Image forming apparatus having a motor to drive a developer retaining unit and a fixing unit

An image forming apparatus includes: a developer retaining unit configured to carry a developer; a fixing unit including a rotatable heating member configured to heat a recording sheet to thermally fix the developer on the recording sheet; a motor configured to drive the developer retaining unit and the fixing unit; a transmission unit configured to transmit a driving force of the motor to the fixing unit; a switching mechanism configured to selectively transmit the driving force of the motor to the developer retaining unit, and shut off the driving force of the motor to the developer retaining unit; and a control unit configured to, in a cooling operation, control the switching mechanism to shut off the driving force of the motor to the developer retaining unit and control the motor to rotate the heating member while the heating member does not heat.

CROSS REFERENCE OF APPLICATION

This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2010-102430 filed on Apr. 27, 2010, the contents of which are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The disclosure relates to an image forming apparatus that includes a fixing unit having a heating member which heats a recording sheet and can be rotated so as to thermally fix a developer on the recording sheet.

As an image forming apparatus, a device is known which drives a fixing unit, a developing device and the like by the same driving source. As such an image forming apparatus, for example, one that drives the fixing unit for a predetermined time after the fixing processing, for the cooling of the fixing unit, is known.

SUMMARY

However, according to a configuration of the above-mentioned related art, there is a need to simultaneously drive the developing device or the like every time the fixing unit is driven after the fixing processing of the fixing unit, whereby there is a problem in that the life of the developing device or the like is shortened.

Thus, an object of the aspect of the disclosure is to provide an image forming apparatus that can use a developing device or the like (a developer retaining unit) over a long period of time.

The aspect of the disclosure provides an image forming apparatus comprising:

a developer retaining unit configured to carry a developer;

a fixing unit including a rotatable heating member configured to heat a recording sheet to thermally fix the developer on the recording sheet;

a motor configured to drive the developer retaining unit and the fixing unit;

a transmission unit configured to transmit a driving force of the motor to the fixing unit;

a switching mechanism configured to selectively transmit the driving force of the motor to the developer retaining unit, and shut off the driving force of the motor to the developer retaining unit; and

a control unit configured to, in a cooling operation, control the switching mechanism to shut off the driving force of the motor to the developer retaining unit and control the motor to rotate the heating member while the heating member does not heat.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Next, a color printer of an example of an image forming apparatus according to an embodiment of the invention will be explained in detail with reference to suitable drawings. In the following description, a direction will be explained as a direction on the basis of a user at the time of using a color printer. That is, inFIG. 1, the left side facing a paper surface is “a front side”, the right side facing the paper surface is “a rear side”, the far side facing the paper surface is “a left side”, and the front facing the paper surface is “a right side”. Furthermore, an up and down direction toward the paper surface is “an up and down direction”.

<The Whole Configuration of Color Printer>

As shown inFIG. 1, a color printer1includes a paper feeding portion20that feeds a paper P as an example of a recording sheet, an image forming portion30that forms an image on a supplied paper P, a discharge portion90that discharges the paper P with an image formed thereon, and a control unit100, within a device main body2.

An opening portion2A is formed on an upper part of the device main body2. Moreover, the opening portion2A is adapted to be opened and closed by an upper cover3that is rotatably supported on the device main body2. An upper surface of the upper cover3is formed of a paper discharging tray4which accumulates a paper P discharged from the device main body2, and on a lower surface thereof, a plurality of LED attachment members5maintaining a LED unit40is provided.

The paper feeding portion20mainly includes a paper feeding tray21which is provided on the lower part of the device main body2and is mounted on the device main body2in an attachable and detachable manner, and a paper supplying mechanism22which transports the paper P from the paper feeding tray21to image forming portion30. The paper supplying mechanism22is provided in the front side of the paper feeding tray21, and mainly includes a paper feeding roller23, a separating roller24and a separating pad25.

In the paper feeding portion20configured in this manner, the papers P within the paper feeding tray21are separated one by one and transported to the upper part, and paper powders are removed in the process of passing between a paper power acquisition roller26and a pinch roller27, and then, the direction of the paper P is changed to a backward direction through the transport path28and the paper P is supplied to the image forming portion30.

