JP2012037258A - Detector and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detector for detecting the concentration of toner, which is capable of correcting the influence of the concentration of the toner on a detection result due to the deviation of the optical axis of reflected light.SOLUTION: In a toner concentration sensor 103, LEDs 104 and 105 are closely arranged and photodiodes 106 and 107 are closely arranged at a predetermined distance from a transfer belt so that the quantities of lights emitted from the LEDs 104 and 105, reflected by the surface of the transfer belt and received by the photodiodes 106 and 107 are equal. The deviation of the optical axis of the reflected light is detected by the balance of the quantity of the light emitted from the LED 105, reflected by the surface of the transfer belt and received by the photodiodes 106 and 107 and the detection result of the concentration of the toner is corrected based on the deviation.

Description

  The present invention relates to a detection device and an image forming apparatus, and more particularly to a detection device for detecting a toner density and an image forming apparatus equipped with the detection device.

  As a toner density detection sensor for detecting toner density in an image forming apparatus, light from a light emitting element is irradiated to a transfer belt and a toner image as single polarized light passing through a polarizing filter, and the reflected light from the light emitting element is irradiated. Some of them detect the toner density by receiving the irradiated single emitted light and polarized light in the parallel direction, and the irradiated light from the light emitting element and the polarized light in the orthogonal direction, respectively.

  For example, Japanese Patent Laid-Open No. 2006-208266 (hereinafter referred to as Patent Document 1) is a toner concentration detection sensor of this type, in which a light emitting element and a light receiving element are arranged on the same substrate, and the light emitting element and the light receiving element are further arranged. The structure which raises the sensor detection precision by making the space | interval with an element and the space | interval between light receiving elements close is disclosed.

JP 2006-208266 A

  By the way, in the toner density detection sensor of this system, the detection sensitivity is improved as the incident angle from the light emitting element to the toner image and the reflection angle from the toner image to the light receiving element are narrower. For this reason, the light emitting element and the light receiving element are arranged between the light receiving elements and the intervals between the light receiving elements are reduced.

  However, the distance and attachment angle between the toner density sensor and the measurement object may differ due to dimensional variations of attachment parts. In this case, there is a problem in that the detection result may be an abnormal value because the optical axis of the reflected light is shifted and the amount of light incident on the light receiving element is changed.

  The present invention has been made in view of such problems, and a detection device for detecting a toner concentration capable of correcting an influence on a detection result of the toner concentration due to a deviation of the optical axis of reflected light, and An object of the present invention is to provide an image forming apparatus equipped with the detection device.

  In order to achieve the above object, according to an aspect of the present invention, a plurality of light emitting elements having different wavelengths arranged with a first polarizing filter in an irradiation direction, and light emitted from the light emitting elements through the first polarizing filter A plurality of light receiving elements arranged in proximity to each other on the first surface for receiving reflected light from the surface of the detection object, the second polarization direction being the same as that of the first polarizing filter; The first light receiving element arranged in a direction toward the detection target surface and the third polarization filter having a polarization direction orthogonal to the polarization direction of the first polarization filter toward the detection target surface And a sensor signal indicating the density of the toner image formed on the surface of the object according to the amount of light received by the first light receiving element and the second light receiving element. Output means for Obtain.

  Preferably, the wavelength of the first light emitting element belongs to the sensitivity region of the second polarizing filter and the third polarizing filter, and the wavelength of the second light emitting device does not belong to the sensitivity region.

  Preferably, the first light receiving element and the second light receiving element are reflected from the second light emitting element when the distance from the second light emitting element to the detection target surface is a predetermined distance on the first surface. It arrange | positions in the position used as the standard irradiation state which is a state in which light is irradiated to the 1st light receiving element and the 2nd light receiving element equally or substantially equally.

  More preferably, the detection device further includes a control device, and the control device is configured based on the amount of light received by the first light receiving element and the amount of light received by the second light receiving element based on the reflected light of the second light emitting element. A value obtained from detection processing for detecting a deviation of the optical axis of reflected light from the irradiation state, and the amount of light received by the first light receiving element and the amount of light received by the second light receiving element of the reflected light of the first light emitting element Is corrected based on the deviation, and an output process for outputting a sensor signal is executed.

  More preferably, the control device causes a deviation when the ratio of the amount of light received by the first light receiving element and the amount of received light by the second light receiving element of the reflected light of the second light emitting element is greater than or equal to a predetermined value. Detects that

  Preferably, the control device uses the ratio of the amount of light received by the first light receiving element and the amount of light received by the second light receiving element of the reflected light of the second light emitting element as a value obtained by the output process. to correct.

  Preferably, the first light-emitting element and the second light-emitting element are disposed on the second surface, and the control device detects a difference between the distance from the second surface to the detection target surface and a predetermined distance as a deviation. .

