JP2005084206A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and accurate color image position detector and an inexpensive color image forming apparatus using the color image position detector. <P>SOLUTION: The image position detector is constituted of a light source part and a light receiving part, when an intermediate transfer body and a toner image pattern are irradiated with light emitted from the light source and the reflected light is received by the light receiving part, a relation of (A/(A+B))<SP>2</SP>≥R/(G×F) is satisfied provided that a distance between the light source part and a detection point on the intermediate transfer body is expressed by A, the light quantity per unit area of the light emitted from the light source part in the distance A is expressed by F, a distance between the detection point on the intermediate transfer body and the light receiving part is expressed by B, a reflectance of the intermediate transfer body is expressed by G and the minimum value of the light quantity per unit area which can be detected in the position of the light receiving part is expressed by R. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus that prints an image in accordance with image data, and more particularly to a color image forming apparatus that includes a color image position detecting device for detecting image positional deviation.

  In general, a tandem color image is formed in which images of different colors are formed by a plurality of image forming units, color toner images of different colors are sequentially transferred to an intermediate transfer member conveyed by a conveyor belt, and then transferred to a recording sheet at a time. Forming devices are known.

  This tandem type color image forming apparatus is provided with a unit for each color, so that it is easy to increase the speed. However, it is difficult to form each color on the recording paper without misalignment, and there is a problem that the image quality is lowered. One of the causes of this displacement is that relative displacement between units occurs due to changes over time and temperature changes.

  In addition, even a slight speed error or fluctuation of the photosensitive member or the intermediate transfer member causes a positional deviation between the images of the respective colors. In order to prevent image quality degradation due to such misregistration, each color toner image for detecting misregistration between colors is formed on the intermediate transfer member, and this toner image is detected by a photodetector to correct the misregistration. A control method is known. This correction control is performed by controlling the timing of the light beam in the scanning direction and the sub-scanning direction when the photosensitive member is scanned with the light beam.

  In order to suppress the above-described positional deviation as small as possible, it is necessary to improve the detection accuracy of the positional deviation. Usually, it is desirable that the positional deviation between the colors is 100 μm or less at maximum and 50 μm or less on average. For this purpose, the image position detector needs to detect a position shift with an accuracy of 10 μm or less.

  Conventionally, this image position detector is composed of a light emitting unit and a detecting unit that reflects light emitted from the light emitting unit with an intermediate transfer member and receives the reflected light. The configuration to detect is known. As an example, the light-emitting part is arranged obliquely, irradiates the pattern image on the intermediate transfer body through a lens at a certain angle, and the specularly reflected light is arranged in a conjugate relationship with the light-emitting point of the light-emitting part. There has been proposed a method of performing position detection with high accuracy by receiving light at a detection unit via a lens (for example, see Patent Document 1).

JP 2002-55572 A

  However, in the case of the above-described conventional technology, a lens is provided between the light source and the intermediate transfer member or between the intermediate transfer member and the detection unit, and there is a problem that the lens is expensive and the lens becomes dirty.

  An object of the present invention is to provide an inexpensive color image forming apparatus using an inexpensive and highly accurate color image position detecting apparatus.

The present invention provides a conveying unit that conveys an intermediate transfer member on which a color image is formed, a plurality of image forming units that are disposed in the vicinity of the conveying unit and that form a color image, and the intermediate transfer member. In a color image forming apparatus including an image position detecting device for detecting a positional shift of each color using a formed toner image pattern, the image position detecting device includes a light source unit and a light receiving unit. When the light is applied to the intermediate transfer member and the toner image pattern and the reflected light is received by the light receiving unit, the light source unit and the intermediate transfer member are not provided with a lens between the light source unit and the intermediate transfer member and between the intermediate transfer member and the light receiving unit. The distance from the detection point on the body is A, the light amount per unit area of light from the light source unit at the distance A is F, the distance between the detection point on the intermediate transfer member and the light receiving unit is B, and the reflectance of the intermediate transfer member Can be detected at G, light receiving position When the minimum value of the light amount is R per a unit area, characterized in that so as to satisfy the relation (A / (A + B) ) 2 ≧ R / (G × F).

  In the present invention, the distance A between the light source unit and the detection point on the intermediate transfer member and the distance B between the detection point on the intermediate transfer member and the light receiving unit are reduced in order to reduce the influence of scratches and inclination of the intermediate transfer member. Characterized by being made smaller.

  Further, the present invention is characterized in that the angle between the normal line of the intermediate transfer member and the center line of the light from the light source unit is set to 30 degrees or less in order to reduce the detection error due to the upper limit fluctuation of the intermediate transfer member.

