Machine Design

A new angle on linear incremental encoders

A new type of linear incremental encoder incorporates a series of optical sensors mounted on a centerline that is tilted with respect to the direction of motion. The arrangement provides high resolution with relatively coarse scales, according to developer Omnific International Ltd., Poughkeepsie, N.Y.

Linear incremental encoders sense mechanical motion, translate linear position, velocity, and acceleration into electrical signals, and then feed the information into a control unit or display. Incremental encoders typically determine the relative position of lines on a linear scale attached to a slide or movable machine element. To provide high resolution, scale lines are usually placed close together. But this setup requires sophisticated engraving processes and expensive optics, which add to the cost of the encoders.

However, Omnific's patented tilted-array method of sensing allows use of a relatively coarse scale with wide spaces between lines while providing high resolution without costly scales or expensive optics or software. The key is an array of simple optical sensors tilted to fit between two adjacent lines on a scale. Each line, as it moves along the array, progressively registers signals at each detector in turn so that resolution depends on the number of detectors, not line spacing alone.

Any point-type sensors, including optical types such as charge-couple devices or photodarlington transistors, or nonoptical types such as Hall-effect devices, can be used in an array, according to Omnific.

Conventional encoders use quadrature principles to determine the direction in which a slide is moving. The new detection method can mimic quadrature action by the addition of a second array to the encoder.

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