JPH0338665A - Image forming device - Google Patents

Abstract

PURPOSE:To accurately know a spot which needs maintenance at appropriate time and to reduce the occurrence of a faulty image by detecting and displaying a loaded condition based on the variation of the duty of an output pulse from a pulse width modulation means. CONSTITUTION:Data to a D/A converter 10 which is a reference voltage generation means for setting the desired output of a power source and the pulse width data of a PWM circuit 3 are fetched in a CPU 1. According to arithmetic operation in the CPU 1, whether or not the pulse width data is within a threshold previously set corresponding to the data to the D/A converter 10 is decided and the normality or abnormality of the loaded condition of high voltage is determined. It is decided whether or not the duty of the output pulse from the PWM circuit 3 is within the variation of the duty of the output pulse from the PWM circuit which is supposed when the loaded condition of high voltage is normal corresponding to the output from the reference voltage generation means at that time. In the case that the decided result shows abnormality, a proper message is given by a display part 11 to designate the maintenance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus such as an electrophotographic copying machine or printer.

[Conventional technology]

In electrophotographic copying machines and printers, charging is a process of forming one image.

In the charging process, high voltage is applied to a charger to charge the photosensitive drum by corona discharge, but usually the high voltage is controlled by the discharge current or applied voltage in order to form a stable image.

[Problem to be solved by the invention]

However, in electrophotographic copiers and printers, the charging wire may become dirty due to toner adhesion or ion products from discharge, and in this case, the dirt on the charging wire may be uneven or excessive. This exceeds the control capability of the power supply, causing problems in image formation and making it impossible to obtain stable images.

The present invention has been made in order to deal with such problems, and it is an object of the present invention to provide an image forming apparatus that detects the above-described malfunctions, displays them, and requests maintenance.

[Means to solve the problem]

In order to achieve the above object, the present invention detects an abnormality in the load condition based on an abnormality in the duty of the output pulse in a pulse width modulation means for electric fX control. It is configured as shown in .

(1) Output setting means for setting a desired power output, power output detection means, comparison means for comparing the output of the output setting means and the output of the power output detection means, and (5) the output of the comparison means. a pulse width modulation means controlled by the pulse width modulation means, an output means driven by the output of the pulse width modulation means, and a duty of the output pulse of the pulse width modulation means corresponding to the output of the output setting means at that time. An image forming apparatus comprising a determining means for determining whether or not the fluctuation is within an allowable range, and a display means for performing a desired display according to the output of the determining means.

[Function] According to the configuration (1) above, abnormalities in the load condition such as toner adhesion to the charging wire and uneven staining of the charging wire can be detected.
It is detected based on an abnormality in the duty of the pulse generated by the pulse width modulation means, and an appropriate display is performed.

〔Example〕

The present invention will be explained below with reference to Examples.

FIG. 1 is a block diagram of the main parts (related to high-voltage power supply) of an image forming apparatus according to a first embodiment of the present invention.

Generally, a microcomputer is used for sequence and process control of RH of copying machines, printers, etc., but this embodiment uses a microcomputer 1 (hereinafter referred to as CPU) for sequence and process control and pulse width modulation. A circuit 3 (hereinafter referred to as a PWM circuit) is connected via a D/A converter 10. In the block marked as high-voltage power supply block 2, the pulses generated by the PWM circuit 3 are supplied to the output circuit 5 via the driver 4 to drive the flyback transformer, and the output is converted to DC high voltage through the smoothing circuit and charged. Power is being supplied to device 7. The high voltage supplied to the charger 7 flows to the ground via the charger shield 8 or the photosensitive drum 9.

In addition, in the high voltage power supply block 2, the output current is detected by the output detection circuit 6, and fed back as a detection input to the comparison means (comparator) 16 in the previous stage of the PWM circuit 3, and the D/A conversion which is the reference voltage generation means. Constant current control is performed by comparing the output of the device 10.

Next, detection of an abnormality in the load state will be explained.

