Laser beam coupling and focusing system

Abstract

The invention provides a laser beam coupling and focusing system which comprises a zoom lens group, a stepping motor, a moving mechanism, a controller and a prediction module. The zoom lens group is used for converging incident laser to a working interface; the stepping motor is used for receiving a command of the controller and driving the moving mechanism to a specified position; the moving mechanism is used for loading the zoom lens group and is driven by the stepping motor to move so as to realize zooming; the controller is used for sending a command to the stepping motor so as to control the stepping motor to move; and the prediction module is used for receiving the size and brightness of the light spot on the working interface, predicting the position of the lens through a neural network, and controlling the moving mechanism through the controller so as to control the lens to move to the corresponding position. By adopting the doublet lens, the spherical aberration of the lens can be eliminated, and the light beam quality and the imaging quality of the optical system are improved; through the zoom lens group, the working distance of machining can be changed by adjusting the focal length, and the degree of production automation is improved.

Description

Technical Field

[0001] The invention relates to the technical field of laser energy convergence, in particular to a laser beam coupling and focusing system. Background Art

[0002] With the development and popularization of laser technology, laser technology has been widely used in mechanical processing, laser cutting, laser rust removal, and laser marking due to its excellent characteristics. The accuracy of laser processing depends not only on the power density of the laser beam, but also on the focusing ability of the focusing lens on the laser beam.

[0003] Laser processing is the process of focusing the energy emitted by the laser on a small target area and transferring heat to the material being processed. The laser processing process is highly dependent on the energy that the material can absorb. The efficiency of the processing process is often a function of the square or cube of the irradiance. Therefore, the total energy and spatial distribution of the focus on the workpiece are the key to the success of the processing process, and are very sensitive to the deformation of the shape of the spatial energy distribution of the laser beam. In laser welding, the gap between the parts must be controlled very accurately, which requires that the energy of the laser beam is always aimed at the same target area without focus drift. If high-speed welding is performed, poor beam structure can cause poor welds. In laser cutting, the quality and focusing ability of the beam are critical to the quality of the cut itself. Poor quality beams can cause parts to be scrapped or reworked, increasing costs. Therefore, obtaining high-quality laser beams is the core issue of laser processing.

[0004] There are often complex environments in the production process of laser processing. In large-scale industrial production, fixed-focus lenses are used when fixed lathes are used for processing, which often require manual mechanical adjustments. This is often inefficient and has low precision. Long working hours are prone to mechanical vibration problems, and cutting consistency is not strong.

[0005] Common zoom lenses generally include a front fixed lens group, a variable magnification lens group, a compensation lens group, and a rear fixed lens group. They usually have a complex structure of several or even more than a dozen lenses, and have high requirements for the working environment. When the mechanical vibration is large, it is easy to cause defocus. When there are too many lenses, a large part of the laser power will be lost, so it is rarely used in the field of laser processing. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a laser beam coupling focusing system, comprising a zoom lens group, a stepper motor, a moving mechanism, a controller and a prediction module, wherein the zoom lens group is used to converge the incident laser to a working interface; the stepper motor is used to receive a command from the controller and drive the moving mechanism to a specified position; the moving mechanism is used to load the zoom lens group and move under the drive of the stepper motor to achieve zooming; the controller is used to send a command to the stepper motor to control the movement of the stepper motor; the prediction module is used to receive the size and brightness of the light spot on the working interface, predict the position of the zoom lens group through a neural network, and control the moving mechanism through the controller to control the lens to move to a corresponding position.

[0007] Furthermore, the zoom lens group includes a fixed lens, a variable magnification lens and a compensating lens; the fixed lens, the variable magnification lens and the compensating lens are all double-crossed lenses.

