A PLC-controlled method for compensating for lead screw errors in laser cutting machines

Abstract

This invention discloses a PLC-controlled laser cutting machine lead screw error compensation method, comprising the following steps: Step 1: Designing a backlash error compensation method and developing it into a PLC-controlled backlash error compensation module; Step 2: Designing a lead screw pitch error compensation method and developing it into a PLC-controlled lead screw pitch error compensation module; Step 3: Determining whether the feed axis has reversed movement; if so, proceeding to Step 4; otherwise, proceeding to Step 5; Step 4: Sending the target position to the backlash error compensation module, correcting the target position, and then sending the corrected target position to the lead screw pitch error compensation module to calculate the given position; Step 5: Sending the target position to the lead screw pitch error compensation module to calculate the given position; Step 6: The lead screw pitch error compensation module sends the given position to the motor controller, and the motor drives the lead screw to rotate, causing the slider and cutting head to move to the target position.

Description

Technical Field

[0001] This invention belongs to the field of laser processing technology and relates to a method for compensating for lead screw errors in a laser cutting machine based on PLC control. Background Technology

[0002] Laser cutting is currently applied in industries such as automotive, shipbuilding, aerospace, nuclear industry, machinery manufacturing, steel, textiles, and petroleum. Due to its advantages, including saving mold and material costs and shortening new product development and processing time, the demand for laser cutting technology is constantly increasing with the development of core technologies such as military and aerospace. In addition to general-purpose laser cutting machines, the demand for high-performance laser cutting systems, such as high-speed, high-precision laser cutting machines, large-format thick plate laser cutting machines, 3D CNC laser cutting machines, and aerospace non-ferrous metal laser cutting machines, is also growing rapidly. However, due to precision limitations, laser cutting equipment cannot yet replace metal cutting machine tools in fields requiring high precision. The penetration rate of laser cutting is relatively low, making improving the precision of laser cutting equipment a key issue. The mechanical error transmitted by the lead screw is the main factor affecting the processing accuracy of laser cutting machines. Therefore, a lead screw error compensation method is urgently needed to reduce the impact of the lead screw's mechanical errors on processing accuracy. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a PLC-controlled laser cutting machine lead screw error compensation method, which can reduce the impact of lead screw mechanical errors on machining accuracy.

[0004] This invention provides a method for compensating for lead screw errors in a laser cutting machine based on PLC control, comprising the following steps:

[0005] Step 1: Use a laser interferometer to measure the lead screw error data and backlash distance for each feed axis;

[0006] Step 2: Design a backlash error compensation method and develop it into a backlash error compensation module for PLC control;

[0007] Step 3: Design a lead screw pitch error compensation method and develop it into a lead screw pitch error compensation module controlled by PLC;

[0008] Step 4: Determine if the feed axis has reversed its movement. If so, proceed to step 5; otherwise, proceed to step 6.

[0009] Step 5: Send the target position to the backlash error compensation module to correct the target position, and then send the corrected target position to the lead screw pitch error compensation module to calculate the given position;

[0010] Step 6: Send the target position to the lead screw pitch error compensation module to calculate the given position;

[0011] Step 7: The lead screw pitch error compensation module sends the given position to the motor controller, and the motor drives the lead screw to rotate, which in turn moves the slider and the cutting head to the target position.

[0012] In the PLC-controlled laser cutting machine lead screw error compensation method of the present invention, the measurement of lead screw error data in step 1 specifically includes:

[0013] Step 1.1: Select N+1 discrete points uniformly on the lead screw. Let the distance between the discrete points be L. Then, the theoretical position of each discrete point on the standard lead screw is P. i =P0+i×L; i=0,1,...,N-1;

[0014] Step 1.2: Due to pitch error, the offset Δ of each discrete point on the lead screw to be compensated is measured using a laser interferometer. i The actual position of each discrete point is obtained as P. i ′=P i +Δ i Record the theoretical and actual positions of each discrete point.

[0015] In the PLC-controlled laser cutting machine lead screw error compensation method of the present invention, step 5, which sends the target position to the backlash error compensation module and modifies the target position, specifically involves:

[0016] Step 5.1: When the feed axis reverses, determine whether the backlash distance is greater than the maximum compensation value for a single control cycle. If it is, proceed to step 5.2; otherwise, proceed to step 5.3.

