GB2085399A

GB2085399A - Robotic manipulator

Info

Publication number: GB2085399A
Application number: GB8129859A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-10-06
Filing date: 1981-10-02
Publication date: 1982-04-28
Also published as: DE3139764C2; DE3139764A1; IT8149432A0; IT1171573B; FR2491380A1; GB2085399B; JPS57127684A; CA1186005A; JPH0246357B2; FR2491380B1

Abstract

A robotic manipulator has three nearly extensible arms 50, 54, 58 mounted on a frame 10 in a triangular array and carrying at their remote ends a connector interface 62 coupling the arms to a tool for manipulating parts to be positioned or for other work. The structure is such that the location of the connector 62 is determined solely by the lengths of the arms 50, 54, 58, while its orientation is determined primarily by the angular rotation of the arms, thereby minimizing the computation required to accurately position a tool. The driving motors, such as 36, for the arms, such as 50, are located at the arm ends adjacent the frame 10; this minimizes the mass, and thus the inertia, located at the connector end, and enables high acceleration and rapid motion of the connector head and its associated tool. Further, a three-point suspension for the arms provides high stiffness enabling the system to carry substantial loads at high speed and with good positioning and orientation accuracy. <IMAGE>

Description

SPECIFICATION Robotic manipulator The invention relates to robotics and, more particularly, to robotic manipulators for robotic positioning and the like.

Robotic positioning machines typically incorporate an articulated arm which moves throughout a defined volume for handling and assembling parts of various devices. These machines are used for various purposes, such as automatic assembly and numerically controlled machining, among others. Increasingly, such machines are placed under the control of a device such as a digital computer which controls the position and orientation of a manipulator element affixed to the arm. Examples of such machines are shown in U.S. Patent No. 3,985,238 issued October 12, 1976 to K. Nakura, et al and U.S. Patent No.

4,068,536 issued January 17, 1978 to T. H.

Stackhaus. These manipulators are essentially cantilevered arms incorporating a number of articulated and sliding joints to provide the requisite motion in space.

Among some of the more important characteristics of such machines are their load carrying capacity, their maximum operating speed (which, in large part, is a function of the inertia of the machine), and the simplicity of the machine, which riot only affects its ease of use but also directly affects its cost. The load carrying capacity of many of the manipulators currently available, particularly those of the cantilevered arm type, are frequently quite limited in relation to the mass of the manipulator itself. Further, the construction of these manipulators is such as to create high translational and rotational moments of inertia with the result that the acceleration of the manipulator head, and thus the maximum speed of the manipulator itself, is unnecessarily limited.

Further, their complexity frequently results in high cost, diminished reliability and consequent greater "down-time", and frequently an increased complexity of the control system for driving these machines.

Accordingly, it is an object of the invention to provide an improved robotic manipulator.

Further, it is an object of the invention to provide a robotic manipulator of simple and efficient design.

Another object of the invention is to provide a robotic manipulator whose moveable portions have comparatively low inertia in relation to the load they can carry.

Yet another object of the invention is to provide a robotic manipulator whose construction minimizes the computation required to position the manipulator head at a desired location.

In a preferred embodiment of the invention, an articulated structure for robotic assembly and the like has three arms, each mounted on a frame for rotation (with respect to the frame) about first and second axis defined in a plane transverse to the corresponding arm, and about a third axis coincident with the longitudinal axis of the arm. The arms terminate in a coupler carrying a connector mounted to rotate (with respect to each arm) about two axes defined in a second plane transverse to the corresponding arm and constrained to rotate with each arm about an axis coincident with the longitudinal axis of the arm. The positional location and orientation of the connector (and thus of any tool or part carried by the connector) is defined by the longitudinal extension of each arm and its rotation about its longitudinal axis.

