WRIST TENDON ACTUATOR

Abstract: The wrist actuator or joint (10) includes a ball (20) having two grooves (22, 24) in its surface, each groove extending circumferentially about the ball and disposed approximately 90<o> from each other. A housing (40) has a socket for receiving the ball and includes two slots (41, 42) located proximately at an equatorial plane of the ball. A frame (32) is secured to the ball at the intersection of the grooves opposite the housing. A first ribbon (52), slidable within the first groove (22), is attached to pivot pins (56, 58) in the slots and is looped aroud a first pulley (70) within the frame. A second ribbon (54), slidable within the second groove (24), is attached to pivot pins (60, 62) mounted in the housing at the approximate midpoints between the slots and is looped around a second pulley (74) within the frame. An output shaft (45) is connected to the housing. Motors (72, 76) provide selective movement of the drive ribbons.

Description: WRIST TENDON ACTUATOR BACKGROUND OF THE INVENTION -*-• Field of the Invention. The present invention relates generally to mechanical joints and in particular relates to a mechanical joint for a robot wrist. 2. Description of the Prior Art. Interest in robotics and the use of robots in industrial applications has greatly increased in recent years. One area in which the use of robots has become important is the replacement of humans in tasks that involve manual work, such as welding, material handling, paint spraying, and assembly. Many of these tasks require working in cramped spaces or performing complex maneuvers. To perform such tasks, a robot arm or wrist should be able to rotationally move in a range similar to a human wrist and at a dwell time acceptable for the particular task involved. One article reviewing the development of robot arms and wrists is entitled, "Robot Wrist Actuators," Robotics Age, November/December 1982, pp. 15-22, and was written by the applicant of the present application. In the article, several characteristics are described that make robot wrists attractive. One characteristic is that a mechanical arm or wrist can be safely used in areas where there is a danger of explosion if the wrist is driven by hydraulic actuators. However, there are several disadvantages with the prior art robot arms and wrists. Some of the disadvantages are also enumerated in the above-mentioned article and include large and bulky mechanical joints, slow dwell time in some rotational directions and low mechanical efficiency. A number of well known universal joints are illustrated and described on pages 16 and 17 of the Pictorial Handbook of Technical Devices by Pete Grafstein and O. Schwarz, published by the Chemical Publishing Company, Inc. of New York, 1971. Although rotational motion can be transmitted through the universal joints illustrated on pages 16 and 17, the universal joints cannot be used in operations for transmitting pitch, yaw and roll motion to an implement or tool member. A rotary actuator mechanism is described in the Higuchi et al U.S. Patent 4,009,644. However, the rotary actuator of the Higuchi et al Patent is not very useful for the transmission of pitch, yaw and roll motion to a tool or implement member. A number of robot joints are illustrated in the Vykukal U.S. Patent 3,405,406 and the Vykukal et al U.S. Patent 4,046,262. The Vykukal patents describe hard-type space suits that permit the user inside the space suit to move around somewhat unrestricted. The Bolner U.S. Patent 3,912,172 describes a back-drivable, direct drive, hydraulically-actuated pitch and roll actuator. The Roshei U.S. Patents 4,194,437 and 4,296,681, which were issued to the applicant of the present application, describe hydraulic servomechanisms which impart rotary movements to a device to -be driven. The Stackhouse U.S. Patent 4,068,536 describes a remotely-driven, mechanical manipulator. The manipulator is controlled by three concentric drive shafts which terminate in a spherically-spaced wrist mechanism. The Totsuka U.S. Patent 3,739,923 and the Niitu et al U.S. Patent 3,784,031 describe a manipu¬ lator arm having two parallel rotating drive shafts in a beveled gear system which translates the drive shaft's rotating motion to a bending pitch motion and rotary roll motion in a tool member. A mechanical wrist is described in German Patent 2,752,236 that includes three electric motors, providing pitch, yaw, and roll, which are mounted on the outside • of a housing with the inside of the housing being hollow. The wrist is used for holding welding tongs and the hollow inside housing permits electrical power lines to be fed through the wrist. The Molaug U.S. Patent 4,107,948 describes a flexible robot arm that is composed of a number of mutually connected rigid links being connected at one end to a drive means and at the other end to a tool member that is to be rotated. Another robot arm is illustrated in the Wells U.S. Patent 3,631,737. The robot arm of the Wells Patent includes a plurality of rigid tubular sections joined end-to-end by flexible joints to form an articulated arm. The rigid sections are manipulated by slender control cables which are attached to the respective sections and selectively extend and retract. SUMMARY OF THE INVENTION The present invention is a ball and socket mechanical joint having pitch, yaw and compound pitch-yaw movement, particularly adaptable for anthropomorphic joint design including hand knuckles and personal robots.