JP3406841B2 - Seam welding method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hermetically sealing a flange formed at a joint portion of a container (work) typified by, for example, an automobile fuel tank. In particular, seam welding , in which an industrial robot grips a workpiece to automatically feed the welding site
About the method. 2. Description of the Related Art As shown in FIG. 2, an automobile fuel tank 2 includes an upper member 2a and a lower member 2 formed by a sheet metal press.
b at the top and bottom, and the joining flange 2c at the periphery of the divided surface
Is temporarily fixed at several places by spot welding, and then the joining flange portion 2c is continuously welded. In this welding operation, a seam welding machine having a pair of upper and lower electrode wheels is generally used, and at this time, the upper member 2a and the lower member 2b are rotatably supported by a lower jig or a robot arm. The method of supporting the fuel tank by the lower jig has a disadvantage that it takes a long time to manufacture the jig, so that it is not possible to quickly respond to a change in the shape of the fuel tank. For this reason,
Recently, a method of supporting a fuel tank by a robot arm is becoming mainstream. For example, Japanese Patent Application Laid-Open Nos. 2-92471 and 61-276782 disclose that a robot control system uses a robot system instead of guiding a welding locus by mechanical cam scanning control. Discloses a method for numerically inducing a welding locus by an operation program stored in a welding program. In detail, as shown in FIG. 7, a C-shaped frame 3 as a holding means of a fuel tank 2 attached to an end of an arm of a main body 1 of an articulated industrial robot is attached to a C-shaped frame by an end axis of the robot. A pair of upper and lower rotating shafts 4a that rotate,
The upper and lower surfaces of the upper and lower members of the fuel tank 2 are pressed and supported by the rotating shafts 4a and 4b. Thereby, the fuel tank 2 pressed and supported on the C-shaped frame 3
Are associated with the rotation of the rotating shafts 4a, 4b.
It will rotate around b. Then, as shown in FIG. 3, the robot is arranged such that the joining flange portion 2c is always fed in a tangential direction to a pair of upper and lower electrode wheels 6a, 6b of the seam welding machine 5 which is rotationally controlled separately from the robot main body 1. The main body 1 is controlled by the robot controller 7, while the pair of upper and lower electrode wheels 6 a and 6 b is controlled by the seam welding machine 5. According to such a configuration, even when the model of the fuel tank is frequently changed, unlike the conventional mechanical cam copying apparatus, only the operation program is changed by teaching or data input. There is an advantage that coping is possible. Further, if a plurality of operation programs corresponding to the types of the fuel tanks are input in advance to the robot controller, there is an advantage that it is possible to produce fuel tanks of various types on the same line. [0005] In the prior art, the work feeding operation performed by the robot body 1 and the rotating operation of the electrode wheels 6a and 6b performed by the seam welding machine 5 are preset so as to be synchronized. Since the control system is independent of the driving of each joint axis of the main body 1 and the driving of the electrode wheels 6a and 6b, for example, when a torque fluctuation occurs between the electrode wheels 6a and 6b and the fuel tank 2, the fuel Tank 2 and electrode wheel 6a,
6b, the stable operation by the regular torque is not performed. To cope with such a problem, Japanese Patent Application Laid-Open No.
In the method disclosed in Japanese Patent Publication No. 380, the rotation speed of the electrode wheel is detected during the welding operation, and the feed speed on the robot body side is controlled so that the rotation speed and the feed speed on the work side are synchronized. ing. Here, the feed speed on the robot body side referred to here is the speed at the end of the arm of the robot. Therefore, in a use mode in which the work is gripped by the tip of the arm, the feed speed on the robot body side is equivalent to the feed speed on the work side. [0006] The object of the invention is to be Solved by the way, the electrode wheels of the anti
As it is a consumable item,
Good. Therefore, the dimensions of the new electrode wheel before wear
Is synchronized with the welding speed of the robot body based on the
The welding of the robot body according to the wear of the electrode wheel.
The peripheral speed of the electrode wheel will be slower than the speed
The robot feed operation and the seam welding performed by the robot body
When the rotation of the electrode wheel performed by the machine is completely out of synchronization
Problem arises. [0008] The present invention has been made to solve the above problems.
Dimensions of new electrode rings before wear
Synchronization with the welding speed of the robot body based on the source
The robot's robot feeds the workpiece
Synchronized with the rotation of the electrode wheel performed by the seam welding machine
The purpose is to provide a seam welding method
You. [0010] [0011] [Means for Solving the Problems] The accomplishment of the foregoing
According to the present invention, a work is held by a work holding device which can be moved in a plurality of axial directions by being connected to an arm tip of an industrial robot, and a welding locus in a flange formed on the work is seam-welded. AC current is intermittently or continuously interposed between the electrode wheels while guiding the welding trajectory between the electrode wheels based on the operation program stored in the robot controller of the industrial robot while being sandwiched between a pair of electrode wheels provided in the machine. Is a seam welding method in which seam welding is performed by flowing an electrode wheel, and the drive of each joint axis of the industrial robot and the drive of the electrode wheel are synchronized by using the electrode wheel as an additional axis of the robot controller. Accordingly, when the welding speed is switched based on the operation program, the seam welding is performed so that the rotation speed of the electrode wheel can be changed in synchronization with the welding speed.
In the contact method, when the electrode wheel is new,
Based on welding work calculated based on past welding results
The wear amount of the electrode wheel per rotation of the electrode wheel is determined in advance by the robot.
The control is stored in the
Current from the new condition of the electrode wheel
Count the total number of rotations up to the current
Diameter of the electrode ring for the product, electrode ring per rotation of the electrode ring
Wear of the electrode wheel and the condition from the new condition of the electrode wheel to the present.
The current electrode wheel diameter is calculated based on the total number of revolutions at
Synchronizes with the welding speed based on the current electrode wheel diameter.
The feature is that the rotation speed of the electrode wheel is corrected.
To provide a seam welding method. Electrodes counted by a revolution counter
N is the total number of revolutions from the new state of the wheel to the present
And the current electrode wheel diameter Dc is the electrode diameter when the electrode wheel is new.
Based on wheel diameter (diameter of electrode wheel) Dn and past welding results
Per rotation of electrode wheel by welding work
Dc = Dn−L × N due to the wear amount L of the electrode wheel.
On the other hand, the feed speed of the fuel tank 2 performed by the robot body 1 is limited.
That is, assuming that the welding speed is Vw,
The rotation speed Ve of the electrode wheel is expressed as Ve = Vw / (π × Dc).
Is required. The calculated rotation speed Ve of the electrode wheel
The dimensions of a new electrode ring before it is worn
Synchronize with the welding speed of the robot body based on the specifications
The robot body moves according to the wear of the electrode wheels.
Workpiece feeding operation (welding speed Vw) and electrode wheel rotation
Synchronization (rotational speed Ve of electrode wheel)
Become. Here, the configuration described in claim 1 is
A description is given below. The term "work" as used herein refers to, for example, containers manufactured by joining two members formed by a sheet metal press or the like, as represented by a fuel tank for an automobile, for example. However, the present invention is not limited to this as long as it has a flange portion for joining to the surface. Also, "based on the operation program" means that the control system of the robot generally performs feedback control, so for example, a movement command for each joint axis of the robot is a raw movement command specified by the operation program. However, this is because feedback data is added. Also, here, "welding speed
"Degree" means that the position of the electrode ring is fixed
Is equivalent to the movement speed of the robot arm tip. "Electrode wheels are used as additional axes of the robot controller" means that the drive axes for rotating the electrode wheels are the same as the respective drive axes for operating the joint axes of the robot body. This means adding as one of the control axes controlled by the robot controller. Generally, in order to efficiently and safely move an attachment (in the present invention, a means for holding a fuel tank) attached to the end of an arm, an industrial robot performs synchronous control on each joint axis of the industrial robot. . Specifically, the drive axis of each joint axis is controlled by one robot controller, and the robot controller distributes and controls the drive axis of each joint axis based on an operation program. As a result, the joint axes of the robot main body operate synchronously based on the operation program. An embodiment of the present invention will be described below with reference to the accompanying drawings. I will explain. FIG. 1 is a schematic diagram showing the overall configuration of a seam welding apparatus to which the present invention is applied, using an articulated robot as an automatic feeder of an automobile fuel tank 2 as a work. Reference numeral 1 denotes a robot main body having a vertical articulated structure;
Reference numerals a and 4b denote an upper rotating shaft and a lower rotating shaft, respectively, which enable the C-shaped frame 3 to rotate around the rotating shaft 4 and support the fuel tank 2 by pressing. The rotating shafts 4a and 4b can be opened and closed by a cylinder mechanism or the like, and the fuel tank 2 is sandwiched by plate-like gripping members provided at the tips of the rotating shafts 4a and 4b. The seam welding machine 5 has an upper electrode wheel 6a and a lower electrode wheel 6b as a pair of upper and lower seam welding electrode wheels, and these electrode wheels 6a and 6b are respectively moped.
