JPH02136247A - Thermal transfer apparatus - Google Patents

Abstract

PURPOSE:To prevent the generation of wrinkles and density irregularity in copy paper by uniformizing pressure contact force by preliminarily supposing the bending deformation of a platen roller and forming the surface shape of a thermal head so as to follow this bending by a control mechanism. CONSTITUTION:In a mechanism for controlling the surface shape of a thermal head 1 when thermal transfer is performed by the pressure contact of the thermal head 1 with a platen roller 3, a plurality of adjusting rivets 10 functioning as the control mechanism so as to tightly bring the surface shape of the thermal head into contact with the peripheral surface of the platen roller 3 bent and deformed into a bow shape under pressure are mounted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal transfer device equipped with a thermal head used in copying machines, facsimile machines, and the like.

[Conventional technology]

For example, a typical thermal transfer type copying apparatus has a structure in which a thermal head is disposed in the path of copying paper, and an ink donor film to which a coloring material is attached or contained is used to transfer an image.

FIG. 15 is a schematic diagram showing a system including a thermal head installed in a color copying apparatus.

In the figure, an ink donor film 52 as a transfer sheet is wound between a supply roll 50 and a take-up roll 51, and the ink donor film 52 fed out from the supply roll 50 is sequentially wound around the take-up roll 51 and collected. We have set up a path for you.

The ink donor film 52 pulled out from the supply roll 50 passes through a portion of the thermal head 1 in which the heat sink 2 is integrated, in close contact with the copy paper 53 supplied from another system. Then, the ink donor film 52 and copy paper 53 are pressed against the heating resistor 1a of the thermal head 1 by the platen roller 3, and the ink on the ink donor film 52 is heated by the heating resistor 1a according to the printing pattern based on the image information. The structure is such that the liquid is fluidized or sublimated and transferred to the copy paper 53.

Further, a stepping motor 54 is arranged as a driving source for feeding and collecting the ink donor film 52. The stepping motor 54 has a drive pulley 55. The drive system includes a belt 56 and a driven pulley 57, and the ink donor film 52 is sandwiched between a drive roller 58 and a pressure roller 59 attached to the driven pulley 57 and sent to the take-up roll 51. Then, the ink donor film 52 and the copy paper 53 are guided by the guide roller 4 and reach the thermal head 1 portion, and after the transfer, the copy paper 53 is separated from the ink donor film 52 by the separation bar 5, and the copy paper 53 is separated from the ink donor film 52 by the arrow Pass in the direction.

The thermal head 1 system having the above configuration is applied to a multi-head single-pass color copying machine as shown in FIG. In the figure, a scanning section 60 that optically scans a document and a thermal transfer section 61 are provided, and thermal transfer based on image information obtained by the scanning section 60 is performed!
1lis61. The thermal i-photograph 1161 has a structure in which thermal transfer heads 62 to 65 each having yellow, magenta, cyan, and black ink donor films are arranged in a ring. Then, the copy paper 53 from the paper cassette 66 is sent in, passed through each of the thermal transfer heads 62 to 65, copied, and then collected into the discharge tray 67.

Furthermore, in such multi-head single-pass color copying, the movement characteristics of the copy paper 53 can be improved without suffering from slippage between the copy paper 53 and the ink donor film 52, expansion and contraction of the ink donor film 52, etc. A system is provided to prevent this from changing. This system is constructed by disposing a detection roller 6 and a pinch roller 7 between a platen roller 3 and a peeling bar 5, as shown in FIG. An encoder 6a is provided at the shaft end of the detection roller 6, and generates a predetermined number of pulse signals during one rotation of the detection roller 6, which rotates as the copy paper 53 passes between the pinch roller 7 and the copy paper 53. is output from this encoder 6a. On the other hand, at both ends of the shaft portion of the pinch roller 7, the pressure contact force with the detection roller 6 can be adjusted and the pressure contact can be canceled by movable arms (1!! not shown).

[Problem to be solved by the invention]

It is already known that the transfer process in a copying device has a large effect on the quality of reproduced images.

For example, if the flatness of the thermal head 1 in direct contact with the ink donor film 52 is poor, wrinkles may occur and density unevenness in the main scanning direction may occur, which may adversely affect image quality. Further, minute waviness of the thermal head 1, lifting in the main scanning direction, etc. may similarly affect image quality.

