JP3080451B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with a laser beam scanner.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus provided with a laser beam scanner, a member for supporting the laser beam scanner with respect to the apparatus main body includes sheet metal stays passed over a frame such as front and rear side plates of the apparatus main body. Such frame structures are used.

[0003]

However, in the above-mentioned prior art, the structure supporting the laser beam scanner is transmitted by the vibration generated by the laser beam scanner itself or from another drive system of the image forming apparatus. Vibrated to some extent by vibration. For this reason, the light beam scanned by the laser beam scanner device vibrates, and the light amount distribution on the photoreceptor fluctuates, causing a density unevenness in the sub-scanning direction on the image, resulting in a decrease in image quality. Was.

The main factors that cause the light beam to be scanned to vibrate are as follows. (1) Since the natural frequency of the structure supporting the laser beam scanner device and the frequency of the vibration generated by the laser beam scanner device are close to each other, resonance occurs and the scanning is performed with a large amplitude vibration. The light beam vibrates. (2) The laser beam scanner is mounted between the "belly" and the "node" of the deformation caused by the vibration of the structure supporting the laser beam scanner. In other words, because the structure supporting the laser beam scanner device is formed at a small angle due to vibration but forms a slope and is deformed, the laser beam scanner device is attached,
The light beam to be scanned causes “flagging”, and the scanning line vibrates largely in the sub-scanning direction on the photoconductor at the focal position. (3) Since the structure supporting the laser beam scanner device is made of a material such as a steel plate having a small vibration damping rate, the applied vibration is hardly attenuated and easily vibrated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an image forming apparatus in which a resonance phenomenon of support means of a laser beam scanner is suppressed.

[0006]

According to the present invention, there is provided a laser beam scanner having a motor.
Supporting the scanner device and the laser beam scanner device.
And a support means fixed to the apparatus main body.
In the forming apparatus, the laser beam scanner device is activated.
And the laser beam scanner device
And the natural frequency of the combined system consisting of
It is characterized by being comprised so that it might become.

Further , a laser beam scanner having a motor is provided.
For supporting the scanner device and the laser beam scanner device.
And a support means fixed to the apparatus main body.
In the forming apparatus, the two opposite sides of the supporting means are
It is substantially perpendicular to the support surface of the laser beam scanner device and
Bent so that the height is almost the same
And the laser via is provided substantially at the center between the two bent portions.
A beam scanner device is provided.

[0008] Laser beam scanner device having motor
Device for supporting the laser beam scanner device
And a support means fixed to the main body.
The laser beam is attached to two opposite sides of the support means.
The height is approximately perpendicular to the support surface of the
Providing differently bent portions, the two
Height of the bent part from the center between the bent parts of
The laser beam scanner device is biased toward the lower side.
It is characterized by being placed.

The supporting means for supporting the laser beam scanner is preferably made of a damping steel plate.

[0010]

According to the present invention having the above structure, the laser beam
Shake can be suppressed.

The positional relationship between the laser beam scanner and the support means is such that the laser beam scanner is disposed at the "rigid center of gravity" of the support means, that is, the support means is symmetrically positioned with respect to the laser beam scanner. By increasing the rigidity, the laser beam scanner device is supported at the "belly" portion of the bending vibration of the support means, and even if it is elastically deformed by the vibration, the inclination does not occur much compared to the reference surface before deformation, The irradiated laser beam does not rotate. As a result, a uniform image without shading is obtained on the photoreceptor.

In addition, the vibration level can be further reduced by forming the support means from a damping steel plate while preventing the resonance phenomenon from occurring.

[0013]

(Embodiment 1) FIG. 1 is a partial perspective view of a digital copying apparatus to which the present invention is applied, 1 is a laser beam scanner, and 2 is a stay as a support means.

The laser beam scanner 1 is composed of a semiconductor laser, a collimator lens, a motor, a polygon mirror, an fθ lens, etc., and scans a laser beam modulated according to a recording signal from a slit-shaped opening 3.

The stay 2 is passed between the front and rear side plates (not shown) of the digital copying machine, is positioned with respect to the front side plate by tongues 4 and 5, and is positioned on the rear side plate by tongues 6 and 7. And are fixed with screws. The stay 2 is a pressed product of a steel plate,
Reference numerals 8 and 9 denote portions bent at right angles from the reference surface of the stay 2 (the surface on which the laser beam scanner device 1 is mounted and fixed). The bending portions 8 and 9 increase the value of the second moment of area when the stay 2 is viewed as a beam in the direction of the arrow Y in the figure. That is, it plays a role of increasing the rigidity and increasing the natural frequency of the stay 2.
Reference numeral 10 denotes a slit-shaped opening provided in the bending and erecting section 9 so that a laser beam scanned from the laser beam scanner 1 can pass therethrough.

FIG. 2 is a schematic sectional view of a digital copying apparatus according to the present embodiment.

The reading optical system includes an original placing glass 11, an original irradiating lamp 12, mirrors 13, 14, 15 and a lens 1.
6, a mirror 17, and a CCD line sensor 18.

