JP2004338894A - Image forming device and speed measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect conveyance speed in each part of a recording medium at real time in an image forming device. <P>SOLUTION: Coherent light is irradiated on a paper P moving by a light source 701 to detect light reflected from the paper P by a plurality of photodiode segments 703a, 703b arranged at a predetermined interval in the direction of conveyance of the paper P. Difference in time of each receive signal detected in the photodiode segments 703a, 703b is measured by a time difference measuring part 706 to calculate conveyance speed of the paper P based on the interval at which the photodiode segments 703a, 703b are arranged and difference in time measured by the time difference measuring part 706 in a conveyance speed calculation part 707. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a printer and a copying machine, and more particularly, to an image forming apparatus that records an image on a recording medium.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an image forming apparatus such as a printer, a copying machine, and a facsimile, an image forming apparatus using an electrophotographic method and an apparatus using an ink jet method are generally well known. In an image forming apparatus using an electrophotographic method, for example, a photosensitive member configured in a drum shape is uniformly charged by a charger, and the photosensitive member is exposed to light controlled based on image information, and the photosensitive member is exposed to light. An electrostatic latent image is formed thereon. Then, the electrostatic latent image is converted into a toner image by a developing device, the toner image is transferred to a recording medium conveyed at the same speed as the photoconductor, and the toner image transferred to the recording medium is fixed by a fixing device. Thus, an image is formed.
On the other hand, in an image forming apparatus using an ink jet method, for example, for a recording medium conveyed at a predetermined speed, an image is formed while scanning a recording head in a direction orthogonal to a conveying direction of the recording medium. I have.
[0003]
In such an image forming apparatus, it is necessary to adjust the conveyance speed of the recording medium to be constant in each part of the recording medium in order to suppress distortion and tilt of the image, to make the image magnification uniform, and the like. . For this reason, it is necessary to control the paper transport system, so that the transport speed of the recording medium is detected.
[0004]
For example, as a conventional technique, a line sensor including a pair of a line light emitting diode (line LED) and a CCD (Charge Coupled Device) sensor or a photodiode array is disposed on the left and right sides of a paper transport path. The paper transport position is detected depending on whether light is received up to the pixel, and the detection of the paper transport speed is performed by periodically performing this detection, and the skew angle of the paper is detected by calculating the left and right transport positions. Technology exists (for example, see Patent Document 1).
In addition, a slit disk that rotates in contact with the passing paper is provided, and the rotational speed of the slit disk is detected by measuring the number of passages of the slits formed in the slit disk. There is a technique for detecting the transport speed of a sheet passing from a rotational speed (for example, see Patent Document 2).
[0005]
[Patent Document 1]
JP-A-5-286611 (page 3, FIG. 4)
[Patent Document 2]
JP-A-9-142697 (page 3, FIG. 1)
[0006]
[Problems to be solved by the invention]
However, in the conventional method of detecting the transport speed of the recording medium, a method of calculating an average transport speed of the entire recording medium from a difference in passage time between the leading edge and the trailing edge of the recording medium, or a rotational speed of a transport roll that transports the recording medium is used. Since the method of detecting and indirectly detecting the transport speed of the recording medium is used, it is possible to partially detect the transport speed in a desired area, for example, the central portion of the recording medium, or to detect the transport speed that occurs every moment. Could not be detected in real time. For this reason, there has been a problem that the conveying speed fluctuates in a part of the recording medium, and the image is partially distorted or shifted, and the image magnification fluctuates.
[0007]
Note that the technique described in Patent Document 1 described above can only detect the transport speed and skew angle of the recording medium at the leading end and the trailing end of the recording medium, and can detect other areas of the recording medium. That is, it is not possible to detect the transport speed and the skew angle in a region where the recording medium covers the entire line sensor. Further, in the technology described in Patent Document 2 described above, depending on the type of the recording medium, a slip occurs between the passing recording medium and the slit disk, and the conveyance speed of the recording medium is accurately detected. There was a problem that may not be possible.
[0008]
The present invention has been made to solve the above-described technical problem, and an object of the present invention is to detect a transport speed in each part of a recording medium in real time.
Another object is to form a high-quality image by controlling a drive system based on the transport speed detected in real time in each section of the recording medium.
[0009]
[Means for Solving the Problems]
With such a purpose, the image forming apparatus of the present invention irradiates a recording medium moved by a light source with coherent light, and a plurality of photodetectors arranged at predetermined intervals in a conveying direction of the recording medium. The light reflected from the recording medium is detected. Then, the time difference between the received signals detected by the light detection unit is measured by the time difference measurement unit, and recorded based on the interval at which the light detection unit is provided in the speed calculation unit and the time difference measured by the time difference measurement unit. It is characterized in that the medium transport speed is calculated. Here, a semiconductor laser can be used as the light source. Further, the light source may irradiate coherent light to a flat portion of the recording medium.
[0010]
Further, in the image forming apparatus of the present invention, in a fixing unit that fixes the toner image transferred from the toner image forming unit that forms the toner image onto the recording medium to the recording medium, coherent light is applied to the recording medium that passes through the fixing unit. Irradiation, the light reflected from the recording medium is detected by a plurality of light detection units arranged at predetermined intervals in the transport direction of the recording medium, and the time difference between the received signals detected by the light detection units is determined. It is characterized in that the transport speed of the recording medium is measured based on the time difference of the received signal and the interval at which the light detecting unit is provided by the transport speed detecting unit.
[0011]
Further, the image forming apparatus may further include a fixing drive control unit that controls a driving speed of the fixing unit. In particular, the fixing drive control unit can control the driving speed of the fixing unit based on the difference between the recording medium conveyance speed detected by the conveyance speed detection unit and the driving speed of the fixing unit. Further, the fixing drive control unit can control the driving speed of the fixing unit when the difference between the recording medium conveyance speed detected by the conveyance speed detection unit and the driving speed of the fixing unit is larger than a predetermined value. Further, the fixing drive control unit can also stop at least the fixing unit when the difference between the recording medium conveyance speed detected by the conveyance speed detection unit and the driving speed of the fixing unit is larger than a predetermined value.
[0012]
Further, the fixing drive control unit controls the driving speed of the fixing unit based on a difference between the conveyance speed of the recording medium detected by the conveyance speed detection unit and the driving speed of the fixing unit, and the type of the recording medium. It can be a feature.
Furthermore, a transport speed recording unit that records a transport speed when a recording medium in which a toner image is not transferred to the fixing unit for each type of recording medium is further provided, and the fixing drive control unit is provided with a transport speed detection unit. The driving speed of the fixing unit may be controlled based on a difference between the detected transport speed of the recording medium and the transport speed recorded in the transport speed recording unit.
[0013]
On the other hand, the present invention is regarded as a speed measuring device, in which a light source irradiates a coherent light to a moving body, and a plurality of lights arranged in parallel with a moving direction of the moving body at a predetermined interval from each other. The detection unit detects the light reflected from the moving body. Then, the time difference between the received signals detected by the light detection unit is measured by the time difference measurement unit, and the movement is performed based on the interval at which the light detection unit is provided in the speed calculation unit and the time difference measured by the time difference measurement unit. It is characterized in that the body transport speed is calculated. Here, the light source irradiates coherent light to a plane portion of the moving body.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus illustrated in FIG. 1 is an image forming apparatus using an electrophotographic method, and includes a plurality of image forming units 10 (10Y, 10M, 10C, and 10K) on each of which a toner image of each color component is formed. An intermediate transfer belt 15 for sequentially transferring (primary transfer) each color component toner image formed by the unit 10 and holding the same, and collectively transferring a superimposed toner image transferred on the intermediate transfer belt 15 to a sheet P as a recording medium ( A secondary transfer unit 20 for performing secondary transfer), a fixing unit 60 for fixing the secondary-transferred image on the sheet P, and a sheet speed detecting unit 70 for detecting a conveyance speed of the sheet P immediately after being fixed by the fixing unit 60. It has. Further, a control unit 40 for controlling the operation of each device (each unit) is provided.
[0015]
In the present embodiment, in each of the image forming units 10 (10Y, 10M, 10C, and 10K), a charger 12 that charges these photosensitive drums 11 is provided around a photosensitive drum 11 that rotates in the direction of arrow A. A laser exposure device 13 (exposure beam Bm is shown in the figure) for forming an electrostatic latent image on the body drum 11, each color component toner is stored, and the electrostatic latent image on the photosensitive drum 11 is made visible by the toner. Electronic devices such as a developing device 14 for forming an image, a primary transfer roll 16 for transferring each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15, and a drum cleaner 17 for removing residual toner on the photosensitive drum 11. Photographic devices are sequentially arranged. These image forming units 10 are arranged substantially linearly in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side of the intermediate transfer belt 15.
[0016]
The intermediate transfer belt 15, which is an intermediate transfer member, is configured by a film-shaped endless belt made of polyimide, polyamide, or the like. The intermediate transfer belt 15 is circulated (rotated) at a predetermined speed in a direction B shown in the figure by various rolls. The various rolls include a drive roll 31 driven by a motor (not shown) having an excellent constant speed to circulate and drive the intermediate transfer belt 15, and an intermediate roller extending substantially linearly along the direction in which the photosensitive drums 11 are arranged. A support roll 32 that supports the transfer belt 15, a tension roll 33 that applies a constant tension to the intermediate transfer belt 15 and functions as a correction roll that prevents the intermediate transfer belt 15 from meandering, and a backup provided in the secondary transfer unit 20. The cleaning unit includes a roll 25 and a cleaning backup roll 34 provided in a cleaning unit that scrapes residual toner on the intermediate transfer belt 15.
[0017]
A voltage having a polarity opposite to the charging polarity of the toner is applied to each of the primary transfer rolls 16 provided inside the intermediate transfer belt 15 which is opposed to each of the photosensitive drums 11 and extends substantially linearly. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15, and a superimposed toner image is formed on the intermediate transfer belt 15.
[0018]
The secondary transfer unit 20 includes a secondary transfer conveyance belt 21 disposed on the toner image bearing surface side of the intermediate transfer belt 15, a backup roll 25, and the like. The backup roll 25 is made of a blend rubber tube of EPDM and NBR in which carbon is dispersed on the surface, and the inside thereof is made of EPDM rubber. ⁷ -10 ¹⁰ The roll is formed to have a roll diameter of 28 mm in Ω / □, and the hardness is set to, for example, 70 ° (Asker C). The backup roll 25 is disposed on the back side of the intermediate transfer belt 15 and forms a counter electrode of the secondary transfer conveyance belt 21, and a metal power supply roll 26 to which a secondary transfer bias is stably applied is abutted. Have been.
[0019]
On the other hand, the secondary transfer conveyance belt 21 is stretched by a drive roll 22 and an idle roll 23 and has a volume resistivity of, for example, 10%. ⁶ -10 ¹⁰ It is a semiconductive endless belt of Ωcm. The secondary transfer conveyance belt 21 is conveyed at a predetermined speed by a drive roll 22, and is given a predetermined tension by an idle roll 23. The drive roll 22 is grounded. Then, the secondary transfer conveyance belt 21 and the intermediate transfer belt 15 are interposed therebetween so as to be pressed against the backup roll 25 and function as a secondary transfer roll for performing secondary transfer on the paper P conveyed on the secondary transfer conveyance belt 21. I have.
[0020]
A belt cleaner 35 that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15 is provided downstream of the secondary transfer unit 20 of the intermediate transfer belt 15. Is provided. On the other hand, on the upstream side of the yellow image forming unit 10Y, a reference sensor (home position sensor) for generating a reference signal serving as a reference for setting an image forming timing in each image forming unit 10 (10Y, 10M, 10C, 10K). ) 42, and an image density sensor 43 for adjusting image quality is provided downstream of the black image forming unit 10K. The reference sensor 42 recognizes a predetermined mark provided on the back side of the intermediate transfer belt 15 and generates a reference signal. Each of the image forming units is controlled by an instruction from the control unit 40 based on the recognition of the reference signal. 10 (10Y, 10M, 10C, 10K) is configured to start image formation.
[0021]
Further, in the present embodiment, a plurality of paper trays 50a and 50b for accommodating the paper P, and a pickup roll 51 for taking out and transporting the paper P stacked on the paper trays 50a and 50b at a predetermined timing, as a paper transport system. And a transport roller 52 for transporting the paper P fed by the pickup roll 51, a transport chute 53 for transporting the paper P transported by the transport roll 52 to the secondary transfer unit 20, and a secondary transfer by the secondary transfer transport belt 21. A transport belt 55 that transports the paper P transported after the transport to the fixing device 60 is provided.
[0022]
The fixing device 60 includes a fixing roll and a pressure roll. The fixing roll and the pressure roll are pressed against each other and rotate at a constant speed while forming a nip portion. When the paper P passes through the nip portion, the toner image transferred onto the paper P is heated and pressed to fix the toner image on the paper P.
In the vicinity of the downstream side of the fixing device 60, a paper speed detecting unit 70 is provided. As shown in FIG. 2, the paper speed detection units 70 are disposed at three positions, that is, at both ends and the center in the width direction of the paper P. The position where the sheet speed detection unit 70 is disposed is an area where the sheet P discharged from the fixing device 60 does not bend and maintains a substantially planar shape. Then, the sheet speed detection unit 70 detects the transport speeds at both ends and the center of the sheet P immediately after being fixed by the fixing unit 60, and transmits the detected values to the control unit 40. The control unit 40 is configured to control the fixing drive unit 61 based on the detection value from the sheet speed detection unit 70 to adjust the rotation speeds of the fixing roll and the pressure roll of the fixing unit 60. I have.
[0023]
Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. Image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is input to the image forming apparatus shown in FIG. In the image forming apparatus, after an image processing device (IPS) (not shown) performs predetermined image processing, an image forming operation is performed by the image forming unit 10 or the like. The image processing apparatus (IPS) performs predetermined processing such as shading correction, positional deviation correction, brightness / color space conversion, gamma correction, various image editing such as frame erasing, color editing, and moving editing on the input reflectance data. Image processing is performed. The image data subjected to the image processing is converted into four color material gradation data of Y, M, C, and K, and output to the laser exposure device 13.
[0024]
The laser exposure device 13 irradiates, for example, an exposure beam Bm emitted from a semiconductor laser to each of the photosensitive drums 11 of the image forming units 10Y, 10M, 10C, and 10K according to the input color material gradation data. I have. In the photoconductor drums 11 of the image forming units 10Y, 10M, 10C, and 10K, after the surface is charged by the charger 12, the surface is scanned and exposed by the laser exposure device 13 to form an electrostatic latent image. The formed electrostatic latent image is developed in each of the image forming units 10Y, 10M, 10C, and 10K as a toner image of each color of Y, M, C, and K.
