Field of the Invention
The present invention relates to a color image forming apparatus, such as a laser printer, a photocopier, or a facsimile, which employs an electrophotography recording method.
Description of the Related Art
In general, in color image forming apparatuses, a phenomenon which is so-called “white gap” in which an irregular white gap, which is not intended to be generated, is generated between adjacent images of different colors has occurred. This phenomenon occurs in the following situation. Specifically, an electrostatic latent image obtained by a rapidly changing potential of a surface of a photoconductor drum, that is an image edge portion, is generated on the photoconductor drum. Then, when this portion is developed by a developing apparatus, a developed image having a width smaller than that of a developed image intended to be formed is generated. In an image including a cyan band and a black band which are adjacent to each other, for example, although the cyan band and the black band should be closely adjacent to each other, a gap is generated between the cyan band and the black band in a final image generated on a recording material since a developed image of the cyan band and a developed image of the black band are formed with smaller widths.
To address this problem, a method for performing minute emission using a light emitting element of a laser scanner on a non-image section (non-toner-image-forming unit) in an entire printable region of the photoconductor drum to the extent that toner attachment does not occur has been used, so that the width of the image is prevented from being small. Hereinafter, this method is referred to as “background exposure”, “non-image-section minute emission”, or the like.
Note that an object for performing the non-image-section minute emission is not limited to the prevention of generation of the white gap. For example, as disclosed in Japanese Patent Laid-Open No. 2003-312050, the non-image-section minute emission is performed for making contrast of a transfer potential smaller and preventing image disturbance which occurs in a gap between the developing roller and the photoconductor drum in accordance with aerial discharge. Specifically, the non-image-section minute emission is not performed for a limited usage.
Here, as a concrete method for performing the non-image-section minute emission, a method for changing a duty ratio of a pulse wave which is referred to as a PWM (Pulse Width Modulation) method has been proposed in Japanese Patent Laid-Open No. 2003-312050. In this method, a light emitting element of a laser scanner emits light in a non-image section with a pulse width corresponding to an intensity of minute emission in synchronization with an image clock which has a fixed frequency.
In recent years, there is a demand for higher-quality images generated by color image forming apparatuses. Therefore, in addition to control of an intensity of emission light corresponding to an image section, appropriate control of an intensity of light of minute emission in the non-image section is required.
According to an embodiment of the present invention, there is provided an image forming apparatus which includes a light emitting element which emits a laser beam, a photoconductor drum, and a charging unit which charges the photoconductor drum, which forms a latent image by radiating light emitted from the light emitting element on the charged photoconductor drum, and in which toner attaches to the latent image so that the image becomes visible. The image forming apparatus comprising a laser driving unit configured to cause the light emitting element to emit light with an intensity corresponding to a first emission level for printing for a period of time corresponding to a pulse duty in an image section of the latent image being formed on the photoconductor drum and to cause the light emitting element to emit light with an intensity corresponding to a second emission level for minute emission on a non-image section of the latent image being formed on the photoconductor drum, a first light-intensity controller configured to control a first driving current used to cause the light emitting element to emit light with an intensity corresponding to the first emission level several times in one job, and a second light-intensity controller configured to control a second driving current used to cause the light emitting element to emit light with an intensity corresponding to the second emission level several times in one job. The laser driving unit adds the first driving current to the second driving current so as to cause the light emitting element to emit light by the intensity of light corresponding to the first emission level. The first light-intensity controller controls the first driving current to be added to the second driving current.
Accordingly, the light emission may be performed in an image section by a stable intensity of light and minute emission may be performed in a non-image section. Consequently, a high-quality image may be obtained.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
First Embodiment
Embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. Note that components disclosed in the embodiments are merely examples and the scope of the present invention is not limited to these.
Schematic Sectional View of Image Forming Apparatus
As shown in
The intermediate transfer belt 3 is an endless belt rotating in a process speed of 115 mm/sec in a direction denoted by an arrow mark shown in
The four photoconductor drums 5 (5Y, 5M, 5C, and 5K) are arranged in series in a direction in which the intermediate transfer belt 3 moves. The photoconductor drum 5Y having a yellow developer 8Y is uniformly subjected to a charge process performed by a primary charge roller 7Y so as to obtain a predetermined polar characteristic and a predetermined potential in a rotation process, and subsequently, is subjected to image exposure 4Y performed by an image exposure unit 9Y. By this, an electrostatic latent image corresponding to a first-color (yellow) component image of a target color image is formed. Next, the first developer (yellow developer) 8Y performs development by attaching a yellow toner which is a first color to the electrostatic latent image. By this, the image becomes visible. As described above, a method for performing development using toner in a portion in which the electrostatic latent image is formed by image exposure is referred to as a “reversal developing method”.
