JP3560114B2 - Optical scanning device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical scanning device, and more particularly, to an optical scanning device that irradiates a photosensitive material while scanning a light beam corresponding to input data.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an optical scanning apparatus using laser light from a single light source (hereinafter, abbreviated as Single Beam), generally, laser light is deflected by a polygon mirror that rotates at high speed by rotation of a driving unit such as a scanner motor. While irradiating the photosensitive material. In such an optical scanning device, the resolution has been switched without lowering the processing capability by switching the rotation speed of the scanner motor according to the resolution. A laser diode (hereinafter, abbreviated as LD) that outputs such a single beam is referred to as a single beam LD.
[0003]
On the other hand, demands for higher speed and higher resolution in recent years have not been met by increasing the speed of the scanner motor. For this reason, a method of irradiating a plurality of laser beams simultaneously in one scanning period has been proposed. The LD capable of simultaneously outputting a plurality of laser beams is provided with a plurality of LD chips. By turning on the plurality of LD chips, a plurality of laser beams (hereinafter, abbreviated as Multi Beam) can be output. . An LD capable of lighting such a plurality of LD chips is called a Multi BeamD. However, when the resolution is switched using the Multi BeamD, the desired resolution cannot be obtained only by changing the rotation speed of the scanner motor because the arrangement interval of the LD chips is constant. In order to solve this problem, it is necessary to switch the number of laser beams to be applied to plural / single (Multi / Single).
[0004]
Japanese Patent Application Laid-Open No. 1-299042 discloses a resolution switching patent relating to Multi BeamLD. In the image forming apparatus according to this patent, when switching the scanning density, the number of laser light sources to be used is switched. This makes it possible to switch the plurality of laser emission sources in accordance with the scanning density and suppress the number of rotations of the polygon mirror to 10,000 or less. Accordingly, it is possible to prevent the cost of the polygon mirror and the scanner motor from increasing, and to reduce the size.
[0005]
By the way, generally, the required light amount of the photosensitive material per unit time is determined by the product of the process speed and the scan length. Since the scan length is not greatly changed if the same photosensitive material is used, it is not necessary to largely change the light amount in the conventional Single Bar LD if the process speed does not change even if the resolution changes.
[0006]
[Problems to be solved by the invention]
However, when using a Multi Beam LD having N LDs and switching the resolution by switching between Multi / Single lighting, Single lighting requires N times as much light quantity as Multi lighting. In a general LD current driving element (hereinafter, abbreviated as LD DRIVER; LDD), the light amount variable range is determined, and there is no light amount variable range that can cope with both Multi / Single lighting. If the amount of light is not the corresponding amount, it is necessary to adjust the irradiation time until the required amount of light is reached, and the processing cannot be sped up.
[0007]
The present invention has been made in view of the above-described facts, and has as its object to provide an optical scanning device capable of easily changing a light amount variable range.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, in an optical scanning device for irradiating a photosensitive material while scanning a light beam corresponding to input data, an LD capable of outputting two or more light beams, and switching of resolution. Accordingly, there is provided a beam number switching unit for switching the number of light beams of the LD, and a light amount switching unit for switching a light amount variable range of the LD in accordance with the switched resolution.
[0009]
According to the present invention, the number of light beams of the LD can be switched according to the switching of the resolution, and the variable light amount range of the LD can be switched by the light amount switching means according to the switched resolution. The light amount variable range can be easily changed based on the number of light beams.
[0010]
Therefore, even in an image forming apparatus in which the resolution is switched by switching the number of beams, the light quantity variable range can be easily changed, and accordingly, high speed and high resolution can be supported.
[0011]
Note that the change in the light amount variable range generally refers to a change in the light amount outside the light amount adjustment range performed according to the deterioration of the optical member or the like. The case where a different range is set is included.
[0012]
According to a second aspect of the present invention, in an optical scanning device that irradiates a photosensitive material while scanning a light beam corresponding to input data, an LD capable of outputting two or more light beams and a rotational drive are performed. A light beam deflecting unit for deflecting the light beam from the LD toward the photosensitive material, a rotation speed switching unit for switching the rotation speed of the light beam deflecting unit in accordance with the switching of the resolution, and a resolution switching unit. Accordingly, there is provided a beam number switching unit for switching the number of light beams of the LD, and a light amount switching unit for switching a light amount variable range of the LD in accordance with the switched resolution.
[0013]
According to the present invention, the number of beams and the number of rotations of the light beam deflecting means are switched in accordance with the switching of the resolution, and the light quantity switching means can switch the light quantity variable range of the LD according to the switched resolution. Therefore, the resolution can be switched in a number of stages, and the light quantity variable range can be easily changed based on the number of light beams and the rotation speed of the light beam deflecting means according to the resolution.
[0014]
Therefore, even in an image forming apparatus in which the resolution is switched by switching the number of beams and the number of rotations of the light beam deflecting means, the variable light amount range can be easily changed. Further, the resolution can be finely switched by switching the resolution by using both the number of beams and the rotation speed of the light beam deflecting means.
