JP2007079414A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having an opening and closing mechanism for a shield member shielding a sensor. <P>SOLUTION: The image forming apparatus is equipped with: a reading section reading information for setting the conditions of an image forming process from a prescribed object; the shield member which is interposed between the object and the reading section and shields the reading section; the opening and closing mechanism switching the shield member to either of an open state for enabling reading by the reading section or a closed state for shielding the reading section, by the driving force of any of drive parts; a butting portion with which the shield member comes into contact, when the shield member is in the open state; and a position maintaining mechanism which is provided in the opening and closing mechanism and prevents the driving force from being transmitted to the shield member, to maintain the shield member in a position in contact with the butting portion, even if the driving force is continuously applied from the drive part, after the shield member comes into contact with the butting portion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a recording medium, and more particularly to an image forming apparatus that forms an image on a recording medium by an electrophotographic process.

  Forming an evaluation pattern made of a developer (hereinafter referred to as toner) on the conveyance belt of the recording medium, detecting the evaluation pattern with a photo sensor, and correcting the color shift and density of the image based on the detection result There is a device. In such an image forming apparatus, if the toner adheres to the surface of the photosensor, the evaluation pattern cannot be detected accurately. Therefore, when the photosensor is not used, it is necessary to cover the surface of the photosensor with a shielding member such as a shutter.

An invention relating to an image forming apparatus having a shielding member that covers the surface of a photosensor is described in Patent Document 1, for example. The image forming apparatus described in Patent Document 1 includes a belt that conveys a recording medium, a photosensor that detects an evaluation pattern transferred onto the belt, and a shutter (shielding member) that covers the surface of the photosensor. . The rotation of the shutter uses, for example, the rotation of a motor that drives the fixing roller. The driving force necessary for rotating the shutter is obtained by transmitting the driving force generated by the motor that drives the fixing roller to the shutter mechanism through a gear train using a planetary gear or the like.
Japanese Unexamined Patent Publication No. 2004-138976 (pages 7-10, FIG. 12)

  Normally, the opening angle of the shutter that covers the photosensor is limited to a predetermined range due to restrictions on the shape of the photosensor. Therefore, the amount of rotation of the motor for driving the shutter needs to be controlled so as to rotate by an amount corresponding to the specified opening angle of the shutter. However, the opening / closing operation of the shutter varies, and the shutter does not always open at the same opening angle with respect to the rotation amount of the motor. For this reason, in the image forming apparatus described in Patent Document 1, it is considered necessary to separately provide a positioning sensor or the like for detecting the opening position of the shutter, and the structure and control may be complicated.

  Also, in consideration of shutter operation variations, the motor is rotated more than the rotation amount of the reference motor that theoretically makes the shutter fully open, so that the shutter is always fully opened when the photosensor is used. It is also possible. In this case, a positioning sensor for detecting the open position of the shutter is not necessary. However, there are various modes of occurrence of shutter operation variations. For example, when a driving gear that transmits the driving force of a motor and a planetary gear for opening and closing the shutter mesh at an earlier stage than a predetermined timing, Even if the shutter opening operation exceeds a physical opening limit point (for example, a frame barrier or a stopper), the drive gear and the planetary gear described above may be damaged.

  An image forming apparatus according to the present invention is an image forming apparatus that forms an image on a recording medium by a predetermined image forming process, and includes an image forming unit that forms an image, a conveyance unit that conveys the recording medium, and image formation A plurality of driving units that drive the scanning unit and the conveyance unit, a reading unit that reads information for setting conditions of the image forming process from a predetermined object, and a target unit and the reading unit. A shielding member that shields, an opening / closing mechanism that switches the shielding member between an open state that enables reading by the reading unit and a closed state that shields the reading unit by any driving force of the driving unit, and a shielding member The abutting part that abuts when in the open state and the opening / closing mechanism, even if the driving force is continuously applied from the driving part after the shielding member abuts against the abutting part, To be transmitted to Characterized in that it comprises a position maintaining mechanism to maintain the contact position with the abutment portion of the shielding member is.

  According to the image forming apparatus of the present invention, the driving force is transmitted to the shielding member even when the driving member is continuously given the driving force after the shielding member is opened and comes into contact with the abutting portion. Since the position maintaining mechanism that can prevent this is provided, the structure and control of the opening and closing mechanism for opening and closing the shielding member can be simplified, and the gears and the like for transmitting the driving force to the shielding member can be prevented from being damaged. it can.

1) First Embodiment [Configuration]
FIG. 1 is a schematic configuration diagram of an image forming apparatus 1000 according to the first embodiment of the present invention.

  The image forming apparatus 1000 forms a color image using an electrophotographic process, and is a so-called tandem in which image forming units 2K, 2Y, 2M, and 2C corresponding to black, yellow, magenta, and cyan are arranged. This is an image forming apparatus of the type.

  The image forming units 2K, 2Y, 2M, and 2C are sequentially arranged in the conveyance direction of the recording medium P (the direction indicated by the arrow A in FIG. 1). In the following description, the left side in FIG. 1, that is, the downstream side in the conveyance direction of the recording medium P is the F direction (forward direction), and the right side in FIG. Backward).

  The image forming unit 2K includes a photosensitive drum 20 as an image carrier that rotates clockwise in the drawing. The photosensitive drum 20 is rotationally driven by a drum motor 308K (FIG. 2). Around the photosensitive drum 20, a charging roller 21, an LED head 22 and a developing unit 23 are disposed. The developing unit 23 includes a toner container 23c that stores black toner, and a developing roller 23a and a supply roller 23b are provided below the toner container 23c. For example, a transfer roller 24 as a transfer device is provided below the photoconductive drum 20 so as to sandwich the recording medium P between the photoconductive drum 20.

