Method and system for checking dimensions or geometric features of a mechanical part
The method addresses the challenge of achieving accurate 3D reconstruction of non-axisymmetric mechanical parts by rotating and calculating spatial coordinates from edge point variations, enabling precise geometric and dimensional checks.
Patent Information
- Application Number
- JP2025515839
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-09-16
- Filing Date
- 2023-09-14
- Publication Date
- 2025-09-04
AI Technical Summary
Existing optoelectronic systems struggle to achieve accurate 3D reconstruction of mechanical parts with variable shapes that do not rotate around their axis of symmetry, limiting the effectiveness of dimensional and geometric feature checking.
A method involving rotation of the mechanical part around an axis, acquiring two-dimensional images, transforming detection profiles into a Cartesian reference system, and calculating spatial coordinates based on edge point variations to reconstruct the 3D model.
Enables accurate and complete checking of geometric and dimensional features by calculating spatial coordinates, overcoming limitations of existing systems in obtaining precise 3D models of non-axisymmetric parts.
Smart Images
Figure 2025529491000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a method and system for checking the dimensions or geometric features of a three-dimensional mechanical part rotating about an axis of rotation by means of an optical system. [Background technology]
[0002] It is known to perform measurement and checking of three-dimensional mechanical parts by any device, which can rotate about a rotation axis, and images of the mechanical part at corresponding cross sections during rotation are acquired by an optoelectronic system. More specifically, to obtain highly accurate results, it is known to employ a shadow-casting type optical measurement system including an emitter with a light source and a telecentric lens, a receiver with a photosensor, and a processing device. It is known that such devices are capable of obtaining highly accurate linear or two-dimensional images of the mechanical part.
[0003] If the part to be checked is axisymmetric and rotates around its own axis of symmetry, it is possible to obtain adequate information regarding the location of points on the entire surface of the part. However, if the part has a variable shape and / or does not rotate around its own axis of symmetry, this is generally not possible. More specifically, it is not possible to obtain an adequate 3D reconstruction of the part's surface from profiles extracted from images acquired during rotation at various cross sections. In fact, each two-dimensional image acquired during rotation of a mechanical part is a detection profile that does not necessarily correspond to the actual profile of the mechanical part on the corresponding cross section. The points that make up the detection profile may not necessarily be on such cross section, but may be at various unknown distances from the cross section, about which there is no information. Because an adequate 3D reconstruction of the part, i.e., evaluation of the location of points on the entire surface of the part, is generally not possible, the checking operations that can be performed are consequently limited. This is done, for example, in connection with a mechanical part featuring an external thread.
[0004] It is pointed out that systems and methods for acquiring 3D numerical objects corresponding to a mechanical part to be checked are known, including, for example, coordinate measuring machines equipped with contact sensors or devices using optoelectronic distance sensors, such as laser scanners, suitably positioned and oriented relative to the mechanical part to be controlled.
[0005] However, although devices with this type of photoelectronic sensor are generally reliable and widely used, they are often unable to obtain three-dimensional numerical objects corresponding to the parts to be controlled with the accuracy required and that can be obtained using shadow-casting measurement systems, which are caused by disturbances, for example, by undesirable reflection phenomena. Summary of the Invention [Problem to be solved by the invention]
[0006] The object of the present invention is to provide a method and an apparatus for checking the dimensions or geometrical characteristics of a mechanical part by means of an optoelectronic system, more particularly an optical measuring system of the shadow-casting type, which allows obtaining a 3D reconstruction of the mechanical part, i.e. calculating the spatial coordinates of the points of the surface of the mechanical part, and thus allowing the part to be measured in an accurate and complete manner. [Means for solving the problem]
[0007] A checking method according to claim 1 and a device according to claim 7 achieve this object.
[0008] In particular, the method according to the invention provides for rotating the mechanical part to be checked around a rotation axis, acquiring two-dimensional images of the mechanical part at successive rotation angles by an optoelectronic system, extracting relative detection profile points from each two-dimensional image, transforming each detection profile point into a measurement profile point in a Cartesian reference system which includes a measurement plane and whose first coordinate axis coincides with the rotation axis, identifying edge points in each measurement profile which correspond to the same value of the first coordinate in the Cartesian reference system, evaluating the variation in the position of these edge points as a function of the rotation angle, and calculating, based on this variation, the position of a point on the surface of the mechanical part which corresponds to that edge point of the measurement profile relative to the measurement plane, and the spatial coordinates of such point.