[0015]
In addition, since the resolution is switched not only by changing the rotation speed of the light beam deflecting means but also by switching the number of beams, it is possible to cope with high speed and high resolution without increasing the rotation speed of the light beam deflecting means. In addition, it is possible to realize a highly reliable optical scanning device by preventing noise and temperature rise.
[0016]
Accordingly, it is possible to change the light amount variable range of the image forming apparatus in which the resolution is changed by switching a plurality of beams without depending only on the rotation speed of the light beam deflecting unit driven by the driving unit.
[0017]
According to a third aspect of the present invention, the light amount switching means includes a light amount adjusting means for adjusting the light emission amount of the LD, and the detection sensitivity of the light amount adjusting means is switched in accordance with the number of beams corresponding to the resolution. The variable light amount range is characterized.
[0018]
According to the present invention, since the light amount variable range is changed by switching the detection sensitivity of the light amount adjusting means according to the number of beams, for example, when the number of beams is changed, the light amount variable range of the LD can be easily changed accordingly. Is changed. Here, since the light amount adjusting unit can adjust the light amount of the light beam output from the LD to maintain the light amount at a constant value, by switching the detection sensitivity of the light amount adjusting unit, the light amount before switching is the same. The output of the LD is controlled so that the amount of light becomes equal to the amount of light. As a result, the amount of light can be easily changed exactly N times. Thereby, the variable range of the light amount of the light beam can be easily and reliably changed without providing a special device. Note that, with the change of the light amount variable range, the light amount adjustment range for adjusting the light amount to a constant value can be changed.
[0019]
At this time, the switching of the detection sensitivity of the light quantity adjusting means can be linked with the switching of the number of beams, as in the ninth aspect of the present invention. Thus, when the beam number is changed by the beam number switching unit and the light amount variable range is changed, the detection sensitivity of the light amount adjustment unit is switched in conjunction with the light amount adjustment unit, so that the output sensitivity can be easily adjusted to the beam number. can do.
[0020]
According to a fourth aspect of the present invention, the light amount switching unit includes a light amount adjustment filter inserted on an optical path of the LD to adjust a transmitted light amount of the LD, and the light amount adjustment filter is switched according to a resolution. It is characterized in that the light amount variable range is changed by adjusting the transmittance so as to be the transmission amount of the light beam corresponding to the number of beams.
[0021]
According to the present invention, the light amount adjustment filter switches the transmittance so that the light beam transmission amount corresponds to the number of beams. Therefore, when the number of beams is changed according to the resolution, the light amount adjustment filter is accordingly changed. Is switched. Thus, a light beam having a light amount after adjustment according to the resolution can be obtained. Therefore, the light amount variable range can be easily adjusted without using complicated control.
[0022]
The invention according to claim 5 is characterized in that it has a synchronous detection sensor amplification switching means for switching the amplification factor of the synchronous detection sensor for detecting the start of scanning of the light beam according to the switching of the resolution.
[0023]
According to the present invention, since the amplification factor of the synchronous detection sensor is switched according to the resolution, for example, even if the light beam is scanned at a high speed according to the resolution, the light beam can be surely increased by increasing the amplification factor. Can be detected.
[0024]
At this time, the synchronization detection sensor amplifying means can be linked with the beam number switching means, as in the ninth aspect of the present invention. Accordingly, when the beam number is changed by the beam number switching means and the light amount variable range is changed, the light amount of the light beam corresponding to this beam number is changed to a synchronous detection sensor of an appropriate operation range in conjunction with the change. Can be reliably detected.
[0025]
Further, as in the invention according to claim 6, when the synchronization detection sensor is operated, the number of light beams detectable by the synchronization detection sensor can be increased.
[0026]
According to this, for example, during high-speed rotation of the light beam deflecting unit in which the amount of light incident on the synchronization detection sensor decreases, the number of light beams can be increased only during the synchronization detection period to increase the amount of light incident on the synchronization detection sensor. it can. As a result, even when the light beam deflecting unit is rotating at a high speed, the synchronization detection sensor can reliably detect the light beam.
[0027]
The invention according to claim 7 is characterized in that there is provided a beam diameter switching means for switching the beam diameter of the light beam from the LD in accordance with the switching of the resolution.
[0028]
According to this, since the beam diameter of the light beam is changed according to the resolution, when the resolution is changed and the light amount is changed, the beam diameter is optimized accordingly. As a result, even when an image is formed using such an optical scanning device, an image having a good finish quality can be formed by a light beam having an appropriate light amount and beam diameter.
[0029]
At this time, the beam diameter switching means can be linked with the beam number switching means, as in the ninth aspect of the present invention. Thus, when the number of beams is changed by the beam number switching means and the light amount is changed, a light beam adjusted to an appropriate beam diameter can be output in conjunction therewith.
[0030]
Further, this beam diameter switching means can be integrated with the above-mentioned light amount adjustment filter as in the invention according to claim 8. For example, when the shape of the light amount adjusting filter is a slit type, when the light beam passes through the light amount adjusting filter, a suitable light amount is adjusted by the transmittance according to the number of beams, and the slit is adapted to the optimum light amount. Beam diameter. This makes it possible to reduce the number of components and downsize the device.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an optical scanning device 100 according to the present embodiment.
