Optics: measuring and testing – Plural test
Reexamination Certificate
1999-10-27
2001-01-30
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Plural test
C359S211200
Reexamination Certificate
active
06181415
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical transmission deflector in which light is deflected by a prism which is mechanically driven via electromagnetic operation, and in particular it relates to a position sensor for detecting the position thereof. The present invention also relates to an optical scanner and a correction apparatus for correcting the scanning position in the sub-scanning direction.
This application is related to the commonly assigned application filed on Jun. 16 1998, entitled “TRANSMISSION TYPE OPTICAL DEFLECTOR”, the disclosure of which is expressly incorporated by reference herein.
2. Description of the Related Art
In a known optical deflector in which an optical element is mechanically driven co deflect light, a mirror which is adapted to deflect light is reciprocally moved or the mirror is rotated. A galvano mirror is one of the typical first type in which the mirror is reciprocally moved. A polygonal mirror is another way of providing an optical deflector in which the mirror is rotated. In theory, a transmission deflector can be realized, for example, by employment of a wedge-shaped prism in place of the galvano mirror. However, in practice, since the wedge-shaped prism is heavier than the planar mirror and the position of the center of gravity of the prism varies depending on the shape thereof, oscillation tends to occur due to a weight imbalance, thus leading to difficulty in realizing a precise and high-speed optical deflector.
To this end, the assignee of the present application has proposed a precise and fast-driven optical transmission deflector using a prism (Japanese Patent Application No. 9-159932). In the proposed optical transmission deflector, the thick portion of the transmission prism is partly cut away so that the position of the center of gravity of the transmission prism is located on the axis about which the transmission prism swings.
In conventional optical scanners which have been widely used in a laser printer, etc., the laser beam emitted from a laser source and modulated in accordance with drawing data (printing data) is made incident upon the polygonal mirror (optical deflector) and is moved in the main scanning direction. The scanning laser beam is made incident upon a photosensitive body which is moved in the sub-scanning direction perpendicular to the main scanning direction through an f&thgr; lens. The photosensitive body is made of, for example, a photosensitive drum or a photosensitive sheet.
In conventional optical scanners, positional deviation of the laser beam on the photosensitive body in the sub-scanning direction tends to occur due to an irregularity in the movement of the photosensitive body or a slim inclination of the reflection surfaces of the polygonal mirror, etc., thus leading to a deteriorated printing quality. The correction of the scanning position in the sub-scanning direction is carried out by the reflection type optical deflector, such as a galvano mirror. However, in the related art in which the reflection type correction system has been only employed, freedom of design is restricted and the size of the optical scanner is increased.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a position sensor for a transmission type optical deflector that uses a prism, which can detect the position of the transmission prism.
Another object of the present invention is to provide a scanning position correcting apparatus for a transmission type optical deflector, which can correct the scanning position in the sub-scanning direction.
Still another object of the present invention is to provide a scanning position correcting apparatus in which chromatic aberrations can be compensated.
According to an aspect of the present invention, there is provided a position sensor for a transmission type optical deflector, including: a prism holder supported by a yoke member to rotate about a principal axis through an elastic member; a wedge-shaped transmission prism provided on the prism holder to transmit and refract light; a coil and a permanent magnet which are provided on the prism holder and the yoke member, respectively, to produce a rotational motion of the prism holder in the forward and reverse directions about the principal axis via electromagnetic operation; a reflection layer which is coated on a surface of the wedge-shaped transmission prism other than the transmission portion thereof through which the light can pass; a light emitter for emitting collimated light onto the reflection layer; and an incident position detector for receiving the light reflected by the reflection layer and detecting the incident position of the light thereon.
Preferably, the reflection layer is formed on the thinner portion of the wedge-shaped transmission prism.
Preferably, the wedge-shaped transmission prism is partly cut away at the thicker portion thereof so that the center of gravity of the wedge-shaped transmission prism is substantially the same as the principal axis in which the principal axis appears as a point and the wedge-shaped transmission prism appears as a wedge-shape in section, and the reflection layer is formed on an incident or emission surface of the thinner portion of the wedge-shaped transmission prism that is opposed to the cut-away portion.
Preferably, the light emitter includes a laser diode and a collimating lens which collimates the laser light emitted from the laser diode and wherein the incident position detector includes a condenser lens and an optical position detector.
According to another aspect of the present invention, there is provided a scanning position correcting apparatus for an optical scanning system, including: a laser source whose output is modified in accordance with drawing data; an optical deflector (e.g , polygonal mirror)) which moves the laser light emitted from the laser source in a main scanning direction; a photosensitive body which is driven in a sub-scanning direction perpendicular to the main scanning direction and which receives the laser light moved in the main scanning direction; a pair of wedge-shaped transmission prisms provided in a light path between the laser source and the optical deflector, the wedge-shaped transmission prisms having a wedge shape in section in the sub-scanning direction and are oriented in opposite directions, one of the wedge-shaped transmission prisms is stationary and the other wedge-shaped transmission prism is rotatable about a principle axis perpendicular to the sub-scanning direction; and an electromagnetic drive device which rotates the rotatable transmission prism about the principle axis.
In an embodiment of this aspect of the present invention, the electromagnetic drive device includes: a yoke member; a prism holder which is supported by the yoke member to rotate about the principal axis through an elastic member and on which the rotatable transmission prism is provided and; a coil and a permanent magnet provided on the prism holder and the yoke member, respectively, to produce rotational motion of the prism holder in the forward and reverse directions about the principal axis via electromagnetic operation. The stationary transmission prism is secured to the yoke member or a member integral therewith.
Preferably, the rotatable transmission prism is partly cut away at the thicker portion thereof so that the center of gravity of the rotatable transmission prism is substantially the same as the principal axis thereof in which the principal axis appears as a point and the rotatable transmission prism appears as a wedge-shape in section.
Preferably, the electromagnetic drive device drives the rotatable transmission prism in accordance with data on the irregular movement of the photosensitive body.
Preferably, the optical deflector includes a polygonal mirror and wherein the electromagnetic drive device drives the rotatable transmission prism in accordance with inclination data of the reflection surfaces of the polygonal mirror.
Preferably, the stationary transmission pr
Iima Mitsunori
Kanazawa Hiroshi
Tanaka Akihiro
Asahi Kogaku Kogyo Kabushiki Kaisha
Font Frank G.
Greenblum & Bernstein P.L.C.
Nguyen Tu T.
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