In the preferred embodiment, the connector is so mounted that its axes of rotation with respect to each arm intersect at a common point to thereby decouple the translational and rotational position equations of the system, whereby the positional location of the connector is defined solely by the longitudinal extension of each arm and its angular orientation is defined primarily by the angular orientation of each arm. This significantly decouples the equations of motion relating the extension and rotation of the arms, and their velocities, to the position and orientation, and their velocities, of the connector. This reduces the computational effort required to control the system and thus reduces cost and complexity of the system.For example, in calcuiating the positional and angular. velocities of the connector from the corresponding velocities of the arms, a computation which must be per- formed repeatedly during movement of the connector, it reduces the computational task from inversion of a six-by-six matrix to that of inverting three three-by-three matrices.

Drive motors are mounted on each arm adjacent their connection to the frame for longitudinally extending and rotating each arm to thereby position the connector at a desired location and with a desired orientation. This positioning of the drive motors greatly minimizes the inertia of the system, and thereby minimizes its response time.

A three poirit ("tripod") mounting system is used for the arms; this provides a stiff structure, capable of moving substantial loads of high speeds.

The design readily lends itself to implementation with any of several different degrees of freedom to suit particular needs. Thus, the preferred embodiment described herein has six degress of freedom (three translational, three rotational) but any one or more of these may readily be constrained to thereby provide a manipulator more particularly adapted to a given purpose. Further, each arm is essentially the same as each other arm, and thus the system can be constructed on a mass-assembly basis, compratively inexpensively, without highly critical tolerances, and with a limited number of different components.

The foregoing and other and further features and objects of the invention will more readily be understood from the following detailed description of the invention, when taken in conjunction with the accompanying drawings in which: Figure 1 is a view in perspective of a robotic manipulator constructed in accordance with the invention; and Figure 2 is a view in perspective of the manipulator head of Fig. 1 with portions broken away for purposes of illustration.

Figure 3 is a view of one type of driving means for the arms; In Fig. 1, a frame 10 has a base 12, vertical pedestals 1 4, 1 6, and a trianguiar platform 18. Gimbal mounts 20, 22 and 24 are fixed to the pedestals 1 4, 1 6 and the platform 18, respectively. Gimbal mount 20 has a first yoke 26 in which a second yoke 28 is pivotally mounted by means of a vertical pivot 30. An electric motor 32 is pivotally mounted within yoke 28 by means of pivot 34, and the frame of a second electric motor, 36, is mounted on the shaft of motor 32 for rotation therewith. As may be seen from Fig.

1, each arm is free to rotate with respect to the frame about three axes. A first of these comprises the longitudinal axis of each arm: the second and third comprises mutually transverse axes defined by the respective pivots and themselves defining respective planes that are transverse to the corresponding arm axis.

An arm 50, having an extensible arm 52, is mounted concentric with the shaft of motor 36. Arm 52 has a rear portion 54 thereof center-bored and internally threaded to mate with a correspondingly threaded screw 56 formed on the shaft of motor 36. A pin 57, connected to an inner wall of arm 50, rides in a longitudinal slot 59 in arm 52 to prevent rotation of arm 52 with respect to arm 50.

Motors 32 and 36 are connected to a controller (not shown), preferably containing a computer for supplying various positional and rotational drive commands to the motors. Each motor is preferably energized independently.

Motor 32 controls the angular orientation of arm 52, while motor 36 controls its longitudinal extension. The construction of the gimbais 22, 24, and their associated arm translation and rotational drives are similar to that of the gimbal 20 and its corresponding drives, and thus these will not be described in detail.

The arms 52, 56, and 60 terminate in a coupling head 62 which is shown in full detail in Fig. 2. Head 62 has an inner member 64, an intermediate member 66, and an outer member 68. Members 64 and 66 are separated by ball bearings 70, while members 66 and 68 are separated by ball bearings 72. A connector 74 is rigidly connected to inner member 64 and rotates with that member independent of members 66, 68.

