| 摘要 |
<p>The apparatus is concerned with generating a quadrature signal for the purpose of deteremining the direction in which the scale is being read. There is provided a primary grating means (11) defining spaced lines and adapted for generating orders of diffraction, secondary grating means (14) defining spaced lines arranged at an angle to those of the primary grating means thereby to separate said orders of diffraction into differing phases, and tertiary grating means (13) movable together with the secondary grating means relative to said primary grating means and adapted for detecting the respective said phases and for generating correspondingly phased light modulations which are detected by respective transducers (18) connected to a quadrature-forming circuit (20).</p> |
