JPS6398624A - Synchronous detecting method - Google Patents

Abstract

PURPOSE:To detect synchronizing light properly all the time and to make a device compact by detecting a light beam which is deflected and travels to an optical scanning area as the synchronizing signal, and timing the start of optical scanning. CONSTITUTION:A lens 18 is arranged between a light receiving element which detects the light beam as the synchronizing light and an image forming lens 12, a synchronizing light detection position Q1 is set on the deflection-directional composite focal plane of the image forming lens 12 and lens 18, and the light receiving element is arranged at the position. The lens 18 has power at least in a deflection direction and the synchronizing light is converged on the light receiving element at least in the deflection direction. The light receiving element is arranged on the composite focal plane, so even if the deflected light beam varies owing to the error of an optical deflector, the synchronizing signal is detected correctly all the time.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a synchronization detection method.

(Prior art) An optical scanning device is a device that optically scans a surface to be scanned by deflecting a light beam, and is used to write optical information on the surface to be scanned and read information on the surface to be scanned. known as a device. Among such optical scanning devices,
Some mechanical optical deflectors such as rotating polygon mirrors, hologram disks, or galvano mirrors are used to deflect the optical beam.If the optical beam is deflected by a mechanical optical deflector, the optical beam may be distorted due to mechanical errors. Since the period of deflection is not completely constant, in order to determine the timing of the start of optical scanning, the deflected light beam heading towards the optical scanning area is detected by a light receiving element as synchronous light.

FIG. 4 schematically shows the main parts of a conventionally known optical scanning device. Reference numeral 10 indicates a rotating polygon mirror, reference numeral 12 indicates an f9 lens as an imaging lens, and reference numeral 14 indicates an imaging surface of an FE lens. This imaging plane 14 coincides with the scanned surface, and the area indicated by reference numeral 16 is the scanned area. The position indicated by the symbol Q on the imaging plane 14 is a synchronous light detection position, and the light receiving element is arranged at this synchronous light detection position Q. The light beam L enters the rotating polygon mirror 10 as a parallel light beam, and the light beam L enters the rotating polygon mirror 10 as a parallel light flux.
The mirror surface of the one-rotation polygon mirror 10 is reflected by the mirror surface of the rotary polygon mirror 10, enters the FE lens 12, and is focused into a spot on the image forming plane 14 by the action of the lens 12. The mirror surfaces SO and SL vary, and the deflected light beam also varies like the beams LO and Ll, but since the synchronized light detection position Q of the light receiving element is set on the imaging plane 14, the above Synchronous light can always be detected correctly despite fluctuations in the light beam. However, on the other hand,
Since the placement position of the light receiving element is limited to the imaging surface of the imaging lens, there are restrictions on the arrangement of optical components, resulting in disadvantages such as an increase in the size of the optical unit and the need for a mirror to bend the optical path of the synchronized light. was there.

(Purpose) The present invention has been made in view of the above-mentioned circumstances, and its purpose is to develop a novel synchronization detection method that can provide flexibility in the arrangement position of a light receiving element for detecting synchronization light. It's on offer.

(Structure) The present invention will be explained below. The synchronization detection method of the present invention uses a rotating polygon mirror, a hologram disk, or a galvano mirror.
In an optical scanning device that performs optical scanning by deflecting a light beam using a mechanical optical deflector such as This is a method for detecting it as synchronous light and timing the start of optical scanning.

The features of the present invention are as follows. That is, a lens is provided between a light receiving element that detects a light beam as synchronous light and an imaging lens, and a synchronous light detection position is set on a composite focal plane of the deflection direction of the imaging lens and the lens. The point is that the light receiving element is disposed at this position. The lens has power at least in the deflection direction. Here, the deflection direction refers to the tangential direction of the ideally deflected light beam when the light beam is defined as the radial direction within the sweep plane of the light beam.

By doing so, the synchronized light is focused on the light receiving element at least in the polarization direction. Since the light receiving element is placed on the above synthetic focal plane, due to the error of the optical deflector,
Even if the polarized light beam fluctuates, synchronized light can always be detected correctly.

Further, by selecting the power in the deflection direction of the lens combined with the imaging lens and the lens position, the arrangement position of the light receiving element can be changed on the synthetic focal plane.

Hereinafter, description will be given based on specific examples.

In order to avoid complication, the same reference numerals as in FIG. 4 will be used in the drawings showing each of the following embodiments for those parts that are considered to be free from confusion.