The yellow image formed on the photoconductor drum 5Y enters a primary transfer nip formed with the intermediate transfer belt 3. In the primary transfer nip, a voltage applying member (primary transfer roller) 10Y abuts on a back surface of the intermediate transfer belt 3. To the voltage applying member 10Y, a primary transfer bias power source, not shown, which is used to apply a bias is connected. The intermediate transfer belt 3 transfers yellow in a first color part, and thereafter, successively performs multiple transfer of magenta, cyan, and black, in this order using the photoconductor drums 5M, 5C, and 5K which correspond to these colors and which have been subjected to the process described above. A toner image which has the four colors and which has been transferred on the intermediate transfer belt 3 revolves along with the intermediate transfer belt 3 in the direction (clockwise direction) denoted by the arrow mark in
On the other hand, a recording member P which is mounted on and stored in a sheet-feeding cassette is fed by a feeding roller 2 so as to be supplied to a nip of a registration roller pair 6, and then, the feeding is temporarily stopped. The recording member P which has been temporarily stopped is supplied to a secondary transfer nip by the registration roller pair 6 in synchronization with a timing when the toner image of four colors formed on the intermediate transfer belt 3 arrives in the secondary transfer nip. Then, the toner image formed on the intermediate transfer belt 3 is transferred on the recording member P by a voltage (approximately 1.5 kV) applied between a secondary transfer roller 11 and the secondary transfer counter roller 18.
The recording member P to which the toner image is transferred is separated from the intermediate transfer belt 3 and supplied to a fixing apparatus 14 through a conveyance guide 19. Here, a fixing roller 15 and a pressure roller 16 perform heating and pressurizing on the recording member P so that the toner image is melted and fixed to a surface of the recording member P. In this way, a full-color image having the four colors is obtained. Thereafter, the recording member P is ejected from the apparatus through an ejection roller pair 20, and one print cycle is terminated. On the other hand, toner which has not been transferred to the recording member P by the secondary transfer unit and accordingly remains in the intermediate transfer belt 3 is removed by a cleaning unit 21 disposed on a downstream side of the secondary transfer unit.
The schematic sectional view of the image forming apparatus has been described hereinabove. Next, hereinafter, as for a laser driving system, an appearance of an optical scanning apparatus (corresponding to the image exposure units 9) will be described first, and thereafter, a circuit configuration of a laser driving system will be described in detail.
Appearance of Optical Apparatus
Then, the laser beam emitted from the LD 107 is shaped by a collimator lens 134 so that a parallel beam is obtained. Then, the parallel beam is scanned by a polygon mirror 133 in a horizontal direction of the photoconductor drums 5. Then the scanned laser beam encounters a surface of a photoconductor drum which is axially rotated, passes through an fθ lens 132 for image formation, and is exposed as dots.
Meanwhile, a reflection mirror 131 is disposed so as to correspond to a scanning position at one end of the photoconductor drums 5. The reflection mirror 131 reflects the laser beam to be projected on a scanning start position toward a BD synchronization detection sensor 121. Then, a timing when the scanning of the laser beam is started is determined in accordance with a signal output from the BD synchronization detection sensor 121. Here, when forcible light emission is performed for the detection of the laser beam, APC (Auto Power Control) which is automatic light intensity control is performed on an intensity of the laser beam so that an emission level of the laser beam is controlled.
Diagram of Laser Driving System Circuit
In
An engine controller 122 incorporates an ASIC, a CPU, a RAM, and an EEPROM. Furthermore, the engine controller 122 controls not only a printer engine but also communication with a video controller 123.
An OR circuit 124 has an input terminal to which an Ldrv signal and a VIDEO signal are supplied from the engine controller 122 and the video controller 123, respectively. A Data signal is supplied to the switching circuit 106 which will be described hereinafter. Note that the VIDEO signal is based on print data supplied from an external apparatus such as an external reader scanner or a host computer.
The VIDEO signal output from the video controller 123 is supplied to a buffer 125 having an enable terminal and an output from the buffer 125 is supplied to the OR circuit 124. Here, the enable terminal is connected to a line which extends from the engine controller 122 and which supplies a Venb signal.
Furthermore, the engine controller 122 outputs an SH1 signal, an SH2 signal, a BASE signal, the Ldrv signal, and the Venb signal. The Venb signal is used to perform a masking process on the Data signal obtained on the basis of the VIDEO signal. When the Venb signal is brought to a disable state (OFF state), a timing of an image mask region (image mask period) is generated.
