JP2009025392A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which surely detects that a sensor such as a toner concentration sensor connected to an A/D converter is not connected to the A/D converter in such a case while achieving improvement in sensitivity of the sensor. <P>SOLUTION: The image forming apparatus includes the A/D converter 62 including: a plurality of detection ports 72 connected to the sensor 24 outputting an analog signal; a capacitor 64 subjecting the analog signal to sample-and-hold; a comparator 66 converting the analog signal subjected to sample-and-hold by the capacitor 64 into a digital signal; and a switch 70 selectively connecting the capacitor 64 and the comparator 66 to the detection ports 72. When a potential difference between first output voltage detected when voltage is controlled to first input voltage and second output voltage detected when the input voltage is controlled to second input voltage different from the first input voltage is smaller than a predetermined value set in advance, it is judged as a situation that the sensor 24 is not connected to the A/D converter 62. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly, to an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having these functions combined.

  With respect to an electrophotographic image forming apparatus, a technique for performing development using a two-component developer composed of a toner and a carrier has been proposed.

  In an image forming apparatus employing such a technique, when development is performed, toner is consumed along with this, so that the toner density (ratio of toner amount to carrier amount) in the housing of the developing device decreases. The toner concentration in the housing of the developing device is detected by a toner concentration sensor, and when it is detected that the toner concentration has decreased, the toner is supplied from the toner cartridge to the developing device.

  The toner density sensor is connected to a detection port of an A / D converter provided in the image forming apparatus via a connector. The toner density sensor outputs an analog signal corresponding to the toner density, and the analog signal is converted into a digital signal by an A / D converter. The voltage of the signal thus digitally converted is detected as the output voltage of the toner density sensor.

  The A / D converter has a detection port connected to the sensor and a capacitor for sample-holding an analog signal output from the sensor. In an A / D converter having a plurality of detection ports, each detection port is connected to a capacitor in a predetermined order by a switch switching operation. Therefore, when detecting the output voltage of a sensor using such an A / D converter, the output voltage of each sensor is detected in a predetermined order.

When detecting the output voltage of the sensor in this way, conventionally, each detection port 172 of the A / D converter is grounded via a pull-down resistor 180 as shown in FIG. Thus, when the detection port 172 connected to the capacitor is switched, if the sensor 124 is not connected to the detection port 172 after switching, the charge accumulated in the capacitor before switching can be released. Therefore, a significantly smaller output voltage is detected for the sensor 124 that is not connected to the detection port 172. Therefore, when the output voltage is less than the predetermined value, it is possible to confirm that the sensor is not connected by setting so that it is determined that the sensor is not connected to the A / D converter. A technique for determining that the toner density sensor is not connected when the output value of the toner density sensor is equal to or less than a predetermined value is disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-133830.
JP-A-10-26876

  However, when it is determined that the sensor is not connected to the A / D converter when an output voltage less than the predetermined value is detected, the voltage having the predetermined value cannot be included in the normal detection range. Therefore, as shown in FIG. 8A, since the minimum value of the normal detection range needs to be larger than the predetermined value (1 V in the figure), the normal detection range is narrowed and the sensitivity of the sensor is lowered. There is a bug.

  On the other hand, as shown in FIG. 8B, if the sensitivity of the sensor is increased to increase the normal detection range, the predetermined value (1 V in the figure) is included in the normal detection range, and the non-detection of the sensor. The connection cannot be detected.

  Therefore, the present invention can reliably detect a sensor such as a toner density sensor connected to the A / D converter when the sensor is not connected to the A / D converter while improving the sensitivity of the sensor. An object is to provide an image forming apparatus.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A plurality of sensors that output analog signals;
A plurality of detection ports connected to the sensor; a capacitor that samples and holds the analog signal; a comparator that converts the analog signal sampled and held by the capacitor into a digital signal; and the capacitor and the comparator An A / D converter including a switch selectively connected to the detection port;
A control unit that controls an input voltage input to the sensor and detects a voltage of the digital signal that changes in accordance with a change in the input voltage as an output voltage of the sensor;
The control unit controls the first output voltage detected when the input voltage is controlled to the first input voltage and the input voltage is controlled to the second input voltage different from the first input voltage. When the potential difference from the second output voltage detected in step (b) is smaller than a predetermined value set in advance, it is determined that the sensor is not connected to the A / D converter.