The writing optical system comprises a laser beam scanner 1, mirrors 19 and 20, and a photosensitive drum 21 as a photosensitive member. The laser beam scanner device 1 is supported and fixed on a stay 2 fixed across the front and rear side plates of the main body of the copying machine. The scanned laser beam passes through a slit-shaped opening 10 provided in the stay 2 and a mirror 19. , 20 and form an image on the photosensitive drum 21 to form a latent image.

A corona charger 22, a developing unit 23, a corona charger 24, and a cleaner 25 are arranged around the photosensitive drum 21 to constitute a well-known electrophotographic process. The transfer paper is fed from the paper feed cassette 26 or 27, and the toner image is transferred to the surface by the corona charger 24. Next, the toner image is conveyed by the conveyance belt 28 and discharged out of the apparatus main body after the toner image is fixed by the fixing device 29.

The relationship between the laser beam scanner 1 and the stay 2 will be described in detail with reference to FIG. The laser beam scanner device 1 is disposed substantially near the center in both the X and Y directions of the stay 2 and is fixed with screws. At the same time, the Z-direction dimensions of the bent and raised portions 8 and 9 of the stay 2 are equalized. The stay 2 can be regarded as a beam whose both ends are fixed by the front and rear side plates of the apparatus main body. The natural frequency when a beam with a uniform cross section is fixed at both ends is fm (m =
1, 2, 3...) Are given as Equation 1 from the equation of the bending motion of the beam.

[0021]

(Equation 1) Where l: length of the beam E: modulus of longitudinal elasticity of the material I: second moment of area ρ: density of the material A: cross-sectional area of the beam The above equation can be applied as it is to the stay 2 alone. In the embodiment, since the laser beam scanner device 1 is fixed substantially at the center of the stay 2, a deviation occurs between the calculated value f and the actual value f. This is because the weight and rigidity of the laser beam scanner device 1 have values that cannot be ignored. Therefore, it is necessary to capture the bending vibration of the beam as a combined system of the laser beam scanner device 1 and the stay 2.

In this embodiment, the stay 2 has a thickness of 3.
The natural frequency of the stay 2 was measured while the laser beam scanner device 1 was made of a 2 mm steel plate and the laser beam scanner device 1 was actually placed and fixed. The measurement was performed by using two acceleration sensors and an FFT analyzer while monitoring the points A and B of the stay 2 and analyzing the vibration when the impulse vibration was applied. FIG. 3 shows the measurement results. The horizontal axis represents frequency (Hz) and the vertical axis represents acceleration (mV). From this, it can be seen that the natural frequency of the combined system of the laser beam scanner device 1 and the stay 2 is 190 Hz for the first order and 360 Hz for the second order.

In this embodiment, the frequency of the vibration generated by the laser beam scanner 1 is 237.5 Hz.
(The rotational speed of the polygon motor is 14.250 rpm), whereas the primary 190 Hz is -20%, and the secondary 190 Hz is
60 Hz is configured with a predetermined value of + 52%.

In general, in bending vibration of a beam, the lower the mode vibration, the larger the amplitude. Further, when the laser beam to be scanned vibrates due to the vibration of the stay 2, the pitch of the density unevenness of the actual image tends to be coarser and visually conspicuous as the frequency is lower.
Therefore, the laser beam scanner device 1 has a positional relationship in which the laser beam does not easily vibrate with respect to the vibration in the lower order mode.
And stay 2 need to be arranged.

In this embodiment, as shown in FIG.
In the X direction (irradiation direction of the laser beam) as well as the Y direction
The laser beam scanner device 1 is disposed substantially at the center of the bending and raising portions 8 and 9 so that the heights of the bending and raising portions 8 and 9 before and after the laser beam irradiation direction are equalized.

FIG. 4 is a model diagram showing the relationship between the laser beam scanner device 1 and the bending vibration deformation of the stay 2. This is shown in a cross-sectional view along the XZ plane in FIG. This shows the relationship between the laser beam scanner device 1 and the stay 2 in this embodiment. Since the stay 2 supports the laser beam scanner device 1 in a symmetrical manner, the stay 2 is deformed due to bending vibration. Even when the laser beam 30 is irradiated, the laser beam 30 is kept horizontal without causing any tilt, and its displacement δ is very small.

In FIG. 4, the positional relationship between the laser beam scanner 1 and the stay 2 will be summarized. The bending height of the bending portion 8 on the rear side of the stay 2 in the laser beam projection direction is h1, the distance from the fixed position of the laser beam scanner 1 to the bending portion 8 is l1, and the stay 2 is on the front side in the laser beam projection direction. Assuming that the height of the bending portion 9 is h2 and the distance from the fixed position of the laser beam scanner 1 to the bending portion 9 is l2, Equation 2 is obtained.

[0028]

(Equation 2) h11h2, l1 ≒ l2 (Embodiment 2) FIG. 5 is a schematic sectional view of a digital copying apparatus according to another embodiment. The second embodiment is different from the first embodiment only in the relationship between the laser beam scanner device 1 and the stay 2, and the other configuration is completely the same as the first embodiment.

