A model unknown workpiece five-axis adaptive scanning measurement path planning method

Abstract

The application provides a model unknown workpiece five-axis adaptive scanning measurement path planning method, comprising: measuring a first face sheet to obtain actual measurement data of the first face sheet; predicting a current to-be-measured face sheet based on actual measurement data of a previous face sheet; planning a scanning path of a five-axis measuring machine according to the to-be-measured face sheet prediction; and the five-axis measuring machine measures according to the scanning path planning to obtain actual measurement data of the current to-be-measured face sheet. The application is suitable for five-axis scanning measurement of a CAD model unknown workpiece or a workpiece with a large machining distortion error, and does not require assistance of other measurement systems in the measurement process.

Description

Technical Field

[0001] This invention relates to a five-axis adaptive scanning path planning method, and more particularly to a five-axis adaptive scanning measurement path planning method for a workpiece with an unknown model. Background Technology

[0002] Freeform surface workpieces, such as impeller blades, are widely used in the aerospace field. Accurate and efficient measurement of these workpieces is crucial for workpiece evaluation and model reconstruction. Coordinate measuring machines (CMMs) offer advantages such as high measurement accuracy and a wide range, making them widely used in the precision measurement of parts. Traditional CMMs primarily perform point-by-point measurements, which consumes a significant amount of time in idle travel between points, making them unsuitable for measuring large numbers of data points. In contrast to traditional point-by-point measurement, five-axis scanning measurement can rapidly acquire a large number of data points through rapid stylus oscillation. Its structure is as follows... Figure 2 As shown, before five-axis scanning measurement, it is necessary to plan the measurement path and perform collision detection based on the workpiece model. However, some workpieces suffer severe wear due to long-term use, and their original CAD models can no longer be directly used to guide the measurement, or the workpiece CAD model cannot be obtained. Therefore, research is urgently needed on how to perform high-precision measurement on such workpieces with unknown models. In existing technologies, an additional non-contact probe is added to detect changes in the workpiece shape, thereby guiding the probe to perform measurements. However, its structure is relatively complex and not suitable for five-axis scanning measurement. Therefore, there is currently no five-axis adaptive scanning measurement path planning algorithm for workpieces with unknown models. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the purpose of this invention is to provide a five-axis adaptive scanning measurement path planning method for workpieces with unknown models.

[0004] According to one aspect of the present invention, a five-axis adaptive scanning measurement path planning method for a model unknown workpiece includes: measuring a first surface patch and obtaining actual measurement data of the first surface patch;

[0005] Also includes: iterative

[0006] Predict the current surface to be measured based on the actual measurement data of the previous surface;

[0007] The scanning path of the five-axis measuring machine is planned based on the predicted surface area to be measured.

[0008] The five-axis measuring machine performs measurements according to the scanning path plan to obtain the actual measurement data of the current surface to be measured.

[0009] Preferably, the first facet is measured to obtain actual measurement data of the first facet, including:

[0010] Measure initial data points on the surface to be tested;

[0011] By fitting the initial data points, the guide lines and cross-sectional lines of the surface to be measured are determined;

[0012] Based on the guide line and the first section line, the first predicted patch is obtained by fitting ruled surfaces.

[0013] Perform scanning path planning on the first predicted patch to determine the first segment of probe base trajectory and the first segment of probe tip trajectory;

[0014] The five-axis machine performs actual measurements based on the first segment of the probe base trajectory and the first segment of the probe tip trajectory to obtain the actual measurement data of the first predicted surface.

[0015] Preferably, the first predicted patch contains at least a segment of scan data;

[0016] The guide line is obtained by fitting a small number (5-7) of data points located near the central axis of the surface to be measured;

[0017] The first cross-sectional line is generated by fitting a small number (5-7) of data points that are generally perpendicular to the tangential direction of the first point of the guide line. The first point is determined by the order in which the guide lines are drawn, which corresponds to the order of the scanning measurements.

