CN107702666B - Method for measuring coaxiality of threads and reference shaft - Google Patents
Method for measuring coaxiality of threads and reference shaft Download PDFInfo
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- CN107702666B CN107702666B CN201710762873.XA CN201710762873A CN107702666B CN 107702666 B CN107702666 B CN 107702666B CN 201710762873 A CN201710762873 A CN 201710762873A CN 107702666 B CN107702666 B CN 107702666B
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- G—PHYSICS
- 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
- G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
- G01B11/27—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes for testing the alignment of axes
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- G—PHYSICS
- 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
- G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates
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- G—PHYSICS
- 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
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/03—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by measuring coordinates of points
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- G—PHYSICS
- 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
- G01B11/08—Measuring arrangements characterised by the use of optical techniques for measuring diameters
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- G—PHYSICS
- 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
- G01B11/14—Measuring arrangements characterised by the use of optical techniques for measuring distance or clearance between spaced objects or spaced apertures
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- G—PHYSICS
- 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
- G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
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- Length Measuring Devices By Optical Means (AREA)
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Abstract
The invention discloses a method for measuring the coaxiality of a thread and a reference shaft, which comprises the following steps: clamping the measured thread on a thread clamp, locking and fixing, taking the position section as a 0-degree position section, and collecting images of each area by a CCD (charge coupled device); respectively obtaining boundary position coordinates of each area through image processing; calculating the upper vertex of each thread form full triangle and the lower vertex of each thread form full triangle; calculating the axis of the reference cylinder; calculating a thread axis; calculating the coaxiality of the cross-section thread at the 0-degree position and the reference cylinder; and rotating the thread clamp once at intervals of n degrees by taking the axis of the reference cylinder as an axis, calculating the coaxiality, and finally obtaining the average value E of the coaxiality as the coaxiality of the final thread and the reference cylinder. According to the invention, the acquired images are processed and calculated, so that the precision measurement of the coaxiality of the threads and the reference shaft is realized.
Description
Technical Field
The invention relates to the field of measurement, in particular to a method for measuring coaxiality of a thread and a reference shaft.
Background
In the precision machining and manufacturing process, the application of the threaded part is very wide, and the high-precision measurement of the threaded part is favorable for improving the assembly quality of the threaded part. The coaxiality error of the thread and the reference shaft refers to the variation of the middle-diameter cylindrical axis of the thread to the axis of the reference shaft, and is a difficult point for detection in the thread manufacturing industry. The traditional contact type thread coaxiality detection method is low in efficiency, low in automation degree and difficult to guarantee precision.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method overcomes the defects of the prior art, and the method for measuring the coaxiality of the thread and the reference shaft is provided, and the precision measurement of the coaxiality of the thread and the reference shaft is realized by processing and calculating the acquired image.
The purpose of the invention is realized by the following technical scheme: a method of measuring the coaxiality of a thread to a reference axis, the method comprising the steps of:
(1) clamping the measured thread on a thread clamp, taking the position section of the measured thread image acquired by the CCD at the moment as a 0-degree position section after locking and fixing, respectively translating the CCD to an upper surface Su area of a reference cylinder, a lower surface Sd area of the reference cylinder, a thread LW4 area, a thread LW2 area, a thread LW1 area and a thread LW3 area in sequence, and acquiring images of the areas;
(2) boundary position coordinates of a Su area of the upper surface of the reference cylinder, a Sd area of the lower surface of the reference cylinder, an LW4 area of the screw thread, an LW2 area of the screw thread, an LW1 area of the screw thread and an LW3 area of the screw thread are obtained through image processing;
(3) calculating the upper vertex of each thread form full triangle and the lower vertex of each thread form full triangle;
(4) calculating the axis of the reference cylinder;
(5) calculating a thread axis;
(6) calculating the coaxiality of the cross-section thread at the 0-degree position and the reference cylinder;
(7) and (3) taking the axis of the reference cylinder as an axis, rotating the thread clamp at intervals of n degrees, calculating the coaxiality according to the steps (1) to (6), and finally obtaining the average value E of a plurality of coaxiality as the coaxiality of the final thread and the reference cylinder.
In the method for measuring the coaxiality of the thread and the reference shaft, in the step (2), the image processing includes: preprocessing and sub-pixel processing.
