Abstract:
A technique for deflecting an actuator belt includes applying a variable deflection force to the actuator belt. 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.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     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 
     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 torque 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. 
     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. 
     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 
     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. 
     A technique for deflecting an actuator belt includes applying a variable amount of deflection to a pair of belts (including, e.g., chains). The deflection distance can be set in multiple ways. For example, deflection distance can vary in a load-dependent manner to reduce the displacement as the load increases as an element of an automatically adjusting VRT. As another example, the deflection distance can be set based on input from a control system or vehicle operator, for instance, to increase torque (via smaller displacements) when acceleration is desired or to reduce the input motor speed (via larger displacements) when better economy or high speed is desired. 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 
       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. 
         FIGS. 1A and 1B  are diagrams illustrating a principle of operation. 
         FIG. 2  depicts a conceptual example of a deflector system. 
         FIGS. 3A and 3B  are flowcharts of methods for actuator-mode operation of a worm-braked actuator. 
         FIG. 4  is a graph illustrating continuous torque as tension is passed from one belt to another belt. 
         FIG. 5  shows an example of a device to deflect an actuator belt. 
         FIG. 6  shows a cam follower mechanism for deflecting a belt. 
         FIGS. 7A ,  7 B,  7 C,  7 D, and  7 E show examples of externally controllable mechanisms for setting the ratio of a variable ratio actuator, generator or transmission. 
         FIGS. 8A ,  8 B, and  8 C depict an example of a variable ratio deflector system. 
         FIGS. 9A and 9B  show a three-link belt with magnetic return mechanism. 
         FIGS. 10A and 10B  depict a complete bi-directional linear slider assembly including a variable ratio deflector mechanism. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
       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. 
     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. 
     U.S. patent application Ser. No. 11,649,403 entitled “Rotary Actuator” by Horst et al. filed concurrently herewith is incorporated by reference. U.S. patent application Ser. No. 11,649,493 entitled “Linear Actuator” by Horst et al. filed concurrently herewith is incorporated by reference. U.S. patent application Ser. No. 11,649,496 entitled “Continuously Variable Transmission” by Horst et al. filed concurrently herewith is incorporated by reference. 
       FIG. 2  depicts a conceptual example of a deflector system  200 . The system  200  includes a deflector  202 , a deflector lever  204 , a repositionable deflector rest  206 , and a time-variable lever lifter  208 . The deflector  202  may include any component that directly deflects an actuator belt. Although the deflector  202  physically touches the actuator belt in a specific embodiment, the deflector  202  could make use of, for example, magnetism, to deflect the actuator belt. Any applicable known or convenient component may be used in this manner. 
     The deflector lever  204  is capable of directing the deflector  202  toward an actuator belt. The deflector lever  204  could have practically any shape, though a rod-shaped deflector lever is used in a specific implementation. The shape could vary dependent upon functional requirements such as available space, or for non-functional reasons, such as aesthetics. 
     The repositionable deflector rest  206  is juxtaposed with the deflector lever  204  at a juxtaposition point. The arrow under the repositionable deflector rest  206  conceptually illustrates that the juxtaposition point could be moved along the deflector lever  204 . The deflector  202  deflects the actuator belt that moves the load to a degree that is at least partially depending upon the position of the juxtaposition point during at least a portion of the increasing deflection period. 
     The time-variable lever lifter  208  is coupled to the deflector lever  204 . The time-variable lever lifter  208  lifts the deflector lever  204  by an amount that varies with time. This is illustrated by the dotted box with an arrow that is connected to the time-variable lever lifter  208  in the example of  FIG. 2 . Although the time-variable lever lifter  208  and the repositionable deflector rest  206  do not appear to be connected to one another in the example of  FIG. 2 , as will be seen in later examples, the repositionable deflector rest  206  may or may not be positioned between the deflector lever  204  and the time-variable lever lifter  208 . The example of  FIG. 2  is conceptual, and is not intended to illustrate actual component positions. 
       FIG. 3A  is a flowchart  300 A showing operation of a worm-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 motor. 
     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 worm motor A. Worm motor A may be either of dual (or more) worm motors that are part of a worm brake assembly of a continuously variable ratio actuator. The result of advancing worm motor A is that belt A is tightened. Belt A may be either of dual (or more) belts that are part of a continuously variable ratio actuator. 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. 
     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 , worm motor B is advanced to tighten belt B. Thus, the cam is rotated to deflect belt A while simultaneously tightening belt B. 
     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 , worm 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. 
     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). 
       FIG. 3B  is a flowchart  300 B showing operation of a worm-braked device in braking mode.  FIG. 3B  is intended to illustrate a braking mode of a continuous variable ratio motor. 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. 3B , the flowchart  300 B starts at module  322  with selecting braking mode. 