On the other hand, not only the thermal head 1 itself but also the relationship with the platen roller 3 that presses the ink donor film 52 and copy paper 53 against the thermal head 1 is a factor that affects image reproduction. This is because the platen roller 3 is supported at both ends by bearings or the like, so that a slight bending deformation occurs in which the central portion becomes convex. That is, the 17th
As shown in the figure, the platen roller 3, which rests on the thermal head 1 and whose both ends are pressed down, bends and deforms upward. For this reason, a gap is created between the thermal head 1 and the platen roller 3 at the center of the pressure contact surface, causing wrinkles on the copy paper 53 and reducing the transfer density at the center, which affects the image. result.

To solve this problem, conventionally, a structure has been adopted in which only the center portion of the thermal head l in the width direction is lifted toward the platen roller 3 side. In other words, platen roller 3
In order to follow the upward bending deformation in a quadratic curve,
The idea is to bring the press-contact surfaces into close contact with each other to suppress gaps and the like.

However, the bending deformation of the platen roller 3 differs depending on its shaft diameter and is also greatly affected by thermal stress. For this reason,
It is necessary to determine the surface shape of the thermal head 1 for each specification of the platen roller 3, making it difficult to standardize the product. Furthermore, simply increasing the height of the central portion of the thermal head 2 to follow the deflection of the platen roller 3 may not necessarily match the deflection shape of the platen roller 3, and an appropriate pressure contact surface cannot be obtained. As described above, in the conventional structure, there still remains a problem with the pressure contact between the thermal head 1 and the platen roller 3, and improvements have been made to prevent wrinkles in the ink donor film 52 and copy paper 53, uneven density of reproduced images, etc. was necessary.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thermal head with a pressure contact surface for proper transfer against the deflection of the platen roller, thereby enabling good image reproduction.

[Means to solve the problem]

In order to achieve the above objectives, the thermal transfer device of the present invention has the following features:
A thermal transfer device in which an ink donor film and copy paper pass in an overlapping manner, and during this pass, thermal transfer is performed by pressure contact between a thermal head and a platen roller, the thermal head having a surface that follows the bending deformation when the platen roller is in pressure contact with the thermal head. It is characterized by having an adjustment mechanism that allows the shape to be set.

In addition, the bending deformation when the platen roller is pressed against the thermal head draws a quartic curve according to a theoretical formula, so if the adjustment mechanism is operated so that the surface shape of the thermal head matches this quartic curve, the platen roller and The pressure contact between the thermal head and the thermal head becomes even better.

[Effect]

The bending deformation of the platen roller is assumed in advance, and the surface shape of the thermal head is set by the adjustment mechanism so as to follow this bending deformation. As a result, the thermal head is set so that there is no gap between the thermal head and the platen roller, and a similar pressing force is exerted, thereby preventing wrinkles and uneven density on the copy paper.

〔Example〕

Hereinafter, features of the present invention will be specifically explained with reference to embodiments shown in the drawings.

FIG. 1 is a bottom view of a thermal head showing an embodiment of the present invention, FIG. 2 is a front view as seen in the path direction, and FIGS. 3 and 4 are left and right side views, respectively.

In the figure, a pair of frames 1b are fixed to both widthwise ends of a thermal head 1 with a heat sink 2 integrated therein. And between these frames 1b, the 15th
Guide rollers 4. A peeling bar 7 and a drive roller 58 rotationally driven by a stepping motor (not shown) are each rotatably attached. The unit of the thermal head 1 including these members is rotatably assembled into a mounting frame F disposed inside the copying apparatus by means of a pivot IC, as shown in FIG.

On the other hand, inside the mounting frame F, a donor carrier 8 shown in FIG. 5 is detachably provided. This donor carrier 8 is provided with a supply roll 50 and a take-up roll 51 to pass an ink donor film 52 for transfer (see FIG. 15).

