JP5423517B2 - Image forming apparatus and toner density sensor connection state determination method - Google Patents

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, a black (K) image forming apparatus for a black and white image forming apparatus and a toner image forming part for each color of Y, M, C, and K for a color image forming apparatus are unitized as an imaging unit. , There are those that facilitate the replacement and maintenance. In this case, the black or each color imaging unit is positioned as an independent consumable member (consumable item), and is exchanged when the service life is reached 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 replenishment 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 unit 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 unit 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 to perform AD conversion (Patent Document 3).

For example, FIG. 12 is a diagram illustrating a configuration of a conventional analog switch and signal processing unit. In the signal processing unit 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 sequentially switched and selected as the output port PT20 by a selection signal (not shown). Connected. The input terminal of the A / D converter 320 is connected to a capacitor C1 and a resistor R1 for smoothing the input analog signal voltage.
JP-A-5-307325 JP-A-10-26876 JP 2009-145701 A

  In FIG. 12, in the signal processing unit 80, 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 is in a high impedance or open state, and therefore the analog signal voltage of the previous input port stored in the capacitor C1. Remains without being discharged, 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. 13A, 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%. If, as shown in FIG. 13B, 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, but the following problem arises. 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 method of Patent Document 3 described above detects the connection state of a toner density sensor by combining the order of a plurality of toner density sensor inputs with the order of other sensor inputs. Therefore, depending on the type of other sensor, the combination thereof may be restricted, or in the case of one toner density sensor as in a black and white image forming apparatus, the order combination with other sensors at the input port is further restricted. Problems occur.

  The present invention has been made in view of such problems, and an object thereof is to reliably detect the connection state of a toner density sensor easily and at low cost.

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 a density detection signal based on each toner density in the plurality of developing units. A plurality of density detection means for outputting the signal, a signal processing means for processing the density detection signal, a switching means for sequentially switching each of the density detection means and selectively connecting to the signal processing means, Difference detection means for detecting a difference between a maximum value and a minimum value of the voltage of the concentration detection signal as a connection determination value, and the signal processing means outputs the voltage of the concentration detection signal of the selected concentration detection means. A density detection unit that processes a voltage representing the toner density and outputs a density detection signal in which the connection determination value is detected when the connection determination value is smaller than a predetermined threshold value. There are those determined not to be successfully connected to said signal processing means, the connection determination value, sampling at a plurality of different periods of the same of the concentration detection means is connected to said signal processing means by said switching means Calculated from the data .

  Preferably, the difference detection means sequentially samples the voltage of the concentration detection signal to acquire sampling data, and calculates a difference between the maximum value and the minimum value of the sampling data as the connection determination value.

  According to the present invention, it is possible to reliably detect the connection state of the toner concentration sensor easily and at low cost.

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 example of the waveform of the detection signal KS. It is a figure which shows an example of a connection with a toner density sensor, an analog switch, and a signal processing part. It is a figure for demonstrating the flow of the sensor output reading process in 1st Embodiment. It is a flowchart which shows the connection state determination process in 1st Embodiment. It is a flowchart which shows the connection state determination process in 1st Embodiment. It is a figure for demonstrating the flow of the sensor output reading process in 2nd Embodiment. It is a flowchart which shows the connection state determination process in 2nd Embodiment. It is a figure which shows an example of the connection of the toner density sensor in another embodiment, an analog switch, and a signal processing part. It is a figure which shows the structure of the conventional analog switch and a signal processing part. FIG. 6 is a diagram for explaining a detection range of a toner density sensor.

  Hereinafter, two embodiments will be described in order with reference to the drawings. A repeated description of common items in these embodiments will be omitted. Of the components depicted in each of the drawings, the same or mutually corresponding components may be assigned the same reference numerals and detailed descriptions thereof may be omitted.

  Although the present invention can be applied to a black and white image forming apparatus having one toner density sensor, a full color image forming apparatus having four toner density sensors will be described as an example.

  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. 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 this embodiment, the connection state (normal or defective) 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. Alternatively, the connection state can be easily detected even when the terminals of the connectors CN1 and CN2 are contaminated by the developer or toner and the electrical contact is deteriorated.

  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.

