Monday, 15 July, 2002

 

A complex polariser assembly has two filter elements, referred to as the Front and Rear filters. Each filter element is driven by a stepper motor, and has its position monitored by a single-speed resolver. Either the motor, or the resolver, or both may be coupled to the filter with its shaft end pointing towards or away from the feed. Further, the electrical direction of rotation of the resolver may or may not be in the same direction as its physical rotation. The ATCU provides facilities on its Calibration display, for compensating for these variations. So in effect our software can, at present handle any electro-mechanical configuration of motors and resolvers on the polariser feed assembly, including limits on rotation.When possible, the control system employed for each filter element is identical. The ATCU produces a Direction control plus a Move control. When the measured angle reaches the required angle +/- 0.05 degrees, the ATCU Move control is removed, and a Lock command is issued. 6RU Rack Mount Stepper
motor driver enclosureMovement is demanded when the measured angle and the required angle differ by more than 0.1 degrees. As the cycle rate of the ATCU program is 1/16 second, the maximum filter rotation speed which can be accommodated without undue overshoot is about 3 degrees per second. This speed is more than sufficient.

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