JPH0675186A - Laser beam scanning device - Google Patents

Abstract

PURPOSE:To correct the unevenness of a pitch without using an (ftheta) lens or an (arc-sin) lens by electrically correcting it. CONSTITUTION:This is the laser light scanning device where a rotary polygon mirror 2 is disposed at the focusing position 1a of a parabolic mirror 1 and which emits a laser beam 9 emitted from a laser diode 3 and made incident on the mirror 2 according to the rotation of the mirror 2, makes the emitted beam incident on the mirror 1 and outputs collimated luminous flux from the mirror 1. The sequence Tn=2arctan(c/t) is stored in a memory 7 and a clock outputted from a clock circuit 4 is counted by a counter 5. When it is decided by a coincidence detection circuit 8 that the sequence Tn stored in the memory 7 and the counted value of the counter 5 coincide with each other, a sampling signal for turning on a laser diode is outputted from the detection circuit 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for collimating light which is incident on the focal point of a parabolic mirror and whose incident angle changes with time, and in particular, a recording device such as a laser printer or the like. The present invention relates to a technique effectively used for a scanning mechanism such as a displacement meter.

[0002]

2. Description of the Related Art A rotary polygonal mirror (polygon mirror) or a rotary plane mirror is arranged at the focal point of a parabolic mirror, and the output angle of a light beam incident on this rotary mirror is changed according to the rotation of the mirror (that is, Scanning) and let this emitted light enter a parabolic mirror,
The laser beam scanning device that obtains a parallel light flux from this parabolic mirror is
It is used in laser printers, laser plotters, laser displays, and laser displacement meters.

By the way, the present inventor examined the occurrence of scanning pitch unevenness in a laser printer or a displacement gauge. The following is a technique studied by the present inventor,
The outline is as follows.

That is, when a rotary mirror such as a rotary polygon mirror is arranged at the focal position of a parabolic mirror to perform optical scanning, the angular velocity of the rotary mirror and the scanning velocity of the parallel light flux from the parabolic mirror. However, when used in a laser printer or a displacement meter, there is a problem in that the scanning pitch becomes uneven. That is, since the angular velocity and the scanning velocity are not in a proportional relationship, the pitch becomes coarse at a place far from the focus and becomes dense at a place close to the focus, resulting in uneven pitch. Therefore, conventionally, the correction is performed using an fθ lens or an arc-sin lens.

[0005]

However, in the laser beam scanning device using the fθ lens or the arc-sin lens as described above, it is difficult to design these lenses, and the cost is increased, and the cost of the device is increased. However, the present inventor has found that there is a problem that accuracy is not obtained due to difficulty in manufacturing.

Therefore, an object of the present invention is to provide an fθ lens and a
It is an object of the present invention to provide a laser light scanning technique capable of correcting pitch unevenness without using an rc-sin lens.

The above and other objects and novel characteristics of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0008]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

That is, a polygonal or plane rotating mirror is arranged at the focal point of the parabolic mirror, the laser beam incident on the rotating mirror is emitted in accordance with its rotation, and the emitted beam is emitted from the parabolic mirror. A laser light scanning device that outputs a parallel light flux from the parabolic mirror upon incidence on a memory, which stores a number sequence, a counter that counts a clock, and a number sequence stored in the memory by the counter. A coincidence detection circuit that outputs a sampling signal for turning on the laser when the numerical values coincide is provided.

[0010]

According to the above means, a sequence of numbers for keeping the scanning speed constant is stored in memory, a clock having a sufficiently high frequency is generated, and the laser is activated when the count value matches the sequence of numbers stored in the memory. A signal to turn on is output. As a result, it is possible to correct the pitch unevenness so that the scanning speed is electrically constant at all times.
It is possible to correct pitch unevenness at low cost without using a c-sin lens.

[0011]

1 is a block diagram showing an embodiment of a laser beam scanning device according to the present invention.

At the focal position 1a of the parabolic mirror 1, a rotary polygon mirror 2 is arranged so that it can rotate at high speed, and a laser diode 3 which is a light emitting source is provided on the incident optical path of the rotary polygon mirror 2.
Is installed. That is, the focus position 1 of the parabolic mirror 1
a coincides with the reflection point of the rotary polygon mirror 2.

A clock circuit 4 for generating a clock signal in order to turn on / off the laser diode 3.
A counter 5 for counting the clock signal from the clock circuit 4, an address generating circuit 6 for generating an address,
A memory 7 for storing the number sequence Tn and a coincidence detection circuit 8 for outputting a coincidence signal when the count value of the memory 7 and the count value of the counter 5 coincide are provided.

In the present invention, the correction of the scanning pitch unevenness is electrically processed instead of the conventional optical means. The method will be described with reference to FIG.

When the rotary polygon mirror 2 rotates at an angular velocity ω, the laser beam reflected by the parabolic mirror 1 has a parabolic surface of y ² = 4p.
If it is x, it is represented by the following formula (where t is a regular number and is a natural number).

