Workpiece measurement method and system based on machining center

Abstract

The application relates to the field of irregular profile measurement, in particular to a workpiece measurement method and system based on a machining center, which comprises the following steps: acquiring a distance set, the set elements of the distance set being the distances between any two adjacent collection points; calculating a qualified interval of the distance set, screening all distances in the distance set according to the qualified interval, marking the position coordinates of the collection points corresponding to the normal distances as normal, and marking the position coordinates of the collection points corresponding to the abnormal distances as abnormal; taking any collection point as a target point, counting the number of times that the position coordinates of the target point are marked as normal and the number of times that the position coordinates of the target point are marked as abnormal, constructing a real coordinate group of the target point according to the counting result, calculating a fitting coordinate of the real coordinate group, acquiring a position evaluation result of the fitting coordinate, calculating the radial distance of the target point according to the position evaluation result, and taking all the radial distances as workpiece measurement results. The application can improve the accuracy of measuring the radial distance of a gear.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of irregular profile measurement. More particularly, the present application relates to a workpiece measurement method and system based on a machining center. BACKGROUND

[0002] The radial distance of a gear refers to the distance from a point on the outer edge profile of the gear to the center of the gear, and the radial distance of the gear includes key dimensions of the gear such as the addendum circle radius and the dedendum circle radius, which directly affect the meshing accuracy, load capacity and transmission stability of the gear. Therefore, it is of great significance to accurately measure the radial distance of the gear. SUMMARY

[0003] The main purpose of the embodiments of the present application is to provide a workpiece measurement method and system based on a machining center, aiming to improve the accuracy of measuring the radial distance of the gear.

[0004] To achieve the above-mentioned purpose, the embodiments of the first aspect of the present application provide a workpiece measurement method based on a machining center, which comprises: collecting the outer edge profile of the workpiece according to a preset trajectory, and obtaining a distance set, the set elements of the distance set being the distance between any two adjacent collection points; calculating the qualified interval of the distance set, screening all distances in the distance set according to the qualified interval, obtaining normal distances and abnormal distances, and marking the position coordinates of the collection points corresponding to the normal distances as normal and marking the position coordinates of the collection points corresponding to the abnormal distances as abnormal; repeatedly collecting and screening multiple times, for each screening to obtain normal distances and abnormal distances, marking the position coordinates of the collection points corresponding to the normal distances as normal and marking the position coordinates of the collection points corresponding to the abnormal distances as abnormal; taking any of the collection points as a target point, counting the number of times the position coordinates of the target point are marked as normal and the number of times the position coordinates of the target point are marked as abnormal, constructing a real coordinate group of the target point according to the statistical result, calculating a fitting coordinate of the real coordinate group, obtaining a position evaluation result of the fitting coordinate, calculating the radial distance of the target point according to the position evaluation result, and traversing to obtain the radial distance of each collection point, taking all the radial distances as the workpiece measurement result.

[0005] In some embodiments, calculating the qualified interval comprises: taking any of the distance sets as a target set, calculating the mean value, the upper limit of the abnormal value and the lower limit of the abnormal value of the target set, taking the difference between the average value of the upper limit of the abnormal value and the lower limit of the abnormal value and the mean value as an offset, calculating a correction coefficient according to the offset, adjusting the upper limit of the abnormal value and the lower limit of the abnormal value to obtain the qualified interval according to the correction coefficient, and traversing to obtain the qualified interval of each distance set.

[0006] In some embodiments, calculating the correction coefficient according to the offset comprises: calculating a quartile range of the target set; taking the ratio of the offset and the quartile range as a shrinkage strength, and taking the difference between 1 and the shrinkage strength as the correction coefficient.

[0007] In some embodiments, adjusting the upper limit of the abnormal value and the lower limit of the abnormal value according to the correction coefficient to obtain an eligible interval comprises: taking the product of the upper limit of the abnormal value and the correction coefficient as an eligible upper limit, taking the product of the lower limit of the abnormal value and the correction coefficient as an eligible lower limit, and constructing an eligible interval according to the eligible upper limit and the eligible lower limit.

[0008] In some embodiments, constructing the real coordinate group according to the statistical result comprises: in response to the number of times that the position coordinates of the target point are marked as normal being greater than the number of times that the position coordinates of the target point are marked as abnormal, taking the target point as having no defects as the statistical result, and including the position coordinates of the target point that are marked as normal into the real coordinate group; in response to the number of times that the position coordinates of the target point are marked as normal being not greater than the number of times that the position coordinates of the target point are marked as abnormal, taking the target point as having defects as the statistical result, and including the position coordinates of the target point that are marked as abnormal into the real coordinate group.

