JPH07306550A - Trayless double-sided printing device - Google Patents

Abstract

PURPOSE:To obtain a trayless double-sided printing device which is small in size and light in weight and provided with a mechanism for supplying and carrying paper so as not to collide with following paper by providing a calculation means obtaining a paper supply interval in a double-sided printing mode. CONSTITUTION:This printing device 1 is constituted of an image forming part 6 consisting of a photoreceptor drum 5, the calculation means, and a paper feeding means for feeding paper from a paper supply tray 2 based on a timing signal outputted from the calculation means. The calculation means calculates the paper supply interval Tdf based on paper carrying loop time Tl, paper passing time Tt and the shortest time of gap between papers Tgmin obtained from a control means controlling the entire device. Tdf=(T1/N)X2. N is the division number of the paper carrying loop time, and a maximum odd number which is equal to or under the quotient of N=[Tl/(Tt+Tgmin)]. The calculation means outputs the timing signal at the interval Tdf to the image forming means 6, the paper feeding means and a paper feeding means driving device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a trayless double-sided printing device.

[0002]

2. Description of the Related Art FIG. 1 is a diagram showing a concept of a sheet conveying system of a trayless double-sided printing apparatus. The paper transport system 1 of the trayless double-sided printing apparatus uses the paper 3 supplied from the paper feed tray 2.
Is conveyed to the image forming unit 6 including the photosensitive drum 5 and the like on the conveying path 4, and after a screen is formed on the sheet,
The image is fixed by the fixing unit 7 including a heat roll, and the division unit B
Then, the sheet is ejected to the ejection tray 8 side and the single-sided printing is completed. When printing on both sides, the paper with the image fixed on one side
It is sent to the reversing unit 9 side in the division unit B and is conveyed from the reversing unit 9 to the transport path 4
Is conveyed toward the confluence A of the sheet feeding tray 2 at the confluence A.
The sheet is alternately arranged with the unprinted sheet supplied from the sheet and sent to the image forming section 6 again, an image on the back side is formed on the back side of the sheet, and is fixed by the fixing section 7. Only the waste paper is discharged to the discharge tray 8 side.

In a conventional trayless double-sided printing apparatus, as shown in Japanese Patent Laid-Open No. 60-73635, the sheet feeding interval for printing a table is set to a time interval twice as long as that for printing only one side, After printing, reverse the paper to print on the back side is configured to be fed in the middle of the unprinted paper on the front side, and the paper to print on the front side and the paper to print on the back side are transported alternately. Was printing. In such a paper feeding method, in the single-sided printing mode in which only one side is printed, as shown in the timing chart (a) of FIG.
Then, the paper having the paper passage time Tt determined by the size of the paper is in a state of sequentially passing with a predetermined inter-paper gap Tg. Further, in the double-sided printing mode, the passing condition of the paper at the same point is as shown in the timing chart of FIG. 2B, in which the first paper is returned to the confluence A via the reverse conveyance loop in which the front surface is printed. Until the time comes, that is, during the paper transport loop time Tl,
Paper is supplied from the paper feed tray 2 to the conveyance path 4 at a time interval twice as long as in single-sided printing, and thereafter, the supply of paper from the paper feed tray 2 and the supply of paper from the reverse conveyance path alternate. Done.

Therefore, at the confluence point A, the sheet transport loop time Tl is set so that the sheet whose one side has been printed and which has been turned upside down arrives in the middle of the unprinted sheet fed from the sheet feeding tray 2. Thus, when the sheet length does not change, these sheets do not overlap and are not fed to the transport path 4.

By the way, when the size of the paper fed from the paper feed tray 2 is changed and the paper length is changed, in the case of single-sided printing, the paper passing time Tt is only increased and the inter-paper gap Tg is changed. Instead, normal printing can be performed without problems as shown in FIG.

