JP2009145701A - Image forming device, and method of determining connection state of toner density 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 sensor 15 for outputting a detection signal KS based on a toner density in a developing device 13, by impressing a control voltage VS by a voltage control part 30, an analog switch 31 having a plurality of input ports for inputting the detection signal KS output from the toner density sensor 15 and a signal other than the detection signal KS and one output port, and for switching each of the plurality of input 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 detection signal KS of each color and the signal other than the detection signal KS are connected to the plurality of input ports, so as to make the signal other than the detection signal KS appear in the output port in advance to the detection signal KS of each color, when the analog switch 31 switches sequentially the connection. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  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. 11, 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. 11, when the output signals of all the 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. 12A, when the predetermined level is, for example, 1 volt, 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%. If, as shown in FIG. 12B, the sensitivity of the toner density sensor is increased to widen the range, the output signal is 1 volt and the toner density is within a normal range of 10 volts. % 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. A plurality of density detection means for outputting density detection signals based on the toner density, a plurality of input ports for inputting density detection signals output from the plurality of density detection means and signals other than the density detection signals, and 1 A switching means having one output port and sequentially switching a plurality of the input ports to the output port, and a signal processing means for processing a signal appearing at the output port, the switching means A plurality of the signals so that signals other than the density detection signal appear at the output port before each density detection signal when the connection is sequentially switched. Signals other than the degree detection signal and the concentration detection signal are connected to the plurality of input ports, and the control voltage is changed to be different at each timing of different switching connections by the switching means in the signal processing means. For the concentration detection means, when the change amount of the concentration detection signal based on the change in the control voltage is equal to or less than a predetermined value, it is determined that the concentration detection means is not normally connected to the switching means. It is configured.

  Preferably, the signal processing means processes the digital signal, a capacitor for holding the signal appearing at the output port, an A / D conversion means for converting the signal held in the capacitor into a digital signal, and the like. And a processor.

  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 is provided with optical IDC sensors (density detection sensors) 22 and 23 for detecting the density of the toner image on the intermediate transfer belt 14 (image density at the time of transfer to the recording paper S). ing. In other words, the IDC sensors 22 and 23 are reflection type photosensors that detect the amount of light that is reflected and reflected by irradiating the surface of the intermediate transfer belt 14 with light. The IDC sensor 22 and the IDC sensor 23 detect different color densities.

  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 22 and 23 confirm the state of the surface of the intermediate transfer belt 14. Depending on the density of the toner image detected by the IDC sensors 22 and 23, 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. Actually, the IDC sensors 22 and 23 detect the density of each pattern (toner patch) of Y, M, C, and K created for image adjustment.

  The image forming apparatus 1 is provided with a temperature sensor 24 for measuring the temperature in the apparatus and a humidity sensor 25 for measuring the relative humidity (humidity) in the apparatus. 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 that forms an image by a process, and a detection signal (output signal) KSY based on the toner density in the developing devices 13Y, 13M, 13C, and 13K when the control voltage VS is applied by the voltage control unit 30 , KSM, KSC, and KSK, respectively, toner density sensors 15Y, 15M, 15C, and 15K, and toner density sensors 15Y, 15M, 15C, and 15K, and detection signals KSY, KSM, KSC, and KSK, and the detection signals, respectively. Plural for inputting signals other than KSY, KSM, KSC, KSK An analog switch 31 having input ports PT0 to PT7 (described later) and one output port PT20 (described later), and sequentially switching the input ports PT0 to PT7 to the output port PT20, and the output port PT20 And a signal processing unit 32 for processing the appearing signal.

  In the image forming apparatus 1, when the analog switch 31 sequentially switches the connection, signals other than the detection signals KSY, KSM, KSC, KSK are output to the output port PT20 before each of the detection signals KSY, KSM, KSC, KSK. As shown, detection signals KSY, KSM, KSC, KSK and signals other than detection signals KSY, KSM, KSC, KSK are connected to a plurality of input ports PT0-7.

  Further, in each of the toner density sensors 15Y, 15M, 15C, and 15K in which the control voltage VS is changed in the signal processing unit 32 so that the control voltage VS is different at each timing of the different switching connection by the analog switch 31, it is based on the change in the control voltage VS. If the amount of change in the detection signals KSY, KSM, KSC, and KSK is less than or equal to a predetermined value, it is determined that one of the toner density sensors 15Y, 15M, 15C, and 15K 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.

