Reflection detection apparatus and apparatus using the same

The reflection detection apparatus includes multiple light-receiving elements configured to detect a pattern formed on an object by receiving a reflected light from the object, and a selector configured to select a first light-receiving element group from the multiple light-receiving elements. The selector is configured to select the first light-receiving element group that includes one or more light-receiving elements each mainly receiving a specularly reflected light from an area of the object where no pattern is formed among the multiple light-receiving elements, on a basis of outputs from the multiple light-receiving elements. The detection of the pattern is made on a basis of an output from the first light-receiving element group.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflection detection apparatus that detects a reflected light from an object and that is suitable for detection of a color shift and a density in a color image forming apparatus such as a color laser printer or a color copier.

2. Description of the Related Art

Of the above-described color image forming apparatuses, a tandem-type image forming apparatus provided with photoreceptors for multiple colors, for example, forms a pattern on an intermediate transfer belt and detects, by using a light-receiving sensor (reflection sensor), a reflected light from the pattern to perform detection of the color shift and density as described below.

In the color shift detection, the tandem-type image forming apparatus uses a color shift detection-purpose image composed of a reference color pattern in which portions of a reference color are cyclically formed and a comparison color pattern in which portions of a comparison color are formed between the reference color portions. The apparatus detects a time at which each color pattern passes above the reflection sensor in response to changes in light amount of a specularly reflected light which is generated by the passage of each color pattern and calculates, from a result of the detection, a color shift amount of the comparison color with respect to the reference color.

On the other hand, in the density detection, the apparatus uses a density-inspection-purpose image (dither pattern) constituted by a toner image expressed by area coverage modulation. The apparatus detects, by the reflection sensor, a light amount of the specularly reflected light from a surface of the intermediate transfer belt on which the toner image is not formed and calculates the density by using a decrease amount of the light amount of the specularly reflected light from the surface of the intermediate transfer belt on which a toner image is formed depending on a tone corresponding to a result of the detection.

In this process, a diffusely reflected light from the toner mixes with the specularly reflected light, which causes an error in detected value of the light amount of the specularly reflected light. For this reason, subtracting a detected light amount of only the diffusely reflected light from a detected light amount of a total reflected light, namely, the mixture of the specularly and diffusely reflected lights enables extracting only the light amount of the specularly reflected light, which enables calculating an exact density. However, in the specularly reflected light from the intermediate transfer belt, a ray fluctuation is generated corresponding to a relative angle that depends on a relative alignment relation between the intermediate transfer belt and the reflection sensor. A large ray fluctuation causes the reflection sensor to erroneously detect the specularly reflected light when only the light amount of the diffusely reflected light is to be detected. This erroneous detection consequently makes it impossible to detect an exact light amount of only the specularly reflected light, namely, the density.

Japanese Patent Laid-Open No. 02-256076 discloses a reflection sensor having a light-receiving region whose area is increased so as to prevent the specularly reflected light from reaching outside of a light-receiving region of the reflection sensor even if the ray fluctuation is generated.

However, such an increase in light-receiving region area for the specularly reflected light like the reflection sensor disclosed in Japanese Patent Laid-Open No. 02-256076 results in an increase in light amount of the diffusely reflected light reaching the light-receiving region from toner. This increase in the light amount of the diffusely reflected light reaching the light-receiving region increases, in density detection, the light amount of the diffusely reflected light compared to that of the specularly reflected light which decreases with an increase of the density, which makes it impossible to acquire, from the reflection sensor, a density detection signal with a sufficient amplitude corresponding to the light amount if the specularly reflected light. In this case, the light amount of the specularly reflected light from the surface of the intermediate transfer belt on which the toner image is not formed, the light amount being a reference for the density, contains an imaging noise component due to reflectance unevenness on the surface and to minute concavities and convexities caused in manufacturing of the intermediate transfer belt. For this reason, a decrease in amplitude of the density detection signal decreases an S/N ratio of the density detection signal.

SUMMARY OF THE INVENTION

The present invention provides a reflection detection apparatus capable of accurately detecting a light amount of a specularly reflected light without an area of a light-receiving region being increased even if a ray fluctuation of the specularly reflected light is generated. The present invention further provides an apparatus using the reflection detection apparatus.

The present invention provides as an aspect thereof a reflection detection apparatus including multiple light-receiving elements configured to detect a pattern formed on an object by receiving a reflected light from the object, and a selector configured to select a first light-receiving element group from the multiple light-receiving elements. The selector is configured to select the first light-receiving element group that includes one or more light-receiving elements each mainly receiving a specularly reflected light from an area of the object where no pattern is formed among the multiple light-receiving elements, on a basis of outputs from the multiple light-receiving elements, and the detection of the pattern is made on a basis of an output from the first light-receiving element group.

The present invention provides as another aspect thereof an apparatus including the above reflection detection apparatus, and an operation portion configured to operate by using an output from the reflection detection apparatus.

The present invention provides as still another aspect thereof an image forming apparatus including the above reflection detection apparatus, a transfer body on which a latent image to which toner is adhered is formed, and a detector configured to detect, by using an output from the reflection detection apparatus, at least one of a density of the toner, a color shift of the toner, a moving speed of the transfer body and a variation in slope of the transfer body.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described below with reference to the attached drawings.

First, description will be made of a color image forming apparatus that is an apparatus using a color shift/density detection apparatus as a reflection detection apparatus of each of embodiments described later, with reference toFIG. 1.

InFIG. 1, constituent elements denoted by reference numerals that end with “Y”, “M”, “C” or “Bk” correspond to yellow, magenta, cyan or black which are colors of developers (toners). However, in the following description, symbols Y, M, C and Bk are omitted for constituent elements common to these colors.

The color image forming apparatus is provided with a charging unit1, a photosensitive drum2, an exposing unit3, a developing unit4and a primary transfer roller5for each of the toner colors: yellow, magenta, cyan and black. The charging unit1electrically charges the photosensitive drum2, which is an image supporting body rotatable in a direction indicated by a thin arrow in the drawing. The exposure unit3projects a laser light onto the photosensitive drum2to form thereon an electrostatic latent image. The developing unit4applies a developing bias to the photosensitive drum2and supplies toner to the electrostatic latent image to develop the electrostatic latent image into a toner image that is a visible image. The primary transfer roller5applies a primary transfer bias to the photosensitive drum2to transfer the toner image formed thereon onto an intermediate transfer belt6.

The intermediate transfer belt6as a transfer body is rotationally driven (transported) by driving rollers7in a direction (X direction) indicated by a thick arrow. The toner images are transferred, onto a surface (object), from the photosensitive drums2for the respective toner colors such that the toner images overlap one another, which results in formation of a color image on the intermediate transfer belt6.

Transporting rollers8,9and10transport a recording material in a cassette20along a transporting path11to a secondary transfer roller12. The secondary transfer roller12applies a secondary transfer bias to the intermediate transfer belt6to transfer the toner images mutually overlapping on the intermediate transfer belt6to the recording material. A residual toner not transferred to the recording material and thus remaining on the intermediate transfer belt6is removed by a cleaning blade13and then collected by a waste toner collection container14.

The recording material to which the toner image is transferred is heated and pressurized by a fuser15. The recording material to which the toner image is fixed thereby is let out by a transporting roller16outside the apparatus.

An engine controller17includes a micro controller installed therein and performs sequence controls of various actuators (not illustrated), various controls using sensors and others in the image forming apparatus.

At a position facing the intermediate transfer belt6(position with a gap from the intermediate transfer belt6in a Z direction in the drawing), a color shift/density sensor18of each embodiment described later is provided.

A first embodiment (Embodiment 1) will describe a configuration of the color shift/density detection apparatus including the color shift/density sensor18, a method of selecting a light-receiving element group to be used for detecting a specularly reflected light amount, a method of detecting a color shift amount and a method of detecting a density in this order.

