JPH02286372A - Thermal printer - Google Patents

Abstract

PURPOSE:To surely retain a paper and prevent the generation of the skew of the paper by a method wherein a pushing roller, pushing an ink sheet against a platen drum at a position before a printing position in the rotating direction of the drum, is provided while the pushing roller is extended all-over the width of the paper. CONSTITUTION:A paper 5 is pushed against a platen drum 1 by a pushing roller 8' through an ink sheet 16 near the printing position of the paper 5. The paper 5 is pushed against the platen drum 1 by the ink sheet 16 which receives a tension between the printing position and the pushing position of the pushing roller 8' and, therefore, the paper may be surely retained until the paper passes through the printing position. When printing on the paper is finished and the paper is discharged, a thermal head 6 and the pushing roller 8' are separated from the platen drum 1 after the tip end of the paper is pinched by a paper discharging roller 30 whereby operation to push the paper against the platen drum by the ink sheet 16 is released. In this case, the paper, pulled by the paper discharging roller in a high speed, may be prevented from being precluded to move by the thermal head and the ink sheet, which are pushing the paper.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a thermal printer, and more particularly to an ink sheet feeding mechanism of a thermal printer.

[Prior art]

It consists of a thermal head, a platen drum that wraps and clamps a sheet of paper, and an n-color sequential ink sheet,
2. Description of the Related Art A thermal transfer color printer that prints n colors while rotating a platen drum n times is conventionally known. In such a color printer, in order to obtain a good color image, it is necessary to improve the accuracy of dot positions so that the dot positions of each color ink coincide when printing is performed using an ink sheet in n color planes sequentially. In order to match the dot positions for each color, it is first necessary to prevent misalignment of the paper. An effective method for this purpose is to clamp the edges of the paper and print on the clamped paper on the platen drum. It was particularly effective in reducing skinny appearance.

However, since the paper is only clamped at the leading end by the platen drum, if the paper is rotated multiple times, it is inevitable that the adhesion of the paper to the platen drum will vary. Although it is required to match the dot positions of a plurality of color inks with even higher accuracy, this requirement cannot currently be met.

Although not known as a thermal printer that satisfies the above requirements and can obtain high dot position accuracy, the applicant has developed a paper that is placed in front of the thermal head in the rotational direction of the platen drum and that presses the paper against the platen drum. a presser member, a clamp claw provided on the platen drum for clamping an edge of the paper, a moving member provided on the paper presser member, and a cam member provided on the platen drum; The present invention has proposed a thermal printer in which the cam member cooperates with the movable moving member at a position where the clamp pawl passes the position of the paper press member to separate the paper press member from the path of the clamp pawl. .

By pressing the paper against the platen drum with a paper press roller, the paper is brought into close contact with the rotation of the platen drum, and the holding power of the paper by the platen drum is improved, making it possible to transfer without skinny and with less color shift. When the platen drum rotates and the trailing edge of the paper comes off the contact/separation member provided on the paper presser member, for example, the paper presser roller, the tension load on the paper between the thermal head and the paper presser roller changes. This causes variations in the rotational load of the platen drum, resulting in uneven pitch of printed dots.

Similarly, after the trailing edge of the paper is removed from the paper holding roller, the thermal 2nd drive loses its holding effect on the paper behind the printing position, causing problems such as skew and color misregistration.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a thermal printer that reliably holds paper on a platen drum and does not cause paper skew.

[Means to solve the problem]

The present invention solves the above problem by having a platen drum around which one page of paper to be printed is wrapped and clamped, and a thermal head disposed opposite to the platen drum with an ink sheet interposed therebetween. In a thermal printer that pressurizes and thermally transfers the paper with a head, a press roller is provided to press the ink sheet against the platen drum at a position on the platen drum before the printing position by the thermal head in the rotational direction, The problem was solved by a thermal printer characterized in that the pressing roller extends over the entire width of the paper.

[Effect]

According to the present invention, the paper is pressed against the platen drum by the presser roller via the ink sheet near the printing position. Since the paper is pressed against the platen drum by the ink sheet under tension between the printing position and the holding position by the pressure roller, the paper can be reliably held until it passes the printing position.

When printing is completed and the paper is to be ejected, after the paper ejection roller has pinched the leading edge of the paper, the thermal head and presser roller are separated from the platen drum, and the ink sheet releases the action of holding the paper against the platen drum. . This prevents the paper being pulled at high speed by the paper discharge roller from being held down by the thermal head and the ink sheet and prevented from moving.

