JPH0517245Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention is applied, for example, to a fax printing device, etc., and is equipped with a platen roller and a thermal head that can approach and separate from the outer peripheral surface of the platen roller. This relates to thermal printers.

[Prior Art] A conventional thermal printer of this type has a configuration as shown in FIGS. 5a and 5b.

In the figure, 1 is a platen roller, 2 is a thermal head, 3 is a thermal head mounting plate, and 4 is a rotation support member that rotatably supports the base end of the thermal head mounting plate 3.
It is placed almost on the setting surface. 5 is an elastic member such as a spring that urges the thermal head 2 toward the outer peripheral surface of the platen roller 1; 6 is a stepping motor that rotationally drives the platen roller 1;
7 and 8 are pulleys, 9 is a timing belt,
The rotational driving force of the stepping motor 6 is transmitted to the platen roller 1. 10 is printing paper such as thermal paper.

In the thermal printer consisting of the above-mentioned components, the printing paper 10 is held between the thermal head 2 and the platen roller 1 under a constant pressure by the urging force of the elastic member 5, and the stepping motor 6 is driven to rotate. When the force is transmitted to the platen roller 1 via the pulleys 7 and 8 and the timing belt 9 and the platen roller 1 rotates, the print paper 10 is sequentially conveyed by friction and the thermal head 2 performs a predetermined print. Then, printing is terminated by a stop signal from a control circuit (not shown).

[Problems to be Solved by the Invention] In the conventional thermal printer configured as described above, when the printing paper 10 is not held between the platen roller 1 and the thermal head 2, the elastic member 5 Due to the biasing force, the thermal head mounting plate 3 is rotated in the Z direction in FIG. The platen roller 1 is directly pressed against the surface, and this pressing force causes the outer circumferential surface of the platen roller 1 to elastically deform in a linear manner, increasing the contact area between the thermal head 2 and the outer circumferential surface of the platen roller 1. As a result, the thermal head 2 and the outer circumferential surface of the platen roller 1 are The frictional force between the platen roller 1 and the print paper 10 becomes larger than that when the print paper 10 is sandwiched, and in order to resist such a large frictional force and reliably rotate the platen roller 1 at a predetermined speed, it is necessary to It is necessary to increase the driving torque of the stepping motor 6, which is disadvantageous in terms of cost. Also,
When setting the print paper 10, as mentioned above, since the frictional force between the thermal head 2 and the platen roller 1 is large, the print paper 10 is moved between the thermal head 2 and the platen roller 1 against the large frictional force. To insert the paper between them, it is necessary to provide an auxiliary roller 15 for forcibly feeding the print paper, as shown by the imaginary line in FIG. 5b.

Furthermore, as described above, the rotating force of the thermal head mounting plate 3 in the Z direction increases the pressing force on the outer peripheral surface of the platen roller 1, so the platen roller 1, which is made of an elastic body such as rubber,
The outer circumferential surface of the printer tends to plastically deform into a non-circular shape after long-term use, resulting in problems such as a gradual deterioration of print quality.

This idea was made to solve the above problems, and it is possible to reduce the driving torque required to rotate the platen roller when the printing paper is not sandwiched between the platen roller and the thermal head. An object of the present invention is to provide a thermal printer that can suppress plastic deformation of a platen roller as much as possible.

[Means for Solving the Problems] The thermal printer according to this invention enables the platen roller to be driven in forward and reverse directions, and when rotating in one direction, the thermal head is brought into contact with the outer peripheral surface of the platen roller, and when rotating in the opposite direction. In some cases, the thermal head is provided with a cam body that rotates the mounting plate in a direction to move the thermal head away from the platen roller, and a pair of rotation support members are provided on both sides above and below the extension of the tangent between the platen roller and the thermal head. The thermal head mounting plate is movably supported by being an upper rotation support member when the platen roller rotates in one direction, and by switching to a lower rotation support member when the platen roller rotates in the opposite direction. It is.

[Function] In this invention, when the platen roller is driven to rotate in the forward direction while the print paper is not sandwiched between the platen roller and the thermal head, the cam rotates in one direction in conjunction with this. The thermal head mounting plate is rotated by the body in a direction to bring the thermal head held therein into contact with the outer peripheral surface of the platen roller, and the thermal head is directly brought into contact with the outer peripheral surface of the platen roller by the biasing force of the elastic member. , and a large frictional force is generated between the two. At this time, the rotational support point that movably supports the base end of the thermal head mounting plate is an upper rotational support located above the contact point between the platen roller and the thermal head with reference to the setting surface of the thermal head. Since the thermal head mounting plate is constructed of members, as the platen roller is driven and rotated, a component force is generated on the tip side of the thermal head mounting plate in a direction away from the platen roller.

