Method and apparatus for reducing crosstalk effects upon phase

Abstract

An angle transducer includes input rotor and reference rotor assemblies that are mounted for rotation upon a common shaft and that cooperate with respective moveable input stator and fixed reference stator assemblies to produce signals whose phase difference represents an input angle. Diametrically opposed sensors in each stator assembly achieve enhanced eccentricity error reduction by producing separate signals whose phases are averaged after the phase of each is individually measured. A phase measurement technique does not rely upon the mechanical accuracy of the angular placement of the poles for the rotor assemblies. A phase measurement between two signals is performed by beginning on an arbitrary zero crossing of the signal from the reference stator and forming, for each rotor, the sum of the times for the zero crossings for one complete revolution. To avoid the effects of crosstalk the rotors may have different numbers of poles. The sums, the different numbers of poles, the time for one revolution, and, for each rotor, the number of poles from the pole corresponding to the first term in the associated sum to an absolute reference pole, are the variables in a phase formula producing a high accuracy and resolution unified answer free of separate coarse and fine components. The absolute reference poles may be missing poles whose absense is detected and replaced with an estimate. State and time of transition data for one revolution's worth of all of the signals from the stators are temporarily captured in a small high speed revolving buffer and then immediately stored in a larger wrap-around memory under the control of an interrupt system of a microprocessor. To perform an angle measurement the microprocessor analyzes the last complete revolution's worth of data, beginning at any point in the revolution.