Robotic welding system

Abstract

A robot welding system capable of appropriately performing welding even when the welding speed is high, even if the gap amount greatly changes. A robot welding system according to an embodiment of the present disclosure includes: a welding torch; a gap detector that detects a gap amount of a welding object in advance in front of the welding torch; a robot that moves the welding torch and the gap detector; a control device that changes a welding condition based on the gap amount detected in advance by the gap detector; and a welding power source that causes welding to be performed based on the welding condition instructed from the control device, wherein the control device changes the welding condition corresponding to an increase in the gap amount before the welding torch reaches a position where the gap amount changes in an increasing trend, and changes the welding condition corresponding to a decrease in the gap amount after the welding torch passes a position where the gap amount changes in a decreasing trend.

Description

Technical Field

[0001] This invention relates to a robotic welding system. Background Technology

[0002] The following system is proposed: In a robotic welding system in which a welding torch is moved by a robot to weld steel plates, a sensor is set for the robot to detect the size of the gap between the steel plates to be welded before the welding torch arrives, and welding conditions such as welding current, welding voltage, wire feed speed, and welding torch moving speed are changed according to the size of the pre-detected gap (see, for example, Patent Document 1).

[0003] In the robot system described in Patent Document 1, the robot control device includes: a welding condition table recording a range of gap lengths and welding conditions corresponding to the range of gap lengths; a region for storing condition mitigation parameters pre-stored as length information; and a condition mitigation calculation unit that, under normal circumstances, changes the welding conditions by referring to the welding condition table and the gap length currently detected by a sensor. The unit maintains the current welding conditions if the gap length currently detected by the sensor is smaller than the lower limit of the range of gap lengths corresponding to the current welding conditions in the welding condition table, but larger than the value obtained by subtracting the length specified by the condition mitigation parameters from the lower limit of the range of gap lengths. It also maintains the current welding conditions if the gap length currently detected by the sensor is larger than the upper limit of the range of gap lengths corresponding to the current welding conditions in the welding condition table, but smaller than the value obtained by adding the length specified by the condition mitigation parameters to the upper limit of the range of gap lengths. In the system of Patent Document 1, welding conditions can be stabilized even when the gap amount changes at short periods by delaying the change in welding conditions.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5428136 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] It is clear that, not only in the case of short-cycle variations, which are considered problematic in Patent Document 1, but also in the case of a large trend in increasing or decreasing gap amount, and in the case of high welding speed, it may be impossible to perform proper welding simply by corresponding the welding conditions to the changes in gap amount. Therefore, there is a need for a robotic welding system that can perform welding properly even when the gap amount changes significantly and when the welding speed is high.

[0009] Solution for solving the problem

[0010] One aspect of this disclosure relates to a robotic welding system comprising: a welding torch; a gap detector that pre-detects the gap amount of the workpiece to be welded in front of the welding torch; a robot for moving the welding torch and the gap detector; a control device that causes welding conditions to change based on the gap amount pre-detected by the gap detector; and a welding power source that causes welding to be performed based on welding conditions indicated by the control device, wherein the control device causes the welding conditions to change in accordance with an increase in the gap amount before the welding torch reaches a position where the gap amount tends to increase, and causes the welding conditions to change in accordance with a decrease in the gap amount after the welding torch passes a position where the gap amount tends to decrease.

[0011] The effects of the invention

[0012] The robotic welding system disclosed herein can perform welding appropriately even when the gap varies greatly and the welding speed is high. Attached Figure Description

[0013] Figure 1 This is a schematic diagram illustrating the structure of the robotic welding system according to the first embodiment of this disclosure.

[0014] Figure 2 It is shown Figure 1 A schematic diagram showing the relationship between the gap amount and welding conditions in a robotic welding system.

[0015] Figure 3 This is a schematic diagram illustrating the structure of the robotic welding system according to the second embodiment of this disclosure. Detailed Implementation

[0016] The embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 This is a schematic diagram showing the structure of the robotic welding system 1 according to the first embodiment of this disclosure.

[0017] Robotic welding system 1 is an apparatus for arc welding a first welding object W1 and a second welding object W2. Typically, the welding objects W1 and W2 are steel plates, arranged such that their facing ends overlap or their ends are butt-jointed. Robotic welding system 1 performs arc welding in a manner that forms a weld bead B along the end edge of one of the welding objects W1 and W2.

