JP2561293B2 - Document scanning device in copier - Google Patents

Description

TECHNICAL FIELD The present invention relates to a document scanning device in a copying machine.

(Prior Art) A copying machine of the type in which an exposure optical system is moved with respect to a document table on which a document is placed, or a document table is illuminated and scanned by moving the document table with respect to an exposure optical system fixed in the apparatus space. Well known.

In the present specification, a copying machine is an analog type which forms an electrostatic latent image by exposing an optical image of an original on a photoconductive photoconductor and an original which is read by a solid-state image sensor such as a CCD. It is a general term for a digital system in which an image is recorded by a multi-needle electrode, an optical scanning device, a thermal head, etc. based on image information. Therefore, the document scanning device is a device for illuminating and scanning the document and projecting an optical image of the document on the photoconductive photoconductor or the solid-state image sensor by the exposure optical system.

As a method of illuminating and scanning an original, as described above, a method of moving the exposure optical system with respect to the original table on which the original is placed, and a method of fixing the exposure optical system in the device space of the copying machine and placing the original There is a method of moving the document table with respect to the exposure optical system. Whichever method is used, a machine having a considerable mass moves reciprocally when the original is illuminated and scanned. In this mass transfer, the speed of the moving mass changes discontinuously. For this reason, when the speed changes discontinuously, a force is applied to the document scanning device, and the document scanning device inevitably vibrates.

Such vibration in the document scanning device causes the document scanning speed to be changed in an oscillating manner, which causes a reduction in the sharpness of the copied image regardless of whether it is digital or analog.

Conventionally, as a method for preventing the above-mentioned vibration in a document scanning apparatus, a method of applying a constant load by friction (Japanese Patent Laid-Open No. Sho 61-206).
58-24166, 58-1168), a method of applying a load corresponding to speed (Japanese Patent Laid-Open No. 58-196344, 58-).
No. 214141) is known. However, the anti-vibration method by friction requires a large load on the motor for moving the movable part of the document scanning device, inevitably requires a high-power motor, and changes in the load with time are extremely durable. There's a problem. In addition, the method of applying a load corresponding to the speed has problems that a large power is required at the time of starting the scanning of the document scanning device, the response characteristic is deteriorated, and the device becomes large.

(Object) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a novel document scanning device having an excellent image stabilizing effect.

(Configuration) Hereinafter, the present invention will be described.

The document scanning device of the present invention is a system for illuminating and scanning a document by moving an exposure optical system with respect to a document table on which a document is placed or by moving the document table with respect to an exposure optical system fixed in the device space. Is a device for illuminating and scanning an original in a copying machine.

The feature of the present invention lies in the following points.

That is, a damper having a mass m is attached by a spring having a spring constant k to a moving member that reciprocates during illumination scanning of an original in the original table and the exposure optical system, and the damper is in the moving direction of the moving member. When the mass of the moving member is M and the spring constant of the elastic force acting on the moving member is K, these m and k are (K / m) ≒ (K / M)

(Example) Hereinafter, an example will be described with reference to the drawings.

FIG. 3 shows only a main part of a document scanning device to which the present invention is applied.

Reference numeral 1 in the drawing indicates a document table. Original O to be copied
Are placed flat on the original table 1. In this embodiment, the document table 1 is fixed, and a part of the exposure optical system reciprocates as a moving member. Reference numerals 2, 3, and 4 are plane mirrors of the exposure optical system, reference numeral 5 is a lamp, and reference numeral 6 is a cover of the lamp 5. The plane mirrors 2, 3, 4, the lamp 5, and the cover 6 are movable parts of the exposure optical system and are movable members.

The lamp 5 is caused to emit light and is moved integrally with the plane mirror 2 and the cover 6 in the arrow direction, and at the same time, the plane mirrors 3 and 4 are integrally formed,
The plane mirror 2 is moved at a moving speed that is half the moving speed. The original O is illuminated by the moving lamp 5, and the reflected light from the original O is sequentially reflected by the plane mirrors 2, 3, 4 and guided to a lens (not shown). On the optical path of the exposure optical system, the lens and the plane mirror on the image side thereof are fixed in the apparatus space, but they can be displaced according to the copy magnification if necessary such as zooming. Now, the reciprocating movement of the moving member is performed by a mechanism as shown in FIG.