On the other hand, a second embodiment will describe a method of detecting a color shift and a density utilizing a 180-degree phase difference arrangement of light-receiving elements of the color shift/density sensor18, and a third embodiment (Embodiment 3) will describe a method of detecting a moving speed of the intermediate transfer belt6.

Furthermore, a fourth embodiment (Embodiment 4) will describe a method of detecting a variation in slope angle of the surface of a detection object (intermediate transfer belt6) utilizing the 180-degree phase difference arrangement of the light-receiving elements.

Finally, a fifth embodiment (Embodiment 5) will describe an optical structure that suppresses an amount of a ray fluctuation due to a slope of a surface of a detection object to shorten required lengths of multiple light-receiving elements.

FIG. 2illustrates a configuration of a color shift/density sensor (reflection sensor)18as a sensor head of the color shift/density detection apparatus that is Embodiment 1 of the present invention. The color shift/density sensor18includes an infrared-wavelength light source201, an aperture member203having an aperture202that limits a width of a light spot204projected from the light source201onto an intermediate transfer belt6and multiple light-receiving elements205each capable of receiving light (reflected light) reflected by the intermediate transfer belt6.

The multiple light-receiving elements205are arranged in line in an x direction inFIG. 2so as to form a line sensor. The x direction is a main direction in which the light emitted from the light source201proceeds while passing through and exiting from the aperture202and then being reflected by a portion204of the surface of the intermediate transfer belt6. In this embodiment, the x direction corresponds to the X direction illustrated inFIG. 1, namely, a direction in which the intermediate transfer belt6is moved (transported). The x direction is hereinafter also referred to as “a transporting direction”. In this embodiment, a width direction orthogonal to the transporting direction of the intermediate transfer belt6is defined as a y direction, and a direction from the color shift/density sensor18toward the intermediate transfer belt6(i.e., a direction orthogonal to the x and y directions) is defined as a z direction corresponding to the Z direction inFIG. 1.

FIGS. 3A and 3Billustrate the configuration of the color shift/density detection apparatus including the color shift/density sensor (hereinafter simply referred to as “a sensor”)18.FIG. 3Aillustrates an operation of the color shift/density detection apparatus performed to select (set) a specular reflection detection region. InFIG. 3A, a region selector305as a selector outputs, to the sensor18, region setting information306used to divide the light-receiving elements205for setting multiple light-receiving element groups. Each of the light-receiving element groups is constituted by two or more light-receiving element.

The sensor18(light-receiving elements205) receives and photoelectrically converts a specularly reflected light from the intermediate transfer belt6and outputs a resulting analog voltage value301corresponding to a light amount detected by the light-receiving elements205to a signal processor302. An A/D converter303of the signal processor302digitalizes the analog voltage value301to produce detected light amount information304and outputs this information to the region selector305.

The region selector305selects from the multiple light-receiving element group, depending on the detected light amount information acquired from the output of each of the light-receiving element groups set in the sensor18, a first light-receiving element group serving as the specular reflection detection region and a second light-receiving element group serving as a diffuse reflection detection region. The first light-receiving element group is a light-receiving element group that mainly receives the specularly reflected light from the intermediate transfer belt6more than a diffusely reflected light therefrom. On the other hand, the second light-receiving element group is a light-receiving element group that mainly receives the diffusely reflected light more than the specularly reflected light from the intermediate transfer belt6. In this embodiment, in a state where no toner image being formed on the intermediate transfer belt6, the region selector305selects one of the multiple light-receiving element groups whose detected light amount is largest as the first light-receiving element group and selects the others as the second light-receiving element group. That is, in this embodiment, the second light-receiving element group is selected so as to have a wider light-receiving area than that of the first light-receiving element group.

FIG. 3Billustrates an operation of the color shift/density detection apparatus performed in a state where a color shift/density detection-purpose image (hereinafter simply referred to as “a detection-purpose image”)307that is a toner image used for color shift/density detection and formed on the surface of the intermediate transfer belt6facing the sensor18. The region selector305first outputs, to the sensor18, the region setting information306to be used for setting the first and second light-receiving element groups selected as illustrated in the state ofFIG. 3A. This output causes the sensor18to set the first and second light-receiving element groups, which are the specular reflection and diffuse reflection detection regions, respectively.

The sensor18photoelectrically converts, by the first light-receiving element group, the specularly reflected light from the detection-purpose image307on the intermediate transfer belt6and outputs the analog voltage value301corresponding to the light amount detected by the first light-receiving element group to the signal processor302. The A/D converter303of the signal processor302digitalizes the analog voltage value301to produce the detected light amount information304and outputs this information to the color shift/density calculator308. The color shift/density calculator308serving as a specular reflection calculator and a pattern interval calculator performs a calculation by using the detected light amount information304to produce color shift/density information309and sends this information to an engine controller17of the image forming apparatus, which is illustrated inFIG. 1, as feedback information for image formation.

Description will now be made of a method of variably selecting the first light-receiving element group of the sensor18so that the specularly reflected light can be detected even if a ray fluctuation is generated.

First, with reference toFIGS. 4A to 4D, description will be made of an example of the ray fluctuation.FIG. 4Aillustrates a state (hereinafter referred to as “a normal state”) in which the sensor18of the image forming apparatus illustrated inFIG. 1is fixed at a normal position at a normal angle. The sensor18is disposed so as to face a surface (hereinafter referred to as “a belt curved surface”) of a curved surface portion of the intermediate transfer belt6along a roller surface of the driving roller7around which the intermediate transfer belt6is wound. In the normal state, a specularly reflected ray402from the belt curved surface enters a center of the light-receiving elements205in the direction (X direction) in which the light-receiving elements205are arranged in line.

FIG. 4Billustrates a case where a fixing position of the sensor18is shifted in the X direction from the normal position illustrated inFIG. 4A. The positional shift of the sensor18in the X direction changes an incident position on the belt curved surface at which a ray401from the sensor18hits. This change in the incident position changes a reflection direction of the specularly reflected ray402, causing the ray fluctuation. As a result, an entrance position of the specularly reflected ray402on the light-receiving elements205is shifted in the X direction from the center of the light-receiving elements205depending on a direction and an amount of the ray fluctuation.

FIG. 4Cillustrates a case where a fixing angle of the sensor18changes from the normal angle illustrated inFIG. 4A. The change in the fixing angle changes an incident angle of the ray401from the sensor18to the belt curved surface and the incident position thereof on the belt curved surface. This change in the incident angle and position changes the reflection direction of the specularly reflected ray402, causing the ray fluctuation. As a result, the entrance position of the specularly reflected ray402on the light-receiving elements205is shifted in the X direction depending on the direction and the amount of the ray fluctuation.

FIG. 4Dillustrates a case where a mount position at which the light source201is mounted in the sensor18is shifted from a proper position. In this case, depending on a positional relation between the light source201and the aperture202, the incident position and angle of the ray401on and to the belt curved surface changes, which changes the reflection direction of the specularly reflected ray402and thereby causes the ray fluctuation. As a result, the entrance position of the specularly reflected ray402on the light-receiving elements205is shifted in the X direction depending on the direction and the amount of the ray fluctuation.

FIGS. 5A to 5Deach illustrate a light-receiving element group501where the specularly reflected ray (a flux of rays having a certain width in the X direction)402enters from the belt curved surface in a corresponding one of the states illustrated inFIGS. 4A to 4D. In addition, in each ofFIGS. 5A to 5D, a light intensity distribution of the specularly reflected ray402on the light-receiving element group501is shown above the light-receiving element group501.

As shown inFIGS. 4A to 4D and 4A to 5D, the fixing position and angle of the sensor18with respect to the intermediate transfer belt6, the shift in the mount position of the light source inside the sensor18and the like cause the ray fluctuation of the specularly reflected ray, which consequently shifts the position at which the specularly reflected ray enters the light-receiving elements205.

Next, with reference toFIGS. 6 and 7 and 8A to 8M, description will be made of a method of selecting (setting) the first light-receiving element group, which is the specular reflection detection region, from the multiple light-receiving elements205.