The thermal head 1 is rotatable relative to the donor carrier 8 by the pivot IC. Further, with respect to the unit of the thermal head 1, as shown in FIG. 15, the drive roller 58 is brought into contact with the pressing roller 59, and the pinch roller 7 is brought into contact with the detection roller 6. Further, the platen roller 3 is similarly set in a posture in contact with the heating resistor 1a of the thermal head 1. These pressure roller 59° detection roller 6 and platen roller 3 are
The rack is arranged with each support shaft passing through the mounting frame F. Incidentally, FIG. 6 shows an outline of the main parts at the time of setting.

The thermal head 1 has a heat sink 2 integrated on its lower surface. In order to make the pressure contact surface between the thermal head l and the platen roller 3 follow the bending deformation of the platen roller 3, the thermal head l is connected by a plurality of fastening screws 9, and the thermal The surface shape of the head 1 can be adjusted. That is, as shown in FIG.
A total of eight fastening screws 9 are arranged in the main scanning direction, and five adjusting screws 10 are arranged on the arrangement line of these fastening screws 9.
is screwed into the heat sink 2 from the bottom surface.

7(a) is a front longitudinal cross-sectional view corresponding to the direction of arrow II in FIG. 1, FIG. 7(b) is an enlarged longitudinal cross-sectional view of the main part,
C) is a side view of the thermal head 1 and the heat sink 2.

As shown in the figure, the heat sink 2 is formed with screw holes 2a, 2b for a fastening screw 9 and an adjusting screw 1O.

The fastening screw 9 passes through the screw hole 2a and is screwed into the screw hole 1d of the thermal head 1, thereby connecting the thermal head 1 and the heat sink 2 together.

On the other hand, the adjustment screw 10 is shaped to be buried in the screw hole 2b, and its tip protrudes from the upper surface of the heat sink 2 so as to press the thermal head 1 upward. Note that the screw hole 2b is
Seven are formed in the extension direction of the thermal head 1,
No adjustment screws 10 are fitted into the two at both ends.

Also, between the thermal head 1 and the heat sink 2,
A spacer 11 made of a stainless steel plate or the like is inserted, and the adjustment screw 10 pushes up the thermal head 1 via this spacer 11. Therefore, the pushing force exerted by the adjusting screw 10 does not act locally only on the tip thereof, but the load acts on the entire lower surface of the thermal head l via the spacer 11 in a distributed manner. In addition, spacer 1
Needless to say, a hole 11a is formed in the hole 11 through which the fastening screw 9 passes.

The shape of the thermal head 1 is set using the adjusting screw 10 so as to correspond to the bending deformation of the platen roller 3. This adjustment is performed on the platen roller 3 as shown in FIG.
The central part of the thermal head 1 is bent and deformed so that it becomes convex upward, so the thermal head 1 is set in a shape that follows this. That is, as shown in FIG. 8(a), since the platen roller 3 bends and deforms in an arched shape so as to be convex upward, the surface shape of the thermal head 1 also closely follows the circumferential surface of the platen roller 3. Adjust to.

Here, the bending deformation of the platen roller 3 can be calculated assuming that it is supported at both ends and receives a load from the entire width direction of the thermal head 1. The calculation formula is given by the following formula, where the X axis is horizontal and the deflection V is vertical, as shown in FIG.

・ ・[1] However, E: Young's modulus of platen roller 3 ■=πd'/64 (a diameter of nib platen roller 3)
w = W / i' 3 From the above equation, the deflection of the platen roller 3 is expressed as a quartic function with respect to the change in length in the axial direction. and,
Setting the shape of the thermal head 1 using the adjusting screws 10 can be done according to the above formula, by changing the amount of protrusion of the five adjusting screws 10 toward the bottom of the thermal head 1, and also by changing the amount of tension on the thermal head 1 caused by the fastening screws 9. Adjust by changing the force. This adjustment work is performed using, for example, a digital electric micrometer M as shown in FIG. This is done by placing the thermal head l with integrated heat sink 2 on top of the reference block,
The measuring spindle 1 is applied to the surface of the thermal head 1, and the downward deflection of the thermal head 1 from the reference plane A-1 to the reference block is measured. At this time, set the position of the contact point of the spindle 1 in the X-axis direction,
The protrusion degree of the adjusting screw 10 and the fastening screw 9 are adjusted so that the amount of deflection corresponding to each value of X satisfies the above formula.
Change the tightness. That is, basically, a quartic curve is obtained by applying downward force to three points on the thermal head 1 and applying upward force to two points between these three points. However, in reality, an optimal curve is obtained by applying downward force at 8 points and applying upward force at 5 points.