[0032]
The optical scanning device 100 includes a dual LD (hereinafter, referred to as a DLD) 112 including two different LD chips 112A and 112B (see FIG. 2). The DLD 112 can output two light beams having different emission angles in the sub-scanning direction from the two LDDs 112A and 112B. In FIG. 1, the two light beams are arranged in the front-rear direction of the drawing sheet, and thus are illustrated in an overlapping manner. The DLD 112 is provided with a DLD light receiving element (hereinafter, abbreviated as PD) 114, and detects the light amount of the light beam output from the DLD 112.
[0033]
A polygon mirror 102 as a light beam deflecting unit is disposed near the emission side of the DLD 112 and on each optical axis of the two light beams from the DLD 112, and two laser beams from the DLD 112 The light reaches the reflection surfaces on the side surfaces of the polygon mirror 102 respectively. The polygon mirror 102 has a predetermined number (for example, six) of reflection surfaces on its side surface. A scanner motor 104 (see FIG. 2) is connected to the polygon mirror 102. The scanner motor 104 rotates the polygon mirror 102 around the axis 102A at a predetermined speed in the direction of arrow R to continuously change the angle of incidence of the light beam on each reflection surface. Thus, the light beam from the DLD 112 is deflected by the polygon mirror 102.
[0034]
On the optical path of the light beam deflected by the polygon mirror 102, a cylindrical photosensitive drum 108 is rotatably disposed with an optical system 106 including a pair of imaging lenses 106A and 106B interposed therebetween. A driving unit (not shown) is connected to the photosensitive drum 108, and the driving force of the driving unit causes the photosensitive drum 108 to rotate in one direction.
[0035]
As shown in FIG. 2, the DLD 112 is connected to the image processing device 150 via the controller 116. The image processing device 150 outputs image data to the controller 116.
[0036]
The controller 116 includes a light amount control unit 118, a scanner rotation speed control unit 134, an SOS gain control unit 126, and a beam diameter switching control unit 136.
[0037]
The light quantity control unit 118 includes a light quantity control circuit 120. The light quantity control circuit 120 is connected to the DLD 112 via LD current driving elements (hereinafter, abbreviated as LDD) 122A and 122B, and converts the image data input from the image processing device 150 into an image data. It can be temporarily stored every two scanning lines.
[0038]
The LDDs 122 </ b> A and 122 </ b> B are turned on / off based on image data, and output light beams of the light amount controlled by the light amount control circuit 120.
[0039]
The light quantity control unit 118 includes a PD light quantity control circuit 124, and is connected between the light quantity control circuit 120 and the DLD 112. The PD light quantity control circuit 124 detects the LD light quantity from the DLD 112, converts the current to voltage, amplifies the output, and outputs it to the light quantity control circuit 120.
[0040]
The light quantity control circuit 120 compares the output value from the PD light quantity control circuit 124 with a reference value and performs light quantity control so as to have a prescribed light quantity.
[0041]
The scanner rotation speed controller 134 is connected to the scanner motor 104 and controls the rotation speed of the polygon mirror 102.
[0042]
The SOS gain control unit 126 is connected to a synchronization detection sensor 128 (hereinafter, referred to as SOS sensor 128) (see FIG. 1).
[0043]
The SOS sensor 128 is disposed on an optical path of a light beam converging at a scanning start position (Start Of Scan; SOS) on the main scanning surface on which the light beam reflected and deflected by the polygon mirror 102 is scanned. . The SOS sensor 128 is connected to the light quantity control circuit 120, and when an SOS beam is detected by the SOS sensor 128, an image writing timing signal is input from the SOS sensor 128 to the light quantity control circuit 120. When a write start timing signal is input from the SOS sensor 128, the light quantity control circuit 120 starts modulating the image signal on the line after a predetermined time has elapsed.
[0044]
As shown in FIG. 5, the SOS gain control unit 126 includes an amplifier 130, and an SOS sensor 128 is connected to one input terminal side of the amplifier 130. Resistances Rf and Rg are connected in parallel between the other input terminal side and the output terminal side, and a gain switch 132 is connected to the resistance Rf side. The gain changeover switch 132 is turned on / off in response to a speed changeover signal from the scanner rotation speed controller 134 of the controller 116. Therefore, when the gain changeover switch 132 is turned on / off, the resistance value is changed.
[0045]
The beam diameter switching control unit 136 is connected to the beam diameter switching driver 138 of the LDDs 112A and 112B. The beam diameter switching driver 138 drives according to a signal from the beam diameter switching control unit 136 to change the beam diameter of the output beams of the LDDs 112A and 112B.
[0046]
Incidentally, a resolution changeover switch 140 is connected to the controller 116. The resolution switch 140 outputs to the controller 116 a resolution switching signal for switching the resolution by a predetermined operation. Here, the resolution is switched between 600 dpi and 300 dpi as an example.
[0047]
The controller changes the number of output beams from the DLD 112 according to the resolution switching signal. That is, when the resolution is 300 dpi, one output beam is used, and when the resolution is 600 dpi, two output beams are used. In response, the LDDs 122A and 122B to be driven are selected.
