JPS6050509A - Optical beam scanning type picture input device - Google Patents

Abstract

PURPOSE:To make a light quantity constant on the surface to be scanned, by varying a light quantity of a laser light source or a sensitivity of a photoelectric converting element, so as to be in inverse proportion to a reflection factor. CONSTITUTION:A laser driving circuit 2 drives on and off a semiconductor laser 3 by switching transistors 30, 31. This semiconductor laser 3 consists of a light emitting element LD and a photodetector PD, and the light emitting quantity of the light emitting element LD is detected by the photodetector PD and fed back to an optical output controlling circuit 32. The optical output controlling circuit 32 controls a current capacity of a current source 33 and makes the semiconductor laser 3 hold an optical output at a constant value.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a scanning type image input device using a laser beam.
% related to the method of forming a reflective trowel surface protective film and the uniformity of image reading signals.

[Background of the invention]

Problems in a laser beam scanning type image input device using a rotating polygon mirror will be explained with reference to FIGS. FIG. 1 is a configuration diagram of a scanning type image input device using a laser beam, and a laser drive circuit 2 drives a semiconductor laser 3 with a constant output in response to a command from a signal processing device 1. Semiconductor laser 3
The emitted laser beam is collimated and turned into a parallel beam by a meter lens 4, deflected and scanned by a rotating polygon mirror 5, and focused onto a scanned surface a by an F0 lens 6. The reflected light from the scanned surface a is converted into an electric signal by the photoelectric conversion element 9, and is transmitted to the signal processing device 1 via the 7th amplifier 13 for signal amplification. The signal processing device 1 digitally encodes the obtained image a and stores it in a storage device (not shown). As a reference signal for capturing image information, a part of the laser beam 7 is guided by a mirror 1 (1) to a beam conversion element 1IVc, and the beam position is detected by a beam position detection circuit 12 from its output. By moving 8 in the direction b, image information can be read.

Here, the amount of light reflected from the surface to be scanned is proportional to the amount of incident light. Therefore, it was necessary to make the amount of light incident on the surface to be scanned uniform, and this was achieved by setting the laser drive circuit 2 to constant output operation. The transmittance of the collimator lens 4 and Fθ lens 6 is uniform unless the influence of dirt etc. is excluded, but
Rotating polygon mirrors are stable because the flexibility of the angle of incidence and reflection varies with rotation, and the reasons for this will be discussed below.

For a rotating polygon mirror, a base material is mirror-finished or a mirror-finished surface is provided on the base material, and a protective film is formed on the lever. In this example, we will discuss a rotating polygon mirror that uses At base material and 5i (12) as a protective film. Figure 2 shows the base material and protection 11! Fully enlarged to analyze the fouling rate against the light beam. The symbol is as follows (represents C foot).

Rs: Reflectance of polygon mirror for S polarization component ,: Reflectance between air and protective film δ: Phase difference of laser beam no: Refractive index of air nl: Refractive index of protective film n2: 〃 ψ of base material , ψ8. ψ2: angle of incident reflection and refraction at each boundary At this time, the reflectance f(, s of the polygon mirror is determined by the formula corrected in Figure 2, and when the number of feet depending on the material is determined, R, It can be seen that s is a function of the incident angle ψ and the protective film thickness dl.

Figure 3 shows maintenance film material S+02, base material At, and laser wavelength 7.
This is an example in which #'i is calculated as 80 nrr+, and its characteristics will be described below. In FIG. 3, the horizontal axis shows the protective film thickness d1, and the vertical axis shows the reflectance R, the s-cutting, and the incident angle ψ as parameters. The main % characteristic here is (1) The reflectance reaches its maximum value near n, d, = λ/2, but the f movement of Rs with a change in 90 also reaches its maximum value.

Change in Rs due to fil 9'o trJd, = 21 (1
Although it takes a minimum value near a person, the rate of change of Rls due to d is quite large in this vicinity.

