JP2009145702A - Image forming device, method of determining connection state of toner density sensor, and method of determining connection state of sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily detect a connection state of a toner density sensor at low cost. <P>SOLUTION: This image forming device 1 is provided with the toner density sensors 15Y, 15M, 15C, 15K for outputting respectively respective detection signals KS based on toner densities in developing devices 13Y, 13M, 13C, 13K, an analog switch 31 having four toner density ports for inputting respectively the respective detection signals KS, four image density ports for inputting respectively respective density signals SI, and one output port, and for switching the respective toner density ports and the respective image density ports sequentially to the output port to be connected selectively, and a signal processing part 32 for processing a signal appearing in the output port. The respective detection signals KS and the respective density signals SI are connected to the respective toner density ports and the respective image density ports, to make each of the density signals SI appear in the output port in advance to each of the detection signals KS, when the analog switch 31 switches sequentially the connection. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an MFP, a toner density sensor connection state determination method, and a sensor connection state determination method.

  In an image forming apparatus that forms an image by an electrophotographic method, such as a copier, a printer, a facsimile machine, a multifunction machine, or a multi-function machine called MFP (Multi Function Peripherals), it is formed on a drum-shaped photoreceptor. The electrostatic latent image is developed to form a toner image, the toner image is primarily transferred to an intermediate transfer belt, and then further transferred to a recording paper, and then fixed, thereby forming an image. The photoreceptor is cleaned by a cleaning device having a cleaning blade or the like after the transfer of the toner image.

  In such an image forming apparatus, there is an apparatus in which a portion for forming a toner image for each color of Y, M, C, and K is unitized as an imaging unit to facilitate replacement and maintenance. In this case, the imaging units of the respective colors are positioned as independent consumable members (consumables), and are exchanged when the service life is reduced by use. The imaging unit includes a photoreceptor and a developing device corresponding to each color.

  The developing device develops the electrostatic latent image on the photoreceptor with a two-component developer composed of toner and carrier. The developing device is supplied with toner (developer) from a toner supply device. The toner and the carrier are charged by stirring. The electrostatic latent image on the photoreceptor is developed by electrostatically attaching toner to the developing device.

  In the image forming apparatus, the toner concentration is detected by detecting the magnetic permeability of the two-component developer in the developing device with a toner concentration sensor. The toner replenishing amount is controlled by the toner replenishing device based on the output value of the toner density from the toner density sensor.

  The toner density sensor is connected to the image forming apparatus main body through a connector. As a result, an output signal from the toner density sensor is input to the signal processing circuit via the connector.

  When there is a connection failure of the developing device or a connection failure of the toner concentration sensor due to a connector disconnection or the like, the toner concentration cannot be detected. As a result, the toner tube may become clogged due to excessive replenishment of toner, or toner may be excessively consumed.

  Therefore, when the output level calculated by the pulse output type toner density sensor becomes a high level, it is determined that the developing device is not attached or the developing device connector is not connected (Patent Document 1), or after the power is turned on. When the output value of the toner density is equal to or less than a predetermined value, it is proposed that the subsequent processing is stopped because the connection failure of the toner density sensor has occurred (Patent Document 2).

  On the other hand, an AD converter for converting an analog output signal into a digital signal is used in a signal processing circuit for output signals of a plurality of toner density sensors. In that case, the output signals of a plurality of toner density sensors are sequentially switched and input to one AD converter by analog switches, and AD conversion is performed.

That is, as shown in FIG. 13, in the signal processing circuit 80, the analog switch 31j has eight input ports PT0 to PT7 and one output port PT20, and the input ports PT0 to PT7 are selected by a selection signal (not shown). They are sequentially switched and selectively connected to the output port PT20. A capacitor C1 for holding an input analog signal voltage and a resistor R1 are connected to the input terminal of the A / D converter 320.
JP-A-5-307325 JP-A-10-26876

  In the signal processing circuit 80 shown in FIG. 13, when the output signals of all toner density sensors are normally connected to the input ports PT0 to PT3, the output signals of these toner density sensors are sent to the A / D converter 320. The data is sequentially input normally, and detection corresponding to the input is performed normally. However, when the connection failure of the toner density sensor as described above occurs, the input port becomes high impedance, so that the analog signal voltage of the previous input port stored in the capacitor C1 is discharged. It remains without being cut, and an indefinite voltage due to the residual voltage is detected.

  In order to solve this problem, a pull-down resistor is connected in parallel with the output port PT20 or the capacitor C1 so that the residual voltage of the capacitor C1 becomes a predetermined level or less even when a connection failure of the toner density sensor occurs. It is conceivable to construct a circuit. However, in that case, an output signal lower than a predetermined level detected by the toner density sensor cannot be set as a normal range of toner density, and as a result, a wide range of the detection range (detection sensitivity) of the toner density sensor. It will be difficult to realize this.

