CN107765426B - Self-focusing laser scanning projection device based on symmetrical out-of-focus double detectors - Google Patents

Abstract

A self-focusing laser scanning projection device based on symmetrical defocusing double detectors belongs to the field of advanced processing and manufacturing technology. The prior art has low focusing accuracy and low lateral resolution of light intensity automatic search scanning. The invention is characterized in that a dual-axis scanning galvanometer is arranged behind the 1/4 wave plate; a symmetrical defocusing double detector light intensity detection module is arranged on the optical path of the calibrated reflected light of the polarization beam splitting prism; In the strong detection module, a set of converging objective lenses, a point detection pinhole and a photodetector are provided on the transmission and reflection optical paths of the beam splitting prism. The point detection pinhole is located between the converging objective lens and the photoelectric detector. The photosensitive surfaces are defocused by +ΔZ, ‑ΔZ respectively relative to the corresponding converging objective lenses; the respective light intensity electrical signal output ends of the two photodetectors are respectively connected to the two light intensity analog signal input ends of the measurement control module; the measurement control module The output terminal of the focusing drive signal is connected to the precise displacement mechanism in the dynamic self-focusing module.

Description

Self-focusing laser scanning projection device based on symmetrical defocusing dual detectors

technical field

The invention relates to a self-focusing laser scanning projection device based on symmetrical defocusing double detectors, which is used for laser-assisted processing of various parts (such as composite material layup, skin drilling and riveting, etc.) in the process of intelligent manufacturing and assembly. Welding, etc.) and indicating positioning and assembly, the scanning galvanometer realizes the laser circular scanning projection, and the laser wireframe of the three-dimensional outline of the parts driven by the three-dimensional CAD digital model is accurately projected and displayed in the target processing and assembly area, which belongs to the field of advanced processing and manufacturing technology.

Background technique

The laser scanning projection device is a kind of device that can convert the parts to be processed or assembled, that is, the three-dimensional outline of the workpiece to be projected into a laser wireframe by cyclic scanning and projection of laser light, and display it in the target processing and assembly area. The area is also called the projection receiving area, so as to realize the precision optoelectronic instrument for various parts processing and assembly auxiliary instructions.

In the existing laser scanning projection device, as shown in FIG. 1 , the laser 1, the focusing module 2, and the beam splitting prism 3 are arranged coaxially in turn; a biaxial scanning galvanometer 4 is arranged on the transmitted light path of the beam splitting prism 3; A light intensity detection module 5 is set on the calibration reflected light optical path of 3; the light intensity electrical signal output end of the light intensity detection module 5 is connected to the analog signal input end of the measurement control module 6; the computer 7 is connected with the measurement control module 6 through the USB port ; The focus drive signal output end of the measurement control module 6 is connected to the precision displacement mechanism 8 in the focusing module 2; The measurement control module 6 is a multifunctional data acquisition card capable of acquiring, storing and processing data, and the processing includes digital-to-analog and analog-to-digital conversion.

During the working process of the laser scanning projection device, the first step is to adjust the focus of the scanning projection laser spot. The scanning projection laser emitted by the laser 1 is successively projected to the projection receiving area 10 through the focusing module 2, the beam splitting prism 3 and the dual-axis scanning galvanometer 4, and the operator observes and judges the focusing situation of the laser spot in the projection receiving area 10 by human eyes. Through keyboard operation, the measurement control module 6 sends a control signal to the precision displacement mechanism 8 in the focusing module 2, and drives the precision displacement mechanism 8 to move back and forth until the observed laser spot reaches the minimum, and the fixed focus along the optical axis direction is guaranteed to the greatest extent. Accuracy, complete the focus adjustment of the scanning projection laser spot.

It can be seen that the prior art fails to use the optical path distribution of the calibration reflected light of the scanning projection laser to automatically feedback control the focus adjustment of the scanning projection laser spot, and the improvement of the focusing accuracy is very limited.

The second is to calculate the conversion relationship between the projection coordinate system (PX ^P Y ^P Z ^P ) of the dual-axis scanning galvanometer 4 and the digital-analog coordinate system (OX ^O Y ^O Z ^O ) of the three-dimensional CAD digital-analog of the workpiece to be projected.

Since the dual-axis scanning galvanometer 4 is a precision corner device, the position of the projection receiving area 10 cannot be known, and it cannot be determined where the laser wire frame 16 reflecting the three-dimensional contour features of the part to be projected should be scanned and projected. This requires determining the position of the projection receiving area 10 and establishing the correspondence between the three-dimensional coordinate value of any point on the three-dimensional CAD digital model of the workpiece to be projected and the scanning angle values of the vertical scanning mirror 12 and the horizontal scanning mirror 13 in the dual-axis scanning galvanometer 4 That is, to establish a conversion relationship between the projection coordinate system (PX ^P Y ^P Z ^P ) of the dual-axis scanning galvanometer 4 and the digital-to-analog coordinate system (OX ^O Y ^O Z ^O ) of the three-dimensional CAD digital-analog of the workpiece to be projected.

According to the needs of solving the multivariate equation, 4 to 6 irregularly distributed scanning calibration positions are selected in the projection receiving area 10, and the three-dimensional coordinates of each scanning calibration position in the digital-analog coordinate system (OX ^O Y ^O Z ^O ) are already Known. A back-reflection cooperative target 11 is arranged at each of the scanning calibration positions for scanning calibration. The scanning drive signal sent by the measurement control module 6 drives the vertical scanning mirror 12 and the horizontal scanning mirror 13 in the dual-axis scanning galvanometer 4 respectively by driving the two precision corner mechanisms 9 in the dual-axis scanning galvanometer 4 to scan back reflection. In the reflective area of the cooperative target 11, a part of the scanning projection laser is reflected by the back-reflection cooperative target 11, returns along the original optical path as the calibration reflected light, and is totally reflected by the beam splitter 3 to the light intensity detection module 5, where the light intensity detection module 5 The converging objective lens 14 converges on the photodetector 15 , and the photodetector 15 performs photoelectric conversion to obtain a light intensity electrical signal, which is transmitted to the measurement control module 6 . The measurement control module 6 detects a light intensity peak area of the reflective area of a back-reflection cooperative target 11 according to the light intensity electrical signal value and the respective deflection angles of the vertical scanning mirror 12 and the horizontal scanning mirror 13 when the light intensity electrical signal is obtained. , the center point of this area is the scanning calibration position, and its three-dimensional coordinate value corresponds to a pair of deflection angle values to complete a high-precision scanning positioning of the center position of the back-reflection cooperative target 11 . Repeat the above process, scan the reflective area of each back-reflection cooperative target 11 one by one, and obtain each group of three-dimensional coordinate values and deflection angle values, so that the projection coordinate system (PX) of the dual-axis scanning galvanometer 4 can be accurately calculated. The transformation relationship between ^P Y ^P Z ^P ) and the digital-analog coordinate system (OX ^O Y ^O Z ^O ) of the three-dimensional CAD digital model of the workpiece to be projected.

It can be seen that if the lateral resolution of the light intensity automatic search scanning of the laser scanning projection device can be enhanced, the projection coordinate system (PX ^P Y ^P Z ^P ) of the dual-axis scanning galvanometer 4 and the three-dimensional workpiece to be projected will be more accurately calculated. The conversion relationship between the digital-to-analog coordinate system (OX ^O Y ^O Z ^O ) of the CAD digital model.

Finally, the laser scanning projection of the three-dimensional outline of the workpiece to be projected on the projection receiving area 10 is completed. Import the three-dimensional CAD digital model of the workpiece to be projected into the measurement control module 6, and drive the dual-axis scanning galvanometer 4 to accurately deflect and rapidly cycle scan according to the contour feature information such as the position, size and shape in the three-dimensional CAD digital model of the workpiece to be projected, According to the definition of the contour feature information such as the position, size and shape of the workpiece to be projected by the 3D CAD digital model, and according to the conversion relationship between the two coordinate systems, the 3D contour of the workpiece to be projected is displayed accurately and cyclically in the projection receiver. In the area 10, a laser wire frame 16 is formed.

