A laser cutting device and method for a vehicle body welding line

Abstract

The application discloses a laser cutting device and method for a vehicle body welding line, and relates to the technical field of laser cutting. A plurality of independent pressing execution units are controlled to press a workpiece at a first preset force value, and a first displacement value is recorded by a displacement sensor built in each pressing execution unit. The pressure of the pressing execution units is increased to a second preset force value to fully press the workpiece, and an actual contour point cloud is obtained by scanning a cutting region of the workpiece by using a contour scanning sensor. Meanwhile, a second displacement value of each pressing execution unit at this time is recorded. The application collects actual contour point cloud data of the workpiece, and completes normal offset compensation of a cutting track in combination with a theoretical model. Relying on displacement collection data of multiple groups of independent pressing execution units in double working conditions, stress release timing and early release distance are dynamically planned according to a cutting speed and a mechanism response characteristic, precise matching of a cutting process and stress release timing is realized, and local residual stress of the workpiece is released from the root.

Description

Technical Field

[0001] This invention relates to the field of laser cutting technology, and in particular to a laser cutting apparatus and method for a car body welding line. Background Technology

[0002] In the production of automotive body-in-white, after large body panels such as side panels, doors, and roofs undergo stamping and multi-station welding processes, issues such as assembly dimensional deviations and accumulated welding deformation commonly arise. These require laser cutting at the final welding station for trimming and precision hole cutting to ensure the assembly accuracy of body parts and the consistency of overall vehicle dimensions. Currently, laser cutting on welding lines generally employs a rigid fixture clamping method. After the workpiece is positioned by a fixed positioning structure, the laser robot completes the cutting operation according to an offline preset trajectory. Some processes utilize fixed pressure rollers to assist in clamping the workpiece and suppress sheet metal vibration during the cutting process.

[0003] Existing processing techniques have several inherent technical defects in actual mass production. First, after multiple welding processes, the workpiece retains a large amount of uneven residual stress. The rigid overall clamping method can only ensure the geometric position of the workpiece is fixed during cutting, but cannot identify the local stress distribution of the workpiece. After the cutting operation is completed and the clamping constraints are released, the residual stress inside the workpiece is released autonomously, causing the cut edge to spring back and deform, resulting in out-of-tolerance dimensions of the finished product and reducing the processing pass rate.

[0004] Secondly, the existing clamping structure uses a fixed pressure clamping method, which cannot adaptively adjust the clamping force according to the stress differences and deformation state of different areas of the workpiece. A uniform clamping force will result in local over-pressure or local under-pressure. Over-pressure will lock the local stress of the workpiece and concentrate it at the cutting gap, aggravating deformation defects after cutting. Under-pressure will cause the plate to vibrate during the cutting process, causing quality problems such as slag on the cut and uneven cut surface, making it difficult to achieve both processing accuracy and cut surface quality.

[0005] Meanwhile, existing laser cutting trajectories mostly use offline fixed programs, relying solely on a fixed height adjustment structure to maintain the distance between the laser head and the sheet metal. They do not perform real-time contour detection and trajectory compensation for post-weld workpiece deformation and assembly deviations. Accumulated welding deformation and workpiece clamping deviations cause the actual cutting path to deviate from the theoretical path, further reducing cutting dimensional accuracy and failing to meet the precision machining requirements of high-end automotive body parts.

[0006] Finally, traditional processes lack an adaptive stress release mechanism. The clamping force and stress release timing are fixed parameters, which cannot be dynamically adapted to the processing parameters based on the actual deformation and displacement data of the workpiece. This results in poor processing versatility, insufficient adaptability to different batches and workpieces with different deformation states, poor quality stability during production, and difficulty in meeting the high-efficiency, high-precision, and high-consistency production requirements of modern welding lines. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a laser cutting device and method for vehicle body welding lines. The technical solution adopted is as follows:

[0008] A laser cutting method for a car body welding line includes the following steps:

[0009] Step 1: The workpiece with the pre-welded parts completed is transported to the cutting station and initially positioned by the preliminary positioning unit;

[0010] Step 2: Control multiple independent clamping actuators to pre-clamp the workpiece with a first preset force value, and record the first displacement value through the displacement sensor built into each clamping actuator;

[0011] Step 3: Increase the pressure of the clamping execution unit to the second preset force value to fully clamp the workpiece, and use the contour scanning sensor to scan the area to be cut on the workpiece to obtain the actual contour point cloud; at the same time, record the second displacement value of each clamping execution unit at this time.

[0012] Step 4: Compare the actual contour point cloud with the theoretical workpiece model, calculate the normal offset of each point on the cutting path, and generate the compensated cutting trajectory; at the same time, assess the local stress near each clamping point based on the displacement change, and plan the clamping execution unit and release control parameters that need to perform pressure release during the cutting process.

[0013] Step 5: The laser cutting robot performs cutting along the compensated cutting trajectory; during the cutting process, the pressure of the corresponding clamping execution unit is reduced to the third preset force value according to the release control parameters in order to actively release local stress.

[0014] Step 6: After cutting is completed, all clamping units are unloaded, and the workpiece leaves the workstation.

[0015] Optionally, the first preset force value is the minimum clamping force required to overcome the workpiece's own weight and conform to the coarse positioning reference; the second preset force value is the full clamping force required to meet the cutting process requirements; the displacement sensor is a grating displacement sensor.