[0009] In some embodiments, calculating the radial distance of the target point according to the position evaluation result comprises: calculating a position evaluation of the fitting coordinate; in response to the position evaluation being not greater than a preset threshold, taking the fitting coordinate as meeting the requirement as the position evaluation result, calculating the radial distance of the fitting coordinate, and taking the radial distance of the fitting coordinate as the radial distance of the target point; in response to the position evaluation being greater than the preset threshold, increasing the number of times of repeated collection and screening to reacquire the fitting coordinate, calculating a position evaluation of the newly acquired fitting coordinate, until the position evaluation is not greater than the preset threshold, calculating the radial distance of the fitting coordinate, and taking the radial distance of the fitting coordinate as the radial distance of the target point.

[0010] In some embodiments, calculating the position evaluation of the fitting coordinate comprises: calculating the dispersion degree of the fitting coordinate in the real coordinate group; performing negative correlation mapping on the number of repetitions by an exponential function, and taking the product of the mapping value and the hyperbolic tangent value of the dispersion degree as the position evaluation.

[0011] Embodiments of the second aspect of the present application propose a workpiece measurement system based on a machining center, the system comprising: a processor and a memory, the memory storing computer program instructions, which, when executed by the processor, implement the workpiece measurement method based on the machining center described above.

[0012] The present application has the following beneficial effects:

[0013] The present application carries out multiple rounds of collection on the outer edge profile of the workpiece, for each round of collection, the qualified interval is calculated according to the distance set, all distances in the distance set are screened through the qualified interval, the normal distance and the abnormal distance are obtained, the position coordinates of the collection points corresponding to the normal distance are marked as normal, and the position coordinates of the collection points corresponding to the abnormal distance are marked as abnormal, after multiple rounds of collection, the sum of the number of times that each collection point is marked as normal and the number of times that each collection point is marked as abnormal is equal to the number of collection rounds, for each collection point, the number of times that the position coordinates are marked as normal and the number of times that the position coordinates are marked as abnormal are counted, the real coordinate group is constructed according to the statistical result, then the fitting coordinates of the real coordinate group are calculated, the position evaluation result of the fitting coordinates is obtained, and the radial distance is calculated according to the position evaluation result, so that the accuracy of measuring the radial distance of the gear can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is the flow chart of steps S1-S3 in the workpiece measurement method based on the machining center according to the embodiments of the present application. DETAILED DESCRIPTION

[0015] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application.

[0016] The specific embodiments of the present application will be described in detail below with reference to the drawings.

[0017] Reference Figure 1 The workpiece measurement method based on the machining center includes steps S1-S3, and specifically as follows:

[0018] Step S1: collecting the outer edge profile of the workpiece according to the preset trajectory, obtaining a distance set, the set elements of the distance set being the distances of any two adjacent collection points; calculating the qualified interval of the distance set, screening all distances in the distance set according to the qualified interval, obtaining the normal distance and the abnormal distance, marking the position coordinates of the collection points corresponding to the normal distance as normal, and marking the position coordinates of the collection points corresponding to the abnormal distance as abnormal.

[0019] It should be noted that the workpiece measurement method of the present application is described by taking gear measurement as an example, and more specifically, by taking the outer edge profile of one end face of the gear as an example.

[0020] It should be noted that after obtaining the gear profile curve by 3D scanning, a CAD model is used to plan the preset trajectory, and the machining center controls the probe to collect on the outer edge profile according to the preset trajectory, the probe can extract the coordinates of the collection points, and the distance between any two adjacent collection points can be calculated through the coordinates of the collection points.

[0021] It should be noted that the distance within the qualified interval is regarded as a normal distance, and the distance not within the qualified interval is regarded as an abnormal distance.

[0022] It can be understood that the calculation of the qualified interval includes: taking any distance set as a target set, calculating the mean value, upper abnormal value limit and lower abnormal value limit of the target set, and taking the difference between the average of the upper abnormal value limit and the lower abnormal value limit and the mean value as an offset; calculating a correction coefficient according to the offset, and adjusting the upper abnormal value limit and the lower abnormal value limit to obtain the qualified interval according to the correction coefficient; and traversing to obtain the qualified interval of each distance set.

[0023] It can be understood that the calculation of the correction coefficient according to the offset includes: calculating the interquartile range of the target set; taking the ratio of the offset and the interquartile range as the contraction degree, and taking the difference between 1 and the contraction degree as the correction coefficient.