However, the paper transport loop time Tl does not change even if the paper length changes unless the process speed or fixing speed changes. Therefore, in the case of double-sided printing in which the paper size is changed, as shown in FIG. As shown
After printing on one side, the sheet turned upside down may overlap with the unprinted sheet fed from the sheet feed tray 2.

In order to avoid this problem, a mechanism for resetting the paper transport loop time Tl every time the paper size (paper length) changes is required. Similarly, when the process speed, the fixing speed, etc. change, a mechanism for adjusting the paper transport loop time is required. As a mechanism for adjusting the paper transport loop time, it is conceivable to provide a weight mechanism for stopping the paper for an arbitrary time after the fixing mechanism. However, if the weight time is increased, a problem such as collision with the succeeding paper may occur. Yes, there are many difficult points. Also,
There is also a problem that the space for providing such a mechanism and the cost increase due to the provision of this mechanism.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is a trayless double-sided printing apparatus having a mechanism that is small and lightweight and that feeds and conveys a sheet so that it does not collide with a succeeding sheet. The purpose is to provide.

[0009]

In order to achieve such an object, the trayless double-sided printing apparatus of the present invention has a sheet feeding interval (periodic timing) for feeding sheets in the double-sided printing mode.
From the time (paper transport loop time) when the paper that passed a certain point prints an image on one side and then returns after being reversed (paper transport loop time), the paper transit time determined by the paper size, and the shortest permissible inter-paper gap time. Equipped with a calculating means for obtaining.

[0010]

According to the present invention, even when the paper length, the process speed, the fixing speed, or the like changes, the paper feed interval is obtained from the paper feed loop time, the paper pass time, and the shortest paper gap time, and the paper feed interval is calculated from this calculation result. It is possible to achieve paper feed timing control that does not overlap the succeeding paper simply by changing the paper feed timing. Therefore, compared to the prior art, it is not necessary to provide a weight mechanism or the like in the transport path, and it has a feature of being advantageous in terms of equipment space and cost.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a trayless double-sided printing device according to the present invention will be described with reference to FIG. Paper transport loop time (Tl) and paper transit time (Tt) compared to similar conventional devices
It is characterized in that a calculation means 10 for calculating the paper feed interval (Td f) from the shortest inter-paper gap time (Tg min) is provided. That is, the trayless double-sided printing device 1 of the present invention is
Paper feed tray 2, paper 3, transport path 4, and photosensitive drum 5
An image forming unit 6 including a heat roller, a fixing unit 7 including a heat roll, a discharge tray 8, a sheet reversing unit 9, and a calculating unit 1
0 and a paper feeding means 11 for feeding the paper from the paper feed tray 2 based on the timing signal output from the calculating means.
Composed of and.

The calculating means 10 is a paper transport loop time (T) obtained from a control means (not shown) for controlling the entire apparatus.
l), the paper passage time (Tt), and the shortest inter-paper gap time (Tg min), the paper feed interval (Td f) is calculated, and the timing signal is sent to the image forming means 6, the paper feeding means 11 and the paper at this interval. It outputs to the transportation device driving device.

In the trayless duplex printing apparatus according to the present invention, the paper transport loop time (Tl) and the paper transit time (Tt).
And the shortest inter-paper gap time (Tg min), the paper feed interval (paper feed timing) is obtained. In the present invention, the paper transport loop time (Tl) means that the paper taken out from the paper feed tray 2 passes through the confluence A and is supplied to the transport path 4 as shown in FIG. The time required for the sheet to be printed at the transfer section 7 and then to be turned upside down by the reversing mechanism 9 provided in the reversing loop so as to pass through the confluence A again. The paper passage time (Tt) is the time required for one sheet of paper to pass through a certain point by the conveyance mechanism, and depends on the paper size and the process speed. The shortest inter-sheet gap time (Tg min) is a value obtained by dividing an interval (minimum inter-sheet gap) that should be kept at a minimum between subsequent sheets by the transport speed. In other words, 1
This is the minimum time required to feed one sheet of paper and feed the next sheet of paper.

