JP2938336B2 - Apparatus and method for laser engraving on steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for engraving a steel surface using a laser beam.

[0002]

2. Description of the Related Art As a method of engraving a product number, a company mark, an inspection institution mark, etc. on a steel sheet surface, there are a method of engraving manually by using a hammer or the like and an automatic engraving machine by a hammer drop type. . However, manual work has the disadvantages that the working environment is poor and it takes a long time, and that the automatic stamping machine cannot deal with noise, consumption of the stamp, and changes in the character size and the stamp direction. For these reasons, laser engraving that has a clear and uniform engraving state and is easy to automate has been studied. Laser-engraved steel sheets are required to have a depth that does not disappear by exposure to air, shot blasting, heat treatment, and the like, and generally have a depth of about 100 μm or more. Therefore, a high-output pulse laser having energy on the order of J per pulse is required. As a laser marking device for steel materials, there is a method of performing marking by scanning a movable carriage equipped with an optical system with a motor as proposed in Japanese Patent Laid-Open No. 57-142785.

[0003] However, such a method has a problem that it takes time to move the mobile trolley, and it takes time to engrave.
A marking device using a galvano scan mirror and a laser has already been put to practical use for ICs and the like. However, the character size is small, the marking depth is about several μm using a Q-switched laser, and this is used as a steel material. It is impossible to use it for engraving. Further, since a Q-switch laser capable of high repetition is used, characters and symbols to be engraved are represented as a dot pattern.
The method of engraving while taking the timing of laser oscillation with a scanning device such as a galvano scan mirror for every one dot as proposed in Japanese Patent Publication No. 4 is adopted, and this method complicates data exchange and repeats. There is a problem that it takes too much time to perform engraving using a normal pulse laser having a low speed.

Further, in the above-described method using a trolley, there is a condition that there is a large space for installing the optical system in front of the engraved portion of the steel material, and engraving is performed on the side surface of the steel plate, the back surface of the steel plate, or the side surface of the roll material or the bar material. It is difficult. In addition, since the beam transmission is performed by a mirror, the optical path of the entire marking device becomes rigid, and not only requires laborious installation work to provide the marking device to the existing equipment, but also clean environment that is inherently clean. There is a restriction that the laser oscillator body that requires the above is installed in the vicinity of a production line of a dusty or vibrating steel plate or the like, which is one of the causes of frequent device failures.

As another example using an optical fiber, as in Japanese Patent Publication No. 62-13117, the laser beam is divided, transmitted by a fiber, collected in a focusing head, and engraved by moving the focusing head. Devices have also been proposed. However, also in the present invention, beam scanning for forming a character is a method in which engraved dots are formed by moving a processing head, and the engraving speed is slow, which is not practical. It is the same as the invention of the above.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for easily and clearly performing laser engraving on a free portion of the surface of a steel material such as a steel plate or a roll material or a bar material.

[0007]

The gist of the present invention for solving the above-mentioned problems is to provide a beam scanning system including a normal pulse laser and a set of galvano scan mirrors for scanning a laser beam. A drive system for driving a galvano scan mirror and fθ for condensing a laser beam
A lens or a mirror, a tapered optical fiber having a smaller exit core diameter for transmitting a beam than the entrance core diameter,
An incident optical system for inputting a laser beam into the tapered optical fiber, a collimating optical system for collimating the laser beam at the tapered optical fiber exit, a control computer for processing marking information, the beam scanning system and the normal pulse A laser marking device comprising: a pulse control system for independently controlling laser oscillation.
And in the method of laser engraving on steel by the above device, the characters to be engraved, the symbol is recognized as a set of line segments,
In addition, at the intersection of a line segment in a character or a symbol, another line segment except one of the intersecting line segments is constituted by a pattern interrupted before and after the intersection, and the galvano scan mirror forms a line constituting each character and symbol. The scanning is performed based on the information of the two points of the start point and the end point of the minute, and the drive signal of the galvano scan mirror is
Assuming that the actual movement of the galvano scan mirror is delayed with respect to the drive signal, a certain waiting time is inserted in advance to scan the beam spot without confirming the position of the galvano scan mirror, and use the normal pulse laser. The pulse control system stops the oscillation only at the interval between each line segment from the end point to the start point of the line segment in the set of line segments at a timing determined in advance according to the galvano scan mirror. Is a laser engraving method for steel material that enables high-speed and clear marking on steel material by independently oscillating independently without recognizing information on the scanning position of the laser beam by the laser beam.