In the method for measuring the coaxiality of the thread and the reference shaft, in the step (3), the step of calculating the upper vertex of each thread form full triangle and the lower vertex of each thread form full triangle includes: establishing a two-dimensional coordinate system, mapping boundary position coordinates of an upper surface Su area of a reference cylinder, a lower surface Sd area of the reference cylinder, an LW4 area of a thread, an LW2 area of the thread, an LW1 area of the thread and an LW3 area of the thread to the two-dimensional coordinate system, respectively obtaining a straight line MN and a straight line RT according to the boundary position coordinates of the upper surface Su area of the reference cylinder and the lower surface Sd area of the reference cylinder, obtaining straight lines F3F4, G3G4, H3H4, I3I4 and J3J4 on two sides of upper and lower thread forms according to the boundary position coordinates of the LW4 area, obtaining straight lines A3A4, B3B4, C3C4, D3D4 and E3E4 on two sides of the upper and lower thread forms according to the boundary position coordinates of the LW2 area of the thread, obtaining straight lines A1A2, B1B2, C1D 3D4, D863E 867 and E8658 and obtaining straight line coordinates of the upper and lower thread forms according to the boundary position coordinates of the boundary positions LW 367F 863F 867 and LW 863E 867, H1H, I1I, J1J, lower vertices o (x, y) are calculated from the straight line A1A and the straight line B1B, upper vertices o (x, y) are calculated from the straight line B1B and the straight line C1C, lower vertices o (x, y) are calculated from the straight line C1C, straight line C1C and the straight line D1D, lower vertices o (x, y) are calculated from the straight line D1D and the straight line E1E, lower vertices o (x, y) are calculated from the straight line F1F and the straight line G1G, upper vertices o (x, y) are calculated from the straight line I1I and the straight line J1J, upper vertices o (x, y) are calculated from the straight line A3A and the straight line B3B, lower vertices o (x, y) are calculated from the straight line B3C and the straight line C3C, upper vertices o (x, y) are calculated from the straight line D3D and the straight line E3D, upper vertices o (x, y) are calculated from the straight line G3C, y16), line G3G4 and line H3H4 calculate lower vertex o19(x19, y19), and line H3H4 and line I3I4 calculate upper vertex o17(x17, y17), line I3I4 and line J3J4 calculate lower vertex o20(x20, y 20).
In the method for measuring the coaxiality of the thread and the reference shaft, in the step (4), the step of calculating the axis of the reference cylinder includes: obtaining the boundary coordinate of a straight line MN of the Su area on the upper surface of the reference cylinder according to the boundary position coordinate of the Su area on the upper surface of the reference cylinder, and obtaining a fitting straight line y which is ku x + bu, wherein ku is the slope of the straight line MN and bu is the intercept of the straight line MN; obtaining the boundary coordinates of a straight line RT of the Sd region of the lower surface of the reference cylinder according to the boundary position coordinates of the Sd region of the lower surface of the reference cylinder, and obtaining a fitting straight line y which is kd x + bd, wherein kd is the slope of the straight line RT, and bd is the intercept of the straight line RT; finally, the axis L0 of the reference cylinder is calculated as y0 ═ k0 × x + b0, where k0 ═ ku + kd)/2 and b0 ═ bu + bd)/2, where k0 is the slope of the straight line L0 and b0 is the intercept of the straight line L0.
In the method for measuring the coaxiality of the thread and the reference shaft, in the step (5), the step of calculating the thread axis includes: obtaining an upper thread pitch diameter line point P ((x + x)/2, (y + y)/2) from the coordinates of the upper vertex o and the lower vertex o, obtaining an upper thread pitch diameter line point P ((x + x)/2) from the coordinates of the upper vertex o and the lower vertex o, (y13+ y15)/2) fitting the upper thread pitch line point P2, the upper thread pitch line point P3, the upper thread pitch line point P4, the upper thread pitch line point P7, the upper thread pitch line point P8 and the upper thread pitch line point P9 to obtain an upper thread pitch line y-k 1 × x + b1, wherein k1 is the slope of the straight line, and b1 is the intercept of the straight line; obtaining a lower thread pitch diameter line point P ((x + x)/2, (y + y)/2) from the coordinates of the upper vertex o and the lower vertex o, obtaining a lower thread pitch diameter line point P ((x + x)/2) from the coordinates of the upper vertex o and the lower vertex o, (y17+ y20)/2) fitting the lower thread pitch line point P12, the lower thread pitch line point P13, the lower thread pitch line point P14, the lower thread pitch line point P17, the lower thread pitch line point P18 and the lower thread pitch line point P19 to obtain a lower thread pitch line y which is k2 × x + b2, wherein k2 is the slope of the straight line, and b2 is the intercept of the straight line; the thread axis L1 is yL ═ k × x + b, where k ═ k1+ k2)/2, and b ═ b1+ b2)/2, where k is the slope of the line L1 and b is the intercept of the line L1, as determined from the upper and lower thread radii.
