A method for real-time compensation of part outer circle size based on off-machine measurement

Abstract

The present application belongs to the field of mechanical processing, and relates to a part outer circle size real-time compensation method based on off-machine measurement. The present application method is as follows: the actual outer circle size and design tolerance of the part are acquired in real time, the real-time calculation of the compensation value is facilitated, and the real-time compensation processing of the part is ensured. The compensation value of the part outer circle size is determined according to the actual outer circle size and design tolerance of the part, the accuracy of the compensation value is ensured, the compensation value calculation efficiency is high, the calculation result is accurate, and then the processing precision of the part is ensured. The compensation value of the part outer circle size is returned to the machine tool to continue processing the part. The whole process realizes automatic closed-loop processing of processing, measurement and compensation processing, avoids the stop-line inspection of the production line, and improves the production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of machining and relates to a method for real-time compensation of the outer diameter of a part based on external measurement. Background Technology

[0002] With the development of industrial automation, the closed-loop production method of "machining-measurement-compensation" in production lines has become a research hotspot both domestically and internationally in recent years. Traditional offline coordinate measuring machine (CMM) inspection methods are often used for precision inspection of parts, but they have limitations such as errors caused by secondary workpiece clamping and excessively long waiting times for measurement results. To avoid these problems, the cutting tool is replaced with a probe after machining, directly measuring the part's errors inside the machine tool. This avoids the problems of secondary CMM clamping and the inability to compensate in real time, facilitating the realization of an integrated "machining-measurement-compensation" production line. However, in-machine measurement introduces machine tool errors, such as geometric and thermal errors, leading to discrepancies between the measurement results and the actual value of the part, which can severely degrade the part.

[0003] Therefore, based on the characteristics of the processed parts, corresponding inspection equipment is installed in the production line to ensure inspection accuracy while measuring part dimensions in real time. Generally, when the accuracy of a part fails to meet design tolerances after inspection due to tool wear, thermal errors, or uncertainties, the robotic arm will pick out the part and trigger an alarm, alerting on-site workers to investigate and handle the issue. On-site workers need to stop the line to check for abnormalities in the process system and adjust the tool compensation value to prevent parts from exceeding tolerances. This method severely impacts the production line's processing cycle time and production efficiency, especially when processing parts with many dimensions and heavy production tasks. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a real-time compensation method for the outer diameter of a part based on external measurement. This method calculates the tool compensation value quickly and accurately based on the measurement results and transmits the compensation value back to the machine tool in real time, thereby achieving automatic compensation and improving production efficiency.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention discloses a method for real-time compensation of the outer diameter of a part based on external measurement, comprising the following steps:

[0007] Real-time acquisition of the actual outer diameter and design tolerances of parts;

[0008] Determine the compensation value for the outer diameter of the part based on its actual outer diameter and design tolerance;

[0009] The compensation value of the outer diameter of the part is sent back to the machine tool to continue processing the part.

[0010] Furthermore, after obtaining the actual outer diameter of the part in real time, it is necessary to determine the reason for the out-of-tolerance of the outer diameter of the part based on the actual outer diameter. If the out-of-tolerance is caused by tool chipping or workpiece chip entanglement, a machine stop alarm operation is required, and processing can only be carried out after the operator has checked and dealt with the problem.

[0011] Furthermore, the criteria for determining tool chipping are as follows:

[0012] If the blade breaks, then

[0013] d i ≥(1+λ)·d ul,i (i∈[1,4])

[0014] If the cutting tool is normal, then

[0015] d i <(1+λ)·d ul,i (i∈[1,4])

[0016] Where, d i This is the actual measured value; d ul λ is the difference between the parts; λ is the adjustment coefficient, λ∈[0.001,0.005].

[0017] Furthermore, the criteria for determining workpiece chip entanglement are as follows:

[0018] If the workpiece is wrapped with chips, then

[0019] d i ≥(1+β)·d ul,i (i∈[1,4])

[0020] If the workpiece is normal, then

[0021] d i <(1+β)·d ul,i (i∈[1,4])

[0022] Where, d i β is the actual measured value, and β is the chip entanglement adjustment coefficient, β∈[2,15].

[0023] Furthermore, the compensation value for the outer diameter of the part is determined based on the actual outer diameter and design tolerance as follows:

[0024] Based on the design tolerance, a control tolerance is set. The control tolerance is smaller than the design tolerance. When the actual outer diameter of the part is larger than the design tolerance, the compensation value of the outer diameter of the part is calculated and the part size is compensated.

