JPH07186430A - Thermal printer - Google Patents

Abstract

PURPOSE: To provide a thermal printer capable of simply and inexpensively performing the alteration and replacement of a print head assembly unit. CONSTITUTION: A thermal printer has a drum designating a printing medium, a detachable print head unit 14 and a circuit module 22. The print head unit 14 has a thermal print head 32 having heating elements 34-1-34-n and a memory device 38 storing a correction number for performing uniform operation. The circuit module 22 has a power supply 56, a data processor 52 transmitting data to be printed from the image data from an image data unit 54, a correction circuit storing the correction number loaded from the memory device 38 and the data from the data processor 52 and a data memory device 50.

Description

Detailed Description of the Invention

[0001]

This invention relates to thermal printers, and in particular to low cost, easily programmable permanent storage devices,
It relates to a removable thermal printing head unit in the overall compensation for the correction of the non-uniformity of the multiple heating elements of the head unit.

[0002]

2. Description of the Related Art Some types of thermal printers have a thermal head
You are using an assembly. This assembly has a number of closely spaced heating elements that are separately excited and, based on input information, from a heat-sensitive dye element to a small media or page. Alternatively, the pixels are printed. The data is a binary word (for example,
It is an 8-bit word) and defines the position and density of each pixel during printing, as well as characters and images. In order to be visually sharp and faithful to the original image, the printed pixels must be very small and have a substantially uniform tonal scale for a wide range of densities. A thermal head assembly is typically a linear, one-dimensional array of thick (thin) film heating elements, individually mounted on a ceramic substrate attached to a heat sink, such as a metal rod. Has been formed. Currently 1 horizontally
A print head with 300 small heating elements per inch (2400 elements for 8-inch wide pages)
It is commonly used. These elements are small enough to provide visual clarity.

[0003]

However, due to slight variations in the printing action of these individual heating elements,
Visually objectionable inhomogeneities (for densities that should be equal) tend to occur in pixels on the lines of the printed page. This non-uniformity manifests itself as visible lines, stripes, or bands parallel to the movement of the page as the thermal head moves.

There are very small random differences in the physical, electrical and thermal properties of the microminiature heating elements of the thermal head assembly as described above. As a result, it is imperative to use the latest manufacturing techniques to produce printhead assemblies with high uniformity of individual elements and avoid visible distortion or smearing on the printed page. It is very difficult, if not possible. In view of this point, a circuit for electronically compensating for print head non-uniformity in a thermal printer is
Developed and currently in use. US Patent No. 4,8
No. 27,279 (assigned to the assignee of the present application) describes a method and apparatus for correcting non-uniformity of printing action between heating elements of a thermal print head. In the compensation method disclosed in this patent, the corrected number of each heating element of the head assembly is obtained by a microdensitometer measurement of the printed line. That is, the correction number is calculated based on a predetermined mathematical formula. The correction number specific to a particular head assembly is entered into the high speed electronic storage circuitry of the overall thermal printer device. The stored number is used thereafter during normal printer operation to produce the desired quality of printing. It is difficult to change or replace the head assembly of a printer (as described in the U.S. Patent) because the correction number for a given head assembly is unique to that assembly. On the other hand, if the head assembly is to be replaced in the field, the correction values for the new head must be entered individually into the printer's electronic memory and correction circuitry. It is difficult to perform this work when no special electronic device is at hand or when there is no engineer. In addition, sending the entire printer to a repair shop to install or readjust a new head can be time consuming and expensive.

The object of the present invention is therefore to solve the abovementioned problems in a simple and cost-effective manner. In the present invention, it is to provide each printhead assembly unit that is permanent and has a unique adjustment,
As a result, the calibrated head can be used in any printer. Equipped with a particular printer, there is no need for further adjustment of a particular head unit. The present invention is also simple and efficient in the first place for head unit fabrication and testing operations, as well as printer final assembly operations.

