Image forming apparatus

An image forming apparatus according to the present invention includes: a discrimination circuit for detecting a conveying load at a time a sheet, on which an image is to be formed, is conveyed through a curved conveying path, for discriminating a thickness of the sheet based on a detected value of the conveying load, and for generating a process control signal in order to carry out a process control suitable for the thickness of the sheet based on the discriminated thickness; and a process control circuit for carrying out the process control suitable for the thickness of the sheet in response to the process control signal received.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus such as a copying machine, a complex machine including a copying machine, facsimile, and printer, etc.

2. Background of the Invention

Image forming apparatuses include copying machines for copying original images, and multifunction peripherals (MFPs) each having functions of a copying machine, a facsimile, a printer, etc. Sometimes, these copying machines and MFPs are used to print images on special paper such as thick paper, instead of ordinary paper. When thick paper is printed on as special paper, the settings of the copying machines and the MFPs should be changed to the “thick paper print setting.” In the thick paper print setting, the process conditions such as the transfer condition, the charging condition, the fixing condition, etc. are changed from those for ordinary paper to those for thick paper. Conventionally, such thickpaper print settings have been adjusted by users.

However, there is a case where a user determines wrongly whether the paper to be printed on is ordinary paper or thick paper, resulting in that he/she does not implement the thick paper print setting when thick paper is used for the printing. In this case, many problems may arise due to the differences between the process conditions for thick paper and the process conditions for ordinary paper. For example, sometimes an image printed on thick paper is thinner than the original image to be copied; sometimes, there is a white portion, to which toner is not adhered, in an image printed on thick paper; and sometimes the appearance of a printed image is inferior to and dirtier than that of the original image.

SUMMARY OF THE INVENTION

The present invention is proposed in view of the above-described problems, and the object of the present invention is to automatically discriminate the thickness of a sheet of paper being conveyed, and to carry out a process control suitable for the thickness of the sheet of paper.

An image forming apparatus according to the present invention includes: a discrimination circuit for detecting a conveying load at a time a sheet, on which an image is to be formed, is conveyed through a curved conveying path, for discriminating a thickness of the sheet based on a detected value of the conveying load, and for generating a process control signal in order to carry out a process control suitable for the thickness of the sheet based on the discriminated thickness; and a process control circuit for carrying out the process control suitable for the thickness of the sheet in response to the process control signal received.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, characteristic features of the embodiment of the present invention will be briefly described below.

In the embodiment of the present invention, the thickness of paper being conveyed is discriminated by detecting the conveying load of the paper when the paper, on which an image is to be formed, is vertically conveyed. Then, the process conditions suitable for the thickness of the paper being conveyed are set based on the discrimination result. Next, according to the set process conditions, an image is formed on the paper. Hereinafter, the embodiment of the present invention will be described in detail.

FIG. 1is a sectional view for explaining the structure and operation of a manual paper feeding unit and its peripherals of a multifunction peripheral (MFP) according to an embodiment of the present invention. In the present specification, an MFP is an apparatus having functions of a copying machine, a facsimile, a printer, etc., all in a single unit. As can be understood fromFIG. 1, the MFP employs a vertical conveying system, with which it is possible to minimize the size and reduce the first copy time.FIG. 2is a partial exploded view of a driving section of the manual paper feeding unit shown inFIG. 1.

As can be understood fromFIG. 1, in the MFP, a sheet of paper set in a manual paper feeding tray3is sent to a resist section8via a vertical conveying path7by a driving section4. An electrostatic latent image formed on the surface of a photoconductive member9is transferred to the sheet of paper to ultimately form an image thereon. This will be described in more detail below.

First, the structure of the MFP will be described below.

As shown inFIG. 1, the MFP includes a manual paper feeding unit1for setting and feeding special paper such as thick paper (e.g., 128, 158, or 209 g/m2), thin paper (e.g., 50 g/m2), OHP sheets, etc. Although ordinary paper (e.g., 64–80 g/m2) is usually fed by a cassette paper feeding unit (not shown) placed within a main section2, it is possible for ordinary paper to be also fed by the manual paper feeding unit1and be printed on. The manual paper feeding unit1is composed of the manual paper feeding tray3and the driving section4.

