JP5265395B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of a process by center of gravity point operation for a patch pattern being complicated. <P>SOLUTION: An optical sensor 8' for detecting the position of a patch pattern 7' on a transfer belt 5 emits a radiation pattern IR' which is almost an oval shape that is orthogonal to a proceeding direction of the patch pattern 7' and receives the reflected light from the same. The optical sensor 8' is inclined at a prescribed inclination angle &theta; on the upstream side in the proceeding direction of the patch pattern 7'. The patch pattern 7' includes a starting end 7'a to be detected which is longer than a major axis length of the oval shape in the radiation pattern IR'. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a multicolor image forming apparatus such as a color electrophotographic apparatus, a color laser beam printer, and a color printing apparatus, and more particularly to an optical sensor for detecting the belt reference position.

  FIG. 13 shows a conventional multicolor image forming apparatus including an optical sensor for detecting a belt reference position (see Patent Document 1). In FIG. 13, a four-drum color laser beam printer is shown.

In FIG. 13, four color image forming units, that is, a magenta image forming unit 1, a cyan image forming unit 2, a yellow image forming unit 3 and a black image forming unit 4 are provided.

  Each color image forming unit 1, 2, 3, 4 includes on / off light signal generating units 11, 21, 31, 41 having a laser oscillator, a polygon mirror, a reflecting mirror, etc., photosensitive drums 12, 22, 32, 42, and charging. The units 13, 23, 33, 43, the developing units 14, 24, 34, 44, the transfer units 15, 25, 35, 45, and the cleaners 16, 26, 36, 46 are included.

  On the other hand, between the photosensitive drums 12, 22, 32, and 42 and the transfer units 15, 25, 35, and 45, there is provided a transfer belt 5 that conveys a transfer member such as paper and carries toner. The transfer belt 5 is driven in the direction of the arrow by a driving roller 6. The photosensitive drums 12, 22, 32, 42 are provided on the transfer belt 5 at equal intervals.

For example, the magenta image transfer is performed by the magenta image forming unit 1 as follows. First, the surface of the photosensitive drum 12 is uniformly charged by the charger 13. Next, the on / off light signal from the on / off light signal generator 11 scans the surface of the photosensitive drum 12 along the direction of the rotation axis. As a result, the electrostatic latent image of the magenta image is scanned on the surface of the photosensitive drum 12. An image is formed. Next, magenta toner adheres to the electrostatic latent image on the surface of the photosensitive drum 12 by the developing device 14, and a magenta toner pattern is formed. Similarly, the cyan toner pattern, the yellow toner pattern, and the black toner pattern are formed by the cyan image forming unit 2, the yellow image forming unit 3, and the black image forming unit 4.

The magenta toner pattern, the cyan toner pattern, the yellow toner pattern, and the black toner pattern are sequentially transferred onto a transfer member such as paper by the transfer units 15, 25, 35, and 45. Finally, the magenta toner pattern, the cyan toner pattern, the yellow toner pattern, and the black toner pattern are thermocompression bonded by a fixing device (not shown).

  In the conventional multicolor image forming apparatus of FIG. 13, it is necessary to detect the reference position of the transfer belt 5 in accordance with switching between the full color print mode, the single color print mode, or the black and white print mode in which the transfer belt 5 has a different speed. Therefore, a patch pattern 7 for detecting the reference position is printed in advance at a predetermined position on the transfer belt 5.

The transfer belt 5 is black, and its optical density (OD) value is, for example, about 1.0 to 1.2. On the other hand, the patch pattern 7 is white ink, and its OD value is, for example, about 0.05 to 0.2. Such a difference in gloss, that is, a difference between the light reflection amount of the transfer belt 5 and the light reflection amount of the patch pattern 7 is detected by a reflection type optical sensor 8, and a control circuit 9 including a CPU is connected to the optical sensor 8. The color image forming units 1, 2, 3, 4 are controlled according to the sensor output V _S.

  FIG. 14 is a perspective view showing the positional relationship between the patch pattern 7 and the optical sensor 8 of FIG.

  As shown in FIG. 14, the optical sensor 8 emits a substantially circular irradiation pattern IR at right angles to the traveling direction of the transfer belt 5, that is, the traveling direction of the patch pattern 7, and the reflected light from the transfer belt 5 and the patch pattern 7. Is received. The patch pattern 7 has a linear detection start end 7a longer than the diameter of the irradiation pattern IR.

