JP2008009060A - Current control circuit and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current control circuit capable of surely preventing a rush current from flowing into a circuit for performing the operation control of driving load, and an image forming apparatus. <P>SOLUTION: The current control circuit 1 is provided with a switching element SW1 having three terminals T1 to T3 between a power supply circuit 2 and a capacitor C1 for supplying power to the driving load M. The first terminal T1, the second terminal T2 and the third terminal T3 of the switching element SW1 are connected to the power supply circuit 2, a resistance element R1 and ground, respectively. The switching element SW1 is constituted so that the first terminal T1 and the second terminal T2 are electrically shut down and the second terminal T2 and the third terminal T3 are electrically connected when a cover 18 is opened, whereby charge accumulated in the capacitor C1 is discharged to the ground instantaneously. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a current control circuit for preventing occurrence of an inrush current in a circuit that controls operation of a drive load, and an image forming apparatus including the current control circuit.

  When a paper jam (hereinafter referred to as jam) occurs in an image forming apparatus such as a copying machine or a printer, a cover is opened to remove the paper. When the cover is opened, it is necessary to stop the operation of each unit installed inside the apparatus in order to ensure the safety of the sheet removing operation by the user. For this reason, conventionally, a current control circuit that supplies power to and cuts off power from the power source to each part (drive load) in the apparatus according to the open / closed state of the cover is mounted. FIG. 7 is a diagram showing a configuration of a conventional current control circuit.

  As shown in FIG. 7, the current control circuit 200 includes a capacitor C11 connected in parallel to the drive load M, a power supply circuit 201 connected in parallel to the drive load M and the capacitor C11, and a cover opening / closing operation. A switching element SW11 that is turned on / off in conjunction with each other, a resistance element R11 for limiting current, and a switch circuit 202 that is connected in parallel to the resistance element R11 and for short-circuiting between both terminals of the resistance element R11, The on / off detection circuit 203 detects the potential at one terminal of the switching element SW11 and detects the on / off of the switching element SW11 according to the potential, and indicates the on / off of the switching element SW11 from the on / off detection circuit 203. And a control unit 204 that receives the detection signal and controls the operation of the switch circuit 202. There.

  As a basic operation of the current control circuit 200, as shown in FIG. 8, when the cover is closed, the switching element SW11 is turned on, and power is supplied from the power supply circuit 201 to the driving load M and the capacitor C11. Is opened, the switching element SW11 is turned off and the power supply by the power supply circuit 201 is cut off.

Further, if the cover is closed and the switching element SW11 is turned on with both terminals of the resistance element R11 being short-circuited by the switch circuit 202, the resistance value of the capacitor C1 is substantially reduced as shown in FIG. Since the current supplied from the power supply circuit 201 is 0, a very large inrush current (current value I ₁ ) flows toward the drive load M and the capacitor C11, and the inrush current causes damage such as burn-in of each element. There is a possibility that the circuit board may be erroneously reset due to generation of ground noise due to the inrush current. Therefore, when the control unit 204 detects that the switching element SW11 is turned on based on the detection signal output from the on / off detection circuit 203, a certain minute period after the switching element SW11 is turned on (from time T13 to time T13 in FIG. 8). During the period T14, the switch circuit 202 is turned off so that the current supplied from the power supply circuit 201 flows through the resistance element R1, thereby suppressing the current flowing toward the capacitor C1 as shown in FIG. Current value I ₂ <I ₁ ).

  In a period other than the certain minute period, the control unit 204 causes the switch circuit 202 to perform a short-circuit operation to reduce the power loss, and the power is supplied from the power supply circuit 201 to the capacitor C11 via the switch circuit 202. Supply.