First and second reference voltages Vref11 and Vref21 are input to positive terminals of the comparator circuits 101 and 111, respectively, and outputs of the comparator circuits 101 and 111 are supplied to the sample-and-hold circuits 102 and 112, respectively. The reference voltage Vref11 is set as a target voltage used to emit light from the LD 107 in a light emission level for normal printing (first emission level or first light intensity). Furthermore, the reference voltage Vref21 is set as a target voltage used to emit light from the LD 107 in a light emission level for minute emission (second emission level or second light intensity). The hold capacitors 103 and 113 are connected to the sample-and-hold circuits 102 and 112, respectively. Outputs of the hold capacitors 103 and 113 are input to positive terminals of the current amplifying circuits 104 and 114, respectively. Note that, although described below in detail, it is necessarily the case that the reference voltages Vref11 and Vref21 correspond to the light emission level for the normal printing and the light emission level for the minute emission, respectively. The reference voltages Vref11 and Vref21 mean settings for realization of the light emission level for the normal printing and the light emission level for the minute emission in the laser driving system circuit.
The reference current sources 105 and 115 are connected to the current amplifying circuits 104 and 114, respectively, and outputs of the current amplifying circuits 104 and 114 are input to the switching circuits 106 and 116, respectively. On the other hand, third and fourth reference voltages Vref12 and Vref22 are input to negative terminals of the current amplifying circuits 104 and 114, respectively. Here, a current Io1 (first driving current) and a current Io2 (second driving current) are determined in accordance with a difference between a voltage output from the sample-and-hold circuit 102 and the reference voltage Vref12 and a difference between a voltage output from the sample-and-hold circuit 112 and the reference voltage Vref22, respectively. Specifically, the reference voltages Vref12 and Vref22 are set to specify the currents.
The switching circuit 106 turns on or off in accordance with the Data signal serving as a pulse modulation data signal. The switching circuit 116 turns on or off in accordance with an input signal Base.
The switching circuits 106 and 116 have output terminals connected to a cathode of the LD 107 and supplies driving currents Idrv and Ib. The driving current Idrv corresponds to the current Io1 whereas the driving current Ib corresponds to the current Io2. The driving current Idrv is used to realize the light emission level for the normal printing whereas the driving circuit Ib is used to realize the light emission level for the minute emission. Therefore, the driving circuits Idrv and Ib may correspond to the first and second driving currents, respectively. An anode of the LD 107 is connected to a power source Vcc. A cathode of the PD 108 which monitors an intensity of light emitted from the LD 107 is connected to the power source Vcc. An anode of the PD 108 is connected to the current-voltage conversion circuit 109 so that a monitor current Im is supplied to the current-voltage conversion circuit 109. By this, a monitor voltage Vm is generated. The monitor voltage Vm is supplied to negative terminals of the comparator circuits 101 and 111 in a non-feedback manner.
Note that, although the engine controller 122 and the video controller 123 are separately shown in
Explanation of APC of P(Idrv)
The engine controller 122 sets the sample-and-hold circuit 112 to a hold state (non-sampling period) using the SH2 signal and brings the switching circuit 116 to an off-operation state using the input signal Base. Furthermore, the engine controller 122 sets the sample-and-hold circuit 102 to a sampling state using the SH1 signal and turns the switching circuit 106 on using the Data signal. More specifically, here, the engine controller 122 controls (instructs) the Ldrv signal so that the Data signal causes the LD 107 to be a light emission state. Note that a period in which the sample-and-hold circuit 102 is in the sampling state corresponds to an APC operation state.
In this state, when the LD 107 is brought to a full emission state, the PD 108 monitors an intensity of light emitted from the LD 107 and generates a monitor current Im1 which is proportional to the light emission intensity. Then, by supplying the monitor current Im1 to the current-voltage conversion circuit 109, a monitor voltage Vm1 is generated. Furthermore, the current amplifying circuit 104 controls the driving current Idrv in accordance with the current Io1 supplied to the reference current source 105 so that the monitor voltage Vm1 coincides with the first reference voltage Vref11 which is a target value.
Note that, although described below in detail, when the LD 107 emits light in the light emission level for the normal printing, the circuit shown in
Explanation of APC of P(Ib)
On the other hand, the engine controller 122 sets the sample-and-hold circuit 102 to a hold state (non-sampling period) using the SH1 signal and brings the switching circuit 106 to an off-operation state using the Data signal. As for the Data signal, the engine controller 122 sets a Venb signal connected to the enable terminal of the buffer 125 to a disable state and controls the Ldrv signal so as to bring the Data signal to an off state. Furthermore, the engine controller 122 sets the sample-and-hold circuit 112 to an APC operation mode using the SH2 signal and turns the switching circuit 116 on using the input signal Base so that the LD 107 is brought to a minute emission state.
