1. Field of the Invention
The present invention relates generally to rotary position sensors, and more particularly to encoders which provide digital representation of angular position.
2. Description of the Prior Art
In many applications it is necessary to identify the positioning of a rotary member, for example, one such type of application is a rotary actuator, such as a valve actuator, which in operation must be able to accurately sense the position of the output shaft. Traditionally, position sensing of a rotary member has been accomplished through use of cam operated switches and/or potentiometers. Absolute encoders are also known which provide a digital representation corresponding to the rotary position. Absolute encoders utilize a sensing mechanism which evaluates rotary displacement relative to a measuring scale. For sensing rotary displacement, the scale is in the form of one or more disks that rotate a plurality of concentric tracks providing respective bits of a multi-bit digital code. The code tracks are typically formed of optically responsive segments which are etched, painted, drilled, or otherwise modified on the rotating disk. Advantageously, absolute encoders have the property that the operating power can be removed without loss of the data corresponding to rotary position since the data is carried by the encoder itself. However, in providing these functions, absolute encoders require a great many parallel scales, the exact number depending upon the range and accuracy requirements. This large number of scales required in absolute encoders causes them to be more delicate in application as well as less reliable. However, in many applications, the reliability and ruggedness are extremely important features. Furthermore, the cost of the typical absolute encoder is rather high for these same reasons. Accordingly, the present invention has been developed in view of the foregoing and to overcome the deficiencies of the prior art.