Parallel kinematic positioning system

• US 20100122602A1
• Filed: 11/17/2008
• Published: 05/20/2010
• Est. Priority Date: 11/17/2008
• Status: Active Grant

• Current Assignee: Andre Perrin, Fred L. Ansaldi, Marc Webster, Robert Domes, Sacha L. Marcroft
• Original Assignee: Andre Perrin, Fred L. Ansaldi, Marc Webster, Robert Domes, Sacha L. Marcroft
• Inventors: Marcroft, Sacha L., Ansaldi, Fred L., Perrin, Andre', Domes, Robert, Webster, Marc
• Granted Patent: US 8,215,199 B2
• Time in Patent Office: Days
• US Class Current: 74/490.30
• CPC Class Codes: B25J 17/0216 comprising a stewart mechanism
• CPC Class Codes: Y10T 74/20305 Robotic arm
• CPC Class Codes: Y10T 74/20317 including electric motor
• CPC Class Codes: Y10T 74/20348 Planar surface with orthogonal movement and rotation
• CPC Class Codes: Y10T 74/20378 Planar surface with orthogonal movement or rotation

Abstract

A parallel kinematic positioning system 10 (PKPS 10) that is comprised of a stationary base plate (12) and an upper movable platform (28) to which is attached a workpiece or an instrument. Between the stationary base plate (12) and the upper movable platform (28) are positionally attached six strut assemblies (50). The six strut assemblies operate a hexapod that include in combination, a counterbalance subassembly (111), a servo motor subassembly (134), a bearing and encoder subassembly (156) and an electronics circuit (190). The combination accurately and repeatably positions the upper movable platform (28) within six degrees of freedom relative to the base plate (12).

Claims

1. A parallel kinematic positioning system comprising:

a) a stationary base plate having an inner surface and an outer surface,

b) an upper movable platform having an inner surface and an outer surface, wherein the outer surface is designed to have attached and positioned a workpiece or instrument,

c) a plurality of strut assemblies that are positionably attached between said stationary base plate and said upper movable platform, wherein said plurality of strut assemblies each have an upper end, a lower end, and are designed to selectively control the position of said upper movable platform relative to said base plate, and

d) an electronics circuit having means for selecting and controlling the position of said plurality of strut assemblies.

2. The system as specified in claim 1 wherein said plurality of strut assemblies are comprised of six strut assemblies that in combination control the movement of said upper movable platform within six degrees of freedom relative to said stationary base plate.

3. The system as specified in claim 2 wherein said stationary base plate can be dimensioned to have a surface area that is greater than, less than or equal to the surface area of said upper movable platform.

4. The system as specified in claim 3 wherein said stationary base plate having means for being rigidly attached to a substantially flat working surface.

5. The system as specified in claim 3 wherein the inner surface of said base plate further comprises a like plurality of base attachment structures that interface with the lower end of said strut assemblies.

6. The system as specified in claim 3 wherein said stationary base plate and said upper movable platform have a corner-truncated triangular shape.

7. The system as specified in claim 3 wherein said stationary base plate and said upper movable platform have a circular shape.

8. The system as specified in claim 2 wherein the inner surface of said upper movable platform further has a like plurality of platform attachment structures that interface with the upper end of said strut assemblies.

9. The system as specified in claim 2 wherein the outer surface of said upper movable platform is designed to have attached a specific workpiece.

10. The system as specified in claim 9 wherein said upper platform further having an opening that facilitates the attachment and adjustment of the workpiece that is attached to the outer surface of said upper platform.

11. The system as specified in claim 9 wherein each said strut assembly further comprises:

a) a linear servo motor that;

(1) can attain a speed of at least five meters per second,

(2) is substantially frictionless,

(3) provides a smooth constant linear velocity,

(4) with the exception of the bearing surface, has no appreciable surface contact, and

(5) has a relatively long useful life.

b) a counterbalance assembly that functions in combination with said linear servo motor to maintain the position of the work piece that is attached to the upper surface of said movable upper platform if electrical power to said system is interrupted or lost, and

c) an encoder that is designed to translate the angular position of a magnetic shaft attached to said linear servo motor into a series of corresponding digital signals that are processed by said electronics circuit.

12. The system as specified in claim 5 wherein the base attachment structure consists of a universal joint that is further selected from the group consisting of a ball and socket U-joint, a single U-joint, a double U-joint, a pin and block U-joint, and a needle bearing U-joint.

13. The system as specified in claim 8 wherein the platform attachment structure consists of a universal joint that is further selected from the group consisting of a of a ball and socket U-joint, a single U-joint, a double U-joint, a pin and block U-joint, and a needle bearing U-joint.

14. The system as specified in claim 11 wherein said linear servo motor is further comprised of a linear servo motor having an ironless motor core.

15. The system as specified in claim 11 wherein said counterbalance assembly is selected from the group consisting of a magnetic counterbalance, an air spring, an active air actuator, a constant-force spring, a pulley type counterbalance, and an air cylinder.