[0006]

SUMMARY OF THE INVENTION In accordance with the present invention, a physically separable thermal printer having a multi-element resistive print head, a mounting substrate, and an electronically erasable read only memory (EEPROM) device. Print head unit is provided. These components are grouped together as an integral unit for all printers, but are also separable.

[0007]

During the assembly process, the head unit is inspected, the individual heating elements of the head are activated and the individual printing characteristics of each element are determined. The print data thus obtained is input to the computer. The computer then calculates the compensation data (correction number) corresponding to each heating element. As a result, when activated by the same data word that requires a uniform density, each element prints with no residual density. These individual correction numbers obtained by the computer are then permanently stored in the EEPROM device corresponding to that particular printhead and constitute a permanent part of the printhead unit. Therefore, the print head unit is in all respects the same as all other head units in production. The EEPROM device incorporated into each printhead unit is a relatively slow and inexpensive device. The correction number permanently stored in the EEPROM device is output to the high-speed correction circuit corresponding to the printer when the printer is powered on. This process takes a few seconds.
Therefore, the correction numbers stored in the EEPROM device are sequentially sent to the memory of the high speed print correction circuit of the printer at a very low speed. With this configuration, each print head unit
When accurately, permanently and inexpensively calibrated and used in a given printer, it is possible to produce a substantially uniform print.
As a result, the initial production cost of the thermal printer according to the present invention can be saved, the efficiency of the maintenance at the subsequent usage site can be improved, and the maintenance cost can be reduced.

According to the invention, the EEPROM used
The price of the device is relatively low. This is because this device does not directly go into the high speed data path of the thermal printer and therefore does not have high speed capability. EEPRO
The correction number from the M device can be output at a very low speed.
The above is performed when the printer is first powered up (it takes some time for the various other elements and circuits to reach equilibrium). The EEPROM device itself is a simple 8-pin dual-in-line (DIP) package and occupies very little space on the circuit board. Furthermore, despite the unavoidable fluctuations for each element,
Since each heating element of the print head has similar printing characteristics, the correction number stored in the EEPROM device is
It provides near-perfect, uniform compensation with a very limited number of ranges. Therefore, if the data words printed by the thermal printer as pixels are in the range 0-255 (8 bits), the compensation range of the individual heating elements of the print head is in the range 0-63 (6 bits). Need only the number of. For a 2400 (300 pixels / inch x 8 inch wide page) printhead, one low cost 2048 byte position (8 bits) EEPROM is needed to read sequentially with the appropriate circuitry. Bit correction number (6
X2400 or 14400) has enough or more single bit positions to store.

The present invention may be better understood with reference to the following description and accompanying drawings.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a schematic structure of a thermal printer 10, which is partially shown in phantom. The thermal printer 10 has a drum 12 that supports a thermal print medium (not shown) and that is adapted to pass the thermal print medium through a printhead unit 14. The drum 12 is mounted within the housing and frame 16 (shown in phantom) and rotates as indicated by the curved arrow 18. Print head unit 1
4 is fixed to the frame 16 by means not shown and is close to the drum 12. As described in detail in connection with FIG. 2, printhead unit 14 is shown in FIG.
, Is electrically connected to the circuit module 22 by the cable connector 20. Mounted in the module 22 (not shown here) are various data and control circuits (described later) of the printer 10.
Is. The printhead unit 14 is easily physically and electrically separated from the other elements of the printer 10.

