CN105928470B - Free form surface surface topography On-machine Test method and device based on holographic method - Google Patents

Abstract

The invention relates to an on-machine detection method and device for the surface topography of a free-form surface based on a holographic method. Accurate and rapid measurement of free-form surfaces is difficult in existing technologies. The composition of the present invention includes: a detection device (15), the detection device includes a base A (2), the probe handle (1) is installed in the hole above the base A, and the base A passes through the slideway (10) Connected to the base B (7), the bottom of the probe handle is connected to the laser seat (3) through threads, the laser (4) is installed at the lower end of the laser seat, and the base B has a The partition (6), the partition is connected to the spatial light filter (5), the inner and lower parts of the base B are respectively connected to the beam splitter (8) and the mirror (14) through the card holder, and the detection method passes The wavefront distortion information of the reflected light beam on the curved surface is collected to obtain the measured spatial coordinate information. The invention is an on-machine detection device for free-form surface topography based on a holographic method.

Description

Method and device for on-machine detection of free-form surface topography based on holographic method

Technical field:

The invention relates to the field of optics and the technical field of on-machine measurement of numerical control machining, in particular to an on-machine detection method and device for free-form surface topography based on a holographic method.

Background technique:

In the existing technology, it is difficult to accurately measure and evaluate unknown free-form surfaces with non-rotating and asymmetric features. For surface measurement of free-form surfaces after processing, most of them use blue-ray digital raster 3D scanners or three-coordinate measuring machines. and other contact measuring instruments to measure it. Although the first two measurement methods are accurate, since the processed parts need to be removed from the processing machine to the measuring instrument, the process of moving and reinstalling the workpiece will not only produce Positioning errors will also prolong the measurement cycle, making the measurement process cumbersome. The contact measurement method not only has requirements for the workpiece material and steepness of the workpiece, but also requires corresponding error compensation and probe compensation for the measured value.

With the rapid development of aerospace, shipbuilding, automobile and mold industries, the application of free-form surfaces has become more and more extensive. At the same time, the requirements for high-efficiency and high-precision measurement and evaluation are also increasing. Therefore, smooth surfaces The measurement and evaluation of (rough) degree is of great significance.

Invention content:

The purpose of the present invention is to provide a method and device for on-machine detection of free-form surface topography based on holographic method.

Above-mentioned purpose realizes by following technical scheme:

An on-machine detection device for free-form surface topography based on a holographic method, which consists of: a detection device, the detection device includes a base A, and a probe handle is installed in a hole above the base A, and the The base A is connected to the base B through a slideway, the underside of the probe handle is connected to the laser seat through threads, the laser is installed at the lower end of the laser seat, and there is a partition in the base B. The partition plate is connected with the spatial light filter, and the inner and lower parts of the base B are respectively connected with the beam splitter and the mirror through the deck.

In the on-machine detection device for free-form surface topography based on the holographic method, the sensor baffle is connected to the upper part of the base A through fastening bolts, and a holographic wavefront sensor is installed on the sensor baffle. A positioning knob is installed on the base A corresponding to the position of the hole on the base B, and a workpiece with a free-form surface to be measured is placed under the beam splitter.

A method for on-machine detection of the surface topography of a free-form surface based on a holographic method by the detection device. The method includes the following steps: firstly, during measurement, the measuring head handle of the device is clamped on the main shaft and connected with the machine tool, and the movement of the detection device is controlled by the machine tool, and the detection device rotates with the main shaft. The axis of the main shaft is coaxial, so the detection device can accurately control the coordinates of the measured points through the machine tool during the working process;

Combining optical measurement with on-machine measurement, fast and accurate measurement of parts with unknown free-form surfaces, the light source provided by the laser in the laser seat, passes through the spatial optical filter in base B, and the spatial optical filter converts the light provided by the laser The light source is collimated into a standard plane wave. After the collimated beam passes through the beam splitter, a separated beam of transmitted light is projected onto the surface of the workpiece to be measured, and after being reflected by the workpiece to be measured, it is reflected back to the beam splitter, and then passes through the beam splitter. The reflection is projected to the mirror, and then it is incident into the holographic wavefront sensor. After the wavefront sensor collects the information of the wavefront distortion of the reflected light beam on the surface of the curved surface, the wavefront aberration and the data information of the measured point are obtained;

There is a positioning slide between base A and base B. During the measurement process, the distance between the laser and the spatial light filter can be precisely adjusted by adjusting the positioning knob on base A to achieve high-quality standard plane wave , thereby improving the detection accuracy.

