A system for controlling laser writing devices

A System for Controlling Laser Writing Devices

V. A. Sluev and K. K. Smirnov

Institute of Automation and Electrometry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia

E-mail: [email protected]

Received April 26, 2006

Abstract—Software and hardware for laser writing systems are presented. A method of multipage

recording with allowance for object motion, aimed at dynamic formation of images on cylindrical

surfaces, is proposed. Tools for creating protective laser marking with the use of the multilevel regime of

laser writing are implemented.

DOI: 10.3103/S8756699007050135

INTRODUCTION

Systems for laser marking are produced by many foreign (and recently, also Russian) companies. Laser

devices with a system for beam sweep by means of two-axis angular electromechanical deflectors (scanners)

are widely used now to form images on the object surface. In many applications, such devices are faster and

more flexible than systems based on using coordinate tables, rotating drums, etc. The size of the scanning

area in devices with two-axis angular deflectors is restricted by optical system capabilities and normally

stays within 10 10� cm [1]. An increase in the recording area makes the system more complicated and expen-

sive, while the output velocity becomes lower. To obtain large-size images, systems with a traversing writ-

ing unit are used: laser gravers with a plane recording field or systems with raster scanning [1, 2]. The output

velocity in such systems, however, is much lower. One possible method to combine the fast operation of de-

flectors and the arbitrary recording area inherent in systems with a traversing writing unit is the division of

the output image into zones limited by the optical system (let us call them pages) with subsequent recording

of each page by deflectors and displacement of the writing unit or element to the next page [3, 4]. The page

size is chosen for the page to be completely within the recording region of the deflectors. It could be neces-

sary to divide the original image into individual pages to apply pictures onto the entire length of cylindrical

elements or onto a part on the conveyer belt extended along one coordinate.

The objective of the present activities was the creation of new hardware and software that allow

multipage laser writing onto cylindrical surfaces and also writing with division of the original image into

fragments and output of each fragment with different levels of laser power (multilevel method of detection),

which offers a certain degree of protection of articles being marked from counterfeit.

DESCRIPTION OF THE CONTROL CODE AND BASIC PARAMETERS OF MARKING

We present a system developed at the Institute of Automation and Electrometry SB RAS for controlling

vector laser writing devices, which includes a specialized MARKER code operating in the WINDOWS en-

vironment and a master controller designed for vector laser writing. With the use of this system, the problem

of image output is divided into three independent problems:

1. Initial preparation of the image in some well-known graphical package, e.g., Corel DRAW, and export

of the ready image in the HPGL vector format into a file.

2. Working with a specialized application, MARKER code, which uses files in the HPGL format as input

data. Preparation of information for direct output of the image with the use of various parameters that take

into account the dynamics of deflectors and material-motion system. The system for data preparation can be

481

ISSN 8756-6990, Optoelectronics, Instrumentation and Data Processing, 2007, Vol. 43, No. 5, pp. 481–487. © Allerton Press Inc., 2007.

Original Russian Text © V A. Sluev, K.K. Smirnov, 2007, published in Avtometriya, 2007, Vol. 43, No. 5, pp. 117–125.

OPTICAL INFORMATION TECHNOLOGIES,

ELEMENTS, AND SYSTEMS

implemented on the basis of a standard computer as an application that transforms these data from the HPGL

vector format to a format for the output controller that directly controls the deflectors.

3. Loading of data together with the control information directly into the controller. The latter is intended

to generate microvectors and various time intervals, which take into account the dynamics of deflectors, la-

ser properties, material motion, etc. The velocity of information transfer from the computer to the master

controller is normally smaller than 50 kB/s. It should also be noted that the laser marking system does not

need a master controller of large computational power, because the control file may be prepared in advance

and remain unchanged for a long time.