[0009] The last two steps are repeated for a predetermined number of values of the first coordinate, and the dimensions or geometric features of the mechanical part are checked based on such spatial coordinates of the point.
[0010] The method and device according to the invention will now be described with reference to the accompanying drawings, given as non-limiting examples, in which: [Brief explanation of the drawings]
[0011] [Figure 1] FIG. 1 shows, in a highly schematic manner, the essential components of a shadow casting system for obtaining two-dimensional images of mechanical parts. [Figure 2A] 2 is a graphical representation of several profiles acquired by the system of FIG. 1 during rotation of a machine part about axis A of FIG. 1; [Figure 2B] 2B is a graph showing how the positions of corresponding points of the profile of FIG. 2A vary during rotation of the machine part about axis A. FIG. [Figure 3] FIG. 1 is a schematic diagram of a shadow casting system for checking a machine part defining an external thread. [Figure 4] 1 is a graphical representation of the output of various steps in a checking process for a machine part having an external thread, as an example. [Figure 5] 1 is a graphical representation of the output of various steps in a checking process for a machine part having an external thread, as an example. [Figure 6] 1 is a graphical representation of the output of various steps in a checking process for a machine part having an external thread, as an example. [Figure 7] 1 is a graphical representation of the output of various steps in a checking process for a machine part having an external thread, as an example. [Figure 8] 1 is a graphical representation of the output of various steps in a checking process for a machine part having an external thread, as an example. [Figure 9] 1 is a graphical representation of the output of various steps in a checking process for a machine part having an external thread, as an example. DETAILED DESCRIPTION OF THE INVENTION
[0012] A checking device including an optoelectronic system of the shadow-casting type is shown very diagrammatically in Figure 1 and is designated by the reference number 1. It comprises an emitter 2 with a light source and a telecentric lens, and a receiver 3 with a sensor, in particular an e-matrix sensor. The mechanical part 4 to be checked is placed in a reference and support device and can be rotated about a rotation axis A, and the sensor 3 obtains a two-dimensional image 5 i The control and processing unit 10 is connected to the reference and support device to control the rotation of the machine part 4 and generates various rotation angles θ i The microscope is connected to an optoelectronic system to acquire two-dimensional images.
[0013] The 2D image 5 i The detected value of the profile position or "edge" E j k , i.e., the same z j The edge points of the profile in coordinates (or heights) are j kare grouped to obtain a curve that shows how the values of θ vary, and more specifically, the rotation angle θ i The x-axis represents the value of each coordinate on the measurement plane XZ as a function of σ (Figure 2B). In the example shown in the figure, the line z = z j and grouped 2D images 5 i The intersection between the profile of and generates two edges (k=1, k=2), but the number of generated edges K varies and depends on the shape of the machine part 4 to be checked. i Detected edge E from measurement plane XZ at j k The distance of the point belonging to the surface of the mechanical part 4 corresponding to is obtained by calculating the variation of said position as a function of the rotation angle θ.
[0014] In reality, the angle θ i For each angle θ, and as the mechanical part 4 rotates clockwise as the angle θ increases (or as the mechanical part 4 rotates counterclockwise as the angle θ decreases), the height z j Point p at i The position in space of each of the points p on the surface of the mechanical part 4 is i The spatial coordinates of are obtained by the following formula, where, as already mentioned, E j k is the height z j is the value of one of the K edges generated by and is one of the degrees k (k = 1, . . . , K).
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[0015] The 3D model is constructed by dividing the 3D model into 3D models with various predetermined heights z j Point p with i=1,...,N obtained at i It consists of a cloud or set of
[0016] A brief description of a particular preferred embodiment of the method according to the invention, including other steps than those mentioned above, follows: In the shadow casting device 1 of Fig. 1, the mechanical part 4 to be controlled, which is arranged between the emitter 2 and the receiver 3, rotates about an axis of rotation A, which is defined by a Cartesian reference system S f This defines the axis of the first coordinate Z.