The manual paper feeding tray3is for setting the sheet of paper on which an image is formed. A pair of sidewalls3afor supporting the set paper from both sides is attached to the manual paper feeding tray3.

The driving section4is for conveying the sheet of paper set in the manual paper feeding tray3toward the resist section8. As shown inFIG. 1, the driving section4includes a paper feeding sensor actuator12and a paper feeding sensor11for detecting the existence of the paper set in the manual paper feeding tray3. As can be understood fromFIG. 1, an end portion of the paper feeding sensor actuator12is pushed toward the left side in the drawing due to the weight of the paper set in the manual paper feeding tray3. As the paper feeding sensor actuator12is pushed, the paper feeding sensor11is turned on. The paper feeding sensor11is connected to the main section2, by which the ON/OFF state of the paper feeding state is recognized.

As shown inFIG. 1, the driving section4includes a pick-up roller6for picking up the uppermost sheet of paper from the stack of sheets paper set in the manual paper feeding tray3. Further, the driving section4includes a paper feeding roller5for conveying the picked-up sheet of paper to the resist section8.

As can be understood fromFIG. 2, a motor15for rotating the paper feeding roller5is provided to the driving section4. The motor15can be any kind of DC motor and AC motor. The motor15is connected to a clutch17avia a connecting member, which is not shown. The clutch17ais connected to a paper feeding roller shaft14for conveying the driving force of the motor15to the paper feeding roller5. That is, whether or not the driving force of the motor15is conveyed to the paper feeding roller shaft14is determined by the ON/OFF states of the clutch17a.

As shown inFIG. 2, the paper feeding roller shaft14penetrates the paper feeding roller5. Further, the pick-up roller6is wound by a belt13together with the paper feeding roller5. With such a structure, the pick-up roller6is rotated in conjunction with the paper feeding roller5. As shown in FIG.1, a tension roller18is positioned so as to contact the belt13, so that the belt13is not loosened.

As shown inFIG. 2, the paper feeding shaft14also penetrates a spring clutch17b, which is opened by the rotation of the paper feeding roller shaft14, resulting in that the pick-up roller6falls in the direction of the arrow due to its own weight, as shown inFIG. 1. That is, in the non-printing state, the spring clutch17bsupports the pick-up roller6at an upper position, and in the printing state, the spring clutch17bdrops the pick-up roller6as shown inFIG. 1. A pick-up roller push-up spring17cfor moving the dropped pick-up roller6back to the original position is also penetrated by the paper feeding roller shaft14.

As shown inFIG. 1, the paper feeding roller5contacts a separating pad16for separating only one sheet of paper when some of the sheets of paper set in the manual paper feeding tray3are simultaneously picked up, overlapping one another.

Next, as shown inFIG. 1, the MFP includes the main section2, to the exterior housing of which the manual paper feeding unit1is attached.

As shown inFIG. 1, the main section2includes a vertical conveying path7serving as a path connecting the manual paper feeding tray3and the resist section8. The sheet of paper sent from the manual paper feeding tray3by the driving section4passes through the vertical paper conveying path7toward the resist section8.

As shown inFIG. 1, the main section2includes the resist section8, which timely sends the received sheet of paper to the photoconductive member9so as to align the sheet of paper with the electrostatic latent image formed on the surface of the photoconductive member9. In more detail, the resist section8includes a resist sensor8a, a resist actuator8b, and resist rollers8cand8d. The sheet of paper having passed through the vertical conveying path7pushes up the tip of the resist actuator8, thereby turning on the resist sensor8a. The resist sensor8ais connected to the clutch17ashown inFIG. 2. When the resist sensor8ais turned on, the clutch17ais turned off, thereby stopping the rotations of the paper feeding roller5and the pick-up roller6. The resist rollers8cand8dhold an end of the sheet of paper having pushed up the actuator8b, and send the sheet of paper to the photoconductive member9in predetermined timings.

The operation of the MFP with the above-described structure will be described next.

As is understood fromFIG. 1, a sheet of paper on which an image will be formed is set in the manual paper feeding tray3. The end of the paper feeding sensor actuator12is pushed down to the left side inFIG. 1due to the weight of the sheet of paper set in the manual paper feeding tray3, thereby turning on the paper feeding sensor11. When the paper feeding sensor11is turned on, the main section2recognizes that a sheet of paper is set in the manual paper feeding tray3. In this state, if the user pushes down a print key button (not shown) of the main section2, the paper feeding operation is started.

That is, as can be understood fromFIG. 2, the motor15starts, and then the clutch17ais turned on, resulting in that the driving force of the motor15is conveyed to the paper feeding roller shaft14, thereby rotating the paper feeding roller shaft14. In conjunction with the rotation of the paper feeding roller shaft14, the paper feeding roller5penetrated by the paper feeding roller shaft14is rotated, thereby rotating the pick-up roller6wound by the belt13together with the paper feeding roller5. On the other hand, as the paper feeding roller shaft14is rotated, the spring clutch17bpenetrated by the paper feeding roller shaft14is opened, resulting in that while still being rotated, the pick-up roller6falls, due to its own weight, on the uppermost sheet of paper P of the stack of sheets of paper set in the manual paper feeding tray3, as can be understood fromFIG. 1. Then, the sheet of paper P is picked up by the rotating pick-up roller6and sent to the paper feeding roller5. Subsequently, the sheet of paper P is fed toward the resist section8by both the pick-up roller6and the paper feeding roller5. After the sheet of paper P completely leaves the pick-up roller6, only the paper feeding roller5continues to feed the sheet of paper P. After passing through the vertical conveying path7to reach the resist section8, the sheet of paper P pushes up the tip portion of the resist actuator8b, thereby turning on the resist sensor8a, resulting in that the clutch17ais turned off. As the clutch17ais turned off, the rotation of the paper feeding roller5and the pick-up roller6is stopped. Further, when the clutch17ais turned off, the pick-up roller6is returned to the original position by the pick-up roller push-up spring18, as can be understood fromFIG. 1. The movement of the sheet of paper P having pushed up the resist actuator8bis stopped, and then the end thereof is held by the resist rollers8cand8d, as can be understood fromFIG. 1. The resist rollers8cand8dsend the sheet of paper P toward the photoconductive member9at a predetermined time.

As can be understood fromFIG. 1, the sheet of paper P having been sent from the manual paper feeding tray3toward the resist section8is bent at an angled portion A of the vertical conveying path7when it is passing through the vertical conveying path connecting the manual paper feeding tray3and the resist section8. Accordingly, the load of the motor15shown inFIG. 2, e.g., the drive current value, increases by the amount required to bend the sheet of paper P. The amount of increase in the drive current value, i.e., the load of the motor, depends on what is being fed, for example, thick paper, ordinary paper, or thin paper. Hereinafter, this will be described in more detail.

FIG. 3shows the transitions of the drive current value of the motor15when thick paper, ordinary paper, and thin paper are fed from the manual paper feeding tray3to the resist section8. The present inventor has drawnFIG. 3based on their own experiments.

First, as can be understood fromFIG. 1, sheets of thick paper, ordinary paper, and thin paper are set in the manual paper feeding tray3. Then, the print key button (not shown) of the main section2is pushed to actuate the motor15shown inFIG. 2. This moment is shown as time t0inFIG. 3. The drive current value of the motor15at this time is the drive current value I0inFIG. 3.

As shown inFIG. 3, at time t1, when a period T0has passed from time t0at which the motor15is actuated, the clutch17ashown inFIG. 2is turned on (CLT-ON). When the clutch17ais turned on, the paper feeding roller5and the pick-up roller6are rotated, as can be understood fromFIG. 2. The pick-up roller6picks up and sends a sheet of paper, as can be understood fromFIG. 1. The sheet of paper having been picked up is fed by only the pick-up roller6during the period T1, i.e., from time1to time2. That is, the sheet of paper does not reach the paper feeding roller5during the period T1, i.e., from time t1to time t2. As a result, during the period T1, the paper feeding roller5is rotated contacting the separating pad16, as can be understood fromFIG. 1. In the period T1, the load of the motor15is increased due to the friction resistance of the separating pad16as compared with the period T0, which is before CLT-ON. Accordingly, as shown inFIG. 3, the drive current value I1of the motor15during the period T1is greater than the drive current value I0of the motor15during the period T0, which is before CLT-ON.

As can be understood fromFIG. 3, the sheet of paper fed by the pick-up roller6at time t1reaches the paper feeding roller5at time t2when the period T1has passed from time t1. During the period T2, i.e., from time t2at which the sheet of paper reached the paper feeding roller5to t3, the sheet of paper is horizontally fed by both the paper feeding roller5and the pick-up roller6to the position immediately before the vertical conveying path7shown inFIG. 1. As shown inFIG. 3, the drive current value I2of the motor15during the period T2is smaller than the drive current value I1of the motor15during the period T1, in which only the pick-up roller6feeds the sheet of paper. That is, since the friction resistance of the sheet of paper is smaller than that of the separating pad16shown inFIG. 1, the load of the motor15, i.e., the drive current value of the motor15, is smaller in the period T2, during which the paper feeding roller5feeds the sheet of paper, than in the period T1during which the paper feeding roller5rotates while contacting the separating pad16.

As can be understood fromFIG. 3, the sheet of paper having reached the paper feeding roller5at time t2reaches the vertical conveying path7shown inFIG. 1at time t3when the period T2has passed from time t2. The sheet of paper having reached the vertical conveying path7at time t3is bent and sent through the vertical conveying path7to the resist section8. Then, at time t4when the period T3has passed from time t3, the resist sensor8ashown inFIG. 1is turned on, and the clutch17ashown inFIG. 2is turned off (CLT-OFF).

As can be understood fromFIG. 3, during the period T3, in which the sheet of paper is passed through the vertical conveying path7, the drive current values I3a–I3cof the motor15are greater than the drive current value I2of the motor during the preceding period T2. The drive current values I3a–I3care those of the motor15for thick paper, ordinary paper, and thin paper, respectively.

As shown inFIG. 3, during the period T3, the sheet of paper is bent and conveyed at the angled portion A shown inFIG. 1. Accordingly, since the sheet of paper is bent, the conveying load of the motor15, i.e., the drive current value of the motor15increases in comparison with the period T2. As can be understood fromFIG. 3, the drive current value I3a, which is obtained when the sheet of thick paper is fed, is the largest. The reason for this is that thick paper is the least flexible, and the load required for bending thick paper is the most. Then, as can be understood fromFIG. 3, the drive current value I3cof the motor15, which is obtained when thin paper is fed, is the smallest. The reason for this is that thin paper is the most flexible, and the load required for bending thin paper is the least. In addition, as can be understood fromFIG. 3, since the flexibility of ordinary paper is between that of thick paper and that of thin paper, the drive current value I3bof the motor15, which is obtained when ordinary paper is fed, is somewhere between the drive current value I3aof the motor15for thick paper and the drive current value I3cof the motor15for thin paper.

With such recognition, the MFP of the present embodiment automatically discriminates the thickness of the sheet of paper, and prints the sheet of paper under the process conditions suitable for the sheet of paper based on the discrimination result. This will be described in more detail below.

FIG. 4is a block diagram showing a discrimination circuit for discriminating which type of paper among thick paper, ordinary paper, and thin paper is being fed.

This discrimination circuit discriminates which type of paper among thick paper, ordinary paper, and thin paper is being conveyed using the detected drive current value of the motor15. Further, this discrimination circuit generates a process control signal corresponding to the thickness of the sheet of paper and sends the signal to a process control circuit.

First, the structure of the discrimination circuit will be described.

As shown inFIG. 4, a motor driver IC22for controlling the motor15is connected to the motor15. A connection signal serving as a signal indicating the start of paper feeding is inputted to the motor driver IC22, as shown inFIG. 4. The motor driver IC22drives the motor15in response to the connection signal. As shown inFIG. 4, the motor driver IC22is connected to a reference voltage REF1, and also connected to a reference voltage REF2via resistors23and24. A first comparator20and a second comparator21are connected in parallel with each other between the resistors23and24, as shown inFIG. 4. The first and second comparators20and21are for monitoring the drive current value of the motor15. For this purpose, the drive current value of the motor15is inputted to each of the first and second comparators20and21from the motor driver IC22. Further, an identical reference current value is inputted to each of the first and second comparators20and21from a microcomputer19of the main section2, as shown inFIG. 4. The reference current value may be set such that the differences among thick paper, ordinary paper, and thin paper can be distinguished. In this case, the reference current value is obtained by adding a design margin to the drive current value of the motor15for ordinary paper. The fist comparator20compares the drive current value of the motor15inputted from the motor driver IC22with the reference current value inputted from the microcomputer19. If the drive current value of the motor15is smaller than the reference current value, the first comparator20outputs a first detection signal representing thin paper, as shown inFIG. 4. On the other hand, the second comparator21compares the drive current value of the motor15inputted from the motor driver IC22with the reference current value inputted from the microcomputer19. If the drive current value of the motor15is greater than the reference current value, the second comparator21outputs a second detection signal representing thick paper, as shown inFIG. 4. In the other cases, no detection signal is outputted from the first and second comparators20and21. The first detection signal outputted from the first comparator20and the second detection signal outputted form the second comparator21are fed back to the microcomputer19, as can be understood fromFIG. 4. If receiving the first detection signal representing thin paper, the microcomputer19recognizes that the paper being conveyed is thin paper. If receiving the second detection signal indicating thick paper, the microcomputer19recognizes that the paper being conveyed is thick paper. If receiving neither the first detection signal nor the second detection signal, the microcomputer19recognizes that the paper being conveyed is ordinary paper. As shown inFIG. 4, the microcomputer outputs a process control signal corresponding to the first detection signal or the second detection signal to a process control circuit (not shown) for performing process control. Receiving the process control signal, the process control circuit performs process control in accordance with the thickness of paper based on the received process signal.

The discrimination circuit according to the present embodiment can discriminate the thickness of thickpaper, ordinary paper, thin paper, and other sheets made of a material other than paper, such as OHP sheets.

Next, the operation of the discrimination circuit and the process control circuit when the discrimination circuit is used for printing will be described with reference toFIGS. 4 and 5.FIG. 5is a flow chart showing the operation of the discrimination circuit and the process control circuit when the printing operation is performed using the discrimination circuit shown inFIG. 4.

First, as shown inFIG. 5, an original image to be copied is set on a glass plate for setting originals of the main section2shown inFIG. 1(Step1). Next, sheets of paper including thick paper, ordinary paper, and thin paper are set in the manual paper feeding tray3shown inFIG. 1(Step2). Then, the print key button of the main section2is turned on (Step3). With this action, a connection signal is inputted to the motor driver IC22(Step4) to start the paper feeding operation (Step5), as can be understood fromFIG. 5. After the paper feeding operation is started, the drive current value of the motor15is inputted from the motor driver IC22to each of the first comparator20and the second comparator21(Step6). Further, a reference current value is inputted from the microcomputer19to each of the first comparator20and the second comparator21. Each of the first comparator20and the second comparator21compares the drive current value of the motor15with the reference current value (Step7). This will be described in more detail below.

If the first comparator20and the second comparator21determine that the drive current value of the motor15and the reference current value are the same (“Same” in Step8), no detection signal is outputted from the first comparator20and the second comparator21. Because of this, the microcomputer19discriminates that the paper being conveyed is ordinary paper (Step9). If the first comparator20and the second comparator21determine that the drive current value of the motor15is smaller than the reference current value (“Smaller” in Step8), only the first comparator20outputs the first detection signal, as shown inFIG. 4. The first detection signal is fed back to the microcomputer19, so that the paper being conveyed is discriminated to be thin paper (Step10). If the first comparator20and the second comparator21determine that the drive current value of the motor15is greater than the reference current value (“Greater” in Step8), only the second detection signal is outputted from the second comparator21, as can be understood fromFIG. 4. The second detection signal is fed back to the microcomputer19, so that the paper being conveyed is discriminated to be thick paper (Step11).

After the thickness of the paper being conveyed is discriminated, the paper is printed under suitable process conditions in accordance with the thickness thereof. This will be described in more detail below.

If the paper being conveyed is discriminated to be ordinary paper, the paper is printed under the process conditions for ordinary paper, which is the initial mode (Step12).

If the paper being fed is judged to be thin paper, a process control signal corresponding to thin paper is sent from the microcomputer19to a process control circuit (not shown), as can be understood fromFIG. 4. The process control circuit changes the process conditions from the initial mode for ordinary paper to the thin paper mode in response to the received process control signal (Step13). The thin paper is printed under the process conditions in the thin paper mode (Step12). For example, when thin paper is printed, in the transfer process, the separating output, which is the force to separate paper adhering to the photoconductive drum from the photoconductive drum, is increased in comparison with the case in which ordinary paper is printed.

If the paper being conveyed is discriminated to be thick paper, a process control signal corresponding to thick paper is outputted from the microcomputer19to the process control circuit (not shown). The process control circuit changes the process conditions from the initial mode for ordinary paper to the thick paper mode in response to the received process control signal (Step14). The thick paper is printed under the process conditions in the thick paper mode (Step12). For example, when the thick paper is printed, in the transfer process, the transfer inflow current value, which is the force to transfer an image formed on the photoconductive drum to a sheet of paper, is increased as compared with the case in which ordinary paper is printed. Further, in the fixing process, the fixing temperature, which is the temperature for fixing toner on the sheet of paper, is increased.

The environment around the area where the MFP is placed is not always the same. For example, the environmental conditions of the area where the MFP is placed, e.g., humidity, change due to the daily weather and/or the operation status of the air conditioner. Generally, the flexibility of printing paper is affected by humidity. For example, the flexibility of a sheet of paper in the area where the humidity is high is increased since the sheet of paper is subjected to moisture. That is, even though the thickness of the paper being conveyed is the same, the conveying load is less in the case where the paper subjected to more moisture is conveyed than in the case where the paper subjected to less moisture is conveyed. Accordingly, when a sheet of paper which is subjected to more moisture than usual is printed, there may arise a problem in that the thickness of paper is discriminated wrongly, and the printing operation is performed under the process conditions suitable for paper having other thickness. In order to avoid this, a humidity sensor for detecting the humidity in the area where the image forming apparatus is placed, or within the image forming apparatus may be provided inside the image forming apparatus to modify the detection data by using the humidity value detected by the humidity sensor when discriminating the thickness of paper. For example, the thickness of paper may be discriminated by modifying the data based on the relationship between the humidity detected by the humidity sensor and the drive current value of the motor. With such an adjustment, the accuracy in discriminating the thickness of paper can be improved.

According to this embodiment, the thickness of paper is automatically discriminated, and based on the discrimination result, a process control is performed which is suitable for the thickness of the paper being printed. Accordingly, a user may print a sheet of paper under the optimum printing conditions for the paper without setting the printing condition in accordance with the thickness of paper by himself/herself. Further, since the drive current value of the motor is used for discriminating the thickness of paper, it is not necessary to newly provide a special sensor to the MFP. Accordingly, since no special modification is made for the existing manual paper feeding unit, the cost for introducing the present embodiment can be minimized.