Speed control system for multiple motor feed of welding wire

Claim 2

In a push-pull wire feed system for supplying welding wire from a wire supply station to a welding station, and having a plurality of direct current wire feed motors in tandem including at least one push motor located along the wire intermediate the stations, and a pull motor having a drooping speed-torque characteristic located at the welding station, the method of controlling the speed of the wire feed motors for uniform wire feed that comprises comparing control quantities representing the speed and load torque respectively of the pull motor with a control quantity representing a selected reference wire feed speed for obtaining a motor control quantity representing deviation of the pull motor speed from the reference speed, applying power to the pull motor according to the parameters of the motor control quantity for correcting speed deviations and maintaining the pull motor at reference speed throughout the normal range of load torque, and slaving the speed of the push motor to that of the pull motor.

Claim 3

The method of wire feed speed control as specified in claim 1 wherein the control quantities are voltage signals and the pull motor speed and torque signals respectively, are of opposite sense and proportioned for compensating the drooping speed-torque characteristic of the pull motor.

Claim 4

The method of wire feed speed control as specified in claim 2 wherein the sum of the magnitudes of the speed reference signal and the pull motor torque signal is normally substantially equal to the magnitude of the pull motor speed signal.

Claim 5

The method of wire feed speed control as specified in claim 1 and including the steps: a. deriving a signal representing a selected reference speed for the wire feed, b. deriving a signal representing the instant speed of the pull motor, c. deriving a signal representing the instant load torque of the pull motor, d. comparing all the derived signals for obtaining an error signal representing deviation of pull motor speed from the reference speed, e. applying power to the pull motor according to the magnitude and sense of the error signal for correcting speed deviations and maintaining the pull motor speed at reference speed, f. deriving a signal representing the instant speed of the push motor, g. comparing the push motor speed signal with the pull motor speed signal for deriving a second error signal representing deviation of the push motor speed from the pull motor speed, h. applying power to the push motor according to the magnitude and sense of the second error signal for correcting the speed deviations and maintaining the push motor speed at the pull motor speed.

Claim 6

Apparatus for controlling the speed of a plurality of wire feed motors for feeding in a push-pull arrangement a welding wire at a uniform rate from a supply source to a welding unit, the feed motors including a pull motor having a drooping speed-torque characteristic located at the welding unit and at least one push motor located between the unit and the wire supply, comprising: a. means for controlling application of power to the pull motor, b. means for deriving a constant reference signal representing a selected wire feed speed, c. means for deriving a pair of control signals representing respectively, the speed and the load torque of the pull motor, d. the pull motor power controlling means being responsive to the reference and control signals jointly for applying power to the pull motor in amount sufficient to maintain its speed at the selected wire feed speed, e. and means operable according to the speed of the pull motor for slaving the speed of the push motor to that of the pull motor.

Claim 7

Apparatus for controlling the speed of a plurality of wire feed motors for feeding in a push-pull arrangement a welding wire at a uniform rate from a supply source to a welding unit, the feed motors including a pull motor having a drooping speed-torque characteristic located at the welding unit and at least one push motor located between the unit and the wire supply, comprising: a. means for controlling application of power to the pull motor, b. means for deriving a constant reference signal representing a selected wire feed speed, c. means for deriving a pair of control signals representing respectively, the speed and the load torque of the pull motor, d. the pull motor power controlling means being responsive to the reference and control signals jointly for applying power to the pull motor in amount sufficient to maintain its speed at the selected wire feed speed, e. and means operable according to the speed of the pull motor for slaving the speed of the push motor to that of the pull motor.

Claim 8

Apparatus as specified in claim 5 wherein comparing means for the reference and control signals produce an error signal representing deviation of the pull motor speed from the selected reference speed, and the pull motor power Controlling means is activated according to a function of the error signal.

Claim 9

Apparatus as specified in claim 6 wherein the comparing means constitutes a summing input network for a high-gain regulating amplifier, and the error signal output of the amplifier is pulse-modulated and polarized for activating the power controlling means.

Claim 10

Apparatus as specified in claim 7, wherein the power controlling means constitutes transistorized switching means that is responsive to the magnitude of the polarized error signal for applying power pulses of corresponding duration to the pull motor.

Claim 11

Apparatus as specified in claim 5 wherein the power controlling means for the pull motor constitutes on-off switching means for applying power pulses of variable duration for maintaining the motor at the selected wire feed speed.

Claim 12

Apparatus as specified in claim 9, wherein the duration of the power pulses is controlled according to the magnitude of the error signal.

Claim 13

Apparatus as specified in claim 5 wherein the pull motor load torque signal is compared with a torque reference signal representing maximum permissible pull motor load for producing a torque limiting signal upon overload, and the overload signal overrides the reference and control signals for reducing application of power to the pull motor.

Claim 14

Apparatus as specified in claim 5 wherein the push motor is energized by separate application of power for maintaining the push motor speed at the pull motor speed, and a signal representing the push motor load torque is compared with a reference signal representing maximum permissible push motor load for producing a torque limiting signal upon overload, and the overload signal overrides the speed slaving means for reducing application of power to the push motor.

Claim 15

Apparatus as specified in claim 5 wherein the wire speed reference signal and the speed and torque control signals are relatively proportioned and polarized for jointly causing application of power to the pull motor throughout its normal load range for establishing therefor a constant speed-torque characteristic.