Therefore, it is best to select a film thickness in the vicinity of KI/'i, d, = 210 OA to minimize the variation in reflectance due to changes in the incident angle, that is, the variation in the amount of light on the scanned surface, and to keep the total reflected light l constant. In that case, there is a problem in that the reflectance of the polygon mirror does not reach its maximum value, and the reflectance changes greatly with changes in the thickness of the protective film d.

[Purpose of the invention]

The purpose of the present invention is to take into consideration the characteristics of the rotating polygon mirror or the oscillating mirror described above, and to create a light beam configured to obtain a uniform light output and an effective spot diameter in the scanning direction, and to maximize the reflection efficiency of the mirror surface. An object of the present invention is to provide a scanning type image input device.

[Summary of the invention]

As can be seen from FIG. 3, when a rotating polygon mirror with a real divisor is used in the range of use, for example ψo -30° to 60°, the reflectance is maximum d, = 3r near 100 people, ψ. The relationship between Can be done at a constant rate.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be explained with reference to FIGS. 4 to 7. In this embodiment, a scanning image input device using a laser beam is incorporated into an electrophotographic laser beam printer. Figure 4 shows its configuration,
The laser beam printer 20 has a paper feed cassette 25 and a paper output tray 24, and passes the paper from the paper feed cassette 25 through the paper feed section 28 to the printing section 27 (consisting of a drum 17, a printer, etc.), and to the regular printer. The paper reaches the paper ejection cassette 24 via the paper ejection transport system 29 via the paper container 26 (+-).A cleaner 22 and a developing device 21 are arranged around the printing section 27.The laser scanning system is
Laser light source (not shown) 2J: Hisono drive circuit (not shown)
, a rotating polygon mirror 5, an Fθ lens 6, a switching mirror 16.2 for scanning and exposing a photosensitive drum 17, and a scanning mirror 16.2 for scanning an original 8 (not shown) on an original platen 23, and a long photoelectric Vm cable for detecting reflected light. The sense amplifier 13 is arranged close to the elongated photoelectric conversion elements 9a and 9b.

FIG. 5 shows the configuration of a laser beam scanning image input device according to an embodiment. Since it is shared with the laser thread of a laser beam printer, the laser drive circuit 2 is driven by the signal generation circuit 14 and has a high-speed switching mechanism for laser light. Fig. 7 shows signals related to G-tone.The laser drive circuit 2 turns on and off the semiconductor laser 3 using switching transistors 30 and 31.The three semiconductor lasers and light emitting elements used in this example It consists of an LD and a light receiving element PD, and the light receiving element PL') detects all the light emitting elements of the light emitting element LD and returns the light output to the light output control circuit 32.

The light output control circuit 32 outputs the current of the current source 33.
ll ill to keep the optical output of the semiconductor laser 3 at a constant value.

As shown in FIG. 7, the laser drive signal from the signal generation circuit 14
J Gotan ■ carefully sets the lighting interval τD for reading and the laser lighting period τBJ for beam position detection, and the other periods are as follows:
Considering the life span of the semiconductor laser, the laser is turned off. One running cycle is 1°, and during this period, the reflection angle ψ. changes by about 30 degrees to 6 (1"!), and the reflectance of the rotating polygon mirror changes accordingly by about 7 degrees from 86% to 93 degrees.

In response to this reflectance change, the laser drive circuit of this embodiment includes a bias current source 34 and a bias control circuit 35.
As a result, as shown in FIG. 7, by reducing the bias force and reducing the current σ, the amount of light on the scanned surface a can be made uniform. In the configuration shown in FIG. 6, the bias current is independent of the switching current and has a value less than or equal to the Threnjord current of the semiconductor laser, so there is no problem.

The timing for applying the bias current is set to the beam detection signal from the beam position detection circuit 12. Since image information is read from the reflected light from the surface to be scanned using the beam detection signal as a reference, the scanning angle jK of the light beam, that is, the angle of incidence and reflection on the rotating polygon mirror 5 ψ. The amount of bias current applied is always constant. The reset timing for changing the bias to ', #r' was set at the beginning of the beam position detection laser lighting period. Unimplemented original output system @11! :
The JM 32 fully captures the laser first output during the beam position detection laser lighting period, determines the capacity of the current source 20, and holds that one target for one running period. As mentioned above, if the bias current change is reset at the beginning of the beam position detection laser lighting period, the optical output open side 1 circuit 32 will be free from the influence of the bias current change I.
# is no longer received, and the bias current change I++ can be adjusted freely.

According to the non-embodiment, the rotating polygon mirror can be used in the range where the reflectance is the highest, and the range of rapid movement of reflected light can be made extremely small regardless of the characteristics of the human skin incidence angle. Further, in the vicinity of the protective film thickness where the rotating polygon mirror has the maximum retraction rate, the change in reflectance due to the change in the protective film thickness is gradual, making quality control easy when manufacturing the polygon mirror.

Furthermore, in the non-example, since the optical system and the laser drive circuit 2 are shared with the laser beam printer, the amount of light straying onto the photosensitive drum 17 is also uniform, and the number of products marked 4 is improved.

In the non-example, compensation for reflectance fluctuation was approximated by a triangular wave bias current, but it is not limited to a triangular wave, and the bias current is not separated as a bias current. Since it is a scanning type image input device built into the
The aim was to compensate for the input/reflection characteristics of the reflective surface and improve the printing quality as a printer.1 As a blood image input device, the laser light source was made constant output, and the sensitivity of Sense Ang 13 was adjusted to the input/reflection angle. Even if you change it, you will get the same effect.

〔Effect of the invention〕

According to the present invention, a rotating polygon mirror or a reciprocating oscillating mirror can be used in the region having the maximum reflectance, which not only reduces the burden on the laser light source but also reduces the scanning area regardless of the angle of incidence and reflection. A uniform amount of scanning light can be obtained over the entire area.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a laser beam scanning type image input device, Fig. 2 is a plan view showing the angle of incidence and reflection of a rotating polygon mirror, and Fig. 3 is a scanning type explanatory example showing the reflectance characteristics of a rotating polygon mirror. FIG. 6 is a block diagram of the laser drive circuit of the embodiment, and FIG. 7 is a signal timing chart in the actual Mu example. 2... Laser drive circuit, 3... Semiconductor laser, 5...
...Rotating polygon mirror, 9a, 9b...Photoelectric conversion collector, 12
...Beam position 1a detection 1! :] Circuit, 13... Sense amplifier, 1... Signal processing device, 32... Optical output side diagonal 1 '91 path, 33... Current source, 34... Bias, 'Tunryu City 11 @1 circuit, 35...Bias 81 Figure 2 T = 51, (nayak) T2 = 5jrL-' (1,000) 5 = (2rrdrcθS5f?) Figure 3

Claims (1)

[Claims] l The light beam output from the laser light source is transferred to a rotating polygon mirror,
Alternatively, a scanning optical system is used to perform scanning deflection using a reciprocating vibrating mirror sound, focus the light beam onto the scanned surface using an optical system, and read information on the scanned surface from the reflected light by a photoelectric conversion device. The optical output of the laser light source or the reflected light is compensated for the reflectance fluctuation caused by the change in the angle of incidence of the light beam on the reflective surface due to the shadow 9 of the thickness of the protective film on the reflective surface of the rotating polygon mirror or the reciprocating mirror. A light beam scanning type image input device characterized in that the sensitivity of a photoelectric conversion element is changed according to an incident angle of a light beam on a reflective surface. 2. A light beam scanning type according to claim 1, characterized in that the thickness of the peritoneal coating on the reflecting surface of the rotating polygon mirror or the oscillating mirror is formed to a thickness that can accommodate the maximum reflectance. Image input device.