Then, by measuring a plurality of measurement points, if the surface of the thermal head 1 is set to have a shape that has a quartic curve that satisfies the above equation, it can be determined that the surface of the thermal head 1 closely follows the deflection deformation of the platen roller 3. Can be done.

As described above, the surface shape of the thermal head 10 can be set in accordance with the deflection of the platen roller 3.

Therefore, compared to the conventional structure in which a gap is likely to occur between the thermal head 1 and the platen roller 3, there is no gap at all, and the distribution of the pressure contact force is uniform throughout. Therefore, there is no fear of wrinkles or density unevenness on the copy paper 53, and good image reproduction is possible.

Furthermore, even if the surface shape of the thermal head 1 is set using the adjustment screw 10 so that the magnitude of the deflection V of the platen roller 3 according to equation (1) corresponds to a value of 1.0 to 1.2V, good.

Even if the platen roller 3 and the thermal head 1 are perfectly aligned, the pressure tends to be concentrated in the axial end area of the platen roller 3 and the pressure contact force tends to be weak in the central area, which tends to reduce the image density in the central area. . Therefore, by setting the surface shape of the thermal head 1 so that the thermal head 1 has a larger deflection than the theoretical deflection of the platen roller 3, the pressure contact force with the platen roller 3, especially in the central portion, becomes greater.

By strengthening the pressure contact force in the central region, uneven density can be prevented.

Not only can good image reproduction be achieved by setting the surface shape of the thermal head 10 as described above, but even better reproduction can be achieved by improving each member. This will be explained below.

When the platen roller 3 has the same diameter as shown in FIG. 10(a), the pressure distribution applied to the copy paper 53 and the ink donor film 52 during transfer is generally as shown in FIG. 10(a).
It is known that it will look like this. This is copy paper 53
This phenomenon is caused by the fact that stress tends to concentrate at the edges of the steel. In this case, the pressure is higher at the edges of the copy paper 53 than at the center, resulting in transfer that tends to be darker on the edges and lighter on the center.

On the other hand, as shown in FIG. 11(a), the platen roller 3 has a large diameter portion 3a at the end, and this is connected to the thermal head 1.
If the copy paper 53 is brought into contact with the surface of the copy paper 53, the pressure distribution applied to the copy paper 53 becomes a negative pressure distribution as shown in FIG.

This is because the end of the platen roller 3 comes off the copy paper 53 and hits the thermal head 1.
This is because stress concentration tends to occur in the large diameter portion 3a, and as a result, no local pressure is applied to the edge of the copy paper 53. Note that FIG. 11(C) shows the measured outer diameters of five platen rollers 3.

In this way, a reproduced image with no difference in density can be obtained with a simple configuration in which the large diameter portions 3a are provided at both ends of the platen roller 3 and the peripheral surface portions thereof are brought into contact with the surface of the thermal head 1.

Further, the guide roller 4 that guides the ink donor film 52 and the copy paper 53 to the thermal transfer position by the thermal head 1 is provided with a crown 4a over the entire guide roller 4 as shown in FIG. The profile of this crown 4a is formed so that the X-Y coordinate axes are taken as shown in the figure and the distance between G and H is expressed by the following equation.

Y=aX' +bX+c...(2) However: a=-1,96X10-', b=6.86X10-
', C=3.8.

When the crown 4a having such a profile is formed over the entire guide roller 4, the circumferential speed at the central portion where the diameter is large is higher than that at the end portions, and the pressing force against the ink donor film 52 and the copy paper 53 is also increased. As mentioned in the case of the platen roller 3, if the rollers have the same diameter, the copy paper 5
Since a large pressure is applied locally to the edge of the third grade, the edge passes before the center. Therefore, the ink donor film 52 and the copy paper 53 are more likely to wrinkle due to differences in pass speed. On the other hand, if the central part is swollen and has a round 4a, the circumferential speed of the central part of the copy paper 53 etc. increases and can be made equal to that of the Ii part, and the pressing force can be equalized, so wrinkles etc. Occurrence can be suppressed.