It can be seen that in practical applications, the laser wireframe of the three-dimensional outline of the parts driven by the three-dimensional CAD digital model is accurately projected and displayed in the target processing and assembly area. The essential factor affecting the accuracy of the scanning projection positioning is the focusing of the scanning projection laser, which affects the The influence of scanning projection positioning accuracy has the following two aspects:

One is the line width of the laser wire frame 16 projected by the laser scanning, that is, the minimum size of the laser spot that can be achieved when scanning and projection is performed in the projection receiving area 10 . The higher the fixed focus accuracy of the scanning projection laser in the projection receiving area 10 along the optical axis direction through the focusing module 2, the smaller the size of the laser spot, and the narrower the line width of the laser wire frame 16 for cyclic scanning and projection of the laser spot. The more accurately it can assist processing and indicate assembly;

The second is the scanning positioning accuracy of the dual-axis scanning galvanometer 4 to the center position of the back-reflection cooperative target 11 . When the size of the laser spot is smaller, the lateral resolution of the laser spot in the automatic search and scanning of the light intensity on the back-reflection cooperative target 11 is stronger, and the dual-axis scanning galvanometer 4 can perform more detailed scanning at a smaller scanning interval. At the same time, the light intensity detection module 5 can also obtain more light intensity information of the calibrated reflected light at the scanning calibration position, and can more accurately obtain a pair of deflection angle values corresponding to the center position of the back-reflection cooperative target 11, Then, a more accurate coordinate system conversion relationship can be calculated.

The laser wavelength emitted by the laser 1 in the existing laser scanning projection device is 532 nm, the diameter of the reflective area of the back-reflection cooperative target 11 is 6 mm, the reflective material is glass beads, and the optimal laser scanning projection positioning distance is 3-5 m , the laser scanning design line width is 0.5mm at a distance of 5m, the laser scanning projection positioning accuracy is defined as the half line width of the laser light, and the positioning accuracy is 0.25mm.

SUMMARY OF THE INVENTION

The purpose of the present invention is to further improve the fixed focus accuracy of the scanning projection laser emitted by the laser 1 along the optical axis on the premise that the scanning accuracy of the dual-axis scanning galvanometer 4 and the control accuracy of the measurement control module 6 are determined, and the obtained size To minimize the laser spot and improve the lateral resolution of the automatic search scanning of light intensity, we have invented a self-focusing laser scanning projection device based on symmetrical defocusing double detectors. Since the positioning accuracy of laser scanning projection is defined by the half-line width of the laser, the improvement of the fixed focus accuracy directly determines the improvement of the positioning accuracy of laser scanning projection; because the lateral resolution of the automatic search and scanning of light intensity is directly related to The calculation accuracy of the conversion relationship between the projection coordinate system (PX ^P Y ^P Z ^P ) and the digital-analog coordinate system (OX ^O Y ^O Z ^O ), therefore, the improvement of the lateral resolution also directly determines the positioning of the laser scanning projection. Accuracy improvements.

As shown in FIG. 2 , the components of the self-focusing laser scanning projection device based on the symmetrical defocusing dual detectors of the present invention include a laser 1, a dual-axis scanning galvanometer 4, a measurement control module 6, a computer 7, and the computer 7 and the measurement The control module 6 is connected; the scanning drive signal output end of the measurement control module 6 is connected to the precision corner mechanism 9 in the dual-axis scanning galvanometer 4, and the measurement control module 6 is a multifunctional data acquisition card; it is characterized in that the laser 1 , beam expander collimating lens group 17, dynamic self-focusing module 18, polarizing beam splitting prism 19, and 1/4 wave plate 20 are arranged coaxially in turn; After 20, a dual-axis scanning galvanometer 4 is set; a symmetrical defocusing double-detector light intensity detection module 21 is set on the calibrated reflected light optical path of the polarization beam splitting prism 19; The transmission and reflection light paths of the prism 22 are each equipped with a set of converging objective lenses 14, point detection pinholes 23 and photodetectors 15. The point detection pinholes 23 are located between the converging objective lens 14 and the photoelectric detectors 15, and two photodetectors 15 The photosensitive surfaces are defocused by +ΔZ and -ΔZ relative to the corresponding converging objective lenses 14 respectively; the respective light intensity electrical signal output ends of the two photodetectors 15 are respectively connected to the two light intensity analog signal input ends of the measurement control module 6 ; The focus drive signal output end of the measurement control module 6 is connected to the precise displacement mechanism 8 in the dynamic self-focusing module 18 .

If any one of the two photodetectors 15 is located at the focal point of the image side, the detected axial light intensity response curve is the axial light intensity response curve at the focal point of the image side, that is, the curve 0 in FIG. 3; The axial light intensity response curves detected by each of the photodetectors 15 are respectively the axial light intensity response curves at the positions deviating from the image-side focus -ΔZ and deviating from the image-side focus +ΔZ, namely curve 1 and curve 2 in FIG. 3 . At this point, at the zero point O, the light intensity values of curve 1 and curve 2 are only equivalent to about 0.707 times of the light intensity value of curve 0, and the light intensity of the calibrated reflected light is originally maintained at tens of picowatts (pW) It seems that the effect of the present invention is counterproductive. However, under this condition, it can be controlled in a differential and additive manner to obtain the desired effect.

The light intensity signals of curve 1 and curve 2 are subtracted point by point by the measurement control module 6 to obtain a differential axial light intensity response curve, that is, curve 3 in FIG. 3, and curve 3 corresponds exactly to the peak point P of curve 0 at zero point O . The slope of curve 0 near point P is close to zero, that is, the change of the light intensity value is not sensitive to the change of the displacement of the precision displacement mechanism 8, even if the measurement control module 6 sends feedback control to the dynamic self-focusing module 18 according to the curve 0 signal, and control the precision displacement mechanism 8 to realize the axial self-focusing of the scanning projection laser spot, instead of manual focusing by human eye observation, it is still difficult to improve the fixed focus accuracy of the scanning projection laser along the optical axis direction. Although the light intensity of curve 3 at zero point O is zero, the slope of curve 3 at zero point O is the largest, that is to say, the change of light intensity with axial displacement is the largest here. The measurement control module 6 sends a feedback control signal to the dynamic self-focusing module 18 to control the precise displacement mechanism 8 to realize the axial self-focusing of the scanning projection laser spot, which can not only replace the existing manual focusing method of human eye observation, but also The focusing accuracy can be significantly improved.

The light intensity signals of curve 1 and curve 2 are added point by point by the measurement control module 6 to obtain the summed axial light intensity response curve, that is, curve 4 in Figure 3; the peak point P″ of curve 4 and the peak point of curve 0 are obtained. P corresponds to P, and the peak value of curve 4 is about 1.414 times that of curve 0. Therefore, compared with the existing single-detector laser scanning projection device and method, the present invention can perform high-precision lateral scanning on the back-reflection cooperative target 11 positioning, so that the conversion relationship between the projection coordinate system (PX ^P Y ^P Z ^P ) and the digital-analog coordinate system (OX ^O Y ^O Z ^O ) can be established more sensitively and accurately.

It can be seen that the present invention combines the differential light intensity detection method with the summation light intensity detection method, and takes into account the improvement of the axial focusing ability and the lateral scanning resolution ability of the laser scanning projection device.