[0008]

FIG. 1 schematically shows a laser marking device used in the present invention. A laser beam 2 emitted from a normal pulse laser oscillator 1 is condensed by an optical system incident on an optical fiber and transmitted by a tapered optical fiber. At the exit of the tapered optical fiber, there is a beam collimating optical system that collimates the output beam, and the laser beam that has exited the tapered optical fiber is collimated into substantially parallel light.
The collimated laser light is guided to a high-speed and high-precision beam scanning system 9 using two sets of galvano scan mirrors 3 and 4. The galvano scan mirrors 3 and 4 include a drive system 10
The laser beam is moved two-dimensionally, and the laser beam is focused on the steel plate surface by the fθ lens (or mirror) 5.

On the other hand, the control computer 6 and the pulse control system 7 are for processing the marking information and controlling the laser oscillator 1. The side nozzle 8 is for blowing a gas such as dry air or argon to a processing point to promote evaporation during processing and to remove a melt. The information of the engraving is composed of the engraving parameters and the engraving data input to the control computer. The engraving parameter specifies the size of the character and the position of the character, and the engraving data specifies the array of characters to be laser-engraved. In response to the two pieces of information and the engraving start command, the control computer operates a pre-made character formation program to convert engraved characters and symbols into patterned data, and drives the galvano scan mirror 3 through the drive system 10. , 4
Scan. The laser oscillator 1 first has a frequency,
After the output is set, an oscillation start signal is received from the control computer through the pulse control system at the start point of the marking, and oscillation is started.

Next, transmission of a laser beam by a tapered optical fiber will be described. FIG. 2 schematically shows a state of a beam when a laser beam emitted from an optical fiber is collimated and then condensed by a condenser lens.
Assuming that the core diameter of the optical fiber exit is d1, the focal length of the collimating optical system is f1, the focal length of the condenser lens is f2, the diameter of the collimated beam is D1, and the diameter of the focused beam spot is d2, the light is condensed. The size d2 of the beam spot diameter is expressed as follows.

D2 = d1 × f1 / f2 When an optical fiber is used as shown in the above equation, the diameter of the focused beam spot is proportional to the diameter of the exit core of the optical fiber. Therefore, when it is desired to condense the beam spot small and make a deeper mark on the steel plate, it is necessary to reduce the exit diameter of the optical fiber. However, since the pulse laser used for engraving on steel materials has a large output and oscillates in multimode, it is difficult to focus the beam.Therefore, there is a limit when the laser beam is incident on the optical fiber. Optical fibers having the same core diameter can transmit data up to a minimum core diameter of about 0.6 mm.

Also, when laser engraving is performed on a steel material, the engraving is usually performed in a range of several tens to hundreds of mm square as a normal engraving range. 100 as the focal length of the lens
mm or more.

Accordingly, f2 in the above equation is about 100 mm. If the fiber core diameter is assumed to be 0.6 mm, the condensing spot diameter required for deep engraving 1.
In order to obtain about 0 mm or less, the focal length f1 of the collimating optical system needs to be as long as about 70 mm or more. Here, the collimated beam diameter D1 in FIG. 6 is expressed as follows by the NA of the optical fiber and the focal length f1 of the collimating light collecting system.

D1 = 2 × NA × f1 The NA of an optical fiber currently used for a high-power pulse laser is about 0.2. Therefore, when the above-mentioned numbers are substituted into the above equation, D1 becomes about 28 mm or more. Such a beam is condensed using an fθ lens. An fθ lens having a focal length of about 100 mm has an effective diameter such that a laser beam having a beam diameter as large as described above is scanned due to its lens configuration. Therefore, it is difficult to manufacture an optical fiber. Therefore, an optical fiber having the same diameter of a normal exit core diameter and an entrance core diameter is used for a laser marking device for scanning a beam with a galvano scan mirror and an fθ lens of the present invention. Is difficult.

The tapered optical fiber which is a component of the present invention has an entrance diameter smaller than an exit core diameter. Therefore, even when transmitting a high-output pulse YAG laser used for engraving a steel material, the diameter of the exit core of the fiber is 0.1 mm.
The diameter of the exit core can be about 1 to 0.4 mm. In the transmission of the laser beam, the diameter of the exit core of about half or less can be used as compared with the optical fiber having the same diameter of the exit core and the entrance core. is there.

In this case, even when a fθ lens having a focal length of about 100 mm is used as described above, if the focused beam spot diameter is to be about 1.0 mm or less, the focal length f1 of the collimating optical system should be up to about 25 mm. Can be shorter. Then, the collimated beam diameter D1 can be set to about 10 mm. With this beam diameter, the effective diameter of the fθ lens having a focal length of about 100 mm can be sufficiently reduced, and deep and clear marking can be formed on the steel material surface at high speed.

