JP2002214854A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus, capable of highly accurately measuring an amount of toner attached to a belt-like image carrier stretched between a plurality of rollers. SOLUTION: Light is emitted from a light-emitting element 601 to a surface area of an intermediate transfer belt wrapped round a roller 43, that is, to a wrapped area 41a. In addition, light reflected from the wrapped area 41a is received by light-receiving units 670p and 670s. Based on the signal outputted from a sensor 6, amount of toner is measured. In the wrapped area 41a, the intermediate transfer belt 41 is prevented from flapping in a direction nearly perpendicular to the direction of the movement of the belt. Therefore, variation in distance (sensing distance) between the sensor 6 and the intermediate transfer belt 41 is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus for detecting an amount of toner adhering to a belt-shaped image carrier stretched over a plurality of rollers.

[0002]

2. Description of the Related Art Some electrophotographic image forming apparatuses such as printers, copiers and facsimile machines form a toner image on a belt-shaped image carrier. For example, in an apparatus described in Japanese Patent Application Laid-Open No. H11-258872,
Four process units are arranged along a transfer belt (belt-shaped image carrier) stretched over two rollers. Each process unit forms a latent image on the photoreceptor and develops the latent image with toner to form a toner image. The toner images formed by these process units have different toner colors (yellow, cyan, magenta, and black), and the toner images are transferred to the transfer belt so as to overlap each other. Thus, a color image is formed on the transfer belt.

In this apparatus, in order to adjust the image density of a toner image, a toner image (patch image) having a predetermined pattern is formed on a transfer belt, and the density is measured by a density sensor. This density sensor includes a light emitting element that irradiates light to the transfer belt and a light receiving element that receives light reflected from the transfer belt, and calculates the amount of toner adhering to the transfer belt based on the output from the light receiving element. Thus, the image density of the toner image is measured.

[0004]

In the prior art, no special attention has been paid to the location of the density sensor. As a result, various noise components are included in the sensor output, and the sensor output adheres to the image carrier. This leads to a decrease in the measurement accuracy of the toner amount. For example, in the above-described conventional device, since the density sensor is disposed at a position relatively far from the roller,
There were the following problems.

At the position away from the roller as described above,
The transfer belt flaps in a direction substantially perpendicular to the belt movement direction, and a distance from the sensor to the transfer belt (belt-shaped image carrier) (hereinafter, referred to as a “sensing distance”).
Fluctuates randomly or unstable, and the sensor output becomes unstable due to the distance fluctuation. As a result, accurate measurement is difficult.

Further, the transfer belt is stretched over a plurality of rollers, and some of the rollers have a certain degree of eccentricity. For this reason, since the transfer belt further fluctuates due to the rotation of the eccentric roller, the sensor output becomes unstable and accurate measurement becomes difficult.

Further, the thickness of the transfer belt is not uniform over the entire circumference of the transfer belt, but may be uneven in thickness. This is one of the causes of the fluctuation of the sensing distance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an object to accurately measure the amount of toner adhering to a belt-shaped image carrier in a structure in which a belt-shaped image carrier is stretched over a plurality of rollers. It is an object of the present invention to provide an image forming apparatus capable of performing the following.

[0009]

SUMMARY OF THE INVENTION According to the present invention, a light emitting element irradiates a belt-shaped image carrier, which is stretched over a plurality of rollers, with light, and a light-receiving element which receives light reflected from the belt-shaped image carrier. An image forming apparatus comprising: a sensor that receives a light beam and outputs a signal corresponding to the amount of received light; and a control unit that calculates an amount of toner attached to the belt-shaped image carrier based on an output from the sensor. In order to achieve the above object, the light-emitting element is arranged to face one of the plurality of rollers so as to sandwich the belt-shaped image carrier, and the light-emitting element is disposed in a surface area of the belt-shaped image carrier. Light is applied to the area around the sensor facing roller.

[0010] In the invention configured as described above, the light is applied to the winding area, and the light reflected by the winding area is received by the light receiving element to measure the toner amount. When the measurement is performed in the wrapping area in this manner, unstable fluttering of the belt-shaped image carrier in a direction substantially orthogonal to the belt moving direction is suppressed, and therefore, the distance between the sensor and the belt-shaped image carrier (sensing Distance) is effectively suppressed.

Here, it is desirable to select a roller fixedly arranged at a predetermined position and rotatable at the predetermined position as the sensor facing roller. This is because, when the sensor is disposed opposite a roller that is rotatably fixed at a predetermined position, the distance between the roller and the sensor is constant.

Further, the belt may be configured to rotate around the belt-shaped image carrier by rotating the sensor facing roller two or more times. Is sampled, and an eccentric component of the sensor facing roller can be obtained based on the plurality of sampled outputs. Since the eccentric component is a fluctuation component of the sensing distance, accurately obtaining the eccentric component is very useful information for eliminating erroneous measurement due to the fluctuation. When a toner image is formed on the belt-shaped image carrier, the output from the light receiving element is corrected by an eccentric component, and the image density of the toner image is obtained based on the correction value. Regardless, the image density of the toner image can be accurately measured.

Further, by subtracting the eccentric component from a plurality of sampling outputs, a periodic profile of the belt-shaped image carrier can be obtained. Since this periodic profile reflects the belt thickness unevenness, the light receiving element for receiving the light reflected by the belt-shaped image carrier when calculating the image density of the toner image on the belt-shaped image carrier. If the output from the printer is corrected based on the periodic profile and the image density of the toner image is obtained based on the correction value, the accuracy of measuring the toner amount can be further improved.

Further, when measuring the amount of toner on the belt-shaped image carrier, there is a possibility that the toner may float off the belt-shaped image carrier and adhere to the sensor. Alternatively, when the sensor is disposed above the horizontal facing position and at a position facing the sensor facing roller, the sensing surface of the sensor becomes vertical or downward, so that contamination of the sensing surface by toner can be prevented, and measurement accuracy can be improved. it can.

[0015]

DETAILED DESCRIPTION OF THE INVENTION First Embodiment FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention. This image forming apparatus forms a full-color image by superimposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K). When an image signal is given to a control unit (reference numeral 1 in FIG. 2), each unit of the engine unit E is controlled by the control unit, and an image corresponding to the image signal is formed on a sheet S such as transfer paper, copy paper, or an OHP sheet. Is formed.

In the engine section E, a toner image can be formed on the photosensitive member 21 of the process unit 2. That is, the process unit 2 includes a photoconductor 21 rotatable in the direction of the arrow in FIG. 1, and further includes a charging roller 22 as a charging unit and a developing roller as a developing unit around the photoconductor 21 along the rotation direction. Developing units 23Y, 23C, 23
M, 23K, and a photoreceptor cleaner blade 24 are arranged, respectively.

In this apparatus, the charging roller 22 is connected to the photosensitive member 2
After the outer peripheral surface of the photoreceptor 21 is uniformly charged by contacting the outer peripheral surface of the photoconductor 1, the exposure unit 3 irradiates the outer peripheral surface of the photoconductor 21 with laser light L. As shown in FIG. 1, the exposure unit 3 includes a light emitting element 31 such as a semiconductor laser that is modulated and driven in accordance with an image signal, and a laser beam L from the light emitting element 31 is rotated by a high-speed motor 32. Incident on a polygon mirror 33 to be formed. The laser beam L reflected by the polygon mirror 33 is transmitted to the lens 34 and the mirror 3
5, the photosensitive drum 21 is scanned in the main scanning direction (a direction perpendicular to the plane of the paper of FIG. 1) to form an electrostatic latent image corresponding to an image signal. Reference numeral 36 denotes a horizontal synchronization reading sensor for obtaining a synchronization signal in the main scanning direction.

The electrostatic latent image thus formed is developed
Is developed with toner. That is, in this embodiment, as the developing unit 23, a developing unit 23Y for yellow, a developing unit 23C for cyan, a developing unit 23M for magenta, and a developing unit 23K for black are arranged along the photoconductor 21 in this order. Have been. These developing units 23Y and 23
C, 23M, and 23K are configured to be freely movable toward and away from the photoreceptor 21, and the four developing units 23Y, 23M, 23C, and 2 according to a command from the control unit 1.
3K selectively contacts the photoconductor 21, and applies a high voltage to apply a toner of a selected color to the surface of the photoconductor 21, thereby causing an electrostatic latent on the photoconductor 21. Reveals an image.

The toner image developed by the developing unit 23 is transferred to the intermediate transfer belt 41 (belt-shaped image carrier) of the transfer unit 4 in a primary transfer area located between the black developing device 23K and the photosensitive member cleaner blade 24. ) Is primarily transferred onto. Also, from the primary transfer area in the circumferential direction (the direction of the arrow in FIG. 1)
A cleaner blade 24 for a photoconductor is disposed at a position where the toner is transferred to the above, and scrapes off toner remaining on the outer peripheral surface of the photoconductor 21 after the primary transfer.

The transfer unit 4 has seven rollers 42 to
The endless intermediate transfer belt 41 is stretched around six rollers 42 to 47 excluding the secondary transfer roller 48. When the color image is transferred to the sheet S, the toner image of each color formed on the photoreceptor 21 is superimposed on the intermediate transfer belt 41 to form a color image, and is taken out from a cassette or a manual feed tray. The sheet S passes through the space between the upper guide member 5U and the lower guide member 5D, is conveyed to the secondary transfer area, and the color image is secondarily transferred to the sheet S to obtain a color image (color printing process). ). When a monochrome image is transferred to the sheet S, only the black toner image on the photoreceptor 21 is formed on the intermediate transfer belt 41, and is conveyed to the secondary transfer area in the same manner as in the case of a color image. The image is transferred to the sheet S to obtain a monochrome image (monochrome printing process).

A belt cleaner 49 is provided to face the roller 46. This belt cleaner 49 is
The cleaning unit removes residual toner remaining on the intermediate transfer belt 41 after the secondary transfer, and has the following configuration. That is, in this belt cleaner 49, the cleaner blade 492 is attached to the cleaner case 491, and the intermediate transfer belt 41 in the cleaner cover 493.
, And driven by a belt cleaner drive unit (not shown).
Reference numeral 494 in FIG. 1 denotes a cleaner rake sheet.

A sensor 40 for detecting a reference position of the intermediate transfer belt 41 is provided below the roller 43, and a synchronization signal in a sub-scanning direction substantially orthogonal to the main scanning direction, that is, a vertical synchronization signal. It functions as a vertical synchronization reading sensor for obtaining a signal. Also, the roller 43
A sensor 6 for detecting the amount of toner adhering on the intermediate transfer belt 41 stretched across the intermediate transfer belt 41 is disposed opposite to the roller 43 with the intermediate transfer belt 41 interposed therebetween. Thus, in this embodiment, the roller 43 is the “sensor facing roller” of the present invention.

FIG. 2 is a diagram showing the structure of a sensor for detecting the amount of toner on the intermediate transfer belt. The sensor 6 has a light emitting element 601 such as an LED that irradiates light to a winding area 41 a wound around the roller 43 in the surface area of the intermediate transfer belt 41. The sensor 6 includes a polarizing beam splitter 603 and a light-receiving unit 60 for monitoring the amount of irradiation light in order to adjust the amount of irradiation light.
4 and an irradiation light amount adjustment unit 605 are provided.

The polarizing beam splitter 603 includes a light emitting element 601 and an intermediate transfer belt 41 as shown in FIG.
And a p-polarized light having a polarization direction parallel to the incident surface of the irradiation light on the intermediate transfer belt 41,
And s-polarized light having a perpendicular polarization direction. Then, while the p-polarized light is incident on the intermediate transfer belt 41 as it is, the s-polarized light is extracted from the polarization beam splitter 603, and then is incident on the light receiving unit 604 for monitoring the irradiation light amount. The proportional signal is the irradiation light amount adjustment unit 605
Is output to

The irradiation light amount adjusting unit 605 performs feedback control of the light emitting element 601 based on a signal from the light receiving unit 604 and a light amount control signal Slc from the control unit 1 which has the CPU 11 and the memory 12 and controls the entire apparatus. From the light emitting element 601 to the intermediate transfer belt 41
Is adjusted to a value corresponding to the light amount control signal Slc. Thus, in this embodiment, the irradiation light amount can be changed and adjusted appropriately over a wide range.

Further, in this embodiment, the input offset voltage 641 is applied to the output side of the light receiving element 642 provided in the irradiation light amount monitoring light receiving unit 604, so long as the light amount control signal Slc does not exceed a certain signal level. , And the light emitting element 601 is configured to be kept off. The specific electrical configuration is as shown in FIG.
FIG. 3 shows a light receiving unit 60 employed in the apparatus of FIG.
4 is a diagram illustrating an electrical configuration of FIG. This light receiving unit 60
In No. 4, the anode terminal of the light receiving element PS such as a photodiode is connected to the non-inverting input terminal of the operational amplifier OP constituting the current-voltage (I / V) conversion circuit, and is connected to the ground potential via the offset voltage 641. Have been. Further, the cathode terminal of the light receiving element PS is connected to an inverting input terminal of the operational amplifier OP and is connected to an output terminal of the operational amplifier OP via a resistor R. Therefore, when light is incident on the light receiving element PS and a photocurrent i flows, the output voltage V0 from the output terminal of the operational amplifier OP becomes V0 = iR + Voff (where Voff is an offset voltage value),
A signal corresponding to the amount of reflected light is output from the light receiving unit 604. The reason for this configuration will be described below.

When the input offset voltage 641 is not applied, the light intensity characteristic shown by the broken line in FIG. That is, when the light amount control signal Slc (0) is supplied from the control unit 1 to the irradiation light amount adjusting unit 605, the light emitting element 601 is turned off, and when the signal level of the light amount control signal Slc is increased, the light emitting element 601 is turned on. The irradiation light amount on the transfer belt 41 also increases almost in proportion to the signal level. However, the light amount characteristic may be shifted in parallel as shown by a one-dot chain line or a two-dot chain line shown in FIG. 4 depending on the influence of the ambient temperature, the configuration of the irradiation light amount adjustment unit 605, and the like. In this case, the light-emitting element 601 may be lit even though the control unit 1 gives the light-off instruction, that is, the light amount control signal Slc (0).

On the other hand, as in the present embodiment, when the input offset voltage 641 is applied and shifted in advance to the right hand side in the figure to provide a dead zone (signal levels Slc (0) to Slc (1)). The light emission command from the control unit 1, that is, the light amount control signal Slc (0) can be surely turned off by giving a light-off instruction from the control unit 1 (solid line in the figure), and malfunction of the device can be prevented beforehand. Can be.

On the other hand, when a light amount control signal Slc exceeding the signal level Slc (1) is given from the control unit 1 to the irradiation light amount adjustment unit 605, the light emitting element 601 is turned on, and p-polarized light is applied to the intermediate transfer belt 41 as irradiation light. Irradiated. Then, the p-polarized light is reflected by the intermediate transfer belt 41, the reflected light amount detection unit 607 detects the amount of p-polarized light and the amount of s-polarized light among the light components of the reflected light, and a signal corresponding to each light amount is transmitted to the control unit. 1 is output.

The reflected light amount detection unit 607 is the same as that shown in FIG.
As shown in the figure, a polarization beam splitter 671 disposed on the optical path of the reflected light, and a polarization beam splitter 671
And a light-receiving unit 670p that receives p-polarized light passing through and outputs a signal corresponding to the amount of p-polarized light, receives s-polarized light split by the polarization beam splitter 671, and outputs a signal corresponding to the amount of s-polarized light. Output light receiving unit 6
70s. In the light receiving unit 670p, the light receiving element 672p includes a polarization beam splitter 671
After receiving the p-polarized light from the light-receiving element 672p and amplifying the output from the light-receiving element 672p by the amplifier circuit 673p, the amplified signal is converted into a signal corresponding to the amount of p-polarized light.
Output from p. The light receiving unit 670s has a light receiving element 672s and an amplifier circuit 673s, like the light receiving unit 670p. For this reason, the light amounts of two component lights (p-polarized light and s-polarized light) different from each other among the light components of the reflected light can be obtained independently.

In this embodiment, the light receiving element 672
The output offset voltage 674p,
674 s is applied to each of the amplifier circuits 673 s
The output voltages Vp and Vs of the signals supplied from p and 73s to the control unit 1 are offset to the positive side as shown in FIG. The specific electrical configuration of each of the light receiving units 670p and 70s is the same as that of the light receiving unit 604, and a description thereof is omitted here. In the light receiving units 670p and 670s configured as described above,
Similarly to the light receiving unit 604, even when the amount of reflected light is zero, each of the output voltages Vp and Vs has a value of zero or more, and further, the output voltages Vp and Vs are proportional to the increase in the amount of reflected light.
Also increase. Thus, the output offset voltage 674p,
By applying 674 s, the influence of the dead zone in FIG. 4 can be reliably eliminated, and an output voltage corresponding to the amount of reflected light can be output.

The signals of these output voltages Vp and Vs are inputted to the control unit 1 and, after A / D conversion, the amount of toner adhering on the intermediate transfer belt 41 is obtained by the control unit 1. In this embodiment, prior to the measurement of the actual toner amount, the eccentric component of the roller 43 and the cycle profile of the intermediate transfer belt 41 are obtained in advance as follows.
It is stored in the memory 12. Here, a procedure for deriving the eccentric component and the periodic profile will be described prior to the toner amount measurement flow.

In the image forming apparatus according to the first embodiment, the peripheral length of the intermediate transfer belt 41 corresponding to the "belt-shaped image carrier" of the present invention is a non-integer multiple of the peripheral length of the sensor facing roller 43. The intermediate transfer belt 41 is configured to make one rotation every time the sensor facing roller 43 makes about 5.2 rotations. It takes 3120 ms for the intermediate transfer belt 41 to make one rotation, and the amount of reflected light from the intermediate transfer belt 41 is sampled at intervals of 10 ms, and the output voltage Vp0 at the time of turning off is subtracted from the output voltage Vp at each sampling position x. The light amount signal SigP (= Vp−Vp0) is obtained, and the output voltage Vs0 when the light is turned off is subtracted from the output voltage Vs at each sampling position x.
(= Vs−Vs0), and then these light quantity signal ratios (=
SigP / SigS) is stored in the memory 12 as sampling data D (x) at each sampling position x. In this embodiment, during the rotation of the intermediate transfer belt 41, 312
The number of sampling data D (x) is obtained,
In this embodiment, the number of samplings is set to 256 in order to execute an arithmetic operation efficiently with a small memory capacity. That is, the sampling data D (0),
D (1),... D (255) are stored in the memory 12.

Here, "output voltage Vp0, Vs0 when light is turned off"
This means that the light amount control signal Slc (0) corresponding to the light-off instruction is output to the irradiation light amount adjustment unit 605 to turn off the light emitting element 601 and output voltages Vp0 and Vs0 indicating the light amounts of the p and s-polarized light in the light-off state. Is stored as the dark output voltage. Then, as described above, the output voltage Vp0, Vs0 is subtracted from the output voltage Vp, Vs, respectively, thereby obtaining the dark output voltage Vp.
Eliminating the adverse effects of 0 and Vs0 enables more accurate measurement.

In this embodiment, as will be described later, the light amount signal ratio (= SigP / SigS) is used as an index of the toner amount.
Is used, the light amount signal ratio is used as the sampling data. However, other data such as the output voltages Vp and Vs and the light amount signals SigP and Sig are used as an index of the toner amount.
S, light amount signal sum (= SigP + SigS) and light amount signal difference (=
When (SigP-SigS) or the like is used, data corresponding to the index may be used as sampling data. Further, both output voltages may be calculated in a circuit and then input to the control unit 1, and the input signals may be stored in the memory 12 as sampling data.

Since the intermediate transfer belt 41 makes one rotation every time the roller 43 makes 5.2 rotations, 60 (= 312 ÷ 5.2) continuous sampling data are taken out from the sampling data D (x). Thus, the components of one round of the roller 43 are included in the 60 pieces of sampling data. Here, focusing on the eccentric component of the roller 43, it is not necessary to consider the eccentric component by taking the average value of one rotation of the sensor facing roller 43. That is, while the sensor opposing roller 43 makes one rotation, both the case where the sensing distance becomes longer and the case where the sensing distance becomes closer due to the eccentricity are included, and by taking the average value, the respective effects cancel each other out. This is because it can be considered to be substantially equivalent to the average value at the above sensing distance.

Therefore, for example, three intervals (1) to (3) are defined as 60 intervals of continuous sampling data from the sampling data D (x) shown in FIG. x (x = 30, 31,...,
210) Average value AV for one round of roller 43 centered on
Find (x). AV (30) = (D (0) + ... + D (30) + ... + D (59)) / 60 AV (31) = (D (1) + ... + D (31) + ... + D (60)) / 60 AV (32) = (D (2) + ... + D (32) + ... + D (61)) / 60 ... AV (210) = (D (180) + ... + D (210) + ... + D (239) ) / 60. In the above equation, the sampling positions “0” to “5”
The center of the 60 pieces of sampling data of "9" is 30. Strictly, the center is between "29" and "30", and the above equation gives AV (29) = (D (0) +... + D (30 ) +... + D (59)) / 60 (the same applies hereinafter).

The average value AV (x) thus obtained
Is the eccentric component of the roller 43 canceled.
The eccentric component E (x) of the roller 43 at each sampling position x can be obtained by subtracting the average value AV (x) from the sampling data D (x). That is, the eccentric component E (x) of the roller 43 can be obtained by E (x) = D (x) -AV (x). However, in this case, the eccentric components for three rotations of the roller 43 while the intermediate transfer belt 41 makes one rotation are obtained.

Here, the sections (1) to (3) are all rollers 4
3 corresponds to one round, so if the phase is the same, the eccentric component E
(x) should show the same value. Therefore, section (1)-(3)
The average value Eav (a) of the eccentric components in each in-phase is given by the following equation: Eav (a) = ｛D (30 + a) −AV (30 + a)｝ + ｛D (90 + a) −AV ( 90 + a)｝ + {D (120 + a) -AV (120 + a)} / 3 (1) (where a = 0, 1,..., 59). Thus, in this embodiment, the intermediate transfer belt 4
Since three eccentric components are obtained during one rotation of 1 and the average value thereof is obtained, the eccentric component of the roller 43 can be obtained with high accuracy. Of course, the number of rotations of the roller 43 per one rotation of the intermediate transfer belt 41 is not limited to “5.2”, and the eccentric component of the roller 43 can be obtained in the same manner as described above if the number of rotations is two or more. it can.

When the eccentric component Eav (a) of the roller 43 at each phase is obtained in accordance with the equation (1), the eccentric component is subtracted from the sampling data D (x) to obtain the thickness unevenness of the intermediate transfer belt 41. Is obtained (FIG. 7). That is, the period profile F (x) is expressed as follows: F (0) = D (0) -Eav (30) F (1) = D (1) -Eav (31) ... F (29) = D (29) -Eav (59) F (30) = D (30) −Eav (0) F (31) = D (31) −Eav (1)

The thus obtained eccentric component Eav (a)
And the cycle profile F (x) is stored in the memory 12. Then, when measuring the actual toner amount, after calculating a light amount signal ratio as an index of the toner amount calculated in a procedure described later, an eccentric component Eav is calculated with respect to this light amount signal ratio.
(a) and correction (distance fluctuation correction) based on the cycle profile F (x), and the toner amount is measured based on the correction result.

FIG. 8 is a flowchart showing the toner amount measuring operation in the image forming apparatus of FIG. In this apparatus, the control unit 1 outputs a light amount control signal Slc (0) corresponding to a light-off instruction to the irradiation light amount adjustment unit 605 and turns off the light-emitting element 601 prior to toner amount measurement (step S1). In particular, in this embodiment, as described above, since the dead zone (the signal levels Slc (0) to Slc (1) in FIG. 4) is set by applying the input offset voltage 641, the light amount control signal Slc (0) is set. ) Gives a light emitting element 6
01 is surely turned off.

Then, the output voltage Vp0 indicating the amount of received p-polarized light and the output voltage Vs0 indicating the amount of received s-polarized light in the unlit state are detected and stored in the memory 12 of the control unit 1 (step S2). That is, the sensor output in the unlit state, that is, the dark output voltage is detected and stored.

Next, a signal Slc (2) having a signal level exceeding the dead zone is set as the light amount control signal Slc, and the light amount control signal Slc (2) is given to the irradiation light amount adjustment unit 605 to turn on the light emitting element 601 ( Step S3). Then
The light from the light emitting element 601 is applied to the intermediate transfer belt 41, and the light reflected by the intermediate transfer belt 41 has a light intensity p.
The amount of polarized light and the amount of s-polarized light are reflected light amount detection unit 607
Output voltage V corresponding to each received light amount
p and Vs are input to the control unit 1. (Step S
4).

The control unit 1 subtracts the dark output voltage Vp0 from the output voltage Vp for the p-polarized light to obtain a light amount signal SigP representing the light amount of the p-polarized light corresponding to the toner amount (step S5). As for the s-polarized light, similarly to the p-polarized light, a light amount signal S representing the light amount of the s-polarized light corresponding to the toner amount by subtracting the dark output voltage Vs0 from the output voltage Vs.
igS is determined (step S5). Further, the ratio between the light quantity signals SigP and SigS corrected in this way is obtained (step S5). As described above, in this embodiment, the dark output voltages Vp0 and Vs0 are removed from the measured output voltages Vp and Vs, respectively, so that the amount of light corresponding to the toner amount can be obtained with high accuracy. Even if the dark output fluctuates due to the surrounding environment of the device or a change over time of the components of the apparatus, the index of the toner amount can be obtained without being affected.

In the next step S6, the light amount signal ratio obtained as described above is corrected by the eccentric component Eav (a) and the periodic profile F (x) (distance fluctuation correction). The procedure for this correction is as follows.

First, in this embodiment, every time the sensor facing roller 43 makes about 5.2 rotations, the intermediate transfer belt 4
1 goes around once. Therefore, the phase of the sensor facing roller 43 differs between when the eccentric component and the cycle profile are obtained and when the detection is performed to obtain the toner amount thereafter. However, the circumferential length ratio between the sensor facing roller 43 and the intermediate transfer belt 41 is known by design. Therefore, the phase of the eccentric component is shifted based on the number of rotations of the intermediate transfer belt 41 from the time when the eccentric component and the cycle profile are obtained to the time when the toner amount is detected, so that the roller facing the sensor at the time of the toner amount detection is shifted. 43. Then, the cycle profile and the eccentric component are combined, and the light amount signal ratio is corrected.

By the above processing, the influence of the eccentric component of the roller and the unevenness of the belt thickness can be corrected. Thereafter, the toner amount is measured based on the correction result (step S7).

As described above, according to this embodiment, light is applied to the surface area of the intermediate transfer belt wound around the roller 43, that is, the winding area 41a, and is reflected by the winding area 41a. Light is received by the light receiving element 672
The amount of toner is measured based on a signal received at p and 672 s and output from the sensor 6. In the wrapping area 41a, there is no unstable flutter of the intermediate transfer belt 41 in a direction substantially perpendicular to the belt moving direction.
Fluctuations in the distance (sensing distance) between the sensor 6 and the intermediate transfer belt 41 can be suppressed only to fluctuations due to the eccentricity of the rollers, and measurement accuracy can be improved.

In this embodiment, the eccentricity component Eav (a) of the roller is obtained, and the fluctuation of the distance (sensing distance) between the sensor 6 and the intermediate transfer belt 41 due to the eccentricity of the roller is corrected. The measurement accuracy can be further improved by suppressing the influence of the eccentricity. In addition, the thickness unevenness of the intermediate transfer belt 41 can be obtained from the above-described periodic profile F (x), and the light amount signal ratio as an index of the toner amount is corrected by the periodic profile F (x). The influence of unevenness can be suppressed, and highly accurate toner amount measurement is possible.

When the amount of toner on the intermediate transfer belt 41 is measured, the toner may float and fall from the intermediate transfer belt 41 and adhere to the sensor 6. Since the sensor is disposed at the opposing position, the sensing surface is vertical, so that the toner that floats and falls can be effectively prevented from adhering to the sensing surface, and the measurement accuracy can be improved. This effect is the same or more when the sensor 6 is arranged above the horizontal opposing position of the roller 43 (FIG. 2) and at a position opposing the roller 43.

In this embodiment, the light amount signal SigP representing the amount of p-polarized light and the light amount signal Sig representing the amount of s-polarized light among the light components of the reflected light from the intermediate transfer belt 41.
S are obtained independently, and their light signal ratios (= SigP / S
Since the amount of toner adhering to the intermediate transfer belt 41 is measured based on igS), the measurement of the amount of toner can be performed with high accuracy without being affected by the influence of noise or the fluctuation of the amount of light applied to the intermediate transfer belt 41. Become.

Further, when the dark output is obtained, it is necessary to surely turn off the light emitting element 601. According to this embodiment, the light emitting element 601 is applied by applying the input offset voltage 641 as described above. The light can be reliably turned off.

In the first embodiment, the light amount signal ratio as an index of the toner amount is corrected based on the eccentricity component Eav (a) of the roller and the cycle profile F (x). If there is a difference, the light amount signal ratio may be corrected based only on the larger correction amount.

In this embodiment, the intermediate transfer belt 41 is used.
And the circumferential length of the sensor opposing roller 43 is a non-integer multiple, so that the phase shift of the sensor opposing roller 43 with respect to the intermediate transfer belt 41 between the time when the eccentric component and the periodic profile are obtained and the time when the toner amount is detected is corrected. However, the phase shift may be eliminated by setting the peripheral length of the intermediate transfer belt 41 and the sensor facing roller 43 to an integer. In this case, since the calculation for correcting the phase shift is not required, the same effect can be obtained with fewer processing steps, and the detection error due to the calculation accuracy can be prevented beforehand.

B. Second Embodiment In an image forming apparatus in which the intermediate transfer belt 41 is an integral multiple of the circumference of the sensor facing roller 43, the amount of toner is measured according to the procedure shown in FIG. In addition, the fluctuation of the distance (sensing distance) between the sensor 6 and the intermediate transfer belt 41 is suppressed, and the amount of toner adhering to the intermediate transfer belt 41 is measured with high accuracy by correcting the effects of the eccentricity of the roller and the unevenness of the belt thickness. can do.

FIG. 9 is a flowchart showing a toner amount measuring operation in the second embodiment of the image forming apparatus according to the present invention. Here, first, output voltages Vp and Vs corresponding to the amount of light reflected from intermediate transfer belt 41 are sampled at predetermined sampling intervals (for example, 10 ms) while intermediate transfer belt 41 on which a toner image is not formed makes one revolution. As described above, the dark output voltage Vp0 is subtracted from the output voltage Vp to obtain the light amount signal SigP representing the amount of p-polarized light corresponding to the toner amount, and the dark output voltage Vs0 is subtracted from the output voltage Vs to correspond to the toner amount. After obtaining the light amount signal SigS representing the light amount of the s-polarized light, the ratio of the light amount signals SigP and SigS thus corrected is obtained, and the light amount signal ratio R (x) at each sampling position x is used as the background data as the memory 1
2 (step S11). The ground data R (x) thus obtained includes the eccentricity component of the roller and the belt thickness unevenness described in detail above.
In addition, since the circumferential length of the intermediate transfer belt 41 and the sensor facing roller 43 is an integral multiple, there is no phase shift between the two regardless of the number of turns.

Then, when actually measuring the toner amount, the same procedure as in steps S1 to S5 of the first embodiment is executed, whereby the light amount signal ratio (= SigP / SigS) serving as an index of the toner amount is obtained. Is calculated as sampling data D (x) and stored in the memory 12 (steps S12 to S12).
S16).

Subsequently, after correcting the sampling data D (x) based on the background data R (x) obtained in step S11 (step S17), the toner amount is detected based on the corrected light amount signal ratio (step S17). Step S18).

As described above, in the second embodiment, by subtracting the base data R (x) from the sampling data D (x), the influence of the eccentric component of the roller and the unevenness of the belt thickness is corrected, and The amount of toner adhering to 41 can be measured with high accuracy. Therefore,
Compared with the first embodiment, highly accurate toner measurement can be performed with fewer processing steps.

C. Others The present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. For example, in the above embodiment, the sensor 6 is arranged so as to face the roller 43, but the sensor 6 is arranged so as to face the other rollers 42, 44 to 47 around which the intermediate transfer belt 41 is stretched. It may be. However, in the above embodiment, since the roller 44 among the plurality of rollers 42 to 47 is a tension roller, one of the other rollers which is fixed to the apparatus main body in advance and is rotatable at the fixed position is used. Is desirably provided with a sensor 6. This is because, when the sensor 6 is arranged to face a roller rotatably fixed at a predetermined position, the distance between the roller and the sensor 6 is constant.

On the other hand, since the tension roller 44 is configured to move forward and backward with respect to the intermediate transfer belt 41, the distance between the sensor 6 and the tension roller 44 fixed in advance is apt to fluctuate. 4
This is because the distance between the belt region and the sensor 6 spanned by the sensor 4 fluctuates, which causes a reduction in measurement accuracy. In order to prevent this, for example, the tension roller 44 and the sensor 6 may be mechanically connected, and the sensor 6 may be configured to interlock with the fluctuation of the tension roller 44.

In the above embodiment, the light amount signal ratio (= SigP / SigS) is used as the index value of the toner amount. However, other index values, for example, the output voltages Vp and Vs, the light amount signals SigP and SigS, and the light amount A signal sum (= SigP + SigS), a light amount signal difference (= SigP−SigS), or the like can be used.

In each of the above embodiments, (1)
By providing a configuration in which the sensor 6 is provided so as to face the roller 43, fluctuations in the sensing distance are suppressed, and
Equipped with (2) a configuration to correct sampling data based on the eccentric component of the roller, and (3) a configuration to correct sampling data based on the periodic profile (belt thickness unevenness). To improve the accuracy of measuring
It goes without saying that (1) to (3) may be used alone or in an appropriate combination.

Further, in the above embodiment, as shown in FIG. 2, the light emitting element 601 is such that the incident surface (the paper surface in FIG. 2) including the irradiation light and the reflected light is substantially orthogonal to the rotation axis of the sensor facing roller 43. And the light receiving elements 672p and 672s are arranged, but the arrangement relationship is not limited to this. For example, the sensor 6 may be configured such that the incident surface is substantially parallel to the roller rotation axis. . If the incident surface and the roller rotation axis are not parallel, not only does the sensing distance fluctuate due to the eccentricity of the roller, but also changes in the amount of reflected light due to changes in the angle of the roller surface (reflection surface). By making the axes parallel, the angle of the reflecting surface can be further stabilized. Further, for the same reason, in order to stabilize the angle of the reflection surface, the entrance surface and the roller rotation axis may be configured to be on the same plane.

In the above embodiment, the present invention is applied to the image forming apparatus in which the intermediate transfer belt 41 is a belt-shaped image carrier, but the present invention is not limited to this. The present invention is also applicable to an image forming apparatus that forms a toner image on a photoreceptor belt, and the present invention can be applied to all image forming apparatuses including a belt-shaped image carrier that is stretched over a plurality of rollers.

Further, in the above embodiment, the image forming apparatus is capable of forming a color image using four color toners. However, the present invention is not limited to this. Naturally, the present invention can also be applied to an image forming apparatus that forms only the image forming apparatus. The image forming apparatus according to the above embodiment is a printer that forms an image given from an external device such as a host computer on a sheet S such as copy paper, transfer paper, paper, and a transparent sheet for OHP. The present invention can be applied to all electrophotographic image forming apparatuses such as copying machines and facsimile machines.

[0068]

As described above, according to the present invention, light is applied to the surface area of the belt-shaped image carrier wound around the sensor facing roller, that is, the winding area.
Since the light reflected by the winding area is received by the light receiving element and the toner amount is measured,
Distance between sensor and belt-shaped image carrier (sensing distance)
Can be suppressed, and the amount of toner adhering to the belt-shaped image carrier can be measured with high accuracy.

Further, the output from the light receiving element is sampled while rotating the belt-shaped image carrier once, and the eccentric component of the driving roller is obtained based on the plurality of sampling outputs. After the correction, the toner amount can be accurately obtained based on the correction value.

Further, since the sensor is disposed at a position facing the sensor facing roller horizontally or above the horizontal facing position and at a position facing the sensor facing roller, the sensing surface of the sensor becomes vertical or downward, It is possible to prevent the sensing surface from being stained by the floating and falling toner, and to improve the measurement accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating a configuration of a sensor that detects an amount of toner on an intermediate transfer belt.

FIG. 3 is a diagram showing an electrical configuration of a light receiving unit employed in the apparatus of FIG.

FIG. 4 is a diagram showing a light amount control characteristic in the toner amount measuring device of FIG. 1;

FIG. 5 is a graph showing how the output voltage changes with respect to the amount of reflected light in the toner amount measuring device of FIG.

FIG. 6 is a graph showing an example of sampling data output from a sensor.

7 is a graph showing a cycle profile of an intermediate transfer belt obtained by removing an eccentric component of a driving roller from the sampling data of FIG. 6;

FIG. 8 is a flowchart illustrating a toner amount measurement operation in the image forming apparatus of FIG. 1;

FIG. 9 is a flowchart illustrating a toner amount measuring operation in the second embodiment of the image forming apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Control unit (control means) 6 ... Sensor 11 ... CPU (control means) 12 ... Memory 41 ... Intermediate transfer belt (belt-shaped image carrier) 41a ... Wrapping area 42-47 ... Roller 43 ... Sensor facing roller 601 ... Light emitting elements 642, 672p, 672s, PS: light receiving element 670p, 670s: light receiving unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA09 DE02 DE07 DE10 EB06 EC03 EC06 EF15 2H032 AA05 AA15 BA09 BA19 BA23 CA15

Claims (6)

[Claims] 1. A light emitting element irradiates light to a belt-shaped image carrier that is stretched over a plurality of rollers, and light reflected by the belt-shaped image carrier is received by a light-receiving element. An image forming apparatus comprising: a sensor that outputs a signal corresponding to the signal; and a control unit that calculates an amount of toner adhering to the belt-shaped image carrier based on an output from the sensor. A light is applied to a winding area of the surface of the belt-shaped image carrier, which is wound around the sensor facing roller, which is disposed to face one of the plurality of rollers so as to sandwich the body. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the sensor facing roller is fixedly arranged at a predetermined position, and is rotatable at the predetermined position. 3. The apparatus according to claim 1, wherein the sensor-facing roller is rotated twice or more to make the belt-shaped image carrier make one rotation.
While rotating, the output from the light receiving element is sampled, the eccentric component of the drive roller is obtained and stored based on the plurality of sampled outputs, and the image density of the toner image on the belt-shaped image carrier is obtained. 3. The method according to claim 1, wherein an output from the light receiving element that receives light reflected by the belt-shaped image carrier is corrected by the eccentric component, and an image density of the toner image is obtained based on the correction value. The image forming apparatus as described in the above. 4. The image forming apparatus according to claim 1, wherein a peripheral length of the belt-shaped image carrier is an integral multiple of a peripheral length of the sensor facing roller. 5. The peripheral length of the belt-shaped image carrier is a non-integer multiple of the peripheral length of the sensor facing roller, and the control means subtracts the eccentric component from the plurality of sampling outputs to produce the eccentric component. The cycle profile of the belt-shaped image carrier is determined and stored, and when the image density of the toner image on the belt-shaped image carrier is determined, the light receiving the light reflected by the belt-shaped image carrier is received. 4. The image forming apparatus according to claim 3, wherein an output from the element is corrected by the eccentric component and the periodic profile, and an image density of the toner image is obtained based on the correction value. 6. The image forming apparatus according to claim 1, wherein the sensor is disposed at a horizontal facing position or above the horizontal facing position and at a position facing the sensor facing roller. .