[0018] The robotic welding system 1 includes: a welding torch 10; a welding power source 20 for supplying welding current to the welding torch 10; a gap detector 30 for pre-detecting the gap between welding objects W1 and W2 in front of the welding torch 10; a robot 40 for moving the welding torch 10 and the gap detector 30; and a control device 50 for adjusting welding conditions based on the gap amount pre-detected by the gap detector 30.

[0019] As for the welding torch 10, a welding torch that uses consumable electrodes for gas-shielded welding, such as CO2 arc welding, MIG welding, and MAG welding, is particularly preferred. In addition, welding torches that use non-consumable electrodes, such as TIG welding, may also be used, and the use of welding torches for other welding methods is not excluded.

[0020] As the welding power source 20, a known power supply device that supplies welding current for performing arc welding to the welding torch 10 can be used. Preferably, the welding power source 20 is configured to adjust the value of the welding current or welding voltage in real time according to a setting signal input from the control device 50 described later.

[0021] The gap detector 30 detects the gap in the thickness direction between the first welding object W1 and the second welding object W2, that is, the height of the gap at the welding position between the first welding object W1 and the second welding object W2. The gap detector 30 can also be used as a tracking sensor to detect the path that the welding torch 10 should move, that is, the position of the welding line between the first welding object W1 and the second welding object W2.

[0022] The gap detector 30 detects the gap between the welding objects W1 and W2 in front of the moving direction of the welding torch 10. The distance between the welding position welded by the welding torch 10 and the gap detection position detected by the gap detector 30 can be set to, for example, 30 mm or more and 100 mm or less.

[0023] As the gap detector 30, for example, a sensor that uses a laser to scan along a direction to measure distance is used. Preferably, the gap detector 30 is held at the front end of the robot 40 that moves the welding torch 10, in a manner that scans along a direction perpendicular to the direction of movement of the robot 40 moving the welding torch 10 as described later to measure distance.

[0024] The robot 40 holds the welding torch 10 at its end portion, where its spatial position and orientation can be changed. Thus, the robot 40 is able to move the welding torch 10 in a manner that follows a desired trajectory. As described above, it is preferable that the robot 40 holds the gap detector 30 integrally with the welding torch 10.

[0025] Robot 40 is not particularly limited, but vertical articulated robots, horizontal articulated (SCARA) robots, parallel linkage robots, and Cartesian coordinate robots can be used. In addition, depending on the shape of the welding objects W1 and W2, robot 40 can also be a simple robot such as a positioner or actuator that feeds along one or two axes using a linear motor or the like.

[0026] The control device 50 controls the movement of the robot 40, causing the welding torch 10 to move along the welding line between the first welding object W1 and the second welding object W2, and changes the welding conditions to enable the first welding object W1 and the second welding object W2 to be welded appropriately. Examples of welding conditions that can be changed by the control device 50 include, for instance, the welding current supplied from the welding power source 20 to the welding torch 10, the welding voltage supplied to the welding torch 10, the moving speed (welding speed) of the welding torch 10, and the wire feed speed of the welding torch 10; one or more of these can be changed by the control device 50.

[0027] The control device 50 can be implemented by importing appropriate control programs into one or more computer devices having a CPU, memory, etc. The constituent elements of the control device 50 described later are derived from a classification of the functions of the control device 50, and their physical and program structures do not necessarily need to be clearly distinguished. Furthermore, the control device 50 may also have more constituent elements for implementing other functions.

[0028] The control device 50 controls the robot 40 and the welding power source 20 based on a welding program created according to the shapes of the welding objects W1 and W2, and the gap amount detected by the gap detector 30. The control device 50 adjusts the welding conditions to correspond to the increase in gap amount before the welding torch 10 reaches a position where the gap amount tends to increase, and adjusts the welding conditions to correspond to the decrease in gap amount after the welding torch 10 passes a position where the gap amount tends to decrease. Furthermore, "increasing trend" and "decreasing trend" mean a continuous increase or decrease at a significant rate of change.

[0029] The control device 50 can be configured to have an approximate output section 51, a variation range determination section 52, a reference value determination section 53, and a welding condition adjustment section 54.

[0030] The approximation derivation unit 51 derives an approximation formula that approximates the change in gap amount as a quadratic function of the welding position. Specifically, the approximation derivation unit 51 fits the measured values ​​of the gap amount at a certain range of welding positions centered on the welding position to be confirmed (hereinafter referred to as the confirmation position) using the least squares method, thereby deriving a quadratic approximation formula representing the change in gap amount near the confirmation position. That is, when the welding position is set as D and the gap amount is set as P, the gap amount P near the confirmation position is approximated as P = a × D using the coefficients a, b, and c calculated by the least squares method. 2 +b×D+c.

