Abstract A driving system for cranes includes a three phase asynchronous motor with a squirrel cage rotor and two stator windings with different numbers of poles. The speed is steplessly controllable within a lower speed range below the synchronous speed corresponding to the higher number of poles in response to the difference between actual and desired speed. This difference quantity passes unidirectional means which, depending on its sign, feeds it as a control signal to a delay angle current varying device inserted between the low speed stator winding and the network, or to a controlled DC source which, during operation in the lower speed range, is connected to the high speed winding, that is, the stator winding with a lower number of poles. This winding is by means of a throwover switch also connectable to the network, in which case the signal circuit of the delay angle current device is intended to be broken by means of a signal current breaker so that no current is fed to the low speed stator winding.
A driving system for cranes and the like comprising a three phase asynchronous electric motor with a squirrel cage and first and second stator windings having a higher and lower number of poles, respectively, a three phase feeding network, a three phase sequence reversing device, a three phase change over switch, a three phase delay angle controlled current varying device comprising a group of antiparallel-connected rectifiers interposed in each phase and control means for simultaneous electrical control of said groups, a control signal breaker for said groups, said groups being connected between the network and the terminals of said first stator winding by means of said reversing device, a controllable DC current source and control means for said current source, said second stator winding being selectively connectable to said network or to said DC current source by means of said change over switch for driving in a higher part of the motor speed range or braking in a lower part, respectively, said driving system further comprising transducer means to express the motor speed in the form of an output quantity, means to supply a reference quantity and to compare the reference quantity with said output quantity to form a difference quantity, and means to supply the numerical value of said difference quantity alternatively as an input to the delay angle or the DC current control means in dependence on the sign of said difference quantity to effect driving or braking respectively in said lower speed range.
Claim 2
Dependent Claim
246 words
A driving system for cranes and the like comprising a three phase asynchronous electric motor with a squirrel cage and first and second stator windings having a higher and lower number of poles, respectively, a three phase feeding network, a three phase sequence reversing device, a three phase change over switch, a three phase delay angle controlled current varying device comprising a group of antiparallel-connected rectifiers interposed in each phase and control means for simultaneous electrical control of said groups, a control signal breaker for said groups, said groups being connected between the network and the terminals of said first stator winding by means of said reversing device, a controllable DC current source and control means for said current source, said second stator winding being selectively connectable to said network or to said DC current source by means of said change over switch for driving in a higher part of the motor speed range or braking in a lower part, respectively, said driving system further comprising transducer means to express the motor speed in the form of an output quantity, means to supply a reference quantity and to compare the reference quantity with said output quantity to form a difference quantity, and means to supply the numerical value of said difference quantity alternatively as an input to the delay angle or the DC current control means in dependence on the sign of said difference quantity to effect driving or braking respectively in said lower speed range.