JPH0250866A - Thermal recording apparatus - Google Patents

Abstract

PURPOSE:To obtain good image quality by using a worm and a worm wheel as a means for decreasing the rotational speed of a stepping motor to transmit said speed to a pressure contact roller. CONSTITUTION:Thermal recording paper 4 is inserted between the heating resistor element group provided to a thermal recording head 1 and a pressure contact roller 3. The rotatory power of a stepping motor 5 is transmitted to a worm wheel 7 through the worm 6 mounted on a stepping motor shaft 5a and further transmitted to the pressure contact roller 3 coaxially mounted in coaxial relation to the worm wheel 7. A bearing 8 is provided in order to prevent the shaking of the stepping motor shaft 5a. As a result, since the rotary state of the stepping motor 5 can be made almost synchronous to that of the pressure contact roller 3, printing inferiority generated by feed irregularity is eliminated and good image quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal recording device such as a facsimile machine, and more particularly to an improvement in a pressure roller conveyance system for eliminating uneven feeding of thermal recording paper.

[Conventional technology]

Conventional devices transmit the driving force of a stepping motor to a pressure roller via a timing pulley and a timing belt, as described in JP-A-56-75881, or as described in JP-A-61-118,283. As described above, a method has been adopted in which the driving force of the stepping motor is transmitted to the pressure roller by connecting gears such as spur gears.

Generally, a differential recording device generates Joule heat by passing a current through a predetermined resistance of a group of heating resistor elements arranged in a line on a thermal recording head, and uses this heat to print one line of thermal recording paper. After printing, the pressure roller is rotated a predetermined amount to print the next line.

In this case, some thermal recording devices aim to improve image quality by further dividing one line and finely feeding the printing and pressure rollers. In any case, matching the printing timing at which current is passed through the heating resistor elements and the rotational characteristics of the pressure roller becomes an important problem in terms of image quality.

For this reason, conventionally, a high-precision, high-torque compound stepping motor, for example, has been used as a stepping motor. Due to the structure of this motor, the rotation angle per pulse can be made small, so the conveyance path to the pressure roller can be simplified, and the rotation of the stepping motor can be faithfully transmitted to the pressure roller. Therefore, there is an advantage that it is easy to synchronize the rotational characteristics of the pressure roller and the printing timing.

However, with the demand for lower prices of thermal recording devices, inexpensive stepping motors are increasingly being used in many thermal recording devices on the market. For example, a permanent magnet stepping motor is often used as such a stepping motor, but due to its structural characteristics, this stepping motor has a relatively small rotational torque.
It also has the characteristic that the rotation angle per pulse is large. For this reason, in order to apply it to a thermal recording device, it is necessary to reduce the rotation angle and increase the rotation torque by using a large number of spur gears, for example. In this case, it is possible to increase the gear reduction ratio per stage or the timing pulley ratio as a reduction mechanism, but permanent magnet stepping motors have a lower rotation per pulse than compound stepping motors. Since the angle is about an order of magnitude larger, the outer diameter of the gear and the timing pulley are larger, resulting in a larger device.

FIG. 4 shows a thermal recording device using a conventional permanent magnet type stepping motor. In FIG. 4, the thermal recording head 1
A thermal recording paper 4 is inserted between a heating resistor element group 2 and a pressure roller 3, and the rotational force of the stepping motor 5 is transmitted to a spur gear 12a attached to the shaft of the stepping motor 5. Furthermore, spur gears 12b and 12c
, 12d.

12e and 1.2f, the speed is transmitted to the pressure roller 3 attached coaxially with the spur gear 12f, and as the pressure roller 3 rotates, the thermal recording paper 4 is transferred to the pressure roller 3.
The structure is such that the material is transported by frictional force with the material. In this device, a permanent magnet type stepping motor with a rotation angle of 7.5 degrees per 1-pulse during two-phase excitation is used as the stepping motor 5, and this rotation is 0.0 degrees with spur gears 12a to 12f.
The speed is reduced six times and transmitted to the pressure roller with an outer diameter of 16.5 mm.

In this device, each line is printed and the stepping motor is fed by two pulses at a predetermined time.

FIG. 5 shows the measured amount of rotation of the pressure roller of the thermal recording apparatus shown in FIG. 4, and the value obtained by multiplying the measured amount of rotation of the stepping motor by a reduction ratio of 0.06.

From the results shown in FIG. 4, in this thermal recording device, there is a large difference in the rotation status of the stepping motor 5 and the pressure roller 3 shown in FIG. 1, and the rotation of the stepping motor 5 is transmitted to the pressure roller 3 in synchronization. do not have. This is because soft plastic is used for the spur gears 12a to 12f, which also serves as a noise countermeasure, and deformation and backlash of the spur gears accumulates, thereby inhibiting synchronization.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, a thermal recording device using a permanent magnet type stepping motor, which has a simple and inexpensive structure, requires the use of a conveyance system that connects a large number of spur gears to reduce speed due to the characteristics of the stepping motor, such as rotation angle and torque. there were. In this case, there is a problem in that the rotation of the stepping motor is not synchronously transmitted to the pressure roller. To solve this problem, reduce the number of spur gears and increase the gear ratio.
Alternatively, increasing the ratio of the timing pulleys increases the size of these conveyance systems, making it difficult to implement them in a thermal recording device. In addition, since the main parts of permanent magnet stepping motors are formed by press processing, they are inexpensive, but due to assembly precision, the rotating shaft tends to shake, and in order to solve the noise caused by this shaking, soft plastic is used. This was due to the fact that many spur gears were connected together, but this was a major hindrance to the image quality of thermal recording devices.