FIG. 6illustrates a switch circuit that switches a light-receiving element group referenced by the sensor18, that is, a light-receiving element group to be subjected to a determination of whether or not to select that group as the first light-receiving element group. The selected light-receiving group is hereinafter referred to respectively as “a referenced element group”. Individual light-receiving elements205ato205pincluded in the light-receiving elements205are connected to the switch circuit601, and their output signals are selectively connected to output terminals Vrefand Vscaby the switch circuit601depending on the region setting information306from the region selector305. Detected voltages of the light-receiving elements (four light-receiving elements illustrated in each ofFIGS. 5A to 5Din this embodiment) selected as elements of the referenced element group are summed, and the summed voltage is output as a detected voltage Vref. On the other hand, detected voltages of the other light-receiving elements are summed, and the summed voltage is output as a detected voltage Vsca.

FIG. 7illustrates output terminals Vrefand Vscato which output signals of the light-receiving elements are selectively connected depending on the region setting information306. In this embodiment, the region setting information306is a 4-bit signal. For instance, a row indicated by symbol SW306(1,1,1,1) in the drawing shows that, when the region setting information306is a 4-bit signal whose all bits are high level, the output signals of the light-receiving elements205ato205dof the referenced element group are connected to the output terminal Vrefand the output signals of the light-receiving elements205eto205pare connected to the output terminal Vsca. In this manner, the referenced element group is switched depending on the 4-bit signal (hereinafter referred to as “a switching signal”) as the region setting information306.

FIGS. 8A to 8Millustrate sequential switching of a referenced element group801in response to changes of the switching signal. For instance,FIG. 8Aillustrates, in black, among the 16 light-receiving elements205ato205p, the referenced element group801constituted by the four light-receiving elements205ato205dselected corresponding to the 4-bit switching signal SW306(1,1,1,1) illustrated inFIG. 7.

In this embodiment, an entire light-receiving region of the sensor18is formed by the 16 light-receiving elements205ato205parranged in line in the X direction such that the entire light-receiving region has a length (entire length of the light-receiving region) of L2. The entire light-receiving region with the length of L2is divided into n=16 small regions (light-receiving elements) in the X direction. The referenced element group801with the length of L1constituted by four of the 16 light-receiving elements is shifted on an element-by-element basis (m=1) in response to the switching signal (region setting information306) while maintaining the length of L1. In this manner, the region selector305sequentially shifts a first number (n/4=4 in this embodiment) of the light-receiving elements mutually adjacent in the X direction in units of light-receiving elements whose number is a second number (m=1 in this embodiment) equal to or less than the first number and thereby sets multiple (13) referenced element groups801. Then, the region selector305selects, as the first light-receiving element group serving as the specular reflection detection region, one of the multiple referenced element groups801which provides a highest detected voltage Vref.

Description will be made of a relation between the states illustrated inFIGS. 5A to 5Dand the referenced element group801selected as the specular reflection detection region. In the normal state illustrated inFIG. 5A, the detected voltage value Vrefof the selected referenced element group801selected at a center of the entire light-receiving region as illustrated inFIG. 8Gbecomes highest. Thereby, this referenced element group801is selected as the specular reflection detection region. In a ray fluctuation state illustrated inFIG. 5B, the detected voltage value Vrefof the referenced element group801shifted from the center depending on a direction and an amount of the ray fluctuation as illustrated, for example, inFIG. 8Ebecomes highest. Thereby, this referenced element group801is selected as the specular reflection detection region. Similarly, in ray fluctuation states illustrated inFIGS. 5C and 5D, the detected voltage value Vrefof the referenced element group801shifted from the center as respectively illustrated, for example, inFIGS. 8L and 8Bbecomes highest. Thereby, one of these referenced element group801is selected as the specular reflection detection region.

As described above, setting the referenced element group801whose detected voltage value Vrefbecomes highest depending on the direction and amount of the ray fluctuation as the specular reflection detection region enables detecting the light amount of the specularly reflected light with good accuracy without an expansion of the specular reflection detection region itself regardless of generation of the ray fluctuation in the specularly reflected light.

Next, description will be made of an effect provided when the light-receiving region (whose entire length is L2) of the sensor18is formed by the multiple light-receiving elements205as illustrated inFIG. 9A(that is, as in this embodiment) by comparison with an effect provided when the light-receiving region is formed by a single light-receiving element901having an entire light-receiving region length identical to the entire length L2as illustrated inFIG. 9B. In the following description, Condition1refers to forming the light-receiving region of the sensor18divided by the multiple light-receiving elements205, and Condition2refers to forming the light-receiving region by the single light-receiving element901.

The entire length L2of the light-receiving elements205and of the single light-receiving element901is sufficiently long so that a specularly reflected light904from the intermediate transfer belt6does not reach outside of the light-receiving region even if the ray fluctuation is generated due to the shift of the fixing position shift and the change of the fixing angle of the sensor18with respect to the intermediate transfer belt6. For instance, in a case where a size of the projected light spot on the intermediate transfer belt6is Φ=0.2 mm, a size of the reflected light spot on the light-receiving elements205is approximately 0.5 to 0.6 mm, the entire length L2of the light-receiving region is 2.41 mm. In this case, a width of each of the 16 light-receiving elements in the x direction in Condition1(FIG. 9A) is 0.15 mm.

FIG. 9Cillustrates an intensity distribution of the specularly reflected light on the entire light-receiving region in a state in which the detection-purpose image is not formed on the intermediate transfer belt6. This intensity distribution has an intensity peak formed by the specularly reflected light904whose center is at a light-receiving position corresponding to a position of the light-receiving element205jin Condition1. In this state, in Condition1, the referenced element group illustrated inFIG. 8His selected as the specular reflection detection region.

FIG. 9Dillustrates an intensity distribution of the specularly reflected light904on the entire light-receiving region in a state in which the detection-purpose image is formed on the intermediate transfer belt6. In this state, a diffusely reflected light903from the detection-purpose image approximately uniformly reaches the entire light-receiving region.

FIG. 9Eillustrates, with time, detected voltage values of density detection signals provided in Conditions1and2when the intensity distributions of the specularly reflected light and the diffusely reflected light respectively illustrated inFIGS. 9C and 9Dare formed on the light-receiving region.

Symbol Vitbrepresents an average value of the density detection signal corresponding to the intensity of the specularly reflected light from the intermediate transfer belt6. The density detection signal corresponding to the intensity of the specularly reflected light contains an amplitude fluctuation Vn as a noise component due to a reflectance variation of the surface of the intermediate transfer belt6and minute concavities and convexities on the surface. This applies to both Conditions1and2.

On the other hand, the diffusely reflected lights from the detection-purpose image on the intermediate transfer belt6in Conditions1and2have a difference in detected light amounts due to a difference in light-receiving areas of regions where the reflected lights are received. In Condition1, the diffuse reflection detection region (second light-receiving element group) other than the specular reflection detection region (first light-receiving element group) receives the diffusely reflected light from the detection-purpose image. This means that the light-receiving area in Condition1is smaller than that in Condition2. For this reason, in Condition1, a voltage value Vton1of the density detection signal provided from the diffuse reflection detection region is lower (in other words, the density is thicker) as compared to that in Condition2, and an amplitude V1is larger than that in Condition2. In contrast thereto, in Condition2in which the light-receiving area of the diffusely reflected light from the detection-purpose image is larger than that in Condition1, a voltage value Vton2of the density detection signal is higher than Vton1(in other words, the density is thinner), and only a smaller amplitude V2than V1is provided.

Comparison in S/N ratios between V1and V2provides a relation of V1/Vn>V2/Vn. This comparison result shows that Condition1, that is, variably selecting the specular reflection detection region in the light-receiving region as in this embodiment, in further other words, separating the specular reflection detection region from the diffuse reflection detection region enables improving the S/N ratio of the density detection signal.

Although this embodiment described the case where all part of the entire light-receiving region other than the specular reflection detection region is selected as the diffuse reflection detection region, only part of the light-receiving region other than the specular reflection detection region may be selected as the diffuse reflection detection region.

