Abstract:
A method for scanning an image of media comprises biasing a scanner carriage for movement relative to a platen and releasing the carriage to move relative to the platen, the carriage scanning an image with a scanner head disposed therein. An image scanner comprises a housing, a platen disposed on the housing, a carriage disposed in the housing, the carriage comprising a scanner head adapted for scanning an image, a biasable drive moving the carriage relative to the platen for high-speed scans, and a drive mechanism loading the biasable drive for the high-speed scans and moving the carriage relative to the platen for low-speed scans. An encoder for sensing position of a scanner carriage comprises a grating disposed in a scanner housing, and an optical sensor for sensing the grating during biased movement of a scanner carriage, the sensor providing carriage position information for rastering an image of scanned media.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is related to digital imaging technology, and more specifically to biasable drives for image scanner carriages.  
         BACKGROUND OF THE INVENTION  
         [0002]    Typical construction of digital image scanners, particularly those described as “flatbed scanners”, employs a generally rectangular-shaped scanner housing supporting a platen glass against which one may lay a piece of media, such as a piece of paper for scanning. An optical scanner head moves opposite the media and scanner associated software and/or firmware typically transforms an optical image of the media into a data file. Other scanners, often called “scroll feed scanners” function similar to a facsimile machine in that they feed sheets of paper through a stationary scanning mechanism one at a time.  
           [0003]    Construction of flatbed scanners typically employs an optical carriage, housing an optical scanning head or the like; a carriage rod that aligns and guides the optical carriage down a scan-path below the platen; and a motorized drive mechanism employing a direct-current (DC) motor and/or stepper motor. The optical carriage has optics, also known as a scanner head, that normally employ mirrors. These optics map light at a location coinciding with the upper surface of the platen glass, where media is typically resting, to a charge couple device (CCD) or the like. The CCD converts optical photons into electrons, used to create a data signal. The data provided by the CCD is processed into a final form such as an image file, for example a bitmap (BMP) file, tag image file format (TIFF) file, Joint Photographics Expert Group (JPEG) file or the like.  
           [0004]    In operation, the optics or scanner head of the carriage usually scans a very thin strip, commonly referred to as a scan line. Then typically the motorized drive mechanism translates the optical carriage one small step, and then the scanner head takes another scan line, followed by another step, and another scan. This step-and-scan process is repeated to create a rastered scan of a whole image of the media disposed against the platen.  
           [0005]    Generally, drive technologies for scanner optical carriages attempt to translate a carriage in some controlled manner to create the scan lines for rastering together to create a digital image file. Multi-speed scanners use dynamic ranges of a drive motor to provide a multiple-speed carriage drive. Depending on the resolution required, some scanners may employ five or more speeds. Other motors may provide an infinite number of speeds, between an upper and a lower limit. In some scanners a pulse frequency to a stepper motor is modified to generate these different speeds. Another existing scanner carriage drive mechanism is a DC motor that employs a servo methodology.  
           [0006]    A stepper motor has a rotor that moves through a fixed angle in response to a pulse from a controlling element. The stepper motor makes discrete steps that are translated to the carriage via a transmission and/or a belt and pulley system. The steps are based on characteristics of the stepper motor and/or a drive-train disposed between the stepper motor and scanner carriage. A stepper motor employs an open loop control system. A stepper motor driving a scanner carriage is sent a pulse and the system assumes the carriage moves one step in response. Therefore, existing stepper motor-based scanner carriage drives do not typically need intermediate position sensing.  
           [0007]    A servo-drive mechanism typically employs a drive belt-and-pulley system to basically pull the carriage back and forth. Since this technology does not employ discrete steps, electronic logic to determine location, often based on velocity and/or acceleration of the carriage, is employed to provide a closed-loop control system. To this end, many DC servo scanner carriage drives include some type of optically-encoded position sensing, or the like. The DC servo, closed-loop system typically employs control algorithms. Otherwise, construction of these two types of existing scanner carriage drive systems are similar, employing a transmission and/or belt assembly.  
           [0008]    Other types of scanner drive mechanisms may include screw drives, gear-wheel and rack drives, or the like. Screw drives may replace or augment the aforementioned carriage rod. A rack may be molded into, or attached to, the bottom of an existing scanner housing for a gear-wheel and rack-drive mechanism. Regardless, drive technologies for scanner carriages are intended to translate a scanner carriage in a controlled manner to facilitate creation of scan lines to be rastered together to develop a digital image.  
           [0009]    Increasing resolution capability demanded by the scanner market translates into smaller and smaller steps between scan lines to provide higher resolutions, that in turn, results in slower scan speeds. However, extremely fast scans at low-resolution, such as used for a preview scan, are in demand as well. Existing scanner carriage drive motors specifically designed for high-resolution, high-accuracy scans typically do not have very fast performance at lower resolutions. DC servo or stepper motors only have a limited dynamic range, limiting the upper speed threshold that a scanner carriage may be moved so as to provide the required precise high-resolution, slow-speed scans. For example, stepper motors can only pulse within a limited range of frequencies. Problematically, use of a dual-speed transmission or two different motors with different drive speeds is not desirable as it raises cost and complexity issues.  