In the method for measuring the coaxiality of the thread and the reference shaft, in the step (6), the step of calculating the coaxiality of the 0-degree position cross-section thread and the reference cylinder includes: calculating the value of x in the length range of the thread, wherein the maximum value s of the distance | yL-y0| between the thread axis L1 and the axis L0 of the reference cylinder is max (| yL-y0|), and taking 2 times of max (| yL-y0|) as the coaxiality E between the cross-section thread at the 0-degree position and the reference cylinder1。
In the method for measuring the coaxiality of the thread and the reference shaft, in the step (7), the formula of the average value E is as follows:
wherein E isiThe coaxiality of the thread and the reference cylinder of the section at the ith position is shown.
In the method for measuring the coaxiality of the screw thread and the reference shaft, in the step (7), the n degree is in the range of 10-90 degrees.
In the method for measuring the coaxiality of the thread and the reference shaft, the pretreatment comprises the following steps: loading the collected image, enhancing the image, nonlinear filtering, binarization processing, edge identification and pixel level edge detection.
In the method for measuring the coaxiality of the thread and the reference shaft, the sub-pixel processing comprises the following steps: and performing sub-pixel calculation on the preprocessed image to obtain the edge contour position of the three-dimensional sub-pixel precision of the image, obtaining the boundary position coordinate and storing the boundary position coordinate.
Compared with the prior art, the invention has the following beneficial effects:
(1) according to the coaxiality measuring method, images of all parts of the thread are obtained by using a CCD (charge coupled device) according to the coaxiality definition of the thread and the reference cylinder by adopting an image measuring method, then the images are processed and calculated, and finally the coaxiality of the thread and the reference cylinder is measured;
(2) the invention can realize the precise measurement of the major diameter, the minor diameter, the pitch, the thread form angle and the thread height of the thread.
Drawings
FIG. 1 is a schematic illustration of an image acquisition process of a measured thread of the present invention;
FIG. 2 is a flow chart of the image processing of the present invention;
FIG. 3 is a schematic illustration of the coaxiality definition and calculation of the threads and the reference axis of the present invention.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
the invention provides a method for measuring coaxiality of a thread and a reference shaft, which comprises the following steps:
(1) clamping the measured screw thread on a screw thread clamp, taking the position section as a 0-degree position section after locking and fixing, respectively translating a CCD (charge coupled device) to an upper surface Su area of a reference cylinder, a lower surface Sd area of the reference cylinder, a screw thread LW4 area, a screw thread LW2 area, a screw thread LW1 area and a screw thread LW3 area in sequence, and acquiring images of the areas; wherein the 0 degree position cross section is taken as the first position cross section.
(2) Boundary position coordinates of a Su area of the upper surface of the reference cylinder, a Sd area of the lower surface of the reference cylinder, an LW4 area of the screw thread, an LW2 area of the screw thread, an LW1 area of the screw thread and an LW3 area of the screw thread are obtained through image processing;
(3) calculating the upper vertex of each thread form full triangle and the lower vertex of each thread form full triangle;
(4) calculating the axis of the reference cylinder;
(5) calculating a thread axis;
(6) calculating the coaxiality of the cross-section thread at the 0-degree position and the reference cylinder;
(7) and (3) taking the axis of the reference cylinder as an axis, rotating the thread clamp at intervals of n degrees, calculating the coaxiality according to the steps (1) to (6), and finally obtaining the average value E of a plurality of coaxiality as the coaxiality of the final thread and the reference cylinder. It should be noted that, a cross section at 0 degree is taken as a first position cross section, a cross section at a second position is taken from 0 degree to n degrees, a cross section at a third position is taken from n degrees, and so on, and a cross section at an ith position is taken from an i-1 th time to n degrees.