[0031] The variation range determination unit 52 determines the increasing range where the gap amount is increasing and the decreasing range where the gap amount is decreasing based on the approximation formula for each confirmed position. For example, the variation range determination unit 52 can be configured as follows: First, based on the quadratic term coefficient 'a' and the position of the extreme value (minimum or maximum value) in the approximation formula, it determines whether the gap amount at the confirmed position is decreasing or increasing. Then, it determines the range where the gap amount at the welding position continuously increases as an increasing range and the range where the gap amount at the welding position continuously decreases as a decreasing range. In the variation range determination unit 52, a minimum value is appropriately set for the continuous amount used to determine the increasing and decreasing ranges to eliminate short-period variations in the gap amount caused by measurement errors, etc.

[0032] As a specific example, the variation range determination unit 52 calculates the welding position where the approximation becomes an extreme value. If the position is confirmed to be to the left of the extreme value (the value of the welding position is small) and the quadratic coefficient 'a' is positive, the variation range determination unit 52 can determine that it is in a decreasing trend. If the position is confirmed to be to the right of the extreme value and the quadratic coefficient 'a' is positive, the variation range determination unit 52 can determine that it is in an increasing trend. If the position is confirmed to be to the left of the extreme value and the quadratic coefficient 'a' is negative, the variation range determination unit 52 can determine that it is in an increasing trend. If the position is confirmed to be to the right of the extreme value and the quadratic coefficient 'a' is negative, the variation range determination unit 52 can determine that it is in a decreasing trend. When the absolute value of the quadratic coefficient 'a' is small, it can also be determined that the gap amount is neither in an increasing trend nor a decreasing trend, but is stable. In the variation range determination unit 52, the value used to determine that the gap amount is stable is set to be sufficiently small compared to the maximum gap amount that can be welded.

[0033] Furthermore, the derivative of the quadratic function P, P' = 2a × D + b, represents the slope of P at the welding position D. Therefore, this derivative can also be used to determine whether the trend is increasing or decreasing. If P' is positive, it can be determined that the trend is increasing; if P' is negative, it can be determined that the trend is decreasing. If the absolute value of P' is small, it can be determined that the gap is neither increasing nor decreasing, but stable. Conversely, if the absolute value of P' is large, it can be determined that the gap is increasing or decreasing significantly.

[0034] The reference value determination unit 53 determines the reference value of the welding conditions for each welding position based on the gap amount. The reference value of the welding conditions is set such that the optimal welding value can be obtained when the gap amount is fixed at an ideal value, that is, when the first welding object W1 and the second welding object W2 are in ideal close contact. Specifically, the reference value determination unit 53 can be configured, for example, to determine the reference value of the welding conditions at each welding position using a reference table that associates the gap amount with the reference value of the welding conditions, or a conversion formula that expresses the welding conditions as a function of the gap amount. In addition, when the moving speed (welding speed) of the welding torch 10 changes, the reference value determination unit 53 can also determine the reference value of the welding conditions for each welding position by considering not only the gap amount but also the welding speed. Generally speaking, when at least one of the gap amount and the welding speed increases, it is necessary to increase at least one of the welding current value, voltage, and wire feed speed.

[0035] The welding condition adjustment unit 54 determines the value of the welding condition for each welding position by moving the reference value of the welding condition in the increasing interval backward in the welding direction (to the position where welding was performed earlier) (overriding the value of the welding condition at the welding position that is the destination of the move) and moving the reference value of the welding condition in the decreasing interval forward in the welding direction. The values ​​of the welding conditions between the starting point and the destination of the reference value movement can all be set to values ​​equal to the values ​​at the end of the data being moved. At the end of the data movement direction towards the destination of the reference value, the value of the welding condition may become discontinuous, but as long as the setting of the variation interval determination unit 52 is appropriate, it will not become a large change that would affect the welding.

[0036] The control device 50 may also include a movement amount setting unit, which is used by the user to preset at least one of the movement amount by which the welding condition adjustment unit 54 moves the reference value backward and the movement amount by which it moves the reference value forward. By providing a unit for setting each movement amount, the operation of the robot welding system 1 can be adjusted to perform more appropriate welding based on external conditions such as the thickness and material of the welding objects W1 and W2. In addition, for example, it is possible to set the following: by setting the forward movement amount to 0, the reference value is moved only when there is an increasing trend (movement backward), or by setting the backward movement amount to 0, the reference value is moved only when there is a decreasing trend (movement forward).

