Increment encoder failure detection

Details Increment encoder failure detection Increment encoder failure detection

1999-03-05

2001-06-12

Moise, Emmanuel L. (Department: 2784)

Coded data generation or conversion

Digital pattern reading type converter

Incremental

C341S006000, C377S017000

Reexamination Certificate

active

06246343

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to encoders and more particularly to detection of errors in increment encoders.
BACKGROUND OF THE INVENTION
A typical use for an encoder is to determine the rotational velocity and/or position of a rotating object, typically a shaft. In certain applications, the need arises to ensure that the encoder has not failed during operation and so error detection is needed. Otherwise, the functional failure of a shaft encoder can cause abnormal behaviors of the machine in which the shaft operates such as shaft speed vibration, wrong rotating direction, undesirable acceleration, and other concerns. The abnormalities can then result in processed parts out of tolerance, damaged parts, as well as wrong direction rotation for moving parts on machines.
One solution is disclosed in U.S. Pat. No. 4,597,081 wherein an optical encoder interface performs error checking on each full revolution of the encoder. The pulses per revolution are counted and compared to a reference number that should occur in one revolution with a properly operating system. This error detection operates on an encoder with a three channel signal where an index revolution bit (a Z-bit) is employed to determine when a complete revolution has occurred. The error detection capability is implemented in the hardware of the electronic assembly itself. However, this solution has limitations that are not always desirable. Such as, the error detection is built into the hardware itself, thus limiting its adaptability and use in retrofitting existing assemblies. Also, this error detection assembly requires a three channel signal, and thus cannot be employed with two channel encoder applications. This adds to the cost and complexity if one wishes to operate an encoder with this error detection. And further, the error detection determination can only be made once every revolution of the shaft, thus limiting how quickly the error will be detected.
Consequently, it is desired to have a system with an encoder that accomplishes error detection but does not have the above noted drawbacks.
SUMMARY OF THE INVENTION
In its embodiments, the present invention contemplates an error checking method for use with a rotating member having a two channel encoder mounted in proximity thereto that produces signals from a first channel and a second channel, each producing pulses. The method comprising the steps of: receiving the signals from one of the first and second channels; determining a counting time interval; counting the number of pulses during the time interval; comparing the number of pulses counted to a predetermined expected number of pulses; and detecting an error if the number of pulses counted is not equal to the expected number of pulses.
Accordingly, an object of the present invention is to provide the capability to detect failures in a two channel increment encoder.
An advantage of the present invention is that a two channel encoder can be monitored during operation over a wide speed range to detect a failure.
Another advantage of the present invention is that the cost associated with the encoder and its error detection is minimized.
A further advantage of the present invention is that the error detection is accomplished with software, thereby allowing for a system that is easily adaptable for other encoder applications, and can be retrofitted to similar existing two channel encoder applications.
An additional advantage of the present invention is that there is not the requirement of a full revolution before each error check, thus allowing for faster error detection.
Another advantage of the present invention is that the error detection system can determine which channel has failed.


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patent: 2249446 (1992-05-01), None
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