JP2850494B2 - Thermal printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding a line dot type thermal printer, when the motor stops and the rotation of the platen stops, the reverse rotation of the motor due to the deflection of the rubber coating of the platen is prevented. A platen driven by a motor and resiliently contacted by a thermal head via a recording medium; and a reverse rotation preventing means. The reverse rotation preventing means follows the rotation stop of the motor and rotates the platen. Is stopped, the reverse rotation of the motor caused by the restoring force of the deflection of the rubber coating of the platen is braked.

[Industrial applications]

The present invention relates to a thermal printer, and more particularly, to a line dot type thermal printer in which a platen is driven by a stepping motor, which prevents a print dot pitch deviation caused by a reverse rotation of the motor due to a restoring force of bending of a rubber portion of a platen. The present invention relates to a thermal printer.

In recent years, with the progress of computerization, the demand for a printer as an information output device has been increasing more and more.

Printers can be classified into various types, and are roughly classified into an impact type and a non-impact type.

In the non-impact method, a laser printer has recently been developing at a rate exceeding that of an impact-type wire dot printer, but it is undeniable that the apparatus will be exaggerated.

In contrast, thermal printers have recently been receiving attention. It is small and lightweight, has a moderately high printing speed, has no noise, and is used not only in the so-called personal use centered on personal computers, but also in the business field.
It seems to have many features such as no maintenance.

There are two types of thermal printers, a serial dot type and a line dot type, depending on the driving method of the thermal head. In the line dot type, there is generally room for improvement in the feeding accuracy of a friction-driven recording medium.

[Conventional technology]

The thermal printing method is classified into two methods depending on the form of the thermal head and how the thermal head scans a recording medium to perform printing.

On the thermal head, several to several tens of heating dots are arranged in parallel to the direction of travel of the recording medium. For example, while the recording medium is intermittently fed line by row, the thermal head is perpendicular to the direction of travel of the recording medium. A method of printing by mechanically moving and scanning the image is called a serial dot method. This method is mainly used for low-end printers.

On the other hand, using a thermal head in which hundreds to thousands of heat-generating dots are arranged in the width direction perpendicular to the direction of travel of the recording medium, the recording medium can be fed continuously or intermittently in dot pitch units. A method in which heating dots are electrically scanned and printed while being fed is called a line dot method. This method is applied to printers that require high-speed printing, and is frequently used in facsimile machines and the like.

FIG. 6 is a configuration diagram of a drive system in the line dot thermal printer.

In the figure, 1 is a motor, 2 is a recording medium, 3 is a thermal head, 4 is a platen, and 6 is a speed reduction mechanism.

As the motor 1, a DC motor or the like is used, but intermittent driving in dot units by a stepping motor is generally performed.

The recording medium 2 is made of, for example, a heat-sensitive paper for directly developing a color or a combination of a thermal transfer ribbon and plain paper.

The thermal head 3 is of a so-called line dot type, in which hundreds to thousands of heating dots are arranged in a line.
Diode matrix driving and, in recent years, direct driving by an integrated circuit are also performed.

The platen 4 includes a metal core 4c and a rubber coating 4a wound on the metal core 4c.

The speed reduction mechanism 6 reduces the rotation speed of the motor 1 and transmits it to the platen 4 in order to feed the recording medium 2 at a predetermined speed, and a structure in which several gears are combined is often used. .

The paper feed of the recording medium 2 is performed by sandwiching the recording medium 2 between a platen 4 and a thermal head 3 elastically contacting a rubber coating 4a of the platen 4 with a spring or the like. This paper feed is also called a friction (friction) drive, and generally, the friction coefficient between the recording medium 2 and the rubber coating 4a is overwhelmingly larger than the friction coefficient between the thermal head 3 and the recording medium 2; As it rotates, the recording medium 2 is fed.

Printing is started by energizing the thermal head 3 while rotating the platen 4 by the motor 1 to move the recording medium 2.

On the other hand, when the printing is completed, in the case of a stepping motor in which the motor 1 is frequently used, heat is generated in a state where the motor is stopped and excited and released, so that the excitation is cut off at the same time as the printing is completed.

