JP2000263827A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the image forming conditions from being varied depending on the position of heating elements. SOLUTION: In an image forming apparatus where the heating elements in a thermal head 91 are driven simultaneously for respective blocks 130A, 130B depending on an image signal, heating elements in each block 130A, 130B are divided into two or more groups 1-4. Heating control signals A1, A2, B1, B2 for driving the heating elements in each group are provided and the heating elements are driven by a drive means with unique energy for each heating control signal A1, A2, B1, B2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a thermal head.

[0002]

2. Description of the Related Art A thermal head is generally used in an image forming apparatus such as a thermal transfer recording apparatus and a plate-making printing apparatus. A thermal transfer recording apparatus presses a thermal head against a platen roller via an ink sheet and an image receiving sheet, conveys the ink sheet and the image receiving sheet, and includes a plurality of heating elements arranged in a line in the main scanning direction of the thermal head. Heat is generated according to the image signal to melt the ink on the ink sheet, and the ink is transferred to an image receiving sheet to perform image recording.

[0003] In addition, the stencil printing apparatus contacts a thermal head having a plurality of heating elements arranged in a line in the main scanning direction with at least a heat-sensitive stencil master having a thermoplastic resin film, and simultaneously contacts the plurality of heating elements. On the other hand, the heat-sensitive stencil master is relatively moved in the sub-scanning direction, and the heating element generates heat in accordance with the image signal to form an image by perforating the heat-sensitive stencil master. The ink is supplied to the stencil master on the printing drum by being wound, and an image is formed on the printing paper by the ink.

In the thermal head, one ends of a plurality of heating elements arranged in a line in the main scanning direction are commonly connected to a common electrode, and the other ends of the common electrode and the plurality of heating elements are connected to a driver. The plurality of heating elements are driven according to the image signal to generate heat. In this case, it is known that a plurality of heating elements are divided into a plurality of blocks and driven by a driver simultaneously for each block.

Conventionally, the thermal head itself has a relatively large outer shape, and the width of the common electrode is such that the thermal efficiency of the thermal head is not significantly affected. For this reason, when the heating element is driven simultaneously for each block, a known heat history control technique or the like is used to drive the heating element without considering the voltage (power) loss at the common electrode. Energy is applied, and the heat-sensitive stencil master is perforated to obtain a printed image.

[0006] It is considered that the thermal head is made narrower and smaller. FIG. 12 shows an example of a thermal head 91 which is narrower and smaller, and FIG. 129 shows a cross section when cut in the sub-scanning direction. Heating element array 13 including a plurality of heating elements
The thermal head 91 having 0 includes a protective film layer 131, a lead electrode 132, a resistor layer 133, a glaze layer 134, a ceramic layer 135, an aluminum radiator plate 136, and the like. A thermal head substrate 125 is provided with a driver IC 137. . A connector 119 is arranged on the thermal head substrate 125, and the thermal head 91 is connected to the connector 1.
19 is wired. FIG. 14 shows a common electrode 138,
The thin film substrate 129 having the heating element array 130 and the lead electrodes 132 is shown in an enlarged manner.

Japanese Patent Application Laid-Open No. 4-163159 discloses a line thermal head, a control circuit for transferring print data necessary for the thermal head, and an optimum print energy for the thermal head according to the density of the print data. And a driving circuit for supplying the thermal head.

An image receiving sheet of B4 size, A3 size, etc.
In a long thermal head having many heating elements capable of forming an image on a sheet, such as a heat-sensitive stencil master, the heating elements are arranged in a row in the main scanning direction in order to reduce electric energy for generating heat. The heating element array made up of the plurality of heating elements is divided into blocks such as four divisions, eight divisions, and the like, and these are divided into blocks, and these blocks are energized in a time division manner for each block in accordance with a heat generation control signal to generate heat, thereby performing image formation. Was.

FIG. 9 shows a conventional thermal head 91a.
10 shows a heating element row of each block which is driven to generate heat simultaneously, FIG. 10 shows a drive timing of the thermal head 91a, and FIG. 11 shows a circuit for driving the thermal head 91a. In the thermal head 91a, a heating element row 130 composed of a plurality of heating elements arranged in one row in the main scanning direction is divided into, for example, two blocks 130A and 130B.

The thermal head 91a includes a block 130
Write data (print data) corresponding to A, block 1
30B, write data (print data) corresponding to 30B, data transfer clock corresponding to write data of each block 130A, 130B at the time of data transfer, each block 130
A data latch signal for latching the write data of A and 130B, and strobe pulses A and B as a heat generation control signal for energizing a heating element that generates heat corresponding to the image data of each of the blocks 130A and 130B are input. . The heat control signals A and B are generated by a heat control signal generation circuit 1
The heat generation control signal generation circuit 141 is input from the thermal head 41 to the thermal head 91 a and is controlled by the CPU 142.

The thermal head 91a captures write data (print data) in synchronization with a data transfer clock, latches the latched data with a data latch signal, and drives the heating element array 130 with the drive ICs by the strobe pulses A and B so that the heating element array 130 is controlled by the blocks 130A and 130B. Each time it is driven according to the latched write data (print data) to generate heat.

As described above, the conventional thermal head 91
a, each block 130 driven to generate heat simultaneously
Even if there is only one heat generation control signal for the heating elements A and 130B, or if there is one or more heat generation control signals for the heating elements of each of the blocks 130A and 130B, the energy for driving the heating elements to generate heat does not increase. The value was the same for each control signal.

[0013]

In recent years, in image forming apparatuses, further improvement in image quality has been desired, and voltage loss due to resistance of a common electrode (hereinafter also referred to as common drop) is a potential problem when using a thermal head. Therefore, there has been a problem that the image forming state differs depending on the position of each heating element. In addition, the influence of the common drop is caused by reducing the number of heat generating elements to reduce the heat generating element (heat generation) in order to secure the width of the energizing time of the heat generating elements in order to increase the speed (reduce the printing cycle) desired in recent image forming apparatuses and plate making apparatuses. (Body split driving).

Further, the demand for downsizing the apparatus and reducing the amount of components constituting the thermal head has made it necessary to downsize the thermal head. As a result, the common electrode resistance increases due to the narrowing of the common electrode width of the thermal head, and the influence of the common drop on the difference in the image forming state due to the difference in the position of the heating element has increased.

When a thermal head having a large number of heating elements is driven, the heating element array is driven in a time-divided manner to reduce the number of heating elements that generate heat at the same time, thereby reducing the power supply capacity for the heating elements. ing. In this case, the heating element row is generally divided into two, four, or eight. Here, for example, when the heating element row is divided into two, due to the influence of the common drop due to the common electrode resistance,
The problem that the image forming state differs depending on the position of the heating element will be described below.

FIG. 7 shows an electric circuit for driving the heating element of the thermal head 91 to generate heat. 7, 130 heat generating element row comprising a plurality of heating elements R ₁ to R _4608, 137 is a drive IC train consisting of a plurality of drive IC for driving the heating element R ₁ to R ₄₆₀₈ each. 138 is a common electrode formed on the thin film substrate of the thermal head 91,
140 power supply supplies current to the heating element R ₁ ~R ₄₆₀₈ (V
hd) 146 is the direction of current flow, ER _{1 to} ER ₄₆₀₈
Represents the voltage value applied to the heating element R ₁ to R ₄₆₀₈ it is. The heating elements R _{1 to} R ₄₆₀₈ are respectively connected between one end of each drive IC of the drive IC row 137 and the common electrode 138, and between the other end of each drive IC of the drive IC row 137 and the common electrode 138. Are commonly connected to a power source 140.

The heating elements R _{1 to} R ₄₆₀₈ are the drive IC row 1
Each of the drive ICs 37 is driven, and when the drive IC is turned on, a current flows to generate heat. Here, although a material having a small electric resistance such as aluminum is used for the common electrode 138, the common electrode 138 actually has a slight electric resistance. The outline of the thermal head will be described below in order to explain the thermal head.

