection of the belt. The change of length of the belt causes the output shaft to move by the same amount. Hence the Y axis of  FIG. 4  can also be considered the movement of the output shaft as it is moved in response to the two belts.  FIG. 4  is plotted for a cam shape in which the radius increases quickly near its minimum radius, increases slowly as it approaches its maximum radius, then quickly decreases back to the minimum radius. This shape has an increasing radius for about 270 degrees and a decreasing radius for the other 90 degrees . By having the increasing radius more than 180 degrees, it is possible to have part of each cam rotation with the load shared between the two belts, allowing smooth operation.  
         [0041]      FIG. 4  also shows that this cam design has a large region where each degree of cam rotation results in a nearly linear change in belt displacement. This shows that the output force will be nearly constant and independent of cam position. The graph for belt B has been displaced by the amount that belt A would have moved the output load. Note that near points where the two graphs intersect, the slope of the belt A line is less than that of belt B, hence belt B is accelerating to catch up and take over the load from belt A. The shape of the cam can be changed to vary the output displacement vs. cam rotation angle as desired.  
         [0042]     In braking mode, the cam moves the opposite direction, so it is like viewing  FIG. 4  from right to left. The load starts out on belt B, but near the points where the two graphs intersect, belt A has a radius changing more slowly than belt B, so its support of the load drops off faster and the load is transferred to belt A.  
         [0043]      FIG. 5  shows another example of a variable ratio linear actuator system  500 .  FIG. 5  is intended to illustrate that different actuators can be used to take advantage of techniques described herein. Specifically, the linear actuator  500  is similar to the actuator  200  ( FIG. 2 ) but replaces a ball screw actuator with a linkage mechanism  502 . Operation of the linkage mechanism  502  is described more fully in the co-pending patent application entitled “Deflector Assembly,” which has been incorporated by reference.  
         [0044]      FIGS. 6A and 6B  show another example of a variable ratio actuator  600  system. The system  600  includes lead screw motors  602 , screw driven slides  604 , driven carriages  606 , passive carriages  608 , cables  610 , an output tendon  612 , a driver motor  614 , and deflectors  616 . The lead screw motors  602  drive the screw driven slides  604  on which the driven carriages  606  and the passive carriages  608  are operationally connected. The cables  610  are coupled between the driven carriages  606  and the passive carriages  608 , and the passive carriages  608  are coupled to the output tendon  612  (which may, in an alternative, be an output linkage). A driver motor  614  drives the deflectors  616  to deflect the cables  610  and the deflection of the cables is provided to the output tendon  612 .  
         [0045]     In an illustrative embodiment, the screw driven slides  604  are Kerk Rapid Guide Screw slides. A screw driven slide, such as the Kerk Rapid Guide Screw, includes a lead screw  618 , a slide  620 , a carriage guided by the bearings and driven by the lead screw ( 606 ), and optional addition passive carriages that are guided by the linear bearing but not driven by the lead screw ( 608 ). In the system  600 , two screw driven slides  604  are used, each with one driven carriage  606  and one passive carriage  608 . The passive carriages  608  are coupled to the output tendon  612 . The cables  610  couple each driven carriage  606  with its corresponding passive carriage  608 . The screw driven slide  604  and cable  610  are long enough to allow both carriages to move back and forth for the maximum displacement of the output.  
         [0046]     In an illustrative embodiment, a driver mechanism (e.g., the driver motor  614  and deflectors  616 ) is fixed at a point between the carriages. When the driver mechanism is activated, one of the cables  610  is deflected and one passive carriage  608  is pulled towards its stopped driven carriage  606 . During this phase, the other lead screw is rotated by its associated motor  602  to pull slack from the other cable  610 . Then the process repeats with the opposite driver. Hence the two driven carriages  606  will take turns pulling the passive carriages  608  as all carriages move to the right.  
         [0047]     In an illustrative embodiment, two belt deflection systems are substantially co-planar. Advantageously, the overall thickness of a co-planar system constructed according to the techniques described here may be the same as for a single one of the deflection systems.  