Here, when the paper transport loop time is (Tl), the paper transit time is (Tt), and the shortest inter-paper gap time (Tg min) is set, the paper transport loop time is first divided from these times. Find the number (N). This value can be calculated by the following equation.

N = [Tl / (Tt + Tg min)]
The largest odd number less than or equal to

Next, the paper feed interval (Td f) is obtained from this division number. That is,

Td f = (Tl / N) × 2

Therefore, when paper is fed from the paper feed tray 2 at this paper feed interval (Td f), the paper whose one side has been printed and then the front and back sides are reversed is exactly the same as the unprinted paper fed from the paper feed tray 2. Since it always arrives in the middle, even if the paper length is changed by changing the paper size, it does not overlap with the succeeding paper.

Next, the operation of the present invention will be described with reference to FIG. FIG. 2E shows a physical paper transport loop length determined by the structure of the apparatus and a paper transport loop time (Tl) obtained based on the process speed and the fixing speed.
And the paper passing time (Tt) obtained based on the paper size and the transport speed, and the shortest paper gap time (Tg min) determined by the structure of the apparatus, the paper feeding interval (Td f) is calculated by the above method. A timing chart in the case of obtaining and feeding a sheet is shown. In this example, the number of divisions (N) of the paper transport loop time obtained by the above calculation,
That is, the case where the maximum number of sheets that can be present on the sheet conveyance loop is 3 (sheets) is shown.

As is clear from this chart, in the trayless double-sided printing apparatus of the present invention, the sheet feeding interval (Td f) is larger than that of the conventional one, so that the adjacent sheets fed alternately to the conveying path 4 at the confluence A. Matching paper sheets do not overlap.
Further, since the number of sheets that can be fed within the predetermined time can be kept as large as possible within the range where the sheets do not overlap each other, it is possible to suppress the reduction in the number of sheets printed per unit time.

[0021]

According to the present invention, even when the paper length, the process speed, the fixing speed, or the like changes, the paper feed interval is obtained from the paper transport loop time, the paper passage time, and the shortest paper gap time, and the paper feed interval is changed. The timing control of trayless double-sided printing can be realized only by
Compared with the conventional technology, there is no need to provide a weight mechanism,
It has excellent effects in terms of saving space for the device and suppressing increase in cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a trayless double-sided printing device according to the present invention.

FIG. 2 is a timing chart showing a paper feeding state.

[Explanation of symbols]

1 Trayless duplex printer, 2 paper feed tray, 3
Paper, 4 conveyance paths, 5 photosensitive drums, 6 image forming section, 7 fixing section, 8 discharge tray, 9 inverting means, 10 calculating means, 11 paper feeding means.

Claims (2)

[Claims] 1. A trayless double-sided printing apparatus having a paper feed unit, a paper transport unit, an image forming unit for forming a toner image, a fixing unit, and a reversing mechanism for reversing the paper after fixing, and an image of one side of the paper is printed. A trayless double-sided printing apparatus comprising a calculating means for obtaining a sheet feeding interval in a double-sided printing mode from a time of reversing after returning (paper feeding loop time), a sheet passing time, and a shortest sheet gap time. 2. The paper feeding loop time, which is the time required for the paper to be fed and printed at the time of double-sided printing after printing an image on one side and then reversing and returning to the same position during the double-sided printing (Tl)
The paper passing time, which is the time required for the paper to pass through one place, is (Tt), and the shortest inter-paper gap time, which is the time required for the shortest interval between adjacent papers to pass, is (Tg min). , The number of divisions of the paper transport loop time is (N), and the paper feed interval for printing the table is (Td f)
And the number of divisions (N) of the paper transport loop time is Tl / (Tt +
The trayless according to claim 1, which is a calculation means for calculating a sheet feeding interval (Td f) of a sheet for printing a table by calculating a formula (Tl / N) × 2, which is a maximum odd number equal to or less than a quotient of (Tg min). Double-sided printing device.