In this embodiment, the CPU 1 includes a D/A which is a reference voltage generating means (output setting means) for setting a desired power output.
The data to the A converter 10 and the pulse width data of the PWM circuit 3 are taken in, and the pulse width data is set in advance according to the data to the D/A converter 10 by calculation within the CPU. D/ determines whether it is within the threshold and determines whether the high pressure load condition is normal or abnormal.
The data to the A converter 10 and the threshold data are the CPU
The data is read from the internal ROM (read-only memory).

In this way, the duty of the output pulse of the PWM circuit 3 is changed according to the output of the reference voltage generating means at that time, and the variation range of the duty of the output pulse of the PWM circuit (duty It is determined whether the high pressure load condition is normal or abnormal (within the permissible variation range), and in the event of an abnormality, an appropriate message is displayed on the display unit 11 to instruct maintenance.

For example, if the charger wire breaks, the PWM circuit loop breaks and the pulse width data becomes the maximum that the circuit can handle. By the way, the reference voltage is set as necessary for a certain process, and the CPU 1 detects that the pulse width data of the PWM circuit exceeds the variation range of pulse width data expected for this reference voltage during normal operation. , display maintenance requests.

Even if the charger wire becomes dirty, the pulse width data of the PWM circuit relative to the reference voltage set from the ROM will change compared to the normal level due to the decrease in charger impedance due to wire dirt C. Taking advantage of this, C
It is possible to import data into the PUI and compare it with the preset data in the CPU to find out if there is an abnormality.

Here, the data in the CPU refers to data on the ROM, which is taken in according to a program. Also,
Dat preset in the ROM in the CPUI
If an abnormal condition is detected by comparison with a, display section 1
1 to notify the user of the abnormality, set the value of the D/A converter 10 to stop the circuit operation, set each register of the Zara IYPWM circuit 3 to the stopped state, and stop the circuit operation. Perform a stop.

Below, an overview of the operations of the PWM circuit 3 and its peripheral parts will be explained.

FIG. 2 is a block diagram of the digital PWM circuit and its peripheral parts used in this embodiment.

In Figure 2,! 6 is a comparison means (corresponding to the comparator 16 in FIG. 1); 15 is a selection means for selecting an external detection input and inputting it manually to the comparison means 16; and 10 is a reference voltage generation means for generating a reference value for comparison. (D in Figure 1/
(equivalent to the A converter 1o), and the reference voltage generating means can be set from the CPUI side by the value of the register A14. 3 is a PWM circuit, and three types of registers, register C, register D, and register E, allow writing and reading of various settings of the PWM circuit to be exchanged with the CPUI via the CPU bus 19. Also, 18
is the timing generator and register B 1
The configuration is such that the status can be set from the CPU via 7, and the selection means 15, comparison means 16, and PWM circuit 3
It generates clock signals and state switching signals for the blocks.

An overview of the operation shown in FIG. 2 will be explained below.

First, the chain channel of the multiplexer 15 is switched in order to take in the variable to be controlled from the external detection input. The switching signal at this time is generated by the timing generator 18 and sent as the signal φ1. Also, base 1 at the same time! It is also necessary to set a comparison reference value for the lightning voltage generation means (D/A converter) 10, and this must be set from the CPU bus 19 from the CPUI side.
The voltage is written into the register A 14 via the reference voltage generating means 10 and inputted to the comparing means 16 as a reference voltage. The comparison means 16 uses a comparator having the configuration shown in FIG. 3, and switches SWI to SW3 are switched by a timing signal φ2 from a timing generator 18. First, with SW2 turned off, SWI and SW3 turned on at the same time, and inverter Q shorted with SW3,
By inputting the external detection input via the multiplexer 15 and SWt to charge the capacitor C, and then turning off SWI and SW3 and turning on SW2, the output value of the D/A conversion used as the reference voltage generation means 10 is determined. A comparison is made with the external sense input. The results are latched and output as digital binary values at predetermined timings.

The PWM circuit 3 has three registers, each of which is a register C that inputs the maximum value of the pulse width.

Register D to input the pulse width modulation threshold level
and a register E for outputting pulse width data.

Further, each register can be written to or read out via the CPU bus 19.