  Further, the present invention satisfies the relationship of C ≦ (D × (A + B)) / A, where C is the size of the light receiving unit body and D is the size of the toner image pattern in order to improve the SN ratio of the toner image pattern portion. It is characterized by doing so.

  Furthermore, in the present invention, in order to improve the S / N ratio of the intermediate transfer member, when the interval between the toner image pattern and the toner image pattern is P, the relationship of C ≦ (P × (A + B)) / A is satisfied. It is characterized by that.

  According to the present invention, it is possible to provide an inexpensive color image forming apparatus that does not require a lens between the light source and the intermediate transfer member or between the intermediate transfer member and the detection unit as in the prior art.

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

  FIG. 1 shows a schematic configuration of an image forming apparatus according to the present invention. An intermediate transfer body 1 that travels at a constant speed and a plurality of color image forming units 2 that are arranged along the travel path of the intermediate transfer body 1 are shown. 3, 4, 5, and a misalignment correction controller 6. The image forming unit 2 forms a color toner image of yellow (hereinafter referred to as Y), 3 forms magenta (hereinafter referred to as M), 4 forms cyan (hereinafter referred to as C), and 5 forms a black image.

  As shown in FIG. 2, each image forming unit includes a photoconductor 10, a charging unit 11, an exposure unit 12, and a developing unit 13, and forms a color toner image on the photoconductor 10 through a series of electrophotographic processes. .

  FIG. 3 shows a configuration example of the exposure means 12. Laser light from a semiconductor laser 20 that emits a laser beam is converted into parallel light by a collimator lens 21 and irradiated onto a polygon mirror 22 that scans the laser beam. The scanning light generated by the rotation of the polygon mirror 22 is converged by the fθ lens 23 and then irradiated to the photosensitive member 10. A part of the light applied to the polygon mirror 22 is reflected by the mirror 24 and then enters the beam detecting means 25 for detecting the reference position in the laser beam scanning.

  Returning to FIG. 1, the description will be continued. The first transfer means 31, 32, 33, and 34 are arranged corresponding to the image forming units 2, 3, 4, and 5, respectively. The M, C, and black color toner images are sequentially transferred to the intermediate transfer body 1. The color toner image transferred to the intermediate transfer body 1 is collectively transferred to the recording paper 36 by the second transfer means 35 and fixed to the recording paper 36 by the fixing means 37.

  This color image forming apparatus performs an operation of correcting a positional deviation between the respective colors when the apparatus starts up or when the temperature in the apparatus changes by a certain level or more. That is, the misregistration detection toner image patterns formed by the image forming units 2, 3, 4, and 5 are transferred to the intermediate transfer body 1, and the toner image patterns conveyed by the intermediate transfer body 1 are image position detection It is detected by the device 38 and enters the misalignment correction control unit 6. In this misregistration correction control unit 6, each time interval between a detection signal of a specific color, for example, a black toner image pattern and a toner image pattern detection signal of other colors Y, M, and C is measured. Then, according to the relative time difference, the rotation speed of the photoconductor 10 in 2, 3, 4, and 5 is changed in each image forming unit, or the light emission timing of the laser beam emitted from the semiconductor laser 20 in each image forming unit. Is controlled so that the relative time difference is kept small. By such control, it is possible to reduce the relative positional deviation of the images of the respective colors.

  FIG. 4 shows a schematic configuration example of the image position detection device 38. Light emitted from the light emitting unit 40 enters the intermediate transfer member 1 at an incident angle θ. Further, the distance between the light emitting unit 40 and the detection point of the intermediate transfer member 1 is A, and the distance between the detection point of the intermediate transfer member 1 and the light detector 41 is B. The reflectance of the intermediate transfer member 1 is G, the dimension of the positioning mark 42 is D, the distance between the positioning mark 42 and the positioning mark 42 is P, and the amount of vertical fluctuation of the intermediate transfer member 1 Is E, C is the dimension of the photodetector 41, and R is the minimum light amount per unit area that can be detected by the photodetector 41.

