Method and apparatus for sensing present position in position control system

A position control system having a control unit for producing a command signal, error storage means for storing an error corresponding to the difference between the magnitude of the command signal and a feedback quantity, a speed control circuit operatively connected to the error storage means for controlling a motor in accordance with the error, and a position sensor provided on the motor shaft or on a movable machine element driven by the motor, the position control system including a position control loop wherein an amount of movement sensed by the position sensor is applied to the error storage means as the feedback quantity, and an apparatus for sensing the present position of the machine element when the connection between the error storage means and speed control circuit is disconnected to place the position control loop in the open state, said control unit comprising:

• a steady deviation register, operatively connected to the error storage means, for storing an error from the error storage means as a steady deviation immediately before the position control loop, connecting the error storage means and the speed control circuit, is switched from the closed state to the open state;
• a present position register, operatively connected to the apparatus for sensing the present position of the machine element, for storing the present position of the machine element;
• and
• updating control means, operatively connected to said present position register, for updating the content of said present position register on the basis of an arithmetic difference obtained by substracting the steady deviation in said steady deviation register from the error in the error storage means read when the position control loop is in the open state, and for delivering the arithmetic difference to the error storage means to revise the content thereof in dependence upon the arithmetic difference.

A method for sensing the present position of a machine element in a position control system, including a motor, error storage means for storing an error and a steady deviation signal, a speed control circuit operatively connected to the error storage means and the motor for controlling the motor in accordance with the error, and a position control loop having an open state or a closed state, said method comprising the steps of:

• (a) reading and storing the error from the error storage means as a steady deviation immediately before the position control loop connecting the error storage means and the speed control circuit is switched from the closed state to the open state;
• (b) reading the error in the error storage means when the position control is in the open state;
• (c) updating the contents of the present position register by storing the present position of the machine elements determined on the basis of an arithmetic difference obtained by subtracting the steady deviation from the error read from the error storage means;
• and
• (d) revising the contents of the error storage means in dependence upon the arithmetic difference.

A position control system including a movable machine element, a motor connected to the movable machine element, an error storage means for storing an error, a speed control circuit operatively connected to the error storage means and the motor for controlling the motor in accordance with the error, and a position control loop connecting the error storage means and the speed control circuit, for applying an amount of movement of the machine element to the error storage means and having an open state or a closed state, and a control unit for producing a command signal, said control unit comprising:

• a steady deviation register, operatively connected to the error storage means, for storing an error from the error storage means as a steady deviation immediately before the position control loop is switched from the closed state to the open state;
• a present position register, operatively connected to the machine element, for storing the present position of the machine element;
• and
• updating control means, operatively connected to the present position register, for updating the contents of said present position register on the basis of an arithmetic difference obtained by subtracting the steady deviation in said steady deviation register from the error in the error storage means read when the position control loop is in the open state, and for delivering the arithmetic difference to the error storage means to revise the contents thereof in dependence upon the arithmetic difference.

A position control system having a control unit for producing a command signal, error storage means for storing an error corresponding to the difference between the magnitude of the command signal and a feedback quantity, a speed control circuit operatively connected to the error storage means for controlling a motor in accordance with the error, and a position sensor provided on the motor shaft or on a movable machine element driven by the motor, the position control system including a position control loop wherein an amount of movement sensed by the position sensor is applied to the error storage means as the feedback quantity, and an apparatus for sensing the present position of the machine element when the connection between the error storage means and speed control circuit is disconnected to place the position control loop in the open state, said control loop comprising:

• a steady deviation register, operatively connected to the error storage means, for storing an error from the error storage means as a steady deviation immediately before the position control loop, connecting the error storage means and the speed control circuit, is switched from the closed state to the open state;
• a present position register, operatively connected to the apparatus for sensing the present position of the machine element, for storing the present position of the machine element;
• and
• updating control means, operatively connected to said present position register, for updating the contents of said present position register on the basis of an arithmetic difference obtained by subtracting the steady deviation in said steady deviation register from the error in the error storage means read when the position control loop is in the open state, and for delivering the arithmetic difference to the error storage means to revise the contents thereof in dependence upon the arithmetic difference, said updating control means comprising:
• a first arithmetic circuit, operatively connected to said steady deviation register and operatively connected to receive the error in the error storage means as an input, for producing a signal indicative of the arithmetic difference;
• and
• a second arithmetic circuit, operatively connected to said steady deviation register and to said present position register and operatively connected to receive the error in the error storage means, for updating the contents of said present position register.

A position control system including a movable machine element, a motor connected to the movable machine element, an error storage means for storing an error, a speed control circuit operatively connected to the error storage means and the motor for controlling the motor in accordance with the error, and a position control loop connecting the error storage means and the speed control circuit, for applying an amount of movement of the machine element to the error storage means and having an open state or a closed state, and a control unit for producing a command signal, said control unit comprising:

• a steady deviation register, operatively connected to the error storage means, for storing an error from the error storage means as a steady deviation immediately before the position control loop is switched from the closed state to the open state;
• a present position register, operatively connected to the machine element, for storing the present position of the machine element;
• and
• updating control means, operatively connected to the present position register, for updating the contents of said present position register on the basis of an arithmetic difference obtained by subtracting the steady deviation in said steady deviation register from the error in the error storage means read when the position control loop is in the open state, and for delivering the arithmetic difference to the error storage means to revise the contents thereof in dependence upon the arithmetic difference, said updating control means comprising:
• a first arithmetic circuit, operatively connected to said steady deviation register and operatively connected to receive the error in the error storage means as an input, for producing a signal indicative of the arithmetic difference;
• and
• a second arithmetic circuit, operatively connected to said steady deviation register and to said present position register and operatively connected to receive the error in the error storage means, for updating the contents of said present position register.