One end of the support 2A that supports the plane mirror 2 and one end of the support 3A that supports the plane mirrors 3 and 4 are movably engaged with the guide rod 10. The other ends of the supports 2A and 3A, which are not shown in FIG. 4, are engaged with the guide through rollers.

A wire 20 is fixed to the end of the support 2A. As shown in the figure, the wire 20 is connected to the connecting tool 18 via the movable pulley 16 and the pulley 15 provided on the support 3A. The wire fixed to the other end of the linking tool 18 is wound around the drive pulley 11 via the fixed pulley 14, the movable pulley 16, and the fixed pulleys 12 and 17. The wire wound around the drive pulley 17 is further connected to the support 2A again via the fixed pulleys 17 and 13 to form a closed loop. The pulley 15 is a tension pulley and applies a necessary tension to the wire 20 by a suitable tension means 19. The drive pulley 11 is connected to a motor (not shown). This motor is a servo motor controlled by a speed loop or a position loop having a speed loop as a minor loop, and rotates forward and backward at a speed according to the document size and copy size to reciprocate the moving member.

An example of the velocity diagram of the motor in this reciprocating motion is shown in FIG.

In the figure, the solid line shows the command value. However, if no anti-vibration measures are taken, the measured value of the motor rotation speed will be as shown by the chain line. This is wire 20
The rigidity of the drive transmission path such as or the support 2A, 3A, the guide rod 1
The moving member vibrates due to the rigidity of 0 and the plane mirrors 2, 3 and 4, etc.
This is because the control system of the motor is affected. The velocity transfer function at this time is shown in FIG. The solid line shows the gain and the broken line shows the phase.

 From this velocity transfer function, the following can be understood.

That is, the resonance frequency of the vibration is about 60 hertz,
The peak of the gain curve appears at this resonance frequency. Also, an anti-resonance point occurs at a frequency about 10 hertz lower than the resonance frequency, and the phase margin (0d
The phase at B) is reduced and the stability is deteriorated. The resonance frequency is generally about 40 to 70 hertz.

By the way, the above description with reference to FIG. 7 and FIG.
The present invention is implemented as follows, although it is not necessary to take any anti-vibration measures in the document scanning device of FIG.

FIG. 1 shows a state of the plane mirror 2 and its support 2A. In the figure, reference numeral 2C indicates a roller, but the roller 2C rotates on the guide 30.

At the engaging portion of the support 2A with the guide rod 10, a regulating member is provided.
23 are fixed. A part of the regulation plate is formed with a bent portion, and one end of the spring 24 is fixed to this bent portion.
A damper 25 is connected to the other end of 24. Therefore, the damper 25 can be moved within a range that allows the elastic force of the spring 24, but the movement direction thereof is regulated by the regulation member 23 in the vertical direction of FIG. 1, that is, in the direction of the guide rod 10. Therefore, the damper 25 can move relative to the plane mirror 2 in the moving direction of the plane mirror 2 as the moving member.

Now, assuming that the mass of the moving member when there is no damper is M, this is determined as a design condition of the document scanning device.

Further, the spring constant K of the elastic force caused by the rigidity of the drive transmission path such as the wire 20 and the supports 2A and 3A and the rigidity of the guide rod 10 and the plane mirrors 2, 3 and 4 that causes the moving member to vibrate.
Is the angular frequency ω corresponding to the above resonance frequency,
Between ω, M, K Therefore, the spring constant K can be known based on the actual measurement of the resonance frequency.

 The mass m and the spring constant k of the damper 25 are determined so as to satisfy (M / K) ≈ (m / k) (2) with respect to the above M and K.

When the condition (2) is satisfied, the resonance frequency of the damper 25 becomes substantially the same as the resonance frequency of the moving member. Therefore, in the vibration of the coupled system of the moving member and the damper, the moving member and the damper vibrate at the same frequency, but the fundamental mode of vibration is that the both vibrate in the same phase and
It becomes a mode that vibrates with a phase difference of degrees.