Printing width: A3 size Resolution: 400 DPI (Dot Per Inch) Heating element size (main scanning direction × sub scanning direction): 30 × 25
μm Heating element total number: 4608 Heating element resistance value: 2145Ω Common electrode resistance value (between both ends of electrode): 0.150Ω In this thermal head 91, a heating element for 2304 dots, which is a half of the total number of heating elements, is divided into two. R _{1 to} R ₂₃₀₄
Are turned on at the same time, a current is supplied from the power supply 140 to each of the heating elements R _{1 to} R ₂₃₀₄ through a current path as shown in FIG. 7, but as described above, the common electrode 138 has a slight electric resistance value. To have the common electrode 1
At 38, a voltage loss occurs. When the heating elements R _{1 to} R ₂₃₀₄ are simultaneously turned on, the combined resistance of the heating elements R _{1 to} R ₂₃₀₄ is 2145Ω ÷ 2304 dots ≒ 0.93Ω, and the voltage loss due to the resistance value of the common electrode 138 of 0.150Ω is image quality. Can not be ignored.

FIG. 8 shows the positions of the heating elements in the thermal head 91 and the state of the voltage loss. Unlike the position of each heating element voltage is applied to the R ₁ ~R ₂₃₀₄ ER ₁ ~ER ₂₃₀₄ each heating element R ₁ to R _2304, as shown in FIG. 8 by the resistance value of the common electrodes 138, the heating element R ₁ ~ R
₂₃₀₄ Voltage ER ₁ to Er ₂₃₀₄ to be applied to each heating element R ₁ to R ₂₃₀₄ by the resistance value of about the common electrode 138 a distance from the power supply 140 is increased is lowered in. As a result, due to the influence of the common drop due to the resistance of the common electrode 138, there is a problem that the image forming state such as perforation differs depending on the position of the heating element.

From the above description, the effect of the common drop is
The greater the current flowing through the common pattern (the pattern of the common electrode 138), that is, the greater the number of heating elements that generate heat simultaneously with time (the number of heating elements for securing the width of the energization time of the heating elements for speeding up). It can be understood that this becomes more pronounced due to the lowering of the division, and becomes more pronounced as the resistance value of the common electrode 138 becomes higher, that is, as the pattern width of the common electrode 138 becomes narrower (the thermal head becomes smaller).

FIG. 15 shows the result of plate making and printing under the following conditions using a copying machine using the thermal head 91. Environment: 25 ° C. 60% Thermal head: Printing width: A3 size Resolution: 400 DPI Heating element size (main scanning direction × sub scanning direction): 30 × 25
μm Heating element total number: 4608 dots Heating element resistance value: 2145Ω Common electrode resistance value (between both ends of electrode): 0.150Ω Power applied to thermal head heating element Applied power: 0.093 W Powering pulse width: 0.468 ms Line Period: 1.5 ms / l Number of thermal head heating element drive divisions: 2 Plate making printing machine: JP5500 (Ricoh) Master: JP50 (Ricoh) Ink: JP10 (black) Ricoh Printing speed: Standard High speed (3rd speed) Printing pattern: 100% printing rate in the main scanning direction, all solid (192 dot continuous plate making in the sub-scanning direction) From FIG. 15, the print density differs depending on the position of the heating element of the thermal head in the main scanning direction. I understand. This concentration difference is
In a copy printing machine, this occurs because the diameter of the dots perforated in the plate-making master differs due to the influence of the common drop.

Further, conventionally, a thermal head mounted on an image forming apparatus such as a thermal transfer recording apparatus or a plate making apparatus has a relatively large outer shape, and the width of a common electrode greatly affects the heat generation efficiency of the thermal head. It is not possible to consider the voltage (power) loss at the common electrode by driving the heating element for each block that is energized at the same time.
A well-known technique such as thermal history control is applied to the driving of the heating element to apply perforation energy to the heating element and to perforate the heat-sensitive stencil master to obtain a printed image.

However, it has become increasingly necessary for users to produce cheaper products and environmentally friendly products on a global scale. For this reason, it is necessary to manufacture parts of the products themselves. It has become essential to increase the efficiency and reduce the amount of materials and the like for parts. Therefore, it is necessary to further reduce the size of the component, and the thermal head mounted on an image forming apparatus such as a thermal transfer recording apparatus and a plate making printing apparatus is required to have a technology for utilizing the reduced size as described above. We must proceed with the establishment.

However, when the size of the thermal head is reduced, the width of the common electrode becomes narrower. Therefore, a voltage drop caused by the resistance of the common electrode, that is, a power loss occurs, which is generated in each heating element. Joule heat fluctuates due to the difference in the position of each heating element in the main scanning direction. For this reason, the quality of the formed image varies, and especially, the quality of the formed image largely varies near the center and both ends in the main scanning direction.

In an image forming apparatus such as a plate-making printing apparatus, if the size of the thermal head is reduced, the quality of the formed image varies due to the above-mentioned phenomenon. Will occur.
For example, in a plate-making printing apparatus, a plurality of heating elements arranged in a line in a main scanning direction provided in a thermal head are used to melt a thermoplastic resin film of a heat-sensitive stencil master with Joule heat to perform perforation. However, the perforated state when the thermoplastic resin film of the heat-sensitive stencil master is melted by the heating element near the end side of the thermal head becomes a large diameter, and the heat-sensitive stencil by the heating element near the center of the thermal head. When the thermoplastic resin film of the master is melted, the perforated state becomes small, and the same perforated state cannot be obtained. For this reason, the print image density is high near the edge of the thermal head at the perforated portion, and conversely, is low near the center portion of the thermal head at the perforated portion. The image quality will deteriorate.

Further, near the end of the thermal head,
By over-perforating the thermoplastic resin film of the heat-sensitive stencil master, in the worst case, a perforated state in which each perforation is not separated is obtained. The peculiar set-off (the transfer of the ink on the printing paper surface of the previous printing unit to the back surface of the printing paper and not on the printing paper front surface but on the back side of the printing paper) deteriorates poorly. In the vicinity of the center of the thermal head, white spots, that is, unperforated portions are considerably increased.

In the case of a plate making printing apparatus, if the thermoplastic resin film of the heat-sensitive stencil master is not uniformly perforated near the center and the end of the thermal head, wrinkles are generated on the heat-sensitive stencil master, and the printed image is printed. Not only does the quality of the stencil deteriorate, but the expensive heat-sensitive stencil master must be discarded and reprinted. In other words, if the diameter of the perforation increases near the end or center of the thermal head, the heat-sensitive stencil master sticks to the thermal head due to heat shrinkage at the time of perforation. This phenomenon tends to increase, and therefore, the wrinkles of the heat-sensitive stencil master easily occur due to the imbalance in the perforation diameter in the width direction of the heat-sensitive stencil master.

It is an object of the present invention to provide an image forming apparatus capable of forming an optimum image even when the position of a heating element in the main scanning direction is different.

Another object of the present invention is to provide an image forming apparatus capable of forming an optimum image even when the heating element has a different position in the main scanning direction and a different printing rate in the main scanning direction.

According to a third aspect of the present invention, there is provided a heating element in the main scanning direction, a printing rate of a heating element driven to generate heat simultaneously for each heating control signal, and a group of other groups corresponding to other heating control signals in the same block. It is an object of the present invention to provide an image forming apparatus capable of forming an optimum image even if the printing rates of the heating element rows are different.

According to the fourth aspect of the present invention, the quality of the formed image can be made uniform by using the downsized thermal head, and high efficiency in manufacturing can be achieved with downsizing of the thermal head. It is an object of the present invention to provide an image forming apparatus in which the cost can be reduced and the price of the product can be reflected, and the amount of materials used can be reduced with the downsizing of the thermal head and the environment can be made more environmentally friendly.

