Precision stop control for motors

An improved stop control system for a motor having a drive mechanism wherein the motor is coupled to a motor controller that controls the speed and position of the drive mechanism using a first signal indicative of a commanded position of the drive mechanism, a second signal indicative of the actual speed of the drive mechanism and a third signal indicative of the actual position of the drive mechanism, wherein the motor controller uses said second signal in conjunction with said third signal to stop the motor, said improved stop control system comprising:

• a differencing circuit receiving said first signal and said third signal for generating one of a positive version and a negative version of an error signal indicative of a difference between said first signal and said third signal;
• and
• an absolute value circuit coupled to said differencing circuit for generating an absolute value of said one of a positive and a negative version of said error signal;
• a comparator circuit coupled to said absolute value circuit for generating a stop control signal when said absolute value is less than a threshold position error;
• and
• a switch having a signal input coupled to the motor for receiving said second signal and having a control input coupled to said comparator circuit for receiving said stop control signal, said switch further having an output coupled to the motor controller, said switch coupling said signal input to said output in response to said stop control signal.

A method of controlling the stoppage of a motor having a drive mechanism wherein the motor is coupled to a motor controller that controls the speed and position of the drive mechanism using a first signal indicative of a commanded position of the drive mechanism, a second signal indicative of the actual speed of the drive mechanism and a third signal indicative of the actual position of the drive mechanism, said method comprising the steps of:

• generating an error signal indicative of a difference between said first signal and said third signal;
• providing a threshold position error;
• and
• supplying said second signal to the motor controller at least whenever said error signal is less than said threshold position error so that the motor controller can use said second signal in conjunction with said third signal to stop the motor.