By the way, looking at the movement of the platen 4, when the mandrel 4c is being driven to rotate, the rubber coating 4a is
Is rotated in a state where a so-called brake is applied by being elastically contacted with the thermal head 3 via the recording medium 2. Therefore, the rubber coating 4a is rotating while constantly bending in the direction opposite to the rotation direction. Therefore, when the rotation of the platen 4 stops, the surface of the rubber coating 4a is firmly supported by the thermal head 3, and the restoring force of the deflection of the rubber coating 4a acts to reversely rotate the metal core 4c.

Thus, in the paper feeding by the friction drive, when the printing is completed and the excitation of the motor 1 is cut off, the motor 1 is frequently rotated in the reverse direction.

FIG. 7 is an explanatory view of the displacement due to the restoring force of the rubber coating.

6 and 7, the relationship between the platen 4, the force between the core 4c of the platen 4, the rubber coating 4a, the recording medium 2, and the thermal head 3 will be examined.

Here, P is the pressing force of the thermal head 3, μ is the coefficient of friction between the thermal head 3 and the recording medium 2, R is the radius of the platen 4, Tr is the restoring force of the rubber coating 4a of the platen 4, and Md is the detent of the motor 1. The torque, C, is the reduction ratio of the reduction mechanism 6, η
Is the efficiency of the speed reduction mechanism 6, and μ × P is the force to send the recording medium 2.

(1) Relation of force when the motor 1 is excited: When Tr <μ × P × R, the recording medium 2 stops.

(2) Relationship between the excitation and cutting forces of the motor 1 after printing: When Tr> Md × C × η, the motor 1 rotates in the reverse direction.

 From the relational expression and the expression, Md × C × η <Tr <μ × P × R is obtained.

From the equation, the motor 1 is rotated in reverse through the speed reduction mechanism 6 until Md × C × η = μ × P × R, that is, until the angle corresponds to the angle θ ′ of the metal core 4c of the platen 4. Can be

Thus, when printing is restarted next time, especially if the motor is a stepping motor, a so-called step-out occurs, so that the recording medium is not started normally, and the recording medium is not normally fed.

[Problems to be solved by the invention]

Thus, in a line dot thermal printer, once printing is completed and the motor stops, the motor is rotated in the opposite direction by the force that restores the deflection of the rubber coating on the platen. Happens.

Then, when the motor is restarted to restart the next printing, the rotation of the platen and, consequently, the paper feeding of the recording medium sometimes become abnormal.

FIG. 8 shows an example of printing by the conventional driving method. FIG. 8A shows a normal state, and FIG.

That is, as shown in FIG. 2B, the head of the print becomes slightly clogged due to the abnormality of the paper feed pitch of the recording medium, and for example, the alphabet “2” is changed to “Z”. There was a problem.

The present invention is to provide a thermal printer that prevents reverse rotation of a motor due to bending of a rubber coating of a platen when printing is completed and rotation of a platen is stopped by stopping a motor. The purpose is.

[Means for solving the problem]

The above-mentioned problem has a platen driven by a motor and resiliently contacted with a thermal head via a recording medium, and a reverse rotation preventing unit, wherein the reverse rotation preventing unit follows the rotation stop of the motor. The problem is solved by a thermal printer configured to brake the reverse rotation of the motor caused by the restoring force of the deflection of the rubber coating of the platen when the rotation of the platen stops.

(Operation)

As described above, in the thermal printer of the line dot type which feeds the recording medium while elastically contacting the recording medium with the platen with the thermal head, the motor is returned in the reverse direction by the restoring force of the bending of the rubber coating of the platen, In particular, when the motor is a stepping motor, a step-out occurs, and the next time printing is resumed, the paper feed pitch becomes abnormal. In the present invention, the motor is prevented from rotating in the reverse direction. .

That is, generally, the rotation of the motor is transmitted to the platen via the reduction mechanism, and the main shaft of the motor is reversed at the largest angle corresponding to the reduction ratio with respect to the return angle due to the restoring force of the deflection of the rubber coating of the platen. Since the motor rotates, the reverse rotation preventing means is attached to the main shaft of the motor so as to be more effective. The main shaft of the motor rotates freely in the forward direction of the paper feed, but does not rotate in the reverse direction.

Further, a one-way clutch is used for the reverse rotation preventing means. The one-way clutch is not used for transmitting the rotation in only one direction, but is fixed so that the driving side or the driven side does not rotate, and the rotation in the reverse direction is braked.

