JP2004284185A - Light source controlling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light source controlling device by which circuit scale can be reduced, designing is facilitated and light quantity control can be performed with high accuracy. <P>SOLUTION: In the light source controlling device, order information showing a light quantity control order of a plurality of LDs contained in the light source 50 is previously stored in a storing section 12A of a light quantity control order setting so as to perform the light quantity control on the order shown by the order information. The device is so constituted that the switching of an LD, a target of the light quantity control, can be performed with a switching section 14A, in synchronization with a light source switching signal being a modulation signal showing the switching timing of the LD, the target of the light quantity control. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light source control device, and more specifically, used in an optical scanning device that scans a surface to be scanned with light beams output from a plurality of light sources that can be independently modulated, and the light source control device The present invention relates to a light source control device that performs light quantity control.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is an image forming apparatus that forms an image by scanning a light beam on a photoconductor by an optical scanning device such as a laser printer or an electrophotographic copying machine. FIG. 16 shows a configuration of a general optical scanning device. As shown in the figure, in this optical scanning device 200, an edge-emitting type semiconductor laser (hereinafter, referred to as “LD”) 202A is used as a light source, and a light beam output from the LD 202 is converted into a parallel light by a lens 204. After being converted, the light is incident on a polygon mirror 206 having a plurality of reflection surfaces on its side surface and rotating at a constant speed. Then, the scanning light beam reflected by the reflection surface of the polygon mirror 206 is transmitted through the fθ lens 208 so that the scanning speed is corrected so that the scanning speed on the surface of the photoconductor becomes constant, and then irradiated onto the photoconductor. It is supposed to be.
[0003]
In an image forming apparatus using such an optical scanning device, in order to obtain good image quality, it is necessary to control the light amount of the light beam to a predetermined amount with high accuracy. For this reason, in such an optical scanning device, the output light quantity of the LD is controlled by detecting the output light quantity of the LD and adjusting the drive current of the LD so that the detection result becomes a predetermined light quantity. For example, in the edge emitting type LD 202A, a photodiode (hereinafter, referred to as a back beam) that receives a light beam (a so-called back beam) output rearward from the LD is provided in the LD package as a detecting unit for detecting the output light amount of the LD. A “PD” is provided, and the amount of output light of the LD can be detected by detecting the back beam of the LD using the PD.
[0004]
Further, in recent years, a surface emitting LD called VCSEL (Vertical Cavity Surface Emitting Laser) can be produced at a low cost. Therefore, as a light source of an optical scanning device, a conventional edge emitting LD is used. Instead, the use of a surface-emitting type LD has been studied. This surface-emitting type LD does not have a back beam as in the case of the edge-emitting type LD, and outputs a light beam only in one direction. Therefore, as shown in FIG. After the output light from the surface-emitting type LD 202B is collimated by the lens 204, a part of the light is guided to the PD 210 by the half mirror 212, and the light is condensed by the lens 214 and incident on the PD 210. A method of detecting the amount of output light by causing the light to be output has been considered (for example, see Patent Document 1).
[0005]
When this technique is applied to the optical scanning device 200 shown in FIG. 16, the configuration becomes as shown in FIG. In the following, when the edge emission type LD and the surface emission type LD are not particularly distinguished, the LD will be referred to as an LD 202.
[0006]
On the other hand, in recent years, an LD array capable of obtaining a plurality of independently modulatable light beams has been used as a light source of an optical scanning device for the purpose of improving image forming speed and resolution in image data. Even in this type of optical scanning device, as described above, in order to obtain good image quality, it is necessary to control the light amount of each light beam to a predetermined amount with high accuracy.
[0007]
Conventionally, as a technique for setting the light amounts of a plurality of light sources to a predetermined light amount, each light source is selectively sequentially turned on in each ineffective scanning period, and the light intensity of laser light emitted from the turned on light source is detected by light. (Hereinafter referred to as "first conventional technology") for controlling the drive current of each light source so as to maintain the light intensity of each light source at a predetermined level by detecting with a light source (for example, Patent Document 2). reference.).
[0008]
In this technique, two drive circuits are provided in the drive current control circuit shown in FIG. 19A corresponding to the two LDs shown in FIG. 19B, and FIG. As shown in the figure, the two light-selection signals S1 and S2, which are effective in a time-sharing manner during the non-effective scanning period, perform light amount control in accordance with an output signal from the light amount sensor for each beam. With this configuration, the light intensity of each light source can be controlled to a predetermined value by a single photodetector (light amount sensor).
[0009]
Further, as a technique for setting the light amounts of the plurality of light sources to a predetermined light amount, a technique of transmitting a control signal of the light amount to the plurality of light sources by serial transmission or encoding (hereinafter, referred to as a “second conventional technique”) is also known. (For example, refer to Patent Document 3).
[0010]
In this technique, as shown in FIG. 20, a control signal is transmitted in a time-division manner in synchronization with a clock signal, and is effective in a light quantity control circuit in synchronization with a control signal switching signal. The light source whose light quantity is to be controlled is sequentially switched. Thereby, the number of control signals for controlling the plurality of light sources can be reduced.
[0011]
[Patent Document 1]
JP-A-4-355986
[Patent Document 2]
JP-A-7-235715
[Patent Document 3]
JP 2000-71514 A
[0012]
[Problems to be solved by the invention]
However, in the first prior art, there is a problem that the circuit scale becomes larger as the number of light beams increases, because the same number of selection signals as the number of light beams is required.
[0013]
In particular, when a VCSEL is applied as a light source, arraying is easier than an edge-emitting type LD, and a multi-beam light source exceeding 10 bits is possible. In this case, the first prior art is applied. In such a case, the circuit scale becomes extremely large.