  According to the present invention, the first output voltage detected when the first input voltage is input to the sensor and the second output voltage detected when the second input voltage is input to the sensor. When the potential difference is smaller than a predetermined value set in advance, it is determined that no sensor is connected to the A / D converter. Therefore, when the output voltage is detected for a sensor not connected to the A / D converter, the output voltage included in the normal detection range is detected under the influence of the potential remaining in the capacitor of the A / D converter. Even in this case, it is possible to reliably detect the disconnection of the sensor.

  In addition, according to the present invention, even if the output voltage of the sensor not connected to the A / D converter is included in the normal detection range, it does not interfere with the detection of the sensor disconnection, so that normal detection is performed. The range can be greatly expanded, and the sensitivity of the sensor can be improved.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In the following description, terms indicating a specific direction (for example, “up”, “down”, “left”, “right”, and other terms including them, “clockwise direction”, “counterclockwise” ”) Is used to facilitate understanding of the invention with reference to the drawings, and the present invention should not be construed as being limited by the meaning of these terms. In the image forming apparatus described below, the same reference numerals are used for the same or similar components.

  FIG. 1 shows a schematic configuration of an image forming apparatus 2 according to an embodiment of the present invention. However, in order to facilitate understanding of the invention by clarifying the characteristic portions of the present invention, the housing of the image forming apparatus is omitted from the drawings.

  The image forming apparatus 2 is an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine having a combination of these functions. Currently, various types of electrophotographic image forming apparatuses have been proposed. The illustrated image forming apparatus is a so-called tandem color image forming apparatus. However, the present invention is not applied only to this type of image forming apparatus. For example, a so-called four-cycle color image forming apparatus or a toner image on an electrostatic latent image carrier is directly applied to a recording sheet. The present invention is equally applicable to a direct transfer type color image forming apparatus for transferring.

  The image forming apparatus 2 includes an endless intermediate transfer belt 30. Under the intermediate transfer belt 30, toners of corresponding colors using yellow (Y), magenta (M), cyan (C), and black (K) developers in order from the left side to the right side in the drawing. Four image forming units 3 (3Y, 3M, 3C, 3K) for generating an image are arranged along the intermediate transfer belt 30.

  Each image forming unit 3 supplies a toner to an electrostatic latent image formed on the outer peripheral surface of the photosensitive member 4 as an electrostatic latent image carrier and develops the electrostatic latent image into a visible image. Device 18. The toner image formed on the photosensitive member 4 by developing the electrostatic latent image is transferred from the photosensitive member 4 to the intermediate transfer belt 30 at the nip portion (primary transfer region) between the photosensitive member 4 and the intermediate transfer belt 30. (Primary transfer). The yellow, magenta, cyan, and black toner images are transferred onto the intermediate transfer belt 30 so as to form a full-color toner image on the belt 30.

  The photoreceptor 4 and the developing device 18 constitute an imaging unit 12 (12Y, 12M, 12C, 12K) together with a charger, a cleaning member, and the like (not shown). The imaging unit 12 is detachable from the image forming apparatus 2.

  The developing device 18 accommodates a two-component developer composed of toner and carrier inside the housing. At the time of development, the developing device 18 supplies only the toner from the developer to the photosensitive member 4 by the developing roller 20 disposed opposite to the photosensitive member 4. Therefore, the toner in the housing of the developing device 18 is consumed along with the development. However, when the toner is replenished from a toner cartridge (not shown), the toner amount in the housing of the developing device 18 with respect to the carrier amount (N). The ratio (M / N) of (M) (hereinafter referred to as “toner density”) is maintained substantially constant.

  A toner concentration sensor 24 for detecting the toner concentration in the housing is provided inside the housing of the developing device 18. The toner density sensor 24 is connected to the connector 26 when the imaging unit 12 is attached to the apparatus 2. As a result, the toner density sensor 24 is connected to an A / D converter 62 described later via the connector 26.

