JPS61105531A - Focusing mechanism - Google Patents

Abstract

PURPOSE:To omit a stage raising and lowering mechanism by moving a mirror in accordance with the thickness of an original to perform focusing. CONSTITUTION:A mirror 3' is moved for focusing, and the length of the hypotenuse (the extent of movement for correction), the length of the base, and the length of the vertical side (the height) of a right triangle formed by mirrors 3 and 3' are denoted as (a), (b), and (c) respectively. Since the increase of the optical path length of the mirror 3' to the mirror 3 is (a+c), a photographic lens 6 is focused correctly if this increase is equal to a thickness (t) of an original 1. Since the length (c) of the vertical side is aXcostheta, the extent (a) of movement for correction is expressed with an equation a=tX(1+costheta). This equation is operated by a microcomputer provided for operation control in each mechanism to control the movement of the mirror 3. Since the center of the original 1 and the optical axis of the photographic lens 6 are shifted from each other by the movement of the mirror 3, the set position of the original 1 is changed for the purpose of compensating this shift.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used in a camera-type copying machine or a plate-making machine, etc.
This invention relates to a focal joint mechanism for correcting movement of the focal plane due to the thickness of a document.

[Prior art]

In a camera-type plate-making machine, a mirror is arranged at an angle above a stage, and the light reflected by this mirror passes through a photographic lens and reaches a focal plane. A photosensitive sheet (master paper) is set on this focal plane,
An image of the original is formed on this. The exposed photosensitive sheet is developed and fixed, and then etched with an etcher to form a sheet-like plate.

Since the stage has its top surface serving as a reference surface,
When a thick original is set on the stage, the object distance becomes shorter, causing blur in the image formed on the focal plane. Conventional camera-type plate making machines are equipped with a stage height adjustment mechanism, and the focus is adjusted by operating this height adjustment mechanism to lower the stage by the thickness of the document. However, with this focus adjustment mechanism, it is necessary to move the stage in parallel with high precision, which makes the structure of the device complicated, the stage is unstable, and the height of the stage changes depending on the document. This has the disadvantage that it is difficult to operate.

[Purpose of the invention]

The present invention makes it possible to easily adjust the focus by using a mirror moving mechanism used for image magnification conversion, and also provides a focus with excellent operability and stability by fixing the stage. The purpose is to provide an adjustment mechanism.

[Features of the invention]

In order to achieve the above-mentioned object, the present invention has the following objectives: the inclination of the mirror placed above the stage is θ, the thickness of the original is t, and the amount of movement of the mirror in the optical axis direction of the photographing lens is a. Then, the following equation (3) is calculated, and the mirror is moved by the corrected movement amount a obtained, thereby increasing the object point distance of the photographing lens by the thickness t of the document.

Embodiments of the present invention will be described in detail below with reference to the drawings.

〔Example〕

In Figure 2, which shows a camera-type electrophotographic engraving machine, original 1
A mirror 3 is placed above the stage 2 on which the lamp is placed, and on both sides of the mirror 3 are placed illumination arms 5 to which rod-shaped light sources 4 are attached.

The reflected light from the original 1 illuminated by the rod-shaped light source 4 is reflected diagonally backward by the mirror 3, passes through the photographic lens 6, reaches the exposure position, and is applied to the original 1 onto the photosensitive sheet 7 positioned at this exposure position. Record the image.

Note that the photographic lens 6 is equipped with a lens shutter as is well known.

The mirror 3 and photographic lens 6 are held by a mirror holder 8 and a lens holder 9, respectively. These mirror holder 8 and lens holder 9 are fitted into a guide rod 11 arranged parallel to the optical axis 10 of the photographic lens 6, and move along this guide rod 11 during image magnification conversion.

Note that, as will be explained in detail later, the mirror holder 8 also moves in order to correct the deviation of the focal plane due to the thickness of the document l. In order to move this mirror holder 8, a feed screw shaft 12 that fits into a part of this is arranged.
When this feed screw shaft 12 is rotated by a stepping motor 13, the mirror holder 8 moves forward or backward depending on the direction of rotation. Similarly, a feed screw shaft 14 that fits into a part of the lens holder 9 is provided, and the lens holder 9 moves back and forth when the stepping motor 15 rotates.