〔Example〕

The structure and operation of the present invention will be explained in detail based on the embodiment shown in the drawings.

In FIG. 1, the platen roller 1 includes a winding transmission member 2,
For example, it is drivingly connected to a drive motor 3 by a timing belt, and is rotated in the direction of the arrow, for example, counterclockwise in the figure.

The platen drum 1 has clamp claws 4. At the home position A, the paper 5 to be printed is clamped at its leading end by the clamp claw 4 of the platen drum 1, wound around the platen drum 1, and rotated together with the platen drum 1.

While being rotated by the platen drum 1, the paper 5 passes through a printing position B by the thermal head 6 and is printed.

A paper pressing member 7 is provided at a position in front of the thermal head 6 in the direction of rotation of the copy paper 1 to bring the paper into close contact with the platen drum 1. The paper pressing member 7 supports and supports a sliding member 8, such as a roller that rotates in contact with the paper, or a member that slides in contact with the sheet, or an elastic plate-shaped member such as a metal leaf spring or a plastic leaf spring. A lever 10 is swingably supported by a shaft 9. The lever 10 is a sliding member 8
is swingable between an operating position in which the paper 5 is brought into close contact with the platen drum 1 and a non-operating position in which the paper 5 is separated from the platen drum 1 by a predetermined distance. An electromagnetic means 11, for example, TRAED, is connected to the end of the lever 10 opposite to the side that supports the sliding member 8, and the lever 10 is energized by the solenoid.
is moved and held in the inactive position. A spring 12 is engaged with the lever 10 near the connecting position of the solenoid 11, and provides a force for tilting the lever 10 to the operating position.

The thermal sludge is arranged so as to be tiltable up and down around a fulcrum 13, and an eccentric cam 1 whose arm 14 fixed to the thermal head 6 is fixed to the output shaft of a thermal head release motor 15
5', and is tilted up and down by the operation of the thermal head release motor 15 between the printing position shown by the solid line and the release position shown by the broken line in the figure. The ink sheet 16 is arranged so as to be in contact with the paper on the platen drum 1 at and before and after the printing position B on the platen drum 1 by the thermal head 6. The ink sheet 16 is sent out from the ink sheet roll 17, and is passed through the guide 18.
The platen drum 1 is guided by 19 at a predetermined position.
The winding roller 20 and the ink sheet winding roll 21 are brought into contact with the winding motor 22, are fed by the winding roller 20, and are wound around the ink sheet winding roll 21. A belt is wound around it, and the rotational driving force of the take-up motor 22 is transmitted.

The ink sheet 16 has a structure in which n color ink sheets each having a size of one page are successively connected to each other for color printing.

A discharge lever 24 is disposed for discharging the clamped leading edge of the paper from the platen drum l.
A presser roller 25 is supported at the tip of the platen roller 1, which contacts the platen roller 1 at a position slightly before the discharge position C in the rotational direction. The ejection lever 24 is supported at a fulcrum 26 so as to be tiltable up and down, and an ejection solenoid 27 is connected to apply a force to the ejection lever 24 in a direction that brings the presser roller 25 into contact with the platen drum 1 . A spring 28 is engaged with the ejection lever 24 so as to apply a force to the ejection lever 24 in a direction away from the ejection lever 24 .

While the paper clamped on the platen drum 1 is rotated the number of times corresponding to each color, the thermal head 6 thermally transfers the paper, and the leading edge of the paper after printing reaches the ejection point, and the ejection lever 24 is activated to eject the paper. When the presser roller 25 is in contact with the platen drum I, the solenoid 27 is activated.
The leading edge of the paper is unclamped and pushed up from the platen drum 1 by the operation of a mechanism that moves the clamp claw 4 provided on the platen drum 1. Thereafter, the leading edge of the paper 5 pushed up by the rotation of the platen drum 1 is guided by a discharge guide 29 and sent to a paper discharge tray by a paper discharge roller 30. As one of the mechanisms for moving the clamp claw provided on the platen drum l, a patent application filed in 1982 by the present applicant
There is something related to No.-278165.

A paper discharge roller 30, which feeds the paper discharged from the discharge position C, feeds the paper under pressure from a presser roller 31. A paper feed roller 32, which feeds paper from a paper feed section (not shown) to a home position A of a platen drum 1 during printing, feeds the paper in cooperation with a presser roller 33. The paper feed roller 32 and the paper discharge roller 30 are driven and connected to a paper feed motor 34 by a winding transmission member 35, such as a timing belt.

The sheet whose leading end is clamped by the clamp claw 4 in the home positive silane A is gradually wound around the platen drum 1 as the platen drum 1 rotates. When the portion clamped by the clamp claw 4 passes the position of the sliding member 8, the electromagnetic means 11, that is, the solenoid is deenergized, and the sliding member 8 presses the paper against the platen drum l by the force of the spring 12, and the paper is pushed against the platen drum. Closely adheres to 1. In this case the pressing force is set in the spring. Furthermore, the paper is printed by a thermal head. The platen drum 1 is rotated by a predetermined number of color inks, and at the printing position B, 0, for example, yellow, Y1, magenta, M, and cyan C are printed by four rotations.

When printing of all colors of black B is completed, the leading edge of the paper is separated from the platen drum 1 at the discharge position C and is discharged by the discharge guide 29. Although the position of the sliding member 8 is shown approximately 90° in front of the printing position B in the figure,
The most preferable condition is when the last line of printing for one page is still holding down the paper when printing is completed, and is at such a position that it is later removed from the paper. In reality, the printing area will be narrowed, so the position should be determined depending on the skew allowance, layout, etc.

The thermal head 6 is used in order to prevent the clamp claw 4 of the platen drum 1 from contacting and damaging it, and to allow the ink to advance to the flame-colored ink sheet after printing one color.
In addition, the thermal head release motor 15 is used for reasons such as eliminating paper running resistance when feeding and discharging paper for purposes other than printing.
The thermal head 6 is moved away from the platen drum 1 at a predetermined position on the platen drum 1 by the rotation of the thermal head 6 and the operation of the eccentric cam 15'.

During printing, the pressurizing force in the line direction of the thermal head 6 becomes unbalanced, causing a difference in the force or amount of movement of the paper, resulting in skew of the paper. Further, the tension in the width direction of the ink sheet 16 or the difference in the amount of movement caused by the tension causes paper skew. However, when the paper is pressed by the paper presser member 7 as described above, when the sliding member 8 of the paper presser member 7 is placed at the position 00 from the pressurizing point by the thermal head 6, the section of θ0 A force corresponding to the force causing the skew can be obtained by the holding force of the paper to the platen drum 1 at . When the pressing force by the sliding member 8 is P, the force holding the paper on the platen drum (
P + 11 I) Here, μm is the coefficient of friction between the paper and the platen roller.

In the case of color printing, the platen drum 1 rotates by the number of colors. At this time, the sliding member 8 of the paper pressing member 7 continues to be in contact with the surface of the platen roller 1. If this happens, each time the clamp claw 4 of the platen roller 1 passes, the clamp claw 4 will abut against the sliding member 8, and at least one of the clamp claw 4 and the sliding member 8 will be damaged. In order to solve this problem, cam members such as raised portions are provided at both ends of the platen roller l, such as the flange portions, although not shown in the drawings. This raised portion contacts a part of the collar provided at both ends of the paper pressing roller 8 which is a sliding member provided on the paper presser member 7, and the raised portion pushes up the collar, so that the paper presser roller 8 is a sliding member. The presser roller 8 is lifted from the platen roller 1 by a predetermined amount. The raised portion is formed so that the pressing roller 8 continues to be raised while the clamp claw 4 passes. In particular, if the raised portion is shaped to have a smooth rising and falling surface, there will be less shock to the paper when the presser roller 8 moves up and down, and the paper will be less likely to change its position.

When the paper 5 is ejected by operating the ejection lever 24, the thermal head 6 is moved to the release position, and the presser member 7 is moved to the release position.
to the inactive position.

As a result, even when the clamp claw 4 of the platen drum 1 moves from the discharge position C to the home position A and the platen drum 1 stops, the trailing edge of the paper is not pressurized by the presser member 8 or the thermal head 6. This prevents paper from becoming difficult to move. This eliminates the wasted time of rotating the platen drum 1 until the paper is completely ejected, shortens the time until the next paper is introduced, and furthermore, the paper is ejected at a speed higher than the circumferential speed of the platen drum 1. The rollers 30 make it possible to discharge the paper.

