Asymmetric six-degree-of-freedom force-transducer system for a computer-controlled manipulator system

#This invention relates to measuring and testing for a computer-controlled manipulator, and more particularly to force transducer measuring devices comprising dynamometers applied to a manipulator system.

#The manipulator gripper of U.S. Pat. No. 3,948,093 of Folchi et al. for a Six-Degree-of-Freedom Force Transducer for a Manipulator System employs pairs of strain gauges mounted on I-beam modules to measure forces on the fingers. It employs a modular approach with x-y-z orthogonality. Stiffness is of the same order in all directions. There is minimum cross-sensitivity, minimum backlash, and there are overload stops.

#An object of this invention is to measure the gripping force and a force vector applied to the object being held by a manipulator finger.

#FIG. 1A shows a perspective view of a computer-controlled manipulator employing the force-sensor apparatus in accordance with this invention.

#FIG. 1B shows a finger drive mechanism for the fingers of FIG. 1A.

#FIG. 2 shows a perspective view of the gripper fingers including the force-sensor apparatus shown in FIG. 1A.

#FIG. 1A shows a manipulator controlled by a central processing unit (CPU) 44 having three mutually perpendicular X, Y and Z arm segments 38, 40 and 42 for providing x, y and z directions of motion of the gripper. Segments 38, 40, and 42 are slidably connected together by holders 39, 41 and 43 to provide an articulated three-part manipulator arm, as shown in U.S. Pat. No. 4,001,556 of Folchi et al. filed Apr. 7, 1975. It is somewhat similar to the manipulator structure shown in U.S. Pat. No. 3,575,301 of Panissidi for a "Manipulator". At the outboard end of the arm segment 38 is shown a gripper 45 connected to X arm segment 38 by roll shaft 46 wrist 47, and finger drive mechanism 48. The X arm segment 38 is slidable in holder 39 affixed to the end of Y arm segment 40. Holder 39 carries a linear motor 50 affixed thereto including actuators adapted for operating upon a parabolic displacement cam 53 in accordance with U.S. Pat. No. 3,848,515 of Gardineer et al. for a "Linear Hydraulic Drive System". Rack 108 drives a potentiometer 114 by its associated pinion. Potentiometer 114 operates to send messages indicating X arm position data to CPU 44 indicating the position of arm 38. Y arm segment 40 is slidable along the Y axis in holder 41 with a similar drive motor 51 secured thereto to operate upon cam 54. Potentiometer 116 is driven by its pinion riding on rack teeth 110, as segment 40 moves by to signal Y arm position data to CPU 44. Z arm segment 42 does not move up and down along the z axis, but instead, holder 43 is rigidly and permanently secured to holder 41 and holder 43 has motor 53 secured thereto to operate upom cam 55 to raise and lower the rest of the arm including segments 38 and 40, etc. on arm segment 42. Z axis position is sensed by potentiometer 118 and rack teeth 112. The entire structure is rotatable about the center of arm segment 42 which is mounted upon a rotatable disc which is driven by a rotary drive inside cylinder 56. Potentiometer 57 driven by rack teeth 107 senses arm rotation. Still another rotary drive turns roll shaft 46, as do motors for the yaw, and pitch axes 58 and 59 of wrist 47. The finger drive mechanism 48 moves fingers 10 and 11 of gripper 45 which can be opened or closed (moved together and apart) by means of the mechanism shown in FIG. 1B.

#As shown in FIG. 1B, the motor 74 is operatively connected by means of gears 76 to a pair of gear racks 80 for driving the finger driver blocks 23 and 24 either toward or away from each other in unison. Gear racks 80 move longitudinally to the left and right as shown by the arrows in FIG. 1B. A potentiometer 78 has its shaft teeth in operative engagement with motor gears 76 so that the motor shaft angular position is reflected in the output of the potentiometer 78 on line 86. This output on line 86 is therefore directly related to the separation of the finger driver blocks 23 and 24.

#Referring to FIG. 2, the gripper 45 consists of two fingers 10 and 11. A three-degree-of-freedom force sensor 12 is connected to the inboard end of the right finger 10. Another three-degree-of-freedom force sensor 13 with a different offset distance, is connected to the inboard end of the left finger 11. In other words, the sensor system for the two fingers is not symmetrical.