JPH05215982A - Optical deflection device - Google Patents

Abstract

PURPOSE:To prevent position precision from decreasing rotation by tapering either of clamping members which champs a rotary polygon mirror to a flange and the contact surface of the rotary polygon mirror. CONSTITUTION:The rotary polygon mirror 12 is engaged with a rotary shaft 9, and the three clamping members (flat countersunk head screw or oval countersunk head screw) 18 having tapered screw heads are run through fitting holes 13 and clamped with female screws 15. Then binder screws (flat head screw) 17 are clamped with three female screws 15 formed in the seat of the rotary shaft 9. By using the flat countersunk heads 18 the tapered parts of the flat countersunk screws 18 is pressed against the corner parts of the screw holes of the rotary polygon mirror 12 to hold the mirror 12 therebetween and fixed with reaction forces generated by the tapered parts of the flat countersunk screws 18 against radius-directional forces. As the tapering angle is made smaller and smaller than 90 deg., the reaction forces from the corner parts of the screw holes are larger and larger to give more effect. The heads of the binder head screws 17 hold the rotary polygon mirror 12 therebetween against the force in the direction of the rotary shaft, thereby preventing the rotary polygon mirror 12 from shifting in position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of fixing a rotary polygon mirror in an optical deflecting device which deflects a light beam from a laser light source or the like and scans an irradiated object.

[0002]

2. Description of the Related Art FIG. 9 is a block diagram of a laser scanning device. The laser element 2 is driven by the current from the laser driver 1.
Is driven to emit light, and the emitted laser beam is collimated by the collimator lens system 3 into a parallel light beam, which is deflected and reflected by the rotating rotary polygon mirror 4, and is combined by the fθ lens group 5 on the photoconductor drum 6 which is the irradiated body. Scan with the imaged spot light. In such a device, the rotary polygon mirror 4 maintains an ultra-high-precision plane for highly accurate deflection for scanning, and is lightweight in order to reduce the power consumption of the motor that rotationally drives the rotary polygon mirror 4. Therefore, an aluminum alloy having a metal vapor-deposition film for preventing oxidation formed on the reflection surface is used.

As shown in FIG. 8, the rotary polygonal mirror 4 is inserted around a rotary shaft 7 in a clearance fit state, and is screwed to a flange provided on the rotary shaft 7 with a screw 8.
That is, the rotary polygon mirror 4 is provided with a plurality of screw insertion holes at equal intervals, the female screw 8 is passed through this hole, and the plurality of female screw portions provided on the flange of the rotary shaft 7 are brought into contact with each other, whereby the screw head of the female screw 8 is The rotary polygon mirror 4 is sandwiched between and the flange. Such a fixing method is a very excellent method in terms of cost and assembling.

[0004]

However, in the above-mentioned conventional example, the fastening force varies depending on the machining accuracy of the screw. When a force exceeding the fastening force of the screw is applied when the rotary polygon mirror rotates, the center of rotation of the rotary polygon mirror shifts. When the amount of deviation is the same, the larger the polygonal mirror, the greater the vibration that occurs, and the quality of the recorded image on the object to be irradiated deteriorates significantly.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide a fixing method for a rotary polygon mirror in which the positional accuracy does not deteriorate during rotation of the rotary polygon mirror.

The optical deflecting device according to the present invention for achieving the above-mentioned object is provided with a rotary polygon mirror when the rotary polygon mirror is positioned in the rotary axis direction by abutting against a flange provided on the rotary shaft. The screw is fixed to the rotary shaft by pressing a screw having a tapered head into the screw hole.

