Patent Application
20090317109
1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method for transferring visible images formed on plural image carriers to the endlessly-moving front surface of an endless movement body or a recording member held on the front surface thereof so as to be superimposed one on another.
2. Description of the Related Art
A known image forming apparatus of this type is one described in Patent Document 1. This image forming apparatus has plural photosensitive bodies serving as image carriers and a belt member serving as an endless movement body that performs an endless movement to successively pass through positions facing the photosensitive bodies. In the image forming apparatus, toner images of different colors are formed on the front surfaces of the respective photosensitive bodies and then transferred to a recording paper held on the front surface of the belt member so as to be superimposed one on another through an electrophotographic process. With the superimposition of the toner images, a multicolor toner image is formed on the front surface of the recording paper.
In the image forming apparatus that forms the multicolor toner image in this manner, displacements in the superimposition of the dots of respective colors may occur due to the off-centering of a photosensitive-body gear fixed to the rotary shaft of a photosensitive body. Specifically, when the maximum-diameter part of the photosensitive-body gear, at which a length from the rotary shaft to a gear tooth tip is the longest with respect to the off-centering of the photosensitive-body gear, is meshed with a driving gear, the linear speed of the photosensitive body per rotation becomes the slowest. Conversely, when the minimum-diameter part of the photosensitive-body gear, at which the distance from the rotary shaft to the gear tooth tip is the shortest with respect to the off-centering of the photosensitive-body gear, is meshed with the driving gear, the linear speed of the photosensitive body per rotation becomes the fastest. Since the maximum- and minimum-diameter parts of the photosensitive-body gear are symmetrical about a point by 180° relative to the rotary shaft, the linear speed of the photosensitive body has a fluctuation characteristic in which a sine curve for one cycle is displayed per cycle of the gear. Among mountain parts and valley parts created when a center line is drawn between the maximum and minimum values of the sine curve, the valley parts of the sine curve indicate that the linear speed of the photosensitive body becomes slower than its original speed (the value of the center line). Thus, dots on the photosensitive body are transferred to a recording paper moving faster than the photosensitive body in a state of being more expanded than usual in a belt movement direction. On the other hand, the mountain parts of the sine curve indicate that the linear speed of the photosensitive body becomes faster than its original speed. Thus, the dots on the photosensitive body are transferred to the recording paper moving slower than the photosensitive body in a state of being more contracted than usual in the belt movement direction. The dots of the respective colors are thus separately expanded and contracted to cause the displacements in the superimposition of the dots of the respective colors.
The image forming apparatus described in Patent Document 1 prevents the displacements in the superimposition of the dots of the respective colors in the following manner. In other words, a pattern image for detecting a speed fluctuation waveform is first formed on the belt member at a predetermined timing. This pattern image is composed of patch-like toner images of the respective colors arranged in a belt-surface movement direction in a predetermined order. If no speed fluctuation occurs in the photosensitive bodies for the respective colors, the toner images are arranged at even intervals. On the other hand, if any speed fluctuation occurs in the photosensitive bodies for the respective colors, the toner images are not arranged on the belt member at even intervals and differences between the intervals reflect the speed fluctuation of the photosensitive bodies for the respective colors. The differences between the intervals are detected based on an output from a photosensor that detects the toner images for the respective colors, whereby the sine-curve-like speed fluctuation waveform is detected for each of the photosensitive bodies for the respective colors. Then, the driving speed variation pattern of each of the photosensitive bodies capable of canceling the sine-curve-like speed fluctuation waveform is determined and stored in a data storage unit. Subsequently, when a print job is performed, reference timing in a one-rotation cycle is recognized for each of the photosensitive bodies for the respective colors based on an output from an encoder fixed to each of the rotary shafts of the photosensitive bodies for the respective colors. Then, the driving speed of each of plural driving motors that separately drive the photosensitive bodies for the respective colors is finely adjusted based on the reference timing and the driving speed fluctuation pattern stored in advance. With this fine adjustment of the driving speed, the speed fluctuations of the photosensitive bodies for the respective colors are reduced, so that the displacements in the superimposition of the dots of the respective colors can be prevented.
Note that in addition to the displacements in the superimposition of the dots due to the speed fluctuations of the photosensitive bodies, the image forming apparatus described in Patent Document 1 detects displacements in the superimposition of the dots due to the speed fluctuation of a driving roller that drives the belt member, or the like. For this reason, the above-described pattern image is formed. However, when only the speed fluctuations of the photosensitive bodies are detected to control the driving motor, the formation of the pattern image can be omitted. This is because the speed fluctuation waveforms of the photosensitive bodies can be detected based on the outputs from the encoders fixed to the rotary shafts of the photosensitive bodies.
