1 2
LASER MARKING SYSTEM AND METHOD piece with a clear and relatively shallow pattern without
USING CONTROLLED PULSE WIDTH OF Q- decreasing the marking performance.
SWITCH Still another object of the present invention is to provide
a laser marking method and system for marking a workpiece
BACKGROUND OF THE INVENTION 5 Sow^epA. ***** "*"
1. Field of the invention According to the present invention, a specific characterThe present invention relates to a laser marking system, istic of a continuous-wave (CW) pumped Q-switch pulse
and in particular to a laser marking system and method for laser is used to generate a pulse laser beam for marking. The
marking a workpiece with a laser beam scanning the surface 10 present invention is based on the fact that laser emission
thereof. pulses vary in intensity and number with the emission period
2. Description of the Related Art of the CW-pumped Q-switch pulse laser. In other words, a Laser marking has been widely used to mark an electronic plurality of laser emission pulses are generated by adjusting
part with a specific pattern such as classification characters. toe emission period of the CW-pumped Q-switch pulse laser Of the laser marking methods, there is known a beam- ^th the laser emission pulses varying in intensity. The scanning marking method in which a laser beam scans the Plural laser emission pulses are caused by the primary laser surface of the part in the specific pattern, which is disclosed oscillation and the relaxation oscillation. Since the relaxin Japanese Patent Unexamined Publication Nos. 59-45091 ation oscillation causes a plurality of secondary emission and 60-221721. Generally, a solid state laser such as pulses wim me prmiaiy emission pulse reducing in intensity. Nd: YAG laser is used as a laser light source. 20 ^ Plural laser emission pulses including the primary emis
The solid state laser is typically provided with a Q-switch fion pulse having a relatively low intensity can be obtained
scheme which causes pulse repetition emission with a rela- bv only adJustlnf *e eim.sslon P"5"0* wlth°ut leasing the
lively high peak output in power. In a beam-scanning r<ffb,lon rate of *e emission pulses or the scanning speed
system, as shown in FIG. 1, the Q switch switches on and off „ of ** ?ulse laser beam. Therefore, a marking pattern having
according to a control signal, which causes the solid state f relatively shallow depth is achieved by using the pulse
laser to emit the laser light beam during the OFF period of laser beam having the plural laser emission pulses to scan a
the Q switch. Conventionally, the OFF period, or the emis- Predetermined surface of the workpiece.
sion period, is set at 10 microseconds (usee) during which According to an aspect of the present invention, there is
me laser beam is emitted instantaneously. 30 used a laser source which comprises a laser medium and a
However, when such a laser beam is focused on a certain Q-<wi** e\eTntn The }aSf medium contillu«usly
position of the electronic part encapsulated in resin, the resin PumPed and Quitch element switches on and off
at that position is vaporized at an instant, and thereby a deep according to a repetition control signal The repetition
hole is formed reaching 50-100 micrometers in depth, as control signal comprises an emission period in a repetition
shown in FIG. 2. For this reason, the conventional laser 35 T' u T* beam through the
marking method cannot be applied to a thin workpiece Q-swfh elemenf dunng the emission period. The emission
encapsulated in resin. Penod or ^ factor of ^ repetition control signal is
. ^ ,' , , . . ^ „ . , adjusted such that the laser source emits a pulse laser beam
In order to reduce me peak level of the Q-switch kser co^sin a of emission lses ^ me emis.
beam, it is considered that the marking is performed by sioJ^io£ ^ beam is ^ged m two orthogo
using the laser beam obtained by setting the repetition rate 40 , r .. , . . . „ _ t
at 50 kHz or more so that the co tinuous av fCW, directions according to a predetermined pattern to gena . ,? or. TM°'e so f con TM?US WaVe. , erate a scanning pulse laser beam. The scanning pulse laser pumped Q-switch laser approaches a CW pumped laser ^ fa focus(* ^ a predetermined surface of the workHowever, since the reduced peak level of toe laser light d ^ a ition. causes the laser beam to decrease in power, it is necessary ;, , . . . r . to lower the scanning speed of the laser beam so as to 45 Inferably, at least (he predetermined surface of the compensate for the power reduction, resulting in reduced workpiece comprises a thermoplastic resin containing carperformance of marking. bon- Bv melm& and vaporizing portions of the predeter„, .,, . , , ,. mined surface of the workpiece with the scanning pulse laser To avoid the reduced performance of marking, the scan- , . . . . . „ X. -u j , ^ • i. , x x j beam scanning in the predetermined pattern, the carbon
nine speed of the laser beam is usually kept at constant, and t . . ■"? „ „ . . ...
.... B ri.i. _ , • • . j. x . - Kt, contained in the thermoplastic resin is deposited on the
fterepeution rate^of the.laser emission is adjusted to achieve 50 ^ before, after removing the deposited carbon
the optimal condition of the laser marking system. However, ^ ^ ^termized surface c| me wo^iece, mose
a distance between adiacent holes produced by the laser _x. <■ , , ,x- • ■ j
, . . _x- x xi. x!x_- x x- ,t portions on the surface are discolored, resulting in improved
beam is in reverse proportion to the repetition rate of the . ...... f A .. „
■ ■ ■ r~ * v xi. x x5 x ■ x visibility of the marking pattern,
laser emission. Therefore, when the repetition rate is too ,' ,. , ,. . „T,,,.„
low, adjacent holes are formed apart from each other. 55 More specifically, the laser medium is a Nd:YAG rod and
resulting in discontinuous marking lines. As the repetition 016 Q"swltfh element 15 an acousto-optic diffraction switch
rate is too high, the laser beam energy becomes denser, such as a ultrasonic Q-switeh element. Further, the repetition
causing deeper holes than necessary. In other words, the control signal has a fixed repetition rate falling within a
conventional laser marking method cannot achieve clear raJ«e ^om 5 ^j0 50.m? and *e emssion period is
marking lines having a relatively shallow depth. 60 adjusted to a penod ranging from 20 usee to 200 uSec.
SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS
An object of the present invention is to provide a laser FIG. 1 is a waveform chart showing an conventional laser
marking method and system which can mark a workpiece driving method in a laser marking system;
with a pattern having a relatively shallow depth. 65 FIG. 2 is a schematic sectional view of a hole produced
Another object of the present invention is to provide a by vaporization according to the laser marking system as
laser marking method and system which can mark a work- shown in FIG. 1;
