JPH02293172A - Image forming device - Google Patents

Abstract

PURPOSE:To restrain the levitation and slack of a sheet at a printing part to prevent stains on a printing surface by inclining small tensile rollers forming tensile roller pairs in the direction of imparting an outward feed force in a sheet width direction. CONSTITUTION:If a sheet S is levitated from a platen 13 in a process of printing, it comes into contact with a printing means to generate a failure of staining a printing surface. However, by rotating tensile roller pairs 17a, 17b, 17c at a speed higher than the peripheral speed of feed roller pairs 5a, 5b, the sheet S is kept appropriately tensed in the feed direction thereof. Furthermore, the upper tensile rollers 17b, 17c are inclined through an angle theta so as to generate a force of tensing the sheet S outward in a sheet width direction. Thus, the sheet S is kept suitably tensed also in the width direction thereof. In this manner, the sheet S loaded on the printing means is made in an ideal condition free from levitation and slack, therefore being prevented from stains on the printing surface caused by a contact with the printing means.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a sheet conveyance mechanism of an image forming apparatus, and more specifically to a sheet conveyance mechanism that prevents sheets from floating. (0) Conventional technology Conventionally, in an image forming apparatus such as an inject printer or a wire dot printer, a sheet is intermittently conveyed between a platen and a printing means, and an image is recorded on the sheet by scanning the printing means. The device prints on the sheet by scanning the printing means in the width direction of the sheet while feeding the sheet intermittently. In this type of image forming apparatus,
Rubbing of the printing section with the printing means due to the sheet lifting may cause scratches on the sheet, and in order to prevent this rubbing and staining, various sheet lifting prevention means are provided in the printing section. For example, as the sheet lifting prevention means,
Generally, an electrostatic adsorption method is used, in which air is removed from the inside of the platen in the printing section using a pump or the like and the sheet is attracted to the platen, or the sheet is adsorbed to the platen using static electricity.

(c) Problems to be solved by the invention However, in recent years, there has been a demand for miniaturization of the devices themselves, and the above-mentioned conventional devices not only take up a very large space, but also require a suction device, high-voltage power supply, etc. It required expensive equipment. Therefore, as a simple method for suppressing sheet floating in the printing section, there is a sheet conveying mechanism as shown in FIGS. 5 and 6. This mechanism includes a printing section 4 having a platen 41 and a printing means (not shown) above it.
A pair of feed rollers 43 and a pair of tension rollers 45 for supporting and conveying the sheet are provided before and after the rollers 2, and the circumferential speed of the pair of pull and feed rollers 45 on the downstream side is higher than the circumferential speed of the pair of feed rollers 43 on the upstream side. Like roller vs. 43
．． 45 has a speed difference to give tension to the seat S. As a result, the sheet S is brought into close contact with the platen 41 and is conveyed in the direction of the arrow 46. In such a horizontal mechanism, in order to accurately feed the sheet S at a constant speed or intermittently by a constant amount, the sheet supporting force of the upstream feed roller pair 43 is transferred to the downstream pull feed roller pair. 45, and this feed roller pair 4
The sheet feeding speed of the pair of pulling and feeding rollers 45 on the downstream side is set higher than the sheet feeding speed of No. 3.

However, according to the above configuration, sheet lifting (sagging) in the direction perpendicular to the traveling direction (arrow 46) of the sheet S can be suppressed as shown in FIG. The sheet floating Sa parallel to , as shown in Figure 6, could not be suppressed sufficiently. For this reason, even in a mechanism in which a pair of pulling rollers 45 is disposed downstream of the printing section 42, friction with printing means such as an inject head often occurs, resulting in staining of the sheet S. .

Furthermore, when a sheet pulling mechanism consisting of two long pulling roller pairs 45 is adopted, one of the pulling roller pairs 45 comes into pressure contact with the sheet S immediately after printing, so that ink, etc. If it is not completely fixed on the sheet S, the image will be distorted.

Therefore, the present invention provides an image forming system that has a sheet conveyance mechanism that can be placed in the printing section and does not cause sheets to float, by providing a pulling roller disposed on the downstream side of the printing section with a function of pulling the sheet S outward. The goal is to provide equipment.

(:) Means for Solving the Problems The present invention has been made in view of the above-mentioned circumstances, and for example, as shown with reference to FIG. , sheet (S) to this printing section (16)
) and the printing unit (16).
), the image forming apparatus includes a pair of pulling rollers (17) for applying tension to the printing area of the sheet (S), the pair of pulling rollers (17) having a long pulling roller (17a) and This consists of short tension rollers (17b, 17c) that are in pressure contact with the outer periphery and partially in pressure contact with the width direction ends of the sheet (S), and each tension roller (17a, 17c) is connected to the sheet width. It is characterized by being inclined in a direction that provides an outward conveying force.

