Linear induction motors controlling carriages moving round a circular track

The paper describes a way of precisely controlling, in a noncontact manner, the position of conducting plates as they move between a series of separate linear induction motors. To establish the method, a circular rig of 0.7m diameter containing eight commercial thrust units driven from a single-phase mains supply has been used. Each carriage running on the circular track is provided with a reaction plate for actuation purposes and a digitally coded perspex strip for position detection. Each thrust unit has its own optical position detector and phase-angle controller, providing a positional control system operational over a 35° arc of the track. A common demand waveform drives all eight controllers so that a number of carriages (up to eight) can rotate continuously at speeds between 10 rev min¿1 and 60 rev min¿1 on the track, maintaining a fixed interspacing within ± 3 mm. Carriage momentum takes it from one thrust unit control region to the next. The carriages (of mass 1kg) can be started and stopped within a 10° arc of movement, while the displacement step response is 0.1 s. This development could lead to the production of a novel type of braiding machine having distinct advantages over existing types.