A non-contact straightness measurement device and method

Abstract

The present invention discloses a device and method for non-contact straightness measurement. The device includes a non-diffraction light emitting mechanism and a linear reference deviation and laser triangulation distance integrated measurement mechanism arranged on a guide rail; the mechanism moves along the guide rail to change the position to be measured and completes the straightness scanning measurement; the lifting frames at both ends of the guide rail can adjust the distance between the mechanism and the surface of the object to be measured to the measuring range; the non-diffraction light emitting mechanism is fixed on the light source lifting frame and can move up and down, laterally and deflect in the direction so that the non-diffraction light linear reference light spot is irradiated on the center of the frosted glass, and its light beam direction is basically parallel to the guide rail. The integrated measurement mechanism can synchronously measure the change in the distance from it to the object to be measured and the deviation of the light spot position on the frosted glass from the linear reference. The difference between the two can compensate for the influence of the guide rail bending error in long-distance straightness measurement. The present invention can solve the problem of straightness measurement of long and open objects with non-smooth surfaces such as pipes and rails.

Description

Technical Field

[0001] The present invention belongs to the technical field related to precision instruments and geometric measurement, and more specifically, relates to a device and method for non-contact straightness measurement. Background Art

[0002] With the development of science and technology, modern industry has increasingly higher requirements for machining accuracy. Straightness measurement is widely used in the fields of machinery manufacturing, aviation, shipbuilding, etc., such as straightness detection of precision machine tool guide rails, straightness detection of high-speed railway tracks, alignment of ship shafting, straightness measurement of pipelines, etc. Therefore, it is very important to improve the measurement accuracy, range, speed and other performance of straightness.

[0003] Straightness measurement methods can be broadly categorized into two types: traditional measurement methods, primarily including the plumb line method, the testing platform method, and the steel wire method; and modern measurement methods, primarily utilizing laser interferometers or sensors such as PSD position sensors and capacitive displacement sensors. While traditional measurement methods are simple to operate and inexpensive, they are inefficient due to manual labor. Furthermore, measurement results are subject to significant errors, influenced by the operator's operational level and subjective influence. Laser interferometers offer high precision through non-contact measurement, but they are expensive and difficult to use, making them unsuitable for harsh working environments. Measurement using sensors is mostly contact measurement. A deep hole straightness detection device is disclosed in Chinese patent CN201510741425.2. The probe is placed in the deep hole to be measured, and the laser outside the deep hole emits laser into the hole to illuminate the PSD sensor of the probe. When the traction line drives the probe to move, the probe will be displaced in the deep hole due to the deformation of the inner hole, resulting in a change in the position of the light spot on the PSD sensor. The data collected by computer analysis is used to evaluate the straightness of the deep hole. However, this method is a contact measurement, which may damage the surface of the object and has limited applicable scenarios. On the other hand, it uses an ordinary Gaussian beam as a straight line reference. When the measured distance is long, the resolution of the light spot position will decrease.

[0004] When performing medium- and long-distance straightness measurements, a linear reference is required. There are usually two options for selecting a linear reference. One is to use an actual object such as a high-precision guide rail or flat crystal as the linear reference. Chinese invention patent CN201710203901.4 discloses a non-contact automatic rail straightness measurement device. This method measures straightness by moving a laser displacement sensor on a high-precision guide rail. This method essentially uses a high-precision guide rail as a linear reference. However, this method requires a precision guide rail that is longer than the object to be measured. The longer the precision guide rail, the more difficult it is to ensure its own straightness. The other is to use laser as a straight line reference. A non-contact inner hole straightness measurement device and method is disclosed in the Chinese invention patent CN201310106703.8. This method uses light as a reference. The photoelectric sensor moves with the center bracket. The center bracket and the inner hole of the object to be measured are separated by an air film generated by an air floating cushion. It moves as the center of the inner hole of the object to be measured changes, realizing non-contact follow-up measurement. When relative movement occurs between the center of the photosensitive surface of the photoelectric sensor and the light beam, the sensor will convert the displacement into an electrical signal, and the measurement result is obtained after computer processing. Although this method is not a contact measurement, it uses air floating to keep a constant distance between the probe and the measured surface equal to the thickness of the air film, which is equivalent to contact measurement. The air floating support is not suitable for straightness measurement of open objects and objects with non-smooth inner holes. In addition, it also uses ordinary Gaussian laser as a straight line reference. Summary of the Invention

[0005] In response to the above defects or improvement needs of the prior art, the present invention provides a non-contact straightness measurement device and method to solve the problem of straightness measurement of long, open objects with non-smooth surfaces such as pipes and rails.

