JPS6237825B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light beam scanning device used in a laser printer or the like, and more particularly to a light beam scanning device configured to detect the passing time of a scanning beam scanned over a scanning surface.

Generally, this type of light beam scanning device is constructed as shown in FIG. 1, and a semiconductor laser 1 is driven by a laser drive circuit 2. Semiconductor laser 1
The laser beam oscillated from the collimator lens 3,
Scanning surface 7 via rotating polygon mirror 4 and condensing lens 5
The light is focused upward and becomes a scanning beam 8, which is repeatedly scanned in the direction of arrow A. Since the cycle of this repetition is not constant due to manufacturing errors, rotational irregularities, etc. of the rotating polygon mirror 4, a photodetector 9 is installed near the scanning start point of the scanning surface 7 to detect the passing time of the scanning beam. , the light beam scanning and the image signal 13 are synchronized by the detection signal 10.

However, this method requires an expensive photodetector 9 with a fast response speed, and when this photodetector 9 is used in an electrophotographic printer, a lot of noise is generated in the detection signal from the photodetector. There were problems such as doing something.

Note that reference numeral 14 is a photodetector that detects the laser output of the semiconductor laser 1.

In consideration of the above points, the present invention utilizes the self-coupling effect of a semiconductor laser to accurately detect the passage time of a scanning beam scanned on a scanning surface using an inexpensive device. The purpose is to provide equipment.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 2, reference numeral 20 indicates a light beam scanning device used in a laser printer or the like. This light beam scanning device 20 has a semiconductor laser 21 .
This semiconductor laser 21 is connected to a semiconductor laser drive circuit 2.
2, and a diverging laser beam 23a is oscillated. The oscillated laser beam 23a is made into parallel light by the collimator lens 24. This parallel laser beam is deflected by a rotating polygon mirror 25. The deflected laser beam is focused onto the scanning surface 27 by the condensing lens 26, and becomes a scanning beam 23b.
The top is scanned in the direction of arrow A.

The scanning beam 23b is repeatedly scanned on the scanning surface 27 by the rotation of the rotating polygon mirror 25. The repetition period is determined according to the number of mirror surfaces and rotation speed of the rotating polygon mirror 25.

On the other hand, a reflection mirror 29 is installed near the scanning start point position of the scanning surface 27. This reflective mirror 2
The laser beam (scanning beam 23b) incident on the laser beam 9 is reflected and returned to the semiconductor laser 21 through the condenser lens 26, the rotating polygon mirror 25, and the collimator lens 24 in this order. The semiconductor laser 21 is affected by this feedback light, and the self-coupling effect causes a change in the output of the semiconductor laser or a change in the semiconductor laser drive current (terminal voltage). Here, the self-coupling effect of a semiconductor laser refers to a phenomenon observed when optically feedbacking the output laser light of a semiconductor laser. Generally, the feedback laser beam acts to decrease the driving current of the semiconductor laser 21 when the laser beam output is constant, and to increase the laser beam output when the driving current is constant.

Further, the output of the semiconductor laser 21 is detected by a photodetector 30.
The detection signal 31 is used to synchronize the image signal 32 and the scanning of the light beam on the scanning surface 27. Specifically, the output change of the semiconductor laser 21 is expressed as shown in FIG. 3, and by detecting this output change with the photodetector 30, the reflection mirror 2
9 is detected. That is, the passing time of the scanning beam 23b is detected at the timing of the rise of the laser output at time _T1 . Note that area R is the reflection mirror 2.
Part 9 is shown.

Incidentally, the detection signal 31 from the photodetector 30 is also fed back to the semiconductor laser drive circuit 22, thereby stabilizing the laser output. Although the semiconductor laser 21 is susceptible to output fluctuations due to ambient temperature or deterioration of itself, this prevents the laser output from changing.

The reflecting mirror 29 provided near the scanning start point of the scanning surface 27 may have rectangular reflecting surfaces 33 and 34 as shown in FIGS. 4 and 5, or may have other shapes. It's okay. Of these, the reflecting mirror 29 shown in FIG. 4 has an elongated reflecting surface 33, and is provided so that its longitudinal direction is orthogonal to the scanning direction (scanning optical path) A of the scanning beam. Further, the reflecting mirror shown in FIG. 5 forms a boundary area 35 extending in a direction perpendicular to the scanning direction of the beam, and the area excluding this boundary area 35 is formed as a scanning surface 34.

Furthermore, as shown in FIG. 6, a transparent member 37 may be provided on the front surface of the reflective mirror 29 in order to protect the reflective surface 36. In this case as well, the scanning beam 2
3b may be focused on the reflective surface 36, and the defocus surface of the scanning beam 23b may be the surface of the transparent member 37. This can prevent the negative effects of debris such as dust and dirt.

In addition, in the description of one embodiment of this invention,
The reflected laser light from the reflecting mirror is converted into a semiconductor laser 2.
1, and the resulting change in the output of the semiconductor laser 21 is detected by the photodetector 30. However, instead of this photodetector, a detection method that detects a change in the drive current (terminal voltage) of the semiconductor laser may be used. A detector may be provided, and this detector may detect the transit time of the scanning beam scanned over the scanning surface, and the image signal and the light beam scanning may be synchronized using this detection signal.

Further, the reflection mirror installed on the scanning optical path of the scanning surface does not necessarily have to be installed at the scanning start position, but may be at a predetermined setting position.

As described above, in the optical beam scanning device according to the present invention, a reflecting mirror is arranged on the scanning surface where the oscillated laser beam from the semiconductor laser is scanned, and the laser beam is returned from the reflecting mirror to the semiconductor laser. By simply providing a detector that detects the presence or absence of light, and by utilizing the self-coupling effect of the semiconductor laser, it is possible to reliably and accurately detect the passage time of the laser light scanned on the scanning surface.

At that time, there is no need to install an expensive photodetector on the scanning surface, so it can be manufactured at low cost.
This provides effects such as an economical optical beam scanning device.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a conventional light beam scanning device, FIG. 2 is a system diagram showing an embodiment of the light beam scanning device according to the present invention, and FIG. 3 is a system diagram showing an embodiment of the light beam scanning device of the present invention. Graphs showing the relationship between the laser output of the semiconductor laser and the scanning position of the scanning beam obtained with the detector, Figures 4, 5, and 6 show examples of reflection mirrors placed on the scanning surface. FIG. 21... Semiconductor laser, 22... Drive circuit, 24...
Collimator lens, 25... Rotating polygon mirror, 26... Condensing lens, 23b... Scanning beam, A... Scanning direction,
27...Scanning surface, 29...Reflection mirror, 30...Photodetector, 31...Detection signal, 32...Image signal, 33,3
4, 36...reflective surface.

Claims (1)

[Claims] 1. In a light beam scanning device that irradiates an oscillated laser beam from a semiconductor laser onto a scanning surface and scans the scanning surface, a reflecting mirror is installed at a predetermined position on the scanning optical path of the scanning surface, and
A detector is provided to detect a change in the laser light output of the semiconductor laser or a change in the semiconductor laser drive current, and the detector returns the reflected laser light from the reflecting mirror to the semiconductor laser and detects the presence or absence of the returned laser light. 1. A light beam scanning device characterized in that the time of passage of a scanning laser beam is detected by detecting the passing time of the scanning laser beam.