Glass bulb for a cathode ray tube and a method for producing a cathode ray tube

Manufacturing steps for a cathode ray tube or a glass bulb for the cathode ray tube are controlled in such a manner that a two-dimensional matrix code 3 comprised of a plurality of dots is marked by laser in an outer side surface of a glass bulb 1, 5, the two-dimensional matrix code 3 containing the information which can identify individually glass bulbs, and the manufacturing steps are conducted by using a computer and the particulars specified by the serial information.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a glass bulb for a cathode ray tube having
 a two-dimensional matrix code comprised of a plurality of dots in a
 predetermined portion of an outer side surface of the glass bulb, a method
 for producing such glass bulb and a method for producing a cathode ray
 tube using such glass bulb.
 2. Discussion of the Background
 There has been known a technique that information on the glass bulb or
 information on operating conditions (including information on the
 particulars of operations) is directly written as marked characters or a
 code in an outer side surface of a glass bulb for a cathode ray tube
 (hereinbelow, referred to as a glass bulb), and manufacturing steps for
 the glass bulb are controlled based on the information read. Generally,
 the writing of such information in the outer side surface of the glass
 bulb is conducted by directly printing a heat-resistant material or
 attaching a heat-resistant label, or marking by sand-blasting or laser.
 For example, JP-A-2-87442 proposes a method for controlling manufacturing
 procedure wherein a bar code is marked by using a CO.sub.2 gas laser
 masking method and the bar code is read whereby a mistake in combining
 parts of a cathode ray tube, which may take place in manufacturing, can be
 prevented. Further, such a technique that the particulars of a product
 manufactured can be obtained from characters marked by laser is also known
 from JP-U-63-20251.
 However, the conventional techniques using printing or laser masking to
 write the characters or the code had a problem that all required
 information had to be separately given to individual products. For
 example, in the laser masking method, since laser beams had to be passed
 through a mask to write information, it was impossible to change the
 particulars of information without changing the mask. Accordingly, it was
 difficult to write information for a relatively short time for a large
 quantity of glass bulbs conveyed during manufacturing steps.
 In the conventional technique, there was a quantitative restriction on
 information to be written in by means of characters and a bar code.
 Accordingly, information inherent to the glass bulb such as the kind
 (size), the transmittance of the glass bulb, application or
 non-application to an anti-reflection treatment, a manufacture line used
 and so on and information on operating conditions have been given to a
 large number of products which were grouped for controlling in mass
 production. That is, the conventional techniques are inappropriate as an
 information means to identify a large number of glass bulbs.
 Heretofore, conventional characters or a bar code marked by laser on the
 outer side surface of glass bulbs by a glass bulb manufacturer are
 insufficient for a cathode ray tube manufacturer to utilize the
 information written by the glass bulb manufacturer. Accordingly, the
 cathode ray tube manufacturer has written its own information by means of
 characters or a bar code so that manufacturing steps can be controlled.
 That is, glass bulb manufacturers and cathode ray tube manufacturers have
 not used common characters or a bar code.
 There has been known a general technique of using a laser to mark
 characters or bar codes on glass products. However, there has not been
 proposed such a technique that characters or the like including a large
 amount of information which can identify individually glass bulbs are
 marked on the surface of a glass product such as a glass bulb which is
 transparent, does not have a flat surface and has a mat-surface-like fine
 recesses and projections, and the information marked therein can be read
 by means of a pick-up device.
 Further, in the steps of producing panels and funnels in the glass bulb
 manufacturers, there are a variety of combinations among a processing
 line, a mold, a forming machine, a hot processing machine and so on.
 Accordingly, if a trouble or a defective product takes place in a step of
 producing, it takes much time to trace the cause, and on the other hand,
 an appropriate way of resolution has not been proposed.
 Further, there is a problem in manufacturing steps for the glass bulb such
 that, for example, it is difficult to supply products manufactured by the
 same mold or the same machine in a forming or hot processing step, in the
 intentionally optimum combination, to the next polishing step at which
 there are a large number of lines for polishing. This difficulty is
 applicable also to cathode ray tube manufacturers.
