Optical deflection device, image printing apparatus, and optical deflection device manufacturing method

This invention relates to an optical deflection device capable of obtaining sufficient durability without any positional error of a polygon mirror even when the rotational speed of the polygon mirror increases to 50,000 rpm or more. An optical deflection device includes a base member, a polygon mirror which is formed into a regular polygon and has a reflecting surface on each peripheral end face, a flange member which holds the polygon mirror and rotates with respect to the base member, and a press member which presses the polygon mirror against the flange member. In this optical deflection device, surface roughening is performed for at least one of the holding surface of the flange member which holds the polygon mirror and the held surface of the polygon mirror which is held by the holding surface, and the holding surface and held surface are bonded with an adhesive.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical deflection device which can be preferably adopted in, e.g., a barcode reader or an image printing apparatus such as a digital copying machine, a printer, a facsimile apparatus, or a multifunction apparatus having the functions of these apparatuses, an image printing apparatus having the optical deflection device, and an optical deflection device manufacturing method.

2. Description of the Prior Art

An image printing apparatus or the like emits on the basis of read information a laser beam to a polygon mirror which rotates at high speed in an optical deflection device, scans a reflected beam to project it on a photosensitive body, and prints an image. Optical deflection devices using a polygon mirror are disclosed in many Japanese patent publications. One example is an optical deflection device shown inFIG. 1(see, e.g., Japanese Unexamined Patent Publication No. 2002-48997).

An optical deflection device disclosed in this reference will be explained with reference toFIG. 1.

A polygon mirror72on which a reflecting surface72afor reflecting and deflecting a laser beam is formed on a peripheral end face having a regular polygonal shape is fitted on a flange member71assembled integrally with an external cylinder bearing73. The polygon mirror72is pressed and biased against the flange member71by a leaf spring74supported by a press plate75, and is integrally held by the flange member71. In this manner, a mirror unit70is formed.

An internal cylinder bearing65which is radially fitted in the external cylinder bearing73, and an upper thrust bearing66′ and lower thrust bearing64which abut against the external cylinder bearing73in the thrust direction are fitted on, a base member60. The internal cylinder bearing65, upper thrust bearing66, and lower thrust bearing64are positioned in the thrust direction by a screw68and stationary plate67.

A stationary yoke61is fixed to the base member60, and a printed wiring board63having a magnet coil62is further fixed. A magnet77which faces the magnet coil62is fixed to the flange member71. When the magnet coil62is energized, the mirror unit70is permitted to rotate at high speed above the base member60via the bearings by the interaction between the magnet coil62and the magnet77.

The polygon mirror72is held by a holding surface71cof the flange member71via a held surface72b(processing reference surface).

To correct the face tangle angle of the reflecting surface72aof the polygon mirror72to a desired value, the held surface72bmust be processed at high precision. The holding surface71cand held surface72bare conventionally so machined as to obtain mirror surfaces with a surface roughness (Ry) of 1 μm or less. When the mirror-finish holding surface71cand held surface72babut against each other to fix the polygon mirror72and flange member71, the polygon mirror72has a positional error due to the centrifugal force of high-speed rotation. As a result of rotating the mirror unit70in this state, the balance may be lost to generate vibrations.

To prevent this, the above-mentioned reference employs surface treatment for one or both of the holding surface71cand held surface72bso as to adjust the surface roughness (Ry) to 3 μm≦Ry≦20 μm. Note that Ry is the maximum height of undulations formed on the surface, and is defined by JIS B0601. With this arrangement, even if centrifugal force acts on the polygon mirror72which rotates at high speed, the polygon mirror72can hardly have a positional error and does not unnecessarily vibrate because of frictional force generated between the holding surface71cand the held surface72b.

Recently, higher speed and higher precision of image printing are required more and more. For this purpose, the polygon mirror must also rotate at higher speed. Even if the rotational speed of the polygon mirror increases to 50,000 to 60,000 rpm, the polygon mirror must have satisfactory durability without any positional error.

Examinations made by the present inventor reveal that the invention described in the above reference can prevent a positional error of the polygon mirror when the rotational speed of the polygon mirror is up to about 50,000 rpm, but when the rotational speed exceeds 50,000 rpm, the polygon mirror may have a positional error.

SUMMARY OF THE INVENTION

The present invention has been made to overcome the conventional drawbacks, and has as its object to provide an optical deflection device capable of obtaining sufficient durability without any positional error of a polygon mirror even when the rotational speed of the polygon mirror increases to 50,000 rpm or more, an image printing apparatus, and an optical deflection device manufacturing method.

To achieve the above object, the first aspect of the present invention provides an optical deflection device comprising a base member, a polygon mirror which is formed into a regular polygon and has a reflecting surface on each peripheral end face, a flange member which holds the polygon mirror and rotates with respect to the base member, and a press member which presses the polygon mirror against the flange member, wherein surface roughening is performed for at least one of a holding surface of the flange member which holds the polygon mirror and a held surface of the polygon mirror which is held by the holding surface, and the holding surface and the held surface are bonded with an adhesive.

The second aspect of the present invention provides an optical deflection device wherein the surface roughening described in the first aspect includes abrasive blasting.

The third aspect of the present invention provides an optical deflection device described in the first aspect wherein a surface roughness (Ry) of the holding surface and/or the held surface having undergone surface roughening satisfies a conditional expression: 3 μm≦Ry≦20 μm (where Ry: maximum height (JIS B0601)).

The fourth aspect of the present invention provides an optical deflection device wherein the adhesive described in the first aspect has a Young's modulus of not more than 1,700 MPa and preferably not more than 1,144 MPa at 25° C.

The fifth aspect of the present invention provides an optical deflection device wherein the polygon mirror described in the first aspect is rotated at a rotational speed of not less than 50,000 rpm.

The sixth aspect of the present invention provides an image printing apparatus comprising the optical deflection device described in the first aspect.

The seventh aspect of the present invention provides an optical deflection device wherein the polygon mirror and the flange member described in the first aspect are formed from aluminum.

The eighth aspect of the present invention provides an optical deflection device manufacturing method comprising the steps of integrally fitting a flange member on a bearing, performing flat work for a holding surface of the flange member arranged to hold a polygon mirror having a plurality of reflecting surfaces so as to become a surface perpendicular to an axis of rotation of the bearing, performing surface roughening for the holding surface of the flange member, applying an adhesive between the holding surface of the flange member and a held surface of the polygon mirror held by the holding surface, and mounting a press member which presses and biases the polygon mirror against the flange member.

The ninth aspect of the present invention provides an optical deflection device manufacturing method wherein the surface roughening described in the eighth aspect includes abrasive blasting.

The 10th aspect of the present invention provides a manufacturing method for an optical deflection device described in the eighth aspect wherein a surface roughness Ry of the holding surface having undergone surface roughening satisfies a conditional expression: 3 μm≦Ry≦20 μm (where Ry: maximum height (JIS B0601)).

The 11th aspect of the present invention provides an optical deflection device manufacturing method wherein the adhesive described in the eighth aspect has a Young's modulus of not-more than 1,700 MPa and preferably not more than 1,144 MPa at 25° C.

The 12th aspect of the present invention provides an optical deflection device manufacturing method wherein the polygon mirror described in the eighth aspect is rotated at a rotational speed of not less than 50,000 rpm.

As is apparent from the above aspects, the optical deflection device, image printing apparatus, and optical deflection device manufacturing method according to the present invention can prevent the positional error of a polygon mirror and obtain sufficient durability even when the polygon mirror is rotated at a very high speed of 50,000 rpm or more.

The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which a preferred embodiment incorporating the principle of the present invention is shown by way of illustrative examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of a beam scanning optical apparatus having an optical deflection device will be described with reference toFIG. 2.

