BRIEF DESCRIPTION OF THE DRAWINGS
These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic perspective view illustrating a spindle motor assembly according to an exemplary embodiment of the present general inventive concept;
FIG. 2 is a cross-sectional view illustrating the spindle motor assembly illustrated in FIG. 1;
FIG. 3 is a plan view illustrating a dynamic pressure generator of FIG. 1;
FIG. 4 diagrammatically illustrates the structure of a helical groove illustrated in FIG. 3;
FIG. 5 is a schematic perspective view illustrating an image forming device according to an exemplary embodiment of the present general inventive concept; and
FIG. 6 is a schematic perspective view illustrating a spindle motor assembly according to another exemplary embodiment of the present, general inventive concept.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures.
Referring to FIGS. 1 and 2, a spindle motor assembly according to an exemplary embodiment of the present general inventive concept may include a spindle motor 100, a polygon mirror 200 supported by the spindle motor 100, and a dynamic pressure generator 300.
FIG. 2 is a cross-sectional view illustrating a state in which the spindle motor 100 is installed in a reverse direction with respect to gravity. As illustrated in FIG. 2, the spindle motor 100 may include a stator 120 mounted on a substrate 110, a shaft 130 rotatably coupled to the stator 120, and a rotor 140 coupled to the shaft 130, thereby rotating together.
The stator 120 may include a bearing housing 121 coupled onto the substrate 110, and a stator core 122 and a coil 123 that are coupled to the outside of the bearing housing 121. The stator core 122 can be fit-pressed to the circumference of the bearing housing 121, and the coil 123 can be wound around the stator core 122. The interior of the bearing housing 121 can be hollow, and a bearing 125 can be installed therein.
The bearing 125 and the shaft 130 are coupled to each other. Therefore, the bearing 125 helps the shaft 130 to be rotatably supported by the stator 120, that is, the bearing housing 121.
The rotor 140 may include a rotor frame 141 coupled to the shaft 130, a rotor housing 142 coupled to the rotor frame 141, and a magnet 143 supported by the rotor housing 142. As the shaft 130 can be fit-pressed into the rotor frame 141, the rotor frame 141 and the shaft 130 rotate together. In addition, as the rotor housing 142 is coupled on the rotor frame 141, it also rotates with the rotor frame 141 and the shaft 130. The magnet 143 can be installed on an inner peripheral surface of the rotor housing 142 correspondingly to the coil 123 of the stator 120.
The polygon mirror 200 is an optical member having a plurality of reflective surfaces (or facets) 210 formed on its outside, and has a hollow 220 in which the rotor frame 141 is inserted. When the rotor frame 141 is inserted in the hollow 220, it can be fixed by a separate fixing piece 150. In detail, the fixing piece 150, being placed outside the polygon mirror 200, is elastically coupled to a stepped portion 141a which is formed on a peripheral surface of the rotor frame 141, to thereby fix the polygon mirror 200 onto the rotor frame 141. I.e., the polygon mirror 200 and the rotor 140 can be coupled to each other by the fixing piece 150, thereby rotating together.
The dynamic pressure generator 300 generates a dynamic pressure P to force the rotor 140 to move toward or to a position close to the stator 120 by an air flow generated around the rotor 140 during its rotation. As illustrated in FIG. 1 and FIG. 3, such a dynamic pressure generator 300 can be provided with a predetermined dynamic pressure generating pattern 310 formed on the rotor 140, or on the outer surface of the rotor frame 141 to be more specific. The dynamic pressure generating pattern 310 can include plural helical grooves 311 helically formed on the outside of the rotor frame 141 from a center C of the rotation.
The helical grooves 311 can be formed at regular intervals to a predetermined curvature in the rotation direction A1 of the rotor frame 141.
As illustrated in FIG. 4, the helical groove 311 can have an increasing depth D as it gets farther from the center C of the rotation. As such, a bottom surface 311a of the helical groove 311 can be inclined towards the center C of the rotation from the outside.
Going back to FIG. 3, a width W of the helical groove 311 may increase as it gets farther from the center C of the rotation. According to the dynamic pressure generating pattern 310 having such helical grooves 311, the rotor 140, including the rotor frame 141, rotates in the A1 direction, while the ambient air of the rotor frame 141 is guided by each of the helical grooves 311 and travels in an A2 direction. At this time, the air that travels in A2 direction along the helical grooves 311 increases in its flow rate and eventually in pressure because the depth D and the width W of the helical groove 311, i.e., the cross-section of the helical groove, are gradually decreased. The dynamic pressure P thus generated increases sharply on a side of the center C of the rotation, as illustrated in FIG. 4 and FIG. 2. This dynamic pressure P restrains the rotor 140 from moving away from the stator 120 in the axial direction of the shaft 130 due to, for example, gravity. Thus, as illustrated in FIG. 2, even if the spindle motor assembly is installed upside down, the polygon mirror 200 and the rotor 140 still rotate, having overcome the influence of gravity, so that the polygon mirror 200 can rotate stably in the axial direction of the shaft 130 without experiencing any displacement. Consequently, it becomes possible to improve the accuracy of scanning light scanned by the polygon mirror 200. While the spindle motor assembly illustrated in FIG. 2 is installed upside-down with respect to gravity to illustrate the effects of the dynamic pressure generator 300, the present general inventive concept is not limited thereto, and the dynamic pressure P can also restrain the rotor 140 from moving away from the stator 120 in the axial direction of the shaft 130 when the spindle motor assembly is mounted in different positions with respect to gravity, for example, when the spindle motor assembly is mounted tilted with respect to gravity.
Meanwhile, reference numeral 160 in FIGS. 1 and 2 denotes a stopper that can be installed on the substrate 110. The stopper 160 is disposed to be overlapped with the outside of the rotor housing 142 in the axial direction of the shaft 130, to thereby structurally prevent the rotor housing 142 from being separated completely from the stator 120.
The dynamic pressure generator 300 of the present general inventive concept prevents the rotor 140 from being separated from the bearing 125 within its movement range between the stopper 160 and the substrate 110. By controlling the rotor 140 to stay at a fixed position about the axial direction of the shaft 130, it becomes possible to stably maintain the rotation force generated between the stator 120 and the rotor 140 and the displacement and rotation speed of the polygon mirror 200.
FIG. 5 is a schematic perspective view illustrating an image forming device employing the spindle motor assembly according to an exemplary embodiment of the present general inventive concept.
Referring to FIG. 5, the image forming device may include a main body 10 of the image forming device, a paper feed unit 20 installed at a lower portion of the main body 10 to supply a printing medium, a laser scanning unit 30, a fixing unit 40, a transfer roller 50, and a developing unit 60.
In this structure, the paper feed unit 20 picks up the printing medium and supplies the printing medium between the transfer roller 50 and an image bearer 61 of the developing unit 60.
The developing unit 60 is provided with the image bearer 61 on which an electrostatic latent image of a desired image is formed by a laser light beam scanned from the laser scanning unit 30 to form an image, a developer supply unit 62 to supply a developer to the image bearer 61, a charging roller 63, and a cleaning blade 64. The developing unit 60 further may include a developer cartridge 65 to contain the developer, a stirrer 66, and so on. Since the construction of the developing unit 60 can easily be learned from the well-known technology, further details will not be provided hereinafter.
Meanwhile, the fixing unit 40 fixes an image onto the printing medium while it passes through the transfer roller 50 and the image bearer 61.
The laser scanning unit 30 can scan a laser light onto the image bearer 61. In the laser scanning unit 30, a spindle motor assembly including the spindle motor 100 and the polygon mirror 200 as illustrated in FIGS. 1 through 4 is installed upside down. The laser scanning unit 30 may include, besides the spindle motor assembly, a series of known optical system that can include a light source (laser diode), a collimating lens, an F-theta lens, a reflective mirror, and so forth.
As such, in a case of employing the laser scanning unit 30 on which the spindle motor assembly is installed upside down, the dynamic pressure generator 300 of the spindle motor 100 serves to prevent the rotating bodies (the polygon mirror 200 and the rotor 140) of the spindle motor assembly from inclining downwards by their unladen weights. In this way, it becomes possible to stably maintain the scanning position of a reflected light through the polygon mirror 200.
FIG. 6 is a schematic perspective view illustrating a spindle motor assembly according to another exemplary embodiment of the present general inventive concept. In FIG. 6, like reference numerals are given to the like elements of the spindle motor assembly illustrated in FIG. 1.
Referring to FIG. 6, a dynamic pressure generator 400 is provided to a rotor frame 141. Here, the dynamic pressure generator 400 is built in a predetermined pattern, for example, a propeller form. The propeller can be integrally formed by processing an outer exposed surface of the rotor frame 141, so that an air flow is generated towards the center of rotation during the rotation of a rotor 140. This increases the dynamic pressure as it goes closer to the center of the rotation. This propeller-type dynamic pressure generator 400 may be integrally formed on the rotor frame 141, or may be formed in a separate form by being coupled to a special propeller member (not illustrated).
While the embodiment of the present invention illustrated in FIG. 6 illustrates a 4-wing propeller, there is no limitation to the number of propeller wings, and different numbers of wings can be used for the propeller-type dynamic pressure generator 400. Similarly, while a helical grove spiral shape was illustrated in the dynamic pressure generator 300 illustrated in FIGS. 1 and 3, the present general inventive concept is not limited thereto, and different shapes can be used to create an effective force P.
According to the spindle motor and the spindle motor assembly, and the image forming device having the same, of the present general inventive concept, helical grooves formed on the upper surface of the rotor frame serve to generate a dynamic pressure in the axial direction of the shaft during the rotation of the rotor to thereby prevent the separation of the rotor without adding a separate part or a subsidiary material.
In addition, as the shaft coupled to the rotor is closely contacted to the bearing, the polygon mirror may operate at a fixed axial position.
Although the exemplary embodiment of the present general inventive concept has been described, it will be understood by those skilled in the art that the present general inventive concept should not be limited to the described exemplary embodiment, but various changes and modifications can be made within the spirit and scope of the present general inventive concept as defined by the appended claims.
Patent Application
20080074011
