Measuring device in small five-axis machine tool space error measuring system based on R-test

Abstract

The invention discloses an R-test-based measuring device in a small five-axis machine tool space error measuring system. The R-test-based measuring device comprises a cutter handle, a shell and a central mounting frame, wherein the central mounting frame is an I-shaped cylindrical component and is divided into a front section, a middle section and a rear section; the front section of the central mounting frame is a mounting part of a sensor; the middle section of the central mounting frame is a connecting column; the rear section of the central mounting frame is a connecting end of the cutter handle; the shell is assembled from the rear section to the front section of the center mounting frame and wraps the center mounting frame. By designing an integrated overall structure (a non-contact measurement system with an I-shaped center frame as a core), the problems that an existing R-test device is difficult to flexibly adapt to automatic tool changing of a small five-axis machine tool, the structural rigidity is insufficient, and the measurement range is small are solved, high integration level, high rigidity and in-situ measurement characteristics of the device are achieved, and the measurement accuracy is improved. And the measurement sensitivity, the measurement stability and the measurement space size are improved through the optimization of the installation poses of the sensors.

Description

Technical Field

[0001] This application belongs to the field of measurement device technology, specifically relating to a measurement device in a small five-axis machine tool spatial error measurement system based on R-test. Background Technology

[0002] A contact-type R-test measuring instrument, disclosed in CN119057567A, specifically includes a mounting ring with three sliding mechanisms slidably connected to it. Each moving mechanism is fixedly connected to a lifting mechanism, each lifting mechanism has a swing arm mechanism, each swing arm mechanism has a oscillating mechanism, each oscillating mechanism has a rotating mechanism, and each rotating mechanism has a telescopic mechanism. A contact displacement sensor is mounted on the telescopic end of each telescopic mechanism. A standard ball is positioned between the three contact displacement sensors and mounted on the rotating spindle tool holder of a machine tool. The positions of the three contact displacement sensors relative to the standard ball can be adjusted according to different measurement and algorithm requirements. However, it has the following technical drawbacks: the contact-type R-test measurement method suffers from decreased measurement accuracy due to wear during measurement; mounting the measuring ball on the spindle and the measuring device on the platform limits measurement to single-point measurement, making it unable to efficiently identify 41 geometric errors; and it does not provide a calibration method for sensor installation errors, affecting measurement accuracy. Summary of the Invention

[0003] In view of the shortcomings or deficiencies of the prior art, the technical problem to be solved by this application is to provide a measuring device in a small five-axis machine tool spatial error measurement system based on R-test.

[0004] To solve the above-mentioned technical problems, this application provides the following technical solution: This application proposes a measuring device in a small five-axis machine tool spatial error measurement system based on R-test, including: a tool holder, a housing, and a central mounting bracket; Wherein: the central mounting frame is an I-shaped cylindrical component, which is divided into three sections: front, middle and rear; The front section of the central mounting bracket is the sensor mounting section; The middle section of the central mounting frame is a connecting column; The rear section of the central mounting bracket is the connecting end of the tool holder; The outer casing is assembled from the rear to the front of the central mounting frame, enclosing the central mounting frame.

[0005] Optionally, the device also includes a battery compartment cover, which covers a battery compartment opening on the outer casing and can be opened when replacing the battery.

[0006] Further optionally, the button switch mounting hole is arranged on the shell and is used for mounting a button switch.

[0007] Further optionally, the first, second and third eddy current sensors are fixed by the first, second and third fixing plates respectively.

[0008] Further optionally, the first, second and third eddy current sensors are uniformly distributed on the center mounting frame at an included angle of 120°, and the axes of the first, second and third eddy current sensors converge at a point, and the elevation angle α of the axes is 45°.

[0009] Further optionally, the error parameter integration calibration method of the pose installation error and the spherical measurement error of the first, second and third eddy current sensors is further included.

