Automatic tuning of a position control circuit for a servo device

A method for tuning a control circuit that positions a servo device in response to a process demand signal, said servo device being connected to an actuation circuit and a position detection means for generating a servo device position signal, said control circuit having:

• (i) a demodulator having a gain determinable by a gain signal for transmitting integer values in a gain range having a lower limit, DGl, and an upper limit, DGh, said integer values corresponding to real number values for said gain, said demodulator operable to receive and respond to said servo device position signal to generate an analog position signal, said analog position signal having a lower voltage value when said servo device is at its 0% mechanical position and an upper voltage value when said servo device is at its 100% mechanical position, said lower voltage value and said upper voltage value being functions of said gain, (ii) an analog to digital converter having an input voltage range, said analog to digital converter operable to convert said analog position signal to a digital position signal, and (iii) calculating means operable to receive and respond to said process demand signal and said digital position signal to calculate a control signal to said actuation circuit, said control signal causing said actuation circuit to move said servo device in response thereto, said method comprising the steps of:
• a) generating said gain signal;
• b) ramping said control signal down until said servo device is at its 0% mechanical position;
• c) determining the largest one of said integer values, SG0, for said gain signal which results in said lower voltage value of said analog position signal being within a lower voltage range which begins with, but does not include, a minimum lower voltage value, LVmin, and extends to, and includes, a maximum lower voltage value, VL, where said lower voltage range is in said input voltage range;
• d) ramping said control signal up until said servo device is at its 100% mechanical position;
• e) determining the largest one of said integer values, SG100, for said gain signal which results in said upper voltage value of said analog position signal being within an upper voltage range which begins with, but does not include, a minimum upper voltage value, UVmin, and extends to, and includes, a maximum upper voltage value, Vh, where said upper voltage range is in said input voltage range;
• and
• f) setting said gain signal to one of said integer values, SG, which corresponds to an optimum value for said gain, SG being selected from SG0 and SG100, where SG100 is selected if SG100 is less than SG0 and where SG0 is selected if SG0 is less than or equal to SG100, provided SG is not less than or equal to an error gain that results in said lower voltage value of said analog position signal being greater than LVmin or said upper voltage value of said analog position signal being less than UVmin.