  In the present embodiment, as signals other than the detection signals KSY, KSM, KSC, and KSK, the temperature signal ST from the temperature sensor 24, the humidity signal SH from the humidity sensor 25, the concentration signal SN1 from the IDC sensor 22, and the IDC The density signal SN2 from the sensor 23 is used.

  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. In the following, for these multiple input ports, the input port to which the detection signal (density detection signal) KS of the toner density sensor 15 as the density detection means is input is “density port”, and the other ports are input to other signals. May be described as “predetermined 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 concentration sensor 15, FIG. 4 is a diagram showing the relationship between the toner concentration and the detection signal KS when the control voltage VS is changed, and FIG. 5 is the analog switch 31 and signal processing. 3 is a diagram illustrating an example of a configuration of a 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 30. The reference voltage is controlled according to VS, and the sensitivity characteristic of the toner density sensor 15 is adjusted.

  The voltage control unit 30 is a part of the control unit 100 and outputs a 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 30, 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 30. 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 VS of the voltage control unit 30. This will be described in detail later.

  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, the toner density and the detection signal KS are proportional, and the detection signal KS decreases linearly as the toner density increases. 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. The control voltage VS is adjusted for each toner density sensor 15 of each color, and is adjusted so that an appropriate toner density 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.

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

  As shown in FIG. 5, the analog switch 31 has eight input ports PT0 to PT7 and one output port PT20. Under the control of the CPU 321, the input ports PT0 to PT7 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.

  To the input ports PT0 to PT7, the temperature sensor 24, the toner concentration sensor 15Y, the humidity sensor 25, the toner concentration sensor 15M, the IDC sensor 22, the toner concentration sensor 15C, the IDC sensor 23, and the toner concentration sensor 15K are sequentially output. Each signal (hereinafter may be 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.

  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 the temperature sensor 24 and the humidity sensor 25. Based on the image stabilization processing performed as necessary, the image density control processing based on the toner pattern density detected by the IDC sensors 22 and 23, 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.

  Note that the temperature sensor 24, the humidity sensor 25, and the IDC sensors 22 and 23 usually do not have a sudden change in the voltage of signals output from them, and the voltage of the signal also increases depending on the state of control by the CPU 321. It is a sensor with a stable output signal voltage that does not change. For example, the output signal voltage hardly changes in a short time such as several milliseconds or several seconds.

  On the other hand, the toner concentration sensor 15 can change the detection signal KS, which is the output signal voltage, almost instantaneously by changing the control voltage VS.

  In this embodiment, the control voltage VS is changed each time the detection signal KS of the toner concentration sensor 15 is sampled, that is, the digital data of the detection signal KS is taken in the connection state determination process, and the detection signal KS is thereby detected. By comparing the amount of change with a predetermined value th, it is determined whether the connection state of each toner density sensor 15 is good or bad.

  Alternatively, the control voltage VS may be changed every time 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.

  6 is a diagram schematically illustrating the flow of the connection state determination process, FIG. 7 is a diagram illustrating the timing of sampling in the connection state determination process, and FIG. 8 is an output voltage and control voltage of the sensor signal before the control voltage VS is changed. FIG. 9 is a flowchart for explaining the connection state determination processing. FIG. 9 is a diagram for explaining the output voltage of the sensor signal after changing VS.

  As shown in FIG. 6, first, a control voltage (hereinafter referred to as “pre-control voltage”) VS1 is applied to the toner density sensor 15 by the voltage control unit 30 at time t1. In the present embodiment, the pre-control voltage VS1 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 VS1 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 voltage control unit 30 changes the pre-control voltage VS1 to the post-control voltage VS2. The post control voltage VS2 is 12.8V, for example. 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 VS2 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 pre-control voltage VS1 or the post-control voltage VS2 is applied to the toner density sensors 15Y, 15M, 15C, and 15K at the same timing.

  Hereinafter, sampling in the pre-control voltage VS1 and the post-control voltage VS2 will be described.

  As described above, switching by the analog switch 31 is performed in the order of the predetermined port PT0, the concentration port PT1, the predetermined port PT2, the concentration port PT3, the predetermined port PT4, the concentration port PT5, the predetermined port PT6, and the concentration port PT7.

  Therefore, as shown in FIG. 7, the order of the sensor signals input to the signal processing unit 32 during the period from the time t2 to the time t3 (period in which the pre-control voltage VS1 is applied) is the temperature signal ST, the detection The signal KSY, the humidity signal SH, the detection signal KSM, the concentration signal SN1, the detection signal KSC, the concentration signal SN2, 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 VS2 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. 7), 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. 8A, when the connection state of the toner density sensor 15Y is good, when the pre-control voltage VS1 is changed to the post-control voltage VS2 by the voltage control unit 30, the voltage of the detection signal KSY is also changed. Change.

