Focal length compensation method for different working distances of front focusing system

Abstract

The invention relates to a focal length compensation method for different working distances of a front focusing system, which belongs to the field of 3D (three-dimensional) printing and comprises the following steps of: S1, calculating a distance Z between focusing lenses corresponding to different printing coordinate positions by taking a working distance L as a reference, establishing a relational data table about the printing coordinate position and the corresponding spacing; s2, for front focusing systems with different working distances, real printing coordinate positions are converted into virtual coordinate positions, and corresponding intervals are found from the relational data table according to the virtual coordinate positions; and S3, adjusting the focusing lens based on the difference between the obtained distance and the actual distance between the current focusing lens and the focusing lens. According to the method, for front focusing printing systems with different working distances, a relational data table is not re-established any more, and the workload and the calculated amount of establishing the relational data table about the printing coordinate position and the corresponding interval Z when the working distance changes are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of 3D printing, and in particular relates to a focal length compensation method for different working distances of a front focusing system. Background Art

[0002] Galvanometer scanning processing is widely used in laser drilling, cutting, welding, 3D printing and other industries. Its principle is to use a galvanometer to reflect the laser beam and perform image scanning and printing on the printing work surface. According to the galvanometer scanning light path, the current laser scanning focusing methods include front focusing galvanometer and rear focusing galvanometer. The rear focusing galvanometer focuses after scanning, and the front focusing galvanometer focuses before scanning.

[0003] Among them, in the front focusing galvanometer method, the laser beam first passes through the collimator and beam expander, then through the dynamic focusing lens that can move in real time, and then through the galvanometer to reflect the laser to achieve the scanning and printing of the laser on the printing work surface. This mechanism needs to use a program compensation algorithm to control the focusing lens in real time, and coordinate the position of the galvanometer scanning to compensate the focal length, so that the laser beam can be imaged on the printing work surface in real time.

[0004] The front focusing solution uses a voice coil motor that is adjusted dynamically in real time to drive the focusing lens to focus the optical path system. Compared with the rear focusing solution, this solution can eliminate the impact of the price and size of the F-Theta flat-field lens. As the 3D printing industry based on galvanometer scanning matures, the galvanometer printing module is developing towards small size, multiple laser heads, and high integration. The front focusing galvanometer system has the above advantages.

[0005] In the front focusing system, different scanning and printing positions require dynamic focusing lenses to perform real-time dynamic focusing to compensate for the focal length. The specific compensation method is: let (x, y) be the coordinate value on the work surface with the origin directly below the print beam, D be the distance between the X-axis galvanometer and the Y-axis galvanometer, and L be the distance between the Y-axis galvanometer and the work surface in a vertical state. When printing the coordinate (x, y), the focal length value that needs to be compensated is expressed as: In conventional printing systems, the focal length compensation value is usually as high as tens of millimeters. In order to compensate the focal length in real time with high frequency response, the focusing lens needs to compensate the focal length value within a very short stroke. Therefore, the front focusing system is usually divided into a focusing lens group and a focusing lens group, such as Figure 1 As shown in the figure, assuming that the focal length of the focusing lens group is f1, the focal length of the focusing lens group is f2, the distance between the two lens groups is Z, and the distance between the focusing lens group and the X-axis galvanometer is H, then when printing the coordinates (x, y), the distance between the two lens groups is expressed as: , according to the calculated focal length value that needs to be compensated, calculate the change value △Z of the distance between the two sets of lenses. In actual engineering applications, in order to simplify the calculation process, numerical simulation will be used to obtain a data table about the relationship between the coordinates (x, y) and the change value △Z of the distance between the two sets of lenses. The data table can be called by the software to quickly obtain the printing coordinates and the values ​​that need to be compensated for the focus motor.

