JPH03182369A - Line thermal printer - Google Patents

Abstract

PURPOSE:To use components in common as much as possible for different printing densities of dots by fixing the relative axial center of a plurality of transmission gears, making the gear ratio variable, and adjusting the feeding pitch of a recording paper to a desired density standard. CONSTITUTION:The reduction gear ratio of a transmission gear array 13 is determined by setting the gear ratio between a second transmission gear 25 and a third transmission gear 26 properly. In other words, a desired feeding pitch is obtained by transmitting the rotational movement of a step motor with a fixed stepping rotary angle to a platen roller with a predetermined reduction gear ratio. A motor frame 14 is provided with a bearing member 28 for supporting coaxial gears 26, 27 in a changeable manner. Moreover, a bearing member 29 is mounted to support different coaxial gears 24, 25 in a changeable manner. The distance between the two bearing members 28 and 29 is kept constant. Therefore, when coaxial gears with different number of teeth are properly changed, a desired gear ratio is obtained. Accordingly, the motor frame 14 can be used in common irrespective of the printing density of dots in the feeding direction of a recording paper.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a small-sized line thermal printer, and particularly to a mechanism for adjusting print dot density in the recording paper feeding direction.

[Conventional technology]

Traditionally, recording paper width standards (60 mm, 80 mm.

112mm, etc.), a platen roller unit arranged on the frame unit along the width direction to feed the recording paper at a desired pitch in the length direction, and a platen roller unit connected to the platen roller unit. A small-sized line thermal printer has been known which is composed of a drive unit for rotationally driving the printer. In this type of small line thermal printer, it is necessary to change the rotation pitch of the platen roller unit in order to select the printing dot density in the recording paper feeding direction. The rotation pitch of this platen roller unit is controlled by a drive unit connected thereto. This drive unit consisted of a step motor that generated rotational power, a wheel train consisting of multiple gears to transmit the power to the platen roller unit, and a motor frame on which the step motor and wheel train were mounted. .

[Problem that the invention seeks to solve]

However, in conventional drive units, the number of teeth and shaft positions of multiple gears are set according to a specific printing dot density (6 dots, 8 dots, 12 dots, 16 dots, etc. per unit), and therefore the motor frame had to be a special part depending on the specific dot density. As described above, conventional drive units have the problem that the component parts such as gears and motor units cannot be used in common for different dot densities, which hinders mass production.

[Means for solving problems]

In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide a compact line thermal printer with a drive unit structure that allows parts to be shared as much as possible even for different printing dot densities.

In order to achieve the above object, in the small line thermal printer according to the present invention, the platen roller unit has a drive gear fixed to one end in the axial direction, and the drive unit has a step motor that rotates in steps at a constant angle. , has a power gear fixed to the rotating shaft of the step motor, and a train consisting of a plurality of transmission gears for connecting the power gear and the drive gear of the platen roller unit, and has a relative relationship between the plurality of transmission gears. By fixing the shaft center position and making the gear ratio variable, the feeding pitch of the recording paper is made to match the desired dot density standard.

Preferably, the gear train includes a first transmission gear directly engaged with the power gear, a second transmission gear coaxially fixed to the first transmission gear, and a second transmission gear connected to the second transmission gear. a third transmission gear in direct engagement; a fourth transmission gear coaxially fixed to the third transmission gear and in engagement with the drive gear; By making only the gear ratio between the three transmission gears variable, the desired recording paper feed pitch is set. More preferably, the drive unit has a motor frame that is separably fixed to the outer side surface of the printer frame in the width direction, and this motor frame is equipped with a step motor and rotatably supports a plurality of transmission gears in a replaceable manner. It is equipped with the following members.

[For production]

According to the present invention, the recording paper feeding pitch is set to a desired standard by fixing the relative axial center positions of the plurality of transmission gears and making only the gear ratio variable.

Therefore, the motor frame on which the step motor and the plurality of transmission gears are mounted can have the same shape regardless of the printing dot density standard, making it possible to share parts. Furthermore, the gear ratio can be easily set to a desired value by simply replacing the gear in the bearing portion of the motor frame, which changes the number of teeth in accordance with a specific printing dot density.