An object of the present invention is to provide a high-quality thermal recording device using an inexpensive permanent magnet type stepping motor.

[Means to solve the problem]

In order to achieve the above purpose, by using a worm and a worm wheel as a means to decelerate the rotation of the stepping motor and transmit it to the pressure roller, a combination of fewer gears can achieve a large deceleration, an accompanying increase in torque, and a stepping motor. The rotation of the motor is synchronously transmitted to the pressure roller.

[Effect]

That is, the rotation of the stepping motor is decelerated by the worm and the worm wheel, and then transmitted to the pressure roller.

Since even one set of the worm and worm wheel can provide a large reduction ratio, uneven conveyance is less likely to occur in these reduction parts. As a result, it becomes possible to synchronously transmit the rotation of the stepping motor to the pressure roller.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, a thermal recording paper 4 is inserted between a heating resistor element group 2 provided on a thermal recording head 1 and a pressure roller 3. As shown in FIG. The rotational force of the stepping motor 5 is transmitted to the worm wheel 7 via the worm 6 attached to the stepping motor shaft 5a.
The structure is such that the pressure is transmitted to the pressure roller 3 coaxially attached to the pressure roller 3. In this embodiment, the stepping motor shaft 5a
A bearing 8 was provided to prevent the vibration.

Although the worm 6 in this embodiment is made of brass in consideration of wear resistance, it is also possible to use plastic as long as it is a material with good wear resistance.

Regarding this example, FIG. 2 shows the measurement results of the rotation amount of the pressure roller and the value obtained by multiplying the measurement value of the rotation amount of the stepping motor by the reduction ratio.

From the results shown in Fig. 2, the stepping motor 5 shown in Fig. 1
It has become possible to synchronize the rotation status of the press roller 3 with the rotation status of the pressure roller 3. As a result, it was possible to eliminate printing defects that occur due to uneven conveyance, which was a problem with conventional thermal recording devices using permanent magnet type stepping motors, and to obtain good image quality.

Further, in this embodiment, since the vibration of the shaft 5a of the stepping motor 5 is suppressed by the bearing 8, it is possible to reduce the noise caused by uneven contact between the gears due to vibration of the shaft 5a.

Furthermore, unlike conventional conveyance systems in which deceleration is achieved by connecting a large number of spur gears, it has become possible to make the thermal recording device compact.

Further, FIG. 3 shows another embodiment of the present invention.

In FIG. 3, the stepping motor 5 is attached to the chassis 10a of the thermal recording device with screws or the like, and the rotational force of the stepping motor 5 is transmitted through a bevel gear 9a.

The pressure is transmitted to the shaft 11 via the shaft 9b, and is further decelerated by the worm wheel 7 from the worm 6 fixed to the shaft 11, thereby rotating the pressure roller.

The pressure roller 3 is a chassis 10a of a thermal recording device.

10b via bearings 8c and 8d for free rotation,
Further, the shaft 11 is rotatably fixed to bearings 8a and 8b.

In this embodiment, since the stepping motor 5 can be fixed to the chassis 10a of the thermal recording apparatus, there is an advantage that the thermal recording apparatus can be made more compact. In addition,
If the vibration of the stepping motor shaft 5a becomes a problem,
By fixing the bevel gear 9a in the middle of the stepping motor shaft 5a and further attaching a bearing to the tip of the stepping motor shaft 5a, it is possible to reduce runout.

〔Effect of the invention〕

Since the present invention is configured as described below, it produces the effects described below.

A simple speed reduction device using a worm and a worm wheel allows the rotational characteristics of the stepping motor to be faithfully and timely transmitted to the pressure roller.

Furthermore, since the speed reduction device is small, the thermal recording device can be designed compactly.

Furthermore, by fixing the stepping motor shaft with a bearing, it is possible to reduce noise generated due to vibration of the stepping motor shaft.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a portion of the thermal recording paper conveyance system of a thermal recording device according to an embodiment of the present invention, and FIG. 2 is a measurement of rotational characteristics of a stepping motor and a pressure roller using the thermal recording device shown in FIG. 1. A characteristic diagram showing the results, FIG. 3 is a top view showing a portion of a thermal recording paper conveyance system according to another embodiment of the present invention, and FIG. 4 is a side view of a portion of a thermal recording paper conveyance system of a conventional thermal recording apparatus. , FIG. 5 is a characteristic diagram showing the results of measurement of the rotational characteristics of the stepping motor and the pressure roller by the thermal recording apparatus shown in FIG. 4. 1...Thermal recording head, 2...Heating resistor element group,
3... Pressure roller, 4... Heat-sensitive recording paper, 5... Stepping motor, 6... Worm, 7... Worm wheel, 8... Bearing.

Claims (1)

[Claims] 1. A thermal recording head having a heating resistor element group, a thermal recording paper provided so as to be in contact with the heating resistor element group of the thermal recording head, the thermal recording head and the thermal recording paper being pressed together, and a thermal recording head having a heating resistor element group; In a thermal recording device consisting of a pressure roller for feeding the recording paper, a stepping motor for driving the pressure roller, and a reduction device for reducing the rotational speed of the stepping motor, the reduction device includes a worm and a worm wheel. A heat-sensitive recording device characterized by using the following.