| 摘要 |
This apparatus utilizes a fixed laser beam as a reference to determine offset error on a movable platform of a layout machine with reference to a fixed frame carrying the movable platform. Essentially, the invention provides at least two photocells mounted on the movable platform with appropriate optical equipment to receive the laser beam and give equal signal readout when the movable platform is in predetermined offset relationship with the laser beam, indicating a zero position with respect to the reference established by the laser beam. When the movable platform because of inherent mechanical defects in the stationary platform upon the movement thereof relative to the stationary platform actually moves out of alignment with respect to the laser beam, the photocells detect varying amounts of light proportional to the offset relationship of the movable platform, and this is converted to displacement in terms of measurement for use in correcting measurements or other position information taken by apparatus located on the movable platform.
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