[0010] Further optionally, the measurement model is determined, for measuring the sphere center, for the distance between the point and the measurement plane of the i-th eddy current sensor, for measuring the minimum distance between the sphere surface and the measurement plane of the i-th eddy current sensor, for measuring the sphere radius, for the unit normal vector of the measurement plane of the i-th eddy current sensor, for the center point of the measurement plane of the i-th eddy current sensor, then formula 1 is obtained, ; determining the error caused by eccentricity when measuring the spherical surface of the eddy current sensor, for the actual display measurement result of the sensor, 、 、 for the error parameter of the i-th eddy current sensor, for the distance between the sphere center and the axis of the i-th eddy current sensor, then formula 2 is obtained, ; and formula 3 is obtained, ; 、 are determined by three parameters respectively, plus , , Therefore, one sensor has nine parameters to be calibrated, three sensors have 27 parameters to be calibrated, and the precise coordinates of 100 measuring points in the measuring space are measured by using a three-coordinate measuring instrument and corresponding sensor data Solve , and , , Thus, the integrated calibration of the installation pose error and the spherical measurement error of the three sensors is completed. After calibration, the precise coordinates of the center of the measuring ball can be solved according to the above formula 1, formula 2, formula 3, error parameter calibration results and eddy current sensor display measurement data.

[0011] Further optionally, the small five-axis machine tool has 41 geometric errors, and the 41 geometric errors can be identified by measuring the position error of the machine tool at multiple measuring points.

[0012] Further optionally, a Jacobian matrix of the center of the measuring ball relative to the 41 geometric errors is determined; and an observability index is determined: the reciprocal of the singular value of the matrix. The index is minimized using the DETMAX algorithm to generate an optimized spatial distribution of the measuring ball.

[0013] The specific steps are as follows: Discretize the five-dimensional parameter space (x, y, z, c, a) of the machine tool to generate 78650 candidate spatial measuring points; Randomly select 10 candidate measuring points as an initial subset; Iterative optimization, each iteration adds a point that minimizes the observability index from the candidate point set, and removes a point that minimizes the observability index, until the added point and the removed point are the same, and the iteration is stopped; Obtain the final set of 10 measuring points, and generate the spatial distribution of the measuring ball according to the optimized 10 measuring points.

[0014] Compared with the prior art, the present application has the following technical effects: The present application solves the problems of the existing R-test device, such as difficulty in flexible adaptation to automatic tool changing of small five-axis machine tools, insufficient structural rigidity, and small measurement range, by designing an integrated structure (an I-shaped center frame as the core of a non-contact measurement system), realizes high integration, high rigidity and in-situ measurement characteristics of the device, and improves measurement sensitivity, stability and measurement space size through sensor installation pose optimization.

[0015] The application solves the key problem of the decline of the accuracy of the calculation of the sphere center caused by the installation deviation and the inherent characteristics of the sensor in the non-contact measurement by designing an integrated calibration method (simultaneously solving the installation pose error and the sensor spherical characteristic parameters), and realizes high-precision calculation of the sphere center coordinates under complex real conditions.

[0016] The application solves the problem of the decline of the measurement accuracy caused by the traditional regular distribution scheme of the measurement points by designing a multi-standard sphere workpiece and optimizing the spatial distribution of the measurement sphere based on the DETMAX algorithm. The measurement method of the application can realize fast measurement of multiple measurement points and can efficiently identify 41 geometric errors of the machine tool. The integrated calibration method of the application for installation errors and spherical measurement errors can effectively improve the measurement accuracy. The non-contact method of the application avoids the decline of the accuracy caused by wear. BRIEF DESCRIPTION OF DRAWINGS

[0017] Other features, objects and advantages of the application will become more apparent after reading the detailed description of the non-limiting embodiments made with reference to the following drawings: Fig. 1 : The overall structure diagram of the non-contact R-test measurement device in an embodiment of the application; Fig. 2 : The structure diagram of the non-contact R-test measurement device after hiding the shell in an embodiment of the application; Fig. 3 : The structure diagram of the center mounting frame in an embodiment of the application; Fig. 4 : The principle diagram of the non-contact R-test measurement in an embodiment of the application; Fig. 5 : The schematic diagram of the sensor installation error and the spherical measurement error in an embodiment of the application; Fig. 6 : The optimized distribution diagram of the multi-standard sphere workpiece in an embodiment of the application.

