Vernier sensor with self calibration
AssigneeSemiconductor Components Industries, LLC
InventorJacques Jean Bertin
Life of this patent
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Abstract
A vernier sensor including a coarse sensor and a fine sensor may require calibration to ensure accurate position measurements. Calibration may include determining coefficients for harmonics that can be added to the coarse sensor output and the fine sensor output to reduce harmonic distortion. The disclosure describes using the offset and variance of a difference signal as the basis for calibration. This approach is possible at least because the frequencies of the coarse sensor and fine sensor can be selected to reduce the complexity of these calculations.
Claims23
A method for calibrating a position sensor, the method comprising:
- moving a movable element of the position sensor over a measurement range to acquire:
- a first output signal from a first sensor, the first output signal having increments repeating at a first frequency, and
- a second output signal from a second sensor, the second output signal having increments repeating at a second frequency;
- computing a difference signal based on the first output signal and the second output signal;
- calculating an offset of the difference signal;
- calculating a value of a variance of the difference signal;
- determining a first calibration and a second calibration to reduce the offset and the value of the variance of the difference signal;
- and
- applying the first calibration to the first output signal and the second calibration to the second output signal.
A position measurement system including:
- a position sensor including:
- a first sensor configured to output a first output signal;
- a first sensor correction circuit configured to apply a first calibration to the first output signal to generate a first corrected signal;
- a second sensor configured to output a second output signal;
- and
- a second sensor correction circuit configured to apply a second calibration to the second output signal to generate a second corrected signal;
- and
- a processor coupled to the position sensor and configured by software instructions to:
- generate a difference signal based on the first corrected signal and the second corrected signal;
- calculate an offset of the difference signal;
- calculate a value of a variance of the difference signal;
- and
- determine a calibration quality based on a first comparison of the offset to a first threshold and a second comparison of the value of the variance to a second threshold.
A method for determining calibration coefficients for a vernier position sensor, the method comprising:
- transforming a first incremental signal from a first sensor of the vernier position sensor to a first absolute signal;
- transforming a second incremental signal from a second sensor of the vernier position sensor to a second absolute signal;
- computing a difference signal of based on the first absolute signal and the second absolute signal;
- calculating an offset and a variability of the difference signal, the variability being a value of a variance of the difference signal;
- and
- performing an optimization routine that includes adjusting calibration coefficients applied to the first incremental signal and the second incremental signal to reduce the offset and the variability of the difference signal.
Dependencies are inferred from the claim text.