JP4886860B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine using an electrophotographic system, and controls the amount of a loop formed on a transfer material such as paper conveyed between a transfer unit and a fixing unit. It is about.

  In a conventional image forming apparatus, a toner image on an image carrier is transferred to a transfer material by a transfer roller or the like, and is guided to a nip portion of a fixing device via a conveyance guide and fixed. There is a state in which the rear end portion of the transfer material has not yet passed through the transfer portion while being introduced into the nip portion of the fixing portion (unit).

  On the other hand, there is a difference between the transfer material conveyance speed of the fixing unit and the transfer material conveyance speed of the transfer unit due to thermal expansion of the fixing roller of the fixing unit, solid difference, or secular change, and the transfer material conveyance speed in the fixing unit is When the transfer material transport speed of the transfer unit is exceeded, a phenomenon occurs in which the transfer material carrying the unfixed toner image is pulled between the fixing unit and the transfer unit, which causes image deterioration such as image blurring. There is a case. Therefore, if a loop as a slack is formed in the transfer material conveyed between the transfer portion and the fixing portion, it is possible to prevent the phenomenon that the transfer material is pulled between them.

  13A shows an overall view of the image forming apparatus, FIG. 13B shows a case where a loop is not formed on the transfer material and the loop is small, and FIG. 13C shows a case where the loop is large. Indicated. Further, an enlarged view between the conveying belt and the fixing device is shown in FIG. 14A, and an entrance guide and a loop amount sensor drawing are shown in FIG. 14B.

  With reference to the drawings, a part relating to a transfer material conveyance configuration between transfer and fixing in a conventional image forming apparatus will be described. As shown in FIG. 14A, the fixing entrance guide 13 has its front end positioned below the transfer surface of the transfer material transport belt, while the rear end of the entrance guide is positioned above the transfer belt. It is inclined to be located at. Furthermore, when the transfer material 4 is formed with a downwardly convex loop, the transport surface between the front and rear ends is a gently convex curved surface so that it can be accommodated.

  Next, as shown in FIG. 14B, a loop amount sensor 15 for detecting the loop amount is arranged on the conveyance surface of the fixing entrance guide 13 so as to be rotatable about one side as a swing center, and the other side is a transfer material. Are arranged so as to be biased by a spring (not shown) so as to rotate according to the amount of the loop formed along the line. Further, a flag linked to the movement of the loop amount sensor 15 extends from the center of swinging of the loop amount sensor 15 to the photo interrupter 14 (hereinafter described as a photo interrupter) which is one of the loop amount detection discriminating means. As shown in FIGS. 13B and 13C, the loop amount exceeds a certain value due to the ON / OFF state of the photo interrupter 14 being changed in conjunction with the movement of the loop amount sensor 15. Whether or not is detected.

  Further, as shown in FIG. 13A, the pressure roller 16 in the fixing device 9 is rotated counterclockwise in the drawing by the fixing motor 18 whose rotation is controlled by the controller 20 and the CPU 21. The conveyor belt 6 is driven by a driving roller 8. The drive source of the drive roller 8 is a conveyor belt drive motor 17 whose rotation is controlled by the controller 19 and the CPU 21, and the rotation direction is counterclockwise in the figure.

  The CPU 21 controls the rotational speed of either the fixing motor 18 and / or the conveyor belt motor 17 based on the detection signal of the photo interrupter 14 that is interlocked with the movement of the loop amount sensor 15 and the print timing, thereby controlling the rotation speed of the conveyor belt. The transfer material conveyance speed between the fixing devices is controlled to control the loop amount.

  A series of flow of loop amount control will be described with reference to the flowchart of FIG.

  First, as step 1 (abbreviated as S1 in the figure, the same applies hereinafter), the transfer material front end passes through the entrance guide 13 from the conveyance belt 6 and begins to be nipped and conveyed by the pressure roller 16 and the heat roller 11 in the fixing device 9. Next, as step 2, the transfer material conveyance control between the conveyance belt and the fixing device is performed, and the control is performed in the direction in which the loop amount is formed (so that the loop is enlarged). In step 3, it is determined whether or not the loop is large and the loop amount is formed up to the loop size (FIG. 13C). The loop formation control in step 2 is continued until the loop formation is determined. If it is determined that the loop is formed, the process proceeds to step 4. In step 4, it is determined whether or not the trailing edge of the transfer material has passed the loop amount sensor 15 shown in FIGS. 14A and 14B. If not, the process proceeds to step 5. Go to step 8.

