Patent Publication Number: US-2011058893-A1

Title: Continuously variable positioning device

Description:
FIELD 
     Positioning device for continuously varying the relative position of two bodies, such as a joint. 
     BACKGROUND 
     Most mechanical positioning devices use a friction-based or pin-in-hole type locking system. These systems suffer from the difficulty in maintaining positions against multilateral forces, their inability of adapting to multidimensional joint applications, the need for a strong locking force, a limited number of locking positions, questionable weight bearing strength, and difficulty in obtaining 3D locking capability. 
     U.S. Pat. No. 6,238,124 (Merlo) describes a repositionable joint that is suitable for use in a prosthetic arm. The joint has two parts with engaging surfaces that can be pulled apart to adjust the relative orientation of each, and lock together to maintain the desired position. 
     SUMMARY 
     According to one aspect, there is provided a continuously variable positioning device. The continuously variable positioning device has a first body having a first engagement surface. At least part of the first engagement surface is covered with a pattern of movable actuators. There is also a second body having a second engagement surface in contact with the first engagement surface. At least a part of the second engagement surface has an actuator engaging profile. At least some of the movable actuators are depressed and others of the movable actuators are extended to conform to the actuator engaging profile. Means are provided for creating relative movement of the first body and the second body while maintaining the first engagement surface continuously engaged with the second engagement surface. The movable actuators move axially during relative movement of the first body and the second body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: 
         FIG. 1  is a perspective view of a prior art joint locking mechanism. 
         FIG. 2  is a perspective view of a continuously variable positioning device. 
         FIG. 3  is a side elevation view in section of the continuously variable positioning device in a first position. 
         FIG. 4  is a side elevation view in section of the continuously variable positioning device in a second position. 
         FIG. 5  is a side elevation view in section of the continuously variable positioning device in a third position. 
         FIG. 6  is a perspective view of the continuously variable positioning device with an actuator. 
         FIG. 7  is a top plan view of an alternative actuator. 
         FIG. 8  is a side elevation view in section of the continuously variable positioning device with an outer enclosure. 
         FIG. 9  is a side elevation view in section of the continuously variable positioning device with an outer enclosure in a disengaged position. 
         FIG. 10  is a side elevation view in section of the continuously variable positioning device with an outer enclosure in a locked position. 
         FIG. 11  is a side elevation view of a planar second body, and position-controllable movable actuators. 
     
    
    
     DETAILED DESCRIPTION 
     A prior art device will be described with reference to  FIG. 1 . The preferred embodiment, a continuously variable positioning device generally identified by reference numeral  10 , will then be described with reference to  FIG. 2 through 11 . 
     Structure and Relationship of Parts: 
     Referring to  FIG. 1 , a prior art “passive-locking” joint is shown. In this joint, a rounded object  102  such as a ball or part thereof has a surface covered with polygonal patterns of spaced apart protuberances  104 . The spaces between protuberances  104  are cavities  105 . When an assembly  106  of closely spaced, pressure sensitive actuators  108  are imprinted against the protuberances  104 , the actuators  108  emulate a mirror image of the opposing surface. Actuators  108  contacting protuberances  104  are pushed back, while unobstructed actuators  108  penetrate into the cavities  105  between protuberances  104 . Once trapped in a cavity  105 , the actuators  108  are unable to move in any direction, thereby freezing the spatial orientation between actuators  108  and ball surface  102  against forces of pitch, yaw and roll (the three degrees of freedom). As soon as the actuator assembly  106  is disengaged from the protuberances  104 , the unhindered ball  102  can be freely moved to another angle. The actuators  108 , compressed to various depths while engaged with the protuberances  104 , regain their fully extended position and are ready to imprint the protuberances  104  at a different locking position. The actuators  108  are surrounded by an upstanding lip  110 , which forms part of an entire structure intended to encapsulate the actuators  108  and the ball surface  102 . This joint has two positions: a disengaged adjustment position that allows the orientation of the joint to be manipulated, and an engaged locking position, where the selected orientation is fixed. 