  As the toner concentration sensor 24, for example, a magnetic sensor configured to detect the toner concentration by detecting the magnetic permeability of the developer is used. The output voltage of the toner concentration sensor 24 changes according to the magnetic permeability of the developer, and increases as the magnetic permeability increases. Since the magnetic permeability of the developer decreases as the toner concentration, that is, the ratio (M / N) of the toner amount (M) to the carrier amount (N) increases, the output voltage of the toner concentration sensor 24 increases the toner concentration. It becomes smaller as needed (see FIG. 6).

  The toner concentration sensor 24 includes a reference coil and a detection coil (not shown) as coils for detecting the magnetic permeability of the developer. An input voltage controlled by the control unit 60 described later is input to the input terminal connected to the reference coil. When this input voltage is input, a current corresponding to the magnitude of the input voltage and the magnetic permeability of the developer flows to the detection coil, and the current flowing to the detection coil passes through a predetermined circuit to the toner concentration sensor. 24. The signal output from the toner density sensor 24 is an analog signal, but is converted into a digital signal by an A / D converter 62 described later.

  A secondary transfer roller 40 that clamps the recording sheet 36 together with the belt 30 is provided outside the belt portion supported by the roller 32 arranged on the right side in the drawing. The recording sheet 36 is conveyed from the paper supply unit 42 to the nip portion (secondary transfer region 41) between the secondary transfer roller 40 and the belt 30. In the secondary transfer area 41, the toner image on the belt 30 is transferred (secondary transfer) to the recording sheet 36.

  After the secondary transfer, the recording sheet 36 is conveyed to the fixing unit 50 where the toner image is fixed on the recording sheet 36. After fixing, the recording sheet 36 is conveyed to a paper discharge unit (not shown).

  The image forming apparatus 2 also includes a control unit 60 that controls various operations of the apparatus 2. The control unit 60 can be arranged at an arbitrary location of the device 2. The control unit 60 has an A / D converter 62. The A / D converter 62 is selectively connected to the toner concentration sensor 24 and other sensors, and converts analog signals output from these sensors into digital signals. In the present invention, the sensors other than the toner density sensor 24 connected to the A / D converter 62 are not particularly limited, and examples thereof include a temperature sensor or an image density sensor (IDC sensor).

  As shown in FIG. 2, the A / D converter 62 outputs a plurality of detection ports (port 0 to port 7) 72 (72a to 72h) connected to the toner density sensor 24 and other sensors and the sensors. A capacitor 64 that samples and holds the analog signal, a comparator 66 that converts the analog signal sampled and held by the capacitor 64 into a digital signal, and the capacitor 64 and the comparator 66 are selectively connected to the detection ports 72 (72a to 72h). Switch 70 and resistor 68.

  For the sensor connected to the detection port 72 selected by the switch 70, the A / D converter 62 samples and holds the analog signal output from the sensor in the capacitor 64, and then compares the analog signal sampled and held in the capacitor 64 with a comparator. 66 to convert to a digital signal. The voltage of the signal thus digitally converted by the A / D converter 62 is detected by the control unit 60 as the output voltage of the sensor. The detection port 72 connected to the capacitor 64 is switched every predetermined time by the switching operation of the switch 70. When the detection port 72 connected to the capacitor 64 is switched, the output voltage of the next sensor is detected in the same manner as described above.

  As shown in FIG. 3, the detection port 72 is switched to the port 0 (72a), the port 1 (72b), the port 2 (72c), the port 3 (72d), the port 4 (72e), the port 70 by the switching operation of the switch 70. 5 (72f), port 6 (72g), and port 7 (72h) are connected to the capacitor 64 in this order. After port 7 (72h), port 0 (72a) is connected to capacitor 64 again. Thereafter, switching of the detection port 72 connected to the capacitor 64 is repeated in the same order as described above.