Setting the beam expander collimating lens group 17 can increase the numerical aperture of the focusing lens group in the dynamic self-focusing module 18 by 3 to 5 times. According to the imaging theory of the converging objective lens, the spot diameter d is obtained by the following formula:

In the formula: λ is the laser wavelength, and n·sinα is the numerical aperture of the converging mirror group. It can be seen that increasing the numerical aperture of the converging lens group can reduce the theoretical diameter of the converging light spot. When the laser wavelength λ is 532nm, the working distance of the converging mirror group is 4600mm, the combined focal length of the converging mirror group is about 2500mm, and the effective aperture of the laser incident on the converging mirror group is 12mm, the theoretical diameter of the Airy disk can be calculated to be about It is 0.27mm, which means that the theoretical positioning accuracy is increased to 0.135mm. The secondary effect of compressing the scanning projection laser spot size and improving the scanning projection laser spot convergence quality is that the smaller the scanning projection laser spot size is, the size of the reflective area in the back-reflection cooperation target 11 can be reduced accordingly. It is as small as 4-5 mm, which means that accurate laser scanning projection can be performed in a more compact and narrow projection receiving area 10, and thus the application field of the present invention can be expanded.

Description of drawings

FIG. 1 is a schematic structural diagram of a conventional laser scanning projection device.

FIG. 2 is a schematic structural diagram of a self-focusing laser scanning projection device based on symmetrical defocusing dual detectors according to the present invention.

Fig. 3 is the axial light intensity response curve diagram obtained by adopting the self-focusing laser scanning projection device based on the symmetrical defocusing double detector of the present invention, the vertical axis is light intensity I, the horizontal axis is the axial normalized coordinate u, Fig. middle:

Curve 0 is the axial light intensity response curve of the detector at the focal point of the image side;

Curve 1 is the axial light intensity response curve of the detector located at -ΔZ deviated from the image square focus;

Curve 2 is the axial light intensity response curve of the detector located at +ΔZ deviated from the image square focus;

Curve 3 is the differential axial light intensity response curve;

Curve 4 is the summed axial light intensity response curve.

Detailed ways

As shown in FIG. 2 , the components of the self-focusing laser scanning projection device based on the symmetrical defocusing dual detectors of the present invention include a laser 1, a dual-axis scanning galvanometer 4, a measurement control module 6, a computer 7, and the computer 7 and the measurement The control module 6 is connected; the scanning drive signal output end of the measurement control module 6 is connected to the precision corner mechanism 9 in the dual-axis scanning galvanometer 4 , and the measurement control module 6 is a multifunctional data acquisition card.

The laser 1 , the beam expander collimating lens group 17 , the dynamic self-focusing module 18 , the polarizing beam splitting prism 19 , and the quarter wave plate 20 are arranged coaxially in sequence.

The beam expander collimating lens group 17 can compress the divergence angle of the scanning projection laser light from the laser 1, and expand the beam to a state close to the full pupil of the converging lens group in the dynamic self-focusing module 18, which increases the size of the dynamic self-focusing module 18. The numerical aperture of the converging mirror group is determined, thereby compressing the spot size of the scanning projection laser irradiated on the projection receiving area 10 . The illumination pinhole 24 is arranged in the beam expanding collimating lens group 17, so that the laser light emitted by the laser 1 works in the way of spot illumination, at the same time eliminating stray light interference, improving the beam quality, and further reducing the spot size, in the projection receiving area 10 Get a more ideal focused spot. In the dynamic self-focusing module 18, the focusing lens 25 is installed on the precise displacement mechanism 8 to realize the axial self-focusing of the scanning projection laser spot. The focusing lens group in the dynamic self-focusing module 18 is an anti-telephoto lens group, so that the laser scanning projection positioning distance range reaches 1-10m, but this will lead to the reduction of the numerical aperture of the focusing lens group, which is about 10 ^-3 , However, due to the existence of the beam expander collimating lens group 17, it can be compensated.

