Spot welding gun and system and method for automatically calibrating welding quality by using spot welding gun

Abstract

A spot welding gun and a system and method for autonomously calibrating welding quality using the same, the system including: a spot welding gun configured to secure a welding target during a welding process, accurately measure a welding indentation depth, and perform autonomous welding quality calibration in response to an applied control signal; the welding robot is provided with a spot welding gun and is configured to move to a specified welding spot position; the welding controller is configured to control the welding current and the welding time of the point welding gun, and the welding quality is checked in real time by monitoring the welding indentation depth and the dynamic resistance in the welding process; and a welding quality manager configured to receive the welding quality inspection result from the welding controller, send a welding condition feedback change, and control autonomous welding quality calibration.

Description

Technical Field

[0001] The present invention relates to a spot welding gun and a system and method for autonomously calibrating welding quality using the spot welding gun. More specifically, the present invention relates to a spot welding gun for accurately measuring welding quality in real time and autonomously calibrating welding quality and a system and method for autonomously calibrating welding quality using the spot welding gun. Background Art

[0002] Typically, production lines at vehicle factories employ a large number of welding robots that automatically perform spot welding to join multiple components.

[0003] Spot welding is a welding method that involves fixing the welding target to the upper and lower welding nozzles provided on the spot welding gun installed on the welding robot, pressing the welding target, and applying high voltage current to the welding target. The welding operation is performed continuously and repeatedly at multiple welding points.

[0004] However, when a welding robot repeats a welding operation over time, welding quality may vary due to changes in materials (eg, welding targets) or equipment (eg, spot welding guns).

[0005] For example, Fig.17 The factors causing the welding quality variation during the welding process of the lower fixed spot welding gun in the prior art are shown.

[0006] Reference Fig.17 , due to changes in the material or thickness of the panel, the position of the panel set between the upper and lower welding tips of the welding gun may be raised or lowered from the normal position. In this case, excessive or insufficient welding indentation will occur, resulting in excessive welding separation and spatter, which will deteriorate the appearance quality of the vehicle.

[0007] Furthermore, in the case of the device, when the spot welding gun performs repeated welding operations, the welding quality may vary due to length changes caused by welding tip wear, length changes of the handle, bending of the welding gun arm, and sagging of the welding gun, etc. In addition, there is a problem that when a work variable occurs due to a change in the material / thickness of the welding target, the welding quality may change or vary depending on the skills of the welding robot teaching operator.

[0008] However, in the prior art, there is no function of checking welding quality problems or defects such as excessive weld indentation, weld separation, weld spatter, etc., or changes in welding quality from main calibration (eg, and implementation) using a spot welding gun.

[0009] Meanwhile, in the prior art, the welding quality is identified by measuring the current value provided from the welding controller and measuring the resistance value output after the welding process. However, in the actual mass production process, various resistance value fluctuations will occur in the welding part, which makes it difficult to accurately predict the welding quality by measuring the resistance value.

[0010] Therefore, in vehicle factories, welding quality managers perform manual offline inspections of welding quality. Alternatively, a separate welding inspection process is set up in the production line, and operators manually inspect welding quality using a semi-destructive sampling method. However, when operators manually perform semi-destructive inspections, there is a possibility that vehicles with welding defects are sent to post-process locations due to human error, resulting in problems such as reduced product reliability due to recalls of finished vehicles.

[0011] In addition, there is a problem that when a welding quality defect occurs, welding conditions are managed based on the experience of the welding quality manager regardless of data, resulting in delays in welding quality assurance and high costs during the new vehicle development stage and / or when factors that change welding quality occur.

[0012] The above information described in this Background section is provided only to enhance the understanding of the background of the present invention. Therefore, the Background section may contain information that does not constitute prior art known to a person of ordinary skill in the art. Summary of the invention

[0013] The present invention is directed to providing a spot welding gun having a mechanical part for fixing a reference surface of a welding part and accurately measuring a welding indentation depth of a welding target during spot welding.

[0014] The present invention is also directed to providing a system and method for autonomously calibrating welding quality, which can evaluate welding quality in real time by measuring the welding indentation depth of a welding target using a spot welding gun and autonomously calibrate the changing welding quality, thereby improving the reliability of welding quality.

[0015] An embodiment of the present invention provides a spot welding gun for autonomously calibrating welding quality. The spot welding gun includes: a first welding nozzle located at the upper part of the welding gun and a second welding nozzle located at the lower part of the welding gun; a robot mounting bracket configured to mount the first welding nozzle and the second welding nozzle on a welding robot; a welding pressing unit configured to press a welding target using compressed air supplied from an air compressor during welding, and accurately measure the welding indentation depth of a welded portion using an encoder directly connected to the rear side of the welding pressing unit; a welding transformer configured to supply a large current required during welding; an air balancing cylinder configured to prevent deformation of a reference measuring surface of a welded portion by realizing a balancing function of moving the second welding nozzle in a straight up and down direction using compressed air; and a linear guide unit configured to assist the straight up and down movement of the second welding nozzle.

[0016] In addition, when the welding target is higher or lower than the reference height, the air balance cylinder can perform a balancing function to raise or lower the lower portion of the welding gun with minimal force until the second welding tip of the lower portion of the welding gun touches the welding target.

[0017] In addition, the air balancing cylinder may include: an electric proportional pressure control valve configured to use a piston to adjust the main pressure of the compressed air to a low pressure corresponding to a minimum force, through which it can be identified whether the rising second welding nozzle touches the lower part of the welding target; a piston position sensor configured to monitor the movement of the piston and identify whether the second welding nozzle touches the welding target; and a pressure detection sensor configured to support feedback control for minimum force derivation by transmitting the pressure measured by the first port (P1) and the second port (P2) embedded in the air balancing cylinder to the electric proportional pressure control valve.

[0018] In addition, the pressure detection sensor can measure the air pressure introduced into the air balance cylinder through the first port (P1) and measure the exhaust pressure discharged to the outside through the second port (P2), and the pressure detection sensor can provide feedback to the electric proportional pressure control valve.

[0019] In addition, the electric proportional pressure control valve may receive feedback related to the air pressure in the first port (P1) and the exhaust pressure in the second port (P2), and control the movement of the second welding nozzle using the derived minimum force. When the movement of the piston stops as detected by the piston position sensor, the electric proportional pressure control valve may stop the movement of the second welding nozzle.

[0020] In addition, the piston position sensor may have a sensor line vertically installed inside the air balance cylinder, and detect whether the piston moves using a Hall effect generated between magnets installed on the piston.

[0021] In addition, the welding pressing unit may include a roller screw configured to convert the rotational motion of the magnetic servo motor into linear motion of the drive shaft, and may include an encoder connected in series to the rear end of the drive shaft and configured to accurately measure the position of the first welding nozzle mounted at the end of the drive shaft.

[0022] In addition, the encoder may measure the distance D of the first welding tip from the welding pressing unit according to the linear motion of the directly connected driving shaft. The welding start distance value D1 and the welding completion distance value D2 may be measured in a state where the first welding tip touches the upper surface of the welding target. The welding indentation depth may be calculated as a value obtained by subtracting the welding start distance value D1 from the welding completion distance value D2.

[0023] In addition, the linear guide unit may include: a linear guide rail arranged in a straight up and down direction; a linear guide bearing having a dual structure and configured to move the second welding nozzle along the linear guide rail; and a linear guide rail brake configured to fix the position of the second welding nozzle to accurately measure the welding indentation depth.

[0024] In addition, the linear guide brake may include: a friction member unit, configured to contact opposite sides of the linear guide and generate a braking force through friction; a friction member sliding unit, configured to guide the friction member unit in the direction of the linear guide; a piston driving unit, configured to apply braking pressure to the friction member unit; and an origin return unit, configured to use a spring to return the friction member unit that has completed the measurement of the welding indentation depth to the origin.

[0025] In addition, the linear guide brake can firmly fix the lower part of the welding gun by setting the braking force to a value higher than the upper pressing force generated by the welding pressing unit during welding.

[0026] Another embodiment of the present invention provides a system for autonomously calibrating welding quality using a spot welding gun. The system includes a spot welding gun, which constitutes a mechanical part that fixes the welding target during the welding process so that the reference measurement surface of the welding part is not deformed. The spot welding gun is configured to accurately measure the welding indentation depth and perform autonomous welding quality calibration in response to the applied control signal. The system also includes a welding robot, which is equipped with a spot welding gun and configured to move to a specified welding point position. The system also includes an air compressor, which is configured to supply high-pressure compressed air for pressing the welding part of the spot welding gun. The system also includes a welding controller, which is configured to control the welding current and welding time of the spot welding gun based on the initial welding conditions, and to check the welding quality in real time by monitoring the welding indentation depth and dynamic resistance measured by the spot welding gun during the welding process. The system also includes a welding quality manager, which is configured to receive the welding quality inspection result from the welding controller, send welding condition feedback changes according to the reference value conditions of the welding indentation depth and the dynamic resistance not being met, and control the autonomous welding quality calibration.

[0027] In addition, the welding quality manager can utilize a minimum force derivation feedback algorithm for realizing a balancing function for moving the lower portion of the welding gun in a straight line up and down direction, taking into account the welding gun direction of the spot welding gun that changes according to a plurality of welding point positions set for the welding target, and storing the minimum force and the minimum gas pressure as set values.