According to the method of fixing the rotary polygon mirror having the above-mentioned structure, since the rotary polygon mirror is fixed by the wedge action of the tapered screw portion and the screw hole of the rotary polygon mirror, the inertia of the rotary polygon mirror is fixed. There is no fear that the center of the rotary polygon mirror will move with respect to the rotation axis due to force or centrifugal force.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical deflecting device of the present invention will be described in detail based on the embodiments shown in FIGS. FIG. 1 shows an exploded view of a rotary polygon mirror and a rotary shaft before being fixed. The rotary polygonal mirror 12 which is a low prism and is made of aluminum and which is a substantially rectangular prism is a rotary shaft 9 made of iron.
The state before being tightened is shown. The rotary polygon mirror 12 has a plurality of side surfaces 11 which are plane reflecting mirrors. At the center of the rotary polygon mirror 12, a hole 10 for engaging with the rotary shaft 9 is opened, and it has a function of aligning the rotary centers of the rotary shaft 9 and the rotary polygon mirror 12. Outside the hole 10, six mounting holes 13 are formed at equal intervals on a substantially circle centered on the center of the rotary polygon mirror 12, and these are coaxial with the hole 10 (the central axes of the holes are parallel to each other). That). The seat 14 of the rotary shaft 9 for receiving the rotary polygonal mirror 12 for positioning and fixing has a flat surface with high precision, and the small hole 1 formed in the rotary polygonal mirror 12
Female screws 15 are cut at six positions equiangularly at positions having the same diameter as 3. Further, there is provided a circular groove 16 for attaching a balance weight that balances the rotation when the rotary polygon mirror 12 and the rotary shaft 9 are fixed while maintaining the coaxiality with the central hole 10.

The above-mentioned components are assembled in the following manner. First, the rotary polygon mirror 12 is engaged with the rotary shaft 9, and three fastening members (generally called a countersunk screw or a round countersunk screw) 18 having a tapered screw head are passed through the mounting hole 13. It is fastened to the female screw 15. Next, three bind head screws 17 are similarly fastened to the female screw 15 provided on the seat of the rotary shaft 9. The bind head is a flat head that is not tapered. 2 and 3 are cross-sectional views of the main part after the rotary polygon mirror is fixed. The following forces act on the rotating polygon mirror.

(1) Inertial force of the rotating polygon mirror itself: T1 (2) Centrifugal force generated by the deviation between the rotating polygon mirror itself and the center of rotation: F1 The inertia moment of the rotating polygon mirror is J (= 1.36 × 10 ^{− Four}
[M ² kg]), and the mass of the rotating polygon mirror is m (= 0.1 [k
g]) the angular acceleration is α (= 5 × 10 4 [rad / s ² ],
Angular velocity ω (= 2094 [rad / s]), binding head screw tightening force P (= 1300 [N]), force Fb for fastening the rotary polygon mirror generated by screw tightening force, binding head screw tightening Torque Tb for fastening the rotary polygon mirror generated by the force, coefficient of static friction μ (= 0.28) between the screw of the bind head and the rotary polygon mirror, distance R (from the center of rotation of the rotating shaft to the fastening portion of the screw of the bind head) = 15 × 10
^-3 [m]), the number N of fastenings of the bind head screw (= 3), and the maximum deviation ε (=) between the center of rotation of the rotating shaft and the center of the rotating polygon mirror.
20 × 10 ⁻⁶ [m]). As shown in FIG. 10, the static friction coefficient between the screw head and the rotary polygon mirror was determined by measuring F and N using the same materials as the rotary polygon mirror (aluminum) and the screw head (iron), respectively. The amount of deviation between the center of rotation of the rotating shaft and the center of gravity of the rotating polygon mirror was determined in consideration of the dimensional tolerance of the inner diameter of the rotating polygon mirror and the dimensional tolerance of the outer shape of the rotating shaft.

The force of (1) is calculated as follows.

The force of T1 = Jα = 6.8 [Nm] (2) is calculated as follows.

F1 = mεω2 = 8.76 [N] Let us consider the case of fastening with only the bind head screw. The bind head screw fastens the rotary polygon mirror by static friction between the screw head 17a and the rotary polygon mirror. Therefore, F
b and Tb are calculated as follows.

Tb = μPRN = 16.3 [Nm] Fb = μPN = 11092 [N] Although Tb> T1 and Fb> F1 are calculated, the coefficient of static friction μ varies depending on the machining accuracy of the screw, and the rotary polygon mirror. There is a possibility that T1 which acts on T will exceed Tb.
Even if the number of binding head screws is increased, the possibility that the center of rotation of the rotary polygon mirror moves with respect to the center of rotation remains.

However, if a countersunk screw is used, the taper portion 18a of the countersunk screw 18 comes into pressure contact with the corner of the screw hole of the rotary polygonal mirror, and the rotary polygonal mirror 12 is clamped to generate a radial force. On the other hand, a reaction force is generated from the taper portion of the screw of the head, and the screw is fixed. The smaller the taper angle is from 90 degrees,
This is effective because the reaction force from the corners of the screw holes increases. The head 17 of the screw 17 of the binding head is
Since a holds the rotary polygon mirror 12, the displacement of the seat of the rotary shaft and the rotary polygon mirror does not occur even when a large rotary polygon mirror is used or when the rotary polygon mirror is rotated at a high speed of 20000 rpm. ..