 In short, due to restrictions to an amount of information to be written in
 and difficulty in writing the characters and so on for glass bulbs, there
 is a limit in using the characters or codes in manufacturing steps in each
 of the glass bulb manufacturers and cathode ray tube manufacturers. Thus,
 there has not been known a method for producing a glass bulb or a cathode
 ray tube wherein marked characters or codes can be used commonly for both
 manufacturers, to make it unnecessary for the cathode ray tube
 manufacturer to use its own characters or codes.
 On the other hand, there has recently been an increased spread of using bar
 codes and needs for coding a greater amount of information and putting
 information in a smaller space. In response to this, a two-dimensional
 matrix code has been known. The two-dimensional matrix code is a code
 system wherein information is written in both directions of longitudinal
 and lateral, i.e., two-dimensional directions. However, the application of
 the two-dimensional matrix code, in particular, a two-dimensional matrix
 code comprised of a plurality of dots, to a glass bulb has not been
 studied. Further, a technique of identifying glass bulbs by using the
 two-dimensional matrix code comprised of a plurality of dots, and a
 technique of controlling manufacturing steps for glass bulbs or cathode
 ray tubes based on the information of the two-dimensional matrix code
 marked in the glass bulbs, have not been known.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to provide a glass bulb wherein a
 two-dimensional matrix code comprised of a plurality of dots which is
 usable commonly for a glass bulb manufacturer and a cathode ray tube
 manufacturer is marked in a predetermined portion of an outer side surface
 of the glass bulb and which is capable of writing information capable of
 identifying individually glass bulbs, and a method for producing a glass
 bulb or a cathode ray tube, wherein manufacturing steps are controlled by
 using the two-dimensional matrix code.
 In accordance with the present invention, there is provided a glass bulb
 for a cathode ray tube which has an outer side surface in which a
 two-dimensional matrix code comprised of a plurality of dots marked by
 laser is formed, wherein each dot has a recess having a depth of 5-100
 .mu.m and a diameter of 50-400 .mu.m.
 Further, in accordance with the present invention, there is provided a
 method for producing a glass bulb for a cathode ray tube which comprises a
 step of marking by laser a two-dimensional matrix code comprised of a
 plurality of dots in an outer side surface of a glass bulb, which is in a
 state of being heated at 200-500.degree. C. after having been formed, a
 step of reading information contained in the two-dimensional matrix code,
 and a step of controlling processing operations after the forming of the
 glass bulb based on the read information, wherein the two-dimensional
 matrix code includes at least the information which can identify
 individually glass bulbs for cathode ray tubes.
 Further, in accordance with the present invention, there is provided a
 method for producing a cathode ray tube which comprises a step of
 identifying a glass bulb for a cathode ray tube by reading a
 two-dimensional matrix code comprised of a plurality of dots formed in an
 outer side surface of the glass bulb, a step of determining by a control
 device at least desirable operating conditions for the identified glass
 bulb in response to the information inherent to the identified glass bulb,
 a step of reading sequentially the two-dimensional matrix code in
 manufacturing steps to extract information for desirable operating
 conditions determined for the glass bulb from the control device, and a
 step of conducting operations instructed by the control device, wherein
 the two-dimensional matrix code includes at least the information which
 can identify individually glass bulbs for cathode ray tubes, and a part or
 all of the manufacturing steps are controlled on the basis of the
 information.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The present invention will be described in more detail.
 In the present invention, a two-dimensional matrix code comprised of a
 plurality of dots is marked in a predetermined portion of an outer side
 surface of a glass bulb for a cathode ray tube. In this text, the glass
 bulb designates a panel for a color cathode ray tube (hereinbelow,
 referred to as a panel), a funnel for a color cathode ray tube
 (hereinbelow, referred to as a funnel), a glass bulb for a monochrome
 cathode ray tube, or a glass bulb for a projection tube. In a case of the
 panel and the funnel, a two-dimensional matrix code is usually marked to
 each of them. However, the marking may be conducted to either one.
