Patent GB-190711070-A (GB)
Title: Improvements in and relating to Switch Mechanism for Controlling Electric Motors.
Filed: 1907-05-11
Granted: 1908-07-13
Abstract: 11,070. British Thomson-Houston Co., [Allgemeine Electricitõts-Ges.]. May 11. Switches.-In a drum controller, the drum is provided with oblique contact vanes which engage a fixed contact spring ; or the vanes may be used as cams to operate spring-controlled contacts. The backward movement of tbe drum disengages the fixed contacts from the vanes, until the drum reaches its initial or any other predetermined position. The contacts b are arranged to overlap each other round the drum a, so that, as the drum is rotated, the contact finger c rides up the inclined surface of one contact b and then drops on to the next one. When the motion of the drum is reversed, the finger c slides down the contact it happens to be on to its normal position, below the lower ends of all the contacts b except the first. The controller must be returned past the first contact b, and the finger c is then in the correct position for the starting motion to be repeated. If it is desired to complete the circuit at another point during the backward motion of the controller, as for instance at the point where the connexions are changed from series to parallel &c., it is only necessary to place an extended contact x<1>, Fig. 2, in the proper position. The underside of these extended contacts or the top of the finger c is insulated. To prevent an interruption of the circuit from occurring when the finger c drops from one contact b to the next, the finger c may be split, as shown in Fig. 8, so that one part springs into position upon the incoming contact before the other part leaves the preceding contact. Instead of this, two fingers c may engage two sets of staggered contacts b, as shown in Fig. 7. Some of the contacts may be provided with extended horizontal portions x<2>, to limit the number of steps at which the motors may be cut out by the reversal of the drum. The oblique segments b may be used as cams to operate auxiliary switches of the type shown in Fig. 12. The cams engage a roller o carried by a rod h working in guides k and raise it against the spring n, thus causing the contact block g to bridge the fingers e, f. The reverse movement of the drum opens the circuit as in the previous case. Two auxiliary switches working over two sets of staggered cams, corresponding to the arrangement shown in Fig. 7, may be used. The connexions for motor starting are shown in Fig. 10. In the first position of the controller, the winding s is energized and the motor circuit is closed through the contacts t. In the next controller position, the spring contact opens a shunt about the resistance u, and so diminishes the current in the winding s. If the line potential drops, the contacts t are disconnected, the contact w closes a braking - circuit, and the controller must be brought back to the 'off' position before the running circuit can be again completed. If an overload occurs, the coil v attracts its armature to short-circuit the coil s. The controller may also be used to govern the actuation of the separate contacts in a master-control system.