Arc welding apparatus

Abstract: An arc welding apparatus comprising a combination of a teaching-playback robot and an arc welding power source is provided. Even when, in changing a welding method, one welding power source for one welding method is replaced by another welding power source for another welding method, the welding apparatus does not require an adjustment between a robot controller and the latter arc welding power source for consistency between them. The arc welding apparatus comprises a teaching -playback robot comprising a robot body and a robot controller and a welding power source including a controller. The robot controller and the controller of the welding power, source both have a communication controller, and communicate with each other using a digital signal. On the basis of information on the welding method transmitted from the welding power source, the welding method is automatically set into the robot controller.

Description: The present invention relates to an arc welding apparatus comprising a combination of a teaching playback robot and an arc welding power source according to the preamble of claim 1 (see, for example, EP-A-911107). BACKGROUND OF THE INVENTION A gas-shielded arc welding has mainly used a helium gas, an argon gas, a carbon dioxide gas, or a mixture of these gases as shielding gas for protecting a welded part from ambient atmosphere. Depending on various gasses, there are a metal inert gas (MIG) arc welding method, a CO 2 gas shielded arc welding method (CO 2 arc welding method), and a metal active gas (MAG) arc welding method. A pulsed arc welding method in which pulse current is periodically made to flow is also known. Each arc welding method employs a welding power source appropriate to the arc welding method. When a welding is performed using a combination with a teaching playback robot (hereinafter simply referred to as a robot), an adjustment for providing a consistency between a robot control apparatus and an arc welding power source is required for each arc welding method. This adjusting operation is required every time the combination with the robot is changed to use the other welding power source for a different welding method. An arc welding apparatus comprises a shielding gas solenoid valve and a shielding gas supply controller in order to continuously supply the shielding gas to a shielded part for a certain period before a welding, during the welding, and for a certain period after the welding. Before a welding working is performed, generally, a shielding gas flow rate is adjusted to a reasonable amount for preparation of the task. A gas flow rate adjuster mounted to a gas cylinder or a gas supply pipe performs this adjustment of the shielding gas flow rate. Most of gas flow rate adjusters to be mounted to the gas cylinder have a structure integrally combined with a gas-pressure regulating valve. The gas flow rate adjuster is generally deposited away from the gas solenoid valve and a gas controller. Because the adjustment of the gas flow rate requires experimental gas supply regardless of the welding, the welding apparatus includes a gas check switch used for supplying gas experimentally. The gas check switch has a function of switching between "supply" and "stop" of the gas. However, if the switch is left set on the "supply" side, the shielding gas continues to be supplied regardless of the welding. Japanese Patent Laid Open No. 11-77309 discloses a gas-shielded arc welding apparatus including a stop mechanism of shielding gas supply for preventing undesired supply of the shielding gas during non-welding. In the technology disclosed in this Japanese Patent Laid Open, a timer starts counting time synchronously with opening of a solenoid valve for supplying and stopping the shielding gas by operation of a gas check switch. After a time-out period set in the timer is achieved, the solenoid valve is closed to stop the shielded gas supply even if the gas check switch is left set to the supply position of the shielded gas. As a result, the disclosed apparatus has an effect of preventing expensive shielding gas from being uselessly consumed even if the gas check switch is not return to the "stop" side. However, in case of the welding power source disclosed in Japanese Patent Laid Open No. 11-77309 supplying or stopping the shielding gas is performed only by the welding power source. Thus, a problem may occur when the welding power source is used for the arc welding apparatus comprising a combination of the welding power source and a teaching playback robot without any adjustment. For example, for adjusting a shielding gas flow rate with the shielding gas flow rate adjuster, an operator must perform the following processes: setting a gas check switch deposited on the welding power source to "supply" side to open a gas solenoid valve into a gas supply state; adjusting the shielding gas flow rate to a desired value with the shielding gas flow rate adjuster at the position of the shielding gas flow rate adjuster; returning the gas check switch to the stop side again at the position of the welding power source; and closing the gas valve to stop the supply of the shielding gas. The operator must troublesomely perform the adjustment every before the welding. The welding power source disclosed in the Laid Open, as discussed above, is used for automatically closing the gas valve to stop the supply of the shielding gas when the timer achieves the set time-out period even if the gas check switch