Data processing: measuring – calibrating – or testing – Measurement system – Speed
Reexamination Certificate
1999-02-17
2001-09-11
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Speed
C702S148000, C250S231130
Reexamination Certificate
active
06289294
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method for determining rotational data from a random pulse pair generated by an encoder device and, more particularly, to a method for determining rotational data that minimizes the effect of a cyclical anomaly that is associated with the output of an encoder device.
2. Discussion
Encoder devices are commonly used to monitor the rotation of instrumented vehicle wheels and other rotating devices. Physical inaccuracies inherent in any real system give rise to an anomaly or scattering in the actual measurement process, which we will refer to as “jitter” in the measured data. Since this jitter is repetitive in nature, it can be cancelled with an appropriate algorithm.
Traditional approaches for deriving angular position or linear displacement in the case of a wheel has been to sum received pulses from the encoder device. This approach is not affected by the jitter contained in the signal, and thus the present invention does not address distance measurements.
There are at least two methods commonly used for determining speed from an encoder signal. The first and most common method is to sum pulses over a fixed period of time (i.e., the frequency method). The calculation for this method is speed=(sum of pulses/time interval)*(rotational distance). In order to get acceptable resolution for the velocity calculation, the time interval must be large enough to see many pulses which in turn has the effect of limiting update rates. The second method uses the time interval between successive pulses to determine an instantaneous speed (i.e., the period method). The period method can give an updated speed value as each pulse arrives from the encoder, but it exhibits jitter in the measured data.
Therefore, it is desirable to provide a method for determining rotational data from a random pulse pair generated by an encoder device that minimizes the effect of the cyclical anomaly or jitter that is associated with the output of an encoder device.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method is provided for determining rotational data from a random pulse pair generated by an encoder device, comprising the steps of: (a) monitoring the rotation of the rotating member using the encoder device; (b) receiving a plurality of pulses from the encoder device, where each of the pulses is indicative of a rotational distance that has been traveled by the rotating member; (c) storing a time value for each of the pulses that has occurred during the previous revolution of the rotating member; (d) identifying a first pulse and a second pulse that have occurred in the current revolution of the rotating member; (e) computing a time difference between the first pulse and the second pulse using a first time value for the first pulse that corresponds to the current revolution of the rotating member and a second time value for the second pulse that corresponds to a previous revolution of the rotating member; and then (f) using the time difference to determine a rotational speed, thereby determining rotational data for the rotating member from the random pulse pair.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.
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Freyre Elliezer P.
Frinkle Marvin L.
Rataj David H.
Bui Bryan
Calcaterra Mark P.
DaimlerChrysler Corporation
Hoff Marc S.
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