CN111336956A - Optical measurement system and method for online measuring workpiece surface roughness - Google Patents
Optical measurement system and method for online measuring workpiece surface roughness Download PDFInfo
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- CN111336956A CN111336956A CN202010095593.XA CN202010095593A CN111336956A CN 111336956 A CN111336956 A CN 111336956A CN 202010095593 A CN202010095593 A CN 202010095593A CN 111336956 A CN111336956 A CN 111336956A
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
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Abstract
The invention provides an optical measurement system and method for online measuring the surface roughness of a workpiece. The transparent window simulation system flushes cooling liquid by means of transparent liquid, and flushes a transparent area above the surface of the workpiece to be measured, so that the measuring laser beam can reach the surface of the workpiece to be measured through the cooling liquid covering layer to realize measurement. The measuring method comprises the following steps: the collimated laser beam passes through a transparent measuring area generated by a transparent window simulation system and is obliquely incident to the surface of the workpiece to be measured at a certain angle; shooting a scattering image on an acquisition screen positioned in the reflection direction of the laser beam, and extracting characteristic parameters; and calculating the roughness value by using a calibration curve between the characteristic parameter and the surface roughness. The invention can realize the online detection of the surface quality of the workpiece under the cooling liquid processing condition by creating a transparent measuring area on the surface of the workpiece.
Description
Technical Field
The invention relates to an optical measurement system and method for online measuring the surface roughness of a workpiece, which are particularly suitable for online detection of the surface roughness of a metal workpiece in a cooling liquid environment.
Background
The online detection of the surface of the workpiece refers to the simultaneous detection of the quality of the workpiece during the processing of the workpiece. The method can actively detect the quality condition of workpiece processing and feed back the quality condition to the control system, thereby forming a closed-loop system to control the whole processing process, greatly improving the production rate and ensuring the product quality.
In modern manufacturing industry, the processing of workpieces is usually performed in a coolant environment. At present, the online detection of the surface of a workpiece under the condition of cooling liquid mainly comprises an ultrasonic method and an optical method. Shin y.c. et al use focused ultrasound beams to enable online detection of surface roughness. However, ultrasonic waves are mechanical waves, the measurement resolution is not sufficient, and the measurement parameters are average effect parameters, and cannot be used for measuring a surface with high precision. And the board sensor, etc. used an optical fiber sensor as a carrier for the laser beam, and the optical fiber was immersed in a cooling liquid to complete the measurement. But rotation of the workpiece and its reduction in size can cause changes in the cooling fluid near the probe, thereby affecting the measurement results. In addition, the measured surface may be blown with compressed air to eliminate the influence of the cooling liquid, but this solution is liable to form mist on the measured surface.
In summary, many scholars have proposed solutions to the problem of online measurement of workpiece surfaces in a coolant environment, but these solutions all have some disadvantages and fail to completely solve the problem. Especially in optical measurement methods, the use of optical methods for online measurement of the surface of a workpiece is limited because the opacity of the cooling liquid prevents the propagation of the light beam.
Disclosure of Invention
The purpose of the invention is as follows: the present invention is directed to solve the above problems of the prior art, and an object of the present invention is to provide an optical measurement system and method for online measuring the surface roughness of a workpiece, so as to realize optical online measurement of the surface roughness of the workpiece processed in a coolant environment, thereby improving productivity and ensuring product quality.
The technical scheme is as follows: in order to achieve the purpose, the invention adopts the following technical scheme:
an optical measurement system for online measurement of workpiece surface roughness, comprising: the device comprises a laser, a transparent window simulation system, a collection screen and a data collection 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 measuring 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 acquisition screen is used for acquiring a scattering image carrying metal surface roughness information, and the data acquisition and processing system is used for shooting the scattering image on the acquisition screen and calculating to obtain a roughness value.
The transparent window simulation device is characterized in that a relatively closed cavity is formed by an end plate, a side plate, a bottom plate and a transparent top plate, cooling liquid is filled in a space between the transparent top plate and the bottom plate, and a transparent area is formed between the upper part of the surface of a workpiece to be measured and the top plate of the transparent window simulation device 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. The data acquisition and processing system comprises: a photographing imaging unit and a data processing unit, wherein: the shooting imaging unit is used for shooting the scattering image on the 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.
