Curved surface tangent detection method

Abstract

The invention relates to the technical field of numerical control machine tool detection, and discloses a curved surface tangent line detection method, which comprises the following steps of: detecting a target curve by adopting a probe on a numerical control machine tool to obtain a tangent line position of the target curve in a specified plane vertical to a detection direction; comprising the following steps: parameter determination: segmenting a target curve according to a division mode, estimating the radius of a detected curve segment, and determining detection parameters according to segmented curves; detection points are obtained, specifically, the detected curve segments are detected according to the detection parameters, and multiple sets of detection points are obtained; tangent point selection: projecting a detection point in a detection normal direction, and calculating a projection maximum point # imgabs0 #; and tangent calculation: determining the position of a detected tangent according to the tangent point # imgabs1 # and the detection normal. The curved surface tangent line detection device can detect the curved surface tangent line on a common machine tool, can adapt to probes with any precision, can eliminate random errors, improves the detection precision, improves the machining efficiency and the product quality, and reduces the machining difficulty and cost.

Description

Technical Field

[0001] The invention relates to the technical field of grinding technology for numerically controlled machine tools, and in particular to a curved surface tangent line detection method. Background Art

[0002] In modern manufacturing, CNC machine tool detection technology plays an important role in improving machining accuracy and efficiency. Through precise detection, key elements such as the position, size and shape of the workpiece can be accurately grasped before machining, providing a strong guarantee for subsequent high-quality machining operations; at the same time, real-time detection during the machining process can also help reduce debugging time, and timely adjust machining parameters based on detection feedback, further improving overall machining efficiency.

[0003] However, most common CNC machine tools in the prior art cannot directly use probes as measuring tools to detect surface tangents. In some processing situations, if the tangent of the workpiece needs to be known, the workpiece needs to be removed and replaced with other testing equipment for testing. This offline measurement method not only makes the processing process more cumbersome and reduces processing efficiency, but more seriously, each re-clamping will introduce new positioning errors, and other errors in subsequent processing will appear, causing the processing accuracy to show a trend of decreasing. Even if a high-precision three-coordinate measuring machine is currently used for testing, its measurement results are difficult to directly feed back to the processing system to form a closed-loop control.

[0004] In addition, in most cases, existing detection technology can only detect one end face, and it is difficult to detect the tangent of complex surfaces. Even though some high-end measurement systems currently have certain surface measurement capabilities, they have strict requirements on the use environment and require special probes and complex compensation algorithms. More importantly, in the actual detection process, due to the influence of various uncontrollable factors, the probe often produces random errors, and the existing detection technology cannot effectively eliminate these random errors automatically. This affects the accuracy of the detection results, which may make it difficult for the processed workpiece to meet the expected accuracy standards, seriously restricting the improvement of processing quality, especially in some parts processing scenarios with extremely high precision requirements. The impact of this error is more prominent. Summary of the invention

[0005] The present invention aims to provide a surface tangent detection method to solve the problem that the existing ordinary CNC machine tools cannot directly use probes as measuring tools to detect surface tangents, resulting in the existing curve tangent detection process being cumbersome, low in accuracy, and prone to errors that affect machining accuracy.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a surface tangent detection method, which uses a probe on a CNC machine tool to detect a target curve to obtain a tangent position of the target curve perpendicular to the detection direction in a specified plane; comprising the following steps: Parameter determination: segment the target curve according to the division method, estimate the radius R of the detected curve segment according to the segmented curve segments, and determine the detection parameters according to the segmented curve; Detection point acquisition: According to the determined detection parameters, the detected curve segments are detected according to the corresponding detection methods to obtain multiple groups of detection points ; Tangent point selection: Project it onto the detection normal n and calculate the maximum projection point As a cut point; Tangent calculation: Based on the obtained tangent point and the detection normal n, determine the tangent position of the detection.