The principle of fixing the rotary polygon mirror will be described below. FIG. 4 is an enlarged view of the mounting portion of the flat head screw. The mounting hole of the rotary polygon mirror 12 has a diameter of 3.5 mm, a chamfer of 0.3 mm, and the taper portion of the countersunk screw 18 is 60 °. When the countersunk screw 18 is tightened, as shown in FIG. 5, the entire circumference of the taper portion 18a of the screw head is pressed against the screw hole. Further, when the countersunk screw is tightened, the rotary shaft and one point of the inner diameter of the rotary polygon mirror come into contact with each other, so that the rotary polygon mirror can be fixed to the rotary shaft by using one or more countersunk screws. The center of rotation of the rotary polygon mirror does not move due to inertial force and centrifugal force. In addition, in the above-described embodiment, an example in which three countersunk screws are used in consideration of safety is shown. In addition, in the above-described embodiment, three bind head screws are also used in consideration of further safety.

FIG. 7 shows changes in the distance of the eccentric center of gravity on the rotary polygon mirror side when the conventional fixing method and the fixing method of the present invention are used. From the stopped state, steady rotation speed 20000r
This is a repeated cycle of reaching pm and stopping. In the conventional fixing method, the eccentric center-of-gravity distance largely changes the first time and continues to change thereafter. However, it was confirmed that the eccentric center-of-gravity distance hardly changed by the fixing method of the present invention.

FIG. 6 shows a structure in which the rotary polygon mirror and the rotary shaft are fastened by using countersunk bolts instead of the three countersunk screws shown in FIG. Similar to the first embodiment, the tapered portion 19a of the bolt 19 having a flat head is pressed against the corner portion of the screw hole of the rotary polygon mirror 12, and the rotary polygon mirror 12 is held.

FIG. 11 shows a modification in which the contact surface of the rotary polygon mirror 12 with the screw head is not tapered, but only the screw head is tapered. The countersunk screw 20 has a tapered portion 20a.

FIG. 12 shows a modification in which only the contact surface of the rotary polygon mirror 12 with the screw head is tapered and the screw head is not tapered. Head 21 of bind head screw 21
a is flat.

[0021]

As described above, according to the method of fixing a rotary polygon mirror according to the present invention, the central axis of the rotary polygon mirror does not shift due to the influence of the rotation, so that the deflected light flux is touched. Does not occur.

[Brief description of drawings]

FIG. 1 is an exploded view of a rotary polygon mirror before being fixed.

FIG. 2 is a cross-sectional view after fixing the rotary polygon mirror.

FIG. 3 is a cross-sectional view after fixing the rotary polygon mirror.

FIG. 4 is an enlarged view of a mounting location of a countersunk screw.

FIG. 5 is a diagram showing how a taper portion of a screw is in contact with a chamfered portion of a screw hole.

FIG. 6 is an enlarged view of a bolt mounting portion.

FIG. 7 is a diagram showing a relationship between the number of times of endurance and an eccentric center of gravity distance.

FIG. 8 is a plan view of a conventional rotary polygon mirror.

FIG. 9 is a configuration diagram of a laser scanning device.

FIG. 10 is a method for measuring the coefficient of static friction.

FIG. 11 is an enlarged view of a mounting position of a flat head screw.

FIG. 12 is an enlarged view of a mounting portion of a binding head screw.

[Explanation of symbols]

 9 rotary shaft 10 hole 11 plane mirror 12 rotary polygon mirror 13 small hole 14 rotary shaft seat 15 female screw 16 circular groove 17 bind head screw 18 countersunk screw

Claims (2)

[Claims] 1. An optical deflecting device for positioning a rotary polygon mirror in the direction of the rotation axis by abutting a flange provided on the rotary shaft, and a fastening member for fastening the rotary polygon mirror to the flange, and the rotary polygon mirror. An optical deflecting device characterized in that at least one of the contact surfaces of the above is tapered. 2. The optical deflector according to claim 1, wherein the rotary polygon mirror is fixed to the flange by using a plurality of the fastening members.