Optical: systems and elements – Deflection using a moving element
Reexamination Certificate
1998-12-31
2001-03-27
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Deflection using a moving element
C359S206100, C359S216100, C359S819000
Reexamination Certificate
active
06208448
ABSTRACT:
RELATED CROSS-REFERENCED APPLICATIONS
This application is based on Application No. 10-61 filed in Japan, the content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to temperature compensation of a scanning optical apparatus using a visible light laser as a light source.
BACKGROUND OF THE INVENTION
In the field of temperature compensation for the light source unit of scanning optical systems, art has been proposed for compensating for the spatial variation between a laser light source
22
and a condensing lens
23
caused by temperature fluctuation by combining a plurality of condensing lens element holding member
21
, as shown in
FIG. 5
, pursuant, for example, to the disclosure of Japanese Laid-Open Patent No.4-107518. Reference number
24
in the same drawing refers to a concave lens, and reference number
25
refers to a lens holder.
Japanese Laid-Open Patent Application No. 61-162014 discloses art for compensating temperature fluctuation caused by the oscillation wavelength of a semiconductor laser by changing the length of the light source support member. Furthermore, when the condensing lens is constructed as a single element lens, the focal length of the light source changes due to change in the oscillation wavelength of the laser induced by a change in temperature, and a method for compensating for the shift of the image forming point on the scanned medium caused by this variation is proposed in Japanese Laid-Open Patent Application No. 61-162014, which discloses a method for selecting the linear expansion coefficient of the support members so that the amount of change in the space between the condensing lens and the light emission point induced by thermal deformation of the light source support member is equal to the amount of change in the focal length.
In the construction disclosed in Japanese Laid-Open Patent No. 4-107518, however, the temperature compensation is applied to the space between the laser light source and the condensing lens, and the focal length of the condensing lens is not changed. In practice, the focal length is changed by a change in the refraction index caused by wavelength and temperature, and although it is possible to suppress this change in focal length by using a plurality of materials for the condensing lens elements, such a solution is disadvantageous from the perspective of increased cost of components and assembly due to the increased number of lens elements.
In the construction disclosed in Japanese Laid-Open Patent Application No. 61-162014, thermal expansion and change of the refractive index of the collimator lens due to temperature, and the influence of temperature on the f&thgr; lens are not considered. Since the change in focal length is particularly great in the case of visible light, the support member must have a large linear expansion coefficient, which narrows the breadth of material selection, and the method only allows for changing the composition ratio of glass fibers in resin. When the support member comprises a member having a single type of linear expansion coefficient, the aforesaid composition ratio must be finely adjusted, thereby making it disadvantageously difficult to obtain resin materials inexpensively.
When the beam diameter is reduced by reducing the oscillation wavelength of the laser light and a single element collimator lens is used to reduce cost, the e reflective index of the material changed greatly due to the change in wavelength caused by the reduction of the oscillation wavelength, so as to disadvantageously be unbeneficial relative to temperature change.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved scanning optical apparatus.
Another object of the present invention is to provide a condensing lens of single element construction or a plurality of lens elements which do not include a negative lens element even in the visible light range in which there is large variation in refractive index depending on the wavelength.
A further object of the present invention is to provide a scanning optical apparatus having a light source capable of compensating for the shift of the image forming point on a scanned medium caused by temperature change.
An even further object of the present invention is to provide a scanning optical apparatus which provides temperature compensation for the entire optical system including temperature change of the f&thgr; lens via a simple construction without using an expensive autofocus mechanism to detect and feedback the mage forming position in a scanning optical system of a scanning optical apparatus.
These objects are attained by providing a scanning optical apparatus having:
a light source which emits a ray in a wavelength range of 460 to 650 nm;
a first lens unit for forming a luminous flux using the ray and having at least one or more positive lens element;
a scanner for scanning the luminous flux;
a second lens unit for forming an image on a scanned medium using the luminous flux; and
a holding structure connecting the light source to the first lens unit via at least two support members having mutually different linear expansion coefficients,
wherein the movement of the image forming point on the scanned medium caused by change in the oscillation wavelength of the light source is compensated by the thermal expansion of the support members.
The invention itself, together with further objects and attendant advantages, will be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4634232 (1987-01-01), Tateoka
patent: 5864739 (1999-01-01), Kaneko
patent: 5870133 (1999-02-01), Naiki
patent: 4-320079 (1992-11-01), None
Boutsikaris Leo
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Spyrou Cassandra
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