  That is, as shown in FIG. 14A, when the predetermined level is 1 volt, for example, the toner concentration is in a normal range when the output signal (output voltage) of the toner concentration sensor is 1 volt. The sensitivity characteristic of the toner density sensor must be set so as to be, for example, 11% or more so as not to fall within ˜11%. As shown in FIG. 14B, when the sensitivity of the toner density sensor is increased to achieve a wide range, when the output signal is 1 volt, the toner density is within the normal range. % Or the toner density sensor cannot be distinguished from each other, and therefore the connection failure of the toner density sensor cannot be detected.

  Further, it is conceivable to reduce the residual voltage by reducing the resistance value of the pull-down resistor. In such a case, it is possible to expand the toner density detection range to a lower voltage. The following problems arise: That is, the output part of the analog output type toner density sensor is usually provided with a smoothing circuit for smoothing the amplitude waveform, and the output resistance (output impedance) of the smoothing circuit is relatively large. When the value is decreased, the sensitivity at the normal detection of the toner density sensor is lowered and the detection capability is lowered.

  Further, the methods of Patent Documents 1 and 2 described above are for detecting the connection state of the toner density sensor corresponding to any one of the color components of yellow, magenta, cyan, and black, for example. It does not propose a method for detecting the connection state of toner density sensors corresponding to all color components easily and at low cost.

  The present invention has been made in view of such a problem, and an object of the present invention is to easily and inexpensively detect the connection state of a toner density sensor.

  An image forming apparatus according to an aspect of the present invention is an image forming apparatus that includes a plurality of developing units and forms an image by an electrophotographic process, and outputs a toner density detection signal based on the toner density in the developing unit. A plurality of input ports and one output port for inputting a plurality of toner concentration detection means, a toner concentration detection signal output from the plurality of toner concentration detection means, and a plurality of predetermined signals other than the toner concentration detection signal Switching means for sequentially switching a plurality of the input ports to the output port and selectively connecting them, and signal processing means for processing a signal appearing at the output ports, the switching means being connected A plurality of toner density detections so that the predetermined signal appears at the output port before each of the toner density detection signals. And the plurality of predetermined signals are connected to the plurality of input ports, and in the signal processing means, immediately after the predetermined signals changed in voltage at different timings of different switching connections by the switching means. For the toner concentration detection means for outputting the toner concentration detection signal appearing at the output port, when the change amount of the toner concentration detection signal based on the change in the voltage of the predetermined signal is equal to or greater than a predetermined value, the toner concentration The detection unit is configured to determine that it is not normally connected to the switching unit.

  Preferably, the predetermined signal includes an image density signal output from an IDC sensor that detects an image density based on a density of a toner image on the image carrier, and a control voltage applied to the IDC sensor by voltage control means. By changing, the voltage of the predetermined signal is changed.

  According to the present invention, the connection state of the toner density sensor can be detected easily and at low cost.

  FIG. 1 is a diagram schematically illustrating an internal configuration of an image forming apparatus 1 according to an embodiment of the present invention, and FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus 1.

  As shown in FIG. 1, an image forming apparatus 1 according to the present embodiment has a tandem image forming unit, and has four colors of yellow (Y), magenta (M), cyan (C), and black (K). A color image is formed by sequentially superposing the toners.

  The image forming apparatus 1 develops an electrostatic latent image formed on a drum-type photoconductor 11 by exposure by a developing device 13, and the obtained toner image is an intermediate transfer as an image carrier by a primary transfer roller 18. The image is transferred to the belt 14 and further transferred to the recording paper S.

  In the image forming apparatus 1, four color imaging units UY, UM, UC, and UK of Y, M, C, and K are arranged in a tandem arrangement, and each color toner image formed by these imaging units U. The (toner image) is superimposed on the intermediate transfer belt 14 and transferred and synthesized. The “imaging unit U” indicates all or part of the “imaging units UY, UM, UC, UK”. The same applies to other elements.

  The surface of the photoreceptor 11 is charged to a predetermined voltage (charging potential) V0 by a charging device (not shown), and an electrostatic latent image is formed by exposure with a print head (not shown). The electrostatic latent image is supplied by toner charged from the developing roller 13a to a potential gap ΔV between the potential of the electrostatic latent image and the developing bias voltage Vdc by the developing roller 13a to which the developing bias voltage Vdc is applied. A toner image is formed and visualized.

  The toner image visualized on the surface of the photoreceptor 11 is primarily transferred to the intermediate transfer belt 14 by the primary transfer roller 18. The toner remaining on the photoreceptor 11 is scraped off by a cleaner (not shown). The toner image on the intermediate transfer belt 14 is secondarily transferred onto the recording sheet S by the secondary transfer roller 19. The recording paper S is fixed by the fixing unit 20 and is discharged onto the paper discharge tray 21 as an electrophotographic image.

  Further, the image forming apparatus 1 includes optical IDC sensors (density detection sensors) 22Y, 22M, and 22C that detect the density of the toner image on the intermediate transfer belt 14 (image density at the time of transfer to the recording paper S). 22K is provided. That is, the IDC sensors 22Y, 22M, 22C, and 22K are reflection type photosensors that irradiate the surface of the intermediate transfer belt 14 and detect the amount of light that is reflected and returned. The IDC sensors 22Y, 22M, 22C, and 22K detect image densities of color components of yellow, magenta, cyan, and black, respectively, and output density signals SIY, SIM, SIC, and SIK based on the image densities. The configuration of the IDC sensors 22Y, 22M, 22C, and 22K will be described later.