  The image forming apparatus 1 includes toner density sensors 15Y, 15M, 15C, and 15K that output detection signals (output signals) KSY, KSM, KSC, and KSK based on the toner density in the developing devices 13Y, 13M, 13C, and 13K, respectively. Have. Further, a plurality of input ports PT0 for inputting detection signals KSY, KSM, KSC, KSK output from the toner density sensors 15Y, 15M, 15C, 15K and signals other than the detection signals KSY, KSM, KSC, KSK, respectively. ˜7 (described later) and an analog switch 31 having one output port PT20 (described later). By the analog switch 31, the plurality of input ports PT0 to PT7 are sequentially switched and selectively connected to the output port PT20. Further, it has a signal processing unit 32 for processing a signal appearing at the output port PT20.

  When the signal processing unit 32 determines that any one of the toner density sensors 15Y, 15M, 15C, and 15K is not normally connected to the analog switch 31 at each timing of the switching connection by the analog switch 31, 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.

  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 concentration signal from the IDC sensor 23 Although SN2 is used, these are only examples, and other types of sensors provided in the actual image forming apparatus 1 may be 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).

  FIG. 3 is a circuit diagram showing an example of the configuration of the toner density sensor 15. 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 the amplifier 152, compared with a reference voltage (not shown) by the 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 receives the control voltage from the voltage control unit 40. The reference voltage is controlled according to VS, and the sensitivity characteristic of the toner density sensor 15 is adjusted.

  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.

  Further, the toner density and the detection signal KS are proportional, and the detection signal KS decreases linearly as the toner density increases. The control voltage VS is adjusted, and 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 detection signal KS output from the toner density sensor 15 will be described.

  FIG. 4 is a diagram illustrating an example of the waveform of the detection signal KS. Each developing device 13 includes a stirring roller (not shown), and the stirring roller rotates at a predetermined timing by a driving force of a driving source (not shown) to stir the developer and the toner. And a detection signal KS is output.

  The detection signal KS illustrated in FIG. 4 is a signal in which an AC component having a maximum value Vp and a minimum value Vv, that is, a so-called ripple voltage component Vr is superimposed on the DC voltage component Vc. The ripple voltage component Vr is generated by the rotation of the stirring roller that stirs the toner, and has a ripple period Tr corresponding to the structure and rotation. In the example of FIG. 4, the ripple period is about 0.29 seconds. Further, the maximum amplitude of the ripple voltage component Vr, that is, the difference Vpv between the maximum value Vp and the minimum value Vv is about 1.0 V in the example of FIG. Note that the waveform of the ripple voltage component Vr varies depending on the flow of the developer during stirring and the mechanism around the stirring roller, and thus is not always as shown in FIG. 4, but the maximum value Vp and the minimum value Vv AC component having

  Note that the DC voltage component Vc of the detection signal KS substantially corresponds to the average value of the ripple waveform that changes every period during one cycle, and changes according to the toner concentration of the developer to be detected. In the example of FIG. 4, it is 1.2-4.2V. When the toner density is high, the voltage is low, and when the toner density is low, the voltage is high.

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

  FIG. 5 is a diagram illustrating an example of a connection between the toner density sensor, the analog switch, and the signal processing unit. 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.

  The toner density sensors 15Y, 15M, 15C, and 15K are sequentially connected to the input ports PT0 to PT7, and then output from the temperature sensor 24, humidity sensor 25, IDC sensor 22, and IDC sensor 23, which are other sensors. Are connected so that each signal (hereinafter sometimes referred to as “sensor signal”) is 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 connection order to the input ports PT0 to PT7 is one example, and connections other than this order are possible.

  The analog signal voltage appearing at the output port PT20 is converted into a digital signal (digital data) by the A / D converter 320 via the resistor R1 and output. The capacitor C1 forms a time constant circuit together with the resistor R1. When high frequency noise is superimposed on the signal voltage, the capacitor C1 introduces noise to the ground, but has a time constant that does not affect the ripple voltage component Vr of the signal voltage. doing. For example, it is configured to introduce noise having a period of about 1 ms or less to the ground. The digital data converted by the A / D converter 320 is processed by the difference detection unit 322, and a maximum value Vp, a minimum value Vv, and a difference Vpv (connection determination value) of sampling data described later are calculated. Note that the difference detection unit 322 is realized in software by a CPU executing an appropriate program or in combination with an appropriate hardware circuit.

  The CPU 321 sequentially switches the input ports PT0 to PT7 of the analog switch 31 at predetermined time intervals, takes in digital data of each sensor signal, and performs necessary processing based on each 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, sensor output reading processing for detecting the value of the detection signal KS representing the toner density of the developer, and other various processing.

[First embodiment]
Next, connection state determination processing and sensor output reading processing related to each toner concentration sensor 15 in the first embodiment will be described with reference to the drawings.