[0017] During the rotation of the mechanical part 4, N 2D images 5 are taken. i is a continuous rotation angle θ that can cover a range of, for example, 180° or 360° at a given frequency. i , which is acquired by the control and processing unit 10 through the sensor 3. In particular, the height z j And when we consider all K edges in a 360° rotation, the angle θ i Each point of the mechanical part 4 obtained by i +180, there is some redundancy in the information. As a result, point p i To calculate all spatial coordinates of , it is possible to consider all K edges in a 180° rotation, or alternatively, K / 2 edges in a full 360° rotation.
[0018] 5 each 2D images i From the point C of the detection profile, a profile ("detection profile") is extracted. i The position (x, z) is on the plane X C Z C The reference system S associated with sensor 3, whose plane coincides with that of sensor 3, c It is identified in
[0019] Point C on the detection profile i (x, z) is transformed into the Cartesian reference system S by the parameters (transformation matrices and vectors) obtained in a known way during the calibration phase. f point F of the corresponding profile ("measurement profile") of i It is converted to (x, z).
[0020] M values of Z coordinate, i.e. height z j (j=1, . . . , M) are chosen so that the measurement profile is “sectioned”, i.e., for points F of such a measurement profile, it is desired to evaluate the position in space of the corresponding points of the actual profile of the machine part 4 and calculate the spatial coordinates. i (x, z), height z j is.
[0021] Edge E of various measurement profiles j k are grouped to obtain up to K traces (K=maximum number of edges that can be detected during the rotation of the mechanical part 4) that describe the profile of the edge (i.e., each coordinate x) as a function of the rotation angle θ. In general, an edge can be detected by the same trace at different angles θ i are grouped so as to include edges that represent the same part of the machine part 4. In general, the edges of two consecutive measurement profiles resulting from the same trace are those that have the closest values (x coordinates) to each other.
[0022] Rotation angle θ i As the value of z changes, jThe trend of the kth order (k=1, , K) edge in E j k (θ i ) is defined as follows:
[0023] The point p generated by the edge defined above i The spatial coordinates of are obtained, as mentioned before, by applying the formula:
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[0024] Height z j The spatial coordinates of the points calculated for each (j=1,...,M) constitute a cloud (or set) of points representing a three-dimensional numerical model of the machine part 4. The necessary checks and measurements, for example of geometric or dimensional features of the machine part 4, are carried out in a manner known per se using or based on such spatial coordinates. The method according to the invention can be implemented by an apparatus including an optoelectronic system with a matrix, a two-dimensional sensor, or different sensors as described above. For example, a linear one-dimensional sensor can be used. In this case, during rotation of the machine part, a two-dimensional image can be acquired by suitable scanning in a direction parallel to the rotation axis A.
[0025] The method according to the invention is carried out by determining a point p on the surface of the machine part 4 to be checked. iThis allows the calculation of the spatial coordinates of the points on the surface of the mechanical part 4, thereby enabling a complete and accurate check / measurement of the geometric and dimensional features of such mechanical part 4, in comparison with known methods employing two-dimensional or linear sensors and optoelectronic systems of the shadow-casting type. This is done by analyzing the instantaneous fluctuations in the position of the profile detected from the image provided by the shadow-casting technique, and identifying with good precision how the points of that profile "move" during the rotation of the mechanical part 4 about axis A. This makes it possible to have the missing information about the distance of the points on the surface of the mechanical part corresponding to the points of the measured profile relative to the measurement plane, and then to calculate the spatial coordinates of the points, which can be used to obtain a three-dimensional model of the mechanical part 4 and to carry out the check / measurement of the geometric and / or dimensional features of such mechanical part 4.
[0026] It should be noted that the formulas used in the preferred embodiment of the method according to the invention are always applicable, regardless of the particular type of part.