[0025]
The toner images formed on the photosensitive drums 11 of the image forming units 10Y, 10M, 10C, and 10K are transferred onto the intermediate transfer belt 15 at a primary transfer section where the respective photosensitive drums 11 and the intermediate transfer belt 15 abut. Transcribed. More specifically, in the primary transfer section, a voltage having a polarity opposite to the charge polarity of the toner is applied from the primary transfer roll 16 to the base material of the intermediate transfer belt 15, and the unfixed toner image is applied to the surface of the intermediate transfer belt 15. The primary transfer is performed by superimposing sequentially. The unfixed toner image primary-transferred in this way is conveyed to the secondary transfer unit 20 as the intermediate transfer belt 15 rotates.
[0026]
On the other hand, in the paper transport system, the pickup roll 51 rotates in synchronization with the timing of image formation, and paper P of a predetermined size is supplied from a selected one of the paper trays 50a and 50b. The paper P supplied by the pickup roll 51 is transported by the transport roll 52, and reaches the secondary transfer unit 20 via the transport chute 53. Before reaching the secondary transfer section 20, the sheet P is temporarily stopped, and the registration roll (not shown) rotates in accordance with the movement timing of the intermediate transfer belt 15 carrying the toner image as described above. Thus, the position of the sheet P and the position of the toner image are aligned.
[0027]
In the secondary transfer section 20, the drive roll 22 is pressed against the backup roll 25 via the semiconductive secondary transfer conveyance belt 21 and the intermediate transfer belt 15. At this time, the sheet P conveyed in a timely manner is sandwiched between the intermediate transfer belt 15 and the secondary transfer conveyance belt 21. When a voltage (regular transfer bias) having the same polarity as the charge polarity of the toner is applied to the power supply roll 26, a transfer electric field is formed on the secondary transfer conveyance belt 21 as a counter electrode, and the transfer electric field is carried on the intermediate transfer belt 15. The unfixed toner image thus formed is electrostatically transferred to the sheet P at a secondary transfer position pressed by the drive roll 22 and the backup roll 25.
[0028]
Thereafter, the sheet P on which the toner image has been electrostatically transferred is separated from the intermediate transfer belt 15 by the secondary transfer conveyance belt 21 and conveyed, and a conveyance belt provided downstream of the secondary transfer conveyance belt 21 in the sheet conveyance direction. It is sent to 55. The transport belt 55 transports the paper P to the fixing device 60 in accordance with the optimal transport speed of the fixing device 60. The unfixed toner image on the sheet P conveyed to the fixing device 60 is fixed on the sheet P by receiving heat and pressure when passing through the nip portion of the fixing device 60. The sheet speed detecting unit 70 detects the conveying speeds at both ends and the center of the sheet P immediately after the sheet P is fixed by the fixing unit 60, and controls the fixing driving unit 61 based on the detected values, thereby controlling the fixing unit 60. The rotation speeds of the fixing roll and the pressure roll are adjusted. Thereafter, the paper P on which the fixed image is formed is discharged outside the apparatus by a discharge roll (not shown).
On the other hand, after the transfer to the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit with the rotation of the intermediate transfer belt 15, and the intermediate toner is transferred by the cleaning backup roll 34 and the belt cleaner 35. It is removed from the transfer belt 15.
[0029]
Next, the paper speed detecting unit 70, which is a feature of the present embodiment, will be described.
FIG. 3 is a diagram illustrating the structure of the sheet speed detection unit 70. As shown in FIG. 3, the paper speed detecting unit 70 includes a light source 701 such as a semiconductor laser that emits coherent light, a condenser lens 702 that collects light from the light source 701 on the paper P, and a transport direction of the paper P. Light receiving sensor 703 as an example of a light detecting unit including two photodiode (PD) segments 703a and 703b arranged at a predetermined distance d along the line, and two PD segments 703a and 703b constituting the light receiving sensor 703 Out of the analog signals from the PD segments 703a, 703b clipped by the clipping circuits 705a, 705b, and the clipping circuits 705a, 705b, which respectively clip the signals from the amplifiers 704a, 704b, the amplifiers 704a, 704b, respectively. Highest voltage signal or most A time difference measuring unit 706 for extracting signals with low pressure and measuring a time difference between the signals, and a conveying speed for calculating a conveying speed of the paper P from a time difference between analog signals from the PD segments 703a and 703b measured by the time difference measuring unit 706. It comprises a calculation unit 707.