[0016] Optionally, the method for generating the compensated cutting trajectory in step 4 is:

[0017] Discretize the theoretical cutting path into a set of points. The normal vectors of each point on the surface of the theoretical workpiece are obtained. Searching for distance in the actual contour point cloud nearest point Calculate the normal offset , ; by compensation point Generate the compensated trajectory and simultaneously adjust the laser head attitude so that the nozzle axis is parallel to the normal of the actual surface at the compensation point.

[0018] Optionally, the method for determining the release control parameters in step 4 is as follows:

[0019] Calculate the displacement change corresponding to each clamping actuator. ,Will Units exceeding a preset threshold are marked as clamping execution units to be released; the positions of the clamping execution units to be released are mapped to the arc length coordinates of the cutting path, and the advance release distance is determined based on the cutting speed and the response time of the actuator. Before the path arc length reaches the associated position At this point, the pressure release of the clamping execution unit to be released is triggered, and the corresponding release control parameters are generated.

[0020] Optionally, the release control parameters also include a third preset force value. The third preset force value is based on the displacement change of the corresponding clamping actuator. With preset threshold The ratio relationship is determined. The calculation method is as follows:

[0021] ;in It is the first preset force value. For the release factor, satisfying , The maximum displacement change among all clamping actuators marked as pending release, or a preset upper displacement limit, when Time to take .

[0022] Optionally, in step 5, the process of controlling the pressure of the clamping actuator to decrease from the second preset force value to the third preset force value is carried out according to a preset pressure release slope. Executed, Determined by the following formula:

[0023] ;

[0024] in For the duration of release, , It is the current cutting speed, so that when the cutting focus reaches the associated position of the clamping execution unit to be released along the path arc length, the pressure drops to the third preset force value.

[0025] Optionally, the pressure release slope remains constant during the release process, when the actual pressure drop rate fed back by the displacement sensor built into the clamping actuator matches the preset pressure release slope. When the deviation exceeds the allowable range, the central controller issues an alarm signal and controls the laser cutting robot to pause cutting.

[0026] A laser cutting device for a car body welding line is provided to implement a laser cutting method for a car body welding line. The laser cutting device includes multiple independently controlled clamping execution units, a preliminary positioning unit, a contour sensor, a laser cutting robot, and a central controller. The preliminary positioning unit includes at least two positioning pins and multiple positioning support blocks. The positioning pins cooperate with positioning holes on the workpiece to achieve planar constraints. The upper surface of the positioning support blocks constitutes the support reference surface of the workpiece.

[0027] Multiple clamping actuators are discretely distributed and installed on the fixture base along the periphery of the area to be cut on the workpiece. Each clamping actuator includes a clamping arm, a clamping head, a drive unit, and a displacement sensor. One end of the clamping arm is hinged to the fixture base, and the clamping head is installed at the other end of the clamping arm. The drive unit is used to drive the clamping arm to swing around the hinge point to apply clamping force. The displacement sensor is installed between the clamping arm and the fixture base to detect the displacement of the clamping head in real time.

[0028] The laser cutting robot is equipped with a laser cutting head at its end; the contour scanning sensor is installed at the movable end of the laser cutting robot and located on one side of the laser cutting head, and is used to scan the area of ​​the workpiece to be cut and obtain the actual contour point cloud.

[0029] The central controller is communicatively connected to the drive unit, displacement sensor, contour sensor, laser cutting robot, and laser cutting head of each clamping execution unit, and is used to execute the following control logic: in the pre-clamping and full-clamping states, the displacement values ​​of each displacement sensor are collected and the displacement change is calculated; release control parameters are generated based on the displacement change; and during the cutting process, each clamping execution unit is controlled to release pressure based on the release control parameters.

[0030] Optionally, the clamping actuator is a servo electric cylinder.

[0031] Optionally, after the central controller completes the cutting trajectory compensation calculation, it sends the compensated cutting trajectory to the laser cutting robot for cutting; during the cutting process, the central controller controls the corresponding drive unit to perform pressure release actions in real time according to the release control parameters corresponding to each clamping execution unit.

[0032] In summary, the present invention has at least one of the following beneficial technical effects:

[0033] This invention provides a laser cutting device for car body welding lines. Through an integrated technical solution of real-time workpiece contour compensation, accurate identification of local stress, and dynamic pressure adaptive release, it solves the core problems of traditional rigid clamping cutting, such as springback deformation, dimensional deviation, and unstable cut surface quality. It has significant technical advantages and production application value.

[0034] By acquiring real-time point cloud data of the actual contour of the workpiece through a contour scanning sensor and combining it with a theoretical model to complete the normal offset compensation of the cutting trajectory, and simultaneously adapting the laser head posture, the cutting path error caused by workpiece deformation and clamping deviation is effectively eliminated, and the dimensional accuracy and contour matching degree of laser cutting are greatly improved.