[0017] Step 5.2: Use the maximum compensation value for a single control cycle as the compensation distance;

[0018] Step 5.3: Use the backlash distance as the compensation distance;

[0019] Step 5.4: Increase the compensation distance to the target position to correct the target position, and send the corrected target position to the lead screw pitch error compensation module.

[0020] In the PLC-controlled laser cutting machine lead screw error compensation method of the present invention, when the backlash distance is greater than the maximum compensation value in a single control cycle, the compensation will be completed in multiple control cycles; the target position after correction in each control cycle is the target position of the previous control cycle plus the maximum compensation value in a single control cycle, and the backlash distance is added to the target position as the compensation distance in the last control cycle.

[0021] In the PLC-controlled laser cutting machine lead screw error compensation method of the present invention, the calculation of the given position through the lead screw pitch error compensation module specifically involves:

[0022] 1) Read the theoretical and actual positions of N+1 discrete points, and compare the target position P with the actual position P of any discrete point. i If P = P' i If P', then execute 2); i ′<P≤P i ′ +1 Then execute 3);

[0023] 2) The theoretical location P of the discrete point i As a given position Send to the driver;

[0024] 3) Assuming that the pitch of two adjacent discrete points is uniform and their positions are linearly related, then given a position Calculated using the following formula:

[0025]

[0026] 4) The given position is sent to the motor controller, and the motor drives the lead screw to rotate, which in turn moves the slider and the cutting head to the target position.

[0027] The PLC-controlled laser cutting machine lead screw error compensation method of the present invention further includes integrating the developed backlash error compensation module and lead screw pitch error compensation module into the IDE of the PLC program development.

[0028] The present invention provides a PLC-controlled method for compensating for lead screw errors in a laser cutting machine, which has at least the following advantages:

[0029] (1) The present invention compensates for the unavoidable mechanical error of the laser cutting machine body, improves the laser processing accuracy, and enables it to be more widely used in fields with high precision requirements.

[0030] (2) The error compensation method of the present invention can be implemented without other sensors, thus saving costs.

[0031] (3) The error compensation method is developed into two standard PLC function blocks, which can be easily reused in all laser cutting machines controlled on the same platform or other products with the same requirements. This saves development time and reduces development costs.

[0032] (4) The operation is simple for users, there is no threshold for use and no special training is required. Attached Figure Description

[0033] Figure 1This is a schematic diagram illustrating the causes of lead screw pitch error;

[0034] Figure 2 This is a schematic diagram of the pitch error compensation principle;

[0035] Figure 3 This is a schematic diagram illustrating the causes of backlash error;

[0036] Figure 4 This is a comparison chart of gap compensation;

[0037] Figure 5 This is a flowchart of a PLC-controlled laser cutting machine lead screw error compensation method according to the present invention;

[0038] Figure 6 It is a comparison curve of the ideal pitch, actual pitch, and compensated pitch for pitch error compensation. Detailed Implementation

[0039] The present invention provides a PLC-controlled laser cutting machine lead screw error compensation method, which mainly compensates for errors caused by two aspects: lead screw pitch error and backlash error.

[0040] Firstly, the X and Y axes of a typical laser cutting machine are the feed axes. Each feed axis motor drives a leadscrew to rotate, causing a slider on the leadscrew to move along it, ultimately moving the cutting head on the slider. Ideally, the threads on the laser cutting machine's leadscrew are evenly distributed, but due to limitations in machining precision, the actual threads are not perfectly uniform. Figure 1 The thread pitch shown has an error and the error varies at different positions of the lead screw. This will cause the actual position of the cutting head to not match the target position. At this time, it is necessary to perform thread pitch error compensation on the given position value sent to the drive controller to reduce or even eliminate the error and make the actual position the same as the target position.

[0041] like Figure 2 As shown, a certain feed axis of the laser cutting machine is made to advance a fixed distance each time, ideally with the position increasing uniformly each time. Due to the error in the thread pitch, the actual position will deviate from the ideal position each time, and a distance deviation value is measured at each step.