[0028] In addition, the welding controller can raise the welding gun lower part with minimum force by inputting the minimum air pressure set by the welding quality manager to the air balance cylinder, and at the same time lower the welding gun upper part by the welding pressing unit, so that the welding gun lower part and the welding gun upper part move until the welding gun lower part and the welding gun upper part contact each other with the welding target placed therebetween. The welding controller can press the upper and lower parts of the welding target in a force-balanced state by increasing the operating pressure of the air balance cylinder to raise the welding gun lower part according to the upper part pressing force of the welding pressing unit.

[0029] In addition, the welding controller can measure the welding current and the dynamic resistance R in real time while maintaining the pressing force of the upper part of the welding gun and the pressing force of the lower part of the welding gun during welding using the spot welding gun. The welding controller can measure the welding indentation depth by subtracting the welding start distance value D1 indicating that the upper part of the welding gun touches the upper part of the welding target from the welding completion distance value D2.

[0030] In addition, when the welding indentation depth and the upper limit value of the dynamic resistance do not meet the preset first reference value and the preset second reference value, the welding controller can determine that a welding separation defect (NG) or excessive spatter and welding defect (NG) occurs. The welding controller can also send the welding quality inspection result to the welding quality manager. The welding controller can also change at least one welding condition of the current value, the pressing force and the welding time according to the welding condition feedback change of the welding quality manager.

[0031] In addition, in the case of a weld separation defect (NG), the welding quality manager may perform welding power-on again at 50% of the initial welding condition, and send a welding condition feedback change message for increasing at least one of the current value and the pressing force to the welding controller. In the case of excessive spatter and a weld defect (NG), the welding quality manager may send a welding condition feedback change message for reducing at least one of the current value, the pressing force, and the welding time to the welding controller.

[0032] Another embodiment of the present invention provides a method for autonomously calibrating welding quality using a spot welding gun. The method includes the following steps: the spot welding gun is moved to a designated welding point position by a welding controller using a welding robot, and the lower part of the welding gun is raised with a minimum force by inputting a minimum air pressure into an air balance cylinder, and the upper part of the welding gun is lowered by a welding pressing unit, so that the lower part of the welding gun and the upper part of the welding gun are moved to contact each other and the welding target is placed between the two. The method also includes a welding step, by increasing the operating pressure of the air balance cylinder to raise the lower part of the welding gun according to the upper pressing force of the welding pressing unit, and pressing the upper and lower parts of the welding target in a force balance state. The method also includes measuring the welding current and dynamic resistance in real time while pressing the upper part of the welding gun during welding, and accurately measuring the welding indentation depth using an encoder directly connected to the rear side of the welding pressing unit. The method also includes sending the welding quality inspection result to the welding quality manager and requesting autonomous welding quality calibration when the welding indentation depth and the upper limit value of the dynamic resistance do not meet the preset first reference value and the preset second reference value. The method further includes analyzing the welding quality inspection result by the welding quality manager and sending a welding condition feedback change message corresponding to a welding separation defect (NG) or excessive spatter and welding defect (NG) to the welding controller.

[0033] In addition, the welding quality manager may execute a minimum force derivation feedback algorithm for a balancing function for moving the lower part of the welding gun in a straight line up and down direction. The minimum force derivation feedback algorithm may include: the welding quality manager inputs the weight of the lower part of the welding gun and the direction of the welding gun relative to the specified welding point; inputs the minimum air pressure of the air balance cylinder corresponding to the weight of the lower part of the welding gun, and uses the piston position sensor to monitor whether the air balance cylinder is operated; when the piston position sensor does not detect movement, it is determined that the lower part of the welding gun cannot move, and the air pressure is increased to a predetermined level; when the piston position sensor detects movement, the current air pressure is determined as the minimum air pressure Pm at which the lower part of the welding gun can move; and the minimum air pressure Pm and the minimum force of the lower part of the welding gun corresponding to the welding point position and the spot welding gun direction conditions are set as set values, and the set values ​​are stored.

[0034] In addition, the step of analyzing the welding quality inspection result may include determining that a welding separation defect (NG) occurs when the welding indentation depth is less than the lower limit value of the first reference value and the upper limit value of the dynamic resistance exceeds the upper limit value of the second reference value, performing welding power-on again at 50% of the initial welding condition, and generating a welding condition feedback change message for increasing at least one of the current value and the pressing force. The step of analyzing the welding quality inspection result may also include determining that excessive spatter and welding defects (NG) occur when the welding indentation depth exceeds the upper limit value of the first reference value and the upper limit value of the dynamic resistance is less than the lower limit value of the second reference value, and generating a welding condition feedback change message for reducing at least one of the current value, the pressing force, and the welding time.

[0035] According to an embodiment of the present invention, the welding quality can be checked in real time by accurately measuring the dynamic resistance and welding indentation depth using a spot welding gun during the welding process. Moreover, the changing welding quality can be calibrated autonomously, thereby preventing product defects and improving the reliability of welding quality.

[0036] In addition, by using the spot welding gun's linear guide unit and air balance cylinder and utilizing the balancing function that moves the lower part of the welding gun in a straight line up and down direction, deformation of the welding reference surface caused by materials and equipment can be prevented.

[0037] In addition, the spot welding gun is provided with a linear guide brake for preventing the lower part of the welding gun from sagging during welding, and the spot welding gun is provided with an encoder directly applied to the driving shaft of the welding pressing unit, so that the welding indentation depth can be accurately measured in real time during welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 : is a view schematically showing the configuration of a spot welding system for autonomously calibrating welding quality according to an embodiment of the present invention.

[0039] Figure 2is a view showing the configuration of a spot welding gun for autonomously calibrating welding quality according to an embodiment of the present invention.

[0040] Figure 3 1 is a view schematically showing the configuration of an air balance cylinder and a linear guide unit according to an embodiment of the present invention.

[0041] Figure 4 is a view showing an example in which a reference surface of a weld portion is deformed due to height fluctuation of the weld portion during spot welding in the related art.

[0042] Figure 5 : is a view showing an application example of the equalization function of the lower portion of the spot welding gun according to the embodiment of the present invention.

[0043] Figure 6 is a flow chart illustrating a minimum force derivation method using a minimum force derivation feedback algorithm according to an embodiment of the present invention.

[0044] Figure 7 is a view showing a minimum force derivation method for each welding gun direction using a minimum force derivation feedback algorithm according to an embodiment of the present invention.

[0045] Figure 8 1 is a view showing a method of controlling the pressing force of the lower portion of the welding gun when the equalizing function is applied according to an embodiment of the present invention.

[0046] Fig. 9 is a view illustrating a method of implementing an equalization function for preventing a welding object from being deformed during spot welding according to an embodiment of the present invention.

[0047] Fig.10 is a view showing the configuration of a mechanical part for accurately measuring a welding indentation depth according to an embodiment of the present invention.

[0048] Fig.11 is a view illustrating a welding quality evaluation method according to a correlation between a welding indentation depth and welding quality according to an embodiment of the present invention.

[0049] Fig.12 : is a view schematically showing a structure for operating a linear guide brake according to an embodiment of the present invention.

[0050] Fig.13 is a graph illustrating a method of inspecting welding quality in real time using a spot welding gun according to an embodiment of the present invention.

[0051] Fig.14 : is a view showing comparison between dynamic resistance graphs and welding indentation depths in a normal welding state, a welding separation state, and an excessive spatter & welding state according to an embodiment of the present invention.

[0052] Fig.15 is a flow chart schematically illustrating a method for autonomously calibrating welding quality using a spot welding gun according to an embodiment of the present invention.

[0053] Fig.16 is a flow chart schematically illustrating autonomous welding quality calibration logic of a welding quality manager according to an embodiment of the present invention.

[0054] Fig.17 : is a view showing welding quality variation factors in a welding process of a lower fixed spot welding gun of the related art.

[0055] <Description of Reference Numerals>

[0056] 10: Welding target 11: Upper panel

[0057] 12: Lower panel 1: System for autonomous calibration of welding quality

[0058] 100: Spot welding gun 111: First welding nozzle

[0059] 112: Second welding nozzle 113: Gun body

[0060] 120: Robot mounting bracket 130: Welding pressing unit

[0061] 131: Roller screw 132: Servo motor

[0062] 133: Encoder 134: Drive shaft

[0063] 140: Welding transformer

[0064] 150: Air balance cylinder 151: Electric proportional pressure control valve

[0065] 152: Piston position sensor 153: Pressure detection sensor

[0066] 154: Piston 155: Magnet

[0067] 160: Linear guide unit 161: Linear guide rail

[0068] 162: Linear guide bearing 163: Linear guide brake

[0069] 1631: Friction member unit 1632: Friction member sliding unit

[0070] 1633: Piston drive unit 1634: Origin return unit

[0071] 170: Cooling unit

[0072] 200: welding robot 300: air compressor

[0073] 400: welding controller 500: welding quality manager. DETAILED DESCRIPTION

[0074] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can practice the described embodiments.

[0075] The terms used herein are only used to illustrate the purpose of specific embodiments and are not intended to limit the present invention. Unless the context clearly states otherwise, the singular expressions used herein are intended to include plural expressions. It should be understood that the words "include" and / or "comprising" used in this specification refer to the presence of the features, integers, steps, operations, constituent elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, constituent elements, components and / or their combinations. The words "and / or" used herein include any one or all of the combinations of the relevant listed items.