  On the other hand, as shown in FIG. 8B, when the connection failure of the toner density sensor 15M occurs, even if the front control voltage VS1 is changed to the rear control voltage VS2 by the voltage control unit 30, The voltage of the detection signal KSM is almost constant.

  In FIG. 9, as described above, first, the pre-control voltage VS1 is applied to the toner density sensor 15 by the voltage controller 30 (# 1). Then, the output voltage of each sensor is sampled from time t2 to time t3 (# 2).

  Next, the control voltage VS applied to the toner density sensor 15 by the voltage controller 30 is changed from the pre-control voltage VS1 to the post-control voltage VS2 (# 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 pre-control voltage VS1 and the output voltage at the post-control voltage VS2 for the toner density sensor 15Y exceeds a predetermined value th that is a threshold value (# 5).

  When the difference is equal to or smaller 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.

  When the difference exceeds the predetermined value th (Yes in # 5), the difference between the output voltage at the front control voltage VS1 and the output voltage at the rear control voltage VS2 for the toner density sensor 15M exceeds the predetermined value th. It is determined whether or not (# 7).

  If the difference is equal to or smaller 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).

  When the difference exceeds the predetermined value th (Yes in # 7), the difference between the output voltage at the front control voltage VS1 and the output voltage at the rear control voltage VS2 for the toner density sensor 15C exceeds the predetermined value th. It is determined whether or not there is (# 9).

  When the difference is equal to or smaller 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).

  When the difference exceeds the predetermined value th (Yes in # 9), the difference between the output voltage at the front control voltage VS1 and the output voltage at the rear control voltage VS2 for the toner density sensor 15K exceeds the predetermined value th. It is determined whether or not there is (# 11).

  When the difference is equal to or smaller 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 exceeds 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. Is 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)
In the present embodiment, in the switching order of the sensor signal input to the analog switch 31, a predetermined value is input before each input of the detection signals KSY, KSM, KSC, KSK received by the density ports PT 1, PT 3, PT 5, PT 7. By inputting any one of the temperature signal ST, the humidity signal SH, the density signal SN1, and the density signal SN2 that are received by the ports PT0, PT2, PT4, and PT6 and have small fluctuation characteristics, the connection state of the toner density sensor 15 is changed. When it is not normal, the voltage appearing at the output port PT20 is prevented from changing. Therefore, it is possible to accurately detect the connection state of the toner density sensor 15.

  In the present embodiment, the pre-control voltage VS1 or the post-control voltage VS2 is applied to each of the toner density sensors 15Y, 15M, 15C, and 15K at the same timing, so that they are applied at different timings. As compared with the above, the difference between the output voltage of each sensor signal at the time of the pre-control voltage VS1 and the output voltage of each sensor signal at the time of the post-control voltage VS2 can be obtained in a short time, and the connection state determination process is performed in a short time. be able to.

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

  In the present embodiment, the connection state of the toner density sensor 15 can be easily detected by a method of changing the control voltage VS.

  In the present embodiment, a decrease in detection sensitivity of the toner density sensor 15 is suppressed by appropriately setting the resistance value of the pull-down resistor R2.

  Further, when the method of inputting the detection signals KSY, KSM, KSC, and KSK in order from the toner density sensors 15Y, 15M, 15C, and 15K to the input side port of the analog switch 31, the control voltage VS is changed. Since the change in the output voltage at that time affects the next input switching target port, it is necessary to shift the timing for changing the control voltage VS 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 than in the past.

(Other embodiments)
The sensor signal input to the concentration ports PT1, PT3, PT5, PT7 and the predetermined ports PT0, PT2, PT4, PT6 of the analog switch 31 described in the above embodiment (FIG. 5) may be as follows.

  FIG. 10 is a diagram illustrating another example of a configuration for inputting a signal to each port of the analog switch 31.

  As shown in FIG. 10, the analog switch 31a has predetermined ports PT0 and PT2, concentration ports PT1 and PT3, predetermined ports PT40, PT41, PT42, and PT43 as input ports, and an output port PT20.

  The temperature signal ST from the temperature sensor 24 is input to the predetermined port PT0 of the analog switch 31a, the detection signal KSY or the detection signal KSM is input to the concentration port PT1, and the concentration signal SN1 from the IDC sensor 22 is input to the predetermined port PT2. The detection signal KSC or the detection signal KSK is input to the concentration port PT3, the signal SA from the A sensor 40 is input to the predetermined port PT40, and the signal SB from the B sensor 41 is input to the predetermined port PT41. Then, 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.