  When the density of the toner image on the intermediate transfer belt 14 is low, that is, when the amount of toner on the intermediate transfer belt 14 is low, the amount of light reflected by the intermediate transfer belt 14 is returned to increase and the amount of light increases, that is, when the density of the toner image is high. When there is a large amount of light, the light is blocked by the toner and the amount of reflected light decreases. In this way, the IDC sensors 22Y, 22M, 22C, and 22K confirm the state of the surface of the intermediate transfer belt 14. Image adjustment is performed by controlling the light amount of a laser diode (not shown) of the print head, developing conditions in the developing device 13, and the like according to the density of the toner image detected by the IDC sensors 22Y, 22M, 22C, and 22K. . Actually, the IDC sensors 22Y, 22M, 22C, and 22K detect the density for each pattern (toner patch) of Y, M, C, and K created for image adjustment.

  Further, the image forming apparatus 1 is provided with a toner replenishing unit (toner bottle) 12 for supplying toner to a developing device (including a developing roller 13a) 13.

  In the vicinity of the developing device 13, a toner concentration sensor 15 for detecting the toner concentration in the developing device 13 is disposed. The toner concentration sensor 15 is connected to the control unit 100 via connectors CN1 and CN2 and electric wires.

  The control unit 100 of the image forming apparatus 1 includes a CPU (Central Processing Unit), a memory, and other peripheral circuit elements. When the connector CN1 and the connector CN2 are connected, the control unit 100 correctly receives the output signal of the toner concentration sensor 15, detects the toner concentration based on the output signal, and detects the toner concentration based on the detection result. Control the replenishment amount.

  As will be described in detail later, in the present embodiment, the connection state (connected and disconnected) between the connector CN1 and the connector CN2 can be detected easily and at low cost. For example, when the connection between the connector CN1 and the connector CN2 is disconnected at the time of replacement of the imaging unit U, the connection state can be easily and reliably confirmed after the operation.

  Here, an outline of functions of the image forming apparatus 1 will be described. As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment includes developing devices 13Y, 13M, 13C, and 13K that respectively include toners and carriers corresponding to the respective color components of yellow, magenta, cyan, and black. An image forming apparatus for forming an image by a process, and a toner density sensor 15Y that outputs detection signals (output signals) KSY, KSM, KSC, and KSK based on the toner density in the developing devices 13Y, 13M, 13C, and 13K. , 15M, 15C, 15K, and toner density ports PT1, PT3, PT5, PT7 (described later) for inputting detection signals KSY, KSM, KSC, KSK, respectively, and density signals SIY, SIM, SIC, SIK, respectively. Image density ports PT0, PT2, PT4, PT6 (described later) and 1 An output port PT20 (to be described later), and an analog switch 31 for selectively switching the toner density ports PT1, PT3, PT5, PT7 and the image density ports PT0, PT2, PT4, PT6 by sequentially switching to the output port PT20. And a signal processing unit 32 for processing a signal appearing at the output port PT20.

  In the image forming apparatus 1, each of the density signals SIY, SIM, SIC, and SIK appears at the output port PT20 before each of the detection signals KSY, KSM, KSC, and KSK when the analog switch 31 sequentially switches connections. In addition, detection signals KSY, KSM, KSC, KSK and density signals SIY, SIM, SIC, SIK are connected to toner density ports PT1, PT3, PT5, PT7 and image density ports PT0, PT2, PT4, PT6, respectively.

  Further, in the signal processing unit 32, the toner concentration sensor 15 that outputs the detection signal KS that appears at the output port PT20 immediately after the concentration signal SI that is changed so that the control voltage VG is different at each timing of different switching connections by the analog switch 31. When the change amount of the detection signal KS based on the change of the density signal SI is equal to or greater than a predetermined value, it is determined that the toner concentration sensor 15 is not normally connected to the analog switch 31. In this case, the operation panel 33 displays a message indicating that the connection is poor on the liquid crystal display. Thereby, the user or service person can recognize the connection failure of the toner density sensor 15.

  The function of the signal processing unit 32 is realized in software by the CPU of the control unit 100 executing an appropriate program or in combination with an appropriate hardware circuit.

  An analog switch or a multiplexer is used as the switching means. Many of these analog switches or multiplexers have a plurality of input ports, for example, 2, 4, 8, 12, 16, etc. input ports and one output port.

  As the signal processing unit 32, an A / D converter, a CPU, a RAM, or the like is used. These analog switches or multiplexers, A / D converters, CPUs, RAMs, and the like may be used as a whole or part of them as a microcomputer or ASIC (Application Specific Integrated Circuit).

  3 is a circuit diagram showing an example of the configuration of the toner density sensor 15, FIG. 4 is a diagram showing the relationship between the toner density and the detection signal when the control voltage VS is changed, and FIG. 5 is a schematic diagram of the IDC sensor 22. FIG. 6 is a diagram illustrating the configuration, FIG. 6 is an explanatory diagram illustrating the relationship between the image density and the voltage of the density signal SI when the control voltage VG is changed, and FIG. 7 illustrates an example of the configuration of the analog switch 31 and the signal processing unit 32. FIG.

  As illustrated in FIG. 3, the toner density sensor 15 includes an oscillation circuit 150, a differential transformer 151, an amplifier 152, a phase comparator 153, a smoothing circuit 154, an output terminal 155, and a sensitivity control unit 156.

  The differential transformer 151 includes a drive coil LT1, a reference coil LT2, and a detection coil LT3. The reference coil LT2 and the detection coil LT3 are differentially wound. By supplying an alternating voltage (high frequency voltage) of about several hundred kHz to the drive coil LT1 by the oscillation circuit 150, the voltage (reference voltage) V2 is applied to the reference coil LT2, and the voltage (detection voltage) V3 is applied to the detection coil LT3. Each occurs. These voltages V2 and V3 have substantially the same value or the same phase, and the magnitude of the differential output signal Vt is almost zero, but the value or phase of the voltage V3 of the detection coil LT3 depending on the magnetic permeability of the developer. Slightly changes, and the minute change ΔV3 is obtained as the differential output signal Vt. Since both the developer concentration and the magnetic permeability change depending on the ratio between the toner amount and the carrier amount, the toner concentration is detected by detecting the magnetic permeability.

  The differential output signal Vt output from the differential transformer 151 is amplified by an amplifier 152, compared with a reference voltage by a phase comparator 153, and phase discrimination is performed. The output from the phase comparator 153 is smoothed by a smoothing circuit 154 including a resistor Rh and a capacitor Ch, and is output from an output terminal 155. As a result, a DC analog signal having a voltage value corresponding to the toner density is obtained as the detection signal KS.

  In order to perform phase discrimination of the differential output signal Vt, a reference voltage having a phase difference of 90 degrees is applied to the differential output signal Vt, but the sensitivity control unit 156 controls the control voltage from the voltage control unit 30a. The reference voltage is controlled according to VG, and the sensitivity characteristic of the toner density sensor 15 is adjusted.

  The voltage control unit 30a is a part of the control unit 100, and outputs the control voltage VS independently to the toner density sensor 15 of each color. That is, the sensitivity characteristics of the toner density sensors 15 of the respective colors are adjusted by the control voltage VS output from the voltage control unit 30a, and accordingly, the voltage level of each detection signal KS is adjusted. That is, it is possible to calibrate the detection signal KS of the toner density sensor 15 of each color by the control voltage VS from the voltage control unit 30a.

  Note that the oscillation circuit 150, the amplifier 152, the sensitivity control unit 156, and the like may be provided independently of each other, but are configured so that their functions are obtained as a whole by connecting a plurality of circuit elements to each other. It is also possible. For example, the sensitivity control unit 156 may be configured using a resistor, a capacitor, a logic element, and the like so that a part of the output of the oscillation circuit 150 is phase-adjusted and applied to the reference coil LT2.

  As shown in FIG. 4, in the toner density sensor having a function capable of changing the output voltage of the detection signal KS by changing the control voltage VS, the toner density and the detection signal KS are proportional to each other. As the value increases, the detection signal KS decreases linearly. By changing the control voltage VS, the voltage value of the detection signal KS changes even if the toner density is the same. When the control voltage VS is increased, the detection signal KS is increased, and when the control voltage VS is decreased, the detection signal KS is decreased. In general, the control voltage VS is adjusted for each toner concentration sensor of each color so that an appropriate toner concentration range is detected. For example, the control voltage VS is adjusted, and the calibration is performed so that the detection signal KS becomes, for example, 2.5V when the toner density is 7% which is an ideal value. From the viewpoint of improving or maintaining the image quality, it is preferable to set the normal range of the toner density to 4% to 11%, for example.

  As shown in FIG. 5, the IDC sensor 22 includes a light emitting element 220 and a light receiving element 221 for detecting the image density of the toner pattern TP formed on the intermediate transfer belt 14. That is, when the light emitted from the light emitting element 220 is reflected by the toner pattern TP and returned by the light receiving element 221, the image density of the toner pattern TP is detected.

  The light quantity control unit 30b is a part of the control unit 100, and outputs a control voltage VG independently to the light emitting element 220 of the IDC sensor 22 of each color. The light quantity control unit 30b can control the amount of light emitted from the light emitting element 220 by changing the control voltage VG. Thereby, the amount of light received by the light receiving element 221 can be controlled. Therefore, the output voltage of the IDC sensor 22 can be controlled.

  As shown in FIG. 6, the sensitivity characteristics of the IDC sensors 22 of the respective colors are adjusted by the control voltage VG output from the light amount control unit 30b, and accordingly, the voltage level of each density signal SI is adjusted. . That is, it is possible to calibrate the density signal SI of the IDC sensor 22 of each color by the control voltage VG from the light quantity control unit 30b. In the present embodiment, it is detected whether or not the connection state of the toner density sensor 15 of each color is normal by changing the control voltage VG of the light amount control unit 30b. This will be described in detail later.