Beneficial effect:

1. The present invention is a method and device for on-machine detection of free-form surface topography based on holographic methods,

The detection device based on the holographic wavefront sensor combines the optical element with the on-machine detection, and all the detection elements are designed in two base shells, so that the optical element is protected and prevents the external environment from affecting the measurement environment of the optical element. influence, improving the measurement accuracy.

The detection device based on the holographic wavefront sensor of the present invention adopts a non-contact measurement method to avoid

Due to the contact force in the measurement, it is impossible to perform contact measurement on soft, fragile objects, etc., avoiding deformation of the workpiece or even forming scratches on the surface during measurement, and avoiding the complicated process of secondary clamping of the workpiece, which improves the measurement efficiency. , At the same time, it has high measurement accuracy, good reliability and stability, and the obtained measurement data does not need to be compensated for the contact radius.

The detection device of the holographic wavefront sensor of the present invention, the shell is composed of two bases, not only convenient

It is convenient to assemble and disassemble all the parts, and the base B can be adjusted by adjusting the knob on the base A, so that the distance between the laser and the spatial light filter can be adjusted precisely, so that the spatial light filter can be used in different situations. Adjust to the most suitable distance from the laser to obtain high-quality parallel light, thereby improving the measurement accuracy and making the output parallel light quality of the spatial light filter.

The invention adopts the holographic wavefront sensor, avoids solving the wavefront through numerical calculation, can realize ultra-high-speed wavefront detection, has fast detection speed, is easy to use, flexible, reliable and has high detection accuracy.

The casing of the present invention adopts a material with light weight and strong rigidity, which not only reduces the load on the main shaft, but also avoids the deformation of the base A and base B, thereby ensuring the measurement accuracy requirements of the device.

The present invention applies the holographic wavefront sensing method to the detection of the surface topography of the freeform surface, and adopts a series of linear combinations of orthogonal Zernike polynomials to represent the wavefront aberration detected by the wavefront sensor, and then represent the entire freeform surface workpiece surface topography.

The present invention adopts the hardened steel free-form surface processed by a three-axis numerical control machine tool, and measures the surface topography of the free-form surface through a non-contact measuring device combined with a laser, a spatial light filter, a beam splitter and a wavefront sensor, and then from the surface smoothness ( roughness) to measure and evaluate the machining accuracy of free-form surface workpieces.

The detection device of the present invention is an optical measuring instrument based on computer vision, which adopts the principle of optical non-contact measurement, which can not only measure the workpiece directly on the processing machine tool after the workpiece is processed, but also avoid the above-mentioned secondary The positioning error caused by card loading is simple, convenient and time-saving.

The non-contact measurement of the present invention uses optical elements to measure without contacting the workpiece, and adopts the method of combining optical principles with on-machine measurement, especially for measuring fragile and deformable workpieces, soft material workpieces, and complicated shapes. Compared with other measurement methods, it has higher resolution, accuracy and efficiency for workpieces, coated surfaces and workpieces requiring high geometric accuracy, and can make up for the shortcomings of contact measurement.

The present invention uses the holographic wavefront sensor as the main optical element of the surface topography detection device. A beam of parallel light is irradiated on the surface of the workpiece and reflects a beam with wavefront distortion information. After being received by the holographic wavefront sensor, the The amplitude and phase information are analyzed, and then the curvature changes at different positions on the workpiece surface are reflected. The surface topography of the processed workpiece is simulated in the computer, and the method of integrating detection and processing has many advantages, and it is also the frontier direction of digital manufacturing.

Description of drawings:

Accompanying drawing 1 is the structural schematic diagram of the detection device of the present invention.

Accompanying drawing 2 is the appearance diagram of the detection device in accompanying drawing 1.

Accompanying drawing 3 is a schematic diagram of the working optical path of the detection device in accompanying drawing 1.

Accompanying drawing 4 is the principle diagram of detecting single mode aberration of the present invention.

Accompanying drawing 5 is the schematic diagram of detecting wavefront aberration by the holographic wavefront sensor of the present invention.

Accompanying drawing 6 is the UG model diagram of the free-form surface of hardened steel of the present invention.

Accompanying drawing 7 is the on-site diagram of the workpiece of hardened steel free-form surface of the present invention.

Accompanying drawing 8 is the simulation figure of workpiece surface of the present invention.

Accompanying drawing 9 is the planning diagram of the detection path of the hardened steel free-form surface of the present invention.

Accompanying drawing 10 is the topography diagram of the workpiece surveyed and drawn by the detection device in the accompanying drawing 1.

Accompanying drawing 11 is the roughness profile surveyed and mapped by the detection device in accompanying drawing 1.

Accompanying drawing 12 is the roughness profile observed by the ultra-depth-of-field microscope of the present invention.

Accompanying drawing 13 is an exploded view of parts of the detection device in accompanying drawing 1.

Detailed ways:

Example 1:

An on-machine detection device for free-form surface topography based on a holographic method, which consists of: a detection device 15, the detection device includes a base A2, and a probe handle 1 is installed in the hole above the base A, The base A is connected to the base B7 through a slideway 10, the bottom of the probe handle is connected to the laser seat 3 through threads, the laser 4 is installed at the lower end of the laser seat, and the base B has a The partition 6, the partition is connected with the spatial light filter 5, and the inner and lower parts of the base B are respectively connected with the beam splitter 8 and the mirror 14 through the card holder.

Example 2:

According to the on-machine detection device for free-form surface topography based on the holographic method described in Embodiment 1, the upper part of the base A is connected to the sensor baffle 12 through fastening bolts 11, and the sensor baffle is installed with For the holographic wavefront sensor 9, the base A is equipped with a positioning knob 13 corresponding to the position of the hole on the base B, and a workpiece 16 with a free-form surface to be measured is placed under the beam splitter.

Example 3:

A method for using the detection device described in Embodiment 1-2 to perform on-machine detection of free-form surface topography based on the holographic method. The method is as follows: firstly, during measurement, the probe handle of the device is clamped on the main shaft And connected with the machine tool, the movement of the detection device is controlled by the machine tool. The detection device rotates with the spindle. Since the installation position of the laser is coaxial with the axis of the machine tool spindle, the detection device can be accurately detected by the machine tool during work. control the coordinates of the measured points;

Combining optical measurement with on-machine measurement, fast and accurate measurement of parts with unknown free-form surfaces, the light source provided by the laser in the laser seat, passes through the spatial optical filter in base B, and the spatial optical filter converts the light provided by the laser The light source is collimated into a standard plane wave. After the collimated beam passes through the beam splitter, a separated beam of transmitted light is projected onto the surface of the workpiece to be measured, and after being reflected by the workpiece to be measured, it is reflected back to the beam splitter, and then passes through the beam splitter. The reflection is projected to the mirror, and then it is incident into the holographic wavefront sensor. After the wavefront sensor collects the information of the wavefront distortion of the reflected light beam on the surface of the curved surface, the wavefront aberration and the data information of the measured point are obtained;

There is a positioning slide between base A and base B. During the measurement process, the distance between the laser and the spatial light filter can be precisely adjusted by adjusting the positioning knob on base A to achieve high-quality standard plane wave , thereby improving the detection accuracy.

Example 4:

According to the method for on-machine detection of free-form surface topography based on the holographic method described in Embodiment 1-3,

1. Detection method based on holographic wavefront sensor

Wavefront sensing technology uses pure optical means to detect wavefront aberrations, and uses avalanche photodiode arrays as peak light intensity detection elements, which not only simplifies the optical path but also avoids the heavy matrix calculation process of traditional wavefront sensors. The detection efficiency and detection accuracy are greatly improved. We first introduce the single-mode phase difference detection method, and then explain the detection method of the wavefront distortion information with multiple aberration modes by the holographic wavefront sensor used in this article. , the principle of detecting single-mode aberrations is shown in Figure 4,

The hologram in the figure reuses two sub-holograms, let (x, y) be the plane coordinates of the hologram, (xA, yA, zA), (xB, yB, zB) are the coordinates of A and B respectively . K1(x, y) and K2(x, y) are reference lights converging on points A and B respectively. The bias light waves P1(x,y), P2(x,y) have positive and negative magnitude aberrations eSi(x,y), -eSi(x,y) respectively. The sub-hologram is formed by the interference between the bias light and the reference light, and its transmittance function is shown in formula (1):

(1)

The formula represents the conjugate relationship, j=√-1 . When a beam of light wave G(x,y) with fSi(x,y) mode aberration reflected by the workpiece enters the wavefront sensor and illuminates the hologram, the beams converging on two points A and B will be reproduced , as shown in formula (2):

(2)

There is a certain relationship between the peak light intensity of the light beam converging on points A and B and the aberration amplitude of the incident light wave. It can be obtained from theoretical analysis that the relationship between the aberrations of incident light waves can be approximately linear. Therefore, the wavefront aberration can be accurately calculated by detecting the peak light intensity of the two points A and B.

In the actual measurement process, since the free-form surface has the characteristics of rapid curvature changes and different curvatures at different positions, it is necessary to detect multiple aberration modes at the same time. According to the characteristics of the holographic element, it can be solved by multiplexing multiple pairs of sub-holograms. this problem. The spherical wave reflected from the workpiece back to the wavefront sensor is split on the peak light intensity detection element of the avalanche photodiode array. By detecting the relative peak intensity of each pair of spots, the overall wavefront aberration detection can be realized. Its basic principle is shown in accompanying drawing 5.

, Measurement of surface topography of free-form surface workpieces

When using the detection device proposed in this paper to detect the shape of the free-form surface of the processed workpiece, since the distorted wavefront reflected by the workpiece to the wavefront sensor is continuous, it can fully reflect the surface shape of the detected workpiece. appearance. Therefore, a continuous function can be chosen to represent the wavefront aberration detected by the holographic wavefront sensor, and further represent the surface shape of the workpiece. The wavefront aberration detected by the wavefront sensor can be expressed by the orthogonal Zernike polynomial as

(3)

In the formula, G ( x, y ) is the wavefront aberration detected by the wavefront sensor, which can reflect the z coordinate value of a certain detection point, Z _j ( x, y ) is the Zernike polynomial, and a _j is the jth polynomial coefficient. The Zernike polynomials are orthogonal in the region, so the specific expression can be expressed in polar coordinates as:

(4)

In the formula, R ^l _n ( ρ ) is expressed as an item related to the radial direction, Θ ^l _n ( θ ) is expressed as an item related to the argument angle, ( ρ, θ ) are polar coordinates in the area, where 0<ρ<1 , 0<θ<2π , n is the order of the polynomial, the value is a positive integer, l is the serial number related to n , and has the same parity as n , | l |≤ n . Let l=n - 2m ( m=0,1,2,… ), R ^l _n ( ρ ) can be expressed as:

(5)

Θ ^l _n ( θ ) can be expressed as:

(6)

Bringing Rln(ρ) and Θln(θ) in formulas (5) and (6) into formula (4), when n takes different values, the specific expression of each Zernike polynomial can be written, To represent various wave aberrations, and then represent the surface topography of the workpiece. This expression not only satisfies the description of complex free-form surfaces, but also achieves the required precision requirements.

