JPS61253193A - Laser beam machine - Google Patents

Abstract

PURPOSE:To absorb the fluctuation in the spreading angle of a laser beam by changing automatically the space between the lenses of a beam expander in the direction where the change of the spread of laser beam emitted from a pulse excited solid-state laser light source is offset. CONSTITUTION:A pulse generating circuit 15 receives the pulse synchronized with the first pulse among the burst pulses which a driving circuit 2 supplies to the solid state laser light source 1. Said circuit generates the pulses of the repeating speed of integer times the speed thereof and supplies the pulses to a pulse motor 14. The motor 14 rotates a cam 13b at the specified speed proportional to the pulse speed. As a result, a concave lens 11 is pushed forward by the movement of a moving plate 13c so as to approach a convex lens 12 at the point of timer for starting burst of the solid-state laser light source. The interative forward and backward movements that the lens begins to retreat again after maintaining the most near position shown by a dotted line for the prescribed time and returns to the home position before the start of the next burst are repeated at the burst period.

Description

[Detailed description of the invention] purpose of invention Industrial applications The present invention relates to a laser processing device.

Some conventional laser processing devices use solid state laser light sources as light sources.

The diameter and divergence angle of the laser beam emitted from a solid-state laser light source depend on the dimensions of the laser medium, its thermal characteristics, the configuration of the resonator, etc., and are usually several mm in diameter and several millimeters in divergence angle.
It is in the range of ad to number + mrad. A beam expander composed of a combination lens is used as a means for converting this emitted laser beam into a desired power density.

Further, in a solid-state laser light source, pulsed excitation is performed.

Problems to be Solved by the Invention While a solid-state laser light source is in steady operation, the laser medium is in a thermal equilibrium state and the divergence angle of the emitted laser beam remains constant.

On the other hand, when a solid-state laser operates intermittently, the beam divergence angle changes in the thermal transient state immediately after the start of operation, and the power density on the workpiece changes accordingly, reducing processing accuracy. There is a problem with the decline.

Means for Solving the Problems in the Structure of the Invention The laser processing apparatus of the present invention has a beam expander including a combination lens disposed between a pulse-excited solid-state laser light source and a workpiece. It is configured to absorb changes in the beam divergence angle during thermal transient states by automatically changing the direction to offset changes in the divergence angle of the laser beam emitted from the solid-state laser light source.

Hereinafter, the operation of the present invention will be explained in detail together with examples.

Embodiment FIG. 1 is a block diagram schematically showing the configuration of a portion around a beam expander in a laser processing apparatus according to an embodiment of the present invention.

This beam expander 10 is installed in front of a solid-state laser light source 1 consisting of a YAG laser oscillator or the like, expands the diameter of the laser beam emitted from the solid-state laser light source, and guides it toward the workpiece.

This beam expander 10 includes a concave lens 11, a convex lens 12 disposed in front of the concave lens, a movable plate 13a that carries the concave lens 11 and moves, and a movable plate that moves between the lenses 11 and 13.
a mechanism section 13 consisting of a cam 13b and a spring 13c that move the cam 13b back and forth in a direction parallel to the optical axis of the mechanism section 12; a pulse motor 14 that rotates the cam 13b of the mechanism section 13 at a predetermined speed;
The pulse motor 14 is provided with a pulse generating circuit 15 that supplies pulses of a predetermined period.

The drive circuit 2 operates the solid-state laser light source 1 in a so-called burst mode by intermittently supplying a group of periodic drive pulses to the solid-state laser light source 1 .

That is, the solid-state laser light source 1 operates in a pulsed manner 10 times at a predetermined period, stops for a predetermined period, and then operates in a pulse manner at a predetermined period, as shown in FIG. It repeats a periodic operation in a burst mode in which it operates in a pulsed manner 10 times and then pauses for a predetermined period of time.

In such a burst mode, the temperature of the laser rod changes periodically, for example, as shown in FIG. 2(B). That is, when the first pulse operation is performed with the start of a burst, the temperature of the laser rod begins to rise.

This temperature rise gradually increases with the second, third, etc. pulse operations, but the amount of heat dissipated from the laser rod also increases at the same time, so eventually a thermal equilibrium is reached where the amount of heat and heat dissipation are evenly balanced. state, and the temperature of the laser rod also becomes a constant value. This increased temperature gradually decreases during the stop period of the solid-state laser light source 1, and when the next burst operation is started, it is equal to the temperature when the previous pulse operation was started.

A spatial temperature distribution occurs within the laser rod such that the center portion is at a high temperature, and the laser rod itself acts as a lens due to the spatial distribution of refractive index based on this temperature distribution. As a result, the divergence angle of the emitted beam changes as the temperature distribution of the laser rod changes. Therefore, as the spatial distribution of temperature changes during thermal imbalance, the divergence angle θ of the emitted laser beam gradually increases to a constant value, as illustrated in FIG. 2(C).

The lens distance d between the concave lens 11 and the convex lens 12 is decreased in a direction that offsets this increase in the divergence angle of the emitted beam.

That is, as shown in FIG. 1(D), the pulse generation circuit 15 receives from the drive circuit 2 a pulse synchronized with the first of the burst pulses that the drive circuit 2 supplies to the solid-state laser beam tX1, and calculates the integer number of the pulses. A pulse with twice the repetition rate is generated and supplied to the pulse motor 14. The pulse motor 14 receiving this pulse rotates the cam 13b at a constant speed proportional to the pulse speed. As a result, at the start of the burst operation of the solid-state laser light source 1, the concave lens 11, which was in the position shown by the solid line in FIG. 1, is gradually pushed forward and approaches the convex lens 12 as the moving plate 13c moves. , after holding the maximum approach position indicated by the dotted line for a predetermined time, it begins to retreat again, and returns to the original position indicated by the solid line by the start of the next burst, repeating the repetitive back and forth movement at the burst cycle.

As a result, the laser beam emitted from the solid-state laser light source 2 passes through the optical path shown by the solid line in Figure 1 at the beginning of each burst, and after reaching a thermal equilibrium state, the laser beam is emitted by the solid line in the figure The light is supplied to the workpiece through such an optical path. Such periodic increase/decrease in the lens interval compensates for the increase in the divergence angle of the laser beam emitted from the solid-state laser light source 1.

The present invention has been exemplified above for the case where the number of pulses included in one burst and the burst period are fixed, but
The present invention can also be applied when these vary. In this case, count the number of pulses in each burst, rotate the pulse motor until it reaches a predetermined value, and then stop the rotation.
When the end of each burst is detected, appropriate corrections may be made, such as quickly returning the rotation angle of the pulse motor to its initial value by supplying a predetermined number of high-speed pulses.

Further, although a configuration in which a cam and a pulse motor are used to change the lens interval has been exemplified, other appropriate methods may be used.

Moreover, although the case where the lens interval is changed by moving the concave lens has been illustrated, a configuration may also be adopted in which the concave lens is fixed and the convex lens is moved.

Effects of the Invention As explained in detail above, the laser processing apparatus of the present invention automatically adjusts the distance between the lenses of the beam expander in a direction that offsets changes in the divergence angle of the laser beam emitted from the pulse-excited solid-state laser light source. Since it is a configuration that can be changed symmetrically, it is possible to absorb fluctuations in the beam divergence angle in a thermal transient state, and it is possible to further improve processing accuracy.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing the configuration of the peripheral portion of a beam expander in a laser processing apparatus according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram for explaining the operation of FIG. 1. ■...Solid laser light source, 2...Drive circuit, 10...Beam expander, 11...Concave lens. 12... Convex lens, 13... Mechanism section, 14... Pulse motor, 15... Pulse generation circuit. Patent distributor NEC Corporation Representative Patent attorney Toshihiko Sakurai

Claims (1)

[Scope of Claims] A beam expander comprising a pulse-excited solid-state laser light source that operates intermittently and a combination lens disposed between the pulse-excited laser light source and the workpiece, A laser processing apparatus characterized in that the interval between the pulse-excited solid-state laser light sources is automatically changed in a direction that offsets a change in the divergence angle of the laser beam emitted from the pulse-excited solid-state laser light source.