* The mechanical joint is singularity-free and back-drivable for walk-through programming. The mechanical joint is a simple and rugged economical design and is easily miniaturized. The mechanical joint includes a. spherical member having a pair of grooves in its outer surface, each groove extending circumferentially about the spherical member and disposed approximately 90° from each other. A housing means has a concave spherical socket for receiving the spherical member. The housing means includes a pair of slots located proximately at an equatorial plane of the spherical member. A frame means is fixedly secured to the spherical member at the intersection of the first and second groove opposite the housing means. A first ribbon means, slidable within the first groove, is attached to pivot pins in the slots of the housing means and is looped around a first pulley within the frame means. A second ribbon means slidable within the second groove, is attached to pivot pins mounted in the housing means at the approximate midpoints between the slots of the housing means. The second ribbon means is attached to a second pulley within the housing means. An output means is fixedly connected to the housing means. A first and second drive means provide selective movement of the first and second ribbon means. In a first alternate embodiment, an integral passageway for fluid is provided in the mechanical joint of the present invention. In a second alternate embodiment, a pair of sleeve assemblies teaches roll movement for the wrist actuator combined with the pitch and yaw movements. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of the apparatus of the present invention, with portions broken away for clarity. Figure 2 is a sectional view taken along line 2-2 of Figure 1. Figure 3 is a sectional view taken along line 3-3 of Figure 1. Figure 4 is a sectional view taken along line 4-4 of Fig. 3 illustrating a ball of the present invention. Figure 5 is an alternate embodiment of the present invention illustrating an internal fluid passageway. Figure 6 is a detailed view of the embodiment of Fig. 5 showing the port in a pivot pin. Figure 7 is an alternate embodiment of the present invention showing a roll axis and a pair of slidable sleeve assemblies. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The mechanical joint or wrist actuator generally indicated at 10 of the present invention is illustrated in Figure 1. Throughout the figures and the embodiments, like reference characters are used to indicate like elements. A ball or spherical member 20 is fixedly connected to a frame member 32. The ball 20 includes a pair of grooves 22 and 24 cut circumferentially and approximately 90° apart from each other in the outer surface of the ball 20. The frame member 32 is preferably an elongated hollow and generally rectangular frame. The frame 32 is connected to the ball 20 at a point where the grooves 22 and 24 intersect. A shaft or rod 30 is fixedly mounted inside the ball 20 and extends into the open central portion of the frame member 32. A housing 40 receives the ball 20 and includes a concave spherical socket or cavity for receiving the ball 20. The housing 40 slides over the outer surface of the ball 20 in a manner similar to a ball-and-socket joint. The housing 40 includes a pair of rectangular slots 41 and 42 as best seen in Figure 4. The slots 41 and 42 are disposed at proximate an equatorial plane of the ball 20. The slots 41 and 42 are diametrically opposed to each other. A retaining flange 43 is secured to the housing by screws 44A and 44F. The housing includes an output shaft 45 secured by a nut 46. If desired, the output shaft may be integral with the housing 40, as illustrated in Figures 5 and 7. It is to be understood that the output shaft 45 in the Figures is representative of any desired tool implement, such as a disk, grippers, and the like. A pair of tendons or ribbons 52 and 54 are wrapped around the ball and disposed within the grooves 22 and 24 respectively. Each ribbon 52 and 54 is movable within its respective groove as will be described subsequently. The ribbons are made of a flexible, yet strong material, such as a reinforced fabric. As illustrated in Figure 3, the ribbon 52 has a first end 52A which is inserted over a first flanged pin 56 and a second end which is inserted over a second flanged pin 58. The pins 56 and 58 along with the ribbon ends 52A and 52B slide in the groove 22. The ribbon 52 extends along the groove 22 of the ball 20 and through the frame member, between the rod 30 and the frame member 32 and exits the frame member 32 at an opening 34. An idler 36 rotatably secured into the frame 32 reduces slack in the ribbon 52 as it exits the opening 34; The ribbon 52 loops around a pulley 70 and passes over a pulley 38. The pulley 38 is mounted within the frame member 32 by pin 39 attached to the frame member at a point where the shaft 30 terminates. The ribbon 52 extends back through the opening 34 inside the frame member 32 and extends upwardly between the rod 30 and the frame