 The two-dimensional matrix code in the present invention is formed by
 arranging a plurality of dots in a two-dimensional direction, i.e.,
 longitudinal and lateral directions. The basics of the two-dimensional
 matrix code will not be described in detail because it is substantially
 the same as one conventionally known. However, the present invention is
 featurized by specifying information by the positional arrangement of
 dots. An amount of information of the two-dimensional matrix code can
 properly be adjusted by increasing or decreasing the number of dots and
 the arrangement of the dots.
 The shape of each of the dots which forms the two-dimensional matrix code
 does not intend the thickness of line as for a so-called bar code, but can
 be recognized as a point of circular or elliptic shape. Use of a circular
 shape is generally preferable. In marking the two-dimensional matrix code
 in a form of arranging dots, a matrix style such as a data matrix, veri
 code matrix or the like is generally utilized. However, another style may
 be employed as far as the two-dimensional matrix code can be formed by
 dots.
 In the present invention, when the two-dimensional matrix code is marked by
 dots as recesses in an outer side surface of the glass bulb, use of a
 laser is in particular preferable. The main reason is as follows. Even
 though there are fine recesses and projections on the glass bulb at the
 portion to be marked by the laser, the laser can mark correctly and
 quickly dots so that they can be read by a sensor in an automatic way
 provided that the recesses of the dots are appropriately formed.
 Further, the two-dimensional matrix code marked in the outer side surface
 of the glass bulb after having been formed should withstand chemically and
 physically to any treatment in the subsequent manufacturing steps for the
 glass bulb or the cathode ray tube. In particular, since the glass bulb
 undergoes a heat treatment at a high temperature of about 440.degree. C.
 in manufacturing steps for the cathode ray tube, it has to withstand heat.
 Marks formed by laser can satisfy substantially all requirements described
 above.
 In the-following, several embodiments of the present invention will be
 described with reference to the drawings.
 Each dot forming a two-dimensional matrix code marked by a laser in a glass
 bulb is formed as a recess 26 of circular or substantially circular shape
 in a glass surface as shown in FIG. 3. In FIG. 3, L designates the
 diameter of the recess 26, and d designates the depth. An annular
 projection 25 is generally formed around the recess 26. The depth d of the
 recess 26 in the case when the projection 25 is formed is measured from
 the top of the projection 25. The shape of the inner surface of the recess
 26 is not in particular limited. However, when a laser is used to glass to
 mark a dot, the shape as shown in FIG. 3 is generally formed.
 FIG. 4 shows another embodiment of the matrix code which is composed of a
 plurality of consecutive recesses 26. The recesses 26 shown in FIG. 4 are
 formed so that adjoining recesses 26 are partly connected when the depth d
 of each recess 26 becomes larger with respect to a pitch between adjacent
 recesses. The diameter L and the depth d of each of the recesses 26 in
 this case are measured as shown in FIG. 4. Generally, each of the recesses
 26 is formed as a dot of substantially circular shape. However, when it is
 not circular, the maximum diameter is used.
 In order to read correctly the two-dimensional matrix code, it is necessary
 to control the depth d and the diameter L of each of the recesses 26 to
 have predetermined dimensions. The reading of the two-dimensional matrix
 code is influenced by the performance of a reading device, the size
 (diameter) of dots, surface appearance of the portion to be marked by
 laser and so on. In generally used glass bulbs, the depth d is preferably
 5-100 .mu.m more preferably, 10-50 .mu.m. Further, the diameter L is
 preferably 50-400 .mu.m, more preferably, 90-250 .mu.m. Generally, when
 the depth d is smaller, the diameter L also becomes smaller. Accordingly,
 when the depth d is less than 5 .mu.m, the diameter L is also less than 50
 .mu.m, which causes difficulty in reading correctly the two-dimensional
 matrix code.
