High torque, low hysteresis, multiple link robot arm mechanism

摘要

A robot arm mechanism (10) maximizes available torque and control accuracy by arranging first and second high torque motors (50, 52) in a concentric relationship about a shoulder axis (16). The first motor is coupled through a 1:1 ratio endless belt to rotate a forearm (22) about an elbow axis (32). The second motor is 1:1 directly coupled to rotate an upper arm (14) about the shoulder axis. A motor controller (100) controls the first and second motors in at least two operational states. The first operational state equally contrarotates the first and second motors to linearly extend or retract a hand (30), and the second operational state equally rotates the first and second motors to angularly displace the hand about the shoulder axis. The robot arm mechanism has a 1:1:1:2 overall drive ratio and an indexing vane (130) for eliminating positional ambiguity problems stemming from a continuous rotation capability of the robot arm mechanism. The indexing vane has four alternating short (132) and long blades (136) evenly spaced around a circle. The indexing vane is detented to rotate into four quadrant rest positions. An indexing pin (144) contacts one of the four blades for each 360 degree rotation of the first motor relative to the second motor such that the long blades break a light beam in an optical switch assembly (148) for each 720 degrees of relative rotation. The indexing vane stores and updates a rotational state of the robot arm mechanism even if the power is off and the robot arm mechanism is manually repositioned or otherwise disturbed.