[0030]
When the sheet speed detection unit 70 irradiates a recording medium such as the sheet P with coherent light having good coherence such as a laser beam, the laser beams reflected from the recording medium interfere with each other and are unique to the recording medium. It utilizes the generation of speckle patterns. That is, the laser beam emitted from the light source 701 to the paper P generates a speckle pattern when reflected from the paper P. This speckle pattern is a peculiar pattern for each sheet of paper P, which is made up of the intensity of the output level generated by the interference of the laser beam, and the speckle pattern moves as the sheet of paper P is conveyed. Accordingly, in the two PD segments 703a and 703b constituting the light receiving sensor 703, signals having the same waveform are detected with a time difference only while the paper P moves at the interval d. From this, if the time difference τ of the signal waveform detected in the PD segments 703a and 703b is measured, the transport speed v of the sheet P can be calculated as v = d / τ.
[0031]
Therefore, the paper speed detecting unit 70 irradiates the laser light from the light source 701 to the area where the paper P is maintained in a substantially flat state, and the laser light reflected from the paper P is detected by the light receiving sensor 703 in the transport direction of the paper P. , Two PD segments 703a and 703b arranged at a predetermined interval d along the line. In each of the PD segments 703a and 703b, a signal waveform as one section of a speckle pattern formed by the paper P is detected. As described above, the signal waveforms detected in the PD segments 703a and 703b have the same waveform, and are detected with a time difference τ only while the paper P moves the interval d. These signals are amplified by amplifiers 704a and 704b, respectively, and further clipped by clipping circuits 705a and 705b. Then, a time difference τ of each signal is measured by a time difference measuring unit 706.
[0032]
The paper speed detecting unit 70 uses the time difference τ of the signal waveforms detected in the PD segments 703a and 703b and the interval d between the PD segments 703a and 703b to determine the transport speed of the paper P in the transport speed calculating unit 707. v is calculated by v = d / τ. Then, the control unit 40 outputs the obtained transport speed v of the paper P to the control unit 40.
[0033]
As described above, in the image forming apparatus of the present embodiment, the laser beam is emitted from the light source 701 to the paper P, and the speckle pattern formed when the light is reflected from the paper P is set along the transport direction of the paper P. The moving speed of the speckle pattern that moves with the conveyance of the paper P is determined by detecting the light with the light receiving sensor 703 including two PD segments 703a and 703b that are arranged at a predetermined interval d. The transport speed v can be measured. For this reason, since the laser light can be emitted from the light source 701 to any place of the paper P, the transport speed v at a desired portion of the paper P can be measured. As a result, the transport speed v can be easily measured even in a portion where it is conventionally difficult to dispose the sensor, such as a central portion of the sheet P. In addition, since the transport speed v of the portion irradiated with the laser beam can be measured in real time, the transport speed v of the paper P, which changes every moment, can be immediately grasped.
[0034]
Next, drive control of the fixing device 60 in the image forming apparatus of the present embodiment will be described.
FIG. 4 is a block diagram illustrating a configuration used for drive control of the fixing device 60 in the image forming apparatus according to the present embodiment. As shown in FIG. 4, in the image forming apparatus, a sheet speed detecting unit 70, a fixing driving unit 61, and a user interface unit (UI unit) 80 for selecting a type of the sheet P are connected to the control unit 40. . The control unit 40 stores a CPU 40a for controlling the entire apparatus, a RAM 40b used as a working memory of the CPU 40a, a ROM 40c storing a control program executed by the CPU 40a, and information about the paper P. And an interface 40e for controlling various devices such as an input / output device connected to the control unit 40. The sheet speed detection unit 70, the fixing drive unit 61, and the UI unit 80 are connected to the control unit 40 via the interface 40e, and are controlled by the CPU 40a connected by a bus line.
[0035]
In such an image forming apparatus, the control unit 40 selects one of the paper tray 50a and the paper tray 50b based on the type of the paper P input from the UI unit 80. At this time, information on the paper P is stored in the RAM 40b in the control unit 40. Then, the control unit 40 starts the image forming operation, causes the sheet P to be fed from the sheet tray 50a or the sheet tray 50b selected according to the image forming timing, and causes the secondary transfer unit 20 to transfer the toner image onto the sheet P. Is secondary transcribed. The sheet P on which the toner image has been secondarily transferred is fixed by the fixing device 60. The sheet speed detecting unit 70 detects the sheet P discharged from the fixing device 60 at both ends in the width direction of the sheet P and at the center. Are measured, and the transport speed v of the sheet P is transmitted to the control unit 40 in real time.
[0036]
Then, the control unit 40 determines the fixing driving unit 61 based on the received conveying speed v of the sheet P, the driving speed V of the fixing unit 60 output from the fixing driving unit 61, and the information on the sheet P recorded in the RAM 40b. Control. That is, the measured transport speed v of the sheet P at three locations is compared with the driving speed V of the fixing device 60, and any one of the measured transport speeds v of the three locations of the sheet P is compared with the fixing device 60. If the difference from the driving speed V of the fixing device 60 decreases by more than 3% with respect to the driving speed V of the fixing device 60, it is determined that the sheet P is in an abnormal state in which a slip has occurred, and information on the sheet P is determined. , The rotational speed of the fixing device 60 is changed. For example, based on the information about the paper P recorded in the RAM 40b, if the paper P being transported is, for example, 127 GSM of a mirror-coated paper having a large weight, the rotation of the fixing device 60 is performed to secure the torque of the fixing device 60. The fixing driving unit 61 is controlled so as to reduce the speed. On the other hand, when the transported paper P is a thin paper of 64 GSM or less with a small weighing amount, the fixing speed may be increased by increasing the rotation speed of the fixing unit 60 because the fixing may be excessive and slippage may occur in the toner layer. Then, the fixing driving unit 61 is controlled to ease the fixing. By controlling the fixing drive unit 61 in this way, it is possible to suppress the slip of the paper P.
[0037]
Here, FIG. 5 is an example of a flowchart showing a flow of processing related to drive control of the fixing device 60 performed by the control unit 40. As shown in FIG. 5, when the driving control process of the fixing device 60 is started, first, the sheet speed detecting unit 70 changes the transport speed v of the sheet P immediately after passing through the fixing device 60 to the both ends in the width direction of the sheet P. Detection is performed at three locations, ie, the central part and the central part (S101). Comparing the detected transport speeds v of the three sheets of paper P with the drive speed V in the fixing device 60, the transport speed v in any part is reduced by 3% or more with respect to the drive speed V of the fixing device 60. Is determined (S102). If the transport speed v of any part is within 3% of the driving speed V of the fixing device 60, the driving speed V of the fixing device 60 is maintained (S103).
[0038]
If it is determined in step S102 that the transport speed v in any part is lower than the driving speed V of the fixing device 60 by 3% or more, the amount of decrease in the transport speed v in that part is determined. It is determined whether the driving speed V of the fixing device 60 is 7% or less (S104). If the amount of decrease in the driving speed V of the fixing device 60 is 7% or more, the image forming apparatus is stopped (S105).
If it is determined in step S104 that the reduction amount of the transport speed v is 7% or less of the drive speed V of the fixing device 60, it is determined whether the transported paper P is a thick paper whose weighing is 127 GSM or more. A determination is made (S106). If the paper P being transported is thick paper of 127 GSM or more, the driving speed V of the fixing unit 60 is set to be the same as the minimum transport speed v of the three transport speeds v of the detected papers P. (S107).
If the paper P being transported is not thick paper of 127 GSM or more in step S106, it is determined whether or not the paper P is thin paper of 64 GSM or less (S108). If the transported sheet P is a thin sheet of 64 GSM or less, the driving speed V of the fixing device 60 is set to a speed increased by 5% (S109). On the other hand, if the paper is not thin paper of 64 GSM or less, that is, if it is plain paper whose weighing is in the range of 64 GSM to 127 GS, the driving speed V of the fixing device 60 is set to be uniformly reduced by 3% (S110).
Then, after step S103, step S107, step S109, and step S110, the process returns to step S101, and the process is repeated.
[0039]
In the present embodiment, the transport speed v of the sheet P is compared with the driving speed V of the fixing device 60 output from the fixing driving unit 61. However, the fixing device 60 does not carry a toner image for each paper type. Are measured in advance in the non-volatile memory 40d of the control unit 40, and the conveyance speed v of the sheet P is compared with the measured value recorded in the non-volatile memory 40d. Thus, the slip amount can be determined.
[0040]
As described above, in the image forming apparatus of the present embodiment, the transport speed v of the paper P can be measured by determining the moving speed of the speckle pattern that moves with the transport of the paper P. Can irradiate the laser light to any place of the paper P, and can measure the transport speed v at a desired portion of the paper P. Therefore, for example, with respect to the conveyance speed v of the sheet P after fixing, it is easy to measure the conveyance speed v even in a portion where it is conventionally difficult to arrange a sensor, such as a central portion of the sheet P where slippage easily occurs. The slip of the sheet P in the fixing device 60 can be reliably detected, and the slip can be fed back to the fixing drive unit 61 of the fixing device 60. As a result, the slip of the sheet P can be reliably suppressed, and a high-quality image can be stably formed. In particular, the real-time measurement of the transport speed v of the portion irradiated with the laser beam becomes possible, so that the driving speed V of the fixing device 60 can be adjusted immediately.
[0041]
In the present embodiment, the sheet speed detection unit 70 is provided near the downstream side of the fixing device 60 to detect the conveyance speed v of the sheet P after fixing. It is also possible to arrange a detection unit 70 to detect the transport speed v of the sheet P before fixing.
[0042]
Further, in the present embodiment, the transport speed v of the sheet P passing through the fixing device 60 is detected, but the transport speed v of the intermediate transfer belt 15 is detected. _belt Can also be detected. As described above, since the intermediate transfer belt 15 is formed of a film-shaped endless belt made of polyimide, polyamide, or the like, a specific speckle pattern is also generated from the intermediate transfer belt 15 by irradiating a laser beam. Accordingly, the transport speed v of the intermediate transfer belt 15 _belt Can be detected, and drive control can be performed on the drive roll 31 that circulates and drives the intermediate transfer belt 15 based on the measured value. In particular, in the sheet speed detection unit 70 of the present embodiment, the changing conveyance speed v of the intermediate transfer belt 15 is used. _belt Can be controlled in real time, so that a constant transport speed v _belt Can be driven.
[0043]
[Embodiment 2]
In the first embodiment, a toner image is formed on a sheet P by an electrophotographic method, and a conveyance speed v of the sheet P passing through a fixing device 60 for heating and fixing the toner image is determined by using a speckle pattern reflected from the sheet P. The description has been given by taking an image forming apparatus for performing measurement as an example. However, such a content is based on an image adopting a so-called inkjet method in which a liquid ink is used instead of the electrophotographic image forming apparatus, and the liquid ink is directly ejected onto the paper P to form an ink image on the paper P. It is also possible to apply to a forming apparatus. In the second embodiment, a case will be described in which such an inkjet system is employed. The same components as those in the first embodiment are denoted by the same reference numerals, and a detailed description thereof will be omitted.
[0044]
FIG. 6 is a diagram showing an image forming apparatus to which the present embodiment is applied. The image forming apparatus shown in FIG. 6 is a so-called inkjet type image forming apparatus, and holds an image on paper P while holding at least yellow (Y), magenta (M), cyan (C), and black (K) inks. A recording unit 400 that forms a color image by applying ink according to data, a paper supply tray 410 that holds paper P on which an image is recorded, and a paper supply tray 410 that is synchronized with the timing at which the recording unit 400 performs image formation. Paper feed roll 420 that feeds paper P, paper transport roll 431 that transports paper P to recording unit 400 in a predetermined amount stepwise, and paper speed detection that detects the transport speed of paper P transported by paper transport roll 431 Unit 70, a paper transport roll 432 that transports the paper P to a discharge unit of the image forming apparatus, and heats and dries the ink image formed on the paper P燥 roll 440, the ink image is formed and a discharge tray 450 for placing the discharged sheet P from the image forming apparatus. In addition, a control unit 460 that controls the operation of each device (each unit) is provided.
[0045]
As shown in FIG. 7, the recording unit 400 includes a recording head 401 that ejects ink droplets according to an image signal, an ink cartridge 402 that stores Y, M, C, and K inks, a housing 403 as a support, The recording head 401 includes a support shaft 404 that slidably supports the recording head 401.
The print head 401 has 832 nozzles for each of the colors Y, M, C, and K, and a total of 3328 nozzles are alternately arranged at a density of 800 dpi. Each nozzle is provided with an ink supply path through which ink of each color of Y, M, C, and K from the ink cartridge 402 is supplied. A piezo element is arranged on each side of the ink supply path, and an electric signal is applied to the piezo element to deform the piezo element, and the deformation applies pressure to the ink supply path and ejects ink droplets from the nozzle. It is configured to be.
The support shaft 404 is fixed to the housing 403 so as to face in a direction orthogonal to the transport direction of the paper P. The support shaft 404 slidably supports the recording head 401. The recording head 401 is configured to reciprocate on a support shaft 404 in a direction perpendicular to the transport direction of the sheet P by a driving device (not shown).
[0046]
The drying roll 440 is rotatably supported by a supporting mechanism (not shown) while the heating roll and the driven roll are pressed against each other, and is rotated at a predetermined speed in a direction indicated by an arrow in the drawing by a driving device (not shown). A halogen heater as a heating source is provided inside the heating roll, and the surface temperature of the heating roll is maintained at a predetermined temperature (for example, 80 ° C.).
The sheet speed detection unit 70 has the same configuration as that described in the first embodiment, and is configured to detect the transport speed of the paper P transported by the paper transport roll 431 in real time.
[0047]
Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. In the image forming apparatus shown in FIG. 6, image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is subjected to predetermined image processing by an image processing device (IPS) not shown. After that, the image is transmitted to the recording unit 400 and the image forming operation is performed.
First, the paper supply roll 420 rotates in synchronization with the timing of image formation, and the paper P held in the paper supply tray 410 is supplied to the recording unit 400. The paper P supplied by the paper feed roll 420 reaches the paper transport roll 431, and the paper transport roll 431 transports the paper P to the recording unit 400 stepwise by a predetermined amount. At this time, the paper speed detecting unit 70 detects the transport speed of the paper P in real time, and integrates the detected speed over time for each step, thereby detecting the transport amount of the paper P in units of steps. By controlling the driving of the paper transport roll 431 based on the detected transport amount, it is possible to transport the paper P accurately.
On the other hand, the recording unit 400 ejects ink droplets onto the paper P while reciprocating in a direction orthogonal to the transport direction of the paper P in synchronization with the paper P moving stepwise by a predetermined amount, Form a color image.
[0048]
The paper P on which the color image has been formed is transported to the drying roll 440 by the paper transport roll 432. The drying roll 440 applies heat to the paper P to dry the color image ink formed on the paper P. Thereafter, the paper P is transported to the discharge tray 450 and is sequentially placed.