Thus, even if the platen is rotated by the restoring force of the rubber coating, reverse rotation of the motor can be prevented.

〔Example〕

FIG. 1 is an explanatory view of a first embodiment of the present invention, FIG. 2 is an explanatory view of an operation of a one-way clutch, FIG. 3 is an explanatory view of driving / braking of FIG. 1, and FIG. FIG. 5 is an explanatory view of the second embodiment, and FIG. 5 is an explanatory view of the driving / braking of FIG.

In the figure, 1 is a motor, 1a is a main shaft, 2 is a recording medium, 3 is a thermal head, 4 is a platen, 4a is a rubber coating, 4b is a platen shaft, 5 is a reverse rotation preventing means, and 6 is a speed reduction mechanism.

Embodiment 1 In FIG. 1, the motor 1 is a stepping motor.

The platen 4 has a rubber coating 4 with an outer diameter of 14.2 mmφ and a thickness of 2.6 mm.
a is covered.

The platen 4 is driven by a motor 1 via a speed reduction mechanism 6 composed of three gears, and a line dot type thermal head 3 is elastically contacted with a recording medium 2 composed of thermal paper.

Now, how much the main shaft 1a of the motor 1 is rotated in the reverse direction by the restoring force due to the bending of the rubber coating 4a of the platen 4 will be examined.

The specifications of the thermal printer are as follows, and the calculation is made with reference to FIG.

(1) Pressing force of thermal head 3: P = 3,000 g, (2) Friction coefficient between recording medium 2 and thermal head 3: μ = 0.4, (3) Radius of platen 4: R = 7.1 mm, (4) Reduction ratio of reduction mechanism 6: C = 11.3, (5) Efficiency of reduction mechanism 6: η = 1.37, (6) Detent torque of motor 1: Md = 35 gcm, Restoring force of rubber coating 4a of platen 4: Tr is 542 gcm <Tr <852 gcm from the equation Md × C × η <Tr <μ × P × R, and the return angle θ at which the main shaft 1a of the motor 1 rotates in the reverse direction is:
The angle becomes as large as θ = 4 degrees.

On the other hand, the reverse rotation preventing means 5 may be, for example, a ratchet or a cam so that the main shaft 1a of the motor 1 does not rotate in the reverse direction. In this case, a one-way clutch is used.

In FIG. 2, the configuration of a one-way clutch (one-way clutch) is divided into a driving side 5a and a driven side 5b. Since the driving side 5a can rotate ahead of the driven side 5b, it is also called an overrunning clutch or the like.

In other words, when driving is indicated by solid arrows, overrunning is indicated by broken arrows in the opposite direction, and the driving 51a of the driving side 5a and the driving 51b of the driven side 5b, and the overrunning 52a of the driving side 5a and the driven side The overrunning 52b of 5b is in a relationship opposite to each other.

In FIG. 3, the direction of the overrunning 52b of the driven side 5b of the one-way clutch is connected via the gear 1b so that the main shaft 1a of the motor 1 rotates in the forward direction, and the driving side 5a is prevented from rotating. Fix it.

Now, as shown in FIG. 3 (A), when the motor 1 rotates in the forward direction, the driven side 5b rotates via the gear 1b, but is fixed because the rotation direction is the direction of the overrunning 52b. It is rotatable without any influence on the driving side 5a.

Next, as shown in FIG. 3 (B), when the motor 1 stops, the gear 1b rotates in the reverse direction due to the restoring force of the rubber coating of the platen (not shown), and the driven side 5b of the one-way clutch is moved. Attempts to rotate in the direction of drive 51b. However,
Since the driving side 5a is fixed, the driven side 5b is braked and cannot rotate. Therefore, the rotation of the main shaft 1a of the motor 1 in the reverse direction is braked.

In this way, since the reverse rotation of the motor is braked, it has been confirmed that there is no obstacle such as an abnormal rotation of the motor by 4 degrees in the angle and an abnormality in the paper feeding of the recording medium.

Second Embodiment In FIGS. 4 and 5, a one-way clutch having the same specifications as those used in the first embodiment is used as the reverse rotation preventing means 5.