The rotational force of the motors 12a and 12b is rotationally driven via the speed reducers 13a and 13b. In the present invention, as will be described later, since the electrode wheels 6a and 6b are set as additional axes of the robot controller, the motors 12a and 12b use servo motors. At least one of the electrode wheels 6a and 6b is provided with a torque detector for detecting a rotational torque of the electrode wheel. Reference numeral 7 denotes a robot controller for controlling the drive of each joint axis of the robot body 1 and the electrode wheels 6a and 6b of the seam welding machine 5. The robot control device 7
A main body axis servo driver 8 for driving each joint axis of the robot main body 1, an electrode axis servo driver 9 for driving the electrode wheels 6a and 6b, and a welding machine timer for controlling a welding current supplied between the electrode wheels 6a and 6b. 10 and a memory 14 for storing welding conditions and the like respectively corresponding to a plurality of types of welding speeds. The CPU 11 outputs a drive command to the body axis servo driver 8 and the electrode axis servo driver 9 based on an operation program stored in advance in a ROM (not shown) or the like and feedback data from each drive axis. In addition, the CPU 11 has a memory 14
Timer 1 based on the welding conditions stored in the
With respect to 0, a command regarding the magnitude of the welding current and the timing of energization is output. Next, the seam welding operation in this embodiment will be described. The operation program is stored in a ROM (not shown) in the robot control device 7 in advance.
This operation program includes the flange 2 of the fuel tank 2.
Numerical control data for guiding a welding trajectory c in two-dimensional or three-dimensional manner between the electrode wheels 6a and 6b is included. The numerical control data indicates that the electrode wheels 6a, 6b
And the feed speed of the fuel tank 2 are numerically matched. In addition, welding conditions corresponding to each of a plurality of types of welding speeds are stored in the memory 14 in the robot control device 7 in advance. Specifically, a table is provided in which a plurality of types of welding speeds and a plurality of types of welding conditions correspond to each other on a one-to-one basis. Here, a predetermined range is provided for each of the plurality of types of welding speeds so that adjacent welding speeds do not overlap each other in the predetermined range, and the welding conditions are uniquely selected at any welding speed. So that In addition, as the welding conditions, at least the pressing force and welding current of the electrode wheel, which are greatly related to the welding quality, are set, but are not limited to these, and in accordance with the welding speed in order to improve the welding quality. Any other elements that need to be changed may be included. Now, when the fuel tank 2 is held between the C-shaped frames, the robot body 1 starts moving based on the operation program, and the fuel tank 2 is placed on the front surface of the electrode wheels 6a and 6b of the seam welding machine 5. The electrode wheel 6a which has been transported and is in an open state,
The flange 2c of the fuel tank 2 is inserted between 6b. Next, the electrode wheels 6a and 6b clamp the welding start position of the welding locus. When the clamping is completed, the electrode wheel 6a,
The robot body 1 moves at a predetermined welding speed while applying a welding current while applying a welding current between the welding wheels 6b and the electrode wheels 6a, 6b corresponding to the welding speed.
Rotates. More specifically, in the present embodiment, not only the joint axes of the robot body 1 but also the drive axes of the electrode wheels 6a and 6b of the seam welding machine 5 are controlled by one robot as hardware. Since the apparatus is controlled, the rotation speed of the electrode wheels 6a and 6b in the operation program as software is numerically equal to the feed speed of the fuel tank 2, that is, the welding speed. This allows the CPU 1 to perform operations based on the operation program and feedback data from each drive axis.
The movement command output by the motor 1 to the servo drivers 8 and 9 is also synchronized with the rotation speed of the electrode wheels 6a and 6b and the feed speed of the fuel tank 2. Also,
With respect to welding conditions such as the pressing force of the electrode wheels 6a and 6b and the welding current, optimal welding conditions corresponding to the welding speed that changes momentarily during welding are uniquely selected from the memory 14, and the CPU 11 The welding conditions are output for. Thereby, the electrode wheel 6 is synchronized with the welding speed.