[0025] Furthermore, the compensation value is calculated using the following formula:

[0026] When the actual outer diameter of the part is larger than the design tolerance

[0027]

[0028] Where: △d ul This is the compensation value for the design error; △d dl d is the compensation value for the under-design error; δ is the actual measured value; ζ is the correction coefficient; and ζ is the control parameter.

[0029] When the actual outer diameter of a part is greater than the control tolerance but less than or equal to the design tolerance...

[0030]

[0031] Where: △d uv This is the compensation value for the over-control upper deviation; △d dv This is the compensation value for the over-control deviation.

[0032] Furthermore, the formula for controlling the tolerance range is as follows:

[0033]

[0034] Where, d uv To control the upper difference; d dv To control the undershoot; d ul For design flaws; d dl To design the lower difference; △α u This is the upper bias; △α d This is the lower bias.

[0035] Furthermore, the compensation value is transmitted back to the machine tool in real time via TCP / IP technology, and the actual outer diameter of the part is obtained in real time via TCP / IP technology.

[0036] Furthermore, the machining errors of the machine tool must be within the design tolerance range.

[0037] Furthermore, the machining error is the sum of machine tool positioning accuracy, thermal error, error caused by tool wear, machine tool dynamic error, and measurement error. Compared with the prior art, the present invention has the following beneficial effects:

[0038] The method of this invention is as follows: The actual outer diameter and design tolerance of the part are acquired in real time, facilitating real-time calculation of the compensation value and ensuring real-time compensation machining of the part. The compensation value for the outer diameter of the part is determined based on the actual outer diameter and design tolerance, ensuring the accuracy of the compensation value. The calculation efficiency is high and the calculation results are accurate, thereby guaranteeing the machining accuracy of the part. The compensation value for the outer diameter of the part is then fed back to the machine tool for further machining. The entire process realizes an automated closed-loop machining process of machining, measurement, and compensation machining, avoiding production line downtime for inspection and improving production efficiency. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the measuring device of the present invention;

[0040] Figure 2 This is a schematic diagram of the compensation method of the present invention;

[0041] Figure 3a XR images of automatic and manual compensation at two locations in this invention;

[0042] Figure 3b XR images of automatic and manual compensation at two other locations of the present invention;

[0043] Figure 4 This is a flowchart of the method of the present invention.

[0044] The components include: 1. Motor; 2. Light source; 3. Measuring platform; 4. Ball screw feed system; 5. Measuring lens; 6. Worktable; 7. Workpiece to be measured; 8. Center. Detailed Implementation

[0045] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0046] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0047] The present invention will now be described in further detail with reference to the accompanying drawings:

[0048] See Figure 4 This invention discloses a real-time compensation method for the outer diameter of a part based on external measurement, comprising the following steps:

[0049] S1. Real-time acquisition of the actual outer diameter and design tolerances of the part;

[0050] After obtaining the actual outer diameter of the part in real time, it is necessary to determine the reason for the out-of-tolerance of the outer diameter based on the actual outer diameter. If the out-of-tolerance is caused by tool chipping or workpiece chip entanglement, a machine stop alarm operation is required, and processing can only be carried out after the operator has checked and dealt with the problem.

[0051] The criteria for determining if a tool is chipped are as follows:

[0052] If the blade breaks, then

[0053] d i ≥(1+λ)·d ul,i (i∈[1,4])

[0054] If the cutting tool is normal, then

[0055] d i <(1+λ)·d ul,i (i∈[1,4])

[0056] Where, d i This is the actual measured value; d ul λ is the difference between the parts; λ is the adjustment coefficient, λ∈[0.001,0.005].

[0057] The criteria for judging chip entanglement on a workpiece are as follows:

[0058] If the workpiece is wrapped with chips, then

[0059] d i ≥(1+β)·d ul,i (i∈[1,4])

[0060] If the workpiece is normal, then

[0061] d i <(1+β)·d ul,i (i∈[1,4])

[0062] Where, d i β is the actual measured value, and β is the chip entanglement adjustment coefficient, β∈[2,15].

