High-precision measurement method and system for screw head dimensions

Abstract

The present application relates to the technical field of screw head size measurement, and specifically to a high-precision screw head size measurement method and system, the method comprising: obtaining the hardness factor of the screw head in each measurement process and the radial coordinate set at each rotation angle; obtaining the groove matching degree of each measurement process based on the difference between the fitting function of the radial coordinate set at each rotation angle of each measurement process and the ideal groove function of the screw head groove; obtaining the current groove risk coefficient of the measured screw based on the difference between the predicted value of the groove matching degree of the next measurement process and the average level of the groove matching degree of all current measurement processes, judging whether to trigger a closed-loop control mechanism, and then obtaining the size of the screw head groove. The present application improves the accuracy of screw head size measurement by analyzing the risk of screw assembly failure and adjusting the angular resolution during laser scanning.

Description

Technical Field

[0001] The present application relates to the technical field of screw head size measurement, and in particular to a high-precision screw head size measurement method and system. Background Art

[0002] The development of high-precision screw head dimensional measurement technology stems from modern industry's stringent requirements for reliability and consistency in the assembly of tiny components. As the most fundamental fastener, even slight deviations in screw head dimensions can lead to assembly failure, inaccurate torque transmission, tool wear, and even equipment damage. Traditional contact measurement methods, such as mechanical calipers and micrometers, are inefficient, prone to scratching workpieces, and difficult to accurately assess complex groove shapes, making them difficult to meet the needs of high-volume, in-line inspection. This has led to the rapid development of non-contact optical measurement and high-precision image measuring instruments. These, combined with precision motion control, high-resolution sensors, and advanced image processing algorithms, enable rapid, automated measurement with micron-level accuracy.

[0003] When measuring the size of the groove on the screw head, the existing mainstream technology uses a high-resolution multi-angle optical scanning imaging system. This system integrates a high-precision rotating stage, a multi-directional controllable light source and a micron-level resolution camera, and uses the rotating stage to drive the screw for multi-angle precision positioning. However, due to the instantaneous fluctuations in the hardness of the screw material, the screw material may experience abnormal wear at different hardness levels, resulting in slight fluctuations in the size of the screw. The existing technology does not take into account the impact of the instantaneous hardness fluctuations of the screw material on the screw shape, which leads to poor accuracy in the final measured screw size. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of this application is to provide a high-precision screw head size measurement method and system. The technical solutions adopted are as follows:

[0005] In a first aspect, an embodiment of the present application provides a method for high-precision measurement of screw head dimensions, the method comprising the following steps:

[0006] Obtaining a radial coordinate set of the screw head plane at each rotation angle during each measurement process according to a preset rotation angle step and an azimuth angle of a preset calibration point; obtaining a hardness factor of the screw head during each measurement process;

[0007] Obtaining a groove profile fitting function of the screw head plane measured at each rotation angle of each measurement process based on a radial coordinate set at each rotation angle of each measurement process; obtaining an ideal groove profile function of the screw head plane measured, and combining the ideal groove profile function with an average level of differences between the ideal groove profile function and the groove profile fitting function of the screw head plane measured at all rotation angles of each measurement process to obtain a groove profile matching degree of each measurement process;

[0008] The assembly risk coefficient of the entire measurement process is obtained based on the fusion results of the groove matching degree and hardness factor of all current measurement processes. The current groove risk coefficient of the measured screw is obtained by combining the difference between the predicted value of the groove matching degree of the next measurement process and the average level of the groove matching degree of all current measurement processes. The coefficient is compared with the preset risk threshold to determine whether the closed-loop control mechanism is triggered. If the closed-loop control mechanism is not triggered, the size of the screw head groove is obtained. If the closed-loop control mechanism is triggered, the groove risk coefficient of the measured screw is recalculated until the closed-loop control mechanism is not triggered and the size of the screw head groove is obtained.

[0009] Preferably, the specific process of obtaining the radial coordinate set of the measured screw head plane at each rotation angle during each measurement process is: setting a preset calibration point in the screw head plane, taking the intersection of the measured screw head plane and the screw center axis as the origin, and taking the direction from the origin to the preset calibration point as the positive direction of the x-axis to establish a polar coordinate system; the rotating stage drives the screw to rotate around its center axis, and the rotation angle starts from 0 degrees, and is incrementally sampled with a preset rotation angle step a as the step length. Every time a degree is rotated, a preset number of random sampling is performed within 360 degrees of the screw head plane where the polar coordinate system is located. The radial distances at different azimuth angles are increased, and the azimuth angle increases in the counterclockwise direction along the x-axis of the polar coordinate system, and a preset number of data coordinates in the [radial distance, azimuth angle] format at the rotation angle are obtained, and then the system is rotated a degree again to collect a preset number of data coordinates at the new rotation angle, until the rotating stage rotates one circle and stops; the measurement process of the rotating stage rotating one circle is recorded as one measurement; the set of all data coordinates collected at each rotation angle in each measurement process in the order of azimuth angle from small to large is recorded as the radial coordinate set at each rotation angle in each measurement process.

[0010] Preferably, the slot fitting function of each rotation angle of each measurement process refers to: taking the radial coordinate set of each rotation angle of each measurement process as the input of the least squares method, taking the radial distance as the dependent variable, and taking the azimuth angle as the independent variable, to obtain the fitting equation of each rotation angle of each measurement process.

[0011] Preferably, the calculation formula for the groove matching degree of each measurement process is: Where, is the groove matching degree of a single measurement process, The rotation angle during a single measurement The slot fitting function under is the azimuth angle, is the rotation angle in a single measurement, and for An integer multiple of N, where N is the preset rotation angle range. is the preset rotation angle step, intmin() is the rounding function, which is used to take the integer smaller than and closest to the input data. It is the ideal groove function of the screw head groove being measured.

[0012] Preferably, the process of obtaining the assembly risk coefficient of the entire measurement process is as follows: the sequence of the groove matching degrees of all current measurement processes in the order of measurement is recorded as the matching degree sequence of the entire measurement process; the sequence of the normalized hardness factors of all measurement processes in the order of measurement is recorded as the hardness factor sequence of the entire measurement process; and the matching degree sequence and hardness factor sequence of the entire measurement process are used as inputs of the weighted linear combination algorithm, and the sum of the product of the mean of the matching degree sequence and its initial weight and the sum of the product of the mean of the hardness factor sequence and its initial weight is used as the initial weighted summation result, and the recursive least squares method is used to update the weight parameters in real time, and the result of the weighted summation of the matching degree sequence and the hardness factor sequence by dynamic weight is output, and the result is recorded as the assembly risk coefficient of the entire measurement process.

[0013] Preferably, the current slot risk coefficient of the measured screw is: Where, is the current slot risk factor of the screw being tested, is the assembly risk factor during the entire measurement process, is the predicted value of the groove matching degree in the next measurement process, is the mean value of the groove matching degree of all measurement processes, is a preset constant, is the sigmoid function.

[0014] Preferably, the specific process of determining whether to trigger the closed-loop control mechanism is: when the current slot risk coefficient of the measured screw is less than or equal to the preset risk threshold, the closed-loop control mechanism is not triggered; otherwise, the closed-loop control mechanism is triggered.

[0015] Preferably, if the closed-loop control mechanism is not triggered, the specific process of obtaining the size of the screw head is: taking the measurement process with the largest groove matching degree among all measurement processes as the precise measurement process, parsing the size data of the screw head groove from the groove surface fitting function obtained at each rotation angle in the precise measurement process, and calculating the average of the size data at all rotation angles in the precise measurement process as the size of the screw head groove.