[0018] Preferably, the step of predicting the current surface to be measured based on the actual measurement data of the previous surface includes:

[0019] By fitting the actual measurement data of the previous patch, the boundary curve is obtained;

[0020] A new boundary curve is generated by combining the direction of the guide line; the guide line here is the same as the guide line of the first patch, which is the surface to be measured of an unknown model, and its guide line is fitted by manual measurement points.

[0021] Based on two boundary curves, predicted patches are obtained by fitting ruled surfaces.

[0022] The length of the predicted patch includes at least a segment of scan data.

[0023] Preferably, S′(u,v)=(1-u)b s (v)+ub e (v)

[0024] S′(u,v) is a ruled surface, b s (v)b e (v) are two boundary curves, where u and v are two directional parameters of the ruled surface.

[0025] Preferably, the step of predicting the current surface to be measured based on the actual measurement data of the previous surface further includes: adjusting the width of the obtained predicted surface by combining the width of the first cross-section line and the width in the actual measurement data of the previous surface.

[0026] Preferably, the adjustment parameter is equal to (width of the first cross-section line - width in the actual measured data of the previous patch) / width in the actual measured data of the previous patch.

[0027] Preferably, the scanning path planning of the five-axis measuring machine includes: probe trajectory planning and stylus trajectory planning for each surface to be measured.

[0028] Preferably, each segment of the measuring trajectory is connected to the previous segment of the measuring trajectory, and a new measuring trajectory is generated by fitting the endpoint of the previous segment of the measuring trajectory with a B-spline curve and the calculated trajectory.

[0029] Preferably, the probe scanning trajectory is obtained by constructing a sphere with the probe length as the radius for each point on the probe trajectory and finding its intersection with the predicted surface.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention proposes a five-axis adaptive scanning measurement path planning method for workpieces with unknown models, which is applicable to five-axis scanning measurement of workpieces with unknown CAD models or workpieces with large machining distortion errors, and no other measurement system is required during the measurement process;

[0032] The present invention proposes a five-axis adaptive scanning measurement path planning method for an unknown workpiece. Considering that the width of the actual measurement data is smaller than the width of the actual surface patch, the width of the predicted surface patch is adjusted, which solves the problem of the measurement width becoming smaller and ensures that the entire surface can be effectively measured.

[0033] The present invention proposes a five-axis adaptive scanning measurement path planning method for an unknown workpiece. The newly generated probe trajectory and the endpoint of the previous trajectory are fitted with a spline curve to ensure the continuity of the probe trajectory, thereby ensuring the continuity of the probe tip scanning trajectory and avoiding the impact of sudden changes in probe position on accuracy.

[0034] The five-axis adaptive scanning measurement path planning method for an unknown workpiece proposed in this invention provides a fast calculation speed while ensuring prediction accuracy, thus meeting the needs of online real-time measurement. Attached Figure Description

[0035] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0036] Figure 1 A flowchart of a five-axis adaptive scanning measurement path planning method for an unknown workpiece model is provided in an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the structure of a five-axis scanning measuring machine provided in an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the adaptive scanning measurement process provided in an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the predicted patch generation provided in an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram illustrating the generation of continuous measurement trajectory corresponding to the predicted surface patch provided in an embodiment of the present invention. Detailed Implementation

[0041] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0042] This invention provides an embodiment of a five-axis adaptive scanning measurement path planning method for a workpiece with an unknown model, comprising:

[0043] S1, Measure the first face piece and obtain the actual measurement data of the first face piece;

[0044] S2, predict the current surface to be measured based on the actual measurement data of the previous surface;

[0045] S3, Based on the predicted surface area to be measured, the scanning path of the five-axis measuring machine is planned;

[0046] S4, the five-axis measuring machine performs measurements according to the scanning path plan to obtain the actual measurement data of the current surface to be measured.

[0047] Repeat steps S2-S4 until the adaptive scanning measurement of the entire surface is completed.