In this state, when the LD 107 is brought to the full minute emission state (lighting maintaining state) in which the LD 107 emits weak light, the PD 108 monitors an intensity of light emitted from the LD 107 and generates a monitor current Im2 (Im1>Im2) which is proportional to the intensity of emitted light. Then, the monitor current Im2 is supplied to the current-voltage conversion circuit 109 so that a monitor voltage Vm2 is generated. Furthermore, the current amplifying circuit 114 controls a driving current Ib in accordance with the current Io2 supplied to the reference current source 115 so that the monitor voltage Vm2 coincides with the second reference voltage Vref21 which is a target value.
Then, during a non-APC operation, that is, during a normal image forming operation (in a period in which an image signal is supplied), the sample-and-hold circuit 112 is brought to a hold period (non-sampling period), the full minute emission state which is a weak light state is maintained.
Note that, when ignoring the normal fogging/reversal fogging of the toner, it is preferable that the intensity of emitted laser beam in the minute emission is set to have appropriate intensity to the extent that a charged potential does not become lower than a development potential. However, this is not possible. Specifically, when taking the normal fogging/reversal fogging of the toner into consideration, when an image is formed, an intensity of light of P(Ib) should be normally stable.
Explanation of Minute Emission Level
In the foregoing description, in the full minute emission state, the driving current Ib is set so as to exceed a threshold value Ith of the LD 107 shown in
On the other hand, when normal image forming is performed, a driving current (Idrv+Ib) is set to have a light emission level corresponding to intensity of a print level P(Idrv+Ib). Note that the print level means an emission intensity level in which electrostatic attachment of the developer to the photoconductor drum becomes a saturation state.
The minute emission level will be further described in detail with reference to
Then, the charged potential Vd is attenuated to a charged potential Vd_bg by laser emission in a minute emission level Ebg1 (second emission level). The attenuation is performed because a potential which is higher than a convergence potential and which is generated in some portions on the surface of the photoconductor drum enhances back contrast Vback and triggers the reversal fogging. Therefore, when the charged potential Vd is attenuated to the charged potential Vd_bg by the laser emission of the minute emission level Ebg1, the potential higher than such a convergence potential is prevented from remaining and at least the occurrence of the reversal fogging is prevented. Furthermore, transfer memory which occurs in the charged potential Vd has been generally known. To address this problem, the transfer memory is made smaller by the laser emission of the minute emission level Ebg1 and at least a ghost image may be prevented from being generated due to the transfer memory.
Furthermore, the laser emission of the minute emission level Ebg1 has a function of correcting the back contrast Vback which is a potential difference with a development potential Vdc. Also from this viewpoint, the normal fogging and the reversal fogging are prevented from being generated. Furthermore, development contrast Vcont (=Vdc−V1) which is a difference value between the development potential Vdc and an exposure potential V1 may be also corrected. By this, deterioration of development efficiency and generation of sweeping may be suppressed and margins for transfer and retransfer may be ensured.
Furthermore, when the charged potential Vd is controlled to be a fixed value, the voltage Vcdc (charged voltage) is set to be variable depending on environment and deterioration (status of use) of the photoconductor drum. Then, in terms of maintenance of image quality, the target intensity of light in the minute emission level (intensity of second emission level) should be set variable in accordance with the variable voltage Vcdc. For example, when a value of the voltage Vcdc becomes large as an integer value (that is, a value of the voltage Vcdc becomes small as an absolute value), an intensity of light in the minute emission level Ebg1 also becomes large whereas when the value of the voltage Vcdc becomes small as an integer value (that is, the value of the voltage Vcdc becomes large), the intensity of light in the minute emission level Ebg1 also becomes small. Note that it is apparent to those who skilled in the art that control of the minute emission level may be achieved by changing the reference voltage Vref21 as described above.
Meanwhile, when the voltage Vcdc is not controlled to a constant value but set as a fixed value, the minute emission level should be controlled as described below. In a case where the voltage Vcdc is a constant value, when deterioration (use status) of the photoconductor drum progresses, for example, the charged potential Vd increases. Therefore, when the charged potential Vd increases, the intensity of light in the minute emission level Ebg1 should be increased. Conversely, the charged potential Vd obtained before the deterioration of the photoconductor drum progresses is smaller than the charged potential Vd obtained after the deterioration progresses. Accordingly, the intensity of light in the minute emission level Ebg1 obtained before the deterioration of the photoconductor drum progresses is smaller than that in the minute emission level Ebg1 obtained after the deterioration of the photoconductor drum progresses. As described above, the emission level for the minute emission (second emission level or second light intensity) may be changed in accordance with change of the charged voltage.