         [0048]      FIG. 6B  shows a cam follower mechanism that can be used with the screw driven slide of  FIG. 6A  or other actuators. As the cam rotates, a follower arm rotates up and down, moving the deflector arm up and down around a pivot point. As the pivot point moves to the right, the pulley has less maximum displacement on each cycle. The arm may also be designed with spring steel to provide and automatic mechanism to reduce the displacement as the load increases. A device such as the cam follower mechanism of  FIG. 6B  is described more thoroughly in the co-pending U.S. patent application entitled “Deflector Assembly,” which has been incorporated by reference.  
         [0049]      FIGS. 7A and 7B  depict an example of linear actuator system  700  with an output piston that is pushed or pulled depending on the position of a lead-screw driven carriage. The system  700  is intended to illustrate a dual direction linear actuator. The system  700  is similar to that of  FIG. 6A . So only a portion of the components have reference numbers; the remainder are sufficiently similar to that of  FIG. 6A  that more detailed explanation is redundant.  
         [0050]     In the example of  FIGS. 7A and 7B , the system  700  includes a passive carriage  702 , a linear bearing  704 , a stop  706 , a driven carriage  708 , a passive carriage  710 , a stop  712 , a linear bearing  714 , and an output piston  716 . A pair of slides each has a driven carriage plus two passive carriages. Where, for illustrative purposes, a distinction is made between the carriages of the two slides, one slide is referred to as the top slide (and the carriages as top carriages) and the other is referred to as the bottom slide (and the carriages as bottom carriages).  
         [0051]     In the example of  FIGS. 7A and 7B , the passive carriages  702  and  710  are connected to each other by a flexible belt, cord, cable, or three-link chain. When the belt between the passive carriages  702 ,  710  is tight, the distance between the passive carriages  702 ,  710  is greater than the width of the driven carriage  708 . The driven carriage  708  may be positioned as a brake for either passive carriage. The output piston  716  is supported by linear bearings  704 ,  714 , allowing it to move in only one dimension. The passive carriages  702 ,  710  can push against stops  706 ,  712  operationally connected to the output piston  716 .  
         [0052]     In the example of  FIG. 7A , the passive carriage  710  is prevented from moving to the right by the position of the driven carriage  708 . When the top belt is deflected, the passive carriage  710  is held in place and the passive carriage  702  moves to the left. The passive carriage  702  rides against the stop  706  of the output piston  716  and the movement of the passive carriage  710  causes the output piston  716  to move to the left. Before the top belt is slack, the bottom belt applies force to the output piston  716  by pulling the bottom right passive carriage toward the stationary bottom left passive carriage braked by the bottom driven carriage. While the bottom belt is driving the load, the top lead-screw motor turns to move its driven carriage in the direction of the output movement, thereby tightening the belt in preparation for the next cycle.  
         [0053]      FIG. 7B  shows the same mechanism as  FIG. 7A , but with the driven carriage riding against the right passive carriages. In this configuration, deflections of the belts cause the left passive carriages to move to the right. The left carriages ride against the left stop of the output piston to couple the force from the carriages and to cause the output piston to move to the right. Thus position of the lead-screw driven carriages control the direction of movement of the output piston. Sensors (not shown) can detect the force on the output piston and these sensors may be used for feedback control of the system  700 .  
         [0054]     When the driven carriage  708  is moved from its position in  FIG. 7A  to its position in  FIG. 7B , it passes through a region where it engages neither passive carriage  702 ,  710 . If both the top and bottom driven carriages are in this mid-position, the output piston can move freely, even if one of the top or bottom stops  706 ,  712  are in contact with a passive carriage. As long as neither driven carriage  708  impedes the movement of one of the passive carriages, the output piston may pull the passive carriages in either direction, or if neither stop is in contact, the movement of the output piston causes no movement in the passive carriages. The actuator thus allows free movement up to the point where the driven carriage again is in contact with a passive carriage. The free movement mode can be extended to the full range of the linear actuator with a control system that senses the position of the output carriages and adjusts the position of the driven carriages via the lead screw motors to keep the driven carriage from coming into contact with a passive carriage.  