     In the example of  FIG. 3B , the flowchart  300 B 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 , worm 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 worm 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. 
     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. 
     In the example of  FIG. 3B , the flowchart  300 B continues at modules  328 - 1  and  328 - 2 , which may be executed simultaneously. At the module  328 - 1 , worm 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. 
       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 output shaft movement in rotations is this belt deflection amount divided by the circumference of the output sprocket.  FIG. 4  is plotted for a cam shape for 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 with very little torque ripple. 
     The shape of the cam also allows for different drive ratios simply by adjusting the angle at which the cam touches and begins to deflect the belt. If the tensioner positions the belt to be tangent to the minimum radius of the cam, then the belt is deflected by the first 180 degrees of cam rotation. If the tensioner moves the belt support such that it contacts the cam only when it reaches 90 degrees of rotation, then the cam deflects the belt between 90 and 270 degrees. With this cam design, the radius delta of the cam between 0 and 180 degrees is greater than between 90 and 270 degrees, hence the belt is deflected less and movement of the tension has the effect of reducing the output speed, effectively dropping into a lower gear. 
       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 torque 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 the 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. 
     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. 
       FIG. 5  shows an example of a device  500  to deflect an actuator belt. The device  500  includes a driver  502 , a plate  504 , a plate  506 , a rocker arm  508 , and a sprocket  510 . For illustrative purposes, a base  512  is also depicted. The driver  502  may include any applicable device that is capable of rotating the plate  504 . In the example of  FIG. 5 , the driver  502  is depicted, conceptually, as coupled to a rotation point  514 . In some implementations, the driver  502  would appear to be behind the base  512  (where  FIG. 1  represents a front view). In some implementations, the driver  502  is affixed to the base  512 . 
     In the example of  FIG. 5 , the driver  502  is coupled to the rotation point  514 , to which the plate  504  is also coupled. Thus, in operation, when the driver  502  rotates the rotation point  514 , the plate  504  is also rotated. 
     In the example of  FIG. 5 , the plate  504  is coupled to the plate  506  at a pivot point  516 . In order for the plate  506  to properly pivot at the pivot point  516 , the pivot point  516  should have some radial distance from the rotation point  514 . 
     In the example of  FIG. 5 , the rocker arm  508  is coupled to the base  512  at a pivot point  518 , and to the plate  506  at a pivot point  520 . Since the rotation point  514  and the pivot point  518  are fixed relative to one another, the rocker arm  508  rocks back and forth around the pivot point  520  when the driver  502  rotates the plate  504 . In a non-limiting embodiment, the rocker arm may be constructed from, for example, spring steel or some other applicable known or convenient material, and formed in such a way that it acts as an extension spring. Thus, when an actuator belt has high tension, the spring extends and the displacement of the belt is reduced. This may be advantageous in an embodiment in which automatic downshifting is desired. 
     In the example of  FIG. 5 , the sprocket  510  is coupled to the plate  506 . The motion of the plate  506 , when the driver  502  causes the plate  504  to rotate and the rocker arm  508  to rock back and forth, is depicted as a dashed line that passes through the center of the sprocket  510 . The net motion is an oval path where the Y direction first changes quickly then slows as the motion is more in the X direction. Finally there is a quick return from the maximum Y displacement back to the minimum Y displacement. 
     In a non-limiting embodiment, the sprocket  510  is coupled to the plate  506  at the sprocket center  522 , and is capable of rotating as it deflects an actuator belt (not shown) engaged by the sprocket  510 . The term “sprocket” implies that the actuator belt is a chain. However, alternatively, the sprocket  510  can be replaced with any applicable deflector, which may or may not rotate around the center. 
       FIG. 6  depicts a deflection device  600  including a cam follower mechanism. The device  600  includes a deflector  602 , a deflector lever  604 , a time-variable lever lifter  606 , and a repositionable deflector rest  608 . In the example of  FIG. 6 , the deflector  602  includes a cable deflector pulley. However, any applicable known or convenient mechanism that can be used to deflect an actuator belt could be used. 
     In the example of  FIG. 6 , the deflector  602  is coupled to the deflector lever  604 . The deflector lever  604  may include, by way of example but not limitation, spring steel that deflects to a lower ratio under a heavy load. However, any applicable known or convenient component that is capable of coupling the time-variable lever lifter  606  to the deflector  602  as described herein could be used. 