  FIG. 15 is a front view, a top view, and a side view showing the optical sensor 8 of FIG.

  As shown in FIG. 15, the optical sensor 8 includes a light emitting unit 81 including a light emitting element 81a and a circular lens 81b, and a light receiving unit 82 including a condensing lens 82a and a light receiving element 82b. The part 82 is incorporated in the support case 84 together with the circuit board 83 so as to have an equiangular inclination with respect to the detection surface S.

  The surface including the optical axis 81 c of the light emitting unit 81 and the optical axis 82 c of the light receiving unit 82 includes an axis 85 perpendicular to the traveling direction of the transfer belt 5, that is, the traveling direction of the patch pattern 7, and perpendicular to the traveling direction of the patch pattern 7. It has become.

  In addition, in order to ensure the tolerance for the distance variation of the detection surface S and the deviation of the optical axes of the light emitting unit 81 and the light receiving unit 82, the light distribution of the light receiving unit 82 is set to be wide with respect to the light emitting unit 81. Has been.

  From the viewpoint of spectral sensitivity and manufacturing cost of the light receiving unit 82, the light emitting element 81a of the light emitting unit 81 is configured by a red or infrared light emitting diode (LED) element of 600 nm to 1000 nm, for example.

  On the other hand, the condensing lens 82a of the light receiving unit 82 has a filter function for cutting a short wavelength region equal to or shorter than the emission wavelength of the LED element, and is configured to improve the detection ratio. In addition, the light receiving element 82b of the light receiving unit 82 is configured by a phototransistor or a photodiode made of silicon having a good response and low manufacturing cost, and adopts a method of detecting in synchronization with the driving waveform of the LED element to cause a pulsed disturbance. It can also be configured to ensure a noise margin for light.

As shown in FIG. 16, when the light emitting portion 81 of the optical sensor 8 irradiates the detection surface S1 of the transfer belt 5 with the incident light I with the irradiation pattern IR, the light receiving portion 82 of the optical sensor 8 receives the weak reflected light R1. . On the other hand, as shown in FIG. 17, when the light emitting portion 81 of the optical sensor 8 irradiates the detection surface S2 of the patch pattern 7 with the incident light IR, the light receiving portion 82 of the optical sensor 8 emits strong reflected light R2. Receive light. As shown in FIG. 18, even if the patch pattern 7 is contaminated with paper powder, toner, or the like, the center point of the sensitized region of the sensor output V _S of the optical sensor 8 does not change. Therefore, the detection ratio P1 due to contamination of the patch pattern 7 is decreased by detecting the center-of-gravity point while the detection position P1, P2 or P1 ′, P2 ′ in the initial state or the contamination state exceeds a certain threshold value TH. Can be reduced. The barycentric point detection described above can be performed by the control circuit 9 such as software (program).

JP-A-1-167769

  However, the conventional optical sensor 8 shown in FIG. 15 has a problem that the processing becomes complicated because it needs to detect the center of gravity.

Further, if the detection of the patch pattern 7 is performed only at the rising timing of the sensor output V _S in order to simplify the processing, the detection position P1 is as large as P1 ′ in the contamination state of the patch pattern 7 as shown in FIG. As a result, the position detection accuracy of the patch pattern 7 is lowered.

Further, in the conventional optical sensor 8 shown in FIG. 15, the surface including the optical axis 81c of the light emitting portion 81 and the optical axis 82c of the light receiving portion 82 is perpendicular to the traveling direction of the patch pattern 7. The variation of the detection ratio is large and therefore the stability is low. That is, the detection ratio is expected to secure a margin against a decrease in the sensor output V _S due to the initial radiation output of the light emitting unit 81, the sensitivity of the light receiving unit 82, contamination of the patch pattern 7 with paper dust, toner, and the like. However, in the case of the optical sensor 8, the variation of the detection ratio due to the installation error is large, and therefore the stability is low. As a result, in order to ensure a detection ratio margin, high sensor mounting accuracy is required. In addition, when the sensor output V _S is adjusted with respect to the above-described threshold TH for detecting the center of gravity, the output of the light emitting unit 81 and the sensitivity of the light receiving unit 82 may vary if the detection ratio margin is not sufficient. It is necessary to reduce the size, and the accuracy of mounting the light emitting unit 81 and the light receiving unit 82 in the support case 84 is also required. For this reason, there is another problem that the manufacturing cost is high.