  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 and output to the density port PT1. 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 formed of an analog switch and output to the density port PT3.

  Under the control of the CPU 321 (FIG. 5), the predetermined port PT0, concentration port PT1, predetermined port PT2, concentration port PT3, predetermined port PT40, predetermined port PT41, predetermined port PT42, and predetermined port PT43 are switched in this order for output. It is selectively connected to port PT20. The next of the predetermined port PT43 returns to the predetermined port PT0 and is switched again in the same order.

  As described above, the temperature sensor 24 and the IDC sensor 22 are sensors with stable output signal voltage (small fluctuation characteristics) in which the signal voltage does not change abruptly depending on the state of control by the CPU 321.

  In contrast, in the A sensor 40, the B sensor 41, the C sensor 42, and the D sensor 43, the difference between the output voltage at the pre-change control voltage VS1 and the output voltage at the post-change post-control voltage VS2 is a predetermined value th. It may be a sensor having a large fluctuation characteristic exceeding.

  As described above, even when the number of sensors with small fluctuation characteristics provided in the image forming apparatus 1 is small, the connection state of the toner density sensor 15 is detected by providing the first switching element 50 and the second switching element 51. can do.

  In the above-described embodiment, the temperature signal ST, the humidity signal SH, and the concentration signals SN1 and SN2 are used as signals other than the detection signal KS. However, the present invention is not limited to these signals. Alternatively, a fixed potential signal may be used.

  In addition, the configuration of the entire image forming apparatus 1 or each part, the processing content, the processing order, and the like can be appropriately changed in accordance with the spirit of the present invention. In this case, the above-described unique and exceptional effects can be obtained. Is done.

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 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 (density detection means)
22, 23 IDC sensor 24 Temperature sensor 25 Humidity sensor 30 Voltage 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 (concentration detection signal)
PT0, PT2, PT4, PT6 Predetermined port PT1, PT3, PT5, PT7 Concentration port SH Humidity signal SN1, SN2 Concentration signal ST Temperature signal VS Control voltage VS1 Pre-control voltage VS2 Post-control voltage th Predetermined value

Claims (7)

An image forming apparatus comprising a plurality of developing means and forming an image by an electrophotographic process,
A plurality of density detection means for outputting a density detection signal based on the toner density in the developing means by applying a control voltage by the voltage control means;
A plurality of input ports and one output port for inputting density detection signals output from the plurality of density detection means and signals other than the density detection signals, and sequentially switching the plurality of input ports to the output ports Switching means for selectively connecting,
Signal processing means for processing a signal appearing at the output port;
Have
A plurality of density detection signals and signals other than the density detection signals so that signals other than the density detection signals appear at the output port before the respective density detection signals when the switching means sequentially switches connections. Are connected to a plurality of the input ports,
In the signal processing means,
When the change amount of the concentration detection signal based on the change in the control voltage is less than or equal to a predetermined value for the concentration detection unit changed so that the control voltage is different at each timing of different switching connections by the switching unit. The concentration detection means is configured to determine that it is not normally connected to the switching means.
An image forming apparatus. 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 stirring 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 is normally connected to the switching unit. To determine whether it is not
The image forming apparatus according to claim 1. The voltage control means changes the control voltage at the same timing for a plurality of the concentration detection means,
The image forming apparatus according to claim 1. The signals other than the density detection signal include a signal from a temperature sensor that measures the temperature in the apparatus, a signal from a humidity sensor that measures the humidity in the apparatus, or a signal from an IDC sensor that detects the density of the toner image. ,
The image forming apparatus according to claim 1. The signal other than the concentration detection signal includes a signal having a fixed potential with respect to a ground potential or a power supply potential.
The image forming apparatus according to claim 1. A connection state determination method for determining a connection state of a plurality of 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 density detection signal based on the toner density in the developing means by a plurality of density detection means by applying a control voltage by the voltage control means;
The switching means having a plurality of input ports and one output port for inputting density detection signals output from the plurality of density detection means and signals other than the density detection signals, before each density detection signal. A step of selectively switching a plurality of the input ports to the output port so that signals other than the concentration detection signal appear at the output port; and
For the concentration detection means that has been changed so that the control voltage is different at each timing of different switching connections by the switching means, the amount of change in the concentration detection signal that appears at the output port based on the change in the control voltage is predetermined. Determining that the concentration detection means is not normally connected to the switching means when the value is less than or equal to the value,
A connection state determination method for density detection means.

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