[0018] Reference signs: 1- handle; 2- shell; 3- battery compartment cover; 4- button switch; 5- center mounting frame; 6- first eddy current sensor; 7- second eddy current sensor; 8- third eddy current sensor; 9- first fixed plate; 10- second fixed plate; 11- third fixed plate; 501- handle connecting end; 502 - Connecting Post; 503 - Sensor mounting hole. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] like Figs. 1 to 3 As shown, in one embodiment of this application, the measuring device in the R-test-based small five-axis machine tool spatial error measurement system includes: a tool holder 1, a housing 2, and a central mounting bracket 5. Wherein: the central mounting frame 5 is an I-shaped cylindrical component, which is divided into three sections: front, middle and rear; The front section of the central mounting bracket 5 is the sensor mounting section; The middle section of the central mounting frame 5 is a connecting column 502, which serves to connect the front and rear sections and ensure the rigidity of the overall structure. The rear section of the central mounting bracket 5 is the tool holder connection end 501 of the tool holder 1, which serves to connect the tool holder 1 and enable the entire device to be installed on the machine tool swing head. The outer shell 2 is assembled from the rear to the front of the central mounting frame 5, enclosing the central mounting frame 5 and providing protection.

[0021] This embodiment solves the problems of existing R-test devices, such as difficulty in flexibly adapting to automatic tool changing on small five-axis machine tools, insufficient structural rigidity, and small measurement range, by designing an integrated overall structure (a non-contact measurement system with an I-shaped central frame as the core). It achieves high integration, high rigidity, and in-situ measurement characteristics of the device, and improves measurement sensitivity, stability, and measurement space size by optimizing the sensor installation posture.

[0022] Furthermore, in this embodiment, a battery compartment cover 3 is also included. The outer shell 2 has a battery compartment hole, which is covered by the battery compartment cover 3. When replacing the battery, the battery compartment cover 3 can be opened to facilitate battery replacement.

[0023] Furthermore, in this embodiment, it also includes: a button switch mounting hole, which is disposed on the housing 2, and is used to install a button switch 4, which is used to control the on / off state of the internal circuit.

[0024] Further, in the present embodiment, the first eddy current sensor 6, the second eddy current sensor 7 and the third eddy current sensor 8 are installed in the sensor installation holes 503 corresponding to the installation portions of the sensors at the front section of the center installation frame 5, and are fixed by the first fixing plate 9, the second fixing plate 10 and the third fixing plate 11.

[0025] In the present embodiment, further optionally, the first eddy current sensor 6, the second eddy current sensor 7 and the third eddy current sensor 8 are uniformly distributed on the center installation frame 5 at an included angle of 120°, and the axes of the first eddy current sensor 6, the second eddy current sensor 7 and the third eddy current sensor 8 converge at a point, with the elevation angle a of the axes being 45°. The distance p from the center point of the measurement plane of the first eddy current sensor 6, the second eddy current sensor 7 and the third eddy current sensor 8 to the axis of the center installation frame 5 is 10.25 mm, which two parameters determine the installation pose of the above-mentioned sensors, and are optimized parameters, ensuring high measurement sensitivity and stability of the above-mentioned sensors, and also ensuring a larger measurement space for the measurement device.

[0026] In the present embodiment, the distance of the measurement sphere is measured by the above-mentioned three eddy current sensors, and the coordinates of the sphere center are calculated according to the measurement data of the three sensors. Due to installation errors of the eddy current sensors and errors caused by deviation from the sphere axis during sphere surface measurement, etc., the calculation accuracy of the sphere center of the measurement sphere will be affected, and for this reason, a 27-item error parameter integrated calibration method for installation errors of the eddy current sensor pose and sphere surface measurement errors is designed.

[0027] Specifically, it further comprises determining a measurement model, for the sphere center of the measurement sphere, for the distance of the point from the measurement plane of the i-th eddy current sensor, the minimum distance of the sphere surface of the measurement sphere from the measurement plane of the i-th eddy current sensor, the radius of the measurement sphere, the unit normal vector of the measurement plane of the i-th eddy current sensor, the center point of the measurement plane of the i-th eddy current sensor, and there is formula 1, ; determining the error caused by eccentricity when the eddy current sensor measures the sphere surface, the actual display measurement result of the sensor, , , the error parameter of the i-th eddy current sensor, To measure the distance between the ball center and the axis of the i-th eddy current sensor, there is formula 2, ; And there is formula 3, ; , Each of which is determined by three parameters, plus , , Therefore, one sensor has nine parameters to be calibrated, and three sensors have 27 parameters to be calibrated. The precise coordinates of 100 measuring points in the measuring space are measured by using a three-coordinate measuring instrument And the corresponding sensor data Solve , And , , Thus, the integrated calibration of the installation pose error of the above three sensors and the spherical surface measurement error is completed. After calibration, the precise coordinates of the ball center of the measured ball can be solved according to the above formula 1, formula 2, formula 3, error parameter calibration results, and eddy current sensor display measurement data.

[0028] In this embodiment, the small five-axis machine tool has 41 geometric errors, which can be identified by measuring the position error of the machine tool at multiple measuring points. A multi-standard ball workpiece is designed for the small five-axis machine tool to measure the ball center positions of multiple standard balls, and the spatial error of the machine tool is identified according to the errors of multiple measuring points measured by the measuring device. An optimization method is designed to optimize the spatial distribution of multiple measuring points, improving the measurement and identification efficiency of spatial error.

[0029] Specifically, the Jacobian matrix of the ball center offset with respect to the 41 geometric errors is determined; the observability index: the reciprocal of the singular value of the matrix and The DETMAX algorithm is used to minimize the index to generate the optimized spatial distribution of the measuring ball.

[0030] The specific steps are as follows: Discretize the five-dimensional parameter space (x, y, z, c, a) of the machine tool to generate 78650 candidate spatial measuring points; Randomly select 10 candidate measuring points as the initial subset; Iterative optimization, each iteration adds a point that minimizes the observability index from the candidate point set, and removes a point that minimizes the observability index, until the added point and the removed point are the same, and the iteration stops; ​Obtain the final 10 measurement point set, and generate the measurement sphere space distribution according to the optimized 10 measurement points.

[0031] The present application solves the problems of the existing R-test device, such as difficult flexible adaptation to small five-axis machine tool automatic tool changing, insufficient structural rigidity, and small measurement range, by designing an integrated overall structure (a non-contact measurement system with a I-shaped center frame as the core), realizes high integration, high rigidity and in-situ measurement characteristics of the device, and improves the measurement sensitivity, stability and measurement space size through sensor installation pose optimization. The present application solves the key problem of the decline of the sphere center calculation accuracy caused by installation deviation and inherent characteristics of the sensor in the non-contact measurement by designing an integrated calibration method (simultaneously solving the installation pose error and the sensor spherical characteristic parameters), realizes high-precision calculation of the sphere center coordinates under complex real conditions. The present application solves the problem of low error identification efficiency caused by the traditional regular distribution scheme of measurement points by designing a multi-standard ball workpiece and optimizing the measurement sphere space distribution based on the DETMAX algorithm, and significantly improves the overall identification accuracy and solving efficiency of the geometric error parameters. In summary, the present application has broad market application prospects.

[0032] In the description of the present application, unless otherwise explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood broadly, for example, can be fixedly connected, or can be detachably connected, or integrated; can be mechanically connected, or electrically connected; can be directly connected, or indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0033] In the present application, unless otherwise explicitly specified and limited, the first feature "on" or "under" the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature "on", "above" and "above" the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "under", "below" and "below" the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0034] In the description of the present embodiments, the terms "upper", "lower", "left", "right", and the like, orientation or positional relationships are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only used to distinguish in the description, and have no special meaning.

[0035] The above embodiments are only used to illustrate the technical solutions of the present application and are not limited. The present application has been described in detail with reference to the preferred embodiments. Those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and all should be covered within the scope of the claims of the present application.

Claims

1. A measuring device in a small five-axis machine tool spatial error measurement system based on R-test, characterized in that, include: Handle, housing, and center mount; Wherein: the central mounting frame is an I-shaped cylindrical component, which is divided into three sections: front, middle and rear; The front section of the central mounting bracket is the sensor mounting section; The middle section of the central mounting frame is a connecting column; The rear section of the central mounting bracket is the connecting end of the tool holder; The outer casing is assembled from the rear to the front of the central mounting frame, enclosing the central mounting frame.