It is assumed that the amount of light from the light emitting unit 40 is F per unit area at a distance A. As the distance A between the detection point of the light emitting unit 40 and the intermediate transfer member 1 and the distance B between the detection point of the intermediate transfer member 1 and the light detector 41 increase, the amount of light reaching the light detector 41 decreases. This amount of light decreases in inverse proportion to the square of the distance. Further, the amount of light reaching the light detector 41 also changes depending on the reflectance G of the intermediate transfer member. If the minimum value of the amount of light per unit area that can be detected by the light detector 41 is R, it cannot be detected by the color image position detection device of the present invention unless Expression (1) is satisfied. It is necessary to arrange the distance A between the detection points and the distance B between the detection point of the intermediate transfer body 1 and the light detector 41 so as to satisfy the relationship of (A / (A + B)) ² ≧ R / (G × F). is there. Hereinafter, this equation is defined as equation (1).

  For example, the distance A between the light emitting unit 40 and the detection point of the intermediate transfer body 1 is 30 mm, the light amount F per unit area at the distance A from the light emitting part is 3 mW, the reflectance G of the intermediate transfer body 1 is 0.04, and the light detector. Assuming that the minimum value R of the amount of light per unit area detectable by 41 is 0.05 mW, the distance B between the detection point of the intermediate transfer body 1 and the light detector 41 is calculated to be 16.48 or less from the equation (1). . Therefore, in this example, detection is possible if the value of B is 16.48 or less, for example, 10 mm.

  The amount of light F per unit area at a distance A from the light emitting portion of the formula (1), the reflectance G of the intermediate transfer body 1, and the minimum value R of the amount of light per unit area detectable by the light detector 41 are the characteristics of the components. Therefore, detection is possible by setting the distance A between the detection point of the light emitting unit 40 and the intermediate transfer body 1 and the distance B between the detection point of the intermediate transfer body 1 and the light detector 41 to the condition of the expression (1). It becomes.

  Furthermore, in the color image position detection apparatus of the present invention, there is a problem that the position at which the light from the light emitting unit 40 is reflected to the light detector 41 changes due to the slight inclination α of the intermediate transfer body 1. When the amount of change is X, X = B × tan α. In addition, part of the reflected light from the intermediate transfer body 1 may not reach the light detector 41 due to the influence of the disturbance of the light beam caused by the surface state (scratches and dirt) of the intermediate transfer body 1. In order to reduce these, in the present invention, the distance B between the detection point of the intermediate transfer body 1 and the light detector 41 is made smaller than the distance A between the light emitting unit 40 and the detection point of the intermediate transfer body 1.

  In addition, in the case of the present invention, when the intermediate transfer member 1 changes E in the vertical direction, the position of the shadow of the positioning mark 42 that reaches the photodetector 41 changes. As shown in FIG. 4, the amount is roughly calculated by Esin θ when the plane of the photodetector 41 and the center line of the incident light beam are orthogonal. This amount should be as small as possible, but detection is difficult unless it is less than or equal to 1/2 of the vertical fluctuation amount E of the intermediate transfer member 1. Therefore, in the present invention, θ is set to 30 degrees or less.

  In addition, the S / N ratio is improved by making the dimension C of the light receiving portion of the photodetector 41 smaller than the dimension of the shadow with respect to the dimension D of the positioning mark 42. Therefore, in the present invention, the relationship between the dimension D of the positioning mark 42 and the dimension C of the light receiving portion of the photodetector 41 satisfies C ≦ (D × (A + B)) / A.

  For example, if A = 40, B = 10, and D = 0.5, C ≦ 0.625.

  In addition, by setting the dimension C of the light receiving portion of the photodetector 41 to be smaller than the interval P between the positioning mark 42 and the positioning mark 42, the SN ratio is improved. Therefore, in the present invention, the relationship between the positioning mark 42, the positioning mark 42 interval P, and the dimension C of the light receiving portion of the photodetector 41 satisfies C ≦ (P × (A + B)) / A. Yes. For example, if A = 40, B = 10, and P = 2, C ≦ 2.5.

  As the light source used in the color image position detection apparatus of the present invention, the use of light close to a point light source allows the edge portion of the positioning toner mark 42 to appear on the light detector 41 as a sharp shadow. It becomes possible to detect with higher accuracy. A semiconductor laser has been proposed as an example of the light source. The output of the photodetector 41 has a circuit configuration in which the output voltage increases as the amount of light incident on the light receiving surface increases. Conversely, the circuit may be such that the output voltage decreases as the amount of light incident on the light receiving surface increases.

  The light detector 41 receives the light regularly reflected from the intermediate transfer body 1 and generates an electric signal corresponding to the light amount. FIG. 5 shows the relationship between the light amount of the light emitting unit 40 and the output of the light detector 41 which is a light receiving unit, and shows a comparison between the reflected light from the intermediate transfer body 1 and the reflected light of each color toner. Since the reflectance of the intermediate transfer body 1 is higher than the reflectance of the toner, the output of the light detector 41 is high even with a small amount of light. In addition, even with the same toner, the Y, M, and C toners have almost the same output, but the black toner has a low reflectivity, so the output voltage is extremely lower than the other color toners. I understand that.