  Preferably, the first light-emitting element and the second light-emitting element are arranged on the second surface, and the control device is configured to adjust the second irradiation angle of the second light-emitting element with respect to the second surface in the standard irradiation state. A difference from the irradiation angle of the second light emitting element with respect to the surface is detected as a deviation.

  According to another aspect of the present invention, an image forming apparatus includes an image carrier, transfer means for transferring a toner image to the surface of the image carrier, and detection for detecting the density of the toner image on the surface of the image carrier. Device. The detection apparatus includes a plurality of light emitting elements having different wavelengths, in which a first polarizing filter is arranged in an irradiation direction toward the image carrier, and an image of light emitted from the light emitting elements through the first polarizing filter. A plurality of light receiving elements arranged close to the first surface for receiving reflected light from the surface of the carrier, wherein the second polarizing filter has the same polarization direction as the first polarizing filter. A first light receiving element disposed in a direction toward the image carrier and a third polarizing filter having a polarization direction orthogonal to the polarization direction of the first polarization filter are disposed in a direction toward the image carrier. And an output means for outputting a sensor signal indicating the density of the toner image in accordance with the amount of light received by the first light receiving element and the second light receiving element.

  According to the present invention, the distance between the toner density sensor and the transfer belt as the measurement object is different, or the attachment angle is different due to dimensional variation of the attachment parts, etc., and the optical axis of the reflected light is shifted and enters the light receiving element. Even when the amount of light changes, the influence of the toner density on the detection result is corrected. Thereby, the accuracy of toner density detection can be improved.

It is a figure which shows the specific example of a structure of the printer concerning this Embodiment. FIG. 3 is a diagram illustrating a specific example of a configuration in the vicinity of a toner density sensor of a printer. It is a figure which shows the specific example of a structure of a toner density sensor. It is a figure which shows the frequency characteristic of the polarizing filter contained in a toner density sensor. FIG. 4 is a diagram illustrating an optical path when one LED of a toner density sensor emits light. It is a figure showing the optical path when the other LED of the toner density sensor is caused to emit light. FIG. 6 is a diagram for explaining a relationship between a distance between a toner density sensor and a transfer belt and an arrangement of light receiving elements. FIG. 6 is a diagram illustrating an irradiation position of reflected light of an LED on a light receiving element when a distance between a toner density sensor and a transfer belt is closer than a normal distance. FIG. 4 is a diagram illustrating a relationship between toner density on a transfer belt and output characteristics of a toner density sensor. It is a figure which shows the specific example of a function structure of a control apparatus which outputs a sensor signal after correcting according to the shift | offset | difference of an optical axis. 7 is a flowchart showing processing for detecting a deviation of an optical axis between a toner density sensor and a transfer belt and determining a sensor output value after performing correction according to the deviation of the optical axis. It is a figure which shows the specific example of the output value of a photodiode.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same.

  In the following description, an example in which the image forming apparatus is a tandem color printer (hereinafter abbreviated as a printer) is shown, but the image forming apparatus is not limited to a printer. The image forming apparatus may be a copying machine, a facsimile, and an MFP (Multi Function Peripheral) that is a device that combines these functions.

<Overall configuration>
FIG. 1 is a diagram illustrating a specific example of the configuration of the printer 1 according to the present embodiment. Referring to the drawing, printer 1 includes an image forming unit and a conveyance unit for paper that is a print medium.

  The image forming unit includes an annular transfer belt 101 that is an intermediate transfer member and is suspended from a plurality of transfer driving rollers 102 from the inside, which is disposed at a substantially central portion inside the printer 1.

  Along the transfer belt 101, cartridges 28y, 28m, 28c, and 28k corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged. These are representatively referred to as a cartridge 28. The cartridge 28 includes a photoreceptor 3, a charging unit 5, an exposure unit 6, and a developing unit 4 as toner image forming mechanisms for forming a toner image by an electrostatic recording method.

  Each developing unit 4 includes a developing roller and a supply roller (not shown). Further, the developing units 4 each include a space for filling toner (not shown). As the developing unit 4 operates and the supply roller rotates, the toner in the space is supplied to the developing roller. The developing roller is disposed at a position corresponding to the photoconductor 3 and carries the supplied toner to a position facing the photoconductor 3. Since the surface of the photoconductor 3 is exposed, the toner on the developing roller moves to the exposed portion of the photoconductor 3 at a position facing the photoconductor 3. As a result, a toner image is formed on the photoreceptor 3.

  The photoreceptor 3 transfers the toner image formed on the transfer belt 101. The charging unit 5 uniformly charges the surface of the photoreceptor 3. The exposure unit 6 exposes the image patterns of the respective colors on the photoreceptor 3 and sequentially forms them. The developing unit 4 supplies toner to the photoconductor 3 and develops a toner image on the photoconductor 3.

  A secondary transfer roller 11 is disposed with a transfer driving roller 102 at a position in contact with a printing paper conveyance path, which will be described later, and the conveyance path therebetween. The secondary transfer roller 11 transfers the toner image transferred onto the transfer belt 101 onto the conveyed paper.

  A toner density sensor 103 is disposed at a position facing the transfer belt 101. The toner density sensor 103 detects the density of the toner image transferred onto the transfer belt 101. This configuration will be described later.

  The transport unit includes a paper feed roller 8, a transport roller 30, a timing roller 10, the above-described secondary transfer roller 11, a pair of fixing rollers 12 a and 12 b (representing these as the fixing roller 12), And a paper discharge roller 13.

  The paper feed roller 8 feeds paper from a storage unit 16, which is a cassette for storing paper, which is disposed at a lower portion inside the printer 1. The transport roller 30 transports the paper supplied by the paper feed roller 8. The timing roller 10 temporarily stops the sheet conveyed by the conveyance roller 30. The fixing roller 12 is arranged with the sheet to be conveyed interposed therebetween, and heats and fixes the toner image transferred onto the sheet. The paper discharge roller 13 discharges the fixed paper.

  The photoreceptor 3, the secondary transfer roller 11, and the timing roller 10 in the cartridge 28 are connected to the main motor 18. Of the developing units 4 in the cartridge 28, the color developing unit 4 is connected to the developing motor 20, and the monochrome developing unit 4 is connected to the developing motor 21. The developing motor 20 drives the color developing unit 4, and the developing motor 21 drives the monochrome developing unit 4. The fixing roller 12 is connected to the fixing motor 19 and is rotated by the rotation driving of the fixing motor 19.

  The printer 1 further includes a control unit 50 and a memory 55. A CPU (Central Processing Unit) (not shown) included in the control unit 50 reads and executes a program stored in the memory 55. Drive mechanisms such as the main motor 18, the fixing motor 19, and the developing motors 20 and 21 are electrically connected to the control unit 50, and driving is controlled according to a control signal from the control unit 50. Further, the toner concentration sensor 103 is electrically connected to the control unit 50 and inputs a sensor signal to the control unit 50. The control unit 50 performs the above control using the sensor signal.

<Configuration of toner density sensor>
FIG. 2 is a diagram illustrating a specific example of the configuration in the vicinity of the toner density sensor 103. Referring to the drawing, toner density sensor 103 is arranged with its detection surface facing the surface of transfer belt 101. The toner image formed on the transfer belt 101 moves in the direction of the arrow in the figure as the transfer driving roller 102 rotates. When the toner image moves on the surface of the transfer belt 101 at a position facing the detection surface, the toner concentration sensor 103 detects the density of the toner image.

  FIG. 3 is a diagram illustrating a specific example of the configuration of the toner density sensor 103. Referring to the figure, toner density sensor 103 includes LED (Light Emitting Diode) 104 as a first light emitting element, LED 105 as a second light emitting element, and a light receiving element. Photodiodes 106, 107, 108, and a control device 117.

  The LED 105, the LED 104, the photodiode 106, and the photodiode 107 are arranged on the printed circuit board 109 so as to be in a straight line in this order. In the following drawings, the straight line on which these components are mounted is also referred to as “component mounting axis”. The photodiode 106 and the photodiode 107 are arranged close to each other with a distance between them as a distance in a range in which the regular reflection light from the transfer belt 101 is irradiated to both the photodiode 106 and the photodiode 107.

  Here, an example in which the LED 105, the LED 104, the photodiode 106, and the photodiode 107 are all arranged on the same printed circuit board 109 is shown. However, the LEDs 105 and 104 and the photodiodes 106 and 107 may be arranged on the same line of different substrates, each of which has a predetermined positional relationship.

  The photodiode 108 is disposed on the printed circuit board 109 in the vicinity of the LEDs 104 and 105. The photodiode 108 is a light receiving element that detects the amount of light emitted from the LEDs 104 and 105 and performs feedback to keep the supply current to the LED 104 or the LED 105 constant. Therefore, the photodiode 108 is not involved in the sensor output.

  A holder 110 is provided above the surface of the printed circuit board 109 on which the LEDs 104 and 105 and the photodiodes 106, 107, and 108 are disposed. Above that, a lens 112 is provided.

  A hole 111 is drilled on the light emitting optical path of the LEDs 104 and 105 of the holder 110. The range of the amount of light from the LEDs 104 and 105 is limited by the hole 111. As a result, erroneous output of the toner density sensor due to surrounding irregular reflection is suppressed.

  A polarizing filter 113 is provided between the LEDs 104 and 105 and the holder 110. Light emitted from the LEDs 104 and 105 is emitted outside the sensor through the polarization filter 113.

  Between the photodiode 106 and the holder 110, a polarization filter 114 for aligning the polarization direction so as to be the same polarization as the polarization filter 113 is provided. The light reflected from the transfer belt 101 passes through the polarizing filter 114 and irradiates the photodiode 106.

  Between the photodiode 107 and the holder 110, a polarization filter 115 is provided for aligning the polarization direction so that the polarization direction is orthogonal to the polarization filter 113. The light reflected from the transfer belt 101 passes through the polarization filter 115 and irradiates the photodiode 107.

  The control device 117 includes a CPU and a memory (not shown). The controller 117 may be provided at a position different from the printed circuit board 109 as illustrated, or may be mounted on the printed circuit board 109.

  The CPU of the control device 117 and the LEDs 105 and 104 are electrically connected. The LEDs 105 and 104 emit light according to a control signal from the CPU, and the light emission ends.

  The CPU of the control device 117 and the photodiodes 106, 107, 108 are electrically connected. The photodiodes 106, 107, and 108 each output a signal corresponding to the amount of received light to the CPU. The control device 117 is further electrically connected to the control unit 50 of the printer 1. The control device 117 performs an operation based on the signals input from the photodiodes 106, 107, and 108 and outputs a sensor signal to the control unit 50.

<Characteristics of polarizing filter>
FIG. 4 is a diagram illustrating the frequency characteristics of the polarization filters 113, 114, and 115. 4A shows frequency characteristics in the transmission axis direction (parallel direction) of the polarizing filters 113, 114, and 115, and FIG. 4B shows frequency characteristics in the absorption axis direction (orthogonal direction).

  Referring to the drawing, polarizing filters 113, 114, and 115 have a transmittance of 80% or more for light having a wavelength of 400 nm or more in the transmission axis direction (parallel direction), and the absorption axis direction (orthogonal direction). Then, the transmittance is almost 0% for light having a wavelength of 400 nm to 700 nm.

<Principle of detection of optical axis deviation between toner density sensor and transfer belt>
Based on this characteristic, the emission wavelength of the LED 104 is a wavelength at which the transmittance in the absorption axis direction of the polarizing filters 113, 114, 115 is 10% or less, and the emission wavelength of the LED 105 is in the absorption axis direction of the polarizing filters 113, 114, 115. The wavelength is set to a transmittance of 80% or more.

  The emission wavelength of the LED 104 belongs to a wavelength region outside the sensitivity region of the polarizing filters 113, 114, and 115 represented by A1 and A2 in FIGS. 4 (A) and 4 (B), and the emission wavelength of the LED 105 is FIG. It belongs to the wavelength region that is within the sensitivity region of the polarization filters 113, 114, and 115 represented by B1 and B2 in FIG. As for the wavelengths of these LEDs 104 and 105, the transmittance in the transmission axis direction of the polarizing filters 113, 114, and 115 is 80% or more. Therefore, the light irradiated from the LED 104 and transmitted through the polarization filter 113 is transmitted through the polarization filter 114 whose transmission axis direction is parallel to the polarization filter 113, but is polarized light whose transmission axis direction is orthogonal to the transmission axis direction of the polarization filter 113. The filter 115 does not transmit. On the other hand, the light emitted from the LED 105 and transmitted through the polarizing filter 113 includes a polarizing filter 114 whose transmission axis direction is parallel to the polarizing filter 113 and a polarizing filter 115 whose transmission axis direction is orthogonal to the transmission axis direction of the polarizing filter 113. To Penetrate.

  FIG. 5 is a diagram showing an optical path when the LED 104 is caused to emit light, and FIG. 6 is a diagram showing an optical path when the LED 105 is caused to emit light.

  Referring to FIG. 5, the irradiation light from LED 104 passes through polarization filter 113 and is linearly polarized, is output from toner density sensor 103, and is reflected by transfer belt 101. The reflected light again enters the toner density sensor 103. The reflected light does not pass through the filter because the polarizing filter 115 is a polarizing filter arranged in the absorption axis direction of light linearly polarized by the polarizing filter 113. Therefore, the reflected light does not reach the photodiode 107, and only the photodiode 106 is irradiated with the reflected light.

  Referring to FIG. 6, the irradiation light from LED 105 passes through polarizing filter 113, is output from toner density sensor 103, and is reflected by transfer belt 101. The reflected light again enters the toner density sensor 103. Since this reflected light passes through both the polarizing filters 114 and 115, both the photodiodes 106 and 107 are irradiated with the reflected light.

  FIG. 7 is a diagram for explaining the relationship between the distance between the toner density sensor 103 and the transfer belt 101 and the arrangement of the light receiving elements.

  Referring to the figure, toner density sensor 103 is installed at a predetermined distance from transfer belt 101. The photodiodes 106 and 107 as light receiving elements are arranged at positions where the light emitted from the LED 105 and reflected from the transfer belt 101 separated by the distance is irradiated almost uniformly between the photodiodes 106 and 107.

  With this arrangement, when the arrangement position (distance) of the toner density sensor 103 with respect to the transfer belt 101 is a normal distance as specified, the output from the photodiode 106 and the output from the photodiode 107 Are equal.

  FIG. 8 is a diagram for explaining the irradiation position of the reflected light of the LED 105 to the light receiving element when the distance between the toner density sensor 103 and the transfer belt 101 is shorter than a normal distance.

  Referring to FIG. 8, when the distance between the toner density sensor 103 and the transfer belt 101 is shorter than the normal distance, the irradiation position of the light emitted from the LED 105 and reflected by the transfer belt 101 is The position is closer to the photodiode 106 than the substantially equal position between the photodiodes 106 and 107. Therefore, in this case, the output from the photodiode 106 is larger than the output from the photodiode 107.

  Similarly, when the distance between the toner density sensor 103 and the transfer belt 101 is longer than the normal distance, the position where the light irradiated from the LED 105 and reflected by the transfer belt 101 is irradiated is the photodiode 106. , 107 is closer to the photodiode 107 side than the substantially uniform position. Therefore, in this case, the output from the photodiode 106 is smaller than the output from the photodiode 107.

<Sensor output characteristics>
The control device 117 performs control (hereinafter also referred to as detection processing) for toner density detection, and calculates a sensor output value based on output values obtained from the photodiodes 106 and 107 under the control. In the detection process, specifically, only the LED 104 is caused to emit light with a light emission amount such that the sensor output value on the surface of the transfer belt 101 without the toner image becomes a predetermined value (for example, 3 V).

  As an example of the calculation method of the sensor output value, a calculation method of multiplying the difference between the output values of the signals from the photodiodes 106 and 107 (output value of the photodiode 106−output value of the photodiode 107) by a coefficient (for example, 5) can be given. It is done.

  FIG. 9 is a diagram illustrating the relationship between the toner density on the transfer belt 101 and the output characteristics of the toner density sensor 103 calculated by the above-described calculation method. The solid line in the figure represents the relationship between the toner density on the transfer belt 101 and the output characteristics of the toner density sensor 103. Furthermore, the dotted line in the figure represents the relationship between the toner density on the transfer belt 101 and the output of the photodiode 106, and the dashed line represents the relationship between the output of the photodiode 107.

  When the distance between the toner density sensor 103 and the transfer belt 101 is shortened, the amount of light incident on the photodiode 106 increases, so that the output value of the photodiode 106 increases. For this reason, when the LED 104 is caused to emit light in the detection process, the amount of emitted light is controlled to be small.

  Therefore, when the toner density is high, the output value of the photodiode 106 is larger than the output value of the photodiode 107. Therefore, the sensor output value of the toner density sensor 103 obtained by the above calculation method is the true sensor output. Higher than the value. On the other hand, when the distance between the toner density sensor 103 and the transfer belt 101 is increased, the sensor output value of the toner density sensor 103 obtained by the above-described calculation method in a state where the toner density is high is lower than the true sensor output value. Become.

<Functional configuration of control device>
Therefore, the controller 117 determines the optical axis between the toner density sensor 103 and the transfer belt 101 based on the balance of the amount of light applied to the photodiodes 106 and 107 that changes depending on the irradiation position of the reflected light when the LED 105 emits light. Detecting deviations. Then, the sensor signal is output after correction based on the deviation amount.

  FIG. 10 is a diagram illustrating a specific example of a functional configuration of the control device 117 that outputs a sensor signal after performing correction according to the deviation of the optical axis. These functions are mainly formed in the CPU by reading and executing a program stored in a memory by a CPU (not shown).

  Referring to the figure, control device 117 generally includes a detection processing unit 70 for detecting a deviation of the optical axis and an output processing unit 80 for outputting a sensor signal.

  The detection processing unit 70 compares these signals with a light emission control unit 71 for controlling the light emission of the LEDs 104 and 105 and an input unit 72 for receiving input of signals from the photodiodes 106 and 107 under the control. And a comparison unit 73 for outputting a comparison result.

  The light emission control unit 71 causes the LED 105 to emit light with a predetermined light amount for a predetermined time during the detection process, and does not cause the LED 104 to emit light. The comparison unit 73 compares the output values corresponding to the amounts of received light indicated by the signals from the photodiodes 106 and 107 under this control, and as a result, the output values of these signals are equal (the extent that they can be handled if they are equal). The comparison result indicating whether it is within the range of (or may be included in “equal”) or not equal is passed to the output processing unit 80. Further, if they are not equal, the comparison unit 73 generates a signal value indicating the ratio of the received light amount obtained by comparing the output values corresponding to the deviation amount of the optical axis between the toner density sensor 103 and the transfer belt 101. The ratio is passed to the output processing unit 80.

  The output processing unit 80 includes a light emission control unit 81 for controlling light emission of the LEDs 104 and 105, an input unit 82 for receiving input of signals from the photodiodes 106 and 107 under the control, and output values of these signals. A calculation unit 83 for calculating the sensor output value from the detection unit 70 and a correction unit 84 for correcting the sensor output value calculated based on the detection result of the detection processing unit 70.

  The light emission control unit 81 causes the LED 104 to emit light for a predetermined time with a light emission amount such that a sensor output value on the surface of the transfer belt 101 without a toner image becomes a predetermined value (for example, 3 V) during output processing, and the LED 105 does not emit light.

  The calculation unit 83 calculates the sensor output value based on the output values of the signals from the photodiodes 106 and 107. As an example, the calculation unit 83 performs the above-described calculation of multiplying the difference between the output values of the signals from the photodiodes 106 and 107 (output value of the photodiode 106−output value of the photodiode 107) by a coefficient (for example, 5). To calculate the sensor output value.

  When the comparison result that the output values of both signals are equal is obtained in the detection process, the correction unit 84 does not correct the calculated sensor output value. When a comparison result is obtained that the output values of both signals are not equal in the detection process, the correction unit 84 calculates the sensor output value calculated based on the output ratio of the photodiodes 106 and 107 included in the comparison result. Correct.

  That is, when the distance between the toner density sensor 103 and the transfer belt 101 is shorter than the normal distance, the amount of light received by the photodiode 106 increases. Therefore, the output value of the photodiode 107 is subtracted from the output value. The resulting difference will be larger. Therefore, the sensor output value obtained by multiplying the difference by the coefficient becomes larger than the true sensor output value. On the contrary, when the distance between the toner density sensor 103 and the transfer belt 101 is longer than the normal distance, the amount of light received by the photodiode 106 decreases. Therefore, the output value of the photodiode 107 is subtracted from the output value. The difference obtained is small. Therefore, the sensor output value obtained by multiplying the difference by the coefficient is smaller than the true sensor output value.

  Therefore, as an example, the correction unit 84 calculates the sensor output value calculated from the difference between the output values of the photodiodes 106 and 107 (output value of the photodiode 106−output value of the photodiode 107) obtained in the output process. The sensor output value is corrected by dividing by the ratio of the output values of the photodiodes 106 and 107 obtained in the detection process (output value of the photodiode 107 / output value of the photodiode 106).

<Processing flow>
FIG. 11 is a flowchart showing a process for detecting a deviation of the optical axis between the toner density sensor 103 and the transfer belt 101 and determining a sensor output value after performing correction according to the deviation of the optical axis. The processing shown in the flowchart of FIG. 11 is realized by a CPU (not shown) of the control device 117 reading and executing a program stored in the memory.

  12 is a diagram illustrating a specific example of output values of the photodiodes 106 and 107. FIG. 12A illustrates a specific example of output values of the photodiodes 106 and 107 in a detection process described later. B) is a diagram showing a specific example of output values of the photodiodes 106 and 107 in the output processing described later.

  Referring to the figure, the CPU first causes the LED 105 to emit light for a predetermined time as a process for detecting a deviation of the optical axis between the toner density sensor 103 and the transfer belt 101 (step S101). Then, the CPU receives signals from the photodiodes 106 and 107 under the light emission and acquires these output values (step S103).

  The CPU compares these output values. As a result, if these output values are equal (“photodiode 106 = photodiode 107” in step S105), the process proceeds to step S107. If these output values are not equal (“photodiode 106 ≠ photodiode 107” in step S105), the process proceeds to step S113. When the output values of the photodiodes 106 and 107 obtained in step S103 are the output values shown in FIG. 12A, these output values are not equal in step S105. The processes in steps S101 to S105 described above correspond to the above-described detection process.

  When the output values from the photodiodes 106 and 107 are equal, the CPU turns off the LED 105 and processes the LED 104 instead of the toner image as a process for obtaining a sensor output value by correcting according to the deviation of the optical axis. Light is emitted for a predetermined time with a light emission amount at which the sensor output value on the surface of the transfer belt 101 not present becomes a predetermined value (for example, 3 V) (step S107). Here, the CPU adjusts the light amount of the LED 104 based on the output values of the photodiodes 106 and 107 obtained from the position where there is no toner image on the surface of the transfer belt 101.

  Then, the CPU calculates a sensor output value from the output values from the photodiodes 106 and 107 under the light emission (step S109). When the output values from the photodiodes 106 and 107 are the output values in FIG. 12B, the CPU adds a coefficient (for example, 5) to the difference (V6−V7) in the output values of the signals from the photodiodes 106 and 107. A sensor output value is calculated by performing a multiplication operation.

  Irradiation light from the LED 104 is polarized by the polarization filter 113 and is not received by the photodiode 107 provided with the polarization filter 115 having a polarization direction orthogonal to the polarization direction. For this reason, it can be said that the output value of the photodiode 107 is due to a so-called dark current (dark current), which is a photocurrent generated by light reception and other current that does not depend on light reception. Therefore, this effect can be eliminated by subtracting the output value of the photodiode 107 from the output value of the photodiode 106.

  If the output values of the photodiodes 106 and 107 are equal, the CPU specifies that the calculated sensor output value is not corrected, assuming that there is no deviation of the optical axis (step S111).

  If the output values of the photodiodes 106 and 107 are not equal, the CPU turns off the LED 105 and emits the LED 104 for a predetermined time as a process for obtaining a sensor output value by correcting according to the deviation of the optical axis. (Step S113). Then, the CPU calculates a sensor output value from the output values from the photodiodes 106 and 107 under the light emission (step S115). The processes in steps S113 and S115 are the same as the processes in steps S107 and S109, respectively.

  If the output values of the photodiodes 106 and 107 are not equal, the CPU assumes that the optical axis has shifted and the calculated sensor output value is obtained by the comparison process in step S105. Correction is performed based on the output ratio of 107 (step S117). When the output values of the photodiodes 106 and 107 obtained in step S103 are the output values shown in FIG. 12A, the CPU obtains the sensor output value calculated in step S115, for example, in step S103. The sensor output value is corrected by dividing by the ratio (L1 / L2) of the output values of the photodiodes 106 and 107.

  Irradiation light from the LED 105 is not polarized by the polarizing filter and is received by any photodiode. Therefore, it can be said that the influence of the so-called dark current in the output values from the photodiodes 106 and 107 is negligible compared to the light reception. Therefore, here, it is assumed that the ratio (L1 / L2) of the output values of the photodiodes 106 and 107 obtained in step S103 represents the amount of deviation of the optical axis.

The processes in steps S107 to S117 described above correspond to the output process described above.
As described above, the deviation of the optical axis between the toner density sensor 103 and the transfer belt 101 is detected, and after correcting according to the deviation of the optical axis, the process of determining the sensor output value is completed. The sensor output value obtained in step S111 or step S117 is output.

  In the above description, an example in which the detection process and the output process are continuously performed as a series of processes is shown. However, the detection process does not necessarily have to be performed before the output process. That is, the control device 117 performs only the detection process at a predetermined timing (for every fixed image formation amount, at the time of starting the printer 1, during the image stabilization process, etc.), and obtains the comparison result and the obtained comparison process. The output ratio of the obtained photodiodes 106 and 107 may be stored.

  Further, in the above description, the CPU performs a comparison process in step S105, and as a result, when the outputs of the photodiodes 106 and 107 are not equal, the correction in step S117 is performed. However, when the output ratio of the photodiodes 106 and 107 is multiplied by the calculated sensor output value in the correction processing as described above, the sensor output value remains even if the correction is performed when the outputs of the photodiodes 106 and 107 are equal. There is no change. Therefore, when performing the correction by multiplying the ratio in this way, the CPU multiplies the calculated sensor output value by the output ratio of the photodiodes 106 and 107 obtained by the detection process without performing the comparison in step S105. It may be. By doing in this way, the sensor output value calculated as needed is corrected, without performing a comparison process.

<Effect of Embodiment>
By performing the above-described processing in the control device 117, even if the optical axis is shifted due to a shift in the distance between the toner density sensor 103 and the transfer belt 101, the toner density of the shift is generated. The influence on detection can be corrected. As a result, the toner density detection result can be kept normal, and the density detection accuracy can be improved.

  In the above description, correction is described when the optical axis of the reflected light is shifted due to the difference in the distance between the toner density sensor 103 and the transfer belt 101 as the measurement object, and the amount of light incident on the light receiving element is changed. is doing. However, when the LEDs 104 and 105 are attached to the printed circuit board 109 at the same irradiation angle, the optical axis of the reflected light is shifted due to the difference in the attachment angle of the LED, which is a light emitting element, due to dimensional variation of the LED, etc. Even when the amount of light incident on the light source changes, the effect is eliminated by applying this correction, and the accuracy of density detection can be improved.

<Other examples>
Further, it is possible to cause the computer to execute a process of detecting the optical axis deviation between the toner density sensor 103 and the transfer belt 101 and determining the sensor output value after performing correction according to the optical axis deviation. A program can also be provided. Such a program is stored in a computer-readable recording medium such as a flexible disk attached to the computer, a CD-ROM (Compact Disk-Read Only Memory), a ROM (Read Only Memory), a RAM (Random Access Memory), and a memory card. And can be provided as a program product. Alternatively, the program can be provided by being recorded on a recording medium such as a hard disk built in the computer. A program can also be provided by downloading via a network.

  The program according to the present invention is a program module that is provided as a part of a computer operating system (OS) and calls necessary modules in a predetermined arrangement at a predetermined timing to execute processing. Also good. In that case, the program itself does not include the module, and the process is executed in cooperation with the OS. A program that does not include such a module can also be included in the program according to the present invention.

