JP2010262024A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce user's discomfort due to vibrating noise, by suppressing continuous occurrence of vibrating noise of a piezoelectric device, when detecting no toner left in a toner storage section. <P>SOLUTION: Toner is supplied to a developing unit 12 from a hopper 102. A first sensor 202 and a second sensor 203 are disposed in the hopper 102 and developing unit 12, respectively. When it is determined, based on an output signal D1 from the comparison circuit 406 of the first sensor 202, that no more tone is left in the hopper 102, a control section 201 turns off the first sensor 202. That is, the control section halts supplying of a switch-on signal Son1 to the transistor 402 of the first sensor 202, thereby supplying of a power Vcc to an oscillating circuit 403 is halted, and the piezoelectric element 401 is prevented from vibrating freely. As a result, vibration noise of the piezoelectric element 401 of the first sensor 202 occurs only temporary. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that employs an electrophotographic system, and more particularly, to an image forming apparatus that includes a piezoelectric element type toner sensor.

  Image forming apparatuses using an electrophotographic process such as an electrophotographic copying machine, an electrostatic printer, and a facsimile are known. In this type of apparatus, an image is formed by applying a developer (hereinafter referred to as “toner”) to an electrostatic latent image obtained by irradiating a photoconductor with light, and the image is formed on a recording medium such as transfer paper. After the image is transferred, an unfixed toner image is fixed on the transfer paper to obtain an image output.

  In the above-described apparatus, in order to detect the remaining amount of toner in a developing unit for supplying toner and a toner storage unit (hereinafter referred to as “hopper”) having a stirring and conveying function for stably supplying toner to the developing unit. Toner sensors are widely used. As this toner sensor, one having a piezoelectric element is known.

  FIG. 9 is a schematic diagram of a toner sensor using a piezoelectric element. This toner sensor includes a piezoelectric element 602 and a remaining amount detection circuit 603. The remaining amount detection circuit 603 includes an oscillation circuit 604, a resonance detection circuit 605, an integration circuit 606, and a comparison circuit 607. The piezoelectric element 602 installed in the opening of the hopper 601 is driven to vibrate (excited) at a specific frequency by the oscillation circuit 604 in the remaining amount detection circuit 603.

  10A to 10C are schematic diagrams of the output drive signal waveform of the oscillation circuit 604 and the vibration waveform of the piezoelectric element 602. FIG.

  The drive signal shown in FIG. 10A is output from the oscillation circuit 604 and tries to vibrate the piezoelectric element 602. In this case, assuming that the toner 608 is not present in the hopper 601 and the piezoelectric element 602 can freely vibrate, the resonance detection circuit 605 detects a signal having a vibration frequency waveform as shown in FIG. Accordingly, in this case, a voltage of a predetermined level or higher is output via the integration circuit 606 and the comparison circuit 607, so that a control unit (not shown) determines that “no toner”.

  On the other hand, when the toner 608 remains in the hopper 601 to some extent, the piezoelectric element 602 is compressed by the toner 608 through the opening and cannot vibrate, so that the vibration frequency as shown in FIG. Almost no waveform signal is detected. Therefore, in this case, since the output voltage via the integration circuit 606 and the comparison circuit 607 is equal to or lower than a predetermined value, a control unit (not shown) determines that “toner is present”.

  When the presence or absence of toner is detected by the operation as described above, a drive signal as shown in FIG. 10A is always output from the oscillation circuit 604, and the piezoelectric element 602 is excited. However, once there is no toner, the piezoelectric element 602 freely vibrates, and the vibration is transmitted to the outside as it is to generate noise, which is unpleasant and uncomfortable for the user and the surroundings.

  Further, in a copying machine that requires a large amount of toner, such as a high-speed copying machine, a hopper is usually provided in front of the developing unit as described above, and a plurality of toners are detected in order to detect the remaining amount of toner at each location. It is set as the structure provided with a sensor. Therefore, the number of toner sensors in the entire apparatus increases, leading to an increase in noise due to vibration of the piezoelectric element.

  In order to solve such a problem, Japanese Patent Application Laid-Open No. 2004-228561 discloses a configuration in which the power supply of the oscillation circuit of the toner sensor can be turned off. Japanese Patent Application Laid-Open Publication No. 2003-228561 discloses a configuration in which a plurality of toner sensors are driven in a time division manner.