[0008] Furthermore, the fixed lens includes a first curved surface, a second curved surface and a third curved surface, and the curvature radii of the three curved surfaces are all positive. The zoom lens includes a fourth curved surface, a fifth curved surface and a sixth curved surface, and the curvature radii of the three curved surfaces are all positive. The compensating lens includes a seventh curved surface, an eighth curved surface and a ninth curved surface, and the curvature radius of the seventh curved surface is positive, the curvature radius of the eighth curved surface is negative, and the curvature radius of the ninth curved surface is negative. The overall effect of the three curved surfaces is to converge the laser beam.

[0009] Furthermore, an aperture is provided between the fixed lens and the variable-magnification lens to control the laser beam into a circular shape, thereby ensuring the distribution of laser energy on the laser working interface.

[0010] Furthermore, the displacement accuracy of the stepper motor is no more than 0.1 mm.

[0011] Furthermore, the moving structure includes a guide rail and two sliders, on which a zoom lens and a compensation lens are respectively mounted. The slider is connected to a stepper motor and moves under the control of the stepper motor, thereby driving the lens to move.

[0012] Furthermore, it also includes a shell, which is provided with a conical, hollow spout at the image end, with air holes on the side of the spout, and glass slides are placed at both ends of the spout.

[0013] Furthermore, it also includes an accuracy control module for receiving the accuracy of the spot size and brightness input by the user, and generating a plurality of preset spot sizes and brightnesses according to the accuracy.

[0014] Furthermore, it also includes a position detector and a position tuning module, which are used to calculate the difference between the lens position generated by the prediction module and the current lens position, and send the lens position corresponding to the minimum difference to the controller, thereby controlling the movement of the moving mechanism.

[0015] Furthermore, the prediction module generates the positions of several lenses according to the size and brightness of the light spot on the received working interface, and sends them to the position tuning module to calculate the minimum difference, thereby controlling the movement of the moving mechanism through the controller.

[0016] Compared with the prior art, the laser beam coupling and focusing system provided by the present invention has the following beneficial effects:

[0017] (1) Using a zoom lens group, the working distance of mechanical processing can be changed by adjusting the focal length to adapt to complex working environments, which can greatly improve detection efficiency and increase the degree of production automation.

[0018] (2) The lenses in this design all use double-cemented lenses, which can eliminate the spherical aberration of the lens, thereby improving the beam quality and imaging quality of the optical system.

[0019] (3) Based on the characteristics of laser, three double-cemented lenses are used to achieve optical zoom. The simplified structure effectively avoids the problem of multiple lenses being easily out of focus.

[0020] (4) Using a linear array CCD device as a light detector, the light spot image is captured to obtain the light intensity data of each pixel, and then the light intensity distribution and the light spot diameter are obtained. The data fed back by the prediction module is sent to the controller, which then controls the position of the mobile module to achieve the zoom result. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of the overall structure of a laser beam coupling and focusing system according to an embodiment of the present invention;

[0022] Figure 2 is a structural schematic diagram of a zoom lens assembly according to an embodiment of the present invention;

[0023] Figure 3 is a flow chart of a control part of an embodiment of the present invention;

[0024] Figure 4 is a schematic structural diagram of a moving mechanism according to an embodiment of the present invention;

[0025] Figure 5 It is a schematic structural diagram of a spout of an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention provides a laser beam coupling and focusing system, such as Figure 1 As shown, it includes a zoom lens group, a stepper motor, a moving mechanism, a controller 8 and a prediction module, wherein the zoom lens group is used to converge the incident laser to the working interface; the stepper motor is used to receive the controller command and drive the moving mechanism to the specified position; the moving mechanism is used to load the zoom lens group and move under the drive of the stepper motors 10 and 15 to achieve zooming; the controller 8 is used to send commands to the stepper motor to control the movement of the stepper motor; the prediction module 30 is used to receive the size and brightness of the light spot on the working interface, predict the position of the zoom lens group through the neural network, and control the moving mechanism through the controller 8, thereby controlling the lens to move to the corresponding position. The size and brightness of the light spot on the working interface can be obtained by using a linear array CCD device as a light detector, shooting a light spot image, obtaining the light intensity data of each pixel, and then obtaining the brightness and the light spot diameter.