[0016] Preferably, if the closed-loop control mechanism is triggered, the slot risk coefficient of the measured screw is recalculated until the closed-loop control mechanism is not triggered, and the specific process of obtaining the size of the screw head is: after the closed-loop control mechanism is triggered, the preset rotation angle step is reduced, and the rotating stage is driven with the reduced new rotation angle step to obtain the hardness factor of the screw head in each measurement process and the radial coordinate set at each rotation angle; the slot risk coefficient of the measured screw is recalculated; if the recalculated slot risk coefficient is less than or equal to the preset risk threshold, the size of the screw head groove is obtained; otherwise, the closed-loop control mechanism is continued to be triggered, and the cycle is repeated until the condition that the slot risk coefficient is less than or equal to the preset risk threshold or the condition that the rotation angle step is less than the preset minimum step limit is met, the size of the screw head groove is obtained, and the cycle is stopped.

[0017] In a second aspect, an embodiment of the present application also provides a high-precision size measurement system for screw heads, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein when the processor executes the computer program, the steps of any one of the above-mentioned high-precision size measurement methods for screw heads are implemented.

[0018] This application has at least the following beneficial effects:

[0019] 1. To address the problem of groove curve reconstruction distortion, a radial basis function interpolation algorithm is used to directly quantify the shape of the groove, solving the problem of low accuracy in optical multi-angle scanning;

[0020] 2. To address the assembly failure risk caused by geometric deviations and material hardness fluctuations, a weighted linear combination + exponential smoothing prediction algorithm is used to integrate current risks and future degradation trends, eliminating the random effects of environmental vibration and local material unevenness. This method constructs a slot risk coefficient and accurately quantifies the immediate and short-term assembly reliability of screws, providing a basis for subsequent screw size measurement.

[0021] 3. Based on the groove risk coefficient, determine whether to trigger the closed-loop control mechanism. When the assembly risk level is serious, reduce the laser scanning angular step, improve the angular resolution, directionally enhance the coordinate coverage of the groove, improve the groove surface reconstruction accuracy, and thus improve the measurement accuracy of the screw head groove size. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] Figure 1 A flowchart of the steps of a high-precision screw head size measurement method provided in one embodiment of the present application;

[0024] Figure 2 A schematic structural diagram of a data acquisition device provided for one embodiment of the present application, wherein 1 is a sensor group consisting of a laser displacement sensor and an eddy current sensor, 2 is a screw, 3 is a rotating platform, the solid arrow is the rotation direction of the rotating platform, and the dotted line is the radial distance. DETAILED DESCRIPTION

[0025] To further illustrate the technical means and effectiveness of this application's objectives, the following, in conjunction with the accompanying drawings and preferred embodiments, details the high-precision screw head dimensional measurement method and system proposed in this application, including its specific implementation, structure, features, and effectiveness. In the following description, references to different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0026] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0027] The specific scheme of the high-precision screw head size measurement method and system provided by the present application is described in detail below with reference to the accompanying drawings.

[0028] See also Figure 1 , which shows a flowchart of a method for high-precision measurement of screw head dimensions provided by an embodiment of the present application, the method comprising the following steps:

[0029] Step 1: Obtain a radial coordinate set of the screw head plane at each rotation angle during each measurement process according to a preset rotation angle step and the azimuth angle of a preset calibration point; and obtain the hardness factor of the screw head during each measurement process.

[0030] A high-precision laser displacement sensor is coaxially installed just above the screw head, and is matched with a high-precision electric rotating stage at the bottom. The initial preset rotation angle step is a degree. In this embodiment, the initial value of a is 30, so as to collect radial cross-sectional profile data at each rotation angle in the cylindrical coordinate system. The structural diagram of the data acquisition device is shown in FIG. Figure 2As shown, the specific process is as follows: taking any screw head plane in the screw head groove as an example, a preset calibration point is set in the screw head plane, the intersection of the plane and the screw center axis is used as the origin, and the direction from the origin to the preset calibration point is used as the positive direction of the x-axis to establish a polar coordinate system; the rotating stage drives the screw to rotate around its center axis at a constant angular velocity, and the rotation angle starts from 0 degrees and is incrementally sampled with a preset rotation angle step as the step size. Every time the rotation is a degree, the laser displacement sensor uses a coaxial laser triangulation method to perform high-speed line scanning along the radial direction of the screw head, and randomly collects b radial distances (in millimeters) at different azimuth angles within 360 degrees of the screw head plane where the polar coordinate system is located. The azimuth angle increases in the counterclockwise direction of the x-axis of the polar coordinate system, and obtains b data coordinates in the [radial distance, azimuth angle] format under the rotation angle. The radial distance refers to the distance between the origin of the polar coordinate system and the groove contour of the screw head plane; then the rotating stage drives the screw to rotate a degree again, and collects b data coordinates under the new rotation angle until the rotating stage stops when it rotates one circle. In this embodiment, b is set to 50. A set of all data coordinates collected at each rotation angle in ascending order of azimuth angle is recorded as a radial coordinate set at each rotation angle.