     The present positioning device  10  uses a similar locking principle to act as a three dimensional mechanical gear drive mechanism that features a permanent linkage between two engaging surfaces. This linkage enables a continuous flow between locking positions. By providing an adaptable surface with individually movable components, the versatility of the device is increased. Furthermore, unlike the multiple unidirectional joint systems commonly used for manipulator arms throughout the robotics industry, the new device is capable of replicating the three dimensional movements of pitch, yaw and roll from a single unit joint mechanism. 
     Referring to  FIG. 2 , continuously variable positioning device  10  includes a first body  12  having a first engagement surface  14  and a second body  16  having a second engagement surface  18 . As depicted, second engagement surface  18  is arcuate, although it will be apparent from the discussion below that other shapes may also be possible. At least part of first engagement surface  14  is covered with a pattern of movable actuators  20 . At least a part of second engagement surface  18  has an actuator engaging profile  22 . As depicted in  FIG. 2 , actuator engaging profile  22  is made up of a pattern of protrusions and concavities. It will be understood that other patterns or designs may be used that involve, for example, ridges, valleys, holes, etc. Second engagement surface  18  is in contact with first engagement surface  14  such that at least some of the movable actuators  20  are depressed and other movable actuators  20  are extended to conform to actuator engaging profile  22 . In so doing, first engagement surface  14  conforms to second engagement surface, such that a larger contact surface area is provided than would otherwise be possible. Second body  16  has a terminal device connection for connecting a device to second body  16 , such as a prosthetic, or a robotic tool. 
     In contrast to the prior art, there is also provided means for creating relative movement of first body  12  and second body  16 , while maintaining first engagement surface  14  continuously engaged with second engagement surface  18 . Movable actuators  20  move axially during relative movement of first body  12  and second body  16 . There may be different means for creating relative movement. In one embodiment, a drive assembly may be used to move either first body  12  or second body  16 . An example of this is depicted in  FIG. 6 . In this embodiment, drive assembly  40  moves first body  12  laterally while second body  16  is secured in a housing to  52  cause it to move about a pivot point. The actuator may also rotate first body  12 . By controlling the lateral movement and rotation of first body  12 , the pitch, yaw and roll of second body  16  is also controlled. Alternatively, a different drive assembly may be provided that adjusts the pitch, yaw and/or roll of second body  16 , which would then control the orientation of first body  12 . In either of these embodiments, movable actuators  20  would be passive, spring loaded actuators to permit first engagement surface  14  to conform to second engagement surface  18  at all times. It will be understood that instead of a physical spring  21  as shown, actuators  20  may use a different type of compressible fluid or solid to provide a spring effect. 
     In another embodiment, referring to  FIG. 11 , some or all of movable actuators  20  are position-controllable, such that the position and orientation of second body  14  could be adjusted in a desired direction by extending some actuators  20 , and retracting others. All actuators  20  need not be position controlled by, for example, a linear actuator  23  or a hydraulic system, with the remainder of actuators  20  being passive, spring loaded actuators. 
     In other embodiments, either or both of first body  12  may have arcuate, planar, or other shapes of engagement surfaces  14  and  18 , depending on the preferences of the user.  FIG. 11  shows an embodiment where both first body  12  and second body  16  are planar. Suitable adjustments to the rest of positioning device  10  will be recognized by those skilled in the art. 
     Referring to  FIG. 6 , additional details on drive mechanism  40  will now be given. Assembly actuator  40  has two linear drive mechanisms  42  and  44  and a rotating drive mechanism  46 . Linear drive mechanism  42  and  44  control the lateral position of first body  12 , while rotating drive mechanism  46  rotates first body  12  about an axis, in the directions indicated by the arrows. Linear drive mechanisms  42  and  44  move along horizontal shafts  48 . Each moves first body  12 , as well as the drive mechanisms between it and first body  12 , in the associated direction. Rotating drive mechanism  46  rotates first body  12 . The three drive mechanisms  42 ,  44 ,  46  work together to control the roll, pitch and yaw of second body  16  and any terminal device attached thereto. These drive mechanisms  42 ,  44 ,  46  may also be programmed to move second body  16  along a specific movement path. In some situations, it may be preferable to provide a computer to control drive mechanisms  42 ,  44 ,  46  to achieve precise movements and positions. 