〔Example〕

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a front view of a small line thermal printer according to the present invention. As shown in the figure, the line thermal printer has a frame unit having a size and shape conforming to the width standard of recording paper. The frame unit consists of a pair of side frames 1 and 2 that are spaced apart from each other in the width direction of the recording paper, a paper feed guide frame 3 that is held between the side frames, and a frame that is installed across the side frames. It consists of a shaft 4. A platen roller unit 5 is arranged in the frame unit along the width direction in order to feed the recording paper in the length direction at a desired feeding pitch. The platen roller unit 5 includes a rotating shaft 6, a platen roller 7 formed around the rotating shaft, a drive gear 8 coaxially fixed to one end of the rotating shaft, and a rotating shaft 6.
A head-up lever 9 is slidably fixed to the other end. A drive unit 10 for rotationally driving the platen roller unit 5 is connected. The drive unit IO includes a step motor 11 that rotates at a constant step rotation angle, and a transmission gear train 13 that transmits the step rotation motion of the step motor 11 to the drive gear 8 of the platen roller unit 5 at a desired reduction ratio. It is composed of a motor frame I4 on which a step motor 11 and a transmission gear train 13 are mounted. The motor frame 14 is detachably attached to the side frame 1.

A thermal head unit 15 is arranged opposite to the platen roller unit 5. The thermal head unit 15 is rotatably supported on the frame shaft 4 so as to be detachable and swingable. Furthermore, thermal head unit 1
Head force/(-16 is attached to cover 5.

The head cover 16 is rotatably secured to the same frame shaft 4.

FIG. 2 is a right side view of the line thermal printer shown in FIG. 1. As shown, the thermal head unit 15
is rotatably supported on the frame shaft 4, and the head cover 16 is also rotatably supported on the frame shaft 4. Thermal head unit I5 and head cover 1
6 are interlocked with each other, and when the head cover 16 is rotated in the opening direction and opened, the thermal head unit 15 is also retracted from the platen roller unit 5, and its heating element is exposed.

FIG. 3 is a sectional view of the line thermal printer taken along line A--A shown in FIG. As shown, a paper feed guide frame 3 is fixed between one side frame 2 and the other side frame 1 (not shown). A U-shaped notch is formed approximately at the center of the side frame 2, and a U-shaped bearing notch is similarly formed at approximately the center of the other side frame 1.

The platen roller unit 5 is inserted into the pair of bearing notches at both ends of its rotating shaft and is removably supported. At the rear part of the platen roller unit 5, a recording paper curl bath (indicated by arrow C) is defined by the first guide surface 17 of the paper feed guide frame 3. , the second guide i1[1j1B of the paper feed guide frame 3 defines a straight bus (indicated by arrow S) of the recording paper.

A thermal head unit 15 is arranged so as to be in pressure contact with the platen roller unit 5, and a recording paper discharge bus (indicated by an arrow) is formed above the platen roller unit 5.

The recording paper is selectively supplied to the platen roller unit 5 through a curl bath or a straight bath according to the shape, material, thickness, etc. of the recording paper. The supplied recording paper is held between the platen roller unit 5 and the thermal head unit 15 and pressure is applied thereto. In other words, the thermal head unit 15 is urged against the platen roller unit 5 in the pressed state. In this state, when the platen roller unit 5 is rotated at a predetermined step rotation angle (indicated by arrow R), the recording paper is intermittently fed at a corresponding predetermined pitch, and the thermal head unit 15 is energized in synchronization with this pitch. Line printing is executed by doing this. The recording paper fed at a predetermined paper feeding pitch is finally ejected to the outside through an ejection bus D. By adjusting the step rotation angle of the platen roller unit 5 in this manner, the paper feeding pitch of the recording paper can be set to a desired standard.

FIG. 4 is a schematic diagram of a recording paper feeding mechanism that constitutes the essential part of the present invention. The structure and operation of the recording paper feeding mechanism will be explained in detail with reference to FIG. As described above, the recording paper feeding mechanism is composed of the platen roller unit 5 and the drive unit 10. The platen roller unit 5 includes a rotating shaft 6, a platen roller 7 formed around the rotating shaft, a driving gear 8 fixed coaxially to one end of the rotating shaft 6, and a sliding gear attached to the other end of the rotating shaft. It is composed of a head up lever 9 that is coaxially locked. The platen roller unit 5 is pivotally supported at both ends of the rotating shaft 6 by a pair of side frames 1 and 2, which are arranged opposite to each other, via bearings 19 and 20. In this embodiment, the platen roller 7
The effective outer diameter φD of is set to 14.324 mm.

