JPH01176746A - Image forming device - Google Patents

Abstract

PURPOSE:To form a stable image simply by sensing the amount of loop generated while a sheet transported moves from a resist roller couple to image forming parts, and by controlling drive of the sheet transport means. CONSTITUTION:A sheet S transported from upstream is sent to between guide plates 6, 7 with the aid of a resist roller couple 1a, 1b, to form an image at image forming parts 11, 12. Part of the guide plate 6 is cut to form a hole 6a, and thereto one of the levers 9a of a Y-shaped sensing means 9 shall face. This lever 9a contacts the sheet S and rotates round a shaft 10, and the other lever 9b is reciprocated between sensors Sa, Sb. The drive speed of the resist roller 1b is controlled on the basis of output of the sensors Sa, Sb. This stabilizes the transport speed without use of high precision resist rollers, and a stable image can be obtained.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to an image forming apparatus such as a copying machine, a printing machine, or a laser beam printer. The present invention relates to an image forming apparatus comprising:

(B) Prior art Conventionally, an image forming apparatus is known in which a sheet is synchronously conveyed to an image forming section by a pair of registration rollers. The dimensional accuracy of the diameter of each roller of the pair of registration rollers is strictly controlled so that they are the same.

9 Problems to be Solved by the Invention By the way, in the above-described image forming apparatus, the drive side rollers (rollers whose iron cores are coated with a rubber material) of the pair of registration rollers are used, and each of the pair of registration rollers is Because the rollers are in pressure contact with each other, the rubber material of the driving roller deforms and changes its diameter, which changes the sheet conveyance speed of the pair of registration rollers and causes the transferred image to shrink or expand. In addition, the rubber material of the drive-side roller gradually wears out, and the diameter of the drive-side roller becomes smaller, which slows down the sheet conveyance speed, resulting in an image that is distorted.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus in which the above-mentioned problems are solved by controlling the sheet conveyance speed of a pair of registration rollers.

(C) 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 FIGS. A pair of rollers (1), an image forming section (11, 12) that forms an image on a sheet h (S) conveyed by the pair of registration rollers (1), and a driving means that fully drives the pair of registration rollers (1). (3) An image forming apparatus comprising: a detection means (9, Sa, Sb) for detecting a loop amount of the sheet (S) from the registration roller pair (1) to the image forming section (11, 121); , and control means (15) for controlling the nine movement means (3) based on the detection signal from the detection means (9, Sa, Sb).

Function: Based on the above configuration, the sheet (S) fed to the registration roller pair (1) is held by the registration roller pair (1) and synchronously conveyed to the image forming section (11, 12). , an image is formed by the image forming section (11, 12). At this time, the sea 1-(S) uses a detection means (
9, Sa, Sb) and the detection means (9, Sb).
The control means (15) which receives the detection signals of a and Sb) controls the drive means (3) based on the detection signals so that the loop amount of the sheet (S) becomes a predetermined amount.

(F) Examples Examples of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, the image forming apparatus includes a pair of distrollers 1 that are in pressure contact with each other. It is composed of a lower roller 1b covered with a rubber material. A gear 2 is fixed to one end of the shaft 1c of the lower roller 1b, and the gear 2 meshes with a gear 5 fixed to the output shaft of the motor 3. Further, a pair of guides 6 and 7 are arranged downstream of the registration roller 1, and the upper guide 6 of the pair of guides 6 and 7 has a hole 6a. Further, on the upper part of the upper guide 6, a sensor lever 9 having a V-shape in front view and a crank shape in plan view is rotatably supported by a shaft 10 fixed to the fuselage (not shown). One end 9a of 9 is adapted to abut against the sea +-S which is conveyed within the guide pair 6.7 through the hole 6a. On the other hand, two photosensors Sa and Sb are arranged near the other end 9b of the lever 9, and these sensors Sa and Sb are turned on and off by the movement of the other end 9b. There is.

A photosensitive drum 1 is provided downstream of the guide pair 6 and 7.
1, a transfer charger 12, and the like, and a conveyor belt 13 for conveying the beam -+-S to a fixing section (not shown) is disposed downstream of the image forming section. has been done.

Further, the image forming apparatus includes a control section 1 as shown in FIG.
5, and the control section 15 includes the photosensor S.
a and Sb are connected through an input circuit 16, and the motor 3 is connected through a motor driver 17.

Next, the operation of this embodiment will be explained along the flowchart of FIG.

