Direct velocity estimation for encoders using nonlinear period measurement
First Claim
1. A method, comprising:
- receiving a signal from a sensor indicating displacement of a moving sensor element based on a movement of an object;
counting down from a first value to a lower value after the signal has been received, the counting being at a predetermined variable rate, the rate decreasing as the count continues; and
outputting a velocity value of said counter as a value related to a velocity of the object, the velocity value being a current value of the counter when a successive signal from the sensor is received.
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Abstract
A method and apparatus for providing a direct velocity of a moving object using nonlinear period measurement. A pulse signal from an encoder indicates the detection of a passage of a point on a moving sensor element, such as a mark on an encoder disk. A counter is then made to count down from a higher value to a lower value, where counts by the counter are made at a variable, nonlinear rate. The rate is faster when the count begins and gets slower as the count continues, reducing the possibility that the counter will overflow before the next encoder signal is received. The counter value is output and the counter is reset when another encoder signal is received, where the output value is directly related to the velocity of the object. In a different method and apparatus, first and second values, such as PWM or DAC commands, are provided to an actuator to output as forces. The values are differenced a rate of change of the force values is determined. A force is output according to the rate of change until another force value is received, allowing more stable and continuous force output.
114 Citations
28 Claims
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1. A method, comprising:
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receiving a signal from a sensor indicating displacement of a moving sensor element based on a movement of an object;
counting down from a first value to a lower value after the signal has been received, the counting being at a predetermined variable rate, the rate decreasing as the count continues; and
outputting a velocity value of said counter as a value related to a velocity of the object, the velocity value being a current value of the counter when a successive signal from the sensor is received. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. An apparatus, comprising:
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a decoder state machine that receives a signal from an encoder, the signal having a pulse indicating movement of an element of the encoder, based on movement of an object; and
a nonlinear period counter coupled to said decoder state machine and configured to receive an indication of said pulse therefrom, said nonlinear period counter configured to count down from a first value to a lower value and configured to be reset to the first value when the indication of the pulse is received, a rate of said counter being predetermined, variable and decreasing as said counter counts down, thereby increasing the dynamic range of velocity estimation, said counter being configured to output the lower value based on a successive pulse being received by said decoder state machine, said lower value being related to said velocity of said object. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23)
a variable frequency divider, said frequency divider configured to send out a count signal at a variable rate; and
a velocity counter coupled to said variable frequency divider, said velocity counter configured to count from said first value to said lower value, after said count signal is received from said variable frequency divider.
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18. The apparatus of claim 17, wherein said nonlinear period counter further includes a lookup table, said lookup table configured to provide different divisors to said variable frequency divider, said variable frequency divider configured to divide a base clock signal by said received divisors to change said rate of outputting said count signal.
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19. The apparatus of claim 18, wherein said lookup table stores divisors that have been determined based on a 1/T2 relationship, T being the time period between successive pulses.
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20. The apparatus of claim 16, wherein said counting rate follows a 1/T relationship, T being a time period between said pulse and the successive pulse.
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21. The apparatus of claim 16, further comprising a velocity register, said counter value being passed to said velocity register when the successive pulse is received.
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22. The apparatus of claim 16, wherein said decoder state machine is a quadrature decoder state machine configured to receive two quadrature detector signals from said encoder.
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23. The apparatus of claim 16, wherein said encoder is an optical encoder that senses motion of said object, a pattern of evenly-spaced marks being provided on an moving encoder element, the passage of one or more of said marks being detected as said object moves.
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24. A method, comprising:
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receiving a signal from a sensor indicating displacement of a moving sensor element based on movement of an object;
counting down from a first value to a lower value after the signal has been received, the counting being at a variable rate, the rate decreasing as the count continues, the counting rate being varied by providing one of different divisors to a frequency divider, the frequency divider controlling when the counter makes another count, the different divisors being stored in a look up table; and
outputting the value of the counter as a value directly related to a velocity of the object, the value being a current value of the counter when a successive signal from the sensor is received. - View Dependent Claims (25, 26, 27, 28)
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Specification