JPS6132835A - Image forming device - Google Patents

Abstract

PURPOSE:To facilitate control over an automatic original feeding device by detecting the feed position of an original by the automatic original feeding device from the number of driving pulses of a motor for original feeding even after a specific sensor detects the original, and detecting it with the invariably constant counted number even when the feed speed varies. CONSTITUTION:The original 1 is fed at a variable speed according to variable magnification. When the original 1 advances by 115mm. after its front end is detected by the sensor 6, transfer paper 14 is sent out from a registration roller 16. In this case, the time up to the driving timing of the roller 16 varies with the variable magnification. A motor which drives a belt 4 for conveying the original 1 has its speed brought under PLL control and variation in speed corresponding to the variable magnification is attained by setting the frequency of oscillation pulses of the oscillator in a PLL loop. Thus, motor driving pulses varying with the variable magnification are counted to detect the feed position of the original, thereby obtaining registration timing.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus with an automatic document feeding system suitable for copying large-sized originals, and particularly to an image forming apparatus capable of copying at variable magnifications such as enlargement and reduction. The present invention relates to an image forming apparatus that is improved in detecting the position of a document when timing registration.

(Prior Art) Conventionally, copying devices as image forming devices capable of copying large-sized originals larger than the original platen glass have fixed optical systems and automatically feed the originals using an automatic document feeder to make copies. In the case of copying at the same magnification, the rotational peripheral speed of the photosensitive drum and the moving speed of the original are made the same, but in the case of enlarged or reduced copying, the feeding speed of the original is changed, and the former In the latter case it is slow, in the latter case it is fast.

On the other hand, the registration timing for aligning the leading edge of the image on the photosensitive drum with the leading edge of the transfer paper is set at the time when the document is sent out a predetermined distance toward the optical system. The position detection of the predetermined distance depends on how much time has passed since the leading edge of the document is first detected by a position sensor provided at a specific position when the document is first sent out, and then the document reaches the position of the predetermined distance.

This time is measured by counting a constant reference clock.

However, as mentioned above, if the magnification is different,
Since the moving speed of the document differs, the time required to reach the position at the predetermined distance changes.

Therefore, the number of counts to be detected is set in advance to be different depending on the variable magnification such as normal magnification, enlargement, reduction, etc., and when a specific magnification is selected, the count number set according to that magnification is set in advance. At the time of counting, it is detected that the document has reached the position at the predetermined distance.

Based on this detection signal, the registration roller is driven to feed the transfer paper, and the timing is set so that the leading edge of the image on the photosensitive drum and the leading edge of the transfer paper are aligned.

Therefore, in the past, it was necessary to set the count number according to the variable magnification ratio, which made control complicated, and especially when the variable magnification ratio could be selected many times, the control became extremely complicated. Ta.

(Object of the Invention) The present invention has been made in view of the above-mentioned points, and it is possible to keep a specific feed position of a document in an automatic document feeder at a constant count even if the feed speed of the document changes. An object of the present invention is to provide an image forming apparatus that can detect images and simplify its control.

(Structure of the Invention) For this purpose, the present invention is configured such that the document feed position in the automatic document feeder is detected by the number of drive pulses of the document feed motor after a predetermined sensor detects the document. are doing.

(Example) Examples of the present invention will be described below. FIG. 1 schematically shows a copying apparatus, which is an image forming apparatus, and is equipped with an automatic document feeder for copying large-sized documents using electrophotography.

The original I is placed on the original plate 2, and when the copy start key is operated, it is fed by the feed roller 3, then conveyed by the feed belt 4 over the surface of the original platen glass 5, where it is optically scanned, and then the original is printed. Uke is sent out to the plate. A sensor 6 detects the document 1. The automatic document feeder is configured as described above.

An exposure light source 7 is fixed below the document table glass 5, and the light image of the document 1 obtained by the light source 7 is transmitted to the photosensitive drum 1 as an image forming photosensitive member via a mirror 8.9.
Guided to the surface of 0. The photosensitive drum 10 is a grounded metal cylinder with a photoconductive layer made of selenium or the like provided on the outer peripheral surface thereof, and rotates in the direction of arrow a in synchronization with the feeding of the original document 1.

In this photosensitive drum 10, before the arrival of the optical image, the photoconductive layer is, for example, uniformly charged by a charging electrode 11 to which a high DC voltage is applied, and the photoconductive layer in this state receives the optical image. Then, the conductivity of the area that receives the light increases, and the electrical charge in that area escapes to the metal cylinder, and positive charges remain in the dark area depending on the degree of brightness, and this causes the photoconductive layer to An electrostatic latent image corresponding to the image of the original is formed on the surface of the document.