[0048]
Further, as shown in FIG. 3, the controller 116 is provided with a light amount switching circuit 142 for switching the light amount of the output beam according to the resolution switching signal. The light amount switching circuit 142 includes a PD light amount control unit 118 and a light amount control circuit 120. The light amount switching circuit 142 is provided in each of the LDDs 122A and 122B, and one of them will be described as an example.
[0049]
In the light amount switching circuit 142, a comparator 144 is provided on the light amount control circuit 120 side. The reference voltage Vref and the PD light amount monitor voltage Vr from the PD 114 are input to the input terminal of the comparator 144.
[0050]
One ends of monitor current detection resistors Ra and Rb as light emission output detection means are respectively connected to the input side of the PD light quantity monitor voltage Vr of the comparator 144. The other end of the monitor current detection resistor Ra is grounded. The other end of the monitor current detection resistor Ra is connected to the other end of the monitor current detection resistor Rb via the resistance value changeover switch 146, and is grounded similarly to the monitor current detection resistor Rb.
[0051]
The monitor current detection resistors Ra and Rb are linked variable resistors, and are adjusted to always have the same resistance value. The monitor current detection resistors Ra and Rb correct the monitor current Is to a constant value. This prevents the monitor current Is from being different due to differences in threshold currents, differential efficiencies, and transmittances of the optical components of the LDDs 112A and 112B.
[0052]
The resistance changeover switch 146 is turned on / off in response to the number of output beams of the DLD 112, that is, a resolution changeover signal for switching between Single (one) and Dual (two). Here, it turns on in the case of Single, and turns off in the case of Dual.
[0053]
The output terminal of the comparator 144 is connected to the LDD 122A or LDD 122B, and outputs a light amount control signal as a result of comparison between the light amount monitor voltage Vr and the reference voltage Vref to the LDD 122A or LDD 122B. The LDD 122A and the LDD 122B output a light beam according to the input light amount control signal.
[0054]
Note that an ENB signal is input to the LDDs 122A and 122B, and the LDDs 122A and 122B whose light amount is controlled by the ENB signal are selected. For example, in the case where the resolution is set to half of that in the case of two beams, data is not divided into the A channel and the B channel, and the light amount is controlled to be twice as large as that in the case of two beams.
[0055]
Further, the reference voltage Vref can be changed according to a factor of a light amount decrease due to a sensitivity deterioration of the photosensitive drum 108 or the like, whereby the light amount set on the optical scanning device 100 can be changed within a predetermined range. .
[0056]
The resolution switching signal input to the controller 116 is input to the SOS gain control unit 126, the scanner rotation speed control unit 134, and the beam diameter switching control unit 136. The SOS gain control unit 126, the scanner rotation speed control unit 134, and the beam diameter switching control unit 136 control the gain of the SOS sensor 128, the rotation speed of the scanner motor 104, and the beam diameter, respectively, so as to be adjusted to values according to the resolution. I do.
[0057]
Next, the operation of the present embodiment will be described.
First, an outline of the optical scanning device 100 will be described.
[0058]
In the optical scanning device 100, the data “A + B” for two scanning lines input from the image processing device 150 is temporarily stored in the light amount control circuit 120 and then divided into A channel and B channel. When an image writing timing signal is input from the SOS sensor 128, the data is divided into “A” and “B” and output to the LDDs 122A and 122B. In the LDDs 122A and 122B, the LDDs 112A and 112B are turned on according to a light amount control signal instructed from the light amount control circuit 120. As a result, two output beams are emitted from the DLD 112. At this time, the light amount of the output beam from the DLD 112 is detected by the PD 114, and the light amount of the output beam is adjusted to an appropriate value by the light amount switching circuit 142, as described later.
[0059]
The output beam from the DLD 112 irradiates and is deflected by irradiating the side surface of the polygon mirror 102 which is driven to rotate in a predetermined direction (the direction of arrow R in FIG. 1) at a set number of rotations. The deflected output beam passes through the optical system 106 and irradiates the photosensitive surface of the photosensitive drum 108. The output beam scans and exposes the photosensitive surface of the photosensitive drum 108 in a predetermined direction by rotating the polygon mirror 102.
[0060]
On the other hand, since the photosensitive drum 108 is rotationally driven by a rotation driving unit (not shown), sub-scanning is performed in a direction different from main scanning by an output beam.
[0061]
Thus, main scanning and sub-scanning are performed, and an image corresponding to the image data is formed on the photosensitive surface of the photosensitive drum 108.
[0062]
Next, control associated with switching of resolution will be described.
The optical scanning device 100 is provided with a resolution changeover switch 140, and outputs a resolution changeover signal by predetermined key scanning. A single mode in which a resolution switching signal is output and a single output beam is selected, and a dual mode in which two output beams are output is selected, and the mode is switched.
[0063]
When the resolution is switched by the resolution switch 140, the rotation speed of the scanner motor 104 is changed according to the set number of output beams. Here, when there is no change in the number of beams, the speed becomes high when the resolution is switched to high, and the speed becomes low when the resolution is switched to low. If the number of beams is changed, the speed is determined according to the number of beams used.