As described above, by providing the guide roller 4 with the crown 4a, the ink donor film 52 and the copy paper 5
3 can be sent to the thermal transfer position of the thermal head 1 in a state where no wrinkles are generated. Therefore, it is possible to proceed to the thermal transfer process under favorable conditions, which is useful for good image reproduction.

Furthermore, FIG. 13 shows an improvement to eliminate roller marks caused by the detection roller 6 and pinch roller 7.

FIG. 13(a) shows a conventional combination of a detection roller 6 and a pinch roller 70, and the detection roller 6 is made of rubber fixed to the outer periphery of the shaft portion 6b. On the other hand, the pinch roller 7 is also provided on the outer periphery of the shaft portion 7a, and is made of metal. The axial length of the detection roller 6 is shorter than that of the pinch roller 7. However, as the copy paper 53 passes, the pressure from the edge of the detection roller 6 is high, as in the case of the platen roller 3, guide roller 4, etc., and the roller traces of the detection roller 6 are left on the copy paper 53. It will remain.

On the other hand, as shown in FIG. 13, etc., the detection roller 6
If the axial length of the pinch roller 7 is made longer than that of the pinch roller 7, and the circumferential surface of both ends of the pinch roller 7 is chamfered to have a chamfered portion 7b, this problem of roller marks can be solved. This is because the ends of the detection roller 6, which have high pressure against the copy paper 53, no longer come into contact with the copy paper 53, and both ends of the pinch roller 7 are not pressed against the copy paper 53 at a steep angle. It is. Note that the circumferential surface of both ends of the detection roller 6 may also be chamfered.

In this way, if the combination of the detection roller 6 and the pinch roller 7 is improved, the copy paper 5 discharged from the transfer process can be
No roller traces from the detection roller 6 are left on the image forming apparatus 3, making it possible to improve the image quality.

Further, when the ink donor is wiped after thermal transfer, the ink donor adheres to the lower surface of the copy paper 53. Therefore, the copy paper 53 tends to curl toward the adhesion side due to contraction of the ink donor.

On the other hand, as shown in FIG. 6, when the path of the copy paper 53 after passing the detection roller 6 is raised compared to the conventional one (indicated by a dashed line in the figure), the curved surface of the detection roller 6 As a result, the copy paper 53 is corrected in a direction opposite to the curl direction, and curling of the copy paper 53 can be suppressed. For example, if the ejection angle of the copy paper 53 with respect to the path direction from the thermal head l to the detection roller 6 is changed from the conventional approximately 5° to 20°, the copy paper 53 can pass without curling. It becomes possible.

Furthermore, as shown in FIGS. 1 and 2, the thermal head 1 with the integrated heat sink 2 is rotatably mounted on a mounting frame F in which a pivot IC is provided inside the copying apparatus. The pivot IC is supported by a bearing 1e fixed to the frame 1b of the thermal head 1. In order to prevent looseness due to assembly errors and parts processing errors, a collar 1 is integrally formed on one of the bearings 1e and the pivot IC.
A wave washer 1g is provided between f. This wave washer 1g is similar to a spring washer and has the function of elastically receiving and stopping force in the thrust direction.

Since such a wave washer 1r is provided on the pivot IC, when assembling the thermal head 1, the frame 1b
The pivot IC can be mounted without wobbling. Therefore, the unit of the thermal head 1 can be incorporated into the mounting frame F of the copying machine without wobbling.

Further, the platen roller 3 has a structure in which it is urged toward the thermal head 1 by a spring 3b, as shown in FIG. The platen roller 3 is attached to the tip of an arm 3d rotatably provided on a support shaft 3C fixed to a mounting frame F, and a spring 3b is suspended between this arm 3d and a support part F-1 provided on the frame F. is passing.

On the other hand, conventionally, the thermal head 1 and the platen roller 3
As a mechanism for bringing them into pressure contact, a structure was adopted in which the thermal head 1 is urged toward the platen roller 3 side by a spring or the like. In this case, thermal head 1
The entire structure has to be energized, which complicates the structure. In addition, the thermal head 1 has to be given a lot of attention, so accuracy tends to be insufficient. On the other hand, if the platen roller 3 is biased toward the thermal head 1 side as shown in FIG. 14, the structure becomes much simpler, which is advantageous in terms of assembly, maintenance, and inspection.