[0048] Based on the above embodiments, the present invention provides a preferred embodiment, such as... Figure 1 The diagram shown is a flowchart of the five-axis adaptive scanning measurement path planning method for an unknown workpiece in this embodiment. Figure 2 This is a schematic diagram of the five-axis scanning measuring machine in this embodiment. Specifically, the five-axis adaptive scanning measurement path planning method for workpieces with unknown models includes:

[0049] S100: Manually measure a small number of data points and fit them to obtain guide lines and cross-sectional lines;

[0050] S200, fit the first patch, perform path planning and measurement;

[0051] S300, based on the measurement data, fits a new surface using ruled surfaces;

[0052] S400, based on the fitted surface patch, path planning determines the probe trajectory and probe trajectory;

[0053] S500, perform actual measurements and obtain a new set of measurement data;

[0054] S600: Determine whether the surface to be measured has been completely measured. If not, repeat S300-S600. If yes, end.

[0055] In a preferred embodiment provided by the present invention, steps S100-S200 are performed, see below. Figure 3 As shown, 5-7 data points are manually measured near the central axis of the surface to be measured, and then the guide line g can be fitted and determined; perpendicular to the guide line, 5-7 data points are manually measured at the beginning of the surface to be measured and the cross-sectional line sc is fitted and determined.

[0056] Based on the section line sc, the first predicted surface patch S is obtained by fitting a ruled surface in the direction of the guide line. 1 To minimize the deviation between the predicted surface patch and the actual surface, the length of the predicted surface patch should be as small as possible, but it should be greater than the length of a scan data segment and the length of a scan trajectory segment. This ensures that at least one complete data segment can be measured when the actual scan measures the surface patch, so that the subsequently planned trajectory can at least measure one data segment and complete the fitting of the next surface patch. Then, based on the path planning with respect to the predicted surface patch, the first segment of the measurement trajectory h is obtained. 1 and the first segment of the probe tip trajectory f 1 The actual measurement data (MP) of the predicted surface patch was obtained using a five-axis measuring machine. 1 .

[0057] A preferred embodiment of the present invention is provided to perform S300. Based on the measurement data, the next surface patch is predicted again, then the trajectory is planned based on the predicted surface patch, and then the actual measurement is performed using a five-axis measuring machine to obtain new measurement data... This process is repeated iteratively through the three steps of surface patch prediction, scanning path planning, and actual surface patch measurement until the adaptive scanning measurement of the entire surface is completed.

[0058] Specifically, S300 includes: except for the first facet, the predictions for subsequent facets are based on the measurement data from the previous segment. For example... Figure 4As shown, based on the measurement data MP from the previous step j-1 The boundary curve b is obtained through fitting. s According to the direction of the guide line in this segment Another boundary curve b can be determined through translation transformation. e Then, based on these two boundary curves, a ruled surface S′(u, v) can be obtained by fitting, as shown below:

[0059] S′(u, v)=(1-u)b s (v)+ub e (v)

[0060] Where u and v are two directional parameters of the ruled surface.

[0061] However, because the width of each measured data point is smaller than the actual width of the surface patch, the width of the fitted ruled surface is also smaller than the actual surface patch width. After multiple iterations, the actual measured width will become increasingly smaller. To prevent this from happening, in a preferred embodiment of the invention, a width adjustment parameter R is used. a The predicted patch S is determined after adjusting the width of S′(u, v). j , where R a The calculation formula is as follows:

[0062]

[0063] Where L w The width of the initial cross-section line; For MP j-1 width.

[0064] Similarly, the length of the predicted patch Sj should also be greater than the length of a scan data segment.

[0065] A preferred embodiment of the present invention is provided to perform S400, see [link to previous document]. Figure 5 As shown, based on Sj determined in the above embodiments, the probe trajectory mj of the predicted patch can be determined using its central axis and probe length, etc.

