Scanning mirror control
First Claim
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1. A method comprising:
- detecting cyclical movement of a scanning mirror to produce position information;
performing a Fourier transform to produce return harmonic coefficients describing frequency content of the position information;
comparing the return harmonic coefficients with harmonic coefficient targets to obtain error values; and
responsive to the error values, modifying a plurality of drive coefficients at different rates.
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Abstract
A scanning beam projection system includes a scanning mirror having a fast-scan axis and a slow-scan axis. Movement on the slow-scan axis is controlled by a slow-scan scanning mirror control system. The control system receives position information describing angular displacement of the mirror. An outer loop of the control system operates in the frequency domain and determines harmonic drive coefficients for a scanning mirror drive signal. An inner loop of the control system operates in the time domain and compensates for a scanning mirror resonant vibration mode at a frequency within the frequency band occupied by the harmonic drive coefficients.
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Citations
25 Claims
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1. A method comprising:
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detecting cyclical movement of a scanning mirror to produce position information; performing a Fourier transform to produce return harmonic coefficients describing frequency content of the position information; comparing the return harmonic coefficients with harmonic coefficient targets to obtain error values; and responsive to the error values, modifying a plurality of drive coefficients at different rates. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method comprising:
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characterizing a scanning mirror by exciting the scanning mirror at different frequencies and measuring a response; determining a weighting array proportional to an inverse of the scanning mirror response; and using the weighting array to weight learning rates of harmonic drive coefficients in a feedback loop, the harmonic drive coefficients to produce angular displacement of the scanning mirror. - View Dependent Claims (10)
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11. A computer-readable medium having instructions stored thereon that when accessed result in a computer performing:
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receiving time domain data describing angular movement of a scanning mirror in a slow-scan direction; performing a fast Fourier transform on the time domain data to produce return harmonic coefficients; comparing the return harmonic coefficients with harmonic coefficient targets to determine errors; modifying a plurality of drive coefficients by differing amounts to reduce the errors; and performing an inverse fast Fourier transform on the drive coefficients to produce a drive waveform to drive the scanning mirror in the slow-scan direction. - View Dependent Claims (12, 13, 14)
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15. An apparatus comprising:
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a scanning mirror having a fast-scan axis and a slow-scan axis, the slow-scan axis having a position detector; an outer control loop that operates in the frequency domain to determine harmonic coefficients of a drive signal in response to position information received from the position detector; and an inner control loop that operates in the time domain to compensate for a scanning mirror resonant vibration mode at a frequency within a frequency band occupied by the harmonic coefficients of the drive signal. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. A mobile device comprising:
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a communications transceiver; a scanning mirror; and a slow-scan scanning mirror control system having an outer loop operating in the frequency domain and an inner loop operating in the time domain. - View Dependent Claims (23, 24, 25)
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Specification