     Referring to  FIG. 7 , an alternative drive mechanism  24  is shown. Drive mechanism  24  is connected to move first body  12 , and has a planar drive mechanism  26  and a rotating drive mechanism  27 . Planar drive mechanism  26  includes a threaded shaft  28  that moves a platform  30  when rotated, or two as shown. Platform  30  is attached to first body  12 . Threaded shafts  28  have a gear  34  mounted at each end, such that, as gears  34  turn, the orientation of threaded shaft  28  is changed. This allows threaded shaft  28  to move first body  12  laterally in any two-dimensional direction. Rotating drive mechanism  27  is carried by, or moves with, planar drive mechanism  26  and rotates first body  12 . By controlling the movement of both planar element  26  and rotating element  27 , the pitch, roll and yaw of second body  16  can be adjusted in a smooth, continuous fashion, and even through a desired path of travel. 
     It can be seen from the two examples given above that drive mechanism controls the lateral and rotational position of first body  12  and thus the roll, pitch and yaw of second body  16 . Other designs that provide the necessary range of motions will be apparent to those skilled in the art beyond those depicted and described. However, the drive mechanisms described above have the advantage of being able to fit within a narrow housing, which may be important if device  10  is used, for example, as a wrist joint for a robotic arm. 
     In a preferred embodiment, a two-dimensional electronic positioning system acts as the control center for positioning device  10 . The positioning system is capable of controlling the directional and rotational movements of first body  12  interlinked with its race counterpart. Simultaneous directional and rotational changes by the actuator assembly triggers a true representation of all the three-dimensional movements while constantly maintaining a true 3D interlock between the ball race  18  and actuators  20  throughout the entire repositioning process. 
     In another embodiment, referring to  FIG. 8 through 10 , the axial position of a movable actuator assembly  32  relative to second body  16  may be controlled. Referring to  FIG. 8 , movable actuator assembly  32  includes first body  12  and an outer enclosure  33 . Outer enclosure  33  may move with first body  12 , independently of first body  12 , or a combination of both. This allows a user to select the intermediate, movable position shown in  FIG. 8 , to disengage first and second engagement surfaces  14  and  18  as shown in  FIG. 9 , or to lock device  10  by causing movable actuator assembly  32  to engage second engagement surface  18  as shown in  FIG. 10 . As movable actuator assembly  32  does not conform to second body  16  as do movable actuators  20 , the relative position of first and second bodies  12  and  16  will become locked. This may be useful in situations where, for example, a large force will be applied to one or the other bodies, or if the user wishes to ensure that the position will not accidentally change. 
     Below is a discussion of the preferred embodiment, where a ball joint is provided that is connected to a suitable terminal device (e.g. a prosthetic hand or robotic tool) by a connector  50 , held in place by a shell-like enclosure, such as a stationary, immovable metal ring (not shown), and is able to move completely around its own axis and/or tilt in all directions within its confines. For example, a tilt of up to 50 degrees from center may be permitted, or using other designs, a tilt of more than 90 degrees from center may be achieved. A portion of the ball  16  is comprised of ball race protuberances that are permanently interlinked with a crown of pressure sensitive, spaced actuators  20 . The resulting coupling is supple and extremely flexible. 
     Bound by that physical linkage, the closely interdependent parts can only move as a union, each part with the other in tow. The actuator assembly thus controls the movement of the ball joint  10 . When the actuator assembly moves within a small horizontal orbital plane, it directs the angular and rotational deviations of the ball-race and consequently the terminal device attached thereto. Every degree of tilt and/or axial rotation by the terminal device is directly proportional to the directional changes made by the actuators. In essence, the two components move in tow, with every directional change by the actuator assembly within the periphery of a horizontal orbital platform directly related to the degree of tilt or axial rotation of the terminal device. 
     This embodiment is able to work due to the unique shape of the ball race protuberances and their ability to interact with the actuators. Directional changes by the drive mechanism triggers a reaction between the two entities, whereby the tips of the pressure sensitive actuators continuously self adjust their various extensions into the concavities between the race protrusions as they yield to the fluctuating pressures of the protuberances in a smooth cam action. To safeguard the unhindered self-adjustment of actuators, the ball-race protuberances must not contact the top rim of the actuator enclosure while being manipulated. The counteracting interdependency between actuators and protuberances tilts the terminal device to the left when the actuator assembly is moved to the right and vise versa. A turning motion of the actuator entity causes the terminal device to tag along a 360 degree pathway whatever the preset angle. 
