Digital control for multiaxis robots

• US 4,786,847 A
• Filed: 11/20/1986
• Issued: 11/22/1988
• Est. Priority Date: 11/20/1986
• Status: Expired due to Term

• Current Assignee: Unimation Incorporated Shelter Rock Lane Danbury 06810
• Original Assignee: Unimation, Inc. (Stäubli Holding AG)
• Inventors: Johnson, Richard A., Penkar, Rajan C., Vercellotti, Leonard C., Casler, Richard J. Jr., Daggett, Kenneth E., Onaga, Eimei M., Booth, Barrett L.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): IP, SHIK LUEN PAUL
• Application Number:
  US06/932,989
• Time in Patent Office: 733 Days
• Field of Search: 318/568, 318/568 C, 318/568 D, 318/568 E, 318/568 G, 318/568 M, 318/566, 318/567, 318/569, 318/573, 318/574, 318/597, 318/598, 318/560, 318/565, 318/570 , 318/576, 318/561, 318/562, 318/577, 318/568 B, 318/599, 901/2-25, 901/27, 901/529, 364/478, 364/513, 364/169
• US Class Current: 318/568.2
• CPC Class Codes: B25J 9/1633 compliant, force, torque control, e.g. combined with position control
• CPC Class Codes: G05B 19/4141 characterised by a controller or microprocessor per axis
• CPC Class Codes: G05B 2219/33337 For each axis a processor, microprocessor
• CPC Class Codes: G05B 2219/41426 Feedforward of torque
• CPC Class Codes: G05B 2219/42237 Pwm pulse width modulation, pulse to position modulation ppm
• CPC Class Codes: G05B 2219/42256 Sampling the signal

Abstract

A completely digital robot control operates at a predetermined sampling rate. The robot arm has a plurality of joints with each driven by an electric brushless or brush-type DC motor which is in turn supplied with drive current by a power amplifier bridge circuit having power switches connected therein to supply motor winding current in the forward or reverse direction.

Incremental or absolute encoders and tachometers provide for generating digital position and velocity feedback signals generated synchronously with the sampling rate. Digital motor current feedback signals are also generated synchronously with the sampling rate.

Paired position/velocity microprocessors generate torque commands for each of the robot axes at the sampling rate in response to the position commands and the position and velocity feedback signals. Paired torque microprocessors generate motor voltage commands for each of the robot axes at the sampling rate in response to the torque commands and the current feedback signals.

Pulse width modulators generate digital motor control signals for each of the robot axes at the sampling rate in response to the voltage commands. The digital control signals for each axis are coupled to control terminals of the corresponding power switches to control on/off switch time and satisfy the motor voltage commands and thereby satisfy the position commands.

Claims

1. A completely digital control for a robot operating at a predetermined sampling rate and having an arm with each of a plurality of joints driven by an electric DC motor, each of said DC motors in turn supplied with drive current by a power amplifier bridge circuit having power switches connected therein to supply motor winding current in the positive direction or the negative direction, said robot control comprising:

digital means for generating position commands at the sampling rate for each of the robot axes in accordance with a stored robot program;

means for sensing the position of each of said motors;

means for generating digital position feedback signals synchronously with the sampling rate in response to said position sensing means;

means for generating digital velocity feedback signals synchronously with the sampling rate for each of said motors;

means for sensing the polarity and magnitude of motor current for each of said joint motors;

means for generating digital current feedback signals synchronously with the sampling rate in response to said current sensing means;

digital means for generating torque commands for each of the robot axes at the sampling rate in response to said position commands and said position and velocity feedback signals;

digital means for generating motor voltage commands for each of the robot axes at the sampling rate in response to said torque commands and said digital current feedback signals;

pulse width modulation means for generating digital motor control signals for each of the robot axes at the sampling rate in response to said voltage commands; and

means for coupling said digital control signals for each axis to control terminals of the corresponding power switches to control on/off switch time and satisfy said motor voltage commands and thereby satisfy said position commands.

2. A digital robot control as set forth in claim 1 wherein said velocity feedback signal generating means includes a tachometer coupled to each of the joint motors.

3. A digital robot control as set forth in claim 1 wherein said digital means for generating torque commands includes a microprocessor system having a data manager microprocessor and a position/velocity calculating microprocessor coupled together, said data manager microprocessor controlling the timing and flow of control data to and from said calculating microprocessor.

4. A digital robot control as set forth in claim 1 wherein said motor voltage command generating means includes a microprocessor system having a data manager microprocessor and a torque calculating microprocessor coupled together, said data manager microprocessor controlling the timing and flow of control data to and from said calculating microprocessor.

5. A digital robot control as set forth in claim 4 wherein said digital means for generating torque commands includes a microprocessor system having a position/velocity data manager microprocessor and a position/velocity calculating microprocessor coupled together, said position/velocity data manager microprocessor controlling the timing and flow of control data to and from said calculating microprocessor.

6. A digital robot control as set forth in claim 3 wherein said position digital means for generating commands includes stored program means for generating position commands from programmed robot moves, said microprocessor system includes said position command generating means, and said data manager microprocessor executes said program means and manages the operation of said microprocessor system to generate said position commands.

7. A digital robot control as set forth in claim 3 wherein said digital means for generating commands includes stored program means for generating position commands from programmed robot moves and further includes a system data manager microprocessor and a system position command calculating microprocessor coupled together, said system data manager microprocessor executing said program means and controlling the timing and flow of control data to and from said position command calculating microprocessor.

8. A digital robot control as set forth in claim 5 wherein said digital means for generating includes stored program means for generating position commands from programmed robot moves and further includes a system data manager microprocessor and a system position command calculating microprocessor coupled together, said system data manager microprocessor executing said program means and controlling the timing and flow of control data to and from said position command calculating microprocessor.