[0007] The principles and advantages of this solution are: This solution can be used on ordinary machine tools to directly detect the curve where the target surface intersects the specified plane in the specified plane and along the specified direction through the probe built into the machine tool to obtain the tangent position of the curve perpendicular to the detection direction, thereby solving the problem that ordinary CNC machine tools cannot use probes as measurement tools to detect surface tangents. By dividing the complex curve into several segments, each segment is probed, and the detection normal n is known for each segment of the curve, a tangent perpendicular to the detection normal n is calculated in the specified plane. Then, by using the probe to detect the target curve, find the The tangent point is detected in the detection range one by one to obtain the contact point position information. The contact point position information is multiplied by the detection normal n, and the maximum value is selected, which is the tangent point information. Calculate the tangent information.

[0008] This solution breaks through the limitations of existing technologies that can only detect one end face and cannot detect the tangent of the surface, and can detect the tangent of the surface on ordinary machine tools. It is no longer limited to specific equipment such as three-coordinate measuring machines, and reduces the accuracy requirements of the probe, greatly expanding its application range in surface processing. It can achieve more accurate processing path planning, thereby improving processing efficiency and product quality, and effectively reducing the processing difficulty and cost caused by detection limitations. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The figure is a flow chart of a curved surface tangent line detection method of the present invention.

[0010] Figure 2 It is a schematic diagram of detection parameters for detecting curve segments of a surface tangent detection method of the present invention.

[0011] Figure 3It is a structural schematic diagram of detecting deviation angle of a curved surface tangent detection method of the present invention.

[0012] Figure 4 It is a schematic diagram of the direction of the detection normal of a detection curve in two different forms of a surface tangent detection method of the present invention.

[0013] Figure 5 It is a schematic diagram of the detection step length of a surface tangent detection method of the present invention.

[0014] Figure 6 It is a schematic diagram of the detection process of Example 1 in a curved surface tangent detection method of the present invention. DETAILED DESCRIPTION

[0015] The following is further described in detail through specific implementation methods: Example A surface tangent detection method in this embodiment cleverly uses the principle of geometric projection to transform complex tangent detection into a mathematical problem of finding projection extreme points, which not only ensures accuracy but also realizes automated detection, thereby realizing a method in which the probe of an ordinary CNC machine tool can be directly used as a measuring tool to detect the surface tangent.

[0016] In the prior art, since the probe of an ordinary CNC machine tool is a spherical probe, the contact point measured is the coordinate of the probe's center of the sphere, not the actual contact point. When the curvature of the surface changes dramatically (such as a sharp edge or a steep slope), the offset between the contact point and the center of the sphere will increase sharply, which leads to measurement distortion, just like using a ping-pong ball to touch the tip of a needle, the position of the center of the sphere cannot reflect the true coordinates of the tip of the needle at all. At the same time, coupled with the fact that ordinary probes cannot adjust the angle adaptively, it is also difficult to compensate for the measurement distortion problem. In addition, the servo system of traditional machine tools is mainly designed for cutting. Its rigid structure and inertial mass make it difficult to achieve the micron-level high-frequency dynamic adjustment required by the probe, making its dynamic response insufficient and unable to handle multiple solutions or singular points. Therefore, in the existing detection operations, it is believed that a special detection instrument with higher accuracy, shorter measurement cycle, and better decision-making algorithm is needed to complete it, such as using a three-coordinate machine equipped with a special probe that can be actively deflected, and a built-in iterative detection protocol (such as ISO10360), which can automatically optimize the detection path and compensate for anisotropic errors. There is an inherent thinking that traditional machine tools cannot be directly used as measurement tools.

[0017] In the face of this problem, existing technologies are also trying to adopt methods such as integrating microscopic visual probes on machine tools to assist in positioning and build hybrid detection systems; or establishing probe-surface contact dynamics models to predict errors in real time and achieve digital twin compensation; or directly reading the contact point position through photon signals. However, all of the above methods require additional auxiliary equipment to further improve the performance of existing machine tools, which undoubtedly increases the manufacturing cost and difficulty of machine tools, and it is difficult to ensure that the measurement accuracy and quality can reach that of dedicated equipment.

[0018] However, the above methods all integrate new technologies into the existing machine tool system to ensure the accuracy and feasibility of detection. This solution breaks the cognitive constraints of traditional machine tools and breaks the original thinking that traditional machine tool probes cannot be used directly to detect complex surface tangents. Without adding additional technology or equipment, a new tangent detection method is creatively proposed, which converts complex tangent detection into the calculation of projection extreme points, greatly reducing the dependence on algorithms and ensuring the accuracy of detection. It realizes the traditional machine tool method of using probes for automated detection, reduces the complexity of the detection operation process, and reduces the errors caused by repeated clamping, thereby improving accuracy. The measurement results are directly fed back to the processing system to form a closed-loop control.