     In the example of  FIG. 6 , the time-variable lever lifter  606  includes a cam device. In an illustrative embodiment, the time-variable lever lifter  606  includes a cam  610  and a cam follower  612 . In this illustrative embodiment, the amount of lift provided by the time-variable lever lifter  606  is at least partially dependent upon the position of the cam  610 . In the example of  FIG. 6 , the cam  610  is positioned at a maximum lift position, which results in the deflector lever  604  being pulled down at one end by the cam follower  612 , while the end of the deflector lever  604  that is coupled to the deflector  602  is raised. In the example of  FIG. 6 , the cam  610  has a minimum lift position illustrated as a dotted line, which results in zero lift (though in an alternative embodiment, there could be some lift). When the cam  610  rotates, the cam follower  612  moves up and down at a pivot point  614 . Since the cam follower  612  is connected to one end of the deflector lever  604 , the deflector lever  604  is pulled up and down in a similar (opposite) manner. In an illustrative embodiment, the pivot point  614  is a rotation point fixed relative to a housing (not shown), while pivot point  616  is a movable pivot point that couples the cam arm to the deflector arm. When the cam forces the left end of the cam arm upward, the right end of the cam arm moves down, moving pivot point  616  down. The downward motion of the pivot point  616  lowers the left end of deflector lever  604  and raises the right end of deflector lever  604 . The amount of upward motion of the right end of deflector lever  604  varies depending on the position of repositionable deflector rest  608 . 
     The amount of distance the deflector  602  actually travels is dependent upon a ratio range select, illustrated in  FIG. 6  as a double-ended arrow near the repositionable deflector rest  608  because the repositionable deflector rest  608  is juxtaposed with the deflector lever  604  at a juxtaposition point. In operation, the deflector  602  is raised by the time-variable lever lifter  606  to a degree that is at least partially dependent upon the position of the juxtaposition point. As the juxtaposition point moves to the right, the deflector  602  has less maximum displacement on each cycle. In another embodiment, the deflector lever  604  may be designed with spring steel to provide and automatic mechanism to reduce the displacement as the load increases. 
       FIGS. 7A ,  7 B, and  7 C show an externally controllable mechanism for setting the ratio of a variable ratio actuator, generator or transmission. The components of  FIGS. 7A ,  7 B, and  7 C are similar to those of  FIG. 6 , but the repositionable deflector rest  608  ( FIG. 6 ) is shown in a bit more detail for the alternative embodiment depicted by  FIGS. 7A ,  7 B, and  7 C.  FIGS. 7A ,  7 B, and  7 C are intended to illustrate a repositionable deflector rest connected to a compression spring to allow for automatic ratio adjustment.  FIG. 7A  shows the minimum cam position where an actuator belt is tangent to the deflector sprocket regardless of the juxtaposition point setting.  FIG. 7B  shows the maximum deflection for a high gear setting, and  FIG. 7C  shows the maximum deflection for a lower gear setting. 
     In an alternative embodiment, the repositionable deflector rest could be controlled by a linear actuator such as a worm motor, hydraulic actuator, or a manually operated mechanism (e.g.,  FIG. 7D ). In cases where an actuator controls the position of the repositionable deflector rest, a control system can precisely set a desired ratio by measuring the rotation speed of the driver and the output to compute the current ratio (e.g.,  FIG. 7E ). When the current ratio is less than the desired ratio, the juxtaposition point is moved left, and when it is more than desired, the juxtaposition point is moved right. 
       FIGS. 8A ,  8 B, and  8 C depict an example of a variable ratio deflector system  800 . The system  800  includes a deflector  802 , a deflector lever  804 , a repositionable deflector rest  806 , a cam arm  808 , a cam  810 , a cam follower  812 , and a driver  814 . A juxtaposition point is identified by the reference number  816 . In the example of  FIGS. 8A ,  8 B, and  8 C, a three link actuator belt is depicted as three links  818 - 1 ,  818 - 2 , and  818 - 2 , referred to collectively as the actuator belt  818 . 
     A system such as is shown in the example of  FIGS. 8A ,  8 B, and  8 C may be suitable for deflecting a belt, chain or linkage as part of a variable ratio transmission or actuator.  FIGS. 8A ,  8 B, and  8 C show how the driver  814  rotates the cam  810 , causing the cam arm  808  coupled to the cam follower  812  to rise. The cam arm  808 , cam  810 , cam follower  812 , and driver  814  may be referred to collectively as a time-variable lever lifter. 
     The time-variable lever lifter pushes at the end of a spring that is part of the repositionable deflector rest  806  to move a track that is also a part of the repositionable deflector rest  806 . It may be noted that in the system  800  the repositionable deflector rest  806  is positioned between the time-variable lever lifter and the deflector lever  804 . 
     The repositionable deflector rest  806  pushes on the deflector lever  804  at the juxtaposition point  816 . In an illustrative embodiment, the juxtaposition point  816  may include a roller coupled to the deflector lever  804 . In alternative embodiments, the juxtaposition point  816  could be any other component (or lack thereof) that is interposed between the repositionable deflector rest  806  and the deflector lever  804 , and may be considered a part of the deflector lever  804  and/or repositionable deflector rest  806 . 