[0006] To achieve the above object, according to one aspect of the present invention, a non-contact straightness measurement device is provided, which includes a light emitting mechanism and an integrated measuring mechanism, wherein:

[0007] The light emitting mechanism is used to emit non-diffracted light as a straight line reference. The integrated measurement mechanism is composed of a non-diffracted light straight line reference deviation measurement optical path and a laser triangulation ranging optical path, and is used to measure the displacement change of the straight line reference light spot and the displacement change of the ranging light spot.

[0008] The integrated measurement mechanism includes frosted glass, a lens group, a camera, a laser, a third plano-convex lens, a fourth plane reflector, and a biconvex lens. The light emitting mechanism, the frosted glass, the lens group, and the camera form a non-diffracted light straight line reference deviation measurement optical path; the laser, the third plano-convex lens, the fourth plane reflector, and the biconvex lens form a laser triangulation distance measurement optical path.

[0009] When the light emitting mechanism emits non-diffracted light, it passes through the frosted glass and reaches the camera, forming a straight reference light spot in the camera. At the same time, the laser emitted by the laser passes through the third plano-convex lens and illuminates the fourth plane reflector. The laser is reflected by the fourth plane reflector and focused on the surface of the object to be measured. The light scattered by the object to be measured enters the double convex lens and is focused to form laser triangulation ranging measurement light, thereby forming a ranging light spot. The measurement light and the non-diffracted light reach the camera at the same time and form an image. The image in the camera is used to calculate the displacement change of the ranging light spot and the displacement change of the straight reference light spot, and the straightness of the object to be measured is obtained by calculation.

[0010] Further preferably, in the laser triangulation ranging optical path, the laser is emitted from the laser, passes through the third plano-convex lens and is irradiated at point B of the fourth plane reflector, and is reflected by the fourth plane reflector and focused at point A on the surface of the object to be measured. The line connecting point A and point B is on the same straight line as the frosted glass, satisfying the Abbe principle.

[0011] Further preferably, the non-diffraction light emitted by the light emitting mechanism is irradiated on the center of the frosted glass.

[0012] Further preferably, the non-diffracted light straight line reference deviation measurement optical path also includes a plurality of plane reflectors for changing the direction and position of the optical path, wherein a first plane reflector and a second plane reflector are arranged between the frosted glass and the lens group.

[0013] Further preferably, a third plane reflector is provided between the lens group and the camera, and the non-diffracted light is reflected by the third plane reflector and enters the camera simultaneously with the laser triangulation ranging light to form an image.

[0014] Further preferably, the lens group is two or more lenses, which are used to adjust the focal length so that the straight reference light spot on the frosted glass is accurately focused on the camera.

[0015] Further preferably, the device also includes a guide rail, a left lifting frame and a right lifting frame, the two ends of the guide rail are arranged on the left lifting frame and the right lifting frame, the integrated measuring mechanism is arranged on the guide rail, the guide rail moves on the left lifting frame and the right lifting frame to drive the integrated measuring mechanism to move so that it meets the range requirements of the integrated measuring mechanism, and the movement of the integrated measuring mechanism on the guide rail enables it to scan and measure straightness.

[0016] According to another aspect of the present invention, a method for measuring the non-contact straightness measurement device described above is provided, the method comprising the following steps:

[0017] S1. The integrated measuring mechanism moves up and down by Δh, and calibrates the relationship Δh(Δy1) between Δh and the displacement change Δy1 of the linear reference light spot in the camera. Simultaneously, the relationship ΔH(Δy2) between the change ΔH in the distance between the integrated measuring mechanism and the surface of the object to be measured and the displacement change Δy2 of the ranging light spot in the camera is calibrated, where ΔH=Δh during calibration.

[0018] S2. For the object to be measured, measuring the displacement change Δy2 of the ranging light spot in the camera, and measuring the displacement change Δy1 of the linear reference light spot in the camera;

[0019] S3. Substitute Δy1 and Δy2 obtained in step S2 into the Δh(Δy1) and ΔH(Δy2) to obtain the actual ΔH and Δh; the difference between the actual ΔH and Δh is the required straightness of the object to be measured, Str = ΔH(Δy2) - Δh(Δy1).