An optical measurement method for online measuring the surface roughness of a workpiece comprises the following steps:
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; the transparent window simulation system generates a transparent measurement area, namely, a transparent area is punched above the surface of the workpiece to be measured by using transparent liquid to blow away cooling liquid, so that a measurement laser beam can reach the surface of the workpiece to be measured through a cooling liquid covering layer to realize measurement.
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; the collected surface scattering image is a scattering image which is formed in a space and distributed in a belt shape after collimated light beams emitted by a laser pass through a transparent measuring area and enter a surface to be measured to be reflected and scattered, and the reflected and scattered light beams pass through the transparent measuring area.
And thirdly, substituting the characteristic parameters into the calibration curve to calculate the surface roughness value of the workpiece to be measured.
Has the advantages that: compared with the prior art, the invention has the beneficial effects that:
1. the transparent window simulation system can create a transparent measurement area in the presence of cooling liquid to eliminate the influence of opaque cooling liquid on optical measurement, so that the online detection of the surface quality of a workpiece in a cooling liquid environment becomes possible.
2. The invention adopts an optical measurement method, the laser beam is obliquely incident, the surface scattering image is collected, and the characteristic parameters are extracted from the surface scattering image to complete the measurement, the measurement precision is high, the speed is high, the operation is convenient, the cost is low, and the prospect of the application to the on-line measurement is good.
Drawings
Fig. 1 is a schematic view of a measurement system according to an embodiment of the present invention.
Fig. 2 is a surface scattering image of a transparent measurement area corresponding to different roughness collected in an embodiment of the present invention.
FIG. 3 is a graph of the relationship 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 point ratio and the surface roughness in the embodiment of the present invention.
FIG. 5 is a graph showing the relationship between the brightness point gray scale ratio and the surface roughness according to the embodiment of the present invention.
Detailed Description
The present invention is further illustrated by the following description in conjunction with the accompanying drawings and the specific embodiments, it is to be understood that these examples are given solely for the purpose of illustration and are not intended as a definition of the limits of the invention, since various equivalent modifications will occur to those skilled in the art upon reading the present invention and fall within the limits of the appended claims.
As shown in fig. 1, in the present embodiment, an optical measurement system for online measuring the surface roughness of a workpiece includes: the device comprises 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, and the collimated laser beam obliquely enters the surface of the metal to be measured at a set angle (such as 30 degrees). The output of the laser is: wavelength lambda is 632.8nm, and power is 5 mW.
The transparent window simulation system 2 comprises: coolant liquid storage tank 5 and transparent liquid storage tank 9, coolant liquid pump 6 and transparent liquid pump 10, coolant liquid flowmeter 7 and transparent liquid flowmeter 11, coolant liquid connects 8 and transparent liquid connects 12, connecting pipe and transparent window analogue means 13, wherein: the cooling liquid storage tank 5, the cooling liquid pump 6, the cooling liquid flowmeter 7 and the cooling liquid connector 8 are sequentially connected in series through connecting pipes, and the cooling liquid connector 8 is arranged on an end plate of the transparent window simulator 13; the transparent liquid storage tank 9, the transparent liquid pump 10, the transparent liquid flowmeter 11 and the transparent liquid connector 12 are sequentially connected in series through connecting pipes, and the transparent liquid connector 12 is arranged on the bottom plate of the transparent window simulator 13; the workpiece to be measured is positioned at the bottom of the transparent window simulator. The transparent window simulation device 13 is a relatively closed cavity formed by an end plate, a side plate, a bottom plate, a transparent top plate and the like, cooling liquid is filled in a 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 simulation device 13 by adjusting the flow rate of the cooling liquid and the transparent liquid (such as water); the used cooling liquid and transparent liquid are discharged from the water outlet of the transparent window simulator 13. The acquisition screen 3 is transmission-type hard ground glass, is placed in the reflection direction, acquires a scattering image carrying metal surface roughness information, and has the height consistent with that of the laser, so that the symmetry of a scattering light band is ensured.