Next, description will be made of a method of detecting the color shift with reference toFIGS. 10A to 10D.FIG. 10Aillustrates the detection-purpose image as the toner image that is formed on the intermediate transfer belt6and is to be used for the color shift detection. For the detection-purpose image to be used for the color shift detection, two toner patch groups111and121tilted mutually oppositely in the X direction are arranged tandemly in the X direction. Each toner patch group includes reference color toner patches (Bk)1001disposed at 0 (360)-degree phase positions in the X direction and having a maximum density, and comparison color toner patches(Y)1002, (M)1003and (C)1004disposed one by one at 180-degree phase positions between the reference color toner patches. In the drawings, reference letters a to h are respectively added after reference numeral1001of the reference color toner patches in order in the X direction, and reference numerals1002,1003and1004of the comparison color toner patches(Y), (M) and (C) are followed by the reference letters of the reference color toner patches disposed across each comparison color toner patch. For instance, the comparison color toner patch(Y)1002abis disposed between the reference color toner patches1001aand1001b. On the other hand, the comparison color toner patch(M)1003fgis disposed between the reference color toner patches1001fand1001g.

The sensor18sequentially detects times at which multiple patterns composed of the color toner patches formed on the intermediate transfer belt6pass through a position where a light spot is formed by the light from the light source201. Thereafter, the sensor18calculates, from the detected passage times, a positional shift of each comparison color toner patch with respect to the reference color toner patch adjacent thereto (that is, a distance between the reference color toner patch and the comparison color toner patch).

Next, description will be made of a method of detecting the passage time of each toner patch.FIG. 10Billustrates partial toner patch groups1011and1021included in regions A and B respectively set for the two toner patch groups111and121inFIG. 10A. The partial toner patch group1011includes the reference color toner patches1001aand1001band the comparison color toner patch(Y)1002abdisposed therebetween. On the other hand, the partial toner patch group1021includes the reference color toner patches1001eand1001fand the comparison color toner patch(Y)1002efdisposed therebetween. These toner patches are transported by the drive of the intermediate transfer belt6in a direction indicated by an arrow in the drawing and respectively pass through the position (hereinafter referred to as “a spot position”)1005at which the light spot is formed by the light from the sensor18.

FIG. 10Cillustrates a voltage value (detected voltage value) Vrefof a color shift detection signal output from the specular reflection detection region of the sensor18in response to the passage of each toner patch through the spot position1005illustrated inFIG. 10B. When no toner patch passes through the spot position1005, the light amount of the specularly reflected light from the intermediate transfer belt6is large, and therefore the voltage value Vrefis high. When the reference color toner patch passes through the spot position1005, the light amount of the specularly reflected light from the intermediate transfer belt6is smallest and the light amount of the diffusely reflected light is also small due to light absorption by that reference color toner patch. Consequently, the voltage value Vrefis approximately zero, and therefore a voltage amplitude value of the color shift detection signal is increased.

On the other hand, the comparison color toner patches(Y)1002aband1002efare formed by light-reflective toner. Since a typical toner patch is formed by toner particles whose particle diameter is several micrometers, the toner patch has a surface with concavities and convexities and thus has light diffusivity as an optical property. The light amount of the diffusely reflected light received by the light-receiving element varies depending on a relation in size between the light-receiving element, the comparison color toner patch and the light spot, and the voltage value Vrefof the color shift detection signal does not become zero. For this reason, the voltage amplitude value of the color shift detection signal is smaller as compared to when the reference color toner patch passes through the spot position1005.

FIG. 10Dillustrates a variation with time of the voltage value Vrefof the color shift detection signal from the sensor18input to the signal processor302and then binarized by the A/D converter303with a threshold voltage Vth. The passage time at which each toner patch passes through the spot position1005is an average value of times at which two polarity changes of the binary signal are detected. Employing such an average passage time enables calculating, without an influence of the difference in the voltage amplitude value of the color shift detection signal caused by a difference in color among the toner patches, a time at which a center of each toner patch passes through the spot position1005. When the times at which the two polarity changes of the binary signal with respect to the reference color toner patch1001aare detected are t1aand t2a, the passage time of the reference color toner patch1001ais calculated by following expression (1):

Similarly, times at which the other toner patches1002ab,1002ef,1001e,1002efand1001fincluded in the partial toner patch groups1011and1021pass through the spot position1005are expressed by following expressions (2) to (6). Times t1ab, t2ab; t1b, t2b; t1e, t2e; t1ef, t2ef; and t1f, t2frepresent times at which the two polarity changes of the binary signal with respect to the toner patches1002ab,1002ef,1001e,1002efand1001fare detected.

Next, description will be made of a method of calculating the color shift. In the following description, the method of calculating the color shift of yellow (Y) with respect to the reference color (Bk) will be shown.

As the color shift, a sub-scan directional color shift that is a color shift in the transporting direction (X direction) of the intermediate transfer belt6and a main scan directional color shift that is a color shift in a direction (Y direction) orthogonal to the transporting direction are generated. Following expressions (7) to (12) are used for calculation of the main scan directional color shift and the sub-scan directional color shift.

When the color shift is generated, a time difference ΔTYis calculated from expression (7) or (8) and sent to the engine controller17. The engine controller17corrects, depending on the time difference ΔTY, the color shift in yellow with respect to the reference color Bk by, for example, correcting an exposure timing at the exposing unit3Y to adjust a transfer position.

Although this embodiment described the detection and the correction of the color shift in yellow that is one of the comparison colors to the reference color, the color shifts in cyan and magenta can also be detected and corrected by the same process as that described above. Therefore, description of the detection and the correction of the color shifts in cyan and magenta is omitted.

Although this embodiment described the case where only the specular reflection detection region is used in the color shift detection, a process to subtract an output corresponding to the diffusely reflected light from the output from the specular reflection detection region may alternatively be performed to suppress a decrease in amplitude caused by the reflective toner patch. Moreover, only the diffuse reflection detection region may be used for the color shift detection for the toner patch color having diffusive reflectivity.

Next, with reference toFIGS. 11A to 11D, description will be made of a method of detecting the density. In this embodiment, the detection-purpose image to be used for the density detection is an image with a dither pattern expressing densities with a minimum unit of 4×4 dots, 1 dot that is a minimum unit of the detection-purpose image having a size of 42.3 μm×42.3 μm.

FIG. 11Aillustrates a graduation pattern1108to be used as the detection-purpose image. Local densities of the graduation pattern1108are expressed by the above-described minute dither pattern.

FIG. 11Billustrates dither patterns in a 0% density region1101, a 25% density region1102, a 50% density region1103, a 75% density region1104and a 100% density region1105of the graduation pattern (toner pattern)1108. Frame lines in each density region illustrated in the drawing are shown for clearly showing each dot and therefore are not actually present. A black portion of the dither pattern indicates, on the surface of the intermediate transfer belt6a, a toner accumulation portion1106on which the toner accumulates (is adhered). On the other hand, a white portion of the dither pattern indicates a region where the toner is not present, that is, an exposed portion (hereinafter referred to as “an exposed surface portion”)1107of the surface of the intermediate transfer belt6.

A change in density of the density region changes an area of the exposed surface portion1107of the intermediate transfer belt6, which results in a change in area of a region in the dither pattern which specularly reflects an incident light and also results in a change in area of the toner accumulation portion1106. Since color of the toner changes a light reflectance of the toner, this embodiment employs a method of calculating the density of the toner by using as an index an increase or a decrease in specularly reflected light amount which is independent of properties of the toner.