The image forming apparatus described in Patent Document 1 refers to the displacements in the superimposition of the dots on the recording paper conveyed in a state of being held on the front surface of the belt member, but a similar displacement in the superimposition of the dots may occur in an image forming apparatus having the following configuration. In other words, the image forming apparatus is configured to transfer the toner images formed on the photosensitive bodies for the respective colors to an intermediate transfer belt serving as the belt member so as to be superimposed one on another and then transferring them to the recording paper in a collective manner.
On the other hand, Patent Document 2 describes an image forming apparatus that reduces the displacements in the superimposition of the dots of the respective colors by matching the phases of the speed fluctuation waveforms of the photosensitive bodies for the respective colors to each other. Specifically, in this image forming apparatus, the arrangement pitches of the photosensitive bodies are set to be an integral multiple of the circumferential length of the photosensitive bodies. Under this setting, the photosensitive-body gears are rotated by an integral number while the belt member is moved from one position facing any one of the photosensitive bodies to another position facing the adjacent photosensitive body. Therefore, when the photosensitive bodies are rotated in a state in which rotational phases at the maximum- and minimum-diameter parts of the photosensitive-body gears are matched to each other, the two adjacent photosensitive bodies transfer the following dots to the recording paper so as to be superimposed one on another. In other words, the dots entering a transfer position when the photosensitive bodies are driven at the maximum linear speed per rotation and those entering the transfer position when the photosensitive bodies are driven at the minimum linear speed per rotation are transferred to the recording paper. In such the superimposition of the dots, the dots transferred in a state of being more expanded than usual and those transferred in a state of being more contracted than usual due to the speed fluctuations of the photosensitive bodies are superimposed one on another, thereby making it possible to prevent the displacements in the superimposition of the dots. To this end, the image forming apparatus described in Patent Document 2 has plural photosensors that detect marks provided at the maximum- and minimum-diameter parts of the photosensitive bodies at predetermined positions. Furthermore, the image forming apparatus controls the driving of the driving motors for the respective colors so that timings for detecting the marks with the photosensors are synchronized with each other.
Patent Document 1: JP-B2-3186610
Patent Document 2: JP-A-2003-194181
Meanwhile, since reduction of manufacturing costs for apparatuses has been in demand recently, it is desired in some cases that the driving motor for driving the photosensitive body be also used as a driving source for members other than the corresponding photosensitive body. For example, it is desired in some cases that, regardless of a monochrome mode and a color mode, the driving motor for black to be driven among plural of the driving motors corresponding to the photosensitive bodies for the respective colors be used as a driving source for the belt member. In this case, when the driving speed of the driving motor for black is finely adjusted based on the predetermined driving speed variation pattern to cancel the speed fluctuation due to the off-centering of the photosensitive body for black, the fluctuation of the speed of the belt member occurs. Accordingly, processing for finely adjusting the driving speed of the driving motor based on the driving speed variation pattern as described in Patent Document 1 is not suitable. Conversely, when performing the processing for matching the rotational phases of the photosensitive-body gears for the respective colors to each other as described in Patent Document 2, the image forming apparatus can prevent the displacements in the superimposition of the dots of the respective colors without causing the speed fluctuation of the belt member described above.
However, while high quality has been in demand in recent technologies, the displacements in the superimposition of the dots of the respective colors exceeding a tolerance level may remain only if the rotational phases of the photosensitive gears for the respective colors are matched to each other. Specifically, the displacements in the superimposition of the dots of the respective colors cannot be eliminated only with the superimposition of the rotational phases of the photosensitive-body gears for the respective colors. It is assumed that speed fluctuation occurs in the photosensitive bodies for the respective colors as shown in
The present invention has been made in view of the above circumstances and may provide an image forming apparatus and an image forming method. Specifically, the present invention may provide the image forming apparatus capable of reducing manufacturing costs with the shared use of a driving source between an image carrier and other members and keeping displacements in the superimposition of dots at a tolerance level.
According to an embodiment of the present invention, there is provided an image forming apparatus including plural image carriers each having a visible image carried on a rotating surface thereof; a first driving source that is a driving source for only any one of the image carriers; a second driving source that is a driving source for another image carrier; a rotation detection unit that separately detects whether the image carrier driven by the first driving source and another image carrier driven by the second driving source have a predetermined rotational angle; an endless movement body that causes a front surface thereof to be endlessly moved; a transfer unit that transfers the visible images formed on front surfaces of the image carriers to the front surface of the endless movement body or a recording member held on the front surface of the endless movement body so as to be superimposed one on another; and a control unit that controls driving of the first and second driving sources based on an output from the rotation detection unit. The image forming apparatus uses the first driving source as a shared driving source between the image carrier and a predetermined member other than a driving transmission unit for driving the image carrier. A waveform recognition unit is provided that recognizes a first waveform as a waveform of a first speed fluctuation and a second waveform as a waveform of a second speed fluctuation based on a result obtained by detecting the first speed fluctuation per rotation of the image carrier driven by a driving force of the first driving source driven at a predetermined speed and the second speed fluctuation per rotation of another image carrier driven by a driving force of the second driving source driven at a predetermined speed. The control unit is configured to recognize a reference timing per rotation of the image carrier driven by the first driving source and a reference timing per rotation of another image carrier driven by the second driving source based on the output from the rotation detection unit and control the driving of the second driving source based on the reference timings and the first and second waveforms recognized by the waveform recognition unit, thereby matching a phase and an amplitude of the second waveform of another image carrier driven by the second driving source to a phase and an amplitude of the first waveform of the image carrier driven by the driving force of the first driving source driven at the predetermined speed.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.
Next, a description is made of an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) as an image forming apparatus to which the present invention is applied.
First, the basic configuration of the printer is described.
The charging unit 4Y uniformly charges the front surface of the photosensitive body 1Y rotated in a clockwise direction in
The development unit 5Y has a development roller 51Y provided so as to be partially exposed from an opening of its casing. In addition, the development unit 5Y has two conveyance screws 55Y provided parallel to each other, a doctor blade 52Y, a toner density sensor (hereinafter referred to as a T sensor) 56Y, and the like.
Inside the casing of the development unit 5Y, the Y developing agent (not shown) containing the magnetic carrier and the Y toner is accommodated. The Y developing agent is friction-charged while being stirred and conveyed by the two conveyance screws 55Y and then carried on the front surface of the development roller 51Y. Next, after its layer thickness is controlled by the doctor blade 52Y, the Y developing agent is conveyed to a development region facing the photosensitive body 1Y. At the development region, the Y toner is attached to the electrostatic latent image on the photosensitive body 1Y. Thus, the Y-toner image is formed on the photosensitive body 1Y. In the development unit 5Y, the Y development agent whose Y toner has been consumed by development is returned to the casing along with the rotation of the development roller 51Y.
A partition wall is provided between the two conveyance screws 55Y. With this partition wall, a first supply unit 53Y that accommodates the development roller 51Y, the conveyance screw 55Y on the right side in
The T sensor 56Y composed of a permeability sensor is provided at the bottom wall of the second supply unit 54Y and outputs the voltage of a value corresponding to the permeability of the Y developing agent that passes through a position above the T sensor 56Y. Since the permeability of a two-component developing agent containing toner and a magnetic carrier shows a good mutual relationship with a toner density, the T sensor 56Y outputs the voltage of a value corresponding to a Y-toner density. The value of the output voltage is transmitted to a control unit (not shown). The control unit has a RAM storing Vtref for the color Y as the target value of the output voltage from the T sensor 56Y. The RAM also stores data of Vtref for the color M, Vtref for the color C, and Vrtref for the color K as the target values of output voltages from T sensors (not shown) provided in other development units. Vtref for the color Y is used for controlling the driving of a Y toner conveyance unit described below. Specifically, the control unit controls the driving of the Y toner conveyance unit (not shown) to replenish the second supply unit 54Y with the Y toner so that the value of the output voltage from the T sensor 56Y approximates Vtref for the color Y. With this replenishment, the Y toner density of the Y developing agent in the development unit 5Y is kept in a predetermined range. The development units of other processing units also perform the same toner replenishment control using M, C, and K toner conveyance units.
In
In
In the vicinity of the terminal end of the paper feeding path 70, a pair of resist rollers 28 is provided. The pair of the resist rollers 28 is rotated to sandwich the transfer paper P but temporarily stopped immediately when the transfer paper P is sandwiched between the rollers 28. Then, the pair of the resist rollers 28 feeds the transfer paper P to a secondary transfer nip described below at an appropriate timing.
Above the processing units 6Y, 6M, 6C, and 6K in
The driving roller 12 sandwiches the intermediate transfer belt 8 between the driving roller 12 and the secondary transfer roller 19 to form the secondary transfer nip. The four-color toner image as a visible image formed on the intermediate transfer belt 8 is transferred to the transfer paper P at the secondary transfer nip. Then, the four-color toner image is combined with white color of the transfer paper P to form a full-color toner image. Remaining transfer toner that has not been transferred to the transfer paper P is attached to the intermediate transfer belt 8 that has passed through the secondary transfer nip. The remaining transfer toner is cleaned by the cleaning unit 10. The transfer paper P to which the four-color toner image is collectively secondarily transferred at the secondary transfer nip is fed to a fixation unit 20 via a conveyance path 71.
The fixation unit 20 forms a fixation nip with a fixation roller 20a having a heat generation source such as a halogen lamp inside it and a pressure roller 20b that rotates in contact with the fixation roller 20a at a predetermined pressure. The transfer paper P fed into the fixation unit 20 is sandwiched at the fixation nip so as to make its unfixed-toner-image carrying surface closely contact the fixation roller 20a. Then, the toner in the full-color toner image is softened by influences of heating and pressure. Thus, a full-color image is fixed.
The transfer paper P on which the full-color image is fixed by the fixation unit 20 is ejected from the fixation unit 20 and then approaches a branch point between a paper discharge path 72 and a pre-inversion conveyance path 73. A first switch claw 75 is provided at the branch point in a state in which it can swing. The movement path of the transfer paper P is switched when the first switch claw 75 is swung. Specifically, when the tip end of the claw 75 is moved in a direction close to the pre-inversion conveyance path 73, the movement path of the transfer paper P is directed to the paper discharge path 72. Furthermore, when the tip end of the claw 75 is moved in a direction away from the pre-inversion conveyance path 73, the movement path of the transfer paper P is directed to the pre-inversion conveyance path 73.
When the movement path directed to the paper discharge path 72 is selected by the first switch claw 75, the transfer paper P passes through the paper discharge path 72 via a pair of paper discharge rollers 100, is discharged outside the apparatus, and is stacked on a stack unit 50a provided at the top surface of a printer housing. On the other hand, when the movement path directed to the pre-inversion conveyance path 73 is selected by the first switch claw 75, the transfer paper P passes through the pre-inversion conveyance path 73 and enters a nip formed at a pair of inversion rollers 21. The pair of the inversion rollers 21 conveys the transfer paper P sandwiched between the inversion rollers 21 toward the stack unit 50a but reverses rotation immediately before the rear end of the transfer paper P enters the nip. Thus, the transfer paper P is conveyed in reverse, and the rear end of the transfer paper P enters an inversion conveyance path 74.
The inversion conveyance path 74 is formed into such a shape as to be extended from an upper side to a lower side in a vertical direction while being curved. In the inversion conveyance path 74, a pair of first inversion conveyance rollers 22, a pair of second inversion conveyance rollers 23, and a pair of third inversion conveyance rollers 24 are provided. The transfer paper P is conveyed while successively passing through nips formed at the pairs of the rollers and thus turned upside-down. The transfer paper P turned upside-down is returned to the paper feeding path 70 and fed to the secondary transfer nip again. Then, the transfer paper P enters the secondary transfer nip so as to make its non-image-carrying surface closely contact the intermediate transfer belt 8, and a second four-color toner image of the intermediate transfer belt 8 is collectively secondarily transferred to the non-image-carrying surface. Then, the transfer paper P passes through the conveyance path 71, the fixation unit 20, the paper discharge path 72, and the pair of the paper discharge rollers 100 and is stacked on the stack unit 50a outside the apparatus. With this inversion conveyance, the full-color images are formed on both surfaces of the transfer paper P.
A bottle support unit 31 is provided between the transfer unit 15 and the stack unit 50a positioned above the transfer unit 15. In the bottle support unit 31, toner bottles 32Y, 32M, 32C, and 32K serving as toner accommodation units that accommodate the Y, M, C, and K toner are installed. The toner bottles 32Y, 32M, 32C, and 32K are provided so as to be arranged at a slightly oblique angle to each other and set in height in the order of the colors Y, M, C, and K. The Y, M, C, and K toner in the toner bottles 32Y, 32M, 32C, and 32K is appropriately supplied to the corresponding development units of the processing units 6Y, 6M, 6C, and 6K by the toner conveyance units described below. The toner bottles 32Y, 32M, 32C, and 32K can be detached from the printer main body independently of the processing units 6Y, 6M, 6C, and 6K.
In a monochrome-mode print job, the printer according to the embodiment drives only the photosensitive body 1K among the four photosensitive bodies 1Y, 1M, 1C, and 1K. In this case, with the adjustment of the posture of the transfer unit 15, the intermediate transfer belt 8 is brought into contact with only the photosensitive body 1K among the four photosensitive bodies 1Y, 1M, 1C, and 1K. On the other hand, in a color-mode print job, all the four photosensitive bodies 1Y, 1M, 1C, and 1K are driven. In this case, with the adjustment of the posture of the transfer unit 15, the intermediate transfer belt 8 is brought into contact with all the four photosensitive bodies 1Y, 1M, 1C, and 1K.
The photosensitive-body driving system composed of a coupling 201 serving as a part of a connection unit, a photosensitive-body gear 202, a driving motor 90, and the like shown in
On the side of the printer main body, the photosensitive-body gear 202 is supported by a support plate so as to be rotatable. The coupling 201 is formed at the rotation center of the photosensitive-body gear 202 and coupled with a coupling (not shown) fixed to the rotary shaft of the photosensitive body 1 in the shaft line direction. With this coupling, the rotational driving force of the photosensitive-body gear 202 is transmitted to the photosensitive body 1 via the two couplings. The gear of the photosensitive-body gear 202 is meshed with the motor gear of the driving motor 90, whereby the rotational driving force of the driving motor 90 is transmitted to the photosensitive-body gear 202. When the processing unit 6 is pulled out from the printer main body, the coupling (not shown) fixed to the rotary shaft member of the photosensitive body 1 and the coupling formed in the photosensitive-body gear 202 are released from each other.
When the driving motor 90 is driven at a constant speed in a configuration where such a coupling is made, a speed fluctuation where the waveforms of-two types of speed fluctuation components are superimposed one on another occurs in the photosensitive body 1. One of the two types of speed fluctuation components is a speed fluctuation due to the off-centering of the photosensitive-body gear 202 described above. Furthermore, the other one of the two types of speed fluctuation components is a speed fluctuation due to a slight displacement (hereinafter referred to as a coupling displacement) in the rotary shaft line of the two couplings coupled with each other. As shown in
In the printer according to the embodiment, the processing unit 6 and the photosensitive-body driving system shown in
The driving of the four driving motors 90Y, 90M, 90C, and 90K is controlled by the control unit (not shown). The control unit has a CPU (Central Processing Unit) that performs arithmetic processing, a ROM (Read Only Memory) that stores a control program and various data, a RAM (Random Access Memory) that temporarily stores the various data, and the like. The control unit performs speed fluctuation waveform recognition processing at a predetermined timing such as a timing immediately after the power of the printer is turned on or a timing immediately after an operation for detaching the processing unit 6 is detected. In the speed fluctuation waveform recognition processing, the control unit first drives the driving motors 90Y, 90M, 90C, and 90K that drive the photosensitive bodies 1Y, 1M, 1C, and 1K, respectively, at a predetermined speed. Then, the control unit detects the speed fluctuation waveforms of the photosensitive bodies 1Y, 1M, 1C, and 1K based on outputs from the rotary encoders 250Y, 250M, 250C, and 250K fixed to the photosensitive bodies 1Y, 1M, 1C, and 1K, respectively.
After the phases of the speed fluctuation waveforms are matched to each other, a driving speed pattern is determined by which the amplitudes of the waveforms (second waveforms) of the photosensitive bodies 1Y, 1M, and 1C can be matched to that of the speed fluctuation waveform (first waveform) of the photosensitive body 1K. In an example shown in
In an example shown in
In an example shown in
After the establishment of the state in which the displacements in the superimposition of the dots of the colors Y, M, C, and K are almost eliminated as described above, optical writing on the photosensitive bodies 1Y, 1M, 1C, and 1K is started. Thus, in the printer according to the embodiment, the displacements in the superimposition of the dots of the respective colors can be kept at a tolerance level.
Note that in the printer according to the embodiment, the combination of the control unit and the rotary encoders 250Y, 250M, 250C, and 250K serves as a waveform recognition unit that recognizes the first waveform as the speed fluctuation waveform per rotation of the photosensitive body 1K driven by the driving force of the driving motor for the color K driving at the constant speed and the second waveforms as the speed fluctuation waveforms per rotation of the photosensitive bodies 1Y, 1M, and 1C driven by the driving forces of the driving motors for the colors Y, M, and C driving at the constant speed. In addition, the combination serves as a rotation detection unit that detects whether each of the photosensitive bodies 1Y, 1M, 1C, and 1K has a predetermined rotational angle.
Next, a description is made of a printer according to examples obtained by adding a more characteristic configuration to the printer according to the embodiment. Note that the configuration of the printer according to the examples is the same as that of the printer according to the embodiment unless otherwise specified.
On the other hand, a motor gear 96 for the colors Y, M, and C is provided between a photosensitive-body gear 202M for the color M and a photosensitive-body gear 202C for the color C so as to be meshed with them. The color motor gear 96 is fixed to the motor shaft of a driving motor 90YMC for the colors Y, M, and C and transmits the driving force of the driving motor 90YMC to the photosensitive-body gears 202M and 202C. Thus, the photosensitive bodies 1M and 1C are rotated and driven. Furthermore, an idler gear 97 is provided between a photosensitive-body gear 202Y for the color Y and the photosensitive-body gear 202M so as to be meshed with them. Thus, the driving force of the driving motor 90YMC is transmitted to the photosensitive body 1Y successively via the color motor gear 96, the photosensitive-body gear 202M, the idler gear 97, and the photosensitive-body gear 202Y.
With this configuration, the three photosensitive bodies 1Y, 1M, and 1C other than the photosensitive body 1K are rotated and driven by the driving motor 90YMC. The photosensitive-body gears 202Y, 202M, and 202C corresponding to the three photosensitive bodies 1Y, 1M,and 1C are meshed with each other so as to rotate in a state in which their maximum off-centering parts (maximum-diameter parts) are positioned at the same rotational angle. Specifically, the photosensitive-body gears 202Y, 202M, and 202C have marks mk inscribed at the maximum off-centering parts. The photosensitive-body gears 202Y, 202M, and 202C are meshed with each other in a state in which the marks mk are positioned at the same rotational angle. In a state shown in
In the printer according to the embodiment, the arrangement pitches of the photosensitive bodies are set to be equal. Therefore, the synchronization of the rotational phases of the photosensitive-body gears can realize the following matter. That is, the expansion and contraction patterns of the dots of the colors Y, M, and C due to the off-centering of the photosensitive-body gears 202Y, 202M, and 202C can be synchronized with each other at the primary transfer nips.
As described above, in the photosensitive-body driving system of the printer, the speed fluctuation component of the photosensitive body due to the off-centering of the photosensitive-body gear (hereinafter referred to as a gear speed fluctuation component) and that of the photosensitive body due to the coupling displacement (hereinafter referred to as a coupling speed fluctuation component) occur. Furthermore, the speed fluctuation waveform actually occurring in the photosensitive body is a waveform where the waveforms of these two speed fluctuation components are superimposed one on another (hereinafter referred to as an actual fluctuation waveform), and the phase of the actual fluctuation waveform is slightly displaced from that of the waveform of the gear speed fluctuation component. However, as described above, since the gear speed fluctuation component is significantly greater than the coupling speed fluctuation component, the phase of the actual fluctuation waveform is very close to that of the gear speed fluctuation component. Thus, the photosensitive-body gears 202Y, 202M, and 202C are meshed with each other so that the rotational phases due to the off-centerings of the photosensitive-body gears 202Y, 202M, and 202C are synchronized with each other. As a result, the actual fluctuation waveforms of the photosensitive bodies 1Y, 1M, and 1C can be almost synchronized with each other.
Any of the photosensitive-body gears 202Y, 202M, and 202C is manufactured by molding a resin through a die, and an off-centering position and a off-centering amount are determined by the die. Therefore, a groove for molding the mark mk is inscribed at the maximum off-centering part of the die in advance. Thus, the mark mk can be formed at the same time when the resin is molded. In this manner, any of the marks mk of the photosensitive-body gears 202Y, 202M, and 202C shown in
The photosensitive body 1K is rotated and driven by the driving motor 90K serving as a driving source that is used for the photosensitive bodies 1Y, 1M, and 1C. Since demand for monochrome printing is higher than that for color printing, only the photosensitive body 1K has the independent driving source. For monochrome printing higher in demand, only the photosensitive body 1K is driven to reduce the waste of the photosensitive bodies 1Y, 1M, and 1C and promote energy savings.
Since only the photosensitive body 1K is rotated and driven for monochrome printing, the phase at the maximum off-centering part of the photosensitive-body gear 202K is different from that at the maximum off-centering parts of the photosensitive-body gears 202Y, 202M, and 202C for any cost. Therefore, when a printing operation is started, the printer is configured to perform phase-difference matching control in which a rotational phase difference between the photosensitive-body gear 202K and the photosensitive-body gears 202Y, 202M, and 202C is made zero.
On the other hand, a rotary disc 203YMC for the colors Y, M, and C is fixed to an end part on the side opposite to the photosensitive-body gear 202C in the coupling 201C of the photosensitive body 1C. The rotary disc 203YMC is also integrally formed with a large-diameter part 204YMC that partially increases the diameter of the rotary disc 203YMC. When the photosensitive-body gears 202Y, 202M, and 202C reach a predetermined rotational position, the large-diameter part 204YMC is detected by a gear sensor 91YMC for the colors Y, M, and C composed of the transmission-type photosensor.
Note that in the printer, the rotary disc 203K and the rotary disc 203YMC are attached so that the large-diameter part 204K and the large-diameter part 204YMC are positioned at the same rotational angle as the maximum-diameter part of the photosensitive-body gear.
The resist motor 92 is a driving source for the pair of the resist rollers 28. The data input port 68 receives image information transmitted from external personal computers (not shown), or the like. The control unit 150 controls the driving of the entire printer and has the CPU 150a, the RAM 150a serving as an information storage unit, a ROM 150b, and the like. The operations display unit 93 is composed of a touch panel or a liquid crystal panel and plural touch keys. Through the operations display unit 93, various information items are displayed in accordance with the control of the control unit 150, and input information from an operator is transmitted to the control unit 150. The four unit sensors 263Y, 263M, 263C, and 263K detect the processing units 6Y, 6M, 6C, and 6K, respectively, provided in the printer main body to output detection signals. Based on the fact that the detection signal from the unit sensor which has not been detected is detected again, the control unit 150 detects the detachment operation of the processing unit corresponding to the unit sensor. In other words, the printer has a detachment detection unit that separately detects the detachment operations of the photosensitive bodies 1Y, 1M, 1C, and 1K from the printer main body with the unit sensors 263Y, 263M, 263C, and 263K and the control unit 150.
When the control unit 150 detects the detachment operation of any of the processing units, it performs waveform acquisition processing for acquiring the actual fluctuation waveform of the photosensitive body of at least the detached processing unit prior to the starting of a print job in accordance with instructions from the user. In the waveform acquisition processing, a pattern image for detecting the speed fluctuation waveform is first formed on the intermediate transfer belt 8. As shown in
Note that when the control unit 150 detects the detachment operations of the two processing units at the same time, it forms the pattern image TP corresponding to one processing unit at one end part in the width direction of the intermediate transfer belt 8 so as to be detected by the first toner-image detection sensor 261 and forms the pattern image TP corresponding to the other processing unit at the other end part in the width direction of the transfer belt 8 so as to be detected by the second toner-image detection sensor 262.
Furthermore, when the control unit 150 detects the detachment operations of the three or four processing units, it first forms the pattern images TP for two of the processing units so as to be detected by the first and second toner-image detection sensors 261 and 262. Then, the control unit 150 forms the pattern images TP for the remaining two or one of the processing units so as to be detected by the first and second toner-image detection sensors 261 and 261 in a similar fashion.
Furthermore, toner-image detection sensors may be provided facing the photosensitive bodies 1Y, 1M, 1C, and 1K so that the pattern image TP is detected on the photosensitive bodies for 1Y, 1M, 1C, and 1K not on the intermediate transfer belt 8.
Next, a description is made of a printer according to specific examples obtained by adding a more characteristic configuration to the printer according to the examples. Note that the configuration of the printer according to the specific examples is the same as that of the printer according to the examples unless otherwise specified.
When the color K of the photosensitive body 1K that uses the driving motor also as the driving source for the driving roller is recognized as a reference color, recognition of a displacement of dots of the color M from the color K among the colors Y, M, and C is the most suitable. Thus, in the printer according to a first specific example, the actual fluctuation waveform of the photosensitive body 1M among the three photosensitive bodies 1Y, 1M, and 1C that share the driving motor 90YMC is matched to that of the photosensitive body 1K.
When the control unit 150 starts the color-mode print job to drive the driving motor 90K and the driving motor 90YMC, it recognizes the phase of the actual fluctuation waveform of the color K and that of the actual fluctuation waveform of the color M based on outputs from the gear sensor 91K and the gear sensor 91YMC. If the previous print job is a monochrome-mode print job, the phase of the actual fluctuation waveform of the color K is greatly displaced from that of the color M as shown in
However, even if the phases are thus matched to each other, the corresponding actual fluctuation waveforms are not completely superimposed one on another. This is because the amplitudes of the actual fluctuation waveforms are different as shown in
Recognition of a displacement of dots from the color K serving as the reference color using the color Y is the most difficult. However, if the displacement amount of the color Y is significant, the displacement between the colors K and Y is easily recognized. The printer according to a second specific example performs the following processing instead of performing the processing for matching the phase and amplitude of any one of the actual fluctuation waveforms of the three photosensitive bodies 1Y, 1M, and 1C that share the driving motor 90YMC to those of the actual fluctuation waveforms of the photosensitive body 1K. In other words, the printer performs the processing for matching the phase and amplitude of an actual fluctuation average waveform obtained by averaging the actual fluctuation waveforms of the three photosensitive bodies 1Y, 1M, and 1C to those of the actual fluctuation waveform of the photosensitive body 1K.