 On the other hand, when d and L exceed 100 .mu.m and 400 .mu.m
 respectively, there will arise problems that the marking by laser becomes
 difficult and fine cracks are formed around the recess 26. Further, the
 formation of a recess having an excessive size will cause strength
 reduction and the glass bulb is destroyed when a stress of vacuum is
 applied thereto. The annular projection 25 formed around the recess 26 is
 projected from the level of glass surface to increase the depth whereby
 the intensity of light and darkness of a reflection light from the dot is
 increased so as to provide easy detection.
 Further, it is preferable for the recesses 26 as the dots for forming the
 two-dimensional matrix code to have a ratio of depth d/diameter L of
 0.04-0.60, in particular, 0.09-0.35. Any recess 26 having d/L less than
 0.04 will have a small recess portion and is not optically conspicuous.
 Accordingly, when the two-dimensional matrix code is to be read, light and
 darkness provided by any dot can not sufficiently be obtained whereby it
 is difficult to recognize the dot correctly. In particular, the case is
 remarkable in a glass bulb, because the surface 28 of the glass bulb is
 generally not a mirrored surface but has minute recesses and projections.
 On the other hand, when any recess has d/L larger than 0.60, the shape of
 the recess is acute whereby fine cracks are resulted around the recess.
 Since the recesses are acute and relatively deep, the strength of the
 glass bulb becomes small. As a result, a cathode ray tube using such glass
 bulb is apt to be broken due to the acute recesses.
 The surface of the glass bulb in which marking is conducted should be as
 smooth as possible regardless of a marking technique used. However, when
 marking is made by laser, the presence of fine recesses and projections in
 the surface to be marked is allowed within the range as described below.
 Namely, it is possible that the surface of glass bulb has minute recesses
 and projections where marking is made so that when light is irradiated
 from an angular direction of 5-85.degree. with respect to a normal line to
 that surface, the S/N ratio of the intensity of contrast between light and
 darkness provided by the minute recesses and projections to the intensity
 of contrast between light and darkness provided by a dot in the
 two-dimensional matrix code marked in that surface is at least 1.5. When
 the S/N ratio is smaller than 1.5, the reading of the two-dimensional
 matrix code becomes difficult.
 In a preferred embodiment of the present invention, the surface of the
 glass bulb in which marking is made should be smooth so as to have locally
 a mirrored surface or a nearly mirror surface, whereby the influence of
 the surface roughness of the surface where marking is made can be
 eliminated or can be minimized. Such a smoothed surface can easily be
 obtained by processing the surface of a mold used or a polishing treatment
 after the forming.
 The position of the surface of the glass bulb in which the two-dimensional
 matrix code is marked is not in particular limited. However, a location in
 a central portion of a longer side of the glass bulb and near the sealing
 edge is generally selected as the optimum position in consideration of the
 easiness of marking and reading as well as its having flatness in the
 outer side surface of the glass bulb. Further, in order to improve the
 flatness of the surface to be marked, a flat or substantially flat bed
 portion as a mound or a sunken spot (or sink) may be provided at the
 portion of the glass bulb to be marked. Further, in order to smooth the
 top surface of the mound or the bottomed surface of the sink, it may be
 finished to be a mirrored surface.
 Description will be made as to information written in the two-dimensional
 matrix code. The two-dimensional matrix code used in the present invention
 includes a specific information such as the information which specifies
 the glass composition, the type, the size, the wall thickness, the date of
 manufacture, the arrangement of parts, the dimensions of product and the
 information which can identify individually glass bulbs or cathode ray
 tubes, and information on processing such as a processing line, processing
 operations, processing conditions in manufacturing steps for glass bulbs
 or cathode ray tubes. In the most preferable embodiment of the
 two-dimensional matrix code, it has information capable of at least
 specifying individually glass bulbs, i.e., a serial information.