Next, the output waveform of digital PWM circuit 3 and register C~
The relationship between each data of E will be explained.

FIG. 4 shows the relationship between the PWM output waveform and each register (C to E). The upper diagram in the figure shows the operation of the counter used internally. In this example, the counter is counted up from 0, reset at point A, and counted up again.
The point is determined by the digital signal determined by the comparison means 16 in FIG. If the output is large, the counter value is decremented.

It always operates so that the detected output value is equal to the set value. Furthermore, in the upper diagram of FIG. 4, B indicates the maximum pulse width determined by register C, and A
The point count value always operates below the set value of B,
It serves as a limiter for A. Also, C is the threshold level set in register D, and C is the threshold level set in register D.
When the value of is exceeded, the output is turned on. In Figure 4,
The pulse is turned on at the point where the count value exceeds the value of C.

In this example, the threshold level of C normally takes a constant value determined in advance by the ROM in the CPU, etc.
The output value of the pulse width of A changes according to the output, thereby realizing a PWM circuit in which the output off-width is constant and the on-width is variable.

In the first embodiment described above, the abnormality detection threshold is set in the ROM in the CPUI, but the RAM (
randoa+-access memory).

FIG. 5 is a block diagram of the main parts of the image forming apparatus according to the second embodiment of the present invention, which is set on this RAM.

As shown in the figure, the RAM 12 in the CPUI is backed up by a voltage holding means 13 with a battery, and data at the time when the assembly of the machine is completed is set in the RAM 12. 1-11
The structure is similar to that of the first embodiment.

Pulse width data for each pulse of the PWM output is taken into cput from register E, and compared with the threshold value of RAMI2 to detect an abnormality.

In this embodiment, since data can be set for each machine, it is possible to deal with variations among machines and to perform detailed detection.

Note that in the first and second embodiments described above, the PWM circuit has a constant off period because the output of the PWM circuit drives the flyback transformer of the high voltage power supply, but the present invention is not limited to this. For example, as shown in FIG. 6, the pulse period may be constant (constant frequency) and the threshold level may be variable, or the on-period may be constant and the off-period may be variable.

In either case, it is sufficient to determine whether the load condition is normal or abnormal depending on whether the duty of the output pulse of the PWM circuit is within the permissible variation range of the duty corresponding to the output of the reference voltage generating means at that time. .

In making the above determination, instead of directly calculating the duty of the output pulse and comparing it with a threshold duty indicating an acceptable range of duty variation, data that is a function of the duty of the output pulse is used as a function of the duty variation of the output pulse. It goes without saying that normality or abnormality may be determined by comparing data that is a duty function of a threshold value indicating a range, and the determination by the determination means of claim 1 may be performed by comparing data that is a function of this duty function. It also includes.

(Effects of the Invention) As explained above, according to the present invention, by detecting and displaying the load condition based on fluctuations in the duty of the output pulse of the pulse width modulation means, maintenance is performed accurately and appropriately. This can reduce the occurrence of image defects.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the main part of the first embodiment, Fig. 2 is a block diagram of the digital PWM circuit used in the same embodiment and its peripheral parts, and Fig. 3 is a connection tube of the comparison means used in the digital PWM circuit. Figure 4 shows the PWM output waveform and each register (
FIG. 5 is a block diagram of the main part of the second embodiment, and FIG. 6 is a diagram showing the relationship between the output waveform and counter operation in PWM with a constant frequency. 1... Microcomputer (CPU) 3...
-PWM circuit 5---Output circuit 6---Output detection circuit 11,---Display section 16---Comparison means

Claims (1)

[Claims] (1) Output setting means for setting a desired power output; power output detection means; comparison means for comparing the output of the output setting means with the output of the power output detection means; A controlled pulse width modulation means, an output means driven by the output of the pulse width modulation means, and a duty variation in which the duty of the output pulse of the pulse width modulation means corresponds to the output of the output setting means at that time. An image forming apparatus comprising: a determining means for determining whether the output is within a permissible range; and a display means for displaying a desired display according to the output of the determining means.