[0076] Throughout the specification, terms such as "first", "second", "A", "B", "(a)", "(b)" and other numerical terms may be used herein only to describe various elements, but these elements should not be limited by these terms. These terms are used only for the purpose of distinguishing one constituent element from another constituent element, and the nature, order or sequence of the constituent elements are not limited by these terms.

[0077] Throughout the specification, when one constituent element is described as being “connected” or “coupled” to another constituent element, it should be understood that one constituent element may be directly connected or coupled to another constituent element, and that intermediate constituent elements may exist between these constituent elements. When one constituent element is described as being “directly connected to” or “directly coupled to” another constituent element, it should be understood that there are no intermediate constituent elements between these constituent elements.

[0078] Throughout the specification, the terms used herein are only used for the purpose of describing specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates a different meaning. When a component, device, element, etc. of the present invention is described as having a purpose or performing an operation, function, etc., the component, device or element should be considered herein as "configured to" meet the purpose or perform the operation or function.

[0079] In addition, it should be understood that one or more of the following methods or aspects thereof may be performed by at least one controller. The term "controller" may refer to a hardware device including a memory and a processor. The memory is configured to store program instructions, and the processor is specifically programmed to execute the program instructions to perform one or more processes described in more detail below. As described herein, a controller may control the operation of a unit, module, component, device, etc. In addition, it should be understood that, as one of ordinary skill in the art should recognize, the following methods may be performed by a device including a controller and one or more other components.

[0080] A spot welding gun according to an embodiment of the present invention and a system and method for autonomously calibrating welding quality using the spot welding gun will be described in detail with reference to the accompanying drawings.

[0081] Figure 1 : is a view schematically showing the configuration of a spot welding system for autonomously calibrating welding quality according to an embodiment of the present invention.

[0082] Reference Figure 1 , a system 1 for autonomously calibrating welding quality according to an embodiment of the present invention is installed to automatically perform spot welding to join welding targets (e.g., body panels) 10 continuously supplied on a production line of a vehicle factory. The welding target 10 may include an upper panel 11 and a lower panel 12, and is set by a jig or a conveyor for welding operation (see Figure 2 ).

[0083] The system 1 for autonomously calibrating welding quality includes a spot welding gun 100 , a welding robot 200 , an air compressor 300 , a welding controller 400 , and a welding quality manager 500 .

[0084] The spot welding gun 100 constitutes a mechanical part that fixes the welding target 10 during spot welding so that the reference measurement surface of the welding portion is not deformed. Therefore, the spot welding gun 100 accurately measures the welding indentation depth (thickness) and autonomously calibrates the welding quality in response to the applied control signal.

[0085] The welding robot 200 mounts the spot welding gun 100 on the arm end of the multi-joint structure and moves the spot welding gun 100 to a designated welding point position.

[0086] The air compressor 300 supplies high-pressure compressed air for pressing a welding portion of the spot welding gun 100 .

[0087] The welding controller 400 controls the welding current and welding time of the spot welding gun 100 based on the preset welding conditions (hereinafter referred to as "initial welding conditions"), and checks the welding quality in real time by monitoring the welding indentation depth and dynamic resistance measured by the spot welding gun 100 during the welding process. In this case, the welding controller 400 can determine whether normal welding quality is achieved by comprehensively evaluating the inspection results of the monitored welding indentation depth and dynamic resistance. In addition, the welding controller 400 may include a robot control device and control the motion posture (e.g., movement) of the welding robot 200 for spot welding.

[0088] The welding quality manager 500 sends welding condition feedback changes according to non-satisfaction (eg, failure to satisfy) of reference value conditions of welding indentation depth and dynamic resistance according to welding quality inspection results received from the welding controller 400, and controls autonomous welding quality calibration.

[0089] Therefore, the welding controller 400 may control the autonomous welding quality calibration by changing at least one of the current value, the pressing force, and the welding time set as the initial welding condition in response to the welding condition feedback change.

[0090] The system 1 for autonomously calibrating spot welding quality according to an embodiment of the present invention uses a spot welding gun 100 to accurately measure the welding indentation depth of a welding target in real time during spot welding. In addition, the system 1 for autonomously calibrating spot welding quality autonomously calibrates the welding quality that changes due to changes in the set position of the welding target and / or the equipment (e.g., the spot welding gun 100), thereby improving the reliability of the welding quality.

[0091] The spot welding gun 100 according to the purpose of the present invention is implemented to accurately measure the welding indentation depth (thickness) of the welding target in real time during the spot welding process and fine-tune the height of the lower portion of the welding gun, thereby autonomously calibrating the change in welding quality.

[0092] Figure 2 is a view showing the configuration of a spot welding gun for autonomously calibrating welding quality according to an embodiment of the present invention.

[0093] Reference Figure 2, the spot welding gun 100 according to the embodiment of the present invention includes a first welding nozzle 111 provided at the upper side of the welding gun, a second welding nozzle 112 provided at the lower side of the welding gun, and a robot mounting bracket 120 configured to mount the first welding nozzle 111 and the second welding nozzle 112 on the welding robot 200. In addition, the spot welding gun 100 includes a welding pressing unit 130 configured to press the welding target 10 using compressed air supplied from the air compressor 300 during welding, and accurately measure the welding indentation depth of the welded portion using an encoder directly connected to the rear side of the welding pressing unit 130. The spot welding gun 100 also includes: a welding transformer (TR) 140 configured to supply a necessary large current during welding; an air balancing cylinder 150 configured to prevent the reference measurement surface of the welded portion from being deformed by realizing a balancing function for moving the second welding nozzle 112 in a straight up and down direction using compressed air; and a linear guide unit 160 configured to guide the straight up and down movement of the second welding nozzle 112. In addition, the spot welding gun 100 may further include a cooling unit 170 configured to cool the first and second welding tips 111 and 112 by performing valve control (ON / OFF) to control the flow of a coolant and / or air during welding.

[0094] The first welding tip 111 disposed on the upper side is vertically connected to the welding pressing unit 130 .

[0095] The second welding nozzle 112 disposed at the lower side is connected to an air balancing cylinder 150 that performs a balancing function through a C-shaped gun body 113 and a linear guide unit 160 .

[0096] During the spot welding process, the first welding tip 111 and the second welding tip 112 are in contact with the upper panel 11 and the lower panel 12 of the welding target 10, respectively.

[0097] Hereinafter, throughout the specification, the first welding tip 111 may be referred to as the upper part of the welding gun, and the second welding tip 112 and the gun body 113 may be referred to as the lower part of the welding gun. However, the terms "upper part" and "lower part" should be understood to mean when based on Figure 2 The positions / directions in which the panels 11 and 12 and the welding tips 111 and 112 are placed are observed, and the directions are not limited thereto.

[0098] The welding robot 200 is equipped with a spot welding gun 100 of a type with a lower portion of the welding gun fixed, moves to a designated welding point, and is fixed in a state where the second welding tip 112 is in contact with the lower panel 12 of the welding target 10 .

[0099] The welding pressing unit 130 presses the upper panel 11 by lowering the first welding tip 111 in a state where the second welding tip 112 is fixed to the lower portion of the lower panel 12. In this case, the spot welding gun 100 fixes (eg, contacts) and presses the welding target 10 using the first welding tip 111 and the second welding tip 112.

[0100] In order to accurately measure the welding indentation depth of the welding target 10, the welding pressing unit 130 is configured as a mechanical part including a pressing actuator having a combination of a roller screw and a magnetic servo motor. A detailed description of the welding pressing unit is provided below.

[0101] In a state where the welding target 10 is fixed and pressed by the first welding nozzle 111 and the second welding nozzle 112 , the welding transformer 140 can convert the welding current supplied from the welding controller 400 into a large current suitable for spot welding and supply the large current to the first welding nozzle 111 and / or the second welding nozzle 112 .

[0102] Meanwhile, the spot welding gun 100 according to the embodiment of the present invention can accurately measure the welding indentation depth during the welding process of the welding target 10. In order to accurately measure the welding indentation depth, the following two conditions need to be met in advance.

[0103] As a first condition, the reference measurement surface of the weld portion for measuring the weld indentation depth needs to be free from deformation.

[0104] As a second condition, a mechanical structure is required that can measure an accurate position without causing the lower portion (ie, the second welding tip) of the spot welding gun 100 to sag during the measurement of the welding indentation depth.

[0105] Next, the first condition will be described.

[0106] The spot welding gun 100 according to the embodiment of the present invention includes an air balance cylinder 150 and a linear guide unit 160 as mechanical parts for preventing a reference measurement surface of a welding target 10 from being deformed during welding.

[0107] Figure 3 1 is a view schematically showing the configuration of an air balance cylinder and a linear guide unit according to an embodiment of the present invention.

[0108] Reference Figure 3 The air balance cylinder 150 includes an electric proportional pressure control valve 151, which is configured to use a piston 154 to adjust the main pressure of the high-pressure compressed air (for example, more than 5 bar) to a low pressure corresponding to the minimum force F3, through which it can be identified whether the rising second welding nozzle 112 touches (contacts) the lower part of the welding target 10. The balance cylinder 150 also includes a piston position sensor 152 and a pressure detection sensor 153, the piston position sensor 152 is configured to detect the movement of the piston and identify whether the second welding nozzle 112 touches the welding target 10, and the pressure detection sensor 153 is configured to transmit the pressure actually measured through the first port P1 and the second port P2 embedded in the air balance cylinder 150 to the electric proportional pressure control valve 151, thereby supporting feedback control for deriving the minimum force.

