Machine position sensing device

A device for sensing the position of a movable machine part, which is driven by a motor, through use of pulses available from a position sensor mounted on the motor directly or indirectly, said device comprising:

• counting means for counting the pulses from the position sensor;
• readout means for reading out the count value of the counting means at predetermined time intervals;
• cancel means for cancelling the contents of the counting means by a value equal to the count value read out by the readout means;
• backlash amount storage means for storing an amount of backlash;
• amount-of-movement computing means for computing the actual amount of movement of the movable machine part for each said predetermined time interval on the basis of the count value read out by the readout means and the amount of backlash;
• integrating means for integrating the amount of movement computed by the amount-of-movement computing means;
• and
• wherein said amount-of-movement computing means comprising:
• backlash discharge storage means for storing a backlash discharge value relative to the movement of the movable machine part in a predetermined direction;
• backlash discharge adding means for adding the stored value of the backlash discharge storage means and the count value read out by the readout means;
• subtracting means for subtracting the amount of backlash from the output value of the adding means;
• first polarity discriminating means for discriminating the polarity of the output of the adding means;
• second polarity discriminating means for discriminating the polarity of the output of the subtracting means;
• amount-of-movement outputting means for outputting either one of the outputs of the adding means and the subtracting means to the integrating means in dependence upon the results of discrimination by the first and second polarity discriminating means;
• and
• updating means for updating the stored value of the backlash discharge storage means on the basis of the results of discrimination by the first and second polarity discriminating means, the output of the adding means, the amount of backlash, and a present value.