Inverter type DC resistance welding machine

• US 4,734,556 A
• Filed: 06/22/1987
• Issued: 03/29/1988
• Est. Priority Date: 10/18/1986
• Status: Expired due to Term

• Current Assignee: Miyachi Electronic Company 95-3 Futatsuzuka Noda-Shi Chiba-Ken Japan
• Original Assignee: Miyachi Electronic Company
• Inventors: Namiki, Mitsuo
• Primary Examiner(s): Shaw, Clifford C.
• Application Number:
  US07/064,606
• Time in Patent Office: 281 Days
• Field of Search: 219/110, 219/109, 219/117.1, 219/130.33, 219/108, 363/97, 363/98
• US Class Current: 219/110
• CPC Class Codes: B23K 11/252 using digital means

Abstract

Disclosed is an inverter type DC welding machine incorporating constant-power control to assure a high and reliable quality of weld. The pulse width of the high-frequency output of the inverter circuit is controlled at the inverter switching rate by the constant-power control on a feedback loop basis in which the value of a weld power actually supplied to the portion to be welded between electrodes is computed and the computed value is compared with the value of a reference weld power to produce an error signal for controlling the operation of the inverter circuit, so that the actual weld power is maintained constant regardless of variations in the resistance of the portion to be welded during a welding operation.

Claims

1. A DC resistance welding machine including a first rectifier circuit for rectifying a commercial AC voltage into a DC voltage, a circuit for converting said DC voltage into a pulse-shaped voltage having a predetermined high-frequency, a welding transformer for transforming said pulse-shaped high-frequency voltage, a second rectifier circuit for rectifying said pulse-shaped high-frequency voltage to a DC weld voltage, said DC weld voltage being applied to workpieces to be welded between electrodes so that a DC weld current for a resistance welding flows through said electrodes and said workpieces, comprising:

means for detecting said DC weld voltage;

means for detecting said DC weld current;

means for computing the value of a weld power actually consumed between said electrodes on the basis of the detection values of said DC weld voltage and of said DC weld current;

means for presetting a reference weld power to any desired constant value;

means for comparing the computed value of said actual weld power with said reference weld power to produce an error signal representative of the comparision error;

means being responsive to said error signal for controlling the pulse width of said pulse-shaped voltage at the rate of said predetermined high-frequency so as to maintain constant said weld power consumed between said electrodes.

2. The DC resistance welding machine as defined in claim 1 wherein said voltage detection means comprises a computing circuit connected to said electrodes for computing the mean value of said weld voltage at the rate of said predetermined high-frequency.

3. The DC resistance welding machine as defined in claim 1 wherein said current detection means comprises:

a toroidal coil for sensing said weld current to generating an output voltage representing the differential waveform of said weld current;

a waveform regeneration circuit for integrating said output voltage from said toroidal coil to generate a voltage signal representing said weld current; and

a computing circuit for computing the mean value of said current at the rate of said predetermined high-frequency.

4. The DC resistance welding machine as defined claim 1 wherein said pulse width control means comprises a pulse wave modulation circuit that responds to said error signal from said comparision means to produce a pulse wave modulation signal for controlling the switching operation of said converting means.

5. A weld power control system for a DC resistance welding machine including an inverter in its power circuit, the inverter producing a pulse-shaped voltage at a switching rate, comprising:

means for detecting a DC weld voltage applied between electrodes being depressed against workpieces;

means for detecting a DC weld current flowing through said electrodes and workpieces;

means for computing the value of a weld power consumed between said electrodes on the basis of the detection values of said DC weld voltage and of said DC weld current;

means for presetting a reference weld power to any desired constant value;

means for comparing the computed value of said actual weld power with said reference weld power to produce an error signal representative of the comparison error; and

means being responsive to said error signal for controlling the pulse width of said pulse-shaped voltage at the rate of inverter switching so as to maintain constant said weld power consumed between said electrodes.