[0035] By leveraging the dual-condition displacement acquisition data from multiple independent clamping actuators, the system accurately identifies the distribution of local residual stress in various areas of the workpiece and quantifies high-stress processing zones. Based on the cutting travel speed and mechanism response characteristics, the system dynamically plans the stress release timing and advance release distance, achieving precise matching between the cutting process and stress release sequence. This addresses the root cause of local residual stress in the workpiece, preventing post-cutting springback deformation and ensuring dimensional consistency in mass production. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of a laser cutting device for a car body welding line according to the present invention;

[0037] Figure 2 This is a schematic diagram illustrating the component connection principle of a laser cutting device for a car body welding line according to the present invention;

[0038] Figure 3 This is a schematic diagram of the pressure release slope in Embodiment 6 of the laser cutting method for a car body welding line of the present invention;

[0039] Figure 4 This is a schematic flowchart of a laser cutting method for a car body welding line according to the present invention;

[0040] Explanation of reference numerals in the attached drawings: 11, clamping execution unit; 111, clamping arm; 112, clamping head; 113, drive unit; 12, displacement sensor; 2, preliminary positioning unit; 3, contour sensor; 4, laser cutting robot; 41, laser cutting head; 10, central controller. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the accompanying drawings.

[0042] This invention discloses a laser cutting device and method for a car body welding line.

[0043] Reference Figures 1-4 Example 1: A laser cutting method for a car body welding line, comprising the following steps:

[0044] Step 1: The workpiece with the pre-welded parts completed is transported to the cutting station and initially positioned by the preliminary positioning unit 2.

[0045] Step 2: Control multiple independent clamping execution units 11 to pre-clamp the workpiece with a first preset force value, and record the first displacement value through the displacement sensor 12 built into each clamping execution unit 11;

[0046] Step 3: Increase the pressure of the clamping execution unit 11 to the second preset force value to fully clamp the workpiece, and use the contour scanning sensor to scan the area to be cut on the workpiece to obtain the actual contour point cloud; at the same time, record the second displacement value of each clamping execution unit at this time.

[0047] Step 4: Compare the actual contour point cloud with the theoretical workpiece model, calculate the normal offset of each point on the cutting path, and generate the compensated cutting trajectory; at the same time, assess the local stress near each clamping point based on the displacement change, and plan the clamping execution unit 11 and release control parameters that need to be executed to release pressure during the cutting process.

[0048] Step 5: The laser cutting robot 4 performs cutting along the compensated cutting trajectory; during the cutting process, the pressure of the corresponding clamping execution unit 11 is reduced to the third preset force value according to the release control parameters, so as to actively release local stress.

[0049] Step 6: After the cutting is completed, all clamping execution units 11 are unloaded, and the workpiece leaves the workstation.

[0050] By adopting the above technical solution, in step 1, the workpiece that has completed the pre-welding process is transported to the cutting station. The workpiece is the outer side panel of the vehicle body, which has been resistance-spot welded to parts such as the sill reinforcement plate and B-pillar reinforcement plate at the pre-welding station. Residual stress exists inside the workpiece due to the welding thermal cycle. After the workpiece is delivered to the cutting station via the conveyor roller or transport robot, it is initially positioned by the preliminary positioning unit 2. The preliminary positioning unit 2 is fixedly installed on the base platform of the cutting station. The workpiece falls or is pushed against the preliminary positioning unit 2 to complete the preliminary geometric constraints in the planar and height directions.

[0051] Step 2: The central controller 10 sends commands to the drive units 113 of each independently controlled clamping execution unit 11, controlling all clamping execution units 11 to operate synchronously with a first preset force value to apply a pre-clamping force to the workpiece. The specific value of the first preset force value is 200N. The clamping heads 112 of each clamping execution unit 11 move downward under the drive unit 113, contact the upper surface of the workpiece, and press the workpiece against the positioning support block of the preliminary positioning unit 2. After the pressure of each clamping execution unit 11 reaches the first preset force value and stabilizes, the central controller 10 collects and records the first displacement value d1_i through the displacement sensor 12 built into each clamping execution unit 11, where i is the number of the clamping execution unit 11, i takes values ​​from 1 to n, and n is the total number of clamping execution units 11.

[0052] Step 3: The central controller 10 increases the target pressure value of each clamping actuator 11 from the first preset force value to the second preset force value. The specific value of the second preset force value is 800N to meet the requirements of the laser cutting process for workpiece clamping stiffness. After the pressure of all clamping actuators 11 reaches the second preset force value and stabilizes, the contour scanning sensor 3 scans the area of ​​the workpiece to be cut. The contour scanning sensor 3 is a line laser contour meter, installed on the end flange of the laser cutting robot 4. Driven by the laser cutting robot 4, it runs along the preset scanning path, projects a laser line onto the workpiece surface and receives the reflected light to obtain the actual contour point cloud data of the area of ​​the workpiece to be cut. The scanning line width of the contour scanning sensor 3 is 50mm, the sampling frequency is 200Hz, and the scanning speed is 100mm / s. At the same time, the central controller 10 reads the values ​​of each displacement sensor 12 again, records them as the second displacement value d2_i, and stores them in the controller memory.

[0053] Step 4: The central controller 10 executes two parallel computing tasks. The first task is to perform best-fit registration between the actual contour point cloud and the theoretical workpiece model pre-stored in the central controller 10, calculate the normal offset of each point on the cutting path, and generate the compensated cutting trajectory. The second task is to calculate the displacement change Δdi corresponding to each displacement sensor 12. Based on the displacement change Δdi, the degree of local stress near the clamping point of each clamping actuator 11 is assessed, and the clamping actuator 11 that needs to perform pressure release during the cutting process and its corresponding release control parameters are planned.

