End effector with load-sensitive digit actuation mechanisms

Abstract

Each of a plurality of digits within a reconfigurable end effector is both rotated and maneuvered for grasping by a single small motor coupled to a drive shaft for the digit through a load-responsive two-speed drive arrangement. The drive arrangement couples the motor directly to the drive shaft through a slip clutch for rapid digit positioning for light load or no load conditions on the digit, then alternatively through an oscillating sprag clutch arrangement for incrementing the drive shaft at a substantially different gear ratio for low speed, high force movement of the digit when substantial loads are encountered. High breakaway friction prevents back drive of the drive shaft without the need for braking apparatus. The motor also rotatably drives a turret in which the digit is mounted through a second slip clutch until a desired rotational position is reached. The turret is locked in the selected rotational position by deenergizing a solenoid to allow a pivoting pawl to wedge a ball into one of a plurality of detents in the turret. An optical sensor responds to the presence of the detents to determine the rotational position of the turret. The drive shaft is axially movable in response to substantial loads on the digit against the resistance of a compressible sprain spring, and a Hall Effect sensor determines the load on the digit by measuring the axial movement. A pair of rotary optical position sensors are employed to determine the rotational positions of the drive shaft and the shaft of the motor.