member 32 into the groove 22 of the ball 20 up to pin 56. The pins 56 and 58 are extended into and slidably engage slots 41 and 42, respectively, of the housing 40. As illustrated in Figure 2, the ribbon 54 extends into the groove' 24 and held at an end 54A by a flanged pin 60 and at an end 54B by a flanged pin 62. The pins 60 and 62 along with the ribbon ends 54A and 54B slide in the groove 24. The pin 60 and 62 rotatably engage bearings 61 and 63, respectively. The bearings 61 and 62 are mounted to the housing and are disposed about the equatorial plane of the ball 20 at midpoints between slots 41 and 42. Thus, the pins 60 and 62 are approximately 180" from one another. The ribbon 54 extends downwardly from the ball 20, through the frame member 32 and is looped around a pulley 74. The pulley 74 is located proximate a bottom end of the frame member 32. The pully 70 is mounted to an output shaft 71 of a motor 72. The ribbon 52 is looped over the pulley '70 and moved by the motor 72 as best illustrated in Figure 1. The pulley 74 is mounted to an output shaft 75 of a motor 76 by a snap ring 77. Ribbon 54 is looped over pulley 74 and activated by motor 76. Any desirable means of connecting ribbons 52 and 54 to a driven shaft is includable within the present invention. It is preferred that the motors be bidirectional, that is capable of driving ribbons 52 and 54 in two directions. Figure 4 is a sectional view taken along the equatorial plane of the ball 20. The ball 20 and grooves 22 and 24 travel intact and the housing 40 is shown in section. The grooves 22 and 24 extend circumferentially around an outer surface of the ball and intersect at the ball's top. The ribbon 52 is connected to the pins 56 and 52 which slide within slots 41 and 42, respectively. The ribbon 54 is connected to pins 60 and 62 which rotate within the bearings 61 and 63, respectively. As the housing is rotated in pitch, yaw or compound pitch-yaw movement on the ball 20, the ribbons 52 and 54 slide within their respective slots and move about their respective pulleys. Simple pitch movement of the wrist actuator 10 is accomplished by pivoting the housing 40 about pins 56 and 58. In this manner, ribbon 54 travels and slides within groove 24. Simple movement about the yaw axis occurs when the housing 40 pivots about pins 60 and 62, causing ribbon 52 to slide within groove 22. In compound pitch-yaw movement, pins 56 and 58 slide within their respective slots 41 and 42 as the housing 40 rotates and pivots about pins 56, 58, 60 and 62. The wrist actuator 10 of the present invention can be adapted to provide a fluid channel or passageway 80 as illustrated in Figures 5 and 6. In the embodiment in Figures 5 and 6, the rod 30 and the ball 20 are shown as an integral structure. Additionally, the housing 40 and the output shaft 43 are shown as an integral structure. An internal bore 82 is provided in the rod 30 and ball 20. The bore 82 leads to an interior fluid chamber 84 defined by the housing 40 and the ball 20. The chamber 84 is sealed by a ring liner 86 which is positioned and slides within groove 24. The ring liner 86 includes a pair of flanged pins 87 and 88 that replace pins 60 and 62 of the embodiment shown in Figures 1-4. In addition, ring liner 86 includes a seal 89 to contain the fluid in the chamber 84. A detailed section view of the ring liner 86 and pin 88 is illustrated in Figure 6. An internal port 90 is provided along the longitudinal axis of pin 88 from the flange portion to a desired position on the outer surface. The port 90 allows fluid to flow from the interior fluid chamber 84 to an internal bore 92 that extends through the housing and the output shaft. A pair of 0-rings 94 and 96 are provided on the pin 88 on opposite sides of the housing bore 92 to prevent leakage from the port 90. The ring liner 86 is secured to the housing 40 by pins 87 and 88 and slides with the housing 40 over the ball 20. The ribbon 54 is held in place by pins 87 and 88 in a manner similar to the embodiment of Figures 1-4. An alternate embodiment of the present invention having a roll axis is depicted in Figure 7. A pair of sleeve assemblies 110 and 150 are slidably connected to the frame- ember 32. The first sleeve assembly 110 includes an inner sleeve 112 and an outer sleeve 114. A peg 113 projecting from the inner sleeve 112 is inserted into the ribbon 54. As the inner sleeve 112 slides along the longitudinal axis of the frame member 32, the pegs travel within the borders of a slot 115 of the frame member 32, causing the ribbon to move through the frame member and about the pulley 38. The outer sleeve 114 is decoupled from the inner sleeve 112 by a pair of ring bearings 118 and 120. The ring bearings permit the outer sleeve 114 to rotate about the inner sleeve 112. A linearally- actuated rod 124 is fixedly connected to the outer sleeve 114. Any suitable drive means, such as an electric motor or hydraulic cylinder, can be used to actuate the drive rod 124 along the arrows 126 and 128. Linear movement of the rod 124 is transmitted to the wrist actuator 10 by the ribbon 52 to provide yaw movement. In a similar manner to the first sleeve assembly 110, a second sleeve assembly 150 is slidable along the longitudinal axis of the frame member 32. An inner sleeve 