[0064]
For example, when the resolution is set to 3/4 of the two-beam lighting, one of the LDDs 112A and 112B is turned on to form one output beam, and the scanner rotation speed control circuit 134 controls the rotation speed of the polygon mirror 102. Increase by 1.5 times. At this time, the image data is not divided into the A channel and the B channel, and the light amount is controlled by one of the LDDs 122A and 122B selected by the ENB signal, and the light amount is controlled to be twice as large as the case of two beams.
[0065]
Accordingly, the resolution can be switched and the rotation speed of the polygon mirror 102 can be set, and an image can be formed on the photosensitive drum 108 at an appropriate scan speed.
[0066]
When the scanner rotation speed is changed according to a resolution switching signal from the resolution switching switch 140, the SOS gain control unit 126 adjusts the gain of the SOS sensor 128 accordingly.
[0067]
As shown in FIG. 5, when the SOS gain control unit 126 switches the scanner rotation speed between high speed and low speed, the gain changeover switch 132 is switched accordingly. That is, it is turned on at a low speed (slow) and turned off at a high speed (fast). As a result, the output voltage Vouts at low speed becomes Vouts = (1 + RfRg / (Rf + Rg)) RhVin, while the output voltage Voutf at high speed becomes Voutf = (1 + Rg / Rh) Vin. At this time, the output voltage Voutf at high speed becomes higher than the output voltage Vouts at low speed.
[0068]
As a result, when the scanning speed is high, the SOS gain increases, and when the scanning speed is low, the SOS gain decreases. Thus, the SOS gain can be easily adjusted according to the scan speed.
[0069]
Therefore, even if the scanning speed becomes high and the amount of incident light on the light receiving surface of the SOS sensor 128 decreases, the amplification factor of the SOS sensor 128 increases, and the SOS sensor 128 can reliably detect one scan of the light beam. it can.
[0070]
Note that if the high resolution is set in the single mode in which the scanner speed is the fastest, one of the LDDs 112A and 112B not used for writing may be turned on for the SOS period instead of increasing the SOS gain. Good. This allows the SOS sensor 128 to more reliably detect the output beam.
[0071]
Next, a description will be given of how the light amount variable range is changed when the resolution is switched.
In the LDDs 122A and 122B to which the image data has been sent, the LDs 122A and 122B are turned on according to the light amount control signal instructed from the light amount control circuit 120. The PD amount provided at the DLD 112 detects the amount of LD light at that time. When detected by the PD 114, the PD 114 outputs a monitor current Is proportional to the amount of emitted light.
[0072]
Here, when the resolution is switched to 600 dpi or 300 dpi by the resolution switching signal, the light amount switching circuit 142 changes the light amount of the output beam output from the DLD 112 by changing the monitor current detection resistance value corresponding to the detection sensitivity. adjust.
[0073]
When the resolution is switched to 600 dpi by the resolution switching signal, the resolution switch 140 of the light amount switching circuit 142 is turned off.
[0074]
When the resolution changeover switch 140 is turned off, the monitor current Is does not flow through the monitor current detection resistor Ra. At this time, since the input voltage of the comparator 144 has a high impedance, the monitor current Is of the PD 114 flows through the monitor current detection resistor Rb. Accordingly, the value of the light amount monitor voltage Vroff of the PD 114 can be obtained by Vroff = Rb × Is. As a result, the light quantity is adjusted by comparing the obtained Vroff with the reference voltage Vref.
[0075]
On the other hand, when the resolution is 300 dpi, the resolution changeover signal turns on the resolution changeover switch 140.
[0076]
When the resolution switch 140 is turned on, the monitor current Is is applied to the combined resistance of the monitor current detection resistances Ra and Rb. Therefore, the light amount monitor voltage Vron can be obtained by Vron = (Ra × Rb / (Ra + Rb)) × Is. As a result, the light amount is adjusted by comparing the obtained Vron with the reference voltage Vref.
[0077]
Here, since the control voltage Vron = Vroff is adjusted by the reference voltage Vref, the monitor current Is is increased until Vroff = Vron when the resolution changeover switch 140 that reduces the combined resistance is off. As a result, the light amounts of the LDDs 112A and 122B increase. Therefore, in the case of 600 dpi, if the monitor current detection resistors Ra and Rb have the same resistance value, the light amount of the LDDs 112A and 112B becomes twice as large as 300 dpi.
[0078]
FIG. 4 is a graph showing the relationship between the light quantity and the control voltage. Here, the X-axis direction indicates a control voltage (Vron, Vroff) for changing the light amount, and the Y-axis direction indicates the light amount. As shown in the graph, the single mode and the dual mode have different light amount variable ranges, and when the same control voltage is applied, the light amount in the single mode is twice that in the dual mode. Further, by switching between the variable light amount range in the Single mode (see arrow S) and the variable light amount range in the Dual mode (see arrow D), the light scanning device 100 has a wider variable light amount range (see arrow E). Will have.