FIG. 6 is a model diagram showing the relationship between the laser beam scanner device 1 and the bending vibration deformation of the stay 2 in this embodiment. This differs from that described in the first embodiment in that the stay 2 is not supported in such a manner as to be symmetrical with respect to the laser beam scanner device 1. But,
Since the height of the bending portion 8 closer to the laser beam scanner 1 is lower and the height of the bending portion 9 farther from the laser beam scanner 1 is higher, the laser beam 30 irradiated even when the stay 2 is deformed due to bending vibration. Is kept horizontal without any tilt, and its displacement δ is very small.

Referring to FIG. 6, the positional relationship between the laser beam scanner 1 and the stay 2 will be summarized.

As described in FIG. 4 in the first embodiment, the heights of the bending portions 8 and 9 are h 1 and h 2, and the distance from the fixed position of the laser beam scanner 1 to the bending portions 8 and 9. Let l 1 and l 2 be Equation 3.

[0032]

(Embodiment 3) h1 <h2, l1 <l2 (Embodiment 3) FIG. 7 is a schematic sectional view of a digital copying apparatus according to another embodiment. The same components as those in the first and second embodiments are denoted by the same reference numerals, and description thereof is omitted.

In this embodiment, unlike the first and second embodiments, the stay 2 is much larger than the laser beam scanner device 1, and the entire copying machine is separated into an upper reading optical system and a lower writing optical system. It also supports the lens 16 and the mirror 19 while fulfilling its role. The stay 2 is reinforced by being provided with a bent portion 8 near the laser beam scanner device 1, and a reinforcing stay 31 is mounted near the opposite side. As described above, the rigidity of the stay 2 is increased and the balance of the rigidity is balanced by devising the shape and attaching the reinforcing member, for example, by bending and bending the vicinity of the fixed position of the laser beam scanner device. The laser beam 30 radiated during the deformation due to the laser beam is unlikely to be tilted, and the amount of displacement is small. (Example 4) In Examples 1 to 3, the stay is made of a damping steel plate. However, when using a general damping steel plate (a type in which a damper material is sandwiched between two steel plates), the rigidity and natural frequency are significantly reduced as compared with a steel plate of the same thickness. It is necessary to prevent deformation and resonance by increasing the size or adding a reinforcing member.

In the above description, one kind of steady vibration generated by the polygon motor has been described. However, a high image quality can be obtained without oscillating the laser beam with respect to the steady vibration and unsteady vibration of other frequencies. Can be

[0035]

As described above, the fluctuation of the laser beam
Can be suppressed.

Further, by increasing the rigidity of the supporting means so as to be symmetrical in the vicinity of the fixed position of the laser beam scanner device, the laser beam scanner device can be made to "bend" the bending vibration while suppressing the displacement due to bending vibration. In this case, the laser beam can be maintained without causing tilting and rotation, so that a uniform and beautiful image without uneven density can be obtained on the photoconductor.

Further, the vibration level can be further reduced by forming the supporting means from a damping steel sheet while preventing the resonance phenomenon from occurring.

[Brief description of the drawings]

FIG. 1 is a partial perspective view of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of the same device.

FIG. 3 is a graph showing a natural vibration of a stay of the device.

FIG. 4 is a model diagram showing a relationship between bending vibration deformation of the device and a stay.

FIG. 5 is a schematic sectional view of an image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a model diagram showing a relationship between bending vibration deformation of the stay and a stay of the same device.

FIG. 7 is a schematic sectional view of an image forming apparatus according to a third embodiment of the present invention.

[Description of Signs] 1 Laser beam scanner device 2 Stay (support means) 21 Photoconductor drum (Photoconductor)

Claims (4)

(57) [Claims] 1. A laser beam scanner having a motor.
The device and the device main body that supports the laser beam scanner device
A fixed support means, and a frequency of vibration generated by the laser beam scanner device in the image forming apparatus having
And the laser beam scanner device and the support means
And the natural frequency of the composite system consisting of
An image forming apparatus, comprising: 2. A laser beam scanner having a motor.
The device and the device main body that supports the laser beam scanner device
And a fixed supporting means, wherein the laser beam scanning is provided on two opposite sides of the supporting means.
Approximately vertical and approximately the same height as the support surface
A bent portion is provided so that the laser beam is scanned substantially in the center between the two bent portions.
Image forming apparatus characterized by having a transfer device
Place. 3. A laser beam scanner having a motor.
The device and the device main body that supports the laser beam scanner device
And a fixed supporting means, wherein the laser beam scanning is provided on two opposite sides of the supporting means.
The height is almost perpendicular to the support surface of the channel device.
A bent portion that is bent like this, and a portion that is bent more than the center between the two bent portions.
The laser beam scanner device
An image forming apparatus, wherein an image forming apparatus is disposed. 4. 請characterized in that the support means for supporting the laser beam scanner unit constituted by the vibration damping steel plate
An image forming apparatus according to claim 1, 2, or 3.