Referring to FIG. 2, printhead unit 14 is shown physically and electrically isolated from the rest of printer 10. Print head
Unit 14 is shown inverted for clarity. The end 20 a of the electrical cable connector 20 (shown in dashed lines) is a permanent part of the printhead unit 14. The other end 20 of the cable connector 20
b is a permanent part of the circuit module 22. The print head unit 14 has a mounting base 30 to which a multi-element thermal printing head 32 is mounted. The printhead 32 has a number of heating elements 34-1 to 34-n (although the reduction ratio is not constant), which elements print the same number of closely spaced pixels on a page of print media. It is like this. These pixels are 3
6-1 to 36-n (reduction ratio is not constant). Print head 32 and its heating element 34-1.
34-n has the construction and operation described in US Pat.
No. 27,279. The storage device 38 is
Adjacent to the head 32 on the mount 30 is an electronically erasable programmable read only memory (EEPROM) device. This storage device 38 is attached as an integral part of the print head unit 14 and is attached to a specific print head 32 (identified by the date and the serial number), and the compensation specific to the print head unit 14 is performed. Print data electronically. If desired, a head drive circuit 40 for supplying electric power to the heating elements 34-1 to 34-n of the head 32 according to the print data sent from the circuit module 22 is attached to the attachment base 30 of the unit 14. It is possible.

To the right of printhead unit 14 is shown another computer 44, which is not part of this unit, but which is used as follows. Printed pixel 3
The actual print data of the head obtained from the density measurements of 6-1 to 36-n is sent to the computer 44, as indicated by the dashed line 46. Based on these actual data, computer 44 causes heating element 34-1 of head 32 to
Calculate individual print compensation data for each of ~ 34-n. These compensation data, which are binary correction numbers, are loaded and permanently stored in the EEPROM, an integral part of the head unit 14, as indicated by the dashed line 48. The correction number is calculated by the above-mentioned US Pat. No. 4,827,
No. 279. These correction numbers are unique to each of the heating elements 34-1 to 34-n of print head 32. This set of correction numbers (specific to a given head unit 14) is then automatically input to the high speed memory and correction circuit of the printer 10 for use. Multiple printhead units 1 used by a given printer 10
Heating element 34-1 regardless of which of the four used.
The non-uniformity of each print operation from .about.34-n is eliminated by these correction numbers and the individual circuits. If another printhead unit 14 is installed, no further printer adjustment is required.

The printhead unit 14 includes the end 20a of the cable connector 20 shown in FIG. Both ends 20a and 20b are connected by a cable connector 20 (shown by a broken line in FIG. 2) and operate with the printer 10 (see FIG. 1).
Mounted on the circuit module 22, the circuit module 22 is electrically connected. The circuit module 22 need not be removed from the printer 10, but is shown removed in FIG. 2 for clarity. The circuit module 22 (shown in FIG. 2 in a block diagram) comprises a correction circuit and data storage device 50 (CCDM), a data processing device 52, an image data unit 54 and a power supply unit 56. The set of correction numbers from the EEPROM device 38 (when the print head unit 14 is attached to the printer 10) is EE
C via the bus 57 from the PROM device 38 and also via the cable connector 20 (shown in phantom in FIG. 2).
It is sent to the CDM unit 50. When the power to the printer 10 is turned on, loading of the correction number into the CCDM unit 50 is started. This is an on-off switch 58.
Is performed by connecting the power source 56 to the input terminal 60 connected to an external power source (not shown). The other input power supply terminal 62 is directly connected to the external power supply and the power supply 56. The lead 64 from the power supply 56 is connected to the EEPROM device 38 via the cable connector 20 and sends an activation signal to the device 38 to load the correction number permanently stored in the device 38 into the CCDM unit 50.
The circuit in the CCDM unit 50 uses the EE
The PROM device 38 sequentially sends the data at low speed via the bus 57 and loads it into the appropriate storage location in the high speed CCDM unit 50. The image data from the image data unit 54 is sent to the data processor 52 and the data to be printed by the processor 52 is sent to the CCDM unit 50. Next, the printer 10 has the above-mentioned US Pat.
827,279 operates with electronic printing compensation (i.e., print head 32 prints print pixels with a high degree of uniformity).

FIG. 3 shows the numbered heating elements 34-1 to 34-3.
It is a graph which shows the printing pixel density corresponding to 34-n.
Line 70 shows the actual density of the printed pixels 36-1 to 36-n, which is printed by each heating element 34-1 to 34-n using the same power supply. It can be seen that the line 70 deviates slightly above and below the dashed line 72. Dashed line 72 represents the desired uniform density level. However, the actual density drawn along line 70 is only slightly offset from the uniform density line 72, but not much from the overall density shown along the ordinate axis. The number of corrections to compensate for the deviation from the desired density level shown by the dashed line 72 in the pixel where each heating element is printed is much smaller than the number of data for the entire area of density. For example, the total area shown in FIG. 3 from “0” to the maximum value is represented by an 8-bit number (data word), and the correction number is small between the line 70 and the value along the flat and uniform line 72. Because of the deviation, it can be represented by a 6-bit number. As previously mentioned, there are as many as 2400 heating elements 34-1 to 34-n on an 8-inch wide page. Therefore, by using one correction number for each heating element of only 6 bits, it is possible to use 2400 heating elements (24
00 × 6 = 14,400, which is 2048 × 8 = 16,
(Less than 384). Each heating element 34-1 stored in the EEPROM device 38 and supplied to the CCDM unit 50 of the printer 10.
Depending on the correction number for ~ 34-n, the print pixel 36-1
~ 36-n will have approximately the desired uniform density along the dashed line 72.

It will be appreciated that the embodiments of the printing apparatus described above represent the general principles of the invention.
Those skilled in the art will be able to make various modifications without departing from the spirit and scope of the present invention. For example, the invention is not limited to use with a particular EEPROM device or with a single device. Furthermore, the number of data other than 8-bit words and the correction number other than 6-bit words can be used. Furthermore, the print head 23 is not limited to a particular number of specific heating elements per inch or per specific page width.

[0016]

This printhead assembly unit can be used in any printer by providing the printhead assembly unit with a memory device that permanently stores the corresponding correction number corresponding to a particular printhead. However, without mounting or readjusting the print head,
It is possible to print at a desired uniform density. Further, it becomes possible to efficiently perform the print head assembly unit in the production and test operations as well as the final assembly operation.

Furthermore, the adjustment work of the print head assembly unit can be performed at low cost.

[Brief description of drawings]

FIG. 1 is a schematic view of a thermal printer according to the present invention.

FIG. 2 is a schematic view of a print head unit of a printer according to a preferred embodiment of the present invention, shown detached from the printer and shown in various scales. In addition, FIG. 2 also shows an external computer for obtaining a correction number that is permanently stored in the printhead unit.

FIG. 3 shows the actual change in density of pixels printed by a thermal head according to the numbered heating elements of the head on one page.

[Explanation of symbols]

 10 Thermal Printer 12 Drum 14 Printing Head Unit 16 Frame 20 Cable Connector 22 Circuit Module 30 Mounting Base 32 Thermal Printing Head 34 Heating Element 38 Storage Device (EEPROM) 40 Head Drive Circuit 44 Computer 50 Correction Circuit and Data Storage Device (CCDM) 52 data processor 54 image data unit 56 power supply unit 57 bus 60, 62 input terminal 64 lead wire

Claims (9)

