Digital signal processing of resolver rotor angle signals

• US 6,754,610 B2
• Filed: 05/16/2001
• Issued: 06/22/2004
• Est. Priority Date: 05/16/2001
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Warner, C. Mike, Dudler, Donald R.
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): Pretlow, Demetrius
• Application Number:
  US09/859,347
• Publication Number:
  US 20020173931A1
• Time in Patent Office: 1,133 Days
• Field of Search: 702/151, 702/127, 702/150, 736/60, 341/116, 341/112, 341/114, 318/661
• US Class Current: 702/151
• CPC Class Codes: G01D 3/022 having an ideal characteristic, map or correction data stored in a digital memory
• CPC Class Codes: H03M 1/645 for position encoding, e.g. using resolvers or synchros H03M1/485 takes precedence

Abstract

An apparatus and method for determining the angular position of a rotor. The rotor is a part of a resolver used to determine the position of a shaft, or the like, in operation in a system such as a shaft in a missile gimbal. A digital signal processor is used advantageously to reduce cost. The inherently poorer performance of a data sampling approach in the presence of noise, as compared to the prior art tracking converter approach, is overcome by novel application of the digital signal processor and related circuitry.

Claims

1. An apparatus for measuring angular position of a rotor, comprising:

a resolver having a rotor, and having a first output for outputting a first signal representative of the sine of the rotor angle and a second output for outputting a second signal representative of the cosine of the rotor angle;

an analog to digital converter having an input coupled to said first and second outputs of said resolver, and having a output;

a digital signal processor having an input coupled to said output of said analog to digital converter, and wherein

said digital signal processor repeatedly samples said output of said analog to digital converter and accumulates a plurality of data points representative of the output signal present on said first and second outputs of said resolver, and wherein

said digital signal processor calculates the rotor angle by averaging a plurality of resultant values derived from said plurality of data points.

2. The invention of claim 1 further comprising:

a first low pass filter disposed to couple said first output of said resolver to said input of said analog to digital converter, and

a second low pass filter disposed to couple said second output of said resolver to said input of said analog to digital converter.

3. The invention of claim 2 wherein said resolver rotor is excited by a reference sinusoidal voltage, and wherein said first and second low pass filters are first order low pass filters having a half power point at a frequency at least ten times the frequency of said reference sinusoidal voltage.

4. The invention of claim 1 further comprising:

a multiplexer having at least a first and second input and an output, and having a control input operable to select which one of said inputs is coupled to said output, said multiplexer disposed between said resolver and said analog to digital converter such that said first and second outputs of said resolver are coupled to said first and second inputs of said multiplexer, and said output of said multiplexer is coupled to said input of said analog to digital converter, and wherein

said digital signal processor has a control output coupled to said control input of said multiplexer.

5. An apparatus for measuring angular position of a rotor, comprising:

a resolver, further comprising;

a rotor having a winding excited by a periodic wave reference voltage;

a first stator winding, excited by energy coupled from said rotor winding, and having an output;

a second stator winding, excited by energy coupled from said rotor winding, having an output, and oriented orthogonal with respect to said first stator winding;

a first low pass filter, with a corner frequency substantially higher than the frequency of said periodic wave reference voltage, having an input coupled to said output of said first stator winding, and having an output;

a second low pass filter, with a corner frequency substantially higher than the frequency of said periodic wave reference voltage, having an input coupled to said output of said second stator winding, and having an output;

a multiplexer having at least a first and second input coupled to said outputs of said first and second low pass filters, and having an output, and having a control input for selecting one of said at least first and second inputs to be coupled to said output;

an analog to digital converter having an input coupled to said output of said multiplexer, and having a output;

a digital signal processor having an input coupled to said output of said analog to digital converter, and having a control output coupled to said control input of said multiplexer for selecting one of said at least first and second inputs of said multiplexer to be coupled to said output of said multiplexer, and wherein

said digital signal processor repeatedly samples said output of said analog to digital converter and accumulates a plurality of data points representative of the output voltage present on said outputs of said first and second stator windings, and wherein

said digital signal processor calculates the rotor angle by averaging a plurality of resultant values derived from said plurality of data points.

6. A method of producing a rotor angle output signal in a system having a resolver with a rotor and a first stator winding outputting a sinusoidal signal representative of the sine of the rotor angle and a second stator winding outputting a sinusoidal signal representative of the cosine of the rotor angle, the system having an analog to digital converter coupled to receive the analog stator winding signals and converting them to digital signals and coupling the digital signals to a digital signal processor, comprising the steps of:

repeatedly sampling, by the digital signal processor, the first and second stator winding signals by reading the output of the analog to digital converter;

accumulating a plurality of data points, by the digital signal processor, corresponding to the analog stator winding signals over time;

repeatedly calculating the rotor angle using a unique subset of said plurality of data points for each calculation, thereby creating a plurality of rotor angle results, and

calculating the average of said plurality of rotor angle results to produce a rotor angle output signal.