152 is connected to the ribbon 52 by a peg 153. As the inner sleeve 153 travels along the longitudinal axis of the frame member 32, the ribbon 52 is rotated inside the frame member 32 about pulley 74 mounted on pin 79. The outer sleeve 154 is decoupled from the inner sleeve 152 by a pair of ring bearings 156 and 158. A rod 160 is fixedly connected to the outer sleeve 154. Any suitable drive means for actuating the rod 160 along arrows 161 and 162 may be utilize and provide pitch movement to the wrist actuator 10. A drive shaft 180 is fixedly connected to a end of the frame member 32 opposite the ball 20. A the drive shaft rotates, sleeve assemblies 110 an 150 decouple the rods 124 and 160 from the fram member 32. Thus, roll movement may be transmitted t the output shaft 45 simultaneously with pitch and ya movement through the actuation rods 124 and 160. The wrist actuator of the present inventio is simple to operate and economical to manufacture. The ball 20 is constructed of any lightweigh material capable of being formed to th specifications described. Plastics and other lik materials such as sold by E. I. DuPont under the mar DELRIN are suitable for the ball 20. The wris actuator 10 is singularity-free and back-drivable fo walk-through programming. The wrist acutator 10 has up to 100 degrees of pitch motion and 100 degrees of yaw motion about a common center point, thereby avoiding gi bal lock in compound pitch-yaw motion. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims: - 13 - WHAT IS CLAIMED IS; 1. A mechanical joint comprising: a spherical member having a first and a second groove in its outer surface, each groove extending circumferentially around the sperical member and the groove disposed approximately 90° from each other; housing means having a concave spherical socket for receiving the spherical member, a pair of slots located proximate an equatorial plane of the spherical member, each slot being disposed diametrically opposite the other slot; frame means fixedly secured to the spherical member at an intersection of the first and second grooves located exteriorly of the housing means; first ribbon means being slidable within the first groove and looped around a first pulley within the frame means, each end of the ribbon means attached to a pin inserted into a slot of the housing means; second ribbon means being slidable within the second groove and looped around a second pulley within the frame means, each end of the ribbon means attached to a fastener means having a pair of pins, the pins pivotally mounted to the housing means located proximately at the equatorial plane of the spherical member and disposed at the approximate midpoints between the slots of the housing means; output means, connected to the housing means opposite the socket; and first and a second drive means for effecting selective movement of the first and second ribbon means. 2. The mechanical joint of claim 1 wherein a rod is fixedly mounted to the interior of the spherical member and extended a desired length into the frame means. 3. The mechanical joint of claim 1 wherein the frame means is an elongated, hollow and generally rectangular frame. 4. The mechanical joint of claim 1 wherein the output means is integral with the housing means. 5. The mechanical joint of claim 1 wherein the drive means comprises: a first and a second motor, the bidirectional rotation of the output shaft of the first motor transmitted to the first ribbon means, the bidirectional rotation of the second motor transmitted to the second ribbon means. - 15 - 6. The mechanical joint of claim 1 and further comprising: rotation means connected to the frame means for bidirectionally rotating the frame means about its longitudinal axis; and a sleeve means slidable along the longi¬ tudinal axis of the frame means and connected to the drive means. 7. The mechanical joint of claim 6 wherein the sleeve means comprises a first and a second sleeve assembly, the first sleeve assembly comprising an inner sleeve attached to the first ribbon means, and an outer sleeve rotatable about the inner sleeve, and a. rod connected at a first end to the outer sleeve and at a second end to the drive means; and the second sleeve assembly comprising an inner sleeve attached to the second ribbon means and an outer sleeve rotatable about the inner sleeve, and a rod connected at a first end to the outer sleeve and at a second end to the drive means. 8. The mechanical joint of claim 2 wherein the fastener means comprises a ring liner slidable within the second groove and terminating at each end in a pivot pin, one of the pins having an internal bore from its base to a desired position in its outer surface along its longitudinal axis. 9. The mechanical joint of claim 8 and further including an integral channel path for fluid comprising: an internal bore along the longitudinal axis of the rod; an internal bore through the interior of the spherical member complementary to the longitudinal axis of the rod; and an internal bore through the housing from the opening for the pin having an internal bore to the output means.

Inventors: ROSHEIM MARK E, ROSHEIM, MARK, E.
Applicants: ROSHEIM MARK E, ROSHEIM, MARK, E.
Application year: 1987
Main classification: G05G11
IPC codes: B25J9, B25J17