Explanation of P(Ib+Idrv) Emission
When the LD 107 is emitted in the emission level for the normal printing, the circuit shown in
Although described below in detail, the print level P(Idrv+Ib) corresponds to an intensity of emission (emission intensity) obtained by superposing a PWM emission level P(Idrv) obtained by pulse width modulation on the minute emission level Pb. More specifically, in a state in which the SH2 signal, the SH1 signal, and the Base signal are set as described above and in a state in which the engine controller 122 brings the Venb signal to an enable state, the switching circuit 106 is turned on or off using the Data signal (VIDEO signal). By this, two-level emission including emission by the driving current Ib and emission by the driving current (Idrv+Ib), that is, emission with the emission intensity P(Ib) and emission with an emission intensity P(Idrv+Ib) may be performed. Furthermore, as for an intensity of light corresponding to the emission intensity P(Idrv+Ib), laser emission in a period of time corresponding to a pulse duty is performed on the basis of the emission intensity P(Ib).
As described above, by driving the circuit shown in
The circuit shown in
In the circuit shown in
As described above, the LD 107 emits light by changing an emission intensity between an emission intensity in the print level P(Idrv+Ib+Ibias) and an emission intensity in the minute emission level P(Ib+Ibias) corresponding to the driving current (Ib+Ibias). More specifically, in a state in which the SH2 signal, the SH1 signal, and the Base signal are set as described above and in a state in which the engine controller 122 brings the Venb signal to an enable state, the switching circuit 106 is turned on or off using the Data signal based on the VIDEO signal. By this, PWM laser emission in two-level emission state including emission by the driving current (Ib+Ibias) and emission by the driving current (Idrv+Ib+Ibias), that is, emission with the emission intensity P(Ib+Ibias) and emission with an emission intensity P(Idrv+Ib+Ibias) may be performed.
Two-Level APC Sequence
Next, a timing when the APC is executed to maintain a laser emission level will be described.
First, at a timing ts, the engine controller 122 turns the SH1 signal and the Ldrv signal on so as to turn the switching circuit 106 on. Note that the term “timing ts” and the like terms are simply referred to as “ts” and the like hereinafter.
Then, a signal output from the synchronization detection sensor 121 is supplied as a horizontal synchronization signal/BD at tb0. When the engine controller 122 detects the horizontal synchronization signal/BD at tb0, the engine controller 122 turns the SH1 signal and the Ldrv signal off at tb1 so as to turn the switching circuit 106 off. By this, the APC for the normal printing level is terminated. Then, after the APC in the print level is terminated, the LD 107 emits a laser beam in the normal print level in accordance with the VIDEO signal. Then, the laser emission is performed in accordance with the VIDEO signal between tb1 and tb2, and a detailed description of this laser emission is omitted.
Next, the engine controller 122 controls the current Io1 (first driving current) with reference to a timing (detection timing) in which the horizontal synchronization signal/BD is output in accordance with a preceding scanning line. More specifically, with reference to the timing (tb0 or tb1) in which the horizontal synchronization signal/BD is output, the SH1 signal and the Ldrv signal are turned on so that the switching circuit 106 is turned on at tb2 which is a timing after predetermined period of time has been elapsed (before the next horizontal synchronization signal/BD is detected). Thereafter, the APC in the print level is started again. Furthermore, before the APC is started, the engine controller 122 turns the Venb signal off and issues a disable instruction to the enable terminal of the buffer 125. Furthermore, the disable instruction is similarly input in APC which is performed immediately before this APC. Then, by this, even when the video controller 123 outputs a signal in error (including noise), a control instruction which is associated with the APC and which is issued from the engine controller 122 may be reflected to the control.
Then, another signal is output from the synchronization detection sensor 121 as a horizontal synchronization signal/BD at tO. When the engine controller 122 detects the horizontal synchronization signal/BD at tO, the SH1 signal and the Ldrv signal are turned off at t1 so as to turn the switching circuit 106 off whereby the APC in the print level is terminated again.
Subsequently, the engine controller 122 turns the SH2 signal and BASE signal on at t1 after detection of the horizontal synchronization signal/BD so as to turn the switching circuit 116 on. By this, the engine controller 122 starts APC in the minute emission level. Note that the APC in the minute emission level may be started at any timing between t1 and t2. The APC in the minute emission level should be performed at least part of an image masking period between t1 to t2. In particular, when the APC in the minute emission level is executed in a margin period from t2 to t3, excellent efficiency is attained.