[0020] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0021] 1. The device of the present invention is a non-contact measurement method using laser triangulation, with a measurement accuracy of up to micron level. It is suitable for measuring the straightness of various measuring surfaces, including pipes, rails and other long and open objects with non-smooth surfaces.

[0022] 2. In the present invention, since the deviation of the integrated measuring mechanism relative to the linear reference during measurement can be calculated from the linear reference spot displacement change Δy1, the accuracy requirement for the guide rail is not high. A general guide rail can be used, and a long-distance high-precision guide rail is not required.

[0023] 3. The present invention uses non-diffracted light as a straight line reference. The cross-sectional shape of the non-diffracted light beam is concentric rings of alternating light and dark. It is a special beam structure that does not change with the propagation distance of the light. Therefore, when calculating the center of the non-diffracted light spot through the corresponding image processing algorithm, the center of the light spot can be determined by considering the concentric rings as a whole. The local impact of noise from the environment on the circular rings in the non-diffracted light spot does not affect the calculation of the center of the concentric rings from the overall consideration. However, for ordinary Gaussian lasers, their light spot is a circle or ellipse, and the center of the light spot is often calculated using the image processing method of the center of mass method. When environmental noise affects the light spot, it will cause the center of mass to change, and the image processing result will change. Its stability and accuracy as a straight line reference will be affected to a certain extent. Therefore, compared with ordinary Gaussian laser beams, non-diffracted light as a straight line reference can have the obvious advantages of both a large range and high precision.

[0024] 4. The device of the present invention structurally combines the measurement of non-diffracted light straight line reference deviation and laser triangulation into one. The two optical paths share one camera. The vibration of the integrated measurement mechanism affects the measurement values ​​of the two optical paths synchronously without time difference. Therefore, the effects can be offset and no measurement error is generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1 is a schematic structural diagram of a non-contact straightness measuring device constructed according to a preferred embodiment of the present invention;

[0026] Figure 2 It is a working principle diagram constructed according to the preferred embodiment of the present invention;

[0027] Figure 3 is a relationship diagram between the displacement change Δy1 of the linear reference light spot constructed according to the preferred embodiment of the present invention and the offset Δh of the entire integrated measurement mechanism relative to the linear reference;

[0028] Figure 4 is a graph showing the relationship between a change ΔH in the distance between the integrated measuring mechanism constructed according to a preferred embodiment of the present invention and the surface of the object to be measured and a change Δy2 in the displacement of the ranging light spot in the camera;

[0029] Figure 5 is an image obtained from a camera constructed according to a preferred embodiment of the present invention.

[0030] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0031] 1-light emitting mechanism, 2-diffraction-free light straight line reference, 3-ground glass, 4-first plane mirror, 5-second plane mirror, 6-first plano-convex lens, 7-second plano-convex lens, 8-third plane mirror, 9-camera, 10-laser, 11-third plano-convex lens, 12-fourth plane mirror, 13-double convex lens, 14-guide rail, 15-integrated measuring mechanism, 16-object to be measured, 17-right lifting frame, 18-left lifting frame, 19-light source lifting frame. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0033] A non-contact straightness measurement device and method include a light emitting mechanism 1, frosted glass 3, a first plane reflector 4, a second plane reflector 5, a first plano-convex lens 6, a second plano-convex lens 7, a third plane reflector 8, a camera 9, a laser 10, a third plano-convex lens 11, a fourth plane reflector 12, a biconvex lens 13, a guide rail 14, an integrated measuring mechanism 15, a right lifting frame 17, a left lifting frame 18, a light source lifting frame 19 and a computer, wherein the computer is connected to the camera 9. The integrated measurement mechanism 15 has two optical paths. One consists of a laser triangulation optical path, which is composed of a camera 9, a laser 10, a third plano-convex lens 11, a fourth plane reflector 12, and a biconvex lens 13. Changes in the distance between the measuring probe and the surface of the object 16 to be measured will change the image position on the camera 9. The other optical path consists of a light emitting mechanism 1, a frosted glass 3, a first plane reflector 4, a second plane reflector 5, a first plano-convex lens 6, a second plano-convex lens 7, a third plane reflector 8, and a camera 9. This optical path primarily enables the camera 9 to receive non-diffracted light and form an image. Upon receiving the light spots from both optical paths, the camera 9 transmits the spot image to a computer, generating a digital image. The computer then performs appropriate image processing to determine the positional changes (Δy1 and Δy2) of the two spot centers. Based on the calibration curve, the changes in the distance between the integrated measurement mechanism 15 and the surface of the object to be measured and the changes relative to the non-diffracted light straight line reference are calculated, thereby determining the surface straightness of the object to be measured.

