JPH0445458A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image of an appropriate density and to improve copying speed at the same time by providing a means estimating the time left standing after output from a fixing temperature sensor, a means timing the time from turning on of power to starting of image formation, and a means timing the time from detection of final paper ejecting signal to turning off of power. CONSTITUTION:The time left standing from when the fixing lamp is turned OFF based on the output from the fixing temperature sensor Th and data of ROM until the power is turned on is estimated by a process control circuit 50. ON signal is fed out when a fixed time (55sec) is elapsed after the circuit 50 is started, a latched state of a latch circuit 70 is released, and a copying start signal is fed out to the circuit 50 by an internal timer TM3 of the circuit 50. The time from the connecting of a main switch until the start of the image formation is timed by the timer TM. The time from the detection of the final paper ejecting signal to turning off of the main switch is timed by the internal timer TM1. Whether preprocessing before the image forming process (electrifying, destaticizing) is necessary or not is judged by the circuit 50 based on these data.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an image forming apparatus using electrophotography, and more particularly to improvement of a copy disk by the charging characteristics of a photoreceptor.

[Background of the invention]

Image forming apparatuses using electrophotography employ a drum-shaped photoreceptor such as Se or OPC as an image forming member. The charging potential characteristics of a typical photoreceptor will be explained. FIG. 9 is a graph showing the band tt position on the OPC photoreceptor during continuous copying. Particularly in the case of an OPC photoreceptor, the charging potential in the initial image forming process tends to be lower than the reference potential (indicated by the dashed line), as shown by the dotted line. Here, the reference potential Vs is a surface potential for forming a latent image by clearly distinguishing the border between an image and a non-image at a document density of 0.2. In order to obtain a toner image with an appropriate density, the rotating photoconductor is charged and the pre-discharge process is performed to adjust the state of the photoconductor so that the charged potential in the initial image forming process also becomes the reference potential VS. Arrange. Next, an image forming process begins in which an image is formed by charging, image exposure, development, separation, and fixing on the photoreceptor, which rotates twice. Finally, post-processing is performed to remove dust and residual toner from the surface of the photoreceptor and remove residual potential. However, when performing book originals or continuous copying, there is a limit to the improvement in copying speed if the above-mentioned preprocessing, image forming process, and postprocessing are performed. Therefore, the present inventor focused on the charging characteristics of the photoreceptor and attempted to improve the image forming process. The wC8 diagram shows OPC used in general analog copiers.
3 is a graph showing charging characteristics of a photoreceptor. In the figure, the vertical axis indicates the surface potential (V) of the photoreceptor, and the horizontal axis indicates the elapsed time after the image forming process is completed. The origin (0) of the w-axis indicates the elapsed time after fixing the 1-niter toner image on the transfer paper and detecting the paper ejection after t by the paper ejection sensor. The present inventor has discovered that the surface potential Vf of the photoreceptor gradually decreases and becomes lower than Vd (for convenience, this is referred to as the boundary potential Vd) after approximately IQmins has elapsed. According to the surface potential characteristics of this photoreceptor, the surface potential Vf
It has been found that the copy density becomes appropriate even without performing pre-processing as long as it exceeds the boundary potential Vd. When making continuous copies, copy images with sufficient image density can be obtained by omitting the preprocessing and performing the image formation process, postprocessing, and then the image formation process. It's going to be out. In other words, the boundary potential Vd is the surface potential of the photoreceptor that is the boundary between whether or not pretreatment is required.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that aims to obtain a copy image of appropriate density and improve copy speed.

[Means to solve the problem]

The present invention achieves the above object by providing a heat fixing roller for heat fixing the toner image formed on the recording a[, and providing a paper discharge sensor and a fixing temperature sensor for detecting paper discharge from the heat fixation roller. The image forming apparatus includes: a leaving time estimating means for estimating a leaving time based on information from the fixing temperature sensor; a first time measuring means for measuring a time from turning on the twin switch to starting image formation; The apparatus is characterized by comprising a second timer for measuring the time from when the paper discharge signal is detected to when the main switch is turned off.

[Example] Next, an example of the present invention will be described based on the accompanying drawings. First, the schematic configuration of the image forming apparatus of this embodiment will be described. FIG. 6(a) is a functional block diagram showing a schematic configuration of the image forming apparatus of this embodiment, and FIG. 6(b) is a functional block diagram showing a process control circuit of this embodiment. The image forming apparatus 100 includes a drum-shaped photoreceptor (hereinafter simply referred to as photoreceptor) 1 that rotates in the direction of an arrow;
A scorotron charger 2 that applies a negative charge to the top, a scanning optical system 3, a developer 4, a scorotron charger 5, a separator 6, a fixing roller 7, a cleaning device 8, a static eliminator 9, and a DC power supply. 60, a latch circuit 70, an operation panel 80, and a process control circuit 50. The process control circuit 50 is, for example, a microprocessor as shown in FIG. 6(b), and has a control unit 51. It is provided with internal timers TM, -TM, a ROM 52 that stores software for executing the image forming process, and a nonvolatile RAM 53 that stores data generated during the execution of the image forming process. Further, the ROM stores data for estimating the leaving time, specifically a table consisting of temperature values and values indicating the corresponding times. Thereby, the process control circuit 50 can obtain the standing time based on the output from the fixing temperature sensor Th. In other words, in this embodiment, the table stored in the RAM and the process control circuit correspond to the leaving time estimating means. The internal timer TM measures the time from when the fixing lamp is turned off until when the main switch is turned off. The internal timer TM is activated at the same time as the process control circuit 50 is activated, and in this embodiment, it sends out an on signal when 55 seconds have elapsed. At this point, the latch circuit 70 is released from the launch state, and a copy start signal from the operation panel 80 is sent to the process control circuit 5o. The internal timer TM measures the time from when the main switch is turned on until the image forming process routine is entered. In this embodiment, the internal timer TM corresponds to the first timekeeping means. The second timer measures the time from when the last paper discharge signal is detected to when the main switch is turned off. The photoreceptor 1 adopted in this example is an oPc photoreceptor,
The reference charging potential is V5-290 (V), and the boundary charging potential Vd is 280 (V). The constant JIF roller 7 includes a fixing lamp (not shown) in the rubber roller, and while the main switch is on, the surface temperature of the fixing roller is controlled by turning on and off the fixing lamp. It is controlled to maintain the temperature at approximately 1900C. The fixing roller 7 also has a paper ejection sensor P on the paper ejection side.
S, and when the recording paper passes therethrough, a paper discharge detection signal indicating that paper discharge has been detected is sent to the process control circuit 50. Furthermore, a fixing temperature sensor Th for detecting the surface temperature of the heat fixing roller 7 is provided, and the fixing temperature sensor T
The output signals of h are sent to the process control circuit 50. Note that the heat fixing roller containing the fixing lamp may be provided at the top or the bottom roller.Also, in this embodiment, the surface temperature of the heat fixing roller containing the fixing lamp is detected. The present invention is not limited to this, and substantially the same effect can be obtained by detecting the temperature of a roller that is not equipped with a heat source such as a fixing lamp. The heat dissipation characteristics of the fixing roller 7, which is a characteristic configuration of this embodiment, will be explained. FIG. 7 is a graph showing the heat dissipation characteristics of the fixing roller detected by the fixing temperature sensor. In the figure, the vertical axis shows the surface temperature ('C) of the fixing roller in this example, and the horizontal axis shows time (a+1ns).
It shows. The fixing temperature at the fixing roller 7 is approximately 19
If the temperature is 0°C and you leave it as it is after turning off the power to the fixing lamp, the temperature will rise to about 60OC after about 20a+ins.
It drops to around. As shown in the figure, the surface temperature of the fixing roller decreases exponentially until about 20 ml ns have passed after the fixing lamp is turned off, so the fixing sensor Th
It is possible to easily estimate the standing time based on the output of the device. In other words, the image forming apparatus 1100 of this embodiment is
From the charging characteristics of the photoreceptor shown in FIG. 8 and the heat dissipation characteristics of the fixing roller shown in FIG. 7, estimate the time from turning off the fixing lamp until turning on the main power (hereinafter referred to as the standing time for convenience). It is characterized by having functions. The operation panel 80 is used to set the number of copies and then command the start of copying. The latch circuit 70 is a circuit that launches a copy start signal from the operation panel 80 while the image forming apparatus 100 is performing initialization processing. The copy star signal is launched for about 55 seconds, and the launch is canceled after 55 seconds have elapsed. As a result, a copy start signal from the operation panel 80 is sent to the process control circuit 50. In addition, the DC power supply 60
When the main switch is turned on, a DC voltage of about 5V is supplied to the process control circuit 50 by AC power from an AC line (not shown). Next, the image forming operation of the image forming apparatus 100 of this embodiment will be explained. FIG. 1 is a flowchart showing the main routine in the image forming process. When the main power source (not shown) is turned on (Sl), power is supplied to the AC line (not shown), and approximately 5V DC power is supplied from the DC power supply 60. As a result, the process control circuit 50 is activated. The process control circuit 5o starts the pre-processing determination routine (S2), starts the pre-processing routine (s3), starts the image forming process routine (s4), and repeats step Z in Snoteb 3 according to the set number of sheets. , the main routine ends when the set number of sheets is reached. The operations of each routine in step 2 to step 4 will be explained below based on FIGS. 2 to 5. FIG. 2 is chart 70 showing the preprocessing determination routine. Here, the preprocessing determination flag is a flag that specifies whether or not to execute this routine during the preprocessing routine orbit,