Next, the actual operation will be described with reference to the timing chart of the signal at the time of engraving shown in FIG. FIG. 3 (a)
(B) is a signal sent from the drive system to the galvano scan mirror based on a command from the control computer, (c) is a signal sent from the control computer to the pulse control system, (d)
Is the signal sent from the pulse control system to the laser oscillator,
(E) is the output of the laser oscillator, and (f) is the actual marking. The control computer anticipates that the actual moving speed of the galvano scan mirror is slower than the moving command speed, and the control computer sets a predetermined waiting time (~,
~, ~, ~) Are incorporated and a pattern command for engraving is transmitted to the drive system. This waiting time is a fixed time set in advance, and when the movement pattern of the beam spot changes, such as the character or symbol to be engraved, the trajectory of the beam spot by the galvano scan mirror passes exactly where it should be engraved It is time to set it up. The galvano scan mirror scans the beam spot according to this signal, and generates
A signal for confirming that the beam spot has certainly arrived at the n / off position is not transmitted. The control computer transmits laser oscillation start and stop instructions to the pulse control system at a predetermined time based on an operation signal to the galvano scan mirror at a location where marking is required and at a location where marking is not required. The pulse control system transmits a signal of a pulse cycle corresponding to laser repetition to the laser oscillator in accordance with the laser oscillation start and end signals. As can be seen, the control computer only unilaterally sends commands to the drive system and the pulse control system, and oscillates and stops the laser without confirming the position of the beam spot by scanning the galvano scan mirror. Proceed with engraving.

In such a method in which the position of the beam spot during engraving is not sensed and controlled sequentially, when there is an intersection in the engraved character or symbol as shown in FIG. 4, the laser beam may be hit twice at the intersection. There is. Alternatively, it is conceivable that the engraved dots partially overlap even if they do not completely overlap. Many of the steel materials to be symmetrical according to the present invention are used for special applications, and their properties are strictly controlled.The depth and curvature of the stamped dot shape are also specified to prevent deterioration of the steel sheet properties. May have been. Therefore, in the present invention, in order to avoid such overlapping of dots, when creating data of characters and symbols to be engraved, as shown in FIG. Use a method that creates a line segment before and after an intersection.
As a result, it is possible to perform marking with uniform dots without changing the depth and shape of the marking dots due to double hitting or partial overlap.

In the conventional engraving method (for example, Japanese Patent Laid-Open No. 58-5 / 1983)
No. 3444) Characters are decomposed into all dot information, and laser irradiation is performed after confirming that the galvano scan mirror has moved to a predetermined dot each time. Therefore, the number of times of transmission / reception becomes extremely large, resulting in marking. The time required for signal exchange in the system increased, and the time required for engraving became longer. On the other hand, in the present invention, since the control computer unilaterally sends a command and independently controls the galvano scan mirror and the laser oscillator, the time required for these can be greatly reduced, and high-speed marking can be performed. Since the distance between dots forming characters and symbols to be engraved is determined by the frequency and the speed of the galvanomirror, the number of pulses is determined according to the size of the character so as not to impair visibility. Generally, this distance is sufficient if the distance between the dot centers is within about 0.2 to 2 times the dot diameter. At this time, the depth of one dot is required to be about 100 μm or more so as not to be lost by shot blasting or the like. Therefore, the energy of the laser pulse is required to be about 1 J or more, and the pulse repetition rate is about 30 Hz or more in consideration of practical use. Is required. Due to such oscillation conditions, engraving on steel is impossible with a Q-switch pulse laser, and it is desirable to use a normal pulse laser.

Although each signal in FIG. 3 is shown as a voltage signal for convenience, it is of course possible to use a non-voltage signal such as TTL.

[0021]

FIG. 6 is a block diagram of the marking device used in the embodiment. In the embodiment, the pulse control system 7 is constituted by the pulse generator 11 and the gate controller 12. Instead of directly controlling the oscillation frequency of the YAG laser oscillator 1 by the pulse generator 11, the control computer 6 sends a laser on / off signal to the gate controller 12, and the gate controller 12 gates the signal of the pulse generator. To produce the signal shown in FIG. 2D, and the laser oscillator was controlled. The galvano scan mirror driving system 10 includes a galvano scan mirror controller 13 and a galvano scan mirror driver 14. The drive signal from the control computer is D / A-converted in the galvano scan mirror controller 13 and sent to the galvano scan mirror driver 14 to generate the signals shown in FIGS. The galvano scan mirror 4 was driven. The control system of the present invention can be constituted by such a simple combination of controllers, and one of its features is that the device can be easily manufactured.