16. The system as specified in claim 11 wherein said encoder is comprised of either a magnetic encoder or an optical encoder that through a feedback circuit produces a feedback signal that is applied to said electronics circuit.

17. The system as specified in claim 11 wherein said electronics circuit comprises:

a) an input circuit that can consist of either a personal computer or a microcontroller circuit,

b) a software program that operates said input circuit, wherein the input circuit produces a first output signal,

c) a multi-axis digital control circuit which is applied and processes the first output signal and that produces a second output signal,

d) a digital amplifier which is applied and processes the second output signal and that produces a third output signal that is applied to the ironless motor coil which forms an element of said servo motor subassembly, wherein from the coil a fourth output signal is produced that is applied to the encoder, that is connected to a feedback circuit from where a feedback signal is developed that is applied to the multi-axis digital circuit, and

e) a power source designed to power said electronics circuit.

18. A parallel kinematic positioning system comprising:

A. a stationary base plate having;

(1) an inner surface and an outer surface, wherein the inner surface has a plurality of base attachment structures, and

(2) means for being rigidly attached to a substantially flat surface,

B. an upper movable platform having;

(1) an inner surface and an outer surface, wherein the inner surface further having a like plurality of platform attachment structures, and

(2) an opening that facilitates the attachment and adjustment of a workpiece or instrument that is attached to the upper surface,

C. a set of six strut assemblies that are each positionably located between said stationary base plate and said upper movable platform, wherein said strut assemblies in combination control the position of said upper platform within six degrees of freedom relative to the base plate, wherein each said strut comprises;

a) a trunnion plate having;

(1) a lower end configured as a bifurcated structure that is rotatably pinned to a corresponding base attachment structure which is located on the upper surface of said stationary base plate,

(2) an upper end,

(3) a first edge having a plurality of clamp mounting bores therethrough,

(4) a second edge,

(5) an inner surface, and

(6) an outer surface,

b) a union plate having;

(1) a lower end,

(2) an upper end,

(3) an inner surface and an outer surface, with each surface having a set of bearing mounting bores therethrough, and

c) a lower counterbalance and coil clamp comprising;

(1) a motor shaft bore

(2) a magnetic shaft bore,

(3) an inner surface,

(4) an outer surface,

d) an upper counterbalance and coil clamp comprising;

(1) a motor shaft bore,

(2) a magnetic shaft bore,

(3) an inner surface

(4) an outer surface,

(5) a universal ball joint mounting structure that is attached to the outer surface, wherein the structure is dimensioned to rotatably accept the U-joint that is attached to the upper end of the strut assembly,

e) a counterbalance subassembly comprising;

(1) a counterbalance split clamp having a sleeve opening and a clamp mounting tab, wherein the mounting tab is attached by bolts that are inserted through a set of tab mounting bores and a set of clamp mounting bores that are located on the first edge of said trunnion plate,

(2) a counterbalance sleeve made of a ferrous material, and having an outside diameter and an inside diameter, wherein the outside diameter of the sleeve is dimensioned to be rigidly held within the sleeve opening,

(3) a magnetic shaft having a lower end that is attached by a bolt inserted into the magnetic shaft bore located on said lower counterbalance and coil clamp, an upper end that is attached by a bolt inserted into the magnetic shaft bore located on said upper counterbalance and coil clamp, wherein the magnetic shaft has a diameter that allows the shaft to be concentrically maintained within an air gap located around the sleeve'"'"'s inside diameter,

d) a servo motor subassembly comprising;

(1) an ironless motor coil having a shaft opening therethrough,

(2) a magnetic motor shaft that is inserted into the shaft opening, wherein the shaft has an upper end that is inserted into the upper motor shaft bore located on the upper counterbalance and coil clamp, and a lower end that is inserted into the lower motor shaft bore located on the lower counterbalance and coil clamp,

e) a bearing and encoder subassembly comprising;

(1) an encoder bearing plate having an inner surface, an outer surface and an inner slot, wherein the inner slot is dimensioned to slideably accept and maintain the second edge located on said trunnion plate,

(2) a linear bearing having an inner surface and an outer surface, wherein the outer surface interfaces with the inner surface of the encoder bearing plate, and the inner surface interfaces with the outer surface of said union plate,

(3) an encoder that interfaces with an encoder tape that is located adjacent to the flat linear bearing, wherein said encoder is attached to the inner surface of the encoder bearing plate, and

D. an electronics circuit having means for controlling the position of said struts.

19. The system as specified in claim 18 wherein said means for attaching said base plate to a substantially flat surface comprises a plurality of attachment bores that are dimensioned to receive a plurality of bolts and nuts that interface with the flat surface.

20. The system as specified in claim 18 wherein said linear bearing is selected from the group consisting of a flat linear bearing, a linear ball-bushing shaft bearing, profile rails, crossed roller bearings, a ball spline, bushings, cam style bearing assemblies and v-cam style bearing assemblies.