Then, the engine controller 122 maintains the SH2 signal to be on state until t3. Specifically, the APC in the minute emission level is continued until t3. Accordingly, a long period of the APC in the minute emission level is ensured.
Here,
Here, a sheet-end timing corresponds to t2, and the relationship “t1<t2<t3” is satisfied. Furthermore, in a case of so-called borderless print, since an image region exceeds a sheet-end portion, the relationship “t1<t3<t2” is satisfied. Note that the period from t2 to t3 is referred to as a margin region interval or a margin region period since laser emission corresponding to a margin region in a recording sheet is performed. Furthermore, a period from t4 to t5 which will be described hereinafter may be similarly referred to.
As described above, although automatic light intensity control of laser beams is performed in the non-image region (out of effective regions of the photoconductor drum) such as a region between scanning lines, when miniaturization of image forming apparatuses and optical scanning apparatuses progresses, a ratio of an image region for one scanning operation in the optical scanning apparatuses becomes large, and accordingly, a time ratio of the non-image region is reduced. Even in such a case, according to the timing chart shown in
Returning back to the description with reference to
Note that a minute emission region in which light is emitted by an emission intensity corresponding to the minute emission level is larger than the largest image region which is scanned by the VIDEO signal and the minute emission is performed in a region larger than an interval between the sheet end timings. Furthermore, the minute emission is performed in the non-image section included in the region of the VIDEO signal.
Referring back to the explanation of the timing chart shown in
Simultaneously, the engine controller 122 inputs an instruction for outputting a disable signal to the enable terminal of the buffer 125 using the Venb signal at t4 which is a timing after a predetermined period of time has been elapsed with reference to the timing (t0 or t1) when the horizontal synchronization signal/BD is output. By this, a image masking cancelling period is terminated. In other words, periods other than the image masking cancelling period correspond to the image masking period.
Furthermore, the engine controller 122 turns the switching circuit 116 off using the BASE signal at t6 which is a timing after a predetermined period of time has been elapsed with reference to the timing (t0 or t1) when the horizontal synchronization signal/BD is output whereby the minute emission is terminated.
Here, a sheet-end timing corresponds to t5, and the relationship “t4<t5<t6” is satisfied. Note that the sheet-end timing represents a timing when the LD 107 performs laser irradiation to positions of the belt (intermediate transfer belt) corresponding to edges of sides which are orthogonal to a conveying direction of the recording sheet. Furthermore, in a case of a so-called borderless print, the relationship “t5<t4<t6” is satisfied. Although the timing t6 when the minute emission is terminated comes before a polygon-end timing tp in this embodiment, the minute emission may be continued until t7.
In this way, the automatic light intensity control may be performed in the minute emission level in a region (from t1 to t6) which is larger than the image region (from t3 to t4) and larger than the region between sheet ends (from t2 to t5).
Furthermore, the engine controller 122 performs again the process performed after tb2 from t7 which comes after a predetermined period of time has been elapsed with reference to the timing (t0 or t1) when the horizontal synchronization signal/BD is output. In this way, various types of APC may be efficiently performed several times when a print job is executed in response to a print request externally supplied. Note that, as for a frequency of execution of the APC, the APC may be performed for each laser scanning, for each page (only first scanning in each page), or for every predetermined number (2 or more) of laser scanning.
As described above, according to the timing chart shown in
Note that, although the minute emission level P(Ib) and the print level P(Idrv+Ib) have been described in the timing chart shown in
Second Embodiment
In a second embodiment, the first embodiment is further expanded and a longer period of time is assigned to two-level APC. Note that a configuration of an image forming apparatus and a configuration of a circuit are basically the same as those described in the first embodiment, and therefore, detailed descriptions thereof are omitted. Furthermore, although a timing chart of APC according to the second embodiment will be described with reference to
Specifically, a video controller 123 scans an image region on the photoconductor drum for dots of a laser beam until t4 which is a timing after a predetermined period of time has been elapsed with reference to a timing (t0 or t1) when a horizontal synchronization signal/BD is output and then terminates the image scanning. A period from t3 to t4 corresponds to an emission period in which an LD 107 performs laser emission on a toner image forming region (latent image forming region).
Simultaneously, an engine controller 122 inputs an instruction for outputting a disable signal to an enable terminal of a buffer 125 using a Venb signal at t4 which is a timing after a predetermined period of time has been elapsed with reference to the timing (t0 or t1) when the horizontal synchronization signal/BD is output.
Furthermore, the engine controller 122 starts APC in a minute emission level by turning an SH2 signal on at t4 after the predetermined period of time has been elapsed with reference to the timing (t0 or t1) when the horizontal synchronization signal/BD is output.