[0042] The idea behind lead screw pitch compensation is to establish a mapping relationship between the theoretical position on an ideal standard lead screw and the actual position on a non-standard lead screw. Through this mapping relationship, the theoretical position of the standard lead screw when the actual position equals the target position is found, and this theoretical position is sent to the driver as a given position value. After compensation, the actual position can be made equal to the target position.

[0043] Secondly, the transmission of force between the moving parts and their driving components, such as the lead screw and nut, in a laser cutting machine can be interrupted or delayed. This is because a completely gapless mechanical structure would significantly increase wear on the machine body, and it is also difficult to achieve from a manufacturing perspective. Figure 3 As shown, mechanical backlash causes a deviation Δe between the motion path of the shaft / spindle and the measurement value of the indirect measurement system. This means that once the direction changes, the shaft will move too far or too close, depending on the size of the backlash.

[0044] The idea behind backlash error compensation is to increase the backlash length by increasing the feed distance when the cutting machine's feed motion changes, thus compensating for the backlash. However, when the given backlash value is large, compensation may cause machine vibration, such as... Figure 4 As shown, compensation will be completed over multiple control cycles. The clearance values ​​for each axis can be measured using a laser interferometer during multiple reverse movements of the laser cutting machine.

[0045] like Figure 5 As shown, the present invention provides a PLC-controlled laser cutting machine lead screw error compensation method, comprising the following steps:

[0046] Step 1: Use a laser interferometer to measure the lead screw error data and backlash distance for each feed axis;

[0047] The specific steps for measuring the lead screw error data are as follows:

[0048] Step 1.1: Select N+1 discrete points uniformly on the lead screw. Let the distance between the discrete points be L. Then, the theoretical position of each discrete point on the standard lead screw is P. i =P0+i×L; i=0,1,...,N-1;

[0049] Step 1.2: Due to pitch error, the offset Δ of each discrete point on the lead screw to be compensated is measured using a laser interferometer. i The actual position of each discrete point is obtained as P. i ′=P i +Δ i Record the theoretical and actual positions of each discrete point.

[0050] Step 2: Design a backlash error compensation method and develop it into a backlash error compensation module for PLC control;

[0051] Step 3: Design a lead screw pitch error compensation method and develop it into a lead screw pitch error compensation module controlled by PLC;

[0052] Step 4: Determine if the feed axis has reversed its movement. If so, proceed to step 5; otherwise, proceed to step 6.

[0053] Step 5: Send the target position to the backlash error compensation module to correct the target position, and then send the corrected target position to the lead screw pitch error compensation module to calculate the given position;

[0054] The specific steps to modify the target location are as follows:

[0055] Step 5.1: When the feed axis reverses, determine whether the backlash distance is greater than the maximum compensation value for a single control cycle. If it is, proceed to step 5.2; otherwise, proceed to step 5.3.

[0056] Step 5.2: Use the backlash distance as the compensation distance;

[0057] In practice, the compensation will be completed in multiple control cycles. The target position after correction in each control cycle is the target position of the previous control cycle plus the maximum compensation value of a single control cycle. In the last control cycle, the backlash distance will be added to the target position as the compensation distance.

[0058] Step 5.3: Use the maximum compensation value for a single control cycle as the compensation distance;

[0059] Step 5.4: Increase the compensation distance to the target position to correct the target position, and send the corrected target position to the lead screw pitch error compensation module.

[0060] Step 6: Send the target position to the lead screw pitch error compensation module to calculate the given position;

[0061] The calculation of the given position using the lead screw pitch error compensation module specifically involves:

[0062] 1) Read the theoretical and actual positions of N+1 discrete points, and compare the target position P with the actual position P of any discrete point. i If P = P' i If P', then execute 2); i ′<P≤P i ′ +1 Then execute 3);

[0063] 2) The theoretical location P of the discrete point i As a given position Send to the driver;

[0064] 3) Assuming that the pitch of two adjacent discrete points is uniform and their positions are linearly related, then given a position Calculated using the following formula:

[0065]

[0066] Figure 6The diagram illustrates three pitch distributions. The dashed line represents the standard pitch distribution, which satisfies a linear relationship; the solid line represents the actual pitch distribution, which can only be considered to be monotonically increasing, but cannot completely and accurately represent any functional law; the asterisked solid line represents the sampled actual pitch distribution, where every two adjacent sampling points are considered linear, and the curve is composed of piecewise linear functions. The denser the sampling points, the closer the curve is to the actual pitch distribution curve.

[0067] 4) The given position is sent to the motor controller, and the motor drives the lead screw to rotate, which in turn moves the slider and the cutting head to the target position.

[0068] Step 7: The lead screw pitch error compensation module sends the given position to the motor controller, and the motor drives the lead screw to rotate, which in turn moves the slider and the cutting head to the target position.

[0069] In practical implementation, the developed backlash error compensation module and lead screw pitch error compensation module are integrated into the IDE for PLC program development. When developing laser products using this platform PLC as the controller, the appropriate module can be selected based on actual needs.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the ideas of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for compensating for lead screw errors in a laser cutting machine based on PLC control, characterized in that, Includes the following steps: Step 1: Use a laser interferometer to measure the lead screw error data and backlash distance for each feed axis; Step 2: Design a backlash error compensation method and develop it into a backlash error compensation module for PLC control; Step 3: Design a lead screw pitch error compensation method and develop it into a lead screw pitch error compensation module controlled by PLC; Step 4: Determine if the feed axis has reversed its movement. If so, proceed to step 5; otherwise, proceed to step 6. Step 5: Send the target position to the backlash error compensation module to correct the target position, and then send the corrected target position to the lead screw pitch error compensation module to calculate the given position; Step 6: Send the target position to the lead screw pitch error compensation module to calculate the given position; Step 7: The lead screw pitch error compensation module sends the given position to the motor controller, and the motor drives the lead screw to rotate, which in turn moves the slider and the cutting head to the target position; The specific steps for measuring the lead screw error data in step 1 are as follows: Step 1.1: Select N+1 discrete points uniformly on the lead screw. Let the distance between the discrete points be L. Then, the theoretical position of each discrete point on the standard lead screw is... ; Step 1.2: Due to pitch error, the offset of each discrete point on the lead screw to be compensated is measured using a laser interferometer. The actual position of each discrete point is obtained as follows: Record the theoretical and actual positions of each discrete point; The lead screw pitch error compensation module calculates the specific position as follows: 1) Read the theoretical and actual positions of N+1 discrete points, and compare the target position P with the actual position of any discrete point. ,like If, then execute 2); Then execute 3); 2) The theoretical location of this discrete point As a given position Send to the driver; 3) Assuming that the pitch of two adjacent discrete points is uniform and their positions are linearly related, then given a position Calculated using the following formula: 4) The given position is sent to the motor controller, and the motor drives the lead screw to rotate, which in turn moves the slider and the cutting head to the target position.

2. The method for compensating for lead screw errors in a laser cutting machine based on PLC control as described in claim 1, characterized in that, In step 5, the target position is sent to the backlash error compensation module, and the target position is modified as follows: Step 5.1: When the feed axis reverses, determine whether the backlash distance is greater than the maximum compensation value for a single control cycle. If it is, proceed to step 5.2; otherwise, proceed to step 5.

3. Step 5.2: Use the maximum compensation value for a single control cycle as the compensation distance; Step 5.3: Use the backlash distance as the compensation distance; Step 5.4: Increase the compensation distance to the target position to correct the target position, and send the corrected target position to the lead screw pitch error compensation module.

3. The method for compensating for lead screw errors in a laser cutting machine based on PLC control as described in claim 2, characterized in that, When the backlash distance is greater than the maximum compensation value in a single control cycle, the compensation will be completed in multiple control cycles. The target position after correction in each control cycle is the target position of the previous control cycle plus the maximum compensation value in a single control cycle. In the last control cycle, the backlash distance is added to the target position as the compensation distance.

4. The method for compensating for lead screw errors in a laser cutting machine based on PLC control as described in claim 1, characterized in that, It also includes integrating the developed backlash error compensation module and lead screw pitch error compensation module into the IDE for PLC program development.

Images