Sequence control for tennis ball throwing machine - uses electronic timing circuit controlling relays to switch drive motors in correct sequence

摘要

To prevent blockage or multiple projection of balls in a tennis ball throwing machine it is essential that the main rollers be at full speed before a ball is introduced and that the supply of balls be cut off before the roller drive is switched off. A sequencing circuit to perform these functions includes an electronic timing circuit (28) which controls both a relay (29) switching the 220 V AC supply and a low tension relay (32) switching 24V AC obtained from a transformer (30). The rollers are driven by two 220V motors (41,42) supplied via the 220V relay contacts (33,34). Speed control circuitry (35,36) is provided for these motors. The low tension relay (32) operates the motor which distributes the balls to the rollers, when instructed by the electronic circuit after operation of the start/stop switch (43).