According to the detection device proposed above, the simulation analysis and experimental verification are designed. Firstly, the hardened steel free-form surface model to be processed is drawn in UG (the model drawn in UG is shown in Figure 6), and then the processing program automatically generated by the software is used to select The three-axis machine tool is used for processing, and then the workpiece is simulated and analyzed to design a detection path. Finally, the detection device of the present invention is used to map the topography of the workpiece and compare it with the surface topography of the workpiece observed by an ultra-depth-of-field microscope.

In this experiment, the VDL1000E vertical machining center produced by Dalian Machine Tool Group Co., Ltd. was selected. Its numerical control system is used as the basis for measuring motion in the machine measurement system and is the carrier of data records. The FANUC Oi-MD numerical control system is adopted. The strokes in the three directions of X, Y and Z are 1200mm , 560mm and 600mm , the maximum spindle speed is 8000r/min , the maximum capacity of the tool magazine is 20 , the positioning accuracy is ± 0.012mm/ full course, the repeat positioning accuracy is ± 0.008mm /full course, and It provides RS232 external control interface. The program automatically generated by UG is used for processing, and the finishing parameters are selected as the spindle speed n: 4000r/ min , the feed rate V _f : 800mm/min , the depth of cut a _p : 0.2mm , the processing site and the processed workpiece are shown in Figure 7 shown.

The workpiece surface simulated according to the surface shape of the workpiece is shown in Figure 8, and the measurement path is planned according to the curved surface shape of the workpiece, and the obtained measurement path simulation results are shown in Figure 9.

Using a measuring device based on a holographic wavefront sensor, the surface of a free-form hardened steel part machined by a three-axis CNC machine tool VDL1000E was experimentally analyzed. Figure 10 shows the workpiece morphology measured by the detection device proposed by the present invention. The experimental results prove that the measurement method of this measuring device is simple, the efficiency is 15% higher than that of other measuring instruments, the speed is increased by 12%, and the speed is fast, and there is no need for secondary clamping of the processed workpiece, and it can be directly in the CNC after processing. Measurements are performed on the machine tool.

In order to verify the feasibility of the detection device based on the holographic wavefront sensor proposed in the present invention, a two-dimensional contour passing through the abnormal region is extracted from the topographic surface of the workpiece surveyed and mapped by the detection device, as shown in Figure 11 . A two-dimensional contour passing through the abnormal region is also extracted from the surface of the workpiece detected by the ultra-depth-of-field microscope, as shown in Figure 12. Comparing Figure 11 and Figure 12, there is a small difference. The reliability and authenticity of the roughness profile shown in Figure 11 are basically the same as those observed by other commonly used instruments such as ultra-depth-of-field microscopes.

The above experimental examples show that although the detection device based on the holographic wavefront sensor proposed above may occasionally produce signal abnormal points in the process of mapping the surface topography of the workpiece, there is no excessive information loss. The surface roughness profile of the workpiece measured by the observation instrument is basically the same. However, the device of the present invention can be directly installed on the machine tool, and can be measured quickly, so it is more practical.

Example 5:

According to the on-machine detection device for free-form surface topography based on the holographic method described in Embodiment 1-4, the functions of each main component are as follows:

1. Measuring head handle: directly connected with the base 1 and the spindle of the machine tool, used to connect the device and the spindle;

2. Base A: directly connected with the probe handle, laser seat, fastening bolt and base 2, as the main body of the whole device, through the connection with the probe handle, so that the whole device can be clamped on the spindle, and With the movement of the spindle, the lower end is connected to the laser seat coaxial with the probe handle, which is convenient for controlling parameters during measurement, and the connection with base B can easily adjust the length of the overall base, thereby changing the distance between the laser and the spatial light filter;

3. Laser base: directly connected with the base A and the laser, so that the laser can be coaxial with the probe handle.

Laser: Installed on the laser seat and coaxial with the laser seat and probe handle, and provides a light source for installing a detection device;