When the portion on which the electrostatic latent image is formed reaches the developing bag f&12, the negatively charged developer is attracted to the remaining positively charged portion of the photosensitive drum 10 by electrostatic force. As a result, a developer image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum 10.

The transfer paper 14 in the paper feeding unit 13 is sent out in the direction of the registration roller 16 by the feeding roller 15 and once stopped, and the leading edge of the transfer paper 14 and the photosensitive drum 1
The surface of the photosensitive drum 10 is sent out again from the registration roller 16 at a timing such that the leading edge of the developer image on the photosensitive drum 10 coincides with the top of the photosensitive drum 10, and the transfer pole 17 to which DC high pressure is applied to the transferred transfer paper The developer image is transferred.

Thereafter, the transfer paper is separated from the photosensitive drum 10 by the second pole 18 to which AC high voltage is applied, and the conveyor belt 19
The developer image is then sent to a fixing device 20, where the developer image is fixed, and then discharged onto a paper discharge tray 21.

Reference numeral 22 represents a removing electrode that removes charges remaining on the photosensitive drum 10 , and 23 represents a cleaning device that removes developer remaining on the surface of the photosensitive drum 10 .

Now, as described above, the photosensitive drum 10 rotates at a constant speed, but the speed at which the document 1 is fed changes depending on the magnification ratio. For example, 1:1 magnification (1: 1)...230 Dragon/S magnification (1:
1.41)...163 Iku/S reduction (1: 0.71)
...324 m/s.

Therefore, in order to align the leading edge of the transfer paper 14 with the leading edge of the developer image on the photosensitive drum 10, the registration roller 16
When determining the driving timing, the transfer paper 14 is sent out from the registration roller 16 when the leading edge of the original 1 is further advanced by 115+n after being detected by the sensor 6. In this case, the time from the time of detection by the sensor 6 to the time when the distance reaches 115 mm, that is, the time to the drive timing of the registration roller 16, is 0.5 seconds (115/230) at the same magnification.
When enlarging...0.7s (115/163) When reducing -0.35s (115/324).

That is, the registration timing of the transfer paper changes depending on the magnification ratio. Conventionally, this interval has been measured by counting constant reference pulses, but as the magnification increases, the control becomes complicated.

By the way, the speed of the motor that drives the belt 4 that conveys the document 1 described above is controlled by PLL control. In this case, the speed change (setting) according to the magnification is PL
This depends on the setting of the frequency of the oscillation pulse of the oscillator in the L loop.

Therefore, in this embodiment, the motor drive pulses that change depending on the magnification ratio are counted to detect the document feeding position and obtain the registration timing.

From the table above, the frequency of the motor drive pulse at equal magnification is 10
Hz, the same frequency when enlarging is 7 Hz, and the same frequency when reducing is 1711 z, and if you count only 5 pulses of these, the time is the above-mentioned time, that is, when it is the same size... 0
．． 58 When enlarging...0.73 When reducing...0.35 s, and the same document feeding position, that is, registration timing, as in the conventional case described above can be obtained.

In this case, the count is 5 pulses regardless of the magnification ratio,
It is no longer necessary to preset the number of pulses to be counted according to the variable magnification ratio as in the conventional case.

(Effects of the Invention) As described above, according to the present invention, a specific feeding position of a document in an automatic document feeder can be detected with a very constant count number even if the feeding speed of the document changes. Even in an image forming apparatus in which a plurality of magnifications can be selected, the registration timing can be easily controlled.

[Brief explanation of the drawing]

The figure is a schematic configuration diagram of a copying apparatus having an electronic automatic document feeder for copying large-sized documents. 1...Large original, 2...Document type, 3...Feeding roller, 4...Feeding belt, 5...Original platen glass, 6
...Sensor 1.7...Light source for exposure, 8.9...Mirror, 1o...Photosensitive drum, 11...Charging electrode, 12
...Developing device, 13...Paper feeding unit, 14...
Transfer paper, 15... Feeding roller, 16... Registration roller, 17... Transfer pole, 18... Separation pole, 19... Conveyance belt, 20 Fixing device for, 21...
- Paper discharge tray, 22... electrode removal, 23... cleaning device.

Claims (1)

[Claims] (1) In an image forming apparatus equipped with an automatic document feeder, the document feed position in the automatic document feeder is detected by the number of drive pulses of the document feed motor after a predetermined sensor detects the document. An image forming apparatus characterized in that: