Drive control including plural a.c. motors coupled to same shaft with d.c. braking

Claim 1

A HOIST SYSTEM FOR POSITIONING A LOAD, COMPRISING POWER SUPPLY MAINS, A PAIR OF MOTORS HAVING ROTORS MECHANICALLY COUPLED TOGETHER FOR COUPLING TO THE LOAD AND HAVING STATORS, EACH OF SAID MOTORS HAVING A STATOR CIRCUIT AND A ROTOR CIRCUIT, ENERGIZING OF THE STATOR CIRCUIT WITH ALTERNATING CURRENT PRODUCING A DRIVE TORQUE AND WITH DIRECT CURRENT PRODUCING A BRAKE TORQUE, A SOURCE OF DIRECT CURRENT INCLUDING A FIRST MEANS CONNECTED TO THE POWER SUPPLY MAINS AND A SECOND MEANS CONNECTED TO THE ROTOR CIRCUIT OF THE FIRST MOTOR, AND CONTROL MEANS INCLUDING CONTACTS AND CIRCUITS FOR CONNECTING THE STATOR CIRCUITS TO THE POWER SUPPLY MAINS AND TO THE SOURCE ENERGIZING SAID MOTORS IN A PLURALITY OF MODES INCLUDING A FIRST MODE WHEREIN BOTH STATORS ARE CONNECTED TO THE POWER SUPPLY MAINS TO PROVIDE A POSITIVE DRIVE TORQUE, A SECOND MODE WHEREIN ONLY ONE STATOR IS CONNECTED TO THE POWER SUPPLY MAINS TO ALONE DRIVE THE LOAD, A THIRD MODE WHEREIN ONE MOTOR IS CONNECTED TO DRIVE THE LOAD AND THE OTHER MOTOR IS CONNECTED TO BRAKE THE LOAD, AND A FOURTH MODE WHEREIN ONE MOTOR IS CONNECTED TO BRAKE THE LOAD AND THE OTHER MOTOR IS INACTIVE.