The image forming apparatus30is mainly constituted by four LED units40, four process cartridges50, a transfer unit70, a belt cleaner10, and a fixing unit80.

The LED units40are connected to the LED attachment member5in a rollable manner, and are suitably positioned and supported by a positioning member that is provided on the device main body2.

The process cartridge50is arranged in a line in a front to rear direction between the upper cover3and the feeding paper portion20, and includes a photoreceptor drum51, a charger52, a developing roller53as an example of a developer retainer, a toner accommodating chamber54that accommodates a toner as an example of the developer, a cleaning roller55or the like.

The process cartridges50are arranged so that those shown by reference numerals50K,50Y,50M and50C, in which the toners of the respective colors for black, yellow, magenta, and cyan are put, are arranged from an upstream of a transport direction of the paper P in this sequence. In addition, in the present description and the drawings, when specifying the photoreceptor drum51, the developing roller53, the cleaning roller55or the like corresponding to the colors of the toners, the reference numerals of K, Y, M and C are denoted so as to correspond to each of black, yellow, magenta, and cyan.

The photoreceptor drums51are provided in each of a plurality of process cartridges50, and the plurality of process cartridges50is disposed as mentioned above, whereby the photoreceptor drums51are arranged along the front to rear direction in a row.

The developing roller53is a roller carrying a toner and comes into contact with the photoreceptor drum51to supply an electrostatic latent image on the photoreceptor drum51with the toners.

Moreover, as shown inFIG. 2, the developing roller53can be separated from the photoreceptor drum51by controlling a known contacting and separating mechanism110by the control unit100. Specifically, as shown inFIG. 1, a developing unit530as an example of the developer retaining unit supporting the developing roller53is movably supported, with respect to a drum unit510that supports the photoreceptor drum51, and the movement of the developing unit530is controlled by the contacting and separating mechanism110, whereby the developing roller53can come into contact with the photoreceptor drum51and can be separated therefrom.

A plurality of cleaning rollers55is provided adjacent to the respective photoreceptor drums51so as to correspond to the respective photoreceptor drums51. A cleaning bias is applied to the cleaning roller55. Moreover, the cleaning bias is suitably controlled, whereby it is possible to maintain (withdraw) the toner to be attached on the photoreceptor drum51by the cleaning roller55or transfer the toner onto the photoreceptor drum51.

The transfer unit70is provided between the paper feeding portion20and the respective process cartridges50, and includes a driving roller71, a driven roller72, a transport belt73, and a transfer roller74.

The driving roller71and the driven roller72are disposed in parallel so as to be separated in the front to rear direction, and a transport belt73formed of an endless-shaped belt is installed therebetween. The transport belt73is adapted to be rotated by the driving roller71so that an outer peripheral surface thereof is moved along the arrangement directions of the respective photoreceptor drums51. Furthermore, at the inside of the transport belt73, four transfer rollers74, which pinch the transport belt73between them and the respective photoreceptor drums51, are disposed so as to face the respective photoreceptor drums51. The transfer bias is applied to the transfer rollers74by a constant current control at the time of the transfer.

The belt cleaner10is a device which comes into sliding-contact with the transport belt73, thereby withdrawing the toner or the like attached on the transport belt73, and is disposed in the lower part of the transport belt73. Specifically, the belt cleaner10includes a slide-contact roller11, a withdrawal roller12, a blade13, and a waste toner receptor14.

The slide-contact roller11is disposed so as to come into contact with the outer peripheral surface of the transport belt73, and withdraws the attached matters on the transport belt73by applying the withdrawal bias between the slide-contact roller11and the back-up roller15disposed on the inner peripheral surface of the transport belt73.

The withdrawal roller12is a roller which comes into slide-contact with the slide-contact roller11, and withdraws the attached matters attached on the slide-contact roller11. Moreover, the attached matters on the withdrawal roller12are removed by the blade13disposed so as to come into slide-contact with the withdrawal roller12, and enter the waste toner receptor14.

The fixing unit80includes a heating roller81as an example of a heating member, which is disposed in the rear side of the respective process cartridges50and the transfer unit70, and a pressing roller82which is disposed oppositely to the heating roller81and presses the heating roller81. The heating roller81is rotatably supported by a housing of the fixing unit80which is formed in a hollow cylindrical shape, and is heated by a halogen heater HH disposed in the inner portion thereof.