[0028] The zoom lens group includes a fixed lens 1, a variable magnification lens 2 and a compensating lens 3. Figure 2 As shown, the optical axis of the visible light beam is coupled to the optical axis of the laser beam, so that the working plane of the laser beam and the imaging plane of the visible light beam are on the same optical axis.

[0029] In the present invention, it is assumed that the incident light can propagate from left to right, the side on the left of the optical lens is the object side, i.e., the object side, and the side on the right of the optical lens is the image side, i.e., the image side. Since the incident light propagates from left to right, based on the intersection of the spherical surface (i.e., the curved surface) and the principal optical axis, if the center of the sphere is to the left of the intersection, the curvature radius is a negative value; conversely, if the center of the sphere is to the right of the intersection, the curvature radius is a positive value. It can be understood that the positive and negative signs of the curvature radius value only indicate the direction of the curved surface, while the size of the number indicates the degree of curvature of the curved surface.

[0030] In one embodiment, the fixed lens 1 , the variable magnification lens 2 and the compensating lens 3 are all double-jointed lenses, and the three lenses can be made of different materials, such as flint glass or crown glass.

[0031] In one embodiment, the fixed lens 2, the variable magnification lens 2 and the compensation lens 3 are converging lenses. After gradual convergence, when the laser beam passes through the last lens and converges to the working interface, the change in beam diameter will be relatively small when the focal length of the laser beam changes.

[0032] The fixed lens 1 includes a first curved surface, a second curved surface and a third curved surface. The first curved surface faces the object side and is concave toward the image side, the second curved surface faces the object side and is concave toward the image side, and the third curved surface faces the object side and is concave toward the image side. The curvature radii of these three curved surfaces are all positive values ​​to initially converge the laser.

[0033] The zoom lens 2 includes a fourth curved surface, a fifth curved surface and a sixth curved surface. The fourth curved surface faces the object side and is concave toward the image side, the fifth curved surface faces the object side and is concave toward the image side, and the sixth curved surface faces the object side and is concave toward the image side. The curvature radii of these three curved surfaces are all positive values ​​to further converge the laser.

[0034] An aperture is provided between the fixed lens 1 and the zoom lens 2 to control the laser beam into a circular shape to ensure the distribution of laser energy on the laser working interface. At the same time, when the laser passes through the field aperture, interference from other frequency lights is eliminated due to the different refractive indices.

[0035] The compensation lens 3 includes a seventh curved surface, an eighth curved surface and a ninth curved surface, wherein the seventh curved surface faces the object side and is concave toward the image side, the eighth curved surface faces the image side and is concave toward the object side, and the ninth curved surface faces the image side and is concave toward the object side. The curvature radii of the three curved surfaces are positive for the seventh curved surface, negative for the eighth curved surface, and negative for the ninth curved surface, but the overall effect is to converge the laser beam and finally converge the laser to the working interface.

[0036] The function of the zoom lens 2 is to achieve the purpose of zooming through its own linear movement. At the same time, the focal length of the zoom group and the focal lengths of other groups jointly affect the total focal length of the system.

[0037] The function of the compensating lens 3 is to compensate for the image plane displacement caused by the linear movement of the zoom lens during the zooming process. The positions of the zoom lens and the compensating lens are one-to-one corresponding. For the zoom lens and the compensating lens at different positions, they need to be moved to specific positions to keep the image plane position stable. In this design, the displacement accuracy of the stepping motors 10 and 15 does not exceed 0.1mm, and they control the movement of the zoom lens and the compensating lens respectively.

[0038] In one embodiment, the curvature radii (R1-R9) of the first to ninth curved surfaces have an allowable tolerance of less than 5%, and upper and lower deviations of less than 2%.

[0039] In one embodiment, the controller 8 can calculate the positions of the zoom lens 2 and the compensation lens 3 according to the spot size of the working interface, and then send commands to the stepper motors 10 and 15 to control the stepper motors to drive the moving mechanism, thereby driving the zoom lens 2 and the compensation lens 3 to move, ultimately achieving the purpose of adjusting the focal length and allowing the laser energy to better converge on the working interface.

