Apparatus and method for minimizing limit cycle using complementary filtering techniques

An apparatus for controlling the positioning of a device in response to a commanded input signal, said apparatus comprising:

• (a) means for moving the device in response to an error signal;
• (b) sensor means for determining the actual position of the device, said sensor means outputting an analog position signal corresponding to the actual position of the device;
• (c) a differentiator means, operatively connected to said sensor means, for generating an analog velocity signal;
• (d) converter means, operatively connected to said sensor means and to said differentiator means, for converting said analog position signal to a digital position signal and said analog velocity signal to a digital velocity signal;
• and
• (e) complementary filter system means, operatively connected to said converter means to receive said digital position signal and said digital velocity signal, for filtering said digital position signal and said digital velocity signal to generate a derived position signal, the derived position signal being combined with the commanded input signal to generate the error signal, whereby the filtering results in effectively increasing the resolution of the sensor means thereby reducing the limit cycle caused by quantization of the sensor means.