[0109] The linear guide unit 160 guides the linear up-and-down movement of the second welding nozzle 112 in conjunction with the air balance cylinder 150 , and fixes the second welding nozzle 112 so that the second welding nozzle 112 does not move during the process of measuring the welding indentation depth.

[0110] The linear guide unit 160 may include a linear guide rail 161 arranged in a straight up-and-down direction, a linear guide bearing 162 configured to move the second welding nozzle 112 along the linear guide rail 161, and a linear guide rail brake 163 configured to fix the position of the second welding nozzle 112 to accurately measure the welding indentation depth.

[0111] Next, the equalization function of the spot welding gun 100 for preventing the welding reference surface from being deformed even if the position of the welding target 10 is changed and / or the equipment is changed according to the first condition will be described.

[0112] first, Figure 4 is a view showing an example in which a reference surface of a weld portion is deformed due to height fluctuation of the weld portion during spot welding in the related art.

[0113] Reference Figure 4 As described above, the welding robot in the prior art performs spot welding while moving the lower welding nozzle fixed spot welding gun to multiple welding points according to the teaching conditions. In this case, when the welding target 10 is at a normal height coinciding with the reference measuring surface c, the welding target 10 is not deformed during the spot welding process. However, when the height of the welding target changes or the equipment changes, the welding quality changes, and the welding reference surface is deformed due to the pressing force of the welding robot (i.e., the pressing force of the welding pressing unit). In addition, in the case where high pressure is applied by the upper part of the welding gun due to the structural characteristics of the lower welding nozzle fixed spot welding gun, the welding reference surface may be deformed due to the sagging of the lower part of the welding gun.

[0114] When the reference surface of the welded portion is deformed due to the change in height of the welding target and the change in equipment as described above, there is a problem that the depth of the weld mark cannot be accurately measured.

[0115] Therefore, the spot welding gun 100 according to the embodiment of the present invention adopts the balancing function of the lower second welding tip 112 using the electric proportional pressure control valve 151, the piston position sensor 152, and the pressure detection sensor 153 included in the air balancing cylinder 150. Therefore, control is performed so as to prevent the welding reference surface from being deformed even if the position of the welding target 10 changes and / or the equipment is changed.

[0116] Next, Figure 5 : is a view showing an application example of the equalization function of the lower portion of the spot welding gun according to the embodiment of the present invention.

[0117] Reference Figure 5, when the welding target 10 is normally located at the reference height, the air balance cylinder 150 of the spot welding gun 100 according to the embodiment of the present invention performs normal welding, and the welded portion is not deformed.

[0118] In addition, even if the welding target 10 is higher or lower than the reference height, the air balance cylinder 150 performs a balancing function of raising or lowering the lower second welding nozzle 112 with a minimum force F3 until the lower second welding nozzle 112 touches the welding target 10, thereby preventing deformation of the weld.

[0119] In this case, the pressure detection sensor 153 measures the air pressure introduced into the air balance cylinder 150 through the first port P1 and measures the exhaust pressure discharged to the outside through the second port P2, and provides feedback to the electric proportional pressure control valve 151.

[0120] The electric proportional pressure control valve 151 receives feedback related to the air pressure in P1 and the exhaust pressure in P2 from the pressure detection sensor 153, and uses the derived minimum force F3 to control the movement of the second welding nozzle 112. In addition, when the piston position sensor 152 detects that the air balance cylinder 150 is stopped, the electric proportional pressure control valve 151 can determine that the second welding nozzle 112 touches the welding target 10, and the electric proportional pressure control valve 151 can stop the movement of the second welding nozzle 112.

[0121] As described above, even if the position of the welding target 10 changes and / or the equipment is changed, the spot welding gun 100 according to the embodiment of the present invention can compensate for the change by using the balancing function of the air balancing cylinder 150 and its electric proportional pressure control valve 151, the piston position sensor 152, and the pressure detection sensor 153. Therefore, the deformation of the welding reference surface during normal welding can be prevented.

[0122] Meanwhile, in order to realize the balancing function, it is necessary to obtain in advance the minimum force for preventing the welding surface from deforming when the second welding tip 112 touches the welding target 10 .

[0123] Return to reference Figure 3 In order to realize the balancing function, the air balancing cylinder 150 detects the time point when the second welding tip 112 touches the welding target 10 and sets a minimum force F3 for preventing the welding target 10 from being deformed.

[0124] For example, the minimum force F3 may be set to a set value derived by a minimum force derivation feedback algorithm of the weld quality manager 500 that supports autonomous weld quality calibration control of the weld controller 400 .

[0125] The welding quality manager 500 derives the minimum force F3 by finding the minimum air pressure that can move the air balance cylinder 150 using the input conditions, i.e., the weight of the second welding tip 112 (the weight of the lower part of the welding gun) and the spot welding gun direction (spot welding gun posture) relative to the welding point of the welding target 10. The minimum force F3 is a small unit of force applied when the second welding tip 112 contacts the weld target 10, and the minimum force F3 can be calculated based on the following equation 1.

[0126] (Equation 1)

[0127] F3=F2-F1=m*gA*Pm

[0128] Here, F3 represents the minimum force, A represents the piston area of ​​the air balance cylinder, Pm= represents the minimum air pressure that can move the lower part of the welding gun, F1=A*Pm represents the force of the air balance cylinder, and F2=m*g(weight of the lower part of the welding gun)*cosT.

[0129] at the same time, Figure 6 is a flow chart illustrating a minimum force derivation method using a minimum force derivation feedback algorithm according to an embodiment of the present invention.

[0130] Reference Figure 6 , the welding quality manager 500 inputs the weight of the lower part of the welding gun including the second welding nozzle 112 and the welding gun direction or orientation of the spot welding gun 100 relative to the specified welding point as the starting condition of the minimum force derivation feedback algorithm (S31). In this case, the welding gun direction can be obtained from the multi-axis angle value in the posture control information of the welding robot 200 that moves the spot welding gun 100 to the welding point.

[0131] The welding quality manager 500 inputs the minimum air pressure (F2≒F1) of the air balance cylinder 150 corresponding to the lower weight of the welding gun (S32), and monitors whether the air balance cylinder 150 is operating based on whether the piston position sensor 152 moves (ON / OFF) (S33).

[0132] In this case, when the movement of the piston position sensor 152 is not detected (S33: No), the welding quality manager 500 determines that the second welding nozzle 112 cannot be moved by the air balance cylinder 150, and increases the air pressure of the air balance cylinder 150 to a predetermined level until the air balance cylinder 150 moves (S34).

[0133] In contrast, when the movement is detected by the piston position sensor 152 (S33: YES), the welding quality manager 500 determines the current air pressure as the minimum air pressure Pm of the air balance cylinder 150 that can move the second welding tip 112 (S35).

[0134] The welding quality manager 500 sets Pm and the minimum force F3 of the second welding tip 112 corresponding to the conditions of the input welding point position and the input spot welding gun direction as set values ​​and stores the set values ​​(S36).

[0135] Meanwhile, using the above method, the welding quality manager 500 may derive and store the setting values ​​of the minimum force F3 and Pm in consideration of the welding gun direction of the spot welding gun that varies according to the plurality of welding point positions set to the welding target 10 .

[0136] For example, Figure 7 is a view showing a minimum force derivation method for each welding gun direction using a minimum force derivation feedback algorithm according to an embodiment of the present invention.

[0137] Reference Figure 7 As in Cases 1 to 4, the minimum force vector direction of the minimum force F3 for moving the air balance cylinder 150 changes according to the direction of the spot welding gun 100 (i.e., the welding robot posture). This is because the magnitude or amplitude and direction of the minimum force vector reaction force change with the change of the welding gun direction of the spot welding gun 100. Therefore, the minimum air pressures Pm1, Pm2, Pm3, and Pm4 for each case change.

[0138] In this case, according to the force and law, the minimum force vector reaction force has the value of the welding gun weight * cosT.

[0139] Therefore, as in Case 1, Case 2, and Case 3, in the case where the welding gun is directed downward, the exhaust pressure in P2 output is higher than the input pressure in P1 input to the air balance cylinder 150 .

[0140] On the contrary, when the welding gun is directed upward as in Case 4, the input pressure in P1 needs to be higher than the exhaust pressure in P2 in the air balance cylinder 150. This is because when the welding gun is directed upward as in Case 4, if the input pressure in P1 is lower than the exhaust pressure in P2, the lower part of the welding gun may fall strongly due to gravity, and the welding target 10 may be deformed.

[0141] Therefore, in order to prevent the welding reference surface from being deformed using the equalization function according to the embodiment of the present invention, it is very important to provide a minimum force derivation method that changes the set value according to the direction of the welding gun.

[0142] Therefore, if Figure 6 As shown, the welding quality manager 500 according to an embodiment of the present invention may consider the welding gun direction as an input condition of the minimum force derivation feedback algorithm to derive the minimum gas pressure Pm, and store the set value of the minimum gas pressure Pm.

[0143] Additionally, the weld quality manager 500 may automatically derive the minimum force F3 for each posture of the spot welding gun 100 through a minimum force derivation feedback algorithm and a piston position sensor 152 monitoring the operation of the air balance cylinder 150 .

[0144] Thus, a prior art teach operator may use the weld quality manager 500 to effectively perform an equalization setting operation without having to manually achieve the minimum force.

[0145] Figure 8 1 is a view showing a method of controlling the pressing force of the lower portion of the welding gun when the equalizing function is applied according to an embodiment of the present invention.

[0146] Reference Figure 8 In the air balance cylinder 150, the pressing force of the lower part of the welding gun regulated by the electric proportional pressure control valve 151 is determined according to the Pascal principle in consideration of the air pressure P and the cross-sectional area A of the cylinder piston.

[0147] The electric proportional pressure control valve 151 may adjust the air pressure input to the air balance cylinder 150 and is operated by a solenoid valve in response to an electric signal.

[0148] The electric proportional pressure control valve 151 can adjust the constant pressure in the cylinder by using a pressure sensor to monitor the air pressure input to the air balance cylinder 150 and the exhaust pressure output in real time. The electric proportional pressure control valve 151 can maintain a constant pressing force during welding or adjust the pressure of each step.

[0149] For example, in the case where the second welding tip 112 is intended to be raised and contact the lower portion of the welding target 10 , the electric proportional pressure control valve 151 may operate the air balance cylinder 150 using the minimum air pressure Pm set by applying the balance function.

[0150] Furthermore, in order to prevent the second welding tip 112 from sagging during the spot welding of the welding object 10 , the electric proportional pressure control valve 151 may operate the air balance cylinder 150 with an increased air pressure (eg, 5 bar).

[0151] The piston position sensor 152 has a sensor line vertically installed inside the air balance cylinder 150, and detects whether the piston moves by using the Hall effect generated between the magnets 155 installed on the piston 154. In other words, the sensor line of the piston position sensor 152 can detect whether the air balance cylinder 150 moves by using the principle of detecting the change of the Lorentz force generated by the Hall effect corresponding to the position change of the magnet 155 installed on the piston 154. In this case, it is obvious that when the piston position sensor 152 detects whether the air balance cylinder 150 moves, it can detect whether the connected second welding nozzle 112 moves up and down.

[0152] at the same time, Fig. 9 is a view illustrating a method of implementing an equalization function for preventing a welding object from being deformed during spot welding according to an embodiment of the present invention.

[0153] Reference Fig. 9 The balancing function according to the embodiment of the present invention can be controlled by the welding controller 400 for each step (section) during the welding process according to the time t when the spot welding gun 100 moves to the welding point position of the welding target 10.

[0154] First, the home position step (t0 to t1) is described.

[0155] When the spot welding gun 100 is moved by the welding robot 200 to the welding point position (original position) on the welding target 10, with the welding gun directed downward, the welding controller 400 maintains the operating pressure (P1-P2) of the air balance cylinder 150 to a predetermined main pressure (e.g., 5 bar).

[0156] Next, the lower panel touching step (t1 to t2) is described.

[0157] The welding controller 400 performs a balancing function so that the lower part of the welding gun is raised with a minimum force F3 by inputting the minimum air pressure Pm set by the minimum force derivation feedback algorithm of the welding quality manager 500 to the air balance cylinder 150, and the lower part of the welding gun is stopped when the lower part of the welding gun touches the lower part of the welding target 10. At the same time, the welding controller 400 lowers the upper part of the welding gun through the welding pressing unit 130 until the upper part of the welding gun contacts the welding target 10. In this case, the welding controller 400 can monitor the time point at which the upper part of the welding gun and the lower part of the welding gun touch the welding target 10 by detecting the motor torque reaction force detected by the servo motor of the welding pressing unit 130 that lowers the upper part of the welding gun, and detecting the stop of the piston position sensor 152 installed on the air balance cylinder 150 that raises the lower part of the welding gun. In this case, the piston position sensor 152 can monitor the piston movement of the air balance cylinder 150 and detect the touch of the lower part of the welding gun to the lower part of the welding target 10.

[0158] According to the balancing function of the present invention, even if any one of the upper part of the welding gun and the lower part of the welding gun first touches the welding target 10, the panel will not be deformed. For example, in the case where the upper part of the welding gun first touches the upper part of the welding target 10, due to the characteristics of the servo motor, the upper part of the welding gun applies a pressing force to the welding target only for a small time t, so that the reaction force generated by the pressing force of the upper part of the welding gun on the welding target 10 is not generated, so that the panel will not be deformed. In addition, in the case where the lower part of the welding gun first touches the lower part of the welding target 10, due to the deviation between the weight of the lower part of the welding gun (m*g) and the total force (△Pm*A) of the air balance cylinder to raise the lower part of the welding gun, the minimum force F3 applied to the lower part of the welding target 10 is very small, so that the panel will not be deformed.

[0159] Next, the welding execution steps (t2 to t3) are described.

[0160] When the welding controller 400 recognizes the time point at which the upper and lower parts of the welding gun contact each other, the welding controller 400 stops the raising of the lower part of the welding gun and changes the operating pressure (P1-P2) of the air balance cylinder 150 to a pressure equal to the weight (m*g) of the lower part of the welding gun. In addition, spot welding is performed by applying current in a bidirectional force balance state in which the upper and lower parts of the welding gun operate with almost equal values ​​of pressing force.

[0161] More specifically, during welding, the welding controller 400 starts pressing the upper portion of the welding target 10 by lowering the upper portion of the welding gun with the help of the welding pressing unit 130. In this case, since the first welding tip 111 of the upper portion of the welding gun presses the upper portion of the welding target 10 with a high pressing force of more than 200 kg, the lower portion of the welding gun may sag in a structure such as a cantilever beam in the prior art.

[0162] Therefore, the welding controller 400 of the present invention presses the two opposite parts of the welding target 10 in a force balance state by increasing the operating pressure of the air balance cylinder 150 to raise the lower part of the welding gun in accordance with the upper pressing force of the welding pressing unit 130. In other words, when the upper part of the welding gun presses the upper part of the welding target 10, the welding controller 400 can maintain the force balance state by increasing the rising pressure (for example, 5 bar) of the air balance cylinder 150 by means of the electric proportional pressure control valve 151, thereby preventing the lower part of the welding gun from sagging.

[0163] Next, the original position returning step (t3 to t4) is described.

[0164] When the spot welding is completed, the welding controller 400 releases the welding gun holding by raising the welding gun upper part and lowering the welding gun lower part, and returns the spot welding gun 100 to the original position or moves the spot welding gun 100 to a subsequent welding point position.

[0165] When lowering the welding gun lower portion, the welding controller 400 may perform control so that the operating pressure (P1-P2) of the air balance cylinder 150 is lower than the welding gun lower portion weight (m*g).

[0166] The first condition for preventing the reference measurement surface of the welded portion from being deformed has been described.

[0167] Hereinafter, a mechanical part capable of measuring an accurate position without causing the lower portion of the spot welding gun 100 to sag when measuring the welding indentation depth according to the second condition according to an embodiment of the present invention will be described.

[0168] First, the necessary background of the second condition is briefly explained.

[0169] Because the spot welding gun in the prior art has a mechanical structure in which the lower part is fixed in the form of a cantilever beam, when the upper part of the welding gun is pressed by the pressing unit during the welding process, the lower part of the welding gun sags excessively due to the torque generated at the lower part. In addition, the pressing unit at the upper part of the welding gun has a servo motor installed in parallel with the drive shaft, which is connected by a synchronous belt, and a ball screw is used to convert the rotational motion of the motor into a linear motion to operate the drive shaft. However, there is a mechanical problem that the data encoder attached to the rear side of the servo motor cannot accurately measure the position of the linear motion drive shaft due to many data measurement error generating factors such as the tension change of the synchronous belt, the wear of the ball screw, and the tolerance of the mechanical assembly.

[0170] Therefore, the spot welding gun 100 according to the embodiment of the present invention includes a welding pressing unit 130 and a linear guide unit 160 as mechanical parts for accurately measuring the welding indentation depth of the welding target 10 during welding. Hereinafter, the welding pressing unit 130 and the linear guide unit 160 will be described in more detail with reference to the accompanying drawings.

[0171] Fig.10 is a view showing the configuration of a mechanical part for accurately measuring a welding indentation depth according to an embodiment of the present invention.

[0172] Reference Fig.10 According to an embodiment of the present invention, the welding pressing unit 130 includes: a roller screw 131, which is configured to convert the rotational motion of the magnetic servo motor 132 into the linear motion of the driving shaft 134; and an encoder 133, which is serially connected to the rear end of the driving shaft 134 and is configured to accurately measure the position of the first welding nozzle 111 installed at the front end of the driving shaft.

[0173] The welding pressing unit 130 directly couples the roller screw 131 that transmits force to the driving shaft 134 in a linear direction to the servo motor 132 , and minimizes (≒zero) the occurrence of assembly tolerance and cumulative tolerance.

[0174] The encoder 133 may measure a distance D between the first welding tip 111 and the welding pressing unit 130 according to a linear motion of the directly connected driving shaft 134 .

[0175] The welding press unit 130 uses the encoder 133 to accurately measure the welding indentation depth a of the welding target 10 during the welding process.

[0176] For example, refer to Fig.10 In the mathematical modeling example in , the welding pressing unit 130 uses the encoder 133 to measure the welding start distance value D1 and the welding completion distance value D2 in the state where the first welding nozzle 111 touches the upper surface of the welding target 10 during the welding process. In addition, the welding indentation depth a can be calculated as a value obtained by subtracting D1 from D2. In essence, D1 represents the welding start position of the first welding nozzle 111, D2 represents the welding completion position of the first welding nozzle 111, and the welding indentation depth a can be measured based on the deviation (D2-D1) between the two positions.

[0177] The welding pressing unit 130 transmits the measured welding indentation depth a to the welding controller 400. The welding controller 400 receiving the measured welding indentation depth a can check whether the normal welding quality standard is met based on the welding indentation depth a and the thickness b of the welding target (upper panel) in consideration of welding quality correlation.

[0178] For example, Fig.11 is a view illustrating a welding quality evaluation method according to a correlation between a welding indentation depth and welding quality according to an embodiment of the present invention.

[0179] Reference Fig.11 , the welding controller 400 may check whether the welding indentation depth a made in consideration of the total thickness b of the welding target satisfies a preset first reference value (e.g., 15%=a / b*100(%)=30%). In this case, the first reference value includes a range of an upper limit value (30%) and a lower limit value (15%) of a normal indentation depth. The first reference value may be set by various experiments performed in consideration of the material, thickness, welding conditions, etc. of the welding target, or by learning using a pre-specified algorithm (e.g., simulation, program, and probability model).

[0180] For example, as in normal welding, when the welding indentation depth a satisfies a range within the range of the first reference value (eg, 15%=a / b*100(%)=30%), the welding controller 400 may determine that the weld nugget diameter and the welding strength are normal (OK).

[0181] On the contrary, like welding separation, when the welding indentation depth a is less than the lower limit value of the first reference value (for example, a / b*100(%)<15%), the welding controller 400 may determine that a welding separation defect (NG) occurs in which the welding indentation depth and the weld core diameter are less than normal values, resulting in deterioration of welding strength.

[0182] In addition, as with excessive indentation & spatter, when the welding indentation depth a exceeds the upper limit value of the first reference value (for example, a / b*100(%)>30%), the welding controller 400 may determine that a hole in the weld core caused by spatter has occurred, causing the welding strength to decrease, and the welding indentation depth is too large compared to the normal value, resulting in excessive spatter & welding defects (NG) with deteriorated appearance aesthetics.

[0183] Return to reference Fig.10 The linear guide unit 160 has the following mechanical part, which replaces the cantilever beam fixing structure in the prior art and uses a linear guide bearing 162 with a double structure coupled to the linear guide rail 161 to fix the second welding nozzle 112 at the lower part of the welding gun, thereby preventing the rotational movement caused by the rotational torque generated by the upper pressing force F1 during the welding process.

[0184] In addition, a linear guide brake 163 is applied between the double-structured linear guide bearings 162 to prevent the vertical movement of the second welding tip 112 caused by the upper pressing force F1 during welding. Therefore, it is possible to provide support for accurately measuring the welding indentation depth without error by preventing the second welding tip 112 from sagging during spot welding.

[0185] Fig.12 : is a view schematically showing a structure for operating a linear guide brake according to an embodiment of the present invention.

[0186] Reference Fig.12 The linear guide brake 163 includes: a friction member unit 1631, which is configured to contact opposite sides of the linear guide 161 and generate a braking force BK_F through friction; a friction member sliding unit 1632, which is configured to guide the friction member unit 1631 in the direction of the linear guide 161; a piston driving unit 1633, which is configured to apply braking pressure to the friction member unit 1631; and an origin return unit 1634, which is configured to use a spring to return the friction member unit 1631 that has completed the measurement of the welding indentation depth to the origin.

[0187] Next, a detailed operation sequence of the linear guide brake 163 will be described with reference to a cross-sectional view taken along line AA.

[0188] The friction member units 1631 disposed on opposite sides of the linear guide rail 161 slide forward horizontally by the air pressures p1 and p2 introduced into the air ports disposed in the piston driving part 1633 to generate a braking force BK_F. The braking force BK_F can fix the second welding nozzle 112 so that the second welding nozzle 112 at the lower portion of the spot welding gun 100 does not sag or move in a straight line direction during welding.

[0189] In this case, the braking force BK_F applied to the linear guide may be set to a value calculated using the following Equation 2.

[0190] (Equation 2)

[0191] BK_F=u1p1+u2p2

[0192] Here, μ1 and μ2 represent the friction coefficient of each friction member unit, and p1 and p2 represent the gas pressure*piston cross-sectional area applied when each friction member unit moves forward.

[0193] The linear guide brake 163 firmly fixes the lower part of the welding gun by setting the braking force BK_F to a value greater than the upper pressing force F1 generated by the welding pressing unit 130 during the welding process (BK_F2>>F1), thereby preventing the second welding tip 112 at the lower part of the welding gun from sagging or moving during the welding process (the process of measuring the welding indentation depth).

[0194] at the same time, Fig.13 is a graph illustrating a method of inspecting welding quality in real time using a spot welding gun according to an embodiment of the present invention.

[0195] Fig.14 : is a view showing comparison between dynamic resistance graphs and welding indentation depths in a normal welding state, a welding separation state, and an excessive spatter & welding state according to an embodiment of the present invention.

[0196] Reference Fig.13 and Fig.14 The welding controller 400 sets the welding time for each welding step (e.g., welding gun pressing, power on, welding gun holding / cooling, and welding gun opening) when setting welding conditions. In addition, the welding quality is checked in real time by collecting state data measured during the welding time, monitoring the welding indentation depth and dynamic resistance during the actual welding process.

[0197] The welding controller 400 can measure the welding indentation depth a corresponding to the axial position of the welding pressing portion during the inspection time in the welding gun holding step. Fig.11 As described above, the welding controller 400 may evaluate whether the normal welding quality standard is met based on the welding indentation depth a measured at the inspection time point in consideration of the welding quality correlation.

[0198] In addition, the welding controller 400 measures the voltage from the time when the welding gun is powered on, and uses Joule's law and Ohm's law to calculate the real-time dynamic resistance. In this case, the welding controller 400 can detect the upper limit value, lower limit value and height of the dynamic resistance through the dynamic resistance curve according to the welding time t, thereby predicting the welding quality according to the resistance change of the welded part.

[0199] In this case, the welding controller 400 may check whether the upper limit value Rp of the dynamic resistance measured until the inspection time of the welding gun holding step satisfies a preset second reference value (e.g., 85%=Rp=120%). In this case, the second reference value includes a range of an upper limit value (120%) and a lower limit value (85%) of normal dynamic resistance during welding. The second reference value may be set by various experiments taking into account the material, thickness, welding conditions (resistance and current) of the welding target, etc., or by learning using a pre-specified algorithm (e.g., simulation, program, and probability model).

[0200] For example, when the dynamic resistance upper limit value Rp satisfies a range within the range of the second reference value (eg, 85%=Rp=120%), the welding controller 400 may determine that the weld nugget diameter and the welding strength are normal (OK).

[0201] On the contrary, when the upper limit value of the dynamic resistance is less than the lower limit value of the second reference value (for example, the upper limit value of the dynamic resistance <85%), the welding controller 400 may determine that excessive spatter & welding defects (NG) have occurred, in which the panel thickness is reduced due to spatter and the welding strength is deteriorated due to the appearance of holes in the weld.

[0202] In addition, when the dynamic resistance upper limit value Rp exceeds the upper limit value of the second reference value (for example, Rp>120%), the welding controller 400 can determine that the welding process is not fully carried out, the panel thickness is increased, and the weld core diameter is small, resulting in a welding separation defect (NG) in which the welding strength is deteriorated.

[0203] The welding controller 400 collects state data measured during the welding process and checks the welding quality in real time based on the welding indentation depth and dynamic resistance. When the reference value condition is not satisfied, the welding controller 400 sends dissatisfaction to the welding quality manager 500 and requests autonomous welding quality calibration. In addition, autonomous welding quality calibration control can be performed by changing the initial welding condition based on the received welding condition feedback change in response to a request from the welding quality manager 500.

[0204] Meanwhile, a method of autonomously calibrating welding quality using a spot welding gun according to an embodiment of the present invention is explained with reference to the configuration of a system 1 for autonomously calibrating welding quality using a spot welding gun 100 .

[0205] The welding controller 400 and the welding quality manager 500 may each be implemented as one or more processors configured to be operated by a preset program. The preset program may be programmed to perform various steps of the method for autonomously calibrating welding quality using a spot welding gun according to an embodiment of the present invention.

[0206] Refer to the following Fig.15 and Fig.16 More specifically, a method for autonomously calibrating welding quality using a spot welding gun is described.

[0207] Fig.15 is a flow chart schematically illustrating a method for autonomously calibrating welding quality using a spot welding gun according to an embodiment of the present invention.

[0208] Reference Fig.15 , the welding controller 400 of the system 1 for autonomously calibrating welding quality using the spot welding gun 100 according to an embodiment of the present invention sets initial welding conditions for a designated welding point of the welding target 10 (S10). For example, the welding controller 400 may set a welding current value, a pressing force, and a welding time corresponding to input information such as a welding point ID of the welding target 10 and a material and a thickness of an upper panel.

[0209] The welding controller 400 moves the spot welding gun 100 to a designated welding point position through the welding robot 200 ( S20 ).

[0210] The welding controller 400 refers to the set value set by the welding quality manager 500 to prevent the weld from deforming (i.e., to achieve the balancing function), and identifies the minimum force F3 and the minimum air pressure Pm of the air balancing cylinder 150 corresponding to the welding point position and the welding gun direction (posture) (S30). In this case, the set value is a preset value derived in advance by the minimum force derivation feedback algorithm of the welding quality manager 500 (see Figure 6 ).

[0211] The welding controller 400 supplies the Pm pressure to the air balance cylinder 150 to raise the welding gun lower part with the minimum force F3, and at the same time lowers the welding gun upper part using the welding pressing unit 130, thereby moving the welding gun lower part and the welding gun upper part until the welding gun lower part and the welding gun upper part contact each other with the welding target 10 placed therebetween (S40).

[0212] In this case, the welding controller 400 monitors the movement of the upper part of the welding gun and the movement of the lower part of the welding gun, and identifies whether the upper part of the welding gun and the lower part of the welding gun both touch the welding target 10 (S50). When the welding controller 400 detects that the motor torque reaction force is generated by the servo motor of the welding pressing unit 130, the welding controller 400 identifies that the upper part of the welding gun touches the upper part of the welding target 10. In addition, the welding controller 400 can identify that the lower part of the welding gun touches the lower part of the welding target 10 by detecting that the movement of the piston stops by the piston position sensor 152 installed on the air balance cylinder 150.

[0213] When the welding gun upper part or the welding gun lower part does not touch the welding target 10 ( S50 : No), the welding controller 400 continues to lower the welding gun upper part or raise the welding gun lower part that does not touch the welding target 10 .

[0214] (S60).

[0215] On the contrary, at the time point when the welding controller 400 recognizes that both the upper part and the lower part of the welding gun touch the welding target 10 (S50: Yes), the welding controller 400 stops the raising of the lower part of the welding gun and changes the operating pressure (P1-P2) of the air balance cylinder 150 to a pressure equal to the weight of the lower part of the welding gun (m*g) (S70).

[0216] The welding controller 400 performs spot welding by applying current in a bidirectional force balance state in which the pressing force of the lower portion of the welding gun increases to be equal to the pressing force of the upper portion of the welding gun ( S80 ).

[0217] The welding controller 400 measures the welding current and the dynamic resistance R in real time while maintaining the pressing force of the upper portion of the welding gun and the pressing force of the lower portion of the welding gun during welding using the spot welding gun 100 ( S90 ).

[0218] In addition, the welding controller 400 operates the linear guide brake 163 for preventing the lower part of the welding gun from sagging at the inspection time point after the welding is completed, and the welding controller 400 accurately measures the welding indentation depth a (S100) using the encoder 133 directly connected to the rear side of the welding pressing unit 130. The welding indentation depth a can be calculated by subtracting the welding start distance value D1 from the welding completion distance value D2, and the welding start distance value D1 represents the distance from the reference position of the welding pressing unit 130 to the position where the upper part of the welding gun touches the upper part of the welding target 10.

[0219] The welding controller 400 checks the welding quality (S110) by determining whether the welding indentation depth a measured during the welding process meets the first reference value set to the normal range considering the welding target thickness (for example, 15% = a / b*100(%) = 30%), and whether the dynamic resistance upper limit value Rp meets the second reference value set to the normal dynamic resistance range (for example, 85% = Rp = 120%).

[0220] In this case, when the welding indentation depth a and the dynamic resistance upper limit value Rp satisfy the first reference value and the second reference value ( S110 : YES), the welding controller 400 opens the upper and lower parts of the welding gun and completes the welding process of the corresponding welding point ( S150 ).

[0221] On the contrary, when the welding indentation depth a and the dynamic resistance upper limit value Rp do not satisfy the preset first reference value and the preset second reference value (S110: No), the welding controller 400 sends the welding quality inspection result to the welding quality manager 500 and requests autonomous welding quality calibration (S120).

[0222] When the welding quality manager 500 receives the welding quality inspection result from the welding controller 400 ( S120 ), the welding quality manager 500 analyzes the received welding quality inspection result by executing the autonomous welding quality calibration logic ( S130 ).

[0223] The welding quality manager 500 determines a welding separation defect (NG) or excessive spatter & welding defect (NG) based on the analysis, generates a welding condition feedback change message for changing at least one of the current value, pressing force and welding time to cope with the defect, and sends the welding condition feedback change message to the welding controller 400 (S140).

[0224] Therefore, the welding quality manager 500 may manage the welding controller 400 so that the welding controller 400 performs autonomous welding quality control using the spot welding gun 100 .

[0225] at the same time, Fig.16 is a flow chart schematically illustrating autonomous welding quality calibration logic of a welding quality manager according to an embodiment of the present invention.

[0226] Reference Fig.16 , the autonomous welding quality calibration logic according to an embodiment of the present invention can be described as embodied Fig.15 Step S130 in .

[0227] The welding quality manager 500 analyzes the welding quality inspection result received from the welding controller 400 ( S130 ).

[0228] In this case, when the welding indentation depth a is less than the lower limit value of the first reference value (for example, a<15%) and the dynamic resistance upper limit value Rp exceeds the upper limit value of the second reference value (for example, Rp>120%) (S131: Yes), the welding quality manager 500 determines that a welding separation defect (NG) occurs in which the welding indentation depth and the weld core diameter are less than normal values, resulting in deterioration of welding strength (S132).

[0229] Therefore, based on the determination of the weld separation defect, the welding quality manager 500 performs welding power-on again with 50% of the initial welding condition (e.g., with 50% of the welding current, 50% of the welding time, and / or 50% of the welding pressing force) (S133), and generates a welding condition feedback change message for increasing at least one of the current value and the pressing force (S134). In addition, the welding quality manager 500 may send the generated welding condition feedback change message to the welding controller 400 (S140). Therefore, the welding controller 400 may cope with the subsequent weld separation defect (NG) by controlling the autonomous welding quality calibration that changes the welding condition according to the welding condition feedback change.

[0230] In addition, when step S131 is not satisfied (S131: No), when the welding indentation depth a exceeds the upper limit value of the first reference value (for example, a>30%) and the dynamic resistance upper limit value Rp is less than the lower limit value of the second reference value (for example, Rp<85%) (S135: Yes), the welding quality manager 500 can determine that excessive spatter & welding defects (NG) have occurred (S136).

[0231] Therefore, in response to the excessive spatter & welding defect (NG), the welding quality manager 500 generates a welding condition feedback change message for reducing at least one of the current value, the pressing force, and the welding time (S137). In addition, the welding quality manager 500 may send the generated welding condition feedback change message to the welding controller 400 (S140). Therefore, the welding controller 400 can cope with the subsequent excessive spatter & welding defect (NG) by controlling the autonomous welding quality calibration that changes the welding condition according to the welding condition feedback change.

[0232] However, the welding quality manager 500 can manage and instruct the welding controller 400 not to perform the welding process again on the welding target 10 that already has excessive spatter & welding defects (NG), but to stop the welding process so that the welding target 10 enters the appearance quality repair process.

[0233] As described above, according to an embodiment of the present invention, the welding quality can be checked in real time by accurately measuring the dynamic resistance and welding indentation depth using a spot welding gun during the welding process, and the changing welding quality can be autonomously calibrated, thereby preventing product defects and improving the reliability of welding quality.

[0234] In addition, by using the spot welding gun's linear guide unit and air balance cylinder and utilizing the balancing function that moves the lower part of the welding gun in a straight line up and down direction, deformation of the welding reference surface caused by materials and equipment can be prevented.

[0235] In addition, the spot welding gun is provided with a linear guide brake for preventing the lower part of the welding gun from sagging during welding, and the spot welding gun is provided with an encoder directly applied to the driving shaft of the welding pressing unit, so that the welding indentation depth can be accurately measured in real time during welding.

[0236] The embodiments of the inventive concept disclosed herein may be implemented by other devices and / or methods, and should not be construed as being limited to being implemented by the above-mentioned devices and methods. Based on the above description of the embodiments, a person of ordinary skill in the art to which the present invention belongs may easily implement the embodiments of the present invention by a program for implementing functions corresponding to the configuration of the embodiments of the present invention or by a recording medium (e.g., a computer-readable medium) having the program recorded thereon.

[0237] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto. It should be understood that various modifications and variations made by ordinary technicians in this field using the basic concept of the present invention defined in the appended claims are also included in the scope of the present invention.

Claims

1. A spot welding gun for autonomously calibrating welding quality, the spot welding gun comprising: A first welding nozzle located at the upper part of the welding gun and a second welding nozzle located at the lower part of the welding gun; a robot mounting bracket, configured to mount the first welding nozzle and the second welding nozzle on a welding robot; a welding press unit configured to press a welding target using compressed air supplied from an air compressor during welding and to accurately measure a welding indentation depth of a welded portion using an encoder directly connected to a rear side of the welding press unit; a welding transformer configured to supply the high current required during welding; an air balancing cylinder configured to prevent deformation of the reference measuring surface of the welding portion by realizing a balancing function of moving the second welding nozzle in a straight line up and down direction using compressed air; as well as A linear guide unit is configured to assist the linear up-and-down movement of the second welding nozzle.

