A Semiautomated Coordinate-Measuring System

The Advanced Payload Transfer Measurement System (APTMS) comprises electromechanical sensors and sensor output-processing circuits. Designed specifically for measuring offsets between spacecraft payload trunnions and trunnion supports during ground-based payload-transfer operations, the APTMS could be adapted to general measurement of offsets for guiding movement of large objects during assembly of heavy machinery or structures. An electromechanical sensor of the type used in the APTMS was described in “Spherical- Coordinates Encoder Module” (KSC- 11973), NASA Tech Briefs, Vol. 24, No. 2 (February 2000), page 52. Initially, the sensor outputs were fed via cables to a portable computer for analysis and display. More recently, the sensors and computer were equipped with wireless transceivers capable of communicating in either a time-division- or a spread spectrum multiplex mode to eliminate the need for cables, thereby contributing to maneuverability and safety in the workspace. An important element of the design and operation of the system is taking calibration measurements and processing of these measurements by curve-fitting software to piecewise-linear offsets to correct for systematic errors in raw sensor outputs in order to obtain accuracy within 0.05 in. (≈1.3 mm) at distances ≤ 40 in. (≈1 m).