Patent GB-500955-A (GB)
Title: Improvements in or relating to electrical driving means
IPC: H02P25/12
Filed: 1937-08-17
Abstract: 500,955. Control of several A.C. motors. HOLMES & CO., Ltd., J. H., and ROBERTSON, A. T. Aug. 17, 1937, No. 22577. [Class 38 (iii)] [Also in Group XXXV] A printing - machine is driven by an alternating- current commutator motor which is connected to a supply of normal frequency and functions as a commutator motor over a substantial range of normal speeds, and is connected to a supply of low frequency and functions as an induction motor for operation at a single crawling speed substantially below the lowest normal speed. For normal speed operation a switch C, Fig. 1, is operated to the left so that the motor primary winding A<1> is connected to a supply D of normal frequency, the secondary winding A<1> being connected to the secondary B<2> of a transformer having a primary winding connected in series with the motor winding A<1>. Thus the motor runs as a commutator motor and is speed controlled in the usual way. For slow speed operation the switch C is thrown over to connect the motor winding A<1> to a supply D<1> of low frequency and the brushes A<3> are short-circuited. Thus the motor runs at low speed as an induction motor. Resistances may be included in the short-circuited connections to the brushes. Instead of the switch contacts C<3> on the switch C, switches may be provided to short-circuit or connect resistances across the primary winding of the transformer. In the case of a shunt motor the primary windings J, Fig. 7, are connected for normal running to a supply of normal frequency N, the secondary winding L being connected to brushes K<1> on a commutator winding K. For slowspeed operation the switch M is operated to connect the primary winding J to a supply of low frequency N<1>, and the secondary windings L are short-circuited. Where several motors O, Fig. 8, form a mechanically synchronized group and each operates a unit of a printing press, the sets of brush-gear are operated in common by a pilot motor O<4> and relays R effecting short-circuiting of the brushes for slow-speed operation are energized in parallel with a switch coil P<5>. The switches effecting connection of the motors to supplies P<3>, P<4>, of normal and low frequency are operated by the coil P<5> and a coil F<6> controlled by means of a switch P<7>. A group of motors may be synchronized by associated interconnected synchronizing machines and the several sets of brush-gear operated by individual interconnected synchronizing machines. A switch in circuit with the switch P<7> may be operated by a coil connected to the supply for the synchronizing machines. The shortcircuiting of the secondary winding of the motor for slow-speed operation may be effected by means of a sleeve F<1>, Fig. 5, operated by a spring G<3> to contact with connections F and operated to an open positon either manually or by means of a centrifugal weight G<2>. When the sleeve F<1> is operated to its non-contacting position the brush-holder F<7> may also be operated to lift the brushes. In an alternative arrangement, Fig. 6, a short-circuiting contact H<1> is moved to an operative position by a spring H<3> and withdrawn by a coil H<4> energized by closure of a switch H<7>. A switch H<8> is also energized by closure of the switch H<7> to disconnect the motor brushes.