  Next, the analog switch 31 and the signal processing unit 32 will be described.

  As shown in FIG. 7, the analog switch 31 has eight input ports PT0 to PT7 and one output port PT20, and these input ports are controlled by the CPU 321 so that these input ports are PT0, PT1, PT2, PT3, PT4. , PT5, PT6, PT7 in this order, and selectively connected to the output port PT20. After the input port PT7, the process returns to the input port PT0 and is switched again in the same order.

  The input ports PT0 to PT7 are, in order from the upper port, from IDC sensor 22Y, toner density sensor 15Y, IDC sensor 22M, toner density sensor 15M, IDC sensor 22C, toner density sensor 15C, IDC sensor 22K, and toner density sensor 15K. Each output signal (hereinafter sometimes referred to as “sensor signal”) is connected so as to be input. Therefore, when the input ports PT0 to PT7 are sequentially switched, the respective signals appear at the output port PT20 in this order. The input ports PT0, PT2, PT4, and PT6 may be referred to as image density ports, and the input ports PT1, PT3, PT5, and PT7 may be referred to as toner density ports.

  A pull-down resistor R2 for discharging the residual voltage of the capacitor C1 is connected to the output port PT20. The pull-down resistor R2 can discharge the residual voltage faster as the resistance value is smaller, but cannot be made too small due to the relationship with the output impedance of each sensor. That is, when the connection state of the toner density sensor 15 is good, the smaller the resistance value of the pull-down resistor R2, the lower the output voltage based on the toner density and the lower the detection sensitivity of the toner density sensor 15. . In the present embodiment, the range is set to about several hundred kΩ to several MΩ, for example, 1 MΩ.

  The signal appearing at the output port PT20 charges the capacitor C1 through the resistor R1 and is input to the A / D converter 320. The A / D converter 320 converts the analog signal voltage (peak voltage) held (sampled and held) by the capacitor C1 into a digital signal (digital data).

  The CPU 321 sequentially switches the input ports PT0 to PT7 of the analog switch 31 in, for example, about several microseconds, takes in digital data of each sensor signal, and performs necessary processing based on the respective digital data.

  The processing of the CPU 321 includes, for example, a toner density control process for controlling the toner density of the developing device 13 based on the toner density detected by the toner density sensor 15, and the temperature and humidity detected by a temperature sensor and a humidity sensor (not shown). Based on the image stabilization processing based on necessity, the image density control processing based on the toner pattern density detected by the IDC sensor 22, and the connection state of the toner density sensor 15 for each color as described above is normal. Connection state determination processing for detecting whether or not, and various other processing.

  The IDC sensor 22 can change the concentration signal SI, which is its output signal voltage, almost instantaneously by changing the control voltage VG.

  In the present embodiment, each time the sampling of the detection signal KS of the toner density sensor 15, that is, the digital data of the detection signal KS is taken in the connection state determination process, each image density port PT0, By changing the control voltage VG of the IDC sensor 22 that outputs the density signal SI input to PT2, PT4, and PT6, and comparing the change amount of the detection signal KS with the predetermined value th, Determine whether the connection is good or bad.

  Further, the control voltage VG may be changed every time the digital data of the detection signal KS is taken a plurality of times. In this case, the detection accuracy is improved by using an average value or median value of a plurality of samplings.

  In the present embodiment, the predetermined value th is set to a range of about 1 volt to a sufficient number of several volts, for example, 0.2 V in a specific example.

  Next, the connection state determination process will be described with reference to the drawings.

  FIG. 8 is a diagram schematically showing the flow of the connection state determination process, FIG. 9 is a diagram showing the sampling timing in the connection state determination process, and FIG. 10 is the output voltage and control voltage of the sensor signal before the control voltage VG is changed. FIG. 11 is a flowchart for explaining a connection state determination process for explaining the output voltage of the sensor signal after changing VG.

  As shown in FIG. 8, first, a control voltage (hereinafter referred to as “pre-control voltage”) VG1 is applied to the IDC sensor 22 by the light quantity control unit 30b at time t1. In the present embodiment, the pre-control voltage VG1 is, for example, 0V. A period from time t1 to time t2 (for example, 220 ms) is a waiting time for stabilizing the output voltage of each sensor.

  When the time t2 is reached, sampling of the output voltage of each sensor at the pre-control voltage VG1 is started. The period from time t2 at which sampling is started to time t3 at which sampling is ended is, for example, 80 ms.

  At time t3, the light control unit 30b changes the front control voltage VG1 to the rear control voltage VG2. The post control voltage VG2 is, for example, 12.8V. A period from time t3 to time t4 (for example, 220 ms) is a waiting time for stabilizing the output voltage of each sensor.

  When time t4 is reached, sampling of the output voltage of each sensor at the post-control voltage VG2 is started. The period from time t4 when sampling is started to time t5 when sampling is ended is, for example, 80 ms. In the present embodiment, the front control voltage VG1 or the rear control voltage VG2 is applied to each IDC sensor 22 at the same timing.