Arm 52 is attached to the outer head member 68 by means of a coupling bracket 80 which is rigidly fixed at one end thereof to the arm 52 and which is pivotally mounted at the other end thereof for rotation about a bearing pin 82. Similarly, arm 60 is connected to the intermediate head member 66 by means of a coupling bracket 86 which is rigidly attached to arm 60 at one end thereof and which is pivotally mounted for rotation about a bearing pin 88 at the other end thereof.Accordingly, connector 74 can rotate with respect to arm 52 about a first axis "a" concentric with the axis of rotation of inner member 64, and about a second axis "b" co-linear with the axis of bearing pin 82; these axes define a plane that is transverse to the longitudinal axis "c" of arm 52. ("Transverse" is herein to be understood as meaning oriented at a non-zero angle such that the line or axis to which the plane is transverse lies outside the plane).

Since bracket 80 is rigidly coupled to arm 52, connector head 74 is precluded from rotating with respect to arm 52 about the longitudinal axis "c" of this arm, but can rotate with this arm about this axis. Similarly, segment 74 rotates with respect to arm 60 about the first axis "a" and about a second axis "d" colinear with the axis of bearing pin 88; these axes define a plane transverse to the longitudinal axis "e" of arm 60. Connector head 74 is precluded from rotating with respect to arm 60 about the axis "e", but can rotate with the arm 60 about this axis.

Head segment 64 is coupled to arm 56 by means of a universal joint shown, for purposes of illustration only, as formed from a first pin 90 extending across a slotted jaw 92 at the lower end of arm 56 and a second pin 94 extending perpendicular to pin 90 and mounted in a slotted jaw 96 of a mounting shaft 98 fixed to the connector head 74. Pins 90 and 94 are pivotally mounted with respect to each other at their intersection to form a universal joint providing rotary motion of connector 74 with respect to arm 56 about a pair of axes coincident with the longitudinal axes "f". "g", respectively of the pins 90, 94.

These axes define a plane transverse to the longitudinal axis "a" of arm 56 and connector 74 thus rotates with respect to arm 56 about axes lying in this plane. Conversely, connector 74 is restrained from rotation with respect to arm 56 about the longitudinal axis "a" this arm, but does rotate with this arm about this axis.

The location and orientation of the connector 74 is defined by the longitudinal extension and angular orientation of each of the arms 52, 56, 60. Further, in the preferred embodiment illustrated herein, the axes of rotation of the connector 74 with respect to the arms are so located as to intersect at a common point (point "I" in Figs. 1 and 2). This decouples the translational and rotational co-ordinates of the respective arms such that the positional location of the connector 74 is defined solely by the longitudinal extension of the arms, while the angular orientation of the connector is defined principally by the rotational state of these arms with respect to an initial zero reference point.This greatly simplifies control systems for the robotic manipulator described herein, as it minimizes the computation that must be undertaken to determine the necessary longitudinal extension and angular orientation of each of the arms in order to position the connector in a desired location and with a specified orientation. Thus, development of the control system is simplified, and the system itself is able to operate more expeditiously.

The arms 52, 56, 60 of the robotic manipulator described above form a tetrahedral figure in space, the arms lying along three converging edges of the tetrahedron and the connector lying at their apex. This provides an especially strong and rigid configuration supporting the connector and the tools attached to it, and allows one to subject it to reiatively high accelerations and decelerations without excessive vibration and extended settling time.

Further, it allows the carrying of a substantial load by the connector. Thus, the manipulator is particularly suited for application such as parts assembly numerically controlled machining, part sorting, part transfer, and the like.