In particular, the method comprises the following steps of,
(1) fig. 1 is an image acquisition flow of a measured thread, fig. 2 is an image processing flow, and fig. 3 is a schematic diagram of coaxiality definition and calculation of the thread and a reference axis. As shown in fig. 1 and 3, the screw to be measured was clamped to the screw clamp, and the cross section at this position was taken as a 0-degree position cross section. The CCD is respectively translated to an upper surface Su area of the reference cylinder, a lower surface Sd area of the reference cylinder, a thread LW4 area, a thread LW2 area, a thread LW1 area and a thread LW3 area in sequence, and images of the areas are collected. Firstly, the CCD is translated to the Su area of the upper surface of the reference cylinder, and the contour image of the Su area is acquired. And moving the CCD to the Sd area on the lower surface of the reference cylinder by taking the Su area on the upper surface of the reference cylinder as a starting zero point, wherein the moving amount of the Sd area relative to the Su area is (delta X1, delta Y1). Then, the CCD is moved from the Sd region to the screw LW4 region and an image is captured, the amount of movement of the screw LW4 region with respect to the Su region being (Δ X2, Δ Y2). And then the CCD is moved from the area of the thread LW4 to the area of the thread LW2, and images are collected, wherein the moving amount of the area of the thread LW2 relative to the Su area is (delta X3, delta Y3). And then the CCD is moved from the LW2 area to the screw LW1 area and images are collected, and the movement amount of the screw LW1 area relative to the Su area is (delta X4, delta Y4). Finally, the CCD is moved from the LW1 area to the screw LW3 area and images are collected, and the moving amount of the screw LW3 area relative to the Su area is (delta X5, delta Y5);
(2) boundary position coordinates of a Su area of the upper surface of the reference cylinder, a Sd area of the lower surface of the reference cylinder, an LW4 area of the screw thread, an LW2 area of the screw thread, an LW1 area of the screw thread and an LW3 area of the screw thread are obtained through image processing; as shown in fig. 2, the image processing specifically includes: loading the collected image, enhancing the image, filtering, thresholding, recognizing the edge, detecting the edge at pixel level, processing the edge at sub-pixel level, and storing the coordinate of the boundary position for calculation in the image. Wherein the area of the upper surface Su of the reference cylinder and the area of the lower surface Sd of the reference cylinder both store linear boundary coordinates, the area of the screw LW1, the area of the screw LW2, the area of the screw LW3 and the area of the screw LW4 all store boundary coordinates of both sides of the thread profile, as shown in fig. 3, the boundary of the Su region of the upper surface of the reference cylinder is a straight line MN, the boundary of the Sd region of the lower surface of the reference cylinder is a straight line RT, the boundaries of both sides of the thread profile obtained from the LW1 region of the thread are straight lines A1a2, B1B2, C1C2, D1D2 and E1E2, the straight lines of both sides of the thread profile obtained from the LW3 region of the thread are straight lines F1F2, G1G2, H1H2, I1I2 and J1J2, the straight lines of both sides of the thread profile obtained from the LW2 region of the thread are straight lines A3a4, B3B4, C3C4, D3D4 and E3E4, and the straight lines obtained from the LW4 region of the thread profile are straight lines F3F4, G3G4, H3H4, I3I4 and J863J 4;
(3) establishing a two-dimensional coordinate system, and mapping all boundary position coordinates of a reference cylinder upper surface Su area, a reference cylinder lower surface Sd area, a thread LW4 area, a thread LW2 area, a thread LW1 area and a thread LW3 area to the two-dimensional coordinate system. In fig. 3, o1, o2, o3, o8, o9, o10, o11, o12, o13, o18, o19, o20 are the upper vertices of the full triangle of the thread profile, o4, o5, o6, o7, o14, o15, o16, o17 are the lower vertices of the full triangle of the thread profile, a1, B1, C1, D1, E1, F1, G1, H1, I1, J1 are the intersections of the large diameter line of the upper thread with the straight lines on both sides of the threads, a4, B4, C4, D4, E4, F4, G4, H4, I4, J4 are the intersections of the large diameter line of the lower thread with the straight lines on both sides of the threads, a4, B68672, C72, C8272, E4, F4, G4, H4, I4, H4, and H4 are the straight lines on both sides of the upper thread. Obtaining straight lines MN and RT respectively according to the boundary position coordinates of the Su area on the upper surface of the reference cylinder and the Sd area on the lower surface of the reference