     The deflector lever  804  pushes the deflector  802  against the actuator belt  818 . In an illustrative embodiment, the deflector  802  may include a roller. In an illustrative embodiment, two mechanisms such as just described are driven by out of phase cams  810  to drive two actuator belts  818 . 
     In an illustrative embodiment, the deflector lever  804  may include a roller at the juxtaposition point  816  that rides on the repositionable deflector rest  806 . When the load on the belt  818  is light or moderate, the spring deflects a small amount, deflecting the belt  818  as if the fulcrum (roller) had shifted to the left. Shifting the fulcrum to the left gives the cam arm  808  more mechanical advantage against the belt  818  and reduces the deflection of the belt  818 . 
     In the example of  FIG. 8A , at the left end of the deflector lever  804  is a contact plate  820  that limits the maximum spring compression and prevents the fulcrum from shifting farther left than this point. When the load is at its maximum, the contact plate  820  is in contact with the repositionable deflector rest  806  throughout the entire deflection cycle as set by the rotation of the cam  810 , as shown in  FIGS. 8A and 8C . The height of the contact plate  820  sets the minimum amount of deflection of the belt  818  on each cycle and hence sets the lowest gear ratio of the actuator. 
       FIG. 8A  depicts the variable ratio deflector assembly in a minimum deflection position. In the example of  FIG. 8A , the cam is at a minimum position, and the belt is actually not deflected at all. Where the belt is not deflected at all, the minimum position may be referred to as a zero position. However, in some embodiments, the minimum position may not be zero (i.e., the belt may be deflected at least slightly. 
       FIG. 8B  depicts the variable ratio deflector assembly in a high gear position. In the example of  FIG. 8B , the cam is at a maximum position, and the belt is deflected a maximum amount. If a stiff resistance is encountered when attempting to move the output shaft, the spring compresses and each deflection moves the actuator belt  818  a shorter distance but with more force, effectively dropping the actuator into a lower gear. 
       FIG. 8C  depicts the variable ratio deflector assembly in a low gear position. In the example of  FIG. 8C , the cam is at a maximum position, as it was in  FIG. 8B . However, the spring is compressed so there is relatively little belt deflection. 
       FIGS. 9A and 9B  depict an example of a three-link actuator belt  902  with magnetic return mechanism  904 - 1 ,  904 - 2  (referred to collectively as the magnetic return mechanism  904 ). A three-link belt is advantageous in linear actuators because it can be made out of a strong material that stretches very little under load (e.g. steel), and because it can incorporate a magnet at each end to pull the belt flat. 
       FIG. 9A  shows a magnetic return mechanism  904  starting position for pulling the belt  902  flat after each actuator cycle.  FIG. 9B  shows the magnetic return mechanism  904  pulling the belt  902  flat. In a deflection based actuator, it is advantageous to pull the belt  902  flat after every stroke. Pulling the belt flat with lead screw motors alone will never pull the belt perfectly flat because the force required becomes infinite (1/sin theta) as the belt approaches perfectly flat. However, the magnets can be placed such that their force increases as the belt  902  is nearly flat, and a relatively small magnet is required. The use of the magnetic return mechanism  904  can reduce the size of the lead screw motors required, and can allow for a lower gear possible than without this mechanism. If the belt  902  is not pulled as flat, then there may be too much slack in the belt  902  to allow it move the output shaft when the deflector mechanism is attempting to deflect the belt  902  by a very small amount (e.g., in very low gear). 
       FIGS. 10A and 10B  depict a complete bi-directional linear slider assembly including a variable ratio deflector mechanism. The examples of  FIGS. 10A and 10B  are intended to respectively illustrate complete actuator and deflector assemblies.  FIG. 10A  shows a complete slider assembly. Only the front belt and slider assembly is shown in this drawing. The front and back belt and slider assemblies operate similarly, but in an embodiment they are out of phase by 180 degrees. 
     In the example of  FIG. 10A , a belt connects left and right belt holders. A lead screw brake engages one of the belt holders to stop its movement. The other belt holder engages a pin connected to the output shaft. When the belt is deflected, the belt pulls the output load. By setting the brake to stop the other belt holder, a belt deflection pulls the output in the opposite direction. 
       FIG. 10B  shows a dual deflection assembly suitable for deflecting the belt in  FIG. 10A . When operationally assembled, the top of the deflector assembly of  FIG. 10B  couples to the bottom of the actuator of  FIG. 10A  with the deflector roller pushing on the belt. The operation of the dual deflection assembly is similar to that described previously with reference to  FIG. 8 . 
     The invention is not limited to the specific embodiments described. 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. 
     As used herein, the term “embodiment” means an embodiment that serves to illustrate by way of example but not limitation. 
     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.