[0024] It can be understood that the adjustment of the upper abnormal value limit and the lower abnormal value limit to obtain the qualified interval according to the correction coefficient includes: taking the product of the upper abnormal value limit and the correction coefficient as the qualified upper limit, taking the product of the lower abnormal value limit and the correction coefficient as the qualified lower limit, and constructing the qualified interval according to the qualified upper limit and the qualified lower limit.

[0025] Exemplarily, the calculation formula of the offset is as follows:

[0026]

[0027] In the formula , is the offset of the target set, is the upper abnormal value limit of the target set, is the lower abnormal value limit of the target set, is the mean value of the target set.

[0028] For the above formula , it should be noted that and can be calculated by the interquartile range method, , wherein, is the upper quartile of the target set, is the lower quartile of the target set, is the interquartile range of the target set. is the original interval for screening abnormal values.

[0029] For the above formula , it is necessary to point out that the average of the upper limit of outliers and the lower limit of outliers is the center of the interquartile range. When the offset is greater than 0, the mean of the target set is on the left of the center of the interquartile range, at this time, the data of the target set is left-skewed distribution, the mean is "pulled down" by a few outliers on the left (small value direction), so that it is less than the center point of the middle 50% data. When the offset is less than 0, the mean of the target set is on the right of the center of the interquartile range, at this time, the data of the target set is right-skewed distribution, the mean is "pulled up" by a few outliers on the right (large value direction), so that it is greater than the center point of the middle 50% data. When the offset is equal to 0, the mean of the target set coincides with the center of the interquartile range, at this time, it is the ideal state.

[0030] Exemplarily, the calculation formula of the qualified upper limit and the qualified lower limit is as follows:

[0031]

[0032]

[0033] In the formula and the formula , is the qualified upper limit of the target set, is the qualified lower limit of the target set, is the upper limit of outliers of the target set, is the lower limit of outliers of the target set, is the offset of the target set, is the interquartile range of the target set, is the shrinkage degree, is the correction coefficient.

[0034] For the above formula and the formula , it is necessary to point out that is the qualified interval for screening normal distance and abnormal distance.

[0035] For the above formula and the formula , it is necessary to point out that when the offset (extreme value exists on the left side), , is left-shifted compared to , therefore, compared to the original interval , the qualified interval is left-shifted in the present application, so as to include the extreme value inside the qualified interval as much as possible, and the extreme value is regarded as a normal distance, and further, the position coordinates of the acquisition point corresponding to the extreme value are marked as normal, which is the basis for the acquisition of statistical results in the subsequent step S3.

[0036] For the above formula and formula , it needs to be noted that when the offset (an extreme value exists on the right side), the , is shifted to the right compared to , therefore, compared to the original interval , the present application shifts the qualified interval to the right because it takes into account the extreme value that exists on the right side, which may be a real value (a real defect of the workpiece), so as to include the extreme value inside the qualified interval as much as possible, take the extreme value as a normal distance, and further mark the position coordinates of the collection point corresponding to the extreme value as normal, which serves as a basis for obtaining the statistical result in the subsequent step S3.

[0037] Step S2: repeatedly collect and screen multiple times, for each screening, mark the position coordinates of the collection point corresponding to the normal distance as normal, and mark the position coordinates of the collection point corresponding to the abnormal distance as abnormal.

[0038] It needs to be noted that the starting point of each collection and the collection step length are the same, and the coordinate system when the probe extracts the coordinates of the collection point is the same.

[0039] It needs to be noted that one collection corresponds to one distance set, one distance set corresponds to one qualified interval, one qualified interval corresponds to one screening process of normal distance and abnormal distance, and one screening process corresponds to one marking process. Specifically, the present application collects ten times at the beginning.

[0040] Step S3: take any collection point as a target point, count the number of times the position coordinates of the target point are marked as normal and the number of times the position coordinates of the target point are marked as abnormal, construct a real coordinate group of the target point according to the statistical result, calculate a fitting coordinate of the real coordinate group, obtain a position evaluation result of the fitting coordinate, calculate a radial distance of the target point according to the position evaluation result, traverse to obtain the radial distance of each collection point, and take all the radial distances as the measurement result of the workpiece.

[0041] It can be understood that constructing the real coordinate group according to the statistical result includes: in response to the number of times the position coordinates of the target point are marked as normal being greater than the number of times the position coordinates of the target point are marked as abnormal, taking the target point as having no defect as the statistical result, and taking the position coordinates of the target point marked as normal into the real coordinate group; and in response to the number of times the position coordinates of the target point are marked as normal being not greater than the number of times the position coordinates of the target point are marked as abnormal, taking the target point as having a defect as the statistical result, and taking the position coordinates of the target point marked as abnormal into the real coordinate group.

[0042] It needs to be explained that each collection point is collected multiple times, taking any collection point as a target point, the position coordinates of the target point marked as normal and the number of times marked as abnormal are counted.

[0043] It needs to be explained that if the number of times the position coordinates of the target point are marked as normal is greater than the number of times marked as abnormal, the real coordinates of the target point are closer to normal, and the target point is marked as abnormal due to the error touch, collision and vibration of the measuring head (these are all measurement noise caused by abnormality), at this time, the position coordinates of the target point marked as abnormal are removed, and the position coordinates of the target point marked as normal are included in the real coordinate group; if the number of times the position coordinates of the target point are marked as normal is not greater than the number of times marked as abnormal, the real coordinates of the target point are closer to abnormal (the gear itself has defects, so that the actual size of the gear deviates from the normal value), at this time, the position coordinates of the target point marked as normal are removed, and the position coordinates of the target point marked as abnormal are included in the real coordinate group.

[0044] It needs to be explained that the least square method is used to calculate the fitting coordinates, the square sum of the Euclidean distance of the fitting coordinates to all position coordinates in the real coordinate group is the smallest, and the consistency of multiple position coordinates is found by fitting an optimal coordinate to improve the measurement accuracy.

[0045] It can be understood that the position evaluation of the fitting coordinates includes: calculating the dispersion degree of the fitting coordinates in the real coordinate group; through the negative correlation mapping of the exponential function, the product of the mapping value and the hyperbolic tangent value of the dispersion degree is taken as the position evaluation.

[0046]

[0047] In the formula , the position evaluation of the fitting coordinates is , the number of position coordinates in the real coordinate group is , the Euclidean distance of the fitting coordinates to the th position coordinate in the real coordinate group is , the average of the Euclidean distance of the fitting coordinates to all position coordinates in the real coordinate group is , the dispersion degree of the fitting coordinates in the real coordinate group is , the hyperbolic tangent function is , the exponential function is , and the repetition number is .

[0048] For the above formula It should be noted that the smaller the position evaluation is, the more valuable the calculation is. The position evaluation is positively correlated with the dispersion degree of the fitting coordinates in the real coordinate group. The smaller the dispersion degree is, the smaller the position evaluation is, and the more stable the fitting result is, and the higher the application value of the fitting coordinates is. The position evaluation is negatively correlated with the repetition number. The more the repetition number is, the higher the measurement accuracy is, and the higher the application value of the fitting coordinates calculated through multiple repetitions is.

[0049] It can be understood that the calculation of the radial distance of the target point according to the position evaluation result includes: calculating the position evaluation of the fitting coordinates; in response to the position evaluation being not greater than a preset threshold, taking that the fitting coordinates meet the requirements as the position evaluation result, calculating the radial distance of the fitting coordinates, and taking the radial distance of the fitting coordinates as the radial distance of the target point; in response to the position evaluation being greater than the preset threshold, increasing the number of repeated acquisition and screening to reacquire the fitting coordinates, calculating the position evaluation of the newly acquired fitting coordinates, and repeating the above steps until the position evaluation is not greater than the preset threshold, calculating the radial distance of the fitting coordinates, and taking the radial distance of the fitting coordinates as the radial distance of the target point.

[0050] It should be noted that the preset threshold is 0.6. If the position evaluation of the fitting coordinates is not greater than the preset threshold, the fitting coordinates can be equivalent to the real coordinates of the target point, the radial distance of the fitting coordinates is calculated, and the radial distance of the fitting coordinates is taken as the radial distance of the target point. If the position evaluation of the fitting coordinates is greater than the preset threshold, the fitting coordinates cannot be equivalent to the real coordinates of the target point, the number of repeated acquisition and screening is increased to reacquire the fitting coordinates, the position evaluation of the newly acquired fitting coordinates is calculated, and the above steps are repeated until the position evaluation is not greater than the preset threshold, the radial distance of the fitting coordinates is calculated, and the radial distance of the fitting coordinates is taken as the radial distance of the target point.

[0051] The application further provides a workpiece measurement system based on a machining center. The system comprises a processor and a memory. The memory stores computer program instructions which, when executed by the processor, implement the workpiece measurement method based on the machining center according to the first aspect of the application. The system further comprises a communication bus, a communication interface and other components familiar to those skilled in the art, the arrangement and functions of which are known in the art, and thus will not be described here.