[0031] Furthermore, during eddy current testing, high-frequency electromagnetic fields act on the conductive surface of the screw head, generating induced eddy currents. Instantaneous fluctuations in the material's hardness can alter its microstructure, leading to changes in electrical conductivity and magnetic permeability, which in turn affect the phase difference and amplitude decay rate of the eddy currents. Therefore, an eddy current sensor is integrated alongside the laser displacement sensor. Its probe is perpendicular to the upper surface of the screw head, transmitting a high-frequency electromagnetic field in a non-contact manner and receiving the induced eddy current signals. The phase difference and amplitude decay rate are calculated based on the eddy current signals. The phase difference describes phase delay (i.e., path distortion), while the amplitude decay rate describes amplitude decay (i.e., energy loss). The product of the two represents the total electromagnetic energy dissipated per unit volume and is positively correlated with hardness. Therefore, the product of the phase difference and amplitude decay rate is used as the hardness factor of the screw head material. The hardness factor is collected once per rotation of the rotating stage. This hardness factor comprehensively reflects the material hardness of the screw head material over the period of one rotation.

[0032] The measurement process of one rotation of the rotating stage is recorded as one measurement. In this embodiment, a design of m consecutive measurements (i.e., the rotating stage rotates continuously for m rounds) is adopted. Continuous measurement is used to balance the random errors introduced by the unevenness, thereby providing a forward-looking decision-making basis for closed-loop control. In this embodiment, m is 10.

[0033] At this point, the hardness factor of each measurement process and the radial coordinate set at all rotation angles in each measurement process are obtained.

[0034] Step 2: Obtain the groove profile fitting function of the screw head plane measured at each rotation angle of each measurement process based on the radial coordinate set at each rotation angle of each measurement process; obtain the ideal groove profile function of the screw head plane measured, and combine it with the average level of the difference between the ideal groove profile function and the groove profile fitting function of the screw head plane measured at all rotation angles of each measurement process to obtain the groove profile matching degree of each measurement process.

[0035] Due to the deep and narrow structural features of the groove inside the screw head, it is difficult for the optical sensor to directly obtain the complete geometric information of the groove bottom and side walls. Traditional contact measurement is prone to scratching the precision surface, resulting in the core problems of inaccurate positioning of the groove corner feature points and distortion of the three-dimensional surface reconstruction.

[0036] Although optical sensors cannot directly capture complete three-dimensional information about the screw head groove, they can divide the screw head groove into multiple horizontal planes, thereby obtaining geometric information about any horizontal plane within the screw head groove. By measuring the groove profile coordinate data of any horizontal plane within the screw head groove, fitting it, and comparing it with the ideal groove profile, the degree of match between the measured screw head groove profile and the ideal groove profile can be determined.

[0037] Therefore, the radial coordinate sets of each rotation angle of each measurement process are respectively used as the input of the least square method, the radial distance is used as the dependent variable, and the azimuth angle is used as the independent variable to obtain the fitting equation of the radial coordinate set under each rotation angle of each measurement process. The fitting equation below is Express it as, and record the fitting equation as the rotation angle The slot fitting function of the screw head plane measured below, where is the rotation angle The radial distance below, The fitting equation represents the relationship between the radial distance from the screw head plane groove to the central axis and the azimuth angle.

