JP3676889B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a printer, and more particularly to an image forming apparatus using a resin transport roller as a recording paper transport unit of a recording paper transport system from a paper feed unit to a paper discharge unit. The present invention relates to a recording paper conveyance speed control technique and a curl correction technique by heating a fixing unit.
[0002]
[Prior art]
In an image forming apparatus, a recording sheet fed from a sheet feeding unit is sent to a transfer unit of a photosensitive member at a registration timing, an image is transferred, and further conveyed downstream, and generally heated. Is fixed and is discharged from the paper discharge unit.
In the recording paper conveyance system (recording paper conveyance path) from the paper supply unit to the paper discharge unit, conveyance rollers are provided at intervals shorter than the minimum sheet passing length in addition to the conveyance belt.
[0003]
Here, instead of the conventional type of transport roller in which a rubber roller is fitted on a metal shaft, a resin transport roller (resin roller) in which a resin roller is also integrally formed on a resin shaft is often used recently. is there. This is mainly for cost reduction, EMI countermeasures, heat countermeasures, appearance, and the like, and is often used for a roller of a paper discharge unit that finally discharges recording paper.
However, in the case of the electrophotographic system, the pre-process for finally discharging the recording paper is generally fixing by heating, and the periphery of the heating and fixing device is very hot.
[0004]
[Problems to be solved by the invention]
The resin roller is easily deformed by heat, and the outer diameter of the roller changes due to heat deformation. Therefore, after a predetermined time has elapsed since the heater of the fixing unit is turned on, the resin roller around the fixing unit is thermally expanded unlike other parts, particularly at a position away from the fixing unit, for example, a conveyance roller near the paper feeding unit. Swells the outer diameter.
[0005]
For this reason, even if it is set so that a normal recording paper conveyance speed can be obtained at a normal temperature, the recording paper conveyance speed around the fixing unit becomes faster than the recording paper conveyance speed on the preceding process side. There is a problem that the recording paper is pulled with the conveyance roller in the process and causes jitter and torque increase. In the worst case, the recording paper may run out.
[0006]
On the other hand, if the temperature around the fixing unit is high and the resin roller in the vicinity expands, the recording paper can be transported when the resin roller is cold. The speed is too slow and the recording paper becomes wrinkled.
[0007]
In addition, when the curling correction of the recording paper after fixing is performed with a pair of rollers, the curling state of the recording paper is different between the case where the fixing portion and its periphery are cooled and the case where it is warm, and even if the same curling correction is performed. There are problems such as lack of correction, or overcorrection and reverse curl.
[0008]
Therefore, the present invention provides an image forming apparatus capable of obtaining a target recording paper conveyance speed even using a resin roller, and performing curl correction according to each state to improve the recording paper conveyance quality. It is intended to provide.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is in pressure contact with the paper feed unit , the heat fixing device, the resin paper discharge roller disposed near the downstream side thereof, and the paper discharge roller. In an image forming apparatus that includes a paper discharge unit having a paper discharge roller and discharges recording paper from a paper supply unit from the paper discharge unit through a heat fixing device, a paper discharge roller and a paper discharge roller in the paper discharge unit. A roller pressure adjusting member is provided that adjusts the pressing force between high and low according to a change in temperature around the heat fixing device from low to high .
[0010]
According to a second aspect of the present invention, in the first aspect of the present invention, the roller pressure adjusting member is provided between the paper discharge roller and the paper discharge roller in the paper discharge unit when the heat fixing device is in a warmed state by turning on the power. The pressing force is adjusted to be lower than the pressing force between the paper discharge roller and the paper discharge roller when the heat fixing device is not in a heated state .
[0011]
According to a third aspect of the invention, in the invention of the second aspect, when the roller pressure adjusting member is made of a shape memory alloy and the heating and fixing device is heated by turning on the power, the shape memory alloy is affected by the heating. Due to the temperature rise and deformation, the pressing force between the discharge roller and the discharge roller becomes lower than the pressing force when the heat fixing device is not in the warmed state .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is an overall configuration diagram of a laser printer as an image forming apparatus.
In the main body case 1 of the laser printer, a photoconductor 2 is provided at a substantially central portion, and around the photoconductor 2, a charger 3, a developing device 4, a transfer device 5, a cleaning device 6 and the like are arranged. Yes.
Below these photoconductors 2 and the like, a paper feed cassette 8 containing recording paper 7, a paper feed roller 9 for feeding the recording paper 7 in the paper feed cassette 8 one by one, and the fed recording A registration roller 10 that feeds the paper 7 to the transfer device 5 side at a predetermined timing is provided.
[0016]
Further, above the photosensitive member 2 and the like, a fixing device 11 that fixes an image transferred to the recording paper 7 by the transfer device 5, and the recording paper 7 on which image fixing has been performed by the fixing device 11 are discharged to a stacker unit described later. A paper discharge unit 12 for paper is provided.
[0017]
Next, a stacker portion 13 for discharging the recording paper 7 on which the image has been formed is formed on the upper surface portion of the main body cover 1a which is a part of the main body case 1. An electrical component 15 housed in a metal case 14 is provided below the stacker portion 13 in the main body case 1, and the electrical component 15 is provided on the controller board 16 and the controller board 16. It is formed by various adjustment switches attached to the control unit, a control unit (not shown), and the like.
[0018]
Further, below the case 14 in the main body case 1, a case 19 containing a power source 17 and an electrical board 18 and an optical device 20 for writing an image on the photoreceptor 2 are provided.
[0019]
The paper discharge unit 12 includes a drive-side discharge roller 101 and a driven-side discharge roller 102 pressed against the discharge roller 101. The roller portion of the discharge roller 101 is molded from resin. The paper discharge roller 102 is held at the tip of a plate spring-like holding member 103, and is pressed against the paper discharge roller 101 side by the holding member 103.
[0020]
FIG. 2 is a perspective view of the paper discharge roller holding member side of the paper discharge unit showing the first embodiment.
A hole 104 is formed in the holding member 103.
3A and 3B are explanatory views of the operation of the paper discharge unit according to the first embodiment.
The fixing structure 110 having the protrusions 111 is made of a heat-resistant resin, and the holding member 103 is attached to the fixing structure 110 with screws 112 or the like. Here, the state shown in FIG. 3A is when the fixing unit 11 and the paper discharge unit 12 are cold (such as shortly after the power is turned on), and the paper discharge roller 101 is also near room temperature. At this time, the fixing structure 110 is also in a state close to room temperature, and the holding member 103 is in a state of riding on the protrusion 111 as shown in the drawing.
[0021]
For this reason, as a result of the paper discharge roller 102 being pressed against the paper discharge roller 101 with a strong pressure (P1), the recording paper conveyed to the paper discharge roller 101 and the paper discharge roller 102 is determined by the outer diameter of the paper discharge roller 101. Sent at a predetermined transport speed.
[0022]
Here, when the fixing device 11 and the paper discharge unit 12 are in a warmed state (time has elapsed since the power was turned on and the peripheral part is warmed by heat generated from the fixing roller), as shown in FIG. The resin-made fixing structure 110 is heated to 100 ° C. or more, and as a result of thermal expansion, the position of the protrusion 111 coincides with the hole 104 of the holding member 103, and the holding member 103 does not ride on the protrusion 111.
[0023]
As a result, the pressing force of the paper discharge roller 102 to the paper discharge roller 101 becomes small (P2). At this time, the paper discharge roller 101 is also warmed, and the resin roller portion is larger than a predetermined outer diameter.
[0024]
Here, since the recording paper 7 to be conveyed has a weak pressing force of the paper discharge roller 102, the recording paper 7 does not follow the paper discharge roller 101 whose outer diameter is larger than a predetermined value, and slips and causes a preceding process (here, a fixing roller). ) According to the transport speed. As a result, it is possible to prevent problems (jitter, torque increase, etc.) that occur because the outer diameter of the paper discharge roller 101 is increased.
[0025]
FIGS. 4A and 4B are explanatory views of the operation of the paper discharge unit according to the second embodiment.
In this example, a roller pressure adjusting member 113 made of a shape memory alloy is provided.
The roller pressure adjusting member 113 has a U-shape, and is disposed inside the fixing structure 110 and below the holding member 103.
[0026]
When the temperature around the fixing device 11 is low, the roller pressure adjusting member 113 spreads outward as shown in FIG. 4A and lifts the holding member 103 upward. Accordingly, the paper discharge roller 102 attached to the tip of the holding member 103 is strongly pressed against the paper discharge roller 101 with the pressing force P1. Thus, as described above, the recording paper 7 is fed at a predetermined conveyance speed determined by the outer diameter of the paper discharge roller 101.
[0027]
Further, when the temperature around the fixing device 11 increases, the roller pressure adjusting member 113 narrows inward as shown in FIG. Accordingly, the front end side of the holding member 103 also moves slightly downward, and the paper discharge roller 102 abuts on the paper discharge roller 101 with the pressing force indicated by the weaker P2.
