JPH0441807B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a beam scanning device for scanning, for example, a photoreceptor of a laser printer while turning a laser beam on and off, and particularly relates to a two-beam scanning device that enables color printers. .

FIG. 1 shows an example of the configuration of a conventional beam scanning device of this type. The laser beam exiting the HeNe laser light source 11 passes through a condenser lens 12 and enters an ultrasonic optical modulator 13 . FIG. 2 is a diagram showing the principle of the ultrasonic optical modulator 13, and when an ultrasonic wave 15 is applied to the crystal 14 of the optical modulating element from a specific direction, the laser beam is directed at an angle (2〓) twice that of the incident direction〓. Bragg diffraction. This diffraction angle 2 is determined by the ultrasound speed v, the ultrasound frequency f, and the laser beam wavelength (2 = f/v). Therefore, when the ultrasonic wave is turned on and off, the laser beam emitted from the ultrasonic optical modulator 13 switches between the zero-order direction and the first-order direction. For example, if masking is performed to cut off the zero-order light, the laser beam This causes the beam to turn on and off. The condenser lens 12 adjusts the laser beam diameter d to the desired response time (d/v).
This is to reduce the diameter to a value that achieves this.

The laser beam exiting the ultrasonic optical modulator 13 passes through a collimator lens 16 to become a parallel beam again, and then its diameter is expanded by a beam expander 17. The beam expander 17 consists of two sets of lenses 17a and 17b, and in principle is equivalent to using a telescope in reverse. The laser beam exiting this beam expander 17 is
After being reflected by the reflecting surface 19 of the rotating polygon mirror 18, it reaches the photosensitive drum 21 via the f= lens 20, and according to the on/off generated by the ultrasonic light modulator 13, an on/off spot is formed on the photosensitive drum 21. , that is, a scanning line 22 is drawn. This scanning line 22 is used to generate, for example, a distribution of charging and non-charging of the photoreceptor constituting the photoreceptor drum 21, and one reflection surface 19 of the rotating polygon mirror 18 is used to generate a distribution of charging and uncharging of the photoreceptor drum 21. One scanning line 22 results in the axial direction. As a result of the continuous rotation of the polygon mirror 18 and the rotation of the photoreceptor drum 21, a latent image pattern of continuous scanning lines 22 is formed on the photoreceptor drum 21. For example, a charged developer is then supplied to the photoreceptor drum 21, and printing is performed according to a conventional printing method that utilizes charging and uncharging of the photoreceptor. Note that the reference numeral 23 in FIG. 1 indicates a mirror for bending the optical path of the laser beam.

The reason why the diameter of the laser beam is expanded by the beam expander 17 is to make the diameter of the beam that reaches the photoreceptor drum 21 appropriate for the size of the photoreceptor drum 21. This beam diameter may be determined by, for example, the material of the photoreceptor drum 21, the material of the photoreceptor drum 21,
The optimum diameter is determined by factors such as corona discharge generated above. Also, unlike a normal photographic lens or a Fourier transform lens, the f= lens 20 has a focal length f,
There is a characteristic that the image height y is y=f with respect to the incident angle, and therefore the laser beam image reflected by the polygon mirror 18 can be linearly reproduced on the photoreceptor drum 21. Widely used in optical systems for seed printing.

By the way, this conventional optical system is monochromatic (usually
It is configured only for printing (black). In other words, conventional laser beam printers are used only for monochromatic printing, and the conventional optical system described above cannot be used as is when printing in color.

The present invention was made for the purpose of creating an optical system that can handle color printing while using the main parts of the conventional optical system as is. An ultrasonic optical deflector is installed to separate the laser beam into two directions at a predetermined period, and the two beams separated by the ultrasonic optical deflector form two scanning lines on the photoreceptor. It is characterized by These two scanning lines are used for different colors,
In addition, by using two sets of these two-beam scanning devices, it becomes possible to use a color laser printer.