[0034] The optical path consists of two parts. One is the non-diffracted light path for measuring the deviation of the linear reference. Light emitting mechanism 1 emits non-diffracted light, which forms an image on frosted glass 3. Light scattered from frosted glass 3 is redirected by first and second plane mirrors 4 and 5, then focused by two plano-convex lenses 6 and 7. Finally, it is redirected by third plane mirror 8 before being imaged onto camera 9. The displacement Δy1 of the linear reference light spot on camera 9 corresponds to the offset Δh of the entire integrated measurement mechanism 15 relative to the linear reference. The other is the laser triangulation optical path. Light emitted by laser 10 passes through third plano-convex lens 11, redirected by fourth plane mirror 12, and then focused onto point A on the surface of the object to be measured 16. Light AB is collinear with frosted glass 3. Laser light scattered from point A is focused onto camera 9 by biconvex lens 13. The displacement Δy2 of the center of the ranging light spot formed on camera 9 by the laser triangulation optical path corresponds to the change in distance ΔH from the object to be measured to the integrated measurement mechanism 15. Since the camera 9 is used directly to detect the image, it is only necessary that the light spots of the two light paths are both within the photosensitive surface of the camera 9 .

[0035] like Figure 1As shown, during operation, the integrated measuring mechanism 15 moves along a guide rail 14. The ends of the guide rail 14 are fixed to left and right lifting frames, allowing simultaneous movement. This allows the guide rail 14 to move up and down, driving the integrated measuring mechanism 15 up and down, ensuring that the distance to the surface of the object under test falls within the measuring range. The object under test is placed below the device, roughly parallel to the guide rail 14. The light emitting mechanism 1 is adjusted so that the non-diffracted light linear reference 2 is substantially parallel to the guide rail 14 and illuminates the center of the frosted glass 3.

[0036] The working principle diagram during measurement is as follows Figure 2 As shown, at the beginning of measurement, the offset of the integrated measuring mechanism 15 relative to the linear reference is 0. At this time, the distance between the object surface and the integrated measuring mechanism 15 is H. After moving a distance Δx, due to vibration or guide rail error, the integrated measuring mechanism 15 will deviate from the linear reference by Δh. The distance between the object surface and the integrated measuring mechanism 15 is H'. The change in the distance between the object surface and the integrated measuring mechanism 15 is ΔH = H'-H. Figure 3 As shown, the displacement change of the linear reference light spot on the camera 9 is Δy1. According to the calibration curve, the offset Δh(Δy1) of the integrated measurement mechanism 15 relative to the linear reference can be obtained. Figure 4 As shown, the displacement of the ranging light spot changes by Δy2. Based on the calibration curve, the change in distance ΔH(Δy2) between the surface of the object to be measured and the integrated measurement mechanism 15 can be calculated. Thus, straightness Str = ΔH(Δy2) - Δh(Δy1). Because the two optical paths share a single camera, the vibration of the integrated measurement mechanism 15 affects the measured values ​​of the two optical paths synchronously, thus canceling out the effects and eliminating measurement errors.

[0037] like Figure 5 As shown in the figure, the circular spot on the left is the ranging spot of the laser triangulation ranging optical path, and the concentric ring spot on the right is the straight line reference spot of the non-diffracted light straight line reference deviation measurement optical path. During the mobile scanning measurement, the two spots will produce a certain displacement change. After the change in the center displacement of the spot is calculated by a certain image processing method, the offset Δh (Δy1) of the integrated measurement mechanism relative to the straight line reference and the distance change ΔH (Δy2) of the object surface distance integrated measurement mechanism can be calculated according to the calibration curve, thereby calculating the straightness Str of the object to be measured.