[0027] With reference to Figures 3 to 9, an example of an apparatus and method according to the invention will be described in relation to checking the geometric and dimensional characteristics of a threaded machine part 4 having an external profile with a helical development defining an external thread T and an axis of operation. Figure 3 shows diagrammatically an optoelectronic system 1 of the shadow-casting type, including an emitter 2 with a light source 21 and a telecentric lens 22, and a receiver 3 with a suitable optical element 32 and a matrix sensor 31. The machine part 4 with the thread T is placed on a reference and support device (not shown in Figure 3) and can be rotated about an axis of rotation A, which, in contrast to what can be shown in Figure 3, is parallel to the coordinate Z and generally does not coincide with the axis of operation. The receiver 3 can be rotated through various rotation angles θ i 1 is connected to a processing and control unit 10 which acquires a two-dimensional image of the thread T at
[0028] It should be noted that due to the spiral development of the surface, the contour of the image of the thread acquired using the shadow casting technique is generated by points that do not belong to a single cross section. That is, the points of the measurement profile obtained from the detection profile extracted from the acquired image (shadow) correspond to points on the surface of the thread T that are not on each cross section or measurement plane, with different unknown distances from the measurement plane (see FIG. 3, the plane XZ includes the axis A). As a result, in order to obtain a profile that approximates the true profile of the thread so as to allow a proper checking / measuring operation, it is necessary to apply an algorithm that corrects this "error" due to the geometry of the part and detects or calculates the distance of each point of the measurement profile from the measurement plane of the optoelectronic system.
[0029] During the rotation of the part 4 with the thread T, not necessarily about the axis of rotation A, a sufficiently large number of images are generated by the sensor 31 and acquired by the processing and control unit 10. i is stored for each image, and for each image, a detection profile is extracted. A curve lying in the XZ plane is obtained. Using axis calibration, the detection profile is rotationally translated so that the Z axis coincides with the rotation axis. The resulting measurement profile is shown in Figure 4.
[0030] Rotation angle θ i The information about is used as the X axis to "pack" the various curves in an XYZ system.
[0031] Height z j The number M of various sections in the j The height is divided into planes (Fig. 5). j and for each edge k, a function is obtained that describes the trend of the points of the measurement profile as the rotation angle θ varies (Fig. 6): E j k (θ i ) The derivative of such a function is calculated using an appropriate procedure and is given at a surface point pi The spatial coordinates of can be obtained using the formulas already cited, which are repeated here.
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[0032] Figure 7B shows the same threaded fastener as it can be reconstructed by the method according to the background art without applying the method of the present invention, i.e., without considering the points of the measurement profile as corresponding to points on the surface of the part that are all in the same measurement plane. The model of Figure 7B has parts that do not correspond to the actual surface of the threaded fastener to be checked, and as a result, the points forming such a model do not allow for the performance of an accurate check of the geometrical and dimensional features of the threaded fastener.
[0033] The spatial coordinates obtained according to the method of the present invention are rotationally translated in a reference system whose Z axis coincides with the axis of motion of the screw. This can be achieved by appropriately segmenting the region of the thread T from the measurement profile to obtain the thread axis. For example, if we manage to isolate the points belonging to the apex of the thread, after applying the above formula, they can be part of a cylinder (or cone) from which the axis can be calculated. The region of the machine part 4 outside the thread region may also be used to obtain the same axis.
[0034] In this way, it is possible to obtain a curve lying on a plane containing the axis of motion, or a point p i (Figure 8) calculate the cylindrical coordinates of each defined angle θ i From the curve thus obtained, it is possible, by means of an appropriate segmentation algorithm, to extract the thread profile (FIG. 9), which represents in a realistic way the true profile of the thread T, thus providing the desired precise information on the dimensions and geometrical features of the machine part 4.
Claims
1. A checking method for checking the dimensions or geometrical characteristics of a mechanical part (4) by means of an apparatus including an optoelectronic system (1) of the shadow-casting type, equipped with a linear or matrix sensor and a telecentric optical element, said method comprising: rotating the machine part (4) to be checked around an axis of rotation (A); The photoelectronic system (1) produces a two-dimensional image (5) of the machine part (4). ｉ ) by the continuous rotation angle (θ ｉ ) and the steps you will earn. Each two-dimensional image (5 ｉ ) to the corresponding detection profile point (C ｉ (x, z) The points (C ｉ (x, z)) is defined in a Cartesian reference system (S) that includes a measurement plane (XZ) and whose axis of the first coordinate (Z) coincides with said axis of rotation (A). ｆ ) at the point (F ｉ (x, z) The Cartesian reference system (S ｆ ) and the same value (Z) of the first coordinate (Z) ｊ ) of the edge points (E ｊ ｋ ) The edge point (E ｊ ｋ ) position fluctuation is calculated by the rotation angle (θ ｉ ) and based on the variation, calculate the edge point (E ｊ ｋ ) on the surface of the mechanical part (4), and the positions of the points on the surface of the mechanical part (4) corresponding to these points (p ｉ ) and calculating the spatial coordinates of The value of the first coordinate (Z) (z ｊ repeating the two previous steps for a predetermined number (M) of These points (p ｉ checking the dimensions or geometric characteristics of the mechanical part (4) based on the spatial coordinates of the including, a check method.
