Image scanner with a single motor providing two-dimensional movement of photosensors

An image scanner has a movable photosensor array that can be moved in two dimensions in a plane. Two dimensional movement is provided using a single motor.

FIELD OF INVENTION

This invention relates generally to image scanners.

BACKGROUND OF THE INVENTION

Image scanners, also known as document scanners, convert an image on a document or photograph, or an image in a transparent medium, into an electronic form suitable for copying, storing or processing by a computer. An image scanner may be a separate device, or an image scanner may be a part of a copier, part of a facsimile machine, or part of a multipurpose device. Reflective image scanners typically have a controlled source of light, and light is reflected off the surface of a document, through an optics system, and onto an array of photosensitive devices. Transparency image scanners pass light through a transparent image, for example a photographic positive slide, through optics, and then onto an array of photosensitive devices. The optics focus at least one line, called a scanline, on the image being scanned, onto the array of photosensitive devices. The photosensitive devices convert received light intensity into an electronic signal. An analog-to-digital converter converts the electronic signal into computer readable binary numbers, with each binary number representing an intensity value.

There are two common types of image scanners. In a first type, a reduction lens system is used to focus the scanline onto the photosensor array, and the length of the photosensor array is much less than the length of the scanline. In a second type, an array of lenses is used to focus the scanline onto the photosensor array, and the length of the photosensor array is the same length as the scanline.

There is an ongoing need to reduce the cost of image scanners. There is also an ongoing need to scan surfaces larger than typical documents.

SUMMARY OF THE INVENTION

An image scanner has a movable photosensor array that can be moved in two dimensions in a plane. In multiple example embodiments, two dimensional movement is provided using a single motor.

Photosensor arrays for image scanners typically have thousands of individual photosensitive elements. Each photosensitive element, in conjunction with the scanner optics system, measures light intensity from an effective area on the document defining a picture element (pixel) on the image being scanned. Optical sampling rate is often expressed as pixels per inch (or mm) as measured on the document (or object, or transparency) being scanned. Optical sampling rate as measured on the document being scanned is also called the input sampling rate. The native input sampling rate is determined by the optics and the pitch of the individual sensors. Given a native input sampling rate, and a scanline length, the total number of photosensor sites required to scan an entire scanline with a single exposure is given by: Number of photosensors=(scanline length)*(native input sampling rate). For example, if the scanline is 25 cm long, and the native sampling rate is 500 pixels per cm, then 12,500 photosites are needed to capture 12,500 pixel intensities with one exposure.

A photosensor array, in conjunction with its associated optics system, is a major portion of the cost of a scanner. In addition, the photosensor array, in conjunction with its associated optics system, typically determines the maximum length of one dimension of a document or other surface to be scanned. In the following example embodiments, given a native input sampling rate and a scanline length, an image scanner has a photosensor array that has fewer photosensors than the number of pixels for the scanline and the native input sampling rate. Multiple swaths are scanned, with each swath providing a subset of the pixels for each scanline. For a given scanline length, reducing the number of photosensors reduces the cost of the photosensor array. Viewed alternatively, given a fixed number of photosensors, multiple swaths per scanline enables longer scanlines to be scanned.

Photosensor arrays for scanners having reduction optics (where the overall length of the photosensor array is much less than the length of the scanline) are typically fabricated as a single integrated circuit die. The cost of an integrated circuit is typically a function of die area. If the die can be made smaller, the cost is typically reduced. The die can be made smaller by reducing the number of photosensor sites.

For scanners having arrays of lenses, the photosensor arrays are typically fabricated as an assembly comprising multiple segments. Given segments of a particular size, the cost of the overall assembly may be reduced by reducing the number of segments.

In the following examples, the number of photosites is reduced, and mechanical displacement of the photosensor array is used to capture all the pixels.

FIG. 1illustrates part of an example embodiment of a scanner as viewed through a transparent platen102. A document (not illustrated) may be positioned face down on top of the platen for scanning. A contiguous photosensor array100is moved, as indicated by arrows106,108, and110. Area104depicts an area that has been previously scanned, and area110depicts an area that is being scanned. In particular, area104depicts an area that was scanned earlier with photosensor array100positioned to the left (as viewed inFIG. 1), and moving in the direction indicated by arrow106. At the end of the scan of area104, the photosensor array was translated to the right (indicated by arrow108), the direction of scanning was reversed (indicated by arrow112), and the photosensor array100started scanning area110. Areas104and110may overlap.

Photosensor array100is approximately one-half the length needed to scan a scanline having a length equal to the combined widths of areas104and110. If photosensor array100is fabricated from a single die, then the array can be less expensive than an array that is approximately twice as long. If photosensor array100is fabricated from multiple segments, then the array can be less expensive than an array that requires approximately twice as many segments. Viewed alternatively, given a photosensor array of a length as depicted by photosensor array100inFIG. 1, the scanline length can be approximately doubled.

