Spot welding apparatus

Abstract: A spot welder apparatus includes: a single welding power source (5); a welding current distributor (7) connected to the single welding power source; and a plurality of spot welders (1A, 1B, 1C) connected to the welding current distributor. Each of a plurality of the spot welders is activated alternately by welding current distributed by the welding current distributor. When two start signals are generated almost simultaneously, a first spot welder which generates the start signal earlier is activated, and a second spot welder which generates the start signal later is kept under pressurized condition. Immediately after the first spot welder is deactivated, the second spot welder is then activated. The spot welder apparatus is low in cost and small in installation space, without increasing the user' current capacity.

Description: The present invention relates to a spot welding apparatus according to the preamble of claim 1. Conventionally, welding power is supplied to the primary coil of a transformer provided for each spot welder. In other words, a single spot welder is generally activated by a single welding power source. In the conventional spot welder, however, since the power is supplied from a single welding power source to a single transformer thereof, when a plurality of spot welders are arranged, a transformer and a spot welding power source must be provided for each spot welder, respectively. As a result, it has been necessary to purchase the transformers and the welding power sources (the most expensive units) together for a plurality of spot welders. In addition, since a plurality of user's breakers (the same as the number of the welding power sources) are necessary, there exists another problem in that the capacity of the incoming power increases and therefore the installation space therefor also increases. From US-A-5 072 090 a spot welding apparatus, comprising a single welding power source, a rectifier, a memory unit for storing a number of welding programs, and a control unit for controlling the spot welding apparatus is known. The apparatus further comprises a plurality of spot welders having each a transformer connected in parallel with single welding power source by selectively actuable switching means. The spot welders according to said document are controlled by a central control unit. Each of the spot welders are controlled by one central program and are activated by one activation signal. The control unit controls the welding current supply time to the several spot welders. Said welding times are not overlapping each other in accordance with the central welding program. It is an objective of the present invention to provide a spot welding apparatus as indicated above ensuring simple structure and having spot welders which can work more independently from each other. According to the present invention, this objective is solved by a spot welding apparatus comprising the features of claim 1. Preferred embodiments of the present invention are laid down in the subclaims. In the spot welding apparatus since a plurality of the spot welders can be activated alternately by welding current distributed by the welding current distributor, it is possible to reduce the number of spot welding power sources, the installation space, and the cost thereof. An embodiment of spot welding apparatus will be described hereinbelow with reference to the attached drawings wherein: Fig. 1 is a schematic block diagram showing the spot welding apparatus; Fig. 2 is a timing chart for assistance in explaining the welding operation sequence, in which welding current is supplied to two spot welders from a single current distributor; and Fig. 3 is a flowchart for assistance in explaining the welding operation sequence. In Fig. 1, the spot welding apparatus provides a user's breaker 15, a welding power source 5 connected to the user's breaker, a welding current distributor 7 connected to the welding power source 5, and a plurality of spot welders 1A, 1B and 1C. The welding power source 5 has a rectifier 9. The welding current distributor 7 includes a branch unit 11, three automatic switches 13A, 13B and 13C, a microprocessor 10, a memory unit 12, etc. Each of the spot welders 1A, 1B and 1C has a welding electrode 3A, 3B or 3C, a transformer 23A, 23B or 23C, a start switch 28A, 28B or 28C, a digital switch 29A, 29B or 29C. The welding electrode 3 is attached to an end of a welding gun (not shown) for pressurizing and spot welding an object to be welded. Further, the current distributor 7 is connected between the welding power source 5 and the respective spot welders 1A, 1B and 1C to supply the welding current to the welding electrodes 3A, 3B and 3C of the spot welders 1A, 1B and 1C, respectively. Further, the user's breaker is connected to the rectifier 9 of the welding power source 5 through a power cable 17. The rectifier 9 is connected to the branch unit 11 through a power cable 19. The branch unit 11 is connected to the respective automatic switches 13A, 13B and 13C via power cables 21A, 21B and 21C, respectively. Further, the respective automatic switches 13A, 13B and 13C are connected to the primary coils of transformers 23A, 23B and 23C housed in the spot welders 