From the foregoing, it will be seen that I have provided an improved robotic manipulator. The manipulator is of the non-cantilevered type and has a plurality of arms supported from a solid frame in a three-point mounting so as to provide high stiffness to a connector head attached to it and carrying a tool or part to be positioned or oriented. This enables the movement of substantial loads at comparatively high speeds. Further, the driving elements for the positioning and orientation are located remote from the effective rotational axes of the connector to thereby minimize the mass, and the consequent inertia, of the structure at the location of the connector; this facilitates high speed motion of the connector and the tools attached to it. The driving means can advantageously be located immediately adjacent the mounting means joining the arms to the frame.However, they can also be positioned, in accordance with the needs of the user, at locations remote from this location, if desired, to counterbalance loads applied to the connector head or for other reaons. The design of the present invention thereby provides great flexibility in the location of the driving elements. The arms of the manipulator are quite simple, are essentially indentical in construction and use no parts of critical tolerance. Thus they can be manufactured with mass-production techniques at low cost and readily assembled together. The design is adapted to provide varying degrees of freedom merely by restricting the extension of rotation of one or more of the arms.

Finally, in the preferred embodiment, the coupling structure interconnecting the connector and the respective arms is such that the effective axes of rotation of the connector with respect to the arms intersect at a common point. This substantially decouples the positional and rotational co-ordinates of the arms such that the equations of motion describing the motion of the connector in terms of the motion of the respective arms are simplified.

Thus, the computations required to accurately control the position and orientation of the connector, and to bring it to a desired location and orientation, are simplified.

Claims

1. A robotic manipulator, comprising A. a frame, B. a plurality of arms affixed to said frame, each arm extensible along a longitudinal axis and pivotally mounted for rotation, C. a connector for attachment to a tool, D. coupling means coupling each said arm to said connector and providing rotation of said connector with respect to each said arm about a plurality of axes defining a plane transverse to the longitudinal axis of said arm, and precluding rotation with respect to said connector about axes transverse to said plane, E. said manipulator positioning said connector at a desired location and angular orientation by extending and rotating said arms.

2. A manipulator according to claim 1 in which one of said arms is connected to said frame by a doubly-articulated joint.

3. A manipulator according to claim 1 in which a first of said coupling means comprises a doubly articulated joint having a first portion thereof mounted for rotation with said connector about an axis transverse to a first connector axis and a second portion thereof connected to said arm and mounted for rotation about an axis transverse to said first connector axis.

4. A manipulator according to claim 3 in which a second and third of said coupling members each includes a first member mounted for rotation with respect to said connector about said first connector axis and a second member connected to said first member and mounted for rotation about an axis transverse to said first connector axis.

5. A manipulator according to claim 4 in which said second and third coupling members are mounted to rotate said connector about axes orthogonal to said first connector axis in response to rotation of the respective arms attached to the said yokes.

6. A manipulator according to claim 1 in which each said arm is mounted on said frame for rotation about longitudinal axis as well as about a pair of axes defining a plane transverse to said longitudinal axis.

7. A manipulator according to claim 6 which includes drive means on at least two of said arms for longitudinally extending said arms and positioning said connector at a predetermined location.

8. A manipulator according to claim 1 which includes drive means on the ends thereof adjacent said frame for extending and rotating said arms.

9. A manipulator according to claim 8 in which said drive means include a first motor for extending a corresponding arm and a second motor operable independently of said first motor, for rotating a corresponding arm.

10. A manipulator according to claim 1 in which said arms comprise three in number and are positioned on said frame in tetrahedral relationship for rigidly supporting said connector head.

11. A robotic manipulator, comprising A. a frame mounting one end of at least three longitudinally extensible arms for motion through a substantial solid angle, pairs of said arms defining separate planes; and B. coupling means joining the other end of each of said arms to a connector for motion through a corresponding substantial solid angle, said coupling means including a first member joined to a first of said arms through a first joint rotatable through a substantial solid angle and second and third members joined to second and third arms, respectively, through respective joints rotatable about nonparallel axes, and means mounting said members for rotation with respect to each other about a common axis transverse to the plane defined by said non-parallel axes.

1 2. A manipulator according to claim 11 in which said first joint comprises a universal joint.

1 3. A manipulator according to claim 11 in which said first joint comprises a constant velocity joint.

14. A manipulator according to claim 11 in which each said arm is mounted for rotation with respect to said frame about a first axis coinciding with the longitudinal axis of said arm.