Tan ψ = 4 py / (y ² -4p ² ) y = 2p (cos ψ + 1) / sin ψ y '=-2p (1 + cos ψ) / sin ψ = -2p / (1-cos ψ) = -2p / (1- cosωt) In order for this speed to be constant, the following differential equation may be solved.

−2p / (1-cosψ) · dωt / dt = c This solution is ωt = Tn = 2arctan (c / t). 2 arctan for a constant scanning speed
If sampling is performed for a time that satisfies (c / t), the scanning speed is always constant (y = 2p / c · t). For this purpose, a counting clock with a sufficiently high frequency (that is, that the resolution is sufficiently large) is generated, and a sequence Tn satisfying 2 arctan (c / t) is stored in the memory 7 by the resolution. Put it in (store the required number in one scan). Then, the coincidence detection circuit 8 determines whether or not the clock generated from the clock circuit 4 coincides with the value of the sequence Tn of the memory 7. At this time, the address generation circuit 6 increments from 0, and returns to 0 when the maximum address is reached, generating an address for bringing data from the memory 7. The coincidence detection circuit 8 outputs a sampling signal when the count value of the counter 5 coincides with the sequence Tn of the memory 7, and when the laser diode 3 is turned on, the generated laser spots are scanned at equal intervals on the image plane. Will be.

The laser beam 9 output from the laser diode 3 is incident on the rotary polygon mirror 2, and the emitted light (laser beam 10) changes its emission angle with the rotation of the rotary polygon mirror 2 to form a parabolic surface. Continuously scan the inner surface of the mirror 1 in the direction of the arrow,
The scanning laser beam 11 is output.

As described above, according to the embodiment of the present invention, since the scanning pitch unevenness can be electrically corrected without using an expensive fθ lens or the like, it is possible to significantly reduce the cost. Further, the accuracy can be improved only by increasing the clock frequency.

The invention made by the present inventor has been specifically described above based on the embodiments, but the present invention is not limited to the embodiments and can be variously modified without departing from the scope of the invention. Needless to say.

For example, as a motor for driving the rotary polygon mirror 2, a motor that rotates at a constant speed is usually used, but if a stepping motor is used and rotation is performed so as to satisfy 2 arctan (c / t), Even if sampling is performed at equal intervals, the pitch can be kept constant.

Further, instead of storing the above-mentioned sequence Tn in the memory 7, 2 arctan (c / t) is sequentially calculated by using a CPU (central processing unit) such as a digital signal processor (DSP). You may do it.

[0023]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.
It is as follows.

That is, a multi-faceted or flat rotating mirror is arranged at the focal point of the parabolic mirror, the laser beam incident on the rotating mirror is emitted according to the rotation, and this emitted beam is emitted from the parabolic mirror. A laser light scanning device that outputs a parallel light flux from the parabolic mirror upon incidence on a memory, which stores a number sequence, a counter that counts a clock, and a number sequence stored in the memory by the counter. Since the coincidence detection circuit that outputs the sampling signal for turning on the laser when the numerical values coincide is provided, the scanning speed is always constant, and the fθ lens and the arc-sin
It is possible to correct the scanning pitch unevenness at low cost without using a lens.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a laser beam scanning device according to the present invention.

FIG. 2 is an explanatory diagram illustrating calculation of a number sequence stored in a memory.

[Explanation of symbols]

 1 Parabolic mirror 1a Focal position 2 Rotating polygonal mirror 3 Laser diode 4 Clock circuit 5 Counter 6 Address generation circuit 7 Memory 8 Match detection circuit 9 Laser beam 10 Laser beam 11 Scanning laser beam

Claims (3)

[Claims] 1. A multifaceted or flat rotating mirror is disposed at a focal point of a parabolic mirror, a laser beam incident on the rotating mirror is emitted according to the rotation, and the emitted beam is the parabolic mirror. A laser light scanning device that outputs a parallel light flux from the parabolic mirror upon incidence on a memory, which stores a number sequence, a counter that counts a clock, and a number sequence stored in the memory by the counter. And a coincidence detection circuit for outputting a sampling signal for turning on the laser when the numerical values coincide with each other. 2. The sequence of numbers is 2 arctan (c / t)
The laser beam scanning device according to claim 1, wherein (c is a constant and t is a natural number). 3. A polygon mirror or a plane rotating mirror is disposed at a focal position of a parabolic mirror, a laser beam incident on the rotating mirror is emitted according to the rotation of the rotating mirror, and the emitted light is emitted from the emitting mirror. A laser beam scanning device for making a paraboloidal beam incident on a parabolic mirror and outputting a parallel luminous flux from the parabolic mirror, wherein
ctan (c / t) (where c is a constant and t is a natural number)
A laser beam scanning device comprising a control means for rotating so as to satisfy the condition.