| 摘要 |
To properly align support elements (17,19), typically support bars or strips of a light curtain formed by a plurality of light beams (21), transmitted between transmitters (13) and receivers (15) on the respective support bars (17,19), a separate alignment light source, typically a laser (29), is provided. The laser (29) projects a light beam (33) to a receiver (35) from one (17) of said bars to the other (19). A counter-directed beam (33') is projected from the other (19) of the bars to the first bar (17). The counter-directed beam (33') spaced from the first direct beam (33), can be generated by a second laser (29'), or by deflecting the received direct beam (33) on or in the second bar (19) by 180 DEG to provide the counter-directed return beam to the first bar (17). This permits rapid alignment of the respective bars, even with respect to five directions of freedom of movement of the respective bars. Preferably, the laser is pulsed at a frequency between 1 and 5 Hz, and a timing circuit is provided to disconnect the laser or lasers after suitable alignment timing intervals, or after a safety interval, so that the lifetime of the laser or lasers will be commensurate with the lifetime of the radiation transmitters (13) and receivers (15) of the light curtain itself.
|