[0038] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A non-contact straightness measurement device, characterized in that: The device comprises a light emitting mechanism (1) and a comprehensive measuring mechanism (15), wherein: The light emitting mechanism is used to emit non-diffracted light as a straight line reference. The integrated measurement mechanism is composed of a non-diffracted light straight line reference deviation measurement optical path and a laser triangulation ranging optical path, and is used to measure the displacement change of the straight line reference light spot and the displacement change of the ranging light spot. The comprehensive measurement mechanism comprises a frosted glass (3), a lens group, a camera (9), a laser (10), a third plano-convex lens (11), a fourth plane reflector (12) and a biconvex lens (13); the light emitting mechanism, the frosted glass (3), the lens group and the camera (9) form a non-diffracted light straight line reference deviation measurement optical path; the laser (10), the third plano-convex lens (11), the fourth plane reflector (12) and the biconvex lens (13) form a laser triangulation distance measurement optical path; When the light emitting mechanism emits non-diffracted light, it passes through the frosted glass (3) and the lens group to reach the camera (9) and forms a linear reference light spot in the camera. At the same time, the laser (10) emits laser light, which passes through the third plano-convex lens (11) and irradiates the fourth plane reflector (12). After being reflected by the fourth plane reflector (12), the laser light is focused on the surface of the object to be measured. The scattered light of the object to be measured enters the biconvex lens (13) and is focused to form laser triangulation distance measurement light, thereby forming a distance measurement light spot. The measurement light and the non-diffracted light simultaneously reach the camera (9) and form an image. The image in the camera (9) is used to calculate the displacement change of the distance measurement light spot and the displacement change of the linear reference light spot, and the straightness of the object to be measured is calculated based on the above. In the laser triangulation distance measurement optical path, laser light is emitted from the laser (10), passes through the third plano-convex lens (11), and is irradiated on point B of the fourth plane reflector (12). The laser light is reflected by the fourth plane reflector (12) and is focused on point A on the surface of the object to be measured. The line connecting point A and point B is on the same straight line as the frosted glass (3), satisfying the Abbe principle. The device further comprises a guide rail (14), a left lifting frame (18) and a right lifting frame (17), wherein both ends of the guide rail are arranged on the left lifting frame (18) and the right lifting frame (17), and the integrated measuring mechanism is arranged on the guide rail (14). The guide rail moves on the left lifting frame and the right lifting frame to drive the integrated measuring mechanism to move so as to meet the range requirement of the integrated measuring mechanism. The movement of the integrated measuring mechanism on the guide rail (14) enables the integrated measuring mechanism to scan and measure straightness.

2. The non-contact straightness measurement device according to claim 1, characterized in that: The non-diffracted light emitted by the light emitting mechanism is irradiated onto the center of the frosted glass (3).

3. The non-contact straightness measurement device according to claim 2, characterized in that: The non-diffracted light straight line reference deviation measurement optical path also includes a plurality of plane reflectors for changing the direction and position of the optical path, wherein a first plane reflector (4) and a second plane reflector (5) are provided between the frosted glass (3) and the lens group.

4. The non-contact straightness measurement device according to claim 3, characterized in that: A third plane reflector (8) is provided between the lens group and the camera (9), and the non-diffracted light is reflected by the third plane reflector and simultaneously enters the camera with the laser triangulation distance measurement light to form an image.

5. The non-contact straightness measurement device according to claim 3, characterized in that: The lens group is two or more lenses, which are used to adjust the focal length so that the straight reference light spot on the frosted glass is accurately focused on the camera.

6. A method for measuring non-contact straightness of a device according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: S1. The integrated measuring mechanism moves up and down by Δh, and calibrates the relationship Δh(Δy1) between Δh and the displacement change Δy1 of the linear reference light spot in the camera. Simultaneously, the relationship ΔH(Δy2) between the change ΔH in the distance between the integrated measuring mechanism and the surface of the object to be measured and the displacement change Δy2 of the ranging light spot in the camera is calibrated, where ΔH=Δh during calibration. S2. For the object to be measured, measuring the displacement change Δy2 of the ranging light spot in the camera, and measuring the displacement change Δy1 of the linear reference light spot in the camera; S3. Substitute Δy1 and Δy2 obtained in step S2 into the Δh(Δy1) and ΔH(Δy2) to obtain the actual ΔH and Δh; the difference between the actual ΔH and Δh is the required straightness of the object to be measured, Str = ΔH(Δy2) - Δh(Δy1).

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