In the structure shown in Fig. 1, the paper 5 is rotated by the rotation of the platen drum 1.
When the trailing edge of the sheet comes off the holder roller 8, the change in the tension load of the paper between the thermal head 6 and the holder roller 8 or the rotational load change of the thermal head 6 causes, for example, the curve shown in FIG. ! This may cause dot pitch fluctuations as shown in IIA, or the holding effect of the holding roller 8 may be lost, resulting in skew as shown in curve A in FIG. 4, which may cause color misregistration.
As shown in FIG. 2, printing position B of the platen drum 10
An ink sheet pressing member having an ink sheet pressing collar 8' is arranged at a position closer to the front in the rotational direction of the platen drum 1 so as to press the ink sheet 16 against the platen drum 10. In addition to the sliding member 8 shown in FIG. 1, an ink sheet pressing roller 8' may also be provided, but the sliding member 8 and the ink sheet pressing roller 8
′ can also be used. FIG. 2 shows an example of dual use. Note that the parts common to FIG. 1 are omitted from the drawing and explanation.

The ink sheet pressing member includes an ink sheet pressing roller 8' extending over the entirety of the ink sheet 16, and a lever 10 that rotatably supports the ink sheet pressing roller 8' and can swing around a support shaft 9'. ′. The lever 10' is connected to an electromagnetic means 11', such as a solenoid, and when the solenoid is energized, the lever 10' rotates around the support shaft 9', and the ink sheet pressing roller 8'
is removed from the platen drum 1. Solenoid 11'
Spring 1 which pulls lever 10' in the direction opposite to the biasing force of
2' is engaged with the lever 10' and the solenoid 11' is deenergized, the lever 10' is rotated by the force of the spring 12' and the ink sheet pressing roller 8' is pressed against the ink sheet 1.
6 onto the platen drum 1. Lever lO', solenoid 11' and spring 12' are lever 1 of the paper pressing member.
o, solenoid 11. It is also possible to form the spring 12 without changing its arrangement.

When the ink sheet 16 is pulled out from the in-sheet roll I7, it is put on the ink sheet pressing roller 8' and is brought into close contact with the platen drum 1 in an arc shape along the surface of the platen drum 1 to the printing position B. After leaving the printing position B, the ink sheet passes through a guide 19 and is wound onto an ink sheet take-up roll 21.

Even if the trailing edge of the paper wound around the platen drum 1 passes the position of the ink sheet pressing roller 8' and is no longer pressed by the ink sheet pressing roller 8', the ink sheet pressing roller 8' is pressed against the platen drum 1. During this time, the paper is pressed against the platen drum 1 by the ink sheet 16, so that the paper is reliably pressed and held by the platen drum 1 until it passes the printing position B.

When the printing is finished and the paper is to be ejected, the thermal head 6 is moved to the release position shown by the broken line by the structural member shown in FIG. 1, and at the same time, the solenoid II' is energized.
The ink sheet pressing roller 8' is released from the platen drum 1. Since tension is applied to the ink sheet 16, the ink sheet 16 leaves the platen drum 1 while being wound around the ink sheet pressing roller 8', and the force pressing the paper against the platen drum 1 is removed. Therefore, even if the paper is fed at high speed under pressure from the paper ejection roller 30 and the presser roller 3I, the paper is smoothly ejected without being subjected to the restraining force of the thermal head 6 or the ink sheet 16 and the ink sheet presser roller 8'. can be done.

〔effect〕

According to the present invention, when the paper is transferred, the ink sheet is pressed against the platen drum by the ink sheet within a predetermined wrapping angle range from the printing position by the action of the ink sheet pressing roller, so that the paper is always pressed against the platen drum until it passes the printing position. The winding is maintained on the platen drum, and there is no change in load or reduction in holding force.

This makes it possible to reduce dot pitch fluctuations and skew.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the main parts of a thermal printer that is the premise of the present invention, FIG. 2 is a schematic explanatory diagram of the thermal printer according to the present invention, and FIG. 3 is a diagram showing the dot pitch fluctuation amount with respect to the line pitch in the sub-scanning direction. 4 are diagrams showing the skew amount with respect to the position in the sub-scanning direction. 1...Platen drum 4...Clamp claw 5...
J [6... Thermal spatula 8'... Ink sheet press roller 9'... Support shaft 10'... Lever 1'...
Electromagnetic means 16...Ink jet diagram 2

Claims (1)

[Scope of Claims] It has a platen drum around which one page of paper to be printed is wrapped and clamped, and a thermal head disposed opposite to the platen drum with an ink sheet interposed therebetween. In a thermal printer that pressurizes and thermally transfers paper, a press roller that presses the ink sheet against the platen drum is provided at a position before the printing position of the thermal head on the platen drum in the rotational direction, and the press roller presses the ink sheet against the platen drum. A thermal printer is characterized in that the width of the paper extends over the entire width of the paper.