In order to solve the above-mentioned problem, a belt reference position detection in an image forming apparatus comprising a belt on which a patch pattern is formed and a belt reference position detection optical sensor for detecting the position of the patch pattern on the belt. The optical sensor includes a light emitting unit that emits a substantially oval irradiation pattern orthogonal to the traveling direction of the patch pattern, and a light receiving unit that receives reflected light from the belt and patch pattern of the irradiation pattern. The light emitting element and an elliptical lens that allows the light of the light emitting element to pass therethrough, the patch pattern has a detection start end longer than the length of the oval shape of the irradiation pattern, and the optical axis of the light emitting part And the surface including the optical axis of the light receiving part is inclined at a predetermined inclination angle upstream of the traveling direction of the patch pattern, and one side of the elliptical shape of the irradiation pattern has a convex arc shape, The detection start end of Tchipatan is one having a recessed circular shape corresponding to the convex arc shape. As a result, the patch pattern can be detected only at the rising timing of the sensor output of the optical sensor. In this case, the patch pattern position detection accuracy is hardly lowered even in a contaminated state of the patch pattern.

  According to the present invention, the calculation of the center of gravity can be performed only at the rising timing of the sensor output without performing the centroid calculation. In addition, the stability of the detection ratio is increased, so that the margin of the detection ratio is increased. Therefore, the high mounting accuracy of the sensor and the high mounting accuracy of the light emitting unit and the light receiving unit in the support case are not required. Cost can be reduced.

1 is a diagram showing a multicolor image forming apparatus including an embodiment of an optical sensor for detecting a belt reference position according to the present invention. It is a perspective view which shows the positional relationship of the patch pattern of FIG. 1, and an optical sensor. It is the front view, top view, and side view which show the optical sensor of FIG. It is the bottom view, front view, and side view of the light emission part of the optical sensor of FIG. It is a figure explaining the main beam and side lobe of the light beam of the light emission part of the optical sensor of FIG. It is a figure which shows the experimental example of the irradiation pattern of FIG. It is the bottom view, front view, and side view which show the example of a change of FIG. It is a figure explaining the reflected light from the transfer belt of the optical sensor of FIG. It is a figure explaining the reflected light from the patch pattern of the optical sensor of FIG. It is a figure explaining the inclination-angle of the optical sensor of FIG. It is a figure which shows the detection ratio characteristic with respect to the inclination-angle of FIG. It is a graph which shows the rise of the sensor output of the optical sensor of FIG. It is a figure which shows the multicolor image forming apparatus containing the conventional optical sensor for belt reference position detection. It is a perspective view which shows the positional relationship of the patch pattern of FIG. 13, and an optical sensor. It is the front view, top view, and side view which show the optical sensor of FIG. It is a figure explaining the reflected light from the transfer belt of the optical sensor of FIG. It is a figure explaining the reflected light from the patch pattern of the optical sensor of FIG. It is a graph which shows the example of the sensor output of the optical sensor of FIG. It is a graph which shows the rise of the sensor output of the optical sensor of FIG.

  FIG. 1 is a diagram showing an embodiment of a multicolor image forming apparatus including an embodiment of an optical sensor for detecting a belt reference position according to the present invention. In FIG. 1, a patch pattern 7 'and an optical sensor 8' are provided in place of the patch pattern 7 and the optical sensor 8 of FIG.

  FIG. 2 is a perspective view showing the positional relationship between the patch pattern 7 'and the optical sensor 8' shown in FIG.

  As shown in FIG. 2, the sensor detection output change (referred to as detection output sensitivity) with respect to the movement amount of the patch pattern 7 ′ is increased, and the detection position with respect to the density change of the patch pattern 7 ′ and the output change of the light emitting portion of the optical sensor 8 ′. In order to suppress fluctuations in the optical sensor 8 ′, the width of the irradiation pattern IR ′ of the optical sensor 8 ′ with respect to the traveling direction of the transfer belt 5 is made smaller than the width of the patch pattern 7 ′, and the traveling direction of the transfer belt 5, ie, the patch pattern 7 ′. It has a substantially oval shape orthogonal to the direction of travel. In consideration of position detection accuracy, the irradiation pattern IR 'is preferably a sufficiently thin beam. However, when an inexpensive sealing resin type LED element described later is used, the size and irradiation pattern of the LED element itself are considered. In this case, it is practically impossible to reduce the beam diameter to be equal to or smaller than the lens diameter. Further, in order to avoid a decrease in detection accuracy of the patch pattern 7 ′ due to the influence of edge scattering due to the thickness of the printed part of the patch pattern 7 ′, the optical sensor 8 ′ is disposed upstream in the traveling direction of the patch pattern 7 ′. It is inclined at an inclination angle θ. The optical sensor 8 'receives the reflected light from the transfer belt 5 and the patch pattern 7'.