In the above laser marking device, the laser oscillator is a normal pulse Y having a maximum rated output of 400 W.
Using an AG laser oscillator, pulse energy 3 J / P,
Marking was repeatedly performed under the condition of 130 pps. The optical system has an entrance core diameter of a tapered optical fiber of 1.0 mm, an exit diameter of 0.3 mm, and a focal length f1 of the collimating optical diameter of f1 = 30 m.
, and a collimated laser beam having a collimated beam diameter of about 12 mm was transmitted to a beam scanning system using a galvano scan mirror. An fθ lens with f = 100 mm was used as a condenser lens.

Using the apparatus having the above configuration, 9 letters of the alphabet “ABCDEFGHI” are put on the side of the roll material,
When engraved with each character size 8mm square, engraving time is about 2.
The stamping was completed in 5 seconds. The laser irradiation mark forming each stamped character has a hole diameter of 500 μm and a hole depth of 500 μm, and sufficiently satisfies the conditions required for stamping a steel sheet.
Furthermore, no overlapping of dots was observed near the intersection of the line segments of the characters, and marking with uniform dots was realized. When the same marking is performed by decomposing the character into dot information, confirming the position of the galvano scan mirror for each dot, and irradiating the laser beam using the marking method used in a conventional IC or the like, the marking is performed. The time is about 8 seconds. According to the present invention, a high-speed engraving three times or more as compared with the conventional engraving technique can be realized.

[0024]

According to the present invention, high-speed and clear laser engraving on steel can be performed.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a laser marking device.

FIG. 2 is a conceptual diagram of a beam focusing state in the case of optical fiber transmission.

FIG. 3 is a conceptual diagram of a laser marking method according to the present invention.

FIG. 4 is a conceptual diagram in a case where imprint dots are not uniform at an intersection.

FIG. 5 is a conceptual diagram of a method for avoiding imprinted dot non-uniformity at an intersection according to the present invention.

FIG. 6 is a configuration diagram of a laser marking device used in an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Normal pulse YAG laser oscillator 2 Laser beam 3, 4 Galvano scan mirror 5 fθ lens (mirror) 6 Control computer 7 Pulse control system 8 Side nozzle 9 Beam scanning system 10 Galvano scan mirror drive system 11 Pulse generator 12 Gate controller 13 Galvano Scan mirror control system 14 Galvano scan mirror driver 15 Incident optical system 16 Tapered optical fiber 17 Collimating optical system

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuo Seito 46-59 Ohara Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Machinery & Plant Business Department (72) Inventor Ichiro Koga 5 Fuchinobe Sagamihara-shi, Kanagawa Prefecture −10-1 Nippon Steel Corporation Electronics Research Laboratory (56) References JP-A-60-106686 (JP, A) JP-A-2-299786 (JP, A) JP-A-3-178462 (JP, A) JP-A-1-224192 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B23K 26/00-26/18

Claims (2)

(57) [Claims] 1. An apparatus for engraving a steel material with a laser, comprising: a normal pulse laser; a beam scanning system including a pair of galvano scan mirrors for scanning a laser beam; a driving system for driving the galvano scan mirror; A fθ lens or mirror for condensing the beam, a tapered optical fiber having an exit core diameter smaller than the entrance core diameter for transmitting the beam, an incident optical system for inputting a laser beam into the tapered optical fiber, A collimating optical system for collimating a laser beam at an optical fiber exit, a control computer for processing marking information, and a pulse control system for independently controlling the oscillation of the beam scanning system and the normal pulse laser are provided. Laser marking device. 2. A method for performing laser engraving on a steel material by a laser engraving apparatus according to claim 1, wherein the laser engraving is performed by a normal pulse laser and a scanning optical system of the laser beam comprising a galvano scan mirror and an fθ optical system. Characters and symbols are recognized as a set of line segments, and at points where lines in a character or a symbol intersect, other lines except one intersecting line are constituted by a pattern interrupted before and after the intersection, Galvano scan mirror for each character,
Scanning is performed based on the information on the two points, the start point and the end point, of the line constituting the symbol, and it is assumed that the actual movement of the galvano scan mirror is delayed with respect to the drive signal of the galvano scan mirror. By inputting a certain waiting time in advance, the beam spot is scanned without confirming the position of the galvano scan mirror, and the line segment set by the pulse control system at the timing determined in advance with the normal pulse laser matched to the galvano scan mirror Oscillation is stopped only at the interval between each line segment from the end point of the line segment to the start point, and free oscillation is performed independently without encouraging any information on the scanning position of the laser beam by the galvano scan mirror during engraving. A laser engraving method for steel that enables high-speed and clear marking on steel.