[0052] It should be noted that the above describes the preferred embodiments of the embodiments of the application with reference to the drawings, and does not limit the scope of the embodiments of the application. Those skilled in the art can make several modifications and improvements without departing from the concept of the application, and these all belong to the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. Method for measuring a workpiece based on a machining center, characterized in that, The method comprises the following steps: Collecting the outer edge profile of the workpiece according to a preset trajectory to obtain a distance set, wherein the set elements of the distance set are the distances between any two adjacent collection points; Calculating the qualified interval of the distance set, screening all distances in the distance set according to the qualified interval to obtain normal distances and abnormal distances, marking the position coordinates of the collection points corresponding to the normal distances as normal, and marking the position coordinates of the collection points corresponding to the abnormal distances as abnormal; Repeating the collection and screening process multiple times, for each screening to obtain normal distances and abnormal distances, marking the position coordinates of the collection points corresponding to the normal distances as normal, and marking the position coordinates of the collection points corresponding to the abnormal distances as abnormal; Taking any of the collection points as a target point, counting the number of times the position coordinates of the target point are marked as normal and the number of times the position coordinates of the target point are marked as abnormal, constructing a real coordinate group of the target point according to the statistical result, calculating a fitting coordinate of the real coordinate group, obtaining a position evaluation result of the fitting coordinate, calculating the radial distance of the target point according to the position evaluation result, and traversing to obtain the radial distance of each collection point, and taking all the radial distances as the workpiece measurement result.

2. The workpiece measurement method based on a machining center according to claim 1, characterized by, The calculation of the qualified interval comprises: Taking any of the distance sets as a target set, calculating the mean value, upper limit of abnormal value and lower limit of abnormal value of the target set, taking the difference between the average value of the upper limit of abnormal value and the lower limit of abnormal value and the mean value as an offset, calculating a correction coefficient according to the offset, adjusting the upper limit of abnormal value and the lower limit of abnormal value to obtain the qualified interval according to the correction coefficient, and traversing to obtain the qualified interval of each distance set. The calculation of the correction coefficient according to the offset comprises: Calculating the interquartile range of the target set; 3. The workpiece measurement method based on a machining center according to claim 2, wherein, Taking the ratio of the offset and the interquartile range as the contraction degree, and taking the difference between 1 and the contraction degree as the correction coefficient. The adjustment of the upper limit of abnormal value and the lower limit of abnormal value to obtain the qualified interval according to the correction coefficient comprises: Taking the product of the upper limit of abnormal value and the correction coefficient as the qualified upper limit, taking the product of the lower limit of abnormal value and the correction coefficient as the qualified lower limit, and constructing the qualified interval according to the qualified upper limit and the qualified lower limit.

4. The workpiece measurement method based on a machining center according to claim 2, characterized by, The construction of the real coordinate group according to the statistical result comprises: In response to the number of times the position coordinates of the target point are marked as normal being greater than the number of times the position coordinates of the target point are marked as abnormal, taking the target point as having no defects as the statistical result, and taking the position coordinates of the target point marked as normal into the real coordinate group; 5. The workpiece measurement method based on a machining center according to claim 1, wherein, In response to the number of times the position coordinates of the target point are marked as normal being not greater than the number of times the position coordinates of the target point are marked as abnormal, taking the target point as having defects as the statistical result, and taking the position coordinates of the target point marked as abnormal into the real coordinate group. The calculation of the radial distance of the target point according to the position evaluation result comprises: Calculating the position evaluation of the fitting coordinate; 6. The workpiece measurement method based on a machining center according to claim 1, wherein, In response to the position evaluation being not greater than a preset threshold, taking the fitting coordinate as meeting the requirements as the position evaluation result, calculating the radial distance of the fitting coordinate, and taking the radial distance of the fitting coordinate as the radial distance of the target point; ​ ​ in response to the position evaluation being greater than a preset threshold, regarding the fitting coordinate not meeting the requirement as a position evaluation result, increasing the number of repeated acquisition and screening to reacquire the fitting coordinate, calculating a position evaluation of the newly acquired fitting coordinate, until the position evaluation is not greater than the preset threshold, calculating a radial distance of the fitting coordinate, and regarding the radial distance of the fitting coordinate as the radial distance of the target point.

7. The workpiece measurement method based on a machining center according to claim 1, wherein, The calculating the position evaluation of the fitting coordinate comprises: calculating a dispersion degree of the fitting coordinate in the real coordinate group; performing negative correlation mapping on the number of repetitions by an exponential function, and regarding a product of the mapping value and a hyperbolic tangent value of the dispersion degree as the position evaluation.

8. A workpiece measurement system based on a machining center, characterized by comprise: a processor and a memory, the memory storing computer program instructions which, when executed by the processor, implement the workpiece measurement method based on a machining center according to any one of claims 1-7.

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