FIG. 11Cillustrates toner density dependencies of the specularly reflected light amount and the diffusely reflected light amount detected in the specular reflection detection region, which is the first light-receiving element group of the sensor18. In the drawing, a vertical axis indicates the detected light amount, and a horizontal axis indicates the density. As to the specularly reflected light amount indicated by a thick solid line (specular reflection) in the drawing, as the density increases, the area of the exposed surface portion1107of the intermediate transfer belt6linearly decreases, so that the detected light amount linearly decreases corresponding thereto. As to the diffusely reflected light amounts respectively indicated by a thin dotted line (diffuse reflection BK) and a thin solid line (diffuse reflection Color) in the drawing, these light amounts change nonlinearly depending on the density; the detected light amounts have a difference due to a difference in spectral characteristics of a color toner and a black toner for a wavelength of the light source. For these reasons, each of the reflected light amounts detected in the specular reflection detection region has a property that, as indicated in the drawing by a thick dotted line (combination BK) and a dashed line (combination Color), nonlinearity of the diffusely reflected light appears with increasing the density. This property causes a density detection error for the diffusely reflected light amount in a medium-to-high density range. Therefore, in order to calculate the density, it is necessary to remove a component of the diffusely reflected light amount from a detected value of the light amount in the specular reflection detection region.

Next, description will be made of a method of removing the component of the diffusely reflected light amount from the detected light amount value in the specular reflection detection region of the sensor18.FIG. 11Dillustrates a side view of the sensor18. Of the ray (light flux)401emitted from the light source201, passing through the aperture202and then projected onto the detection-purpose image307, the specularly reflected light904enters the specular reflection detection region1109, which is the first light-receiving element group. Meanwhile, the diffusely reflected light903generated by the toner pattern1108of the detection-purpose image307also enters the specular reflection detection region1109.

The specularly reflected light904does not enter a diffuse reflection detection region1110, which is the second light-receiving element group and is adjacent to the specular reflection detection region1109, but only the diffusely reflected light903enters that region1110. Therefore, the color shift/density calculator308performs a calculation using following expression (13) to calculate a difference between a detected voltage value Vrefcorresponding to the detected light amount value in the specular reflection detection region1109where both the specularly reflected light904and the diffusely reflected light903enter and a detected voltage value Vscacorresponding to the detected light amount in the diffuse reflection detection region1110where only the diffusely reflected light903enters. This calculation enables extracting a voltage value V corresponding only to the specularly reflected light amount. In other words, the color shift/density calculator308can calculate, by using the outputs (Vrefand Vsca) from the first and second light-receiving element groups, an output component (V) corresponding to the specularly reflected light in the output from the first light-receiving element group.
V(SPECULAR REFLECTION)=Vref(SPECULAR+DIFFUSE REFLECTION S)−Vsca(DIFFUSE REFLECTION)(13)

However, when the specular reflection detection region1109and the diffuse reflection detection region1110between which the difference in the voltage values corresponding to their detected light amounts is calculated have a difference in detection sensitivity for the diffusely reflected light amount corresponding to an identical density, it is necessary to correct at least one of those voltage values.

For this reason, the color shift/density calculator308calculates, from a ratio between the detected voltage value Vrefcorresponding to the diffusely reflected light amount and the voltage value Vscacorresponding to the diffusely reflected light amount in a state where the specularly reflected light is not present when a maximum density is detected, a correction coefficient α based on the detection sensitivity difference as expressed by following expression (14):
0(MAXIMUM DENSITY)=Vref(DIFFUSE REFLECTION AT MAXIMUM DENSITY)−α×Vsca(DIFFUSE REFLECTION AT MAXIMUM DENSITY)(14)

In the density calculation, as expressed by following expression (15), the color shift/density calculator308subtracts a value acquired by multiplying the voltage value Vscain the diffuse reflection detection region by the correction coefficient α from the detected voltage value Vrefin the specular reflection detection region. This calculation enables removing the component of the diffusely reflected light for which these detection regions have mutually different detection sensitivities.
V(SPECULAR REFLECTION)=Vref(SPECULAR+DIFFUSE REFLECTIONS)−α×Vsca(DIFFUSE REFLECTION)(15)

The above-described method enables calculating, by performing the calculation using the detected light amount values (voltage values) in the specular reflection detection region (first light-receiving element group) and the diffuse reflection detection region (second light-receiving element group), only the specularly reflected light amount in the specular reflection detection region and thereby enables detecting the density with good accuracy.

As described above, this embodiment variably selects the specular reflection detection region to enable improving the S/N ratio of the density detection signal acquired from the specular reflection detection region. This improvement in S/N ratio makes it possible to reduce the detection error due to the diffusely reflected light undesirably entering the specular reflection detection region and thus to improve a detection accuracy for the specularly reflected light.

The number of the light-receiving elements provided in the light-receiving region of the sensor18and the setting of the multiple light-receiving element groups, both described above, are merely an example. For instance, the light-receiving region may alternatively be constituted by using a larger number of the light-receiving elements (that is, by dividing the light-receiving region into a larger number of the small regions). Furthermore, the multiple light-receiving element groups may alternatively be set by shifting the light-receiving element group in units of light-receiving elements whose number is another second number which is two or more, but equal to or less than the first number. These alternatives enable detecting the specularly reflected light with a higher accuracy and detecting the specularly reflected light in a shorter period of time.

Moreover, the diffuse reflection detection region may be set, in part of the multiple light-receiving elements other than the specular reflection detection region, as a region for detecting the diffusely reflected light amount equivalent to that in the specular reflection detection region. This setting enables omitting the process of calculating the correction coefficient α in the density detection.

Furthermore, when detecting a target that can be determined only by the detection of the diffusely reflected light amount such as density unevenness in a high-density toner patch, the diffusely reflected light amount may only be detected to make the determination.

Next, with reference toFIGS. 12A to 12C and 13A to 13F, description will be made of a color shift/density detection apparatus that is Embodiment 2 of the present invention. A color shift/density sensor (hereinafter simply referred to as “a sensor”)18A in the color shift/density detection apparatus of this embodiment sets two sets of light-receiving element groups having a 180-degree phase difference.

In this embodiment, the sensor18A is capable of setting a specular reflection detection region and a diffuse reflection detection region to enable responding to a large ray fluctuation with a small number of input channels and also of detecting a transporting speed (moving speed) of the intermediate transfer belt6. The detection of the transporting speed of the intermediate transfer belt6enables monitoring an operation status of the image forming apparatus and detecting a sudden speed variation of the intermediate transfer belt6.

FIGS. 12A to 12Cillustrate a configuration of the color shift/density detection apparatus of this embodiment, andFIG. 12Aillustrates an operation of the color shift/density detection apparatus in selecting (setting) the specular reflection detection region. A signal processor302A includes an A/D converter303, a region selector305A and a color shift/density calculator308.

Although definitions of the specular reflection detection region and the diffuse reflection detection region in this embodiment are same as those in Embodiment 1, a switch circuit included in the sensor18A is different from that in Embodiment 1.FIG. 13Aillustrates the switch circuit. A basic configuration of the switch circuit in this embodiment is same as that of the switch circuit in Embodiment 1 and is different from that in Embodiment 1 in that output terminals to which outputs of 16 light-receiving elements (n=16) are connected are Va and Vb. On the other hand,FIG. 13Billustrates a relation between the output terminals connected with the output signals of the respective light-receiving elements and 2-bit switching signals each being region setting information306A. For instance, a row indicated by a switching signal SW306(1,1) inFIG. 13Bshows that, when the region setting information306A is a 2-bit signal whose all bits are high level, the output signals of the light-receiving elements205ato205dand205ito205lare connected to the output terminal Va, and the output signals of the light-receiving elements205eto205hand205mto205pare connected to the output terminal Vb.

In this manner, the light-receiving element groups (referenced element groups) referenced by the sensor18are switched depending on the 2-bit switching signal as the region setting information306A.

FIGS. 13C to 13Feach illustrate the two sets of the referenced element groups1301and1302switched depending on the switching signal (region setting information306A). Each set of the referenced element groups is constituted by two light-receiving element groups set so as to have an interval therebetween. A length of the referenced element group1301in an X direction is L1, and a length of the referenced element group1302in the X direction is L3.