cylinder, obtaining straight lines A1A, B1B, C1C, D1D, E1E, F1F, G1G, H1H, I1I, J1J, A3A, B3B, C3C, D3D, E3E, F3F, G3G, H3H, I3I, J3J on both sides of the upper thread profile and the lower thread profile according to the boundary position coordinates of the LW area on the upper surface of the reference cylinder, the LW area on the thread and the LW area on the lower surface of the reference cylinder, obtaining straight lines A1A, B1B, C3C, D3D, E3E, E3H, I3I, J3J, obtaining o (x, y) according to the straight lines A1A and B1B, obtaining o (x, y) according to the straight lines B1C and C1C, obtaining o (x, y) according to the straight lines B1C, obtaining o (x, y) and o (x, obtaining o (y) to the straight lines C1C and the straight lines C1C, and the x (, y13), straight line A3a4 and straight line B3B4 calculate o6(x6, y6), straight line B3B4 and straight line C3C3 calculate o9(x9, y9), straight line C3C4 and straight line D3D4 calculate o7(x7, y7), straight line D3D4 and straight line E3E4 calculate o10(x10, y10), straight line F3F4 and straight line G3G4 calculate o16(x16, y16), straight line G3G4 and straight line H3H4 calculate o19(x19, y19), straight line H3H4 and straight line I4 calculate o17(x17, y17), straight line I3I4 and straight line J3J4 calculate o20(x20, y 20);
(4) and obtaining the boundary coordinate of the straight line MN of the Su area of the upper surface of the reference cylinder according to the boundary position coordinate of the Su area of the upper surface of the reference cylinder, and obtaining a fitting straight line y which is ku x + bu, wherein ku is the slope of the straight line MN and bu is the intercept of the straight line MN. And obtaining the boundary coordinates of a straight line RT of the Sd region of the lower surface of the reference cylinder according to the boundary position coordinates of the Sd region of the lower surface of the reference cylinder, and obtaining a fitting straight line y which is kd x + bd, wherein kd is the slope of the straight line RT, and bd is the intercept of the straight line RT. Finally, the axis L0 of the reference cylinder is calculated as y0 ═ k0 × x + b0, where k0 ═ ku + kd)/2 and b0 ═ bu + bd)/2, where k0 is the slope of the straight line L0 and b0 is the intercept of the straight line L0;
(5) obtaining P ((x + x)/2, (y + y)/2) according to the coordinates of o and o, and obtaining P ((x + x)/2, (y + y)/2) according to the coordinates of o and o), and fitting P, P and P to obtain a middle diameter line y k x + b in the formula, wherein k is the slope of the straight line and b is the intercept of the straight line; obtaining P ((x + x)/2, (y + y)/2) according to the coordinates of o and o, and obtaining P ((x + x)/2, (y + y)/2) according to the coordinates of o and o); fitting P12, P13, P14, P17, P18 and P19 to obtain a lower thread pitch diameter line y which is k2 x + b2, wherein k2 is the slope of the straight line, and b2 is the intercept of the straight line; obtaining a thread axis L1 as yL ═ k × x + b from the upper thread pitch line and the lower thread pitch line, where k ═ k1+ k2)/2, b ═ b1+ b2)/2, where k is the slope of a straight line L1 and b is the intercept of a straight line L1;
(6) calculating the value of x in the length range of the thread, wherein the maximum value s of the distance | yL-y0| between the thread axis L1 and the axis L0 of the reference cylinder is max (| yL-y0|), and taking 2 times of max (| yL-y0|) as the coaxiality E between the cross-section thread at the 0-degree position and the reference cylinder1；
(7) And (3) taking the axis of the reference cylinder as an axis, rotating the thread clamp at intervals of n degrees, calculating the coaxiality according to the steps (1) to (6), and finally obtaining the average value E of the coaxiality of the multiple sides as the coaxiality of the final thread and the reference cylinder. Represented by the following formula:
wherein E isiThe coaxiality of the thread and the reference cylinder of the section at the ith position is shown.
According to the coaxiality measuring method, images of all parts of the thread are obtained by using a CCD (charge coupled device) according to the coaxiality definition of the thread and the reference cylinder by adopting an image measuring method, then the images are processed and calculated, and finally the coaxiality of the thread and the reference cylinder is measured; the invention can realize the precise measurement of the major diameter, the minor diameter, the pitch, the thread form angle and the thread height of the thread.
The above-described embodiments are merely preferred embodiments of the present invention, and general changes and substitutions by those skilled in the art within the technical scope of the present invention are included in the protection scope of the present invention.