[0038] Based on the international standard parameters of the screw slot of the measured model, the preset slot width, slot depth and angle tolerances are obtained by directly calling the standard geometry library, and then the ideal slot function of the measured screw head plane under the theoretical design size is generated by modeling, which is recorded as .

[0039] As a preferred embodiment, the groove matching degree of each measurement process is obtained according to the average level of the difference between the ideal groove function of the measured screw head plane and the groove fitting function of all rotation angles of each measurement process, which is used to characterize the degree of matching between the actual measured groove shape of the measured screw head plane and the ideal groove shape.

[0040] In this embodiment, the groove matching degree during a single measurement is recorded as A, and its calculation relationship is: Where, is the groove matching degree of a single measurement process, The rotation angle during a single measurement The slot fitting function under is the azimuth angle, is the rotation angle in a single measurement, and for Integer multiples of N, N is the preset rotation angle range, in this embodiment, N is 360, is the preset rotation angle step, intmin() is the rounding function, which is used to take the integer smaller than and closest to the input data. It is the ideal groove function of the screw head groove being measured.

[0041] The larger the integral value is, the closer the screw head plane is to the rotation angle The deviation between the measured and ideal slots is large. The deviations at each rotation angle during a single measurement are averaged to assess the overall slot deviation of the screw head plane measured during that single measurement. The slot matching degree A reflects the shape difference between the actual measured slot and the ideal slot in a single measurement. This directly reflects slot geometry mismatch defects caused by surface reconstruction distortion, thereby assessing the assembly compatibility of the screw slot with standard tools. A greater slot matching degree A indicates a greater mismatch between the actual measured slot curve and the ideal slot curve on the screw head plane.

[0042] Step 3: Obtain the assembly risk coefficient of the entire measurement process based on the fusion results of the groove matching and hardness factor of all current measurement processes, and combine the difference between the predicted value of the groove matching of the next measurement process and the average level of the groove matching of all current measurement processes to obtain the current groove risk coefficient of the measured screw, and compare it with the preset risk threshold to determine whether to trigger the closed-loop control mechanism; if the closed-loop control mechanism is not triggered, obtain the size of the screw head groove; if the closed-loop control mechanism is triggered, recalculate the groove risk coefficient of the measured screw until the closed-loop control mechanism is not triggered, and obtain the size of the screw head groove.

[0043] Due to the accumulation of geometric deviations in the screw head groove and fluctuations in material hardness, there are risks of failure such as inaccurate torque transmission and abnormal tool wear during the assembly process. Especially in high-precision assembly scenarios such as automobile engines, micron-level deviations in the groove angle may cause sealing failure.

[0044] Therefore, the sequence of the groove matching degrees A of all current measurement processes in the order of measurement is recorded as the matching degree sequence of the entire measurement process; the sequence of the normalized hardness factors of all current measurement processes in the order of measurement is recorded as the hardness factor sequence of the entire measurement process; and the matching degree sequence and the hardness factor sequence are used as input. The weighted linear combination algorithm is used to set the initial weight of the matching degree sequence to 0.75 and the initial weight of the hardness factor sequence to 0.25. The sum of the product of the mean of the matching degree sequence and its initial weight and the product of the mean of the hardness factor sequence and its initial weight is taken as the initial weighted summation result. The recursive least squares method (RLS) is used to update the weight parameters in real time, and the result of the dynamic weighted summation of the matching degree sequence and the hardness factor sequence is output. The result is recorded as the assembly risk coefficient of the entire measurement process. , which is used to quantify the instantaneous assembly failure probability of the screw under the current size and material. The calculation formula for the weighted sum of the matching degree sequence and the hardness factor sequence in each recursive process is: Where, Represents the weighted sum of the matching degree sequence and the hardness factor sequence in the i-th recursive process, is the weight of the matching sequence in the i-th recursive process, is the matching degree sequence, is the weight of the hardness factor sequence in the i-th recursive process, is the hardness factor sequence.

