JPH0780325B2 - Platen pressing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a platen press used for heat-sensitive recording in which a recording medium (for example, an ink sheet and a recording paper or a thermal recording paper) is pressed against a thermal head by a platen. Regarding the device.

2. Description of the Related Art As this type of platen pressing device, for example, a heat-sensitive recording device used in a recording portion of a facsimile device has been widely used in recent years.

As shown in FIG. 3, the heat-sensitive recording device has a thermal recording paper 13 sandwiched between the thermal head 12 and the platen 11 which are biased by the platen 11 by the left and right pressure springs 10a and 10b. By heating the heating element of the head 12, heat-sensitive color development is performed for recording.

The problem to be solved by the invention However, in such a heat-sensitive recording apparatus, if the biasing force of the left and right pressure springs is different, the color density of the thermal recording paper differs depending on the location, and uneven density occurs. It was This is for the following reason.

In other words, when the biasing force of the left and right pressure springs is different, the contact state of the thermal head and the thermal recording paper changes, and the heat quantity of the heating element of the thermal head is good at the places where the contact state is good (that is, where the biasing force of the pressure spring is strong). The recording density is high because it is effectively transferred to the thermal recording paper, and the one with a poor contact state (that is, the place where the biasing force of the pressure spring is weak) does not effectively transfer the heat amount of the heating element of the thermal head to the thermal recording paper. As a result, the density unevenness was generated.

In view of this point, the present invention makes the contact state between the thermal head and the thermal recording paper non-uniform even when the biasing force changes due to manufacturing variations of the left and right pressure springs, variations in the length of insertion into the device, and the like. It is intended to provide a platen pressing device which prevents the occurrence of the above and uniformizes the recording density.

Means for Solving the Problems The present invention provides a pair of platen bearings that rotatably support a platen with polygonal spring seating surfaces having different distances from the axis of the platen.

Action The action of this technical means is as follows. That is, when the contact state between the thermal head and the thermal recording paper differs on the left and right, the biasing force of the pressure spring is changed by rotating the right or left platen bearing and inserting the pressure spring on the other spring seat surface. The contact state between the thermal head and the thermal recording paper is the same on the left and right so that uniform recording can be performed without density unevenness.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIGS. 1 and 2, 1 is a thermal head in which heating elements are linearly arranged, 2 is an ink sheet on which thermal transfer ink is evenly applied, 3 is recording paper, 4 is thermal ink sheet 2 and recording paper 3. The platen 5 that presses against the head 1 is a pair of platen bearings that rotatably support both end shafts of the platen 4, and 5a to 5f are distances from the axis of the platen 4 provided on the outer peripheral surface of the platen bearing 5 to the axis: Different polygonal spring seat surfaces, 6 are inserted between the spring seat surface 5a and the housing 7 of the apparatus, and are a pair of pair for pressing the platen 4 against the thermal head 1 through the pair of platen bearings 5. The pressing spring 8 is a guide for preventing the pressing spring 6 from buckling and restricting its position.
1 shows the case where the distance from the axis of the platen to the spring seat surface 5a is the minimum: 1 (that is, the state where the biasing force of the pressing spring 6 is the minimum), and FIG. 2 shows the axis of the platen. The maximum distance from the spring seat surface 5f is l '(that is, the pressure spring 6
The state in which the urging force of is minimum) is shown. Further, the distance from the axis of the platen to the spring seat surfaces 5a to 5f is configured to change at a constant distance: Δl.
= L + 5Δl. That is, the pressing force can be obtained in 6 levels.

Next, the operation of the configuration of this embodiment will be described.

First, the left and right pressure springs are in the state shown in FIG. 1 (that is, the left and right pressure springs 6 are attached between the spring seat surfaces 5a of the pair of platen bearings 5 that engage with both end shafts of the platen 4 and the apparatus housing 7. Ink sheet 2 and recording paper 3
Recording is performed by pressing the thermal head 1 by the platen 4 which is biased by the left and right pressing springs 6, and at this time, the spring constant of the pressing spring 6 is varied, and the space between the one spring seat 5a and the housing 7 is reduced. Insertion length of the pressure spring 6 and the other spring seat 5
In some cases, the pressing balance of the platen 4 with respect to the thermal head cannot be balanced due to the difference in the insertion length of the pressing spring 6'between a'and the housing 7, and this causes uneven recording density.

When the recording density becomes uneven, for example, when the density on the left side is low, the platen bearing 6 (bearing on the left side) is moved clockwise by 1
Rotate the stage (in this embodiment, it becomes 60 ° because of 6 divisions),
When the pressing spring 6 is received by the spring seat surface 5b, the used length of the pressing spring 6 is shortened by Δl, and the biasing force of the platen on the left side increases. After that, recording is performed and the variation in recording density on the left and right is observed. The above operation is repeated to balance the pressure of the platen and make the recording density uniform. Further, even when the recording density is uniform, if the overall density is insufficient, the left and right platen bearings 6 are simultaneously rotated to uniformly increase the pressing force of the platen 4 to increase and decrease the recording density. be able to.

In this embodiment, the spring seat surface is divided into six steps to form a hexagon, but it may be divided into other steps.
It goes without saying that the same effect can be obtained even with a curved cam-shaped spring seat surface whose distance from the shaft center changes continuously.

EFFECTS OF THE INVENTION As described above, according to the present invention, the outer peripheral surface of the platen bearing is provided with the spring seat surface in which the distance from the shaft core changes sequentially. Therefore, even when the pressure balance of the platen is different, the platen bearing is different. The pressing balance can be easily adjusted simply by rotating, which is extremely useful in practice.

[Brief description of drawings]

1 and 2 are side views of a platen pressing device according to an embodiment of the present invention, and FIG. 3 is a perspective view of a thermal recording device using a conventional platen pressing device. 1,12 ... Thermal head, 2 ... Ink sheet, 3 ...
Chart paper, 4,11 …… Platen, 5 …… Platen bearing, 5a to 5f …… Spring seat surface, 6,10a, 10b …… Pressing spring, 7 ……
Device case, 8 ... Guide, 13 ... Thermal recording paper.

Claims (3)

[Claims] 1. A thermal head in which heating elements are linearly arranged, and a platen for pressing a recording medium against the thermal head,
A pair of platen bearings that rotatably support the platen,
A spring seat surface provided on the outer peripheral surface of the platen bearing, the distance from the axis of the platen varying sequentially, and a biasing force for pressing the platen against the thermal head via the platen bearing between the spring seat surface and the apparatus housing. A platen pressing device with a pressing spring inserted. 2. The platen pressing device according to claim 1, wherein the spring seat surface is a polygonal seat surface having different distances from the axis of the platen. 3. The platen pressing device according to claim 1, wherein the spring bearing surface is a curved cam-shaped bearing surface whose distance from the axis of the platen continuously changes.