 By means of the serial information, each glass bulb is provided with, for
 example, an identification number. Accordingly, each glass bulb can
 clearly be distinguished from others in manufacturing steps for glass
 bulbs or cathode ray tubes. As a result, when the identification number is
 made correspondent to a control device such as a computer, the inherent
 information of a glass bulb such as the size, the wall thickness, the date
 of manufacture, the glass composition, the mold used for forming, the
 application or non-application of surface treatment and/or information on
 processing such as processing line, processing-operations, processing
 conditions and so on in manufacturing steps for the glass bulb or the
 cathode ray tube can properly be taken from the control unit so that the
 manufacturing steps can be controlled with use of the serial information.
 For example, in a case that a glass bulb manufacturer supplies a serial
 information including a dimensional information on a glass bulb to a
 cathode ray tube manufacturer, the cathode ray tube manufacturer can read
 the supplied information during manufacturing steps for a cathode ray tube
 so that the cathode ray tube can be assembled by utilizing the dimensional
 information. As a result, the quality of the cathode ray tube and yield
 for the tube can be improved.
 In this case, a part or all of the inherent information excluding the
 serial information and the information on processing for glass bulbs may
 be inputted to an appropriate recording medium so as to correspond to the
 serial information, and the information recorded in the recording medium
 may be taken out on the basis of the serial information marked in the
 glass bulbs.
 There is another example of marking the two-dimensional matrix code.
 Namely, at least a part of the above-mentioned inherent information and
 the information on processing are incorporated along with the serial
 information in a single two-dimensional matrix code. According to this
 technique, the information on the glass bulb can be taken out and utilized
 at any time when the two-dimensional matrix code is read. Further, the
 two-dimensional matrix code and characters and/or figures which show the
 content of the information of the code may be marked together so that the
 inherent information in the two-dimensional matrix code can be confirmed
 by eyes. The characters and figures which correspond to the
 two-dimensional matrix code may previously be inputted in a laser print
 machine for marking two-dimensional matrix codes. Then, the characters and
 figures can be marked at the same time of marking a two-dimensional matrix
 code without requiring a special equipment.
 The present invention is applicable not only to a glass bulb but also a
 glass product such as a window glass for automobile, a glass substrate for
 a TFT display and so on.
 EXAMPLE
 An example of the present invention will be described with reference to the
 drawings.
 FIG. 1 is a diagram showing a funnel 1 having an outer side surface in
 which a data matrix type two-dimensional matrix code 3 and characters and
 figures (hereinbelow, referred to as characters) 4 representing an
 inherent information on the funnel, which is incorporated in the
 two-dimensional matrix code are marked by laser at a position 20 mm higher
 than the edge surface 2 to be sealed and a central portion of a longer
 side of the funnel. A serial information for identifying the funnel is
 incorporated in the two-dimensional matrix code comprised of a plurality
 of dots. The size of the two-dimensional matrix code 3 is 6 mm square, the
 depth of each dot is about 20 .mu.m and the diameter is about 150 .mu.m.
 FIG. 2 is a diagram showing a panel 5 in which a data matrix type
 two-dimensional matrix code 3 and characters 4 are marked, in the same
 manner as the funnel 1 in FIG. 1, at a position 30 mm apart from a mold
 match portion 6 in a central portion of a longer side of the panel. The
 size of the two-dimensional matrix code 3, the depth and the diameter of
 each dot are the same as those of the funnel 1. On the dots of the panel
 or the funnel, the ratio of depth/diameter was 0.15.
 FIG. 5 is a diagram showing a two-dimensional matrix code marking apparatus
 for marking the two-dimensional matrix code 3 in the panel 5.
 Molten glass is formed in a forming device (not shown) into the panel 5.
 The panel 5 was transferred on a conveyor to the next step, during which a
 two-dimensional matrix code 3 was marked at the same position as in FIG. 2
 by means of a laser marking device 8 in a state that surface temperature
 was about 380.degree. C. Two-dimensional matrix codes were marked
 successively to 50 panels 5 by the device, and there no cracks were found
 in dots for the two-dimensional matrix codes.