(E) Function Based on the above configuration, the printing section (
The sheet (S) conveyed to the sheet (S) is transported by a plurality of inclined bow tension rollers (17b
, 17c), a conveying force in the outward direction is applied to the sheet width, and the sheet (S) in the printing section (16) is
This suppresses the occurrence of lifting and sagging parallel to the traveling direction of the sheet (S), and thereby prevents the printing surface of the sheet (S) from rubbing against the printing means (15) placed in the printing section (16) and the sheet (S). Contamination is prevented.

Note that the above-mentioned numbers in brackets are shown for reference to the drawings and do not limit the structure of the present invention in any way.

(F) Example A first example of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a plan view of a sheet conveying mechanism in the vicinity of a printing section in an image forming apparatus showing a first embodiment of the present invention, and FIG. 2 is a longitudinal side view thereof. In the same figure,
A shaft 6 to which a lower conveyance roller 5a is fixed is rotatably mounted on the left and right side plates 2 and 3 via a bearing 7, respectively. The upper transport roller 5b, which is in pressure contact with the upper peripheral surface of the lower transport roller 5a, is fixed to a shaft 9, and both ends of the shaft 9 are engaged with recesses formed at one end of the pressure arm 10. Retained. The pressure arm 10 is pivotally connected to the side plates 2 and 3 by a shaft 11, and the upper conveying roller 5b is moved by the elasticity of a tension spring 12 whose both ends are locked to the pressure arm 10 and the side plate 2 or 3, respectively. It is rotationally biased in the direction of being brought into pressure contact with the lower conveyance roller 5a. The lower conveying roller 5a and the upper conveying roller 5b constitute a conveying roller pair 5. On the downstream side of the pair of conveying rollers 5, a printing unit 16 is provided which includes a platen 13 whose both ends are fixed to the side plates 2 and 3, and a printing unit 15 arranged above the platen. When the image forming apparatus is an inject printer, the printing means 15 is an inject head, and this inject head uses thermal energy to cause a change in the state of the liquid, including the formation of bubbles. An image is recorded by forming droplets.

The tension roller pair 17 arranged downstream of the printing section 16 includes a lower tension roller 17a and a plurality of upper tension rollers 17b that are in pressure contact with both ends of the upper peripheral surface of the lower tension roller 17a.
, 17c. Both ends of the shaft 19a to which the lower tension roller 17a is fixed are rotatably attached to the side plates 2 and 3 via bearings 20, respectively. The upper tension rollers 17b, 17c are rotatably mounted on one end of a pressure lever 22, 23 which is pivotally connected to the side plates 2, 3 via a shaft 21 via shafts 19b, 19c,
The pressure levers 22 and 23 are pulled by tension springs 26 whose other ends and both ends are locked to raised cutouts 25 formed on the side plates 2 and 3, respectively, to pull the upper rollers 17b and 17.
c are each biased in the direction of pressure contact with the lower tension roller 17a.

Further, the axes 26b, 26c of the upper tension rollers 17b, 17c are aligned with the axis 26b of the lower tension roller 17a.
The shafts 19b and 19c are inclined at an angle θ with respect to a, and the inner ends of the shafts 19b and 19c are located on the downstream side. As a result, the lower tension roller 17a and the upper tension roller 17b
, 17c are directed slightly outward as shown by arrows B and C. A gear 2 fixed to one end of the shaft 6 of the lower conveyance roller 5a
7 is connected to a gear 30 fixed to the shaft of the lower tension roller 17a via an idle gear 29 supported by the side plate 3, and is driven in the direction of the arrow by the lower transport roller 5a or a drive source (not shown). In conjunction with this, the lower pulling roller 17a rotates in the direction of the arrow. Here, the circumferential speeds of the lower tension roller 17a and the upper tension roller 17b that rotate following this are set to be greater than the peripheral speeds of the lower conveyance roller 5a and the upper conveyance roller 5b that rotates following this. There is.

Further, the force with which the sheet S is held by the pair of conveying rollers 5 by the tension spring 12 is greater than the force with which the sheet S is held by the pair of tension rollers 17 by the tension spring 26. The upper tension rollers 17b and 17c are arranged such that a part of the upper tension rollers 17b and 17c are in pressure contact with each end of the sheet S being conveyed, and the other part is in pressure contact with the outer peripheral surface of the lower tension roller 17a. .

Next, the operation of the above-mentioned device will be explained. The sheet S sent to the pair of transport rollers 5 by a transport roller (not shown) is conveyed onto the platen 13 while being sandwiched between a lower transport roller 5a and an upper transport roller 5b, and is further conveyed onto the platen 13 by a lower tension roller 17a and an upper tension roller 17b. , 17c. At this point, the driving of the sheet S is temporarily stopped, and printing is performed on the sheet S while scanning 15 printing stages of an inject or the like, and printing for one line is completed. . Thereafter, sheet feeding by a predetermined amount and printing of each line are repeated to print the entire area of the sheet.