[0079]
Thereby, the light amount variable range of the LDDs 112A and 112B can be easily changed according to the number of output beams according to the resolution. As a result, the LDDs 112A and 112B emit a predetermined amount of light for changing the set amount of light on the optical scanning device according to factors such as deterioration in the sensitivity of the photosensitive drum 108, contamination of optical components, and reduction in the amount of light due to deterioration of the LDDs 112A and 112. Not only the variable range but also the variable amount of light can be further changed in accordance with the resolution switching. For this reason, even the LDDs 122A and 112B having a small light amount variable range can have a large light amount variable range.
[0080]
Therefore, by switching the monitor current detection resistance value in conjunction with the resolution switching signal, the light amount variable range of the LDDs 112A and 112B can be easily changed.
[0081]
In the present embodiment, the case of two beams has been described as an example. However, even in the case of three or more beams, the light amount can be similarly changed by increasing the number of interlocking resistors R according to the resolution switching signal. If N interlocking resistors are used for N beams, a variable light amount range of N times can be obtained.
[0082]
In the present embodiment, the monitor current detection resistors Ra and Rb, which are interlocking variable resistors, are used to switch the light amount of the output beam output from the DLD 112 by the resolution switching signal. However, the present invention is not limited to this.
[0083]
FIG. 6 shows another light amount switching circuit 160.
The light amount switching circuit 160 includes a PD light amount control circuit 162 and a light amount control circuit 120. The PD light amount control circuit 162 includes an electronic volume (hereinafter abbreviated as EVR) 164. One end of the EVR 164 is connected to the PD 114, whereby the monitor current Is is applied to the EVR 164. The other end of the EVR 164 is connected to the comparator 144 of the light amount control circuit 120, so that the light amount monitor voltage Vr is input to the comparator 144. The EVR 164 changes a resistance value according to a voltage applied from the outside.
[0084]
The beam switch 166 is connected to the EVR 164. The beam switch 166 switches between a single mode and a dual mode by switching a terminal that is turned on in response to a resolution switching signal. Hereinafter, the side that is turned on in the Single mode is called the Single side, and the side that is turned on in the Dual mode is called the Dual side.
[0085]
Monitor current detection resistors Rc and Rd are connected to the beam switch 166. The monitor current detection resistor Rc is connected to the Dual side and the Single side of the beam switch 166, respectively. On the other hand, the monitor current detection resistor Rd is connected to the Single side at one end, and is grounded at the other end. The monitor current detection resistors Rc and Rd have the same resistance value.
[0086]
A resistance Re is connected to the dual side of the beam switch 166. When the beam switch 166 is switched to the dual mode, the voltage applied to the EVR 164 can be set by adjusting the value of the resistor Re. .
[0087]
When such a light amount switching circuit 160 is used, when the beam switch 166 is in the dual mode, a voltage is applied to both the monitor current detection resistors Rc and Rd.
[0088]
On the other hand, in the single mode, the voltage is a half of that in the dual mode because it is divided by the monitor current detection resistors Rc and Rd. When this voltage is applied to the EVR 164, the resistance value of the EVR 164 becomes half, so that the light amount is increased until the monitor current Is doubles. As a result, the amount of light becomes a double value. Similarly, in the case of three beams or more, the number of terminals of the monitor current detection resistor R and the resolution switch 140 can be increased, and the light amount can be changed according to the resolution switch signal.
[0089]
Thus, similarly to the above, the light amount and the light amount variable range can be easily changed, and a light beam with an appropriate light amount can be output even when the resolution is switched.
[0090]
In the present embodiment, the light amount of the light beam output from the DLD 112 is adjusted by the light amount switching circuits 142 and 160, but the method of adjusting the light amount of the light beam for scanning and exposing the photosensitive drum 108 is not limited thereto.
[0091]
7 and 8 show an optical scanning device 170 according to another embodiment. Note that components having the same functions and effects as those of the optical scanning device 100 described above are denoted by the same reference numerals and description thereof will be omitted.
[0092]
The optical scanning device 170 is disposed between the DLD 112 and the polygon mirror 102 such that the light beam can be inserted into or removed from the optical path of the light beam output from the DLD 112. Further, the light amount adjustment filter 172 is arranged in the vicinity of the optical path of the light beam and where the light is focused. The light amount adjustment filter 172 has a transmittance of 50% for the light beam output from the DLD 112.
[0093]
As shown in FIG. 8, the controller 176 of the optical scanning device 170 is provided with a PD light amount control unit 180 that performs light amount control so as to maintain the light amount detected by the PD 114 at a predetermined value.
[0094]
Further, the controller 176 is provided with a filter insertion control unit 178, and the filter insertion control unit 178 is connected to the light amount adjustment filter 172 via the driver 174. Filter insertion control section 178 outputs a filter insertion signal to driver 174 according to the resolution switching signal. The driver 174 is driven in accordance with a signal from the filter insertion control unit 178 to move the light amount adjustment filter 172.
[0095]
Next, the light amount adjustment processing in the optical scanning device 170 will be described.
When a resolution switching signal is input to the controller 176, a Single mode or a Dual mode is selected according to the resolution switching signal.