Since the image point distance is uniquely determined by specifying the image magnification using the lens formula and the magnification equation, the stepping motor 15 is rotated to position the photographing lens 6 so that the image point distance is determined. At the same time, since the object point distance is determined by a function of the image point distance, the stepping motor 13 is driven so as to obtain this distance. In reality, the relationship between the number of drive pulses supplied to the stepping motor and the image magnification based on the origin position is stored in a table memory, and the number of drive pulses for the current magnification and the relationship for the set magnification are stored in table memory. The rotation direction of the stepping motor is determined based on the magnitude relationship with the number of drive pulses, and drive pulses are supplied to the stepping motor by the difference in re-drive pulses. Note that when the power is turned on,
Limit switches 16 and 17 are provided for detecting the origin position of the mirror 3 and the origin position of the photographing lens 6, respectively. A bellows 19 is connected to the lens holder 9 and the plate 18 so that only the photographing light that has passed through the photographing lens 6 passes through the opening 18a of the light shielding plate 18. Note that numerals 20 to 25 are bearings.

The photosensitive sheet 7 wound around the supply roll 30 is pulled out by a pair of feed rollers 31, 32 and sent to a cutting position. A cutter consisting of a movable blade 33 and a fixed blade 34 is disposed at this cutting position, and cuts the paper into a predetermined length depending on the size of the drum of the printing press. The photosensitive sheet 7 that has passed the cutting position is transferred to a pair of feed rollers 35.3.
6, it is transported towards a charger 37, where it is charged and given photosensitivity, and then reaches a suction belt 39 in which a large number of suction holes are formed, where it is sucked and held and transported to the exposure position. . A plurality of suction belts 39 are used, and each of the suction belts 39 is hung on rollers 41 and 42 attached to a suction box 40, and a punch board 4
3 is arranged to maintain the flatness of the suction belt 39. The suction box 40 is connected to a suction plow 45 via a hose 44.

After the photosensitive sheet 7 is exposed at the exposure position, it is guided by a guide 47 and sent to a developing section 48, where it is developed. The developed photosensitive sheet 7 is sent to a fixing section 49 where it is fixed, and then discharged onto a tray 50.

Next, the photographing operation will be explained. First, specify the image magnification using the keyboard. When this image magnification is specified,
The address corresponding to the image magnification stored in the table memory is compared with the current address, and the rotational direction of the stepping motor 13, 15 and the number of drive pulses are calculated so that the two addresses match. Since the stepping motors 13 and 15 rotate according to the result of this calculation, the mirror 3 and the photographing lens 6 move to positions determined according to the image magnification.

Next, if you operate the exposure switch, the feed roller 31.3
5 rotates, the photosensitive sheet 7 wound around the supply roll 30 is drawn out, and when it is drawn out by a predetermined length, the movable blade 33 is activated to cut the photosensitive sheet 7. The photosensitive sheet 7 cut by the cutter is charged with a charger 37 to impart photosensitivity, and then is suction-held and conveyed by a suction belt 39, and is correctly positioned at an exposure position. Next, the rod-shaped light source 4 is turned on for a certain period of time to illuminate the original 1. During this illumination, the shutter operates and the document 1 is placed on the photosensitive sheet 7 set at the exposure position.
record the image. After this recording, a new photosensitive sheet is conveyed toward the exposure position, and the exposed photosensitive sheet 7 is sent to the developing section 48. The photosensitive sheet 7 that has entered the developing section 48 is developed there, then sent to the fixing section 49 where it is fixed, and then discharged onto the tray 50.

Next, focus adjustment for correcting image blur due to the thickness of the document will be described with reference to FIG. In a camera-type camera in which the mirror 3 is placed on the stage 2, the focus of the photographic lens 6 is adjusted so that the upper surface 2a of the stage 2 is imaged on the focal plane (exposure position) F. Therefore, in the case of a document having a thickness of t, the object point distance of the photographing lens 6 becomes longer by t, and the image at the focal plane F becomes blurred. In the present invention, the focus of the photographing lens 6 is adjusted by moving the mirror 3 according to the thickness t of the original 1.

This focus adjustment can utilize a mirror moving mechanism for image magnification conversion, which is advantageous in terms of cost.