[0006] However, in actual engineering applications, when different laser print heads are installed on machines of different models, the working distances L are different and the differences are relatively large. Based on different working distances, the relationship data table between the coordinates (x, y) and the change value △Z of the distance between the two sets of lenses will also be different. This relationship data table requires precise numerical calculation simulation to obtain a complete table, and in order to meet the accuracy requirements, the table usually has more than thousands of data. Therefore, when the working distance L changes, the corresponding table must be modified, which requires a huge workload and calculation. Summary of the invention

[0007] The purpose of the present invention is to provide a focal length compensation method for a front focusing system with different working distances, so as to solve the problem of huge workload and calculation amount in re-obtaining the data table of the relationship between the coordinates (x, y) and the change value △Z of the distance between two groups of lenses when the working distance changes in the existing front focusing system.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows: The present invention relates to a focal length compensation method for different working distances of a front focusing system, wherein the front focusing system comprises a focusing lens, a focusing lens, a reflection galvanometer group and a printing working surface arranged in sequence along an optical path, wherein the reflection galvanometer group further comprises an X-axis galvanometer and a Y-axis galvanometer arranged in sequence along the optical path, and the vertical optical path from the Y-axis galvanometer to the printing working surface is taken as the working distance of the front focusing system, and the method comprises the following steps: S1. Based on the working distance L, calculate the change in focal length of the focusing lens corresponding to different printing coordinate positions, and establish a data table on the relationship between the printing coordinate position and the corresponding change; S2. For the front focusing system with different working distances, the real printing coordinate position is converted into a virtual coordinate position, and the corresponding change in the focal length of the focusing lens is found from the relationship data table in S1 according to the virtual coordinate position, and the focusing lens is adjusted based on the change.

[0009] Preferably, the step of calculating the change in focal length of the focusing lens corresponding to different printing coordinate positions in S1 is: S1.1. Calculate the focus distance corresponding to different printing coordinate positions. The calculation formula is: (1), Where (x, y) is the coordinate value of the point on the printing work surface directly below the printing beam as the origin, D is the distance between the X-axis galvanometer and the Y-axis galvanometer, and △L is the focusing distance required when printing (x, y); S1.2. Calculate the change in focal length of the focusing lens based on the focusing distance. The calculation formula is: (2), Among them, △Z is the change in focal length of the focusing lens, H is the horizontal distance between the focusing lens and the X-axis galvanometer, and f1 and f2 represent the focal lengths of the focusing lens and the focusing lens, respectively.

[0010] Preferably, the calculation formula for converting the real printing coordinate position into the virtual coordinate position in S2 is: (3), (4), Wherein, (x, y) is the coordinate value of the point on the printing work surface directly below the printing beam as the origin, (x', y') is the virtual coordinate position, and L' is the actual working distance.

[0011] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: The focal length compensation method for different working distances of the front focusing system of the present invention does not re-establish the relationship data table about the printing coordinate position and the corresponding spacing Z for the front focusing printing system with different working distances, but converts the real printing coordinate position into a virtual coordinate position, and finds the corresponding spacing between the focusing lens and the focusing lens from the original relationship data table according to the virtual coordinate position, and finally adjusts the focusing lens according to the difference between the obtained spacing and the actual spacing between the current focusing lens and the focusing lens, thereby reducing the workload and calculation amount of establishing the relationship data table about the printing coordinate position and the corresponding spacing Z when the working distance L changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG1 is a structural diagram of a front focus printing system according to the present invention; Among them, 1-focusing lens, 2-focusing lens, 3-reflection galvanometer group, 4-printing work surface. DETAILED DESCRIPTION

[0013] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with examples. The following examples are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0014] The present invention relates to a method for compensating focal lengths of a front focusing system at different working distances. Figure 1As shown, the front focusing system includes a focusing lens 1, a focusing lens 2, a reflective galvanometer group 3 and a printing work surface 4 which are sequentially arranged along the optical path. The reflective galvanometer group 3 further includes an X-axis galvanometer and a Y-axis galvanometer which are sequentially arranged along the optical path. The vertical optical path from the Y-axis galvanometer to the printing work surface 4 is the working distance of the front focusing system.

[0015] The focal length compensation method of the front focusing system at different working distances includes the following steps: S1. Based on the working distance L, calculate the change in focal length of the focusing lens corresponding to different printing coordinate positions. The calculation steps are as follows: S1.1. Calculate the focus distance corresponding to different printing coordinate positions. The calculation formula is: (1), Where (x, y) is the coordinate value of the point on the printing work surface directly below the printing beam as the origin, D is the distance between the X-axis galvanometer and the Y-axis galvanometer, and △L is the focusing distance required when printing (x, y); S1.2. Calculate the change in focal length of the focusing lens based on the focusing distance. The calculation formula is: (2), Among them, △Z is the change in focal length of the focusing lens, H is the horizontal distance between the focusing lens and the X-axis galvanometer, f1 and f2 represent the focal lengths of the focusing lens and the focusing lens respectively; Then, the relationship between the printing coordinate position and the corresponding change value △Z is established, and the corresponding relationship is: , Furthermore, a relational data table about the printing coordinate position and the corresponding change value ΔZ is established.

[0016] S2. For the front focusing system with different working distances, the real printing coordinate position is converted into the virtual coordinate position. The calculation formula is: (3), (4), Wherein, (x, y) is the coordinate value of the point on the printing work surface directly below the printing beam as the origin, (x', y') is the virtual coordinate position, and L' is the actual working distance.

[0017] At this time, the relationship between the virtual coordinate position and the distance change value △Z between the focusing lens and the focusing lens is expressed as: , Then, the corresponding change amount of the focus lens for adjusting the focal length is found from the relationship data table in S1 according to the virtual coordinate position, and the focus lens is adjusted based on the change amount.

[0018] The present invention is described in detail above in conjunction with the embodiments, but the contents described are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of application of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A focal length compensation method for different working distances of a front focusing system, wherein the front focusing system comprises a focusing lens, a focusing lens, a reflective galvanometer group and a printing work surface arranged in sequence along an optical path, wherein the reflective galvanometer group further comprises an X-axis galvanometer and a Y-axis galvanometer arranged in sequence along the optical path, and the vertical optical path from the Y-axis galvanometer to the printing work surface is the working distance of the front focusing system, characterized in that: It includes the following steps: S1. Based on the working distance L, calculate the change in focal length of the focusing lens corresponding to different printing coordinate positions, and establish a data table on the relationship between the printing coordinate position and the corresponding change; S2. For the front focusing system with different working distances, the real printing coordinate position is converted into a virtual coordinate position, and the corresponding change in the focal length of the focusing lens is found from the relationship data table in S1 according to the virtual coordinate position, and the focusing lens is adjusted based on the change.

2. The focal length compensation method for different working distances of the front focusing system according to claim 1, characterized in that: The steps for calculating the change in focal length of the focusing lens corresponding to different printing coordinate positions in S1 are as follows: S1.

1. Calculate the focus distance corresponding to different printing coordinate positions. The calculation formula is: （1）， Where (x, y) is the coordinate value of the point on the printing work surface directly below the printing beam as the origin, D is the distance between the X-axis galvanometer and the Y-axis galvanometer, and △L is the focusing distance required when printing (x, y); S1.

2. Calculate the change in focal length of the focusing lens based on the focusing distance. The calculation formula is: （2）， Among them, △Z is the change in focal length of the focusing lens, H is the horizontal distance between the focusing lens and the X-axis galvanometer, and f1 and f2 represent the focal lengths of the focusing lens and the focusing lens, respectively.

3. The focal length compensation method for different working distances of the front focusing system according to claim 1, characterized in that: The calculation formula for converting the real printing coordinate position into the virtual coordinate position in S2 is: （3）， （4）， Wherein, (x, y) is the coordinate value of the point on the printing work surface directly below the printing beam as the origin, (x', y') is the virtual coordinate position, and L' is the actual working distance.

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