[Claims] 1. A frame, a support means mounted on the frame for supporting a medium to be printed and moving the medium to a printing position, and a circuit module means mounted on the frame for driving a thermal printer. The circuit module means includes a power supply means, an image and data processing means, and a stored print data correction means for controlling a printing operation of a plurality of heating elements of the thermal print head, a substrate, and A thermal head mounted on a substrate and having a number of small heating elements for thermally printing individual pixels on the print medium; and a multi-head corresponding to the plurality of heating elements of the thermal head mounted on the substrate, respectively. An electronic storage device for permanently storing the bit correction number, each multi-bit correction number being supplied with print compensation data to an individual heating element to provide a uniform image. A printhead unit for printing all heating elements at a uniform density when excited in response to a data, and in the vicinity of the support means in a printing position for printing an image on the print medium, Mounting means for mounting the print head on a frame so that the print head unit can be easily removed from the frame and the printer; and a correction number permanently stored in the electronic storage device for the storage printing. Having a data bus for outputting to the data correcting means, the thermal printer is activated, the printer uniformly prints using a given head unit and does not require adjustment after mounting the head unit. And a means for automatically transferring a correction number from the electronic storage device to the stored print data correction means. Printer. 2. The thermal printer according to claim 1, wherein the storage device in the print head unit is an electronically erasable programmable read only memory (EEPROM), and the individual heating elements are corrected. The number is characterized in that it is stored at a sequential address of the EEPROM device. 3. The thermal printer according to claim 2, wherein when the thermal printer is activated, the data for outputting the correction numbers stored in the EEPROM device to the stored print data correction means in order at low speed. -Characterized by having a bus. 4. The thermal printer of claim 3, wherein each correction number stored in the EEPROM is a digital data word containing a maximum weighted word that is significantly less than the maximum weighted value of the image data word. Characterize. 5. A thermal printer comprising a circuit module having a frame, means for moving the thermal print medium to a printing position, and electronic correction data storage means for driving a plurality of heating elements of the thermal print head, The thermal print head unit includes: a print head having a large number of heating elements that are arranged close to each other in the length direction to print on the thermal print medium; and the print head is mounted on the thermal print medium. A substrate removably attached to the frame at a printing position of the print head and its heating element for corresponding printing, and a correction that is integral with the substrate and the print head and that corresponds to each of the heating elements of the print head. Storage means for permanently storing print compensation data in the form of a number, the correction number being the print characteristics of the heating elements of the print head. The thermal printer is made to print at a substantially uniform density regardless of some changes, the circuit module means is connected to the storage means of the print head unit, and the print head is mounted on the thermal printer. When the thermal printer is activated, the correction number stored in the storage means is downloaded to the electronic correction data storage means, and as a result, all print head units are mounted on a predetermined printer, and the thermal printer is desired. And a circuit means for printing at the same uniform density. 6. The thermal print head unit according to claim 5, wherein said storage means is an electronically erasable programmable
Read Only Memory (EEPROM), characterized in that the correction numbers are stored as 6 bit words in the EEPROM device. 7. The thermal print head unit according to claim 5, wherein a correction number is loaded into the storage means by a computer installed separately, and when the thermal printer is activated, the correction number is stored. It is characterized in that the data is sequentially downloaded to the electronic correction data storage means at a low speed. 8. A thermal printer comprising a circuit module having a frame, means for moving the thermal print medium to a printing position, and electronic correction data storage means for driving a plurality of heating elements of the thermal print head, The thermal print head unit includes: a print head having a large number of heating elements that are arranged close to each other in the length direction to print on the thermal print medium; and the print head is mounted on the thermal print medium. A substrate removably attached to the frame at a printing position of the print head and its heating element for corresponding printing, and a correction that is integral with the substrate and the print head and that corresponds to each of the heating elements of the print head. Electronically erasable programmable read only memory (E) that permanently stores print compensation data in the form of a number EPROM) device, and the correction number causes the thermal printer to print at a substantially uniform density regardless of any changes in the printing characteristics of the heating elements of the printhead, the circuit module means for printing the printhead unit. Connected to an EEPROM device, the print head is mounted on the thermal printer, and when the thermal printer is activated, the correction number stored in the EEPROM device is downloaded to the electronic correction data storage means, As a result, there is provided a circuit means for mounting any print head unit on a predetermined printer, and for causing the thermal printer to print at a desired uniform and uniform density. 9. The thermal printhead unit according to claim 8, wherein the heating elements are positioned at 300 / inch, and the EEPROM device has 2048 byte positions. The number of corrections for each is
Each is stored as a 6-bit data word.