2. The edge point (E ｊ ｋ ) position fluctuation is calculated by the rotation angle (θ ｉ ) and based on the variation, calculate the edge point (E ｊ ｋ ) on the surface of the mechanical part (4), and the positions of the points on the surface of the mechanical part (4) corresponding to these points (p ｉ ) comprising applying the following formula: [Equation 1] where: E ｊ ｋ (θ ｉ ) is the rotation angle (θ ｉ ) varies, the same value (z ｊ ), and represents the tendency of edge points of degree k (k=1, . . . , K) in The ± sign is a positive sign if the mechanical part (4) rotates clockwise as the rotation angle (θ) increases, or if the mechanical part (4) rotates counterclockwise as the rotation angle (θ) decreases; 2. The checking method according to claim 1, wherein the sign is negative if the mechanical part (4) rotates counterclockwise as the rotation angle (θ) increases, or if the mechanical part (4) rotates clockwise as the rotation angle (θ) decreases.
3. The two-dimensional image (5) of the mechanical part (4) ｉ 3. A method according to claim 1 or 2, wherein the distance between the optical axis and the optical fiber is obtained by a two-dimensional sensor (3) of the optoelectronic system (1).
4. The two-dimensional image (5) of the mechanical part (4) ｉ 3. A checking method according to claim 1 or 2, wherein the rotational axis (A) is obtained by a linear sensor of the optoelectronic system (1) and by scanning the mechanical part (4) in a direction parallel to the rotational axis (A).
5. 5. A method according to any one of claims 1 to 4, for checking dimensions or geometrical features of machine parts that define an external thread (T) and an axis of movement.
6. Rotating and translating the calculated spatial coordinates in a reference system in which the axis of the first coordinate (Z) coincides with the axis of motion; Extracting the exact contour of the male thread (T); The checking method according to claim 5 , further comprising:
7. 1. A device for checking the dimensions or geometrical characteristics of a machine part (4), comprising: a reference and support device adapted to rotatably support said machine part (4) to be checked and to define an axis of rotation (A); A shadow-casting type optoelectronic system (1) comprising a linear or matrix sensor and a telecentric optical element; a control and processing unit connected to said reference and support device and said optoelectronic system, controlling the rotation of the machine part (4) to be checked about the axis of rotation (A); The photoelectronic system (1) produces a two-dimensional image (5) of the machine part (4). ｉ ) by the continuous rotation angle (θ ｉ ) and the steps you will earn. Each two-dimensional image (5 ｉ ) from the point (C ｉ (x, z) The points (C ｉ (x, z)) in a Cartesian reference system (S) that includes a measurement plane (XZ) and in which the axis of the first coordinate (Z) coincides with the axis of rotation (A). ｆ ) at the point (F ｉ (x, z) The Cartesian reference system (S ｆ ) and the same value of the first coordinate (Z) (z ｊ ) of the edge points (E ｊ ｋ ) The edge point (E ｊ ｋ ) is calculated by dividing the position of the ｉ ) and based on the variation, calculate the edge point (E ｊ ｋ ) and the positions of the points on the surface of the mechanical part (4) corresponding to these points (p ｉ ) and calculating the spatial coordinates of The value of the first coordinate (Z) (z ｊ repeating the two previous steps for a predetermined number (M) of These points (p ｉ and checking the dimensions or geometrical characteristics of said machine part (4) based on said spatial coordinates of said part (4).
1. An apparatus comprising: