CN111336956A - Optical measurement system and method for online measurement of workpiece surface roughness - Google Patents

Abstract

The invention provides an optical measurement system and method for online measurement of workpiece surface roughness. The measurement system includes a laser, a transparent window simulation system, an acquisition screen and a data acquisition and processing system. The transparent window simulation system uses the transparent liquid to flush out the cooling liquid, and a transparent area is punched out above the surface of the workpiece to be measured, so that the measurement laser beam can reach the surface of the workpiece to be measured through the cooling liquid coating to achieve measurement. The measurement method is as follows: the collimated laser beam passes through the transparent measurement area generated by the transparent window simulation system, and is obliquely incident on the surface of the workpiece to be measured at a certain angle; the scattering image on the acquisition screen located in the reflection direction of the laser beam is taken, and the characteristic parameters are extracted; Using the calibration curve between the characteristic parameters and the surface roughness, the roughness value is calculated. By creating a transparent measurement area on the surface of the workpiece, the invention can realize the on-line detection of the surface quality of the workpiece under the cooling liquid processing condition.

Description

Optical measurement system and method for online measurement of workpiece surface roughness

technical field

The invention relates to an optical measurement system and method for online measurement of workpiece surface roughness, which is especially suitable for online detection of metal workpiece surface roughness in a cooling liquid environment.

Background technique

The online inspection of the workpiece surface refers to the quality of the workpiece during the process of machining the workpiece. It can actively detect the quality of workpiece processing and feed it back to the control system, thus forming a closed-loop system to control the entire processing process, which can greatly improve productivity and ensure product quality.

In the modern manufacturing industry, the machining of workpieces is usually carried out in a coolant environment. At present, there are mainly ultrasonic methods and optical methods for on-line detection of workpiece surfaces under the condition of coolant. Shin Y.C. et al. used a focused ultrasonic beam to achieve on-line inspection of surface roughness. But ultrasonic is a kind of mechanical wave, its measurement resolution is not enough, and its measurement parameters are average effect parameters, which cannot be used for high-precision surface measurement. Dong Min et al. used the optical fiber sensor as the carrier of the laser beam, and immersed the optical fiber in the cooling liquid to complete the measurement. However, the rotation of the workpiece and its reduction in size may cause changes in the coolant near the probe, which can affect the measurement results. In addition, compressed air can also be used to spray the measured surface to eliminate the influence of the cooling liquid, but this solution is prone to fog on the measured surface.

To sum up, many scholars have put forward some solutions for the problem of online measurement of workpiece surface in the coolant environment, but these solutions have some shortcomings and cannot completely solve the problem. Especially in the optical measurement method, the opacity of the cooling liquid hinders the propagation of the beam, which limits the application of the optical method in the on-line measurement of the workpiece surface.

SUMMARY OF THE INVENTION

Purpose of the invention: The purpose of the present invention is to provide a kind of optical measurement system and method for online measurement of workpiece surface roughness in view of the problems existing in the above-mentioned prior art, so as to realize the optical online measurement of workpiece surface roughness under cooling liquid environment, This increases productivity and guarantees product quality.

Technical scheme: the present invention adopts the following technical scheme for realizing the above-mentioned purpose:

An optical measurement system for online measurement of workpiece surface roughness, comprising: laser, transparent window simulation system, acquisition screen, data acquisition and processing system. Among them, the laser is used to emit a collimated laser beam, and the transparent window simulation system is used to simulate the transparent window measurement method in the cooling liquid environment, including: the cooling liquid storage tank, the cooling liquid pump, the cooling liquid flow meter, the cooling liquid joint, the cooling liquid Fluid Connection Pipe, Clear Liquid Reservoir, Clear Liquid Pump, Clear Liquid Flow Meter, Clear Liquid Connector, Clear Liquid Connection Pipe and Clear Window Simulation Device, the Coolant Tank, Coolant Pump, Coolant Flow Meter and The cooling liquid joint is connected in series through the cooling liquid connecting pipe, and the cooling liquid joint is arranged on the end plate of the transparent window simulation device; the transparent liquid liquid storage tank, the transparent liquid pump, the transparent liquid flowmeter and the transparent liquid joint are connected in series through the transparent liquid connecting pipe. The transparent liquid joint is arranged on the bottom plate of the transparent window simulation device; the workpiece to be tested is located at the bottom of the transparent window simulation device; the acquisition screen is used to collect the scattered images carrying the roughness information of the metal surface, and the data acquisition and processing system is used to take pictures on the acquisition screen scatter image and calculate the roughness value.

The transparent window simulation device is composed of an end plate, a side plate, a bottom plate and a transparent top plate to form a relatively closed cavity, and the cooling liquid is filled in the space between the transparent top plate and the bottom plate. A transparent area is formed between the surface of the workpiece to be tested and the top plate of the transparent window simulation device; the used cooling liquid and transparent liquid are discharged from the water outlet of the transparent window simulation device. The data acquisition and processing system includes: a photographing and imaging unit and a data processing unit, wherein: the photographing and imaging unit is used for photographing the scattered image on the acquisition screen and output to the data processing unit; the data processing unit is used for processing the image to extract features parameters to obtain the calibration curve and the roughness value.

An optical measurement method for online measurement of workpiece surface roughness, comprising the following steps:

In the first step, the collimated beam emitted by the laser passes through the transparent measurement area generated by the transparent window simulation system, and is incident on the surface of the workpiece to be measured at a certain angle; The cooling liquid punches out a transparent area above the surface of the workpiece to be measured, so that the measurement laser beam can reach the surface of the workpiece to be measured through the cooling liquid coating to achieve measurement.

The second step is to use the imaging unit of the data acquisition and processing system to collect the surface scattering image, process it, and extract the characteristic parameters; the collected surface scattering image is the reflection of the collimated beam emitted by the laser and incident on the surface to be measured through the transparent measurement area. And scattered, reflected and scattered light after passing through the transparent measurement area in the spatial distribution of the scattered image in the form of a band.

The third step is to substitute the characteristic parameters into the calibration curve to calculate the surface roughness value of the workpiece to be measured.

Beneficial effects: Compared with the prior art, the present invention has the beneficial effects as follows:

1. The transparent window simulation system of the present invention can create a transparent measurement area in the presence of cooling liquid, so as to eliminate the influence of opaque cooling liquid on optical measurement, and make it possible to detect the surface quality of the workpiece on-line in the cooling liquid environment. .

2. The present invention adopts the optical measurement method, the laser beam is incident obliquely, the surface scattering image is collected and the characteristic parameters are extracted to complete the measurement.

Description of drawings

FIG. 1 is a schematic diagram of a measurement system disclosed in an embodiment of the present invention.

FIG. 2 is a surface scattering image corresponding to different roughnesses of a transparent measurement area collected in an embodiment of the present invention.

FIG. 3 is a relationship diagram between scattering characteristic parameters and surface roughness in an embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the bright spot ratio and the surface roughness in an embodiment of the present invention.

FIG. 5 is a graph showing the relationship between the gray scale ratio of the bright spots and the surface roughness in an embodiment of the present invention.

Detailed ways

Below in conjunction with the accompanying drawings and specific embodiments, the present invention will be further clarified. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Modifications in the form of valence all fall within the scope defined by the appended claims of the present application.

As shown in FIG. 1 , in this embodiment, an optical measurement system for online measurement of workpiece surface roughness includes: a laser 1 , a transparent window simulation system 2 , an acquisition screen 3 , and a data acquisition and processing system 4 .

The laser 1 emits a collimated laser beam, which is obliquely incident on the metal surface to be measured at a set angle (eg, 30°). The output of the laser is: wavelength λ=632.8nm, power 5mW.

The transparent window simulation system 2 includes: a cooling liquid storage tank 5 and a transparent liquid storage tank 9, a cooling liquid pump 6 and a transparent liquid pump 10, a cooling liquid flowmeter 7 and a transparent liquid flowmeter 11, and a cooling liquid connector 8 And the transparent liquid joint 12, the connecting pipe and the transparent window simulation device 13, wherein: the cooling liquid storage tank 5, the cooling liquid pump 6, the cooling liquid flow meter 7 and the cooling liquid joint 8 are connected in series through the connecting pipe in sequence, and the cooling liquid joint 8 is set connected to the end plate of the transparent window simulation device 13; the transparent liquid storage tank 9, the transparent liquid pump 10, the transparent liquid flowmeter 11 and the transparent liquid joint 12 are connected in series through the connecting pipe in sequence, and the transparent liquid joint 12 is arranged on the side of the transparent window simulation device 13. Bottom plate; the workpiece to be tested is located at the bottom of the transparent window simulation device. The transparent window simulation device 13 is composed of end plates, side plates, bottom plates and transparent top plates, etc. to form a relatively closed cavity. The cooling liquid is filled in the space between the transparent top plate and the bottom plate. The flow rate is such that a transparent area is formed between the surface of the workpiece to be tested and the top plate of the transparent window simulation device 13 ; the used cooling liquid and transparent liquid are discharged from the water outlet of the transparent window simulation device 13 . The collection screen 3 is a transmissive hard frosted glass, which is placed in the reflection direction to collect scattered images carrying metal surface roughness information, and the height of the collection screen is consistent with the height of the laser, thereby ensuring the symmetry of the scattered light band.

The data acquisition and processing system 4 includes: a photographing and imaging unit and a data processing unit, wherein: the photographing and imaging unit is used to photograph the scattered image on the acquisition screen and output to the data processing unit; the data processing unit is used to process and extract the image Characteristic parameters, get the calibration curve and roughness value.

In this embodiment, an optical measurement method for online measurement of the surface roughness of a workpiece is carried out according to the following steps:

In the first step, the collimated beam emitted by the laser passes through the transparent window to simulate the transparent measurement area generated by the system, and is incident on the surface of the workpiece to be measured at a certain angle;

The transparent measurement area refers to: using the transparent window simulation system to simulate the transparent window measurement method in the cooling liquid environment, flushing the cooling liquid with the transparent liquid, and punching out a transparent area above the surface of the workpiece to be measured, so that the measurement laser beam can be measured. The measurement is achieved by the cooling liquid coating reaching the surface of the workpiece to be measured.

The second step is to use the imaging unit to collect surface scattering images, process them, and extract characteristic parameters;

The surface scattering image refers to: in the first step, the laser beam incident on the workpiece surface is reflected and scattered, and the reflected and scattered light passes through the transparent measurement area to form a scattered image with a band-like distribution in space.

The characteristic parameters refer to: scattering characteristic parameters, bright spot ratio and bright spot gray ratio. These three parameters are calculated according to certain algorithms after preprocessing the scattering image.

The scattering characteristic parameters are calculated according to the following formula:

是长轴方向散射线上灰度数值的平均值，k是常数；其中长轴方向为散射图像中狭长光带的主方向，长轴方向散射线是通过计算垂直于长轴方向上不同位置处的灰度平均值得到的；where n is the number of pixels on the long-axis scattering line, I _i is the gray value of the ith pixel on the long-axis scattering line, and P _i is the normalized gray value of the ith pixel on the long-axis scattering line degree value,

is the average value of the gray value on the long-axis direction scattering line, and k is a constant; the long-axis direction is the main direction of the narrow and long light band in the scattering image, and the long-axis direction scattering line is calculated by calculating the different positions perpendicular to the long-axis direction. The grayscale average value of ;

The bright spot ratio is the ratio of the number of bright spots to the number of sampling points in the entire image, and the bright spot gray ratio is the ratio of the sum of the gray values of the bright spots to the sum of the gray values of the entire image.

The third step is to substitute the characteristic parameters into the calibration curve to calculate the surface roughness value of the workpiece to be measured.

The calibration curve is obtained by using a standard roughness sample block. The grinding standard samples with known roughness values were selected for measurement, and multiple images were collected for each sample. For each image, according to the method described in the second step, the feature parameters are extracted respectively, and then the average value of each feature parameter is obtained. According to the change of the average value of each characteristic parameter with the roughness value, curve fitting is performed respectively to obtain the calibration curve between each characteristic parameter and the surface roughness. In the actual measurement, the surface roughness value can be calculated by analyzing the collected surface scattering images, extracting the characteristic parameters, and substituting them into the calibration curves respectively.

As shown in Fig. 3, Fig. 4 and Fig. 5, for the calibration curve obtained by the above steps in this embodiment, the surface grinding roughness standard sample block conforming to the GB6060.2-85 standard is selected, and the corresponding roughness value is They are: _Ra =0.025 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.8 μm. For each scatter image, first filter preprocessing to eliminate noise, and then calculate three characteristic parameters according to the second step.