The data acquisition and processing system 4 comprises: a photographing imaging unit and a data processing unit, wherein: the shooting imaging unit is used for shooting the scattering image on the 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.
In this embodiment, an optical measurement method for online measuring the surface roughness of a workpiece is performed according to the following steps:
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;
the transparent measuring area refers to: a transparent window simulation system is utilized to simulate a transparent window measuring method under a cooling liquid environment, cooling liquid is flushed away by means of transparent liquid, a transparent area is flushed above the surface of a workpiece to be measured, and measuring laser beams can reach the surface of the workpiece to be measured through a cooling liquid covering layer to achieve measurement.
Secondly, collecting a surface scattering image by using a shooting imaging unit, processing the surface scattering image and extracting characteristic parameters;
the surface scattering image is as follows: the laser beam in the first step is incident to the surface of the workpiece to be reflected and scattered, and the reflected and scattered light passes through the transparent measuring area to form a band-shaped distributed scattering image in space.
The characteristic parameters are as follows: scattering characteristic parameters, bright point ratio and bright point gray scale ratio. The three parameters are calculated according to a certain algorithm after preprocessing the scattering image.
The scattering characteristic parameter is calculated according to the following formula:
where n is the number of pixels on the scattered ray in the long axis direction, IiIs the gray value of the ith pixel on the scattering line in the long axis direction, PiIs the normalized gray value of the ith pixel on the scattering line in the long axis direction,
is the average value of the gray scale values on the scattering lines in the long axis direction, and k is a constant; the long axis direction is the main direction of the long and narrow light band in the scattering image, and the scattering rays in the long axis direction are obtained by calculating the gray level average value at different positions in the direction perpendicular to the long axis;
the bright point ratio is the ratio of the number of bright points to the number of sampling points of the whole image, and the bright point gray ratio is the ratio of the sum of the gray values of the bright points to the sum of the gray values of the whole image.
And thirdly, substituting 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 measuring a standard roughness sample block. And selecting standard grinding sample blocks with known roughness values for measurement, and acquiring a plurality of images for each sample block. And (4) respectively extracting characteristic parameters for each image according to the method in the second step, and then solving the average value of each characteristic parameter. And respectively carrying out curve fitting according to the change condition of the average value of each characteristic parameter along with the roughness value to obtain a calibration curve between each characteristic parameter and the surface roughness. During actual measurement, the collected surface scattering image is analyzed, characteristic parameters are extracted, and the characteristic parameters are respectively substituted into the calibration curve to calculate the surface roughness value.
As shown in fig. 3, 4 and 5, for the calibration curve obtained by the above steps in this embodiment, the sample block of the surface grinding roughness standard conforming to the GB6060.2-85 standard is selected, and the corresponding roughness values are: ra0.025 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.8 μm. For each scattering image, firstly, filtering pretreatment is carried out to eliminate noise, and then, the noise is respectively eliminated according to the second stepThree characteristic parameters are calculated.
And (4) during calibration, acquiring a plurality of images by each sample block, and obtaining the average value of each characteristic parameter. The roughness value is taken as an abscissa, the average value of each characteristic parameter is taken as an ordinate, the change conditions of each characteristic parameter along with the roughness value are listed, curve fitting is respectively carried out, and the scattering characteristic parameter S, the bright point ratio BPR, the bright point gray scale ratio BGR and the roughness R are obtainedaThe expressions in between are:
wherein R is a correlation coefficient.
In actual measurement, the surface roughness value can be obtained by respectively calculating characteristic parameters according to the scattering images of the surface of the workpiece to be measured (or calculating the mean value of the characteristic parameters by collecting a plurality of images) and substituting the characteristic parameters into corresponding expressions. Under the condition that the roughness values can be accurately determined by the three characteristic parameters and the difference of the roughness values is not large, one of the characteristic parameters is used; in addition, two or three characteristic parameters can be used simultaneously to calculate roughness values for comparison and verification.
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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