JPH0811365A - Head gap-regulating mechanism - Google Patents

Abstract

PURPOSE:To provide a head gap-regulating mechanism in which an obstacle of a printing form is reduced in a mechanism for performing head gap regulation by a platen having an eccentric shaft. CONSTITUTION:A platen 4 is constituted of an outer circumferential part 5 and a core part 6 and both parts 5, 6 are rotated for each other. A gear part is formed in the inside of the end part 5a of the outer circumferential part 5 and engaged with a gear 12 which is freely rotatably fitted to the core part 6. An eccentric shaft 8 is fixed to the core part 6 and a gear pulley 9 is loose- fitted to the eccentric shaft 8 and a gear pulley 10 is fixed thereto. Furthermore a slit disk 18 is fitted to the eccentric shaft 8. A gear part 11a engaged with the gear 12 is formed in the gear pulley 9 and rotated by a pulse motor 14. The gear pulley 10 is rotated by a pulse motor 16 and the eccentric shaft 8 is rotated. A slit sensor 20 for detecting the rotational amount of the eccentric shaft 8 is provided in the slit disk 18. Further a position sensor 22 is provided which detects the home position of the platen 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer that prints on printing papers having different thicknesses, or a printer that prints by stacking a plurality of papers. Head gap adjustment mechanism for holding the gap constant).

[0002]

2. Description of the Related Art Conventionally, as a mechanism for moving a platen to adjust a head gap, an eccentric shaft is provided on the platen, and by rotating the eccentric shaft, the platen is moved toward and away from a print head for adjustment. There is something like this. An example of this is disclosed in JP-A-55-118884.

[0003]

However, the above-mentioned prior art has the following problems. That is, since the above-mentioned conventional platen does not rotate, there is a possibility that a paper jam may occur due to friction between the platen and the paper when the paper is conveyed during the printing operation. Further, when the head gap is adjusted, since the platen is rotated around the eccentric shaft, there is a problem that the paper wound around the platen is displaced from the print head, and as a result, the print displacement occurs.

[0004]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is directed to a cylindrical platen outer peripheral portion which is arranged so as to face a print head and winds a print sheet, and slides inside the platen outer peripheral portion. A platen composed of a platen core part which is fitted so as to be fixed and has an eccentric shaft fixed thereto, a first drive part which rotates the eccentric shaft to rotate the platen, and a detection means for detecting a rotation amount of the platen. And a second drive unit for rotating the outer peripheral portion of the platen, wherein the first drive unit rotates the platen while the print sheet is wound around the platen, and the second drive unit causes the platen to rotate. The outer peripheral portion of the platen is rotated to bring the print sheet into contact with the print head, and then the first drive unit separates the platen by a predetermined amount.

[0005]

According to the present invention having the above-described structure, in a state in which the printing paper is wound around the platen, the first driving unit rotates the platen about the eccentric shaft in the direction of approaching the printing head. At this time, the outer peripheral portion of the platen is simultaneously rotated by the second drive unit so that the outer peripheral portion of the platen is not displaced with respect to the print head. When the print sheet comes into contact with the print head due to the rotation of the platen, the first drive unit rotates the platen about the eccentric shaft in the opposite direction to the above by a predetermined amount to separate the print sheet from the print head. The amount of rotation of the platen is controlled by the detection means. As a result, an appropriate head gap can be obtained. Further, during the printing operation, the outer peripheral portion of the platen rotates in the direction in which the printing paper is conveyed by the second driving unit.

[0006]

Embodiments of the present invention will be described in detail below with reference to the drawings. Note that elements common to the drawings are given the same reference numerals. 1 is a perspective view showing an embodiment according to the present invention,
FIG. 2 is an enlarged perspective view showing a main part of the embodiment.

1 and 2, a print head 1 for printing is mounted on a carriage 2, and the carriage 2 is slidably supported by a carriage shaft 3. The carriage 2 reciprocates along the carriage shaft 3 by a power source (not shown).

The platen 4 is disposed so as to face the print head 1, and is composed of a cylindrical outer peripheral portion 5 and a core portion 6 slidably fitted in the outer peripheral portion 5. The outer peripheral portion 5 is movable in the outer peripheral direction with respect to the core portion 6. The outer peripheral portion 5 is slightly longer than the core portion 6, and a tooth portion 7 is formed inside the end portion 5 a of the outer peripheral portion 5. An eccentric shaft 8 is fixed to an end portion 6a of the core portion 6, a gear pulley 9 is loosely fitted to the eccentric shaft 8, and a gear pulley 10 is fixed.