FIG. 2illustrates an alternative embodiment of a scanner as viewed through a transparent platen204. InFIG. 2, a segmented photosensor assembly202comprises three separated photosensor array segments200. The number three is arbitrary and is for illustration purposes only. Areas206depict areas that have been scanned, and areas212depict areas that are being scanned. In particular, areas206depict areas that were scanned earlier with photosensor assembly202positioned to the left (as viewed inFIG. 2) and moving in a direction indicated by arrows208. At the end of the scan of areas206, the photosensor assembly202was translated to the right (indicated by arrows210), the direction of scanning was reversed (indicated by arrows214), and the photosensor array segments200started scanning areas212. Areas206and212may overlap.

Approximately half as many segments are needed relative to a contiguous assembly that is the width of areas206and212combined, thereby reducing cost. Viewed alternatively, given three photosensor array segments of a total length as depicted inFIG. 2, the scanline length can be approximately doubled.

A motor, a solenoid, a voice coil, or other active device, may be used to move a photosensor array in a first dimension (for example,FIG. 1, directions106and112, orFIG. 2, directions208and214). A separate motor, solenoid, voice coil, or other active device may be used to move a photosensor array in a second dimension, (for example,FIG. 1, direction108, orFIG. 2, direction210). However, preferably, as illustrated in the following example embodiments, a single motor or other active device is used to move a photosensor array in two dimensions, further reducing cost by eliminating one motor or other active device.

One example is to mount a photosensor array or assembly, as inFIG. 1,100, orFIG. 2,202, onto a two-dimensional linear stepper motor. For example, a scanner base may be formed with a toothed surface, and active coils may be implemented on the photosensor array, with teeth on the bottom surface of the photosensor array. The array can then be stepped to any X-Y location on the base of the scanner.

In each of the following examples, a single rotational motor is used to move a photosensor array in two dimensions.

FIG. 3Aillustrates a first example scanner in which a single rotational motor can move a photosensor array in two dimensions. A photosensor array (or assembly)300is attached to two flexible drive members (for example, belts, cables, chains, etc.). In particular, one end of the photosensor array300is attached to a first flexible drive member302by a rotating tab308(additional detail is provided inFIG. 3B), and a second end of the photosensor array300is attached to a second flexible drive member304by a second rotating tab308. Each flexible drive member (302,304) passes around four pulleys306. For scanning motion, any of the pulleys may be driven, or one of the flexible drive members may be separately driven. In the example illustrated inFIG. 3A, a single motor320directly drives one pulley306. If motor320drives one pulley counter-clockwise (as viewed inFIG. 3A), the photosensor array300is moved in the direction indicated by arrow310. At the end of the scanner, the photosensor array is translated to the right, and then the direction of scanning is reversed, and the photosensor array is positioned as depicted by reference number300a. The scanning path of the photosensor array300is defined by the path of the flexible drive members. In the example embodiment ofFIG. 3A, and in the other example embodiments below, the direction of travel of the photosensor array may be reversed. That is, a generally counter-clockwise motion is used for illustration, but the motion may be generally clock-wise or any other path that scans the area of interest.

FIG. 3Billustrates a cross section of part of the scanner ofFIG. 3A, depicting the photosensor array positioned over one of the pulleys306. The tab308connecting the photosensor array300to the flexible drive member302rotates around a post312. This prevents twisting of the tab308as the tab travels around the pulleys306. In addition, note that the thickness of the flexible drive member302enables the tab308to clear a flange on the pulley. Optionally, the photosensor array300may be held at a constant distance from a platen316by a low friction spacer318. In the example ofFIG. 3B, a wheeled support314is spring loaded into the photosensor array300, illustrating one example of a way to hold the photosensor array against the platen. The support314may roll on a base of the scanner.

FIG. 4Aillustrates a second example embodiment of a scanner in which a single rotational motor can move a photosensor array in two dimensions. A photosensor array (or assembly)400has two wheels or gears406(additional detail is provided inFIG. 4B) that travel along rigid guide walls402and404. A single motor, mounted on the photosensor array, may drive one or both wheels or gears406. If one of the wheels or gears406is driven clockwise (as viewed inFIG. 4A), the photosensor array400moves toward the bottom of the figure, is then translated to the right, and the direction of scanning is then reversed, and the photosensor array is positioned as depicted by reference number400a. In the embodiment ofFIG. 4A, the path of the movement of the photosensor array is defined by the path of a rigid wall.

FIG. 4Bprovides additional detail. In the example ofFIG. 4B, a motor408directly drives a gear406, which meshes with matching teeth in a rigid wall404. Motor408may optionally also drive another wheel or gear406which engages wall402(FIG. 4A). The rigid walls (402,404), with or without teeth, may optionally be molded as part of a base of the scanner. The photosensor array400may optionally be held at a constant distance from a platen, as illustrated inFIG. 3B.