During this printing process, if the sheet S floats off the platen 13, there is a problem that the sheet S will come into contact with the printing means 15 and stain the printing surface. As the tension roller pair 17 rotates at a circumferential speed higher than the circumferential speed of the transport roller pair 5, an appropriate tension state is maintained in the traveling direction of the sheet S, and furthermore, the upper tension roller 17b , 17c are tilted by an angle θ to generate a force that pulls the sheet outward relative to the sheet width, so that a moderate tension is maintained also in the direction in which the sheet travels.

As a result, the sheet S on the printing means 15 is in a good condition without lifting or sagging, so that the printing surface can be prevented from being stained due to contact with the printing means 15. Furthermore, in an image forming apparatus having a non-image area (image missing width) at both ends of the sheet width, the upper tension roller 17c can be arranged in the area of the non-image area, so that the image quality of the recording sheet can be improved. It is advantageous to hold. In addition, the angle θ at which the upper tension rollers 17b and 17c are tilted is
If this value is too small, the effect of pulling the sheet S outward will be weakened, and if it is too large, the rotational followability with the lower pulling roller 17a will be poor, so the appropriate value of θ is about 2''.

3 and 4 respectively show a second embodiment of the invention. This embodiment differs from the first embodiment described above in the support structure of the upper tension roller. A notched shaft 33 having a notched circular cross section is rotatably attached to the side plates 2 and 3, and a pressure member 3 is attached to this notched shaft 33.
5 and 36 are mounted so as to be non-rotatable and slidable. Upper tension rollers 17b and 17c similar to those in the first embodiment are attached to the free ends of the pressure members 35 and 36 in an inclined manner, respectively. Leg pieces 35a and 36a parallel to the notch shaft 33 are formed at the base of the pressure members 35 and 36, respectively, and racks 35b and 36b formed opposite to the leg pieces 35a and 36a are Notch shaft 3
The pinions 37 are respectively meshed with the pinions 37 which are pivotally supported in the center of the pinions 3. The notch shaft 33 is a cut-and-raise 2 of the side plate 2.
5 and the notched shaft 33 at both ends thereof, the upper tension rollers 17b, 17c are urged to rotate in a direction in which they come into pressure contact with the lower tension roller 17a.

With the above configuration, if one of the pressure members 35, 36 is slid along the notch shaft 33 in the directions of arrows D and E to match the desired sheet size, the other pressure member 36, 36 can be adjusted to the desired sheet size.
5 can also be linked and aligned. That is,
Even in a device that feeds sheets S of various sizes with a central reference, prevention of sheet floating can be achieved by simply moving the pressure members 35 and 36. Note that in an apparatus that feeds sheets on a one-sided basis, it goes without saying that only one side of the pressure members 35 and 36 may be made movable.

In each of the above embodiments, since the printing device 15 is a downward printing device in which the printing means 15 faces downward, the pulling roller pair 1
7 is necessarily in a vertical relationship, and the lower tension roller 17a is a long roller and the upper roller is divided into a plurality of parts (two in the embodiment). The arrangement relationship may be reversed.

Also, the printing direction of the printing means 15 and the pull opening-ra pair 1
7 is not limited to the above embodiment; for example, in the case of horizontal printing in which the sheet S is conveyed in the vertical direction, the tension roller pair 17 may be arranged in parallel in the horizontal direction. It is also possible to achieve the same effects with the same configuration as in each of the embodiments described above.

(G) Effects of the Invention As explained above, according to the present invention, one of the pair of tension rollers disposed on the downstream side of the printing section is divided into a plurality of parts and disposed at both ends of the sheet, and By arranging the plurality of tension rollers in an inclined state so as to generate a conveying force in an outward direction with respect to the width of the sheet, lifting and sagging of the sheet in the printing section can be suppressed. This can prevent the printing means on the sheet from rubbing against the sheet, making it possible to provide high-quality printed matter.

[Brief explanation of drawings]

FIG. 1 is a plan view of a sheet conveying mechanism in an image forming apparatus showing a first embodiment of the present invention, FIG. 2 is a vertical side view thereof, and FIG. 3 is an image forming mechanism showing a second embodiment of the present invention FIG. 4 is a plan view of the sheet conveyance mechanism in the apparatus, FIG. 4 is a vertical side view, and FIGS. 5 and 6 are sheet conveyance mechanisms 1! in the conventional image forming apparatus. ! This is a side perspective view. One angle of inclination.

Claims (1)

[Scope of Claims] 1. A printing section that prints on a sheet, a pair of feed rollers that conveys the sheet to this printing section, and a tensioning device located downstream of the printing section that applies tension to the printing area of the sheet. In an image forming apparatus having a pair of rollers, the pair of pulling rollers includes a long pulling roller and a small pulling roller that presses against the outer periphery of the long pulling roller and a part of which presses against the widthwise end of the sheet, and each small An image forming apparatus characterized in that the tension roller is turned off in a direction that applies an outward conveying force to the sheet width. 2. The image forming apparatus according to claim 1, wherein at least one of the small pulling rollers is configured to be movable in the width direction of the sheet. 3. The image forming apparatus according to claim 1, wherein the printing means records an image by causing a state change including air bubbles in the liquid using thermal energy to form droplets.