2. The measuring device in the small five-axis machine tool spatial error measurement system based on R-test according to claim 1, characterized in that, It also includes a battery compartment cover, which covers the battery compartment opening on the outer shell and can be opened when replacing the battery.

3. The measuring device in the small five-axis machine tool spatial error measurement system based on R-test according to claim 1, characterized in that, Also includes: A push-button switch mounting hole is provided on the housing for mounting a push-button switch.

4. The measuring device in the small five-axis machine tool spatial error measurement system based on R-test according to claim 1, characterized in that, Also includes: The first eddy current sensor, the second eddy current sensor, and the third eddy current sensor are respectively installed in the sensor mounting holes corresponding to the sensor mounting parts at the front of the central mounting frame, and are respectively fixed by the first fixing plate, the second fixing plate, and the third fixing plate.

5. The measuring device in the small five-axis machine tool spatial error measurement system based on R-test according to claim 4, characterized in that, The first eddy current sensor, the second eddy current sensor, and the third eddy current sensor are evenly distributed on the central mounting frame at an angle of 120°, and the axes of the first eddy current sensor, the second eddy current sensor, and the third eddy current sensor converge at a point, with an elevation angle α of 45°.

6. The measuring device in the small five-axis machine tool spatial error measurement system based on R-test according to claim 5, characterized in that, Also includes: A calibration method integrating the error parameters of the pose installation error and spherical measurement error of the first eddy current sensor, the second eddy current sensor, and the third eddy current sensor.

7. The measuring device in the small five-axis machine tool spatial error measurement system based on R-test according to claim 6, characterized in that, Also includes: Determine the measurement model. To measure the center of the ball, for The distance from point i to the measurement plane of the eddy current sensor. To measure the minimum distance between the spherical surface and the measurement plane of the i-th eddy current sensor, To measure the radius of the sphere, Let be the unit normal vector of the measurement plane of the i-th eddy current sensor. Let be the center point of the measurement plane of the i-th eddy current sensor, then we have Equation 1. ； Determine the error caused by eccentricity when using an eddy current sensor to measure a spherical surface. For the actual measurement results displayed by the sensor, , , Let be the error parameter of the i-th eddy current sensor. To measure the distance from the center of the sphere to the axis of the i-th eddy current sensor, we have Formula 2. ； And there is formula 3, ； , Determined by three parameters, plus , , Therefore, one sensor has nine parameters to be calibrated, and three sensors have a total of 27 parameters to be calibrated. A coordinate measuring machine is used to determine the precise coordinates of 100 measuring points in the measurement space. and corresponding sensor data Solve , as well as , , This completes the integrated calibration of the installation posture error and spherical measurement error of the above three sensors; After calibration, the center of the sphere can be determined by applying the above formulas 1, 2, and 3, the calibration results of the error parameters, and the measurement data displayed by the eddy current sensor. The precise coordinates.

8. The measuring device in the small five-axis machine tool spatial error measurement system based on R-test according to claim 1, characterized in that, The small five-axis machine tool has 41 geometric errors, which can be identified by measuring the positional error of the machine tool at multiple measurement points.

9. The measuring device in the small five-axis machine tool spatial error measurement system based on R-test according to claim 8, characterized in that, Determine the Jacobian matrix of the sphere's center offset with respect to 41 geometric errors; Determine the observability index: the sum of the reciprocals of the singular values ​​of the matrix; The DETMAX algorithm is used to minimize the index, generating an optimized spatial distribution of the measurement sphere.

10. The measuring device in the small five-axis machine tool spatial error measurement system based on R-test according to claim 9, characterized in that, The specific steps are as follows: Discretize the five-dimensional parameter space (x, y, z, c, a) of the machine tool to generate 78,650 candidate spatial measurement points; Ten candidate measurement points were randomly selected as the initial subset; Iterative optimization involves adding a point that minimizes the observability index from the candidate point set in each iteration and removing a point that has the least impact on the observability index, until the points to be added and removed are the same, at which point the iteration stops. The final set of 10 measurement points is obtained, and the spatial distribution of the measurement sphere is generated based on the optimized set of 10 measurement points.

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