In the image forming apparatus30configured in this manner, in the case of the color mode, firstly, after the surfaces of the respective photoreceptor drums51are similarly positively charged by the charger52, the surfaces are exposed by the respective LED units40. As a result, the electric potential of the exposed portion declines, and the electrostatic latent image based on the image data is formed on the respective photoreceptor drums51. Thereafter, the toner is supplied to the electrostatic latent image by the developing roller53, whereby the toner image is carried on the photoreceptor drum51.

The paper P supplied onto the transport belt73passes between the respective photoreceptor drums51and the respective transfer rollers74to be disposed inside the transport belt73, whereby the toner images formed on the respective photoreceptor drums51are transferred onto the paper P. Moreover, the paper P passes between the heating roller81and the pressing roller82, whereby the toner images transferred onto the paper P are thermally fixed.

The paper discharging portion90mainly includes a paper discharging side transport path91, which extends from an exit of the fixing unit80toward an upper part thereof and is formed so as to be reversed frontward, and a plurality of pairs of transport rollers92which transports the paper P. The paper P, onto which the toner image is transferred and thermally fixed, is transported along the paper discharging side transport path91by the transport roller92, discharged to the outside of the device main body2, and accumulated on the paper discharging tray4.

Next, a structure for giving the above-mentioned respective components a driving force will be described.

As shown inFIG. 3, a plurality of developing units530and the fixing unit80are configured to be driven by one motor200. Specifically, between the motor200and the fixing unit80, a transmission unit210including a plurality of gears211for transmitting the driving force from the motor200to the fixing unit80is provided.

Furthermore, between the motor200and the respective developing units530, a transmission switch-over mechanism220is provided which can selectively transmit and shut off the driving force of the motor200to the respective developing units530. The transmission switch-over mechanism220is a known friction gear mechanism, but, briefly described, the transmission switch-over mechanism220mainly includes a predetermined gear221, a maintenance arm222which can roll around a rotation axis of the gear221, and a friction gear223which is rotatably maintained in the maintenance arm222and is engaged with the gear221.

As a result, the friction gear223can rotate around the gear221in a direction depending on the rotation direction of the gear221. Furthermore, a stepped engagement portion224is provided on the maintenance arm222, and a hook member226rolled by a solenoid225is suitably engaged with the engagement portion224.

Moreover, the solenoid225or the motor200is controlled by the control unit100, whereby the transmission and the shutoff of the driving force from the motor200to the respective developing units530is switched over.

Specifically, when a control unit100rotates the motor200forward (shown clockwise) from the state ofFIG. 3and controls the solenoid225to disengage the hook member226from the engagement portion224, as shown inFIG. 4, the friction gear223is engaged near a gear row230that is connected to the respective developing units530. As a result, it is possible to concurrently drive the respective developing units530and the fixing unit80.

Furthermore, when the motor200is rotated backward from the state ofFIG. 4by the control unit100, as shown inFIG. 3, the friction gear223is moved so as to be separated from the gear row230, whereby the connection of the gear row230and the motor200is disconnected.

In addition, the driving of the drum unit510, the transport belt73or the like is performed by a motor different from the above-mentioned motor200.

Hereinafter, the control unit100will be described.

The control unit100has a CPU, a ROM, a RAM or the like, and is configured so as to perform the reception of a print command (a printing data) according to a prepared program, and the control of the paper feeding portion20, the image forming apparatus30, the paper discharging portion90, the contacting and separating mechanism110, the motor200and the transmission switch-over mechanism220.

Specifically, as shown inFIG. 2, the control unit100is configured so as to carry out a known control of separating the developing roller53from the photoreceptor drum51depending on the respective modes. Particularly, the control unit100brings the respective developing rollers53in contact with the respective photoreceptor drums51at the time of the color mode, and separates the respective developing rollers53Y,53M, and53C corresponding to the three colors other than black from the respective photoreceptor drums51Y,51M and51C at the time of the monochrome mode.

Furthermore, the control unit100separates the respective developing drums53from the respective photoreceptor drums51at the time of the cleaning mode. Herein, the cleaning mode is a known control, and, briefly described, as shown inFIG. 1, performs a control of transferring the toner withdrawn by the cleaning roller55onto the photoreceptor drum51, thereby withdrawing the toners by the belt cleaner10via the photoreceptor drum51and the transport belt73.

Furthermore, the control unit100is configured so as to turn OFF the halogen heater HH after the fixing processing in the fixing unit80and continues to rotate the motor200in this state, thereby carrying out the cooling operation by the rotation of the heating roller81. Moreover, upon carrying out the cooling operation, the control unit100is configured so as to carry out a cut-off control of controlling the transmission switch-over mechanism220to disconnect the transmission of the driving force to the respective developing units530.

When a predetermined condition is included, the control unit100carries out only the cooling operation without carrying out the cut-off control during a first time period after the fixing processing, and after the first time period, the control unit100restarts the cooling operation after carrying out the cut-off control. Moreover, the control unit100is configured so as to carry out the above-mentioned cooling operation and cut-off control together with another control operation performed in the state of prohibiting the printing control.

In addition, as “another control operation performed in the state of prohibiting the printing control”, any control may be adopted, but, in the present embodiment, the control operation for carrying out the above-mentioned cleaning mode is adopted. Furthermore, when the number of continuous prints becomes equal to or greater than a predetermined number, the cleaning mode in the present embodiment is carried out at two different timings when the printing control is finished.

Moreover, depending on the respective timing when the cleaning mode is started, the timing starting the above-mentioned cut-off control is changed. That is, as shown inFIG. 5, when the number of continuous prints is equal to or greater than a predetermined number, the control unit100waits for the above-mentioned first time period after the printing processing finish (after the fixing processing), and then, performs the cut-off control and the re-driving of the motor200. Furthermore, after an ordinary printing in which the number of continuous prints does not exceed a predetermined number, the control unit100immediately carries out the cut-off control without waiting for the first time period after the printing processing finish, thereby performing the re-driving of the motor200.

Specifically, the control unit100performs the control according to the flow chart shown inFIG. 6. In addition, while the flow chart ofFIG. 6is carried out, the control according to the known flow chart corresponding to the cleaning mode is also concurrently carried out.

As shown inFIG. 6, the control unit100firstly decides whether or not the print command exists (S1). When there is a print command (Yes), the known printing control, that is, a control is carried out in which the motor200is rotated forward, thereby connecting the transmission switch-over mechanism220(S2).

After the printing control is finished, the control unit100turns the halogen heater HH OFF (S3), and decides whether or not the number of continuous prints in the printing control is equal to or greater than a predetermined number (S4). When the number of continuous prints is equal to or greater than a predetermined number in step S4(Yes), the control unit100decides whether or not the elapsed time after the printing finish exceeds the first time period (S5), and after waiting for the first time period (Yes), carries out the cut-off control (S6).

Moreover, in step S4, when the number of continuous prints is less than a predetermined number, the control unit100immediately carries out the cut-off control without waiting for the first time period (S6). Specifically, in step S6, the control unit100firstly stops the motor200and reversely rotates the motor200, thereby stopping the motor200by disconnecting the connection by the transmission switch-over mechanism220.

After step S6, the control unit100restarts the cooling operation by rotating the motor200forward for a predetermined time (S7), and after a predetermined time has elapsed, finishes the main control.

In addition, in the present embodiment, after disconnecting the connection by the transmission switch-over mechanism220in step S6, the motor200is stopped and the stopped motor200is rotated forward in step S7, but, the invention is not limited thereto. For example, after disconnecting the connection by the transmission switch-over mechanism220in step S6, by continuously rotating the motor200backward in this state, the cooling operation may be carried out.

Next, a change in temperature in the fixing unit80by the control of the above-mentioned control will be described with reference toFIG. 7.

Herein, the temperature change shown by a chain double-dashed line inFIG. 7Ais a temperature change of a case of not carrying out the cooling operation (not the case of the invention), and the control of the motor of this time is shown in the timing chart ofFIG. 7B. That is, in the case of not carrying out the cooling operation, since the motor is immediately turned OFF at the time t1after the fixing processing, the temperature in the fixing unit increases relatively rapidly.

On the other hand, as shown inFIG. 7C, in the control of carrying out the cooling operation after immediately performing the cut-off control after the fixing processing (S4; No→S6), after performing the cut-off control (after a time t2), the heating roller81is rotated by the driving of the motor200, whereby the inner portion of the fixing unit80is cooled (see dotted line ofFIG. 7A). For that reason, after the time t2, the temperature increases in a gentle gradient, whereby the temperature is prevented from rising too high.

Furthermore, as shown inFIG. 7D, in the control of carrying out the cut-off operation after waiting for the first time period after the fixing processing (S4; Yes→S5; Yes→S6), the cooling due to the rotation of the heating roller81is immediately started after the fixing processing, and the cooling is continued during the first time period (during times t1to t3) (see solid line ofFIG. 7A). As a result, since the temperature increases in a gentle gradient from the time t1earlier than the time of the control in which the first time period is not waited for, the temperature is prevented from rising too high.

According to the above, it is possible to obtain the following effects in the present embodiment.

When carrying out the cooling operation, the control unit100controls the transmission switch-over mechanism220, whereby the transmission of the driving force to the developing unit530is disconnected. Thus, it is possible to suppress the deterioration due to the driving of the developing unit530.

Since the control unit100can carry out the cut-off control after waiting for the first time period after the fixing processing, it is possible to effectively cool the fixing unit80becoming the highest temperature after the fixing processing.

Since the cooling operation or the cut-off control is performed together with the cleaning mode to be performed in the state in which the printing control is prohibited, it is possible to reduce the frequency in which the color printer1cannot be used.

In addition, the invention is not limited to the above-mentioned embodiment but can be used in various forms as described later.

In the above-mentioned embodiment, the cleaning mode is performed at two different timings and the timing of the cut-off control is changed accordingly. However, the invention is not limited thereto, for example, in addition to the two different timings of the above-mentioned embodiment, the cleaning mode may be carried out at the timing when the printing mode is changed to the other mode (for example, from the color to the monochrome). In this case, for example, as shown inFIG. 8, the cut-off control, which is performed concurrently with the cleaning mode to be carried out after the mode switch-over, may be performed without waiting for the first time period after the mode switch-over.

In the above-mentioned embodiment, as the developer retainer and the developer retaining unit, the developing roller53and the developing unit530were adopted, but the invention is not limited thereto, for example, the photoreceptor drum and the drum unit may be adopted.

In the above-mentioned embodiment, the invention was applied to the color printer1, but the invention is not limited thereto, the invention may be applied to other image forming apparatus, for example, a copier, a multifunction printer, or the like.

In the above-mentioned embodiment, as an example of the recording sheet, a paper P such as a thick paper, a postcard, or a thin paper was adopted, but the invention is not limited thereto, for example, an OHP sheet may be adopted.

In the above-mentioned embodiment, as the heating member, the heating roller81heated by the halogen heater HH was adopted, but the invention is not limited thereto, for example, one may be adopted in which the heating roller itself is heated by the means of an IH (Induction Heating) method or the like. Furthermore, the transmission unit, the motor, or the like also are not limited to the above-mentioned embodiment, but can use various types.

In the above-mentioned embodiment, the mechanism using the friction gear223as the transmission switch-over mechanism was adopted, but the invention is not limited thereto, for example, a one-way clutch, which transmits the driving force in only one direction, may be adopted. Furthermore, in the above-mentioned embodiment, the transmission switch-over mechanism is disposed adjacent to the motor, but the invention is not limited thereto, if the transmission switch-over mechanism is built in a part of the transmission mechanism from the motor to the developer retaining unit, the same may be disposed in any position.

In the above-mentioned embodiment, the control of waiting for the first time period after the fixing processing and performing the cut-off control, and the control without waiting were selectively carried out depending on the condition, but the invention is not limited thereto, and only any one of two controls may be carried out.

In the above-mentioned embodiment, as “another control operation performed in the state of prohibiting the printing control”, the cleaning mode was adopted, but the invention is not limited thereto, for example, the toner is directly printed on the transport belt, and a patch test for investigating whether or not the printed toner is printed on a correct position may be adopted.