[0037] exist Figure 2 In the example of changing the welding current value as the welding condition, the relationship between the gap amount detected by the gap detector 30, the increase range, decrease range and stable range determined by the variation range determination unit 52, the reference value of the welding condition determined by the reference value determination unit 53, and the final welding condition adjusted by the welding condition adjustment unit 54 is shown.

[0038] The waveform of the reference value for welding conditions at the welding position, determined by the reference value determination unit 53, is based on the waveform of the gap amount detected by the gap detector 30 and the positional change. The variation range determination unit 52 determines the range where the slope of the gap amount waveform is above a predetermined positive value as the increasing range, the range where the slope of the gap amount waveform is below a predetermined negative value as the decreasing range, and all other ranges as the stable range.

[0039] The welding condition adjustment unit 54 moves the reference value of the welding condition in the increased interval backward and moves the reference value of the welding condition in the decreased interval forward, and replenishes the value of the interval that disappears due to the movement, thereby determining the waveform of the welding condition, that is, the welding current value that the welding power source 20 should output.

[0040] The welding condition at each welding position is also affected by the welding conditions at the welding positions immediately before and after that welding position. However, the control device 50 with the structure described above increases the deposition rate by adjusting the welding conditions at the welding positions immediately before and after the welding positions with large gaps, thus preventing poor connection of the welded objects W1 and W2. In other words, the robotic welding system 1 can perform welding appropriately even when the gap between the welded objects W1 and W2 changes with a large trend and when the welding speed is high.

[0041] Figure 3 This is a schematic diagram showing the structure of the robotic welding system 1A according to the second embodiment of this disclosure. Figure 3The robotic welding system 1A is used with Figure 1 The same purpose as the robotic welding system 1. Furthermore, for Figure 3 The robotic welding system 1A, sometimes for use with Figure 1 The same components of the robotic welding system 1 are labeled with the same reference numerals, and repeated descriptions are omitted.

[0042] The robotic welding system 1A includes: a welding torch 10; a welding power source 20 for supplying welding current to the welding torch 10; a gap detector 30 for pre-detecting the gap between welding objects W1 and W2 in front of the welding torch 10; a robot 40 for moving the welding torch 10 and the gap detector 30; and a control device 50A for adjusting the welding conditions of the welding power source 20 based on the gap amount pre-detected by the gap detector 30.

[0043] The control device 50A controls the movement of the robot 40 to move the welding torch 10 along the welding line between the first welding object W1 and the second welding object W2, and controls the output of the welding power supply 20 to supply welding conditions to the welding torch 10 that allow the first welding object W1 and the second welding object W2 to be properly welded. The control device 50A can be implemented by importing an appropriate control program into one or more computer devices having a CPU, memory, etc.

[0044] The control device 50A controls the robot 40 and the welding power source 20 based on a welding program created according to the shapes of the welding objects W1 and W2, and the gap amount detected by the gap detector 30. The control device 50A changes the welding conditions in accordance with the increase in gap amount before the welding torch 10 reaches the position where the gap amount tends to increase, and changes the welding conditions in accordance with the decrease in gap amount after the welding torch 10 passes the position where the gap amount tends to decrease.

[0045] The control device 50A includes a welding condition determination unit 55, which determines the welding conditions based on the maximum value of the gap amount within a predetermined setting range including the welding position. The welding condition determination unit 55 confirms the gap amount of the welding position within a predetermined range before and after the welding direction of the reference welding position where the welding conditions should be determined, and sets the welding condition corresponding to the maximum value of the gap amount as the welding condition at the reference welding position.

[0046] The welding condition determination unit 55 sets the welding conditions to the maximum value corresponding to the gap amount within the set range. Therefore, when the gap amount in the welding direction begins to increase, the welding conditions are quickly changed to match the increased gap amount. Conversely, if the gap amount in the current welding position begins to decrease but the gap amount in the welding direction does not begin to decrease, the welding conditions are not changed to match the gap amount before the decrease. This prevents poor connection of welded objects W1 and W2 at welding positions with large gap amounts or at high welding speeds.