For instance,FIG. 13Cshows a first set of (two) referenced element groups1301connected to the detected voltage value Va depending on the switching signal SW306(1,1) illustrated inFIG. 13Bare filled in black, and a second set of (two) referenced element groups1302connected to the detected voltage value Vb depending thereon are filled in white. On the other hand, inFIG. 13D, a first set of (two) referenced element groups1301connected to the detected voltage value Va depending on a switching signal SW306(1,0) are filled in black, and a second set of (one) referenced element group1302connected to the detected voltage value Vb depending thereon is filled in white. In this case, one light-receiving element and three light-receiving elements, both of which are filled in white at left and right ends, are not used as ones constituting the referenced element group1302.

As illustrated inFIGS. 13C to 13F, the region selector305A inFIG. 12Asequentially shifts the light-receiving element groups each composed of a first number of (n/4=4 in this embodiment) light-receiving elements mutually adjacent in the X direction in units of light-receiving elements whose number is a second number (m=1 in this embodiment) equal to or less than the first number. Thereby, the region selector305A sets four patterns of the two sets of the referenced element groups. Next, description will be made of a method of setting the specular reflection detection region in this embodiment. The region selector305A compares, while shifting the two sets of (four or three) referenced element groups as described above, the detected voltage values Va and Vb output from the respective referenced element groups. Then, the region selector305A selects (sets), as the specular reflection detection region that is a first light-receiving element group, one of the four or three referenced element groups from which a largest detected voltage value is output. The region selector305A sets the other three or two referenced element groups as the diffuse reflection detection region as a second light-receiving element group. The sensor18A outputs, as analog voltage values301, the detected voltage value from the first light-receiving element group set to the specular reflection detection region as Vrefand outputs the detected voltage value from the second light-receiving element group set to the diffuse reflection detection region as Vscato the signal processor302A.

Since in this embodiment the two sets of the referenced element groups are arranged so as to have the 180-degree phase difference, shifting each referenced element group in units of light-receiving elements whose number is equal to or more than the number (4 in this embodiment) of the light-receiving elements constituting each referenced element group results in repetition of a state equivalent to a state in which the detected voltage values have been already compared to each other. This enables setting the specular reflection detection region with a smaller number of setting bits as compared to that in Embodiment 1.

For instance, the state illustrated inFIG. 5Ain Embodiment 1 corresponds to a state illustrated inFIG. 13Ein this embodiment. That is, of the referenced element groups1301and1302set corresponding to the switching signal SW(0,1), the referenced element group1302filled in white is set to the specular reflection detection region, and the light-receiving element group filled in black is set to the diffuse reflection detection region. As just described, in this embodiment, it is possible to set at least the specular reflection detection region equivalently to that in Embodiment 1.

FIG. 12Billustrates an operation of the color shift/density detection apparatus performed in a state in which a color shift/density detection-purpose image (hereinafter simply referred to as “a detection-purpose image”)307, which is a toner image to be used for color shift/density detection, is formed on a surface of the intermediate transfer belt6facing the sensor18A. In a same manner as that in Embodiment 1, the color shift/density calculator308detects a color shift and a density by using the detected voltage value Vrefoutput from the specular reflection detection region in the sensor18A and the detected voltage value Vscaoutput from the diffuse reflection detection region in the sensor18A.

Next, description will be made of a method of detecting a speed variation of the intermediate transfer belt6with reference toFIG. 12C,FIGS. 14A and 14B,FIGS. 15A to 15NandFIGS. 16A and 16B.FIG. 12Cillustrates an operation of the color shift/density detection apparatus in the detection of the speed variation of the intermediate transfer belt6. The signal processor302A includes a binarizer1201and a speed calculator1203.

The region selector305A outputs, depending on the setting result of the specular reflection detection region, the region setting information (switching signal)306A to the sensor18to set the specular reflection detection region in the multiple light-receiving elements on the sensor18A. A detection-purpose image1205to be used to detect the speed variation of the intermediate transfer belt6is an image with a line-and-space patch pattern in which multiple lines are periodically formed in the X direction with spaces therebetween as illustrated inFIGS. 15A to 15N. The sensor18A detects a variation in light amount of the reflected light caused by passage of the pattern, by light-receiving element groups switchably set as described later.

An analog single1206indicating the variation in reflected light amount detected by each light-receiving element group is input to the binarizer1201of the signal processor302A and converted into a binary signal1202. The binary signal1202is input to the speed calculator1203.

The speed calculator1203detects times at which the binary signal1202changes between zero and one and calculates speed information1204of the intermediate transfer belt6from the detected times. The speed information1204is sent to the engine controller17. The speed information1204is used as information for suppressing color shift in a formed image, such as information for controlling a timing at which the toner image is formed on the intermediate transfer belt6or information for controlling a rotational speed of the driving roller7. Furthermore, in a product development stage, the image forming apparatus is designed to cancel various adverse effects of a rotational drive system on the color shift, such as eccentricities of rollers and an engagement period of gears. The speed information1204of the intermediate transfer belt6is used for evaluating the design.

Next, with reference toFIGS. 14A and 14B, description will be made of switching setting of the multiple light-receiving element groups for detecting the speed variation of the intermediate transfer belt6.FIG. 14Aillustrates an example of an intensity distribution of the reflected light from the intermediate transfer belt6on the multiple light-receiving elements205in the sensor18A. In this example, of the referenced element groups corresponding to the switching signal SW(0,1) which are illustrated inFIG. 13E, one referenced element group located at a center is selected as a first light-receiving element group (specular reflection detection region)1401. Furthermore, the referenced element groups located across the first light-receiving element group are selected as the second light-receiving element group (diffuse reflection detection region)1402.

Thereafter, the region selector305A shifts, from this state, a phase of the light-receiving element groups by 90 degrees as illustrated inFIG. 14Bin order to detect the speed variation of the intermediate transfer belt6. InFIG. 14B, a dotted circle indicates a reflected light spot1403formed by a reflected light from a light spot projected onto the intermediate transfer belt6. The 90-degree phase shift sets a third light-receiving element group1404and a fourth light-receiving element group1405such that a boundary1406thereof is included in the reflected light spot1403on the first light-receiving element group1401. The region selector305A sets the third and fourth light-receiving element groups1404and1405as a detection region for detecting the speed (speed variation). In the example inFIG. 14B, the setting state of the referenced element groups corresponding to the switching signal SW(1,1), which is illustrated inFIG. 13C, corresponds to a setting state for detecting the speed variation.

In the state illustrated inFIG. 14B, a detection-purpose image1501for detecting the speed variation is formed on the intermediate transfer belt6.FIGS. 15A to 15Gillustrate a variation with time of a relation between the detection-purpose image1501moved together with the intermediate transfer belt6by which the detection-purpose image1501is transported and the light spot1502projected onto the intermediate transfer belt6. On the other hand,FIGS. 15H to 15Nillustrate a variation with time of a relation between the third and fourth light-receiving element groups (detection regions)1404and1405and a projected image (black portion)1503of the detection-purpose image1501in the reflected light spot1403formed by the reflected light from the light spot1502.

With the movement of the intermediate transfer belt6, the line-and-space pattern that is the detection-purpose image1501transported thereby sequentially passes through a position of the light spot1502. Since no light is detected at a projection portion in the detection region at which the projected image1503is present, the detected voltage value output from the detection region including the projection portion decreases. On the other hand, since the specularly reflected light from the intermediate transfer belt6is detected at a non-projection portion at which the projected image1503is not present, the detected voltage value output from the detection region not including the projection portion increases. The movement of the projected image1503on the detection regions (third and fourth light-receiving element groups1404and1405) changes the detected voltage values output from these detection regions like periodic signals whose phases are mutually shifted.

Next, with reference toFIGS. 16A and 16B, description will be made of a method of detecting the speed variation of the intermediate transfer belt6.FIG. 16Aillustrates variations with time of the voltage values (detected voltage values) Vb and Va of the analog signals1206output from the third and fourth light-receiving element groups1404and1405as the detection regions. Times denoted by symbols (h) to (n) respectively correspond to those inFIGS. 15H to 15N.FIG. 16Billustrates signal waveforms acquired by binarizing the detected voltage values Vb and Va with a threshold voltage value Vth (not illustrated). The speed calculator1203calculates a detection time at which the third light-receiving element group1404detects the projected image1503is calculated by averaging times T1601and T1602at which a polarity of the detected voltage value Vb changes. Similarly, the speed calculator1203calculates a detection time at which the fourth light-receiving element group1405detects the projected image1503by averaging times T1611and T1612at which a polarity of the detected voltage value Va changes. A projected image passage time ΔT expressed by following expression (16), which is a difference between the two projected image detection times Average (T1612,T1611) and Average(T1602,T1601) varies depending on a transported speed of the detection-purpose image1501for producing the projected image1503, that is, a transporting speed V of the intermediate transfer belt6.
V∝ΔT=Average(T1612,T1611)−Average(T1602,T1601)  (16)

For this reason, monitoring the projected image passage time ΔT and detecting its variation enables detecting a variation in the transporting speed V of the intermediate transfer belt6due to any abnormal transportation by the intermediate transfer belt6.

Next, as Embodiment 3 of the present invention, description will be made of an alternative to the method of detecting the transporting speed of the intermediate transfer belt6using the sensor18A that sets the two sets of the referenced element groups having the 180-degree phase difference, which was described in Embodiment 2. This embodiment enables detecting the transporting speed of the intermediate transfer belt6that is closer to an actual one as compared to that in Embodiment 2.

FIG. 17Aillustrates setting of detection regions of the reflected light spot1403in the sensor18A for detecting the transporting speed of the intermediate transfer belt6. This embodiment is same as Embodiment 2 in that the reflected light spot1403is set so as to be formed across two detection regions. However, this embodiment is different from Embodiment 2 in number of light-receiving elements constituting each detection region. Specifically, this embodiment sets a width of each light-receiving element in a speed detection direction (x direction) to be smaller than a diameter of the reflected light spot1403on the sensor18A to make detection times and detection positions of projected images1702aand1702bof detection-purpose images1701aand1701billustrated inFIGS. 17B to 17Ecorrespond to each other.

FIGS. 17B to 17Eillustrate movement of the detection-purpose images1701aand1701btransported by the intermediate transfer belt6with respect to a light spot1703projected onto the intermediate transfer belt6.FIGS. 17F to 17Iillustrate the projected images1702aand1702bon light-receiving elements205hand205ias two detection regions across their boundary included in the reflected light spot1403on the sensor18A in states respectively corresponding toFIGS. 17B to 17E. The light-receiving elements205hand205icorrespond to third and fourth light-receiving element groups.

FIG. 17Jillustrates detected voltage values Vb and Va output from the light-receiving elements205hand205iin the states illustrated inFIGS. 17F to 17I. Symbols (f) to (i) in the drawing represent times in the states illustrated inFIGS. 17F to 17I.FIG. 17Jshows that amplitudes of the detected voltage values Vb and Va become smallest respectively in the state illustrated inFIG. 17Gwhere the projected image1702ais projected at a center of the light-receiving element205hand in the state illustrated inFIG. 17Iwhere the projected image1702bis projected at a center of the light-receiving element205i(in other words, one of the projected images overlaps one of the light-receiving elements).FIG. 17Gillustrates a result of binarization of the detected voltage values Vb and Va. The speed calculator1203in this embodiment calculates average times Tb and Ta at which the projected images1702aand1702bpass through the centers of the light-receiving elements (detection regions)205hand205iby using times tb1, tb2, ta1, and ta2at which polarities of the binary signals Vb and Va change. When a width of each light-receiving element in the x direction is D, the transporting speed of the intermediate transfer belt6is calculated by following expression (17):

FIGS. 18A to 18Iillustrate output terminals to which output signals of the light-receiving elements are connected and detection regions (hereinafter each referred to as “a speed detection region”) for detecting the transporting speed of the intermediate transfer belt6; the output terminals are switched depending on switching signals (region setting information).FIG. 18Aillustrates a configuration for speed detection in this embodiment corresponding to the setting of the specular reflection detection region described in Embodiment 2.FIGS. 18B to 18Iillustrate a speed detection region set corresponding to the output terminals for the output signals illustrated inFIG. 18A.

Depending on an entrance position of a specularly reflected light from the intermediate transfer belt6on the multiple light-receiving elements, a specular reflection detection region (black-filled region) illustrated inFIGS. 18B to 18Eand a diffuse reflection detection region (white-filled region) are set. Then, the speed detection region is set for the respective region settings as illustrated inFIGS. 18F to 18I.

The speed detection region illustrated inFIGS. 18F to 18Iis set, regardless of which light-receiving element group is selected as the specular reflection detection region, such that a calculation of a difference between the times to be used for calculating the transporting speed of the intermediate transfer belt6can be performed uniquely depending on a transporting direction of the intermediate transfer belt6. For instance, the calculation of the time difference is expressed as (Ta−Tb) when the intermediate transfer belt6is transported in a +X direction and is expressed as (Tb−Ta) when the intermediate transfer belt6is transported in a −X direction.

This embodiment enables providing a color shift/density sensor18A capable of detecting the transporting speed of the intermediate transfer belt6.

When color shift detection and density detection are to be performed in this embodiment, same setting and process as those in Embodiment 2 may be performed.

Next, as Embodiment 4 of the present invention, description will be made of a method of detecting a variation in slope angle of a detection object surface (surface of the intermediate transfer belt6) by utilizing the two sets of the light-receiving element groups arranged so as to have the 180-degree phase difference, which were described in Embodiment 2. This embodiment enables detecting, without using a patch, the variation in slope angle of the detection object surface and feeding a detection result back to an image forming process and a control process of a drive system in an image forming apparatus to improve an image quality.

A reflection sensor of this embodiment is capable of detecting the color shift and the density in the same manner as that in Embodiment 2 and of detecting the transporting speed of the intermediate transfer belt6in the same manner as that in Embodiment 3. This means that the single reflection sensor can achieve multiple types of detection functions.

With reference toFIGS. 19A to 19C, description will be made of the method of detecting the variation in slope angle of the detection object surface.FIG. 19Aillustrates a color shift/density sensor (hereinafter simply referred to as “a sensor”)18B disposed so as to face a surface (hereinafter referred to as “a belt curved surface”) of a curved surface portion of the intermediate transfer belt6along a roller surface of a driving roller7around which the intermediate transfer belt6is wound.

A ray401emitted from a light source is reflected by the belt curved surface to enter a light-receiving element group205as a specularly reflected light402. In this light entrance, an eccentric component1901of the driving roller7varies the slope angle of the belt curved surface as a tangent angle thereto, which causes a ray fluctuation1902in the reflected light.

FIG. 19Billustrates detection regions set in multiple light-receiving elements on the sensor18B and a reflected light spot1403formed by the specularly reflected light402on the multiple light-receiving elements.

Since setting of the detection regions is identical to the setting of the detection regions to detect the speed variation described in Embodiment 2, a detailed description thereof is omitted. In the light-receiving elements on the sensor18B, two third light-receiving element groups1404and two fourth light-receiving element groups1405are set. Outputs of the two third light-receiving element groups1404and outputs of the two fourth light-receiving element groups1405are respectively combined and input to a subtractor1904. The subtractor1904subtracts the combined output of the third light-receiving element groups1404from the combined output of the fourth light-receiving element groups1405and outputs a subtraction result as a differential output voltage value Vpp.

The ray fluctuation1902caused by the eccentricity of the driving roller7results in a variation in position of the reflected light spot1403. A positional shift of the reflected light spot1403from its normal position toward the third light-receiving element group1401increases the combined output of the third light-receiving element groups1404to be subtracted, which decreases the differential output voltage value Vpp. On the other hand, a positional shift of the light spot1403from the normal position toward the fourth-light-receiving element group1405decreases the combined output of the third light-receiving element groups1404, which increases the differential output voltage value Vpp.

