Magnetically levitated fine motion robot wrist with programmable compliance

• US 4,874,998 A
• Filed: 06/21/1988
• Issued: 10/17/1989
• Est. Priority Date: 06/11/1987
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Hollis, Ralph L. Jr.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): IP, SHIK LUEN PAUL
• Application Number:
  US07/211,113
• Time in Patent Office: 483 Days
• Field of Search: 318/568, 318/640, 318/687, 318/565-572, 901/14-16, 901/9, 901/20, 901/24, 901/26, 901/21, 901/23, 901/29, 901/30-39, 901/48, 414/719, 414/735, 414/736, 414/741, 414/751, 310/166, 310/90.5, 364/513
• US Class Current: 318/568.21
• CPC Class Codes: B23Q 5/28 Electric drives
• CPC Class Codes: B25J 17/0208 Compliance devices
• CPC Class Codes: B25J 17/0283 Three-dimensional joints
• CPC Class Codes: B25J 7/00 Micromanipulators specimen supports for investigating or analysing materials G01N23/2204; associated with microscopes G02B21/32; means for supporting or positioning the objects or the material in discharge tubes H01J37/20
• CPC Class Codes: B25J 9/12 electric
• CPC Class Codes: F16C 2322/39 General build up of machine tools, e.g. spindles, slides, actuators in general B23Q
• CPC Class Codes: F16C 32/0444 Details of devices to control the actuation of the electromagnets
• CPC Class Codes: F16C 32/0493 integrated in an electrodynamic machine, e.g. self-bearing motor
• CPC Class Codes: H02N 15/00 Holding or levitation devices using magnetic attraction or repulsion, not otherwise provided for electric or magnetic devices for holding work on machine tools B23Q3/15 ; monorail vehicle propulsion or suspension B60L13/00; sliding or levitation devices for railway systems B61B13/08; material handling devices associated with conveyors incorporating devices with electrostatic or magnetic grippers B65G47/92; separating thin or filamentary articles from piles using magnetic force B65H3/16; delivering thin or filamentary articles from magnetic holders by air blast or suction B65H29/24; bearings using magnetic or electric supporting means F16C32/04; relieving bearing loads using magnetic means F16C39/06; magnets H01F7/00; dynamo-electric clutches or brakes H02K49/00 ; electric furnaces with simultaneous levitation and heating H05B6/32

Abstract

Selective compliance in up to six degress of freedom in a magnetically levitated fine motion device, or robot wrist, with limited motion in X,Y,Z, ROLL, PITCH, YAW, is provided by controlled actuation currents applied to six electrodynamic forcer elements. The wrist has a stator support base defining a dual periphery, carrying a number of stator magnet units. A shell flotor unit nests within the stator support base dual periphery, and carries forcer coils at locations corresponding to respective magnet units. The magnet unit and related flotor coil form a forcer element. There are a number of forcer elements. The vector sum of all the translational forces and rotational torques established at the forcer elements determines the X,Y,Z, ROLL, PITCH, and YAW motion of the flotor. The flotor carries an end effector which may be a tool. Position and orientation of the flotor is monitored by light emitting diodes and lateral effect cells. Coil currents are controlled as a composite of present position, desired final position, and desired compliance. As the fine motion device approaches its final position, the control unit changes forcer coil current patterns at various sets of forcer elements, to provide selected compliance in one or more degrees of freedom while approaching and finally while maintaining the desired position. Cooling is provided as needed; docking and locking provision is made to allow de-energizing the coils for cooling, motion of the base, or shutdown.

Claims

1. A six-degree-of-freedom fine motion device, having but a single moving part, comprising:

(a) a stator support unit (9) defining a base and a dual enclosure having dual walls upthrust from the base to define a dual periphery;

(b) a multiplicity of forcer magnets (4) disposed at spaced positions about said dual periphery;

(c) a flotor unit (1) having a related periphery nested in said dual periphery of said stator support unit (9);

(d) forcer elements (5) including a multiplicity of forcer element flotor coils (3) arrayed about said periphery of said flotor unit (1) in active juxtaposition with said forcer magnets (4);

(e) position and orientation sensing means (6) arrayed about said dual periphery of said stator support unit (9) and about said periphery of said flotor unit (1) to sense the relative positions and orientations of said stator support unit and said flotor unit; and

(f) control means connected to said position and orientation sensing means (6) in feedback mode, for providing respective forcer elements (5) with electrodynamic actuation appropriate to maintain equilibrium at a desired starting position and orientation, appropriate to cause motion to a desired final position and orientation according to a force-to-displacement ratio K, and appropriate to provide a desired compliance in at least one degree of freedom by selectively lessening the force-to-displacement ratio K in a related set of forcer elements (5).