[0040] The prediction module is used to receive the size and brightness of the light spot on the working interface, predict the position of the zoom lens group through a neural network, and control the moving mechanism through the controller 8 to control the lens to move to the corresponding position.

[0041] Neural network is a prior art and has many models. In the present invention, for example, a multi-layer perceptron (MLP) architecture can be used, which includes an input layer, a hidden layer and an output layer, wherein:

[0042] Input layer: used to receive the size and brightness of the light spot on the working interface. The accuracy of the preset light spot size and brightness can be manually specified according to the processing needs, or it can be automatically generated, and then the light spot size and brightness that meet the accuracy are randomly generated or all generated within the accuracy range. These methods will be introduced one by one in the following embodiments.

[0043] Hidden layer: includes multiple neurons, which are used to extract features and establish nonlinear mapping;

[0044] Output layer: Output the position of the lens. If there are multiple lenses, the position information of each lens. If the position of the front lens, modulation lens and rear lens.

[0045] In practical applications, we can collect a large number of training samples, each of which contains an input vector and the corresponding expected output. The input vector includes the spot size and brightness, and the output is the position information of the lens. During the training process, it is necessary to define a loss function to measure the difference between the network output and the expected output. Common loss functions include mean square error (MSE) or root mean square error (RMSE). In order to minimize the loss function, the back propagation algorithm is used to update the weights and bias terms. The above training is a common method and will not be repeated here.

[0046] Even with the same spot size and brightness, different lens positions may correspond. Therefore, in order to improve the response speed, a preferred embodiment of the present invention also includes a position detector for sending the position information of the lens to a position tuning module, and a position tuning module for calculating the difference between the distances of several lens positions generated by the prediction module and the current lens position, and sending the lens position corresponding to the smallest difference to the controller, thereby controlling the movement of the moving mechanism.

[0047] In one embodiment, a spot size and brightness are set, but there can be multiple groups of predicted results, that is, different results have different predicted probabilities. Ten groups of data can be selected and sent to the position tuning module, and the lens position with the smallest distance from the current lens position is sent to the controller, and then the controller controls the moving mechanism to control the lens to move to the corresponding position.

[0048] In one embodiment, a precision control module is further included, which is used to receive the precision of the spot size and brightness input by the user, and generate a number of preset spot sizes and brightnesses according to the precision, and then send them to the prediction module to generate the position information of multiple groups of lenses. For example, assuming that the spot brightness is 100, the precision is 1, and the range is 5, then the preset spot brightness that can be generated is: 101, 102, 103, 104, 105; if the precision is 0.1 and the range is 5, then the preset laser power density generated is: 100.1, 100.2...105.

[0049] The controller 8 receives the position of the lens sent by the prediction module or the position tuning module, and then adjusts the electric slider to change the size and brightness of the light spot on the working interface, thereby achieving precise control of the light spot used for processing.

[0050] The control part of the present invention, such as the data flow of the prediction module, the position optimization module, etc. Figure 3 shown.

[0051] The zoom lens 2 and the compensating lens 3 are mounted on a moving mechanism, and the moving structure can be made of existing technology, such as a guide rail and a slider. The guide rail is fixed on the ground or a table, and then the zoom lens or the compensating lens is mounted on the slider. The slider is connected to a stepper motor and moves under the control of the stepper motor, thereby driving the lens to move.

[0052] In one embodiment, a housing 16 is further included, and a guide rail and a slider 12 and a slider 13 are arranged at the bottom of the housing 16. Figure 4 As shown, a zoom lens 2 is disposed on the slider 12 and connected to a stepping motor 10, and a compensating lens 3 is disposed on the slider 13 and connected to a stepping motor 15, so that the zoom lens and the compensating lens are driven to move in the housing through the movement of the stepping motor.