is forgotten about being returned to the stop side. This function is useful as measures for the forgetting. However, this function may unfortunately allow the operator to leave the check switch as it is without noticing the forgetting about returning thereof. Additionally, the entire stop mechanism of shielding gas supply is hardware. When the return of the check switch is forgotten, the check switch is left set to the gas supply side while an input switch on the welding power source side is turned off and then turned on. The non-operation of the switch prohibits a trigger from starting the time counting by the timer, which results in continuing the shielding gas supply. In an arc welding apparatus comprising a combination of a robot-only arc welding power source and the teaching playback robot, a robot controller side dominates the control of the shielding gas supply. Therefore, when the operator, during teaching for the robot, forgets to register a shielding gas control sequence or teaches an inappropriate sequence at the start or completion of the welding, a welding defect such as a blowhole disadvantageously occurs. Reference may be made to EP-A-0911107 which discloses the precharacterising features of the present invention. Reference may also be made to US-A-5932123. Reference is made under Article 54(3) EPC to EP-A-0993896. SUMMARY OF THE INVENTION The present invention is defined in claim 1. An advantage of the present invention is that it can provide an arc welding apparatus comprising a combination of a teaching-playback robot and a welding power source, considering the conventional problems discussed above. This arc welding apparatus may avoid any requirement for adjustment for providing consistency between a robot controller and the arc welding power source, even when replacement of one arc welding power source for one welding method to another welding power source for another welding method is performed during changing the welding method. One of the features of the present invention is that a robot controller and a welding power source both have an external interface, and can communicate with each other using a digital signal. Based on information on the welding method transmitted from the welding power source, the welding method is automatically set in the robot controller. Even when the welding power source combined with the robot is replaced by the other welding power source for a different welding method, the robot controller corresponds to the latter welding power source on the basis information on the latter welding method sent from the latter welding power source. Therefore, an operator needs not adjust between the welding power source side and the robot controller side. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing a configuration of an arc welding apparatus in accordance with an exemplary embodiment 1 of the present invention. Fig. 2 is a schematic diagram of the configuration of the arc welding apparatus in accordance with the embodiment 1, which describes the present invention as defined in the appended claims. Fig. 3(A) is an explanatory table for a part of a communication protocol from a robot controller to a welding power source in the arc welding apparatus in accordance with the embodiment 1, which describes the present invention as defined in the appended claims. Fig. 3(B) is an explanatory table for a part of a communication protocol from the welding power source to the robot controller in the arc welding apparatus in accordance with the embodiment 1, which describes the present invention as defined in the appended claims. Fig. 4 is a block diagram showing an input switch and a lighting device in a teach pendant of an arc welding apparatus in accordance with an exemplary embodiment 2. Fig. 5 is a front view of the teach pendant of the arc welding apparatus in accordance with the exemplary embodiment 2. Fig. 6 is an explanatory drawing of a liquid crystal screen of the teach pendant for setting a predetermined time at which shielding gas is shut off. Fig. 7 is a hardware block diagram of a part for controlling the opening/closing of a gas valve in the arc welding apparatus in accordance with the exemplary embodiment 2. Fig. 8(A) is a timing chart of the opening/closing of the gas valve at the start of the welding in an arc welding apparatus in accordance with an exemplary embodiment 4. Fig. 8(B) is a timing chart of the opening/closing of the gas valve at the start of the welding in a conventional arc welding apparatus. Fig. 9(A) is a timing chart of the opening/closing of the gas valve at the completion of the welding in an arc welding apparatus in accordance with an exemplary embodiment 5. Fig. 9(B) is a timing chart of the opening/closing of the gas valve at the completion of the welding in the conventional arc welding apparatus. Fig. 10 shows an algorism of an operation of the arc welding apparatus. Fig. 11 shows an algorism of the operation of the arc welding apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment (Embodiment 1) of the present invention will be described hereinafter with reference to the accompanying drawings. Embodiments 2-6 do not form part of the invention, but are presented for additional technical information. Embodiment 1, which represents the present invention : Referring now to Fig. 2, there is shown an entire configuration of an arc welding apparatus for performing the arc welding by combining a teaching-playback industrial robot and a welding power source. Robot