According to the fifth to ninth aspects of the present invention, it is possible to form an appropriate image in accordance with the resolution in the main scanning direction and the sub-scanning direction and to form an optimum formed image with less formed image density unevenness for any image. At the same time, high efficiency in manufacturing can be achieved with the downsizing of the thermal head, which can be reflected in the price of products as the thermal head is inexpensive. It is an object of the present invention to provide an image forming apparatus capable of reducing the amount and the like and making it more environmentally friendly.

[0033]

In order to achieve the above object, the invention according to claim 1 divides a plurality of heating elements arranged in one example in a main scanning direction of a thermal head into a plurality of blocks. In an image forming apparatus in which a heating element is simultaneously driven for each block in accordance with an image signal to form an image on a sheet, the heating element for each block that is simultaneously driven for heating is divided into at least two or more parts. A plurality of heat generation control signals for driving heat generation are provided for each of the divided heating elements,
There is provided driving means for driving the heat generating element with heat unique to each heat control signal.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, there is provided a counting means for counting the number of the heat generating elements which are driven to generate heat simultaneously for each heat control signal. The energy for driving the heating at the same time for each control signal is determined by the count value of the counting means.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, there is provided a counting means for counting the number of the heating elements which are driven to generate heat simultaneously for each heat generation control signal, and the heating element is provided with each heating element. Based on the count value of the counting means, the number of heating elements driven simultaneously by one heating control signal is determined based on the count value of the counting means. It is determined by the number of heating elements that are driven to generate heat simultaneously by a heat control signal other than the control signal.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second or third aspect, the block is a center of the plurality of heating elements arranged in a line in a main scanning direction of the thermal head. The heating element near the unit and the heating element near both ends are formed as independent blocks.

According to a fifth aspect of the present invention, in the image forming apparatus of the first, second or third aspect, the block is a positive integer, wherein Rn / the number Nb of the heating elements is a positive integer.
The value of Nb is set to an even number of 4 or more, and the division of the heating elements is not limited to the equal division, but also to the division in which the number of heating elements permitted in each block is different.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the heating element is divided into blocks at or near the location of the heating element number divided at an interval of Rn / Nb. The location of Rn / 2 or a location in the vicinity of the location is a boundary, and the combination of the heating elements for each block symmetrical from the boundary is regarded as one block.

According to a seventh aspect of the present invention, in the image forming apparatus according to the first, second or third aspect, the total number of heating elements Rn
/ The number Nb of the blocks is a non-positive integer value, the Nb
Is an even number or an odd number, and the division of the heating elements is not only a division close to equal division, but also a division in which the number of heating elements permitted in each block is different.

According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, a combination of the heating elements for each block symmetrical to the right and left from the boundary is set at or near Rn / 2. This is one block.

According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, at least a thermal head having a plurality of heating elements arranged in a line in the main scanning direction is heated. While being in contact with the heat-sensitive stencil master having a plastic resin film, the heat-sensitive stencil master is relatively moved in the sub-scanning direction with respect to the plurality of heating elements, and the heating elements are heated according to image signals. And a stencil printing machine for forming an image on the thermosensitive stencil master.

[0042]

FIG. 5 shows a first embodiment of the present invention. The first embodiment is an embodiment of an image forming apparatus including a heat-sensitive stencil printing apparatus. First, the configuration of the heat-sensitive stencil printing apparatus will be briefly described. This thermosensitive stencil printing apparatus includes an apparatus main body cabinet 50, a document reading section 80 at an upper portion of the apparatus main body cabinet 50, a plate making and feeding section 90 therebelow, and a porous printing drum 101 on the left side thereof.
Is arranged on the printing drum unit 100 and the plate discharge unit 7 on the left side thereof.
0, a sheet feeding unit 110 below the plate making and feeding unit 90, a printing pressure unit 120 below the printing drum 101, and a sheet discharging unit 130 at the lower left of the apparatus main body cabinet 50.

Next, the operation of the thermosensitive stencil printing apparatus will be described. First, a document 60 having an image to be printed is placed on a document placing table (not shown) arranged above the document reading unit 80, and a plate making start key (not shown) is pressed.
With the press of the plate making start key, a plate discharging process is first executed. That is, in this state, the used heat-sensitive stencil master 61b used in the previous printing remains mounted on the outer peripheral surface of the printing drum 101 of the printing drum unit 100.

When the printing drum 101 rotates in the counterclockwise direction and the rear end of the used heat-sensitive stencil master 61b on the outer peripheral surface of the printing drum 101 approaches the pair of plate-release rollers 71a, 71b, the pair of rollers 71a, 71b. Is used and heat-sensitive stencil master 61b is used by one of the stencil release rollers 71b while rotating.
Scoop up the rear end of the used heat-sensitive stencil master 6
1b is a plate discharging roller pair 73a, 73b and a plate discharging peeling roller pair 71 disposed to the left of the plate discharging roller pairs 71a, 71b.
a, 71b, and a pair of plate discharging transport belts 72
a and 72b, the plate discharging box 7 while being conveyed in the direction of arrow Y1.
4, the used heat-sensitive stencil master 61b is peeled off from the outer peripheral surface of the printing drum 101, and the stencil discharging process is completed. At this time, the print drum 101 continues to rotate in the counterclockwise direction. Discharged used thermosensitive stencil master 61
Thereafter, b is compressed inside the plate discharge box 74 by the compression plate 75.

In parallel with the plate discharging process, the original reading section 80 reads the original. That is, the original 60 placed on an original mounting table (not shown) is separated by a separation roller 81, a pair of front original transport rollers 82 a and 82 b, and a pair of rear original transport rollers 83.
The image is read while being conveyed in the directions of arrows Y2 to Y3 by the respective rotations of a and 83b. At this time, when there are many originals 60, only the lowermost original is conveyed by the action of the separation blade 84. Image reading of the document 60 is performed by reflecting light reflected from the surface of the document 60 illuminated by the fluorescent lamp 86 while being conveyed on the contact glass 85,
The light is reflected by a mirror 87, passes through a lens 88, is incident on an image sensor 89 composed of a CCD (charge coupled device), and is photoelectrically converted. That is, the image reading of the document 60 is performed by a known reduced document reading method, and the document 60 from which the image has been read is placed in the document tray 80.
It is discharged on A. An electric signal (analog image signal) from the image sensor 89 is input to an analog / digital conversion unit (described later) in the apparatus main body cabinet 50, converted into a digital image signal, and subjected to predetermined processing by an image processing unit (described later). You.

On the other hand, in parallel with this image reading operation,
A plate making and plate feeding process is performed based on the digital image signal. That is, the heat-sensitive stencil master 61 set at a predetermined portion of the plate making and feeding unit 90 is pulled out from the rolled state and pressed against the above-described thermal head 91 via the heat-sensitive stencil master 61. The sheet is conveyed to the downstream side of the conveyance path by the rotation of the platen roller 92 and the pair of feed rollers 93a and 93b. For the heat-sensitive stencil master 61 conveyed in this way, a plurality of heating elements provided in the thermal head 91 and arranged in a line in the main scanning direction are sent from the image processing unit to a digital image signal. , And the thermoplastic resin film of the heat-sensitive stencil master 61 that moves in the sub-scanning direction in contact with the heating element is melt-punched. As described above, the image signal is written into the heat-sensitive stencil master 61 as a perforation pattern by the position-selective melting and punching of the heat-sensitive stencil master 61 according to the image signal. The heat-sensitive stencil master 6
No. 1 uses a material obtained by laminating a thermoplastic resin film on Japanese paper as a porous support.

The leading end of the prepressed thermosensitive stencil master 61a on which the image signal has been written is sent out toward the outer peripheral side of the printing drum 101 by the pair of stencil feeding rollers 94a and 94b. And the print drum 101 in the plate feeding position state hangs down toward the expanded master clamper 102 (shown by a virtual line). At this time, the used heat-sensitive stencil master 61b has already been removed from the printing drum 101 by the plate discharging process.