[0053] In one embodiment, the shell is also provided with a spout at the end close to the working interface to protect the converged light from being disturbed in the distance from the compensation lens to the working interface (the shell also has a corresponding function). At the same time, the spout is also affected by the sputtering of the processing material during the laser processing. Figure 5 As shown, the spout is a conical, hollow structure with air holes 6 on the side. After placing the filters at both ends of the spout, air is inflated through the air holes 6. The air pressure in the spout tightly fits the two filters at both ends of the spout to form a closed structure. When replacing a new filter, you only need to flush in the protective gas and add negative pressure to complete the replacement, which improves the product utilization rate. After the laser comes out of the compensation lens group, it passes through the filter and enters the air chamber. The gas in the air chamber protects the laser beam, and the filter is used to isolate the reflected light to protect the laser and prevent sputtering during the laser processing process.

[0054] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A laser beam coupling and focusing system, characterized in that: The invention comprises a zoom lens group, a stepper motor, a moving mechanism, a controller and a prediction module, wherein the zoom lens group is used to converge the incident laser to the working interface; the stepper motor is used to receive the controller command and drive the moving mechanism to the specified position; the moving mechanism is used to load the zoom lens group and move under the drive of the stepper motor to achieve zooming; the controller is used to send commands to the stepper motor to control the movement of the stepper motor; the prediction module is used to receive the size and brightness of the light spot on the working interface, predict the position of the zoom lens group through the neural network, and control the moving mechanism through the controller to control the zoom lens group to move to the corresponding position.

2. The laser beam coupling and focusing system according to claim 1, characterized in that: The zoom lens group includes a fixed lens, a variable magnification lens and a compensating lens. Preferably, the fixed lens, the variable magnification lens and the compensating lens are all double-crossed lenses.

3. The laser beam coupling and focusing system according to claim 2, characterized in that: The fixed lens includes a first curved surface, a second curved surface and a third curved surface, and the curvature radii of the three surfaces are all positive; the zoom lens includes a fourth curved surface, a fifth curved surface and a sixth curved surface, and the curvature radii of the three surfaces are all positive; the compensation lens includes a seventh curved surface, an eighth curved surface and a ninth curved surface, the curvature radius of the seventh curved surface is a positive value, the curvature radius of the eighth curved surface is a negative value, and the curvature radius of the ninth curved surface is a negative value. The overall effect of the three curved surfaces is to converge the laser beam.

4. The laser beam coupling and focusing system according to claim 2, characterized in that: An aperture is arranged between the fixed lens and the variable-magnification lens to control the laser beam into a circular shape and ensure the distribution of laser energy on the laser working interface.

5. The laser beam coupling and focusing system according to claim 1, characterized in that: The displacement accuracy of the stepper motor is no more than 0.1mm.

6. The laser beam coupling and focusing system according to claim 2, characterized in that: The moving structure includes a guide rail and two sliders, on which a zoom lens and a compensation lens are respectively mounted. The sliders are connected to a stepper motor and move under the control of the stepper motor, thereby driving the lens to move.

7. The laser beam coupling and focusing system according to claim 2, characterized in that: The invention also comprises a shell, which is provided with a conical, hollow spout at the image end, air holes are opened on the side of the spout, and glass slides are placed at both ends of the spout.

8. The laser beam coupling and focusing system according to claim 1, characterized in that: It also includes an accuracy control module for receiving the accuracy of the spot size and brightness input by the user, and generating a plurality of preset spot sizes and brightnesses according to the accuracy.

9. The laser beam coupling and focusing system according to claim 1, characterized in that: It also includes a position detector and a position tuning module, which are used to calculate the difference between the lens position generated by the prediction module and the current lens position, and send the lens position corresponding to the minimum difference to the controller, thereby controlling the movement of the moving mechanism.

10. The laser beam coupling and focusing system according to claim 9, characterized in that: The prediction module generates the positions of several lenses according to the received spot size and brightness on the working interface, and sends them to the position tuning module to calculate the minimum difference, thereby controlling the movement of the moving mechanism through the controller.

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