7. The invention of claim 6 further comprising the step of filtering the first and second stator winding sinusoidal signals through a first order low pass filter having a half-power frequency at least ten times the frequency of the sinusoidal signals.

8. An apparatus for measuring angular position of a rotor, comprising:

a resolver having a rotor, and having a first output for outputting a first signal representative of the sine of the rotor angle and a second output for outputting a second signal representative of the cosine of the rotor angle;

an analog to digital converter having an input coupled to said first and second outputs of said resolver, and having a output;

a digital signal processor having an input coupled to said output of said analog to digital converter, and wherein

said digital signal processor samples said output of said analog to digital converter and accumulates a plurality of data points representative of the voltages present on said first and second outputs of said resolver, and wherein

said digital signal processor calculates a series of spectral coefficients with a fast Fourier transform applied to said plurality of data points thereby isolating the majority of noise energy from the desired signal energy by selecting a group of pertinent Fourier coefficients, and subsequently calculates the rotor angle using said pertinent Fourier coefficients.

9. The invention of claim 8 further comprising:

a first low pass filter disposed to couple said first output of said resolver to said input of said analog to digital converter, and

a second low pass filter disposed to couple said second output of said resolver to said input of said analog to digital converter.

10. The invention of claim 9 wherein said resolver rotor is excited by a reference sinusoidal voltage, and wherein said first and second low pass filters are first order low pass filters having a half power point at a frequency at least ten times the frequency of said reference sinusoidal voltage.

11. The invention of claim 8 further comprising:

a multiplexer having at least a first and second input and an output, and having a control input operable to select which one of said inputs is coupled to said output, said multiplexer disposed between said resolver and said analog to digital converter such that said first and second outputs of said resolver are coupled to said first and second inputs of said multiplexer, and said output of said multiplexer is coupled to said input of said analog to digital converter, and wherein

said digital signal processor has a control output coupled to said control input of said multiplexer.

12. An apparatus for measuring angular position of a rotor, comprising:

a resolver, further comprising;

a rotor having a winding excited by a periodic wave reference voltage;

a first stator winding, excited by energy coupled from said rotor winding, and having an output;

a second stator winding, excited by energy coupled from said rotor winding, having an output, and oriented orthogonal with respect to said first stator winding;

a first low pass filter, with a corner frequency substantially higher than the frequency of said periodic wave reference voltage, having an input coupled to said output of said first stator winding, and having an output;

a second low pass filter, with a corner frequency substantially higher that the frequency of said periodic wave reference voltage, having an input coupled to said output of said second stator winding, and having an output;

a multiplexer having a least a first and second input coupled to said outputs of said first and second low pass filters, and having an output, and having a control input for selecting one of said at least first and second inputs to be coupled to said output;

an analog to digital converter having an input coupled to said output of said multiplexer, and having a output;

a digital signal processor having an input coupled to said output of said analog to digital converter, and having a control output coupled to said control input of said multiplexer for selecting one of said at least first and second inputs of said multiplexer to be coupled to said output of said multiplexer, and wherein

said digital signal processor samples said output of said analog to digital converter and accumulates a plurality of data points representative of the output voltage present on said outputs of said first and second stator windings, and wherein

said digital signal processor calculates a series of spectral coefficients with a fast Fourier transform applied to said plurality of data points thereby isolating the majority of noise energy from the desired signal energy by selecting a group of pertinent Fourier coefficients, and subsequently calculates the rotor angle using said pertinent Fourier coefficients.

13. A method of producing a rotor angle output signal in a system having a resolver with a rotor and a first stator winding outputting a sinusoidal signal representative of the sine of the rotor angle and a second stator winding outputting a sinusoidal signal representative of the cosine of the rotor angle, the system having an analog to digital converter coupled to receive the analog stator winding signals and converting them to digital signals and coupling the digital signals to a digital signal processor, comprising the steps of:

repeatedly sampling, by the digital signal processor, the first and second stator winding signals by reading the output of the analog to digital converter;

accumulating a plurality of data points, by the digital signal processor, corresponding to the analog stator winding signals over time;

calculating a series of spectral coefficients using said plurality of data points as input to a fast Fourier transform algorithm;

calculating the rotor angle using the spectral coefficients centered around the frequency of the sinusoidal signal frequencies, and

outputting the calculated rotor angle.

14. The invention of claim 13 further comprising the step of filtering the first and second stator winding sinusoidal signals through a first order low pass filter having a half-power frequency at least ten times the frequency of the sinusoidal signals.

