Motion control system having adaptive feedforward path tracking

• US 4,761,595 A
• Filed: 05/01/1987
• Issued: 08/02/1988
• Est. Priority Date: 05/01/1987
• Status: Expired due to Term

• Current Assignee: General Motors Auto OOO (General Motors Company)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Goor, Robert M.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): YOUNG, BRIAN K
• Application Number:
  US07/045,129
• Time in Patent Office: 459 Days
• Field of Search: 318/568, 318/569, 318/567, 318/574, 318/600, 318/685, 318/687, 364/513, 364/130, 364/464, 364/468, 364/200, 364/300
• US Class Current: 318/568.1
• CPC Class Codes: G05B 19/19 characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
• CPC Class Codes: G05B 2219/35237 Under four is 0xxx, over four is 1xxx
• CPC Class Codes: G05B 2219/41177 Repetitive control, adaptive, previous error during actual positioning
• CPC Class Codes: G05B 2219/41427 Feedforward of position
• CPC Class Codes: G05B 2219/41435 Adapt coefficients, parameters of feedforward
• CPC Class Codes: G05B 2219/41437 Feedforward of speed
• CPC Class Codes: G05B 2219/42337 Tracking control
• CPC Class Codes: G05B 2219/42342 Path, trajectory tracking control
• CPC Class Codes: G05B 2219/43162 Motion control, movement speed combined with position

Abstract

A feedforward path following routine for a motion control system, where the feedforward parameters are adaptively adjusted in real time during system operation for substantially error-free tracking of a third-order command path.

Claims

1. In a motion control system including a DC servomotor adapted to adjust the position of an output member in relation to a control voltage applied thereto, path generation means for defining third order trajectory position, velocity and acceleration parameters y, y'"'"', and y" for steering the servo output member from its current position to a target position, and path tracking means for supplying a control voltage to the servomotor for causing the output member to track the trajectory, the improvement wherein:

the path tracking means includes;

feedback means for computing the tracking error e according to the deviation of the output member from the trajectory position parameter y, and for generating a feedback term in relation thereto;

feedforward means for generating a feedforward term to be combined with the feedback term to form the servomotor control voltage, the feedforward term being determined substantially in accordance with the expression;

space="preserve" listing-type="equation">v.sub.1 y'"'"'+v.sub.2 y"+v.sub.3 y"'"'"'+v.sub.f,

where the coefficients v₁, v₂, v₃ and v_f relate to characteristic operating parameters of said motion control system, whereby the dynamics of said trajectory are immediately reflected in the servomotor control voltage; and

adaptive means for adjusting the value of the feedforward coefficients v₁, v₂, v₃ and v_f substantially according to the expression;

space="preserve" listing-type="equation">v.sub.1 =v.sub.1 +k.sub.1 *e*y'"'"'

space="preserve" listing-type="equation">v.sub.2 =v.sub.2 +k.sub.2 *e*y"

space="preserve" listing-type="equation">v.sub.3 =v.sub.3 +k.sub.3 *e*y"'"'"'

space="preserve" listing-type="equation">v.sub.f =v.sub.f +k.sub.f *e

where k₁, k₂, k₃ and k_f are constants, thereby to adaptively tune the feedforward coefficients v₁, v₂, v₃ and v_f for a specific motion control system, and to compensate for variations in the characteristic operating parameters thereof, allowing the trajectory to be tracked with minimum tracking error.

2. The improvement set forth in claim 1, wherein:

the servomotor is operated in both forward and reverse directions;

the coefficient v_f generated by the feedforward means represents the static friction of the servomotor and comprises first and second additive terms v₄ and v₅ pertaining to forward and reverse operation of the servomotor, respectively; and

the adaptive means includes means effective (1) when the sign of the trajectory velocity parameter y'"'"' corresponds to forward movement of the servomotor to adjust the term v₄ substantially according to the expression;

space="preserve" listing-type="equation">v.sub.4 =v.sub.4 +k.sub.4 *e

where k₄ is a constant, and (2) when the sign of the trajectory velocity parameter y'"'"' corresponds to reverse movement of the servomotor to adjust the term v₅ substantially according to the expression;

space="preserve" listing-type="equation">v.sub.5 =v.sub.5 -k.sub.5 * e

where k₅ is a constant.