[0019] In this embodiment, the surface tangent detection method is as shown in the attached Figure 1 As shown, by using a contact probe on a CNC machine tool, the target surface is detected according to fixed steps to obtain an intersection curve between a specified plane and the target surface, and a tangent position perpendicular to the detection direction is obtained on the intersection curve, including the following steps: S1, segmenting the target curve according to the division method, estimating the radius of the detected curve segment according to the segmented curve segments, and determining the detection parameters according to the segmented curve.

[0020] In this embodiment, the target curve is the intersection curve of the specified plane and the target surface. The division method is to project the complex target curve onto the detection normal n, and segment the detection curve according to the shape of the projected detection curve, and divide it into K curve segments containing at most one arc, K≥1; that is, each curve segment contains at most one convex line segment or concave line segment, so that each projection curve has one and only one highest point or lowest point, that is, the extreme point, to ensure the uniqueness of the tangent of each curve segment. After the division, the radius of the segmented curve segment is estimated to obtain the local radius R of the detected curve.

[0021] For each divided curve segment, the detection parameters of the curve segment are determined respectively. In this embodiment, the detection parameters include the detection contact surface, the detection direction m, the detection normal direction n, the tangent direction (ie, the tangent direction) , the probe ball radius r and the detection step length S.

[0022] Combined with Figure 2 The detection curve segment is shown in Figure 1, where the detection direction m is the direction in which the probe is perpendicular to the target surface, which is generally the direction in which the probe moves vertically. The detection normal n is parallel to the detection direction m. Based on the known detection normal n, the tangent , where the tangential is a tangent direction perpendicular to the detection normal n in the specified plane In this embodiment, the geometric algorithm tangent It is obtained by rotating the detected normal n by +90° or -90° in the specified plane.

[0023] The detection contact surface is the surface where the probe contacts the target curved surface. In this embodiment, the detection deviation angle θ needs to be determined before detection. When the detection deviation angle θ ≤ 45°, the detection method in this solution is applicable. Figure 3 As shown, in this embodiment, the probe has a spherical probe. During the detection process, the spherical probe contacts the target curved surface. The detection deviation angle θ is the angle between the probe contact surface normal f (i.e., the ball head contact surface normal) and the detection normal n. When the contact surface normal f is parallel to the detection normal n, it means that θ is 0 at this time, and the deviation is the smallest, so the probe position at the contact point can be accurately obtained; when the contact surface normal f is not parallel to the detection normal n, the detection result will be biased. In this embodiment, by The deviation is determined by calculating the detection deviation angle θ, where r is the radius of the probe ball head. If the detection deviation angle θ is too large, it means that the detected position error is large and it is difficult to meet the detection accuracy requirements. This method can avoid the problem of errors caused by the positioning of traditional machine tool probes, thereby ensuring that the measured contact point is closer to the actual contact point coordinates, rather than just the probe ball center position, improving the detection accuracy and ensuring the applicability of traditional probes.

[0024] After the detection deviation angle θ is met, the detection normal n, the probe ball head radius r and the detection step length S are determined according to the concave and convex direction of the curve segment to be detected.

[0025] In this embodiment, although the diameter of the probe ball head is not limited, a moderate probe ball head can be selected for detection according to the shape of the detection curve to improve the effectiveness and accuracy of the detection. In this embodiment, the detection curve includes the following two shapes: Morphology 1. The detected curve segment is a convex line segment.

[0026] Morphology 2. The detected curve segment is a concave line segment.

[0027] When the detected curve is a convex line segment of form 1, then, as shown in the attached Figure 4As shown in (a), the detection normal n is set to be opposite to the detection direction m. At this time, a probe ball with a larger probe ball head radius r can be selected at the convex part of the detection curve. The detection step length S is calculated based on the determined probe ball head radius r and the local radius R of the detected curve, as shown in the attached figure. Figure 5 In this embodiment, the detection step length S is calculated as follows: ; (Formula 1) In the formula, It is the position deviation along the detection normal. In actual operation, the position deviation is determined according to actual requirements and directly input as a known value. At the same time, the set detection deviation is achieved by adjusting the step size.

[0028] When the detected curve is a concave line segment of form 2, at this time, as shown in the attached Figure 4 As shown in (b), the detection normal n is set to be in the same direction as the detection direction m. At this time, a probe ball with a ball head radius smaller than the local radius R of the curved surface is selected at the concave part of the detection curve. The detection step length S is calculated based on the determined probe ball head radius r and the local radius R of the detected curve. In this embodiment, the effective range of the detection step length S is the range near the extreme value of the curve segment, and its calculation method is as follows: ; (Formula 2) According to formulas 1 and 2, when r and R are determined, the smaller the step size S is, the smaller the deviation e is. Figure 5 As shown, the above formula can only be satisfied near the estimated local radius of the detected curve, thereby determining the step length S. The value of S will affect the detection deviation and detection speed. When S is too large, the tangent point to be detected may be skipped. When S is too small, the detection time will increase, and the probability of random errors in the local area will increase. According to Formula 1, when detecting convex curves, the local radius R remains unchanged. When the probe r of the probe is increased, the deviation can be reduced. At the same time, the detection step length S can be increased to reduce the detection time and improve the detection efficiency. According to Formula 2, when detecting concave curves, the probe r of the probe needs to be smaller than the estimated local radius R to avoid failure to detect the target tangent point during detection. At this time, the step length S cannot be too large.

[0029] S2, detecting the detected curve segments according to the determined detection parameters and corresponding detection methods, and obtaining multiple groups of detection points.

[0030] Before detection, the detection range is set according to the intersection curve of the target surface, that is, the curve range of the detected curve segment. In this embodiment, the detection range needs to include the farthest point on the curve segment, and the detection range cannot have two or more extreme values ​​on the detection normal n. When determining the specific range, the detection range is defined as the range area including the farthest point by projecting the curve segment on the detection normal n.

[0031] According to the designated detection range, detection is performed in the detection range according to the detection method. In this embodiment, the detection method is scanning segmented combined detection. When detecting, the center of the probe head is moved to the specified plane and placed at the initial position of the detection range, that is, the tangent n t The endpoint of can be set as the initial detection position, and the intersecting curve of the target surface to be detected, that is, the detected curve segment, is scanned according to the determined detection step length S, and its detection direction is parallel to the detection normal n. That is, after detecting a point on the curve, the probe is moved along the tangent direction. Move a distance S, and then detect along the detection direction m, and repeat this process until the detection range covers the entire range to be detected. Then detect the next curve segment to be detected.

[0032] During the detection process, each detected position information is recorded, that is, the position information of the contact point between the probe and the curve, and the recorded position information is projected to the detection normal n and organized into coordinate points, which are recorded as detection points. After detecting each curve segment respectively, the coordinate point information of multiple groups of detection points is obtained.

[0033] In this embodiment, random errors in detection are also eliminated to ensure the accuracy of the measurement data. The random errors are eliminated by repeatedly detecting the position information at the tangent point to obtain multiple detection points, and averaging the detection point data measured at the point. If the projection in the detection direction is farther than the previous detection, the point is repeatedly detected three times, and the middle value is taken as the detection value of the position, so as to eliminate the random errors in the detection of the tangent.

[0034] S3, calculating the maximum value of the upward projection of the detection method according to the obtained detection points; determining the tangent position of the detection according to the projection maximum point and the detection normal.

[0035] In this embodiment, through segmented combined detection, multiple curves with extreme values ​​can be detected in the detection normal direction. Based on the acquired detection points, the maximum value point in the projection direction is calculated, and this point is identified as the point on the tangent line of the target curve perpendicular to the detection direction. Specifically, the acquired detection points After doing point multiplication with the detection normal n, the maximum value is taken as the maximum value point in the projection direction, expressed as [ ·n] max , recorded as the maximum point , which is the tangent point that needs to be found.

[0036] Then according to the found tangent point P m With tangential n t Calculate and merge the required tangent information, expressed as Therefore, according to the set detection normal direction, the tangent information of the concave or convex part of the curve can be obtained respectively, ensuring the accuracy and uniqueness of the tangent information.

[0037] Specific implementation process description Example 1 In this embodiment, a five-axis CNC machine tool is used as an example to detect the tangent of a roller fillet using a spherical probe of the five-axis CNC machine tool, which is used to solve the problem that the tangent of a small fillet at any angle cannot be detected by the probe on the CNC machine tool. The implementation steps are as shown in the attached figure. Figure 6 shown.

[0038] Preparation: Install a probe with a spherical probe on the five-axis CNC machine tool. This probe can capture the machine tool coordinate information of the detection point when it is triggered by contact along the direction of movement.

[0039] It is known that the radius r of the ball head of the probe is 1.5 mm, the roller corner is a convex curve, the estimated radius R of the roller corner to be detected is 0.1-0.2 mm, and the detection deviation e is required to be less than 0.001 mm.

[0040] The detection step length S can be calculated according to Formula 1, and the maximum step length S can be obtained to be 0.062 mm.

[0041] Setting parameters: Set the initial detection position near the roller corner, and set the detection scanning range to include the roller corner. Figure 6 As shown in Figures 1 and 2, the detection direction m is set according to the roller radius, and the detection normal n is opposite to m. The tangent direction of the radius to be detected is calculated based on the detection normal n. , that is, detect the tangential direction, set the detection scanning direction along the tangential direction sports.

[0042] During detection, if Figure 6 As shown in Figures 3 to 6, the probe ball head is used to gradually detect from the initial position according to the set detection step length, and the contact points along the detection normal n are recorded. Points. Compare with the detection method by multiplying n and get the maximum value, that is, [ ·n] max , denoted as By P m and The tangent information can be obtained, that is . To realize the spherical probe of a five-axis CNC machine tool to detect the tangent of a roller radius.

[0043] From the attached Figure 6 It can be seen intuitively that the probe ball head of the five-axis CNC machine tool found the point on the tangent direction and further determined a tangent line of the roller radius.

[0044] Example 2 In this embodiment, different from Embodiment 1, taking a three-axis CNC machine tool as an example, a spherical probe of the three-axis CNC machine tool is used to detect the tangent of a concave surface of a workpiece and a specified section in a specific direction, thereby solving the problem that the three-axis CNC machine tool cannot accurately detect the tangent of a surface and a specified section in a specific direction.

[0045] Preparation: Install a probe with a spherical probe on the three-axis CNC machine tool. This probe can capture the machine tool coordinate information of the detection point when it is triggered by contact along the direction of movement.

[0046] It is known that the radius r of the ball head of the probe is 2 mm, the workpiece is a concave surface, the estimated radius R of the surface to be detected is 50 mm, and the detection deviation e is required to be less than 0.001 mm.

[0047] The detection step length S can be calculated according to Formula 2, and the maximum step length S is 4.794 mm.

[0048] Set parameters: Set the initial detection position near the surface to be detected, set the scanning detection range to include the position to be detected, set the detection direction m, the detection normal to n, n and m are in the same direction, and calculate the tangent direction of the surface to be detected based on the detection normal n , set the detection scanning direction along the tangential direction The remaining steps are consistent with those in Example 1, so as to realize the detection of a tangent line of a concave surface of a workpiece and a specified cross section in a specific tangent direction by using a spherical probe of a three-axis CNC machine tool.

[0049] Example 3 In this embodiment, different from Embodiment 1, taking the continuous detection of the tangent of a curve with multiple concave and convex segments on a CNC machine tool as an example, the technical bottleneck that the CNC machine tool cannot realize high-precision real-time detection of the tangent of a complex continuous curve with multiple concave and convex segments is solved.

[0050] It is known that the radius r of the ball head of the probe is 2 mm, the minimum local radius R of the curve to be detected is 50 mm in the concave part, the maximum local radius R is 30 mm in the convex part, and the detection deviation e is required to be less than 0.001 mm.

[0051] Then the detection step length S of the convex line segment is calculated according to formula 1 1 , the maximum step length S can be obtained 1 It is 1.012mm.

[0052] The detection step length S of the concave segment is calculated according to formula 2. 2 , the maximum step length S can be obtained 2 It is 4.794 mm.

[0053] Set parameters: Set detection parameters for each curve segment separately. For convex line segments, the detection normal n is opposite to the detection direction m, and the corresponding fillet tangent direction to be detected is calculated. ; For concave line segments, set the detection normal n to be the same as the detection direction m, and calculate the corresponding fillet tangent direction to be detected .

[0054] During detection, the probes are respectively The remaining steps are the same as those in Example 1, so as to achieve high-precision tangent real-time detection of complex continuous curves with multiple concave and convex shapes.

[0055] In this embodiment, by processing the complex curve in sections and using a sectioned combination for detection, it can adapt to probes of arbitrary precision and has the ability to eliminate random errors, which greatly improves the accuracy and reliability of the detection results. The present invention breaks through the limitations of the prior art that only one end face can be detected and the tangent of the surface cannot be detected. It can realize the detection of the tangent of the surface on an ordinary machine tool and is no longer limited to the specific equipment of the three-coordinate measuring instrument. It also greatly reduces the requirements for the accuracy of the probe and greatly expands its application range in surface processing. For fields such as mold manufacturing and impeller processing that involve a large number of complex surface processing, this means that the processing path can be planned more accurately, the processing efficiency and product quality can be improved, and the processing difficulty and cost caused by detection limitations can be reduced.

[0056] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for detecting a curved surface tangent line, characterized in that: The target curve is detected by using a probe on a CNC machine tool to obtain the tangent position of the target curve perpendicular to the detection direction in a specified plane; The following steps are included: Parameter determination: segment the target curve according to the division method, estimate the radius R of the detected curve segment according to the segmented curve segments, and determine the detection parameters according to the segmented curve; Detection point acquisition: According to the determined detection parameters, the detected curve segments are detected according to the corresponding detection methods to obtain multiple groups of detection points ; Tangent point selection: Project it onto the detection normal n and calculate the maximum projection point As a cut point; Tangent calculation: Based on the obtained tangent point and the detection normal n, determine the tangent position of the detection.

2. A curved surface tangent detection method according to claim 1, characterized in that: The detection parameters include the detection contact surface, the detection direction m, the detection normal n, the tangent direction , the probe ball radius r and the detection step length S.

3. A curved surface tangent detection method according to claim 1, characterized in that: The target curve is the intersection curve of the specified plane and the target surface; the division method is to project the target curve onto the detection normal n, segment it according to the shape of the projected detection curve, and divide it into K curve segments containing at most one arc, where K≥1.

4. A curved surface tangent detection method according to claim 2, characterized in that: The detection direction m is parallel to the detection normal n; the tangent direction is a tangent direction perpendicular to the detection normal n in the specified plane .

5. A curved surface tangent detection method according to claim 2, characterized in that: It also includes determining the detection deviation angle θ before detection, so that θ≤45°; the detection deviation angle θ is the angle between the normal f of the probe contact surface and the detection normal n, where ; Where r is the radius of the probe ball head, is the position deviation along the detection normal.

6. A curved surface tangent detection method according to claim 2, characterized in that: The detection step length S is calculated according to the shape of the detected curve segment. When the detected curve segment is a convex line segment, the detection step length S is calculated as ； When the detected curve segment is a concave segment, the detection step length S is calculated as: ； In the formula, is the position deviation along the detection normal.

7. A curved surface tangent detection method according to claim 4, characterized in that: The tangent position information is expressed as .

8. A curved surface tangent detection method according to claim 4, characterized in that: The tangent direction To detect the normal n, rotate it by +90° or -90° in the specified plane.

9. A curved surface tangent detection method according to claim 1, characterized in that: The method also includes eliminating random errors of detection during detection. The random errors are eliminated by repeatedly detecting the position information of the tangent point of the tangent line for multiple times and averaging the measured detection point data.

10. A curved surface tangent detection method according to claim 1, characterized in that: It also includes setting a detection range according to the detected curve segment before detection; the detection range includes the farthest point on the curve segment, and the detection range cannot have two or more extreme values ​​on the detection normal n.

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