  FIG. 6 is a diagram for explaining the flow of the sensor output reading process in the first embodiment, and FIGS. 7 and 8 are flowcharts showing the connection state determination process in the first embodiment. 6 to 8, the description of the processes of sensors other than the toner density sensor 15 is omitted.

  First, as shown in FIG. 6, first, a predetermined control voltage VS is applied to each toner concentration sensor 15 by the voltage controller 40 at time t1 (# 1). A period T1 (for example, 220 ms) from time t1 to time t2 is a waiting time for stabilizing the output voltage of each toner density sensor 15 (# 2).

  The sampling of the output voltage is performed in the order of the density port port PT0, the density port PT1, the density port PT2, the density port PT3, the predetermined port PT4, the predetermined port PT5, the predetermined port PT6, and the predetermined port PT7 by switching by the analog switch 31. However, the order of the sensors connected to the ports PT0 to PT7 is not particularly important.

  When time t2 is reached, the first port switching is performed, and the input port PT0 to which the toner density sensor 15Y is connected is connected to the output port PT20 (# 3). The detection signal KSY is sampled during the period from time t3 to t4.

  Note that the period T2 from time t3 to t4, t5 to t6, t7 to t8, t9 to t10 is, for example, 0.3 seconds. The length of the period T2 is a period slightly longer than the ripple period Tr shown in FIG. 4, and may be changed according to the actual ripple period Tr of the detection signal KS.

  The CPU 321 can perform sampling of the maximum value Vp and the minimum value Vv of the ripple voltage component Vr in one cycle of the output voltage of the toner density sensor 15 during the period from time t3 to t4 N times (for example, 50 times). Data sampling is performed on the detection signal KSY appearing at the output port PT0. Therefore, for example, the counter is reset (# 4), the detection signal KSY is sampled (# 5), the counter value is incremented by one (# 6), and it is checked whether the counter value is a predetermined number N or not ( # 7). If it is smaller than the number N (No in # 7), the period T2 is delayed by N divided times (# 8), and the next sampling of the detection signal KSY is performed (# 5). The process of sampling the signal within one period N times is performed by the CPU 321 and its peripheral circuit (not shown) by a program.

  When the counter value is N (Yes in # 7), the difference detection unit 322 acquires the maximum value Vp and the minimum value Vv among the N pieces of sampling data, and calculates the difference pv (connection determination value) between them. Calculate (# 9). Thereafter, the CPU 321 calculates an average value of the N pieces of data and sets it as the DC component Vc of the detection signal KSY (# 10). Note that the above processing (# 9, # 10) when the counter value is N is not shown in FIG. 6, but is a period from time t4 to time t5 when the next port switching ends. At high speed.

  Here, for example, when the connection state of the toner density sensor 15Y is defective, the input port PT0 of the analog switch 31 is in an open state. Therefore, the difference Vpv obtained by performing the data sampling in the period from time t3 to t4 is almost zero. Note that the difference Vpv is substantially zero even when the charge due to the signal input from the previous input port remains in the capacitor C1 of the signal processing unit 32.

  From this, the connection state of the toner density sensor 15 can be easily determined by determining the value of the difference Vpv. In the present embodiment, as the predetermined threshold th for this determination, the waveform of the detection signal KS illustrated in FIG. 4 is measured in advance, and for example, a value of 1/2 of the difference Vpv, specifically, for example, , 0.5V. Therefore, if the difference Vpv is greater than or equal to the threshold th, it can be determined that the connection state of the toner density sensor 15 is normal, and if the difference Vpv is smaller than the threshold th, it can be determined that the connection state of the toner density sensor 15 is defective. .

  Reference is again made to FIGS. When 50 times of data sampling and its processing are completed, the signal processing unit 32 compares and determines the difference Vpv with a predetermined threshold th (0.5 V in this embodiment) (# 11). When the difference Vpv is smaller than the predetermined threshold th (Yes in # 11), the signal processing unit 32 determines that the connection state of the toner density sensor 15Y is defective.

  If it is determined that the connection state of the toner concentration sensor 15Y is defective, the DC component Vc stored for each toner concentration sensor 15 is discarded and the connection state of the toner concentration sensor 15Y is not normal. The message is displayed on the liquid crystal display of the operation panel 33 (# 80). Thereby, the user or the service person can recognize the connection failure. At the same time, all subsequent connection state determination processing, sensor output reading processing, toner density control processing, and the like are stopped, and toner is not oversupplied based on the wrong toner density detection value.