As the rotational speeds of a and 6b change, appropriate welding conditions according to the welding speed are selected. With the above configuration, unstable operation caused by the synchronization of the feed operation of the fuel tank 2 performed by the robot body 1 and the rotation of the electrode wheels 6a and 6b performed by the seam welding machine 5 is prevented. However, when an unexpected situation occurs, for example, when the workpiece holding device 3 is out of grip with the fuel tank 2 or when a different type of fuel tank is erroneously mixed, the welding is performed. This may cause a defect or, in the worst case, damage the drive shaft of the electrode wheel. Therefore, in order to cope with this, by providing a torque detector on the drive shaft of the electrode wheels 6a, 6b, the rotation torque of the electrode wheels 6a, 6b is constantly monitored, and the rotation torque is set to a preset torque limit value. When it exceeds, or when the applied pressure converted from the rotational torque exceeds a preset applied pressure limit value, the robot control device 7 detects an abnormality. When the robot control device 7 detects this abnormality, the robot control device 7 immediately releases the sandwiching state of the fuel tank 2 by the electrode wheels 6a and 6b, and the robot body 1 holding the fuel tank 2 performs seam welding. The operation control is performed so as to separate from the machine 5, whereby the abnormal state is eliminated in a short time. Since the electrode wheel is a consumable item,
As the welding operation is performed, the wear will occur. Due to this, for example, if the rotation speed of the electrode wheel is synchronized with the welding speed of the robot body based on the dimensions of the new electrode wheel before wear, the electrode wheel The peripheral speed of the electrode wheel becomes slower than the welding speed of the robot body due to the wear of the robot body. Occurs. Therefore, in order to cope with this problem, the wear amount of the electrode wheel, which wears as the welding operation is performed, is estimated from the welding results, and the rotation speed of the electrode wheel is corrected by the wear amount. In detail, the diameter of the electrode wheel (diameter of the electrode wheel) Dn when the electrode wheel is new and the amount of decrease in the electrode wheel diameter per rotation of the electrode wheel due to welding work, ie, the amount of wear L, are determined in advance by the robot. It is stored in the memory 14 in the control device 7.
The wear amount L per one rotation of the electrode wheel may be calculated based on, for example, past welding results. And
The following calculation is performed by using a rotation counter that counts each rotation of the electrode wheel. Assuming that the total number of revolutions from the new state of the electrode wheel counted by the revolution counter to the present is N, the current electrode wheel diameter Dc is Dc
= Dn-L x N. Assuming that the feed speed of the fuel tank 2 performed by the robot body 1, that is, the welding speed, is Vw, the rotation speed Ve of the electrode wheel for synchronizing with Vw is Ve = Vw.
/ (Π × Dc). By using the calculated rotation speed Ve of the electrode wheel, even if synchronization with the welding speed of the robot body is attempted based on the dimensions of the new electrode wheel before abrasion, the electrode wheel is worn according to the wear. Synchronization between the work feeding operation performed by the robot body and the rotation operation of the electrode wheels is achieved. It is not necessary to separately provide a counter as hardware for the rotation speed counter, and it is sufficient to use a soft counter provided in the control circuit of the robot controller 7. Needless to say, the rotation speed counter is reset when the electrode wheel is replaced with a new one. Further, in the present embodiment, the wear amount of the electrode wheel is calculated based on the wear amount per one rotation of the electrode wheel and the total number of rotations of the electrode wheel. However, as another means, a visual device or a touch sensor is used. Thus, the current electrode wheel diameter Dc may be directly measured, and the rotation speed Ve of the electrode wheel may be calculated. The embodiment of the present invention has been described above. In the present invention, the work feeding operation is performed by the industrial robot. However, the operation can be performed by, for example, a machining center, which can be easily diverted from the technology of the present invention. In detail, in general, each drive shaft is controlled under the control of one control device so that each drive shaft is also synchronously controlled in the machining center. For example, a work center is controlled by a three-axis controlled spindle of the machining center. If the control system is configured so that the holding device is attached and the drive shaft of the electrode wheel of the seam welding machine is an additional axis of the control device of the machining center, compared to the case where an industrial robot is used for the workpiece feeding operation, Therefore, the degree of freedom of the work is somewhat limited, but the same function can be provided. In the present embodiment, FIG.
Since the electrode axis servo driver 9 and the welding machine timer 10 are under the control of the robot controller 7 for controlling the robot body 1 as shown in FIG. 1, the feed operation of the fuel tank 2 and the operation of the electrode wheels 6a and 6b are performed. There is no time lag with respect to the synchronization with the rotation operation, and the change in the rotation speed of the electrode wheels 6a and 6b and the change in the welding conditions due to the change in the feed speed of the fuel tank 2 are based on the operation program stored in the robot controller 7. A plurality of types of welding speeds and a plurality of types of welding conditions are set to correspond to each other on a one-to-one basis.