controller 1 in Fig. 2 includes teach pendant 2 for teaching, teach pendant 2 is connected to robot controller 1 through communication control line L1, and robot controller 1 is connected to welding power source 3 including a controller through communication control line L2. An operator, while directly looking at welding torch 4 deposited at an effect point of the industrial robot, finely moves robot body 5 and teaches tasks to be performed by the robot in an execution order using teach pendant 2. The operator fixes work 6 to be welded onto table 7, operates teach pendant 2 to move welding torch 4 to a welding start point (not shown). The operator then uses a welding register key on teach pendant 2 to register the following information: teach position data; the fact that the present point of welding torch 4 is the welding start point; welding condition commands (welding current and welding voltage); and welding start commands (a sequence of supplying shielding gas, turning on a welding switch, and the like). The welding switch, which is embedded in the robot controller, is turned on to start the welding or turned off to finish the welding. Next, the operator moves welding torch 4 using robot body 5 to a welding completion point (not shown) along a welding route, and teaches the route. The operator, at the welding completion point, teaches the teach position data and the fact that the present point is the welding completion point. Also, the operator uses a welding completion key on teach pendant 2 to register crater welding condition commands (welding current and welding voltage) and welding completion commands (a sequence of turning off the welding switch, stopping the shielding gas supply, and the like). Central processing unit (CPU) 1b shown in Fig. 1 stores the taught data as a program on random access memory (RAM) 1a responsive to an algorism stored on read only memory (ROM) 1c. RAM 1a is a static RAM and can store the taught data and hold them by battery 1d even if a main power source is shut off. The program, the taught data, automatically operates the welding apparatus in Fig. 2. When robot body 5 moves welding torch 4 to a predetermined welding start point of work 6, robot controller 1 transmits the previously stored welding conditions (welding current and welding voltage) to welding power source 3 through communication control line L2, and then executes the welding start commands. When a response of the arc generation is returned from welding power source 3, robot controller 1 moves welding torch 4 along the welding route of work 6 and executes the arc welding at a taught and stored welding speed. When welding torch 4 reaches the welding completion point, robot controller 1 transmits the taught and stored crater welding condition commands (welding current and welding voltage), stops the robot, executes a crater process, and makes welding torch 4 execute the welding completion commands. The robot controller then performs a known wire stick check, and when an expendable electrode (wire) is not fused with work 6, proceeds to the next teaching point. The crater process means a welding for filling a crater (a recess) formed at the welding end with depositing metal. Referring now to Fig. 1, there is shown transmission and control of signals between robot controller 1 and welding power source 3 in an arc welding apparatus of the present invention. Fig. 1 is a block diagram illustrating a control system of the arc welding apparatus comprising a combination of a teaching-playback robot and a welding power source. As shown in Fig. 1, the robot controller 1 and the welding power source 3 responsively have communication controller le and communication controller 3a as external interfaces, and communicate with each other using a digital signal. After a main power source of the arc welding apparatus is turned on, robot controller 1 and a controller in welding power source 3 execute an initial process upon actuation. After the completion thereof, CPU 1b of robot controller 1, in response to the algorism on ROM 1c, transmits command cord "44h" representing "Good-morning (start of transmitting/receiving)" command to welding power source 3 through communication controller le responsive to a communication protocol shown in Fig. 3(A). Welding power source 3 receives the transmitted command with CPU 3b in response to the algorism stored on ROM 3c through communication controller 3a. When the receiving process is normal, welding power source 3 transmits command cord "71h", which represents a communication protocol "communication acknowledge (ACK)" shown in Fig. 3(B), to robot controller 1 through communication controller 3a. The communication protocols in Fig. 3(A) and Fig. 3(B) are respectively stored on ROM 1c and ROM 3c. The hitherto transmitting/receiving shows an establishment of communication control line L2 between robot controller 1 and welding power source 3. Next, welding power source 3 transmits set wire diameter, welding method, wire material, and kind of wire to robot controller 1. For example, it is assumed that the wire diameter is 1.2, the welding method is CO2, the wire material is mild steel, and the kind of wire is A. First, command cord "7Bh" and its accompanying data "40h" are continuously transmitted responsive to the communication protocol in Fig. 3(B). Reasons why the accompanying data of command cord "7Bh" is "40h" are the followings: Only bit D6 is 1 in the accompanying data for wire diameter 1.2, so that the accompanying