[0014]
On the other hand, in the second prior art, as the number of light beams increases, the number of bits of the control signal increases, and the modulation frequency of the clock signal also increases with the increase in the number of light beams. And the amount of noise increases as the number of light beams increases, which makes it difficult to design the system as a whole, and furthermore, when the output signal from the light amount sensor is affected by noise, the light amount is controlled. However, there is a problem that the accuracy of the method is reduced.
[0015]
The present invention has been made in order to solve the above problems, and provides a light source control device capable of reducing the circuit scale, easily designing, and performing light amount control with high accuracy. The purpose is to:
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the light source control device according to claim 1 is used in an optical scanning device that scans a surface to be scanned with light beams output from a plurality of light sources that can be independently modulated, A light source control device that performs light amount control so that the light amounts of a plurality of light sources become a preset set light amount, wherein a storage unit that stores in advance order information indicating a light amount control order of the plurality of light sources, Switching means for switching a light source to be subjected to light quantity control in synchronization with a light source switching signal which is a modulation signal indicating a switching timing of a light source to be subjected to light quantity control so as to perform light quantity control in the order shown. I have.
[0017]
According to the light source control device of the first aspect, the order information indicating the light amount control order of the plurality of light sources is stored in advance by the storage unit, and the light amount control is performed in the order indicated by the order information. Accordingly, the light source to be subjected to the light amount control is switched in synchronization with the light source switching signal which is a modulation signal indicating the switching timing of the light source to be subjected to the light amount control. The storage means may include a nonvolatile memory such as a flash memory and an EEPROM in addition to a volatile memory such as a DRAM and an SDRAM.
[0018]
As described above, according to the light source control device of the first aspect, the order information indicating the light amount control order of the plurality of light sources is stored in advance, and the light amount control is performed in the order indicated by the order information. Since the light source to be subjected to light quantity control is switched in synchronization with a light source switching signal which is a modulation signal indicating the switching timing of the light source to be subjected to light quantity control, the light source to be subjected to light quantity control irrespective of the number of light beams Can be reduced, and as a result, the circuit scale can be reduced.
[0019]
It is preferable that the present invention further includes a change unit that changes a modulation cycle of the light source switching signal, as in the second aspect of the present invention. Thus, by increasing the modulation period of the light source switching signal by the changing means, it is not necessary to take high-frequency countermeasures on the circuit board, and the design becomes easy and the radiation amount of noise can be reduced. In addition, the output signal from the light amount sensor is hardly affected by noise, and the accuracy of light amount control can be improved. Further, by shortening the modulation cycle of the light source switching signal by the changing means, the light amount control time for each light source can be shortened, and the total lighting time of each light source can be shortened, so that the life of each light source can be extended.
[0020]
Further, the present invention may further include a specific pulse changing unit that changes a modulation cycle of a pulse corresponding to a specific light source in the light source switching signal, as in the invention described in claim 3. Thus, the accuracy of light quantity control can be improved by lengthening the modulation period of the pulse corresponding to the specific light source in the light source switching signal by the specific pulse changing unit. In addition, by shortening the modulation period of the pulse by the specific pulse changing unit, the light amount control time can be shortened, and the total lighting time of each light source can be shortened, so that the life of each light source can be extended.
[0021]
Further, the present invention further comprises a counting means for counting the number of light source switching by the light source switching signal and resetting the count value at a predetermined timing, as in the invention according to claim 4, The switching means may switch the light sources such that the light sources of the order indicated by the count value of the counting means are subject to light quantity control. Thus, even if noise enters the light source switching signal and the count value of the counting means becomes abnormal, a normal count value can be obtained at the next light amount control, and normal light amount control can be performed.
[0022]
Further, according to the present invention, after controlling the light amount so that the light amounts of the plurality of light sources become a preset set light amount, the present invention switches the set light amount to another light amount and again performs the light amount control. The image processing apparatus may further include a light amount control unit configured to perform light amount control of the plurality of light sources.
[0023]
Thereby, a plurality of driving amounts corresponding to a plurality of light amount levels in the plurality of light sources according to the present invention are measured, and the plurality of light sources are driven at a light intensity corresponding to an intensity signal input from the outside. By obtaining the relationship between the light amount and the drive amount from the drive amount and driving each light source with the drive amount calculated to be the light amount indicated by the intensity signal, intensity modulation can be performed.
[0024]
As a result, for example, when the exposure amount distribution on the scanned surface is not uniform, the light amount can be controlled by the intensity signal corresponding to the scanning position, and the exposure amount distribution can be made uniform.
[0025]
Further, when the surface to be scanned is the photoconductor surface, the image density becomes non-uniform corresponding to the scanning position due to uneven sensitivity of the photoconductor, uneven charging of the photoconductor, uneven potential of the transfer unit, and the like. However, at this time, the image density distribution in the scanning direction can be made uniform by controlling the amount of light with the intensity signal corresponding to the scanning position.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, a case will be described in which the present invention is applied to a light amount control device that controls the emission light amounts of the plurality of light sources in an optical scanning device that performs scanning exposure on a photoconductor with a plurality of light sources.
[0027]
[First Embodiment]
First, the configuration of a light quantity control device 10A according to the present embodiment will be described with reference to FIG. As shown in the figure, the light amount control device 10A is configured to include n (n is an integer of 2 or more; in the present embodiment, 128) LDs as a light source of the optical scanning device. In addition, the light source unit 50 is connected to a light source unit 50 that emits exposure light to the photoconductor 54 and a light amount sensor 52 including a PD that detects the amount of light output from each LD of the light source unit 50. When the plurality of LDs included in the light source unit 50 are of the edge emission type, the light amount sensor 52 includes a photodiode built in the LD package so as to detect a rear output (back beam) of the LD. It may be used. In the case where the LD is a surface-emitting type, that is, a VCSEL, as shown in FIG. 18, a part of the output light of the LD is extracted by the half mirror 212, and the light amount sensor is configured to receive the extracted output light. 52 may be arranged.