  Various sensors are connected to each detection port 72. In the embodiment, the toner density sensor 24Y for yellow toner is connected to the port 1 (72b), the toner density sensor 24M for magenta toner is connected to the port 2 (72c), and the cyan toner toner sensor 24M is connected to the port 3 (72d). The toner density sensor 24C is connected, and the toner density sensor 24K for black toner is connected to the port 4 (72e). Any sensor other than the toner density sensor 24 can be connected to the port 0 (72a), the port 5 (72f), the port 6 (72g), and the port 7 (72h). However, it is preferable that the sensor 80 connected to the port 0 (72a) is a sensor with a small variation in output voltage for the reason described later. An example of a sensor having a small fluctuation in output voltage is a temperature sensor.

  Since each sensor is connected to the detection port 72 as described above, the toner density sensor 24 is connected to the capacitor 64 with respect to the yellow toner density sensor 24Y, the magenta toner density sensor 24M, and the cyan toner density sensor. 24C and black toner density sensor 24K are connected in this order. Switching of the detection port 72 connected to the capacitor 64 is performed in units of several microseconds. Therefore, the sensor connected to the capacitor 64 is switched in units of several microseconds.

  By the way, when the power of the image forming apparatus 2 is turned on, the control unit 60 performs control for confirming whether or not the sensors are connected to the A / D converter 62 in order to confirm the presence or absence of various sensors. Do.

  Hereinafter, control for confirming whether the toner density sensor 24 is connected to the A / D converter 62 will be described.

  In the present invention, the following control is performed by the control unit 60 for each toner density sensor 24. The controller 60 first inputs the first input voltage Vi1 to the toner concentration sensor 24, and detects the first output voltage Vo1 corresponding to the first input voltage Vi1. Thereafter, at a predetermined timing, the input voltage to the sensor 24 is switched from the first input voltage Vi1 to the second input voltage Vi2, and the second output voltage Vo2 corresponding to the second input voltage Vi2 is detected. If the sensor 24 is connected to the A / D converter 62, the output voltages Vo1 and Vo2 change according to changes in the input voltages Vi1 and Vi2, but the sensor 24 is not attached or is not connected due to a connection failure. Is not connected to the A / D converter 62, even if the input voltages Vi1 and Vi2 change, the output voltages Vo1 and Vo2 do not change correspondingly. From this point of view, in the present invention, after detecting the first and second output voltages Vo1 and Vo2, the control unit 60 calculates the potential difference (Vo2-Vo1), and the potential difference (Vo2-Vo1) is set in advance. When the value is smaller than the predetermined value, it is determined that the sensor 24 is not connected to the A / D converter 62.

  When the output voltage is detected for the sensor 24 not connected to the A / D converter 62, it is affected by the output of the sensor that has been detected before the detection. For example, it is assumed that the magenta toner density sensor 24M is not connected to the A / D converter 62 for reasons such as sensor non-mounting or poor connection. Since the detection port 72 of the A / D converter 62 is connected to the capacitor 64 in the above-described order, the sensor to be detected before detection by the magenta toner density sensor 24M is the yellow toner density sensor 24Y (FIG. 3). reference). Therefore, when detecting the output voltage of the magenta toner density sensor 24M, the potential at the time of connection with the yellow toner density sensor 24Y remains in the capacitor 64, so that the output voltage affected by this is detected. The Rukoto. In this case, the input voltages Vi1 and Vi2 for the yellow toner density sensor 24Y are switched between the time when the first output voltage Vo1 of the magenta toner density sensor 24M is detected and the time when the second output voltage Vo2 is detected. If the first output voltage Vo1 of the magenta toner density sensor 24M is detected and the second output voltage Vo2 is detected, the capacitor 64 has the same or similar potential. It will be left. Therefore, in this case, since the potential difference (Vo2−Vo1) between the first output voltage Vo1 and the second output voltage Vo2 is zero or an extremely small value, the magenta toner density sensor 24M is supplied to the A / D converter 62. It is possible to accurately detect that it is not connected. However, the input voltages Vi1 and Vi2 are switched for the yellow toner density sensor 24Y between the time when the first output voltage Vo1 of the magenta toner density sensor 24M is detected and the time when the second output voltage Vo2 is detected. If this happens, the disconnection of the magenta toner density sensor 24M may not be detected.

  In order to avoid such a problem, the control unit 60 performs control so that the switching from the first input voltage Vi1 to the second input voltage Vi2 is performed for each sensor 24 while shifting the time. Specifically, the control unit 60 switches the input voltages Vi1 and Vi2 in the order of the black sensor 24K, the cyan sensor 24C, the magenta sensor 24M, and the yellow sensor 24Y. Further, after detecting the second output voltage Vo2 for one sensor 24, control is performed so as to switch the input voltages Vi1 and Vi2 for the next sensor 24. Thereby, the disconnection of the sensor 24 can be accurately detected. Further, by switching the input voltages Vi1 and Vi2 of the sensor 24 in the reverse order to the order of connection to the capacitor 64 by the operation of the switch 70, the output voltage is changed after switching from the port where the output voltage is Vo2. Since the state of measuring Vo1 does not occur, it is not necessary to wait until the capacitor 64 is discharged, and the detection time can be shortened.

  The sensor connected to the capacitor 64 before the yellow sensor 24Y is a sensor 80 that is not a toner density sensor (see FIG. 3). As described above, the sensor 80 has a small output voltage variation. Thus, if the yellow sensor 24Y is disconnected, the influence of the potential remaining on the capacitor 64 when connected to the sensor 80 is reduced, and the disconnection of the yellow sensor 24Y can be reliably detected.

  Hereinafter, the control for confirming whether or not the toner density sensor 24 is connected to the A / D converter 62 will be specifically described with reference to FIGS. 4 and 5 together.

  FIG. 4 shows the flow of each process of control for confirming whether or not the toner density sensor 24 is connected to the A / D converter 62. On the other hand, FIG. 5 is a timing chart of the control shown in FIG. Note that the numbers shown at the bottom of FIG. 5 are the symbols attached to the timing of each process.

  When the power of the image forming apparatus 2 is turned on, first, in step S1 (FIG. 4), the toner density sensors 24 for all colors (yellow, magenta, cyan, and black) are connected to the reference coil of the sensor 24. The first input voltage Vi1 is simultaneously input to the input terminals (timing 1 in FIG. 5). The magnitude of the first input voltage Vi1 can be arbitrarily set, but is set to 0 V, for example.

  For example, 0.22 seconds after the first input voltage Vi1 is input to the toner density sensor 24 for each color (time 2 in FIG. 5) waits for the output of the black toner density sensor 24K to stabilize. It is time for.

  When this time has elapsed, in step S2 (FIG. 4), the first output voltage Vo1 corresponding to the first input voltage Vi1 is sampled for 0.08 seconds, for example, for the black toner density sensor 24K (FIG. 5). Of time 3). The first output voltage Vo1 is, for example, an average value of output voltages acquired five times at intervals of 0.016 seconds. Thereafter, the sampling of the output voltages Vo1 and Vo2 performed for each color sensor 24 is similarly performed.

  When the first output voltage Vo1 is detected for the black sensor 24K, immediately after that, in step S3 (FIG. 4), the voltage input to the black sensor 24K is changed from the first input voltage Vi1 to the second input. The voltage is switched to the voltage Vi2 (timing 4 in FIG. 5). The magnitude of the second input voltage Vi2 can be arbitrarily set, but is set to 12.8V, for example. The second input voltage Vi2 of the yellow, magenta, and cyan sensors 24Y, 24M, and 24C to be input later is similarly set.

  0.22 seconds (the time indicated by reference numeral 5 in FIG. 5) after the input voltage to the black sensor 24K is switched is a time for waiting for the output of the black sensor 24K to stabilize.

  When this time elapses, in step S4 (FIG. 4), the second output voltage Vo2 corresponding to the second input voltage Vi2 is sampled for the black sensor 24K, and in parallel, the cyan sensor 24C is sampled. The first output voltage Vo1 corresponding to the first input voltage Vi1 is sampled (time 6 in FIG. 5).

  When the second output voltage Vo2 is detected for the black sensor 24K, in step S5 (FIG. 4), the potential difference (Vo2-) between the first output voltage Vo1 and the second output voltage Vo2 for the black sensor 24K. It is determined whether or not (Vo1) is a predetermined value (for example, 0.2V) or more. If it is determined in step S5 that the potential difference (Vo2-Vo1) is greater than or equal to a predetermined value, it is detected that the black sensor 24K is connected to the A / D converter 62 (step S6 in FIG. 4). If it is determined that (Vo2-Vo1) is less than the predetermined value, it is detected that the black sensor 24K is not connected to the A / D converter 62 (step S7 in FIG. 4).

  Immediately after the second output voltage Vo2 is detected for the black sensor 24K, in step S8 (FIG. 4), the voltage input to the cyan sensor 24C is changed from the first input voltage Vi1 to the second input voltage Vi2. It is switched (timing 7 in FIG. 5).

  0.22 seconds (time indicated by reference numeral 8 in FIG. 5) after the input voltage to the cyan sensor 24C is switched is a time for waiting for the output of the cyan sensor 24C to stabilize.

  When this time has elapsed, in step S9 (FIG. 4), the second output voltage Vo2 corresponding to the second input voltage Vi2 is sampled for the cyan sensor 24C, and in parallel with this, for the magenta sensor 24M. The first output voltage Vo1 corresponding to the first input voltage Vi1 is sampled (time 9 in FIG. 5).

  When the second output voltage Vo2 is detected for the cyan sensor 24C, in step S10 (FIG. 4), the potential difference (Vo2−) between the first output voltage Vo1 and the second output voltage Vo2 for the cyan sensor 24C. It is determined whether or not (Vo1) is a predetermined value (for example, 0.2V) or more. If it is determined in step S10 that the potential difference (Vo2-Vo1) is greater than or equal to a predetermined value, it is detected that the cyan sensor 24C is connected to the A / D converter 62 (step S11 in FIG. 4). If it is determined that (Vo2-Vo1) is less than the predetermined value, it is detected that the cyan sensor 24C is not connected to the A / D converter 62 (step S12 in FIG. 4).

  Immediately after the second output voltage Vo2 is detected for the cyan sensor 24C, in step S13 (FIG. 4), the voltage input to the magenta sensor 24M is changed from the first input voltage Vi1 to the second input voltage Vi2. It is switched (timing 10 in FIG. 5).

  0.22 seconds (time indicated by reference numeral 11 in FIG. 5) after the input voltage to the magenta sensor 24M is switched is a time for waiting for the output of the magenta sensor 24M to stabilize.

  When this time has elapsed, in step S14 (FIG. 4), the second output voltage Vo2 corresponding to the second input voltage Vi2 is sampled for the magenta sensor 24M, and in parallel, the yellow sensor 24Y is sampled. The first output voltage Vo1 corresponding to the first input voltage Vi1 is sampled (time indicated by reference numeral 12 in FIG. 5).

  When the second output voltage Vo2 is detected for the magenta sensor 24M, in step S15 (FIG. 4), the potential difference (Vo2−) between the first output voltage Vo1 and the second output voltage Vo2 for the magenta sensor 24M. It is determined whether or not (Vo1) is a predetermined value (for example, 0.2V) or more. If it is determined in step S15 that the potential difference (Vo2-Vo1) is greater than or equal to a predetermined value, it is detected that the magenta sensor 24M is connected to the A / D converter 62 (step S16 in FIG. 4). If it is determined that (Vo2-Vo1) is less than the predetermined value, it is detected that the magenta sensor 24M is not connected to the A / D converter 62 (step S17 in FIG. 4).

  Immediately after the second output voltage Vo2 is detected for the magenta sensor 24M, in step S18 (FIG. 4), the voltage input to the yellow sensor 24Y is changed from the first input voltage Vi1 to the second input voltage Vi2. It is switched (timing 13 in FIG. 5).

  0.22 seconds (time indicated by reference numeral 14 in FIG. 5) after the input voltage to the yellow sensor 24Y is switched is a time for waiting for the output of the yellow sensor 24Y to stabilize.

  When this time elapses, in step S19 (FIG. 4), the second output voltage Vo2 corresponding to the second input voltage Vi2 is sampled for the yellow sensor 24M (time indicated by reference numeral 15 in FIG. 5).

  When the second output voltage Vo2 is detected for the yellow sensor 24Y, the potential difference (Vo2−) between the first output voltage Vo1 and the second output voltage Vo2 is detected for the yellow sensor 24Y in step S20 (FIG. 4). It is determined whether or not (Vo1) is a predetermined value (for example, 0.2V) or more. If it is determined in step S20 that the potential difference (Vo2-Vo1) is greater than or equal to a predetermined value, it is detected that the yellow sensor 24Y is connected to the A / D converter 62 (step S21 in FIG. 4). When the processing is completed and it is determined that the potential difference (Vo2-Vo1) is less than the predetermined value, it is detected that the yellow sensor 24Y is not connected to the A / D converter 62 (step S22 in FIG. 4). , The process ends.

  When it is confirmed that the yellow, magenta, cyan, and black toner density sensors 24 are all connected to the A / D converter 62 by the above control, the developer stirring operation of the developing device 18 and the image forming apparatus 2 are performed. The warm-up operation is started.

  While the present invention has been described with reference to the above-described embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiment, the configuration in which the toner density sensor is used as the sensor that changes the output voltage in accordance with the change in the input voltage has been described. However, the present invention can be similarly applied to sensors other than the toner density sensor. It is. As a sensor other than the toner density sensor to which the present invention can be applied, for example, an image density sensor (IDC sensor) can be considered.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention. It is a figure which shows the structure of an A / D converter. It is a figure which shows the example of a connection of a detection port and each sensor. 6 is a flowchart illustrating a flow of control processing for confirming connection of a toner density sensor. 5 is a timing chart of the control shown in FIG. 6 is a graph showing a relationship between toner density and output voltage. It is a figure which shows the example of a connection of the detection port and sensor of the conventional A / D converter. It is a graph which shows the relationship between the output voltage at the time of the conventional sensor non-connecting, and a normal detection range.

Explanation of symbols

2: image forming apparatus, 3: image forming unit, 4: photoconductor (electrostatic latent image carrier), 12: imaging unit, 18: developing device, 24: toner density sensor, 26: connector, 30: intermediate transfer belt 36: recording sheet, 40: secondary transfer roller, 41: secondary transfer area, 60: control unit, 62: A / D converter, 64: capacitor, 66: comparator, 68: resistor, 70: switch, Detection port 72, 80: sensor.

Claims (5)

A plurality of sensors that output analog signals;
A plurality of detection ports connected to the sensor; a capacitor that samples and holds the analog signal; a comparator that converts the analog signal sampled and held by the capacitor into a digital signal; and the capacitor and the comparator An A / D converter including a switch selectively connected to the detection port;
A control unit that controls an input voltage input to the sensor and detects a voltage of the digital signal that changes in accordance with a change in the input voltage as an output voltage of the sensor;
The control unit controls the first output voltage detected when the input voltage is controlled to the first input voltage and the input voltage is controlled to the second input voltage different from the first input voltage. An image forming apparatus that determines that the sensor is not connected to the A / D converter when a potential difference from the second output voltage detected in the step is smaller than a predetermined value set in advance. The control unit performs control so that the switching of the input voltage from the first input voltage to the second input voltage is performed with a time shift for each sensor,
When the switching of the input voltage is performed for the second sensor next to the first sensor, the control unit detects the second output voltage for the first sensor and then inputs the input for the second sensor. The image forming apparatus according to claim 1, wherein the voltage is switched.   The image forming apparatus according to claim 2, wherein the control unit switches the input voltage for the second sensor immediately after detecting the second output voltage for the first sensor. The plurality of sensors can be connected to the capacitor in a first order by the operation of the switch,
The image forming apparatus according to claim 2, wherein the control unit switches the input voltage in a second order opposite to the first order.   The image forming apparatus according to claim 1, wherein the sensor is a toner concentration sensor that detects a toner concentration in a housing of the developing device.

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