The invention will now be described with reference to the illustrated embodiments. 3 and 4 show an embodiment of a two-beam scanning device according to the present invention, and the same components as in FIG. 1 are given the same reference numerals. Reference numeral 30 is an ultrasonic optical deflector added in the present invention, and 31 is an optical angle amplifier installed to enlarge the separation angle of the beam separated by the ultrasonic optical deflector 30 to make the present invention more effective. Both are installed between the collimating lens 16 and the beam expander 17.

The ultrasonic optical deflector 30 has the same structure as the ultrasonic optical modulator 13 in principle, but the response speed for diffracting the laser beam is much slower than that of the ultrasonic optical modulator 13. By doing so, the ultrasonic optical modulator 1 at the point where the diffraction angle is large is
It is different from 3. Specifically, such properties are obtained by changing the crystal axis direction of the elements constituting the deflector. This ultrasonic light deflector 30 is further different from the ultrasonic light modulator 13 in that the Bragg diffracted laser beam is also irradiated onto the photoreceptor drum 21. In the ultrasonic light modulator 13, the plug-diffracted laser beam is masked, so it does not reach the photosensitive drum 21. Bragg diffraction in the ultrasonic light deflector 30 is timed so that it occurs every time one scanning line 22 is drawn on the photoreceptor drum 21. This timing can be determined depending on factors such as the number of rotations of the polygon mirror 18 and the number of reflective surfaces 19;
A beam sensor may be provided on the incident side in the axial direction, and the ultrasonic waves applied to the ultrasonic light deflector 30 may be controlled so that diffraction occurs when the beam is incident on the sensor.

When the laser beam is deflected at a predetermined period by the ultrasonic light deflector 30 in this manner, two scanning lines 22 are drawn alternately on the photosensitive drum 21 at a distance l (FIG. 4) apart. Therefore, for example, if one of these two beams is used for red and the other for blue, and another two-beam scanning device is installed to draw scanning lines 22 for yellow and black, by combining the two, Can print in color. Specifically, this color printing involves, for example, charging two scanning lines with positive and negative charging with different on/off polarities;
Alternatively, the first development in two-color development can be realized by non-contact development without contacting with toner, but the present invention does not require this printing method.

The optical angle amplifier 31 is necessary when the separation angle of the laser beam by the ultrasonic optical deflector 30 cannot be set sufficiently due to the relationship with the beam expander 17. As mentioned above, the beam expander 17 is used to expand the laser beam diameter, but when the beam diameter is expanded, the separation angle of the two beams that were separated in the previous stage becomes smaller. That is, in FIG. 5, if the separation angle of the two beams B1 and B2 entering the beam expander 17 is 〓 ₂ and the separation angle of the two beams emitted from the beam expander 17 is 〓 ₃ , then the magnification of the beam expander 17 is As m, there is a relationship of 〓 ₃ (1/m)・〓 ₂ . For this reason, if the separation angle by the ultrasonic light deflector 30 is small, a case may occur in which the two beams incident on the polygon mirror 18 cannot have the separation angle necessary for colorization. Optical angle amplifier 31
In order to prevent such a situation, the beam is provided to expand (amplify) the separation angle of the beam before it enters the beam expander 17.

FIG. 6 shows a specific example of this optical angle amplifier 31. This optical angle amplifier 31 includes two reflecting mirrors 32,
33, and these reflecting mirrors 32, 33
A space is formed between them through which the first beam B1 passing through the optical axis passes. The reflecting mirrors 32 and 33 function to reflect the other beam and increase the separation angle from the original beam by the angle of reflection. Beam B1 that now passes between the reflecting mirrors 32 and 33, and beam B that is reflected by the reflecting mirrors 32 and 33.
Assuming that the separation angle 〓 ₁ between the beam B1 and the beam before entering the optical angle amplifier 31 is 2.7°, the angles that the reflecting surfaces of the reflecting mirrors 32 and 33 make with the plane perpendicular to the beam B1 are 16.35° and 22.5°, respectively.゜, this optical angle amplifier 31
The separation angle of the two beams exiting 〓 ₂ is 15°. By appropriately setting the angles of the reflecting mirrors 32 and 33 in this manner, the separation angle of the two separated beams can be increased. Further, in the illustrated example, by making the angle of the reflecting mirror 33 adjustable, the amplification angle can be changed.

