CN1814390A - Flight optical focusing characteristic control system - Google Patents

Abstract

A flying optical focusing characteristic control system for a laser processing machine is characterized in that it is composed of a convex deformable mirror, a concave deformable mirror, a focusing mirror and a control system arranged in sequence on the optical path of the laser processing machine, wherein the convex deformable mirror, the concave deformable mirror and the focusing mirror are combined in a motion system, wherein the control system includes a computer, a stepping motor, a control block and a pressure system, wherein the motion system is controlled by a computer through the step length of the stepping motor; on the other hand, the computer controls the curvature radius of the convex deformable mirror and the concave deformable mirror through a pressure system via a control block, and controls the actual focal length and focal spot size in long-distance laser processing in real time. The present invention can overcome the change in the focusing characteristic of the Gaussian laser beam caused by the movement of the focusing mirror in the laser processing of super-large and super-heavy workpieces.

Description

Flight optics focusing characteristic control system

technical field

The invention relates to a laser processing machine, in particular to a control system for the flying optical focusing characteristics of the laser processing machine, which uses two deformable mirrors to monitor the flying optical focusing characteristics (focus position and focal spot size) in real time during the laser processing of large workpieces. On-line control, applied to the quality control system of high-power laser precision machining of ultra-large and overweight workpieces.

technical background

For laser processing of ultra-large and overweight workpieces, the workpieces are sometimes as long as 10 meters or longer and weigh several tons or more. If the workpiece moves with a large area and large inertia, it is difficult to control. If the workpiece does not move, the light-weight focusing lens system moves along the optical axis in a large range, which can avoid the above-mentioned disadvantages, but the resulting change in the focusing characteristics of flying optics brings new problems to laser precision machining.

The focusing characteristics of flying optics mainly include the difference between the actual focal length and the geometric focal length (ideal parallel light focal length), the change of focal spot size and focal depth. Due to the large-scale movement of the focusing mirror of the processing system along the optical axis, the actual focus position and the size of the focal spot will change greatly, which will have a serious impact on the quality of laser processing. For example, although the beam divergence angle of He-Ne light is on the order of milliradians and the beam waist size is on the order of millimeters, if the geometric focal length of the focusing lens is 100mm, the maximum value of the focal length change of its flying optics can reach the order of tens of millimeters . For the high-power CO ₂ lasers currently used in the industry, the maximum value of the focal length of the flight optics can reach the order of several millimeters or more (depending on the quality of the beam). To study and solve this key problem is of great significance to laser technology and its application.

technical content

The object of the present invention is to provide a control system for the focus characteristic of flying optics, which solves the problem of the change of focus characteristic in the laser processing of large workpieces of flying optics, so as to improve the processing accuracy.

Theoretical research shows that Δf is related to the distance z (ie flight distance) of the focusing mirror relative to the light waist of the laser Gaussian beam. The maximum change Δf of the geometric focal length of the focusing mirror is:

Δf _max =f ² θ/2w,

Where w is the waist size (radius) of the laser beam, θ is the divergence angle (half angle) of the beam, and the geometric focal length of the pseudo-focusing mirror. From this, the maximum focal length change value of various typical lasers can be calculated, as shown in Table 1.

Table 1 The maximum focal length change value of various typical lasers (f=200mm) laser name Light waist radius w/mm Beam divergence half angle θ/mrad Rayleigh length Z _R /mm Maximum focal length variation Δf _max /mm kW- _CO2 20 5 4000 5 100W-YAG 10 10 1000 20 He-Ne 1 3 333 60

In order to control the change of laser focusing characteristics and improve the quality of laser processing of large workpieces, the basic idea of the present invention is:

A control system for the focus characteristics of flying optics, the system makes the motion system including two deformable mirrors and focusing mirrors move along the optical axis in a large range to realize long-distance laser processing quality control; two concave-convex with relatively fixed positions are used The deformable mirror uses a computer to control the radius of curvature of the two deformable mirrors separately, and performs real-time control of the focal length and focal spot size respectively, thereby controlling the focusing characteristics of the flying optics.

Technical solution of the present invention is as follows:

A flying optical focusing characteristic control system for a laser processing machine, characterized in that it is composed of a convex deformable mirror, a concave deformable mirror, a focusing mirror and a control system thereof arranged sequentially on the optical path of the laser processing machine, the convex deformable mirror, the concave deformable mirror The deformable mirror and the focusing mirror are combined in a motion system, and the control system includes a computer, a stepping motor, a control block and a pressure system, and the motion system is controlled by the computer through the step length of the stepping motor. On the other hand, the computer controls the radius of curvature of the convex deformable mirror and the concave deformable mirror through a pressure system through a control block, and controls the actual focal length and focal spot size in long-distance laser processing in real time.

The pressure system is a system composed of hydraulic pressure, air pressure or piezoelectric ceramics.

Working process of the present invention is as follows:

The high-power Gaussian laser beam emitted by the laser of the laser processing machine passes through the convex deformable mirror and the concave deformable mirror in sequence, and then enters the focusing mirror and focuses on the large workpiece. Convex deformable mirrors, concave deformable mirrors and focusing mirrors are combined in one kinematic system. The motion system can move in a large range along the optical axis. The computer controls the motion system through the step length of the stepping motor; the computer and the control system control the curvature radius of the convex deformable mirror and the concave deformable mirror through hydraulic, pneumatic or piezoelectric ceramic pressure systems, and real-time control of the actual focal length and focal spot of long-distance laser processing size.

The present invention has following technical characteristics:

1. Make the motion system move along the optical axis in a large range to realize laser processing of large workpieces without moving heavy workpieces or lasers, which increases the flexibility of processing and reduces the processing site.

2. Use two relatively fixed convex deformable mirrors and concave deformable mirrors, respectively control the radius of curvature through the computer, and control the actual focal length and focal spot size of long-distance laser processing in real time.

3. The positions of the two relatively fixed convex deformable mirrors and concave deformable mirrors and the focusing mirror (4) are relatively fixed to avoid dragging of pipelines during movement and improve the safety and stability of the system.

Description of drawings

Fig. 1 is a schematic diagram of the principle of the connection between the control system of the flying optics focusing characteristics of the present invention and the laser processing machine.

Detailed ways

The technical solution of the present invention will be described below in conjunction with the accompanying drawings.

Please refer to FIG. 1 first. FIG. 1 is a schematic diagram of the connection between the flying optical focusing characteristic control system of the present invention and the laser processing machine. The flying optics focusing characteristic control system of the present invention is composed of a convex deformable mirror 5, a concave deformable mirror 3, a focusing mirror 4 and a control system thereof arranged in sequence on the optical path of a laser processing machine, the convex deformable mirror 5, the concave deformable mirror 3 and The focusing mirror 4 is combined in a motion system 6, and the control system includes a computer 8, a stepper motor 7, a control block 9 and a pressure system 10, and the motion system 6 is controlled by the computer 8 through the steps of the step motor 7. Long-term control and movement; the computer 8 controls the radius of curvature of the convex deformable mirror 5 and the concave deformable mirror 3 through a pressure system 10 through a control block 9, and real-time control of the actual focal length and focal spot size in long-distance laser processing.

The pressure system 10 is a hydraulic, pneumatic or piezoelectric ceramic system.

When working, the 5kW high-power laser beam emitted by the _CO2 laser 1 of the laser processing machine passes through the convex deformable mirror 5 and the concave deformable mirror 3 in sequence, and then enters the focusing mirror 4 and focuses on the large workpiece 2 for processing. The convex deformable mirror 5 , the concave deformable mirror 3 and the focusing mirror 4 are combined in a motion system 6 . The motion system 6 is driven by the laser processing machine to move in a large range along the direction of the optical axis. The computer 8 controls the motion system 6 through the stepping motor 7; the computer 8 and the control system 9 control the curvature radius of the convex deformable mirror 5 and the concave deformable mirror 3 through a pressure system 10 such as hydraulic pressure, air pressure or piezoelectric ceramics, so as to control the long distance in real time Actual focal length and focal spot size for laser processing.

On the premise that the large workpiece and the laser do not move, to achieve large-scale processing, the motion system 6 needs to move in a large range, and the position of the focusing mirror relative to the light waist of the Gaussian beam will move, causing changes in the actual focal length and focal spot size , Even make laser processing (such as laser welding, cutting, etc.) impossible. In order to keep the focal length and the size of the focal spot unchanged, a convex deformable mirror 5 and a concave deformable mirror 3 are used. The two deformable mirrors are made of copper with a diameter of 60 mm and a thickness of 2 mm through optical polishing. The external force system 10 such as hydraulic pressure, air pressure or piezoelectric ceramics controls the curvature radius of the two deformable mirrors through the computer 8 and the PLC control system 9, so that the curvature radius of the two deformable mirrors changes with the movement of the focusing mirror. The invention achieves the purpose of real-time control of the actual focal length and focal spot size of long-distance laser processing through computer-controlled hydraulic pressure.

The calculation method of the radius of curvature of the concave mirror and the convex mirror is as follows,

${\mathrm{<span\; class="notranslate">\; f</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; aL</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; ac</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; w</span>}}^{<span\; class="notranslate">\; \&prime;</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; w</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, f' and w' are the actual focal length and the radius of the focal spot, respectively, which are the quantities that need to be controlled; L is the distance between the focusing mirror and the laser Gaussian beam waist, Z _R is the Rayleigh length of the Gaussian beam, and w is the focused Gaussian beam Light waist size (radius), a, b, c, d are the following matrix elements:

$\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; a</span>}& \mathrm{<span\; class="notranslate">\; b</span>}\\ \mathrm{<span\; class="notranslate">\; c</span>}& \mathrm{<span\; class="notranslate">\; d</span>}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; \&CenterDot;</span>\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 1</span>}& {\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; \&Center\; Dot;</span>\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; \&Center\; Dot;</span>\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 1</span>}& {\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; \&CenterDot;</span>\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ \frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Where f ₁ and f ₂ are the focal lengths (half of the radius of curvature) of the convex mirror and the concave mirror respectively, f is the geometric focal length of the focusing mirror, L ₁ is the distance between the concave mirror and the convex mirror, L ₂ is the concave mirror and the focusing distance between mirrors.

When the motion system starts from a certain reference point, it is controlled by the stepping motor step and moves to point L. The radius of curvature of the two deformable mirrors corresponding to point L has been determined by experiments and theory, and stored in the computer. Computer control The hydraulic system sensor changes the pressure on the back of the deformable mirror. Since the curvature radius of the deformable mirror is related to the hydraulic pressure, the convex mirror and the concave mirror have a curvature radius related to the moving distance L, which is determined by (1), (2), (3) It can be seen from the formula that the actual focal length f' and the focal spot size w' can be kept relatively unchanged.

Experiments have shown that when the motion system including the two deformable mirrors and the focusing mirror moves a long distance along the optical axis, the actual focal length change Δf can be controlled within 5%, which meets the needs of laser precision machining of super large and heavy workpieces.

Claims (2)

1. A flight optical focusing characteristic control system for a laser processing machine, characterized in that a convex deformable mirror (5), a concave deformable mirror (3), a focusing mirror (4) and Its control system is composed of, the convex deformable mirror (5), concave deformable mirror (3) and focusing mirror (4) are combined in a motion system (6), and the described control system includes a computer (8), a stepping motor (7), control block (9) and pressure system (10), this kinematic system (6) is by the motion of the step-length control kinematic system (6) of stepper motor (7) by computer (8); This computer (8) ) control the radius of curvature of the convex deformable mirror (5) and the concave deformable mirror (3) through a pressure system (10) through a control block (9), real-time control of the actual focal length and focal spot size in long-distance laser processing . 2. The focusing characteristic control system of flying optics according to claim 1, characterized in that the pressure system (10) is a hydraulic, pneumatic or piezoelectric ceramic system.