When the leading end of the prepressed thermosensitive stencil master 61a is clamped at a predetermined timing by the master clamper 102, the printing drum 101 rotates in the direction A (clockwise) in FIG. The heat-sensitive stencil master 61a is gradually wound. The rear end of the perforated heat-sensitive stencil master 61a is cut to a predetermined length by the cutter 95.

When the one-plate-made heat-sensitive stencil master 61a is wound around the outer peripheral surface of the printing drum 101, the stencil making and plate feeding steps are completed, and the printing step is started. First, the paper feed table 51
The uppermost one of the printing papers 62 stacked on the upper side is moved by the feed roller 111 and the separation roller pairs 112a and 112b toward the feed roller pairs 113a and 113b with an arrow Y4.
In the direction, and further feed roller pair 113a,
The print data is sent to the printing pressure unit 120 at a predetermined timing synchronized with the rotation of the printing drum unit 113 by 113b. Printing paper 6
When the roller 2 comes between the print drum 101 and the press roller 103, the press roller 103, which has been separated from the lower part of the outer peripheral surface of the print drum 101, is moved upward to be wound around the outer peripheral surface of the print drum 101. The press roller 103 is pressed against the prepressed thermosensitive stencil master 61a. Then, the ink oozes out from the opening portion of the print drum 101 and the perforation pattern portion of the prepressed thermosensitive stencil master 61a, and the oozed ink is transferred to the surface of the printing paper 62 to form a print image.

At this time, on the inner peripheral side of the printing drum 101, an ink reservoir 107 formed between the ink roller 105 and the doctor roller 106 from the ink supply pipe 104.
The ink is supplied to the printing drum 101, and the ink is rolled into the printing drum 101 by the ink roller 105 that rotates in the same direction as the rotation direction of the printing drum 101 and in synchronization with the rotation speed of the printing drum 101 and contacts the inner circumferential surface. It is supplied to the peripheral side.

The printing paper 62 on which the printing image has been formed in the printing pressure section 120 is peeled off from the printing drum 101 by the paper discharge peeling claw 114 and is suctioned by the suction fan 118 while being sucked and discharged by the suction discharge paper inlet roller 115 and the suction discharge paper. Due to the counterclockwise rotation of the conveyance belt 117 stretched over the paper exit roller 116, the conveyance belt 117 is conveyed toward the paper discharge unit 130 as indicated by an arrow Y5, and is sequentially discharged and stacked on the paper discharge table 52. In this way, the so-called printing is completed. After that, so-called trial printing is similarly performed as necessary.

Next, when the number of prints is set using a ten-key (not shown) and a print start key (not shown) is depressed, the steps of feeding, printing and discharging are repeated in the same steps as the set number of prints. All the steps of stencil printing are completed.

FIG. 1 shows a part of the electrical system of the first embodiment. As shown in FIG. 1, the heat generation control signal is input to the thermal head 91 from the heat generation control signal generation circuit 143, and the heat generation control signal generation circuit 143.
Is controlled by the CPU 144 as control means. The thermal head 91 may be any of a flat type, a partial grace type, and an end face type, and the heating element may be a rectangular type or a heat concentrated type. In this embodiment, a flat thermal head having a rectangular heating element is used.

As shown in FIG. 7, the thermal head 91 has a plurality of heating elements R ₁ to R ₁ arranged in a line in the main scanning direction.
Each heating element of the heating element row 130 consisting of R ₄₆₀₈ R ₁ ~R ₄₆₀₈
Are connected between one end of each drive IC of the drive IC row 137 and the common electrode 138, respectively.
The other end of each drive IC in the C column 137 and the common electrode 13
8 and a power supply 140 is commonly connected. Heating element R ₁
To R ₄₆₀₈ are driven by the respective drive ICs in the drive IC row 137.

As shown in FIG. 2, the thermal head 91 includes a plurality of heating elements R _{1 to} R ₄₆₀₈ , for example, heating elements R _{1 to} R ₂₃₀₄ , R of two blocks 130 A and 130 B.
_{2305 to} R ₄₆₀₈ . The thermal head 91 is at the same time blocks 130A which is heated and driven, the heating element R ₁ to R ₂₃₀₄ per 130B, R ₂₃₀₅ to R ₄₆₀₈ at least two or more, for example, heating elements of a group-of two by two R ₁ -
_{R 1152, R 1153 ~R 230 4} , R 2305 ~R 3456, R 3457 ~R
Heating elements were each divided by dividing the ₄₆₀₈ R _{1 ~R 1152,} R ₁₁₅₃
~R _2304, R ₂₃₀₅ ~R _3456, a plurality of heat generating control signals for heating driving each _{R 3457 ~R 4608 A1, A2,} B1, B
2 is provided, the heating element R ₁ to R ₄₆₀₈ each heating control signals A1,
A2, B1, and B2 (each group to each) are driven to generate heat with their own energy.

That is, the heating elements R _{1 to} R ₁₁₅₂ of the group corresponding to the heat control signal A 1 are driven according to the write data (print data) by the heat control signal A 1, and the heat elements of the group corresponding to the heat control signal A 2. R _{1153 to} R ₂₃₀₄
Is write data (print data) according to the heat generation control signal A2.
Driven according to the write data (printing data) is driven, the heating element R ₂₃₀₅ to R ₃₄₅₆ of the group corresponding to the heating control signal B1 by heat generation control signal B1 in accordance with the heat generation of the group corresponding to the heat generation control signal B2 The bodies R _{3457 to} R ₄₆₀₈ are driven according to the write data (print data) by the heat generation control signal B2.

FIG. 3 shows the drive timing of the thermal head 91. The thermal head 91 includes write data (print data) corresponding to the block 130A,
B, write data (print data) corresponding to B, a data transfer clock corresponding to the write data of each block 130A, 130B at the time of data transfer, each block 130A,
Heating elements R _{1 to} R ₁₁₅₂ and R ₁₁₅₃ to generate heat corresponding to the data latch signal for latching the write data of 30B and the image data of each of the blocks 130A and 130B.
_{R 2304, R 2305 ~R 3456,} R 3457 ~R 4608 strobe pulse A1 as a heat generating control signals for energizing the, A
2, B1 and B2 are input from the plate making unit to each of the blocks 130A and 130B of the heating element array 130.

The heat generation control signals A1, A2, B1, and B2 are input to the thermal head 91 from a heat generation control signal generation circuit 143 included in the plate making section, and the heat generation control signal generation circuits
3 is controlled by the CPU 144 to generate heat control signals A1,
A2, B1 and B2 are placed on the thermal head 91 by the heating element array 13
Input is performed for each of two groups of each of the blocks 130A and 130B. Write data (print data)
After converting an analog image signal from the image sensor 89 (FIG. 5) into a digital image signal by an analog / digital (A / D) converter (not shown) and performing predetermined image processing by an image processor (not shown) Heat history control and the like and various signal controls and the like are performed by a plate making unit (not shown).

The thermal head 91 captures write data (print data) in synchronization with a data transfer clock, latches the data with a data latch signal, and outputs a strobe pulse A
1, A2, B1, and B2, the heating element array 130 is driven by the drive IC array 137 to generate heat generation control signals A1, A2, B1, and B2.
In each case (for each heating element of each group), heat is generated by driving in accordance with the latched write data (print data) with unique energy.