[0028]
The light amount control device 10A includes a light amount control order setting storage unit 12A, a switching unit 14A, a drive amount control unit 16, and the same number of sample hold circuits (hereinafter, “S / H”) as the number of LDs to be controlled. ) And a modulation unit 20.
[0029]
The light amount control order setting storage unit 12A is connected to the switching unit 14A. The light amount control order setting storage unit 12A previously stores order information indicating the order of the light amount control for the n LDs included in the light source unit 50, and the switching unit 14A stores the order from the light amount control order setting storage unit 12A. Information can be read.
[0030]
Further, n video IN signals are input to the switching unit 14A from the outside (for example, the image forming apparatus main body side equipped with the optical scanning device in which the light amount of the LD included in the light source unit 50 is controlled by the light amount control device 10). The switching unit 14A outputs n video OUT signals based on the video IN signal. Note that, when an image is formed on the photoconductor 54, the video IN signal is a signal for turning on and off each LD of the light source unit 50 according to the image and forming the image. When controlling the light amount of each LD, the signal is a signal for turning off all LDs. The video OUT signal is the same signal as the input video IN signal when an image is formed on the photoreceptor 54. However, when the light amount of each LD is controlled, the LD to be subjected to light amount control is controlled. It is a signal for turning on only the signal.
[0031]
Further, the switching section 14A receives the light quantity control permission signal and the light source switching signal from the outside, and the switching section 14A includes a light quantity control permission signal and a light source switching signal, and a light quantity control order setting storage section. Based on the sequence information read from 12A, n sample / hold signals (hereinafter, referred to as “S / H signals”) corresponding to any one of the n S / Hs 18 are output. .
[0032]
Note that the light amount control permission signal is a signal indicating a period during which execution of the light amount control of each LD included in the light source unit 50 is permitted. In the present embodiment, the signal is set to a low level during the period and set to a high level during another period. This is a signal that is taken as a level. Further, the light source switching signal is a signal indicating the switching timing of the LD to be subjected to the light amount control, and in the present embodiment, the timing when the level shifts from the low level to the high level is the switching timing. Further, the S / H signal is a signal for setting a sample state and a hold state of the corresponding S / H 18.
[0033]
On the other hand, the drive amount control unit 16 receives a light amount instruction signal indicating the set light amount of each LD from the outside and a light amount sensor 52 connected thereto. The drive amount setting signal indicating the drive amount of the LD is output to make the light amount signal indicating the output light amount of the LD equal to the light amount instruction signal.
[0034]
Further, output terminals of the switching unit 14A for outputting n S / H signals are connected to one input terminals of the corresponding S / Hs 18, respectively, and output a driving amount setting signal of the driving amount control unit 16. The output terminal is connected to the other input terminal of each S / H 18. In each S / H 18, in accordance with the setting state of the S / H signal input from one input terminal, the sample state and the hold state for the drive amount setting signal input from the other input terminal are switched and held. Is output as a drive amount signal indicating the drive amount of the corresponding LD.
[0035]
Further, the output terminal of the switching unit 14A for outputting the n video OUT signals and the output terminal for outputting the drive amount signal of each S / H 18 are connected to the modulation unit 20, respectively. The ends are connected to corresponding LDs of the light source unit 50, respectively. In the modulation unit 20, the LD whose lighting is instructed by the video OUT signal input from the switching unit 14A is turned on by the driving amount indicated by the driving amount signal input from the S / H 18 corresponding to the LD. .
[0036]
The light amount control order setting storage unit 12A corresponds to the storage unit of the present invention, and the switching unit 14A corresponds to the switching unit of the present invention.
[0037]
Next, as an operation of the light amount control device 10A according to the present embodiment, an operation of the light amount control device 10A during light amount control of each LD particularly related to the present invention will be described in detail with reference to FIG. FIG. 2 is a time chart showing transition of the light amount control permission signal, the light source switching signal, and the control state during the light amount control. Here, a case will be described in which a light amount instruction signal indicating a set light amount at the time of light amount control of each LD is input from outside.
[0038]
First, when the light amount control permission signal is in a state (low level in the present embodiment) indicating the light amount control permission period of each LD, the switching unit 14A determines the light amount at the first rising edge of the light source switching signal. The order information is read from the control order setting storage unit 12A, and first, an LD (hereinafter, referred to as a "first light amount control light source") for performing light amount control is selected.
[0039]
Then, the switching unit 14A generates a video OUT signal to turn on only the first light amount control light source, outputs the video OUT signal to the modulation unit 20, and sets the S / H 18 corresponding to the first light amount control light source to a sample state. / H signal is output.
[0040]
In this state, the drive amount controller 16 sets the first light amount control light source, which is input from the light amount sensor 52, indicating the output light amount of the first light amount control light source, and the first light amount control signal so that the first light amount control signal is input from the outside. The light amount output from the light amount control light source is feedback-controlled.
[0041]
As shown in FIG. 2, the light source switching signal is modulated at a predetermined cycle, and the switching unit 14A sets the S / H 18 corresponding to the first light amount control light source to the hold state at the next rising edge of the light source switching signal. / H signal is output. In response, the S / H 18 shifts to the hold state.
[0042]
At the same time, the switching unit 14A reads from the light amount control order setting storage unit 12A an LD for performing light amount control (hereinafter, referred to as a “second light amount control light source”), and similarly performs light amount control on the second light amount control light source. Do. Thereafter, the light amount control of all LDs is performed by continuously performing the light amount control while sequentially switching the LDs to be subjected to the light amount control.