During calibration, multiple images are collected for each sample block, and the average value of each feature parameter is obtained. Taking the roughness value as the abscissa and the average value of each feature parameter as the ordinate, the changes of each feature parameter with the roughness value are listed, and curve fitting is performed respectively to obtain the scattering feature parameter S, the bright spot ratio BPR and the bright spot gray. The expressions between the degree ratio BGR and the roughness _Ra are:

R²＝0.99823

R ² =0.99823

R²＝0.99503

R ² =0.99503

R²＝0.99964

R ² =0.99964

where R is the correlation coefficient.

In actual measurement, as long as the characteristic parameters are calculated according to the surface scattering image of the workpiece to be measured (multiple images can also be collected to calculate the average value of the characteristic parameters), and the corresponding expression is substituted, the surface roughness value can be obtained. In the case that the three feature parameters can accurately determine the roughness value and the roughness values are not much different, one of the feature parameters can be used; in addition, two or three feature parameters can be used to calculate the roughness value for Compare and verify each other.

Claims (6)

1. An optical measurement system for online measurement of surface roughness of a workpiece, comprising: the device comprises a laser, a transparent window simulation system, an acquisition screen and a data acquisition and processing system; the laser is used for emitting a collimated laser beam, and the transparent window simulation system is used for simulating a transparent window measurement method under a cooling liquid environment, and comprises the following steps: the cooling liquid storage tank, the cooling liquid pump, the cooling liquid flowmeter and the cooling liquid joint are sequentially connected in series through the cooling liquid connecting pipe, and the cooling liquid joint is arranged on an end plate of the transparent window simulation device; the transparent liquid storage tank, the transparent liquid pump, the transparent liquid flowmeter and the transparent liquid connector are sequentially connected in series through a transparent liquid connecting pipe, and the transparent liquid connector is arranged on a bottom plate of the transparent window simulation device; the workpiece to be measured is positioned at the bottom of the transparent window simulation device; the data acquisition and processing system is used for shooting the scattering image on the acquisition screen and calculating to obtain a roughness value.

2. The optical measurement system for on-line measurement of the surface roughness of the workpiece according to claim 1, wherein the transparent window simulator comprises an end plate, a side plate, a bottom plate and a transparent top plate, which form a relatively closed cavity, the cooling liquid is filled in the space between the transparent top plate and the bottom plate, and a transparent area is formed between the upper part of the surface of the workpiece to be measured and the top plate of the transparent window simulator by adjusting the flow rates of the cooling liquid and the transparent liquid; and the used cooling liquid and the transparent liquid are discharged from a water outlet of the transparent window simulator.

3. An optical measurement system for on-line measurement of workpiece surface roughness according to claim 1, wherein the data acquisition and processing system comprises: the device comprises a shooting imaging unit and a data processing unit, wherein the shooting imaging unit is used for shooting a scattering image on an acquisition screen and outputting the scattering image to the data processing unit; the data processing unit is used for processing the image and extracting characteristic parameters to obtain a calibration curve and a roughness value.

4. An optical measuring method for on-line measuring the surface roughness of a workpiece using an optical measuring system for on-line measuring the surface roughness of a workpiece according to any one of claims 1 to 3, comprising the steps of:

firstly, collimated light beams emitted by a laser pass through a transparent measurement area generated by a transparent window simulation system and are incident to the surface of a workpiece to be measured at a certain angle;

secondly, collecting a surface scattering image by using a shooting imaging unit of a data collecting and processing system, processing the surface scattering image and extracting characteristic parameters;

and thirdly, substituting the characteristic parameters into the calibration curve to calculate the surface roughness value of the workpiece to be measured.

5. The method as claimed in claim 4, wherein the transparent window simulation system generates a transparent measurement area by using a transparent liquid to blow away the cooling liquid, and a transparent area is punched above the surface of the workpiece to be measured, so that the measurement laser beam can reach the surface of the workpiece to be measured through the cooling liquid covering layer to realize measurement.

6. An optical measurement method for on-line measuring the surface roughness of a workpiece according to claim 4, characterized in that the collected surface scattering image is a scattering image which is formed in a band shape after collimated light beam emitted by a laser passes through a transparent measuring area and is incident to the surface to be measured to be reflected and scattered, and the reflected and scattered light passes through the transparent measuring area and is formed in space.

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