The thermal head 91 has the following configuration. Printing width: A3 size Resolution: 400 DPI Heating element size (main scanning direction x sub scanning direction): 30 x 25
μm Heating element total number: 4608 dots Heating element resistance value: 2145Ω Common electrode resistance value (between both ends of electrode): 0.150Ω As described above, the common drop is the heating element position of the thermal head, that is, for heating element heating. Common pattern from power supply 140 to heating element (pattern of common electrode 138)
And the longer the length, the greater the influence on the image.
It falls below the voltage value of 40. Although the first embodiment is an embodiment in which the heating element array 130 of the thermal head 91 is driven by dividing the heating element array 130 into two parts, the heating elements of the block 130A in the heating element array 130 that are simultaneously driven to generate heat are further divided into two groups, Heating control signals A1 and A2 for controlling the heating element conduction time are provided for each group. Similarly, the heating elements of the block 130B that are simultaneously driven to generate heat in the heating element row 130 are divided into two groups, and each group is provided with heat control signals B1 and B2 for controlling the heating element energizing time. I have.

The resistance value of the common electrode 138 according to the position of the heating element will be described with reference to FIG. 4. The common electrode 138 is connected to the center of the heating element row of the group corresponding to the heating control signal A 1 in the heating element row 130. Resistance Ra of the common electrode 138 from the point to the point c on one end of the power supply 140
c is 19.0 mΩ, which is between the point b of the common electrode 138 to which the center of the group of heating elements corresponding to the heating control signal A2 in the heating element row 130 is connected and the point c on one end of the power supply 140. Resistance Rb of the common electrode 138
c is 35.4 mΩ.

Therefore, the heat generation control signal generation circuit 143
In consideration of the resistance values Rac and Rbc of the common electrode 138, in the heating element array 130 of the thermal head 91, the applied energy is controlled by the heating control signal A2. By setting the heating control signal A1 so that the applied energy is slightly lower for the heating element row of the group to be corrected, the difference in image quality (perforation) in the main scanning direction due to the difference in the resistance value of the common electrode 138 is corrected. I do.

Similarly, the heat generation control signal generation circuit 143
The resistance value of the common electrode 138 from the point at which the center of the heating element row of the group corresponding to the heat control signal B1 is connected to the point c on one end of the power supply 140, and the heat control at the common electrode 138. The common electrode 13 between the point at which the center of the heating element row of the group corresponding to the signal B2 is connected and the point c on one end of the power supply 140
Taking into account the resistance value of 8, the applied energy of the group of heating elements of which the applied energy is controlled by the heating control signal B2 in the heating element row 130 of the thermal head 91 is slightly lower than the applied energy to the group of heating elements. By setting the heat generation control signal B2 so as to satisfy the following condition, a difference in image quality (perforation) in the main scanning direction due to a difference in resistance value of the common electrode 138 is corrected. Note that the detailed conditions of the applied energy to the heating element rows of each group to may be obtained by experiments.

The first embodiment is an embodiment of the first aspect of the present invention, in which a plurality of heating elements arranged in one line in the main scanning direction of the thermal head 91 are divided into a plurality of blocks 1.
30A and 130B, and this heating element is
In an image forming apparatus including a heat-sensitive stencil printing apparatus that heats and drives in accordance with an image signal for each of 30A and 130B to form an image on a sheet including the heat-sensitive stencil master 61,
A plurality of heat control signals A for dividing the heat generating element for each of the blocks 130A and 130B, which are simultaneously driven to generate heat, into at least two parts and driving heat generation for each of the divided heat generating elements.
1, A2, B1 and B2 are provided, and a drive IC array 137 is provided as a driving means for driving the heating element to generate heat with its own energy for each of the heat control signals A1, A2, B1 and B2. Optimal energy can be applied to the heating elements allocated to the heating element row for each signal, and an optimum image can be formed even if the heating elements are located at different positions in the main scanning direction.

FIG. 6 shows a part of an electrical system according to a second embodiment of the present invention. In the first embodiment, the influence of the common drop becomes more remarkable as the current flowing through the common pattern increases as described above, that is, as the number of heating elements that generate heat simultaneously with time increases. Therefore, in the second embodiment, in the first embodiment, a print dot number counter 145 is provided as a counting means for counting the number of heating elements driven to generate heat simultaneously for each heat generation control signal. The print data input to the head 91 is also input to the print dot number counter 145.

The print dot number counter 145 counts the print data of each heat control signal A 1, A 2, B 1, B 2 for each sheet composed of one heat-sensitive stencil master 61, and thereby generates each heat control signal A 1. The number of print dots (the number of heating elements driven to generate heat) of the heating element row for each of the groups corresponding to A2, B1, and B2 is counted,
The count result is input to the CPU 144. CPU1
Reference numeral 44 indicates the number of print dots in the heating element array for each of the groups corresponding to the heat control signals A1, A2, B1, and B2 counted by the print dot number counter 145, and controls the heat control signal generation circuit 143 to operate the thermal head 91. Is controlled so that the optimal energy is applied to each of the heating element rows 130 for each group.

That is, the CPU 144 controls the heat generation control signals A 1, A 1 counted by the print dot number counter 145.
2, the energy applied to the heating element in each group is controlled in accordance with the number of print dots in the heating element array for each group corresponding to B1 and B2, and the applied energy of each heating element is controlled by the number of print dots in the group. Group is controlled so as to increase when the number of print dots in the group is large (when the current flowing through the common electrode 138 is large) as compared with when the number is small (when the current flowing through the common electrode 138 is small). Difference in resistance value of common electrode 138 (difference in current flowing through common electrode 138)
Of the image quality (perforation) in the main scanning direction due to Note that the detailed conditions of the applied energy to the heating element rows of each group to may be obtained by experiments.

This second embodiment is an embodiment of the invention according to claim 2, and in the image forming apparatus according to claim 1, heat generation drive is simultaneously performed for each heat generation control signal A1, A2, B1, B2. A print dot number counter 145 as a counting means for counting the number of the heating elements to be heated. The counting means 14 generates energy for simultaneously driving the heating elements for each of the heating control signals A1, A2, B1, and B2.
5, the energy applied simultaneously to the heating element array for each heating control signal can be determined and controlled by the number of simultaneously energized heating elements for each heating control signal, and the position of the heating element in the main scanning direction and the main An optimum image can be formed even if the printing ratio in the scanning direction is different.

In the second embodiment, the heating element array 13
0 is the number of print dots corresponding to the number of heating elements that are driven to generate heat for each of the blocks 130A and 130B in the main scanning direction and the number of heating elements that are simultaneously driven for each of the heat control signals A1, A2, B1, and B2. (Current flowing through the common electrode) was corrected by the difference, but each block 130A,
Heat generation control signals A1, A2, B1, B within 130B
The current flowing through the common electrode 138 differs depending on not only the number of heating elements driven to be heated simultaneously by any one of the two, but also the number of heating elements driven to be heated by another heating control signal in the same block.

Therefore, in order to form a more optimal image (perforation), only the number of heating elements driven to generate heat simultaneously by one of the heat generation control signals A1, A2, B1, B2 in each of the blocks 130A, 130B. In addition, taking into account the number of heating elements driven to be heated by other heating control signals in the same block, the heating element row 130 is divided into the blocks 130A and 13A.
It is necessary to correct the heat driving energy for each 0B.

Therefore, in the third embodiment of the present invention, in the above-described second embodiment, the CPU 144 controls each heating control signal A counted by the print dot number counter 145.
1, A2, B1, and B2, the number of print dots of the heating element array for each group is recognized, and each heat generation control signal A1, A2, which is counted by the print dot number counter 145, as in the second embodiment. Controlling the applied energy of the heating element in each group to each of the heating elements according to the number of print dots of the heating element row in each of the groups corresponding to B1 and B2;
When the number of print dots in each group is small (the common electrode 138).
When the current flowing through the group is small)
Is controlled not only for each group to increase the number of print dots when the number of print dots is large (when the current flowing through the common electrode 138 is large), but also the applied energy of the heating element for each group is controlled by another heat generation in the same block. Control is performed in accordance with the count value of the print dot number counter 145 with respect to the print dot number of the heating element row for each other group corresponding to the control signal, and the applied energy of each heating element is changed to another heating control signal in the same block. Compared to the case where the number of print dots of the corresponding heating element array of each other group is small (when the current flowing through the common electrode 138 is small), the heat generation of each other group corresponding to another heating control signal in the same block. Control is performed so as to increase when the number of print dots in the body row is large (the current flowing through the common electrode 138 is large).