[0054] Step 5: The laser cutting robot 4, carrying the laser cutting head 41, performs laser cutting on the workpiece along the compensated cutting trajectory. The laser cutting head 41 is a fiber laser cutting head, equipped with a focusing lens with a focal length of 125mm and a single-layer nozzle with a nozzle diameter of 1.5mm. The auxiliary gas is compressed air at a pressure of 0.8MPa. During the cutting process, the central controller 10 compares the arc length position of the current tool center point of the laser cutting robot 4 on the cutting trajectory with the trigger position recorded in the release control parameters in real time. When the arc length position reaches the trigger position of a certain pressure-releasing execution unit 11, the central controller 10 sends a command to the drive unit 113 of the pressure-releasing execution unit 11, controlling its pressure to decrease from a second preset force value to a corresponding third preset force value, so as to actively release the local internal stress in the area while the cutting contour is generated.

[0055] Step 6: After the entire cutting contour is processed, the central controller 10 sends an unloading command to the drive units 113 of all clamping execution units 11. The pressure of the clamping execution units 11 drops to zero, the clamping arms 111 are raised, and the clamping heads 112 are removed from the workpiece surface. The workpiece is then conveyed out of the cutting station by the conveying device and enters the next welding process.

[0056] Example 2: The first preset force value is the minimum clamping force required to overcome the workpiece's own weight and conform to the coarse positioning reference; the second preset force value is the full clamping force required to meet the cutting process requirements; the displacement sensor 12 is a grating displacement sensor.

[0057] By adopting the above technical solution, the first preset force value is the minimum clamping force required to overcome the workpiece's own weight and reliably fit the positioning support block of the preliminary positioning unit 2, as determined through experiments. The determination method is as follows: after coarse positioning is completed, the output force of each clamping execution unit 11 is gradually increased in increments of 10N. The displacement change of the clamping head 112 is monitored by the displacement sensor 12. When the displacement tends to stabilize and no longer increases significantly, the corresponding force value is the first preset force value.

[0058] The second preset force value is the full clamping force required by the laser cutting process. It is determined through modal hammer test and trial cutting test to ensure that the workpiece does not produce visible chatter marks under cutting excitation.

[0059] The displacement sensor 12 is a grating-type displacement sensor, and the output signal is an orthogonal differential TTL signal, which is acquired by the high-speed counting module in the central controller 10. The reading head of the grating-type displacement sensor 12 is installed on the side of the clamping arm 111, and the scale grating is attached to the fixed bracket of the fixture base. The relative movement between the reading head and the scale grating reflects the lifting displacement of the clamping head 112.

[0060] Example 3, the method for generating the compensated cutting trajectory in step 4 is as follows:

[0061] Discretize the theoretical cutting path into a set of points. The normal vectors of each point on the surface of the theoretical workpiece are obtained. Searching for distance in the actual contour point cloud nearest point Calculate the normal offset , ; by compensation point Generate the compensated trajectory and simultaneously adjust the laser head attitude so that the nozzle axis is parallel to the normal of the actual surface at the compensation point.

[0062] By adopting the above technical solution, firstly, the theoretical cutting path on the theoretical workpiece model stored in the central controller 10 is discretized with the arc length as the step size, and the step size Δs is 0.5mm, thus obtaining an ordered set of path points. j is numbered from 1 to m, where m is the total number of path points.

[0063] Secondly, query each path point in the surface data of the theoretical workpiece model. The surface normal vector at point , after normalization, is denoted as . .

[0064] Then, in the actual contour point cloud obtained in step 3, the nearest neighbor search algorithm is used to find the distance. The nearest point is denoted as The search radius is 2mm. If no valid point is found within this radius, then... Mark the point as uncompensable and trigger an alarm to prompt the operator to check the scan data.

[0065] Next, the normal offset is calculated. The calculation formula is: equal to vector minus With normal vector The dot product. If If the absolute value is greater than the preset maximum allowable compensation amount of 1.5mm, then... Cut off to ±1.5mm and generate an over-compensation alarm record.

[0066] Next, calculate the compensated path points. The calculation formula is: equal Plus and The product of all. Connect them in sequence to form the compensated cutting trajectory.

[0067] Finally, for each path point on the compensated cutting trajectory Re-estimate the normal direction. The specific method is as follows: In... A micro-cutting plane is fitted within the local neighborhood of the nearby actual contour point cloud, and the unit normal vector of this micro-cutting plane is taken as the normal of the actual surface of the workpiece at that point. The nozzle axis direction of the laser cutting head 41 is set to be parallel to this normal, thus completing the synchronous adjustment of the laser head attitude.

[0068] Example 4, the method for determining the release control parameter in step 4 is as follows:

[0069] Calculate the displacement change corresponding to each clamping actuator 11 ,Will Units exceeding a preset threshold are marked as clamping execution units 11 to be released; the position of the clamping execution unit 11 to be released is mapped to the arc length coordinate of the cutting path, and the advance release distance is determined based on the cutting speed and the response time of the actuator. Before the path arc length reaches the associated position At this point, the pressure release of the clamping execution unit 11 to be released is triggered, and the corresponding release control parameters are generated.

[0070] By adopting the above technical solution, the release control parameters include the marker of the unit to be released and the advance release distance. And the trigger arc length position. First, the central controller 10 reads the first displacement value of each displacement sensor 12 recorded in step 3 from memory. Second displacement value Calculate the displacement change Δ point by point. Δ equal minus The change in displacement Δ The physical meaning is: the absolute downward displacement generated by the clamping head 112 of the clamping actuator 11 during the transition from the pre-clamping state to the full clamping state in order to overcome the local elastic deformation and structural deflection of the workpiece.

