JP2006078824A - Toner image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate color shifts in an electrophotographic device, by eliminating the time differences due to the output level differences of the toner image sensor and obtaining the stable toner image outputs. <P>SOLUTION: This detector comprises a light source, a photodetector to detect the amount of the reflected light of the light source, a differential amplifier to amplify the time series differences in the photodetector output, and a comparator to compare the output of the differential amplifier with the predetermined level, and detects the toner image adhering on a recording medium. It changes the amplification factor of the differential amplifier and the predetermined level, depending on the color of the toner image. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a toner image detector for detecting a toner image on a recording medium in an electrophotographic apparatus.

Hereinafter, conventional techniques will be described with reference to the drawings.
FIG. 3 is a schematic configuration diagram of a color printer using an electrophotographic system.
In FIG. 3, the photosensitive belt 31 rotates at a speed corresponding to the printing speed of the printer, and continues to rotate from the start of the printing operation to the end of the printing operation. When the photosensitive belt 31 starts to rotate, a high voltage is applied to the corona charger 32, and negative charges are uniformly charged on the surface of the photosensitive belt 31, for example. When character data or graphic data converted into a dot image is sent as an on / off signal of the LED head 33 from a controller (not shown) to the printer, there are portions where the surface of the photosensitive belt 31 is irradiated with LED light and portions where it is not irradiated. The so-called electrostatic latent image is formed. When the photosensitive belt region holding the electrostatic latent image reaches a position facing the developing device 34, toner is supplied to the electrostatic latent image, and in the portion where the charge on the photosensitive belt 31 disappears due to the irradiation of LED light, For example, toner charged to a negative charge is attracted by static electricity and a toner image is formed on the photosensitive belt 31. The continuous paper 35 is conveyed between the photosensitive belt 31 and the transfer device 36 in synchronization with the timing at which the toner image of the print data formed on the photosensitive belt 31 reaches the transfer position. The toner image formed on the photosensitive belt 31 is sucked onto the sheet 35 by the action of the transfer unit 36 that applies a charge having a polarity opposite to that of the toner image to the back side of the sheet 35. In the color printer, the black developer unit 37K, the cyan developer unit 37C, the magenta developer unit 37M, and the yellow developer unit 37Y perform the same operation, and a color toner image is formed on the paper 35 by combining these. Form.
In a color printer that forms a color toner image by superimposing toner images in this way, color misregistration due to misregistration (registration) of each color becomes a problem.
Accordingly, the toner image formed by each developing unit is detected using the toner image detector 38, and the positional deviation of each color is detected by measuring the time difference, and the light emission timing of the LED head 33 and the rotational speed of the photosensitive belt 31 are detected. In addition, the color misregistration is eliminated by feeding back to the conveyance speed of the paper 35.
Next, the configuration of the conventional toner image detector 38 will be described with reference to FIGS.
FIG. 4 is a schematic configuration diagram of the toner image detector, FIG. 5 is a circuit diagram thereof, and FIG. 6 is a diagram showing the relationship between the differential amplification unit output and the comparison unit output for each color toner image in the toner image detector.
In FIG. 4, an LED 42 serving as a light source of the detector is mounted on the toner image detection substrate 41 and irradiates a paper 43 and a toner image 44 on the paper 43. The reflected light of the paper 43 or the toner image 44 is received by the light receiving element 45 on the toner image detection substrate 41.
As shown in FIG. 5, the photodiode D1 is used for the light receiving element 45, and the photocurrent of the photodiode D1 is I / V converted by R1 and amplified by the operational amplifier Z1. The amplified output is differentially amplified by a differential amplifying unit of the operational amplifier Z5 with respect to a difference from a signal through a peak hold circuit including the operational amplifier Z3, the diode D2, and the capacitor C1. The differentially amplified signal is compared with a reference voltage by a comparator by a comparator Z6 to obtain a toner image detector output.
With this configuration, if there is a toner image 44 of each color on the paper 43, the toner image is detected by the output of the photodiode D1 being reduced for the portion of the paper 43 where there is no toner image 44 (white paper).
In the above configuration, as shown in FIG. 6, the output level of the differential amplifier differs for each color toner image 44. If the output level of the differential amplifier is different, a time difference is generated in the output of the comparator. Since the time difference is recognized as a positional shift of each color as it is, it is desirable that the differential amplifier output level is equal for each color, or that the ratio between the differential amplifier output level and the comparison unit reference voltage is equal. .
For this reason, a method of detecting a toner image by a plurality of light receiving elements has been proposed (see, for example, Patent Document 1). However, in the above-described method, it is necessary to adjust the output levels of a plurality of light receiving elements to be equal, and there is a problem that chattering occurs in the output when a toner image longer than a specified value is detected.

