Position feedback control system for a numerically controlled machine tool

A feedback position control system controlling the displacement of at least one movable member of a numerical control apparatus and further having transducer means, responsive to excitation signals, operatively connected to each movable member for generating an output signal having a cyclically recurring phase relationship with respect to the excitation signals that is correlatable with the displacement of the at least one movable member, the feedback position control system comprising:

• command means for generating a command signal indicative of the desired position of the at least one movable member;
• feedback means for generating a feedback signal indicative of the motion of said at least one member comprising:
• phase detecting means for determining the phase of said output signal relative to a determinable reference irrespective of the d.c. bias level of the output signal including:
• reference counter means for generating a recurring real time count having a predetermined period;
• phase means responsive to the output signal of said transducer means for determining the phase relationship between said output signal relative to the transducer excitation signals;
• first zero crossing means responsive to zero crossings of said output signal in a determinable direction for generating an indicator signal indicative of the first of said zero crossings in said determinable direction occurring during a predetermined interval of the excitation signals;
• second zero crossing means responsive to said output signal for generating a second signal upon the occurrence of the next zero crossing of said output signal;
• first means responsive to said indicator signal for storing a first count having the value of the count within said reference counter means at the occurrence of said indicator signal;
• second means responsive to said second signal for generating a summed count by adding to said stored first count the value of the count within said reference counter means at the occurrence of said second signal;
• and
• dividing means for dividing said summed count by a determinable factor to generate a number indicative of the phase relationship between a predetermined point with the excitation signals and the first maximum of the output signal occurring after said indicator signal;
• conversion means for converting said determined phase during a particular cycle of said output signal into a first signal indicative of the motion of said at least one movable member;
• and wherein said system further includes:
• comparator means for comparing said command signal and said feedback signal and for generating an error signal for driving said at least one member to the desired position.

A method of determining the displacement of a movable member of a numerically controlled apparatus having a transducer linked to and movable with the number and where the phase of the output signal of the transducer is correlatable to the position of the member, the method comprising:

• a. exciting the transducer with a periodic first reference signal of known frequency, and exciting the transducer with a second reference signal shifted in phase relative to the first reference signal to generate a transducer output signal;
• b. starting a reference counter having a counting period twice that of the period of either reference signal;
• c. monitoring the first positive zero crossing of said transducer output signal in a determinable direction after or in concurrence with the starting of said reference counter;
• d. storing the value of the count within said reference counter corresponding to the first positive zero crossing in step c;
• e. storing the value of the count within said reference counter corresponding to the next zero crossing of the resolver output signal;
• and
• f. determining the phase of said output signal by adding the counts stored in step d and step e and dividing by 2.

A feedback position control system for controlling the displacement of at least one movable member of a numerical control apparatus and further having transducer means, responsive to excitation signals, operatively connected to each movable member for generating an output signal having a cyclically recurring phase relationship with respect to the excitations signals that is correlatable with the displacement of the at least one movable member, the feedback position control system comprising:

• command means for generating a command signal indicative of the desired position of the at least one movable member;
• feedback means for generating a feedback signal indicative of the motion of said at least one member comprising:
• phase detecting means for determining the phase of said output signal relative to a determinable reference irrespective of the d.c. bias level of the output signal, including:
• reference counter means for generating a recurring real time signal having a determinable period;
• wherein said recurring real time signal is a recurring digital count;
• reference means responsive to said real time signal for generating a periodically repeating first reference signal to excite said transducer means;
• quadrature means responsive to said real time signal for generating a periodically repeating second reference signal, to further excite said transducer means, that is shifted in phase from and has the same frequency as said first reference signal;
• first means responsive to said output signal for sampling the count within said reference counter means and for storing a first number corresponding to said count upon the occurrence of a first zero crossing of said output signal in a determinable direction;
• second means responsive to the next zero crossing of said output signal for sampling the count within said reference counter means and for storing a second number corresponding to the count within said reference means at said next zero crossing;
• third means for generating a third number that is equal to the sum of said first and said second number and for dividing said third number by a factor;
• conversion means for converting said determined phase into a first signal indicative of the motion of said at least one movable member during a particular cycle of said output signal;
• and wherein said system further includes:
• comparator means for comparing said command signal and said feedback signal and for generating an error signal for driving said at least one member to the desired position.