If the flag is in the on state, the program returns to normal, and if the flag is in the off state, the preprocessing routine is returned to the main routine without being executed even if the flag is in the off state. The process control circuit 50 starts the internal timer TM (5201). As a result, the internal timer TM continues counting until the next preprocessing determination routine is reached. The process control circuit 50 reads the count value of the internal timer TM from the nonvolatile memory (S202), and determines whether the count value TMI is shorter than IO+n ins (S202).
203). If the count value TMI is shorter than lomins,
The process control circuit 50 reads the output from the fixing temperature sensor Th (5204), and controls the ROM based on the temperature.
The standing time is obtained from (S205). Process control circuit 5
(5206)
, waits for input of a copy start signal from the latch circuit 70 (S207). When the process control circuit 50 detects the copy star signal, the count value T of the internal timer TM is
M3 is read (s208), and the time T is obtained by adding the count value TMI, the standing time TM2, and the count value TM3 (S209). The process control circuit 5o compares the time T and the set time T0 (here, 10m1ns).
210), if the set time is T. If it is less than L, the preprocessing flag is turned off (S211), the preprocessing determination routine is ended, and the process returns to the main routine. On the other hand, if the time T exceeds the set time T0, the process control circuit 50 turns on the preprocessing flag in S21, ends the preprocessing determination routine, and returns to the main routine. If the count value TMI exceeds 10mlns in step 203, the process control circuit 50 turns on the preprocessing flag (5211), ends the preprocessing determination routine, and returns to the main routine. FIG. 3 is a flowchart showing the preprocessing routine. After completing the pre-processing routine, the process control circuit 50 determines the state of the pre-processing flag (531), and if the flag is on, charges the rotating photoreceptor l with the scorotron charger 2 (532); Thereafter, the photoreceptor 1 is neutralized by the static eliminator 9 (S33) and the process returns to the main routine. On the other hand, if preprocessing 7 lag is off, step 3
The process returns to the main routine without executing steps 3 and 34. The preprocessing routine in this embodiment has a function of determining whether or not to execute the routine depending on the state of the preprocessing flag, thereby improving the copying speed. FIG. 4 is a flowchart showing the image forming process routine. When the image forming process routine (S4) is started, the process control circuit 50 drives the scorotron charger 2 to cause the photoreceptor I to rotate in the direction of the arrow shown in FIG.
is charged (5401). Next, the scanning optical system 3 performs image exposure to form an electrostatic latent image on the photoreceptor l (S402).
. The process control circuit 50 drives the developing device 4 to develop the electrostatic latent image on the photoreceptor 1 (5403), forming a toner image on the photoreceptor l. Process control circuit 5
0, the recording paper P from the paper feed tray is moved to the registration roller 10.
The toner image on the photoreceptor 1 is separated and transferred onto the recording paper P by feeding the paper at the appropriate timing and further driving the separator 5 and the transfer device 6 (S404). Next, the toner image is transferred I; the recording paper P is conveyed to the fixing roller 7, and the fixing roller 7 fixes the toner image on the recording paper P using pressure and heat (5405), and then discharges the paper. At this time, the recording paper pushes down the sensor section of the paper discharge sensor PS, and a paper discharge signal is sent from the paper discharge sensor PS to the process control circuit 50. This causes the number of copies to be counted (5408). Thereafter, when the process control circuit 50 detects the paper discharge signal, it executes the post-processing routine (5407). When the process control circuit 50 returns from the post-processing routine, the process control circuit 50 returns to the pre-processing determination routine (S2
), and after executing the routine, returns to the main routine. Further, the processing from step 9 to step IO is a loop for detecting the occurrence of a jam, and since it is not directly related to the invention, a detailed explanation will be omitted. Note that the preprocessing determination routine has already been explained in R and F. The post-processing routine will be described later. FIG. 5 is a flowchart showing the post-processing routine. After completing the post-processing routine, the process control circuit 50 resets the internal timer TM (S441). As a result, the internal timer TM restarts counting and writes the count value to the nonvolatile memory (S442
). The post-processing routine is a routine that only performs the function of resetting the internal timer TM.
The purpose of the internal timer TM is to measure the time from when the last paper discharge signal is detected until the main switch is turned off. The internal timer TM is reset each time the post-processing routine is executed. In other words, the count value TMI written in the ROM has meaning only when the value is read at the beginning when the main switch is turned on. It shows the time. This time is the same value as the time used to detect a jam. With the above-described configuration, the image forming apparatus 100 of this embodiment has the following features:
Omitting preprocessing from the second time onwards during continuous copying,
By performing image formation, the copying speed can be improved and a copied image with appropriate density can be obtained. In addition, in the image forming apparatus 100 of this embodiment, when performing a copy operation within a predetermined time (10 mins), for example, when making continuous copies from different manuscripts from magazines or books, preprocessing can be omitted. As a result, the copying speed could be improved, and a copied image with appropriate density could be obtained even though pre-processing was omitted. Effects of the Invention As described above, the present invention includes a heat fixing roller that heat-fixes a toner image formed on a recording paper, and a paper discharge sensor and a fixing temperature sensor that detect paper discharge from the heat fixation roller. In the image forming apparatus provided, the left time estimating means estimates the left time from the output from the fixing temperature sensor, the first time measuring means measures the time from turning on the main switch to starting image formation, and the last An image forming apparatus that is equipped with a second timer that measures the time from when a paper discharge signal is detected to when the main switch is turned off, thereby increasing the copying speed and obtaining a copied image with an appropriate density. We can provide two.