This component force increases proportionally as the above-mentioned frictional force increases, and acts to reduce the pressing force of the thermal head against the outer peripheral surface of the platen roller. This makes it possible to reduce the required drive torque for the platen roller when setting the print paper.

Furthermore, when the platen roller is driven in reverse at the end of printing, the rotational support point of the base end of the thermal head mounting plate will be located below the contact point between the platen roller and the thermal head with respect to the setting surface of the thermal head. Since it is constituted by the existing lower rotation support member, as the platen roller is driven to rotate, the thermal head mounting plate has a pressure force on the outer peripheral surface of the platen roller on the front end side of the thermal head mounting plate. A component force that reduces the pressure acts, and the torque required to reverse the platen roller can also be reduced. As the cam body rotates in the opposite direction in conjunction with the reverse rotation of the platen roller, the thermal head mounting plate is rotated in a direction that moves the thermal head held thereon away from the platen roller.
A thermal head is held apart from the outer peripheral surface of the platen roller. This makes it possible to prevent distortion of the platen roller due to the thermal head being left pressed against the outer peripheral surface of the platen roller due to the biasing force of the elastic member when printing is stopped.

[Example] Hereinafter, an example of this invention will be described based on the drawings.

1A and 1B are a front view and a side view of the thermal printer during printing, and FIGS. 2A and 2B are a front view and a side view of the thermal printer when the platen roller is reversed; In a, b and FIGS. 2a, b, the same constituent members as those of the conventional example shown in FIGS.

1 and 2, 11 is an eccentric cam body, and this cam body 11 is similar to that shown in FIGS. 3 and 4.
As clearly shown in the figure, the core 1 of the platen roller 1
On the outside of the clutch spring 12 wrapped around a,
A protrusion 11b is attached coaxially to the shaft 1A of the platen roller 1, and is located approximately 90 degrees out of phase with the eccentric portion 11a of the cam body 11.
is installed protrudingly. Reference numeral 3a denotes a hook formed near the tip of the lower side of the thermal head mounting plate 3. When the cam body 11 rotates in one direction, the protrusion 11b of the cam body 11 engages with the latching part 3a. body 11
This locking portion 3a, the projection portion 11b, and the clutch spring 12 constitute a one-way rotation clutch between the cam body 11 and the platen roller 1.

Reference numerals 13 and 14 denote a pair of rotational support members that rotatably support the base end of the thermal head mounting plate 3, and these rotational support members 13 and 14 support the thermal head 2 and the platen roller 1. The rotation support members 13 are disposed on both sides of the extension of the tangent to the thermal head, and one of the rotation support members 13 is loosely fitted into the recess 3b formed at the base end of the thermal head mounting plate 3. The other rotation support member 14 movably supports the mounting plate 3, and the other rotation support member 14 supports the thermal head mounting plate 3 when the platen roller 1 is reversed.
The thermal head mounting plate 3 is movably supported so as to come into contact with the rear edge of the protrusion 3c protruding from the base end of the platen roller 1, and to be separated from the rear edge of the protrusion 3c when the platen roller 1 rotates normally. It is configured as follows.

Next, the operation of the thermal printer having the above configuration will be explained.

When the printing paper 10 is not sandwiched between the platen roller 1 and the thermal head 2, the stepping motor 6 is driven and its rotational force is applied to the platen roller 1 via the pulleys 7, 8 and the timing belt 9. This platen roller 1
When the cam body 11 rotates in the forward direction, that is, in the X direction in FIG. The thermal head 2 is rotated in the direction of contacting the outer circumferential surface of the platen roller 1, and the thermal head 2 is pressed against the outer circumferential surface of the platen roller 1 by the urging force of the elastic member 5, and a frictional force is generated between the two. Subsequently, the protruding portion 11b of the cam body 11 engages with the catch portion 3a of the thermal head mounting plate 3, so that the cam body 11 is stopped rotating by the action of the clutch spring 12. In this state, the thermal head mounting plate 3 is in a position that connects one rotation support member 13 and the contact surface of the thermal head 2 with the outer peripheral surface of the platen roller 1, that is, it is inclined with respect to the setting surface of the thermal head 2. Due to the position, as the platen roller 1 is driven to rotate,
Depending on the magnitude of the frictional force between the thermal head 2 and the platen roller 1, a component force F1 in the direction away from the platen roller 1 is generated on the tip side of the thermal head mounting plate 3. Due to the component force F1, the pressing force of the thermal head 2 against the outer peripheral surface of the platen roller 1 is reduced.
As a result, the required driving torque of the platen roller 1 is small even when the print paper 10, which increases the frictional force described above, is not sandwiched, and an auxiliary roller or the like is not required to move the print paper 10 when setting the platen roller. Even if the printer is not in use, it can be smoothly inserted between the platen roller 1 and the thermal head 2 to perform predetermined printing.

