JPS63312772A - Picture reader - Google Patents

Abstract

PURPOSE:To prevent the resonance phenomenon of a mirror by setting the number of the oscillations of the optical mirror so as to dislocate the basic driving frequency of a stepping motor or the higher harmonic wave component thereof. CONSTITUTION:The mirrors 7, 9a, 9b reflect and guide an original optical image obtained by scanning and exposure light source in an image pickup unit. The mirrors 7, 9a, 9b are supported by both the longitudinal ends thereof and the stepping motor 10 is rotated and driven in normal ad and reverse directions by a driving circuit. A side wall 90 is an internal partition constituting the frame enclosure of a picture reader and the stepping motor 10 is mounted on the external side of the side wall of this frame casing. The natural frequency of the mirror is set to f0<0.85nf1 and f0>1.35nf1 in a higher harmonic area of (n) times. (Herein, f1 is the basic driving frequency of the motor 10).

Description

[Detailed description of the invention] [Industrial application field]

The present invention is characterized in that a document is irradiated with an exposure light source of an optical system, and a light image of the document is formed in an imaging unit.
For example, it relates to an image reading device such as a facsimile machine or a copying machine.

[Background of the invention]

In an image reading device, an optical image of a document surface obtained by exposure scanning is generally formed on a solid-state imaging device such as an image sensor installed around an optical axis via an imaging lens system. For example, in an image reading device of a multicolor image forming device, an optical image of the document surface obtained by exposure scanning is passed through an imaging lens system, and then separated into spectra by a light splitting means such as a prism installed behind it. , the image is formed on an image sensor that receives light in each channel. In an image reading device in which a document table is fixed and an optical system is moved, a document placed on a document table glass is illuminated in a strip shape by a moving light source. A document light image obtained by irradiation with the light source is transmitted to a first mirror that moves together with the light source, and a second mirror that is provided on a movable mirror unit. It is reflected and guided by the third mirror. Then, one image of the reflected and guided document light passes through a fixed imaging lens and is imaged on an image sensor also fixed behind it. A rod-shaped halogen lamp or fluorescent tube is used as a light source that illuminates the document surface. Fluorescent lamps are often used because halogen lamps generate a large amount of heat when continuously lit. 2. Description of the Related Art In an image reading device that scans and exposes a document on a document platen glass using an exposure light source of an optical system, a drive motor for driving a scanning movement section of the optical system is provided inside the device. Although DC motors, induction motors, and the like are generally used as the drive motors, stepping motors have recently come into widespread use due to the trend toward miniaturization of devices and the demand for accurate positioning. When the stepping motor rotates, since the rotation of the motor is controlled in steps using pulses, vibrations having a reference frequency related to the step angle are generated. The frequency f1 of this vibration is fl·68/, where the number of rotations of the stepping motor is N rpm and the step angle is θS.
It can be expressed as θS. This fl is the basic drive frequency of the stepping motor. Fig. 6 shows a spectral analysis diagram of vibration waves when driving a stepping motor with rotation speed N = 83.3 rpm and step angle θs: 0.9''. In the figure, the horizontal axis represents the frequency; The vertical axis represents the amplitude.The vibration wave during driving of this stepping motor has the fundamental driving frequency f, =
6x 83.310.9°=555Hz and harmonic component 1/2 of this fundamental drive frequency ・f+478Hz, 1/
4. f, 138Hz, etc. The natural frequency of the mirror of the optical system may match the fundamental drive frequency of the drive motor and its harmonic components, causing a resonance phenomenon of the mirror. At the time of such a resonance phenomenon, the mirror leads to the solid-state image sensor CCD.
This causes a so-called pre-state in which the formed original optical image is disturbed. If the pre-amount of the original light image formed on the CCD exceeds 18, which is 1 pixel pitch = 62.5 μm, the reproduced image will be affected by this, resulting in deterioration of the reproduced image. When the mirror of the optical system generates a resonance phenomenon in accordance with the fundamental drive frequency of the drive motor and its harmonic components, the original optical image derived by the mirror is 1/4 of the above-mentioned 1/4.
- If the amount of play exceeds the pixel pitch, it may become distorted and cause deterioration of the reproduced image.

[Problems to be solved by the invention]

The present invention has been made in view of the above-mentioned drawbacks of the prior art. to prevent the mirror resonance phenomenon,
It is an object of the present invention to provide an image reading device capable of preventing deterioration of a reproduced image by eliminating distortion of a projected image due to mirror vibration.