data representing wire diameter 1.2 is "4"; and All bits are 0 in the accompanying data for the CO2 welding method, so that the accompanying data representing the CO2 welding method is "0". Incidentally, the last digit "h" shows that the data is written in hexadecimal notation. The robot controller recognizes in advance, referring to a value in column "W" in Fig. 3(B), that command cord "7Bh" has one word of accompanying data. The robot controller 1 receives accompanying data "40h" of the command cord as a set of command cord and accompanying data, and then transmits command cord "41h" as "communication ACK" to welding power source 3. Here, command cord "41h" shows that this set of command cord and accompanying data is received. Similarly, the robot controller receives one word of accompanying data "00h" for command cord "7Ch", and then transmits command cord "41h" as "communication ACK" for the set of command cord and accompanying data to welding power source 3. Reasons why the one word of accompanying data of command cord "7Ch" is "00h" are the followings: all bits are 0 in the accompanying data for mild steel in wire material; and all bits are 0 in the accompanying data for "A" kind of wire. Based on the command cords and their accompanying data transmitted from welding power source 3, the welding method and the like corresponding to the welding power source are automatically set in robot controller 1. The welding method is specific to the welding power source and is fixed, but the wire diameter, the wire material, and the kind of wire, if necessary, can be changed by the communication through communication control line L2 using teach pendant 2 of robot controller 1. The set values after the change are stored on RAM 3d, namely, a static RAM of welding power source 3. Information stored on RAM 3d is backed up by battery 3e and held even during a shutdown of the main power source. (Embodiment 2) A manual control of shielding gas supply during the non-welding will be described in an arc welding apparatus comprising combination of teaching-playback robot controller 1 and welding power source 3. Referring now to Fig. 4, a main configuration of teach pendant 2 on the robot controller 1 is shown. Robot controller, as shown in Fig. 1, comprises RAM 1a, CPU 1b, ROM 1c, and teach pendant interface 1f for controlling communication with teach pendant 2. Teach pendant 2, as shown in Fig. 4, comprises key-block 2a comprising instant ON contacts (pressed to be closed or released to be opened) for performing an robot operation, controller 2b for performing a key input process and the control of the entire teach pendant, a communication controller 2c for performing a communication process of data with robot controller 1, display panel 2d, and memory 2e. CPU 1b in robot controller 1 can recognize a state of each key in key-block 2a through controller 2b, communication controller 2c, and teach pendant interface 1f. Referring now to Fig. 5, a key operation unit of teach pendant 2 is shown. When an operator pushes "gas" key 5a in Fig.5, only during the non-welding, the robot controller recognizes the pushed state of the "gas" key 5a of teach pendant 2, starts to count time with a timer in CPU 1b synchronously with the pressed timing of the "gas" key 5a, and transmits a command (not shown) to welding power source 3 so as to open gas valve 8 controlled by welding power source 3. Gas valve 8 in this embodiment is deposited on robot body 5 as shown in Fig. 2. Referring now to Fig. 7, a hardware configuration for controlling gas valve 8 is shown. When "gas" key 5a of the teach pendant 2 is pushed, CPU 3b of welding power source 3 sets data into data bus "gas on/off = 0/1" and then feeds a LOW logic pulse into a writing signal terminal CK to control relay CR. The data bus "gas on/off = 0/1" is connected to a data input unit in latch circuit 3f through a bus. When relay CR is excited, a contact of relay CR closes to energize solenoid SOL of gas valve 8. Gas valve 8 opens upon energizing solenoid SOL, and shielding gas flows from "gas inlet" toward "gas outlet". Controlling gas valve 8 described above can supply and stop shielding gas. One key in key-block 2a shown in Fig. 4 is assigned as "gas" key 5a of teach pendant 2 in Fig. 5. When "gas" key 5a is pushed, CPU 1b in Fig. 1 stores a value (state) logically showing "1" on a memory region in RAM 1a that is assigned for recognizing the state of the key. When the key is pushed again, CPU 1b replaces the value by a value logically showing "0". In other words, every time "gas" key 5a is pushed, CPU 1b replaces the value in the memory region like 1, 0, 1, 0. Teach pendant 2, as shown in Fig. 4 and Fig. 5, includes LED 5b corresponding to "gas" key 5a. CPU 1b controls turning on/off of LED 5b through teach pendant interface 1f, communication controller 2c, and controller 2b. Controller 2b sets data into data buses LED 1, LED 2, ..., LED m, then feeds a LOW logic pulse into a writing signal terminal WR, and turns on or off LED 5b corresponding to "gas" key 5a. Data buses LED 1, LED 2, ..., LED m are connected to an data input unit in latch circuit 2f through buses. CPU 1b inverts the logic stored in RAM 1a every time "gas" key 5a is pushed. When the value in the memory region assigned for recognizing the state of "gas" key 5a is "1" CPU 1b turns on LED 5b, and when the value is "0" CPU 1b turns off LED 5b. The value in the memory region that inverts its logic for each pushing of "gas" key 5a depends on not only