[0063] S2. Determine the compensation value for the outer diameter of the part based on the actual outer diameter of the part and the design tolerance;

[0064] The compensation value for the outer diameter of the part is determined based on the actual outer diameter and design tolerance as follows:

[0065] Based on the design tolerance, a control tolerance is set. The control tolerance is smaller than the design tolerance. When the actual outer diameter of the part is larger than the design tolerance, the compensation value of the outer diameter of the part is calculated and the part size is compensated.

[0066] The formula for calculating the compensation value is as follows:

[0067] When the actual outer diameter of the part is larger than the design tolerance

[0068]

[0069] Where: △d ul This is the compensation value for the design error; △d dl d is the compensation value for the under-design error; δ is the actual measured value; ζ is the correction coefficient; and ζ is the control parameter.

[0070] When the actual outer diameter of a part is greater than the control tolerance but less than or equal to the design tolerance...

[0071]

[0072] Where: △d uv This is the compensation value for the over-control upper deviation; △d dv This is the compensation value for the over-control deviation.

[0073] The formula for controlling the tolerance range is as follows:

[0074]

[0075] Where, d uv To control the upper difference; d dv To control the undershoot; d ul For design flaws; d dl To design the lower difference; △α u This is the upper bias; △α d This is the lower bias.

[0076] S3. The compensation value of the outer diameter of the part is sent back to the machine tool to continue processing the part.

[0077] The compensation value is transmitted back to the machine tool in real time via TCP / IP technology, and the actual outer diameter of the part is obtained in real time via TCP / IP technology.

[0078] The machining error of the machine tool must be within the design tolerance range.

[0079] Machining error is the sum of machine tool positioning accuracy, thermal error, error caused by tool wear, machine tool dynamic error, and measurement error.

[0080] See Figure 4In another feasible embodiment of the present invention, the following modifications are made as needed. Real-time acquisition of the actual outer diameter and design tolerance of the part facilitates real-time calculation of the compensation value, ensuring real-time compensation machining of the part. The compensation value for the outer diameter of the part is determined based on the actual outer diameter and design tolerance, ensuring the accuracy of the compensation value. The compensation value calculation is efficient and accurate, thus guaranteeing the machining accuracy of the part. The compensation value for the outer diameter of the part is then fed back to the machine tool for continued part machining. The entire process achieves automatic closed-loop machining of machining, measurement, and compensation machining, avoiding production line downtime for inspection and improving production efficiency. Based on the measurement results, the present invention quickly and accurately calculates the tool compensation value and rapidly feeds it back to the machine tool in real time, achieving automatic compensation and improving production efficiency.

[0081] Example 1:

[0082] See Figure 4 This invention discloses a real-time compensation method for the outer diameter of a part based on external measurement, as detailed below:

[0083] Step 1: Analysis of factors causing out-of-tolerance dimensions of the part's outer diameter;

[0084] During external cylindrical turning, cutting force and cutting heat are generated when the tool and workpiece come into contact. The heat generated during cutting can cause local deformation of the machine tool, thus affecting the machining accuracy of the part; while changes in cutting force can cause displacement changes in the weak points of the machine tool, i.e., the parts with weak rigidity, thus affecting the shape error of the part. In addition, the tool wears under the action of thermo-mechanical coupling, which will cause the outer diameter to increase, and in severe cases, the cutting teeth will break. Therefore, taking the outer diameter as an example, the machining error Δδ can be expressed by equation (1):

[0085] △δ=△δ g +△δ t +△δ w +△δ s +△δ m (1)

[0086] Where: △δ g For machine tool positioning accuracy; △δ t For thermal error; Δδ w Error caused by tool wear; △δ s The dynamic error of the machine tool is the error caused by the flexible parts of the machine tool; △δ m This is for measurement error.

[0087] If the sum of all machine tool errors is within the design tolerance range, compensation can be made; otherwise, a new machine tool must be selected or the machine tool must be repaired.

[0088] Step 2: Acquisition of external measurement data;

[0089] Analysis of the factors causing dimensional deviations in the outer diameter of the part shows that machining can proceed when the machine tool's machining error meets the part's dimensional tolerance requirements. The machined workpiece is then moved from the machine tool to the measuring device by a robotic arm. Figure 1 As shown, the measuring platform 3 is equipped with two centers 8, which are used to position the workpiece 7 to be measured, thereby reducing clamping errors. After the workpiece is fixed, the motor 1 drives the ball screw feed system 4, which in turn drives the light source 2 and the measuring lens 5 to move, measuring the four outer diameters [d1, d2, d3, d4] of the part. The obtained measurement data can be used to measure the diameters of the four outer diameters of the workpiece. i}(i∈[1,4]) represents.