Next, the drive unit 10 includes a step motor 1, a power gear 12 fixed to the rotating shaft 21 of the step motor 1, and a drive gear 8 that decelerates the step rotation of the step motor 1.
It consists of a transmission gear train 13 for transmitting data to the motor, and a motor frame 14 for mounting these components. In this embodiment, the step angle θ of the step motor 1 is set to 15 degrees. That is, the step motor 1 performs step rotation every 15 degrees.

The motor frame 14 has a positioning hole 2 having a predetermined inner diameter.
2, and the step motor 1 is equipped with a bearing 23 having an outer diameter matching the inner diameter of the positioning hole 22. By fitting this bearing 23 into the positioning hole 22, the step motor 1 is positioned. Further, the outer diameter of the power gear 12 fixed to the rotating shaft 21 of the step motor 1 is set smaller than the inner diameter of the positioning hole 22. With this structure, the power gear 12 can be inserted through the positioning hole 22, and the step motor 1 can be easily positioned and assembled into the motor frame 14.

The transmission gear train 13 includes a first transmission gear 24 that is directly engaged with the power gear 12, a second transmission gear 25 that is coaxially fixed to the first transmission gear 24, and a second transmission gear 25 that is coaxially fixed to the first transmission gear 24. a third transmission gear 26 that is directly engaged with the transmission gear 25; and a fourth transmission gear that is coaxially fixed to the third transmission gear 26 and engaged with the drive gear 8. It consists of 27. In this embodiment, the reduction ratio G of the transmission gear train 13 is determined by appropriately setting the gear ratio between the second transmission gear 25 and the third transmission gear 26. In other words, the constant step rotation angle θm of the step motor
The desired paper feeding pitch P is obtained by transmitting the rotational motion of the paper to the platen roller at a predetermined reduction ratio.

A bearing member 28 is mounted on the motor frame 14 for exchangeably supporting the coaxial gears 26 and 27, and a bearing member 29 is installed for exchangeably supporting the other coaxial gears 24 and 25. It is planted. According to the present invention, the distance between the two bearing members 28 and 29 is kept constant, and a desired gear ratio can be obtained simply by appropriately replacing coaxial gears with different numbers of teeth. . Therefore, the motor frame L4 can be used in common regardless of the print dot density in the recording paper feeding direction.

In this embodiment, the printing dot density in the recording paper feeding direction can be selectively set in four ways: 6 dots per mm, 8 dots, 12 dots, and 16 dots per mm. This selection is based on the platen effective outer diameter φD1 power gear I2
without changing the number of teeth 2 degrees, the number Z of the first transmission gear 24, the number 24 of teeth of the fourth transmission gear 27, and the number of teeth 25 of the drive gear 8 fixed to the platen roller unit. The number of teeth of the second transmission gear 25 is 2 and the third transmission gear 26
By changing only the number of teeth 23, the actual reduction ratio G' can be appropriately set, and a paper feed pitch P that provides the selected print dot density can be realized.

Parameters such as the optimum number of teeth obtained in this example are shown below as a table.

In the table above, the calculated reduction ratio Gr is the following relational expression It is determined by (1).

G-θ Platen equivalent to 7 paper feed pitch
The rotation angle of the roller or the actual reduction ratio G' is determined by the following relational expression (2).Furthermore, the distance between the shafts of each gear is determined by the following expression (3).

However, M is a gear module.