The biaxial scanning galvanometer 4 is arranged on the optical path of the scanning transmitted light of the polarizing beam splitter prism 19 and behind the 1/4 wave plate 20 . A symmetrical defocusing double detector light intensity detection module 21 is arranged on the optical path of the calibrated reflected light of the polarization beam splitting prism 19 . A notch converging objective lens 26 and a notch filter 27 are arranged on the optical path opposite to the optical path of the calibrated reflected light by the polarization beam splitting prism 19 to eliminate stray light interference. In the symmetrical defocusing double detector light intensity detection module 21, a set of converging objective lenses 14, a point detection pinhole 23 and a photodetector 15 are respectively provided on the transmission and reflection light paths of the beam splitting prism 22, and the point detection pinhole 23 is located in the convergence point. Between the objective lens 14 and the photodetector 15 , the photosensitive surfaces of the two photodetectors 15 are defocused by +ΔZ, -ΔZ respectively relative to the corresponding converging objective lens 14; the respective light intensity electrical signal output ends of the two photodetectors 15 They are respectively connected to the two light intensity analog signal input ends of the measurement control module 6 . The focus drive signal output end of the measurement control module 6 is connected to the precise displacement mechanism 8 in the dynamic self-focusing module 18 .

Claims (5)

1. A self-focusing laser scanning projection device based on a symmetrical out-of-focus double detector comprises a laser (1), a double-shaft scanning galvanometer (4), a measurement control module (6) and a computer (7), wherein the computer (7) is connected with the measurement control module (6); the scanning driving signal output end of the measurement control module (6) is connected to a precise corner mechanism (9) in the double-shaft scanning galvanometer (4), and the measurement control module (6) is a multifunctional data acquisition card; the device is characterized in that a laser (1), a beam expanding collimating lens group (17), a dynamic self-focusing module (18), a polarization beam splitter prism (19) and an 1/4 wave plate (20) are coaxially arranged in sequence; a biaxial scanning galvanometer (4) is arranged on a scanning transmission light path of the polarization beam splitter prism (19) and behind the 1/4 wave plate (20); a symmetrical defocusing double-detector light intensity detection module (21) is arranged on a calibration reflected light path of the polarization beam splitter prism (19); in a symmetrical defocusing double-detector light intensity detection module (21), a group of converging objective lens (14), a point detection pinhole (23) and a photoelectric detector (15) are respectively arranged on a transmission light path and a reflection light path of a beam splitter prism (22), the point detection pinhole (23) is positioned between the converging objective lens (14) and the photoelectric detector (15), and the light sensing surfaces of the two photoelectric detectors (15) are respectively defocused + delta Z and delta Z relative to the corresponding converging objective lens (14); the light intensity electric signal output ends of the two photoelectric detectors (15) are respectively connected to the two light intensity analog signal input ends of the measurement control module (6); the focusing driving signal output end of the measurement control module (6) is connected to a precision displacement mechanism (8) in the dynamic self-focusing module (18).

2. The self-focusing laser scanning projection device based on the symmetric out-of-focus dual detector as claimed in claim 1, wherein the beam expanding collimating lens group (17) can compress the divergence angle of the scanning projection laser from the laser (1) and expand the beam to a state close to the full pupil of the converging lens group in the dynamic self-focusing module (18), thereby increasing the numerical aperture of the converging lens group in the dynamic self-focusing module (18) and further compressing the spot size of the scanning projection laser irradiated on the projection receiving area (10).

3. The self-focusing laser scanning projection device based on the symmetric out-of-focus double detectors as claimed in claim 1, characterized in that an illumination pinhole (24) is arranged in the beam expanding collimating lens group (17), so that the laser emitted by the laser (1) works in a point illumination mode, stray light interference is eliminated, beam quality is improved, spot size is further reduced, and a more ideal focused spot is obtained in the projection bearing area (10).

4. The self-focusing laser scanning projection device based on the symmetrical out-of-focus dual detectors is characterized in that in the dynamic self-focusing module (18), a focusing lens (25) is installed on a precise displacement mechanism (8) to realize axial self-focusing of a scanning projection laser spot.

5. The self-focusing laser scanning projection device based on the symmetrical out-of-focus double detectors is characterized in that a notch converging objective lens (26) and a notch filter (27) are arranged on the optical path opposite to the optical path of the calibration reflected light of the polarization splitting prism (19) and used for eliminating stray light interference.

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