Japanese Patent Laid-Open No. 5-100572 Japanese Patent Laid-Open No. 10-326038

  However, in the configuration of Patent Document 1, since the toner sensor is turned on when printing is started and the agitator in the toner tank rotates, noise generation continues if the toner sensor is turned on. . In addition, measures are taken only for the case of having a single sensor circuit, but noise countermeasures in the case of having a plurality of toner sensors are not considered. small.

  Also in the above-mentioned Patent Document 2, it is impossible to prevent the generation of noise in the absence of toner. Further, since the plurality of toner sensors are configured to always apply the respective resonance frequencies simultaneously in a time-sharing manner, this is insufficient to reduce the total vibration noise of the plurality of toner sensors.

  The present invention has been made to solve the above-described problems of the prior art, and its purpose is to suppress the continuation of generation of vibration noise of the piezoelectric element when no toner remaining in the toner storage unit is detected, An object of the present invention is to provide an image forming apparatus capable of reducing discomfort caused by vibration noise.

  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention is excited by being turned on with a toner storage section for storing toner, and a developing device to which toner is supplied from the toner storage section. A first sensor that has a piezoelectric element and is disposed in the toner storage unit and outputs a signal for detecting the presence or absence of the remaining amount of toner in the toner storage unit, and a signal output from the first sensor And controlling means for controlling the first sensor to be turned off when it is detected that there is no toner in the toner storage unit.

  According to the present invention, it is possible to reduce the discomfort caused by the vibration noise by suppressing the continuation of the vibration noise of the piezoelectric element when the toner storage unit detects that there is no toner remaining.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. It is a schematic diagram which shows the structure around a hopper and a developing device. It is a block diagram (Drawing (a) and (b)) showing each circuit composition of the 1st sensor and the 2nd sensor. 6 is a flowchart of toner sensor on / off control processing based on the remaining amount of toner. FIG. 5 is a schematic diagram illustrating a configuration around a hopper and a developing device in an image forming apparatus according to a second embodiment of the present invention. FIG. 2 is a block diagram illustrating a circuit configuration of a toner sensor of the image forming apparatus. It is a figure (Drawing (a), (b)) which shows a waveform of vibration sound of each piezoelectric element of the 1st and 2nd sensor, and a figure (figure (c)) showing a synthetic waveform of vibration sound of both piezoelectric elements. 6 is a flowchart of toner sensor on / off control processing based on the remaining amount of toner. It is a schematic diagram of a toner sensor using a piezoelectric element. It is a schematic diagram of the output drive signal waveform of an oscillation circuit and the vibration waveform of a piezoelectric element.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus 100 is configured as, for example, an electrophotographic digital copying apparatus having a composite function, and roughly includes a document feeding apparatus 1, a reader unit 200, and a printer unit 300. The image forming apparatus 100 includes a power supply source (not shown) that can be charged.

  In FIG. 1, a document feeding device 1 has a document feeding function, and feeds placed documents one by one or two consecutively to a predetermined position on a platen glass surface 2. The document feeder 1 is an RDF (circulation type automatic document feeder) that circulates documents and discharges them to the original document stack, or an ADF (automatic document feeder) that conveys documents in one direction and discharges them to the sheet discharge table. -Document feeder) may be used.

  In the reader unit 200, the scanner 4 includes a document illumination lamp 3, a scanning mirror 5, and the like. When the original is placed on the original table glass surface 2 by the original feeder 1, the scanner 4 is reciprocally scanned in a predetermined direction, and the original reflected light passes through the lens 8 through the scanning mirrors 5 to 7, and the image sensor. The image is formed on the portion 101.

  In the printer unit 300, the exposure control unit 10 is configured by a laser scanner, and irradiates the photoconductor 11 with a light beam modulated based on image data output from the image signal control unit of the controller unit CONT. The developing device 12 visualizes the electrostatic latent image formed on the photoreceptor 11 with a developer (hereinafter referred to as “toner”) accommodated therein. A toner storage unit (hereinafter referred to as “hopper”) 102 for supplying toner to the developing device 12 is disposed in the preceding stage (upstream of the supply path) of the developing device 12.

  A recording medium P having a standard size is stacked and stored in the transfer paper stacking units (pedestals) 14 and 15. The recording medium P on the transfer paper stacking sections 14 and 15 is fed to the position where the registration roller 25 is arranged by driving the feeding roller, temporarily stops, and then the image leading edge with the image formed on the photosensitive member 11 is stopped. The paper is fed again with the timing for matching.

