Patent GB-190013048-A (GB)
Title: Improvements in and relating to Means for Controlling the Speed of Electro Motors.
Inventor: ELLIOTT WILLIAM BREWSTER
Filed: 1900-07-19
Granted: 1900-11-03
Abstract: 13,048. Elliott, W. B., and Eskholme, J. W. July 19. Driving machines by electromotors. -Relates to means for controlling the speed of electric motors, particularly in the operation of printing-machines, whereby the motor may be started at an extremely low speed with great torque and the speed gradually increased without jerks, preferably by means of a single handlever. To obtain the necessary starting torque, while avoiding the danger of sparking at full speed, the motor has two separate armature windings, which are connected in series when starting the machine, and thrown into parallel before the machine reaches its full speed. Fig. 1 is a diagram of the motor and its connections, the controlling switch being shown with its contact arcs 8, 30, 31, 32 extended into straight lines, and provided with a controlling lever 9 carrying the necessary bridging contacts. When the lever 9 is moved from the extreme left into the position shown, an electromagnetic switch 47 in the main circuit is thrown into the position shown in full lines so as to close the armature circuit, this movement of the switch being brought about by bridging the terminals 26 and 27 of an actuating solenoid 59. Should the two armature windings happen to be in parallel, a second switch 48 will be thrown at the same time so as to connect them in series. By further movement of the controlling lever, resistances are gradually cut out and the speed of the armature slowly increased. When the said lever comes into contact with the contact block D, it strikes a switch lever 37 and short circuits a portion of the series field winding, thereby reducing the strength' of the field and causing a further increase of speed. The remainder of the series winding is then short-circuited and the motor speed still further increased. After pushing aside a spring contact 41, the movement of the controlling lever causes the switch lever 48 to be thrown over into the parallel position, its operating solenoid 60 being energized by bridging the contacts 28, 29. To prevent too sudden an increase of speed, resistances are inserted between the remaining contact blocks, nearly sufficient to compensate for the decreased resistance due to throwing the armature windings into parallel. These resistances are gradually cut out by the continued movement of the controlling lever. Finally, resistances connected with the contacts 30, 30<a>, 30<b>, are gradually thrown into the shunt field circuit, thereby further weakening the field and causing the motor to run at full speed. By a reverse movement of the lever, the shunt field resistances are first cut out and a series of resistances introduced into the armature circuit. On a further backward movement, the armature circuit is opened by closing the spring contact 41, the armature windings are thrown back from parallel to series and the motor is gradually slowed down. In order to stop the machine suddenly, a number of emergency switches 80 may be provided. In the main circuit is also arranged a hand switch 46 provided with three contact blades 45, 45<a>, 45<b>, for closing or opening the connections with the switch 47 and the shunt field winding in three successive stages. To avoid danger to the insulation of the shunt windings when the switch 46 is opened, the said winding is temporally short-circuited through choking coils 78.