  The charging roller 21 uniformly charges the surface of the photosensitive drum 20. The LED head 22 selectively exposes the uniformly charged surface of the photosensitive drum 20 according to image information. Of the surface of the photosensitive drum 20, the exposed portion is removed from the electric charge, and the unexposed portion is left with an electric charge to form an electrostatic latent image. The developing unit 23 supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum 20 to form a visible image (hereinafter referred to as a toner image) made of toner. The transfer roller 24 applies a voltage having a polarity opposite to that of the toner from the back surface of the recording medium P, and transfers the toner image formed on the surface of the photosensitive drum 20 to the recording medium P by an electric suction force.

  The image forming units 2Y, 2M, 2C all have the same configuration as the image forming unit 2K. However, the developing units 23 of the image forming units 2Y, 2M, and 2C contain yellow, magenta, and cyan toners, respectively.

  The belt 1 that conveys the recording medium P is a so-called endless belt, and is stretched between a pair of rollers 25 and 26. The rollers 25 and 26 are provided so that the rotation axis direction coincides with the width direction of the belt 1 and the transfer roller 24 is sandwiched therebetween. The roller 25 is a belt driving roller that is rotationally driven by a belt driving motor 306 (FIG. 2), and the roller 26 is a driven roller that rotates in conjunction with the belt driving roller 25. Due to the rotation of the belt driving roller 25, the belt 1 moves in the direction indicated by the arrow A in FIG.

  On the left side of the belt driving roller 25 in the drawing, that is, on the downstream side in the conveyance direction of the recording medium P, a fixing unit 16 for fixing the toner image by heat-pressing the recording medium P carrying an unfixed toner image is disposed. Has been. The fixing unit 16 includes a fixing roller 16a including a heater 305 (FIG. 2), a pressure roller 16b that sandwiches and presses the recording medium P between the fixing roller 16a, and a driving force for rotating the fixing roller 16a. And a mechanism (for example, a gear train) that transmits the driving force of the fixing motor 200 to the fixing roller 16a.

  On the left side of the fixing unit 16 in the drawing, that is, on the downstream side in the conveyance direction of the recording medium P, two pairs of discharge rollers 17 and 18 that guide the recording medium P to a discharge unit 19 provided at the upper part of the image forming apparatus 1000. Is provided.

  A storage unit 10 that stores the recording medium P is provided below the image forming apparatus 1000. A small-diameter auxiliary roller 12 for taking out the recording medium P from the storage unit 10 and a large-diameter paper feed roller 13 are arranged in parallel on the right side of the storage unit 10 in the drawing, that is, on the downstream side in the conveyance direction of the recording medium P. Yes. The auxiliary roller 12 and the paper feed roller 13 are rotationally driven by a paper feed motor 307 (FIG. 2). On the auxiliary roller 12 side of the storage unit 10, an inclined plate 11 for pressing the leading end of the recording medium P against the auxiliary roller 12 and the paper feed roller 13 is provided. Two pairs of transport rollers 14 and 15 for transporting the recording medium P are provided in the transport path of the recording medium P from the storage unit 10 to the image forming unit 2K.

  The image forming apparatus 1000 is provided with medium sensors 27a, 27b, 27c, and 27d that detect the passage of the recording medium P along the conveyance path. The medium sensor 27 a is disposed on the upstream side of the conveyance roller pair 14, and the medium sensor 27 b is disposed on the upstream side of the conveyance roller pair 15. The medium sensor 27 c is disposed on the upstream side of the driven roller 26, and the medium sensor 27 d is disposed on the downstream side of the fixing unit 16.

  In the vicinity of the belt driving roller 25, color misregistration sensors 3a and 3b are provided as reading units that detect information regarding color misregistration. The color misregistration sensors 3 a and 3 b optically detect an evaluation pattern for color misregistration detection composed of a toner image formed on the belt 1. The color misregistration sensors 3a and 3b are disposed below the belt driving roller 25 so as to face both ends of the belt 1 in the width direction. Each of these color misregistration sensors 3a and 3b has a light emitting element and a light receiving element. The light emitting element irradiates the evaluation pattern for color misregistration detection formed on the belt 1 with light. The light receiving element detects reflected light from the evaluation pattern and outputs a voltage signal corresponding to the intensity of the reflected light.

  Further, in the vicinity of the belt driving roller 25, a density sensor 4 is provided as a reading unit that detects information about density. The density sensor 4 optically detects an evaluation pattern for density detection composed of toner images formed on the belt 1 by the image forming units 2K, 2Y, 2M, and 2C. The density sensor 6 has a light emitting element and a light receiving element. The light emitting element irradiates the evaluation pattern for density detection formed on the belt 1 with light. The light receiving element detects reflected light from the evaluation pattern and outputs a voltage signal corresponding to the intensity of the reflected light.

  Further, in the image forming apparatus 1000, when the color misregistration sensors 3a and 3b and the density sensor 4 are not used, a shutter as a shielding member for covering these sensors and a shutter opening / closing mechanism (configuration 100 indicated by a broken line in FIG. 1). Is provided.

  FIG. 3 is a perspective view showing the configuration 100 shown in FIG. 1, that is, the configuration including the color misregistration sensors 3a and 3b and the density sensor 4, a shutter covering these sensors, and a shutter opening / closing mechanism. FIG. 4 is an exploded perspective view showing the configuration 100. FIG. 5 is a plan view showing the configuration 100.

  The frame 110 that supports the color misregistration sensors 3a and 3b and the density sensor 4 includes a support plate 111 that extends substantially parallel to the rotation axis direction of the belt driving roller 25 (FIG. 1). A pair of side plates 112 a and 112 b parallel to each other are attached to both ends of the support plate 11 in the longitudinal direction. The side plates 112a and 112b are formed with roller mounting portions 113a and 113b to which the belt driving roller 25 is mounted via bearings (not shown).