         [0055]      FIGS. 8A and 8B  depict drawings of a specific implementation of a linear actuator system  800 . The system  800  is conceptually similar to that of  FIGS. 7A and 7B , but the sliders are placed back-to-back instead of in the same plane as shown in  FIGS. 7A and 7B . Advantageously, when first and second belt deflection systems are substantially in parallel, the overall height of the system may be the same as for a single deflection system.  
         [0056]     In the example of  FIGS. 8A and 8B , the belt includes a three-link chain. Advantageously, the three-link chain, dependent upon the implementation, can be stronger, lighter, quieter, and less stretchy than a flexible belt. The three-link chain can have improved durability, control, or other characteristics, as well.  
         [0057]     In the example of  FIGS. 8A and 8B , in an illustrative embodiment, the deflector assembly enables bidirectional operation with a single deflector on each belt. With a rotary actuator, for example, two deflectors may be needed per belt (e.g., one on an upper belt and one on a lower belt) to apply force in both output directions. The moving fulcrum design of the example of  FIGS. 8A and 8B  is capable of continuous force over a wide range of ratios. It may be noted that although the deflector assembly depicted in the example of  FIGS. 8A and 8B  is significantly different from that of  FIGS. 7A and 7B , the deflector assembly uses the principle of a moving fulcrum, as in the example of  FIGS. 7A and 7B .  
         [0058]     In an illustrative embodiment, belt support bearings are arranged above the belt instead of next to the belt. This cuts the thickness of the device. It may be noted that the support bearings could be arranged below the belt to gain similar advantages. Moreover, the drive motor can be arranged with its longest dimension in parallel to the belt. This facilitates construction of a thinner actuator and may allow a standard gearhead to be used on the drive motor. The gearhead ratio can be picked to keep the highest speed of the cam low enough to avoid problems with vibration or noise.  
         [0059]     In the example of  FIGS. 8A and 8B , the top of the deflector assembly ( FIG. 8B ) couples to the bottom of the actuator assembly ( FIG. 8A ) with the deflector roller  804  pushing on the belt  802 . Not shown are the back side sliders and belt. However, the front and back belts look similar and operate similarly, but 180 degrees out of phase.  
         [0060]     The invention is not limited to the specific embodiments described. The number of belts, brakes and drivers are not restricted to the number shown and may be increased. The belts can be implemented by chains, timing belts, steel belts, V-belts, cables, or any other type of flexible material. The materials used in construction are not limited to the ones described. In an embodiment, the ratio adjusting mechanism allows for an external control to set the desired ratio via mechanical, electrical, hydraulic or other means for adjusting the pivot point of a cam follower mechanism or other applicable device.  
         [0061]     As used herein, the term “cam device” means a cam or a cam with a follower. Accordingly, if a cam device is coterminous with, for example, an actuator belt, that means the cam may or may not be coterminous, but a cam follower or some other component of the cam device is coterminous with the, for example, actuator belt.  
         [0062]     As used herein, the term “belt support” means a mechanism that holds the end of a belt. By way of example but not limitation, a belt support may include a passive carriage riding on a linear bearing.  
         [0063]     As used herein, the term “embodiment” means an embodiment that serves to illustrate by way of example but not limitation.  
         [0064]     It will be appreciated to those skilled in the art that the preceding examples and embodiments are exemplary and not limiting to the scope of the present invention. It is intended that all permutations, enhancements, equivalents, and improvements thereto that are apparent to those skilled in the art upon a reading of the specification and a study of the drawings are included within the true spirit and scope of the present invention. It is therefore intended that the following appended claims include all such modifications, permutations and equivalents as fall within the true spirit and scope of the present invention.