JP7174344B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, an image forming apparatus using a timing belt for drive transmission is known.
For example, Japanese Patent Application Laid-Open No. 2002-200002 describes a device that uses a timing belt to transmit drive to a conveying member that conveys a transfer material at a secondary transfer portion that transfers an image from an intermediate transfer member to a transfer material.

However, there remains the problem that it is difficult to obtain an appropriate tension of the timing belt regardless of changes in the driving load of the object to be driven.

In order to solve the above-described problems, the present invention provides an image forming apparatus using a timing belt for drive transmission, in which an idler pulley is provided between a drive source side pulley and a driven side pulley, and a A timing belt is stretched between the idler pulley and between the idler pulley and the driven pulley, and the tension of the timing belt stretched between the idler pulley and the driven pulley is determined. A change means is provided, and an object to which the timing belt drives and transmits the transfer material is a conveying member that conveys the transfer material in a transfer section that transfers an image onto the transfer material, and the change means movably holds the idler pulley. a holding member; a spring having one end engaged with the idler pulley held by the holding member and having the other end connected to a tensioner to exert a biasing force to pull the idler pulley toward the connection point of the tensioner; A drive means for changing the attitude of the tensioner so that the position of the connection point of the tensioner changes the biasing force, and a drive control means for controlling the drive means, wherein the drive control means is operated by an operator. The drive means is controlled based on transfer material type information that is input or detected by a detection means, and the posture of the tensioner is changed to change the urging force of the spring . It is.

According to the present invention, the proper tension of the timing belt can be obtained regardless of the driving load fluctuation of the driven object.

1 is a schematic configuration diagram of an image forming apparatus; FIG. FIG. 2 is an enlarged view of a secondary transfer belt unit of the image forming apparatus; FIG. 4 is an explanatory diagram of a mechanism for varying the tension of the secondary transfer unit; FIG. 2 is a block diagram of control of the image forming apparatus; 7 is a graph showing experimental results of examining the tension of the image forming apparatus. FIG. 4 is an explanatory diagram of a state in which the cleaning blade is turned over; Explanatory drawing of other embodiment.

An embodiment in which the present invention is applied to an image forming apparatus using a timing belt for transmitting drive to a conveying member that conveys a transfer material at a secondary transfer portion that transfers an image from an intermediate transfer member to a transfer material will be described. do.
FIG. 1 is a schematic configuration diagram of the image forming apparatus. An intermediate transfer belt 10 as an intermediate transfer member is supported by a drive roller 11 and two driven rollers 12 and 13 . The drive roller 11 is driven by a drive motor 14 . An arrow A indicates the moving direction of the intermediate transfer belt 10 by this driving. A total of four photoreceptors 20, 21, 22, 23 for black and each color (Y, M, C) are arranged so as to face the horizontal stretched portion of the intermediate transfer belt 10 above.

A charging member, a developing member, and a cleaning member are arranged around each photoreceptor for carrying out the electrophotographic process. A writing unit 30 for irradiating each photosensitive member with exposure light for latent image formation is arranged on the upper part of the apparatus. Primary transfer members (transfer rollers) 24, 25, 26, and 27 are arranged on the back side of the belt of the primary transfer portion where the intermediate transfer belt and each photosensitive member face each other. Appropriate current is applied to each primary transfer member to move the charged toner developed on the photosensitive drum onto the intermediate transfer belt. In this primary transfer section, the intermediate transfer belt is pressed against the lower portion of the photosensitive drum by a spring.

A secondary transfer belt unit 40 is arranged below the apparatus so as to face the portion of the intermediate transfer belt 10 wound around the driven roller 12 that supports the intermediate transfer belt 10 . The secondary transfer belt unit 40 supports the secondary transfer belt 41 with a secondary transfer driving roller 42 and three driven rollers 43 , 44 and 45 . A portion of the secondary transfer belt 41 wound around the secondary transfer driving roller faces the intermediate transfer belt to form a secondary transfer portion. A paper sheet P, which is a transfer material, is sent from a paper feed cassette or the like to the secondary transfer portion. A fixing device 50 is arranged to fix the toner image onto the paper P to which the toner image has been transferred after passing through the secondary transfer portion. A cleaning unit 51 is also arranged for cleaning the surface of the intermediate transfer belt 10 to which the secondary transfer portion is added.