2. A six-degree-of-freedom fine motion device according to claim 1, wherein said stator support unit (9) dual periphery and said flotor unit (1) periphery are in similar closed configuration, and said forcer elements (5) are six in number arrayed about said dual periphery and said flotor unit periphery of the closed configurations.

3. A six-degree-of-freedom fine motion device according to claim 2, wherein the closed configuration of said dual periphery of said stator support unit (9) and said periphery of said flotor unit (1) are hexagonal in section.

4. A six-degree-of-freedom fine motion device according to claim 2, wherein the closed configuration of said dual periphery of said stator support unit (9) and said periphery of said flotor unit (1) are substantially spherical.

5. A six-degree-of-freedom fine motion device according to claim 1, wherein

said stator support unit (9) dual periphery and said flotor unit (1) periphery are hexagonal prisms in configuration;

said forcer elements (5) are six in number, arrayed one to each rectangular surface of the hexagonal prism; and

said control means provides control values related as a 6×

6 square matrix T, with eigenvalues defining that the matrix T is non-singular.

6. A six-degree-of-freedom fine motion device according to claim 1, wherein

said stator support unit (9) dual periphery and said flotor unit (1) periphery have reactive surfaces which generally follow the surface of a sphere, with the centroid of the sphere internal to and close to the axis of each of said stator support unit (9) and said flotor unit (1) and said forcer elements (5) being arrayed about the surface of the sphere.

7. A six-degrees-of-freedom fine motion device according to claim 1, wherein said forcer elements (5) include forcer magnets (4) on said stator support unit(9) and flotor coils (3) in said flotor unit (1), and said flotor coils (3) generally following the configuration of the periphery of said flotor unit (1) and the positions of respective forcer magnets (4);

and

sets of said forcer magnets (4) disposed substantially opposite each other on the dual periphery of said stator support unit (9) having substantial gaps in which gaps said flotor coils (3) can move during levitated fine motion of said flotor (1) with respect to said stator support unit (9).

8. A six-degrees-of-freedom fine motion device according to claim 1, wherein said forcer elements (5) include forcer magnets (4) on said stator support unit (9) and flotor coils (3) in said flotor unit (1), and said flotor coils (3) generally following the configuration of the periphery of said flotor unit (1) and the positions of respective forcer magnets (4), and said forcer elements further including passive damping means;

and

sets of said forcer magnets (4) disposed substantially opposite each other on the dual periphery of said stator support unit (9) have substantial gaps in which gaps flotor coils (3) can move during levitated fine motion of said flotor (1) with respect to said stator support unit (9).

9. A six-degrees-of-freedom fine motion device according to claim 1, wherein said forcer elements (5) include forcer magnets (4) on said stator support unit (9) and flotor coils (3) in said flotor (1), and said flotor coils (3) generally following the configuration of the periphery of said flotor (1) and the positions of respective forcer magnets (4), and said forcer magnets (4) being configured with sufficient magnetic gap to permit flotor coil movement within the gap sufficient for a desired range of motion.

11. A six-degrees-of-freedom fine motion device according to claim 1, wherein

said stator support unit (9) and said flotor (1) include docking means.

12. A six-degrees-of-freedom fine motion device according to claim 11, wherein

said docking means includes mechanical detenting means (18-19) and locking means (16-17).

13. A six-degrees-of-freedom fine motion device according to claim 1, wherein

said stator support unit (9) includes heat transfer means.

14. A six-degrees-of-freedom fine motion device according to claim 1, wherein said stator support unit (9) undergoes motion and said flotor unit (1) remains fixed.

10. A six-degrees-of-freedom fine motion device according to claim wherein

said forcer elements are arrayed in two orthogonal groups.

15. A motion and compliance emulation system comprising:

a matched electrodynamically levitated flotor and stator combination, having clearance gaps between flotor and stator sufficient for a desired range of relative motion and greater than required for electrodynamic efficiency;

electrodynamic forcer means for receiving coil currents for applying controlled magnetic forces mutual to the flotor and stator and analogous to a number of synthetic springs, each synthetic spring having a zero-point and a stiffness value; and

programmable means for controlling both zero-point and stiffness value by controlling the coil currents in sets applied to said forcer elements during the entire range of mutual motion, thereby controlling position, orientation and compliance.

16. A motion and compliance emulation system according to claim 15, wherein

said programmable means for controlling both zero-point and stiffness value includes software settable limit stops, of significant stiffness, near the limits of mechanical motion.