  As shown in FIG. 4, the bottom 114 extends from the lower end of the support plate 111 toward the rear (in the direction indicated by the arrow R in FIG. 4), and rearward from the rear end at both ends in the longitudinal direction of the bottom 114 (the direction of the arrow R). Sensor support portions 115a and 115b extend toward the end. Further, shutter support portions 116a and 116b extend downward from the lower ends of the side plates 112a and 112b.

  The color misregistration sensors 3a and 3b are attached to the attachment plate 120 with the detection surface, that is, the surface on which the light emitting element and the light receiving element are formed facing upward. The mounting plate 120 is fixed to the lower side of the sensor support portions 115a and 115b by screws 121a and 121b. The color misregistration sensors 3a and 3b have holes 117a and 117b formed in the sensor support portions 115a and 115b, respectively. It penetrates and protrudes upward. Further, the upper and side surfaces of the color misregistration sensors 3a and 3b are covered with transparent covers 122a and 122b made of, for example, acrylic resin via the sensor support portions 115a and 115b, respectively.

  Vertical portions 118a and 118b extend upward from the rear end of the center portion in the longitudinal direction of the bottom portion 114, and the concentration sensor 4 is attached to the vertical portions 118a and 118b via an attachment plate 119.

  A shutter (shielding member) 130 that covers the color misregistration sensors 3a and 3b and the density sensor 4 is provided between the side plates 112a and 112b. The shutter 130 includes a sensor cover 131 and rotation shafts 132a and 132b, and is attached to be rotatable within a predetermined angle with the shutter support portions 116a and 116b as rotation centers.

  At the center of the sensor cover 131, there is provided a stopper 133 that contacts the mounting plate 119 of the density sensor 4 when the shutter 130 is opened and defines the maximum opening angle of the shutter 130. A wiper 134 as a removing member is attached to the stopper portion 133 to remove foreign matters such as toner adhering to the upper surface of the density sensor 4 as the shutter 130 rotates.

  The sensor cover 131 has three openings 135a, 135b, and 135c. The openings 135a and 135b are positioned above the color misregistration sensors 3a and 3b when the shutter 130 is in the open position shown in FIG. 3, and open the upper surfaces of the color misregistration sensors 3a and 3b, respectively. On the other hand, when the shutter 130 is rotated backward (in the direction indicated by the arrow R in FIG. 3) to the closed position, the openings 135a and 135b are separated from the upper positions of the color misregistration sensors 3a and 3b, respectively, and the sensor cover 131. Shields the upper surfaces of the color misregistration sensors 3a and 3b. Similarly, the opening 135c is located above the density sensor 4 and opens the upper surface of the density sensor 4 when the shutter 130 is in the open position shown in FIG. On the other hand, when the shutter 130 is rotated backward (in the direction indicated by the arrow R in FIG. 3) to the closed position, the opening 135 c is separated from the upper position of the density sensor 4, and the sensor cover 131 is placed on the upper surface of the density sensor 4. Shield.

  In the vicinity of the openings 135a and 135b, there are blades 136a and 136b as removal members that remove foreign matters such as toner adhering to the upper surfaces of the color misregistration sensors 3a and 3b as the shutter 130 rotates. Each is installed. The blades 136a and 136b are formed of an elastic body such as silicon rubber, for example.

  A coil spring 137 is provided between the shutter 130 and the support plate 111 to urge the shutter 130 in a direction away from the support plate 111 (a direction indicated by an arrow R in FIG. 4).

  Next, a drive system for opening and closing the shutter 130 will be described. FIGS. 6A and 6B are diagrams showing a drive system for opening and closing the shutter 130. 6A and 6B, each gear constituting the drive system is represented by an actual tooth shape and pitch circle.

  A shutter gear 140 is attached to the rotation shaft 132 a of the shutter 130. The shutter gear 140 has a key groove portion (not shown) that engages with a key portion 138 formed on the rotation shaft 132a. With these key structures, the shutter gear 140 can rotate integrally with the shutter 130. The shutter gear 140 is a kind of sector gear in which gear teeth 141 are partially formed.

  The shutter gear 140 is provided with a dummy gear 150. A flexible arm portion 152 is formed at the upper end of the dummy gear 150, and a gear tooth 151 having the same shape as the gear teeth 141 is formed at the tip of the arm portion 152. The dummy gear 150 is fixed in a state of being urged against and abutted against the abutting portion 142 of the shutter gear 140.

  For example, the shutter 130 is opened and closed by using the driving force of the fixing motor 200 that drives the fixing roller 16a. A motor gear 201 is attached to the output shaft of the fixing motor 200. A main gear 202 is provided so as to engage with the motor gear 201. A small-diameter gear 203 having a diameter smaller than that of the main gear 202 is formed integrally with the main gear 202 so as to be coaxial with the main gear 202. The main gear 202 and the small diameter gear 203 are rotatably supported by a common rotation shaft S. A rocking gear 204 and a rocking gear 205 supported by a rocking lever 208 are provided so as to engage with the small-diameter gear 203. The swing lever 208 has a shape in which a long member is bent at a substantially central portion, and the above-described rotation shaft S passes through the substantially central portion, and can swing around the rotation shaft S. It has become. At both ends of the swing lever 208, support shaft portions 204a and 205a for supporting the swing gears 204 and 205 are formed to protrude. Stopper pins 208a and 208b are respectively provided at positions that restrict the swing range of the swing lever 208 in the clockwise direction and the counterclockwise direction.