Then, as described above, slipping occurs when the recording paper 7 is sandwiched between the discharge roller 101 and the discharge roller 102 and discharged, and the conveyance speed of the previous process is followed.
Note that the holding member 103 itself may be made of a shape memory alloy.
[0028]
FIGS. 5A and 5B are explanatory views of the operation of the paper discharge unit according to the third embodiment.
In this example, two discharge rollers 102 are brought into contact with a discharge roller 101 (not necessarily made of resin), and curling is performed using thermal expansion of the fixing structure 110.
[0029]
FIG. 5A shows a state where the periphery of the fixing device 11 is not warmed. At this time, the curl amount of the recording paper 7 is generally small. Therefore, at this time, the curling force is weakened by reducing the pressing force of the paper discharge roller 102, and reverse curl is not generated.
[0030]
FIG. 5B shows a state in which the periphery of the fixing device 11 is warmed. At this time, the holding member 103 rides on the protrusion 111 due to thermal expansion of the fixing structure 110, and the discharge roller 102 has a strong force. Is pressed by the paper discharge roller 101, and the curl removal force acts greatly as in the recording paper conveyance path 114 indicated by the arrow in the figure, so that the curl removal function is sufficiently effective.
[0031]
FIGS. 6A and 6B are explanatory views of the operation of the paper discharge unit according to the fourth embodiment.
In this example, two discharge rollers 102 are brought into contact with the discharge roller 101, and the curl removal is performed using a roller pressure adjusting member 115 made of a shape memory alloy.
[0032]
When the periphery of the fixing device 11 is not warm, the curling amount of the recording paper 7 is small, so that the pressing force of the paper discharge roller 102 to the paper discharge roller 101 may be small. Therefore, the U-shaped roller pressure adjusting member 115 is narrowed inward as shown in FIG.
[0033]
As the periphery of the fixing device 11 warms up, the curl amount of the recording paper 7 increases. However, at this time, as shown in FIG. 6B, the roller pressure adjusting member 115 expands outward to push up the holding member 103. As a result, a strong pressing force in the curl removing direction is generated between the two paper discharge rollers 102 and 102 and the paper discharge roller 101, and the curl is efficiently removed.
[0034]
【The invention's effect】
In the present invention, when the fixing device is warmed and the surrounding temperature is high, the pressing force between the paper discharge roller and the paper discharge roller of the paper discharge unit is reduced, and the nip between the paper discharge roller and the paper discharge roller is held. Since the recording paper transport speed is made to follow the transport speed of the previous process by slipping the recording paper to be recorded , a desired recording paper transport speed can be obtained even if a resin roller is used in the paper discharge unit. can, jitter and torque increase, more Ru can avoid various problems such as occurrence of wrinkles of the recording paper.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a laser printer as an image forming apparatus.
FIG. 2 is a perspective view of a paper discharge roller holding member side in a paper discharge unit according to the first embodiment of the present invention.
FIG. 3 is an operation explanatory diagram of a paper discharge unit according to the first embodiment of this invention.
FIG. 4 is an operation explanatory diagram of a paper discharge unit according to a second embodiment of this invention.
FIG. 5 is an operation explanatory diagram of a paper discharge unit according to a third embodiment of the present invention.
FIG. 6 is an operation explanatory diagram of a paper discharge unit according to a fourth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Fixing device 12 Paper discharge part 101 Paper discharge roller 102 Paper discharge roller 103 Holding member 110 Fixing structure 113,115 Roller pressure adjustment member

Claims (3)

A paper discharge unit having a paper discharge unit having a paper discharge roller disposed in the vicinity of the downstream side thereof, and a paper discharge roller pressed against the paper discharge roller; In an image forming apparatus in which recording paper is discharged from a paper discharge unit via a heat fixing device,
A roller pressure adjusting member is provided for adjusting the pressing force between the paper discharge roller and the paper discharge roller in the paper discharge unit from high to low according to the change from low to high in the temperature around the heat fixing device. An image forming apparatus. The roller pressure adjustment member is used to discharge paper when the heating and fixing device is not in the warming state because the pressing force between the paper discharge roller and the paper discharge roller in the paper discharge unit when the heating and fixing device is in the warming state when the power is turned on. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is adjusted so as to be lower than a pressing force between the roller and the paper discharge roller . The roller pressure adjusting member is made of a shape memory alloy. When the heating and fixing device is heated by turning on the power, the shape memory alloy is heated and deformed due to the heating, so that the discharge roller and the discharge roller are deformed. The image forming apparatus according to claim 2, wherein the pressing force between them is lower than the pressing force when the heat fixing device is not in a heated state .

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