[0090] Step 3: Determining the cause of out-of-tolerance dimensions of the part's outer diameter

[0091] As can be seen from the analysis in step 1, the machining error △δ is caused by the machine tool positioning accuracy △δ g Thermal error Δδ t Error Δδ caused by tool wear w Machine tool dynamic error △δ s and measurement error Δδ m The process consists of five parts, but it does not take into account abnormal situations such as tool chipping or workpiece chip entanglement during machining. Therefore, after obtaining the measurement data in step 2, it is necessary to determine whether any abnormal situations occurred during the workpiece machining process.

[0092] Regarding tool chipping, for finishing, tool chipping will have a slight impact on the accuracy of the part. When the tolerance requirements are strict, it will cause the outer diameter of the part to exceed the upper tolerance. Therefore, the judgment condition can be determined by equation (2).

[0093]

[0094] Where: d is the actual measured value; d ul λ is the difference between the parts; λ is the adjustment coefficient, λ∈[0.001,0.005].

[0095] Regarding the issue of chip entanglement on a workpiece, the chips from the machined surface wrapping around the workpiece shaft are caused by tool dulling, such as when the tool is in a severely worn stage. Although this does not affect the dimensional accuracy of the workpiece, it has a significant impact on measurement, leading to the mistaken belief that the workpiece is unqualified and thus treated as scrap. Therefore, whether a workpiece is entangled in chips can be determined by equation (3).

[0096]

[0097] Where: d is the actual measured value; β is the chip entanglement adjustment coefficient, β∈[2,15].

[0098] The two situations described above are abnormal conditions during processing. If not handled manually, they will affect the quality and precision of the parts. Therefore, no compensation will be provided for these two situations; instead, a machine stop alarm should be triggered, and processing can only resume after the operator has inspected and addressed the issue.

[0099] Step 4: Calculation of the compensation value for the outer diameter of the part

[0100] Based on the characteristics of the parts being processed and considering the actual processing conditions, as well as the influence of thermal errors and uncertainties, control tolerances are set on top of the design tolerances to ensure the part pass rate. When the measured dimension exceeds the control tolerance, the part dimension needs to be compensated. A compensation diagram is shown below. Figure 2 As shown.

[0101] The control tolerance range can be expressed by equation (4).

[0102]

[0103] Where: d uv To control the upper difference; d dv To control the undershoot; d ul For design flaws; d dl To design the lower difference; △α u This is the upper bias; △α d This is the lower bias.

[0104] Considering that the present invention involves turning the outer diameter of a part, and the proposed compensation scheme is to set a control tolerance on the basis of the design tolerance for compensation. In order to reduce the influence of measurement error and make the compensation scheme more universal, the calculation of the compensation value will be divided into two cases: exceeding the design tolerance and exceeding the control tolerance. The calculation of the compensation value exceeding the design tolerance can be expressed by equation (5), and the calculation of the compensation value exceeding the control tolerance can be expressed by equation (6).

[0105]

[0106] Where: △d ul This is the compensation value for the design error; △d dl d is the compensation value for the over-design tolerance; δ is the actual measured value; δ is the correction coefficient, which is used to adjust the size of the compensation value; ζ is the control parameter, which is used to control the range of the over-design tolerance.

[0107]

[0108] Where: △d uv This is the compensation value for the over-control upper deviation; △d dv The compensation value for the over-control deviation

[0109] Step 5: Evaluation of automatic compensation strategy;

[0110] XR images with automatic and manual compensation are shown below. Figure 3a and Figure 3b As shown, automatic compensation can effectively control the dimensions within a certain range, avoiding workpiece scrap due to untimely manual compensation, and improving the first-pass yield and processing efficiency of products.

[0111] To further compare the differences between automatic and manual compensation, and to quantify the processing capabilities of the two compensation methods, a process capability index (C) was selected. pk As a quantitative evaluation indicator, it can be represented by equation (7).

[0112]

[0113] In the formula: C pk C is the evaluation indicator. p For process precision; C a For process accuracy; T is the tolerance center value; σ is the sample standard deviation; C is the sample mean; C is the design tolerance.

[0114] Considering that the workpiece to be processed has multiple dimensions, its comprehensive evaluation index is represented by equation (8).

[0115]

[0116] If K ≥ ψ, then the requirement is met; if K < ψ, then the requirement is not met.

[0117] In the formula: K is the comprehensive processing capacity index; ψ is the expected processing capacity threshold.

[0118] The comprehensive processing capacity index under different compensation methods during the processing is compared with the expected processing capacity threshold. If the judgment condition is met, the current compensation method is implemented; if the requirement is not met, the compensation method needs to be improved.

[0119] This invention analyzes the influence of factors such as tool chipping, tool wear, geometric errors, and thermal errors on the form and position errors of parts during the external cylindrical turning process, identifying the main causes affecting the dimensional accuracy of the external diameter. Then, based on the measurement results from the production line's internal inspection equipment and the part's tolerance requirements, compensation strategies and schemes are proposed. Finally, according to the actual processing conditions on the production line, a feedback compensation method is proposed. The calculated compensation value is fed back to the machine tool in real time and quickly, achieving the goal of automatic continuous processing on the production line without manual intervention.

[0120] The method proposed in this invention eliminates the need for dedicated testing equipment and is not limited by the installation or model of the testing instruments. It automatically acquires measurement results in real time using TCP / IP technology and sends the compensation values ​​back to the machine tool, thus bridging the communication gap between the machine tool and the testing equipment.

[0121] This invention considers the impact of chip entanglement and tool breakage during turning on the measurement results, avoiding inaccurate results due to machining abnormalities. Furthermore, the compensation value can be adjusted according to the specific machining conditions on site, resulting in high calculation efficiency and accurate results. This invention improves the first-pass yield of products and extends tool life, demonstrating significant engineering application value.

[0122] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for real-time compensation of the outer diameter of a part based on external measurement, characterized in that, Includes the following steps: Real-time acquisition of the actual outer diameter and design tolerances of parts; After obtaining the actual outer diameter of the part in real time, it is necessary to determine the reason for the out-of-tolerance of the outer diameter of the part based on the actual outer diameter. If the reason for the out-of-tolerance is due to tool chipping or workpiece chip entanglement, a machine stop alarm operation is required, and processing can only be carried out after the operator has checked and dealt with the problem. The compensation value for the outer diameter of the part is determined based on the actual outer diameter and design tolerance, as follows: Based on the design tolerance, a control tolerance is set. The control tolerance is smaller than the design tolerance. When the actual outer diameter of the part exceeds the design tolerance, the compensation value of the outer diameter of the part is calculated and the part size is compensated. The compensation value for the outer diameter of the part is sent back to the machine tool to continue machining the part. The formula for calculating the compensation value is as follows: When the actual outer diameter of a part exceeds the design tolerance in: This is the compensation value for deviations in the design; This is the compensation value for deviations exceeding the design specifications; These are actual measured values; This is a correction factor; For control parameters; When the actual outer diameter of a part exceeds the control tolerance but does not exceed the design tolerance in: This is the compensation value for the over-control deviation; This is the compensation value for the deviation under over-control conditions; The formula for the range of the control tolerance is as follows: in, To control the upper deviation; To control the lower deviation; Due to design deviations; To design the lower deviation; This is the upper deviation bias amount; This is the lower bias offset.

2. The method for real-time compensation of the outer diameter of a part based on external measurement as described in claim 1, characterized in that, The criteria for determining tool chipping are as follows: If the blade breaks, then If the cutting tool is normal, then in, These are actual measured values; For deviations on parts; For adjustment coefficients, .

3. The method for real-time compensation of the outer diameter of a part based on external measurement as described in claim 1, characterized in that, The criteria for determining chip entanglement on the workpiece are as follows: If the workpiece is wrapped with chips, then If the workpiece is normal, then in, These are actual measured values. This is the chip entanglement adjustment coefficient. .

4. The method for real-time compensation of the outer diameter of a part based on external measurement as described in claim 1, characterized in that, The compensation value is transmitted back to the machine tool in real time via TCP / IP technology, and the actual outer diameter of the part is obtained in real time via TCP / IP technology.

5. The method for real-time compensation of the outer diameter of a part based on external measurement as described in claim 1, characterized in that, The machining error of the machine tool must be within the design tolerance range.

6. The method for real-time compensation of the outer diameter of a part based on external measurement as described in claim 5, characterized in that, The machining error is the sum of machine tool positioning accuracy, thermal error, error caused by tool wear, machine tool dynamic error, and measurement error.

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