  The transfer separation charger 16 transfers the toner image developed on the photoconductor 11 to a recording medium P that is a transfer sheet. Thereafter, the recording medium P is separated from the photoconductor 11 and conveyed to the fixing unit 103 via the conveyance belt. The fixing unit 103 includes a fixing heating roller and a pressure roller 17 that face each other. The recording medium P passes through a nip formed by these rollers, whereby an unfixed toner image is heated and fixed on the surface of the recording medium P. Is done.

  The paper discharge roller 18 stacks and discharges the recording medium P on which image formation has been completed as described above to the tray 20. The direction flapper 21 switches the transport direction of the recording medium P on which image formation has been completed to the paper discharge port and the internal transport path direction, and prepares for the multiplex / double-side image forming process. The paper discharge sensor 19 monitors the paper discharge conveyance state of the recording medium P.

  FIG. 2 is a schematic diagram showing a configuration around the hopper 102 and the developing device 12 described above.

  The hopper 102 has a supply port 208 for supplying toner from the outside, and a hopper lid 204 that can open and close the supply port 208. When the toner is replenished from the outside, the user opens the hopper lid 204 and supplies the toner from the replenishing port 208. A mechanism may be provided in which the hopper lid 204 is automatically opened and closed and toner is automatically supplied into the hopper 102 through the supply port 208. A toner transport screw 207 is disposed in the hopper 102. The toner conveying screw 207 is rotated by the motor 206 to uniformly replenish the developer 12 in the developing unit 12 while conveying the toner stored in the hopper 102 in the conveying direction.

  As described above, the developing device 12 develops the electrostatic latent image by supplying toner onto the photoconductor 11 via a developing roller that is driven by a drive motor (not shown) during image formation. The image forming apparatus 100 includes a control unit 201 as a control unit.

  The hopper 102 is provided with an open / close detection sensor 205 as detection means for detecting the open / close of the hopper lid 204 (that is, the open / close state of the supply port 208). The open / close detection sensor 205 may be a mechanical type or an optical type, and the configuration is not limited. A detection signal D3 from the open / close detection sensor 205 is supplied to the control unit 201. The hopper 102 is provided with a first sensor 202 that is a toner sensor for detecting the remaining amount of toner in the hopper 102. The developing device 12 is provided with a second sensor 203 that is a toner sensor for detecting the remaining amount of toner in the developing device 12.

  FIGS. 3A and 3B are block diagrams showing circuit configurations of the first sensor 202 and the second sensor 203, respectively.

  As shown in FIG. 3A, the first sensor 202 includes an oscillation circuit 403 and a piezoelectric element 401, and a resonance detection circuit 404, an integration circuit 405, and a comparison circuit 406 are connected in series to the piezoelectric element 401. . A transistor 402 is connected to the oscillation circuit 403. The transistor 402 functions as a switch that can turn on / off the supply of the power supply Vcc to the oscillation circuit 403 by supplying / stopping the switch-on signal Son1 supplied from the control unit 201 (see FIG. 2). From the comparison circuit 406, an output signal D1 for detecting the presence or absence of toner in the hopper 102 is output and supplied to the control unit 201 (see FIG. 2).

  As shown in FIG. 3B, the second sensor 203 includes an oscillation circuit 413 and a piezoelectric element 411, and a resonance detection circuit 414, an integration circuit 415, and a comparison circuit 416 are connected in series to the piezoelectric element 411. . A transistor 412 is connected to the oscillation circuit 413. The transistor 412 functions as a switch that can turn on / off the supply of the power supply Vcc to the oscillation circuit 413 by supplying / stopping the switch-on signal Son2 supplied from the control unit 201. From the comparison circuit 416, an output signal D2 for detecting the presence or absence of toner in the developing device 12 is output and supplied to the control unit 201 (see FIG. 2).

  The configuration and arrangement of the first and second sensors 202 and 203 are basically the same as those of the conventional toner sensor (the piezoelectric element 602 and the remaining amount detection circuit 603 in FIG. 9). However, the difference is that the oscillation circuits 403 and 413 are turned on / off by the switch-on signals Son1 and Son2 through the transistors 402 and 412, respectively. The drive signals supplied from the oscillation circuits 403 and 413 to the first and second sensors 202 and 203 are the same as those shown in FIG. Further, the resonance detection circuits 404 and 414 output a vibration frequency waveform signal as shown in FIG. 10B or 10C. The output signals D1 and D2 are output voltages that are greater than or less than a predetermined threshold for defining the presence or absence of toner. Note that the configuration is not limited to the configuration using the switch-on signal, the transistor, and the oscillation circuit as long as the configuration can control the on / off of the operations of the first and second sensors 202 and 203.

  When it is detected from the output signal D1 that the toner in the hopper 102 has run out, the control unit 201 notifies the user of the fact by voice or display. When it is detected from the output signal D2 that the toner in the developing device 12 has run out, the control unit 201 drives the motor 206 to rotate the toner conveying screw 207, so that the toner is transferred from the hopper 102 to the developing device 12. Let them replenish.

  FIG. 4 is a flowchart of toner sensor on / off control processing based on the remaining amount of toner. This process is started when the image forming apparatus 100 is turned on, and is executed by the control unit 201.

  First, the control unit 201 turns on both the first sensor 202 and the second sensor 203 (step S101). That is, by supplying the switch-on signals Son1 and Son2 to the transistors 402 and 412, the power supply Vcc is supplied to the oscillation circuits 403 and 413 so that the piezoelectric elements 401 and 411 are excited. At this time, if the toner is sufficiently present in the hopper 102 and the developing device 12, the piezoelectric elements 401 and 411 are pressed by the toner and do not vibrate and no vibration noise is generated.

  Next, the control unit 201 determines whether or not the hopper lid 204 is open based on the detection signal D3 from the open / close detection sensor 205 (step S102). If the hopper lid 204 is not in the open state, the control unit 201 determines whether or not the toner in the hopper 102 has run out based on the output signal D1 from the comparison circuit 406 (step S103).

  If the control unit 201 determines in step S102 that the hopper lid 204 is in an open state, the control unit 201 returns the process to step S101. The control unit 201 also returns the process to step S101 when it is determined in step S103 that there is toner in the hopper 102. Accordingly, as long as there is toner in the hopper 102, the first sensor 202 and the second sensor 203 are kept on.

  When the image forming operation is performed, the toner in the developing device 12 is consumed, so that the toner is supplied from the hopper 102 to the developing device 12 as described above. If the image forming operation is repeated, the toner in the hopper 102 will eventually disappear. If the control unit 201 determines in step S103 that the toner in the hopper 102 has run out, in this state, it is not necessary to detect the remaining amount of toner with the first sensor 202 unless the toner is replenished from the outside.

  Therefore, the control unit 201 turns off the first sensor 202 (step S104). That is, the supply of the power supply Vcc to the oscillation circuit 403 is stopped by stopping the supply of the switch-on signal Son1 to the transistor 402 (see FIG. 3A), so that the piezoelectric element 401 does not freely vibrate. Thereby, generation | occurrence | production of the vibration sound of the piezoelectric element 401 can be temporary.

  Next, the control unit 201 determines whether or not the hopper lid 204 is in an open state based on the detection signal D3 from the open / close detection sensor 205 (step S105). If the hopper cover 204 is not in the open state, the control unit 201 determines whether or not the toner in the developing device 12 has run out based on the output signal D2 from the comparison circuit 416 (step S106). If there is toner in the developing device 12, the control unit 201 returns the process to step S105. When the control unit 201 detects that the hopper cover 204 is open in step S105 before the toner in the developing device 12 runs out (step S105), the process returns to step S101. This is because it is determined that additional toner is supplied to the hopper 102, and the first sensor 202 that has been in the off state is turned on again.

  On the other hand, when the image forming operation is further repeated, the toner in the developing device 12 is eventually consumed and no toner is used. If the controller 201 determines in step S106 that the toner in the developing device 12 has run out, the controller 201 turns off the second sensor 203 (step S107). That is, the supply of the power supply Vcc to the oscillation circuit 413 is stopped by stopping the supply of the switch-on signal Son2 to the transistor 412 (see FIG. 3B) so that the piezoelectric element 411 does not freely vibrate. Thereby, generation | occurrence | production of the vibration sound of the piezoelectric element 411 is sufficient temporarily.

  Next, the control unit 201 determines whether or not the hopper lid 204 is in an open state based on the detection signal D3 from the open / close detection sensor 205 (step S108). And the control part 201 continues the determination, and will return a process to said step S101, if the hopper cover 204 will be in an open state. This is because it is determined that additional toner is supplied to the hopper 102, and both the first and second sensors 202 and 203, which are in the off state, are turned on again.

  Thus, in the processing in this sequence, when the control unit 201 sequentially detects “no toner” with the first sensor 202 and the second sensor 203, it is not necessary to detect the presence or absence of toner thereafter. Therefore, the power supply of each sensor is turned off so that noise due to vibration of the piezoelectric elements 401 and 411 is not generated unnecessarily. On the other hand, when the control unit 201 determines in steps S102, S105, and S108 that the hopper cover 204 has been opened, the control unit 201 turns on the first sensor 202 and the second sensor 203 again. Thereby, in the case where additional toner can be replenished, there is no problem in restarting detection of the presence or absence of toner.

  According to the present embodiment, when the toner in hopper 102 runs out, first sensor 202 is turned off. When the toner in the developing device 12 runs out, the second sensor 203 is turned off. As a result, it is possible to suppress the generation of vibration noise of the piezoelectric element 401 of the first sensor 202 and the piezoelectric element 411 of the first sensor 202, and to reduce discomfort due to the vibration sound.

  When the open state of the hopper lid 204 is detected, the first sensor 202 and the second sensor 203 are turned on again. Therefore, when the open state of the hopper lid 204 is detected, the first sensor 202 and the second sensor 203 that are in the off state are turned on. As a result, when there is a possibility that the hopper 102 has been replenished with toner, the detection of the remaining amount of toner in the hopper 102 and the developing device 12 can be automatically and promptly restarted.

(Second Embodiment)
FIG. 5 is a schematic diagram showing a configuration around the hopper and the developing device in the image forming apparatus according to the second embodiment of the present invention. FIG. 6 is a block diagram showing a circuit configuration of the toner sensor of the image forming apparatus according to the present embodiment.

  As the toner sensor in the present embodiment, a first sensor 702 and a second sensor 703 are employed instead of the first sensor 202 and the second sensor 203 in the first embodiment (see FIGS. 5 and 6). . 5 and 6, the same components as those shown in FIGS. 2 and 3 are denoted by the same reference numerals.

  As shown in FIG. 6, in the toner sensor, the first sensor 702 is different from the first sensor 202 in that the oscillation circuit 403 and the transistor 402 are eliminated and the transistor 705 is connected to the piezoelectric element 401. Different. Further, the second sensor 703 is different from the second sensor 203 in that the oscillation circuit 413 and the transistor 412 are eliminated and the inverting circuit 701 is connected to the piezoelectric element 411. Further, unlike the first embodiment, the toner sensor in the present embodiment is provided with one oscillation circuit 704 common to the first and second sensors 702 and 703.

  The first sensor 702 is configured such that the drive signal from the oscillation circuit 704 is given to the piezoelectric element 401 via the transistor 705. When the image forming apparatus 100 is powered on, a drive signal is constantly output from the oscillation circuit 704. Therefore, the excitation drive of the piezoelectric element 401 can be turned on / off by supplying / stopping the switch-on signal Son1 supplied from the control unit 201 to the transistor 705. On the other hand, the drive signal from the oscillation circuit 704 is given to the second sensor 203 in reverse phase via the inversion circuit 701.

  Therefore, the vibration sound generated from the piezoelectric elements 401 and 411 has an opposite phase. Here, when the first and second sensors 702 and 703 are simultaneously turned on, if a point equidistant from each sensor is taken as a measurement point, the vibration sound from the piezoelectric elements 401 and 411 is detected at the measurement point. Since they are in opposite phase, they cancel each other.

  FIG. 7A is a diagram illustrating a vibration sound waveform of the piezoelectric element 401 of the first sensor 702, and FIG. 7B is a diagram illustrating a vibration sound waveform of the piezoelectric element 411 of the second sensor 703. At the measurement point, as shown in FIG. 7C, the vibration sounds of both the piezoelectric elements 401 and 411 of the first and second sensors 702 and 703 are combined to form a sound having a waveform with almost no amplitude. In order to make the best use of such a silencing effect, the point at which the vibration sound is emitted to the outside may be the measurement point, that is, the waveform synthesis point.

  As shown in FIG. 5, in the image forming apparatus of the present embodiment, a soundproof cover 801 is provided. In the soundproof cover 801, an opening 802 as a sound emitting part opens toward the user side. The first sensor 702 and the second sensor 703 are located in the soundproof cover 801.

  The distances L1 and L2 from the first sensor 702 and the second sensor 703 to the center point P1 of the opening 802 are designed to be as equal as possible. This center point P1 is the above-described measurement point or waveform synthesis point. Accordingly, vibration sounds from the first sensor 702 and the second sensor 703 emitted from the opening 802 to the outside cancel each other and become minimal, and are hardly heard by the user. The distances L1 and L2 are preferably completely the same, and the closer to the distance, the greater the silencing effect.

  FIG. 8 is a flowchart of toner sensor on / off control processing based on the remaining amount of toner in the present embodiment. The processing from step S201 to S206 is the same as the processing from step S101 to S106 in FIG.

  If the toner in the developing device 12 runs out in step S206, the piezoelectric element 411 of the second sensor 703 in the on state vibrates. On the other hand, the first sensor 702 has already been turned off (step S204). Therefore, in this state, only the vibration sound of the piezoelectric element 411 is released.

  Therefore, in the subsequent step S207, the control unit 201 turns on the first sensor 702 again. That is, the piezoelectric element 401 is excited by supplying a switch-on signal Son1 to the transistor 705. As a result, the first and second sensors 702 and 703 are both turned on, so that vibration sounds from both cancel each other and become the minimum. Thereafter, this process is terminated.

  Note that the process of FIG. 8 may be configured to automatically resume when the open state of the hopper lid 204 is detected. Alternatively, step S207 may be abolished, and if the toner in the developing device 12 runs out in step S206, the control unit 201 may return the process to step S201.

  According to the present embodiment, first, when the toner in the hopper 102 runs out, the same effect as the first embodiment can be achieved with respect to reducing the discomfort caused by the vibration sound of the piezoelectric element 401. . The same effect as that of the first embodiment is provided for automatically and promptly restarting detection of the remaining amount of toner in the hopper 102 and the developing device 12 when there is a possibility that the hopper 102 has been replenished with toner. Can be played.

  According to the present embodiment, when the first sensor 702 is off and the second sensor 703 is on, the first sensor 702 is turned on when the toner in the developing device 12 runs out. . As a result, when both the hopper 102 and the developing device 12 run out of toner, the vibration sound of the piezoelectric elements 401 and 411 is canceled by the opposite phase drive signals, and the magnitude of the vibration sound emitted is reduced. Can be reduced.

  In particular, since the distances L1 and L2 from the first sensor 702 and the second sensor 703 to the center point P1 of the opening 802 are equal, the effect of canceling the vibration noise of the piezoelectric elements 401 and 411 is enhanced and the vibration noise is minimized. Can be.

DESCRIPTION OF SYMBOLS 12 Developing device 100 Image forming apparatus 102 Hopper 201 Control part 202,702 1st sensor 203,703 2nd sensor 204 Hopper lid 205 Opening / closing detection sensor 208 Supply port 401,411 Piezoelectric element D1, D2 Output signal L1, L2 Distance

Claims (6)

A toner storage unit for storing toner;
A developing device to which toner is supplied from the toner storage unit;
A first sensor that has a piezoelectric element that is excited by being turned on and is disposed in the toner storage unit and outputs a signal for detecting the presence or absence of the remaining amount of toner in the toner storage unit;
Control means for controlling the first sensor to be turned off when it is detected from the signal output from the first sensor that there is no toner in the toner storage unit. Forming equipment.   A second sensor that has a piezoelectric element that is excited by being turned on and that is disposed in the developing unit and outputs a signal for detecting the presence or absence of the remaining amount of toner in the developing unit; The control means controls the second sensor to be turned off when it is detected from the signal output from the second sensor that there is no toner in the developing device. The image forming apparatus according to 1.   The toner storage unit is provided with a supply port for supplying toner from the outside, and further includes detection means for detecting opening and closing of the supply port, and the control means is in a state where the first sensor is in an off state. 3. The image forming apparatus according to claim 1, wherein when the detection unit detects an open state of the replenishing port, the first sensor is controlled to be turned on.   The toner storage unit is provided with a supply port for supplying toner from the outside, and further includes detection means for detecting opening and closing of the supply port, and the control means is configured so that the second sensor is in an off state. The image forming apparatus according to claim 2, wherein the second sensor is controlled to be turned on when the detection unit detects an open state of the supply port.   A second sensor that has a piezoelectric element that is excited by being turned on and that is disposed in the developing unit and outputs a signal for detecting the presence or absence of the remaining amount of toner in the developing unit; The first and second sensors are configured to be turned on when supplied with driving signals having opposite phases to each other, and the control means is configured such that the first sensor is in an off state and the second sensor is in an on state. In this case, when it is detected that there is no toner in the developing device based on a signal output from the second sensor, control is performed so that the first sensor is turned on. Image forming apparatus.   A sound emitting portion for emitting the vibration sound of each piezoelectric element of the first and second sensors to the outside; a distance from the piezoelectric element of the first sensor to the sound emitting portion; and the second sensor 6. The image forming apparatus according to claim 5, wherein a distance from the piezoelectric element to the sound emitting unit is the same.