1 5. A manipulator according to claim 14 in which said arms are mounted such that a second axis of rotation of each arm is perpendicular to the first axis of rotation of the corresponding arm.

1 6. A manipulator according to claim 1 4 in which said arms are mounted such that a third axis of rotation of each arm is transverse to the first and second axes of rotation of the corresponding arm.

1 7. A manipulator according to claim 1 6 in which said arms are mounted such that the axes of rotation of each said arm intersect at a common center.

1 8. A manipulator according to claim 11 in which said arms are mounted on said frame by means of a universal joint.

1 9. A manipulator according to claim 11 which includes drive means connected to each arm at the end adjacent said frame for extending said arms.

20. A manipulator according to claim 1 9 in which said drive means includes means for rotating said arms.

21. A manipulator according to claim 11 in which said member is mounted on said arms to define three principal axes of rotation of said connector with respect to said arms, which axes intersect at a common point to thereby decouple the positional equations from the rotational equations of motion of said connector.

22. A manipulator according to claim 21 which includes first drive means on each said arm for controllably rotating said arms and second drive means on at least two of said arms for controllably extending said arms longitudinally.

23. A manipulator according to claim 21 which includes drive means on each arm, adjacent the mounting location of said arm on said frame, for controllably positioning said connector by longitudinally extending and rotating each arm by predetermined amounts.

24. A robotic manipulator comprising A. a connector to be positioned at a selected location B. a frame C. first, second, and third longitudinally extensible non-coplanar arms, each mounted on said frame for rotation with respect to said frame about a plurality of axes D. means rotatably coupling each said arm to said connector for rotation of said connector with respect to said arm about at least one axis but precluding rotation of said connector with respect to said arm about at least a second axis.

25. A manipulator according to claim 24 in which said rotatable coupling means includes means coupling each said arm to said connector for rotation of said connector with respect to said arm about two axes defining a plane transverse to the longitudinal axis of said arm.

26. A manipulator according to claim 25 in which said coupling means is configured to orient each said axis for intersection at a common point such that the position of said connector is defined by the longitudinal extension of each said arm and the orientation of said connector is defined substantially by the orientation of each said arm.

27. A manipulator according to claim 24 in which said coupling means comprises first, second and third collars connected to said first, second, and third arms, respectively, and mounted for rotation relative to each other about a first common axis coincident with a first axis of said connector; first and second pivot means interconnecting said first and second arms and said first and second collars, respectively, and mounted to rotate said connector with respect to said arms about axes defined in a plane orthogonal to said first axis; and a universal joint connected to a third arm and providing rotation of said connector about a pair of axes defined in a plane transverse to' said first axis.

28. A manipulator according to claim 27 which includes drive means mounted on at least two of said arms for longitudinally extending said arms by defined amounts.

29. A manipulator according to claim 27 which includes drive means mounted on each said arm adjacent said frame for rotating each said arm about its longitudinal axis.

30. A manipulator according to claim 27 which includes drive means mounted on each said arm adjacent said frame for rotating each said arm about said longitudinal axis and for independently extending it along said axis.

31. A manipulator according to claim 21 which includes an electric motor mounted on each said arm adjacent point of mounting on said frame for rotating said arm about said longitudinal axis.

32. An articulated structure according to claim 21 wich includes at least one electric motor mounted on each said arm adjacent said frame for rotating said arms about said longitudinal axis and for independently extending it along said axis.

33. A manipulator according to claim 27 in which each said arm about which said connector rotates with respect to said arm is positioned to intersect the other said axes at a common point.

34. A robotic manipulator according to claim 1 which further comprises drive means on said arms for extending and rotating said arms, and a controller for supplying drive commands to the drive means.

34. A robotic manipulator substantially as described herein with reference to Figs. 1 and 2 of the accompanying drawings.

CLAIMS (18 Dec 1981) Claim 34 renumbered as claim 35 and new claim 34 added: