Position pickup for numerically controlled machine tools

Claim 2

In a position pickup for use in numerically controlled machine tools comprising a resolver coupled to the machine part to be moved and having a primary side and a secondary side in which the phase of the voltage on the secondary side relative to the phase of the voltage on the primary side is a measure of position value, a digital sine-cosine generator made up of divider stages for generating two voltages which are electrically shifted 90° relative to each other from a clock frequency and supplying them to the primary side, and means for generating a value proportional to the signal states of the sine-cosine generator at the time of zero crossing of the voltage on the secondary side as a measure of the actual position, including a filter having its input coupled to said secondary side and a comparator having its input coupled to the output of said filter for detecting the zero cross-over of the filter output, the improvement comprising: means for deriving a voltage from the primary side; and means to detect the signal state of the sine-cosine generator at the time of zero crossing of the output of said filter when coupled to said means providing a voltage derived by the primary voltage whereby, in successive switching operations the change of the signals state of said sine-cosine generator as so detected may be used for correcting said value proportional to the signal states.

Claim 3

In a method of generating a digital signal value proportional to angular rotation which comprises the steps of: generating two voltages electrically shifted 90° from each other in a sine-cosine generator by dividing a signal from a clock generator; generating a binary value for storage in a register by dividing a signal from the clock generator in resettable binary counters; generating a signal whose phase is a function of angular position by applying the outputs of the sine-cosine generator to the primary windings of an angle resolver, clearing the storage register and resetting the counters at the start of a counting period of the sine-cosine generator; generating a signal at the time the signal on the secondary winding of the angle resolver goes through zero by coupling said secondary winding to a filter followed by a comparator, and transferring the count from the binary dividers at the time of the zero crossing to establish a value proportional to the position angle of the resolver, the improvement comprising: alternately coupling said filter to said secondary winding and to a voltage derived from the primary side voltage at fixed intervals; aslo transferring the count from the binary dividers at zero crossover when said filter is coupled to said voltage derived from said primary side voltage; and using the values so obtained in successive switching operations to correct said value proportional to the position angle of the resolver.

Claim 4

In a method of generating a digital signal value proportional to angular rotation which comprises the steps of: generating two voltages electrically shifted 90° from each other in a sine-cosine generator by dividing a signal from a clock generator; generating a binary value for storage in a register by dividing a signal from the clock generator in resettable binary counters; generating a signal whose phase is a function of angular position by applying the outputs of the sine-cosine generator to the primary windings of an angle resolver, clearing the storage register and resetting the counters at the start of a counting period of the sine-cosine generator; generating a signal at the time the signal on the secondary winding of the angle resolver goes through zero by coupling said secondary winding to a filter followed by a comparator, and transferring the count from the binary dividers at the time of the zero crossing to establish a value proportional to the position angle of the resolver, the improvement comprising: alternately coupling said filter to said secondary winding and to a voltage derived from the primary side voltage at fixed intervals; aslo transferring the count from the binary dividers at zero crossover when said filter is coupled to said voltage derived from said primary side voltage; and using the values so obtained in successive switching operations to correct said value proportional to the position angle of the resolver.