[Means to solve the problem]

The above object is to provide an image reading apparatus in which a light image of a document on a document table glass is scanned and exposed by an exposure light source of an optical system and an optical image of the document is guided into an imaging unit by a plurality of mirrors of the optical system. , the natural frequency f0 of the mirror, and the fundamental drive frequency f of the drive motor that drives the moving part of the optical system. This is achieved by an image reading device characterized in that the values of the harmonic components of the frequency f and the frequency f are configured to be different from each other. Preferably, the natural frequency f0 of the mirror is ro<o, as Hn-f1 and fo>1.35.
This is achieved by an image reading device characterized in that the range is set to n·f. More preferably, the natural frequency f of the mirror. , fo<0.65・
This is achieved by an image reading apparatus characterized in that the range is set to 1/n-f1 and fo>1.35-1/n-f+. However, n is an integer 1, 2, 3, . ...represents...

【Example】

Prior to a detailed explanation of the present invention, the general functions of the image reading device will be explained. FIG. 3 is a block diagram of the image reading device.
Reference numeral 1 denotes a document table glass, and an original document 2 is placed on this document table glass 1. The original 2 is illuminated by fluorescent lamps 5 and 6 provided in an exposure light source unit 40 that moves on the slide rail 3. The movable mirror unit 80 is provided with mirrors 9a and 9b and moves on the slide rail 3,
In combination with the first mirror 7 provided in the exposure light source unit 40, a light image of the document 2 on the document table glass 1 is guided to the imaging unit 20. The exposure light source unit 40 and the movable mirror unit 80 are
Stepping motor 10. Pulley 11, 12, 13, 1
4. They are driven in the same direction at speeds of 1 and 1/2 by a driving device composed of wires 15 and the like. A standard white plate 17 is provided on the back side of the document abutting member 16 at the tip of the document platen glass 1, and is used for document reading scanning iI.
The configuration is such that a standard white signal can be obtained before the beginning of n. The imaging unit 20 includes a lens 21 as an imaging lens system.
, a prism 22 as a photolysis means, a first reading board 24, a red channel (hereinafter referred to as R-ah) CCD 27 as a line image sensor, and a second reading board 26.
, cyan channel (hereinafter referred to as C-ch) CC[12
Consists of 5. The original optical image transmitted by the first mirror 7, mirror 9a, and mirror 9b is focused by the lens 21, and separated into a C-ch image and an R-ch image by the guichroic mirror provided in the prism 22. Then, the C-ch image is formed on the light receiving surface of the C-ch CCD 25 provided on the first reading board 24, and the R
-ch image is the R-C image provided on the second reading board 26.
h The image is formed on the light receiving surface of the CCD 27. As the fluorescent lamp 5.6 for illuminating the document, a commercially available warm white fluorescent lamp is used to prevent emphasis or attenuation of specific colors based on the light source when reading a color document. In addition, the lights are powered by a 40KHz high frequency power source to prevent flickering.
It is heated by a heater using a POSISTOR to maintain a constant temperature of the tube wall or to promote warm-up. FIG. 1 is a perspective view of an image reading apparatus according to an embodiment of the invention, and FIG. 2 is a side sectional view of the image reading apparatus according to an embodiment of the invention. In these figures, 3 is a slide rail, 7.9a, 9b are mirrors, 10 is a stepping motor, 20 is an imaging unit, 25°27 is a CCD, 9
0 is the side wall of the skeletal casing of the device. Mirrors 7.9a and 9b reflect and guide the original light image obtained by scanning exposure of the exposure light source into the imaging unit 20. Mirrors 7.9a, 9b are both supported at their longitudinal ends. The natural frequency of these mirrors 7.9a and 9b used in the optical system is 2πfo・(α)2・(El/ρ^)05r・ωt
/ 12A; where ρ is the density of the mirror, E is the Young's modulus, t is the thickness, α is π/L when both ends are supported, and L is the distance between the supporting parts. Figure 4 is , is a characteristic diagram showing the natural frequency of the mirror. In the diagram, the horizontal axis represents the distance between the supporting parts in the longitudinal direction of the mirror, and the vertical axis represents the mirror primary resonance frequency. What is shown in the diagram is , mirror thickness t is 3mm, 3.5TI
II11, 4II1m, 4.5n+m, 5n
This is a characteristic curve obtained by measuring the primary resonance frequency when the diameter was changed to +m, 5.5 mm, and 6 mm. The stepping motor 10 is driven to rotate in both forward and reverse directions at a step angle of 0.9° and a rotation speed of 83 rpm by a drive circuit (not shown). The vibration wave when the stepping motor is driven is the basic drive frequency f1・6X 83.310.9°
・555Hz and harmonic components of this fundamental drive frequency 1/
2・f,=27811z,1/4-f,,=138
11z, 2f, □111011z, etc. Solid-state image sensor C-ch CCD 25 and R-ch C
The CD 27 is a line image sensor composed of pixel elements with a pixel width of approximately 7 μm. The side wall 90 is an internal partition that constitutes a skeletal casing of the image reading device, and the stepping motor 10 is attached to the outside of the side wall of the skeletal casing. That is, the two-taper winding portion covered by the motor body of the stepping motor 10 is located outside the side wall 90, and the drive shaft end of the stepping motor 10 and the pulley (not shown) at the drive shaft end are located outside the side wall 90. It is installed so that it is located inside. The exposure light source unit 40 and the movable mirror unit 80 are
Slide dowels 31 made of polyacetal or PPT resin, etc., which are housed on the bottom surfaces of both wing parts, respectively, slide on slide rails 3 made of high-density polyethylene laid on the horizontal parts of both sides of the side wall 90 of the frame casing. . The vibration when the stepping motor 10 is driven is as follows:
The light is transmitted to the exposure light source unit 40 and the movable mirror unit 80 via the frame housing side wall 90, the slide/f trail 3, and the slide dowel 31, and is further transmitted to the mirror both end support protrusions 32,
33 to each mirror 7.9a, 9b. FIG. 5 is a characteristic diagram showing the relationship between the natural frequency of the mirror and the displacement when the stepping motor 10 is driven. In the figure, the horizontal axis represents the natural frequency, and the vertical axis represents the amount of displacement at the center of the mirror. Several combinations are provided by changing the thickness t of the mirror and the distance between the supporting parts at both ends, respectively, to obtain a plurality of natural frequencies. The plurality of mirrors having each frequency resonate with the fundamental drive frequency of the stepping motor 10 and its harmonic components. For example, as a result of an experiment using a mirror with a pressure gfL of 240 mm between the support parts at both ends of the mirror, the conditions are worst when the distance between the mirror and the document is about 350 mm. The amount of displacement in the vicinity is 5μm
If it exceeds the 1/4 pixel pitch, the pre-amount of the original optical image projected onto the CCD will become larger than the 1/4 pixel pitch, and the reproduced image will be distorted. In Fig. 5, if the natural frequency of the mirror is set to a region below this value with the mirror center displacement amount 5μ as the boundary value, the amount of original light image projected on the CCD is generally It was found that the pitch never exceeds about 1/4 pixel pitch. The natural frequency corresponding to this mirror displacement amount of 5μ is 65z of the fundamental drive frequency fl of the stepping motor 10 or its harmonic components 1/n-f, , n-f, and 1351
It is. Therefore, the natural frequency f0 of the mirror is ro<0.65 ・n−f1 and L>t, 35Hn−f in the n-times harmonic region.
In the 11/n harmonic region, fo<0.65 1/n-r1 and fo>1.35 ・
It may be set within the range of 1/n - f+.

【Effect of the invention】

According to the present invention, the frequency of the mirror of the optical system is set to be shifted from the fundamental driving frequency of the stepping motor or its harmonic components, so that the resonance phenomenon of the mirror is prevented, and the original optical image derived by these mirrors is It has become possible to provide an image reading device that can reduce blurring and obtain clear reproduced images without disturbance.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an image reading device according to an embodiment of the present invention;
Fig. 2 is a side sectional view of an image reading device according to an embodiment of the present invention, and Fig. 3 is a configuration diagram of the image reading device. Figure 5 is a characteristic diagram showing the relationship between the natural frequency of the mirror and the amount of displacement, and Figure 6 is a spectrum analysis diagram of the vibration frequency of the stepping motor. DESCRIPTION OF SYMBOLS 1... Original platen glass 2... Original 3... Slide rail 7... First mirror 9a, 9b... Mirror 10... Stepping motor 20... Imaging unit 40... Exposure light source Unit 80...Movable mirror unit 90...Side wall fo of skeleton casing...Mirror natural frequency f1...Basic drive frequency n...Integer Applicant Konishiroku Photo Industry Co., Ltd. Figure 4 Mirror angle Tomb Keisu Imabe to Gate Work ε Negative L (mm) Figure 5 Figure 6 Surroundings CHz)

Claims (4)

[Claims] (1) In an image reading device in which a light image of the document obtained by scanning and exposing a document on a document platen glass with an exposure light source of an optical system is guided into an imaging unit by a plurality of mirrors of the optical system, Natural frequency f_ of the mirror
0 and a value obtained by multiplying a basic drive frequency f_1 of a drive motor that drives a moving part of the optical system by an integer n are configured to be different from each other. (2) The natural frequency f_0 of the mirror and the value obtained by dividing the basic drive frequency f_1 of the drive motor by an integer n are configured to be different from each other.
The image reading device described in Section 1. (3) Let the natural frequency f_0 of the mirror be f_0<0.
65.n.f_1 and f_0>1.35.n.f_1. (4) Let the natural frequency f_0 of the mirror be f_0<0.
65・1/n・f_1 and f_0>1.35・1/n・
3. The image reading device according to claim 2, wherein the image reading device is set to a range represented by f_1. However, n represents an integer 1, 2, 3, . . .