15. An apparatus for measuring angular position of a rotor, comprising:

a resolver having a rotor, and having a first output for outputting a first signal representative of the sine of the rotor angle and a second output for outputting a second signal representative of the cosine of the rotor angle;

a sigma-delta converter having an input coupled to said first and second outputs of said resolver, and having an output;

a digital signal processor having an input coupled to said output of said sigma-delta converter, and wherein

said digital signal processor samples said output of said sigma-delta converter and accumulates a plurality of data points representative of the output voltage present on said first and second outputs of said resolver, and wherein

said digital signal processor calculates the rotor angle by averaging a plurality of resultant values derived from said plurality of data points.

16. The invention of claim 15 further comprising:

a first low pass filter disposed to couple said first output of said resolver to said input of said analog to digital converter, and

a second low pass filter disposed to couple said second output of said resolver to said input of said analog to digital converter.

17. The invention of claim 16 wherein said resolver rotor is excited by a reference sinusoidal voltage, and wherein said first and second low pass filters are first order low pass filters having a half power point at a frequency at least ten times the frequency of said reference sinusoidal voltage.

18. The invention of claim 15 further comprising:

a multiplexer having at least a first and second input and an output, and having a control input operable to select which one of said inputs is coupled to said output, said multiplexer disposed between said resolver and said analog to digital converter such that said first and second outputs of said resolver are coupled to said first and second inputs of said multiplexer, and said output of said multiplexer is coupled to said input of said analog to digital converter, and wherein

said digital signal processor has a control output coupled to said control input of said multiplexer.

19. An apparatus for measuring angular position of a rotor, comprising:

a resolver, further comprising;

a rotor having a winding excited by a periodic wave reference voltage;

a first stator winding, excited by energy coupled from said rotor winding, and having an output;

a second stator winding, excited by energy coupled from said rotor winding, having an output, and oriented orthogonal with respect to said first stator winding;

a first low pass filter, with a corner frequency substantially higher than the frequency of said periodic wave reference voltage, having an input coupled to said output of said first stator winding, and having an output;

a second low pass filter, with a corner frequency substantially higher that the frequency of said periodic wave reference voltage, having an input coupled to said output of said second stator winding, and having an output;

a first sigma-delta converter having an input coupled to said output of said first low pass filter, and having an output;

a second sigma-delta converter having an input coupled to said output of said second low pass filter, and having an output;

a digital signal processor having a first input coupled to said output of said first sigma-delta converter and a second input coupled to said output of said second sigma-delta converter, and wherein

said digital signal processor samples said outputs of said first and second sigma-delta converters and accumulates a plurality of data points representative of the output voltage present on said outputs of said first and second stator windings, and wherein

said digital signal processor calculates the rotor angle by averaging a plurality of resultant values derived from said plurality of data points.

20. A method of producing a rotor angle output signal in a system having a resolver with a rotor and a first stator winding outputting a sinusoidal signal representative of the sine of the rotor angle and a second stator winding outputting a sinusoidal signal representative of the cosine of the rotor angle, the system having an sigma-delta converter coupled to receive the analog stator winding signals and converting them to digital signals and coupling the digital signals to a digital signal processor, comprising the steps of:

repeatedly sampling, by the digital signal processor, the first and second stator winding signals by reading the output of the sigma-delta converter;

accumulating a plurality of data points, by the digital signal processor, corresponding to the analog stator winding signals over time;

calculating the rotor angle using said plurality of data points, and

outputting the rotor angle.

21. The invention of claim 20 further comprising the step of filtering the first and second stator winding sinusoidal signals through a first order low pass filter having a half-power frequency at least ten times the frequency of the sinusoidal signals.

22. A method of producing a rotor angle output signal in a system having a resolver with a rotor and a first stator winding outputting a sinusoidal signal representative of the sine of the-rotor angle and a second stator winding outputting a sinusoidal signal representative of the cosine of the rotor angle, the system having an sigma-delta converter coupled to receive the analog stator winding signals and converting them to digital signals and coupling the digital signals to a digital signal processor, comprising the steps of:

repeatedly sampling, by the digital signal processor, the first and second stator winding signals by reading the output of the sigma-delta converter;

accumulating a plurality of data points, by the digital signal processor, corresponding to the analog stator winding signals over time;

repeatedly calculating the rotor angle using a unique subset of said plurality of data points for each calculation, thereby creating a plurality of rotor angle results, and

calculating the average of said plurality of rotor angle results to produce a rotor angle output signal.

23. The invention of claim 22 further comprising the step of filtering the first and second stator winding sinusoidal signals through a first order low pass filter having a half-power frequency at least ten times the frequency of the sinusoidal signals.