Patent Application
20130153746
The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2011-278223 filed in Japan on Dec. 20, 2011 and Japanese Patent Application No. 2012-271549 filed in Japan on Dec. 12, 2012.
1. Field of the Invention
The present invention relates to a light scanning device that is used in a laser printer, a digital copying machine, a plain paper facsimile apparatus, or the like; as well as relates to and a light intensity adjustment method of the optical scanning device and a computer program product.
2. Description of the Related Art
As illustrated in
Meanwhile, in order to form an electrostatic latent image on the photosensitive member 16, it is necessary to have a predetermined light intensity that matches with the sensitivity characteristic of the photosensitive member 16. Regarding the light intensity adjustment of the LD 101 that is the laser light source of the optical scanning device 1, the light received by the light receiving element 102, which is embedded in the LD unit 10, is subjected to photoelectric conversion; the current (monitor current) that is obtained by means of photoelectric conversion is converted into voltage using an external volume resistance; the voltage obtained by means of current-to-voltage conversion is input to a comparator; a comparison between the voltage and a reference voltage is performed in the comparator; and control is performed accordingly using APC. In this case, the light intensity adjustment is performed by rotating the volume resistance (i.e., by changing the resistance value) by changing the driving current of the LD so as to increase or decrease the light emitting power of the LD and by maintaining the volume resistance value obtained at the point of time when a predetermined light intensity is achieved.
In this LD light intensity adjustment device, when the LD 101a or the LD 101b is made to emit light; the PD 102 embedded in the LD unit 10 detects, inside the LD unit 10, the light on the back beam side of the LD reflection end face and accordingly outputs a monitor current. Then, the volume resistance 205 performs current-to-voltage conversion with respect to the monitor current and outputs a monitor voltage to the LD drive circuit 200. Subsequently, depending on the switching performed by the switching unit S, the monitor voltage is compared with an output reference voltage Vs of either the reference voltage DAC 201a or the reference voltage DAC 201b of the LD drive circuit 200. The comparison result is input either to the driving current DAC 203a or the driving current DAC 203b. Then, the volume resistance 205 is so adjusted that, based on the comparison result, the driving current DAC 203a or the driving current DAC 203b increases or decreases the driving current to the LD 101a or the LD 101b, respectively, and alters the light intensity of that LD. Once the volume resistance value is fixed to a value at which a predetermined (or an appropriate) light intensity is obtained; feedback control is performed thereafter for automatically maintaining that particular light intensity.
Meanwhile, there are times when the rest energy for laser exposure that is required to form an electrostatic latent image on the photosensitive member 16 differs depending on imaging conditions such as the sub-scanning speed of the photosensitive member 16, the writing speed of formed images, and the number of rotations of the polygon mirror 12. In such a case, it becomes necessary to change the light intensity of the LDs 101a and 101b for each imaging condition. In a conventional LD light intensity adjustment device, the LD light intensity can be altered by adjusting the volume resistance 205 in the above-mentioned manner, and accordingly the light intensity of the LDs 101a and 101b can be adjusted to a predetermined light intensity in concert with the imaging conditions. However, in an optical scanning device, consider a case when imaging conditions, such as the linear velocity of the photosensitive member, undergo a change; and the required light intensity also changes for each imaging condition. In such a case, if adjustment is performed using the volume resistance 205, only a single adjustment value can be held for a single resistance. Hence, light intensity adjustment cannot be performed according to a plurality of adjustment specifications for light intensity.
There, in the case of performing different light intensity adjustments according to different imaging conditions; in the conventional LD light intensity adjustment device, the reference voltage DAC 201a or the reference voltage DAC 201b is changed and a new adjustment value is set. However, if the reference voltage DAC 201a or the reference voltage DAC 201b is changed, then the linearity error of the reference voltage DAC 201a or the reference voltage DAC 201b, or the linearity error of the driving current DAC 203a or the driving current DAC 203b gets included by necessity. Besides, the output characteristics of the monitor current with respect to the LD light intensity are controlled on the assumption that linearity is almost secured. Hence, in a conventional LD light intensity adjustment device, in the case of performing control with a light intensity that is different than the light intensity with which light intensity adjustment was previously performed, there occurs a light intensity error of several percent.
For example, once the LD light intensity has been adjusted, if the light intensity is to be exactly halved, then it is ought to be sufficient to halve the values of the driving current DACs (i.e., halve the driving current values). However, because of the linearity error of the monitor current and the light intensity or because of the linearity error of the driving current DACs; the LD light intensity is not exactly halved in actuality, and there occurs a light intensity error of about several percent as described above.
Besides, in the first place, the scope of control for controlling reference voltage DACs is restricted by the setting of the DAC dynamic range. In the case of performing light intensity control using reference voltage DACs; a greater scope of light intensity control needs to be secured because, apart from performing correction of the rest energy for laser exposure that is different according to the imaging conditions, a light intensity correction control is also performed for correcting the variation in the imaging conditions that is caused by device operations and a shading correction control is also performed for correcting the exposure energy unevenness that is caused by the optical characteristic of the scanning optical system (i.e., the shading characteristic of the scanning optical system). However, if a greater scope is secured for light intensity control performed using reference voltage DACs, then the light intensity control resolution per bit (per digit) of the reference voltage DACs becomes coarse. Thus, in order to achieve a fine light intensity control resolution while securing a greater scope of control, it becomes necessary to increase the bit count of the reference voltage DACs. That leads to an increase in the circuit size.
In order to resolve such issues and eliminate the errors; it is thinkable to provide external volume resistances that are equal in number to the number of light control specifications resulting from the differences in imaging conditions, and to use an analog switch for switching between the volume resistances to be connected to a PD for each imaging condition. With that, it becomes possible to perform the most suitable light intensity adjustment for each imaging condition.
In this LD light intensity adjustment device, a plurality of adjustment values can be held using the volume resistances 205a, 205b, and 205c. As a result, it becomes possible to perform an error-free and most suitable light intensity adjustment for each different imaging condition. Moreover, it also becomes possible to resolve the issues that arise from increasing the scope of light intensity control, which is performed by the reference voltage DACs as described above.
However, in this LD light intensity adjustment device, it is a cumbersome task to manually adjust the light intensity by adjusting the volume resistances 205a, 205b, and 205c. Moreover, the addition of the volume resistances 205 (205a, 205b, and 205c) as well as the light intensity switching circuit 204 results in an increase in the manufacturing cost of the light intensity adjustment device. Hence, this configuration is not implementable under normal conditions.
In Japanese Patent Application Laid-open No. 2011-098494, an optical scanning device and an image forming apparatus are disclosed in which a monitor current is used in performing feedback control of the driving currents of LDs; the gain of feedback control is stored in a memory; and readjustment is performed if there is malfunctioning in the post-adjustment operations. The configuration of this optical scanning device is such that the volume resistances are decreased in number and the gain of feedback control is held in a memory. That is a point of similarity to the present invention described below. However, in that optical scanning device, if a different LD light intensity is used that is different from the adjustment point used previously for light intensity adjustment; then there is no resolution to the issue that an LD light intensity error occurs due to the linearity error of the monitor current and the light intensity, or due to the linearity error of the driving current DACs.
Therefore, there is a need for a light scanning device and a light intensity adjustment method thereof capable of performing a highly-accurate and error-free light intensity adjustment in a case of changing to a light intensity that is different than the light intensity which has been previously adjusted depending on the imaging conditions of an image forming apparatus and which has been output by the optical writing light source during light intensity adjustment of an optical writing light source.
According to an embodiment, there is provided an optical scanning device that includes a light source; a light source driving unit that drives the light source; a light intensity detecting unit that detects light intensity emitted from the light source; a light intensity adjustment determining unit, a detected-light-intensity determining unit, and a light intensity adjusting unit. The light intensity adjustment determining unit determines, based on the presence or absence of a change in a predetermined imaging condition, whether or not it is necessary to adjust the light intensity emitted from the light source. The detected-light-intensity determining unit determines whether or not the light intensity emitted from the light source detected by the light intensity detecting unit is at a predetermined light intensity. When the light intensity adjustment determining unit determines that the light intensity emitted from the light source needs to be adjusted, the light intensity adjusting unit amplifies the light intensity emitted from the light source with an amplification factor that is set according to the imaging condition to adjust a driving current of the light source driving unit and to thereby adjust the light intensity emitted from the light source, which is determined by the detected-light-intensity determining unit, to the predetermined light intensity.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Exemplary embodiments of an optical scanning device, a light intensity adjustment method of the optical scanning device, and a computer program product according to the present invention are described in detail below with reference to the accompanying drawings.
Prior to the explanation regarding the embodiments, firstly, a rundown of the features of the optical scanning device is given. In a conventional optical scanning device described above, the current output of the PD 102, which is a light intensity detecting unit (a light receiving element) embedded in an LD unit, is subjected to current-to-voltage conversion using a volume resistance; and the volume resistance is altered with the aim of performing light intensity adjustment. Regarding the adjustment of a volume resistance; typically, a person manually rotates the volume resistance so as to achieve a predetermined light intensity. In that regard, as described earlier, the embodiments are given with the aim of achieving a highly-accurate light intensity adjustment as well as making an improvement in the conventional LD light intensity adjustment device in which light intensity adjustment is a cumbersome task. More particularly, the constituent element that corresponds to a volume resistance is turned into a digitized circuit so as to eliminate the manual operations required in the past, and the volume resistance value is replaced with the amplification factor of an amplifier circuit that amplifies the monitor current of an LD light intensity adjustment device. Such a configuration makes it possible to achieve automation of light intensity adjustment. Meanwhile, in the explanation of the embodiments, a laser diode is used as an optical writing light source, and is abbreviated as LD.
The LD light intensity adjustment device is essentially the same as the conventional LD light intensity adjustment device illustrated in
In the LD light intensity adjustment device according to the first embodiment, if the amplification factor of the current amplifying circuit 209 is increased or decreased, then the monitor voltage that is the output voltage of the current amplifying circuit 209 undergoes a change. Then, depending on the switching performed by the switching unit S, the monitor voltage is compared with an output reference voltage Vs of either the reference voltage DAC 201a or the reference voltage DAC 201b of the LD drive circuit 200. The comparison result is input either to the driving current DAC 203a or the driving current DAC 203b. Thereat, by adjusting the amplification factor, the driving current DAC 203a or the driving current DAC 203b can increase or decrease the driving current to the LD 101a or the LD 101b and alter the light intensity of that LD.
Meanwhile, if there is a plurality of target light intensities due to the differences in imaging conditions in the image forming apparatus (herein, the optical scanning device), then the following operations are performed. In order to be able to obtain a plurality of target light intensities, the amplification factor is changed and the light intensity adjustment is performed. Then, based on the result of the light intensity adjustment, a plurality of digitized gain values that are based on the amplification factor used in the adjustment is stored in the nonvolatile memory 207.
In the first embodiment, the configuration is such that the light intensity adjustment is performed for each imaging condition; each adjusted gain value is independently stored in a nonvolatile memory; and a suitable gain value for each imaging condition is made selectable. Herein, predetermined imaging conditions point to the conditions under which the optical energy falling on the surface of the photosensitive member 16 undergoes a change. Thus, the imaging conditions include, for example, the speed in the sub-scanning direction of the photosensitive member 16 (the process speed), the writing density for image formation, and the number of rotations of the polygon mirror 12.
The operations of the LD light intensity adjustment device for performing light intensity adjustment are controlled by the optical writing control unit 22 or by an image forming apparatus having an optical scanning device installed therein.
The optical writing control unit 22 includes a microcomputer system having a central processing unit (CPU) 30, a read only memory (ROM) 31, and a random access memory (RAM) 32. As described later, the CPU 30 has functions of a light intensity adjustment determining unit 35, a detected-light-intensity determining unit 36, and a light intensity adjusting unit 37.
The light intensity adjustment determining unit 35 determines, based on the presence or absence of a change in the predetermined imaging conditions, whether or not it is possible to adjust the light intensity emitted from the LD 101a or the LD 101b. The detected-light-intensity determining unit 36 determines whether or not the light intensity emitted from the LD 101a or the LD 101b, which is detected by the PD 102 serving as the light intensity detecting unit, is equal to a predetermined light intensity. The light intensity adjusting unit 37 performs the following adjustment if the light intensity adjustment determining unit 35 determines that the light intensity emitted from of the LD 101a or the LD 101b needs to be adjusted. More particularly, the light intensity adjusting unit 37 causes the current amplifying circuit 209 to calculate an amplification factor from a gain value set in advance corresponding to the imaging conditions and to amplify the monitor current from the PD 102 with the amplification factor, thereby adjusting the output of the LD 101a or the LD 101b in a such way that an adjusted light intensity matches with the light intensity that is targeted by the detected-light-intensity determining unit 36.
Given below is the explanation regarding the operations performed by the LD light intensity adjustment device after the light intensity adjustment is performed in the manner described above.
Then, in order to relate to the imaging condition identified at Step S102, the digital gain value representing the target light intensity based on a predetermined imaging condition of the image forming apparatus is read from the nonvolatile memory 207 (Step S103). Subsequently, the gain value that is read is set in the amplification factor setting register 206, which is a temporary storage register (Step S104). Then, the light intensity adjusting unit 37 amplifies the monitor current from the PD 102 with the amplification factor set in the current amplifying circuit 209; and adjusts the driving currents of the driving current DACs 203a and 203b (Step S105).
Once the driving currents are adjusted, the LDs 101a and 101b are made to emit light as a result of adjusting the driving currents of the driving current DACs 203a and 203b. Then, the detected-light-intensity determining unit 36 determines whether or not the LDs 101a and 101b are at a predetermined light intensity (Step S106). Until the LDs 101a and 101b reach the predetermined light intensity, the detected-light-intensity determining unit 36 repeatedly performs the determination. Once the detected-light-intensity determining unit 36 determines that the LDs 101a and 101b are at a predetermined light intensity (Yes at Step S106), the adjusted light intensity is set and output (Step S107).
In this way, in order to achieve a light intensity required under a predetermined imaging condition, that is, in order to achieve a predetermined light intensity; the optical writing control unit 22 reads, from the nonvolatile memory 207, the digital gain value that represents the target light intensity based on the predetermined imaging condition of the image forming apparatus. Then, the optical writing control unit 22 sets the gain value, which has been read, in the amplification factor setting register 206, which is a temporary storage register. Then, with the amplification factor, the current amplifying circuit 209 amplifies the monitor current from the PD 102. With that, the driving currents of the driving current DACs 203a and 203b are adjusted; the LDs 101a and 101b are adjusted to a predetermined light intensity that is in accordance with the light intensity specifications set in advance; and feedback control is performed thereafter for automatically maintaining that particular light intensity.
Thus, in the LD light intensity adjustment device that is used in the optical scanning device according to the first embodiment, a gain value that represents a predetermined light intensity corresponding to an imaging condition is stored in the nonvolatile memory 207. Then, during image formation, the optical writing control unit 22 reads the gain value according to the imaging condition from the nonvolatile memory 207, and then sets that gain value in the amplification factor setting register 206 used for setting the amplification factor. With that, the current amplifying circuit 209 calculates the amplification factor from the gain value that has been set, amplifies the monitor current, and can follow the abovementioned sequence to accurately perform light intensity control (adjustment) in which the light intensity adjustment result is reflected.
Meanwhile, in the first embodiment, at the time of performing LD light intensity adjustment, the light intensity adjustment is performed based on the gain value that is adjusted and set in advance. Consequently, according to the first embodiment, it becomes possible to perform control that is not affected by the linearity error with respect to the monitor current or by the linearity error with respect to the driving current DACs used in performing the LD current control. That makes it possible to reduce the LD light intensity error. Thus, even in the case of an operation mode such as a half-speed mode of an optical scanning device in which the LD light intensity specifications are different for the same optical scanning device; it becomes possible to automatically perform light intensity control that has only a small LD light intensity error and that is equivalent to light intensity control performed using a plurality of volume resistances.
In this example, as illustrated in
In this way, as compared to the LD light intensity adjustment device having the configuration illustrated in
Then, in order to relate to the imaging condition identified at Step S202, the light intensity switching instructing unit 38 performs the following operation. More particularly, of the gain values set in the amplification factor setting register 206 by controlling the light intensity switching selector 208, the light intensity switching instructing unit 38 selects the gain value corresponding to the identified imaging condition (Step S203). Then, the light intensity adjusting unit 37 causes the current amplifying circuit 209 to amplify the monitor current from the PD 102 with the selected gain value and accordingly adjusts the driving currents of the driving current DACs 203a and 203b (Step S204).
Once the driving currents are adjusted, the LDs 101a and 101b are made to emit light as a result of adjusting the driving currents of the driving current DACs 203a and 203b. Then, the detected-light-intensity determining unit 36 determines whether or not the LDs 101a and 101b are at a predetermined light intensity (Step S205). Until the LDs 101a and 101b reach the predetermined light intensity, the detected-light-intensity determining unit 36 repeatedly performs the determination. Once the detected-light-intensity determining unit 36 determines that the LDs 101a and 101b are at a predetermined light intensity (Yes at Step S205), the adjusted light intensity is set and output (Step S206).
In the LD light intensity adjustment device used in the optical scanning device according to the first embodiment, every time there is a change in an imaging condition, it is a requisite task for the optical writing control unit 22 to read a predetermined digital gain value from the nonvolatile memory 207 and to set the gain value in the amplification factor setting register 206. In contrast, in the second embodiment, the gain value for each imaging condition is set in advance in the amplification factor setting registers 206 as illustrated in
Meanwhile, in the LD light intensity adjustment device described above, the two LDs 101a and 101b are arranged in an array-like manner in a single package. Alternatively, a laser diode array (LD array) can be used in which three or more LDs are arranged close to each other in an array-like manner; and the LD light intensity adjustment device can be configured to perform light intensity adjustment and light intensity control independently with respect each of the three or more LDs.
The light intensity adjusting unit 37 performs light intensity adjustment independently with respect each of a plurality of LDs. Meanwhile, if an LD array is used in which light intensity detection is performed using at least one or more PDs used in common for a plurality of LDs, it becomes possible to deal with the speeding up and high productivity of optical scanning devices. In this case, as illustrated in
Moreover, in the second embodiment, the number of amplification factor setting registers 206 is increased to be equal to or greater than the number of laser light sources. Besides this, the nonvolatile memory 207, the amplification factor setting registers 206, and the driving current DACs 203a and 203b serving as LD driving circuits are enclosed in a single semiconductor device. Thus, by configuring as a single semiconductor device; not only the load of the optical scanning device is not increased, but the need to provide a new nonvolatile memory is also eliminated. Moreover, it becomes possible to achieve a simple configuration without causing an increase in the manufacturing cost. Thus, in addition to achieving simplification and automation of the light intensity adjustment as well as achieving enhancement in the accuracy of the light intensity control, it becomes possible to reduce the component cost.
Furthermore, in the second embodiment, the gain values (amplification factors) that serve as light intensity adjustment values are digitized before being incorporated in a laser driving circuit. For that reason, even in the case when a plurality of different laser light intensity specifications are demanded within a single device; light intensity adjustment and light intensity control appropriate for each imaging condition can be performed in an accurate manner.
In addition, according to the second embodiment, the conventional volume resistances are digitized, and gain values for feedback control are used in place of resistance values. As a result, in comparison to the conventional LD light intensity adjustment; light intensity control in which the result of LD light intensity adjustment most suitable for a plurality of imaging conditions is reflected can be performed more accurately with a relatively simple configuration and without causing an increase in the manufacturing cost.
Meanwhile, in the second embodiment, although a current amplifying circuit is assumed to function as the amplifying unit, it is also possible to use a voltage amplifying circuit as long as predetermined gain values can be obtained.
Moreover, the optical scanning device 1 according to the embodiments that includes the laser driving device 20 and the optical writing control unit 22 is applied in an image forming apparatus such as a copying machine performing an electrophotographic process, a printer, or a facsimileing device; or is applied in a multifunction peripheral having the copying function, the printing function, and the facsimileing function. With that, the abovementioned light intensity control can be achieved. Moreover, in the embodiments, although a laser diode is used as an optical writing light source, that is not the only possible case. Alternatively, it is possible to use any light source such as an LED light source (LED stands for light emitting diode) or a liquid crystal light source that can perform optical writing on a photosensitive member.
Meanwhile, it is assumed that a computer program executed in the embodiments is stored in advance in the ROM 31. However, that is not the only possible case. Alternatively, the computer program executed in the embodiments can be recorded in the form of an installable or executable file on a computer-readable recording medium such as a compact disk read only memory (CD-ROM), a flexible disk (FD), a compact disk recordable (CD-R), or a digital versatile disk (DVD), and can be provided as a computer program product.
Still alternatively, the computer program executed in the embodiments can be saved in a downloadable manner on a computer connected to the Internet. Still alternatively, the computer program executed in the embodiments can be distributed over a network such as the Internet.
The computer program executed in the embodiments contains modules for each of the light intensity adjustment determining unit 35, the detected-light-intensity determining unit 36, the light intensity adjusting unit 37, and the light intensity switching instructing unit 38. In practice, for example, the CPU 30 (processor) reads the computer program from the recording medium mentioned above and runs it so that the computer program is loaded in a main memory device such as the RAM 32. As a result, the module for each of the light intensity adjustment determining unit 35, the detected-light-intensity determining unit 36, the light intensity adjusting unit 37, and the light intensity switching instructing unit 38 is generated in the main memory device.
According to an aspect of the present invention, during light intensity adjustment of an optical writing light source; in the case of switching to a light intensity, which is different than the light intensity with which light intensity adjustment was previously performed, depending on the imaging condition in an image forming apparatus, it becomes possible to perform a highly-accurate and error-free light intensity adjustment.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-278223 | Dec 2011 | JP | national |
| 2012-271549 | Dec 2012 | JP | national |