[0045] Then, the matching degree sequence is used as input, and the exponential smoothing prediction algorithm is used to set the smoothing factor. To reduce noise interference while retaining recent change trends, output the predicted value of slot matching , to predict the evolution direction of the slot deviation in the next measurement, The larger the value is, the more serious the trend of slot degradation is.

[0046] As a preferred embodiment, the current slot risk coefficient of the measured screw is obtained based on the assembly risk coefficient of the entire measurement process and the difference between the predicted value of the slot matching degree of the next measurement process and the average level of the slot matching degree of all current measurement processes, which is used to characterize the degree of failure risk of the screw due to geometric matching defects and material hardness fluctuations.

[0047] In this embodiment, the current groove risk coefficient of the screw being measured is recorded as B, and its expression is: Where, is the current slot risk factor of the screw being tested, The assembly risk coefficient for the entire measurement process quantifies the probability of immediate assembly failure of the screw under the current size and material. It is directly related to the risk in the assembly process. The larger the value, the worse the compatibility of the screw with the standard tool and the higher the failure risk. It is the predicted value of the groove matching degree in the next measurement process, indicating the predicted value of the future groove geometry deviation and reflecting the groove degradation trend; It is the mean value of the groove matching degree of all measurement processes, which is used to quantify the average matching degree between the screw head groove and the ideal groove; is a preset constant used to avoid the denominator being 0. Its optimal value range is arrive , in this embodiment The value is , is the sigmoid function, which is used to normalize the input data. , it indicates that the slot type is deteriorating at an accelerated rate, otherwise, it means that the slot type is stable.

[0048] The slot risk factor B combines the current assembly risk and the predicted trend of slot geometry deviation to quantify the overall assembly risk of the screw at present. The higher the value, the greater the risk of failure of the screw due to geometric matching defects and material hardness fluctuations.

[0049] Furthermore, the groove inside the screw head has complex curved surface features, and the traditional multi-angle scanning method cannot meet the requirements of high-precision measurement in dimensional measurement. Factors such as groove bottom deformation, material softening and environmental vibration will cause cumulative measurement deviations, making it difficult to ensure measurement accuracy during online detection, and ultimately resulting in an increase in the missed detection rate of assembly failures.

[0050] Therefore, it is necessary to perform closed-loop improvement based on the slot risk factor B. The specific closed-loop improvement design is as follows:

[0051] In this embodiment, the preset risk threshold is set to 0.8. When the current groove risk coefficient B of the measured screw is ≤ 0.8, it means that the risk of failure of the dimensional measurement result of the screw during the entire measurement process is smaller. The measurement process with the largest groove matching degree in the current m measurement processes is taken as the precise measurement process, and the dimensional data of the screw head groove is parsed from the groove surface fitting function obtained at each rotation angle in the precise measurement process, and the average of the dimensional data at all rotation angles in the precise measurement process is taken as the size of the screw head groove.

[0052] When the current groove risk coefficient B of the measured screw is greater than 0.8, the system triggers the closed-loop control mechanism. The specific operation is: reduce the current preset rotation angle step value to make the scanning angle denser. Specifically, in this embodiment, the reduced step value is 3° (for example, if the current reference step is 30°, it is adjusted to 27°). The angular division parameters are reset by the micro-stepping motor of the high-precision rotary stage to increase the scanning posture of the single screw. This step enhances the coordinate coverage of the groove profile by gradually improving the angular resolution, and can more accurately reconstruct the fitting curve of the groove profile. After triggering the adaptive closed-loop control, the rotary stage is first driven with the adjusted new rotation angle step, and the high-precision laser displacement sensor is used to re-collect high-density radial distance data within a 360° range of the screw head. At this time, the number of scanning poses of the screw increases. Subsequently, based on the newly collected high-density data coordinates, a more accurate groove fitting function is generated. The fitting function is used to recalculate the groove matching degree A of each measurement process to eliminate the measurement deviation caused by insufficient sampling in the early stage. Then, the updated A value is combined with the real-time hardness factor to recalculate the groove risk coefficient B of the screw.