The gear pulley 9 has two tooth portions 11a, 1
1b is formed, and the gear 12 meshes with the tooth portion 11a. The gear 12 is rotatably attached to the core portion 6 and meshes with the tooth portion 7 of the platen outer peripheral portion 5. That is, gear 1
2 transmits the rotation of the gear pulley 9 to the platen outer peripheral portion 5. A toothed belt 13 is wound around the tooth portion 11 b of the gear pulley 9, and the toothed belt 13 transmits the rotation of the pulse motor 14 to the gear pulley 9. Eccentric shaft 8
The tooth portion 15 is formed on the gear pulley 10 fixed to
This tooth portion 15 and the motor pulley 16a of the pulse motor 16
The toothed belt 17 is wound between and. When the toothed belt 17 is rotated by the pulse motor 16, the eccentric shaft 8 rotates and the distance between the platen 4 and the print head 1 changes.

A circular slit disk 18 is fixed to the tip of the eccentric shaft 8. A plurality of slits 19 are formed circumferentially on the slit disk 18, and the slit sensor 20 detects these slits 19. A shield plate 21 is fixed on the slit disk 18 and rotates together with the slit disk 18. Shield portion 21a of the shield plate 21
The position sensor 22 is arranged at a position facing to. The position sensor 22 is an optical sensor and is attached to a device frame (not shown). The eccentric shaft 8 is rotatably supported by a frame (not shown).

FIG. 3 is a side sectional view showing the main part of this embodiment. In the figure, point P indicates the center of the core portion 6, and is displaced from the center of the eccentric shaft 8 by a distance a. Platen 4
Pressing rollers 23 and 24 are disposed on the upper part of the sheet, and the print sheet 25 is pressed by springs 26 and 27 so that the sheet 25 can be conveyed.

FIG. 4 is a block diagram showing the control system of this embodiment. In the figure, a control unit 31 controls the entire operation of the head gap adjusting mechanism of the present embodiment, and comprises a microprocessor or the like. The slit sensor 20 and the position sensor 22 are connected to the control unit 31 and receive these signals. A drive circuit 32 and a storage unit 33 are connected to the control unit 31, and the drive circuit 32 drives the pulse motors 14 and 16 described above. The storage unit 33 stores in advance a predetermined number of pulses for rotating the pulse motor 16 by a predetermined amount when the head gap is adjusted.

Next, the head gap adjusting operation of this embodiment will be described. First, the platen 4 is retracted to the position farthest from the print head 1 by rotating the eccentric shaft 8 by the pulse motor 16. The position farthest from the print head 1 is set so that the shield plate 21 is at the position detected by the position sensor 22. In this state, the printing paper 25 is pressed by the pressing rollers 23 and 24 and is transported to the printing unit (between the print head 1 and the platen 4) by a transporting device (not shown). At this time, the pulse motor 14 is rotated so that the platen outer peripheral portion 5 is rotated in the same direction as the conveyance direction of the sheet 25 and at the same speed as the conveyance speed of the sheet 25. As a result, the paper 25 is conveyed to the printing unit without causing a jam.

Next, the controller 31 rotates the pulse motor 16 so that the platen 4 approaches the print head 1. In FIG. 3, when the pulse motor 16 is rotated, the eccentric shaft 8 rotates in the counterclockwise direction, and the platen core portion 6 rotates about the eccentric shaft 8 in the counterclockwise direction. As a result, the platen 4 approaches the print head 1 with the paper 25 being wound. At this time, the pulse motor 14 is simultaneously rotated, and the platen outer peripheral portion 5 is rotated in the clockwise direction in FIG. 3 via the gear pulley 9 and the gear 12. The rotation speed of the pulse motor 14 is set to a speed at which the positional deviation of the print paper 25 with respect to the print head 1 due to the rotation of the platen 4 is returned. Therefore, the rotation of the pulse motor 14 does not cause the paper 25 to be displaced relative to the print head 1. If the pulse motor 14 is not rotated, the paper 25 will be the pressing rollers 23, 24 shown in FIG.
This may cause twisting, scratches and stains.