  As shown in FIG. 6A, when the fixing motor 200 rotates clockwise (positive direction) in the figure, the motor gear 201 attached to the output shaft rotates clockwise and engages with this. The main gear 202 rotates counterclockwise in the figure. The small-diameter gear 203 formed integrally with the main gear 202 also rotates counterclockwise in the figure. The swing lever 208 swings counterclockwise in the figure due to the engagement between the small-diameter gear 203 and the swing gears 204 and 205 and the friction between the swing gears 204 and 205 and the support shaft portions 204a and 205a. . A fixing roller drive gear 206 for rotating the fixing roller 16a (FIG. 1) is provided at a position where the swing gear 205 engages when the swing lever 208 swings counterclockwise in the drawing. A discharge roller drive gear 207 for rotating the discharge roller pair 17 and 18 is engaged with the fixing roller drive gear 206.

  On the other hand, as shown in FIG. 6B, when the fixing motor 200 rotates counterclockwise (reverse direction) in the figure, the motor gear 201 attached to the output shaft rotates counterclockwise in the figure. The main gear 202 engaged with the gear rotates in the clockwise direction in the figure. The small diameter gear 203 formed integrally with the main gear 202 also rotates clockwise in the figure. As a result, the swing lever 208 swings clockwise in the figure. A shutter gear 140 is provided at a position where the swing gear 205 is engaged when the swing lever 208 swings clockwise in the drawing.

  Next, a control system of the image forming apparatus 1000 will be described. FIG. 2 is a block diagram showing a control system of the image forming apparatus 1000 according to the first embodiment of the present invention.

  The control unit 300 of the image forming apparatus 1000 is connected to the command / image processing unit 302 in addition to the color misregistration sensors 3a and 3b, the density sensor 4 and the medium sensors 27a to 27d described above. A command / image processing unit 302 processes commands and image data input from an external computer via the interface 301. The control unit 300 is connected to and controls the LED control unit 303, the high-voltage control unit 304, and the heater 305. The LED control unit 303 controls the LED heads 22 of the image forming units 2K, 2Y, 2M, and 2C. Further, the control unit 300 includes a fixing motor 200 that rotationally drives the fixing roller 16a, a belt driving motor 306 that rotationally drives the belt driving roller 25, a paper feeding motor 307 that rotationally drives the paper feeding roller 13, and the like, and each image forming unit 2K. , 2Y, 2M, and 2C, drum motors 308K, 308Y, 308M, and 308C that rotate and drive the photosensitive drum 20 are controlled.

[Operation]
Next, the operation of the image forming apparatus 1000 will be described.

  The controller 300 of the image forming apparatus 1000 heats the heater 305 of the fixing roller 16a after turning on the power of the image forming apparatus 1000 or replacing the developing unit 23 and the like, and then opens the shutter 130 from the closed position. Process to move to position.

  That is, first, as shown in FIG. 6A, the controller 300 first rotates the fixing motor 200 clockwise in the drawing and swings the swing lever 208 counterclockwise in the drawing to stop the stopper pin 208b. Abut.

  Next, as shown in FIG. 6B, the controller 300 rotates the fixing motor 200 by a predetermined number of pulses counterclockwise in the figure, and swings the swing lever 208 clockwise in the figure to stop the stopper. It abuts on the pin 208a. As a result, the swing gear 204 is engaged with the shutter gear 140. By engaging the swing gear 204 and the shutter gear 140, the driving force of the fixing motor 200 is transmitted to the shutter 130 via the motor gear 201, the main gear 202, the small diameter gear 203, the swing gear 204, and the shutter gear 140. The

  When fixing motor 200 further rotates counterclockwise in the drawing, shutter 130 moves forward (in the direction indicated by arrow F in FIG. 6B) against the biasing force of coil spring 137. Accordingly, the openings 135a and 135b of the shutter 130 are positioned above the color misregistration sensors 3a and 3b, and the upper surfaces of the color misregistration sensors 3a and 3b are opened. The opening 135c of the shutter 130 is located above the density sensor 4 and opens the upper surface of the density sensor 4. At this time, the shutter 130 is fully opened, and the stopper portion 133 of the shutter 130 is in contact with the mounting plate 119 of the density sensor 4.

  The rotation control of the fixing motor 200 by the control unit 300 is so-called open loop control based only on the count of the number of motor pulses. As shown in FIG. 6A, the fixing motor 200 is once rotated clockwise in the drawing, and the swing lever 208 is brought into contact with the stopper pin 208b, so that the swing lever 208 is once moved to the home position. Because.

  Here, the swing lever 208 is, for example, a balance between the friction generated between the swing gear 204 and the support shaft portion 204a and the friction generated between the swing gear 205 and the support shaft portion 205a. It does not necessarily swing at the same ratio as the number of motor pulses input from the fixing motor 200. That is, there is always some variation in the operation of the swing lever 208. If the operation amount of the swing lever 208 is smaller than the specified amount of motor pulses, and the swing gear 204 and the shutter gear 140 are engaged at a later stage than the predetermined timing, the shutter 130 is not fully opened. There is a fear. Therefore, in this open loop control, it is necessary to rotate the fixing motor 200 with a slightly higher number of motor pulses than the reference number of motor pulses that theoretically opens the shutter 130 in anticipation of variations in the operation of the swing lever 208. There is.

  As described above, if the number of motor pulses of the fixing motor 200 is set to be large, the movement amount of the rocking lever 208 is larger than the specified amount of the motor pulse due to the variation of the rocking lever 208, and the rocking motion is caused. When the gear 204 and the shutter gear 140 mesh with each other at an earlier stage than the predetermined timing, the driving force from the fixing motor 200 is maintained even after the stopper portion 133 of the shutter 130 contacts the mounting plate 119 of the density sensor 4. It is transmitted to the shutter gear 140. However, in the present embodiment, the gear teeth 151 of the dummy gear 150 are displaced in the direction indicated by the arrow B in FIG. The driving force transmitted from the gear 204 to the shutter gear 140 can be released. As a result, even when a driving force greater than the amount of rotation necessary for fully opening the shutter 130 is applied to the shutter gear 140, the shutter 130 can always be maintained at the fully open position without damaging the shutter gear 140.