[Brief explanation of drawings]

FIG. 1 shows the image forming process. 2 is a flowchart showing the preprocessing determination routine; FIG. 3 is a flowchart showing the preprocessing routine; and FIG. 4 is a flowchart showing the image forming process routine.
5 is a flowchart showing the post-processing routine, FIG. 6(a) is a functional block diagram showing the schematic configuration of the image forming apparatus of this embodiment, and FIG. 6(b) is a process control diagram of this embodiment. A functional diagram showing the circuit, Figure 7 is a graph showing the heat dissipation characteristics of the fixing roller detected by the fixing temperature sensor, and Figure 8 is a graph showing the charging characteristics of the OPC photoreceptor used in general analog copying machines. The graph shown in FIG. 9 is a graph showing the band position on the OPC photoreceptor during continuous copying. 7-Fixing roller 50 Process control circuit 51 Control unit 53 RAM P Recording paper Th Fixing temperature sensor TM, -TM Internal tie 52 ROM 100 ...Image forming device PS...Sheet discharge sensor

Claims (1)

[Claims] In an image forming apparatus provided with a thermal fixing roller that thermally fixes a toner image formed on a recording paper, and a paper discharge sensor and a fixing temperature sensor that detect paper discharge from the thermal fixing roller, an output from the fixing temperature sensor is provided. a first timer for measuring the time from turning on the main switch to starting image formation;
An image forming apparatus comprising: a second timer that measures the time from when the last sheet discharge signal is detected to when the main switch is turned off.