  Therefore, when the positioning marks 42 are formed on the intermediate transfer member 1 at positions spaced at equal intervals in the order of black toner, Y toner, M toner, and C toner, the light detector 41 shows as shown in FIG. Output is obtained. That is, since the intermediate transfer body 1 has the highest reflectance, the output voltage is high. Next, when the black toner mark formed on the intermediate transfer body 1 passes through the image position detection device 38, the reflectance is the lowest. The voltage has the smallest value as shown in the figure. Next, when the intermediate transfer member 1 is transported and the Y toner mark passes through the image position detecting device 38, the reflectance of the Y toner mark is between the reflectance of the intermediate transfer member and the black toner. The size is also between the intermediate transfer member and the black toner. Further, when the intermediate transfer body 1 is conveyed, the M toner and C toner marks pass through the image position detecting device 38 in sequence, and an output voltage similar to that of the Y toner can be obtained. After comparing the output voltage with a predetermined voltage, the waveform is shaped into a rectangular wave, and the time interval is measured to calculate the position of each toner mark. If the positions of the toner marks of the respective colors are known, the amount of shift when the positions are shifted can also be known.

  The image position detection device 38 shown in FIG. 4 has been described so far, but the same applies to the image position detection device 38 shown in FIG. In FIG. 7, the photodetector 41 is mounted in parallel with the intermediate transfer member 1 for the convenience of mounting.

1 is a schematic configuration diagram showing an embodiment of a color image forming apparatus of the present invention. FIG. 3 is a configuration diagram of each image forming unit used in the apparatus of the present invention. The block diagram of the exposure means used for this invention apparatus. The block diagram which shows one Example of the image position detection apparatus concerning this invention. Explanatory drawing which shows the relationship between the light quantity of the light emission part in this invention apparatus, and the output of a light-receiving part. Explanatory drawing which shows the output voltage of the light-receiving part in this invention apparatus. The block diagram which shows the other Example of the image position detection apparatus concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Intermediate transfer body 2, 3, 4, 5 ... Color image forming unit 6 ... Position shift correction control part 10 ... Photoconductor 11 ... Charging means 12 ... Exposure means 13 ... Developing means 20 ... Semiconductor laser 21 ... Collimating lens 22 ... Polygon mirror 23 ... Fθ lens 24 ... Mirror 25 ... Beam detection means 31, 32, 33, 34 ... First transfer means 35 ... Second transfer means 36 ... Recording paper 37 ... Fixing means 40 ... Light emitting part 41 ... Photo detector 42 ... Marks for positioning

Claims (5)

Conveying means for conveying an intermediate transfer member on which a color image is to be formed; a plurality of image forming units arranged in the vicinity of the conveying means for forming a color image; and toner formed on the intermediate transfer member In a color image forming apparatus including an image position detection device for detecting a positional shift of each color using an image pattern, the image position detection device includes a light source unit and a light receiving unit, and the light from the light source is transmitted to the color image forming device. When the intermediate transfer member and the toner image pattern are irradiated and the reflected light is received by the light receiving unit, a lens is not provided between the light source unit and the intermediate transfer member and between the intermediate transfer member and the light receiving unit. The distance from the detection point is A, the light amount per unit area of the light from the light source unit at the distance A is F, the distance between the detection point on the intermediate transfer member and the light receiving unit is B, the reflectance of the intermediate transfer member is G, Units that can be detected at the light receiving position When the minimum value of the light amount per product and R, (A / (A + B)) 2 ≧ R / color image forming apparatus characterized by satisfying the relation of (G × F).   2. The color image formation according to claim 1, wherein a distance B between the detection point on the intermediate transfer member and the light receiving unit is made smaller than a distance A between the light source unit and the detection point on the intermediate transfer member. apparatus.   2. The color image forming apparatus according to claim 1, wherein an angle between a normal line of the intermediate transfer member and a center line of light from the light source unit is 30 degrees or less.   2. The color image forming apparatus according to claim 1, wherein the relationship C ≦ (D × (A + B)) / A is satisfied, where C is the dimension of the light receiving unit main body and D is the toner image pattern dimension. 2. The color image forming apparatus according to claim 1, wherein a relationship of C ≦ (P × (A + B)) / A is satisfied, where P is a distance between the toner image pattern and the toner image pattern.

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