Then, the engine controller 122 maintains the SH2 signal to be an on state until t6 so that the APC in the minute emission level is continued. Then, the engine controller 122 turns the SH2 signal off and turns the switching circuit 116 off using the Base signal at t6 so that the APC in the minute emission level is terminated. It is assumed that a timing tp when a face of a polygon mirror is changed is included in a forcible emission period of automatic light intensity control. At this timing (from t6 to tpe), the laser emission is stopped to avoid generation of stray light and the like caused by reflection in edge portions of a polygon.
Furthermore, the engine controller 122 starts the APC in the minute emission level again by turning the SH2 signal on at tpe after a predetermined period of time has been elapsed with reference to the timing (t0 or t1) when the horizontal synchronization signal/BD is output.
Then, the engine controller 122 maintains the SH2 signal to be an on state until t7 so that the APC in the minute emission level is continued. Then, the engine controller 122 turns the SH2 signal off and turns the switching circuit 116 off using the Base signal at t7 so that the APC in the minute emission level is terminated.
Furthermore, the engine controller 122 starts APC in a printing level by turning an SH1 signal on and turning a switching circuit 106 on using an Ldrv signal at t7 after a predetermined period of time has been elapsed with reference to the timing (t0 or t1) when the horizontal synchronization signal/BD is output.
Then, a signal output from a synchronization detection sensor 121 is supplied as a horizontal synchronization signal/BD at t8. When detecting the horizontal synchronization signal/BD at t8, the engine controller 122 performs again the sequence starting from t0 described hereinabove.
As described above, in the second embodiment, in addition to the advantages of the first embodiment, the following advantage is obtained. Specifically, the emission intensity setting in the minute emission level may be performed in a period from a sheet margin section t4 which is a timing of the non-image region including the effective image region of the photoconductor drum (after the image region) to a timing t7 when an emission intensity setting in a normal emission level is started. Accordingly, a longer period of the automatic light intensity control in the minute emission level is ensured.
Note that, although the minute emission level P(Ib) and the print level P(Idrv+Ib) have been described in the timing chart shown in
Third Embodiment
In the foregoing embodiments, the APC in the PWM emission level P(Idrv) and the APC in the minute emission level P(Ib) have been described. However, the APC in the minute emission level P(Ib) may be performed first so that APC in the print emission level P(Ib+Idrv) is performed.
Specifically, the APC in the minute emission level P(Ib) according to the first embodiment is executed first. Thereafter, the engine controller 122 sets a sample-and-hold circuit 112 to a hold state using an SH2 signal and turns a switching circuit 116 on using an input signal Base. That is, the LD 107 is brought to a bias emission (laser emission region) state.
Simultaneously, as with the foregoing embodiments, the engine controller 122 sets a sample-and-hold circuit 102 to a sampling state and turns a switching circuit 106 on using a Data signal so that the LD 107 performs full emission.
In the state in which the LD 107 is in a full emission state, a PD 108 monitors an intensity of light emitted from the LD 107. Furthermore, the PD 108 generates a monitor current Im1′ which is proportional to the actual emission intensity and supplies the monitor current Im1′ to the current-voltage conversion circuit 109 so that a monitor voltage Vm1′ is generated.
A current amplifying circuit 104 controls a driving current Idrv′ in accordance with a current Io1′ supplied to a reference current source 105 so that the monitor voltage Vm1′ coincides with a first reference voltage Vref11′ which is a target value. Here, the reference voltage Vref11′ has a value corresponding to the print emission level P(Ib+Idrv). In addition, the driving current Idrv′ represents a difference between a current which emits light having an intensity corresponding to the print emission level P(Ib+Idrv) and a current which emits light having an intensity corresponding to the minute emission level P(Ib).
Furthermore, as for an executing timing, the APC in the print emission level P(Ib+Idrv) may be executed at a timing when the APC in the PWM emission level P(Idrv) is performed. Furthermore, the APC in the minute emission level P(Ib) should be performed before the APC in the print emission level P(Ib+Idrv) is performed and may be performed before forcible emission when a horizontal synchronization signal/BD is detected. Furthermore, although the minute emission level P(Ib) and the print level P(Idrv+Ib) have been described in the foregoing description, the minute emission level P(Ib) and the print level P(Idrv+Ib) may be replaced by the minute emission level P(Ib+Ibias) and the print level P(Idrv+Ib+Ibias), respectively. In this case, the same advantages may be obtained in the circuit shown in
Modifications
In the first embodiment, the APC in the PWM emission level P(Idrv) and the APC in the minute emission level P(Ib) are separately executed. However, the present invention is not limited to this. For example, APC in a print emission level P(Ib+Idrv) may be performed instead of the APC in the minute emission level P(Ib).
Specifically, after APC in a PWM emission level P(Idrv) is executed, a sample-and-hold circuit 102 is brought to a hold period (non-sampling period) using an SH1 signal in accordance with an instruction issued by an engine controller 122 and a switching circuit 106 is turned on. Furthermore, a sample-and-hold circuit 112 is brought to an APC operation state using an SH2 signal and a switching circuit 116 is turned on using an input signal Base.
In the state in which a LD 107 is in a full emission state, a PD 108 monitors an intensity of light emitted from the LD 107. Then, a monitor current Im2′ which is proportional to the actual emission intensity is generated (Im1<Im2′) and the monitor current Im2′ is supplied to a current-voltage conversion circuit 109 so that a monitor voltage Vm2′ is generated.
Furthermore, a current amplifying circuit 114 controls a driving current Ib in accordance with a current Io2′ supplied to a reference current source 115 so that the monitor voltage Vm2′ corresponds to a voltage Vref21′ having a potential corresponding to a sum of first and second reference voltages which are target values. Then, the SH2 signal is turned off and the sample-and-hold circuit 112 is brought to a hold state, a voltage corresponding to a driving current Ib is charged to a capacitor 113. Thereafter, after a non-APC operation state is entered, that is, the sample-and-hold circuit 112 is brought to the hold state (non-sampling period), when the Base signal is an on state, a full emission state in which emission is performed by an intensity of light corresponding to the driving current Ib is entered.
Furthermore, the following modification may be employed. For example, an automatic light intensity control circuit including components the same as the comparator circuit 101 to the switching circuit 106 which are described above is additionally provided, for example.
When the components are added, outputs of switching circuits are connected to immediately below a LD 107 and a negative terminal of a comparator circuit corresponding to the comparator circuit 101 is connected to a current-voltage conversion circuit 109. Then, a voltage value corresponding to the driving current (Idrv+Ib) in the foregoing embodiments is set as a reference voltage Vref01 to the negative terminal of the comparator circuit corresponding to the comparator circuit 101 in advance. Furthermore, here, the engine controller 122 turns the input signal Base and the Ldrv signal off. Note that the sampling described here may be performed between tb2 to t1 shown in
Then, the output of the sample-and-hold circuit (output of the hold capacitor) is supplied to the engine controller 122 through an A/D port, not shown, and temporarily stores the output in a RAM as a driving current (VIdrv+Ib).
Subsequently, the engine controller 122 turns a switching circuit of the added automatic light intensity control circuit and the switching circuit 116 off and the APC in the PWM emission level P(Idrv) according to the first and second embodiments is performed. Detailed operation has been described hereinabove. Then, the output of the sample-and-hold circuit 102 (output of the hold capacitor) is supplied to the A/D port, not shown, and is temporarily stored in the RAM as a driving current VIdrv.
A CPU included in the engine controller 122 obtains a driving current VIb using a difference between the currents (VIdrv+Ib) and VIdrv stored in the RAM and inputs (sets) the obtained voltage value to a positive terminal of the current amplifying circuit 114 through a D/A port, not shown. Note that the sampling described here may be performed between t1 to the sheet edge timing t2 shown in
As described above, according to the modifications described above, the automatic light intensity control may be performed by not only a direct method such as those described in the first and second embodiments but also an indirect method. Furthermore, although the minute emission level P(Ib) and the print level P(Idrv+Ib) have been described in the foregoing description, the minute emission level P(Ib) and the print level P(Idrv+Ib) may be replaced by the minute emission level P(Ib+Ibias) and the print level P(Idrv+Ib+Ibias), respectively. Also in this case, the same advantages may be obtained in the circuit shown in
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
Number | Date | Country | Kind |
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2010-276173 | Dec 2010 | JP | national |
2011-249918 | Nov 2011 | JP | national |
This application is a Continuation of U.S. application Ser. No. 13/312708, filed Dec. 6, 2011, which claims priority from Japanese Patent Application No. 2010-276173 filed Dec. 10, 2010 and No. 2011-249918 filed Nov. 15, 2011, which are hereby incorporated by reference herein in their entireties.
Number | Name | Date | Kind |
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5983045 | Suzuki | Nov 1999 | A |
6549265 | Sakakibara | Apr 2003 | B1 |
20110032323 | Yamashita | Feb 2011 | A1 |
Number | Date | Country | |
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20170357175 A1 | Dec 2017 | US |
Number | Date | Country | |
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Parent | 13312708 | Dec 2011 | US |
Child | 15669784 | US |