| 摘要 |
<p>A photoelectric sensing device is disclosed for sensing when an object that travels a predefined path, which crosses a straight line a plurality of times, most closely approaches a selected end of the line. The device includes a light detector located at the selected end of the line having a relatively narrow angle of light acceptance; and a light source at the non-selected end of the line to produce a beam of light wider than the widest portion of the object directed along the line and striking the light detector, whereby only when the object crosses the line closest to the light detector does the object entirely block the light beam from striking the light detector.</p> |