2. The spot welding gun according to claim 1, wherein: When the welding target is higher or lower than a reference height, the air balance cylinder performs the balancing function, wherein the welding gun lower portion is raised or lowered with a minimum force until the second welding tip of the welding gun lower portion touches the welding target.

3. The spot welding gun according to claim 1, wherein: The air balance cylinder comprises: an electric proportional pressure control valve configured to adjust the main pressure of the compressed air to a low pressure corresponding to a minimum force by means of a piston, by which it is possible to identify whether the ascending second welding tip touches the lower part of the welding target; a piston position sensor configured to monitor the movement of the piston and identify whether the second welding tip touches the welding target; and A pressure detection sensor is configured to support feedback control for minimum force derivation by transmitting pressure measured using a first port (P1) and a second port (P2) embedded in the air balance cylinder to the electric proportional pressure control valve.

4. The spot welding gun according to claim 3, wherein: The pressure detection sensor measures the air pressure introduced into the air balance cylinder through the first port (P1) and measures the exhaust pressure discharged to the outside through the second port (P2), and provides feedback to the electric proportional pressure control valve.

5. The spot welding gun according to claim 3, wherein: The electric proportional pressure control valve receives feedback related to the gas pressure in the first port (P1) and the exhaust pressure in the second port (P2), and controls the movement of the second welding nozzle using the derived minimum force, and wherein, when the movement of the piston stops as detected by the piston position sensor, the electric proportional pressure control valve stops the movement of the second welding nozzle.

6. The spot welding gun according to claim 3, wherein: The piston position sensor has a sensor line vertically installed in the air balance cylinder, and detects whether the piston moves using a Hall effect generated between magnets installed on the piston.

7. The spot welding gun according to claim 1, wherein: The welding pressing unit comprises: a roller screw configured to convert the rotational motion of the magnetic servo motor into linear motion of the drive shaft; and The encoder is serially connected to the rear end of the driving shaft and is configured to accurately measure the position of the first welding nozzle installed at the end of the driving shaft.

8. The spot welding gun according to claim 7, wherein: The encoder measures the distance D between the first welding nozzle and the welding pressing unit according to the linear motion of the directly connected driving shaft, measures the welding start distance value D1 and the welding completion distance value D2 when the first welding nozzle touches the upper surface of the welding target, and calculates the welding indentation depth as the value obtained by subtracting the welding start distance value D1 from the welding completion distance value D2.

9. The spot welding gun according to claim 1, wherein: The linear guide unit comprises: Linear guides are set in a straight line up and down direction; a linear guide bearing having a dual structure and configured to move the second welding nozzle along the linear guide rail; and A linear guide brake is configured to fix the position of the second welding nozzle to accurately measure the welding indentation depth.

10. The spot welding gun according to claim 9, wherein: The linear guide brake comprises: a friction member unit configured to contact opposite sides of the linear guide rail and generate a braking force by friction; a friction member sliding unit configured to guide the friction member unit along the direction of the linear guide rail; a piston driving portion configured to apply a braking pressure to the friction member unit; and The origin returning unit is configured to return the friction member unit after the measurement of the welding indentation depth has been completed to the origin by using a spring.

11. The spot welding gun according to claim 9, wherein The linear guide brake firmly fixes the lower portion of the welding gun by setting the braking force to a value higher than the upper pressing force generated by the welding pressing unit during welding.

12. A system for autonomously calibrating welding quality using a spot welding gun, the system comprising: a spot welding gun constituting a mechanical portion for fixing a welding target during welding so that a reference measurement surface of a weld portion is not deformed, the spot welding gun being configured to accurately measure a welding indentation depth and to perform autonomous welding quality calibration in response to an applied control signal; a welding robot equipped with the spot welding gun and configured to move to a designated welding point position; an air compressor configured to supply high-pressure compressed air for pressing a welding portion of the spot welding gun; a welding controller configured to control a welding current and a welding time of the spot welding gun based on an initial welding condition, and to check welding quality in real time by monitoring a welding indentation depth and a dynamic resistance measured by the spot welding gun during welding; as well as A weld quality manager is configured to receive weld quality inspection results from the weld controller, send weld condition feedback changes according to the base value conditions of weld indentation depth and dynamic resistance not being satisfied, and control autonomous weld quality calibration.

13. The system according to claim 12, wherein: The welding quality manager utilizes a minimum force derivation feedback algorithm for realizing a balancing function of moving the lower portion of the welding gun in a straight line up and down direction, considers the welding gun direction of the spot welding gun that changes according to the positions of a plurality of welding points set for the welding target, and stores the minimum force and the minimum gas pressure as set values.

14. The system according to claim 12, wherein: The welding controller raises the lower part of the welding gun with minimum force by inputting the minimum air pressure set by the welding quality manager into the air balance cylinder, and lowers the upper part of the welding gun using the welding pressing unit, so that the lower part of the welding gun and the upper part of the welding gun are moved until the lower part of the welding gun and the upper part of the welding gun are in contact with each other and the welding target is placed therebetween, and wherein the welding controller presses the upper and lower parts of the welding target in a force-balanced state by increasing the operating pressure of the air balance cylinder to raise the lower part of the welding gun according to the upper pressing force of the welding pressing unit.

15. The system of claim 14, wherein: The welding controller measures the welding current and the dynamic resistance R in real time while maintaining the pressing force of the upper part of the welding gun and the pressing force of the lower part of the welding gun during welding using the spot welding gun, and wherein the welding controller measures the welding indentation depth by subtracting the welding start distance value D1 indicating that the upper part of the welding gun touches the upper part of the welding target from the welding completion distance value D2.

16. The system of claim 15, wherein: When the welding indentation depth and the upper limit value of the dynamic resistance do not meet the preset first reference value and the preset second reference value, the welding controller determines that a welding separation defect (NG) or excessive spatter and welding defect (NG) has occurred, and the welding controller sends the welding quality inspection result to the welding quality manager, and the welding controller changes at least one welding condition among the current value, pressing force and welding time according to the welding condition feedback change of the welding quality manager.

17. The system of claim 16, wherein: In the case of the welding separation defect (NG), the welding quality manager performs welding power-on again with 50% of the initial welding conditions, and sends a welding condition feedback change message for increasing at least one of the current value and the pressing force to the welding controller, and wherein, in the case of the excessive spatter and welding defect (NG), the welding quality manager sends a welding condition feedback change message for reducing at least one of the current value, the pressing force and the welding time to the welding controller.

18. A method for autonomously calibrating welding quality using a spot welding gun, the method comprising the following steps: The welding controller uses the welding robot to move the spot welding gun to a designated welding point position, and raises the lower part of the welding gun with a minimum force by inputting a minimum air pressure into the air balance cylinder, and lowers the upper part of the welding gun by using a welding pressing unit, so that the lower part of the welding gun and the upper part of the welding gun are moved to contact each other with a welding target placed therebetween; a welding step, wherein the upper and lower parts of the welding target are pressed in a force-balanced state by increasing the operating pressure of the air balance cylinder to raise the lower part of the welding gun according to the upper pressing force of the welding pressing unit; The welding current and dynamic resistance are measured in real time while pressing the upper part of the welding gun during welding, and the welding indentation depth is accurately measured using an encoder directly connected to the rear side of the welding pressing unit; When the welding indentation depth and the upper limit value of the dynamic resistance do not meet the preset first reference value and the preset second reference value, the welding quality inspection result is sent to the welding quality manager, and an autonomous welding quality calibration is requested; as well as The welding quality manager analyzes the welding quality inspection result and sends a welding condition feedback change message corresponding to a welding separation defect (NG) or excessive spatter and welding defect (NG) to the welding controller.

19. The method of claim 18, wherein: The welding quality manager implements a minimum force derived feedback algorithm for an equalizing function to move the lower portion of the welding gun in a straight up and down direction; and The minimum force derived feedback algorithm includes The welding quality manager inputs the weight of the lower part of the welding gun and the direction of the welding gun relative to the specified welding point, Input the minimum air pressure of the air balance cylinder corresponding to the weight of the lower part of the welding gun, and use the piston position sensor to monitor whether the air balance cylinder is operating, When the piston position sensor detects no movement, it is determined that the lower portion of the welding gun cannot move, and the gas pressure is increased to a predetermined level, When the piston position sensor detects movement, the current gas pressure is determined as the minimum gas pressure Pm at which the lower part of the welding gun can move, and The minimum gas pressure Pm and the minimum force at the lower part of the welding gun corresponding to the welding point position and the spot welding gun direction conditions are set as set values, and the set values ​​are stored.

20. The method according to claim 18, wherein: The step of analyzing the welding quality inspection result comprises: When the welding indentation depth is less than the lower limit value of the first reference value and the upper limit value of the dynamic resistance exceeds the upper limit value of the second reference value, it is determined that the welding separation defect (NG) occurs, welding energization is performed again at 50% of the initial welding condition, and a welding condition feedback change message for increasing at least one of a current value and a pressing force is generated; and When the welding indentation depth exceeds the upper limit value of the first reference value and the upper limit value of the dynamic resistance is less than the lower limit value of the second reference value, it is determined that excessive spatter and welding defect (NG) have occurred, and a welding condition feedback change message is generated to reduce at least one of the current value, pressing force and welding time.

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