Dual mode position control system with speed profiling

A method of positioning a load at a target position by means of an electrical actuator, the method comprising:

• deriving a position signal indicative of the load position;
• deriving a speed signal indicative of the speed of the actuator;
• controlling the actuator in response to the position signal in a speed control mode when the load is relatively remote from the target position and in a stepping control mode when the load is relatively closer to the target position;
• and
• decelerating the actuator when the position signal and the speed signal fall on a predetermined position/speed deceleration curve defining a braking profile of the actuator under the control of the controller for a given load.

A load positioning assembly comprising:

• (a) an electrical actuator
• (b) a load to be positioned at a target position;
• (c) an interface operatively coupling said actuator to said load, said actuator controlling the position of said load via said interface so that said load is in its target position when said actuator is in a predetermined position;
• (d) an actuator control system providing at least one control signal to said actuator to control the operation of said actuator;
• (e) a position detector for providing data about the actual position of said actuator;
• (f) said control system comprising position control circuitry for operating said actuator in one of at least two control modes including a speed control mode and a stepping mode;
• and
• (g) said control system further comprising speed detection circuitry for deriving a speed signal indicative of the speed of the actuator, the control system being arranged to decelerate the actuator when the actual position of the actuator and the speed signal fall on a predetermined position/speed deceleration curve programmed into the control system, the curve defining a braking profile of the actuator under the control of the controller for a given load.

A position control system for use in driving an electrical machine to a predetermined position, said position control system comprising:

• (a) means for determining an actual position of said machine and generating an actual position signal corresponding thereto;
• (b) means for receiving said actual position signal and comparing said actual position to said predetermined position and generating a position error signal indicative of the difference between said positions;
• (c) means for receiving said position error signal and selecting a mode of operation for said machine from a plurality of possible modes including at least a speed control mode and a stepping mode;
• and
• (d) means for receiving said position error signal and storing and retrieving a plurality of speed demand values, each of said speed demand parameters corresponding to one of a plurality of possible states of said position error signal, said means generating a speed demand signal corresponding to the current state of said position error signal when said machine is being operated in a speed control mode.

A method of driving an electrical machine to a predetermined position, comprising the steps of:

• (a) generating a plurality of predetermined speed demands corresponding to a plurality of possible states of position errors;
• (b) determining the actual position of said machine;
• (c) comparing said actual position of said machine to said predetermined position and generating an actual position error indicative of the difference between said positions;
• (d) comparing said actual position error to a predetermined minimum threshold distance;
• and
• (e) operating said machine at a speed indicated by said predetermined speed demand corresponding to said actual position error if said position error is greater than said minimum threshold and operating said motor in a stepping mode if said position error is less than said minimum threshold.