| 摘要 |
<p>An incremental measuring device is described which includes a measuring scale and a scanning unit. The measuring scale includes a division grid, a reference track which includes a plurality of reference marks, and a control track which includes a plurality of control regions. Each of the control regions is associated with a respective one of the reference marks, but the precise alignment between each reference mark and its respective control region is unique. The scanning unit includes a scanning plate which defines two separate scanning regions for scanning separate portions of the scale. Each scanning region defines reading fields for reading the division grid as well as a reference track reading field and a control track reading field. The precise alignment between the reference track reading field and the control track reading field of each of the scanning regions is different such that, for each of the scanning regions, there is only a single position of the scale with respect to the scanning plate which produces simultaneous alignment between the reference track reading field and one of the reference marks and the control track reading field and one of the control regions. In the disclosed embodiment photosensitive elements are associated with each of the reference track and control track reading fields, and each produces a respective signal. The four signals are summed in an analog manner to produce a composite signal which unambiguously indicates when the measuring scale is in a single, preselected position with respect to the scanning plate. In this embodiment, when one of two light sources included in the scanning unit fails such that scanning of one of the two scanning regions is interrupted, the device still functions to generate a reference signal unambiguously when the measuring scale reaches the predetermined position with respect to the scanning plate.</p> |