[0049]
As described above, according to the image forming apparatus of the present embodiment, the transport speed of the paper P is detected in real time by the paper speed detection unit 70, and the transport speed is integrated over time for each step. Is detected, and the driving of the paper transport roll 431 is controlled based on the detected transport amount, so that the paper P can be transported accurately. As a result, it is possible to form an image with high quality without image shift or distortion.
[0050]
【The invention's effect】
As described above, according to the present invention, it is possible to detect the transport speed in each part of the recording medium in real time, and to form a high-quality image by controlling the drive system based on the detected transport speed. It became possible.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an image forming apparatus to which an exemplary embodiment is applied;
FIG. 2 is a diagram illustrating an arrangement of a sheet speed detection unit.
FIG. 3 is a diagram illustrating a structure of a sheet speed detection unit.
FIG. 4 is a block diagram illustrating a configuration used for drive control of a fixing device.
FIG. 5 is an example of a flowchart illustrating a flow of processing related to drive control of a fixing device performed by a control unit.
FIG. 6 is a diagram illustrating an image forming apparatus to which the exemplary embodiment is applied;
FIG. 7 is a diagram illustrating a configuration of a recording unit.
[Explanation of symbols]
10Y, 10M, 10C, 10K: image forming unit, 11: photosensitive drum, 12: charger, 13: laser exposure device, 14: developing device, 15: intermediate transfer belt, 16: primary transfer roll, 17: drum cleaner , 20: secondary transfer unit, 21: secondary transfer conveyance belt, 40: control unit, 50a, 50b: paper tray, 60: fixing device, 61: fixing drive unit, 70: paper speed detection unit, 80: UI unit Reference numeral 701: light source 702: condenser lens 703: light receiving sensor 703a, 703b: photodiode (PD) segment; 704a, 704b: amplifier; 705a, 705b: clipping circuit; 706: time difference measuring unit; Calculator

Claims (12)

A light source that emits coherent light to a moving recording medium;
A plurality of light detection units disposed at predetermined intervals in the conveyance direction of the recording medium, and detects light reflected from the recording medium,
A time difference measurement unit that measures a time difference between the received signals detected by the light detection unit,
An image forming apparatus comprising: a speed calculation unit that calculates a transport speed of the recording medium based on an interval at which the light detection unit is provided and a time difference measured by the time difference measurement unit. The image forming apparatus according to claim 1, wherein the light source is a semiconductor laser. The image forming apparatus according to claim 1, wherein the light source irradiates the light onto a flat portion of the recording medium. A toner image forming unit for forming a toner image,
A fixing unit for fixing the toner image transferred from the toner image forming unit to a recording medium on the recording medium,
The recording medium passing through the fixing unit is irradiated with coherent light, and the light reflected from the recording medium is reflected by a plurality of light detection units arranged at predetermined intervals in the conveyance direction of the recording medium. Detecting the time difference between the received signals detected by the light detection unit, and detecting the conveyance speed of the recording medium based on the time difference between the received signals and the interval at which the light detection unit is provided. An image forming apparatus comprising: a speed detection unit. The image forming apparatus according to claim 4, further comprising a fixing drive control unit that controls a driving speed of the fixing unit. The fixing drive control unit controls a driving speed of the fixing unit based on a difference between a conveyance speed of the recording medium detected by the conveyance speed detection unit and a driving speed of the fixing unit. Item 6. The image forming apparatus according to Item 5. The fixing drive control unit controls the driving speed of the fixing unit when a difference between the recording medium conveyance speed detected by the conveyance speed detection unit and the driving speed of the fixing unit is larger than a predetermined value. The image forming apparatus according to claim 6, wherein: The fixing drive control unit stops at least the fixing unit when a difference between the conveyance speed of the recording medium detected by the conveyance speed detection unit and the driving speed of the fixing unit is larger than a predetermined value. The image forming apparatus according to claim 6. The fixing drive control unit controls a driving speed of the fixing unit based on a difference between a conveyance speed of the recording medium detected by the conveyance speed detection unit and a driving speed of the fixing unit, and a type of the recording medium. The image forming apparatus according to claim 5, wherein the control is performed. The fixing drive control unit further includes a conveyance speed recording unit that records a conveyance speed when the recording medium in which the toner image is not transferred is passed through the fixing unit for each type of the recording medium. The driving speed of the fixing unit is controlled based on a difference between a conveyance speed of the recording medium detected by a speed detection unit and the conveyance speed recorded in the conveyance speed recording unit. Image forming apparatus. A light source for irradiating coherent light to the moving object,
A plurality of light detection units that are parallel along the transport direction of the moving body, are disposed at a predetermined interval from each other, and detect light reflected from the moving body,
A time difference measurement unit that measures a time difference between the received signals detected by the light detection unit,
A speed measurement device, comprising: a speed calculation unit that calculates a transport speed of the moving body based on an interval at which the light detection unit is provided and a time difference measured by the time difference measurement unit. The speed measuring device according to claim 11, wherein the light source irradiates the light to a plane portion of the moving body.

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