  If it is detected in step 5 that the loop has been formed up to the large loop (FIG. 13C), this time, the conveyor belt in the direction of reducing (releasing) the loop so that the loop is small (FIG. 13B). ~ Transfer material transfer control between fixing units. In Step 6, it is determined whether or not the loop amount has been eliminated up to the small loop (FIG. 13B). If it has not been eliminated, the state of Step 5 is continued, and if it is determined that it has been eliminated, the process proceeds to Step 7. When the rear end of the material has not passed the loop amount sensor 15 shown in FIGS. 14A and 14B, the process returns to step 2 again and a series of control is repeated.

  If it has passed, the control of the loop amount of the transfer material is completed, and then the process proceeds to Step 8, where the rear end of the transfer material is nipped and conveyed in the fixing device and output from the image forming apparatus.

  Next, FIG. 15 shows a time chart of loop amount control.

  Among these signals, the uppermost signal indicates the signal of the loop amount sensor 15. When a loop is formed, this signal shows a large value of the loop when the photo interrupter is interrupted, and shows a small value when the loop is reduced and eliminated and the photo interrupter is not interrupted. The next signal indicates the transfer material conveyance speed between the conveyance belt and the fixing device, and a loop is formed. When the loop amount sensor 15 determines that the loop amount is large, the conveyance speed of the fixing unit is large to eliminate the loop. It becomes. After that, when the loop is canceled and it is determined that the loop amount is small, the loop is formed again, so that the conveyance speed of the fixing unit is low.

  The last signal indicates the actual loop amount of the transfer material. In this figure, the loop amount that can be detected as a large loop amount indicates R large, and the loop amount that can be detected as a small loop amount indicates R small.

  In other words, the loop amount of the transfer material is controlled while repeating a series of loop amount changes toward R large when the conveyance speed of the fixing unit is low, and toward R small when the conveyance speed of the fixing unit is high.

  As a conventional example as described above, for example, in Patent Document 1 described below, a loop amount sensor that detects a loop of a transfer material is provided in a conveyance guide unit between the fixing unit and the transfer unit, and fixing is performed according to the result. There has been proposed an image forming apparatus in which the driving speed control of a roller driving motor is switched stepwise to control the loop amount of a transfer material.

  Also, in Patent Document 2 below, a loop amount sensor that detects a loop of a transfer material is provided in a conveyance guide unit between the fixing unit and the transfer unit, and based on the result, transfer material conveyance of the fixing unit or the transfer unit is performed. There has been proposed an image forming apparatus in which the speed is switched so that the loop amount of the transfer material is within a predetermined range.

  On the other hand, in Patent Document 3 below, a conveyance guide that conveys a transfer material from a transfer portion toward a fixing nip portion of a fixing device is disposed so that the conveyance surface is inclined upward toward the fixing nip portion, and the transfer material is directed downward. Proposes an image forming device that forms a convex loop, detects the loop amount, and controls the transfer material conveyance speed of the fixing unit to make the loop amount constant, enabling subtle speed control. Has been.

  Furthermore, in Patent Document 4 below, two sensors are provided for detecting the loop amount of the transfer material conveyed from the transfer portion toward the fixing nip portion of the fixing device, and one of the sensors detects the loop amount. In this case, the transfer material conveyance speed is controlled in the direction to decrease the loop amount, and the loop amount is increased in the direction in which the other sensor detects the loop amount, and the transfer material loop amount is controlled within a certain range. A forming apparatus has been proposed.

JP-A-10-97154 JP-A-10-340012 JP 2000-344385 A JP 2001-282072 A

  By the way, in the case of the above-described conventional example, the transfer material conveyance speed control is performed so that a constant loop amount or a loop amount within a predetermined range is formed for a transfer material having all physical property values conveyed between transfer and fixing. It is.

  However, when trying to form the same loop amount regardless of the physical property value of the transfer material, the rate of change in the loop amount of the transfer material varies depending on the physical property value of the transfer material, for example, strain due to basis weight, thickness, etc. As a result, the loop amount may not be within a predetermined range depending on the type of transfer material. Therefore, when it is desired to select a different optimum loop amount for each type of transfer material to be used, it has been difficult to cope with the conventional control. (Here, the basis weight is the weight of a piece of paper per square meter expressed in grams. Paper with a low basis weight is "light paper" or "thin paper", and paper with a high basis weight is " Heavy paper "or" thick paper ").

  For example, as shown in FIG. 17, when a strong transfer material is used, the transfer material is strong when the loop is formed between the transfer and fixing, so that the transfer material is pushed back to the image carrier side and the image is rubbed or fixed to the fixing device side. There is a possibility that an image defect occurs when it is pushed in. On the other hand, if a weak transfer material is used, the transfer material is weak at the time of loop formation between transfer and fixing.If the transfer material loop amount becomes too large and the deformation to the transfer material occurs significantly, There is a possibility that unfixed toner on the transfer material is disturbed.

  For example, as a means for solving such a problem due to the difference in strain of the transfer material, the problem is solved by increasing the distance between transfer and fixing (a configuration in which the sheet is sent to the fixing unit after passing through the transfer unit). However, increasing the transport distance between transfer and fixing increases the overall configuration of the apparatus, and increases the transport distance, thereby increasing the paper throughput (number of prints per unit time). ) Will be delayed.

  The present invention has been made under such circumstances, and an object thereof is to obtain a good image by appropriately controlling the loop amount in accordance with the type and physical properties of the transfer material.

  Further, the present invention controls the transfer material loop amount to an appropriate loop amount size according to the type and physical properties of the transfer material without increasing the distance between the transfer belt and the fixing device, thereby preventing image blurring. Prevention is another issue.

  In addition, the present invention can obtain a good image by controlling the loop amount within the optimum range in accordance with the type and physical properties of the transfer material even in a color image forming apparatus in which image disturbance due to color misregistration is conspicuous. It is an issue.

  In order to solve the above problems, in the present invention, an image forming apparatus is configured as follows.

(1) The detection result by the image carrier, the image forming unit for forming an image according to the image information on the image carrier, and the detection unit for detecting the type of the transfer material, or the type of the transfer material is input. An identification means for identifying the type of transfer material according to the input result from the input means, a transfer means for transferring an image formed on the image carrier by the image forming means to the transfer material, Fixing means for fixing the image transferred by the transfer means, and detection means for detecting the amount of loop of the transfer material formed while the transfer material is being conveyed by the transfer means and the fixing means. The detecting means includes a first flag and a second flag that can contact the transfer material on which the loop is formed, and a loop amount that can detect each variation of the first flag and the second flag. And a detection sensor The first flag and the second flag before detecting the loop of the transfer material contact the transfer material in the second flag with respect to the transfer material conveyed from the transfer unit to the fixing unit. In accordance with the type of the transfer material identified by the identification means, the leading end on the side is set so as to be farther from the transfer material than the leading end on the side in contact with the transfer material in the first flag. Is determined to be the first transfer material, the detection result of only the loop amount detection sensor corresponding to the first flag is used, and the transfer material is weaker than the first transfer material. If it is determined that the transfer material is a second transfer material, the transfer speed of the transfer material in the fixing unit is controlled using the detection result of only the loop amount detection sensor corresponding to the second flag. Image forming equipment .

  According to the present invention, a good image can be obtained by appropriately controlling the loop amount in accordance with the type and physical properties of the transfer material. In addition, without increasing the distance between the transfer belt and the fixing device, the transfer material loop amount can be controlled to an appropriate loop amount size according to the type and physical properties of the transfer material to prevent image blurring. it can. Further, even in a color image forming apparatus in which image disturbance due to color misregistration is conspicuous, a good image can be obtained by controlling the loop amount within the optimum range in accordance with the physical properties of the transfer material.

1 is a diagram illustrating a schematic configuration of an image forming apparatus that is Embodiment 1. FIG. FIG. 3 is a diagram illustrating a conveyance belt to a fixing device, an entrance guide, and a loop amount sensor in Embodiment 1. Operation explanatory diagram of the loop amount sensor in the first embodiment. Timing chart of loop amount control in embodiment 1 Flow chart of loop amount control in embodiment 1 Diagram showing the presence or absence of image defects The figure which shows between a conveyance belt-fixing device in Example 2, an entrance guide, and a loop amount sensor. Operation explanatory diagram of the loop amount sensor in the second embodiment The figure which shows between a conveyance belt-fixing device in Example 3, an entrance guide, and a loop amount sensor. Operation explanatory diagram of the loop amount sensor in the third embodiment The figure which shows the difference in the detection sensitivity by the shape of the loop detection part in Example 3. The figure which shows schematic structure of the color image forming apparatus which is an application example The figure which shows schematic structure of the image forming apparatus which is a prior art example The figure which shows between a conveyance belt-a fixing device in a prior art example, an entrance guide, and a loop amount sensor. Timing chart of loop amount control in the conventional example Flow chart of loop amount control in the conventional example The figure which shows between a conveyance belt-a fixing device in a prior art example, an entrance guide, and a loop amount sensor.

  The mode for carrying out the present invention will be described in detail below with reference to examples.

  First, a schematic configuration of an “image forming apparatus” (laser beam printer) according to the first embodiment will be described with reference to FIG. A scanner unit 1 includes a semiconductor laser (not shown) and a rotating polygon mirror. Reference numeral 2 denotes an image carrier for forming a latent image, and 3 denotes a developing device for supplying a developer to the image carrier 2. Reference numeral 4 denotes a transfer material (paper or the like), and 5 denotes a charging roller for charging the image carrier 2. Reference numeral 6 denotes a conveyance belt constituted by an endless belt for conveying the transfer material 4. A transfer roller 7 is used to transfer the toner image on the image carrier 2 onto the transfer material 4. 8 is a conveyance belt driving roller for driving the conveyance belt 6, 9 is a fixing unit for fixing the toner image on the transfer material 4 to the transfer material 4, and 10 is a cleaning member for excess toner on the image carrier 2 and cleaning. It is a cleaning unit including a storage unit for excess toner to be collected. Reference numeral 11 denotes a heat roller in the fixing device 9 for melting the unfixed toner on the transfer material 4, and reference numeral 12 denotes a heat source for the heat roller 11. 13 is an entrance guide for conveying and guiding the transfer material 4 from the conveyance belt 6 to the fixing device 9, 14 is a photo interrupter for detecting the position of the loop amount detection flag, and 15 is a transfer between the conveyance belt 6 and the fixing device 9. As an example of the conveyance state of the material 4, a loop amount sensor 16 for detecting the loop amount, and a pressure roller 16 for conveying the transfer material 4 in the fixing device 9. Reference numeral 17 denotes a conveyance belt drive motor for driving the conveyance belt 6, and 18 denotes a pressure roller drive motor for driving the pressure roller 16 for conveying the transfer material 4 in the fixing device 9. Reference numeral 19 denotes a motor controller for the transport belt drive motor, 20 denotes a motor controller for the pressure roller drive motor, 21 denotes a CPU for operating the image forming apparatus, and 40 denotes the type of the transfer material P fed and transported from the paper feed unit T. Is a paper type sensor for identifying As the paper type sensor 40, a CMOS sensor or the like that detects the state of the surface of the transfer material by photographing can be used.

  In FIG. 1, the transport roller 8 is driven by a motor 17, and an encoder (not shown) that outputs a signal synchronized with the rotation of the motor is attached to the shaft of the motor 17. It is possible to detect the rotational speed of the motor by detecting how many encoder signals are detected at regular intervals. Therefore, the rotational speed can be detected more accurately as the encoder has higher definition. For detection of the rotation speed, an optical sensor that outputs one pulse for one rotation of the motor may be used. In this case, the rotational speed of the motor can be detected by measuring the time between pulses.

  Reference numeral 21 denotes a CPU for operating the image forming apparatus, which is a control unit for executing control of the entire image forming process, and controls timings such as driving start and stop of the conveying belt motor 17 and the fixing roller 11 of the fixing device 9. Thus, the conveyance control of the transfer material 4 is also performed. Reference numeral 19 denotes a motor controller that sends a control signal to a motor drive driver (not shown), and uses a digital signal processor or the like capable of high-speed product-sum operation to control the speed of the motor. Reference numeral 18 denotes a motor for driving the pressure roller 16 for transporting the transfer material 4 in the fixing device 9. The motor 18 has a means for detecting the rotational speed like the motor 17, and the CPU 21 and the motor controller 20 can control the speed. It is a motor.

  2A is an enlarged view of a transfer material conveyance portion mainly between the conveyance belt and the fixing device in FIG. 1, and FIG. 2B shows an entrance guide, a loop amount sensor, and a photo interrupter.

  As shown in FIG. 2B, the photo interrupters 14-a and 14-b are configured to have a slit between the light receiving and light emitting elements, and two loop amount detection flags 15-a and 15- A sensor of a type that detects the amount of the loop amount depending on whether b blocks the slit or not is used.

  Next, referring to FIG. 2B, when the loop amount is small, that is, when the loop amount is small, the behavior of the loop amount sensor when the optimum transfer material (for example, a strong transfer material) is conveyed. The control will be described. When the transfer material is an optimal transfer material (for example, a strong transfer material) when the loop amount is small, a loop amount sensor 15-a in the drawing is used. The loop amount sensor 15-a includes a transfer material loop detection unit 151-a having a length of Ha, a loop amount sensor support unit 152-a, and a loop amount detection flag 153-a that blocks the photo interrupter 14-a. Has been. FIG. 3A shows the loop amount when this loop amount sensor is used and when the transfer amount is optimally controlled when the loop amount is small.

  In FIG. 3A, when the loop amount is small and the optimum transfer material has a small loop amount (R4), the loop amount detection flag 153-a is set to the photo interrupter 14 as shown in FIG. The transfer material is controlled in the direction in which the loop amount is formed. On the other hand, when the loop amount is large (R3), the result is as shown in FIG. 3A-2, and the loop amount detection flag 153-a is in a direction to eliminate the loop amount as a result of the state where the photo interrupter 14-a is blocked. Control transfer of transfer material. With the above control, transfer material conveyance control is performed so that the loop amount is within the range of R3 to R4 when the optimum transfer material (for example, a strong transfer material) is conveyed when the loop amount is small.

  In this case, the independent loop amount sensor 15-b different from the above shown in FIG. 2B is also operated in accordance with the loop amount of the transfer material. However, when the loop amount is small, the optimum transfer material ( For example, when a strong transfer material) is conveyed, the CPU 21 determines that the signal of the photo interrupter 14-b output by the loop amount detection flag 153-b is not fed back to the transfer material conveyance control and is controlled. Done.

  On the other hand, when an optimal transfer material (for example, a weak transfer material) is conveyed when the loop amount is large, the loop amount sensor 15-b in FIG. 2B is used. The loop amount sensor 15-b includes a transfer material loop detection unit 151-b having a length of Hb, a loop amount sensor support unit 152-b, and a loop amount detection flag 153-b that blocks the photo interrupter 14-b. ing.

  FIG. 3B shows the loop amount when this loop amount sensor is used and an optimum transfer material (for example, a weak transfer material) is conveyed when the loop amount is large.

  Next, the behavior of the loop amount sensor when an optimal transfer material (for example, a weak transfer material) is conveyed when the loop amount is large will be described. In FIG. 3B, when the loop amount is large, an optimum transfer material (for example, a weak transfer material), and when the loop amount is small (R2), the loop is as shown in FIG. The amount detection flag 153-b is in a state where the photo interrupter 14-b is not blocked, and performs transfer control of the transfer material in the direction in which the loop amount is formed. On the other hand, when the loop amount is large (R1), the result is as shown in FIG. 3 (b-2), and the loop amount detection flag 153-b is transferred in a direction to cancel the loop amount as a result of blocking the photo interrupter 14-b. Controls material conveyance. With the above control, the transfer material conveyance control is performed by the photo interrupter 14-b so that the loop amount of the optimal transfer material (for example, a weak transfer material) is within the range of R1 to R2 when the loop amount is large. Control is performed by the CPU 21 so that the signal from the photo interrupter 14-a is not fed back to the conveyance control.

  As described above, the feature of the configuration of this embodiment is that different loop amount sensors are used properly according to the optimum loop amount of the transfer material. Further, in the configuration of the present embodiment, as a method for detecting different loop amounts, a method is used in which different loop amounts can be detected by setting the length of the transfer material loop detection unit to different lengths Ha> Hb. A similar object may be achieved by providing a loop amount detection flag at an optimum position where a different loop amount can be detected regardless of the length of the portion.

  In the present embodiment, as an example of controlling the control with different loop amounts, an embodiment in which two independent loop amount sensors are provided in FIG. 2 is described. Note that the number of loop amount sensors may be increased to three or more as necessary in accordance with the type of transfer material.

  A time chart relating to a series of controls in this embodiment is shown in FIG. In the chart, the uppermost signal indicates a signal of a photo interrupter 14-b) that detects a loop amount at the time of conveyance control of a transfer material (for example, a weak transfer material) having an optimum large loop amount. The next signal represents the transfer material conveyance speed between the conveyance belt and the fixing device controlled based on the signal. The third signal indicates a signal from the photo interrupter 14-a that detects the loop amount during conveyance control of a transfer material (for example, a strong transfer material) having a small loop amount. The fourth signal is The transfer material conveyance speed between the conveyance belt and the fixing device controlled based on the signal is shown. The upper part of the next line is the actual loop amount of the transfer material when the large loop amount is optimal (weak transfer material), and below that is the transfer material when the small loop amount is optimal This shows the actual loop amount of (strong transfer material).

  Therefore, the difference between this example and the conventional example is that in this example, in order to realize the optimum loop amount control according to the type (characteristic and physical property) of the transfer material, that is, the type and characteristic of the transfer material. In order to set a plurality of control ranges that differ according to the loop amount control level, the loop amount control level is one step (level) in the conventional example, whereas two steps (levels) are provided in different loop amount control ranges. It is. In this embodiment, the case of two stages is shown, but the number of control stages may be further increased according to the necessity of diversification of physical properties of the transfer material.

  Furthermore, the flowchart of the present Example was described in FIG.

  First, as step 21, it is determined whether the optimum transfer material loop amount is large or small. This determination is made based on the result of detecting the paper type of the transfer material P by the paper type sensor 40 (FIG. 1). Alternatively, when the user inputs the type and physical properties (thickness, basis weight, size, etc.) of the transfer material from the operation panel (not shown) of the image forming apparatus, the determination is made at the control unit (CPU) 21 of the image forming apparatus. Is done. Based on the determination result, when it is determined that the transfer material is optimal when the loop amount is large (for example, the transfer material is weak), the flow of steps 22 to 28 is performed. On the other hand, when it is determined that the transfer material is optimal when the loop amount is small (for example, a transfer material having a strong strain), the flow from 30 to 36 is performed.

  That is, when it is determined that the optimal transfer material loop amount is large, the flow proceeds to step 22 where the transfer material front end passes through the entrance guide 13 from the conveyance belt 6 and is pressed by the pressure roller 16 and the heat roller 11 in the fixing device 9. Start nipping conveyance. Next, in step 23, transfer material conveyance control between the conveyance belt and the fixing device is performed to control in a direction in which a loop amount is formed. In step 24, it is determined whether or not the loop amount is formed up to the loop large (R1) (FIG. 3 (b-2)). The loop formation state in step 23 is continued until loop formation is determined. If it is determined that a loop is formed, the process proceeds to step 25. In step 25, it is determined whether or not the trailing edge of the transfer material has passed the tip of the transfer material loop detection unit 151-b (FIG. 2B). If not, the process proceeds to step 26. Proceed to step 29. In step 26, transfer material conveyance control between the conveyance belt and the fixing device is performed in a direction to eliminate the loop so that the loop is small (FIG. 3B-1). In step 27, it is determined whether or not the loop has been canceled to the small loop (FIG. 3B-1). If not, the state of step 26 is continued, and if it is determined that the loop has been canceled, the process proceeds to step 28. If the rear end of the transfer material does not pass through the front end of the transfer material loop detection unit 151b (FIG. 2B), the process returns to step 23 to repeat the series of controls.

  If it has passed, the loop amount control of the transfer material is finished, and then the process proceeds to step 29, where the rear end of the transfer material is nipped and conveyed in the fixing device 9 and output from the image forming apparatus.

  When the transfer material optimum loop amount is small, the same control flow as 22 to 28 when the optimum loop amount is large is repeated for steps 30 to 36 with different loop amounts.

  As described above, depending on the type and physical properties of the transfer material, it is possible to achieve optimal loop amount control by using different loop amount sensors. For example, when a strong transfer material is used, image holding is possible. The possibility that the transfer material is pushed into the body or the fixing device and the image is rubbed is avoided.

  Also, the physical properties of the transfer material often depend on the type of transfer material. Therefore, FIG. 6 shows the result of examining whether or not an image defect occurs when the transfer material conveyance control is used. From this result, we can avoid the phenomenon that the unfixed image of the transfer material is rubbed against the image carrier or heat roller by increasing the loop amount for a transfer material with a small basis weight and decreasing the loop amount for a transfer material with a large basis weight. It turns out that it is possible.

  Accordingly, as described above, the loop amount control can be switched according to the type of the transfer material, so that the optimum loop amount control can be performed. At that time, as a method for recognizing the transfer material type, as the paper type sensor 40 provided in the image forming apparatus described above, the thickness and size are detected by using a transfer material thickness sensor, a transfer material size sensor, and the like. The result is taken into a controller (CPU) of the image forming apparatus and discriminated, and a transfer material conveyance control that automatically sets the optimum loop amount based on the discrimination result is selected. Further, when the user of the image forming apparatus sets an image forming condition, a type of transfer material, physical properties (for example, basis weight, thickness, size), etc. using an image output device such as a personal computer, the image forming condition and the transfer material The control configuration may be such that transfer material conveyance control is performed based on the setting contents such as the type and physical properties.

  An “image forming apparatus” that is Embodiment 2 will be described. The configuration of the main part of the present embodiment is shown in FIG. FIG. 7A shows an enlarged view between the conveyance belt and the fixing device, and FIG. 7B shows an entrance guide and a loop amount sensor drawing.

  In this embodiment, as a technique for detecting the optimum loop amount with different transfer materials, one loop amount sensor 15-2 is used as shown in FIG. 7B. As its configuration, it is composed of a transfer material loop detection unit 151, a loop amount sensor support unit 152, and loop amount detection flags 153-a and 153-b, and when no loop is formed, the loop amount detection flag 153-a. The angle θa of the photo interrupter 14-a blocked by the loop 153-a at the time of loop formation is different from the angle θb of the photo interrupter 14-b blocked by the loop amount detection flag 153-b and 153-b at the time of loop formation. .

  In this embodiment, even if there is one loop amount sensor, the transfer material loop amount between transfer and fixing can be controlled with different loop amounts by providing a plurality of loop amount detection flags of the loop amount sensor and shifting the phase. A possible example is shown.

  Further, although the present embodiment shows an example in which the loop amount detection flag has two detection points having different phases, the detection points may be increased to three or more stages as necessary.

  Next, the operation of the behavior of the loop amount sensor having the above configuration will be described with reference to FIG.

  When the loop amount is small and the transfer material is optimal (for example, a transfer material having a strong strain), when the loop amount is small (R4), the result is as shown in FIG. In this state, the interrupter 14-a is not blocked, and the transfer material conveyance control is performed in the direction in which the loop amount is formed. Thereafter, when the loop amount becomes large (R3), the result is as shown in FIG. 8A-2, and the loop amount detection flag 153-a is transferred in a direction to eliminate the loop amount as a result of blocking the photo interrupter 14-a. Controls material conveyance.

  By repeating the above control, the transfer material conveyance control is performed so that the loop amount when the optimum loop amount of the transfer material is small is within the range of R3 to R4.

  In this control, the output result of the photo interrupter 14-b is not taken into account, and the controller (CPU) of the image forming apparatus judges and controls so that only the output signal of the one photo interrupter 4-a is fed back to the loop amount control. To do.

  On the other hand, when the loop amount is large, the optimum transfer material (for example, a transfer material having a weak strain) and the loop amount is small (R2) is as shown in FIG. 8B-1, and the loop amount detection flag 153-b. Is a state in which the photo interrupter 14-b is not obstructed, and transport control of the transfer material is performed in the direction in which the loop amount is formed. Thereafter, when the loop amount is large (R1), the result is as shown in FIG. 8 (b-2). As a result of the loop amount detection flag 153-b being in a state of blocking the photo interrupter 14-b, Transport control is performed.

  By repeating the above control, the transfer material conveyance control is performed by the loop amount detection flag 153-b so that the loop amount when the optimum loop amount of the transfer material is large is within the range of R1 to R2.

  Further, during this control, the output result of the photo interrupter 14-a is not considered, and only the output signal of the photo interrupter 14-b is determined and controlled by the controller (CPU) of the image forming apparatus so as to feed back to the loop amount control.

  The series of controls in this embodiment is the same as the time chart of FIG. 4 and the flowchart of FIG. 5 shown in the first embodiment.

  As described above, the transfer material conveyance control for controlling a plurality of loop amounts according to the type and physical properties of the transfer material is configured such that one loop amount sensor has a plurality of detection points, so that the loop amount for each detection point. Compared with the case where a sensor is used, the size of the sensor can be suppressed to half or less, so that the apparatus configuration can be further simplified.

  An “image forming apparatus” that is Embodiment 3 will be described.

  The main configuration of the present example is shown in FIG. FIG. 9A shows an enlarged view between the conveyance belt and the fixing device, and FIG. 9B shows an entrance guide and a loop amount sensor drawing.

  In this embodiment, as a method for detecting the optimum loop amount of different transfer materials, one loop amount sensor 15-3 is used as shown in FIG. 9B. The configuration includes a transfer material loop detection unit 151, a loop amount sensor support unit 152, and loop amount detection flags 153-a and 153-b. In this configuration, the transfer material loop detection unit 151 is refracted.

  Further, in this configuration, the loop amount detection flag 153-a in a state where a loop is not formed, the angle θa of the photo interrupter 14-a that is interrupted by 153-a at the time of loop formation, and the loop amount detection flag 153-b and at the time of loop formation The angle θb of the photo interrupter 14-b blocked by 153-b is different in size.

  In this embodiment, even if there is one loop amount sensor, the transfer material loop amount between transfer and fixing can be controlled with different loop amounts by providing a plurality of loop amount detection flags of the loop amount sensor and shifting the phase. A possible example is shown.

  Further, although the present embodiment shows an example in which the loop amount detection flag has two detection points having different phases, the detection points may be increased to three or more stages as necessary.

  Next, the operation of the behavior of the loop amount sensor having the above configuration will be described with reference to FIG.

  When the loop amount is small and the transfer material is optimal (for example, a strong transfer material) and the loop amount is small (R4), the loop amount detection flag 153-a is shown in FIG. In this state, the interrupter 14-a is not blocked, and the transfer material conveyance control is performed in the direction in which the loop amount is formed. Thereafter, when the loop amount is large (R3), the result is as shown in FIG. 10A-2, and the loop amount detection flag 153-a is transferred in a direction to cancel the loop amount as a result of the state where the photo interrupter 14-a is blocked. Controls material conveyance.

  By repeating the above control, the transfer material conveyance control is performed so that the optimum loop amount of the transfer material is within the range of R3 to R4 when the transfer material is small.

  In this control, the output result of the photo interrupter 14-b is not taken into consideration, and the controller (CPU) of the image forming apparatus determines and controls only the output signal of the photo interrupter 14-a to be fed back to the loop amount control.

  On the other hand, when the loop amount is large, the optimum transfer material (for example, a transfer material having a weak strain) and when the loop amount is small (R2), the loop amount detection flag 153-b is obtained as shown in FIG. Is a state in which the photo interrupter 14-b is not obstructed, and transport control of the transfer material is performed in the direction in which the loop amount is formed. Thereafter, when the loop amount is large (R1), the state is as shown in FIG. 10B-2, and the loop amount detection flag 153-b is in a state of blocking the photo interrupter 14-b. Take control.

  By repeating the above control, the transfer material conveyance control is performed by the loop amount sensor 15-3 so that the loop amount when the optimum loop amount of the transfer material is within the range of R1 to R2.

  Further, during this control, the output result of the photo interrupter 14-a is not taken into account, and the controller (CPU) of the image forming apparatus judges and controls to transfer only the output signal of the photo interrupter 14-b to the loop amount control. The loop detection part of the material is used as the detection point of the refraction part of the loop detection unit.

  The loop amount control method for the optimum loop amount of the transfer material in this embodiment is the same as that in the second embodiment.

  On the other hand, as shown in FIG. 11, the effect of the present embodiment is that the detection location of the loop amount sensor is a refraction location, and the refraction location is used at a place where the rate of change in loop amount of the transfer material is large (θ1 <θ2). The detection sensitivity is the highest with respect to the loop amount control of the transfer material, and feedback to the loop amount control can be performed with higher responsiveness than in the second embodiment.

  The series of controls in this embodiment is the same as the time chart of FIG. 4 and the flowchart of FIG. 5 shown in the first embodiment.

(Application examples)
The effect when the first to third embodiments are applied to the color image forming apparatus shown in FIG. 12 (application example) will be described.

  FIG. 12A is a schematic diagram illustrating a partial configuration of an example of a color image forming apparatus. Actually, a developing unit and a cleaning unit (not illustrated) exist as in the first embodiment. In the figure, 9 is a fixing device, 22, 23, 24, and 25 are scanner units, and 26, 27, 28, and 29 are yellow, cyan, magenta, and black image carriers. It doesn't matter. Reference numeral 30 denotes a transfer material conveyance belt, and 31 denotes a transfer material conveyance path. FIG. 12B is an enlarged view of the space between the conveyance belt and the fixing device.

  A thick line indicates an actual loop amount of the transfer material when the transfer material is nipped and conveyed in the fixing device.

  Incidentally, in the case of a color image forming apparatus that conveys a transfer material in the vertical direction as in this application example, gravity acts on the transfer material in the direction of arrow A as shown in FIG. As a result, if the loop amount is increased to the same loop amount as usual without using the control of the embodiment with strong paper (for example, thick paper) or the like, the action due to gravity is further added to the action due to gravity, and the broken line state is obtained. The transfer material loop amount changes, the transfer material-like unfixed toner image is disturbed by the heat roller 11, or the transfer material is pushed into the image carrier 26 side shown in FIG. Image defects such as image rubbing similar to FIG. 17 and color misregistration specific to a color machine occur.

  Accordingly, it is more effective to use the control of the first to third embodiments for a color image forming apparatus that conveys a transfer material in the vertical direction as in the configuration of this application example.

2 Image carrier 4 Transfer material 6 Conveying belt 7 Transfer roller 9 Fixing device 15-a Loop amount sensor 15-b Loop amount sensor 21 CPU for image forming apparatus operation
40 Paper type sensor

Claims (2)

An image carrier;
Image forming means for forming an image on the image carrier in accordance with image information;
An identification means for identifying the type of transfer material based on the detection result by the detection means for detecting the type of transfer material or the input result from the input means to which the type of transfer material is input;
Transfer means for transferring an image formed on the image carrier by the image forming means to a transfer material;
Fixing means for fixing the image transferred by the transfer means on the transfer material;
Detecting means for detecting the amount of a loop of the transfer material formed while the transfer material is being conveyed by the transfer means and the fixing means,
The detection means includes a first flag and a second flag that can contact a transfer material on which a loop is formed, and a loop amount detection sensor that can detect each variation of the first flag and the second flag. And having
The first flag and the second flag before detecting the loop of the transfer material contact the transfer material in the second flag with respect to the transfer material conveyed from the transfer unit to the fixing unit. The tip on the side is set to be at a position farther from the transfer material than the tip on the side in contact with the transfer material in the first flag,
If it is determined that the transfer material is the first transfer material according to the type of the transfer material identified by the identification means, the detection result of only the loop amount detection sensor corresponding to the first flag is displayed. If it is determined that the transfer material is a second transfer material that is weaker than the first transfer material, the detection result of only the loop amount detection sensor corresponding to the second flag is used. An image forming apparatus that controls a transfer speed of a transfer material in the fixing unit.   The image forming apparatus according to claim 1, wherein the first flag is longer than the second flag.

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