  On the other hand, when the signal processing unit 32 determines that the connection state of the toner density sensor 15Y is normal (No in # 11), the DC component Vc of the detection signal KSY calculated during the period from time t3 to t5 is obtained. The data is temporarily stored in a storage unit (not shown) and used as data indicating the toner density described later. Thereafter, the next input port PT1 is connected to the output port PT20 (# 23), and during the period from time t5 to t7, the same processing and determination (# 24 to # 31) as above are performed for the toner concentration sensor 15M and the detection signal KSM. To be done.

  When it is determined that the connection of the toner concentration sensor 15M is normal (No in # 31), the DC component Vc of the detection signal KSM calculated during the period from time t5 to time t7 is temporarily stored by a storage unit (not shown). These are used as values for a toner density control process to be described later. Thereafter, the next input port PT2 is connected to the output port PT20 (# 43), and during the period from time t7 to t9, the same processing and determination (# 44 to # 51) as described above are performed for the toner density sensor 15C and the detection signal KSC. To be done.

  When it is determined that the connection of the toner concentration sensor 15C is normal (No in # 51), the DC component Vc of the detection signal KSC calculated during the period from time t7 to t9 is temporarily stored by a storage unit (not shown). These are used as values for a toner density control process to be described later. Thereafter, the next input port PT3 is connected to the output port PT20 (# 63), and during the period from time t9 to t11, the processing and determination similar to the above (# 64 to # 71) are the toner density sensor 15K and the detection signal KSC. To be done.

  When it is determined that the connection of the toner concentration sensor 15K is normal (No in # 71), the connection state determination process of the toner concentration sensor 15 is finished, the next input port PT4 is connected to the output port PT20, and the other sensors are connected. Although processing is performed (after time t11 in FIG. 6), the description thereof is omitted.

  In the connection state determination process of the toner density sensor 15 described above, only when it is determined that the connection state of all the toner density sensors 15 of each color is normal, the CPU 321 detects each detected during the period of the connection state determination process. In accordance with the direct current component Vc of the toner density sensor 15, the toner density control processing of the developer is performed in the developing devices 13 Y, 13 M, 13 C, and 13 K.

[Second Embodiment]
In the first embodiment, whether the connection state of each toner concentration sensor 15 is good or not is determined based on sampling data of a period from the start to the end of one ripple cycle of each detection signal KS. Therefore, to determine whether the four toner density sensors 15 are connected or not, at least about four times the ripple period Tr is required. However, there are cases where it is desired to shorten the quality determination time of the connection state of the toner density sensor 15.

  The second embodiment takes the above background into consideration and intends to shorten the time for determining the quality of the connection state as compared to the first embodiment. Hereinafter, connection state determination processing and sensor output reading processing related to each toner concentration sensor 15 in the second embodiment will be described with reference to the drawings.

  FIG. 9 is a diagram for explaining the flow of the sensor output reading process in the second embodiment, and FIG. 10 is a flowchart showing the connection state determination process in the second embodiment. A description of the processing of sensors other than the toner density sensor 15 of FIGS. 9 and 10 is omitted.

  First, as shown in FIG. 9, first, at time t1, the voltage control unit 40 applies a predetermined control voltage VS to each toner density sensor 15 (# 101). A period T1 (for example, 220 ms) from time t1 to time t2 is a waiting time for stabilizing the output voltage of each toner density sensor 15 (# 102).

  The sampling of the output voltage is performed in the order of the density port port PT0 to the predetermined port PT7 by switching by the analog switch 31, but the order of the sensors connected to the ports PT0 to PT7 is not particularly important.

  When time t2 is reached, the first port switching is performed, and the input port PT0 to which the toner density sensor 15Y is connected is connected to the output port PT20 (# 103). Immediately thereafter, sampling of the detection signal KSY is started (# 104). When the first sampling data of the detection signal KSY is acquired, the difference detection unit 322 sets the data as the maximum value Vp and the minimum value Vv of the detection signal KSY, and sets the maximum value Vp and the minimum value Vv of the detection signal KSY. The difference Vpv (connection determination value) is calculated (# 105). However, since this is the first time, the maximum value Vp and the minimum value Vv are the same value, and the difference Vpv between them is zero.

  Next, the signal processing unit 32 calculates the average value (DC component Vc) of the sampling data of the detection signal KSY obtained so far (# 106). Then, the difference Vpv of the detection signal KSY is compared with a predetermined threshold th (# 107). When the number of times when the difference Vpv is smaller than the threshold th is n, for example, four, it is determined that the connection state of the toner density sensor 15Y is bad (Yes in # 108), and a trouble message is displayed on the operation panel 33. Is displayed on the liquid crystal display (# 150). Thereby, the user or the service person can recognize the connection failure. At the same time, all subsequent connection state determination processing, sensor output reading processing, toner density control processing, and the like are stopped, and toner is not oversupplied based on the wrong toner density detection value. Note that the predetermined number n plays a role of a safety valve for avoiding that the connection is determined to be poor by one determination when the connection is erroneously determined to be bad due to factors such as noise. Therefore, it may be set according to the actual use state.

  The predetermined threshold th compared with the difference Vpv is the same as that described in the first embodiment. If the threshold value th is too large, even if the connection state is actually bad, a lot of sampling data is required until it is judged as bad, and it takes time. On the other hand, if the threshold value th is set too small, there is a possibility that the toner density sensor 15 is erroneously determined to be defective even though the connection state of the toner density sensor 15 is normal. It is necessary to set a threshold value.

  If the difference Vpv is greater than or equal to the threshold th in step # 107 (No in # 107), the next input port is selected, and the input port PT1 to which the toner density sensor 15M is connected is connected to the output port PT20 ( # 113). Immediately thereafter, sampling of the detection signal KSM is started (# 114). Such a connection state determination process (# 113 to # 118) of the toner density sensor 15M, a connection state determination process (# 123 to 128) of the toner density sensor 15C, and a connection state determination process (# 133 to # 133) of the toner density sensor 15K. Since # 138) is the same as the connection state determination process (# 103 to 108) for the toner density sensor 15Y, description thereof will be omitted.

  If “No” in step # 107, the above processing (# 103 to # 138) is repeated a predetermined number of times for the toner density sensor 15 (# 140). When the predetermined number of times is increased, the accuracy of the maximum value Vp, the minimum value Vv, the difference Vpv (connection determination value), and the average value (DC component Vc) obtained from the detection signal KS of each color increases. Accordingly, the predetermined number of times may be set in consideration of the time and accuracy of the connection state determination process.

[Third embodiment]
In the first and second embodiments, the detection signal KS of the toner concentration sensor 15 is sampled while the predetermined toner concentration sensor 15 is connected to the output port PT20. The difference detection unit 322 included in the signal processing unit 32 detects the maximum value Vp, the minimum value Vv, and their difference Vpv, and uses them for the connection state determination process. The voltage value of the toner concentration detection signal KS is also detected simultaneously by the signal processing unit 32 in the form of an average value (DC component Vc). For this reason, the load on the CPU 321 increases, and the design margin for using the CPU 321 for other control may decrease.

  A third embodiment capable of reducing the load on the CPU 321 will be briefly described with reference to FIG. FIG. 11 is a diagram illustrating an example of connections among the toner density sensor 15, the analog switch 31, and the signal processing unit 32 according to the third embodiment.

  Compared to the configuration shown in FIG. 5, the configuration shown in FIG. 11 is a configuration in which the difference detection circuit 30 is connected to the signal lines of the toner density sensor 15 of each color and the input ports PT <b> 0 to PT <b> 3 of the analog switch 31. It has become. In addition, a comparison circuit 322 a that compares the output of the difference detection circuit 30 with a predetermined threshold is added to the signal processing unit 32.

  In the configuration shown in FIG. 11, a separately provided difference detection circuit 30 detects the maximum value Vp, the minimum value Vv, and the difference Vpv during the period of the ripple cycle Tr of the detection signal KS. That is, if the toner density sensor 15 is not normally connected, the signal line connected to the difference detection circuit 30 is in an open state, and a difference Vpv greater than the threshold th is not generated. The threshold th is set in the same way as in the first and second embodiments. Further, the difference detection circuit 30 itself can be constituted by a conventional ripple voltage detection circuit or the like. Also, a known circuit can be used as the comparison circuit 322a.

  In the configuration shown in FIG. 11, the average value of the detection signals KS used for the toner density control process is read by the signal processing unit 32 via the analog switch 31. Therefore, the time constants of the resistor R1 and the capacitor C1 constituting the signal processing unit 32 may be set larger than those in the first and second embodiments. For example, the ripple voltage component Vr of the detection signal KS shown in FIG. 4 may be set to a value that is smoothed.

The comparison circuit 322a of the signal processing unit 32 compares the difference Vpv (connection determination value) output from each difference detection circuit 30 with the threshold th, and the signal processing unit 32 applies when the connection determination value is smaller than the threshold th. It is determined that the toner density sensor 15 to be connected is not normally connected. If it is determined that at least one toner density sensor 15 is not normally connected, the toner density control process is not performed, so that the toner is not oversupplied (effect in each embodiment).
In the first embodiment, since the detection signal KS is sampled a predetermined number of times over one ripple cycle Tr of the detection signal KS, an accurate difference Vpv (connection determination value) can be obtained.

  In the configuration of the first embodiment, the detection signal KS is not divided by the pull-down resistor, and the detection range (detection sensitivity) of the toner density sensor 15 can be widened. Further, since the sampling data for the connection state determination process and the sampling data for the sensor output reading process are common to the respective toner density sensors 15, the time can be shortened and the control can be simplified.

  In the first 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 first embodiment, for example, even if a single toner density sensor of a black and white image forming apparatus including one developing device is connected to the analog switch 31 together with other sensors other than the toner density sensor, Connection state determination processing and toner concentration control processing can be performed.

  In the second embodiment, it is not necessary to sample the detection signal KS over the ripple period Tr, and the connection state determination process can be performed faster than in the first embodiment. Other effects are the same as in the first embodiment.

  In the third embodiment, since the difference detection unit for the detection signal KS is provided separately from the analog switch 31 and the signal processing unit 32, the load on the CPU 321 can be reduced.

  As described above, according to the image forming apparatus 1 according to the above-described embodiment, the connection state of the toner density sensor 15 can be detected with ease, lower cost, and more reliably than in the past.

  In addition, the configuration of the entire image forming apparatus 1 or each unit, the processing content, the processing order, and the like can be appropriately changed in accordance with the spirit of the present invention.

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 Difference detection circuit (difference detection 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)
322 Difference detection unit (difference detection means)
322a comparison circuit 40 voltage control unit C1 capacitor KS detection signal (concentration detection signal)
PT0, PT1, PT2, PT3 Concentration port PT4, PT5, PT6, PT7 Predetermined port SH Humidity signal SN1, SN2 Concentration signal ST Temperature signal Vp Maximum value Vpv Difference (connection determination value)
VS control voltage Vv minimum value th threshold

Claims (4)

An image forming apparatus comprising a plurality of developing means and forming an image by an electrophotographic process,
A plurality of density detecting means for outputting density detection signals based on respective toner densities in the plurality of developing means;
Signal processing means for processing the concentration detection signal;
Switching means for sequentially switching each of the concentration detection means to selectively connect to the signal processing means;
Differential detection means for detecting a difference between the maximum value and the minimum value of the voltage of each concentration detection signal as a connection determination value ;
The signal processing means processes the voltage of the density detection signal of the selected density detection means as a voltage representing toner density, and detects the connection judgment value when the connection judgment value is smaller than a predetermined threshold value. Determining that the concentration detection means for outputting the concentration detection signal is not normally connected to the signal processing means ,
The connection determination value is calculated from sampling data in a plurality of different periods in which the same concentration detection unit is connected to the signal processing unit by the switching unit .
An image forming apparatus. The difference detection means sequentially samples the voltage of the concentration detection signal to obtain sampling data, and calculates a difference between the maximum value and the minimum value of the sampling data as the connection determination value.
The image forming apparatus according to claim 1. The signal processing means calculates an average value of the sampling data for the plurality of density detection means as a voltage representing the toner density, respectively.
Only when it is determined that all of the plurality of density detection units are normally connected to the signal processing unit, the toner density control processing of the developer in the plurality of development units is performed based on the voltage representing the toner density. ,
The image forming apparatus according to claim 1 or 2 wherein. A connection state determination method for determining a connection state of a plurality of density detection means for outputting density detection signals based on respective toner densities in the development means,
Sequentially switching the plurality of concentration detection means and selectively connecting to the signal processing means;
Obtaining a voltage value representing the toner density of each density detection means by sequentially processing the density detection signals of the density detection means selectively connected;
Detecting a difference between a maximum value and a minimum value of a voltage of each of the concentration detection signals;
When the detected difference is smaller than a predetermined threshold value, the step of determining that the concentration detection means for outputting the concentration detection signal from which the difference is detected is not normally connected is included.
Is,
The difference is calculated from sampling data in a plurality of different periods when the same concentration detection unit is switched and connected to the signal processing unit .
The connection state determination method characterized by the above-mentioned.

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