Patent ID: 8245748

Claim:
A vibration welding system for welding first and second workpieces by effecting reciprocating movement of the first workpiece relative to the second workpiece while urging the workpieces together, said vibration welding system comprising first and second workpiece supports, said first workpiece support being mounted for linear reciprocating movement relative to said second workpiece support, a pair of electromagnets coupled to said first workpiece support for effecting linear reciprocating movement of said first workpiece support, each of said electromagnets including a drive coil and an electrical drive system including a pair of two-phase drive systems each of which is coupled to one of said drive coils for successively energizing and de-energizing said electromagnets 180 degrees out of phase with each other to effect said linear reciprocating movement of said first workpiece support, each of said two-phase drive systems including a source of DC current, multiple controllable electronic switching devices for controllably coupling said source to, and de-coupling said source from, each of said electromagnets, first and second of said controllable electronic switching devices being connected between said source of DC current and a first end of the drive coil, and third and fourth of said controllable electronic switching devices being connected between said source of DC current and a second end of the drive coil, current sensors coupled to said electromagnets and producing signals representing the currents supplied to said electromagnets, and control circuitry coupled to said electronic switching devices and receiving the signals produced by said current sensors for turning said switching devices on and off to control the energizing and de-energizing of said electromagnets to effect reciprocating movement of said first workpiece support, said control circuitry controlling said first, second, third and fourth switching devices to increase the current supplied to the associated drive coil to a preset level and to maintain that current at said preset level for a first preset time interval, and to then reduce that current to zero and to maintain the zero level for a second preset time interval, the current supplied to the drive coil of the first electromagnet being 180 degrees out of phase with the current supplied to the drive coil of the second electromagnet.