JP3365029B2 - Image reading device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for reading a book original or the like from above, and measures the distance to the original to focus on reading the image. It relates to a technology for performing processing. 2. Description of the Related Art Conventionally, as an image reading apparatus for reading a spatially curved original such as a book, for example, Japanese Unexamined Patent Publication No.
As disclosed in Japanese Patent Application Laid-Open No. 0-254869, there is known an apparatus that detects the height of a document placed on a document table and scans a document image while performing a focusing process based on this detection. This image reading device supports a CCD unit including a line sensor that performs photoelectric conversion and a lens that forms an image of an original on the line sensor so as to be movable in the optical axis direction with a ball screw. Is rotated to move the CCD unit in the optical axis direction, thereby performing focusing. However, in the above-described conventional image reading apparatus, focus adjustment is simply performed in accordance with the result of detecting the height of the document corresponding to the reading position. Complex control to focus was needed. In addition, the adjustment speed at the time of focus adjustment is not considered,
Depending on the state of the document, a rapid speed change may occur depending on the result of the height detection, and smooth speed control is not performed. For this reason, there has been a problem that an excessive load is applied to the motor for adjusting the focus and the drive transmission system. SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an image reading apparatus for reading a document placed on a platen by optical scanning. A lens that forms an image on the image sensor, a scanning unit that optically scans the document by the image sensor, a moving unit that moves the lens along the optical axis, and a height of the document placed on the platen And control means for controlling the moving speed of the lens by the moving means based on the output of the detecting means at regular intervals of scanning by the scanning means. According to the above arrangement, it is possible to focus on a spatially curved original such as a book when reading by the image pickup device by simple movement control of the optical system. Also,
Smooth control with little load on the motor can be performed. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of the image reading apparatus. In FIG. 1, a document such as a book or a file is placed upward on a document table 1 of an image reading apparatus, and a reading unit 2 that reads the document by scanning is provided at a position where the document can be read from above. A work space having a predetermined space is formed between the document table 1 and the reading unit 2. In addition, this device
Illumination unit 3 arranged at the upper back of platen 1 to illuminate the original
Operating unit 4 for setting image reading conditions and the like;
A mirror 5 which is positioned in the sub-scanning direction at the end within the reading range at the back of the mirror and which positions the document 10 and captures the shape of the end of the document, and a control unit described later are provided. The mirror 5 captures an end shape of the document, that is, an image of the document viewed from the horizontal direction (hereinafter, referred to as a mirror image).
By reading this mirror image by the reading unit 2, the height of the document surface is detected. FIGS. 2 and 3 show schematic structures of the present apparatus as viewed from the front and side, respectively. The reading unit 2 is an optical system for forming an original image on an image sensor that performs photoelectric conversion, and includes a lens 6 driven by a focusing motor, and a sub-scanning direction on a focal plane on which the original image is formed. It comprises a CCD line sensor (hereinafter, referred to as CCD) 7 as an image sensor that moves in the direction indicated by the arrow in FIG. This CCD7
Has n pixels arranged in the main scanning direction orthogonal to the above-described sub-scanning direction, and a part of the CCD 7 reads a mirror image which is an image of the end portion of the document reflected on the mirror 5. The document 10 placed on the platen 1 is, for example, a book or a file which is closed at one end and has a columnar shape in which each page is spatially curved when opened right and left. The mirror 5 is a platen 1
The document also serves as a document positioning stopper extending in the left-right direction on the back side of the document table, and is installed at an angle of 45 degrees with respect to the surface of the document table 1. The original 1 is placed on the lower end of the mirror 5.
The original 10 is aligned by touching the upper end of 0.
The document table 1 is colored more darkly than the background density of the document. FIG. 4 is a block diagram showing a configuration of a control unit of the present apparatus. The output of the CCD 7 is A / D converted by the A / D converter 21 and then input to the comparator 22 and also to the temporary memory 29. The comparator 22 has C
The threshold value L1 is set in advance by the PU 23. When an output that crosses the threshold value L1 is input to the comparator 22, the counter 24 is set. The CPU 23 stores the minimum / maximum count value of the counter 24.
Based on the output of the counter 24, the CPU 23 obtains the height of the document. Based on these inputs, the CPU 23
A command is output to the scanner drive unit 25 to move the D7 in the sub-scanning direction, and a command is output to the lens drive unit 26 to drive the lens 6 so that the image of the document is focused on the sensor 7; The light source control unit 27 controls the lighting of the illumination unit 3.
To output the command. FIG. 5 shows a configuration of a lens support mechanism and a drive unit. The movable lens barrel 31 has a lens 6 inside, and moves inside the fixed lens barrel 33 along the optical axis by pins 32 provided above and below. The pin 32 is installed near the center of gravity of the movable barrel 31 to reduce the rotational moment. In addition, in order to prevent the reading position from being shifted due to the inclination of the lens 6 with respect to the optical axis, the rotation center (middle point) of the movable lens barrel 31 is arranged near a point that internally divides the lens principal point HH ′ by the reading magnification. The length of the movable lens barrel 31 is longer than a certain distance as compared with the distance from the fixed lens barrel 33. The cam ring 34 is disposed outside the fixed lens barrel 33 and has a cam groove on the periphery. By connecting the pin 32 to the cam groove by a spring 35, the rotational movement of the cam ring 34 can be converted to the linear movement of the movable lens barrel 31.