This optical angle amplifier 31 is theoretically not necessary if the separation angle of the two beams obtained by the ultrasonic optical deflector 30 is large, but at present, depending on the ultrasonic optical deflector 30, the angle of separation is at most several degrees. Only a separation angle of . Therefore, it is highly necessary to use the optical angle amplifier 31, but if an ultrasonic optical deflector 30 that can provide a large separation angle is obtained, the optical angle amplifier 31 will become unnecessary.

Note that one of the two beams B1 and B2, for example beam B1, which is separated by the ultrasonic optical deflector 30 and whose separation angle is increased by the optical angle amplifier 31, is connected to the f〓 lens as shown by the solid line in FIG. However, the beam B2 passes through a plane that does not include the optical axis of the f= lens 20, as shown by a broken line. Therefore, scanning line 2 by beam B2
2 is not a straight line but curved as shown exaggerated in the figure, but this curvature can be corrected by adjusting the Bragg diffraction angle by the ultrasonic optical deflector 30, so it does not pose a practical problem. do not have. Similarly, an error in the surface tilt of the reflective surface 19 of the polygon mirror 18 also causes a pitch error in the scanning line 22, but this error can also be corrected by the ultrasonic light deflector 30.

In the above embodiments, the present invention was explained by taking as an example a case in which a photoconductor drum is irradiated with a beam separated into two beams, but the present invention also describes a case in which a laser beam is irradiated onto an irradiation body other than a photoconductor. The same applies to cases where In other words, it is applicable to all cases where the laser beam irradiated onto the irradiator is separated into two beams.

As described above, in the present invention, a laser beam emitted from a single laser light source is on-off modulated by an ultrasonic optical modulator, and this on-off modulated laser beam is divided into two by another ultrasonic optical deflector. Since the laser beam is separated into two beams, for example, scanning lines for different colors can be drawn using these two beams, and a color laser beam printer can be realized. Since the present invention performs the on/off modulation of the laser beam and the splitting of the laser beam using separate ultrasonic modulators, there is no need to increase the on/off modulation speed and the distance between the split beams. It is possible to simultaneously satisfy the demand for increasing the size accordingly.

[Brief explanation of drawings]

Fig. 1 is a plan view showing an example of an optical system used in a conventional laser beam printer, Fig. 2 is a schematic diagram showing the operation of an ultrasonic optical modulator, and Fig. 3 is a two-beam scanning optical system of the present invention. FIG. 4 is a plan view showing an embodiment of the system, FIG. 4 is a perspective view of the main parts, FIG. 5 is an optical path diagram illustrating the phenomenon of reducing the beam separation angle by a beam expander, and FIG. 6 is an example of an optical angle amplifier. Optical path diagram shown,
FIG. 7 is a perspective view schematically showing the state of curvature of the scanning line of two beams by the f lens. 11... HeNe laser light source, 12... Condensing lens, 13... Ultrasonic light modulator, 16... Collimating lens, 17... Beam expander, 18...
...Rotating polygon mirror, 19...Reflecting surface, 20...f
Lens, 21... Photosensitive drum, 22... Scanning line, 30... Ultrasonic optical deflector, 31... Optical angle amplifier, 32, 33... Reflecting mirror.

Claims (1)

[Claims] 1. A laser light source; An ultrasonic light modulator that modulates the laser beam from this laser light source on and off; An ultrasonic light deflector that deflects the turned on and off laser beam and separates it into two directions; and A two-beam scanning device comprising: beam scanning means for scanning two separated beams onto an irradiation body. 2. In claim 1, an optical angle amplifier is disposed behind the ultrasonic optical deflector to expand the separation angle of the laser beam separated by the ultrasonic optical deflector. Beam scanning device.