     The chaotic interplay between protuberances and the closely spaced actuators can be replaced by two highly compatible interlinking surfaces. Spacing the actuators to fit the openings between protuberances modeled according to the divisions of a platonic solid. For example, the shape of actuators and protuberances may be optimized by using an icosahedron geometry. Furthermore, changing the height of protuberances and lengthening the protruding actuators, will alter the depth of penetration between the two entities. Various depths of penetration as well as enhanced locking characteristics can also be achieved by raising or lowering the actuator assembly. 
     ADVANTAGES 
     This device may be used in a multitude of robotic applications. A vital key to the successful development of compact, single unit 3D joint modules is the ability to power a robotic joint between locking positions. It is anticipated that this technology could replace the successive pitch, yaw and roll movements used in the wrist assemblies of current manipulator arms in appropriate circumstances. 
     In theory, a minimum of two actuators are required to block all three degrees of physical freedom. The advantage of increasing that number several times assures the distribution of external forces over a broad surface area. Large numbers of penetrating actuators also give a significant boost to the weight bearing ability of the joint system. Depending on the application the actuator assembly may be closely spaced or individually guided. According to the FEA (Finite Element Analysis) report, the overall joint strength doubles by increasing the diameter of actuators and protuberances 26%. 
     Other advantages of this design include:
         Unlimited 3D locking positions at any plane or angle within operating range   Self-varying, self engaging core surfaces   Suitable for 1D, 2D &amp; 3D joint applications   Instant 3D locking at all locking sites/Manual or electronic control   Unequalled locking &amp; weight bearing strength against forces of pitch, yaw and roll       

     Variations: 
     The above description and drawings have described an embodiment where the locking profile is made up primarily of a series of protuberances and concavities. It has been found that this provides an economical and practical solution for providing two surface that interlock when engaged. It will be understood, however, that other locking profiles may also be used. For example, the locking profile may consist of a series of ridges or valleys that would depress some actuators and engage others. The locking profile may be designed with depressions, extensions, or combinations of the two. Other patterns for locking profile and actuators will be apparent to those skilled in the art. 
     The above description also focused on the situation where the first body is moved laterally in order to change the pitch and yaw of the second body. However, different movements are also possible. For example referring to  FIG. 11 , the height of some or all pistons may be controlled, such that the second body may be “pushed” in a certain direction to obtain the desired movement. In this case, the first body would remain stationary, and the second body you move laterally in addition to changing its pitch and yaw. Furthermore, using this design, it would be possible to control the orientation of a body with a flat surface, rather than a rounded surface as depicted. The position-controlled actuators would push the body and cause its orientation to change. 
     It is also possible to have a rounded second body control the position of the first body by adjusting the orientation of the first body. As the second body moved about its pivot point, the moving locking engagement would apply a force to the actuators to cause them, and thus the first body, to move laterally. 
     To better follow the curvature of the ball, the assembly of actuators may consist of three different actuator lengths, the outermost being the tallest. The interaction between actuators and protuberances causes the tips of the motion sensitive spring-loaded actuators to yield to the varying pressures of the conically shaped ball-race protuberances. While the steel enclosed actuator assembly is in motion, the actuators continuously self adjust their varying extensions into the cluster of protuberances in a smooth cam action like fashion. To assure the unhindered self adjustment of the actuators it is of critical importance that the protuberances on full impact with the actuators stay spaced from the top rim of the steel actuator enclosure. Throughout this entire repositioning process, the union between actuators and protuberances retains its 3D interlock against external multilateral forces. The ball-race for a possible wrist-joint application could feature an open central core to accommodate wire harness connections, while the crown of actuators may be ring-shaped to allow unimpeded access for electronic circuitry. 
     In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. 
     The following claims are to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the described embodiments can be configured without departing from the scope of the claims. The illustrated embodiments have been set forth only as examples and should not be taken as limiting the invention. It is to be understood that, within the scope of the following claims, the invention may be practiced other than as specifically illustrated and described.