That is, for the heating element array of the block 130A, for example, the CPU 144 determines each heating element of the group according to the number of printing dots of the heating element array of the group corresponding to the heating control signal A1 counted by the print dot number counter 145. Is controlled, and the applied energy of each heating element in the group is controlled when the number of print dots in the group is larger (when the current flowing through the common electrode 138 is small). (When the current flowing through 138 is large), the applied energy of each of the heating elements of the group is controlled by increasing the applied energy of each of the heating elements of another group corresponding to another heating control signal A2 in the same block 130A. Control according to the count value of the print dot number counter 145 with respect to the print dot number, Other heat generation control signal A in the same block 130A the applied energy of the thermal body
The other group corresponding to another heat generation control signal A2 in the same block 130A as compared with the case where the number of print dots of the heating element row of the other group corresponding to No. 2 is small (when the current flowing through the common electrode 138 is small). Is controlled to increase when the number of print dots in the heating element row is large (when the current flowing through the common electrode 138 is large).

The CPU 144 controls the applied energy of each heating element of the group according to the number of printing dots of the heating element row of the group corresponding to the heating control signal A2 counted by the printing dot number counter 145, and The energy applied to the heating element is increased when the number of print dots in the group is large (when the current flowing through the common electrode 138 is large) as compared with when the number of print dots in the group is small (when the current flowing through the common electrode 138 is small). In addition to the above-described control, the applied energy of each heating element of the group is controlled by the printing dot number counter 145 for the printing dot number of the heating element row of another group corresponding to another heating control signal A1 in the same block 130A. Control is performed according to the count value, and the applied energy of each heating element in the group is controlled in the same block 130A. Heat generation control signal A
The other groups corresponding to the other heat generation control signals A1 in the same block 130A as compared with the case where the number of print dots of the heating element row of the other group corresponding to 1 is small (when the current flowing through the common electrode 138 is small). Is controlled to increase when the number of print dots in the heating element row is large (when the current flowing through the common electrode 138 is large).

Further, the CPU 144 executes the processing in the block 130B.
Block 130 for the applied energy of the heating element row
The control is performed in the same manner as the control of the applied energy of the heating element row A.
Thus, the heating element main scanning direction position, the number of print dots (printing rate) corresponding to the number of heating elements driven simultaneously for each heating control signal, and other groups corresponding to other heating control signals in the same block. An optimal image (perforation) can be formed even if the number of printing dots (printing ratio) of the heating element row differs.

The detailed setting conditions and effects of the third embodiment are as follows. Environment: 25 ° C. 60% Thermal head 91: Printing width: A3 size Resolution: 400 DPI Heating element size (main scanning direction × sub scanning direction): 30 × 25
μm Heating element total number: 4608 dots Heating element resistance value: 2145Ω Common electrode resistance value (between both ends of electrode): 0.150Ω Power applied to heating element of thermal head 91 Applied power: 0.093W Powering pulse width: Heating control Signals A1, B2: 0.468 ms Heat generation control signals A2, B1: 0.512 ms Line cycle: 1.5 ms / l Heating element drive division number of thermal head 91: 2 Plate making printing machine: JP5500 Ricoh Master: JP50 (manufactured by Ricoh Co., Ltd.) Ink: JP10 (black) manufactured by Ricoh Co., Ltd. Printing speed: standard speed (3rd speed) Printing pattern: 100% printing rate in the main scanning direction (solid printing with 192 dots in the sub-scanning direction) FIG. 16 shows the result of plate-making printing under the above conditions in the third embodiment in which the position of the thermal head 91 in the heating element main scanning direction and the printing density (Macbeth density) are shown. (Measured value by a densitometer). It can be seen that the change in print density depending on the position of the heating element in the main scanning direction of the thermal head 91 is smaller than in a conventional plate making apparatus. Further, the above-mentioned energy condition is such that the printing pattern is all solid, but it is sufficient that the optimum value is obtained through experiments for various printing patterns.

This third embodiment is an embodiment of the invention according to claim 3, and in the image forming apparatus according to claim 1, the heat generation drive signals A1, A2, B1, B2 are simultaneously driven for heat generation. A print dot number counter 145 as a counting means for counting the number of the heating elements to be heated. The counting means 14 generates energy for simultaneously driving the heating elements for each of the heating control signals A1, A2, B1, and B2.
On the basis of the count value of 5, the number of heating elements that are simultaneously driven by one heating control signal and the number of heating elements that are simultaneously driven by a heating control signal other than the one heating control signal in a block including this heating element. The number of printing dots (printing rate) corresponding to the number of heating elements driven simultaneously for each heating control signal for each heating control signal, and other heating controls in the same block. An optimum image can be formed even if the number of printing dots (printing rate) of the heating element rows of the other groups corresponding to the signals are different.

Next, the fourth to sixth embodiments of the present invention will be described. In the fourth to sixth embodiments, the heating elements of the thermal head are divided as described below in the first to third embodiments, respectively. In the fourth to sixth embodiments, the heating element array 13 provided in the thermal head 91 at the position of the heating element number of the total number of heating elements / 2 by the two-division driving method as the division driving method of the thermal head 91.
Instead of dividing 0 into two, as shown in FIG. 17, a heating element row 130 including a plurality of heating elements arranged in a line in the main scanning direction provided in the thermal head 91 is blocked near both ends and near the center. 130C and 130D are made independent.

That is, in the thermal head 91,
The heating element corresponding to the heating element number 1 is the heating element at the left end in FIG. 17, and the heating element corresponding to the final heating element number is FIG.
7 is the rightmost heating element. Thermal head 91
Is the total number of heating elements Rn: 4608 dots, and is a boundary between the location of the heating element number 1 from the heating element number 1 of the thermal head 91 and the location of 3 × the total heating element number Rn / 4. 1 to 1152 and heating element numbers 3457 to 4
Block 13 on both ends of thermal head 91 up to 608
0C, and the heating element numbers 1153 to 3456 at other positions (near the center) of the thermal head 91 are set as a block 130D. Heating element row 13 of thermal head 91
0 is divided into, for example, two groups for each of the blocks 130C and 130D, that is, the heating elements of the heating element numbers 1 to 1152 are the heating elements of the group, and the heating elements of the heating element numbers 1153 to 2304 are the groups. And the heating elements of heating element numbers 2305 to 3456 are the heating elements of the group, and heating element numbers 3457 to 460.
The heating elements up to 8 are the heating elements of the group. Also,
As in the first to third embodiments, a plurality of heat control signals A1, A2, B1, and B2 for driving the heat generators for each group are provided. The control signal A1, A2, B1, and B2 are driven to generate heat with unique energy for each group (each group).

The fourth to sixth embodiments are one embodiment of the invention according to claim 4 of the present invention.
4. The image forming apparatus according to claim 1, wherein the block is one block in a main scanning direction of the thermal head 91. 5.
Heating element array 13 including the plurality of heating elements arranged in a row
Since the heating elements near the center and the heating elements near both ends at 0 are formed as independent blocks 130D and 130C, the quality of the formed image can be made uniform using a miniaturized thermal head, and the thermal head Higher manufacturing efficiency can be achieved with miniaturization, and thermal heads can be made inexpensive and reflected in product prices.Moreover, with the miniaturization of thermal heads, the amount of materials used can be reduced. More environmentally friendly.