  On the other hand, there is, for example, Patent Document 1 as a technical document related to this technical field. In Patent Document 1, in a dot matrix printer including a piezoelectric head and a piezoelectric head control circuit that drives the piezoelectric head, an interlock switch that is mechanically turned on and off according to opening and closing of the printer cover includes a piezoelectric head control circuit, a power source, and the like. A parallel circuit of a resistor element and a triac connected in series with the interlock switch is installed between the interlock switch and the piezoelectric head control circuit, and the interlock switch is switched from OFF to ON. Immediately after that, a technique is disclosed in which a switching circuit for turning on and off the triac is controlled to maintain a current supplied from a power source in a state of flowing through the resistive element among the triac and the resistive element.

Patent Document 1 discloses a capacitor for supplying a current together with a power source to a piezoelectric head control circuit when the piezoelectric head control circuit instantaneously requires a large current, and a discharge control circuit connected in parallel to the capacitor. It is described that when a cover open is detected, the interlock switch is turned off and the capacitor is discharged.
Japanese Patent Laid-Open No. 5-111149

  Incidentally, the current control circuit shown in FIG. 7 has the following problems. That is, conventionally, the potential at one terminal of the switching element SW11 connected to the capacitor C11 is compared with the threshold value of the potential, and the potential at the one terminal of the switching element SW11 is less than the threshold value. By detecting, it is detected that the switching element SW11 is switched from on to off.

  Here, the potential at one terminal of the switching element SW11 decreases as the charge accumulated in the capacitor C11 is discharged. However, since the discharge is performed relatively slowly, the potential is reduced. The timing for detecting switching of the switching element SW11 from on to off is delayed by the time required for discharging until the voltage falls below the threshold value. When the switching element SW11 is turned on again (when the switching element SW11 is closed immediately after the cover is opened) during such a delay period (period T11 to T12 in FIG. 8), the switch circuit 202 is still turned off at that time. Since it is not switched (the short circuit operation is not released), an inrush current flows toward the capacitor C11.

  In order to avoid this, a configuration is conceivable in which a sensor for detecting the opening and closing of the cover is separately provided and the operation of the switch circuit 202 is controlled based on the detection signal of the sensor. Will incur a cost increase.

  In Patent Document 1, the potential at one terminal of the switching element connected to the capacitor C11 is detected, and it is determined whether or not the two terminals of the resistance element R11 are conducted according to this potential. No solution has been proposed for the above problems.

  The present invention has been made to solve the above-described problems, and provides a current control circuit and an image forming apparatus that can reliably prevent an inrush current from flowing through a circuit that controls the operation of a drive load. The purpose is to do.

  According to the first aspect of the present invention, the current for controlling the current supplied from the power source to the capacitor for supplying power to the driving load in the electronic device according to the position of the predetermined member provided in the electronic device. A control circuit comprising three terminals connected to the power source, the capacitor and ground, and a first switching state for electrically connecting the power source and the capacitor according to the position of the predetermined member And a switching element that can alternatively take a second switching state that electrically connects the capacitor and the ground, and a potential of a terminal connected to the capacitor among the terminals of the switching element. An on / off detection circuit for detecting whether the switching element is in the first switching state or the second switching state; Based on a current limiting element for limiting the current supplied from the power source to the capacitor, a switch circuit for short-circuiting both terminals of the current limiting element, and a detection signal output from the on / off detection circuit, And a control means for controlling a short-circuit operation by the switch circuit.

  According to the present invention, when the predetermined member is set at a certain position, the switching element enters the second switching state in conjunction with the predetermined member, and the charge accumulated in the capacitor is discharged to the ground. Is done. As a result, the potential at the terminal of the switching element connected to the capacitor changes instantaneously, and the ON / OFF detection circuit quickly detects that the switching element is in the second switching state.

  According to a second aspect of the present invention, in the current control circuit according to the first aspect, the on / off detection circuit includes a potential of a terminal connected to the capacitor among the terminals of the switching element and a threshold value for the potential. And detecting whether the switching element is in the first switching state or the second switching state based on a comparison with the size.

  According to the present invention, when the switching element enters the second switching state in conjunction with the predetermined member, the charge accumulated in the capacitor is discharged to the ground, thereby being connected to the capacitor of the switching element. The on / off detection circuit quickly detects that the potential at the terminal immediately falls below the threshold value and the switching element is in the second switching state.