A gear 36 is formed around the cam ring 34 and a belt 37
Thus, the drive from the stepping motor 38 is transmitted. The stepping motor 38 is connected to the CPU 2 described above.
3 is driven by a motor control signal output from the drive unit 26 based on the pulse generated. Also, the belt 37
By transmitting the drive, the backlash generated by the gear 36 can be reduced. Cam ring 34
Is biased by a spring 35 to an adjacent focus ring 39. The inside of the focus ring 39 is threaded, and by rotating the piston ring 39, it can move itself in the optical axis direction. As a result, the focus can be roughly adjusted. FIG. 6 shows the distribution of the reading position and the height of the original. That is, assuming that the reading position in the scanning direction of the document is the X axis and the height direction is the Y axis, the height of the document is represented by an XY diagram as shown. Here, since the line sensor scans at a constant speed in the X direction, the X axis in this figure is the time axis (T axis).
Can be replaced by The moving speed of the lens is obtained by differentiating the height of the document with respect to time, and the lens moving diagram required to keep the document in focus is the TV diagram of FIG. However, in order to move the lens 6 according to the TV diagram shown in FIG. 7, it is necessary to change the control pulse of the motor 38 as needed, and the control software becomes complicated. Further, a sudden speed change may occur, and an excessive load may be applied to the motor 38. On the other hand, when reading a document, it is not necessary to accurately focus on the document surface, and if the document surface is within the depth of field, reading of an image is not affected. Therefore, as shown in FIG. 8, the shape of the document actually detected (FIG. 6) is divided at regular intervals, and the shape of the document is approximated by a straight line. Further, the shape of the document approximated by the straight line, that is, the one obtained by differentiating the XY diagram shown in FIG. 8 with time is the movement speed of the lens. When the XY diagram shown in FIG. 8 is differentiated with respect to time, it becomes a rectangular shape as shown in FIG. 9, and the motor 38 may be controlled by changing the control pulse at regular time intervals. Since a certain acceleration time is required when the speed of the motor 38 changes, it is necessary to change the speed smoothly where a sudden change in speed occurs. Therefore, as shown in FIG. 10, the midpoint between the current block speed and the next block speed divided at regular intervals is obtained, and a speed curve that changes at a constant acceleration through this midpoint is obtained. The motor speed should be controlled accordingly. By performing such acceleration / deceleration control, the absolute value of the lens movement amount within a certain period of time will be smaller than the required value, but the lens movement amount will be more than the required value in the next time block. Is the same as By controlling the speed of the motor as described above, it is possible to keep the focus on the document surface with simple control. Since the control method is simplified as described above, a deviation occurs between the in-focus surface of the lens and the actual document surface. If this shift deviates from the depth-of-field area, it causes blurring of the image. However, by shortening a certain time, which is a time block of the speed change, the amount of the shift can be reduced. In practice, it is necessary to set the time interval in consideration of the maximum amount of curvature of the document, the depth of field of the lens, the required focus accuracy, and the like. In the above-described embodiment, the lens is driven by the stepping motor. However, when the lens is driven by the DC motor, the same control is performed by detecting the lens position and adding feedback control. be able to. As described above, according to the present invention, when a spatially curved document such as a book is scanned and read by the image sensor, the speed is changed at regular time intervals by a simple control. Since the movement of the optical system is controlled so that all surfaces on the document surface are in focus, a beautiful image without blur can be obtained. In addition, since acceleration / deceleration is performed based on the speed values of the front and rear blocks, smooth control with little load on the motor can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an image reading apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram viewed from the front of the image reading apparatus. FIG. 3 is a schematic configuration diagram viewed from a side of the image reading apparatus. FIG. 4 is a block diagram of a control unit of the image reading apparatus. FIG. 5 is a diagram illustrating a configuration of a lens support mechanism and a driving unit. FIG. 6 is a diagram illustrating a height distribution of a document. FIG. 7 is a diagram showing a moving speed of a lens according to an actual document height. FIG. 8 is a diagram showing a distribution in which the height distribution of a document is approximated by a straight line. FIG. 9 is a diagram illustrating a moving speed of a lens according to the embodiment. FIG. 10 is a diagram showing a speed change during acceleration / deceleration of a motor. [Description of Signs] 1 platen 2 reading unit 5 mirror 6 lens 7 CCD 10 document 23 CPU 38 motor

Claims (1)

(57) [Claim 1] In an image reading apparatus for reading a document placed on a platen by optical scanning, an image pickup device and a lens for forming an image of the document on the image pickup device Scanning means for optically scanning a document by the image sensor, moving means for moving the lens along the optical axis, detecting means for detecting the height of the document placed on the document table, Control means for controlling the moving speed of the lens by the moving means based on the output of the detecting means at regular intervals of scanning by the scanning means.