  The program according to the present invention may be provided by being incorporated in a part of another program. Even in this case, the program itself does not include the module included in the other program, and the process is executed in cooperation with the other program. Such a program incorporated in another program can also be included in the program according to the present invention.

  The provided program product is installed in a program storage unit such as a hard disk and executed. The program product includes the program itself and a recording medium on which the program is recorded.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Printer, 3 photoreceptor, 4 image development part, 5 charging part, 6 exposure part, 8 paper feed roller, 10 timing roller, 11 secondary transfer roller, 12, 12a, 12b fixing roller, 13 paper discharge roller, 16 storage part , 18 main motor, 19 fixing motor, 20, 21 developing motor, 28, 28y, 28m, 28c, 28k cartridge, 30 transport roller, 50 control unit, 55 memory, 70 detection processing unit, 71, 81 light emission control unit, 72 , 82 Input unit, 73 Comparison unit, 80 Output processing unit, 83 Calculation unit, 84 Correction unit, 101 Transfer belt, 102 Transfer drive roller, 103 Toner density sensor, 106, 107, 108 Photodiode, 109 Print board, 110 Holder , 111 holes, 112 lenses, 113, 114, 115 polarizing filters, 17 control device.

Claims (9)

A plurality of light emitting elements having different wavelengths, the first polarizing filter being disposed in the irradiation direction;
A plurality of light receiving elements arranged in proximity to a first surface for receiving reflected light from the surface of a detection object of light irradiated from the light emitting element through the first polarizing filter; A first light receiving element in which a second polarizing filter having the same polarization direction as the first polarizing filter is disposed in a direction toward the surface of the detection object, and a polarization direction of the first polarizing filter are orthogonal to each other. A second light receiving element in which a third polarizing filter having a polarization direction is disposed in a direction toward the surface of the detection target;
Output means for outputting a sensor signal indicating the density of a toner image formed on the surface of the object in accordance with the amount of the reflected light received by the first light receiving element and the second light receiving element; A detection device. The wavelength of the first light emitting element belongs to a sensitivity region of the second polarizing filter and the third polarizing filter,
The detection device according to claim 1, wherein a wavelength of the second light emitting element does not belong to the sensitivity region.   The first light receiving element and the second light receiving element are on the first surface, the second light emitting element when the distance from the second light emitting element to the detection target surface is a predetermined distance. 3. The detection according to claim 1, wherein the light reflected from the first light receiving element is disposed at a position where the first light receiving element and the second light receiving element are evenly or substantially uniformly irradiated in a standard irradiation state. apparatus. A control device,
The controller is
The deviation of the optical axis of the reflected light from the standard irradiation state based on the amount of light received by the first light receiving element and the amount of light received by the second light receiving element of the reflected light of the second light emitting element. Detection processing to detect,
The sensor signal is output by correcting a value obtained from the amount of light received by the first light receiving element and the amount of light received by the second light receiving element of the reflected light of the first light emitting element based on the deviation. The detection apparatus according to claim 3, wherein the output process is executed.   The control device detects the deviation when the ratio of the amount of light received by the first light receiving element and the amount of light received by the second light receiving element of the reflected light of the second light emitting element is equal to or greater than a predetermined value. The detection device according to claim 4, wherein the detection device detects that occurrence has occurred.   The control device corrects the obtained value by using a ratio between a received light amount of the reflected light of the second light emitting element at the first light receiving element and a received light amount of the second light receiving element. The detection device according to claim 4 or 5. The first light emitting element and the second light emitting element are disposed on a second surface,
The said control apparatus is a detection apparatus in any one of Claims 4-6 which detects the difference with the said predetermined distance of the distance from the said 2nd surface to the said detection target surface as the said shift | offset | difference. The first light emitting element and the second light emitting element are disposed on a second surface,
The control device calculates a difference between an irradiation angle of the second light emitting element with respect to the second surface from an irradiation angle of the second light emitting element with respect to the second surface in the standard irradiation state. The detection device according to claim 4, wherein the detection device is detected as: An image carrier;
Transfer means for transferring a toner image to the surface of the image carrier;
A detection device for detecting the density of the toner image on the surface of the image carrier,
The detection device includes:
A plurality of light emitting elements having different wavelengths, wherein a first polarizing filter is disposed in an irradiation direction that is a direction toward the image carrier;
A plurality of light receiving elements disposed in proximity to a first surface for receiving reflected light from the surface of the image carrier of light emitted from the light emitting element through the first polarizing filter; A first light receiving element in which a second polarizing filter having the same polarization direction as that of the first polarizing filter is disposed in a direction toward the image carrier, and a polarization direction of the first polarizing filter are orthogonal to each other. A second light receiving element in which a third polarizing filter having a polarization direction is disposed in a direction toward the image carrier;
And an output unit configured to output a sensor signal indicating the density of the toner image in accordance with the amount of the reflected light received by the first light receiving element and the second light receiving element.

Images