InFIG. 2, reference numeral1denotes an optical deflection device having a polygon mirror1a;2, a semiconductor laser;3, a collimator lens for a beam shaping optical system;4, a first cylindrical lens;5and6, f-θ lenses;7, a second cylindrical lens;8, a mirror;9, a cover glass; and10, a photosensitive drum. Reference numeral11denotes an index mirror for detecting synchronization; and12, an index sensor for detecting synchronization.

A beam emitted by the semiconductor laser2is collimated into parallel light via the collimator lens3. Parallel light passes through the first cylindrical lens4of the first imaging optical system, and impinges on the reflecting surface of the polygon mirror1awhich-rotates at high uniform speed in the optical deflection device1. Light reflected by the reflecting surface of the polygon mirror1apasses through the second imaging optical system comprised of the f-θ lenses5and6and second cylindrical lens7. Light reaches the outer surface of the photosensitive drum10via the mirror8and cover glass9. Main scanning of reflected light is done at a predetermined spot diameter on the outer surface of the photosensitive drum10.

Fine adjustment is performed by an adjustment mechanism (not shown) in the main scanning direction. Sync detection for each line is executed by emitting a beam before the start of scanning to the index sensor12via the index mirror11.

To obtain a high-quality latent image on the photosensitive drum10in the beam scanning optical apparatus, the polygon mirror1amust be shaped into a regular polygon, have a plurality of high-precision reflecting surfaces, and rotate at high speed without any inclination from the axis of rotation and any positional error along the axis of rotation.

The optical deflection device mounted in the beam scanning optical apparatus will be explained in detail with reference toFIG. 3.FIG. 3is a longitudinal sectional view showing the optical deflection device.

Reference numeral20denotes a base member which is formed of a metal such as aluminum, holds each member (to be described below), and is fixed to the beam scanning optical apparatus. A stationary yoke21is buried in the upper surface of the base member20such that the upper surface of the stationary yoke21becomes flush with the upper surface of the base member20. A printed wiring board23on which a plurality of magnet coils22are arranged within the same plane is further fixed to the upper surface of the base member20.

Reference numeral31denotes a flange member which is formed of aluminum, brass, stainless steel, or the like, and comprised of a disk-like flange31aand cylindrical portion31b. The lower surface of the flange31ais formed into a holding surface31cfor holding a polygon mirror32. An external cylinder bearing33of a mirror unit30is integrally fitted by shrink fitting or press fitting in a hole formed at the center of the cylindrical portion31bof the flange member31.

The polygon mirror32is formed of a metal such as aluminum into a high-precision regular polygon. A reflecting surface32afor reflecting and deflecting a laser beam is formed on each peripheral end face. The polygon mirror32is fitted around the cylindrical portion31bof the flange member31. A held surface32bof the polygon mirror32is abutted against the holding surface31c. The held surface32bof the polygon mirror32serves as a reference surface used to process the reflecting surface32a, and is mirror-finish.

A leaf spring (press member)34formed by press work of a stainless steel sheet, phosphor bronze steel sheet, or beryllium steel sheet is fitted on the cylindrical portion31b. A mirror press plate35is fastened and fixed to the cylindrical portion31bof the flange member31by a machine screw36so as to press the press member34against the lower surface of the polygon mirror32. The leaf spring34presses the polygon mirror32, and the held surface32bof the polygon mirror32is pressed against the holding surface31cof the flange member31. This can prevent deformation of the polygon mirror32without applying any excessive stress to the polygon mirror32.

A permanent magnet37which faces the magnet coil22and generates a running torque is bonded with an adhesive to the lower portion of the mirror press plate35.

The mirror unit30is comprised of the flange member31, polygon mirror32, external cylinder bearing33, leaf spring34, mirror press plate35, machine screw36, and permanent magnet37.

A shaft20astands at the center of the base member20. A lower thrust bearing24and upper thrust bearing26are fitted on the shaft20aat an interval along the axis of the shaft20a. An, internal cylinder bearing25is fitted on the shaft20abetween the lower thrust bearing24and upper thrust bearing26of the shaft20a. The external cylinder bearing33of the mirror unit30is fitted on the internal cylinder bearing25, and fixed to the shaft20aby threadably fixing a machine screw28extending through a plate27to the shaft20a. The internal cylinder bearing25, external cylinder bearing33, lower thrust bearing24, and upper thrust bearing26are formed of alumina or ceramic (e.g., silicon nitride).

The external cylinder bearing33which holds the mirror unit30performs radial dynamic-pressure rotation on a radial bearing formed by the internal cylinder bearing25, and thrust dynamic-pressure rotation on a thrust bearing formed by the lower thrust bearing24and upper thrust bearing26. A dynamic-pressure generation groove is formed in at least any one of the bearing surface of the lower thrust bearing24, the bearing surface of the upper thrust bearing26, and the outer surface of the internal cylinder bearing25. A wind generated upon high-speed rotation flows into the dynamic-pressure generation groove. A strong wind pressure generated in the dynamic-pressure generation groove forms a gap of about 3 to 10 μm between each fixed bearing and the external cylinder bearing33, decreasing the resistance between these bearings. The mirror unit30can smoothly rotate at high speed in a non-contact state.

The optical deflection device is formed in the above way. High-speed rotation of the mirror unit30generates a harsh wind sound due to disturbance of the air flow or noise due to vibrations. In particular, an office or the like in which quietness is necessary must take any measure for silence. It is therefore desirable to employ a cover facing the base member20and cover the mirror unit30and the like. A cover as disclosed in Japanese Unexamined Patent Publication No. 11-84296 may be arranged.

A method of manufacturing the mirror unit30will be explained with reference toFIGS. 4 and 5.FIG. 4is an enlarged sectional view showing the mirror unit30.FIG. 5is an enlarged view showing the contact between'the holding surface31cof the flange member31and the held surface32bof the polygon mirror32.

The external cylinder bearing33is mirror-finish such that an upper end face33aand lower end face33bform right angles with the central axis, and an inner surface33cand outer surface33dbecome concentric with the central axis. The external cylinder bearing33is integrally fitted by shrink fitting or press fitting in the central hole of the flange member31.

The holding surface31cof the flange member31undergoes flat work using the upper end face33aor lower end face33bof the external cylinder bearing33as a reference so as to become parallel to the upper end face33aand lower end face33b. As a result, the holding surface31cperpendicular to the axis of rotation of the external cylinder bearing33can be attained.

After the flange member31except the holding surface31cis masked, the holding surface31cis subjected to surface roughening such as abrasive blasting, and processed into a rough surface.

An adhesive is applied to the holding surface31cof the flange member31, and the polygon mirror32is fitted on the cylindrical portion31bof the flange member31. The held surface32bof the polygon mirror32is press-bonded to the holding surface31cof the flange member31. In some cases, the adhesive may be applied to the held surface32bof the polygon mirror32.

The leaf spring34is inserted into the cylindrical portion31bof the flange member31, and the mirror press plate35is fastened and fixed to the cylindrical portion31bof the flange member31by the machine screw36. If the adhesive is applied to the contact between the mirror press plate35and the cylindrical portion31bof the flange member31, the mirror press plate35is more firmly fixed to the flange member31.

Consequently, the held surface32bof the polygon mirror32is pressed against the holding surface31cof the flange member31by the leaf spring34. As shown inFIG. 5, projections formed by abrasive blasting on the holding surface31ccatch into the held surface32b, and an adhesive40flows into recesses formed by abrasive blasting on the holding surface31c.

The contact between the holding surface31cof the flange member31and the held surface32bof the polygon mirror32is very firm. Even if the polygon mirror32rotates at a very high speed of 50,000 rpm or more, the polygon mirror32does not shift from the flange member31, and satisfactory durability can be obtained.

The same effects can also be achieved when not the flange member31but the held surface32bof the polygon mirror32undergoes abrasive blasting in the above manufacturing method.

Abrasive blasting may also be performed for both the holding surface31cand held surface32b.

In addition, the holding surface31cof the flange member31may be processed into a rough surface by cutting instead of mirror finish.

The influence of a change in the rough surface of the holding surface31cof the flange member31on an initial face tangle angle (inclination of the polygon mirror from the axis of rotation) and vibration change (balance) will be explained on the basis of Table 1.

Table 1 exhibits nine flange members which were formed by surface roughening according to various methods and had different rough surfaces. After the surface roughness Ry (μm) of each flange member was measured, the flange member was assembled into a polygon mirror unit by the above-described method. The initial face tangle angle (sec) of the polygon mirror and the vibration change (m/s2) upon rotation at 60,000 rpm for 1,000 h were measured. The surface roughness (Ry) before surface roughening was a mirror surface roughness of 0.1 μm or less, and the adhesive used to bond the polygon mirror was Cemedine Super X. The number of samples was 10 for each polygon mirror, and each value was a mean value.

Flange member {circle around (1)} by form rolling had an excessively rough processed surface, and the polygon mirror greatly inclined. Flange members {circle around (7)} to {circle around (9)} by cutting into a mirror surface or almost the mirror surface did not have any projection regardless of abrasive blasting, and no adhesive entered the bonded surface. Only simple bonding between flat surfaces could not suppress a positional error of the polygon mirror. For practical use, the initial face tangle angle of the polygon mirror is desirably 150 sec or less, and the vibration change is 2 m/s2or less.

Flange members {circle around (2)} to {circle around (6)} by abrasive blasting were found preferable with small face tangle angles and small vibration changes.

Hence, the flange member is desirably so processed as to set the surface roughness of the holding surface of the flange member to 3 μm≦Ry≦20 μm.

Note that Ry is a maximum height defined by JIS B0601, and is a value obtained by extracting a profile by only the reference length along the mean line from the roughness profile and measuring the spacing between the peak line and the valley line of the extracted part in the direction of the longitudinal magnification of the roughness profile.

The influence on the vibration change (balance) upon changing the adhesive used to bond the holding surface31cof the flange member31and the held surface32bof the polygon mirror32and the flatness of the reflecting surface32aof the polygon mirror32upon assembly into the polygon mirror unit30will be explained on the basis of Table 2.

Table 2 represents the use of four types of adhesives. After the Young's modulus (MPa) was measured for each adhesive, the flange member was assembled into a polygon mirror Unit30by the above-described method. The vibration change (m/s2) upon rotation at 60,000 rpm for 1,000 h and the flatness of the reflecting surface of the polygon mirror were measured. The surface roughness (Ry) before surface roughening was, a mirror surface roughness of 0.1 μm or less, the surface roughness (Ry) of the holding surface of the flange member was 6.7 μm (abrasive blasting: abrasive grain #230), and the adhesive was cured at 80° C. after assembly. The number of samples was 10 for each polygon mirror, and each value was a mean value.

The vibration change was preferably 2 m/s2or less for each flange member. The flatness of the polygon mirror was as low as λ/4 or more for adhesive {circle around (4)}, but both the vibration change and flatness were good for adhesives {circle around (1)} to {circle around (3)}. Adhesives {circle around (1)} to {circle around (3)} were flexible and deformed to prevent shrinkage upon curing the adhesive or thermal deformation of the flange member from transmitting to the reflecting surface of the polygon mirror. As a result, the flatness of the reflecting surface was kept high.

From this, an adhesive having a Young's modulus of 1,700 Mpa or less, and more preferably 1,144 MPa or less at room temperature (25° C.) is desirably adopted.