[0053] If the recalculated B is less than or equal to 0.8, the size of the screw head groove is calculated and output. If the recalculated B is still greater than 0.8, the adaptive closed-loop control mechanism is triggered again, and this cycle continues until the condition of B less than or equal to 0.8 is met, or the rotation angle step is less than the preset minimum step limit. The size of the screw head groove is calculated and output, and the cycle stops. In this embodiment, the preset minimum step limit is set to 10°. If B is still greater than 0.8 when the rotation angle step is less than the minimum step limit, the screw is marked as a high-risk workpiece, indicating that urgent intervention or offline processing is required. This strategy ensures that while improving dimensional measurement accuracy, the measurement density is dynamically adjusted to maximize the accuracy of online dimensional inspection.

[0054] Based on the same inventive concept as the above method, an embodiment of the present application also provides a high-precision size measurement system for screw heads, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of any one of the above-mentioned high-precision size measurement methods for screw heads are implemented.

[0055] It should be noted that the order in which the embodiments of the present application are presented is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. Furthermore, the foregoing descriptions of specific embodiments of this specification are provided. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential sequence shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0056] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0057] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A high-precision measurement method for the size of a screw head, characterized in that: The method comprises the following steps: Obtaining a radial coordinate set of the screw head plane at each rotation angle during each measurement process according to a preset rotation angle step and an azimuth angle of a preset calibration point; obtaining a hardness factor of the screw head during each measurement process; Obtaining a groove profile fitting function of the screw head plane measured at each rotation angle of each measurement process based on a radial coordinate set at each rotation angle of each measurement process; obtaining an ideal groove profile function of the screw head plane measured, and combining the ideal groove profile function with an average level of differences between the ideal groove profile function and the groove profile fitting function of the screw head plane measured at all rotation angles of each measurement process to obtain a groove profile matching degree of each measurement process; The assembly risk coefficient of the entire measurement process is obtained based on the fusion results of the groove matching degree and hardness factor of all current measurement processes. The current groove risk coefficient of the measured screw is obtained by combining the difference between the predicted value of the groove matching degree of the next measurement process and the average level of the groove matching degree of all current measurement processes. The coefficient is compared with the preset risk threshold to determine whether the closed-loop control mechanism is triggered. If the closed-loop control mechanism is not triggered, the size of the screw head groove is obtained. If the closed-loop control mechanism is triggered, the groove risk coefficient of the measured screw is recalculated until the closed-loop control mechanism is not triggered and the size of the screw head groove is obtained.

2. The high-precision screw head size measurement method according to claim 1, characterized in that: The specific process of obtaining the radial coordinate set of the measured screw head plane at each rotation angle in each measurement process is as follows: setting a preset calibration point in the screw head plane, taking the intersection of the measured screw head plane and the screw center axis as the origin, and taking the direction from the origin to the preset calibration point as the positive direction of the x-axis to establish a polar coordinate system; the rotating stage drives the screw to rotate around its center axis, and the rotation angle starts from 0 degrees, and is incrementally sampled with a preset rotation angle step a as the step length. Every time a degree is rotated, a preset number of different values ​​are randomly collected within 360 degrees of the screw head plane where the polar coordinate system is located. For the radial distance at the same azimuth angle, the azimuth angle increases in the counterclockwise direction along the x-axis of the polar coordinate system, and a preset number of data coordinates in the [radial distance, azimuth angle] format at the rotation angle are obtained, and then the system is rotated a degree again to collect a preset number of data coordinates at the new rotation angle until the rotating stage rotates one circle and stops; the measurement process of one rotation of the rotating stage is recorded as one measurement; the set of all data coordinates collected at each rotation angle in each measurement process in the order of azimuth angle from small to large is recorded as the radial coordinate set at each rotation angle in each measurement process.

