Method and apparatus for measuring angular displacement

• US 4,691,192 A
• Filed: 08/27/1986
• Issued: 09/01/1987
• Est. Priority Date: 03/25/1983
• Status: Expired due to Fees

• Current Assignee: Alan J. Baker
• Original Assignee: Alan J. Baker
• Inventors: Baker, Alan J.
• Primary Examiner(s): Miska, Vit W.
• Application Number:
  US06/901,094
• Time in Patent Office: 370 Days
• Field of Search: 340/347 P, 340/347 M, 250/231 SE, 324/83 D, 364/475, 364/559
• US Class Current: 341/11
• CPC Class Codes: G01L 3/109 involving measuring phase difference of two signals or pulse trains
• CPC Class Codes: G01P 3/565 by measuring or by comparing the phase of generated current or voltage phase comparators per se H03D13/00; phase measurement G01R25/00
• CPC Class Codes: H03M 1/645 for position encoding, e.g. using resolvers or synchros H03M1/485 takes precedence

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 absence 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.

Claims

1. A method of measuring angular displacement comprising the step of:

rotating a multi-pole rotor about an axis;

producing a periodic signal from the passage of poles on the rotor past a sensor journalled about the axis for orbital movement along the periphery of the rotor;

generating an index mark once each revolution of the rotor as a selected pole passes a selected location on the periphery;

positioning the sensor to a reference orbital position;

measuring for an integral number of revolutions beginning upon and relative to a first index mark the times at which each pole passes the sensor at the reference orbital position;

averaging the times obtained by the measuring step at the reference orbital position to obtain a reference average time of occurrence of a pole passing the sensor;

positioning the sensor to an input orbital position;

measuring for an integral number of revolutions beginning upon and relative to a second index mark the times at which each pole passes the sensor at the input orbital position;

averaging the times obtained by the measuring step at the input orbita1 position to obtain an input average time of occurrence of a pole passing the sensor; and

expressing the difference between the reference average time of occurrence and the input average time of occurrence as a fraction of the time required for one revolution.

2. A method of measuring angular displacement comprising the step of:

rotating multi-pole reference and input rotors about an axis, the rotation being simultaneous and identical;

producing a periodic reference signal from the passage of poles on the reference rotor past a reference sensor disposed adjacent the periphery of the reference rotor;

generating a reference index mark once each revolution of the reference rotor as a selected pole thereon passes a selected location on the periphery of the reference rotor;

producing a periodic input signal from the passage of poles on the input rotor past an input sensor journalled about the axis for orbital travel along the periphery of the input rotor;

generating an input index mark once each revolution of the input rotor as a selected pole thereon passes a selected location on the periphery of the input rotor;

positioning the input sensor to a reference orbital position;

measuring for a first integral number of revolutions and relative to a first reference point in time those times at which each pole on the reference rotor passes the reference sensor;

averaging the times measured in the preceding step to obtain a first average time of occurrence of a reference pole;

measuring for the first integral number of revolutions and relative to the first reference point in time those times at which each pole on the input rotor passes the input sensor at the reference orbital position;

averaging the times measured in the preceding step to obtain a first average time of occurrence of an input pole;

forming the difference between the first average times of occurrence of the input and reference poles to obtain a reference difference;

positioning the input sensor to an input orbital position;

measuring for a second integral number of revolutions and relative to a second reference point in time those times at which each pole on the reference rotor passes the reference sensor;

averaging the times measured in the preceding step to obtain a second average time of occurrence of a reference pole;

measuring for the second integral number of revolutions and relative to the second reference point in time those times at which each pole on the input rotor passes the input sensor at the input orbital position;

averaging the times measured in the preceding step to obtain a second average time of occurrence of an input pole;

forming the difference between the second average times of occurrence of the input and reference poles to obtain an input difference; and

expressing as an angular portion of one revolution the difference between the input and reference differences.

3. A method as in claim 2 wherein each measuring step for the reference rotor begins only upon the occurrence of a reference index mark.

4. A method as in claim 2 wherein each measuring step for the input rotor begins only upon the occurrence of an input index mark.

5. A method as in claim 2 wherein each measuring step begins only upon the occurrence of a corresponding reference or input index mark according to whether the measuring step is for the reference or input rotor respectively.

6. A method as in claim 2 wherein the measuring steps for the reference rotor can begin upon arbitrary cycles of the reference signal and wherein the associated average times of occurrence are adjusted to be what they would have been had those measuring steps begun upon reference index marks.

7. A method as in claim 2 wherein the measuring steps for the input rotor can begin upon arbitrary cycles of the input signal and wherein the associated average times of occurrence are adjusted to be what they would have been had those measuring steps begun upon input index marks.

8. A method as in claim 2 wherein the measuring steps for the reference rotor can be upon arbitrary cycles of the reference signal and the associated average times of occurrence are adjusted to be what they would have been had those measuring steps begun upon reference index marks, and wherein the measuring steps for the input rotor can begin upon arbitrary cycles of the input signal and the associated average times of occurrence are adjusted to be what they would have been had those measuring steps begun upon input index marks.