Next, at the end of printing, print paper 1
After conveying a certain amount of 0, the stepping motor 6
When the platen roller 1 is rotated in the opposite direction and the platen roller 1 is reversely rotated in the Y direction in FIG. The rear edge of the protrusion 3c of the plate 3 abuts on the other rotary support member 14. In this state, the thermal head mounting plate 3
is the other rotation support member 14 and the thermal head 2.
Since the thermal head mounting plate 3 is in an inclined position connecting the contact surface with the outer circumferential surface of the platen roller 1, as the platen roller 1 is rotated in the reverse direction, the tip side of the thermal head mounting plate 3 is separated from the platen roller 1. A component force F2 in the direction is generated, and this component force F2 reduces the pressing force of the thermal head 2 against the outer peripheral surface of the platen roller 1. As a result, the platen roller 1 is rotated in the reverse direction with a small torque even if there is no print paper 10. Along with this reverse rotation, the cam body 11 also rotates a certain amount in the opposite direction due to the action of the clutch spring 12, and the thermal head mounting plate 3 and the thermal head 2 held thereon are moved from the platen roller 1 by its eccentric portion 11a. Printing is completed with a gap G created between the thermal head 2 and the platen roller 1 by rotating them in the direction of separation, thereby preventing distortion and deformation of the outer circumferential surface of the platen roller 1 at the end of printing.

In the above embodiment, the cam body 11 is mounted coaxially with the platen roller 1, but they may be provided on separate shafts and both may be synchronously interlocked.

Further, in the above embodiment, the stepping motor 6
Although a timing belt is used to transmit the rotational driving force from the platen roller 1 to the platen roller 1, the transmission may be performed using a chain or gears.

[Effects of the invention] As explained above, according to this invention, when the printing paper is not sandwiched between the platen roller and the thermal head, that is, when the frictional force between them is large, the elastic member By reducing the pressing force, the driving torque required for forward and reverse rotation of the platen roller can be reduced, power consumption can be reduced, and the stepping motor can be made smaller, which is advantageous in terms of cost.

Furthermore, since the pressing force on the outer peripheral surface of the platen roller can be reduced and plastic deformation due to long-term use can be suppressed, printing quality can be guaranteed over a long period of time.

[Brief explanation of the drawing]

Figures 1a and b and Figures 2a and b show an embodiment of this invention. Figures 1a and b are front and side views of the thermal printer during printing, Figures 2a and 2b are b is a front view and side view of the thermal printer when the platen roller is reversed, Fig. 3 is an enlarged perspective view of the main parts, Fig. 4 is a sectional view of Fig. 3, and Figs. 5 a and b are views of a conventional thermal printer. They are a front view and a side view. DESCRIPTION OF SYMBOLS 1...Platen roller, 2...Thermal head, 3...Thermal head mounting plate, 5...Elastic member, 10...Print paper, 11...Cam body, 12
...Clutch spring, 13, 14...Rotation support member. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of utility model registration request] A platen roller that can be driven in forward and reverse directions; a thermal head mounting plate that holds a thermal head so as to be able to approach and separate from the outer peripheral surface of the platen roller, and whose base end is rotatably supported; an elastic member biasing toward the outer peripheral surface of the
The thermal head is arranged so as to be able to come into contact with the outer peripheral surface of the platen roller when rotating in one direction, and
In a thermal printer equipped with a cam body that rotates the thermal head mounting plate in a direction that moves the thermal head away from the outer peripheral surface of the platen roller when the thermal head rotates in the reverse direction, the extension of the tangent between the platen roller and the thermal head A pair of rotation support members for the thermal head mounting plate are provided on both the upper and lower sides, and the upper rotation support member is used when the platen roller rotates in one direction, and the lower rotation support member is used when the platen roller rotates in the opposite direction. A thermal printer characterized in that the thermal head mounting plate is movably supported by switching.