[0047] The size of the setting range for the maximum value of the search gap can be, for example, set to twice the amount of movement of the welding torch 10 (twice as far forward and backward) until the amount of weld deposit (weld bead size) required when the gap is fixed at the assumed maximum value, thereby enabling reliable connection of the welding objects W1 and W2. Furthermore, if the welding condition determination unit 55 includes the moving speed of the welding torch 10 in the varying welding conditions, the size of the setting range can also be set to the size of the setting range that maximizes the moving speed of the welding torch 10.

[0048] Alternatively, the control device 50 may also have a size setting unit for presetting the size of a setting range, allowing the user to appropriately adjust the size of the setting range based on external conditions such as the thickness and material of the welding objects W1 and W2. Alternatively, the size of this setting range may be set to different sizes for the front and rear directions of the welding direction.

[0049] The welding condition determination unit 55 can also adjust the size of the setting range according to the welding speed. Specifically, the welding condition determination unit 55 can also increase or decrease the size of the setting range, that is, the length of the welding direction, proportionally to the moving speed of the welding torch 10.

[0050] The embodiments of the robotic welding system disclosed herein have been described above, but the scope of this disclosure is not limited to the above-described embodiments. Furthermore, the effects described in the above embodiments are merely examples of the optimal effects produced by the robotic welding system disclosed herein, and the effects of the robotic welding system disclosed herein are not limited to those described in the above embodiments.

[0051] In the robotic welding system disclosed herein, instead of deriving an approximation, a moving average or similar method can be used to eliminate short-period variations in the gap amount. Furthermore, when welding conditions are determined based on the maximum value of the gap amount within a set range, data after eliminating short-period variations through a moving average or similar method can be used as the gap amount value for each welding position.

[0052] Furthermore, in the robotic welding system disclosed herein, the welding power source enables welding to be performed based on welding conditions indicated by the control device, or it may not be necessary to directly supply current to the welding torch.

[0053] Explanation of reference numerals in the attached figures

[0054] 1, 1A: Welding system; 10: Welding torch; 20: Welding power source; 30: Gap detector; 40: Robot; 50, 50A: Control device; 51: Approximate output unit; 52: Variation range determination unit; 53: Reference value determination unit; 54: Welding condition adjustment unit; 55: Welding condition determination unit; W1, W2: Welding object.

Claims

1. A robotic welding system, comprising: Welding torch; A gap detector that pre-detects the gap amount of the workpiece to be welded in front of the welding torch; A robot is used to move the welding torch and the gap detector; A control device that adjusts welding conditions based on changes in the gap amount pre-detected by the gap detector; and A welding power source that enables welding to be performed based on welding conditions indicated from the control device. in, The control device causes the welding conditions to change in accordance with the increase of the gap amount before the welding torch reaches the position where the gap amount changes to an increasing trend, and causes the welding conditions to change in accordance with the decrease of the gap amount after the welding torch passes the position where the gap amount changes to a decreasing trend.

2. The robotic welding system according to claim 1, wherein, The control device has: The approximation derivation section derives an approximation that approximates the change in the gap amount as a quadratic function of the welding position; The variation range determination unit determines, based on the approximation formula, the increasing range where the gap amount is on an increasing trend and the decreasing range where the gap amount is on a decreasing trend; The reference value determination unit determines a reference value for the welding conditions based on the gap amount for each of the welding positions; as well as The welding condition adjustment unit determines the welding conditions for each welding position by moving the reference value of the increasing interval backward and moving the reference value of the decreasing interval forward.

3. The robotic welding system according to claim 2, wherein, The variable interval determination unit determines the increasing interval and the decreasing interval based on the coefficient of the quadratic term and the position of the extreme value in the approximation.

4. The robotic welding system according to claim 2 or 3, wherein, The control device further includes a movement amount setting unit, which is used to preset at least one of the backward movement amount of the reference value and the forward movement amount of the reference value.

5. The robotic welding system according to claim 2 or 3, wherein, The welding condition adjustment unit adjusts the movement amount of the reference value according to the moving speed of the welding torch.

6. The robotic welding system according to claim 1, wherein, The control device has a welding condition determination unit that determines the welding conditions based on the maximum value of the gap amount within a predetermined set range including the welding position.

7. The robotic welding system according to claim 6, wherein, The control device also has a size setting unit, which is used to preset the size of the set range.

8. The robotic welding system according to claim 6, wherein, The welding condition determination unit adjusts the size of the set range according to the moving speed of the welding torch.

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