3. The high-precision screw head size measurement method according to claim 1, characterized in that: The groove fitting function of the screw head plane measured at each rotation angle in each measurement process refers to: taking the radial coordinate set of the measured screw head plane at each rotation angle in each measurement process as the input of the least squares method, taking the radial distance as the dependent variable, and taking the azimuth angle as the independent variable, to obtain the fitting equation of the screw head plane measured at each rotation angle in each measurement process.

4. The high-precision screw head size measurement method according to claim 1, characterized in that: The calculation formula for the groove matching degree of each measurement process is: Where, is the groove matching degree of a single measurement process, The rotation angle during a single measurement The slot fitting function under is the azimuth angle, is the rotation angle in a single measurement, and for An integer multiple of N, where N is the preset rotation angle range. is the preset rotation angle step, intmin() is the rounding function, which is used to take the integer smaller than and closest to the input data. It is the ideal groove function of the screw head groove being measured.

5. The high-precision measurement method for screw head dimensions according to claim 1, characterized in that: The assembly risk coefficient of the entire measurement process is obtained by recording the sequence of the groove matching degrees of all current measurement processes in the order of measurement as the matching degree sequence of the entire measurement process; and recording the sequence of the normalized hardness factors of all measurement processes in the order of measurement as the hardness factor sequence of the entire measurement process; The matching degree sequence and hardness factor sequence of the entire measurement process are used as the input of the weighted linear combination algorithm. The sum of the product of the mean of the matching degree sequence and its initial weight and the product of the mean of the hardness factor sequence and its initial weight is used as the initial weighted summation result. The recursive least squares method is used to update the weight parameters in real time, and the result of the dynamic weighted summation of the matching degree sequence and the hardness factor sequence is output. The result is recorded as the assembly risk coefficient of the entire measurement process.

6. The high-precision screw head size measurement method according to claim 1, characterized in that: The current slot risk factor of the screw being tested is: Where, is the current slot risk factor of the screw being tested, is the assembly risk factor during the entire measurement process, is the predicted value of the groove matching degree in the next measurement process, is the mean value of the groove matching degree of all measurement processes, is a preset constant, is the sigmoid function.

7. The high-precision screw head size measurement method according to claim 1, characterized in that: The specific process of determining whether to trigger the closed-loop control mechanism is as follows: when the current slot risk coefficient of the measured screw is less than or equal to the preset risk threshold, the closed-loop control mechanism is not triggered; otherwise, the closed-loop control mechanism is triggered.

8. The high-precision screw head size measurement method according to claim 1, characterized in that: If the closed-loop control mechanism is not triggered, the specific process of obtaining the size of the screw head is: the measurement process with the largest groove matching degree in all measurement processes is regarded as the precise measurement process, the size data of the screw head groove is parsed from the groove surface fitting function obtained at each rotation angle in the precise measurement process, and the size data at all rotation angles in the precise measurement process are averaged as the size of the screw head groove.

9. The high-precision screw head size measurement method according to claim 1, characterized in that: If the closed-loop control mechanism is triggered, the slot risk coefficient of the measured screw is recalculated until the closed-loop control mechanism is not triggered, and the specific process of obtaining the size of the screw head is as follows: after the closed-loop control mechanism is triggered, the preset rotation angle step is reduced, and the rotating stage is driven with the reduced new rotation angle step to obtain the hardness factor of the screw head in each measurement process and the radial coordinate set at each rotation angle; the slot risk coefficient of the measured screw is recalculated; if the recalculated slot risk coefficient is less than or equal to the preset risk threshold, the size of the screw head groove is obtained; otherwise, the closed-loop control mechanism is continued to be triggered, and the cycle is repeated until the condition that the slot risk coefficient is less than or equal to the preset risk threshold or the condition that the rotation angle step is less than the preset minimum step limit is met, the size of the screw head groove is obtained, and the cycle is stopped.

10. A high-precision screw head dimensional measurement system, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the steps of the high-precision screw head size measurement method according to any one of claims 1 to 9 are implemented.

Images