Motion control

A digital motion and position control for a system that includes:

• prime mover means for moving a controlled device relative to a master reference X and a secondary reference Y, first sensor means for sensing the position of the controlled device relative to the reference X and generating a first sensor signal S.sub.x representative of the position of the controlled device relative to reference X, and second sensor means for sensing the position of the controlled device relative to the reference Y and generating a second sensor signal S.sub.y representative of the position of the controlled device relative to reference Y, the control comprising:
• sensor signal processor means for receiving the sensor signals S.sub.x and S.sub.y and producing two sequences of pulse position count signals P.sub.x and P.sub.y, each position pulse count signal being representative of the actual position of the controlled device relative to one reference at a given instant;
• counter means for recording successive pulse position count signals, from the sensor signal processor means;
• computing circuit means connected to the counter means and including position data storage means for recording position data for the controlled device relative to the reference X and Y, for generating a sequence of command signals C.sub.ny for the Y axis, at a command signal sequence frequency F.sub.s, in accordance with the basic relationship:
• ##EQU8## in which:
• C.sub.ny is the command signal relative to reference Y,
• P.sub.x is the current pulse position count signal relative to the X reference,
• P.sub.xo was the starting pulse position count relative to the X reference,
• P.sub.y is the current pulse position count signal relative to the Y reference,
• P.sub.yo was the starting pulse position count relative to the Y reference,
• R.sub.x and R.sub.y are predetermined ratios,
• N.sub.x and N.sub.y are predetermined ratio normalizers,
• D is a drift factor representative of inertia of the controlled device;
• and
• C.sub.ny-1 is the last previous command signal;
• and command signal output means for supplying the command signals C.sub.ny to the prime mover means for the Y reference to control operation of the primer mover means in accordance with those command signals.