Passively activated prehensile digit for a robotic end effector

• US 4,770,455 A
• Filed: 10/21/1986
• Issued: 09/13/1988
• Est. Priority Date: 10/21/1986
• Status: Expired due to Fees

• Current Assignee: The Government Of The United States Of America, As Represented By The Secretary Of The Navy
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Collins, Earl R. Jr.
• Primary Examiner(s): Marbert, James B.
• Application Number:
  US06/921,577
• Time in Patent Office: 693 Days
• Field of Search: 294/88, 294/86.4, 294/116, 294/902, 294/95, 294/106, 294/97, 294/115, 294/119.3, 294/89.1, 294/99.1, 901/30, 901/31, 901/39, 269/32, 269/90, 269/224, 269/265, 269/266, 269/267, 269/275, 414/729, 414/744 A, 623/65, 623/66, 623/57
• US Class Current: 294/213
• CPC Class Codes: B25J 15/106 moving in parallel relationship
• CPC Class Codes: B25J 17/0275 Universal joints, e.g. Hooke, Cardan, ball joints
• CPC Class Codes: B25J 19/02 Sensing devices
• CPC Class Codes: B25J 9/14 fluid
• CPC Class Codes: Y10S 294/902 Gripping element

Abstract

A common hydraulic reservoir holds one or more rows of slidable pistons or "fingers" in a base, or "hand". The individual fingers in each row expose graduated cross-sectional fluid application areas to the hydraulic fluid in the reservoir, with the smallest fluid application area in the center of the row and graduating to progressive larger fluid areas towards both ends of each row. The fingers are elongated pistons. Exposed outer ends of each piston extending away from the reservoir, house a transverse pad to contact an object to be held. The transverse pads are universally ball-joint and spring-center mounted in a longitudinally located opening at the outer tapered end of each finger. Simple and effective capacitance metering in the reservoir is provided for each finger.

Claims

1. A workpiece holder having a plurality of pistons slidably mounted in a row of bores in a closed hydraulic reservoir system, with one end of each piston extending into and urged out of hydraulic fluid in the reservoir by pressure thereon and the other end of each piston extending outwardly away from the hydraulic reservoir to receive an object to be held, said holder comprising:

a plurality of pistons each of which have individual hydraulic pressure areas in the ends thereof exposed to said hydraulic pressure and differeing in size from piston to piston; and

a plurality of spring loaded workpiece contact pads, each pad universally mounted on the outer ends of said plurality of pistons and tiltable through substantial spherical angles for contact with irregular shaped objects.

2. A workpiece holder as defined in claim 1 and further comprising:

a graduated series of different sized pressure areas on said row of pistons with the largest hydraulic pressure areas on the outer end of said row and the smallest hydraulic pressure areas near the center of said row.

3. A workpiece holder as defined in claim 1 and further comprising:

a coaxial bore in the outwardly exposed end of each piston and terminating in an outwardly facing spherical seat;

a mated spherical ball formed on the underside of a contact pad and universally seated in said spherical bore; and

a centering spring connected between said bore and said spherical ball for biasing said contact pad into a normally transverse position to said piston.

4. A workpiece holder as defined in claim 3 and further wherein:

said centering spring is an elongated cylinder seated at one end in the center of the base of said bore and seated at the other end in the center of said ball.

5. A workpiece holder as defined in claim 1 and further wherein:

said outer ends of said pistons are tapered at said universally mounted area to provide essentially 270°

of spherical movement by said contact pads.

6. A workpiece holder as defined in claim 1 and further comprising:

means in said reservoir for sensing the degree of movement of each of said pistons in said reservoir housing.

7. A workpiece holder as defined in claim 6 and further wherein:

said movement sensing means comprises a capacitance having one capacitor plate formed on said piston end and spaced away from another capacitor plate held in said reservoir.

8. A workpiece holder as defined in claim 7 and further wherein:

said capacitor relies upon said hydraulic fluid as a dielectric.

9. A workpiece holder as defined in claim 7 and further wherein:

said one capacitor plate is formed by an outside circumference on the lower end of said piston and the other capacitor plate is a slightly oversized metal sleeve coaxially aligned and spaced from said lower end.

10. A workpiece holder as defined in claim 7 and further wherein:

said one capacitor plate is formed by an inner surface of a longitudinal bore in the lower end of said piston and the other capacitor plate is a slightly undersized post coaxially aligned with and spaced from said bore.

11. A workpiece holder as defined in claim 7 and further wherein:

said movement sensing means comprises a capacitance having one capacitor plate formed on said piston end and spaced away from another capacitor plate held in said reservoir.

12. A workpiece holder as defined in claim 11 and further wherein:

said capacitor relies upon said hydraulic fluid as a dielectric.

13. A workpiece holding device having a common hydraulic fluid reservoir with a plurality of cylinder bores slidably housing a plurality of pistons extending into said reservoir and extending outwardly away therefrom, said device comprising:

a plurality of pistons each of which expose graduated pressure areas to said fluid with the areas differing in size from piston to piston, and

spring loaded workpiece gripping pads universally mounted on the outer ends of said pistons for exerting a graduated reaction force to an object to be held.

14. A workpiece holder as defined in claim 13 and further comprising:

a coaxial bore in the outwardly exposed end of each piston and terminating in an outwardly facing spherical seat;

a mated spherical ball formed on the underside of a contact pad and universally seated in said spherical bore; and

said spring loaded gripping pad further comprises a centering spring connected between said bore and said spherical ball for biasing said contact pad into a normally transverse position to said piston.

15. A workpiece holder as defined in claim 14 and further wherein:

said centering spring is an elongated cylinder seated at one end in the center of the base of said bore and seated at the other end in the center of said ball.

16. A workpiece holder as defined in claim 13 and further wherein:

said outer ends of said pistons are tapered at said universally mounted area to provide essentially 270°

of spherical movement by said contact pads.

17. A workpiece holder as defined in claim 13 and further comprising:

means in said reservoir for sensing the degree of movement of each of said pistons in said reservoir housing.

18. A workpiece holding device having a common hydraulic fluid reservoir with a plurality of cylinder bores slidably housing a plurality of pistons extending into said reservoir and extending outwardly away therefrom, said device comprising:

a row of pistons each of which expose graduated pressure areas to said fluid;

a graduated series of different sized pressure areas on said row of pistons with the largest hydraulic pressure areas on the outer end of said row and the smallest hydraulic pressure areas near the center of said row, and

spring loaded workpiece gripping pads universally mounted on the outer ends of said pistons for exerting a graduated reaction force to an object to be held.

19. A workpiece holder in accordance with claim 18 wherein:

the upper surface of the base forming the hydraulic reservoir is concave with the smallest area piston located in the low point of the concave surface and the largest sized area pistons located at the highest points of the concave surface.