  As described later, by decentering the position of the LED element of the light emitting element 81'a, the irradiation pattern IR 'actually has a convex arc-shaped bias on one side in the minor axis direction of the ellipse. Therefore, the patch pattern 7 'has a detected start end 7'a having a convex arc shape corresponding to the concave arc shape, thereby improving the detection accuracy.

  3 is a front view, a top view, and a side view showing the optical sensor 8 'of FIG.

  As shown in FIG. 3, the optical sensor 8 ′ includes a light emitting unit 81 ′ composed of a light emitting element 81′a and an elliptic lens 81′b, and a light receiving unit 82 composed of a condensing lens 82′a and a light receiving element 82′b. The light emitting unit 81 ′ and the light receiving unit 82 ′ are incorporated in the support case 84 ′ together with the circuit board 83 ′ so as to have an equiangular inclination with respect to the detection surface S.

  The surface including the optical axis 81'c of the light emitting portion 81 'and the optical axis 82'c of the light receiving portion 82' is inclined at a predetermined inclination angle θ on the upstream side in the traveling direction of the patch pattern 7 '.

  Further, in order to ensure the tolerance for the distance variation of the detection surface S and the deviation of the optical axes of the light emitting unit 81 ′ and the light receiving unit 82 ′, the light distribution of the light receiving unit 82 ′ is wide with respect to the light emitting unit 81 ′. It is set to be.

  FIG. 4 is a bottom view, a front view, and a side view showing the light emitting portion 81 ′ of FIG. 3.

  As shown in FIG. 4, the light emitting element 81'a and the elliptical lens 81'b are configured by red or infrared light emitting diodes (LEDs) formed with a sealing resin-integrated oval lens. At this time, the LED element is offset from the center of the minor axis of the elliptic lens 81 ′ b in order to generate a bias on one side of the minor axis direction of the irradiation pattern along the traveling direction of the transfer belt 5. This can suppress the generation of side lobes on the radiation intensity bias side in the light distribution pattern shown in FIG. 5, and as a result, as shown in FIG. 6, the irradiation pattern IR ′ has a short diameter along the traveling direction of the transfer belt 5. A distribution having a bias on one side is formed. As described above, the irradiation pattern IR 'is not affected by the side lobe, so that the detection accuracy can be improved.

  As shown in FIG. 4, instead of offsetting the LED element from the center of the minor axis of the elliptic lens 81′b, as shown in FIG. 7, the LED element is shielded around the elliptic lens 81′b (resin), that is, in the side lobe generation direction. Even if the frame 81c is provided, generation of side lobes can be suppressed.

  In FIG. 4, a toric surface lens may be used instead of the elliptical lens 81'b. Furthermore, a mask function for suppressing the light beam spread in the traveling direction of the transfer belt 5 by a shielding window, printing, or the like may be added to the circular lens.

  As shown in FIG. 8, when the light emitting part 81 ′ of the optical sensor 8 ′ irradiates the detection surface S1 of the transfer belt 5 with the irradiation pattern IR ′, the regular reflection light R1 is received by the light receiving part of the optical sensor 8 ′. No light is received at 82 '. On the other hand, as shown in FIG. 9, when the light emitting portion 81 ′ of the optical sensor 8 ′ irradiates the detection surface S2 of the patch pattern 7 with the irradiation pattern IR ′, a part of the reflected light R2 is reflected by the optical sensor 8. The light receiving unit 82 receives the light.

  In order to improve the detection accuracy of the optical sensor 8 ′, the inclination angle θ of the optical sensor 8 ′ is appropriately set, and the amount of light received by the light receiving unit 82 ′ of the optical sensor 8 ′ of FIG. What is necessary is just to enlarge ratio (henceforth detection ratio) with the light-receiving amount of light-receiving part 82 'of the target sensor 8'.