Claims (10)
1. A method of measuring the coaxiality of a thread with a reference axis, the method comprising the steps of:
(1) clamping the measured thread on a thread clamp, taking the position section of the measured thread image acquired by the CCD at the moment as a 0-degree position section after locking and fixing, respectively translating the CCD to an upper surface Su area of a reference cylinder, a lower surface Sd area of the reference cylinder, a thread LW4 area, a thread LW2 area, a thread LW1 area and a thread LW3 area in sequence, and acquiring images of the areas;
(2) boundary position coordinates of a Su area of the upper surface of the reference cylinder, a Sd area of the lower surface of the reference cylinder, an LW4 area of the screw thread, an LW2 area of the screw thread, an LW1 area of the screw thread and an LW3 area of the screw thread are obtained through image processing;
(3) calculating the upper vertex of each thread form full triangle and the lower vertex of each thread form full triangle;
(4) calculating the axis of the reference cylinder;
(5) calculating a thread axis;
(6) calculating the coaxiality of the cross-section thread at the 0-degree position and the reference cylinder;
(7) and (3) taking the axis of the reference cylinder as an axis, rotating the thread clamp at intervals of n degrees, calculating the coaxiality according to the steps (1) to (6), and finally obtaining the average value E of a plurality of coaxiality as the coaxiality of the final thread and the reference cylinder.
2. A method for measuring the coaxiality of a thread and a reference shaft according to claim 1, wherein: in step (2), the image processing includes: preprocessing and sub-pixel processing.
3. A method for measuring the coaxiality of a thread and a reference shaft according to claim 1, wherein: in step (3), calculating the upper vertex of each full triangle of thread profile and the lower vertex of each full triangle of thread profile comprises: establishing a two-dimensional coordinate system, mapping boundary position coordinates of an upper surface Su area of a reference cylinder, a lower surface Sd area of the reference cylinder, an LW4 area of a thread, an LW2 area of the thread, an LW1 area of the thread and an LW3 area of the thread to the two-dimensional coordinate system, respectively obtaining a straight line MN and a straight line RT according to the boundary position coordinates of the upper surface Su area of the reference cylinder and the lower surface Sd area of the reference cylinder, obtaining straight lines F3F4, G3G4, H3H4, I3I4 and J3J4 on two sides of upper and lower thread forms according to the boundary position coordinates of the LW4 area, obtaining straight lines A3A4, B3B4, C3C4, D3D4 and E3E4 on two sides of the upper and lower thread forms according to the boundary position coordinates of the LW2 area of the thread, obtaining straight lines A1A2, B1B2, C1D 3D4, D863E 867 and E8658 and obtaining straight line coordinates of the upper and lower thread forms according to the boundary position coordinates of the boundary positions LW 367F 863F 867 and LW 863E 867, H1H, I1I, J1J, lower vertices o (x, y) are calculated from line A1A and line B1B, upper vertices o (x, y) are calculated from line B1B and line C1C, lower vertices o (x, y) are calculated from line C1C and line D1D, lower vertices o (x, y) are calculated from line D1D and line E1E, lower vertices o (x, y) are calculated from line F1F and line G1G, upper vertices o (x, y) are calculated from line G1G and line H1H, lower vertices o (x, y) are calculated from line H1H and line I1I, upper vertices o (x, y) are calculated from line I1I and line J1J, upper vertices o (x, y) are calculated from line A3A and line B3B, lower vertices o (x, y) are calculated from line B3B and line C, upper vertices o (x, y) are calculated from line C3D and line D3D, upper vertices o (x, y) are calculated from line D3D and line E3C, upper vertices o (x, y) are calculated from line G3C and line G3C, y16), the straight line G3G4 and the straight line H3H4 calculate the lower vertex o19(x19, y19), the straight line H3H4 and the straight line I3I4 calculate the upper vertex o17(x17, y17), and the straight line I3I4 and the straight line J3J4 calculate the lower vertex o20(x20, y 20).