In the embodiment shown in FIG. 1, reference numeral 18 indicates a lens. The lens 18 is a plano-convex lens, and the imaging lens f
It is arranged between the Q lens 12 and the synchronous light detection position Q1. The light receiving element is arranged at the synchronous light detection position Q1, which is a position on the synthetic focal plane of the synthetic optical system of the fθ lens 12 and the lens 18, and in this example, is the position of the synthetic focal point. . The light beam L enters the rotating polygon mirror 10 as a parallel light beam, and after being reflected, it passes through the f9 lens 12 and becomes a convergent light beam, condensing into a spot on the imaging plane 14. , and is focused on the position Q1 where the light receiving element is placed and detected. In this embodiment, the synchronous light detection position is from the imaging plane 14 to the fθ lens 12.
It is set in a position that is off to the side.

In the embodiment shown in FIG. 2, the lens 20 combined with the TG lens 12 has negative power, and therefore the synchronous light detection position Q2 where the light receiving element is to be disposed is set further back than the imaging plane 14. ing. Position Q2 is fθ lens 1
2 and the lens 20, and in this example, it is the position of the composite focal point, and the light beam L incident on the rotating polygon mirror 10 is a parallel light flux. In these embodiments, the synchronization light detection positions Ql and Q2 are on the synthetic focal plane, so even if the synchronization light changes to LO and Ll due to the reflection surfaces SO and SL of the rotating polygon mirror 10, correct synchronization is possible. Detection is possible.

The embodiment shown in FIG. 3 is an example in which correction of surface inclination is also performed. A cylinder lens 13 is combined with an fθ lens 12 for an image forming surface 14 which is a surface to be scanned, and the mirror surface of a rotating polygon mirror 10 is tilted like Sol or SIO as shown in FIG. Even if the deflected light beam changes like LOI or Llo, it is possible to prevent the scanning position from changing in the direction perpendicular to the deflection direction, that is, the direction perpendicular to the ideal sweep plane.

On the other hand, regarding the synchronized light detection position Q3 where the light receiving element is to be arranged, the lens 22 is combined with the fθ lens 12. The lenses 22 have different powers in the deflection direction and in a direction perpendicular thereto, that is, in a direction perpendicular to the ideal sweep plane.

In other words, the synchronous light detection position Q3 where the light receiving element should be placed
As shown in FIG. 3 (=), in the direction orthogonal to the deflection direction, the synchronous light is connected in a conjugate relationship by the deflection point P of the synchronous light, that is, the starting point of deflection, by the fθ lens 12 and the lens 22. Therefore, even if the surface of the rotating polygon mirror 10 is tilted, the detection of the synchronous light is not affected by the surface tilt.In addition, in the direction perpendicular to the deflection direction, the incident light beam LA on the rotating polygon mirror 10 is Focus on the position of the deflection point mentioned above. On the other hand, when viewed from a direction perpendicular to the ideal sweep plane, the incident light beam LA is a parallel light beam.

The synchronous light detection position Q3 where the light receiving element is to be disposed is the focal point of the synchronous light in terms of the deflection direction, that is, the synthetic focal point on the focal plane of the synthetic optical system of the f9 lens 12 and the lens 22. Therefore, correct synchronization detection is possible even if the synchronization light varies as LO and Ll due to the reflecting surfaces SO and S1 of the rotating polygon mirror 10.

(Effects) As described above, according to the present invention, a novel synchronization detection method can be provided. Since this method has the above-mentioned configuration, it is possible to always properly detect the synchronized light, and since a large degree of freedom is given to the placement position of the light-receiving element, it is possible to make the optical scanning device more compact. This also has the effect of reducing costs. Note that in FIGS. 1 to 4, each light beam is represented by a principal ray.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing another actual flow side of the present invention, FIG. 3 is a diagram showing another embodiment of the present invention, and FIG. 4 is a diagram showing another embodiment of the present invention. FIG. 2 is a diagram for explaining a conventional technique.

Claims (1)

[Claims] 1. In an optical scanning device that performs optical scanning by deflecting a light beam using a mechanical optical deflector and converging the light beam into a spot on a surface to be scanned using an imaging lens, the optical beam is deflected into an optical scanning area. A method for detecting an oncoming light beam as a synchronous light and timing the start of optical scanning, the method comprising applying power at least in the direction of deflection between a light receiving element that detects the light beam as a synchronous light and the imaging lens. A synchronous light detection position is set on a composite focal plane of the deflection directions of the imaging lens and the lens, and the light receiving element is arranged at this synchronous light detection position to detect the synchronous light. A synchronous detection method characterized by: 2. In claim 1, the lenses have different powers in the direction of deflection and in the direction orthogonal thereto, and in the direction orthogonal to the direction of deflection, the deflection point of the optical deflector and the light receiving element are different from each other. A synchronization detection method characterized in that the position is in a conjugate relationship with the position.