US 4,200,827 AGranted

Positioning system employing feedforward and feedback control

AssigneeInternational Business Machines Corporation

InventorRichard K. Oswald

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Abstract

A positioning system for moving a member between positions in time optimal fashion employs concurrent "feedforward" and "feedback" control. The feedforward control system provides major control and the feedback control system provides minor control to correct for deviations between the actual and a nominal system. The feedback loop may thus be of low bandwidth permitting desensitization to high frequency disturbances or the employment of inherently low bandwidth controlled variables. The "feedforward" control function includes successive portions of opposite polarity corresponding to acceleration and deceleration of the member and also includes a subtractive velocity related component. This function represents the approximate current input to an electromagnetic coil actuator of a nominal system required to move such a member between positions in time optimal fashion.

Claims13

Dependent claims

A position control system for moving a member with time optimal motion between a current position and a target position in response to a single input command which defines the distance between said positions, comprising in combination:

(a) an electromagnetic actuator coupled to said member and having a load acceleration characteristic which is proportional to the input current supplied thereto for accelerating and decelerating said member with said time optimal motion in response to an electric drive signal applied to the input circuit of said actuator;
(b) means including a power source and a first summing junction connected to said actuator for providing to said actuator said drive signal to cause said member to tend to follow a predetermined acceleration and deceleration profile for said distance to be moved specified by said single input command;
(c) a first generator for supplying to said first summing junction a first time varying signal corresponding to the profile of the actuator current required to move said member the distance specified by said input command with time optimal motion in an ideal system;
(d) an error amplifier connected to supply an error signal to said first summing junction concurrently with said first time varying signal and having means for limiting the value of its output to no more than 15% of the value of said current drive signal;
(e) a second order position control system in which position is the controlled variable and acceleration is the manipulated variable for providing to said error amplifier an error signal representing the difference in the instantaneous position of said member in said actual system and said ideal system, said error signal varying the instantaneous acceleration and deceleration of said member in a direction tending to reduce said instantaneous position error, and further including a position transducer connected thereto for providing a signal to said second order position control system corresponding to the instantaneous actual position of said member during said time optimal motion;
and
(f) means for controlling the operation of said first generator in response to the operation of said second order position control system to cause the respective signals generated thereby to be supplied concurrently to said first summing junction to achieve time optimal movement of said member.

4 more elements

A position control system for moving a member along a predetermined path of travel in response to a single input command representing the distance to be moved between a current and target position, said movement being in a minimum of time consistent with performance constraints of the system, comprising in combination:

(a) an electromagnetic actuator having a load acceleration characteristic which is proportional to the input current supplied thereto for accelerating and decelerating said member along said predetermined path in response to an electric current drive signal applied to the input circuit of said actuator;
(b) means including a power source and a first summing junction connected to the input of said actuator for providing to said actuator said current drive signal to cause said member to tend to follow a predetermined acceleration and deceleration profile for said distance to be moved specified by said input command;
(c) a first generator for supplying to said first summing junction a first time varying signal corresponding to the profile of the current required to move said member the distance specified by said input command in said minimum time in an ideal system;
(d) said first time varying signal comprising at least an acceleration portion and a deceleration portion, the respective amplitudes of which at any instant of time reflect the effect of the back EMF which is generated in the coil of the actuator during movement of said member whereby the profile of said first time varying signal is proportional to said predetermined acceleration-deceleration profile;
(e) an error amplifier having its output connected to said first summing junction;
(f) means for providing an error signal to said error amplifier concurrently with said first time varying signal, comprising
(g) means for generating an error signal representing the difference between a reference signal and a feedback signal, said error signal being applied to the input of said actuator to finely control the actual instantaneous position of said member by changing the instantaneous deceleration of said member in a direction to reduce said error, said error signal generating means comprising:
(h) means for generating said reference signal in response to said input command, said reference signal corresponding to the velocity position remaining profile of said member in said ideal system;
(i) a feedback loop including a transducer for generating a signal representing the instantaneous actual position of said member during said movement;
and
(j) a second summing junction having an output connected to said error amplifier;
(k) one input connected to said feedback loop to receive a signal from said transducer and another input connected to receive the output of said reference signal generator;
and
(l) means connected from said error signal generator for controlling the operation of said first generator in accordance with the operation of said error signal generator and in response to said input command to achieve time optimal movement of said member over the distance specified by said input command.

11 more elements

Dependencies are inferred from the claim text.