1A, 1B and 1C through the power cables 25A, 25B and 25C, respectively. On the other hand, the secondary coils of the transformers 23A, 23B and 23C are connected to the spot welding electrodes 3A, 3B and 3C of the spot welders through power cables 27A, 27B and 27C, respectively. Further, the spot welders 1A, 1B and 1C are provided with digital switches 29A, 29B and 29C, respectively. When each of these digital switches 29A, 29B and 29C is turned on, any one of a plurality of welding programs stored in the memory unit 12 of the current distributor 7 can be selected. The welding program determines the welding sequence (priority) of the spot welders, the welding pressure (inclusive of the dressing pressure), the welding pressure duration time, the welding current value, the welding current duration time, etc., so that the welding current distributor 7 can be controlled by the microprocessor 10 thereof in accordance with the selected program. For instance, when two spot welders 1A and 1B are arranged, 1st to 8th programs can be selected by the digital switch 29A, and 9th to 15th programs can be selected by the digital switch 29B. However, when programs other than 1st to 8th programs are selected by the digital switch 29A, the current distributor 7 will not supply current, and when programs other than 9th to 15th programs are selected by the digital switch 29B, the current distributor 7 will not supply current. Here, a plurality of the spot welders are activated in parallel to each other alternately as follows: As shown in Fig. 2, when two spot welders 1A and 1B of the three spot welders 1A, 1B and 1C are used and further when a start signal Ss is generated by the start switch 28A of the spot welder 1A at time t1 a little before the start switch 28B of the spot welder 1B generates a start signal Ss at time t2, the pressure of the spot welder 1A is set to a dressing pressure Pd as shown by (A). On the other hand, the pressure of the spot welder 1B is set to a welding pressure Pw at time t2 as shown by (B). After that, in the spot welder 1A, the dressing pressure Pd changes to the welding pressure Pw (pressurized state) at time t3, and further welding current Iw is passed through the welding electrode 3A of the spot welder 1A at time t4. During this time, in the spot welder 1B, a welding pressure Pw is kept after time t2. However, immediately after the spot welder 1A is deactivated and the welding current Iw ends at time t5, welding current Iw is passed through the welding electrode 3B of the spot welder 1B at time t6. During the welding operation of the spot welder 1B, since a succeeding start signal Ss is generated by the spot welder 1A at time t7 as shown in by (D), in the spot welder 1A, the dressing pressure Pd is generated at time t7 and further the welding pressure Pw is generated at time t8. Under these conditions, when the spot welder 1B is deactivated and the welding current Iw ends at time t9, in the spot welder 1A, the pressure is once dropped down to the dressing pressure Pd at time t10 and then raised-up to the welding pressure Pw at time 11. After that, welding current Iw is passed therethrough at time t12 again, as shown by (F). With reference to Fig. 3, the more generic welding procedure of the spot welding apparatus will be described hereinbelow. First, when one of the welding program stored in the memory unit 12 of the welding current distributor 7 is selected by the digital switch 28 of the spot welder 3, the microprocessor 10 control the total welding operation (the pressure value, the pressure duration time, the current value, the current duration time, etc.) of the spot welding apparatus in accordance with the selected program. The microprocessor (referred to as a control, hereinafter) 10 checks whether start signals Ss are generated by the respective spot welders 1 (in step ST1), and further whether a plurality of start signals Ss have been generated simultaneously (in step ST2). If NO; that is, if only one start signal Ss has been generated, control. proceeds to step ST8 to activate the spot welder 1 which generates the start signal Ss. To activate the spot welder, first a low dressing pressure and then a high welding pressure is applied to the electrode. After that, welding current Iw is passed through the spot welder. Further, control checks whether a predetermined time duration (determined by the program) has elapsed and thereby the spot welder is deactivated (in step ST9). If YES, control ends. In step ST2, if YES; that is, if a plurality of start signals have been generated simultaneously, control stores the sequence of the generated start signals Ss (in step S3). Further, control activates the spot welder which has first generated the start signal (first-start signal spot welder), and sets the other remaining spot welders to the welding pressure condition (in step ST4). Further, control checks whether the first-start signal spot welder has been deactivated after a predetermined time has elapsed (in step ST5). If YES, control activates the spot welder which has secondly generated the start signal (second-start signal spot welder), and sets the other remaining spot welders to the welding pressure condition (in step ST6). Further, control checks whether the second-start