JPS6249315A - Laser recording device - Google Patents

Abstract

PURPOSE:To vary the diameter of a spot of a semiconductor laser beam on a recording medium with a simple constitution by changing the optical intensity of the laser beam in accordance with recording magnification. CONSTITUTION:The electric potential VA of a point A is changed in accordance with the recording magnification. Namely, since the VA is increased and the output voltage of a comparator 17 is reduced in accordance with the increase of the recording magnification, the collector current of a transistor (TR) 14 is increased and the diameter of a spot is increased. When the recording medium is decreased on the contrary, the VA is reduced, the output voltage of the comparator 17 is increased, the collector current of the TR 14 is reduced, and 17 is increased, the collector current of the TR 14 is reduced, and the driving current of a semiconductor laser 13 is reduced. Consequently, the optical intensity is reduced and the diameter of the spot is reduced. Since the driving current of the laser 13 is continuously changed by continuously changing the recording magnification, the diameter of the beam spot is also continuously changed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a laser recording device that can change the spot diameter of a laser beam with a simple configuration.

(Prior Art) Recently, laser recording devices (so-called laser printers) that record images using laser beams have been developed and put into practical use. A laser recording device modulates a laser beam with an electric signal representing image information, forms image information on a photoreceptor with the laser beam, and records the image information as a visible image by electrophotographic processing or the like.

When changing the recording magnification in this type of laser recording device, it is desirable to make the spot diameter of the laser beam on the recording medium variable in accordance with the magnification.

, Fig. 2 shows a schematic configuration of a scanning optical system of a conventional laser recording device, where l is a laser light source such as a semiconductor laser, 2 is a collimator lens that makes the beam parallel and gives it a desired shape, and 3 is a beam 4 is a rotating polygon mirror for scanning that rotates at high speed and deflects the beam; 5 is an fO lens that forms an image at a distance proportional to 0 with respect to the optical axis; 6 is a photoreceptor that is a recording medium. Then, an electrostatic latent image of a recorded image is formed on this.

Conventionally, in order to change the spot diameter of the laser beam, a second
As shown in the figure, a method has been proposed in which the beam expander 3 is configured with, for example, two sets of lens systems 3a, 3b and 3c, 3d, and these are selectively switched and used by a rotation operation according to the recording magnification. (For example, Japanese Patent Application Publication No. 1986-
No. 17716). A method of using a zoom lens instead of the beam expander 3 is also known.

In all of these methods, the switching mechanism and device itself are large, and the method using a beam expander by switching makes it impossible to continuously vary the beam spot diameter, and the method using a zoom lens requires a zoom lens mechanism. The problem is that it becomes very expensive.

Incidentally, the light intensity of the laser beam has a Gaussian distribution as shown in FIG. 3, and the intensity distribution is expressed by the following equation.

-a2!2 I=I. e (a is a constant here) The beam diameter at that time can be determined from the value of X when the light intensity I becomes l/e2 of the maximum intensity ■o, and the beam diameter in this case is Do=2X1 /a This value is constant regardless of the maximum light intensity Ik.

However, if the threshold value of the light intensity necessary for the laser beam to be recorded on the recording medium is α, then the actual recorded slot diameter d is quite difficult to understand from Figure 4, even if the beam diameter is constant. It can be seen that it varies depending on the strength. In other words, the greater the light intensity I (II
>I. ) Spot diameter d also increases (dB > dO)
.

(Objective and Structure of the Invention) The present invention has been made in view of the above points, and an object of the present invention is to make it possible to vary the spot diameter of a semiconductor laser beam on a recording medium with a simple configuration. In order to achieve this, the optical intensity of the laser beam was changed according to the recording magnification.

(Example) The present invention will be explained below based on the drawings.

FIG. 1 shows a semiconductor laser drive circuit used in a laser recording device according to the present invention, and 10 is a magnification selection lever;
The resistance value R of the variable resistor 11 changes by lever scanning.

The recording magnification may be varied stepwise or continuously, and the resistance value R increases as the recording magnification increases. A fixed resistor 12 is connected in series with the variable resistor 11, and the potential VA at the connection point A is determined depending on the selected recording magnification. On the other hand, 13 is a semiconductor laser, and the drive current flowing through the laser 13 is controlled by the transistor 14 connected in series.

The optical output, that is, the amount of light from the semiconductor laser 13 is detected by the photodiode 15, and a voltage drop proportional to the current flowing through the photodiode 15 is caused by the resistor 16, thereby determining the potential at point B.

17 compares the potential VA at point A and the potential VB at point B, and
When B>VA(7), the comparator drives the transistor 14 according to (VB - VA), and the drive current of the semiconductor laser 13 is controlled by the output of this comparator 17.

In this case, the potential VA at one point A changes depending on the recording magnification, and as the recording magnification increases, VA increases.At this time, the output voltage of the comparator 17 decreases, so the transistor 14
The collector current increases, and the drive current of the semiconductor laser 13 increases. As a result, the light intensity increases and the spot diameter becomes larger as shown in FIG. Conversely, when the recording magnification is lowered, VA becomes smaller, the output voltage of the comparator 17 becomes larger, the collector current of the transistor 14 decreases, and the drive current of the semiconductor laser 13 decreases. As a result, the light intensity decreases and the spot diameter becomes smaller as shown in FIG. Since the driving current of the semiconductor laser 13 changes continuously by continuously changing the recording magnification, the beam spot diameter also changes continuously.

Note that the drive circuit shown in FIG. 1 performs automatic feedback control of the laser light output and has an automatic light amount adjustment function, but since this point is not the gist of the present invention, a description thereof will be omitted.

(Effects of the Invention) As explained above, in the present invention, since the light intensity of the laser beam is changed according to the recording magnification, the laser beam can be generated by using an inexpensive and simple circuit configuration without increasing the size of the device or mechanism. The spot diameter can be made variable.

[Brief explanation of the drawing]

Fig. 1 shows the semiconductor laser drive circuit of the laser recording device according to the present invention, Fig. 2 shows the schematic structure I & diagram of the scanning optical system of the laser recording device, and Fig. 3 shows the relationship between the beam diameter and light intensity of the laser beam. The intensity distribution diagram shown in FIG. 4 is a diagram showing changes in the spot diameter depending on the light intensity of the laser beam. 1... Laser light source, 2, 4... Collimator lens,
3... Beam expander, 4... Rotating polygon mirror, 5
...fO lens, 6...photoreceptor, lO...magnification selection/<-, 13...semiconductor laser, 15...photodiode, 17...comparator patent applicant Roku Konishi Photography Kogyo Co., Ltd. Agent Patent Attorney Hiroshi Suzuki Figure 1 Figure #12 Figure

Claims (1)

[Claims] 1. A laser recording device that records an image by scanning a laser beam, characterized in that the device is provided with means for changing the light intensity of the laser beam in accordance with a recording magnification.