  Hereinafter, sampling in the pre-control voltage VG1 and the post-control voltage VG2 will be described.

  As described above, the switching by the analog switch 31 is performed by the image density port PT0, the toner density port PT1, the image density port PT2, the toner density port PT3, the image density port PT4, the toner density port PT5, the image density port PT6, and the toner density. This is done in the order of port PT7.

  Therefore, as shown in FIG. 9, the order of the sensor signals input to the signal processing unit 32 during the period from time t2 to time t3 (period during which the previous control voltage VG1 is applied) is the density signal SIY, detection The signal KSY, the density signal SIM, the detection signal KSM, the density signal SIC, the detection signal KSC, the density signal SIK, and the detection signal KSK. The order of the sensor signals input to the signal processing unit 32 in the period from time t4 to time t5 (period in which the post-control voltage VG2 is applied) is the same.

  In this embodiment, sampling of each sensor signal in each of the above periods is performed, for example, 3 to 10 times (three times are shown in FIG. 9), and the average value of these output voltages is the output of each sensor signal in each of the above periods. The voltage.

  Here, the connector CN1Y on the toner concentration sensor 15Y side and the connector CN2Y on the control unit 100 side are electrically connected, and the connector CN1M on the toner concentration sensor 15M side and the connector CN2M on the control unit 100 side are electrically connected. As an example of the case where they are not connected, changes in the voltages of the detection signals KSY and KSM of the toner density sensors 15Y and 15M will be described.

  As shown in FIG. 10A, when the connection failure of the toner density sensor 15Y occurs, when the front control voltage VG1 is changed to the rear control voltage VG2 by the light quantity control unit 30b, the voltage of the detection signal KSY. Also changes.

  On the other hand, as shown in FIG. 10B, when the connection state of the toner density sensor 15M is good, even if the front control voltage VG1 is changed to the rear control voltage VG2 by the light amount control unit 30b, The voltage of the detection signal KSM does not change.

  In FIG. 11, as described above, first, the pre-control voltage VG1 is applied to the light emitting element 220 of the IDC sensor 22 by the light quantity control unit 30b (# 1). Then, the output voltage of each sensor is sampled from time t2 to time t3 (# 2).

  Next, the control voltage VG applied to the IDC sensor 22 by the light quantity control unit 30b is changed from the front control voltage VG1 to the rear control voltage VG2 (# 3). Then, the output voltage of each sensor is sampled from time t4 to time t5 (# 4).

  Subsequently, it is determined whether or not the difference between the output voltage at the front control voltage VG1 and the output voltage at the rear control voltage VG2 is less than a predetermined value th that is a threshold (# 5).

  When the difference is equal to or greater than the predetermined value th (No in # 5), a trouble message indicating that the connection state of the toner density sensor 15Y is not normal is displayed on the liquid crystal display of the operation panel 33 (# 6). Thereby, the user or the service person can recognize the connection failure.

  If the difference is less than the predetermined value th (Yes in # 5), whether the difference between the output voltage at the front control voltage VG1 and the output voltage at the rear control voltage VG2 for the toner density sensor 15M is less than the predetermined value th. It is determined whether or not (# 7).

  When the difference is equal to or greater than the predetermined value th (No in # 7), a trouble message indicating that the connection state of the toner density sensor 15M is not normal is displayed on the liquid crystal display of the operation panel 33 (# 8).

  If the difference is less than the predetermined value th (Yes in # 7), is the difference between the output voltage at the front control voltage VG1 and the output voltage at the rear control voltage VG2 less than the predetermined value th for the toner density sensor 15C? It is determined whether or not (# 9).

  When the difference is equal to or greater than the predetermined value th (No in # 9), a trouble message indicating that the connection state of the toner density sensor 15C is not normal is displayed on the liquid crystal display of the operation panel 33 (# 10).

  If the difference is less than the predetermined value th (Yes in # 9), is the difference between the output voltage at the front control voltage VG1 and the output voltage at the rear control voltage VG2 for the toner density sensor 15K less than the predetermined value th? It is determined whether or not (# 11).

  When the difference is equal to or greater than the predetermined value th (No in # 11), a trouble message indicating that the connection state of the toner density sensor 15K is not normal is displayed on the liquid crystal display of the operation panel 33 (# 12).

  When the difference is less than the predetermined value th (Yes in # 11), since the connection states of the toner density sensors 15Y, 15M, 15C, and 15K are all good, the toner and the carrier are agitated in each developing device 13. Implemented (# 13). As described above, when any one of the toner density sensors 15Y, 15M, 15C, and 15K is not in a normal connection state, the stirring process is not performed and a trouble message is displayed. This prevents the developing device 13 from performing the stirring process with an inappropriate toner concentration.

(Effect in this embodiment)
As a method of detecting the connection state of the toner concentration sensor, there is a method of changing the applied voltage to the toner concentration sensor and determining the connection state based on the output voltage before and after the change. In this embodiment, the output voltage is changed. Even when an expensive toner concentration sensor having the function of using the toner concentration sensor is not used, the connection state of the toner concentration sensor 15 is detected using the following method. Therefore, it is advantageous in terms of cost.

  That is, in this embodiment, before the detection signals KSY, KSM, KSC, and KSK input to the toner density ports PT1, PT3, PT5, and PT7 appear at the output port 20, the image density ports PT0, PT2,. The input ports PT0 to PT7 are sequentially switched by the analog switch 31 so that the density signals SIY, SIM, SIC and SIK input to the PT4 and PT6 respectively appear at the output port 20.

  Then, when the control voltage VG of the IDC sensor 22 is changed and the output voltage is changed, when the output voltage of the detection signal KS changes along with the change of the output voltage of the IDC sensor 22, the previous one ( The connection state of the toner density sensor 15 is not normal, assuming that it is affected by the residual voltage (undefined voltage) of the density signal SI input to any one of the image density ports PT0, PT2, PT4, and PT6, which is one level higher. Judge. On the other hand, when the output voltage of the detection signal KS does not change before and after the change of the output voltage of the IDC sensor 22, it is determined that the connection state of the toner density sensor 15 is good.

  By such a method, the connection state of the toner density sensor 15 can be accurately detected.

  Further, in this embodiment, it is not necessary to provide a plurality of A / D converters 320 that A / D convert each sensor signal by switching the input ports PT0 to PT7 by the analog switch 31. Therefore, it is further advantageous in terms of cost.

  In this embodiment, the connection state of the toner density sensor 15 can be easily detected by a method of changing the control voltage VG to the IDC sensor 22.

  Further, when the method of sequentially inputting the detection signals KSY, KSM, KSC, and KSK from the toner density sensors 15Y, 15M, 15C, and 15K to the input port of the analog switch 31, the control voltage VS is changed. Therefore, the timing of changing the control voltage VS needs to be shifted for each toner density sensor 15. As a result, by shifting the timing, the processing time for detecting the connection state of the toner density sensor 15 becomes longer. For example, the initial warm-up time of the image forming apparatus 1 becomes longer. Accordingly, since it is not necessary to shift the timing, it is possible to prevent the initial warm-up time and the like from becoming long.

  As described above, according to the image forming apparatus 1 of the present embodiment, the connection state of the toner density sensor 15 can be detected more easily and at a lower cost.

(Other embodiments)
The sensor signal input method for the toner density ports PT1, PT3, PT5, PT7 and the image density ports PT0, PT2, PT4, PT6 of the analog switch 31 described in the above embodiment (FIG. 7) may be as follows. .

  FIG. 12 is a diagram showing another example of a configuration for inputting a signal to each port of the analog switch 31.

  As shown in FIG. 12, the analog switch 31a has image density ports PT0 and PT2, toner density ports PT1 and PT3, predetermined ports PT40, PT41, PT42, and PT43 as input ports, and an output port PT20.

  The density signal SIY from the IDC sensor 22Y is input to the image density port PT0 of the analog switch 31a, the detection signal KSY or the detection signal KSM is input to the toner density port PT1, and the image density port PT2 is input from the IDC sensor 22M. The density signal SIM is inputted, the detection signal KSC or the detection signal KSK is inputted to the toner density port PT3, the signal SA from the A sensor 40 is inputted to the predetermined port PT40, and the B sensor 41 is inputted to the predetermined port PT41. The signal SB is input, the signal SC from the C sensor 42 is input to the predetermined port PT42, and the signal SD from the D sensor 43 is input to the predetermined port PT43. The A sensor 40, the B sensor 41, the C sensor 42, and the D sensor 43 may be a temperature sensor that measures the temperature in the apparatus, a humidity sensor that measures humidity, or the like.

  In this example, the detection signal KSY from the toner density sensor 15Y and the detection signal KSM from the toner density sensor 15M are selectively switched by the first switching element 50 made of an analog switch or the like and input to the toner density port PT1. The Further, the detection signal KSC from the toner density sensor 15C and the detection signal KSK from the toner density sensor 15K are selectively switched by the second switching element 51 made of an analog switch or the like and input to the toner density port PT3.

  By the analog switch 31a, the input port is switched in the order of the image density port PT0, the toner density port PT1, the image density port PT2, the toner density port PT3, the predetermined port PT40, the predetermined port PT41, the predetermined port PT42, and the predetermined port PT43. It is selectively connected to port PT20. After the predetermined port 43, the process returns to the image density port PT0 and is switched again in the same order.

  As described above, even when the number of IDC sensors 22 provided in the image forming apparatus 1 is small, the connection state of the toner density sensor 15 can be detected by providing the first switching element 50 and the second switching element 51. It becomes possible.

  In the above embodiment, the concentration signal SI from the IDC sensor 22 that can change the output voltage is input before the input of the detection signal KS is switched. However, the output voltage can be changed. Signals from other possible voltage output circuits may be input.

  In the above embodiment, the connection state of the toner density sensor 15 is detected by changing the control voltage VG of the IDC sensor 22, but the present invention is also applied to the case of detecting the connection state of other sensors. It is possible to apply.

1 is a diagram schematically illustrating an internal configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a block diagram illustrating a functional configuration of the image forming apparatus. FIG. FIG. 3 is a circuit diagram illustrating an example of a configuration of a toner density sensor. It is a figure which shows the relationship between a toner density | concentration when a control voltage is changed, and a detection signal. It is a figure which shows the schematic structure of an IDC sensor. It is explanatory drawing which shows the relationship between the image density at the time of changing a control voltage, and the voltage of a density signal. It is a figure which shows an example of a structure of an analog switch and a signal processing part. It is a figure which shows the flow of a connection state determination process roughly. It is a figure which shows the timing of the sampling in a connection state determination process. It is a figure for demonstrating the output voltage of the sensor signal after changing the output voltage of the sensor signal before changing a control voltage, and a control voltage. It is a flowchart which shows a connection state determination process. It is a figure which shows the other example of the structure which inputs the signal with respect to each input port of an analog switch. It is a figure which shows the structure of the conventional analog switch and a signal processing circuit. FIG. 6 is a diagram for explaining a detection range of a toner density sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Photoconductor 13 Developing device (Developing means)
15 Toner density sensor (toner density detection means)
22 IDC sensor 30b Light quantity control unit (voltage control means)
31 Analog switch (switching means)
32 Signal processing unit (signal processing means)
100 Control Unit 320 A / D Converter (A / D Conversion Unit)
321 CPU (processor)
C1 Capacitor KS detection signal (toner concentration detection signal)
PT0, PT2, PT4, PT6 Image density port PT1, PT3, PT5, PT7 Toner density port SI Density signal (image density signal)
VG control voltage VG1 before control voltage VG2 after control voltage th predetermined value

Claims (6)

An image forming apparatus comprising a plurality of developing means and forming an image by an electrophotographic process,
A plurality of toner density detection means for outputting a toner density detection signal based on the toner density in the developing means;
A plurality of input ports each having a plurality of input ports and one output port for inputting toner concentration detection signals output from the plurality of toner concentration detection means and a plurality of predetermined signals other than the toner concentration detection signals; Switching means for sequentially switching the ports to the output ports and selectively connecting them;
Signal processing means for processing a signal appearing at the output port;
Have
The plurality of toner concentration detection signals and the plurality of predetermined signals are a plurality of the plurality of predetermined signals so that the predetermined signal appears at the output port before each of the toner concentration detection signals when the switching unit sequentially switches the connection. Connected to the input port,
In the signal processing means,
For the toner concentration detection means for outputting the toner concentration detection signal appearing at the output port immediately after the predetermined signal changed so that the voltage differs at each timing of different switching connections by the switching means, the voltage of the predetermined signal When the amount of change in the toner density detection signal based on the change in the value is equal to or greater than a predetermined value, it is determined that the toner density detection means is not normally connected to the switching means.
An image forming apparatus. The predetermined signal includes an image density signal output from an IDC sensor that detects an image density based on the density of the toner image on the image carrier,
By changing the control voltage applied to the IDC sensor by the voltage control means, the voltage of the predetermined signal is changed to be different.
The image forming apparatus according to claim 1. The signal processing means includes
A capacitor for holding the signal appearing at the output port;
A / D conversion means for converting the signal held in the capacitor into a digital signal;
A processor for processing the digital signal;
The image forming apparatus according to claim 1. Before the agitation operation of the toner and the carrier is performed in the plurality of developing units, the voltage control unit changes the control voltage, so that the signal processing unit can normally operate the toner concentration detection unit with the switching unit. Determine if it is not connected,
The image forming apparatus according to claim 1. A connection state determination method for determining a connection state of a plurality of toner density detection units used in an image forming apparatus that includes a plurality of development units and forms an image by an electrophotographic process,
Outputting a toner density detection signal based on the toner density in the developing means by a plurality of toner density detecting means;
The switching means having a plurality of input ports and one output port for inputting a plurality of toner density detection signals output from the plurality of toner density detection means and a plurality of predetermined signals other than the toner density detection signals, respectively. Sequentially switching a plurality of the input ports to the output port so that the predetermined signal appears at the output port before the toner concentration detection signal of
For the toner concentration detection means for outputting the toner concentration detection signal appearing at the output port immediately after the predetermined signal changed so that the voltage differs at each timing of different switching connections by the switching means, the voltage of the predetermined signal Determining that the toner density detection means is not normally connected to the switching means when the amount of change in the toner density detection signal based on the change is greater than or equal to a predetermined value.
A connection state determination method for toner density detection means. A connection state determination method for determining a connection state of a sensor,
The predetermined signal is output before the sensor signal by switching means having a plurality of input ports and one output port for inputting a sensor signal output from the sensor and a predetermined signal other than the sensor signal. Selectively switching a plurality of the input ports to the output ports so as to appear at the ports; and
The sensor that outputs the sensor signal that appears at the output port immediately after the predetermined signal that has been changed so that the voltage differs at each timing of different switching connections by the switching means, based on the change in the voltage of the predetermined signal. Determining that the sensor is not normally connected to the switching means when the change amount of the sensor signal is equal to or greater than a predetermined value.
A method for determining a connection state of a sensor.

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