[0043]
As described in detail above, the light quantity control device 10A according to the present embodiment stores the order information indicating the light quantity control order of the plurality of LDs in advance in the light quantity control order setting storage unit 12A, and uses the order information to store the order information. The switching unit 14A switches the LD to be subjected to the light quantity control in synchronization with the light source switching signal which is a modulation signal indicating the switching timing of the LD to be subjected to the light quantity control so that the light quantity is controlled in the order shown. Therefore, it is possible to reduce the number of control signals for setting the light source to be the light amount control target irrespective of the number of light beams, and as a result, it is possible to reduce the circuit scale.
[0044]
[Second embodiment]
In the first embodiment, the case where the period of the light source switching signal is fixed has been described. In the second embodiment, the case where the period of the light source switching signal is variable will be described.
[0045]
First, the configuration of a light quantity control device 10B according to the second embodiment will be described with reference to FIG. Note that the same components as those in FIG. 1 of FIG. 3 are denoted by the same reference numerals as those in FIG. 1, and descriptions thereof are omitted.
[0046]
The light amount control device 10B according to the second embodiment differs from the light amount control device according to the first embodiment only in that the light source switching signal input to the switching unit 14A is output by the modulation cycle changing unit 22A. It is different from the device 10A.
[0047]
A reference clock signal, a clock frequency-divided signal, and an output permission signal are externally input to the modulation cycle changing unit 22A, and the modulation cycle changing unit 22A outputs a light source switching signal based on these signals. Generate and output to the switching unit 14A.
[0048]
Note that the reference clock signal is a signal that modulates at a higher speed than the light source switching signal, the clock frequency division signal is a signal indicating the frequency division ratio with respect to the reference clock signal, and the output permission signal is the output of the light source switching signal to the switching unit 14A. Is a signal indicating a period during which the permission is granted.
[0049]
That is, the modulation cycle changing unit 22A is controlled according to the output permission signal so as to modulate the light source switching signal only at the time of the light amount control, and in the state where the output is permitted, the reference clock signal is divided by the clock division signal designated by the clock division signal. The signal divided by the frequency ratio is output as a light source switching signal.
[0050]
Even if the light amount is constant on the photoconductor 54, the light amount incident on the light amount sensor 52 differs depending on the design of the optical scanning device and the like. When the amount of light incident on the light quantity sensor 52 is large, the output current from the light quantity sensor 52 is large, and even when the capacity load is large, the rise and fall of the light quantity signal change quickly, and the convergence of the light quantity control becomes fast. Further, if the high-speed light amount sensor 52 is used, or if the wiring pattern on the substrate from the light amount sensor 52 to the drive amount control unit 16 can be shortened, the change of the rise and fall of the light amount signal similarly becomes faster, and Convergence is faster.
[0051]
Therefore, as shown by an example of the light amount signal in FIG. 4, when the convergence of the light amount control is fast due to a relatively large amount of light incident on the light amount sensor 52, the modulation period of the light source switching signal is shortened. Set the clock divided signal to. As a result, the light control time per each LD can be shortened, and the time required for the light control can be shortened. As a result, the total lighting time of each LD can be shortened, and the life of each LD can be prolonged. Can be.
[0052]
On the other hand, when the amount of light incident on the light quantity sensor 52 is small, the output current from the light quantity sensor 52 is small, and when the capacity load is large, the change of the rise and fall of the light quantity signal is delayed, and the convergence of the light quantity control is delayed. Also, when a low-speed light amount sensor 52 is used, or when the wiring pattern on the substrate from the light amount sensor 52 to the drive amount control unit 16 is long, the change of the rise and fall of the light amount signal similarly becomes slow, and Convergence slows down.
[0053]
In this way, as shown in FIG. 5 as an example, when the convergence of the light amount control is slower than the convergence shown in FIG. 4, the clock dividing signal is set so that the modulation cycle of the light source switching signal becomes a cycle T2 longer than the cycle T1. Set. As a result, it is possible to prevent a decrease in the accuracy of the light amount control.
[0054]
Note that the operation of the light quantity control device 10B at the time of light quantity control of each LD is the same as that of the light quantity control device 10A according to the first embodiment, and a description thereof will be omitted. The modulation cycle changing unit 22A corresponds to a changing unit of the present invention.
[0055]
As described in detail above, the light quantity control device 10B according to the present embodiment can achieve the same effects as the light quantity control device 10A according to the first embodiment, and can change the modulation cycle of the light source switching signal. Since the modulation period changing unit 22A performs the modulation cycle changing unit 22A, the modulation period changing unit 22A extends the modulation period of the light source switching signal. Since the amount of radiation can be reduced, the design of the entire system becomes easy, and the output signal (light amount signal) from the light amount sensor 52 is hardly affected by noise, so that the accuracy of light amount control can be improved. In addition, by shortening the modulation cycle of the light source switching signal by the modulation cycle changing unit 22A, the light amount control time of each LD can be shortened, and the total lighting time of each LD can be shortened, thereby extending the life of each LD. Can be.
[0056]
[Third embodiment]
In the second embodiment, the case where the period of the light source switching signal corresponding to all LDs is variable has been described. However, in the third embodiment, only the period of the light source switching signal corresponding to a specific LD is changed. An embodiment in the case of being variable will be described.
[0057]
First, a configuration of a light quantity control device 10C according to the third embodiment will be described with reference to FIG. 6 that are the same as those in FIG. 1 are assigned the same reference numerals as in FIG. 1, and descriptions thereof are omitted.
[0058]
The light quantity control device 10C according to the third embodiment is different from the switching unit having the function of outputting a clock frequency division signal instead of the switching unit 14A in that the light source switching signal is output by the modulation period changing unit 22B. 14B, and instead of the light amount control order setting storage unit 12A, the light amount control order setting storage unit 12B in which time information indicating the time required for the light amount control for each LD is stored in advance in addition to the above order information. Is different from the light quantity control device 10A according to the first embodiment.