JP 2000-231233 A

  An object of the present invention is to eliminate a color difference of an electrophotographic apparatus by eliminating a time difference due to a difference in toner image detector output level and obtaining a stable toner image detector output.

  The object is to provide a light source, a light receiving element for detecting the amount of reflected light of the light source, a differential amplifying part for amplifying a time-series fluctuation difference amount of the output of the light receiving element, and an output of the differential amplifying part to a specified level. This is achieved by switching the amplification factor and the specified level of the differential amplification unit in accordance with the color of the toner image in a detector comprising a comparison unit for comparison and detecting a toner image adhering to the recording medium.

  By eliminating the time difference due to the difference in the output level of the toner image detector and obtaining a stable toner image detector output, the color shift of the electrophotographic apparatus can be eliminated.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. During the initial adjustment, the output of the operational amplifier Z1 at the time of paper detection is adjusted to the target value by adjusting the variable resistor VR1. Depending on the color of the toner image to be detected, for example, when yellow toner is detected, the analog switch S1y is turned on to select the resistor R6y. Like each color, the circuit can select a resistance value corresponding to the output level. Here, the output of the operational amplifier Z1 when detecting the yellow toner image is Vy, the output of the operational amplifier Z1 when detecting paper (blank) (equal to the output of the operational amplifier Z4) is Vp, and the target output value of the operational amplifier Z5 when detecting the toner image is Assuming Vo, R6y is expressed by Equation 1.

R6m, R6c, and R6k can be similarly obtained.
By determining the resistance values of R6y, R6m, R6c, and R6k using Equation 1, and selecting the resistance value according to the color of the toner image to be detected, the output of the operational amplifier Z5 can be made equal for each color. The time difference due to the difference in the output level of the image detector can be eliminated.

FIG. 2 is a circuit diagram showing another embodiment of the present invention. During the initial adjustment, the output of the operational amplifier Z1 at the time of paper detection is adjusted to the target value by adjusting the variable resistor VR1. Depending on the color of the toner image to be detected, for example, when yellow toner is detected, the analog switch S2y is turned on to select the resistor R10y. Like each color, the circuit can select a resistance value corresponding to the output level. Here, if the target value of the reference voltage at the time of detecting the yellow toner image is Vty, R10y is expressed by Equation 2.

However, the output of the operational amplifier Z1 when detecting the yellow toner image is Vy, the output of the operational amplifier Z1 when detecting the magenta toner image is Vm, the reference voltage when detecting the magenta toner image is Vtm, and the output of the operational amplifier Z1 when detecting the cyan toner image. When Vc is the reference voltage when detecting the cyan toner image and Vtk is the output of the operational amplifier Z1 when detecting the black toner image and Vtk is the reference voltage when detecting the black toner image, R10y, R10m, R10c and R10k are determined.

  The resistance values of R10y, R10m, R10c, and R10k are determined by Expressions 2 and 3, and the ratio of the output of the operational amplifier Z5 to the reference voltage is made equal by selecting the resistance value according to the color of the toner image to be detected. The time difference due to the difference in the output level of the toner image detector can be eliminated.

It is a circuit diagram which shows one Example of this invention. It is a circuit diagram which shows the other Example of this invention. 1 is a schematic configuration diagram of a color printer using an electrophotographic system. It is a schematic block diagram of a toner image detector. It is a circuit diagram of a toner image detector. It is a figure which shows the relationship between the differential amplifier part output and the comparison part output for every color toner image in a toner image detector.

Explanation of symbols

31 is a photosensitive belt, 32 is a corona charger, 33 is an LED head, 34 is a developing device, 35 is paper, 36 is a transfer device, 37 is a developing unit, 38 is a toner image detector, 41 is a toner image detection substrate, Reference numeral 42 denotes an LED, 43 denotes paper, 44 denotes a toner image, and 45 denotes a light receiving element.

Claims (1)

A light source;
A light receiving element for detecting a reflected light amount of the light source;
A differential amplifier for amplifying a time-series fluctuation difference amount of the output of the light receiving element;
A detector configured to compare the output of the differential amplifier with a specified level and detect a toner image attached to a recording medium.
A toner image detector, wherein the gain of the differential amplifier and the specified level are switched according to the color of the toner image.

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