[0066]

[0067] Where L s For probe length, The probe direction can be calculated using the following formula:

[0068]

[0069] Where β and γ are set to 30° and 0° respectively, taking into account the actual five-axis scanning constraints.

[0070] The starting point of mj corresponds to point P in the measurement data, and the previous segment of the measuring trajectory h j-1 The endpoint corresponds to the endpoint of the measurement data, therefore mj and h j-1 There are overlapping parts, such as Figure 5 As shown. After removing the overlapping parts, the B-spline curve is used to analyze h. j-1 The endpoint and the remaining m j By performing fitting, a continuous positioning trajectory h can be obtained. j .

[0071] Then, at each point on the probe trajectory, a sphere with the probe length as the radius is drawn, and the intersection with the predicted surface is obtained to obtain the probe scanning trajectory f. j .

[0072] The five-axis measuring machine follows the probe trajectory h j and probe scanning trajectory f j Perform actual measurements on the surface.

[0073] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0074] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A five-axis adaptive scanning measurement path planning method for a workpiece with an unknown model, characterized in that, include: S1, Measure the first facet to obtain the actual measurement data of the first facet, including: S11, Measure the initial data points on the surface to be measured; S12, Fit the initial data points to determine the guide line and cross-sectional line of the surface to be measured; wherein the guide line and cross-sectional line are perpendicular to each other; S13, Based on the guide line and the cross-section line, the first predicted patch is obtained by fitting ruled surfaces; S14, Perform scanning path planning on the first predicted patch to determine the first segment of probe base trajectory and the first segment of probe tip trajectory; S15, the five-axis measuring machine performs actual measurement based on the first segment of the probe base trajectory and the first segment of the probe tip trajectory to obtain the actual measurement data of the first predicted surface; And iterative: S2, based on the actual measurement data of the previous patch, predicts the current patch to be measured, including: S21, Fit the actual measurement data of the previous patch to obtain the boundary curve; S22, generate another new boundary curve by combining the direction of the guide line; S23, based on two boundary curves, the predicted patch is obtained by fitting ruled surfaces; S24, combine the width of the cross-section line with the width in the actual measurement data of the previous patch, and adjust the width of the obtained predicted patch; Wherein, the adjustment parameter = (width of the cross-section line - width in the actual measurement data of the previous patch) / width in the actual measurement data of the previous patch; S3, Based on the predicted surface area to be measured, the scanning path of the five-axis measuring machine is planned; S4, the five-axis measuring machine performs measurements according to the scanning path plan to obtain the actual measurement data of the current surface to be measured.

2. The five-axis adaptive scanning measurement path planning method for an unknown workpiece according to claim 1, characterized in that, The length of the first predicted patch includes at least a segment of scan data; The guide line g is obtained by fitting several data points located near the central axis of the surface to be measured; The first section line sc is generated by fitting several data points in the tangential direction perpendicular to the first point of the guide line.

3. The five-axis adaptive scanning measurement path planning method for an unknown workpiece according to claim 1, characterized in that, ,in, It is a ruled surface. These are two boundary curves, among which , These are the two directional parameters of a ruled surface.

4. The five-axis adaptive scanning measurement path planning method for an unknown workpiece according to claim 1, characterized in that, The scanning path planning of the five-axis measuring machine includes: the probe trajectory planning and the stylus trajectory planning for each surface to be measured.

5. The five-axis adaptive scanning measurement path planning method for an unknown workpiece according to claim 4, characterized in that, Each segment of the probe trajectory is connected to the previous segment. A new probe trajectory is generated by fitting the endpoint of the previous probe trajectory with a B-spline curve and calculating the probe trajectory.

6. The five-axis adaptive scanning measurement path planning method for an unknown workpiece according to claim 4, characterized in that, The probe scanning trajectory can be obtained by constructing a sphere with the probe length as the radius for each point on the new probe trajectory and finding its intersection with the predicted surface.

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