[0071] Secondly, the displacement change Δ of each clamping actuator 11 With the preset threshold Δ A comparison is made. In this embodiment, a preset threshold Δ is used. The value is set at 0.3 mm. This value was obtained through extensive statistical measurements on the same batch of workpieces, and the upper limit of the normal process fluctuation range is set as the threshold. Δ A clamping actuator 11 with a diameter greater than 0.3 mm is marked as a clamping actuator 11 to be released.

[0072] Then, the coordinates of the projection point of the center of the clamping head 112 of the clamping execution unit 11 to be released onto the workpiece surface are mapped to the compensated arc length coordinates of the cutting trajectory. The nearest point of the arc length is taken as the associated position of the unit, and denoted as the associated arc length. If a unit to be released has a corresponding arc length point within a preset range on both sides of the cutting trajectory, it will be preferentially mapped to the side that is reached first in the cutting sequence.

[0073] Next, calculate the early release distance. The calculation formula is: equal Multiply Plus .in The current cutting speed, in this example Take 40 mm / s. For the response time of the implementing agency, Take 0.1s. To allow for a safe distance, Take 5mm. Substitute into the calculation to get... It equals 40 multiplied by 0.1 plus 5, which equals 9mm.

[0074] Finally, the trigger arc length position is generated. , Equal to the associated arc length minus When the tool center point of the laser cutting robot 4 moves along the compensated cutting trajectory to the arc length coordinate... At that time, the central controller 10 triggers the pressure release procedure of the pressure release execution unit 11 to be released.

[0075] Example 5: The release control parameters also include a third preset force value. The third preset force value is based on the displacement change of the corresponding clamping actuator 11. With preset threshold The ratio relationship is determined. The calculation method is as follows:

[0076] ;in It is the first preset force value. For the release factor, satisfying , The maximum value among all displacement changes of the clamping actuators 11 marked as to be released, or the preset upper limit value of displacement, when Time to take .

[0077] By adopting the above technical solution, the release control parameters also include a third preset force value. Each clamping actuator 11 marked as to be released corresponds to an independently calculated third preset force value, denoted as... .

[0078] The calculation formula is: equal Multiply by bracket 1, subtract α, multiply by the fraction, and the numerator of the fraction is... minus The denominator is minus The brackets indicate the end of the text.

[0079] The meanings and values ​​of each parameter in the formula are as follows: The first preset force value is set to 200N. α is the release factor, set to 0.8. The preset threshold is set to 0.3 mm. This represents the displacement change of the clamping actuator 11 to be released, as currently calculated. The determination rule is as follows: iterate through the displacement changes of all clamping actuators 11 marked as to be released, and take the maximum value as... If the displacement change of all units to be released is less than the preset upper displacement limit of 2.0 mm, then the maximum value will be used directly. If the maximum value exceeds 2.0 mm, then take... It equals 2.0mm.

[0080] When a certain clamping execution unit 11 to be released Greater than or equal to At that time, take Equal to 0N, meaning that the unit applies no pressure after release, and the clamping head 112 can detach from the workpiece surface.

[0081] The calculation process is illustrated using three typical units to be released as examples. The first unit... It is 0.5mm. It is 1.2mm, substituting it into the formula gives... Approximately 164N. (Second unit) It is 0.9mm. Approximately 93N. (Unit 3) It is 1.2mm. equal , It equals 0N.

[0082] Through this linear mapping, the larger the displacement change in a region, the smaller the residual clamping force after release, thus achieving the goal of actively releasing the force proportionally based on the degree of local stress.

[0083] In Example 6, the process of controlling the pressure of the clamping execution unit 11 to decrease from the second preset force value to the third preset force value in step 5 is based on a preset pressure release slope. Executed, Determined by the following formula:

[0084] ;

[0085] in For the duration of release, , It is the current cutting speed, so that when the cutting focus reaches the associated position of the clamping execution unit 11 to be released along the path arc length, the pressure drops to the third preset force value.

[0086] By adopting the above technical solution, the pressure of the clamping actuator 11 is controlled from the second preset force value. Reduce to the corresponding third preset force value The process is executed according to the preset pressure release slope Rs.

[0087] Pressure release slope The calculation formula is: equal minus Divide by F2 is the second preset force value, which is 800N. The formula for calculating the release duration is as follows: Equivalent to releasing distance in advance Divide by the current cutting speed . Take 9mm, Take 40mm / s, 9 divided by 40 equals 0.225s. The physical meaning of tr is: from the moment of release triggering, the cutting focus still needs 0.225s to reach the associated position of the clamping execution unit 11. This 0.225s is the available time window for pressure release.

[0088] Taking the first unit to be released in Example 5 as an example, The value is 164N, substituting it into the equation gives... This equals approximately 2827 N / s (800 minus 164 divided by 0.225). After triggering the release of this unit, the central controller 10 sends a force control command to the drive unit 113, causing the output force to decrease from 800 N to 164 N at a constant rate of 2827 N per second. The pressure reaches the target value at 0.225 s, at which point the cutting focus also moves to the associated position of the unit.

[0089] This timing matching ensures the smoothness of the release process, avoids pressure abrupt changes from disturbing the cutting quality, and ensures that local stress release is completed at the same time as the cutting contour is generated.

[0090] In Example 7, the pressure release slope remains constant during the release process. When the actual pressure drop rate fed back by the displacement sensor 12 built into the clamping actuator 11 is equal to the preset pressure release slope... When the deviation exceeds the allowable range, the central controller 10 issues an alarm signal and controls the laser cutting robot 4 to suspend cutting.

[0091] By adopting the above technical solution, the pressure release slope is... During the release process, the force is kept constant, meaning the central controller 10 controls the drive unit 113 to reduce force at a uniform rate. (Referring to Example 6) Taking the case of 2827 N / s as an example, the target pressure decreases by 2.827 N every 1 ms, the control cycle is 2 ms, and the force control command decreases by about 5.65 N per cycle.

[0092] During the release process, the displacement sensor 12 continuously feeds back the actual displacement value of the clamping head 112 to the central controller 10. The central controller 10 calculates the actual pressure drop rate in real time through differential calculation. Specifically, it performs linear fitting on the displacement values ​​of 10 consecutive sampling cycles and converts the fitting slope and the stiffness coefficient of the clamping actuator 11 into the force change rate.

[0093] If the calculated actual pressure drop rate is different from the preset pressure release slope The deviation exceeds the allowable range, that is, the absolute value of the deviation exceeds... 20% of, Taking 2827 N / s as an example, the allowable range is 2262 N / s to 3392 N / s. The central controller 10 determines that the pressure release execution is abnormal. The abnormality may be caused by the servo valve or cylinder of the drive unit 113 being stuck, the clamping head 112 sticking to the surface of the workpiece, or fluctuations in the air source pressure.

[0094] Upon detecting an anomaly, the central controller 10 executes the following safety action sequence: immediately issues an alarm signal, including an audible alarm and a flashing red indicator light; simultaneously, it controls the laser cutting robot 4 to pause its movement after completing the current cutting segment at the current trajectory point, and the laser stops emitting light. After the operator intervenes to check and troubleshoot the fault, and confirms the reset through the human-machine interface, the central controller 10 controls the laser cutting robot 4 to return to the pause point to continue cutting and subsequent pressure release actions.

[0095] Example 8: A laser cutting device for a car body welding line, used to implement a laser cutting method for a car body welding line. The laser cutting device includes multiple independently controlled clamping execution units 11, a preliminary positioning unit 2, a contour sensor 3, a laser cutting robot 4, and a central controller 10. The preliminary positioning unit 2 includes at least two positioning pins and multiple positioning support blocks. The positioning pins cooperate with the positioning holes on the workpiece to achieve planar constraints. The upper surface of the positioning support block constitutes the support reference surface of the workpiece.

[0096] Multiple clamping actuators 11 are discretely distributed and installed on the fixture base along the periphery of the area to be cut on the workpiece. Each clamping actuator 11 includes a clamping arm 111, a clamping head 112, a drive unit 113, and a displacement sensor 12. One end of the clamping arm 111 is hinged to the fixture base, and the clamping head 112 is installed at the other end of the clamping arm 111. The drive unit 113 is used to drive the clamping arm 111 to swing around the hinge point to apply clamping force. The displacement sensor 12 is installed between the clamping arm 111 and the fixture base to detect the displacement of the clamping head 112 in real time.

[0097] The laser cutting robot 4 is equipped with a laser cutting head 41 at its end; the contour scanning sensor 3 is installed at the movable end of the laser cutting robot 4 and located on one side of the laser cutting head 41, and is used to scan the area of ​​the workpiece to be cut and obtain the actual contour point cloud.

[0098] The central controller 10 is communicatively connected to the drive unit 113, displacement sensor 12, contour sensor 3, laser cutting robot 4, and laser cutting head 41 of each clamping execution unit 11, and is used to execute the following control logic: in the pre-clamping and full-clamping states, the displacement values ​​of each displacement sensor 12 are collected and the displacement change is calculated, the release control parameters are generated based on the displacement change, and during the cutting process, the pressure release is controlled by each clamping execution unit 11 according to the release control parameters.

[0099] By adopting the above technical solution, the central controller 10 is a CNC system with an industrial PC architecture, equipped with a real-time operating system, and has an EtherCAT fieldbus communication interface and at least 16 analog input channels for communication with each subsystem and signal acquisition.

[0100] The preliminary positioning unit 2 is fixedly installed on the base table of the cutting station. The preliminary positioning unit 2 includes two positioning pins and four positioning support blocks. One of the two positioning pins is a cylindrical pin, and the other is a diamond-shaped pin, which respectively mate with the main positioning hole and the secondary positioning hole on the workpiece to achieve complete constraint of the workpiece in the horizontal plane. The four positioning support blocks are rectangularly distributed, and their upper surfaces are precision-machined with a flatness better than 0.05mm. The upper surfaces of the four support blocks together constitute the support reference surface of the workpiece.

[0101] There are 12 clamping actuators 11, discretely distributed around the periphery of the workpiece to be cut area, and bolted to the fixture base. Each clamping actuator 11 includes a clamping arm 111, a clamping head 112, a drive unit 113, and a displacement sensor 12. The clamping arm 111 is a welded steel structure, one end of which is hinged to the support lug of the fixture base by a pin, and the other end has a threaded hole for mounting the clamping head 112. The clamping head 112 is made of brass, and a polyurethane gasket is embedded at the end to avoid scratching the workpiece surface. The drive unit 113 is a servo electric cylinder, with the tail of the cylinder hinged to the fixture base, and the piston rod end hinged to the middle of the clamping arm 111 by a spherical bearing. When the drive unit 113 extends or retracts, it drives the clamping arm 111 to swing around its hinge point, so that the clamping head 112 presses against the workpiece surface in an approximately vertical direction.

[0102] The displacement sensor 12 is a grating-type displacement sensor. The reading head is installed on the lower side of the clamping arm 111, and the scale grating is pasted on the vertical surface of the L-shaped bracket that is fixedly connected to the fixture base.

[0103] The contour scanning sensor 3 is a line laser contour transducer, model Keyence LJ-X8000 series or equivalent. The contour scanning sensor 3 is fixed to the end flange of the laser cutting robot 4 by a mounting bracket, located on one side of the laser cutting head 41, with the two axes offset by 150mm.

[0104] The laser cutting robot 4 is a six-axis industrial robot with a payload of no less than 50 kg and a repeatability better than 0.05 mm. A laser cutting head 41 and a contour scanning sensor 3 are simultaneously mounted on the end flange of the laser cutting robot 4. The six-axis rotation allows both to be aligned with the working position.

[0105] The central controller 10 is connected via EtherCAT bus to the servo driver of the drive unit 113 of each clamping execution unit 11, the signal acquisition module of the displacement sensor 12, the controller of the contour scanning sensor 3, the robot controller of the laser cutting robot 4, and the laser control unit of the laser cutting head 41.

[0106] The storage control logic executed by the central controller 10 is as follows: in the pre-compression state, force control commands are sent to the servo drivers of each drive unit 113, and the values ​​of each displacement sensor 12 are collected as the first displacement value. And store; under full compression, collect the values ​​of each displacement sensor 12 again as the second displacement value. And store; calculate the change in displacement. equal reduce Based on the displacement change Generate release control parameters for each clamping actuator 11 to be released. The release control parameters include the trigger arc length position. and the third preset force value During the cutting process of the laser cutting robot 4, the arc length coordinates of the current tool center point of the laser cutting robot 4 on the compensated cutting trajectory are read in real time. When the arc length coordinates reach a certain value... At that time, a pressure release slope is sent to the corresponding drive unit 113 according to the preset pressure release rate. The force reduction command was executed.

[0107] In Example 9, the clamping execution unit 11 is a servo electric cylinder.

[0108] By adopting the above technical solution, the drive unit 113 of the clamping actuator 11 is a servo electric cylinder. The servo electric cylinder is selected from models with built-in force sensors and consists of an AC servo motor, a planetary roller screw pair, a cylinder barrel, a piston rod, and a built-in force sensor, achieving high control precision.

[0109] In Example 10, after the central controller 10 completes the cutting trajectory compensation calculation, it sends the compensated cutting trajectory to the laser cutting robot 4 to perform cutting. During the cutting process, the central controller 10 controls the corresponding drive unit 113 to perform pressure release actions in real time according to the release control parameters corresponding to each clamping execution unit 11.

[0110] By adopting the above technical solution, after the central controller 10 completes the cutting trajectory compensation calculation, it converts the compensated cutting trajectory into a robot motion program executable by the laser cutting robot 4. The conversion process includes: converting the Cartesian coordinates and normal vectors of each path point on the compensated cutting trajectory into the pose matrix of the tool coordinate system of the laser cutting robot 4; performing TCP tool center point offset compensation considering the tool size of the laser cutting head 41; generating a continuous motion trajectory with an interpolation step size of 0.5mm; and sending the complete motion program to the robot controller of the laser cutting robot 4 via the EtherCAT bus.

[0111] During the cutting process, the central controller 10 controls the corresponding drive unit 113 to perform pressure release actions in real time according to the release control parameters corresponding to each clamping execution unit 11. Specifically, the central controller 10 maintains a release event table, and each record in the table includes the trigger arc length position. The target clamping execution unit 11 is numbered i, and the third preset force value is... and pressure release slope The central controller 10 operates on a 2ms control cycle. Within each cycle, it reads the current tool center point arc length coordinates fed back by the laser cutting robot 4, iterates through the release event table, and checks if there is a recorded trigger arc length position s_trig_i whose difference from the current arc length coordinate is less than or equal to zero and which has not yet been executed. If a record meeting these conditions exists, the central controller 10 sends a force control mode switching command and target force curve parameters to the servo driver of the clamping execution unit 11 (numbered i) via the EtherCAT bus. The servo driver then releases the pressure according to the received pressure release slope. Autonomous uniform rate force reduction control is implemented. During the force reduction process, the servo driver performs closed-loop force adjustment with a servo cycle of 0.5ms to ensure that the deviation between the actual output force and the target force curve does not exceed 10N.

[0112] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A laser cutting method for a car body welding line, characterized in that, Includes the following steps: Step 1: The workpiece with the pre-welded parts completed is transported to the cutting station and initially positioned by the preliminary positioning unit (2); Step 2: Control multiple independent clamping actuators (11) to pre-clamp the workpiece with a first preset force value, and record the first displacement value through the displacement sensor (12) built into each clamping actuator (11); Step 3: Increase the pressure of the clamping execution unit (11) to the second preset force value to fully clamp the workpiece, and use the contour scanning sensor to scan the area to be cut of the workpiece to obtain the actual contour point cloud; at the same time, record the second displacement value of each clamping execution unit at this time. Step 4: Compare the actual contour point cloud with the theoretical workpiece model, calculate the normal offset of each point on the cutting path, and generate the compensated cutting trajectory; at the same time, evaluate the local stress near each clamping point based on the displacement change, and plan the clamping execution unit (11) and release control parameters that need to be executed to release pressure during the cutting process. Step 5, the laser cutting robot (4) performs cutting along the compensated cutting trajectory; During the cutting process, the pressure of the corresponding clamping execution unit (11) is reduced to the third preset force value according to the release control parameters in order to actively release local stress; Step 6: After the cutting is completed, all clamping execution units (11) are unloaded and the workpiece leaves the workstation.

2. The laser cutting method for a car body welding line according to claim 1, characterized in that, The first preset force value is the minimum clamping force required to overcome the workpiece's own weight and conform to the coarse positioning reference; the second preset force value is the full clamping force to meet the cutting process requirements; the displacement sensor (12) is a grating displacement sensor.

3. The laser cutting method for a car body welding line according to claim 2, characterized in that, The method for generating the compensated cutting trajectory in step 4 is as follows: Discretize the theoretical cutting path into a set of points. The normal vectors of each point on the surface of the theoretical workpiece are obtained. Searching for distance in the actual contour point cloud nearest point Calculate the normal offset , ; by compensation point Generate the compensated trajectory and simultaneously adjust the laser head attitude so that the nozzle axis is parallel to the normal of the actual surface at the compensation point.

4. The laser cutting method for a car body welding line according to claim 3, characterized in that, The method for determining the release control parameters in step 4 is as follows: Calculate the displacement change corresponding to each clamping actuator (11) ,Will Units exceeding a preset threshold are marked as clamping execution units (11) to be released; the position of the clamping execution unit (11) to be released is mapped to the arc length coordinate of the cutting path, and the advance release distance is determined according to the cutting speed and the response time of the actuator. Before the path arc length reaches the associated position At this point, the pressure release of the clamping execution unit (11) to be released is triggered, and the corresponding release control parameters are generated.

5. The laser cutting method for a car body welding line according to claim 4, characterized in that, The release control parameters also include a third preset force value. The third preset force value is based on the displacement change of the corresponding clamping actuator (11). With preset threshold The ratio relationship is determined. The calculation method is as follows: ;in It is the first preset force value. For the release factor, satisfying , The maximum value among the displacement changes of all clamping actuators (11) marked as to be released, or the preset upper limit value of displacement, when Time to take .

6. The laser cutting method for a car body welding line according to claim 5, characterized in that, In step 5, the process of controlling the pressure of the clamping actuator (11) to decrease from the second preset force value to the third preset force value is carried out according to the preset pressure release slope. Executed, Determined by the following formula: ； in For the duration of release, , The current cutting speed is such that when the cutting focus reaches the associated position of the clamping actuator (11) to be released along the path arc length, the pressure drops to the third preset force value.

7. The laser cutting method for a car body welding line according to claim 6, characterized in that, The pressure release slope remains constant during the release process. When the actual pressure drop rate fed back by the displacement sensor (12) built into the clamping actuator (11) is equal to the preset pressure release slope... When the deviation exceeds the allowable range, the central controller (10) issues an alarm signal and controls the laser cutting robot (4) to suspend cutting.

8. A laser cutting device for a car body welding line, characterized in that, To implement the laser cutting method for a car body welding line as described in claim 7, the laser cutting device includes multiple independently controlled clamping execution units (11), a preliminary positioning unit (2), a contour sensor (3), a laser cutting robot (4), and a central controller (10). The preliminary positioning unit (2) includes at least two positioning pins and multiple positioning support blocks. The positioning pins cooperate with the positioning holes on the workpiece to achieve planar constraints. The upper surface of the positioning support block constitutes the support reference surface of the workpiece. Multiple clamping actuators (11) are discretely distributed and installed on the fixture base along the periphery of the workpiece to be cut area; the clamping actuator (11) includes a clamping arm (111), a clamping head (112), a drive unit (113), and a displacement sensor (12). One end of the clamping arm (111) is hinged to the fixture base, and the clamping head (112) is installed at the other end of the clamping arm (111). The drive unit (113) is used to drive the clamping arm (111) to swing around the hinge point to apply clamping force; the displacement sensor (12) is installed between the clamping arm (111) and the fixture base to detect the displacement of the clamping head (112) in real time. The laser cutting robot (4) is equipped with a laser cutting head (41) at its end; the contour scanning sensor (3) is installed at the movable end of the laser cutting robot (4) and located on one side of the laser cutting head (41), and is used to scan the area of ​​the workpiece to be cut and obtain the actual contour point cloud. The central controller (10) is connected to the drive unit (113), displacement sensor (12), contour sensor (3), laser cutting robot (4), and laser cutting head (41) of each clamping execution unit (11) respectively, and is used to execute the following control logic: in the pre-clamping and full-clamping states, the displacement values ​​of each displacement sensor (12) are collected and the displacement change is calculated, the release control parameters are generated according to the displacement change, and in the cutting process, the pressure release is controlled by each clamping execution unit (11) according to the release control parameters.

9. A laser cutting device for a car body welding line according to claim 8, characterized in that, The clamping actuator (11) is a servo electric cylinder.

10. A laser cutting device for a car body welding line according to claim 8, characterized in that, After the central controller (10) completes the cutting trajectory compensation calculation, it sends the compensated cutting trajectory to the laser cutting robot (4) to perform cutting. During the cutting process, the central controller (10) controls the corresponding drive unit (113) to perform pressure release action in real time according to the release control parameters corresponding to each clamping execution unit (11).

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