When the sheet S is conveyed from upstream to the pair of registration rollers 1, the sensor S comes into contact with the nip of the pair of rollers 1 and is moved obliquely, and then, after a predetermined time, the pair of registration rollers 1 starts rotating, and the sensor S is conveyed to the pair of guide rollers 6. 7 and is conveyed to the image forming sections 11 and 12. At this time, one end 9a of the sensor lever 9 comes into contact with the sheet S, the lever 9 rotates due to the loop of the sheet S, and the other end 9b of the lever 9 turns the photosensors Sa and Sb ON/OFF. The loop amount of the sheet S is measured (Sl). Then, the control unit 15, which receives signals from the photosensors Sa and Sb via the input circuit 16, determines whether the loop amount is smaller than the appropriate value (52
), is large (Sa), and if it is determined to be appropriate, that is, if one end 9b of the sensor lever 9 is not detected by both photosensors Sa and Sb (see Fig. 2), move the registration roller pair 1 at the same speed. Drive. after that,
The sheet S has an image formed on a photosensitive drum 11 in an image forming section transferred thereto by a transfer charger 12, and is conveyed to a fixing device by a conveyor belt 13 to have the image fixed thereon. At this time, the control unit 15 stops the motor 3 via the motor driver 17 after a sufficient time for the rear end of the sheet S to pass through the nip of the registration roller pair 1, and stops the sheet S from being fed by the registration roller pair 1. The process ends (S4).

Further, in S2 described above, if it is determined that the loop amount of the sheet S is smaller than the appropriate value, that is, one end 9b of the sensor lever 9 is detected by the photo sensor sb, and the sensor sb
is 0FFI (see FIG. 5), the control unit 1 receives the OFF signal from the sensor sb via the input circuit 16.
5 connects the motor 3 to the seat S via the motor driver 17.
The sheet conveying speed of pair 1 of registration rollers is increased by increasing the speed (for example, 1 to 6%) until the loop amount becomes appropriate (S5
). Then, the operation from S1 described above is performed again.

Further, in S3 described above, if it is determined that the loop amount of the sheet S is larger than the appropriate value, that is, one end 9b of the sensor lever 9 is detected by the photo sensor Sa, and the sensor Sa
is 0FFt (see FIG. 6), the control unit 15, which receives the OFF (g) from the sensor Sa via the input circuit 16, controls the motor 3 via the motor driver 17 so that the loop amount of the sheet S is Reduce speed until appropriate (e.g. 1-6%)
to lower the sheet conveyance speed of registration roller pair 1 (S
c). Then, the operation from S1 described above is performed again.

In the above embodiment, the sensor lever 9 and the photosensors Sa, Sb were used as the detection means for detecting the loop amount of the sheet S, but the present invention is not limited to this, and as shown in FIG. The optical sensor 16 may also be used.

In this case, the speed increase or decrease of the registration roller pair 1 can be linearly controlled based on the output voltage of the optical sensor 16.

In addition, in the above embodiment, the number of photosensors for detecting the large and small loop amounts of the sheet was one each, but the number is not limited to this, and as shown in FIG. Individual Sa.

Sb, Sc, and Sd may be arranged, and the sheet conveyance speed of the pair of registration rollers 1 may be changed in multiple stages depending on the size of the loop.

Further, in the above embodiment, the sensor lever 9 was used as a component of the detection means, but the present invention is not limited to this, and a cam or the like may be used.

(1.) As described in detail, according to the present invention, the loop amount of the sheet from the registration roller pair to the image forming section is detected, and the sheet conveyance speed of the registration roller pair is controlled based on the loop amount. With this configuration, the sheet conveyance speed of the pair of registration rollers can be stabilized, and stable image formation can be performed. As a result, the sheet conveyance speed can be stabilized without using a pair of registration rollers with good dimensional accuracy, and the life of the pair of registration rollers can be extended.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the main parts of an image forming apparatus according to the present invention, and FIG. 2 is a front view thereof. Further, FIG. 3 is a block diagram showing a control means according to the present invention. Furthermore, FIG. 4 is a flowchart showing the operation of the present invention. 5 and 6 are front views showing the operation of the present invention. 7 and 8 are front views showing other embodiments of the present invention. 1. Registration roller pair, 3. Drive means, 9
．． 16. Sa, Sb, Sc, Sd - detection means, 11.1
2... Image forming unit, 15... Control means, S...
sheet.

Claims (1)

[Claims] (1) An image forming apparatus including a pair of registration rollers that synchronously conveys a sheet, an image forming section that forms an image on the sheet conveyed by the pair of registration rollers, and a drive unit that drives the pair of registration rollers, a detection means for detecting a loop amount of the sheet from the pair of registration rollers to the image forming section; and a control means for controlling the drive means based on a detection signal from the detection means;
An image forming apparatus comprising: