JPS6392156A - Automatic focus detector for image reader - Google Patents

Abstract

PURPOSE:To perform focus detection regardless of power variation by comparing contrast values at two lengthwise positions of a line sensor with each other while holding an image forming lens inclined, and calculating a focus error. CONSTITUTION:While the image forming lens 8 slants to an optical axis 34, the combination of peak values of contrast waveforms outputted at >=2 lengthwise positions of the sensor 4 is different according to an in-focus, a front-focus, and a rear-focus state. This difference is decided through the arithmetic of an arithmetic means 38 to detect a focus state. A driving circuit 40 is controlled according to the detection signal to stop a driving motor 39 for focus adjustment in the in focus state, rotate the motor 39 forward in the front-focus state so as to move an image forming lens 8 toward the sensor 4, or reverse the motor 39 in the rear-focus state to move the lens 8 away from the sensor 4. Consequently, the lens 4 is slanted temporarily by a solenoid 37 to make an automatic focus adjustment.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an automatic focus detection device in an image reading device that scans and forms an image of a document onto a line sensor via an imaging lens and reads the image. It is used for automatic focus adjustment when projecting the original image onto the line sensor for J& reading.

(Prior Art) In general, an image reading device, as shown in FIG. death,
The image is guided to an imaging optical system i via mirrors r, g, and h, and the image is formed on a solid-state image sensor j by the optical system i, and the original image p is scanned by a mirror scan method, an original platen scan method, or an original conveyance method. However, this is read by a solid-state image sensor j and converted into an electrical signal.

By the way, when variable-magnification reading is performed using an image reading device such as the one described above, it is necessary to perform the variable-magnification process optically, since deterioration in image quality cannot be avoided with electrical variable-magnification processing.

In the case of optical magnification processing, it is sufficient to change the conjugate length of the optical path, but at the same time, it is necessary to adjust the focus by changing the distance between the imaging optical system i and the solid-state image sensor j. .

At this time, the depth of focus of the imaging optical system i was very shallow, approximately ±0.01 mfi, so it was difficult to mechanically set an appropriate focal position.

Therefore, the striation pattern k, that is, black and white vertical stripes (ladder)
Using a focus adjustment original (focus adjustment pattern) on which is printed, a striation pattern k is imaged on a solid-state image sensor j by an imaging optical system i, and the pitch of the solid-state image sensor j is caused to interfere with the projected image. A focus adjustment device has been proposed that adjusts the focus based on the output signal of the solid-state image sensor j so that the density is maximized (Japanese Patent Application Laid-Open No. 173705/1983).
(see publication).

(Problems to be Solved by the Invention) However, in the conventional method, the line pattern must be formed with high precision.

Furthermore, when performing variable magnification reading, if the variable magnification range becomes large, interference may not occur with one type of striation pattern, and focus adjustment cannot be performed stably.

(Means for Solving the Problems) The present invention provides a focus detection device for an image reading device that performs focus detection only by temporarily moving the imaging lens of the image reading device, and does not have the above-mentioned conventional problems. In an image reading device that scans and forms an image of a document onto a line sensor via an imaging lens and reads the image, the imaging lens is temporarily tilted with respect to the document image in the longitudinal direction of the line sensor. and a calculation means for calculating a focus error by comparing the contrast of at least two portions in the longitudinal direction of the line sensor with the imaging lens tilted. It is something.

(Function) Normally, the original image, the imaging lens, and the line sensor are located parallel to each other and on the optical axis, and the original image is scanned and imaged in the same focus state by the imaging lens over the entire longitudinal range of the line sensor. As a result, in the focused state, the entire range of the original image can be clearly read.

When the line sensor is tilted in the longitudinal direction with respect to the original image with the optical axis position as the center using the imaging lens and the lens attitude adjustment means, a focus state that is almost the same as in the normal attitude can be obtained at the approximate center position of the line sensor; Due to the inclination of the line sensor, on the side where the imaging lens approaches, as the distance from the optical axis position increases, a state becomes more rear focused than the normal focus state, and also on the side where the imaging lens moves away due to the inclination of the line sensor. In the half of , it is possible to obtain a state in which the farther from the optical axis position the front focus state is than the normal focus state. Here, the relationship between the difference in contrast due to the difference in focus state at two or more locations on the line sensor in the longitudinal direction is
The focus state changes depending on the normal focus state at the optical axis position, and by calculating the above relationship by the calculation means, the focus state determined by the three positional relationships of the original image, the imaging lens, and the line sensor is in focus. Alternatively, it is possible to determine whether it is a front pin or a rear pin.

At the time of focus determination, when the imaging lens is returned to its original position parallel to the document image in the longitudinal direction by the posture control means, a focused state in which the document image is clearly scanned and imaged can be obtained.

(Example) An example of the present invention shown in FIGS. 1 to 5 will be described. In this embodiment, as shown in FIG. 4, a microfilm M is used as a manuscript, and an arbitrary frame of the manuscript image P is enlarged and projected onto a screen 2 through a league optical path 1 for reading, or a printer optical path (scanning projection system) 3 CC as an image sensor in
This shows the case of a printer that enlarges and projects the image while scanning it onto the D-line sensor 4, electrically reads the image, and uses it to print the original image P.

The microfilm M is held between film carriers that are a pair of upper and lower glass plates, so that any frame of the original image P can be moved to a projection position. The original image P at the projection position is illuminated from below by a light source 6 through a condenser lens 7, and enlarged and projected upward by an imaging lens 8 through a prism 9 for image rotation.

In the reader mode, a reader optical path 1 is formed. That is, the light that has passed through the imaging lens 8 and the prism 9 is bent by the first reader mirror 11 and the second reader mirror 12 located at the reader position (solid line position in the figure), and is enlarged and projected onto the screen 2 at the upper front of the main body. .

In print mode, a printer optical path 3 is formed. That is, first, the second reader mirror 12 moves to the retracted position (the imaginary line position shown in the figure), and in the reader mode, the first print mirror 14, which was in the retracted position (not shown) outside the reader optical path 1, moves to the image-forming position. It moves between the lens 8 and the first leader mirror 11. Thereafter, the first print mirror 14 and the second print mirror 15 scan and move in synchronization from their respective scan start positions toward their scan end positions. In this way, the light from the imaging lens 8 passes through the prism 9 to the printed first mirror 14 and the printed second mirror 1.
5 and is slit-projected onto the CCD line sensor 4.

The CCD line sensor 4 converts the original image P sequentially projected onto the slit into an electrical signal, and performs electrical image reading. This image reading signal is input to a known laser beam printer (not shown) and used for printing.

The prism 9 rotates the projected image P from the imaging lens 8 by rotating the imaging lens 8 around the optical axis. This prism 9 is fitted and held in a lens barrel 20, and this lens barrel 20
is held so that it can rotate independently. 22 is an outer peripheral gear, and this outer peripheral gear 22 is fitted and fixed to the lens barrel 20. This outer gear 22 meshes with a drive gear 24 of a rotating device 23 (FIG. 1). A trapezoidal prism is used as the prism 9, and at the position shown by the solid line in FIG.
When the original image P on the microfilm M is faced as it is toward the screen 2, CCD line sensor 4, etc., and rotated 45 degrees as indicated by the broken line in FIG.
It is rotated around the optical axis by 0 degrees and directed toward the screen 2 and CCD line sensor 4.

The prism 9 is used not only to change the projection direction of the original image P by 90 degrees, but also to correct the tilt of the projected image. A photoelectric sensor 30 is provided at the zero point around the optical axis of the prism 9, and a detection mark (not shown) attached to the lens barrel 20 is blinded when the prism 9 rotates, and is used to control the operation of the reader/printer. Microcomputer 37 (Figure 1)
The orientation of the prism 9 is detected by calculating
The projection direction of the original image P can be controlled.

The imaging lens 8 is a base 8a to which it is fixed, as shown in FIG.
As shown in FIGS. 2 and 3, a movable stage 31 for focus adjustment, which is movable in the optical axis direction for focus adjustment, is pivoted by a tilting center axis 32 whose axis line is orthogonal to the optical axis 33. The line sensor 4 is made tiltable so as to swing the optical axis 33 in the longitudinal direction.

A spring 35 is applied between the imaging lens 8 and a first positioning pin 34a on a movable stage 31 which abuts one end side of the base 8a and restricts the imaging lens 8 to the original position without tilting. It is designed to always remain stable at the origin position where it comes into contact. An operating rod 36a of a solenoid (lens attitude adjustment means) 36 is in contact with the other end side of the imaging lens 8.
When the solenoid 36 is activated, the projection of the operating rod 36a pushes the other end of the imaging lens 8, and rotates the imaging lens 8 against the spring 35 until the base 8a abuts the second positioning pin 34b. The imaging lens 8 is tilted at a predetermined angle with respect to the optical axis 33 as shown in FIG.

Here, when the original image P is projected onto the CCD line sensor 4 by the imaging lens 8, the CCD line sensor 4 is at the focus position A as shown in FIG. When the CCD line sensor 4 is at the front bin position AI or the rear bin position A2, the peak value of the received light contrast waveform R0 of the slit-projected image is higher, whereas the received light contrast waveform R+ of the slit-projected image is higher when the CCD line sensor 4 is at the front bin position AI or the rear bin position A2. , the peak value of Rz becomes low.

Contrast waveforms R0 and R corresponding to this focus state,
, R, since the depth of field of the imaging lens 8 is about 0.01 m5, a small difference in the focus state will appear relatively large and can be sufficiently detected.

Therefore, the imaging lens 8 is tilted with respect to the optical axis 33 by operating the solenoid 36 when detecting the focus, but the tilt may be as small as a political change that can detect the difference between the peak values of the contrast waveforms R6, R+, and Rz. . FIG. 7 shows tilted postures for obtaining three focusing states as shown in FIG.

The table below shows the relationship between the contrast waveforms obtained at the center position 4° and the positions 4114□ on both ends of the CCD line sensor 4 in this tilted posture and the actual focus state.

As can be seen from this table, when in focus, the peak value at the center position of 4° is large, while at both end positions of 41.4□, the front and back are in focus, and both are slightly out of focus from the in-focus position. As a result, both of the peak values are lower than the peak value at the center position of 4 degrees.

In contrast, in the front focus state, the CCD line sensor 4 is focused or close to it at the other end position 4□ and exhibits the maximum peak value; The peak value decreases as you move towards .

In addition, in the rear pinned state, one end position of the CCD line sensor 4 is 4. In contrast, a state at or close to in-focus is obtained and the maximum peak value is shown, whereas the peak value decreases as it moves from the center position 40 to the other end position 4□.

In this manner, when the imaging lens 8 is tilted with respect to the optical axis 33, the combination of peak values of the contrast waveforms output at two or more locations in the longitudinal direction of the CCD line sensor 4 determines whether the focus state is in focus or not. It differs depending on whether it is a front pin or a rear pin. This difference can be determined by calculation by a microcomputer (calculation means) 37 for controlling the operation of the league printer, and the focus state can be detected.

The drive circuit 39 of the drive motor 38 for focus adjustment of the imaging lens 8 is controlled according to this detection signal, and as shown in the table above, the motor 38 is stopped when the focus is achieved, and the imaging lens 8 is moved to the line when the front focus is achieved. The motor 38 is rotated forward so as to move it toward the sensor 4 side, and when the rear focus is on, the imaging lens 8 is moved toward the line sensor 4 side.
The motor 38 is reversed so as to move the object away from the object.

As a result, automatic focusing can be performed by temporarily tilting the imaging lens 8 using the solenoid 36, and by returning the imaging lens 8 to its original position after automatic focusing, the document image P can be read in the focused state. You can start. It is best to perform automatic focus adjustment when starting to use the League printer, after changing lenses, after zooming, and after changing film. An example of a control flowchart for automatic focus adjustment is shown in FIG.

Note that the contrast portion of the original image P must correspond to each location where the peak value of the contrast is detected by the CCD line sensor 4, but in the microfilm M on which characters and figures are recorded, there are no contrast areas In such cases, focus detection becomes impossible.

Therefore, as shown in FIG. 9, a detection grid 41 in which contrast areas are arranged uniformly in the scanning direction is provided immediately beside each original image P on the microfilm M but outside the projection area, and this detection grid is used to detect the focus during focus detection. The grating 41 may be scanned and projected onto the CCD line sensor 4.

The microfilm M shown in FIG. 10 is provided with a detection grid 41 on the side edge of the film corresponding to each original image P, so that the detection grid 41 can also be used as a bar code for frame retrieval.

In this case, the arrangement direction of the detection gratings 41 does not match the scanning direction, but this means that the original image P is
This can be avoided by rotating and scanning and imaging on the CCD line sensor 4.

The detection grating 41 may be formed, for example, on one surface of a film carrier that coincides with the image surface of the microfilm M, and the CCD line sensor 4 may scan and image it to perform focus detection.

(Effects of the Invention) Since the present invention has the above-described structure and operation, focus detection can be performed by simply tilting the imaging lens for image reading, regardless of the magnification change, and a special It does not require a sensor or an optical system, has a simple structure, and can be provided as a small and inexpensive device.

[Brief explanation of the drawing]

FIG. 1 is a main configuration diagram showing an embodiment of the present invention applied to a reader printer in which an image reading device is provided in the printer section, and FIGS. 2 and 3 are a side view and a plan view of the image reading device. , Fig. 4 is a perspective view showing the schematic configuration of the beam printer, Fig. 5 is a perspective view of the imaging lens section, and Fig. 6 is the CCD.
Figure 7 is a developed view of the optical system showing the focus state on the line sensor and the contrast waveform of the corresponding output. Figure 7 is a developed view of the optical system showing how the imaging lens is tilted with respect to the optical axis to obtain various focus states simultaneously. , FIG. 8 is a flowchart of automatic focus adjustment, FIGS. 9 and 10 are plan views showing an example of a microfilm suitable for the present invention, and FIG. 11 is a developed view of an optical system showing a conventional image reading device. FIG. 12 is a side view showing the internal structure of a conventional image reading device. P −−−−−−−−−−−−−−−−−−−−−−
−−−−−One original image 3−・−・−・−・−・・−・−
・−・Scanning projection system 4−−−−1・−−−−−−−1−−
・----------- Line sensor 8----
−−・−1−−−−−−−−・・−・−−−−−1・Imaging lens 32−・−1−−−・・−1−−−−
−1−−−−−−・・−Tilt center axis 33−−−−−−
-1--
1--Lens attitude adjustment means 37------m-
−−・−・−−1−−・−・−Calculating means Fig. 1 P−−Ichisae, Saikaga I & 36−
---Len Z-ζr4 exposed-14 Sho 8ξFigure 2Figure 3Figure 5Figure 8

Claims (1)

[Claims] (1) In an image reading device that scans and forms a document image onto a line sensor via an imaging lens to read the image, a lens that temporarily tilts the imaging lens with respect to the document image in the longitudinal direction of the line sensor. An image reading device characterized by comprising: attitude adjustment means; and calculation means for calculating a focus error by comparing the contrast of at least two portions in the longitudinal direction of the line sensor with the imaging lens tilted. Automatic focus detection device in the device.