FIG. 2 is an enlarged view of the secondary transfer belt unit 40. As shown in FIG.
This unit 40 has a spring 46 that biases and presses the supporting portion of the secondary transfer driving roller 42 toward the supporting roller 12 of the intermediate transfer belt in the secondary transfer portion. The lower end of this spring 46 is attached to a follower portion which is vertically moved by a pressure cam 47 . The pressurizing cam 47 is designed such that its rotational attitude is changed by the secondary transfer pressurizing motor 48 . As a result of the change in the rotational posture (rotation amount) of the pressure cam 47, the amount by which the support portion of the secondary transfer driving roller 42 is lifted by the force of the spring 46 changes, and as a result, the secondary transfer driving roller 42 and the intermediate transfer belt 10 are driven. The pressure between the rollers 12 changes. This pressure is changed according to the thickness of the paper. Specifically, as the thickness of the paper increases, the weight of the paper also increases. Therefore, in order to reliably hold and convey the paper in a high-speed machine, the roller pressure is set high. Hereinafter, this pressure control by controlling the amount of rotation of the secondary transfer pressure motor 48 will be referred to as secondary transfer nip pressure control.

A cleaning blade 49 made of urethane is arranged so as to contact the surface of the secondary transfer belt 41 . A collection container 49a for collecting the toner removed by the cleaning blade 49 is also arranged. Since residual toner transferred from the intermediate transfer belt 10 and toner scattered inside the apparatus may adhere to the surface of the secondary transfer belt 41, this is removed. While the secondary transfer belt is rotating, it is constantly cleaned, but most of the static load of the secondary transfer unit is due to contact between the cleaning blade 49 and the secondary transfer belt 41 .

The secondary transfer belt 41 rotates when the rotational force of the roller 42 is transmitted to the belt 41 by friction with the rubber layer forming the outer peripheral surface of the secondary transfer drive roller 42 . A roller-side pulley 60 is fixed to the end of the shaft of the secondary transfer driving roller 42 by a parallel pin. Normally, the roller-side pulley 60 and the motor-side pulley on the motor shaft are stretched by a timing belt. there is

That is, a two-stage idler pulley 61 is prepared in which a first pulley 61a and a second pulley 61b having different pit circle radii are integrated. A roller-side timing belt 62 is stretched between the roller-side pulley 60 and a first pulley 61 a of the idler pulley 61 having a relatively small radius. A motor-side timing belt 65 is stretched between a second pulley 61 b of the idler pulley 61 having a relatively large radius and a motor-side pulley 64 connected to the shaft of the secondary transfer drive motor 63 . . That is, the secondary transfer belt is driven from the secondary transfer drive motor through two timing belts and two stages of idler pulleys.

FIG. 3 is an explanatory diagram of a mechanism for varying the tension of the roller-side timing belt. The idler pulley 61 is held by a guide, which is a holding member having a long groove-shaped space into which the shaft 61c of the idler pulley 61 is inserted, so that the idler pulley 61 can move on the extension line between the shafts connecting the idler pulley 61 and the roller-side pulley 60. ing. One end of a spring 71 as an urging member is engaged with the shaft 61c of the idler pulley 61. As shown in FIG. The other end of this spring 71 is connected to a tensioner 72 . The tensioner 72 is rotatable around a central axis 72a. The tensioner 72 is rotationally driven by a belt tension motor 73 via the central shaft 72a. When the tensioner 72 rotates, the idler pulley 61 moves via the spring 71 and the tension of the roller-side timing belt 62 changes. Even at the rotational position of the tensioner 72 where the tension is the smallest, the tension of the spring 71 applies tension to the roller-side timing belt 62 (increases the tension).

An actuator 74 is attached to the center shaft 72 a of the tensioner 72 . An optical sensor 75 for detecting the actuator 74 is arranged near the actuator 74 . This optical sensor 75 is not interlocked with the operation of the tensioner 72 and takes a fixed position. The actuator 74 moved by the rotation of the tensioner 72 shields the optical path between the light emitting element and the light receiving element of the optical sensor 75, thereby detecting the rotational position of the actuator. Then, for example, a stepping motor is used as the secondary transfer driving motor 63 , and counting of the step angle number of the belt tension motor 73 is started at the timing when the optical sensor 75 is shielded by the actuator 74 on the tensioner 72 . The rotational position of the tensioner 72 is grasped from the number of step angles counted thereafter. In this embodiment, the tension of the roller-side timing belt 62 is controlled by controlling the rotation position of the tensioner 72 according to the thickness of the paper. This control (hereinafter referred to as timing belt tension control) will be described in detail later.

FIG. 4 is a control block diagram for the secondary transfer unit.
The control section 100 comprises a sheet thickness selecting means 101 , an optical sensor 75 for grasping the rotational posture of the tensioner 72 , and a controller section 102 . The paper thickness selection means 101 uses a table that stores the relationship between the paper type and the paper thickness based on the paper type selection input (type selection input) input from the operation panel by the operator of the image forming apparatus. It is possible to select the paper thickness by selecting the paper pressure or by using a detecting device for detecting the paper thickness and using the future detection result. Signals from the paper thickness selection means 101 and the optical sensor 75 are input to the controller unit 102 (signals from the sensor for detecting the rotation attitude of the cam 47 are also input if necessary). The output of the controller section 102 is input to the driver 48 a of the secondary transfer pressure motor 48 and the driver 73 a of the belt tension motor 73 . The control unit 100 performs secondary transfer nip pressure control and timing belt tension control according to the paper thickness.

The secondary transfer nip pressure control according to the thickness of the paper will be described.
In this embodiment, the secondary transfer nip pressure control according to the paper thickness is performed as follows. As the thickness of the paper increases, the roller pressure is increased. At this time, the amount of crushing of the roller increases and the contact resistance with the paper increases, so the load on the secondary transfer driving roller increases. Thus, the load of the secondary transfer drive roller fluctuates due to the secondary transfer nip pressure control according to the paper thickness. Depending on the load on the secondary transfer drive roller, the range of appropriate tension of, for example, a roller-side timing belt for driving the secondary transfer roller changes. The lower limit of the appropriate tension range is a value that does not cause tooth skipping, and the upper limit is a value that is unnecessarily large and does not cause a reduction in life due to wear of the tension belt or pulley.

Note that when tooth skipping occurs, color unevenness also occurs in a color image forming apparatus. Also, if the tension far exceeds the upper limit, the pulley shaft may fall. In order to avoid this axial inclination, it is not possible to always use a large tension that does not cause tooth jumping, considering only the prevention of tooth jumping.

FIG. 5 shows the experimental result of investigating the tension of the roller-side timing belt at which tooth skipping occurs under various secondary transfer nip pressures without passing the paper through the secondary transfer nip. Specifically, at each secondary transfer nip pressure, the tension was changed from a small value to a large value, and the belt tension at which tooth skipping first occurred at that secondary transfer nip pressure was examined. A graph shows the points of the belt tension (horizontal axis) at which tooth jumping first occurred and the dynamic torque (vertical axis) obtained from the current supplied to the secondary transfer drive motor 63 at that time. This is indicated by x above.

The points of x are connected by a solid line, and the dynamic torque on the vertical axis that causes x corresponding to the belt tension on the horizontal axis can be understood as follows. That is, it can be seen that the lower the tension, the lower the torque at which tooth jumping starts to occur, and the higher the tension, the higher the torque at which tooth jumping starts to occur. Tooth jumping can be avoided by using a combination of dynamic torque and tension in the region on the right side of the solid line connecting the points of x. For reference, the horizontal axis of the graph indicates the values at the lower and upper limits of the recommended range for use of the timing belt as appropriate values for thin paper and appropriate values for thick paper.

Therefore, in this embodiment, the rotation angle of the tensioner 72 is controlled by timing belt tension control so that the tension is weakened for thin paper and the tension is strengthened for thick paper, depending on the thickness of the paper. Therefore, the proper tension corresponding to the paper thickness is always selected, and the shortened life of the pulleys and timing belts, shaft breakage, and tooth jumping can be suppressed, and the concerns about color unevenness can be eliminated.

Moreover, according to this embodiment, it is possible to eliminate power transmission failure due to pulley melting. This pulley melting may occur in the following manner.

A cleaning blade 49 for cleaning the secondary transfer belt shown in FIG. 2 is always in contact with the belt 41 . For this reason, the toner collected from the belt 41 remains at the tip of the blade, and the lubricity is maintained due to the presence of the toner. As a result, the lubricating property tends to decrease, the frictional force between the secondary transfer belt 41 and the cleaning blade 49 is high, and the tip portion of the cleaning blade 49 is curled toward the rotation downstream side of the secondary transfer belt 41, causing the secondary transfer belt 41 to rotate. A situation may arise in which the surface of the transfer belt 41 is pressed.

FIG. 6 shows a state in which the cleaning blade 49 is turned over. In this state, the surface of the secondary transfer belt cannot be rotated because the frictional force with the cleaning blade 49 made of urethane greatly exceeds the driving force. In the secondary transfer driving roller, since the frictional force between the outer peripheral surface of the roller made of rubber and the inner peripheral surface of the secondary transfer belt greatly exceeds, the roller side pulley 60 added to the shaft end and the roller side timing Belt 62 does not work. On the other hand, power is transmitted to the motor-side timing belt 65 by the rotation of the motor-side pulley 64 on the shaft of the secondary transfer drive motor 63 . At this time, the roller-side timing belt 62, which cannot operate due to overload, and the first pulley 61a of the idler pulley 61, which can operate, are engaged.

The relationship between the first pulley 61a, the roller-side pulley 60, and the roller-side timing belt 62 is such that the tension is determined only by variation in part tolerance. Therefore, if the engagement between the roller-side timing belt 62 and the first pulley 61a is maintained at an appropriate tension or a tension higher than the appropriate tension, the secondary transfer drive motor 63 cannot operate due to the overload. An error is detected.

However, if the mesh is engaged with a tension lower than appropriate, the mesh will be disengaged and tooth skipping will easily occur. If tooth skipping occurs, the actual static load on the secondary transfer section will be overloaded, but the dynamic load (dynamic torque) will increase. is determined from the current value of the secondary transfer drive motor 63, it is not a very high value. Therefore, the overcurrent detection of the secondary transfer drive motor 63 is not reached and no error is detected, so the secondary transfer drive motor 63 continues to rotate without stopping. If the idler pulley 61 is made of resin, contact wear between the roller-side timing belt 62 and the first pulley 61a made of resin may cause the first pulley 61a to reach a melting temperature in a short period of time, resulting in melting. Once melted, drive transmission is no longer possible.

According to the present embodiment, gear meshing occurs with appropriate tension and tooth skipping does not occur. It can be determined from the current value of the transfer drive motor 63, an error is detected from the secondary transfer drive motor 63, and the motor is stopped. Therefore, melting of the idler pulley 61 can be avoided.

FIG. 7 is an explanatory diagram of another embodiment. In order to change the tension of the roller-side timing belt 62, in the previous embodiment, the biasing force in the tension direction is changed so that the idler pulley 61 can move. A tension roller 80, which is a tension imparting member that abuts on the stretched portion between the pulleys, is provided, and the tension imparted by the roller 80 is changed. Other points are the same as the previous embodiment.

One end of a spring 81 is engaged with the shaft 80 c of the tension roller 80 . The other end of this spring 81 is connected to a tensioner 82 . The tensioner 82 is rotatable around a central axis 82a. The tensioner 82 is rotationally driven by a belt tension motor 83 through the central shaft 82a. When the tensioner 82 rotates, the tension applied to the roller-side timing belt 62 by the tension roller 80 via the spring 81 changes.

An actuator 84 is attached to the center shaft 82 a of the tensioner 82 . An optical sensor 85 for detecting the actuator 84 is arranged near the actuator 84 . This optical sensor 85 is not interlocked with the operation of the tensioner 82 and takes a fixed position. The actuator 84 moved by the rotation of the tensioner 82 shields the optical path between the light emitting element and the light receiving element of the optical sensor 85, so that the rotational position of the actuator 84 can be detected and the rotational position of the tensioner 82 can be grasped.

In the above two embodiments, the tension of the roller-side timing belt 62 is changed in order to prevent tooth skipping of the timing belt. can be Depending on the paper thickness, control is performed so that the thicker the paper, the greater the winding angle.

The invention of this embodiment also has the following background.
In recent years, color image forming apparatuses have advanced. A color image forming apparatus is equipped with multiple image forming mechanisms consisting of a latent image carrier and a developing mechanism. form an image. In the secondary transfer section, the color image is transferred onto the recording medium by a secondary transfer belt or the like.

Since the secondary transfer belt for forming the composite color image is an endless belt, it is very important to stabilize the moving speed during transfer. This is because if the speed fluctuation with respect to the intermediate transfer belt is large, uneven colors will be output on the recording medium.

In addition, there is a belt cleaning mechanism, and a cleaning blade is arranged near the belt surface so that there is no toner left unwiped on the surface of the secondary transfer belt due to toner scattering or the like. The toner is scraped off and collected by coming into contact with the .

Driving force is transmitted to the endless secondary transfer belt by power transmission to pulleys attached to shaft ends of rubber rollers arranged in contact with the inner side of the belt. It is already known that the power transmission to the pulleys is done by means of timing belts.

In the conventional power transmission between pulleys, power is transmitted by the meshing of the teeth formed on the outer periphery of the pulley and the tooth formed on the inside of the timing belt. Or it was constructed by connecting two or more pulleys with a toothed timing belt.

As one means for reducing the occurrence of color unevenness on the recording medium, the driving portion of the secondary transfer belt is driven by a timing belt instead of gears. It was meant to mitigate the negative impact on the image.

The specifications of the timing belt, which is used to transmit power between pulleys, are based on the assumed load torque, operating time, and other usage conditions, with a safety factor added to determine the pitch and face width of the tooth profile. was.

The timing belt had to be properly tensioned when it was wound around the pulleys. There was an effective means of applying tension to the timing belt by urging a flat pulley to optimize the tension.

Large, high-speed image forming devices are designed to handle a wide range of paper thicknesses, so the amount of pressure applied from the secondary transfer belt, which is in contact with the intermediate transfer belt, to the intermediate transfer belt varies depending on the paper thickness. It is possible. Thick paper has the highest pressure, so the load torque for driving the secondary transfer belt is high. Thin paper has the lowest pressure, so the load torque for driving the secondary transfer belt is low.

If the timing belt is designed according to the load torque when thick paper is used, excessive tension will be applied to the timing belt if thin paper is used frequently, and the mechanism itself will be over-engineered. In addition, there is concern about shortening the life of pulleys and timing belts due to wear from excessive tension, and about breakage of the shafts that support the pulleys.

When the timing belt is designed according to the load torque when thin paper is used, if thick paper is used frequently, the tension of the timing belt is low, which increases the possibility of teeth skipping of the timing belt. There is concern about short life due to wear of pulleys and timing belts over time due to tooth jumping.

Also, if the cleaning blade that cleans the secondary transfer belt of the secondary transfer section is turned over and the teeth are skipped, the actual static load is very high, but the belt tension is low, so the dynamic load will cause overcurrent of the motor. The value will not be high enough to reach detection. Therefore, an error due to overcurrent detection of the motor is not detected, and the motor continues to rotate without stopping. As a result, contact wear between the timing belt, which cannot operate due to overload, and the pulley, which continues to rotate while skipping teeth, may reach the melting temperature of the material in a short period of time, and in the case of a resin pulley, may even lead to melting.

As described above, in a large-sized, high-speed image forming apparatus, the load torque fluctuates depending on the thickness of the paper to be printed. There are concerns about the short life of the timing belt, shaft breakage, and color unevenness due to tooth skipping. Furthermore, the pulley melts and power cannot be transmitted.
There was a problem.

Therefore, in a large, high-speed image forming apparatus, the load torque fluctuates depending on the thickness of the paper to be printed, and the range of torque fluctuation is large. It is required to suppress the short life of pulleys and timing belts, shaft breakage, and tooth jumping, to eliminate concerns about color unevenness, and power failure due to pulley melting.

It is known that in a large-sized, high-speed image forming apparatus, the load torque varies depending on the thickness of the paper to be printed, and the torque variation range is large. Moreover, the pressure from the secondary transfer belt to the intermediate transfer belt is predetermined according to the thickness of the paper to be printed, and the load torque can also be assumed. Therefore, it is conceivable that an appropriate tension corresponding to the load torque should be determined in advance. To always select a proper tension corresponding to paper thickness. This prevents pulleys and timing belts from being subjected to excessively high or excessively low tension.

10: intermediate transfer belt 11: drive roller 12: driven roller 13: driven roller 14: drive motor 20: photoreceptor 21: photoreceptor 22: photoreceptor 23: photoreceptor 30: writing unit 40: secondary transfer belt unit 41 : Secondary transfer belt 42 : Secondary transfer drive roller 43 : Driven roller 44 : Driven roller 45 : Driven roller 46 : Spring 47 : Pressure cam 48 : Secondary transfer pressure motor 48a : Driver 49 : Cleaning blade 49a : Recovery Container 50 : Fixing device 51 : Cleaning unit 60 : Roller side pulley 61 : Idler pulley 61 a : First pulley 61 b : Second pulley 61 c : Shaft 62 : Roller side timing belt 63 : Secondary transfer driving motor 64 : Motor side pulley 65 : Motor side timing belt 71 : Spring 72 : Tensioner 72a : Central shaft 73 : Belt tension motor 73a : Driver 74 : Actuator 75 : Optical sensor 80 : Tension roller 80c : Shaft 81 : Spring 82 : Tensioner 82a : Central shaft 83 : Belt Tension motor 84 : Actuator 85 : Optical sensor 100 : Control section 101 : Paper thickness selection means 102 : Controller section P : Paper

JP 2006-18518 A

Claims (3)

In an image forming apparatus using a timing belt for drive transmission,
An idler pulley is provided between the drive source side pulley and the driven side pulley, and a timing belt is stretched between the drive source side pulley and the idler pulley and between the idler pulley and the driven side pulley. hanging,
providing means for changing the tension of the timing belt stretched between the idler pulley and the driven side pulley;
an object to which the driving force is transmitted by the timing belt is a conveying member that conveys the transfer material in a transfer unit that transfers the image onto the transfer material;
The changing means includes a holding member that movably holds the idler pulley , one end of which is locked by the idler pulley held by the holding member, and the other end of which is connected to a tensioner to move the idler pulley to the tensioner. a spring that exerts a pulling force on the connecting portion side of the tensioner; a driving means that changes the posture of the tensioner so that the position of the connecting portion of the tensioner changes the biasing force; and a drive control that controls the driving means. means and
The drive control means controls the drive means based on transfer material type information input by an operator or detected by the detection means, and changes the attitude of the tensioner so that the tensioner is applied by the spring . An image forming apparatus characterized by changing power. The image forming apparatus according to claim 1,
The idler pulley is a two-stage idler pulley in which a first pulley and a second pulley having different radii are integrated. An image forming apparatus, which is connected to a driving source side pulley by the timing belt . The image forming apparatus according to claim 1 or 2 ,
The image forming apparatus, wherein the transfer section is a secondary transfer section for transferring the image from the intermediate transfer member to the transfer material .

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