4. Spatial light filter: It is directly connected to the base B, and directly fixed on the partition inside the base B by fastening screws, so as to ensure that the filter is coaxial with the laser as much as possible. It is mainly used to collimate the light source emitted by the laser into a standard plane wave;

Optical lens: Both the beam splitter and the reflector are installed in the groove of the base B, so that the lens always maintains a 45° angle with the optical path to ensure the integrity of the optical path. The beam splitter is mainly used to transmit the light source to the On the workpiece, and reflect the reflected light from the workpiece to the reflector. The mirror is mainly used to reflect the test light reflected from the workpiece back to the detection device to the wavefront sensor;

5. Base B: It is directly connected with the spatial light filter, optical lens and base 1. There are partitions and grooves inside the base B, so that the spatial light filter and optical lens can be fixed in the base 2 as required. , to ensure the stability of the measurement, the base B is provided with a hole at a precise position, by adjusting the positioning knob on the base A and stretching the base B, the length of the detection device can be accurately adjusted, and the laser and the spatial light can be precisely controlled at the same time. Filter distance to obtain high-quality standard plane waves and improve detection accuracy;

6. Sensor baffle: directly connected with fastening bolts to fix the wavefront sensor;

7. Fastening bolts: directly connected to the sensor baffle and base A, and connected to the base A through the baffle, so that the wavefront sensor can be stably fixed on the base;

8. Wavefront sensor: fixed on the base A by the sensor baffle and fastening bolts. The wavefront sensor receives the test light from the mirror, detects the wavefront aberration by analyzing the test light, and simulates the surface topography of the measured workpiece through the connection with the experimental computer.

Claims (3)

1. An on-machine detection device for free-form surface topography based on a holographic method, comprising: a detection device, characterized in that: the detection device includes a base A, and the hole above the base A is equipped with Probe handle, the base A is connected to the base B through a slideway, the bottom of the probe handle is connected to the laser seat through threads, the laser is installed at the lower end of the laser seat, and the base B is There is a partition, and the partition is connected with the spatial light filter, and the inner and lower parts of the base B are respectively connected with the beam splitter and the mirror through the card holder. 2. The on-machine detection device for free-form surface topography based on holographic method according to claim 1, characterized in that: the upper part of the base A is connected to the sensor baffle by fastening bolts, and the sensor baffle is A holographic wavefront sensor is installed on the base A, a positioning knob is installed on the base A corresponding to the position of the hole on the base B, and a free-form surface workpiece to be measured is placed under the beam splitter. 3. A method for utilizing the detection device according to claim 1 or 2 to carry out on-machine detection of free-form surface topography based on a holographic method, characterized in that: the method comprises the steps of: First of all, when measuring, the probe handle of the device is clamped on the main shaft and connected to the machine tool. The machine tool controls the movement of the detection device. The detection device rotates with the main shaft. Since the installation position of the laser is the same as the axis of the machine tool main shaft axis, so the detection device can accurately control the coordinates of the measured points through the machine tool during work; Combining optical measurement with on-machine measurement, fast and accurate measurement of parts with unknown free-form surfaces, the light source provided by the laser in the laser seat, passes through the spatial optical filter in base B, and the spatial optical filter converts the light provided by the laser The light source is collimated into a standard plane wave. After the collimated beam passes through the beam splitter, a separated beam of transmitted light is projected onto the surface of the workpiece to be measured, and after being reflected by the workpiece to be measured, it is reflected back to the beam splitter, and then passes through the beam splitter. The reflection is projected to the mirror, and then it is incident into the holographic wavefront sensor. After the wavefront sensor collects the information of the wavefront distortion of the reflected light beam on the surface of the curved surface, the wavefront aberration and the data information of the measured point are obtained; There is a positioning slide between base A and base B. During the measurement process, the distance between the laser and the spatial light filter can be precisely adjusted by adjusting the positioning knob on base A to achieve high-quality standard plane wave , thereby improving the detection accuracy.