1. Field of the Invention
The present invention relates in general to a scanning beam generating unit normally employed in a printing apparatus such as a laser printer, a laser facsimile, and the like. In particular, the invention relates to a scanning beam generating unit comprising: a base frame defining an emitting or output window; a motor drive supported on the base frame; a rotating mirror attached to the drive shaft of the motor drive and capable of reflecting a beam emitted from a light source; and an optical component mounted on the base frame and designed to direct the beam from the mirror to the output window.
2. Description of the Prior Art
A laser printer utilizes a laser beam irradiated on an optical photoconductor, namely, an optical photoconductive drum. The laser beam is designed to draw an electrostatic image on a photoconductive cylindrical surface of the drum. Particles of toner supplied to the drum serve to visualize the electrostatic image on the photoconductive cylindrical surface. The visible image of the toner can be transferred to the printing medium, such as a sheet of paper, from the photoconductive cylindrical surface of the drum. When the transferred toner is subjected to heat, the particles of the toner are fused so that the fused toner is deposited onto the printing medium. A fuser, such as a heat roller, may be employed to fuse and deposit the particles of the toner.
The laser beam is in general supplied from a scanning beam generating unit or optical unit. The rotating mirror having a shape, such as a polygon, causes the laser beam, emitted from a laser, to scan across the optical photoconductive drum along the meridian. Each facet of the polygon thus generates a scanning laser beam directed to the optical photoconductive drum. A motor drive is usually employed to generate rotation of the polygon.
In general, the fuser is preferably disposed adjacent or closer to the optical photoconductive drum in a laser printer. Such location of the fuser and drum enables a rapid fusion of the particles of the toner which have been transferred onto the printing medium. The toner can be fused soon after it has been transferred onto the printing medium. On the other hand, it is likewise preferable that the optical unit is disposed adjacent or closer to the optical photoconductive drum. Accordingly, the optical unit is usually disposed closer to the fuser. The smaller the size of the laser printer gets, the closer to the fuser the optical unit is disposed. However, if heat generated at the fuser is conducted to the optical unit, the motor drive tends to suffer from the deficiency of rotation, such as a jitter, because of an increased temperature in the bearing supporting the drive shaft, in particular. In addition, the bearing also suffers from a shortened lifetime or a deterioration.
It is accordingly an object of the present invention to provide a scanning beam generating unit, in general employed in a printing apparatus, capable of avoiding a deterioration and a jitter of a motor drive induced by thermal conduction.
According to the present invention, there is provided a scanning beam generating unit comprising: a base frame defining an output window; a motor drive disposed at a position spaced from the base frame and designed to rotate its drive shaft; a scanning mechanism attached to the drive shaft of the motor drive so as to allow a beam, emitted from a light source, to scan; and an optical component mounted on the base frame and designed to direct the beam from the scanning mechanism to the output window.
For example, the base frame serves to interrupt heat radiated toward the motor drive in the scanning beam generating unit. As compared with the case where a motor drive is mounted directly upon a base frame, the motor drive is prevented from receiving heat through the base frame. It is possible to avoid an increase in the temperature of the motor drive to the utmost. In particular, a rise in temperature can be prevented in the bearing supporting the drive shaft in the motor drive, so that a deterioration can be avoided in the bearing. At the same time, a deficiency in rotation, such as a jitter, can reliably be avoided in the motor drive.
The scanning beam generating unit may further comprise: an attachment member fixed on the base frame; and a basement member supported on the attachment member and spaced from the base frame so as to support the motor drive at a surface opposed to the base frame. The motor drive is located within a space defined between the base frame and the basement member. The basement member can be kept spaced enough from the base frame. Accordingly, heat is hardly conducted to the basement member from the base frame. Increases in temperature can still efficiently be avoided in the motor drive, in particular, at the bearing.
A heat radiation member may be attached on the basement member at a surface opposite to the surface on which the motor drive is attached. The radiation member serves to efficiently radiate heat staying at the basement member. Rises in temperature can still efficiently be avoided in the motor drive.
The scanning beam generating unit may further comprise: a thermal conductive frame cover coupled to the base frame so as to define a space for accommodating at least the optical component; and a conductive member connecting the frame cover to the basement member. The thermal conductive frame cover and the conductive member serve to increase the radiation area for heat staying at the basement member. Such an increase in the radiation area contributes to an accelerated heat radiation from the basement member.
In general, a printing apparatus employing the aforementioned scanning beam generating unit includes a heat source represented by a fuser such as a heat roller, for example. The scanning beam generating unit is often disposed adjacent or closer to the heat source. If the base frame is designed to oppose its back surface to the heat source, while the base frame receives the attachment member at the front surface, it is possible to avoid an increase in temperature of the motor drive spaced apart from the base frame. Accordingly, a deterioration can be avoided in the bearing supporting the drive shaft in the motor drive. At the same time, a deficiency in rotation, such as a jitter, can reliably be avoided in the motor drive.
In addition, the scanning beam generating unit is often located above an optical photoconductor such as an optical photoconductive drum within a housing or enclosure of the printing apparatus. If the output window is defined in the base frame, the base frame is allowed to keep facing the front surface upward when the scanning beam generating unit is assembled within the housing of the printing apparatus. The base frame can be received on a stationary support or stay within the housing of the printing apparatus. In this case, the scanning beam generating unit may simply be mounted from the above onto the upper surface of the stationary support, so that an operator is allowed to assemble the scanning beam generating unit within the housing of the printing apparatus in a facilitated manner.
A conductive connecting member may be employed to connect the basement member to the conductive stationary support. The connecting member and the stationary support contribute to an increased radiation area for heat staying at the basement member. Such an increase in the radiation area enables an accelerated heat radiation from the basement member.
Furthermore, a heat insulator may be attached to the base frame at a location between the motor drive and the fuser. The heat insulator serves to still efficiently interrupt or block heat radiated from the fuser. Less heat energy reaches the motor drive. In this way, an increase in the temperature can still efficiently be avoided in the motor drive.
Furthermore, the aforementioned printing apparatus may further comprise a ventilator designed to generate an air stream directed at least toward the motor drive. The generated air stream can be utilized to drive heat in the vicinity of the motor drive away, so that an increase in the temperature can still efficiently be avoided in the motor drive.
It should be noted that the printed apparatus may be represented by a laser printer, a laser facsimile, and the like. Any types of beam may be employed, instead of a laser beam, to electrically charge the optical photoconductor in the printer and facsimile.