When the platen 4 comes into pressure contact with the tip of the print head 1 via the paper 25, the pulse motor 16 loses synchronization and the eccentric shaft 8 stops rotating. Slit disk 1 at the same time
8 also stops, and this stop is detected by the slit sensor 20. In response to the detection signal from the slit sensor 20, the control unit 31 stops driving the pulse motor 16 and then rotates the pulse motor 16 in the clockwise direction in FIG. 3 by a predetermined amount to rotate the platen 4 in the clockwise direction. It is rotated and separated from the print head 1. At this time, the control unit 31 reads out the data of the predetermined number of pulses stored from the storage unit 33, rotates the pulse motor 16 based on this data, and stops the pulse motor 16. That is, the number of pulses output from the slit sensor 20 is counted by the rotation of the pulse motor 16, and the pulse motor 16 is stopped when the count value reaches the read number of pulses. As a result, the platen 4 is separated from the print head 1 by a predetermined distance, and the print head 1 and the printing paper 25
The gap between and becomes the optimal distance.

After the pulse motor 16 is stopped, the control unit 31 applies a holding current to each phase of the pulse motor 16 to hold the position of the platen 4. Printing is performed on the printing paper 25 in this state. When printing, the sheet 25 is conveyed, but the platen outer peripheral portion 5 is rotated by the pulse motor 14 in the same direction as the sheet 25 is conveyed. As a result, the resistance of the platen 4 with respect to the paper 25 is reduced, and the possibility that the paper 25 is jammed or the like is reduced.

In the above-described embodiment, in the head gap adjusting operation, when the platen 4 approaches the print head 1 while the paper 25 is wound, the platen outer peripheral portion 5 is rotated and abuts on the print head 1. When the platen 4 is separated, the platen outer peripheral part 5 does not rotate, but since the rotation distance of the platen 4 after contact is shorter than the rotation distance of the platen 4 before contact, the platen outer peripheral part 5 is rotated. Even if it does not, the positional deviation of the printing paper 25 is extremely small. However, the platen outer peripheral portion 5 may be rotated even when the platen 4 is rotated after the contact.

[0018]

As described above in detail, according to the present invention, the platen is divided into the outer peripheral portion and the core portion so that they can be separately driven, and only the outer peripheral portion is rotated when the printing paper is conveyed in the printing operation. As a result, the resistance to the paper is reduced, and jams and other obstacles can be reduced. Also,
In the head gap adjustment operation, when the platen approaches the print head while the paper is wound, the outer periphery of the platen is rotated, so that the print position is not displaced and the paper is not scratched or dirty. it can.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment according to the present invention.

FIG. 2 is an enlarged perspective view showing a main part of the embodiment.

FIG. 3 is a side sectional view showing a main part of the embodiment.

FIG. 4 is a block diagram showing a control system of the embodiment.

[Explanation of symbols] 1 print head 4 platen 5 platen outer peripheral portion 6 platen core portion 7 tooth portion 8 eccentric shaft 14 pulse motor 16 pulse motor 18 slit disk 20 slit sensor 22 position sensor 31 controller

Claims (3)

[Claims] 1. A cylindrical platen outer peripheral portion that is arranged to face a print head and winds a print sheet, and a platen core portion that is slidably fitted inside the platen outer peripheral portion and has an eccentric shaft fixed thereto. A configured platen, a first drive unit that rotates an eccentric shaft to rotate the platen, a detection unit that detects a rotation amount of the platen, and a second drive unit that rotates the platen outer peripheral portion. Is provided, the platen is rotated by the first drive section while the print sheet is wound around the platen, and the outer peripheral section of the platen is rotated by the second drive section to bring the print sheet into contact with the print head. The head gap adjusting mechanism is characterized in that the platen is then separated by a predetermined amount by the first driving unit. 2. The head gap adjusting mechanism according to claim 1, wherein the position of the platen after the head gap adjustment is held by the first drive unit. 3. The second drive unit is formed inside the outer peripheral portion of the platen, a motor, a gear pulley loosely fitted to the eccentric shaft, a transmission member for transmitting the rotation of the motor to the gear pulley, and The head gap adjusting mechanism according to claim 1 or 2, further comprising a tooth portion that receives rotation from a gear pulley.