[0059]
A reference clock signal and an output permission signal are externally input to the modulation period changing unit 22B, and a clock divided signal is input from the switching unit 14B. The modulation period changing unit 22B A light source switching signal is generated based on the signal and output to the switching unit 14B.
[0060]
Note that the reference clock signal is a signal that modulates at a higher speed than the light source switching signal, the clock frequency division signal is a signal indicating the frequency division ratio with respect to the reference clock signal, and the output permission signal is the output of the light source switching signal to the switching unit 14B. Is a signal indicating a period during which the permission is granted.
[0061]
That is, the modulation cycle changing unit 22B is controlled according to the output permission signal so as to modulate the light source switching signal only at the time of light amount control, and in a state where the output is permitted, changes the reference clock signal by the clock input from the switching unit 14B. A signal divided by the division ratio designated by the division signal is output as a light source switching signal.
[0062]
On the other hand, the switching unit 14B reads information indicating the time required for the light amount control of the LD to be subjected to the light amount control from the light amount control order setting storage unit 12B, and modulates the clock frequency-divided signal corresponding to the time indicated by the information. Output to the cycle changing unit 22B. The operation of the switching unit 14B other than the operation of outputting the clock frequency-divided signal is the same as that of the switching unit 14A, and the operation of the other parts of the light amount control device 10C when controlling the light amount of each LD is also the same as in the first embodiment. And the description is omitted here.
[0063]
As described above, even if the convergence of the light amount control of only a specific LD is slow due to the influence of the wiring pattern on the substrate or the like, as shown in FIG. 7 as an example, the LD (in FIG. Since the modulation period T2 of the light source switching signal corresponding to the LD to be performed is lengthened, it is possible to prevent a decrease in the accuracy of the light amount control.
[0064]
Conversely, for an LD with a fast convergence of the light amount control, the modulation period T1 of the light source switching signal corresponding to the LD is shortened, so that the light amount control time can be selectively shortened, and the light amount control is performed. The time can be shortened, and as a result, the total lighting time of each LD can be shortened, and the life of each LD can be prolonged.
[0065]
The light quantity control order setting storage unit 12B corresponds to the storage unit of the present invention, the switching unit 14B corresponds to the switching unit of the present invention, and the modulation cycle changing unit 22B corresponds to the specific pulse changing unit of the present invention.
[0066]
As described in detail above, the light amount control device 10C according to the present embodiment can provide the same effects as the light amount control device 10A according to the first embodiment, and can also be used for a specific LD in the light source switching signal. Since the modulation period changing unit 22B for changing the modulation period of the corresponding pulse is provided, the modulation period changing unit 22B increases the modulation period of the pulse corresponding to the specific LD in the light source switching signal, thereby improving the accuracy of the light amount control. Can be improved. Further, by shortening the pulse modulation period by the modulation period changing unit 22B, the light amount control time can be shortened, and the total lighting time of each LD can be shortened, so that the life of each LD can be extended.
[0067]
[Fourth embodiment]
In the fourth embodiment, a mode in which a light amount control device is provided with a counter (hereinafter, referred to as a “light source counter”) that counts the number of LD switching by a light source switching signal will be described.
[0068]
First, the configuration of a light quantity control device 10D according to the fourth embodiment will be described with reference to FIG. Note that the same reference numerals as in FIG. 1 denote the same components as in FIG. 1, and a description thereof will be omitted.
[0069]
The light amount control device 10D according to the fourth embodiment has a light source counter 24 newly provided, a light amount control order setting storage unit 12C provided in place of the light amount control order setting storage unit 12A, and a switching unit 14A. Only the point that a switching unit 14C is provided is different from the light amount control device 10A according to the first embodiment.
[0070]
A light source switching signal and a counter reset signal are externally input to the light source counter 24. The light source counter 24 counts the number of LD switching at the time of light amount control, and outputs a count signal indicating the count value. The data is sequentially output to the light quantity control order setting storage unit 12C.
[0071]
The light source switching signal is a signal indicating a switching timing of the LD to be subjected to the light amount control. In the present embodiment, the timing at which the light level shifts from the low level to the high level is the same as in each of the above embodiments. This is the switching timing. The counter reset signal is a signal for resetting the count by the light source counter 24. In the present embodiment, the counter reset signal is set to a high level when resetting the count, and is set to a low level when executing the count. Signal.
[0072]
Therefore, the light source counter 24 performs counting in synchronization with the rising edge of the light source switching signal when the counter reset signal is at a low level, and resets the count value when the counter reset signal is at a high level.
[0073]
In the light amount control device 10D according to the present embodiment, the light source counter 24 is reset by the counter reset signal immediately before the light amount control.
[0074]
Further, in the light amount control device 10D according to the present embodiment, if it is not possible to secure a sufficient amount of time for controlling the light amounts of all the LDs as the light amount control period during image formation, some LDs are controlled during the first light amount control. Only the light quantity control is performed, the count value of the light source counter 24 is held without resetting until the next light quantity control, and the light quantity control of the remaining LDs is performed at the next and subsequent light quantity control, and the light quantity control of all LDs is performed. After the end, the count value of the light source counter 24 is reset.
[0075]
On the other hand, an APC order control signal indicating the above-described order information (information indicating the order of the light amount control for each LD) is externally input to the light amount control order setting storage unit 12C. When an APC order control signal is input from the outside, storage unit 12C stores order information indicated by the signal.
[0076]
Further, the light quantity control order setting storage unit 12C outputs to the switching unit 14C an LD signal that can specify an LD that performs light quantity control in the order of the count value indicated by the count signal input from the light source counter 24. For example, when the count value is “1”, an LD signal that can specify the LD for which the light amount control is performed first is output to the switching unit 14C.
[0077]
When the LD signal is input from the light amount control order setting storage unit 12C, the switching unit 14C modulates the video OUT signal that can turn on the LD specified by the LD signal, that is, the LD to be subjected to light amount control. The S / H signal is output to the section 20 and the S / H 18 corresponding to the LD is set to a sample state. The other operations of the switching unit 14C at the time of controlling the light amount are the same as those of the switching unit 14A according to the first embodiment, and thus the description thereof will be omitted.
[0078]
The light amount control device 10D according to the present embodiment includes the light source counter 24 that operates as described above, and the light source counter 24 is reset by the counter reset signal immediately before the light amount control. Even if some noise is included in the signal and the count value of the light source counter 24 advances, and the count value becomes equal to or more than the number of LDs subject to light amount control or the count value returns to the initial value, the next light amount control Sometimes, the count value can be set to a normal value, and normal light amount control can be performed.
[0079]
In addition, in the light amount control device 10D according to the present embodiment, as described above, if it is not possible to secure a sufficient amount of time for performing the light amount control of all LDs as one light amount control period, a plurality of light amount control periods Since the light amount control is performed separately, it is possible to cope with an increase in the number of LDs to be controlled.
[0080]
FIG. 9 shows an example of a time chart in a case where the light quantity control is performed by dividing the six LDs into three LDs twice.
[0081]
In this case, the counter reset signal is reset immediately before the start of the period during which the execution of the first light amount control indicated by the light amount control permission signal (in this embodiment, the period during which the light amount control permission signal is at a low level). Is shifted from the state indicating to the state in which counting is permitted (in this embodiment, the state is shifted from a high level to a low level).
[0082]
As a result, the light source counter 24 starts counting in synchronization with the rising edge of the light source switching signal. However, in one light amount control period, only three LDs can perform light amount control. For this reason, in the present embodiment, the counter reset signal is not set to the reset state even after the light amount control period ends, and the count value of the light source counter 24 is kept at “3”. Therefore, at the time of the next light amount control, the count of the light source counter 24 is increased from '3', so that the light amount control for the remaining three LDs for which the light amount control is to be performed after the fourth light is performed. This is performed at the time of light quantity control.
[0083]
After the light amount control of all LDs to be controlled is completed, the count value of the light source counter 24 is reset by shifting the counter reset signal to a state indicating reset.
[0084]
The light quantity control order setting storage unit 12C corresponds to the storage unit of the present invention, the switching unit 14C corresponds to the switching unit of the present invention, and the light source counter 24 corresponds to the counting unit of the present invention.
[0085]
As described in detail above, the light amount control device 10D according to the present embodiment can provide the same effects as the light amount control device 10A according to the first embodiment, and can also switch the number of switching of the LD by the light source switching signal. And a light source counter 24 whose count value is reset at a predetermined timing. The switching unit 14C controls the LD so that the LD of the order indicated by the count value of the light source counter 24 becomes a target of light quantity control. Therefore, even if noise enters the light source switching signal and the count value of the light source counter 24 becomes abnormal, a normal count value can be obtained at the next light amount control, and normal light amount control is performed. be able to.
[0086]
[Fifth Embodiment]
In the fifth embodiment, light quantity control is performed on a plurality of LDs to be subjected to light quantity control at a predetermined set light quantity, and thereafter, the set light quantity is switched and light quantity control is again performed on the plurality of light sources. A mode for performing the operation will be described.
[0087]
First, the configuration of a light quantity control device 10E according to the fifth embodiment will be described with reference to FIG. Note that the same components as those in FIG. 8 of FIG. 10 are denoted by the same reference numerals as in FIG. 8, and description thereof will be omitted.
[0088]
The light quantity control device 10E according to the fifth embodiment newly includes an S / H 18B instead of the S / H 18, a modulation section 20B instead of the modulation section 20, and a set light quantity selection section 26. Only the point provided is different from the light quantity control device 10D according to the fourth embodiment.
[0089]
The S / H 18B receives an S / H signal, a light amount switching signal, and a drive amount setting signal. The S / H 18B receives two drive amount signals 1 and a drive amount signal based on these signals. 2 to the modulator 20B.
[0090]
Note that the light amount switching signal is a signal indicating the timing of switching the set light amount for each LD, and in the present embodiment, the timing of shifting from the low level to the high level is the timing of switching the set light amount. . The S / H signal and the drive amount setting signal are the same as the signals having the same names in the above embodiments.
[0091]
Further, m intensity signals are externally input to the modulation unit 20B, and n video OUT signals are input from the switching unit 14C, and two driving amount signals 1 and two driving amount signals 1 are output from each S / H 18B. The amount signal 2 is input, and the modulation unit 20B outputs a drive signal to n LDs included in the light source unit 50 based on these signals. The intensity signal is a signal indicating the light intensity when each LD is driven.
[0092]
On the other hand, the set light quantity selection unit 26 is configured to receive a light quantity switching signal and a light quantity instruction signal from outside, and the set light quantity selection unit 26 sends a drive quantity control signal to the drive quantity control unit 16B based on these signals. A set light quantity signal indicating the set light quantity of each LD during light quantity control is output. The light amount instruction signal according to the present embodiment is a signal indicating a light amount (hereinafter, referred to as a “reference light amount”) that is a reference of the set light amount of each LD during the light amount control.
[0093]
When the light amount switching signal is at a low level, the set light amount selection unit 26 according to the present embodiment sets the output light amount of the LD to be subjected to the light amount control to a reference light amount indicated by the light amount instruction signal by a predetermined coefficient (this embodiment). In the embodiment, the drive amount control unit 16B is controlled so that the set light amount is multiplied by '1'), and when the light amount switching signal is at a high level, the output light amount of the LD becomes the reference light amount indicated by the light amount instruction signal. The drive amount control unit 16B is controlled so that the set light amount 2 is multiplied by a coefficient (in this embodiment, “2”) larger than the predetermined coefficient.
[0094]
Next, the configuration of the S / H 18B according to the present embodiment will be described in detail with reference to FIG. As shown in the figure, the S / H 18B is configured to include a selection unit 30 and two S / Hs 32A and S / H 32B.
[0095]
A drive amount setting signal is input to the S / H 32A and the S / H 32B from the drive amount control unit 16B. The drive amount 1 is sampled and held, and the S / H 32B samples and holds the drive amount 2 at which the output light amount of the LD to be light amount controlled becomes the set light amount 2.
[0096]
Further, the selection unit 30 receives the S / H signal from the switching unit 14C and the light amount switching signal from outside, and the selection unit 30 responds to the state of the light amount switching signal. By selecting S / H32A and S / H32B, a driving amount signal 1 indicating driving amount 1 and a driving amount signal 2 indicating driving amount 2 are output to the modulation unit 20B.
[0097]
Next, with reference to FIG. 12, the configuration of modulation section 20B according to the present embodiment will be described in detail. As shown in the figure, the modulation section 20B includes n modulation sections 40 each corresponding to one of the LDs and including a drive amount calculation section 40A and a modulation circuit 40B. It is configured.
[0098]
The driving amount calculating unit 40A receives m intensity signals from the outside and receives the driving amount signal 1 and the driving amount signal 2 from the corresponding S / H 18B. 40A calculates a drive amount at which the output light amount indicated by the intensity signal is obtained, and outputs a drive amount signal indicating the drive amount to the modulation circuit 40B.
[0099]
To the modulation circuit 40B, in addition to the drive amount signal, a video OUT signal is input from the switching unit 14C. When the video OUT signal indicates that the LD is turned on, the modulation circuit 40B outputs The corresponding LD is turned on with a predetermined drive amount.
[0100]
The drive amount calculation performed by the drive amount calculation unit 40A is performed, as an example, as shown in FIG. 13, when the set light amount 1 is the minimum value of the intensity modulation range and the set light amount 2 is the maximum value of the intensity modulation range. The driving amount control range at the time of intensity modulation ranges from the driving amount 1 to the driving amount 2, and the driving amount when the intensity signal indicates X% of the maximum light amount can be obtained by the following equation (1).
[0101]
(Drive amount 2−drive amount 1) × (X / 100) + drive amount 1 (1)
Therefore, the driving amount calculating section 40A according to the present embodiment calculates the driving amount by the equation (1). Here, when the relationship between the light amount and the driving amount is linear, it is possible to cope with the relationship by obtaining a relational expression, not particularly the upper and lower limits of the intensity modulation range.
[0102]
Due to the configuration and operation of each unit described above, as shown in FIG. 14, the setting of each LD is performed for each cycle of the light source switching signal during the period in which the light intensity switching signal is at the low level and the light intensity control permission signal is at the low level. The light amount control at the set light amount 2 of each LD is performed for each cycle of the light source switching signal within a period in which the light amount control at the light amount 1 is performed, the light amount switching signal is at the high level, and the light amount control permission signal is at the low level. Is performed.
[0103]
The set light amount selection unit 26 and the drive amount control unit 16B correspond to a light amount control unit of the present invention.
[0104]
As described in detail above, the light amount control device 10E according to the present embodiment can provide the same effects as the light amount control device 10D according to the fourth embodiment, and the light amounts of the plurality of LDs are set in advance. After the light amount is controlled so that the set light amount is obtained, the set light amount is switched to another light amount and the light amount control of the plurality of LDs is performed again. A plurality of driving amounts are measured, and a relationship between the light amount and the driving amount is obtained from the plurality of driving amounts so that each LD can be driven with a light intensity corresponding to an intensity signal input from the outside. By driving each LD with a drive amount calculated so as to obtain a light amount, intensity modulation can be performed. As a result, for example, it is possible to prevent the occurrence of unevenness in the formed image due to the unevenness in the sensitivity of the photoconductor 54.
[0105]
Note that the time charts (see FIGS. 2, 4, 5, 7, 9, and 14) shown in each of the above embodiments are merely examples, and may be appropriately changed without departing from the gist of the present invention. It goes without saying that it is possible.
[0106]
The configurations of the light amount control devices 10A to 10E described in the above embodiments (see FIGS. 1, 3, 6, 8, and 10 to 12) are also examples, and depart from the gist of the present invention. Needless to say, it can be appropriately changed within a range not to be performed.
[0107]
For example, a new light amount control device can be realized by appropriately combining the configurations of the light amount control devices 10A to 10E.
[0108]
In the modulation cycle changing units 22A and 22B shown in the second and third embodiments, the configuration is such that the frequency of the reference clock signal to be modulated at high speed is divided. However, the same effect can be obtained by using a configuration such as a voltage controlled oscillator. Can be played.
[0109]
The information stored in the light amount control order setting storage units 12A to 12C may be fixed in hardware as described in the first to third embodiments, or may be fixed in the fourth and fifth embodiments. As in the embodiment, an external interface may be provided and updated at a predetermined timing. At this time, there is an advantage that information can be updated with a small number of control signals even if the number of LDs to be controlled increases by using the interface to transmit information by serial communication. Further, the light amount control order setting storage unit may be mounted as a removable storage device so as to be easily exchangeable via a socket or the like, and the storage device may be replaced when it is desired to change the order of the light amount control.
[0110]
In the light amount control devices described in the fourth and fifth embodiments (see FIGS. 8 and 10), if a noise is applied to the light source switching signal during permission of the light amount control, the light source counter 24 malfunctions, and It is expected that an instruction to switch the LD to be subjected to light quantity control will be given before the timing comes. Here, when the maximum value that can be counted by the light source counter 24 is larger than the LD number, an invalid count number is input to the light amount control order setting storage unit 12C, and the light amount control may not be performed normally.
[0111]
The problem is that the light source counter 24 controls the LD so as not to switch the LD to be controlled when the light source switching instruction is input more than the number of LDs when the light amount control is permitted, or sets the light source to be controlled. This can be prevented by setting the LD to the LD for which the light amount control was performed when the light amount control is started again, and performing control so as to perform the light amount control again. This problem can also be prevented by controlling to stop the light quantity control of all LDs when a count number greater than the LD number is input to the switching unit 14C.
[0112]
Further, the intensity modulation of the plurality of LDs in the light amount control device 10E according to the fifth embodiment is performed by inputting an intensity signal (m bits × LD number) that independently indicates the light emission amount of each LD. Intensity modulation can be performed independently to form a finer image. A common m-bit intensity signal is input to a plurality of LDs, and intensity modulation is performed on a plurality of LDs in common. When the light intensity profile at the laser scanning position on the photosensitive member is reduced as shown in FIG. 15 as in the technique described in Japanese Unexamined Patent Publication No. 11-291548, the output of the LD is set to the same value. It is also possible to realize a technique in which the profile is changed like a “correction coefficient” in the figure to make a uniform profile after correction.
[0113]
【The invention's effect】
As described above in detail, according to the light source control device of the present invention, the order information indicating the order of controlling the light amounts of the plurality of light sources is stored in advance, and the light amount control is performed in the order indicated by the order information. Since the light source to be subjected to the light amount control is switched in synchronization with the light source switching signal which is a modulation signal indicating the switching timing of the light source to be subjected to the light amount control, the light source to be controlled is independent of the number of light beams. Therefore, the number of control signals for setting the light source to be set can be reduced, and as a result, the effect that the circuit scale can be reduced can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a light quantity control device 10A according to a first embodiment.
FIG. 2 is a time chart for explaining the operation of the light quantity control device 10A according to the first embodiment.
FIG. 3 is a block diagram illustrating a configuration of a light quantity control device 10B according to a second embodiment.
FIG. 4 is a time chart for explaining the operation of a light quantity control device 10B according to a second embodiment.
FIG. 5 is another time chart for explaining the operation of the light quantity control device 10B according to the second embodiment.
FIG. 6 is a block diagram illustrating a configuration of a light quantity control device 10C according to a third embodiment.
FIG. 7 is a time chart for explaining the operation of a light quantity control device 10C according to a third embodiment.
FIG. 8 is a block diagram illustrating a configuration of a light quantity control device 10D according to a fourth embodiment.
FIG. 9 is a time chart for explaining the operation of a light quantity control device 10D according to a fourth embodiment.
FIG. 10 is a block diagram illustrating a configuration of a light quantity control device 10E according to a fifth embodiment.
FIG. 11 is a block diagram showing a configuration of an S / H 18B included in the light quantity control device 10E.
FIG. 12 is a block diagram showing a configuration of a modulation unit 20B included in the light quantity control device 10E.
FIG. 13 is a graph for explaining the operation of the light amount control device 10E according to the fifth embodiment, and illustrates a light source (LD) drive amount vs. a light source (LD) drive amount for explaining an LD drive amount control range during intensity modulation of the light amount control device 10E. It is a graph of a set light quantity.
FIG. 14 is a time chart for explaining the operation of a light quantity control device 10E according to a fifth embodiment.
FIG. 15 is a configuration diagram of an optical scanning device for explaining a case in which a light intensity control device 10E according to a fifth embodiment is applied to a conventional technique for correcting uneven light intensity due to a scanning position by intensity modulation.
FIG. 16 is a configuration diagram of an optical scanning device using a conventional edge emitting LD as a light source.
FIG. 17 is a configuration diagram of a conventional optical scanning device using a surface emitting LD as a light source.
18 is a configuration diagram of the optical scanning device when the optical scanning device shown in FIG. 17 is applied to the optical scanning device shown in FIG.
FIG. 19 is a diagram provided for explanation of a conventional technique.
FIG. 20 is a diagram provided for explanation of another conventional technique.
[Explanation of symbols]
10A-10E Light intensity control device
12A to 12C light amount control order setting storage unit (storage means)
14A to 14C switching unit (switching means)
16 Drive amount control unit
16B drive amount control unit (light amount control means)
18, 18B S / H
20, 20B modulator
22A Modulation cycle change unit (change means)
22B Modulation cycle changing unit (specific pulse changing means)
24 light source counter (counting means)
26 Set light quantity selection unit (light quantity control means)
30 Selector
32A, 32B S / H
40 Modulation section
40A drive amount calculation unit
40B modulation circuit
50 Light source
52 light intensity sensor
54 Photoconductor

Claims (5)

Used in an optical scanning device that scans a surface to be scanned with light beams output from a plurality of light sources that can be independently modulated, and controls the light amount so that the light amounts of the plurality of light sources become a preset set light amount. Light source control device,
Storage means for storing in advance order information indicating the light quantity control order of the plurality of light sources,
Switching means for switching a light source to be subjected to light quantity control in synchronization with a light source switching signal which is a modulation signal indicating a switching timing of a light source to be subjected to light quantity control so as to perform light quantity control in the order indicated by the order information; ,
Light source control device provided with 2. The light source control device according to claim 1, further comprising changing means for changing a modulation cycle of the light source switching signal. The light source control device according to claim 1, further comprising a specific pulse changing unit that changes a modulation cycle of a pulse corresponding to a specific light source in the light source switching signal. Counting means for counting the number of light sources switched by the light source switching signal and resetting the count value at a predetermined timing,
4. The light source control device according to claim 1, wherein the switching unit switches the light sources such that the light sources of the order indicated by the count value of the counting unit are subjected to light amount control. 5. After controlling the light amount so that the light amounts of the plurality of light sources become a preset set light amount, switching the set light amount to another light amount and controlling the light amount control of the plurality of light sources again to perform light amount control means. The light source control device according to claim 1, further comprising:

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