In FIG. 4, the direction of overrunning 52a on the drive side 5a of the one-way clutch is connected to the platen shaft 4b so that the platen 4 rotates in the forward direction, and the driven side 5b is fixed so as not to rotate.

Now, as shown in FIG. 5 (A), when the motor 1 rotates in the forward direction, the platen shaft 4b is connected to the overrunning 52a of the driving side 5a and becomes independent of the driven side 5b. The platen 4 also rotates in the forward direction via the mechanism 6.

Next, as shown in FIG. 5B, when the motor 1 stops, the platen shaft 4b tries to rotate in the opposite direction due to the restoring force of the rubber coating of the platen 4. However, the drive 51a, which corresponds to the reverse rotation of the drive side 5a to which the platen shaft 4b is connected, cannot rotate and is braked because the driven side 5b is fixed so as not to rotate.

In this way, since the reverse rotation of the platen shaft is braked, the reverse rotation of the motor via the speed reduction mechanism is also braked, and it has been confirmed that there is no obstacle such as an abnormality in paper feeding of the recording medium.

Here, a one-way clutch is used as reverse rotation preventing means, a drive side is fixed to the main shaft of the motor to make it impossible to rotate, a mechanism for overrunning the driven side connected to the main shaft of the motor, and a platen Two examples have been described in which the driven side is fixed to the shaft, and the driving side is connected to the platen shaft to perform overrun. However, as long as the forward rotation of the motor or the platen satisfies the condition of the overrunning of the one-way clutch, for example, it can be incorporated in a reduction mechanism combining a plurality of gears,
Various modifications are possible from the configuration.

Further, the specifications of the thermal printer are merely examples, and the characteristics of the present invention are not affected by these numerical values.

〔The invention's effect〕

As described above, in the conventional line dot thermal printer that drives the recording medium frictionally, the motor is turned in the opposite direction due to the restoring force of the deflection of the rubber coating on the platen. In particular, step-out occurs when the motor is a stepping motor. For this reason, an abnormality has occurred in the paper feeding of the recording medium, and when the next printing is restarted, there has been a problem that the printing becomes slightly clogged.

On the other hand, in the present invention, such obstacles can be completely eliminated by providing reverse rotation preventing means such as a one-way clutch.

Thus, the present invention greatly contributes to the improvement of the print quality of the thermal printer of the line dot system, and further to the expansion of the use of the thermal printer.

[Brief description of the drawings]

1 is an explanatory view of a first embodiment of the present invention, FIG. 2 is an explanatory view of the operation of a one-way clutch, FIG. 3 is an explanatory view of driving / braking of FIG. 1, and FIG. FIG. 5 is an explanatory view of the driving / braking of FIG. 4, FIG. 6 is a structural view of a driving system in a line dot thermal printer, and FIG. FIG. 8 shows an example of printing by a conventional driving method. In the figure, 1 is a motor, 1a is a main shaft, 2 is a recording medium, 3 is a thermal head, 4 is a platen, 4a is a rubber coating, 4b is a platen shaft, 5 is a reverse rotation preventing means, 5a is a driving side, and 5b is a driven side. Side.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 11/00 B41J 11/42

Claims (3)

(57) [Claims] A platen (4) driven by a motor (1) and resiliently contacted with a thermal head (2) via a recording medium (3); and a reverse rotation preventing means (5). When the rotation of the platen (4) stops following the rotation stop of the motor (1), the prevention means (5) is caused by the restoring force of the bending of the rubber coating (4a) of the platen (4). A thermal printer for braking the reverse rotation of the motor (1). The reverse rotation preventing means (5) is provided on a driving side (5).
a) or the driven side (5b) is connected to the main shaft (1a) of the motor (1) so that the overrunning direction of the driven side (5b) coincides with the forward rotation of the motor (1); The thermal printer according to claim 1, wherein the side (5a) is a one-way clutch fixed so as not to rotate. The reverse rotation preventing means (5) is provided on a driving side (5).
a) or the driven side (5b) is connected to the platen shaft (4b) of the platen (4) so that the overrunning direction of the driven side (5b) coincides with the forward rotation of the motor (1), and the driven side (5b) or The thermal printer according to claim 1, wherein the drive side (5a) is a one-way clutch fixed non-rotatably.