FIG. 10 is a diagram illustrating the setting of the inclination angle θ of the optical sensor 8 ′. That is, if the light spreading angle of the optical sensor 8 ′ is 2α,
β = π / 2-α + θ (1)
It is. Therefore, in FIG. 8, in order that the regularly reflected reflected light R1 is not received by the light receiving portion 82 ′ of the optical sensor 8 ′,
β-π / 2> 0 (2)
It is. From equations (1) and (2)
θ> α (3)
It becomes.

  Note that the angle α in FIG. 10 is not synonymous with a half-value angle (an inclination angle that decreases by −3 dB from the maximum radiant energy on the optical axis), which is a general representative value indicating the sharpness of directivity. This is because the above-described detection ratio of the optical sensor 8 'can be ensured even in an angle range exceeding the half-value angle. Therefore, the angle α in FIG. 10 is set to a value at which the maximum radiation energy drop on the optical axis is at least −5 dB, preferably −10 dB. In practice, the inclination angle θ is different from the optical axis when the light emitting portion 81 ′ of the optical sensor 8 ′ is installed in the support case 84 ′, when the optical sensor 8 ′ is installed in the apparatus, etc. It is set in anticipation of tolerance against. Further, the detection angle of the light receiving unit 82 ′ of the optical sensor 8 ′ is set to be larger than the light beam spreading angle 2α of the light emitting unit 81 ′ so as to correspond to the light beam spreading angle 2α of the light emitting unit 81 ′.

  FIG. 11 shows the result of measuring the detection ratio of the optical sensor 8 ′ with respect to the inclination angle θ of the optical sensor 8 ′ when the light spread angle α of the light emitting portion 81 ′ of the optical sensor 8 ′ is approximately 15 °. It is a graph to show. In this case, as shown in FIG. 11, the optimum value of the inclination angle θ is 20 ° to 30 °, and it can be seen that the expression (3) is satisfied.

  FIG. 12 is a graph for explaining the position detection accuracy of the patch pattern 7 'according to the present invention.

  As shown in FIG. 12, even if the patch pattern 7 ′ is contaminated, the detection position P1 is shifted to P1 ′. However, the amount of deviation is smaller than that of the conventional case shown in FIG. The decrease in accuracy is small.

  In the above-described embodiment, the irradiation pattern IR ′ has a substantially oval shape, and the optical sensor 8 ′ is inclined at an inclination angle θ upstream of the traveling direction of the patch pattern 7 ′. Even if the pattern IR ′ is made into an almost oval shape, the above-described position detection accuracy is inferior.

1: magenta image forming unit 2: cyan image forming unit 3: yellow image forming unit 4: black image forming unit 5: transfer belt 6: drive roller 7, 7 ′: patch pattern 7a, 7′a: detection start end 8 8 ′: Optical sensor 9: Control circuit 10: Transfer belt cleaner blade 11: Position detection color image pattern trailing edge detection circuit 81, 81 ′: Light emitting portion 81a, 81′a: Light emitting element 81b: Circular lens 81 ′ b: Ellipse lenses 82, 82 ': Light receiving portions 82a, 82'a: Condensing lenses 82b, 82'b: Light receiving elements
IR, IR ': Irradiation pattern θ: Inclination angle

Claims (2)

A belt on which a patch pattern is formed;
An optical sensor for detecting a belt reference position for detecting a position of a patch pattern on the belt;
In an image forming apparatus comprising:
The belt reference position detecting optical sensor comprises:
A light emitting unit that emits a substantially oval-shaped irradiation pattern orthogonal to the traveling direction of the patch pattern;
A light receiving portion for receiving reflected light from the belt and the patch pattern of the irradiation pattern;
Comprising
The light emitting unit is
A light emitting element;
An elliptic lens that allows the light of the light emitting element to pass through;
Comprising
The patch pattern has a detection start end longer than the elliptical length of the oval shape of the irradiation pattern;
The surface including the optical axis of the light emitting unit and the optical axis of the light receiving unit is inclined at a predetermined inclination angle upstream of the traveling direction of the patch pattern, and one side of the oval shape in the minor axis direction of the irradiation pattern is a convex arc An image forming apparatus, wherein the detected start end of the patch pattern has a concave arc shape corresponding to the convex arc shape. The image forming apparatus according to claim 1, wherein the multi-color image forming apparatus.

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