the input of "gas" key 5a but also an actual opening/closing state of the gas valve. In other words, when a sequence command during driving the robot generates a command for opening or closing a gas valve, the command also changes the value in the memory region. The operator, during the operation of "gas" key 5a, can recognize an opening/closing state of the gas valve; "open" when LED 5b is turned on, or "close" when LED 5b is turned off. The operator can thus easily adjust gas flow rate at the start of the working by going to a place of flow rate adjuster 10 with teach pendant 2. A switch that has an instant close contact and is not directly connected to solenoid SOL of the gas valve is used as a gas check switch, and a normally close type valve is used as gas valve 8. Solenoid SOL therefore goes into non-excitation state when the main power source is shut off, so that gas valve 8 closes to stop the supply of shielding gas for arc welding. Even if the main power source of the arc welding apparatus is shut off during the shielding gas supply, the supply of the shielding gas is automatically stopped in this structure. (Embodiment 3) A shielding gas control during non-welding will be described in an arc welding apparatus comprising a combination of teaching-playback robot controller 1 and welding power source 3. In this arc welding apparatus, the robot controller 1 and the welding power source 3 respectively have communication controller 1e and communication controller 3a as external interfaces, and communicate with each other using a digital signal. A circuit shown in Fig. 7 controls and opens gas valve 8 synchronously with an operator's ON operation of "gas" key 5a at an instant ON contact on teach pendant 2 on the robot controller side. The gas valve 8 controls shielding gas supply for welding under the control of welding power source 3. When "gas" key 5a is pushed, CPU 1b on the robot controller 1 shown in Fig. 1 stores a value logically showing "1" (represents a gas supply state) on a memory region assigned for recognizing the state of the key. Synchronously with this storing, a timer in CPU 1b starts counting time, and CPU 1b makes controller 2b turn on LED 5b deposited on teach pendant 2 through communication control line L1. After the time counting operation by the timer in CPU 1b finishes, robot controller 1 transmits a signal for closing gas valve 8 (for stopping gas supply) to welding power source 3 during the non-welding even while LED 5b has been in a gas supply state. In other words, the gas supply stops even if an operation for stopping gas supply has not been performed with "gas" key 5a. At this time, CPU 1b stores "0" on the memory region and turns off LED 5b deposited on teach pendant 2. The timer on the robot controller 1 thus starts counting time synchronously with setting the opening of gas valve 8 by "gas" key 5a, and the gas valve is closed after a predetermined period, during the non-welding even in the gas supply state. Therefore, even when the operator operates "gas" key 5a to supply gas during a check of gas flow rate and then forgets about an operation for stopping the gas supply with "gas" key 5a, the gas supply automatically stops. This prevents useless supply of the shielding gas. The operator, using teach pendant 2, sets the time counting period of the timer in CPU 1b that starts synchronously with the ON operation of "gas" key 5a. Fig. 6 shows a screen used for setting the period as a gas shut-off period (a period until gas shut-off) with teach pendant 2. First for setting a predetermined period during the non-welding as a predetermined period until shielding gas shuts off, the operator operates teach pendant 2 to display contents screen shown in Fig. 6 on a liquid crystal display screen of teach pendant 2. An algorism for this operation and a screen design are stored on ROM 1c. When the contents shown in Fig. 6 are displayed on liquid crystal display screen 5c in the teach pendant in Fig. 5, cursor 5g originally lies at the position "0" of "0.5 (min.)". The operator shifts cursor 5g to a desired digit position with "cursor shift" key 5d shown in Fig. 5, and then inputs a figure using "digit key group" 5e. A figure displayed at the time when "store" key 5f is pushed serves as the counting period. Each set value is stored and held on RAM 1a. RAM 1a is backed up by battery 1d, and the stored data can be held even while the main power source of the arc welding apparatus is shut off. (Embodiment 4) A control sequence of shielding gas at the start of welding will be described. In an arc welding apparatus comprising a combination of teaching-playback robot controller 1 and welding power source 3, as shown in Fig. 1 and Fig. 2, the robot controller land the welding power source 3 respectively have communication controller le and communication controller 3a as external interfaces, and communicate with each other using a digital signal. When welding torch 4 deposited at an effect point of industrial robot body 5 reaches a welding start point (not shown) of work 6 to be welded that is fixed onto table 7, robot controller 1 transmits to welding power source 3 welding condition commands (welding current and welding voltage) and welding start commands (a sequence of supplying shielding gas, turning on a welding switch, and the like) and starts the welding. Referring now to Fig. 8(A) and Fig. 8(B), the present embodiment (Fig. 8(A)) and a conventional example (Fig. 8(B)) will be described comparing them with each other. Robot controller 1 in a conventional arc welding apparatus dominates the control of commands related to welding control. In the conventional example in Fig. 8(B), "gas control signal on robot controller side" is generated for period t1, and synchronously with this generation "gas valve open signal" is generated for period t2 to supply shielding gas for period t2. In this case, "gas control signal on welding power source side" ON of welding power source 3 caused by the command "welding switch" ON from robot controller 1 is neglected. In other words, period t2 depends on period t1, and period t2 is controlled so that period t2 certainly starts synchronously with the start of period t1. Accordingly, when an operator fails the operation, shielding gas is not supplied at the start of the welding, which causes a welding working failure. The operation misses by the operator comprise the following misses: Forgetting about registration of a "gas control signal on robot controller side" ON sequence at the start of the welding; Accidentally deleting the sequence during an editing operation of teaching data; and Setting an unsuitable sequence (for example, a sequence in which "gas control signal on the robot controller side" is turned on at a time lag after turning on the welding switch.) An arc welding apparatus, as shown in Fig. 8(A), uses "gas control signal on welding power source side" of welding power source 3 synchronous to the "welding switch" ON command at the start of the welding. The arc welding apparatus also opens a gas valve to start shielding gas supply, depending on an OR state of an ON signal of "gas control signal on welding power source side" and an ON signal of "gas control signal on robot controller side" of robot controller 1 generated for period t1. In this case, "gas control signal on robot controller side" is in the ON state for period t3, so that shielding gas supply certainly is in the ON state. Even when an operator fails the operation, "gas control signal on welding power source side" turns on synchronously with "welding switch" ON as timing of finishing t3, so that the shielding gas is certainly supplied to prevent a welding working failure. The operation misses by the operator, as discussed above, comprise the following misses: Forgetting about registration of a "gas control signal on robot controller side" ON sequence at the start of the welding; Accidentally deleting "gas control signal on robot controller side" during an editing operation of teaching data; and Setting an unsuitable sequence. The arc welding apparatus of the present embodiment starts to supply shielding gas, by opening the gas valve at the start of the welding depending on an OR state of the gas valve open command on the welding power source 3 and the gas valve open command on the robot controller 1 that is sent for period t1. Incidentally, the gas valve open command on the welding power source 3 is synchronous with the "welding switch" ON command from robot controller 1. (Embodiment 5) A control sequence of shielding gas at the completion of welding will be described. In an arc welding apparatus comprising a combination of a teaching-playback robot and a welding power source, a robot controller and the welding power source both have an external interface, and communicate with each other using a digital signal. The arc welding apparatus of the present invention operates opening/closing of a gas valve with the welding power source depending on an open command or a close command of the gas valve from robot controller, and performs an arc welding working according to teaching data taught to the robot by the operator. In addition, the arc welding apparatus, at the completion of the welding, stops shielding gas supply by closing the gas valve depending on an AND state of a welding completion state on the welding power source and a gas valve close command on the robot controller. The welding completion state starts in response to a welding switch OFF command. When welding torch 4 deposited at an effect point of industrial robot body 5 reaches a welding completion point (not shown) of welded work 6 that is fixed onto table 7, robot controller 1 transmits to welding power source 3 crater welding condition commands (welding current and welding voltage) and welding completion commands (a sequence of turning off a welding switch, stopping the shielding gas supply, and the like) and finishes the welding. Referring now to Fig. 9(A) and Fig. 9(B), the present embodiment will be described in detail. Fig. 9(A) shows an operation sequence not falling under the scope of the appended claims and Fig. 9(B) shows a conventional operation sequence. Robot controller 1 dominates the welding control in a conventional arc welding apparatus. In the conventional example in Fig. 9(B), "gas control signal on robot controller side" is generated for period t5, and "gas valve close signal" is generated upon the completion of period t6 to stop shielding gas supply at this time. In this case, "gas control signal on welding power source side" OFF of welding power source 3 after the completion of a burn back process (period t4) starting with a "welding switch" OFF command from robot controller 1 is neglected. In other words, period t6 depends on period t5, and period t6 is controlled so that period t6 certainly starts synchronously with the start of period t5. Accordingly, when an operator sets "gas control signal on robot controller side" OFF sequence at the completion of the welding to an unsuitable sequence, the burn back process (period t4) is performed in an atmosphere without shielding gas. This generates a blowhole or the like and causes a welding working failure. Here, the operator's unsuitable setting, for example, includes setting a sequence in which "gas control signal on robot controller side" is turned off before turning off the welding switch. The burn back process described above means a process of continuing to apply a low welding voltage between a torch and a base material for a short period after the welding switch is turned off. Because an consumable electrode is supplied due to inertia and the arc continues even after the welding switch is turned off, rapid stop of the application of the welding voltage during the arc continuation causes the consumable electrode to stick into the base material. An arc welding apparatus as shown in Fig. 9(A), at the completion of the welding, uses "gas control signal on welding power source side" OFF after the completion of a burn back process on welding power source 3 side. The burn back process starts with "welding switch" OFF command. The arc welding apparatus also closes a gas valve to stop shielding gas supply, depending on an AND state of an OFF state of "gas control signal on welding power source side" and an OFF state (gas valve close command) of "gas control signal on robot controller side" from robot controller 1. Thus, shielding gas supply is stopped after the completion of period t7. Accordingly, even when an operator sets and registers an unsuitable "gas control signal on robot controller side" OFF sequence at the completion of the welding, the shielding gas supply is stopped only after the completion timing of period t4 after the burn back process. This prevents a welding working failure. The arc welding apparatus as discussed above, closes the gas valve to stop the shielding gas supply, depending on an AND state of the completion state of the burn back process on the welding power source side that starts with the welding switch OFF command (i.e. the OFF state of "gas control signal on welding power source side") and gas valve close command on the robot controller side. (Embodiment 6) It is an object of this embodiment to prevent useless supply of shielding gas even when an operator misses registration of a "gas control signal on robot controller side" OFF sequence at the completion of the welding, accidentally deletes the sequence during an editing operation of teaching data, or sets an unsuitable sequence. In an arc welding apparatus in accordance with the present embodiment comprising a combination of a teaching-playback robot and a welding power source, a robot controller and the welding power source both have an external interface, and communicate with each other using a digital signal. The arc welding apparatus operates opening/closing of a gas valve with the welding power source depending on an open command or a close command of the gas valve from the robot controller, and performs an arc welding working according to teaching data taught to the robot by the operator. Even when any gas valve close command is not sent from the robot controller after welding switch OFF is commanded at the completion of the welding, the arc welding apparatus makes a timer on the welding power source start counting time, and closes the gas valve after a predetermined period to stop the shielding gas supply. The start of the time counting is synchronous with the completion (i.e. turning off "gas control signal on welding power source side") of a burn back process on the welding power source that starts with the welding switch OFF command. When welding torch 4 deposited at an effect point of industrial robot body 5 reaches a welding completion point (not shown) of welded work 6 that is fixed onto table 7, robot controller 1 transmits to welding power source 3 crater welding condition commands (welding current and welding voltage) and welding completion commands (a sequence of turning off a welding switch, stopping the shielding gas supply, and the like) and finishes the welding. An arc welding apparatus of embodiment 5, as shown in Fig. 9(A), at the completion of the welding, closes the gas valve to stop the shielding gas supply depending on an AND state of an OFF signal of "gas control signal output on welding power source side" after the burn back process on welding power source 3 and an OFF signal (gas valve close command) of "gas control signal output on robot controller side" from robot controller 1. The burn back process starts with a "welding switch" OFF command. If an operator forgets about the registration of the "gas control signal output on robot controller side" OFF sequence at the completion of the welding, the "gas control signal output on robot controller side" OFF signal is not generated. Therefore, the AND state of the OFF signal of "gas control signal output on welding power source side" and the OFF signal (gas valve close command) of "gas control signal output on robot controller side" from robot controller 1 does not become 1, so that the shielding gas supply is not stopped. Such case does not cause any welding working failure, but uselessly consumes the shielding gas regardless of the welding working. The arc welding apparatus of this embodiment is used for preventing useless consumption of the shielding gas regardless of the welding working even when the operator forgets about registration of the "gas control signal on robot controller