[0096]
Here, the amount of light in the Dual mode is half the amount of light per LDD 112A, 112B compared to the amount of light in the Single mode. That is, compared to the case where one of the two LDDs 112A and 112B is used, if both are used, the amount of light per unit becomes １ ／.
[0097]
Therefore, the light amount is set in the single mode, the LDDs 112A and 112B are driven together, and the light amount adjusting filter 172 is inserted on the optical path to reduce the light amount of the light beam to 50%.
[0098]
Therefore, by adjusting the light amount in the single mode and driving the LDDs 112A and 112B, it is not necessary to greatly change the light amount variation per LDD 112A and 112B, and the light amount adjustment filter 172 is inserted on the optical path of the light beam. -The light amount can be easily adjusted simply by detaching.
[0099]
When the light amount adjustment is performed using the light amount adjustment filter 172, the width of the light amount variable range and the light amount adjustment range can be changed according to the light amount adjusted by the light amount adjustment filter 172.
[0100]
FIG. 9 shows another example of the light amount adjustment filter 172.
As shown in FIGS. 9A and 9B, the light amount adjusting filter 172 may be configured by a plurality of different filters 180 to form a set of light amount adjusting filters 182 and 184. The number of such filters 180 can be appropriately determined according to the number of light sources. Further, depending on the form of such a pair of light amount adjusting filters 182 and 184, the form of insertion / removal of the light beam onto / from the optical path can be appropriately changed. In the light amount adjustment filter 182 shown in FIG. 9A, each filter 180 is inserted on the optical path of the output beam by rotating in the direction of arrow M about the axis 181. In the light amount adjustment filter 184 shown in FIG. 9B, each filter 180 is inserted on the optical path of the output beam by rotating in the direction of arrow L around the axis 185.
[0101]
Further, as shown in FIG. 8C, a light amount adjustment filter 186 using both the filter 180 and the slit 188 may be used. Thus, the light amount can be adjusted using the filter 180 and the beam diameter can be easily changed according to the resolution using the slit 188. In the light amount adjustment filter 186, each filter 180 is inserted on the optical path of the output beam by moving in the direction of arrow K.
In the optical scanning device 170, the position of the light amount adjustment filter 172 is set between the DLD 112 and the polygon mirror 102, but is not limited to this. The insertion place is economical because the filter near the LD is condensed and the filter can be made small, but it can be placed between the DLD 112 and the photosensitive drum 108. Further, the change of the transmittance by such a filter may be performed by mechanically inserting the filter on the optical path of the light beam, or may be electrically changed by using a liquid crystal or the like.
[0102]
In the present embodiment, the controller 116 can be provided with a resolution switching prohibition unit that prohibits a change in resolution during the formation of an image that is one section, for example, for each page.
[0103]
During the resolution switching, the SOS cycle is also undefined because the rotation speed of the scanner motor is undefined. In such a state, accurate synchronization cannot be achieved, and rotation abnormality detection is activated or two images are output on the same sheet despite the normal operation. When the resolution is switched within the same page, the resolution switching prohibition unit can prohibit images having different resolutions from being present on the same sheet. Also, it can be provided.
[0104]
Further, the controllers 116 and 176 according to the present embodiment include a beam output prohibiting unit that prohibits the output of the light beam by the DLD 112 during resolution switching and an SOS detection prohibiting unit that prohibits SOS detection during resolution switching. Each or both can be provided.
[0105]
Switching the resolution often involves changing the number of revolutions of the scanner motor, and it takes time to change. For this reason, the beam output prohibiting unit and the SOS detection prohibiting unit prohibit the output of the light beam and the SOS detection during such invalid time, respectively, and cause the fatigue of the photosensitive drum 108 due to the LD emission during this period. Waste of toner can be prevented.
[0106]
When a resolution change request is issued according to the resolution switching prohibiting means and the SOS detection prohibiting means, the LDDs 112A and 112B can be turned off and the LDDs 112A and 112B can be turned on after the resolution changing step is completed.
[0107]
In the present embodiment, the case of the DLD 112 including the two LDDs 112A and 112B has been described as an example. However, the same can be applied to a Multi Beam LD having three or more beams.
[0108]
In the present embodiment, the resolution is switched using both the number of light beams output from the DLD 112 and the number of rotations of the scanner motor 104. However, even when the resolution can be switched only by the number of light beams. The same effect as described above can be obtained.
[0109]
Further, in the present embodiment, the number of beams is switched according to the resolution switching signal, and the light amount switching processing and the like are performed in conjunction therewith, but the invention is not limited to this. For example, the switching of the number of beams and the switching of the resolution may be performed separately, and the light amount switching processing may be performed only in response to the switching of the number of beams.
[0110]
【The invention's effect】
According to the present invention, even in an optical scanning device in which the resolution is changed by switching the number of beams, the light amount variable range can be easily changed, so that the rotation speed of the light beam deflecting unit is not increased, It is possible to cope with higher speed and higher resolution, and it is possible to prevent noise and temperature rise due to an increase in the rotation speed of the light beam deflecting means. Further, even in an optical scanning device capable of switching the resolution by using both the number of rotations and the number of beams of the light beam deflecting means, the light quantity variable range can be easily changed, and the resolution can be changed in accordance with the fine resolution switching step. It can be easily changed to an appropriate light amount variable range.
[0111]
Further, by switching the amplification factor of the synchronization detection sensor according to the resolution, the synchronization detection sensor can reliably detect the light beam, and the synchronization detection sensor generated by changing the light amount variable range can be changed. Malfunction can be prevented.
[0112]
Furthermore, by having the beam diameter switching means, the beam diameter of the output beam can be changed according to the resolution, and a light beam having an appropriate beam diameter according to the light amount can be output.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an optical scanning device according to an embodiment of the present invention.
FIG. 2 is a block diagram of the optical scanning device according to the embodiment.
FIG. 3 is a circuit diagram of a light quantity switching circuit according to the present embodiment.
FIG. 4 is a graph showing an example of a relationship between a control voltage and a light amount in the optical scanning device according to the present embodiment.
FIG. 5 is a circuit diagram of an SOS gain control unit of the optical scanning device according to the present embodiment.
FIG. 6 is a circuit diagram of another light amount switching circuit according to the present embodiment.
FIG. 7 is a schematic diagram of another optical scanning device according to the embodiment of the present invention.
FIG. 8 is a block diagram of another optical scanning device according to the present embodiment.
9A is a schematic perspective view of a light amount adjustment filter according to the embodiment, FIG. 9B is a schematic plan view of another light amount adjustment filter according to the embodiment, and FIG. FIG. 9 is a schematic plan view of another light amount adjustment filter according to the embodiment.
[Explanation of symbols]
100 Optical scanning device
102 Polygon mirror (light beam deflecting means)
104 Scanner motor (drive means)
108 Photosensitive drum (photosensitive material)
112 DLD (Laser Diode)
114 PD (light emission output detection means)
116 controller
118 Light control unit
120 Light intensity control circuit (beam number switching means)
122 LDD
124 PD light intensity control circuit
126 SOS gain control unit
128 SOS sensor (synchronous detection sensor)
134 Scanner rotation speed controller
136 Beam diameter switching control unit
142 Light intensity switching circuit (light intensity switching means)
160 light quantity switching circuit (light quantity switching means)
162 PD light quantity control circuit
172 Light intensity adjustment filter (light intensity switching means)
178 Filter insertion control unit

Claims (9)

In an optical scanning device that irradiates a photosensitive material while scanning a light beam corresponding to input data,
A laser diode capable of outputting two or more light beams,
Beam number switching means for switching the number of light beams of the laser diode in accordance with switching of resolution;
Light amount switching means for switching a light amount variable range of the laser diode according to the switched resolution;
An optical scanning device, comprising: In an optical scanning device that irradiates a photosensitive material while scanning a light beam corresponding to input data,
A laser diode capable of outputting two or more light beams,
By rotating and driving, a light beam deflecting unit that deflects the light beam from the laser diode toward the photosensitive material,
Rotation speed switching means for switching the rotation speed of the light beam deflecting means in accordance with the switching of resolution;
Beam number switching means for switching the number of light beams of the laser diode in accordance with switching of resolution;
Light amount switching means for switching a light amount variable range of the laser diode according to the switched resolution;
An optical scanning device, comprising: The light amount switching unit includes a light amount adjusting unit that adjusts a light emitting amount of the laser diode, and changes a light amount variable range by switching a detection sensitivity of the light amount adjusting unit in accordance with a number of beams according to a resolution. The optical scanning device according to claim 1 or 2, wherein: The light amount switching means includes a light amount adjustment filter inserted on an optical path of the laser diode to adjust a transmitted light amount of the laser diode, and the light amount adjustment filter has a light amount corresponding to the number of beams switched according to a resolution. 3. The optical scanning device according to claim 1, wherein the light amount variable range is changed by adjusting the transmittance so as to be a beam transmission amount. 5. The apparatus according to claim 1, further comprising: a synchronous detection sensor amplification switching unit that switches an amplification factor of a synchronous detection sensor that detects a start of scanning of the light beam in accordance with a change in resolution. 6. An optical scanning device according to claim 1. 6. The optical scanning device according to claim 5, wherein, when the synchronization detection sensor operates, the number of light beams detectable by the synchronization detection sensor is increased. The optical scanning device according to claim 1, further comprising a beam diameter switching unit configured to switch a beam diameter of the light beam from the laser diode in accordance with a change in resolution. The beam diameter switching means is inserted on the optical path of the laser diode to adjust the amount of light transmitted by the laser diode, and transmits the light beam so as to have a light beam transmission amount corresponding to the number of beams switched according to the resolution. 8. The optical scanning device according to claim 7, wherein the optical scanning device is integrated with a light amount adjusting filter for adjusting a ratio. In conjunction with the switching of the beam number switching means of the laser diode, switching of the detection sensitivity of the light quantity adjusting means, switching of the light quantity adjusting filter, switching of the amplification factor of the synchronous detection sensor, or switching of the beam diameter of the light beam. 8. The optical scanning device according to claim 3, wherein the optical scanning device performs:

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