In the above table, the calculated reduction ratio G 1 indicates the ideal reduction ratio calculated according to relational expression (1). Further, the actual reduction ratio G' is determined by the relational expression (2), and is an actual reduction ratio determined by the actually set number of teeth 2 to z5. As is clear from the table, the actual reduction ratio G relative to the calculated reduction ratio G
The error of ゛ is less than 1% r
r and does not affect print quality. When the printing dot density is 66 pm, the number of teeth 22 is 30 and the number of teeth 23 is 44. Print dot density is 8clp*
In this case, the number of teeth Z is 25 and the number of teeth 23 is 49. When the printing dot density is 12 dpm, the number of teeth 22 is 1.
9, and the number of teeth 23 is 55. Also, the printing dot density is 1
In the case of 6dpm, the number of teeth 22 is 15 and the number of teeth 23 is 5.
It is 9. In either case, the total number of teeth 22 and 23 is 74. Therefore, as is clear from relational expression (3), the distance between the axes of the second transmission gear 25 and the third transmission gear 2B is always constant. Therefore, the distance between the pair of bearing members 28 and 29 mounted on the motor frame t4 is always constant. This shows that the motor frame 14 can be used in common regardless of the printing dot density standard. By the way, as is clear from relational expression (3), in order to set the distance between the shafts of each gear, it is necessary to determine the module of the gear. In this example, module M is 0
．． It is set within the range of 2 to 0.5. When the module M is smaller than 0.2, the strength of each gear is not sufficient and the processing accuracy is also poor. Also, module M is 0.5
If the above setting is made, the overall size of the drive unit becomes too large and is not suitable for a small line thermal printer.

〔Effect of the invention〕

As described above, according to the present invention, a predetermined printing dot density can be set simply by changing the relative gear ratio of a pair of transmission gears, and the dimensions and shape of the motor frame can be set according to the dot density standard. There is no need to dedicate each
This makes it possible to share parts, which has the effect of mass production.

That is, according to the present invention, the outer diameter of the platen roller and the number of teeth of the drive gear can be kept constant regardless of the standard of printing dot density, and the step angle of the step motor and the number of teeth of the power gear can be kept constant. In addition, since the axial center distance between each gear can be made constant, a large number of parts can be used for multiple purposes.

[Brief explanation of drawings]

FIG. 1 is a front view of a line thermal printer according to the present invention, FIG. 2 is a side view of the line thermal printer, and FIG. 3 is a line cut along line A-A shown in FIG. 4 is a sectional view of the thermal printer, and FIG. 4 is a schematic diagram of a recording paper feeding mechanism built into the line thermal printer. 1... Side frame 2... Side frame 3... Paper feed guide frame 5... Platen roller unit 6... Rotating shaft 7... Platen roller 8... Drive gear 1O... Drive Unit 11...Step motor 12...Power gear I
3...Transmission gear train 24...First transmission gear 25...Second transmission gear 2G...Third transmission gear 27...Fourth transmission gear ゝ-\Q

Claims (1)

[Claims] 1. A frame unit having dimensions matching the width direction of recording paper, and a platen arranged on the frame unit along the width direction to feed the recording paper at a desired pitch in the length direction. In a line thermal printer including a roller unit and a drive unit connected to the platen roller unit for rotational driving, the platen roller unit has a drive gear fixed to one end in the width direction, and the drive unit rotates at a certain angle. It has a step motor that rotates step by step, a power gear fixed to the rotating shaft of the step motor, and a train consisting of a plurality of transmission gears for connecting the power gear and the drive gear of the platen roller unit. A line thermal printer characterized by fixing the relative axial center positions of a plurality of transmission gears and making the gear ratio variable to set the recording paper feeding pitch to a desired standard. 2. The gear train includes a first transmission gear that is directly engaged with the power gear, a second transmission gear that is coaxially fixed to the first transmission gear, and a second transmission gear that is coaxially fixed to the first transmission gear. a third transmission gear in direct engagement; a fourth transmission gear coaxially fixed to the third transmission gear and in engagement with the drive gear; The line thermal printer according to claim 1, characterized in that the gear ratio between the three transmission gears is variable. 3. The drive unit has a motor frame that is separably fixed to the outer side surface in the width direction of the frame unit, and the motor frame is equipped with a step motor and rotatably supports a plurality of transmission gears in a replaceable manner. 2. The line thermal printer according to claim 1, further comprising the following members. 4. The motor frame has a positioning hole with a predetermined inner diameter, and the step motor is equipped with a bearing having an outer diameter that matches the inner diameter of the positioning hole, and by installing the bearing in the positioning hole, the step motor 4. The line thermal printer according to claim 3, wherein the line thermal printer can be inserted by performing positioning and setting the outer diameter of the power gear fixed to the shaft of the step motor to be smaller than the inner diameter of the positioning hole. 6. The line thermal printer according to claim 1, wherein the gear module is set within a range of 0.2 to 0.5.