In this way, by devising the configuration of each member, significant improvements can be made in all aspects, from image reproduction to supplying the original paper 53.

〔Effect of the invention〕

As described above, in the thermal transfer device of the present invention, the thermal head is provided with an adjustment mechanism so that the surface shape follows the bending deformation of the platen roller during pressure contact.

As a result, a pressure-contact state is achieved with no gaps between the thermal head and the platen roller, and image reproduction is prevented from becoming thinner in the center or wrinkled on the copy paper or ink donor film. is performed optimally. Furthermore, since the deflection deformation of the platen roller theoretically forms a quartic curve, the planar shape of the thermal head can be set by assuming this quartic curve and making adjustments, making the work easy. Even if the platen roller has different specifications in terms of diameter, weight, etc., the adjustment mechanism of the thermal head can be operated in accordance with the specifications. Therefore, even if the model is different, it can be handled by setting the shape of the thermal head.
There is no need to increase the specifications of the thermal head.

[Brief explanation of the drawing]

FIG. 1 is a bottom view showing the entire thermal head unit incorporated in the thermal transfer device of the present invention, FIG. 2 is a front view thereof, FIGS. 3 and 4 are left and right side views, respectively, and FIG.
The figure is a side view showing the assembly into the donor carrier and platen roller, etc., and FIG. 6 is a schematic diagram showing the arrangement of each member.
FIG. 7(a) is a front vertical sectional view corresponding to the direction of the arrow I-I in FIG. 1, FIG. Figure (C) is a side view of the thermal head with an integrated heat sink, Figure 8 (a) is a schematic diagram of the thermal head shape setting for platen roller deflection deformation, Figure 8 et al.) is for calculating platen roller deflection. , FIG. 9 is a diagram showing an example of a measuring method for setting the shape of the thermal head, FIG. 10 is an explanatory diagram of copy paper pressure contact and pressure distribution using rollers of equal diameter, and FIG. An example with a large diameter part and an explanatory diagram of pressure distribution,
FIG. 12 is a front view of a guide roller provided with a crown, FIG. 13 is a diagram showing improvements to the detection roller and pinch roller,
FIG. 14 is a side view showing a structure for biasing the platen roller with a spring; FIG. 15 is a schematic diagram showing a conventional thermal head system; FIG. 16 is a schematic diagram showing the arrangement of the thermal head in a copying machine; FIG. 17 is a schematic diagram showing the deflection of the platen roller when it comes into pressure contact with the thermal head. 1: Thermal head 1b: Frame 1d: Screw hole 1f: Collar 2: Heat sink la: Heat generating resistor IC = Pivot 1e: Bearing 18 Two wave washers 2a, 2+): Screw hole 3; Platen roller 3a: Large diameter portion 3b - Spring 3c: Support shaft 3d; Arm 4 Guide roller 4a: Crown 5: Peeling bar 6: Detection roller 6a: Encoder 6b: Shaft portion
7: Pinch roller 7a: Shaft portion 7b
: Chamfered portion 8; Donor carrier 9: Fastening screw 10: Adjustment screw 11 Varnish spacer 11a; Hole 50; Supply roll 51: Winding roll 52: Ink donor film 53: Copy paper 54 Varnish chipping motor 55
: Drive pulley 56: Belt 57; Followed pulley 58 Ni drive roller 59: Press roller 60: Scanning section 61: Thermal transfer section 62-65: Thermal transfer head 66
: Paper cassette 67: Ejection tray A: Reference block ^-1 Two-base table surface M: Digital electric micrometer M-1 Nissin spindle F-1 = Support part

Claims (1)

[Scope of Claims] 1. A thermal transfer device in which an ink donor film and copy paper pass in an overlapping manner, and during this pass, thermal transfer is performed by pressure contact between a thermal head and a platen roller, wherein the thermal head is connected to the platen roller. A thermal transfer device characterized by having an adjustment mechanism that can set the surface shape to follow the bending deformation during pressure welding. 2. The thermal transfer apparatus according to claim 1, wherein the adjustment mechanism is capable of setting the surface shape of the thermal head so as to match the deflection deformation of the quartic curve of the platen roller.