 Each of the panels 5 with the two-dimensional matrix code was transferred
 to a reading device shown in FIG. 6. The two-dimensional matrix code was
 read on a conveyor 9 by means of a CCD camera 11 as an image pick-up
 device, and the read data were decoded by an image processing device 12.
 In this case, the angle of a diffusion light source 10 (an angle 13 to a
 normal line 27 in FIG. 7) was determined to 30.degree.. As a result, the
 two-dimensional matrix code of all 50 panels could correctly be read, and
 it was confirmed that each of the panels could be identified by the serial
 information put in the two-dimensional matrix code 3.
 In the next, description will be made as to an example of treating panels
 in a glass bulb manufacturer.
 FIG. 8 is a diagram showing a case of using panels. Two-dimensional matrix
 codes are marked to panels (not shown) after having been formed, in a
 state that surface temperature is about 380.degree. C., by using the laser
 marking device 8. Then, the two-dimensional matrix code reading device is
 set for each step of processing, polishing, inspecting and packaging for
 the panels. In FIG. 8, reading devices 23 are set for a processing step 21
 and reading devices 24 are set for a polishing step 22 respectively. In
 this case, a host computer 16 is operated so as to correspond the number
 of processing machines or the polishing machines to the panels.
 At the final stage of packaging a panel, the history of processing of the
 panel can be obtained by inquiring to the host computer 16 on the basis of
 the identification number of the panel which is provided by the
 two-dimensional matrix code. If there arises any trouble on a product, the
 cause of the trouble can quickly be obtained by examining the
 two-dimensional matrix code given to the product. Accordingly, the yield
 of manufacture can be improved. The above-mentioned way of using the
 two-dimensional matrix code is applicable to the funnel.
 FIG. 9 is a diagram showing another example of treating panels in the glass
 bulb manufacturer. Two-dimensional matrix codes are marked to panels after
 having been formed in a state that surface temperature is about
 380.degree. C. by using the laser marking devices 8. Reading devices 23
 each provided for each processing step 21 read the two-dimensional matrix
 code of each panel so that the two-dimensional matrix code is made related
 to the machine used for processing the panel, the mold used for pressing
 the panel, in the host computer 16. Each of the panels with the
 two-dimensional matrix code is successively supplied from the processing
 step to a polishing step 22 as the next step.
 FIG. 9 shows an embodiment of a processing apparatus wherein there are
 three lines for processing step 21 and four lines for polishing step 22.
 The reference numerals are given for only each line. When panels are sent
 to polishing steps 22, a reading device 24 installed in each of the
 polishing steps 22 reads the two-dimensional matrix code marked in each of
 the panels. For example, a panel having a type most suitable to a certain
 polishing step or produced by a mold or a processing machine most suitable
 to the certain polishing step is checked and selected in the host computer
 16, and the panel is selectively fed to a related polishing line.
 Thus, since glass bulbs (panels, or funnels) can be produced in the optimum
 combination of manufacturing devices, yield for manufacturing can be
 increased, and the conventional operations wherein the glass bulbs have
 been confirmed by human eyes to select polishing lines can be eliminated.
 Further, the number of transferring equipments for connecting the
 processing steps to the polishing steps can be reduced.
 The above-mentioned is an example of a combination of the processing step
 and the polishing step. However, substantially the same description is
 applicable also to the steps in combination of forming and processing,
 polishing and inspecting, inspecting and packaging and so on. Further, the
 application to the funnels is also possible.
 FIG. 10 shows an embodiment of utilizing two-dimensional matrix codes
 marked in glass bulbs (panels or funnels) by the present invention, which
 can commonly be used by a glass bulb manufacturer 14 and a cathode ray
 tube manufacturer 19. The glass bulb manufacturer 14 marks by using a
 laser marking device 8 a two-dimensional matrix code 3 which contains
 information inherent to a glass bulb such as the date of production, the
 glass composition, the characteristics of the product and so on and a
 serial information for identifying individually glass bulbs and characters
 4 representing the inherent information (v. FIGS. 1 and 2).
