| 摘要 |
In a method of determining the location of at least one point on an object boundary a beam of light (12) is directed at a detector (14) which provides a signal (16) related to the intensity of the spot (13) falling on it. The object (22) is located between the light source (10) and the detector (14), and the light beam (12) is deflectable, under the control of a signal (18) from a controller (20), over an angle alpha so that at some point the light beam crosses the boundary (24) of the object so that the detected intensity of the spot (13) falls from a maximum to a minimum. The signal (16) is fed back to the controller which adjusts the control signal (18) in an attempt to deflect the spot to a position wherein the signal (16) equals a reference value corresponding to the light intensity detected by the detector (14) when the beam is partially obscured by the edge (24). In another embodiment the spot (13) falls on a translucent screen viewed by the detector. The beam may be reflected from the object instead of being transmitted past it. |