In Figure 1, the mirror moved for focus adjustment is 3
In the right triangle formed by mirror 3 and mirror 3'', the length of the hypotenuse (corrected movement amount) is a, the length of the base is b, and the length of the vertical side (height) is C.

The increase in the optical path length of mirror 3'' with respect to mirror 3 is (a+
c), if this becomes equal to the thickness t of the document 1, the focus of the photographic lens 6 will be appropriate. Here, since the length C of the vertical side is aXCO3θ, the corrected movement amount a can be expressed by the following equation.

aFtX (1+cosθ) This calculation is performed by a microcomputer provided for calculation control of each mechanism, and the movement of the mirror 3 is controlled. Note that the movement of the mirror 3 causes a misalignment between the center of the document 1 and the optical axis of the photographic lens 6.
To correct this, either change the cent position of document 1, or
Alternatively, it is of course necessary to change the center position of the photosensitive sheet 7.

FIG. 3 shows the functions of a microcomputer for implementing the present invention. If you operate the magnification designation key 54 and then input the image magnification value by operating the numeric keypad 55,
As described above, the reference mirror position and lens position according to the image magnification are calculated by the calculation unit 56. Furthermore, by operating the document thickness correction key 57 and then operating the numeric keypad 55 to input the thickness, the calculation unit 58 calculates the correction movement amount of the mirror 3. This corrected movement amount and the reference mirror position are added by an adding section 59 to calculate the mirror position taking into account the thickness of the document 1. In addition, if the limit switch 16 is provided on the bearing 22 side in FIG. 2 and the origin position of the mirror 3 is changed, it is necessary to subtract the corrected movement amount.

The counter 60 counts drive pulses generated by software from the pulse generator 61 to detect the current address of the mirror 3. When the power is turned on, the stepping motor 13
．． 15 is forcibly reversed and the limit switch 16.1
When the limit switches 16 and 17 are turned on, the stepping motors 13 and 15 rotate normally, and the mirror 3 and the photographing lens 6 are positioned at the same magnification position. When the limit switch 16 is turned on, the counter 60 is reset.

When setting the image magnification or adjusting the focus according to the thickness of the document, the contents of the counter 60 and the addition result of the addition section 59 are compared in the comparison section 62, and the direction of rotation of the stepping motor 13 is determined from the magnitude relationship. The number of generated drive pulses is determined from the difference. When the stepping motor 13 is driven by the driver 63, the counter 60 counts up the driving pulses if the stepping motor 13 is rotating in the forward direction, and counts down the driving pulses if the stepping motor 13 is rotating in the reverse direction. During the rotation of the stepping motor 13, if the contents of the counter 60 and the contents of the adding section 62 match, the stepping motor 13 stops. Note that the portion surrounded by a dotted line indicates the mirror position control section 64.

A lens position control section 65 having the same configuration as the mirror position control section 64 is also provided for the photographing lens 6, and the direction and amount of rotation of the stepping motor 15 is controlled via a driver 66 according to the obtained position data. and positions the photographing lens 6 at a position corresponding to the image magnification.

〔Effect of the invention〕

In the present invention having the above configuration, the focus is adjusted by moving the mirror according to the thickness of the document, so the stage elevating mechanism can be omitted, and an image magnification conversion mechanism can be used. This allows the structure to be simplified and costs to be reduced. In addition, since the stage can be fixed, the stability of the stage is improved, and the height of the stage remains constant, making it easier to operate.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the principle of the present invention. FIG. 2 is a sectional view showing a camera-type electrophotographic printing machine embodying the present invention. FIG. 3 is a functional block diagram of a microcomputer that calculates the mirror position. 1...Original 2...Stage 3...Mirror 6...Photographing lens 7...Photosensitive sheet
11...Guide rod 12.14...Feed screw shaft 13.15...Stepping motor 16.17...Limit switch.

Claims (1)

[Claims] (1) A stage on which an original is placed, a mirror arranged above the stage at an angle of θ, and a photographic lens that forms an image recorded on the original onto a focal plane via this mirror. , a means for specifying the thickness of the document, a means for calculating the following formula a=t/(1+cosθ), where a is the amount of correction movement of the mirror in the optical axis direction of the photographing lens; A focus adjustment mechanism comprising means for moving a mirror in the optical axis direction of a photographing lens by a correction movement amount a.