The MARKER code is implemented as a Win32 graphical application and can be run in the environment

of any 32-bit operation system of the Microsoft company, such as Windows 9x/Windows ME, Windows

NT/Windows 2000, or Windows XP. The original file in the HPGL format is a list of vectors over which the

laser beam has to move. Each vector is assigned an identifier (ID) of the laser beam switched on or off. The

system is indifferent to the range of the original coordinates and their dimension. They only should be inte-

gers and should stay within � �32 767 32 767, ... , . An example of the application window with editable ele-

ments is shown in Fig. 1. The field allowed for marking is schematically shown at the center of the document

window. The vertical size of this field is determined by the parameters of the scanning system (focal distance

of the lens and angular range of displacement of the scanning mirror). The horizontal size of the field for

article processing on the table equals the vertical size; for circular articles, the horizontal size equals the

length of the unfolded cylindrical surface to be treated.

The MARKER application has a number of built-in means for editing graphical elements of the docu-

ment. All editing functions are applied to elements that are chosen at the moment. The element may be

scaled or moved to the document field in a standard manner by the mouse. Additional editing operations are

available: centering of chosen elements in the marking field or their displacement to the left edge of the field,

mirror mapping in the horizontal and vertical directions, clockwise or anticlockwise rotation by 90�, and

doubling of elements. To facilitate the positioning operations, it is possible to change the scale of document

viewing or to use an appropriate grid in the document marking field. The maximum magnification of the

document approximately corresponds to a step of lines in the document window, which is equal to 0.1 mm.

The default grid step is 2.5 mm in both directions and can be changed in a corresponding dialog box.

The basic parameters of marking are defined in the windows of the MARKER code:

1. Velocity of motion of the laser beam.

2. Power of laser radiation.

3. Size of the picture page. The image cannot be applied onto a circular surface as a whole and, as a conse-

quence, is divided into pages of an identical length. The page width is limited by the curvature of the article

OPTOELECTRONICS, INSTRUMENTATION AND DATA PROCESSING Vol. 43 No. 5 2007

482 SLUEV, SMIRNOV

Fig. 1.

surface (diameter) and has to be as large as possible to restrict the loss of image quality because of the error

due to page matching. The quality of page matching is also affected by the eccentricity of the marked article

with respect to the axis of revolution of the article.

4. Diameter of the article to be marked. For correct matching of the image pages, this parameter has to be

introduced into the system with an accuracy of tenth fractions of a millimeter.

The inertial mass of deflectors and mirrors and the delays in controlling electronics induce a delay be-

tween the positioning control signal and the beginning (or end) of motion. To compensate for the positioning

delay, two control parameters are added: delays of laser switching on and off. Manipulating with the values

of these parameters, one can fairly accurately compensate for the influence of system inertia on the image

quality.

DIVISION OF THE TOTAL IMAGE INTO PAGES

An example of image division into individual pages is shown in Fig. 2. The vectors intersecting the page

boundaries are separated; new additional vectors indicated by the dotted lines are added so that the image on

each page is a completed picture and could be output independent of other pages. Thus, the picture of each

page has to start always from one point O (central point) and to end at the same point. This requirement for

the beginning and end of the page to be at one point is dictated by the necessity of accurate knowledge of de-

flector positions at the beginning of drawing and by the inhibit of uncontrolled motion of deflectors. After

the output of one page, the writing unit with the deflector moves strictly by one page. Thus, the point O ar-

rives at the center of the next page. It is also possible that the deflectors return to the point O only at the end

of the output of the last page. In this case, the total length of the vectors necessary for the picture to be di-

vided into individual pages becomes smaller, but the pages become connected; as a result, the prepared file

of each page cannot be used as a separate picture.

The total image has to be output page by page without visible boundaries of page matching. The images

are assumed to be vector files in the HPGL format prepared by using an arbitrary application program with

the output in this format. With the help of the MARKER code, the image is divided into separate pages, and

each vector of the HPGL format is divided into microvectors whose size is determined by the required out-

put velocity and dynamic parameters of the system.

In straightline marking, the picture normally consists of two parts: an invariable part, which is common

for most articles (e.g., manufacturer’s logo), and a variable part (this is assumed to be the article number

only) (Fig. 3).

In this case, the invariable picture, a set of vector files containing numbers from 0 to 9, and the initial

value of the number are loaded into the memory of the master controller. After that, the controller is discon-

nected from the computer and can operate independently.

The page size L can differ from the number length Lnum

. The following variants are possible:

1. L L�num

. The controller writes the image pages consecutively and replaces L by Lnum

when it passes to

writing the number.