side" OFF sequence at the completion of the welding. At the completion of the welding in Fig. 9(A), the timer in CPU 3b starts counting time for a predetermined period synchronously to a "gas control signal on welding power source side" OFF timing after the burn back process on welding power source 3 that starts with the "welding switch" OFF command If the time counting operation is completed without the "gas control signal on robot controller side" OFF sequence at the completion of the welding, CPU 3b of welding power source 3 forcibly closes the gas valve (i.e. stop of gas supply) with a circuit shown in Fig. 7 during non-welding even in the gas supply state. CPU 3b also notifies robot controller 1 of the closing of the gas valve through communication control line L2. CPU 1b of robot controller 1 replaces the value in a memory region of RAM 1a that represents an actual opening/closing state of the gas valve by "0" representing the closing state of the gas valve, and also turns off LED 5b deposited on teach pendant 2. In addition, CPU 1b displays a warning (not shown) of no gas OFF sequence on a liquid crystal screen. At this time, the robot operation is not stopped but continued. If an operator forgets about the registration of the "gas control signal on robot controller side" OFF sequence, the gas valve close command on the robot controller 1 does not exist. The arc welding apparatus with a structure discussed above, however, makes the timer of welding power source 3 start the counting time synchronously with the completion of the burn back process of the welding after the welding switch OFF command is sent, and forcibly closes the gas valve after a predetermined period to stop the shielding gas supply. This can prevent useless consumption of the shielding gas regardless of the welding working. The time counting period (a period until stop of the gas supply) of the timer of welding power source 3 will be hereinafter described. The operator, using teach pendant 2, sets the time counting period of the timer of welding power source 3. Referring now to Fig. 6, there is shown a screen used for setting the period as a gas shut-off period with teach pendant 2. First for setting a predetermined period, the operator operates teach pendant 2 to display screen 5c shown in Fig. 6 on a liquid crystal display screen on teach pendant 2. The time counting period in accordance with the present embodiment is displayed in second as a shut-off period of the shielding gas during the welding like "during welding 0.5 (sec.)" on screen 5c on teach pendant 2. Cursor 5g originally lies at the position "0" of "during non-welding 0.5 (min.)". The operator shifts cursor 5g to a desired digit position on the "during welding 0.5 (seconds)" side with "cursor shift key" 5d shown in Fig. 5, and then inputs a figure using "digit key group" 5e. A figure displayed at the time when "store key" 5f is pushed serves as the time counting period. Each set value is transmitted to welding power source 3 through communication control line L2, and stored and held as data of the time counting period on RAM 3d. RAM 3d is backed up by battery 3e, and the stored data can be held even when the main power source of the arc welding apparatus is shut off. Referring now to Fig. 10 and Fig. 11, flow charts of algorisms from embodiment 2 through embodiment 6, which are not part of the present invention, are shown. Steps represented by circled figures in Fig. 10 are continued to steps with the same figures in Fig. 11. Individual flow of each algorism is not described because the contents are the same as discussed above. The software processes comprise multiple tasks and are driven by respective events, namely, in "event driven" types.

Claims: An arc welding apparatus comprising: a teaching-playback robot comprising a robot body (5) and a robot controller (1); a welding power source (3) including a controller; a first external interface (1e) deposited in said robot controller; a second external interface (3e) deposited in said controller of said welding power source; and a communication control line (L2) coupling the first and second external interfaces; characterised in that said first and second external interfaces communicate with each other through communication control line (L2) using a digital signal, said second external interface (3e) is operable to send to the first external interface (1e), conditions including a welding method and at least one of wire diameter, kind of wire, kind of wire material stored in the controller of the welding power source (3), and on the basis of said conditions transmitted from said welding power source (3) to the robot controller (1), the robot controller is operable to set said conditions to execute the welding method. The arc-welding apparatus according to claim 1, further comprising a gas valve (8) for controlling a shielding gas supply, the gas valve being opened or closed based on a gas valve open/close command from said robot controller (1), wherein said gas valve (8) is a normally-close-type solenoid valve. The arc welding apparatus according to claim 1 or 2, further comprising a teach pendant (2) operable to change, via the communication control line (L2), said at least one of the wire diameter, the kind of wire, and the kind of wire material stored in the controller of the welding power source (3).

Inventors: SHIMOGAMA SHIGERU, SHIMOGAMA, SHIGERU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 2001
Main classification: B23K9
IPC codes: B23K9