When the control unit detects the detachment operation of any one of the three photosensitive bodies 1Y, 1M, and 1C that share the driving motor 90YMC, it performs average waveform update processing for updating the actual fluctuation average waveform in addition to the waveform acquisition processing for acquiring the actual fluctuation waveform of the detached photosensitive body. This is because if any one of the actual fluctuation waveforms of the three photosensitive bodies 1Y, 1M, and 1C is changed, the actual fluctuation average waveform as an average of the three actual fluctuation waveforms is also changed. Therefore, when the control unit 150 detects the detachment operation of any of the photosensitive bodies 1Y, 1M, and 1C, it acquires the actual fluctuation waveform of the detached photosensitive body and updates the same. Then, the control unit determines the actual fluctuation average waveform obtained by averaging the actual fluctuation waveforms of the photosensitive bodies 1Y, 1M, and 1C based on the updated actual fluctuation waveform.
When the control unit 150 drives the driving motor 90K and the driving motor 90YMC along with the starting of the color-mode print job, it recognizes the phase of the actual fluctuation waveform of the color K and that of the actual fluctuation average waveform Aymc based on outputs from the gear sensor. 91K and the gear sensor 91YMC. If the previous print job is a monochrome-mode print job, the phase of the actual fluctuation waveform of the color K is greatly displaced from that of the actual fluctuation average waveform Aymc as shown in
The above description refers to the printer in which the toner images on the photosensitive bodies 1Y, 1M, 1C, and 1K are transferred to the intermediate transfer belt 8 so as to be superimposed one on another. However, the present invention can also be applied to the following image forming apparatus. In other words, the present invention can be applied to an image forming apparatus in which toner images on plural photosensitive bodies are transferred to the front surface of the recording paper, which is held and conveyed on the front surface of the endless movement body such as the belt member that performs the endless movement, so as to be superimposed one on another.
As described above, the printer according to the first specific example has the control unit 150 that uses the driving motor 90YMC, which serves as a second driving source, also as the driving source for the two or more photosensitive bodies 1Y, 1M, and 1C and constitutes the waveform recognition unit for recognizing the actual fluctuation waveform of the specified photosensitive body 1M as the second waveform. The control unit 150 performs the processing for matching the phase and amplitude of the photosensitive body 1M to those of the photosensitive body 1K. With this configuration, the displacement in the superimposition of the dots of the colors K and M can be kept at a tolerance level.
Furthermore, the printer according to the second specific example has the control unit that performs the processing for matching the phase and amplitude of the actual fluctuation average waveform Aymc obtained by averaging the three actual fluctuation waveforms of the colors Y, M, and C to those of the actual fluctuation waveform of the color K instead of performing the processing for matching the phase and amplitude of any of the actual fluctuation waveforms of the three photosensitive bodies 1Y, 1M, and 1C to those of the actual fluctuation waveform of the color K. With this configuration, the displacements in the superimposition of the dots of the colors Y, M, and C and the dot of the color K can be prevented.
According to the present invention, with the shared use of the first driving source between any one of the plural image carriers and the members other than the image carriers and the driving transmission unit for driving the image carriers, manufacturing costs can be reduced.
Furthermore, the driving of the first and second driving sources is controlled so that the phase of the second waveform as the speed fluctuation waveform occurring when the image carrier to be driven by the second driving source is driven by the second driving source at a predetermined speed is matched to that of the first waveform as the speed fluctuation waveform occurring when the image carrier to be driven by the first driving source is driven by the first driving source at a predetermined speed. At this time, if only the phases of the first and second waveforms are matched to each other, displacements in the superimposition corresponding to a difference between the amplitudes of the first and second waveforms remain. Therefore, not only the phases but also the amplitudes of the first and second waveforms are matched to each other. Thus, the displacement in the superimposition corresponding to the difference between the amplitudes of the first and second waveforms is almost eliminated. Specifically, when the amplitude of the second waveform is greater than that of the first waveform, the driving speed of the second driving source is adjusted so that the amplitude of the second waveform is made smaller to be equal to the amplitude of the first waveform. On the other hand, when the amplitude of the second waveform is smaller than that of the first waveform, the driving speed of the second driving source is adjusted so that the amplitude of the second waveform is made greater to be equal to the amplitude of the first waveform. When the amplitude of the second waveform is made equal to that of the first waveform in a state in which the phase of the second waveform is matched to that of the first waveform, the difference between the amplitudes of the first and second waveforms is almost eliminated. Thus, the displacement in the superimposition corresponding to the difference can be almost eliminated. As a result, the displacement in the superimposition of the dots can be kept at a tolerance level.
The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.
The present application is based on Japanese Priority Application No. 2008-164970 filed on Jun. 24, 2008, the entire contents of which are hereby incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-164970 | Jun 2008 | JP | national |