FIG. 19Cillustrates a relation between the eccentricity1901of the driving roller7and the differential output voltage value Vpp. Depending on the variation in position of the reflected light spot1403caused by the variation in slope angle of the belt curved surface due to the eccentricity1901of the driving roller7, the differential output voltage value Vpp varies. For this reason, a variation in eccentric state of the driving roller7can be detected from the variation of the differential output voltage value Vpp during the transportation of the intermediate transfer belt6. The detection of the variation in eccentric state of the driving roller7enables detecting the variation in transporting speed of the intermediate transfer belt6caused by the eccentricity of the driving roller7. Utilizing detected information on the speed variation to control a forming timing of a toner image and a rotational speed of the driving roller7enables suppressing generation of the color shift.

Differently from Embodiments 2 and 3, this embodiment enables detecting the variation in transporting speed of the intermediate transfer belt6due to the eccentricity of the driving roller7without using a detection-purpose image, namely, a toner image. This enables speed variation detection with fewer toner consumption and fewer system-related limitations on detection sequence.

Next, as Embodiment 5 of the present invention, description will be made of a detection structure which suppresses an amount of a ray fluctuation generated by a variation in slope angle of a surface of a detection object (a surface of an intermediate transfer belt6) that is an object and which suppresses undesirable entrance of a diffusely reflected light into a specular refection detection region. This embodiment enables shortening a required length of a light-receiving region, miniaturizing a reflection detection apparatus and improving an S/N ratio.

This embodiment enables detecting color shift and density in the same manner as that in Embodiment 2 and detecting a transporting speed of the intermediate transfer belt6in the same manner as that in Embodiment 3. In addition, this embodiment enables detecting the variation in slope angle of the surface of the detection object at a sensitivity lower than that in Embodiment 4 in the same manner as that in Embodiment 4. Moreover, this embodiment enables achieving multiple detection functions by a single reflection sensor and miniaturizing the refection sensor.

With reference toFIGS. 20A to 20C, description will be made of a mechanism of the generation of the ray fluctuation of a reflected light in a configuration of the refection sensor of this embodiment.FIG. 20Ais a drawing illustrating the configuration of the reflection sensor of this embodiment.FIG. 20Aillustrates a color shift/density sensor (hereinafter simply referred to as “a sensor”) disposed so as to face a surface (hereinafter referred to as “a belt curved surface”) of a driving roller7around which the intermediate transfer belt is wound. Of a diverging light flux2002emitted from a light source2001, a specularly reflected light2003is reflected by a belt curved surface2004to pass through an aperture portion2005and then enter multiple light-receiving elements.

FIGS. 20B and 20Cillustrate a difference between ray fluctuations generated on an A-A cross section shown inFIG. 20Acaused by a relative positional difference between the sensor and the roller.

InFIG. 20B, a rotation axis of the driving roller7and a center of the sensor are on an identical axis in a Z axis direction. The specularly reflected light2003on the belt curved surface2004is reflected at a light-reflecting point2007on the axis to enter a center of the multiple light-receiving elements.

FIG. 20Cillustrates a state in which the center of the sensor is shifted in parallel to the rotation axis of the driving roller7by a distance ΔX in an X axis direction. In this state, a position of a light-reflecting point2008of the specularly reflected light2003to reach the multiple light-receiving elements that is located on the belt curved surface2004depends on a state of the slope of the belt curved surface2004. This embodiment provides no aperture limitation on a light-source-side light flux or allows the light flux to be sufficiently introduced to a region including the light-reflecting point2008even if the aperture limitation is provided. This structure enables the detection with the multiple light-receiving elements from the specularly reflected light passing through the aperture portion2005.

Although a point at which the specularly reflected light enters the multiple light-receiving elements varies depending on a positional relation among constituent elements that may affect the above-described light-reflecting point2008, it is only necessary to select, by the method described in Embodiment 1, a first light-receiving element group that the specularly reflected light2006enters. The diffusely reflected light reaching the first light-receiving element group is suppressed by the aperture portion2005, which suppresses a decrease in a detection spatial frequency and improves an S/N ratio of a signal. Since a diffusely reflected light2009indicated as an example by a solid line reaches other light-receiving element groups different from the first light-receiving element group, a second light-receiving element group may be freely selected from the light-receiving element groups other than the first light-receiving element group. When a light amount of the specularly reflected light is to be detected, multiplying the light amount detected by the second light-receiving element group by a coefficient corresponding to a diffusely reflected light component detected by the first light-receiving element group and subtracting a value of the coefficient from the light amount detected by the first light-receiving element group enables calculating, with a higher accuracy, the light amount of the specularly reflected light detected by the first light-receiving element group.

As described above, the configuration in this embodiment enables, because of an effect provided by the aperture portion2005and the light source2001widely illuminating the object, suppressing the amount of the ray fluctuation generated on the multiple light-receiving elements, suppressing the diffusely reflected light reaching the selected first light-receiving element group, miniaturizing the sensor and improving the S/N ratio.

Instead of the diverging light flux described in this embodiment, a collimated light flux may be emitted from the light source.

An additional description will now be made of an effect provided, in a relation among the light source, the belt curved surface onto which the light is to be projected and the light-receiving elements, by miniaturization of the light-receiving elements in a configuration having a so-called light-receiving aperture in which the aperture is provided between the belt curved surface and the light-receiving elements. In the configuration of this embodiment having the light-receiving aperture, a geometrical ray path of the specularly reflected light depends on a size and a position of the light source, the slope of the belt curved surface as the object, and a position and a size of the aperture as described above. In this configuration, although the ray path varies depending on a positional relation among the light source, the belt curved surface as the object and the light-receiving aperture with a tolerance, a position at which the ray reaches the light-receiving elements on a ray return path varies in principle with the light-receiving aperture being a reference point.

On the other hand, in a configuration having a light source aperture in which the aperture is provided between the light source and the belt curved surface, a geometrical ray forward path depends on a positional relation between the light source and the light source aperture. Consequently, a return geometrical ray path depends on the slope of the belt curved surface onto which the ray is projected, which defines a position at which the ray reaches the light-receiving elements.

A comparison of the configuration having the light receiving aperture and the configuration having the light source aperture shows that the former has an optical path from the aperture portion to the light-receiving elements which is obviously shorter than that of the latter and that the former in which the aperture is provided on a return-path side with respect to the belt curved surface reflecting the ray that largely affects the ray path, suppresses a ray path fluctuation on the light-receiving elements more compared to the latter and thus suppresses a variation in the position at which the ray enters the light-receiving elements. For this reason, employing the configuration having the light-receiving aperture enables miniaturizing the light-receiving elements.

Although each of the above embodiments described the case where the line sensor constituted by the multiple light-receiving elements arranged in line in a one-dimensional direction is used as the color shift/density sensor (reflection sensor), an area image sensor constituted by two-dimensionally arranged multiple light-receiving elements may alternatively be used as the color shift/density sensor. Furthermore, although each of the above embodiments described the case where the diffuse reflection detection region is set on the multiple light-receiving elements of the color shift/density sensor, a light-receiving unit may be provided outside a path of the specularly reflected light different from that for the multiple light-receiving elements and used as the diffuse reflection detection region.

Moreover, although each of the above embodiments described the case where the reflection detection apparatus is used to detect the density and color shift of the toner and others in the image forming apparatus, the reflection detection apparatus may be used for various apparatuses each including an operation portion performing its operation by using output of the reflection detection apparatus.

Each of the above embodiments enables accurately detecting the light amount of the specularly reflected light without an increase of the area of the light-receiving region even if the ray fluctuation of the specularly reflected light is generated. Using the detection result enables detecting, with high accuracy, the density of the toner, the color shift of the toner, the movement speed of the transferred body, a variation of the slope of the transfer body and others in an image forming apparatus.

This application claims the benefit of Japanese Patent Application No. 2014-096319, filed on May 7, 2014, which is hereby incorporated by reference herein in its entirety.