In the mode in which the moving member and the damper vibrate in the same phase, the vibration of the damper 25 acts in the direction of increasing the vibration amplitude of the moving member. This means that in such a mode, the mass of the moving member apparently increased,
As understood from the equation (1), in this mode, the resonance frequency of the moving member increases.

In the mode in which the moving member and the damper move with a phase difference of 180 degrees, the vibration of the damper 25 acts in the direction of reducing the vibration amplitude of the moving member. This means that in such a mode, the mass of the moving member apparently decreased, and in this mode, the resonant frequency of the moving member decreases.

Therefore, by providing the damper 25 via the spring 24, the resonance frequency of the moving member deviates from the original frequency determined according to the equation (1) in the direction of increasing the frequency and the direction of decreasing the frequency.

When the present invention is applied to the example described with reference to FIGS. 7 and 8 and the damper 25 is provided as shown in FIG. 1 to satisfy the above equation (2), the velocity line The figure and velocity transfer function are as shown in FIGS. 5 and 6, respectively. At this time, M = 500 g and m = 50 g.

As is apparent from comparison of the actual speed value indicated by the chain line in FIG. 5 with the actual value curve (chain line in FIG. 7) when the present invention is not applied, the speed at the time of illuminating and scanning the original document It can be seen that the fluctuation characteristic of is improved and the speed fluctuation is reduced.

Also, as can be seen from the velocity transfer function diagram (Fig. 8), the resonance point shifts to 80 to 90 Hertz (peak P1 of the gain curve) on one side and to 40 to 50 Hertz on the other side. (Gain curve peak P2). Further, the lower resonance point overlaps with the anti-resonance point, so that the resonance is relaxed.

The position of the damper is not particularly limited, and may be, for example, the first position.
It may be provided at the position indicated by reference numeral 2B in the figure. Further, the damper 25 may be attached by a leaf spring 26 as shown in FIG.

Further, the damper may not be a dedicated one, but a part of the scanning device may be used.

For example, as shown in FIG. 9, the cover 6 of the lamp 5 may be used as a damper, and the lamp 5 may be connected by a spring.

(Effect) As described above, according to the present invention, it is possible to provide a novel document scanning device in a copying machine.

Since the present invention is configured as described above, the resonance frequency of the moving member deviates from the original frequency, the phase margin increases, and the control system stabilizes. As a result, the quality of original scanning is improved, and a good copy image with excellent sharpness can be obtained.

Further, since there is no change over time, serviceability is also improved.

Furthermore, unlike the vibration isolation method by friction, it is not necessary to increase the output of the motor so much, and since there is no frictional force, the approach distance for rising can be short, so the device can be made compact. Is.

It should be noted that how much the resonance frequency shifts depends on M / m, but in the practice of the present invention, M / m = about 3 to 15 is appropriate, and M / m
= 3, the resonance frequency shifts by about 40%.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention, and FIG.
FIG. 5 is a diagram for explaining another embodiment, FIGS. 3 and 4 are diagrams for explaining an example of a document scanning apparatus to which the embodiment of FIG. 1 is applied, FIGS. 5 and 6. FIG. 7 is a diagram for explaining the effect of the present invention, FIG. 7 and FIG.
FIG. 9 is a diagram for explaining the necessity of image stabilization, and FIG. 9 is a diagram for explaining another embodiment. 2 ... Planar mirror as a part of moving member, 2A ... Support,
10 …… Guide rod, 24 …… Spring, 25 …… Damper

Claims (1)

(57) [Claims] 1. A copying machine of a type in which an exposure optical system is moved with respect to a document table on which a document is placed, or an original table is moved with respect to an exposure optical system fixed in an apparatus space to illuminate and scan the document. In the document table and the exposure optical system, a damper having a mass m is attached by a spring having a spring constant k to a moving member that reciprocates during illumination scanning of the document, and the damper is arranged in the moving direction of the moving member. When the mass of the moving member is M and the spring constant of the elastic force acting on the moving member is K, the above m, k
The document scanning device is characterized by satisfying the following conditions: (k / m) ≈ (K / M).