In the above-described fourth to sixth embodiments, the heating elements of the thermal head are divided into blocks near the both ends and near the center of the thermal head, but the print image quality is further improved. As a measure, the number of divisions can be further increased in the above-described fourth to sixth embodiments. This means that increasing the number of divisions means that the number of heating elements in the block decreases, and the voltage at the above-mentioned common electrode due to the location of the heating elements generated in each group in the block. This is because the influence of (power) loss is reduced. The reason is that
This is because the energy value for perforation can be adjusted in more detail by reducing the value of the current flowing through the common electrode and increasing the number of divisions of the heating element. In addition, as a division method at that time, the number of heating elements does not have to be the same in each block, and the number of heating elements is divided by an optimum number in consideration of the influence of voltage (power) loss at the common electrode. No problem.

Next, the seventh to ninth embodiments of the present invention will be described. In the seventh to ninth embodiments, the heating element rows of the thermal head in the first to third embodiments are divided as follows. In the seventh to ninth embodiments, the heating element array 130 including a plurality of heating elements arranged in a line in the main scanning direction of the thermal head 91 is used.
Is divided into a plurality of blocks, the total number of heating elements Rn / the number Nb of the blocks is a positive integer, and the value of Nb is an even number of 4 or more. It is assumed that the allowable number of heating elements Rn is different. Further, similarly to the first to third embodiments, the heating element is divided into a plurality of groups for each block, and a plurality of heating controls for driving the heating for each of the divided heating elements. A signal is provided, and each heating element is driven to generate heat with unique energy for each heat generation control signal (for each group).

The seventh to ninth embodiments are one embodiment of the invention according to claim 5 of the present invention.
4. The image forming apparatus according to claim 1, wherein the block has a total number Rn of the heating elements / a number Nb of the blocks as a positive integer, and a value of Nb as an even number of 4 or more. Since the division is not limited to equal division, the number of heating elements allowed for each block is assumed to be different, so that any image can be formed by forming an appropriate image according to the resolution in the main scanning direction and sub-scanning direction. It is possible to form an optimal formed image with less unevenness in formed image density, and at the same time, to achieve higher efficiency in manufacturing with downsizing of the thermal head, which is reflected in the price of the product by making the thermal head cheaper In addition, the size of the thermal head can be reduced, and the amount of materials used can be reduced, thereby making the thermal head more environmentally friendly.

Next, the tenth embodiment to the first embodiment of the present invention will be described.
A second embodiment will be described. The tenth to twelfth embodiments correspond to the seventh to ninth embodiments.
In each of the embodiments, the heating element array of the thermal head is divided as follows. In the tenth to twelfth embodiments, the heating element row 130 is divided into a plurality of blocks at the location of the heating element number divided at the interval of Rn / Nb or in the vicinity of the location, and Rn / 2
Or a location in the vicinity thereof is defined as a boundary, and a combination of the above-described heating elements for each block symmetrical with respect to this boundary is defined as a heating element of each block. Note that, similarly to the seventh to ninth embodiments, the heating element is divided into a plurality of groups for each block, and a plurality of heating controls for driving the heating for each of the divided heating elements. A signal is provided, and each heating element is driven to generate heat with unique energy for each heat generation control signal (for each group).

The tenth to twelfth embodiments are one embodiment of the invention according to claim 6, and in the image forming apparatus according to claim 5, the heat generation divided at an interval of Rn / Nb. The heating element is divided into a plurality of blocks at the location of the body number or in the vicinity of the location, and the location of Rn / 2 or the location in the vicinity thereof is used as a boundary. Since one block is used, it is possible to form an appropriate image in accordance with the resolution in the main scanning direction and the sub-scanning direction, and to form an optimum formed image with less formed image density unevenness for any image. Higher manufacturing efficiency can be achieved with miniaturization, and thermal heads can be made cheaper and reflected in product prices. It can be more environmentally friendly by reduces the amount of materials used, such as with the.

In the tenth to twelfth embodiments, the width and length of the common electrode 138 change depending on the position of the connector 119 of the thermal head 91,
30 and the heating element of each block is
Since the combination of the heating elements for each block in the left-right symmetry in 1 is used, it is not possible to suppress the variation in print image quality due to the plurality of heating elements arranged in a line in the main scanning direction of the thermal head 91. However, in the seventh to ninth embodiments,
In the embodiment, the heating element row 130 is not only divided equally but also the number of heating elements Rn allowed for each block is different, and the heating element row 130 has a unique drilling energy for each group of blocks. , And can be used for various thermal head specifications.

Therefore, in the thirteenth to fifteenth embodiments of the present invention, the heating elements of the thermal head are divided as described below in the first to third embodiments, respectively. Things. In the thirteenth to fifteenth embodiments, the heating element array 1 includes a plurality of heating elements arranged in a line in the main scanning direction of the thermal head 91.
30 is divided into a plurality of blocks, the total number of heating elements Rn / the number Nb of the blocks is a non-positive integer, and the value of Nb is an even or odd number. Instead, the division is made with a different number of heating elements allowed for each block. As in the first to third embodiments, the heating element is divided into a plurality of groups for each block, and a plurality of heating controls for driving the heating for each of the divided heating elements. Signal,
Each heating element is driven to generate heat with unique energy for each heating control signal (for each group).

The thirteenth to fifteenth embodiments are one embodiment of the invention according to claim 7, and in the image forming apparatus according to claim 1, 2, or 3, the total number of heating elements Rn The number Nb of the blocks is not a positive integer and the value of Nb is an even number or an odd number, and the division of the heating elements is not limited to a division close to equal division, and the number of heating elements permitted for each block is different. Since the image is divided, it is possible to form an appropriate image in accordance with the resolution in the main scanning direction and the sub-scanning direction and to form an optimum formed image with less formed image density unevenness for any image. With the miniaturization of thermal heads, higher efficiency in manufacturing can be achieved, and thermal heads can be made cheaper and reflected in product prices. It can be more environmentally friendly and can reduce the amount or the like.

Next, the sixteenth embodiment to the first embodiment of the present invention will be described.
Eighth embodiment will be described. In the sixteenth to eighteenth embodiments, the heating element rows of the thermal head in the thirteenth to fifteenth embodiments are divided as follows. In the sixteenth to eighteenth embodiments, the location of Rn / 2 or a location near the location is defined as a boundary, and a combination of heating elements for each block symmetrically from the boundary is determined as a heating element of each block. Note that, similarly to the thirteenth to fifteenth embodiments, the heating element is divided into a plurality of groups for each block, and a plurality of heating controls for driving the heating for each of the divided heating elements. A signal is provided, and each heating element is driven to generate heat with unique energy for each heat generation control signal (for each group).

The sixteenth to eighteenth embodiments are one embodiment of the invention according to claim 8, and in the image forming apparatus according to claim 7, the position of Rn / 2 or the vicinity thereof Is used as a boundary, and a combination of the heating elements for each block which is symmetrical with respect to the left and right is defined as one block. Therefore, an appropriate image is formed according to the resolution in the main scanning direction and the sub-scanning direction, and any image is formed. An optimal formed image with less density unevenness can be formed, and at the same time, high efficiency can be achieved in manufacturing due to downsizing of the thermal head. In addition, the size of the thermal head can be reduced and the amount of materials used can be reduced, and the environment can be made more environmentally friendly.

Further, the first to eighteenth embodiments are one embodiment of the invention according to claim 9, and are the image forming apparatus according to any one of claims 1 to 8, A thermal head 91 having a plurality of heating elements arranged in a line in the main scanning direction is brought into contact with a heat-sensitive stencil master having at least a thermoplastic resin film,
A stencil printing apparatus that relatively moves the heat-sensitive stencil master in the sub-scanning direction with respect to the plurality of heating elements, generates heat in accordance with an image signal, and forms an image on the heat-sensitive stencil master. Therefore, the effect of the voltage (power) loss at the common electrode due to the location of the heating element can be considerably reduced by using a miniaturized thermal head. Each of the perforations can be obtained independently and uniformly at any place of the plurality of heating elements arranged in a line in the main scanning direction of the thermal head. It is possible to form an optimal print image with less unevenness in print image density, regardless of the image to be made, by forming a perforated image. At the same time, excessive transfer of the ink to the printing paper can be reduced, and the occurrence of set-off peculiar to the plate-making printing apparatus can be prevented. In addition, the miniaturization of the thermal head can achieve higher efficiency in manufacturing, and the thermal head can be made cheaper and reflected in the price of the product. The amount and the like can be reduced, and a more environmentally friendly product can be provided.