It will be done easily. [0037] [0038] [0039] [0040] [0041] According to the present invention, when the electrode wheel is new
Calculated based on electrode wheel diameter and past welding results
The amount of wear of the electrode wheel per revolution of the electrode wheel due to welding work
One rotation of the electrode wheel, stored in advance in the robot controller
New electrode wheel with rotation counter that counts each time
Count the total number of rotations from the state to the present, and
Electrode wheel diameter when the electrode wheel is new
Current from the wear amount of the electrode wheel and the new condition of the electrode wheel.
Based on the total number of rotations up to the current
Calculated and synchronized with the welding speed based on the current electrode wheel diameter
Since the rotational speed of the electrode wheels and to correct to,
Even when the welding speed of the robot body is synchronized with the welding speed of the robot body based on the dimensions of the new electrode wheel before wear, the workpiece feeding operation (welding speed) performed by the robot body and the electrode wheel performed by the seam welding machine (Rotation speed of the electrode wheel) .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall configuration of a seam welding apparatus according to an embodiment of the present invention, which uses an articulated robot as an automatic feeder of an automobile fuel tank 2 as a work. FIG. FIG. 2 is a sectional view of a fuel tank 2. FIG. 3 shows a flange portion 2c of the fuel tank 2 and an electrode wheel 6a;
It is a perspective view which shows the positional relationship with 6b. FIG. 4 is a top view showing a state where the electrode wheel 6a is welding a straight line portion on a welding locus. FIG. 5 is a top view showing a state where an electrode wheel 6a is welding a corner portion on a welding locus. FIG. 6 is a diagram showing a changed part of a welding condition. FIG. 7 is a schematic diagram showing the overall configuration of a seam welding apparatus using an articulated robot as an automatic feeder of an automotive fuel tank 2 as a work in the prior art. [Description of Signs] 1 Robot main body 2 Fuel tank (work) 2a Upper member 2b of fuel tank 2 Lower member 2c of fuel tank 2 Welding locus 3 of fuel tank 2 Holding means of fuel tank 2 (C type frame) 4a, 4b Rotating shaft 5 for press-fitting support of fuel tank 2 Seam welding machine 6a, 6b Electrode wheel 7 Robot controller 8 Body axis servo driver 9 Electrode axis servo driver 10 Welding machine timer 11 CPU 12a, 12b Electrode wheel driving motor 13a, 13b Reduction gear 14 memory

Continuation of the front page (56) References JP-A-10-99972 (JP, A) JP-A-9-108843 (JP, A) JP-A-6-31463 (JP, A) JP-A-5-161980 (JP) JP-A-9-85452 (JP, A) JP-A-11-33734 (JP, A) JP-A-7-164160 (JP, A) JP-A-4-54577 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) B23K 11/24 B23K 1/06

Claims (1)

(57) [Claim 1] A work is held by a work holding device which is connected to the tip of an arm of an industrial robot and is movable in a plurality of axial directions, and is formed on the work. The welding locus in the flange is sandwiched between a pair of electrode wheels provided in the seam welding machine, and the welding locus is guided between the electrode wheels based on an operation program stored in a robot controller of an industrial robot. This is a seam welding method in which seam welding is performed by intermittently or continuously flowing an alternating current, in which an electrode wheel is used as an additional axis of a robot controller to drive each joint axis of an industrial robot. seam is synchronized with the driving of the electrode wheel, which when the welding speed switched based on the operation program by the to allow changing the rotational speed of the electrode wheels is synchronized with the welding speed In contact method, group electrode wheels to electrodes Wa径and past welding results when the new
One rotation of electrode wheel by welding work calculated based on
The wear amount of the electrode wheel is stored in advance in the robot controller.
In addition, a rotation counter that counts each rotation of the electrode wheel
The total number of revolutions from the new condition of the electrode wheel to the current
And und electrode Wa径when the electrode wheel is new, the electrode wheel 1 rotating
The amount of wear on the electrode wheel and whether the electrode wheel is new
Current electrode wheel based on the total number of revolutions from
Calculate the diameter and synchronize with the welding speed based on the current electrode wheel diameter.
The feature is that the rotation speed of the electrode wheel is corrected.
To seam welding method.