  After rotating the shutter 130 to the open position, the control unit 300 performs color misregistration correction processing. That is, the control unit 300 drives the LED control unit 303 and the high voltage control unit 304 to form toner images for color misregistration detection by the image forming units 2K, 2Y, 2M, and 2C, and the width of the belt 1 by the transfer roller 24. Evaluation patterns for detecting color misregistration are sequentially transferred in the vicinity of both ends in the direction. Next, the evaluation pattern formed on the belt 1 is detected by the color misregistration sensors 3a and 3b. Light reflectance of a pattern formed with black toner, light reflectance of a pattern formed with yellow toner, light reflectance of a pattern formed with magenta toner, light reflectance of a pattern formed with cyan toner, and belt The light reflectance of one surface is different. The color misregistration sensors 3a and 3b output a voltage signal having a waveform corresponding to the position and color of the evaluation pattern for color misregistration detection formed on the belt 1. The controller 300 receives the voltage signals output from the color misregistration sensors 3a and 3b, detects the amount of deviation of each evaluation pattern formed on the belt 1 based on the received voltage signal, and detects the amount of deviation detected. The toner image forming timing in the image forming units 2K, 2Y, 2M, and 2C is adjusted based on the above. This adjustment is performed by adjusting the timing of forming the electrostatic latent image by the LED heads 22 of the image forming units 2K, 2Y, 2M, and 2C. That is, the control unit 300 scans the position of each LED head 22 and starts scanning in order to correct the deviation of each color pattern in the main scanning direction (the width direction of the belt 1) and the sub-scanning direction (the traveling direction of the belt 1). Adjust timing.

  While the color misregistration correction process is being executed, the fixing motor 200 is not rotated, but a holding current flows through the fixing motor 200, and a holding torque for holding the current position is generated. Further, since the urging force due to the bending reaction force of the arm portion 152 of the dummy gear 150 is larger than the urging force of the coil spring 137, the shutter 130 can be maintained in the fully opened state while the fixing motor 200 is stopped.

  After the color misregistration correction process is completed, the control unit 300 performs a process of moving the shutter 130 to the closed position. That is, the controller 300 rotates the fixing motor 200 clockwise as shown in FIG. 6A. The shutter 130 moves backward (in the direction indicated by the arrow R in FIG. 6A) by the urging force of the coil spring 137. Thereby, the openings 135a and 135b of the shutter 130 are separated from the upper positions of the color misregistration sensors 3a and 3b, and the sensor cover 131 shields the upper surfaces of the color misregistration sensors 3a and 3b. Similarly, the opening 135 c is separated from the position above the density sensor 4, and the sensor cover 131 shields the upper surface of the density sensor 4. At this time, the coil spring 137 is fully extended, and the urging force does not act between the shutter gear 140 and the swing gear 204, so that the swing gear 204 is separated from the shutter gear 140 and the swing lever 208 is moved. Swings counterclockwise in the figure. As a result, the swing gear 205 is engaged with the fixing roller driving gear 206, and the fixing roller 16a and the discharge rollers 17 and 18 start to rotate.

  Further, density correction processing is performed as necessary. The density correction process is executed, for example, when the cumulative number of printed sheets reaches a certain value. In this density correction process, the control unit 300 drives the LED control unit 303 and the high voltage control unit 304 to form toner images for density detection by the image forming units 2K, 2Y, 2M, and 2C, and by the transfer roller 24. An evaluation pattern for density detection is sequentially transferred to the central portion in the width direction of the belt 1. Next, the evaluation pattern formed on the belt 1 is detected by the density sensor 4. The density sensor 4 outputs a voltage signal having a waveform corresponding to the position and density of the evaluation pattern for density detection formed on the belt 1. Based on the voltage signal output from the density sensor 4, the control unit 300 transmits an instruction to adjust development parameters and the like to the development units 23 of the image forming units 2 </ b> K, 2 </ b> Y, 2 </ b> M, and 2 </ b> C.

  In this embodiment, as shown in FIGS. 6A and 6B, the blades 136a and 136b attached to the shutter 130 are attached to the upper surfaces of the color misregistration sensors 3a and 3b as the shutter 130 is opened and closed. Remove the foreign material adhering to the surface while touching. Further, for convenience of explanation, although not shown in FIGS. 6A and 6B, the wiper 134 attached to the shutter 130 in accordance with the opening / closing operation of the shutter 130, like the blades 136a and 136b described above. Removes foreign matter adhering to the surface while contacting the upper surface of the density sensor 4. As described above, since the surfaces of the density sensor 4 and the color misregistration sensors 3a and 3b can be cleaned by the wiper 134 and the blades 136a and 136b, the sensitivity of the sensor can always be maintained in an optimum state.

  Thereafter, an image is formed on the recording medium P by a known image forming process. Note that the above-described opening / closing operation of the shutter 130 is desirably performed within a time period after the heater 305 starts energization until the heater 305 reaches a predetermined temperature, for example, 100 ° C. In this way, after the heater 305 reaches a predetermined temperature, the image forming process can be performed promptly.

[Function and effect]
According to the first embodiment of the present invention, the shutter gear 140 is provided with the flexible dummy gear 150, and even if a driving force greater than the rotation amount necessary for fully opening the shutter 130 is applied to the shutter gear 140, the shutter gear 140 is provided. The driving force transmitted to 140 is released to prevent the driving force from being transmitted to the shutter 130. Thereby, it is possible to prevent the gear and the like for transmitting the driving force to the shutter 130 from being damaged while simplifying the structure and control for opening and closing the shutter 130. Further, when the density sensor 4 and the color misregistration sensors 3a and 3b are used, the shutter 130 can always be kept fully open, so that color misregistration correction or density correction can be reliably performed.

2) Second Embodiment In the second embodiment of the present invention, a shutter gear 160 is used instead of the shutter gear 140 in the first embodiment. Since other configurations are the same as those of the first embodiment, the same reference numerals are given to configurations common to the first embodiment, and the description thereof is partially omitted.

〔Constitution〕
FIGS. 7A to 7C are a perspective view, a plan view, and an exploded perspective view, respectively, showing the configuration of the shutter gear 160 in the second embodiment of the present invention.

  The shutter gear 160 is a kind of sector gear in which gear teeth 161 are partially formed. The shutter gear 160 is separately provided with a boss 170 that forms the rotating shaft of the shutter gear 160. A torsion spring 180 is wound around the boss 170. An end portion 180 a of the torsion spring 180 is hooked to the key groove portion 171 of the boss 170. Further, the end portion 180 b of the torsion spring 180 is hooked to the abutting portion 162 of the shutter gear 160.

  As shown in FIG. 7B, the torsion spring 180 generates an urging force to rotate the shutter gear 160 in the direction indicated by the arrow C, and the shutter gear 160 is abutted on the boss 170. The parts 172a and 172b are pressed with a constant force. The rotation angle of the shutter gear 160 relative to the boss 170 maintains the state shown in FIG. 7 unless a driving force is applied from the outside.

  Next, a drive system for opening and closing the shutter 130 will be described. FIGS. 8A to 8C are diagrams showing a drive system for opening and closing the shutter 130. In FIGS. 6A to 6C, the gears constituting the drive system are represented by actual tooth shapes and pitch circles.

  A shutter gear 160 is attached to a rotation shaft 132 a of the shutter 130 via a boss 170. The boss 170 has a key groove portion 171 that engages with a key portion (not shown) formed on the rotating shaft 132a. With these key structures, the boss 170 and the shutter gear 160 can rotate together with the shutter 130.

  The configuration of the shutter gear 160 is as described in FIG. That is, the shutter gear 160 and the boss 170 are formed separately, and the shutter gear 160 is fixed in a state of being biased with respect to the boss 170 by a torsion spring 180 wound around the boss 170. .

  For example, the shutter 130 is opened and closed by using the driving force of the fixing motor 200 that drives the fixing roller 16a. A motor gear 201 is attached to the output shaft of the fixing motor 200. A main gear 202 is provided so as to engage with the motor gear 201. A small-diameter gear 203 having a diameter smaller than that of the main gear 202 is formed integrally with the main gear 202 so as to be coaxial with the main gear 202. The main gear 202 and the small diameter gear 203 are rotatably supported by a common rotation shaft S. A rocking gear 204 and a rocking gear 205 supported by a rocking lever 208 are provided so as to engage with the small-diameter gear 203. The swing lever 208 has a shape in which a long member is bent at a substantially central portion, and the above-described rotation shaft S passes through the substantially central portion, and can swing around the rotation shaft S. It has become. At both ends of the swing lever 208, support shaft portions 204a and 205a for supporting the swing gears 204 and 205 are formed to protrude. Stopper pins 208a and 208b are respectively provided at positions that restrict the swing range of the swing lever 208 in the clockwise direction and the counterclockwise direction.

  As shown in FIG. 8A, when the fixing motor 200 rotates clockwise (positive direction) in the figure, the motor gear 201 attached to the output shaft rotates clockwise and engages with this. The main gear 202 rotates counterclockwise in the figure. The small-diameter gear 203 formed integrally with the main gear 202 also rotates counterclockwise in the figure. The swing lever 208 swings counterclockwise in the figure due to the engagement between the small-diameter gear 203 and the swing gears 204 and 205 and the friction between the swing gears 204 and 205 and the support shaft portions 204a and 205a. . A fixing roller drive gear 206 for rotating the fixing roller 16a (FIG. 1) is provided at a position where the swing gear 205 engages when the swing lever 208 swings counterclockwise in the drawing. A discharge roller drive gear 207 for rotating the discharge roller pair 17 and 18 is engaged with the fixing roller drive gear 206.

  On the other hand, as shown in FIG. 8B, when the fixing motor 200 rotates counterclockwise (reverse direction) in the figure, the motor gear 201 attached to the output shaft rotates counterclockwise in the figure. The main gear 202 engaged with the gear rotates in the clockwise direction in the figure. The small diameter gear 203 formed integrally with the main gear 202 also rotates clockwise in the figure. As a result, the swing lever 208 swings clockwise in the figure. A shutter gear 160 is provided at a position where the swing gear 205 is engaged when the swing lever 208 swings clockwise in the drawing.

[Operation]
Next, the operation of the image forming apparatus 1000 will be described.

  The controller 300 of the image forming apparatus 1000 heats the heater 305 of the fixing roller 16a after turning on the power of the image forming apparatus 1000 or replacing the developing unit 23 and the like, and then opens the shutter 130 from the closed position. Process to move to position.

  That is, first, as shown in FIG. 8A, the controller 300 first rotates the fixing motor 200 clockwise in the drawing, and swings the swing lever 208 counterclockwise in the drawing to stop the stopper pin 208b. Abut.

  Next, as shown in FIG. 8B, the control unit 300 rotates the fixing motor 200 by a predetermined number of pulses counterclockwise in the figure, and swings the swing lever 208 clockwise in the figure to stop the stopper. It abuts on the pin 208a. As a result, the swing gear 204 is engaged with the shutter gear 160. By engaging the swing gear 204 and the shutter gear 160, the driving force of the fixing motor 200 is transmitted to the shutter 130 via the motor gear 201, the main gear 202, the small diameter gear 203, the swing gear 204, and the shutter gear 160. The

  When fixing motor 200 further rotates counterclockwise in the figure, shutter 130 moves forward (in the direction indicated by arrow F in FIG. 8B) against the biasing force of coil spring 137. Accordingly, the openings 135a and 135b of the shutter 130 are positioned above the color misregistration sensors 3a and 3b, and the upper surfaces of the color misregistration sensors 3a and 3b are opened. The opening 135c of the shutter 130 is located above the density sensor 4 and opens the upper surface of the density sensor 4. At this time, the shutter 130 is fully opened, and the stopper portion 133 of the shutter 130 is in contact with the mounting plate 119 of the density sensor 4.

  The rotation control of the fixing motor 200 by the control unit 300 is so-called open loop control based only on the count of the number of motor pulses. As shown in FIG. 8A, the fixing motor 200 is once rotated clockwise in the drawing, and the swing lever 208 is brought into contact with the stopper pin 208b, so that the swing lever 208 is once moved to the origin position. Because.

  Here, the swing lever 208 is, for example, a balance between the friction generated between the swing gear 204 and the support shaft portion 204a and the friction generated between the swing gear 205 and the support shaft portion 205a. It does not necessarily swing at the same ratio as the number of motor pulses input from the fixing motor 200. That is, there is always some variation in the operation of the swing lever 208. If the operation amount of the swing lever 208 is smaller than the specified amount of motor pulses, and the swing gear 204 and the shutter gear 140 are engaged at a later stage than the predetermined timing, the shutter 130 is not fully opened. There is a fear. Therefore, in this open loop control, it is necessary to rotate the fixing motor 200 with a slightly higher number of motor pulses than the reference number of motor pulses that theoretically opens the shutter 130 in anticipation of variations in the operation of the swing lever 208. There is.

  As described above, if the number of motor pulses of the fixing motor 200 is set to be large, the movement amount of the rocking lever 208 is larger than the specified amount of the motor pulse due to the variation of the rocking lever 208, and the rocking motion is caused. When the gear 204 and the shutter gear 160 are engaged at a stage earlier than a predetermined timing, the driving force from the fixing motor 200 is maintained even after the stopper portion 133 of the shutter 130 contacts the mounting plate 119 of the density sensor 4. It is transmitted to the gear 160 (state shown in FIG. 8C). However, in this embodiment, the shutter gear 160 can be displaced in the direction indicated by the arrow B in FIG. 8C against the urging force of the torsion spring 180 with respect to the boss 170 connected to the shutter 130. That is, after the stopper portion 133 of the shutter 130 comes into contact with the mounting plate 119 of the density sensor 4, the shutter gear 160 idles with respect to the boss 170, thereby driving transmitted from the swing gear 204 to the shutter gear 160. Can absorb power. As a result, even when a driving force greater than the amount of rotation necessary for fully opening the shutter 130 is applied to the shutter gear 160, the shutter 130 can always be maintained at the fully open position without damaging the shutter gear 160.

  It should be noted that the number of teeth of the gear teeth 161 in the shutter gear 160 is the rotation of the fixing motor 200 even when the fixing motor 200 is rotated with a larger number of motor pulses in consideration of variations in the operation of the swing lever 208. It is sufficient to form a sufficient number so that the meshing between the rocking gear 204 and the shutter gear 160 is maintained until the rotation stops.

  After rotating the shutter 130 to the open position, the control unit 300 performs color misregistration correction processing. Since the color misregistration correction processing has already been described in the first embodiment, the description thereof is omitted here.

  While the color misregistration correction process is being executed, the fixing motor 200 is not rotated, but a holding current flows through the fixing motor 200 and a holding torque for holding the current position is generated. For this reason, even when the fixing motor 200 is stopped, the meshing of the swing gear 204 and the shutter gear 160 can maintain the fully opened state of FIG.

  After the color misregistration correction process is completed, the control unit 300 performs a process of moving the shutter 130 to the closed position. That is, the control unit 300 rotates the fixing motor 200 clockwise as shown in FIG. 8A. The shutter 130 moves backward (in the direction indicated by the arrow R in FIG. 8A) by the biasing force of the coil spring 137. Thereby, the openings 135a and 135b of the shutter 130 are separated from the upper positions of the color misregistration sensors 3a and 3b, and the sensor cover 131 shields the upper surfaces of the color misregistration sensors 3a and 3b. Similarly, the opening 135 c is separated from the position above the density sensor 4, and the sensor cover 131 shields the upper surface of the density sensor 4. At this time, the coil spring 137 is fully extended, and the urging force does not act between the shutter gear 140 and the swing gear 204, so that the swing gear 204 is separated from the shutter gear 140 and the swing lever 208 is moved. Swings counterclockwise in the figure. As a result, the swing gear 205 is engaged with the fixing roller driving gear 206, and the fixing roller 16a and the discharge rollers 17 and 18 start to rotate.

  Further, density correction processing is performed as necessary. Since the density correction processing has already been described in the first embodiment, the description thereof is omitted here.

  In the present embodiment, as shown in FIGS. 8A and 8B, the blades 136a and 136b attached to the shutter 130 are attached to the upper surfaces of the color misregistration sensors 3a and 3b as the shutter 130 is opened and closed. Remove the foreign material adhering to the surface while touching. Further, for convenience of explanation, although not shown in FIGS. 8A and 8B, the wiper 134 attached to the shutter 130 in accordance with the opening / closing operation of the shutter 130, like the blades 136a and 136b described above. Removes foreign matter adhering to the surface while contacting the upper surface of the density sensor 4. As described above, since the surfaces of the density sensor 4 and the color misregistration sensors 3a and 3b can be cleaned by the wiper 134 and the blades 136a and 136b, the sensitivity of the sensor can always be maintained in an optimum state.

  Thereafter, an image is formed on the recording medium P by a known image forming process. Note that the above-described opening / closing operation of the shutter 130 is desirably performed within a time period after the heater 305 starts energization until the heater 305 reaches a predetermined temperature, for example, 100 ° C. In this way, after the heater 305 reaches a predetermined temperature, the image forming process can be performed promptly.

[Function and effect]
According to the second embodiment of the present invention, the boss 170 is formed separately from the shutter gear 160, the torsion spring 180 is provided between the shutter gear 160 and the boss 170, and the rotation amount necessary for fully opening the shutter 130 is exceeded. Even if the driving force is applied to the shutter gear 160, the driving force transmitted to the shutter gear 160 is absorbed to prevent the driving force from being transmitted to the shutter 130. Thereby, it is possible to prevent the gear and the like for transmitting the driving force to the shutter 130 from being damaged while simplifying the structure and control for opening and closing the shutter 130. In addition, when the density sensor 4 and the color misregistration sensors 3a and 3b are used, the shutter 130 can always be kept fully open, so that color misregistration correction or density correction can be reliably performed. Furthermore, even if a driving force greater than the amount of rotation necessary for fully opening the shutter 130 is applied to the shutter gear 160, the gear teeth 161 of the shutter gear 160 will not fly out, so that abnormal noise may occur during operation. Absent.

(Other embodiments)
In the first and second embodiments, the shutter 130 is driven using the driving force of the fixing motor 200. However, the belt driving motor 306 and other motors (for example, drum motors 308K, 308Y, 308M, and 308C). The driving force may be used. In the first and second embodiments, the case where the image forming apparatus 1000 is a tandem type image forming apparatus has been described as an example. However, an intermediate transfer system, that is, a toner image formed by a photoconductor is used as an intermediate transfer body. It is also possible to apply to an image forming apparatus of a type in which the toner images superimposed on the belt are sequentially superimposed and the toner images superimposed on the belt are collectively transferred to a recording medium.

  Further, in the first and second embodiments, the case where the present invention is applied to the shutter opening / closing mechanism for the color misregistration sensor or the density sensor of the image forming apparatus has been described. However, the present invention can be applied to a shutter opening / closing mechanism for other sensors such as a sensor for detecting a medium, and other sensors used in the image forming apparatus.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. 2 is a block diagram illustrating a control system of the image forming apparatus according to the first embodiment. FIG. FIG. 2 is a perspective view illustrating a shutter and a configuration for opening and closing the shutter in the image forming apparatus according to the first embodiment. FIG. 2 is an exploded perspective view illustrating a shutter and a configuration for opening and closing the shutter in the image forming apparatus according to the first embodiment. 2 is a plan view illustrating a shutter and a configuration for opening and closing the shutter in the image forming apparatus according to the first embodiment. FIG. 3 is a diagram illustrating a drive system for opening and closing a shutter in the image forming apparatus according to the first embodiment. FIG. 6 is a configuration diagram of a shutter gear in an image forming apparatus according to a second embodiment. FIG. 6 is a diagram illustrating a drive system for opening and closing a shutter in an image forming apparatus according to a second embodiment.

Explanation of symbols

1 ... Belts 2K, 2Y, 2M. 2C: Image forming unit 3a, 3b: Color shift sensor 4 ... Density sensor 110 ... Frame 130 ... Shutter 133 ... Stopper 140, 160 ... Shutter gear 150 ... Dummy gear 170 ... boss 180 ... torsion spring 200 ... fixing motor 201 ... motor gear 202 ... main gear 203 ... small diameter gears 204, 205 ... oscillating gear 208 ... oscillating lever

Claims (5)

An image forming apparatus for forming an image on a recording medium by a predetermined image forming process,
An image forming unit for forming the image;
A transport unit for transporting the recording medium;
A plurality of drive units for driving the image forming unit and the transport unit;
A reading unit that reads information for setting conditions of the image forming process from a predetermined object;
A shielding member that is interposed between the object and the reading unit and shields the reading unit;
An opening / closing mechanism that switches the shielding member between an open state that enables reading by the reading unit and a closed state that shields the reading unit, by any driving force of the driving unit;
An abutting part that abuts when the shielding member is in the open state;
Even if a driving force is continuously applied from the driving unit after the shielding member comes into contact with the abutting part, the driving force is prevented from being transmitted to the shielding member. A position maintaining mechanism for maintaining the shielding member in a contact position with the abutting portion;
An image forming apparatus comprising: The object is an image carrier on which a toner image is formed by the image forming process,
The image forming apparatus according to claim 1, wherein the information is information related to a color of the toner image. The image carrier is a transport belt for transporting the recording medium;
The image forming apparatus according to claim 2, wherein the information relating to the color is color misregistration information or density information. The opening / closing mechanism has a gear train that transmits a driving force from the driving unit to the shielding member,
The position maintaining mechanism is a gear constituting the gear train,
The image forming apparatus according to claim 1, wherein a part of a tooth row constituting the gear is flexibly displaced. The opening / closing mechanism has a gear train that transmits a driving force from the driving unit to the shielding member,
The position maintaining mechanism is a gear constituting the gear train,
The image forming apparatus according to claim 1, wherein the gear is connected to a rotation shaft of the gear via an elastic member.

Images