In each of the above embodiments, two heat generation control signals are provided for the heat generating elements of each block which are driven to generate heat at the same time, and the optimum energy is applied to the heat generating elements for each heat control signal. However, if two or more heating control signals are provided for the heating element rows of each block that are driven to generate heat at the same time, and optimal energy is applied to the heating element for each heating control signal, Since the energy applied to the heating element can be controlled more precisely, the change in print density depending on the position of the thermal head heating element in the main scanning direction is smaller than in the above embodiment. Further, the present invention can be applied to an image forming apparatus other than the plate-making printing apparatus.

[0092]

As described above, according to the first aspect of the present invention, it is possible to form an optimal image even if the heating element has different positions in the main scanning direction. According to the second aspect of the present invention, an optimum image can be formed even if the heating element has a different position in the main scanning direction and a different printing rate in the main scanning direction.

According to the third aspect of the present invention, with the above-described structure, the heating element main scanning direction position, the printing rate of the heating element that is simultaneously driven for each heating control signal, and the other heating control signals in the same block are controlled. An optimum image can be formed even if the printing ratios of the heating element rows of other corresponding groups are different.

According to the fourth aspect of the present invention, with the above configuration, the quality of the formed image can be made uniform by using the downsized thermal head, and high efficiency in manufacturing can be achieved with downsizing of the thermal head. Can be reflected in the product price as a cheap thermal head,
Further, with the downsizing of the thermal head, the amount of materials used can be reduced, and the environment can be made more environmentally friendly.

According to the fifth to ninth aspects of the present invention, an optimum image is formed with less unevenness in the formed image density in any image by forming an appropriate image according to the resolution in the main scanning direction and the sub-scanning direction. Images can be formed, and at the same time, high efficiency in manufacturing can be achieved with the miniaturization of thermal heads, and thermal heads can be made inexpensive and reflected in product prices. With the miniaturization, the amount of materials used can be reduced and the environment can be made more environmentally friendly.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a part of an electrical system according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a heating element array of each block of the thermal head according to the first embodiment.

FIG. 3 is a diagram showing driving timings of the thermal head.

FIG. 4 is a diagram for explaining a resistance value of a common electrode according to a position of a heating element of the thermal head.

FIG. 5 is a cross-sectional view schematically illustrating the thermosensitive stencil printing apparatus according to the first embodiment.

FIG. 6 is a block diagram showing a part of an electrical system according to a second embodiment of the present invention.

FIG. 7 is a circuit diagram showing an electric circuit for driving a heating element of the thermal head to generate heat.

FIG. 8 is a diagram showing a position of a heating element of the thermal head and a state of voltage loss thereof.

FIG. 9 is a diagram showing a heating element array of each block of a conventional thermal head.

FIG. 10 is a timing chart showing driving timings of the thermal head.

FIG. 11 is a block diagram showing a circuit for driving the thermal head.

FIG. 12 is a front view schematically showing an example of a thermal head that is reduced in size by being narrower.

FIG. 13 is a sectional view showing the thermal head cut in a sub-scanning direction of the thin film substrate.

FIG. 14 is an enlarged schematic view showing a thin film substrate having a common electrode, a heating element, and a lead electrode of the thermal head.

FIG. 15 is a diagram showing a result of plate making and printing performed by a conventional technology using a copying machine using the thermal head.

FIG. 16 is a diagram showing the result of plate-making printing according to a third embodiment of the present invention in comparison with the prior art in the relationship between the position of the heating element of the thermal head in the main scanning direction and the print density.

FIG. 17 is a diagram illustrating a divided state of a row of heating elements of a thermal head according to a fourth embodiment to a sixth embodiment of the present invention.

[Explanation of symbols]

 91 Thermal head 130 Heating element array 130A, 130B Block A1, A2, B1, B2 Heating control signal 137 Drive IC array 138 Common electrode 140 Power supply 143 Heating control signal generating circuit 144 CPU 145 Print dot number counter

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hajime Kato 3 Shinmei-do, Shimada-cho, Shibata-cho, Shibata-gun, Miyagi 1 ・ Tohoku Ricoh Co., Ltd. No. 3 of Nakamei Ichimido Shinmei-do No.1, Tohoku Ricoh Co., Ltd. F-term (reference) 2C066 AA03 AB02 BC01 BC14 BC15 CF03 CF06 CF07 CF12 2H084 AA02 AA13

Claims (9)

[Claims] A plurality of heating elements arranged in one line in a main scanning direction of a thermal head are divided into a plurality of blocks, and the heating elements are simultaneously driven for each block in accordance with an image signal to be driven on a sheet. In an image forming apparatus for forming an image, a plurality of heat generation control signals are provided for driving the heat generation for each of the divided heating elements by dividing the heating element for each block simultaneously driven to generate heat into at least two or more, An image forming apparatus comprising: a driving unit that drives the heating element to generate heat with unique energy for each heat generation control signal. 2. An image forming apparatus according to claim 1, further comprising a counting means for counting the number of said heat generating elements which are driven to generate heat simultaneously for each heat generation control signal, wherein said heat generating elements are simultaneously heated for each heat generation control signal. An image forming apparatus, wherein the driving energy is determined by the count value of the counting means. 3. An image forming apparatus according to claim 1, further comprising a counting means for counting the number of said heat generating elements which are driven to generate heat simultaneously for each heat generation control signal, and wherein said heat generating elements are simultaneously heated for each heat generation control signal. Based on the count value of the counting means, the number of heating elements driven simultaneously by one heat control signal based on the count value of the counting means, and the heat control other than the one heat control signal in the block including this heat element. An image forming apparatus, wherein the number of heating elements is determined by the number of heating elements driven to generate heat simultaneously by a signal. 4. The image forming apparatus according to claim 1, wherein the block comprises a heating element near a central portion of the plurality of heating elements arranged in a line in a main scanning direction of the thermal head. An image forming apparatus, wherein heat generating elements near both ends are formed as independent blocks. 5. The image forming apparatus according to claim 1, wherein the number of the heating elements Rn / the number Nb of the blocks is a positive integer, and the value of the number Nb is an even number of 4 or more. The image forming apparatus is characterized in that the heating elements are not only divided equally but also divided into different numbers of heating elements per block. 6. The image forming apparatus according to claim 5, wherein R
The heating element is divided into blocks at or near the location of the heating element number divided at intervals of n / Nb, and Rn
An image forming apparatus, wherein a combination of the heating elements for each block symmetrical to the left and right from the boundary is defined as one block. 7. The image forming apparatus according to claim 1, 2 or 3, wherein the total number of heating elements Rn / the number of blocks Nb.
Is a non-positive integer, the value of Nb is an even number or an odd number, and the division of the heating elements is not only a division close to equal division but also a division in which the number of heating elements allowed in each block is different. An image forming apparatus comprising: 8. The image forming apparatus according to claim 7, wherein R
An image forming apparatus, wherein a boundary of n / 2 points or a point in the vicinity thereof is a boundary, and a combination of the heating elements for each block symmetrical from the boundary is one block. 9. An image forming apparatus according to claim 1, wherein a thermal head having a plurality of heating elements arranged in a line in the main scanning direction has at least a thermoplastic resin film. While being in contact with the stencil master, the heat-sensitive stencil master is relatively moved in the sub-scanning direction with respect to the plurality of heating elements, and the heating elements are caused to generate heat in accordance with an image signal to be applied to the heat-sensitive stencil master. An image forming apparatus comprising a plate-making printing apparatus for forming an image.