JPS6392155A - 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 the line sensor inclined, and calculating a focus error. CONSTITUTION:While the line sensor 4 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, rotates the motor 30 forward so as to move an image forming lens 8 toward the sensor 4 in the front-focus state, and reverse the motor 39 so as to move the lens 8 away from the sensor 4 in the rear-focus state. Consequently, the sensor 4 is slanted temporarily by a solenoid 37 to make an automatic focus adjustment.

Description

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

(Prior Art) In general, an image reading device, as shown in FIG. and guide it to the imaging optical system i through mirrors r, g, h, and the optical system i
The image is formed on the solid-state image sensor j by the solid-state image sensor j, and while the original image p is scanned by a mirror scan method, an original platen scan method, or an original transport method, the image is read by the 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, about ±0.01 mm, 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 striation pattern must be formed with high precision.

Further, when performing variable magnification reading, if the variable magnification range becomes large, interference may not occur with one type of striation backcoup, 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 by only temporarily moving a line sensor of the image reading device and does not have the above-mentioned conventional problems. For the purpose of
In an image reading device that scans and forms a document image on a line sensor to read the image, the line sensor posture adjusting means temporarily tilts the line sensor with respect to the document image in the longitudinal direction, and the line sensor is tilted. The present invention is characterized by comprising 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.

(Function) Normally, the elongated direction of the line sensor is parallel to the original image and the imaging lens of the imaging optical system, and the original image is imaged in equal focus over the entire longitudinal direction of the line sensor. In this state, the entire document image can be read clearly.

When the line sensor is tilted in its longitudinal direction with respect to the original image with the optical axis position as the center using the line sensor attitude adjustment means, the same focus state as in the normal attitude is obtained at the optical axis position, and the inclination causes the imaging lens to In the half part that is inclined towards the side, as it moves away from the optical axis position, a state becomes more rear focused than the normal focus state at the optical axis position,
In addition, in the half portion that is inclined toward the side away from the imaging lens, as it moves away from the optical axis position, it is possible to obtain a state in which it is closer to the front bin than the normal focus state at the optical axis position. Here, the relationship between contrast differences due to differences in focus states at two or more locations in the longitudinal direction on the line sensor changes depending on the normal focus state at the optical axis position, and the relationship is calculated by a calculation means to obtain the original document. It is possible to determine whether the focus state determined by the three positional relationships among the image, the imaging lens, and the line sensor is in focus, front focus, or back focus.

At the time of focus determination, when the line sensor is returned to its original posture 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 on the line sensor 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 O-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 1) and the second reader mirror 12 located at the reader position (the solid line position in the figure), and is enlarged and projected onto the screen 2 at the upper front of the main body. Ru.

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 leader first mirror 1). 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 is sequentially slit projected (
The original image P is converted into an electrical signal, and the image is read electrically. 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 independently rotatably attached to the upper part of the lens holder part 21 that holds the imaging lens 8. 22 is an outer peripheral gear, and this outer peripheral gear 22 is also part of the lens holder 21.
It is rotatably attached to the upper part of the lens barrel 20 and 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). The lens barrel 20 and the lens holder portion 21 are rotatably held in an opening formed in a support plate 25. In addition, a trapezoidal prism is used as the prism 9, and at the solid line position in FIG. 4, the document image P on the microfilm M is directed as it is toward the screen 2, the CCD line sensor 4, etc., and the broken line in FIG. When the original image P is rotated by <45 degrees for each position, the original image P is rotated 90 degrees around the optical axis and the screen 2,
Aim at the CCD line sensor 4.

The prism 9 is used not only to change the projection direction of the original image P by 90", 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 is attached to the lens barrel 20. The detection mark (not shown) is attached to the prism 90.
During the rotation, a microcomputer 38 (Fig. 1) controls the operation of the reader/printer.
The orientation of the prism 9 is detected by calculating
The projection direction of the original image P can be controlled.

As shown in FIGS. 2 and 3, the CCD line sensor 4 has CCDs 4b arranged horizontally on a substrate 4a, and is fixed to the base 31a of an L-shaped holder 31 via a spacer 32. The holder 31 holds the CCD 4b at the side piece 31b.
The line sensor 4 is pivoted by a tilting center axis 33 whose center axis coincides with the surface at the center position in the longitudinal direction, and the line sensor 4 can be tilted about 1 degree in the longitudinal direction with respect to the projection optical axis 34, or the inclination can be eliminated. It's Nishide. The holder 31 has a spring acting between the base side 31a and the first positioning pin 35a that abuts against the side piece 31b and regulates the holder 31 to an origin position perpendicular to the optical axis 34 of the CCD line sensor 4 at one rotation end side. 3
6, the side edge 31b is stabilized at the original position where it abuts on the first positioning pin 35a.

On the other rotating end side of the holder 31, an operating rod 37a of a solenoid (line sensor attitude adjustment means) 37 is in contact with the lower surface of the base 31a, and when the solenoid 37 is activated, the operating rod 37a protrudes and the base is 31b, the holder 31 is rotated against the spring 36 until it comes into contact with the second positioning pin 35b, and the line sensor 4 is tilted at a predetermined angle with respect to the optical axis 34 as shown in FIG. be.

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 A1 or the rear focus position A2, the peak value of the received light contrast waveform R8 of the slit-projected image becomes high. ,, the peak value of R2 becomes lower.

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 mm, a small difference in the focus state will appear relatively large and can be sufficiently detected.

Therefore, the CCD line sensor 4 activates the solenoid 37 to tilt the optical axis 34 when detecting the focus, but the tilt is only a few degrees, which is enough to detect the difference between the peak values of the contrast waveforms R6, R1, and R2. good. 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 of the CCD line sensor 4 at 4 degrees and the positions at both ends at 41.4t 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 at one end position 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 the lens moves from the center position of 4° to the other end position of 4□.

In the rear focus state, the CCD line sensor 4 is in focus or close to it at the other end position 42 and exhibits the maximum peak value, whereas at the center position 4°, at the -manendo position 4. The peak value decreases as you move towards .

In this way, when the CCI) line sensor 4 is tilted with respect to the optical axis 34, two of the longitudinal directions of the CCD line sensor 4 are
The combination of peak values of the contrast waveforms output at the above locations differs depending on whether the focus state is in-focus, front focus, or rear focus. This difference is explained by the microcomputer (calculating means) used to control the operation of readers and printers.
It is possible to determine the focus state by performing calculations based on 38.

The drive circuit 40 of the drive motor 39 for focus adjustment of the imaging lens 8 is controlled in accordance with this detection signal, and as shown in the table above, the motor 39 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 39 is rotated forward so as to float toward the sensor 4 side, and the imaging lens 8 is moved toward the line sensor 4 when rear focusing.
The motor 39 is reversed so as to move the object away from the object.

As a result, automatic focus adjustment can be performed by temporarily tilting the CCD line sensor 4 using the solenoid 37, and by returning the CCD line sensor 4 to its original position after automatic focus adjustment, the document image P can be read in the focused state. can be started. It is best to perform automatic focus adjustment when starting to use the 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, it is necessary to The parts may correspond, and in such a case, 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 projecting onto 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 line sensor for image reading regardless of magnification, and a special sensor for focus detection can be used. Since the structure is simple and no optical system is required, it 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 league 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. , Figure 4 is a perspective view showing the schematic configuration of the League printer, Figure 5 is a perspective view of the imaging lens section, and Figure 6 is the CCO.
A developed diagram of the optical system showing the CC line sensor focus state and the corresponding output contrast waveform, Figure 7 is the CCD
The tilt of the line sensor with respect to the optical axis is a developed view of the optical system showing the state in which various focusing states are obtained simultaneously. Figure 8 is a flowchart of automatic focus adjustment. Figures 9 and 10 are microfilms suitable for the present invention. FIG. 1) is a plan view showing an example; FIG. 1) 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 the conventional image reading device.

Claims (1)

[Claims] (1) In an image reading device that scans and forms a document image on a line sensor to read the image, the line sensor posture adjustment means temporarily tilts the line sensor with respect to the document image in its longitudinal direction; 1. An automatic focus detection device for an image reading device, comprising: 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 in a state where the line sensor is tilted.