A SYSTEM FOR CONTROLLING LASER WRITING DEVICES 483

Fig. 2.

2. L L�num

. The files with numbers contain numerous pages, and writing of each number is similar to

writing of a multipage image.

The minimum possible step of material displacement, which is defined by the coordinate sweep actuator,

in the general case does not coincide with the minimum step of deflectors determined by the digit capacity of

the controlling digit-to-analog converters (DACs) of the deflectors and optical and mechanical properties of

the system. For this reason, visible defects can appear in matching of the neighboring pages of the image. In

the MARKER code, the page size is prescribed to be multiple to the minimum step of material displacement.

TIME RELATIONS IN MULTIPAGE OUTPUT

As the laser head moves with respect of a motionless material or the article to be marked is rotated with

respect to a motionless laser head, one has to determine the time of the output beginning for each page. The

page positions before and after drawing have to be symmetric with respect to the centerline of the drawing

region O (Fig. 4). If this condition is satisfied, the output of the image pages is symmetric about the central

axis of the deflectors. Let us introduce the following notation:T T T TN1 2 3

, , , ..., is the time of page output de-

termined by the velocity of motion of the deflectors and by image complexity; TS

is the time between the

moments when the first page of the picture is established at the center of the drawing region and when the

conveyer starts moving or the end stop is actuated; V is the velocity of material motion with respect to the la-

ser head.

Then the time prior to the beginning of page drawing can be expressed as

T T T T T L V TS S S S1 1 2 2

2 2� � � � �, ,

T T L V T T T N L V TS S NS S N3 3

2 2 1 2� � � � � � �( ) , ( )( ) .


484 SLUEV, SMIRNOV

Fig. 3.

Fig. 4.

To minimize the measurement error and prevent its accumulation, however, it is better to perform all cal-

culations in units of material displacement rather than in time units, because the page size L is also expressed

in the former units.

In this case, V is found as the number of elementary displacements of the material per unit time. TS

trans-

forms to N T VS S

� , the number of material-displacement units (e.g., the number of engine strokes). Let N be

the page length in units of elementary steps and P P PN1 2

, , ... , be the distance covered by the laser head with

respect to the article being marked during the output time of the first, second, and Nth pages. Then we have

P T V P T V P T V P T Vi i1 1 2 2 3 3

� � � �, , , .

The path prior to the beginning of page drawing is

S N P S N N PS S1 1 2 2

2 2� � � � �, ( ) ,

S N N P S N i N PS i S i3 3

2 2 1 2� � � � � � �( ) [ ( ) ] ,

or

S S N Pi i i

� � ��1

2.

Thus, for a multipage file of the image to be displayed correctly, either each page being transferred to the

output has to be accompanied by information on the time of page output or the master controller has to calcu-

late the output time on the basis of other transferred parameters.

PAGE FILE FORMAT

A file that describes the page is a set of data containing microvectors of deflector displacements and also

information on displacement dynamics and parameters of the laser power. The file structure is illustrated in

Fig. 5. Each microvector is encoded by four bytes. The digit capacity of the output DACs is assumed to equal

12.The first three bytes contain the values of the X and Y coordinates, while the fourth (key) byte contains

service information for controlling the deflectors. The four low bits control loading of one of the 16 values of

laser power. The power of CO2

lasers is understood as the duration of the laser switch on/off pulse; the

power of pulsed continuous lasers is understood as the generation-controlling frequency. This control pa-

rameter is analogous to the number of the stylus for plotters. As was mentioned in [5], this parameter offers a

certain degree of protection of the marked article from counterfeit, in addition to marking proper. If the lines

are drawn by the stylus with the numbers 0, 1, 2, and 3, a corresponding ID of changes in the laser-beam

power is set, which actually ensures either different depths of engraving or different physical and chemical



Fig. 5.

reactions in the material being marked. The end-of-page ID digit equals unity only in the last microvector of

the file. The digits of the acute angle and end-of vector IDs make it possible to introduce displacement delays

in the case the motion direction is changed.

