Reaction sensing torque actuator

• US 5,327,790 A
• Filed: 06/19/1992
• Issued: 07/12/1994
• Est. Priority Date: 06/19/1992
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Levin, Michael, Salisbury, J. Kenneth Jr.
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): Dougherty, Elizabeth L.
• Application Number:
  US07/900,663
• Time in Patent Office: 753 Days
• Field of Search: 73/862.191, 73/862.193, 73/862.29, 73/862.31, 73/862.325, 73/862.326, 73/862.34, 73/862.321
• US Class Current: 73/862.325
• CPC Class Codes: B25J 13/085 Force or torque sensors B25J13/082, B25J13/084 take precedence
• CPC Class Codes: B25J 9/12 electric
• CPC Class Codes: B25J 9/1633 compliant, force, torque control, e.g. combined with position control
• CPC Class Codes: G05B 2219/37344 Torque, thrust, twist, machining force measurement
• CPC Class Codes: G05B 2219/37473 Resolver
• CPC Class Codes: H02K 26/00 Machines adapted to function as torque motors, i.e. to exert a torque when stalled
• CPC Class Codes: H02K 29/06 with position sensing devices H02K29/03 takes precedence

Abstract

A reaction torque actuator has a sensor operatively coupled between a motor housing and an outer housing. A pair of bearings support the motor within the outer housing in a spaced, concentric relationship. The bearings allow a mutual angular displacement of the housing about the axis of rotation of the output shaft of the motor, but they isolate the sensor from the axial and radial moments. A resolver surrounds the shaft at its output end to produce a signal that accurately measures the angular position of the shaft. A controller regulates power to the motor windings as a function of signals from the resolver and the sensor and torque commands. In a preferred form for use in robotics where very accurate force control is desired, the motor: is a brushless D.C. motor, the sensor is of the strain gauge type, and the controller uses high quality amplifiers, sine wave commutation, cable shielding, and filtering to limit the noise generated by electronic switching.

Claims

1. A torque actuator for sensing the torque output of a motor having a rigid housing and an output shaft rotatable about a first axis, comprising

an outer housing that surrounds the motor housing in a spaced relationship and is grounded,

first and second support means mounted between said outer housing and said motor housing, said first and second support means being mutually spaced along the first axis and constructed and positioned to resist axial and radial moments while allowing only a mutual angular displacement of said motor housing and outer housing about said first axis in reaction to the actual output torque of said shaft, and

sensor means operatively coupled between said motor housing and said grounded outer housing that converts said angular displacement caused by said reaction toque into a first electrical signal that corresponds to the output torque of the shaft, said sensor means having no moving parts and limiting said mutual angular displacement to a fraction of a degree.

2. The torque actuator of claim 1 wherein said outer housing substantially has a side wall and front and rear end walls that together enclose said motor housing also having a side wall and front and rear end walls.

3. The torque actuator of claim 2 wherein said outer housing seals its interior.

4. The torque actuator of claim 1 wherein said first and second support means each comprise a bearing.

5. The torque actuator of claim 4 wherein a first one of said bearings is rigidly secured between said shaft and said outer housing and the second of said bearings is rigidly secured between said motor housing and said outer housing.

6. The torque actuator of claim 2 wherein said sensor comprises a strain gauge sensor rigidly secured to the rear end wall of said outer housing and having an angularly movable input shaft rigidly secured to the rear end wall of said motor housing.

7. The torque actuator of claim 1 wherein said motor comprises a brushless D.C. motor.

8. The torque actuator of claim 1 wherein said motor is an electric motor and further comprising a current controller for said motor and means for producing a second electrical signal indicative of said angular position of said shaft, said controller receiving said first and second electrical signals and producing an output current to said motor that results in a pre-selected output torque.

9. The torque actuator according to claim 8 wherein said controller includes means for producing a pulse width modulated current with sine wave commutation.