  According to a third aspect of the present invention, there is provided an image forming apparatus that reads an image of a document by a photoelectric conversion operation and forms an image on a sheet based on an image signal obtained by the reading operation. The electronic device is the image forming apparatus, and the position of the cover member is the open position. The current control circuit according to claim 1, wherein a current supplied from the power source to the capacitor is controlled depending on whether the power supply is in a closed position.

  According to the present invention, in the image forming apparatus that supplies and cuts off the current from the power source to the capacitor according to the open / closed state of the cover member, the power is supplied from the power source even when the cover is closed immediately after the cover is opened. Current can flow through the current limiting element to the capacitor.

  According to the present invention, it is possible to reliably prevent the occurrence of an inrush current to the capacitor for supplying power to the drive load.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a side view schematically showing an internal configuration of a copying machine which is an embodiment of an image forming apparatus according to the present invention.

  As shown in FIG. 1, the copying machine 10 includes a sheet feeding unit 12 disposed at a lower portion of a box-shaped apparatus main body (housing) 11 and an image forming unit disposed above the sheet feeding unit 12. 13, a fixing unit 14 disposed on the left side of FIG. 1 of the image forming unit 13, an image reading unit 15 having an optical system member disposed above the image forming unit 13 and the fixing unit 14, And a paper transport unit 16 from the paper supply unit 12 to the paper discharge through the image forming unit 13 and the fixing unit 14.

  The image reading unit 15 irradiates the document placed on the contact glass 151 with light from an exposure lamp (not shown), and guides the reflected light to the photoelectric conversion unit via the reflecting mirror, thereby allowing the document to be scanned. The image information is read, and this image information is transmitted to an exposure unit 133 described later.

  The sheet feeding unit 12 feeds a bundle of sheets P stacked on the sheet feeding cassette 121 to the sheet conveying unit 16 one by one. The paper transport unit 16 transports the paper P fed from the paper feed unit 12 toward the image forming unit 13 by the transport roller pair 161 and the registration roller pair 162, and further passes through the image forming unit 13 and the fixing unit 14. After that, the discharge roller pair 163 is driven to discharge toward the discharge tray 164 provided on the outer wall of the apparatus main body 11.

  The image forming unit 13 transfers a predetermined toner image onto the paper P by an electrophotographic process. The photosensitive drum 131 is rotatable around an axis, and around the photosensitive drum 131 along the rotation direction. A charging unit 132, an exposure unit 133, a developing unit 134, a transfer unit 135, a cleaner 136, and a charge eliminating unit 137.

  The charging unit 132 applies a predetermined potential to the surface of the photosensitive drum 131 by corona discharge. The exposure unit 133 selectively attenuates the potential of the surface of the photosensitive drum 131 by irradiating the photosensitive drum 131 with laser light based on the image data of the original read by the image reading unit 15. An electrostatic latent image is formed on the surface of the photosensitive drum 131.

  The developing unit 134 develops the electrostatic latent image with toner to form a toner image on the surface of the photosensitive drum 131. The transfer unit 135 transfers the toner image on the surface of the photosensitive drum 131 onto the paper P. The cleaner 136 removes toner remaining on the surface of the photosensitive drum 131 after transfer, and the charge removal unit 137 removes residual charge on the surface of the photosensitive drum 131.

  The fixing unit 14 performs a process of fixing the toner transferred onto the paper P by the image forming unit 13 to the paper P. The fixing unit 14 includes a fixing unit 20 disposed downstream of the image forming unit 13 in the paper transport direction. The guide member 30 is provided on the downstream side of the fixing unit 20 and guides the paper P discharged from the fixing unit 20 toward the discharge roller pair 163. The fixing unit 20 includes a box-shaped fixing device main body 21, a heat roller 22 rotatably supported around the axis of the fixing device main body 21, and a peripheral surface pressing the peripheral surface of the heat roller 22. A pressure roller 23 in contact therewith.

  The paper P conveyed from the image forming unit 13 is heated by the rotation of the heat roller 22 while being nipped between the heat roller 22 and the pressure roller 23 while being pressed and held between them. The fixing process of the image onto the paper P is performed, and the image is discharged toward the discharge tray 164 via the guide member 30 and the discharge roller pair 163.

  2 and 3 are perspective views showing the appearance of the copying machine 10 shown in FIG. 1, FIG. 2 shows a state in which the cover 18 is closed, and FIG. 3 shows a state in which the cover 18 is opened. Yes.

  As shown in FIG. 2, the copying machine 10 is provided with the paper feeding unit 12 including a plurality of paper feeding cassettes 121 at the lower part of the apparatus main body 11 having a vertically long rectangular parallelepiped shape. It can be pulled forward. The fixing unit 14 and the paper transport unit 16 are internally provided at a position directly above the paper feeding unit 12, and the image forming unit 13 is formed at an upper position thereof. In addition, an operation panel 111 having a numeric keypad, a liquid crystal display panel, and various operation keys is provided at the front position of the top panel of the apparatus body 11, and at the rear position of the top panel, An automatic document feeder 152 that can be opened and closed is provided so as to cover the contact glass 151 (FIG. 1).

  A cover 18 that can be opened and closed laterally is provided at a position above the front sheet feeding unit 12 in the apparatus main body 11. The cover 18 is normally closed as shown in FIG. 2, and is opened toward the right as shown in FIG. 3 during a paper jam clearing operation or various maintenance operations.

  In the present embodiment, when the cover 18 is opened in order to ensure safety when a user of the copying machine 10 performs a paper jam clearing operation or various maintenance operations, a current control circuit described below is provided. 1, power supply to each part (image forming part 13, fixing part 14, etc.) inside the copying machine 10 is cut off, and the operation of each part is stopped. The cover 18 is an example of the predetermined member, and corresponds to the cover member.

  FIG. 4 is a diagram showing a circuit configuration of the current limiting circuit. As shown in FIG. 4, the current control circuit 1 supplies a current to the driving load M and the capacitor C1 for supplying power to the driving load M that is a power supply target of each part of the copying machine 10. Power supply circuit 2, a switching element SW1 provided between the power supply circuit 2 and the capacitor C1, a terminal (second terminal T2 described later) of the switching element SW1 and one electrode of the capacitor C1. A connected current limiting resistance element R1 (an example of the current limiting element), a switch circuit 3 connected in parallel to the resistance element R1, an on / off detection circuit 4 for detecting on / off of the switching element SW1, A control unit 5 that receives a detection signal indicating on / off of the switching element SW1 from the on / off detection circuit 4 and controls the operation of the switch circuit 3; To have.

  The capacitor C1 is one element that constitutes a circuit that controls the operation of the drive load M, and supplies a current together with the power supply circuit 2 when a relatively large current is required for the drive load M. One electrode of the capacitor C1 is connected to one terminal (a second terminal T2 described later) of the switching element SW1 via the resistance element R1, and the other electrode is connected to the ground.

  The switching element SW1 has three terminals T1 to T3 (hereinafter, these terminals are referred to as first to third terminals T1 to T3). The first terminal T1 is a power supply circuit 2 and the second terminal T2 is a resistance element. The third terminal T3 is connected to R1 and ground. In the switching element SW1, when the cover 18 is closed, the first terminal T1 and the second terminal T2 are electrically connected, and the second terminal T2 and the third terminal T3 are electrically disconnected (the first terminal T3). On the other hand, when the cover 18 is opened, the first terminal T1 and the second terminal T2 are electrically disconnected, and the second terminal T2 and the third terminal T3 are electrically connected. As described above (corresponding to the second switching state), the switching state is mechanically switched in conjunction with the opening / closing operation of the cover 18.

  The switch circuit 3 is a circuit for short-circuiting both terminals of the resistance element R1, and according to an instruction from the control unit 5, the ON operation for short-circuiting both terminals of the resistance element R1 and the short-circuit state. Performs an off operation to cancel.

  The on / off detection circuit 4 is a circuit for detecting the on / off operation of the switching element SW1 based on the potential at the second terminal T2 of the switching element SW1. FIG. 5 is a circuit diagram showing a circuit configuration of the on / off detection circuit 4. As shown in FIG. 5, the on / off detection circuit 4 includes a switching element Tr1 such as a transistor and resistance elements R2 to R5. A series circuit of a resistance element R2 and a resistance element R3 is connected between the second terminal T2 of the switching element SW1 and the ground, and a connection point A between the resistance element R2 and the resistance element R3 and the switching element Tr1. A resistor element R4 is connected between the base terminal of the first and second base terminals. The collector terminal of the switching element Tr1 is connected to the power source Vcc via the control unit 5 and the resistance element R5, while the emitter terminal is connected to the ground.

  In the on / off detection circuit 4 having such a circuit configuration, the potential of the second terminal T2 of the switching element SW1, that is, the voltage across the capacitor C1, is a threshold value based on the element characteristics of the switching element Tr1 and the resistance elements R2 to R5. In the above case, the switching element Tr1 is turned on and an L (low) signal is output to the control unit 5, while when the voltage across the capacitor C1 is less than the threshold value, the switching element Tr1 is turned off and the H (high) signal Is output to the control unit 5.

  The control unit 5 reads a ROM (Read Only Memory) that stores each control program, a RAM (Random Access Memory) that temporarily stores data such as arithmetic processing and control processing, and the control program from the ROM. It comprises a CPU (central processing unit) to be executed and controls the operation of the switch circuit 3 based on the output signal of the on / off detection circuit 4.

  That is, when the control unit 5 receives an H (high) signal indicating that the potential of the second terminal T2 of the switching element SW1 is less than the threshold value from the on / off detection circuit 4, the control unit 5 performs an off operation on the switch circuit 3. On the other hand, when the L (low) signal indicating that the potential of the second terminal T2 is equal to or higher than the threshold value is received from the on / off detection circuit 4, the switch circuit 3 is caused to perform the on operation.

  The operation of the current control circuit 1 having the above configuration will be described. FIG. 6 is a time chart showing the operation of the current control circuit 1.

  As shown in FIG. 6, the cover 18 is now closed, and the first terminal T1 and the second terminal T2 of the switching element SW1 are electrically connected, while the second terminal T2 and the third terminal T3 are electrically connected. Are electrically cut off, and the power supply operation from the power supply circuit 2 to the capacitor C1 (charging operation of the capacitor C1) is performed. At this time, the control unit 5 causes the switch circuit 3 to perform an on operation (short circuit operation of both terminals of the resistance element R1).

  At time T = t1, when the cover 18 is opened, the first terminal T1 and the second terminal T2 of the switching element SW1 are electrically disconnected, while the second terminal T2 and the third terminal T3. The terminal T3 is electrically connected. Thereby, the power supply operation from the power supply circuit 2 to the capacitor C1 (charging operation of the capacitor C1) is stopped, and the discharging operation from the capacitor C1 to the ground is performed. Here, since the electric charge accumulated in the capacitor C1 is instantaneously discharged to the ground, and the voltage of the capacitor C1, and hence the potential of the second terminal T2 of the switching element SW1, instantaneously falls below the threshold value, the on / off detection circuit 4 At time T = t2 after a lapse of a minute time from time T = t1, an H (high) signal is output to the control unit 5. The control unit 5 causes the switch circuit 3 to perform an off operation (non-short-circuit operation of both terminals of the resistance element R1) based on the H (high) signal.

  When the cover 18 is closed again at time T = t3, the first terminal T1 and the second terminal T2 of the switching element SW1 are electrically connected with the second terminal T2 and the second terminal T2. The three terminals T3 are electrically disconnected. Thereby, the power supply operation from the power supply circuit 2 to the capacitor C1 (charging operation of the capacitor C1) is performed.

  When the voltage at both ends of the capacitor C1 rises to the threshold value at time T = t4 after the time Δt determined by the time constant of the capacitor C1 from the time T = t3, the on / off detection circuit 4 detects the time T = t4. The L (low) signal is output to the control unit 5, and the control unit 5 causes the switch circuit 3 to perform an ON operation based on the L (low) signal.

  As described above, in the present embodiment, when the cover 18 is opened, the electric charge accumulated in the capacitor C1 is discharged to the ground. Therefore, the operation of the switch circuit 3 is instantaneously switched from the on operation to the off operation. That is, both terminals of the resistance element R1 can be switched from the short-circuited state to the non-short-circuited state. Thus, even when the cover 18 is closed immediately after opening, both terminals of the resistance element R1 are not short-circuited at that time, so that the power is supplied from the power supply circuit 2 toward the capacitor C1. The current flows through the resistance element R1. As a result, it is possible to prevent the occurrence of an inrush current to the capacitor C1 that occurs when the cover 18 is closed immediately after the cover 18 is opened in the conventional configuration.

  The present case is applicable not only to the copying machine but also to an apparatus such as a multifunction machine or a facsimile machine. In the above-described embodiment, the type in which the paper feeding unit 12, the image forming unit 13, and the like are built in the apparatus main body 11 has been described. The present case is also applicable to those separated from the apparatus main body 11 so as to be controllable. Further, the function of the control unit 5 may be realized by hardware (circuit) instead of the form realized by a program as in the first embodiment.

1 is a side view schematically showing an internal configuration of a copying machine which is an embodiment of an image forming apparatus according to the present invention. 1 is a perspective view showing an external appearance of a copying machine in a state where a cover is closed. 1 is a perspective view showing an external appearance of a copying machine in a state where a cover is opened. It is a figure which shows the circuit structure of a current limiting circuit. It is a circuit diagram which shows the circuit structure of an on-off detection circuit. It is a time chart which shows operation | movement of a current control circuit. It is a figure which shows the structure of the conventional current control circuit. It is a time chart which shows operation | movement of the conventional current control circuit. It is explanatory drawing of an inrush current. It is a figure explaining the effect | action by the conventional current control circuit.

Explanation of symbols

1,200 Current control circuit 2,201 Power supply circuit 3,202 Switch circuit 4,203 On-off detection circuit 5,204 Control unit 10 Copying machine 18 Cover

Claims (3)

A current control circuit for controlling a current supplied from a power source to a capacitor for supplying power to a driving load in the electronic device according to a position of a predetermined member provided in the electronic device,
A first switching state including three terminals connected to the power source, the capacitor and the ground, and electrically connecting the power source and the capacitor in accordance with a position of the predetermined member; and the capacitor and the ground A switching element that can alternatively take a second switching state that electrically connects
An on / off detection circuit that detects whether the switching element is in the first switching state or the second switching state based on a potential of a terminal connected to the capacitor among the terminals of the switching element. When,
A current limiting element for limiting a current supplied from the power source to the capacitor;
A switch circuit for short-circuiting both terminals of the current limiting element;
A current control circuit comprising: control means for controlling a short circuit operation by the switch circuit based on a detection signal output from the on / off detection circuit.   The on / off detection circuit determines whether the switching element is in the first switching state based on a magnitude comparison between a potential of a terminal connected to the capacitor among the terminals of the switching element and a threshold value for the potential. The current control circuit according to claim 1, wherein the current control circuit detects whether the second switching state is set. An image forming apparatus that reads an image of a document by a photoelectric conversion operation and forms an image on a sheet based on an image signal obtained by the reading operation,
A cover member capable of taking an open position for exposing the inside of the image forming apparatus to the outside and a closed position for covering the inside of the image forming apparatus;
The electronic device is the image forming apparatus;
The image forming apparatus having a current control circuit according to claim 1, wherein a current supplied from the power source to the capacitor is controlled according to whether the cover member is in the open position or the closed position. .

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