4. A method for measuring the coaxiality of a thread and a reference shaft according to claim 3, wherein: in step (4), the calculating the axis of the reference cylinder includes: obtaining the boundary coordinate of a straight line MN of the Su area on the upper surface of the reference cylinder according to the boundary position coordinate of the Su area on the upper surface of the reference cylinder, and obtaining a fitting straight line y which is ku x + bu, wherein ku is the slope of the straight line MN and bu is the intercept of the straight line MN;
obtaining the boundary coordinates of a straight line RT of the Sd region of the lower surface of the reference cylinder according to the boundary position coordinates of the Sd region of the lower surface of the reference cylinder, and obtaining a fitting straight line y which is kd x + bd, wherein kd is the slope of the straight line RT, and bd is the intercept of the straight line RT;
finally, the axis L0 of the reference cylinder is calculated as y0 ═ k0 × x + b0, where k0 ═ ku + kd)/2 and b0 ═ bu + bd)/2, where k0 is the slope of the straight line L0 and b0 is the intercept of the straight line L0.
5. The method for measuring the coaxiality of the thread and the reference shaft according to claim 4, wherein: in step (5), calculating the thread axis includes: obtaining an upper thread pitch diameter line point P ((x + x)/2, (y + y)/2) from the coordinates of the upper vertex o and the lower vertex o, obtaining an upper thread pitch diameter line point P ((x + x)/2) from the coordinates of the upper vertex o and the lower vertex o, (y13+ y15)/2) fitting the upper thread pitch line point P2, the upper thread pitch line point P3, the upper thread pitch line point P4, the upper thread pitch line point P7, the upper thread pitch line point P8 and the upper thread pitch line point P9 to obtain an upper thread pitch line y-k 1 × x + b1, wherein k1 is the slope of the straight line, and b1 is the intercept of the straight line;
obtaining a lower thread pitch diameter line point P ((x + x)/2, (y + y)/2) from the coordinates of the upper vertex o and the lower vertex o, obtaining a lower thread pitch diameter line point P ((x + x)/2) from the coordinates of the upper vertex o and the lower vertex o, (y17+ y20)/2) fitting the lower thread pitch line point P12, the lower thread pitch line point P13, the lower thread pitch line point P14, the lower thread pitch line point P17, the lower thread pitch line point P18 and the lower thread pitch line point P19 to obtain a lower thread pitch line y which is k2 × x + b2, wherein k2 is the slope of the straight line, and b2 is the intercept of the straight line;
the thread axis L1 is yL ═ k × x + b, where k ═ k1+ k2)/2, and b ═ b1+ b2)/2, where k is the slope of the line L1 and b is the intercept of the line L1, as determined from the upper and lower thread radii.
6. The method for measuring the coaxiality of the thread and the reference shaft according to claim 5, wherein: in the step (6), the calculating the coaxiality of the 0-degree position cross-sectional thread and the reference cylinder includes: calculating the value of x in the length range of the thread, wherein the maximum value s of the distance | yL-y0| between the thread axis L1 and the axis L0 of the reference cylinder is max (| yL-y0|), and taking 2 times of max (| yL-y0|) as the coaxiality E between the cross-section thread at the 0-degree position and the reference cylinder1。
7. The method for measuring the coaxiality of the thread and the reference shaft according to claim 5, wherein: in step (7), the average value E is formulated as follows:
wherein E isiThe coaxiality of the thread and the reference cylinder of the section at the ith position is shown.
8. A method for measuring the coaxiality of a thread and a reference shaft according to claim 1, wherein: in step (7), the n degree is in the range of 10 ° to 90 °.
9. A method for measuring the coaxiality of a thread and a reference shaft according to claim 2, wherein: the pretreatment comprises the following steps: loading the collected image, enhancing the image, nonlinear filtering, binarization processing, edge identification and pixel level edge detection.
10. A method for measuring the coaxiality of a thread and a reference shaft according to claim 2, wherein: the sub-pixel processing includes: and performing sub-pixel calculation on the preprocessed image to obtain the edge contour position of the three-dimensional sub-pixel precision of the image, obtaining the boundary position coordinate and storing the boundary position coordinate.
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| CN110260825B (en) * | 2019-07-10 | 2020-12-25 | 陕西理工大学 | Image method thread form angle solving method |
| CN110631534B (en) * | 2019-10-28 | 2021-03-16 | 西安石油大学 | Method for detecting pitch diameter and pitch of taper thread of oil sleeve joint |
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| CN110849287B (en) * | 2019-11-27 | 2021-05-25 | 陕西理工大学 | Machine vision thread form angle compensation method |
| CN111982044B (en) * | 2020-08-12 | 2022-10-28 | 宁波江丰电子材料股份有限公司 | Three-coordinate detection method for threaded hole |
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