HARDWARE IMPLEMENTATION

The controller chart is shown in Fig. 6. The master controller in the laser marking system is a microcom-

puter chip with an 8-bit master microprocessor. This is an element of a more global system for controlling la-

ser technological systems [4]. In addition to the microprocessor, the microcomputer includes a microchip of

the RAM-type memory with a capacity of 128 kB, two 8-bit DACs, four 12-bit DACs, two microchips of

timers, a microchip of a serial interface, two parallel interfaces, drivers of stepper motors, and other

nonprincipal elements. The controller is connected to the computer by a serial interface cable connected to

the serial port of the computer and to the inputs of the serial interface of the microprocessor microchip. The

outputs of the 8-bit DACs are connected to the inputs of the reference voltage of the 12-bit DACs to establish

the X and Y scales of the output image. The outputs of four 12-bit DACs are connected to the inputs for de-

flector controlling with respect to the X and Y coordinates and X and Y displacement coordinates. The digit

capacity of DACs determines the discreteness of the output image. The frequency of pulses controlling the

laser power and their duration are defined by the timer microchips and are programmed by the microproces-

sor. The controller is controlled by a set of commands, which is a block of symbols beginning by the starting

marker and ending by checksum transfer. One of these commands is the command of image file transfer.

With the help of the MARKER code, the computer transfers the required file, and the microprocessor re-

ceives the transferred data and loads them into a previously allocated RAM region. For image output, the

code controlling the controller consecutively loads DACs controlling the deflectors with respect to the X and

Y coordinates and data from the image-description file transferred through a serial connection channel.

The above-described control system was used under real conditions, for instance, in a system for laser

marking of alcoholic beverages [6]. An enlarged fragment of the label with marking is shown in Fig. 7a.

Another example of application is a system of laser marking designed for automatic application of alphanu-

meric and graphic information onto the surface of articles in tool production by the method of laser engrav-

ing. For semi-automatic marking of circular articles in the form of key heads, the system contains a

rotor-type semiautomatic device with manual installation of the article to be marked, automatic marking,

and article removal with a set of holders of marked articles. The output system allows marking over the


486 SLUEV, SMIRNOV

Fig. 6.

entire circumference of the article with the use of the method for image division into individual pages. The

fully marked article is shown in Fig. 7b.

CONCLUSIONS

Division of the marking image into individual pages makes it possible to apply marking onto cylindrical

surfaces in the vector regime and substantially increases the area of the marking zone. If a previously pre-

pared vector file of the image in the form of microvectors and the numbers and alphabet are fed into the mas-

ter controller in advance, the controller can be used autonomously (without its connection to the computer),

and the cost of most units of the system is reduced. The multilevel regime of laser writing ensures a certain

degree of protection from counterfeit, which is necessary in many fields of industry.

REFERENCES

1. 3D Laser Information Technologies, Ed. by P. E. Tverdokhleb, [in Russian], (Inst. Automation Electrometry,

Novosibirsk, 2003).

2. V. P. Bessmeltsev and V. A. Sluev, “Dual-processor controller for laser technological systems,” in Proceedings of

IASTED International Conference on Automation, Control, and Information Technology, (ACTA Press,

Anaheim-Calgary-Zurich, 2002), p. 34.

3. V. P. Bessmeltsev and N. V. Goloshevskii, “Control System for Complementary Two-Coordinate Scanning

Devices,” Optoelectr., Instrum., Data Process. 43 (1), 90 (2007).

4. A. A. Kravtsov and A. M. Leonov, “Prospects of mass application of laser marking,” in Proceeding of the Fifth

International Conference Beam Technologies and Laser Application, (Publishing House SPbSPU, St. Petersburg,

2006), p. 132.

5. V. P. Bessmeltsev, G. N. Alferov, S. G. Baev, and V. A. Sluev, RF Patent No. 2146200 RF, Byull. No. 7 (2001).

6. G. N. Alferov, S. G. Baev, V. P. Bessmeltsev, et al., “Application of Laser Marking for Protection of Alcoholic

Beverages,” in Beer and Other Beverages (Izd. Pishchevaya Promyshlennost, Moscow, 1999) [in Russian].



(a) (b)

Fig. 7.

Documents

A system for controlling laser writing devices