signal spot welder has been deactivated after a predetermined time has elapsed (in step ST7). The similar procedure as describe above is repeated by the number of the spot welders. Further, control proceeds to step ST8 to activate the spot welder which generates the last start signal Ss. Further, control checks whether a predetermined time duration has elapsed and thereby the last spot welder is deactivated (in step ST9). If YES, control ends. As described above, a plurality of the spot welders can be activated alternately by activating only one spot welder (which generates the start signal earlier) and by setting the other remaining spot welders to the welding pressure (pressurized) condition in the sequence of the start signals. Here, since the current duration time is usually from 200 to 400 ms, even if a plurality of spot welder are activated at the same time, there exists no substantial time delay (the waiting time), as compared with the conventional spot welder each having an individual welding power source. In the spot welder apparatus, since the current distributor 7 is provided, even if a plurality of spot welders 1A, 1B and 1C are used, it is possible to supply welding current to a plurality of spot welders 1A, 1B and 1C alternately, by selectively closing any one of the automatic switches 13A, 13B and 13C. In more detail, when a start signal is generated and applied to the current distributor 7, only the automatic switch 13A is closed, for instance to supply welding current to only the spot welder 1A, without closing the automatic switches 13B and 13C, so that it is possible to prevent welding current from being supplied to the other spot welder simultaneously. Further, in the spot welder apparatus, since the primary current (e.g., 600 A) of each of the transformers 23A, 23B and 23C is passed or interrupted by each of the automatic switches 13A, 13B and 13C, it is possible to prevent the contacts of the automatic switches from being consumed and therefore to reduce the size of the contacts. This is because since the secondary current of each of the transformers 23A, 23B and 23C is as large as about 20,000 A, a large switch must be used to pass or interrupt a large current. As described above, in the spot welder apparatus, since the current distributor 7 is connected to a single welding power source 5 and further a plurality of spot welders 1A, 1B and 1C are activated alternately by the single welding power source through the single distributing welding current appropriately, it is possible to reduce the manufacturing cost of the plural spot welders, the capacity of the user's breaker, the number of the breaker and installation space.

Claims: Spot welding apparatus, comprising: a single welding power source (5), a rectifer (9), a memory unit (12) for storing a number of welding programs, a plurality of spot welders (1A, 1B, 1C) having each a transformer (23A, 23B, 23C) connected in parallel with said single welding power source (5) by selectively actuable switching means (13A, 13B, 13C), a control unit (10) for controlling said plurality of spot welders (1A, 1B, 1C), and which applies pressure in accordance with programs stored in the memory when a welding start signal is detected and keeps a welding pressure until the welder is deactivated, characterized in that each of the spot welders (1A, 1B, 1C) comprises a start switch (28A, 28B, 28C) for generating a welding start signal and a digital switch (29A, 29B, 29C) for selecting one of the welding programs, and in that said control unit (10) activates the spot welders (1A, 1B, 1C) in the following way: cyclical checking start signals generated by said plurality of the spot welders, and if only one start signal has been generated during one check cycle: activating the spot welder which generated the start signal, or if a plurality of start signals are generated almost simultaneously: storing the sequence of start signals in the order they were generated, setting the spot welders that generated the start signals under welding pressure condition, passing welding current in the spot welder corresponding to the first start signal in the sequence, passing welding current in the spot welder corresponding to the second start signal in the sequence after the current in the first spot welder has ended, and repeating the latter step to pass current in the spot welders in the sequence that the start signals are generated. Spot welding apparatus according to claim 1, characterized in that the control unit comprises a micro-processor. Spot welding apparatus according to claim 1 or 2, characterized in that the selectively actuable switching means comprises a plurality of automatic switches (13A, 13B, 13C) wherein each transformer (23A, 23B, 23C) of the plurality of spot welders (1A, 1B, 1C) is connected with one of the automatic switches (13A, 13B, 13C). Spot welding apparatus according to claim 3, characterized in that a branch unit (11) is provided for connecting the rectifier (9) with each of the automatic switches (13A, 13B, 13C).

Inventors: KITAGUCHI SHINICHI, TSUYUKI SHIGEO, KITAGUCHI, SHINICHI, TSUYUKI, SHIGEO
Applicants: AMADA METRECS CO, AMADA METRECS COMPANY, LIMITED
Application year: 1995
Main classification: B23K11
IPC codes: B23K11