 When the panels 5 and the funnels 1 are brought into the cathode ray tube
 manufacturer 19, the identification number specified by the
 two-dimensional matrix code 3 of each product is read by a reading device
 15. Inherent information (for example the type, the transmittance, data on
 the position of pins and thickness and so on) of the glass bulbs, which is
 necessary for the cathode ray tube manufacturer, is extracted in response
 to the identification number, among information stored in the host
 computer 16. These data are recorded in floppy disks 17, and the glass
 bulbs are supplied along with the floppy disks 17 to the cathode ray tube
 manufacturer 19.
 The cathode ray tube manufacturer 19 extracts information necessary for
 administration of control based on the information in the floppy disks and
 makes such information correspondent with the identification number of the
 two-dimensional matrix code of the glass bulbs by a host computer 18.
 Then, the panels 5 or the funnels 1 are subjected to administration for
 manufacturing by exchanging-information necessary for controlling by the
 host computer 18 in accordance with the two-dimensional matrix code 3 read
 in the reading device 20 in every occasion. Any means for transmitting
 information may be used instead of the floppy disk 17, for example,
 necessary information can be supplied through a network.
 There is another way of administrating the manufacture of the glass bulbs
 in the cathode ray tube manufacturer 19. When the panels 5 or the funnels
 1 with the two-dimensional matrix code 3 are received by the cathode ray
 tube manufacturer 19, the content of the two-dimensional matrix code 3 is
 mechanically read by the reading device 20. The host computer 18 checks
 information necessary for administration for manufacturing in the cathode
 ray tube manufacturer so that the panels or the funnels are specified so
 as to correspond to the read information. In manufacturing steps for
 cathode ray tubes in the cathode ray tube manufacturer, information
 necessary for controlling is taken through the host computer 18 on the
 basis of the two-dimensional matrix code 3 read by the reading device 20,
 and every step of the manufacturing is controlled by suitable information.
 According to the present invention, information or data on a glass bulb are
 marked in a glass bulb by means of a two-dimensional matrix code comprised
 of a plurality of dots wherein each of the dots is in a form of recess
 having predetermined depth and diameter, whereby the two-dimensional
 matrix code can correctly be marked by laser and can be read by a pick-up
 device. As a result, a glass bulb manufacturer and a cathode ray tube
 manufacturer can use commonly the information marked by the
 two-dimensional matrix code. Accordingly, efficiency of manufacturing can
 be increased; flexibility for manufacturing in each of the manufacturers
 can be expanded, and the reduction of manufacturing cost and the
 improvement of yield can be expected.
 Because of marking by laser, the marking by a relatively expensive
 sand-blasting method which was conventionally used by glass bulb
 manufacturers becomes unnecessary. On the other hand, it is unnecessary
 for cathode ray tube manufacturers to attach an expensive heat-resistant
 label or the like.
 Further, by incorporating a serial information of glass bulb in the
 two-dimensional matrix code, both the manufacturers can have commonly the
 serial information which can be related to information necessary for each
 of the manufacturers in their computers when they use the information for
 manufacturing. As a result, it is possible to supply, by means of floppy
 disks, the data of glass bulbs specified by two-dimensional matrix codes
 from glass bulb manufacturers to cathode ray tube manufacturers.
 Accordingly, operations for preparing and inputting the marking which have
 been conducted by the cathode ray tube manufacturers can be omitted.
 Further, the glass bulb manufacturers or the cathode ray tube manufacturers
 can easily confirm the history of each glass bulb based on the serial
 information by operating the host computers. Accordingly, when any trouble
 takes place, the cause of the trouble can quickly be obtained in
 comparison with the conventional method, and the yield of manufacturing
 can be improved.