FIG. 5illustrates a third example embodiment of a scanner in which a single rotational motor can move a photosensor array in two dimensions. A photosensor array (or assembly)500is moveably supported on a movable rigid support502. The support502may be mounted on one or more guides (not illustrated) for movement in one dimension. The photosensor array500is attached to a flexible drive member504, using a rotating tab508(for example, as illustrated by tab308inFIG. 3B). The flexible drive member504rotates around four pulleys506. Any of the pulleys may be driven by a motor (not illustrated) to move the flexible drive member504. If the flexible drive member is moved counterclockwise (as viewed inFIG. 5), photosensor array500is moved downward, then is translated to the right along the support502as tab508is pulled around a first pulley506, then upward after tab508is pulled around a second pulley506, and so forth. Note that in the example ofFIG. 5, a motor drives a flexible drive member, which in turn drives a photosensor array (or assembly), which in turn drives a support. The photosensor array is held at predetermined positions on the support by the flexible guide member, and the scan path is determined by the path of the flexible guide member.

FIG. 6illustrates a fourth example embodiment of a scanner in which a single rotational motor can move a photosensor array in two dimensions. A photosensor array (or assembly)600is moveably supported on a movable rigid support602. The support602may be mounted on one or more guides (not illustrated) and may be moved by use of a motor and cables. As illustrated in the example depicted inFIG. 6, a motor608drives a belt that passes over a pulley, and the support602is attached to the belt. There are numerous other ways in which a scanner support may be moved, as is well known in image scanner mechanisms.

InFIG. 6, the photosensor array600is held at one of multiple predetermined positions on the support602by rigid guide walls (608,610, and612). Rollers604and606, mounted on the photosensor array600, roll on the rigid guide walls. The motor618moves the support602, and the support602moves the photosensor array in one dimension, with the position of the photosensor array on the support determined by guide walls608and610. When the photosensor array nears the end of the scanner, roller604on the photosensor array follows the guide wall608, forcing the photosensor to translate to the right along the support602. The direction of travel of the support602is then reversed, and the position of the photosensor array on the support is determined by the guide walls610and612.

InFIGS. 3A,4A,5, and6, the photosensor array is depicted as completing a scan of an overall area in two swaths. It may be preferable to provide an even lower cost, by reducing the number of photosensors further, and requiring more than two swaths to complete each scanline. Alternatively, given a photosensor length, more than two swaths enables scanning of even larger documents.

FIG. 7illustrates a photosensor array (or assembly)700capable of making four swaths for each scanline. Photosensor array700is illustrated with three rollers (702,704, and706). When photosensor array700is moving in the direction depicted by arrow708, roller706contacts a deflector710, and the photosensor array is translated to the right (as viewed inFIG. 7). The scanning direction is then reversed and eventually roller704contacts a deflector712, and the photosensor array is translated further to the right. The scanning direction is reversed again, and eventually roller706contacts a deflector714, and the photosensor array is translated further to the right. The scanning direction is reversed again, and eventually roller702contacts a deflector716, and the photosensor array is translated to the left to the starting position.

Optionally, the photosensor array700ofFIG. 7may be held at predetermined positions on a support by guide walls as depicted inFIG. 6. Alternatively, as discussed in more detail below, the photosensor array may be lightly held at predetermined positions, and the holding force may be overcome by the translation force provided by forcing the photosensor array rollers against the deflectors. If the photosensor array is lightly held at predetermined positions, then as illustrated inFIG. 7, where the guide walls bend to translate the photosensor along the support, the guide walls may have an initial region where the deflection is relatively small, but where the deflection force is relatively large to overcome the force keeping the photosensor array lightly held at one of the predetermined positions on the support. Once the photosensor array is freed from the retaining force, the deflection of the photosensor array may be increased relative to the distance moved by the support to reduce the distance the support has to travel to translate the photosensor array along the support. A parabolic shape may be used to provide a constant force and smooth motion.

FIG. 8Aillustrates two alternative ways to hold a photosensor array at a predetermined position on a support (without guide walls). A photosensor array800can move along a support802. Reference804depicts a magnet, where one end of the photosensor array800may be held against the magnet. The photosensor array may have matching magnets, or the photosensor array may have end surfaces of a ferrous or other material that may be attracted to a magnet. As an alternative, a detent806in the support802may be used to receive a flexible protrusion on the photosensor array (further illustrated inFIG. 8C).

FIG. 8Bis a side view, illustrating the magnet804. In addition,FIG. 8Billustrates a roller808on the bottom of the photosensor array800and a guide wall or deflector810. Note that the photosensor array can clear the top of the guide wall or deflector while the roller is in contact. A roller is used for illustration, but it is not necessary. A low friction pad may be used, or the deflector may simply contact a projection on the lower part of the photosensor array.

FIG. 8Cillustrates an example embodiment of a flexible protrusion. InFIG. 8C, the flexible protrusion is a spherical bearing812being held by a spring into the notch806in the support. The force of the spring may be overcome by the force of the photosensor array being forced against a guide wall or deflector.