           [0010]    Uses for springs in the scanner or copier industry abound. For example, springs of various types are used to provide vibration or oscillation for universal product code (UPC) scanners or the like as disclosed in Goto, U.S. Pat. No. 5,245,463; Giordano, U.S. Pat. No. 5,594,232; and Dvorkis, U.S. Pat. Nos. 5,621,371 and 5,412,198. A spring may be employed in conjunction with a motor-driven cable to tension a carriage drive cable and/or to stabilize a scan head by dampening vibration in such a cable. U.S. Patents related to such use of a spring in a scanner or copier include: Yoshida, U.S. Pat. No. 5,392,100; Takizawa, U.S. Pat. No. 4,171,901; Hediger, U.S. Pat. No. 4,965,638; Satomi, U.S. Pat. No. 4,771,315; Hayashi, U.S. Pat. No. 6,108,505; Peng, U.S. Pat. No. 6,026,261; and Costanza, U.S. Pat. No. 4,218,127. Forrester, U.S. Pat. No. 4,460,268, and Cook, U.S. Pat. No. 3,918,806 are examples of copier mechanisms driven by dash pots that use a spring to rapidly return the copier head to a start position, without copying during the return.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    An embodiment of a method for scanning an image of media using a scanner comprises biasing a scanner carriage for movement relative to a platen and releasing the carriage to move relative to the platen, the carriage scanning an image with a scanner head disposed therein.  
           [0012]    An embodiment of an image scanner comprises a housing, a platen disposed on the housing, a carriage disposed in the housing, the carriage comprising a scanner head adapted for scanning an image, a biasable drive moving the carriage relative to the platen for high-speed scans, and a drive mechanism loading the biasable drive for the high-speed scans and moving the carriage relative to the platen for low-speed scans.  
           [0013]    An encoder for sensing position of an image scanner carriage comprises a grating disposed in a scanner housing, and an optical sensor for sensing the grating during biased movement of a scanner carriage, the sensor providing carriage position information for rastering an image of scanned media. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0014]    [0014]FIG. 1 is a partially-fragmented perspective view of an embodiment of a flatbed optical image scanner with a bias-driven scanner carriage, in accordance with the present invention;  
         [0015]    [0015]FIG. 2 is a further fragmented side view of the scanner of FIG. 1, showing an embodiment of an alternative releasable latch mechanism for the scanner carriage;  
         [0016]    [0016]FIG. 3 is a flow chart of an embodiment of a method for providing a biasable drive to an optical image scanner carriage in accordance with the present invention; and  
         [0017]    [0017]FIG. 4 is a partially-fragmented perspective view of an embodiment of a flatbed optical image scanner with a bias-driven scanner carriage employing a stepper motor as an encoder, in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    The present invention is directed to systems and methods that provide a mechanism to facilitate fast-preview speeds for a scanner, while enabling the scanner to use a drive mechanism that may make accurate, high-resolution scans. The present invention provides a solution to the aforementioned disparate preview and high-resolution scanner carriage translation speed dichotomy that is cost-effective and mechanically sound, requiring little, if any, additional space.  
         [0019]    Preferably a flatbed scanner employing the present invention has a motorized drive mechanism that may employ a stepper motor, a DC servo-motor, or the like, for high-resolution scans, with a biasable drive, such as a spring-loaded drive or spring drive mechanism, to drive the carriage for high-speed scans, as detailed below. Preferably, both of these drives are connected to a single scanner carriage. The biasable drive is preferably used to drive the carriage or other optical mechanism of the scanner at a relatively high-rate of speed during low-resolution scans, such as preview scans. These low-resolution scans may also be used to produce image files where lower resolution is acceptable.  
         [0020]    In operation, the biasable drive is preferably loaded, such as by stretching a spring, using the stepper motor or servo-motor that drives the carriage during higher resolution scans. Advantageously, use of such a biasable drive enables a scanner with very high-resolution capability, and a main drive that is geared for such high-resolution use, to have very fast performance for at least one lower resolution. A further advantage of using a biasable drive, in contrast to other possible alternate solutions to the above-described dichotomy for scanner carriage speeds, is that such a biasable drive is very low cost and employs a reliable mechanism that is highly tunable, such as a spring.  
         [0021]    [0021]FIG. 1 is a partially-fragmented perspective view of an embodiment of a flatbed scanner  100  showing optical carriage  101  and two drive mechanisms  102  and  103 . Optical carriage  101  preferably contains an optical head that may include optical mirrors and CCD components typical in flatbed scanners. Carriage rod  104  is one manner of providing alignment and direction of travel to a carriage during a scan, whether it be a high-resolution or a low-resolution scan. Flatbed scanner  100  may have housing  111  wherein carriage  101 , drive mechanisms  102  and  103 , and carriage rod  104  are disposed. Platen  112  is preferably supported by housing  111 . Cover  113  may be hinged, preferably removably-hinged, to housing  111  to close over platen  112  and media disposed thereupon to shut out ambient light and/or to hold media in place on platen  112  during scanning operations.  
         [0022]    Motorized drive mechanism  102  is shown in the form of a pulley  105  and belt  106  mechanism attached to either a DC servo or stepper motor  107 , via transmission system  108 . Other primary drive mechanisms known to those skilled in the art may be employed by a scanner employing the present invention.  
         [0023]    In accordance with the present invention, biasable or spring drive  103  may be employed for high-speed, low-resolution scans, such as a fast-preview scan. As illustrated in FIG. 1, spring drive  103  may employ cable  109  and spiral spring spool  110 . However, biasable drive  103  may take other forms such as a coil, tension, helical or compression spring. Cable and spiral spring spool system  103 , or any other spring employed in accordance with the present invention, preferably provides relatively constant tension throughout traversal of optical carriage  101 , after overcoming initial inertia. Additionally, a variety of spring-deployment configurations may be used. For example, the spring may be attached or integrated into the carriage. As a further example, such a carriage-mounted spring may employ a spring-driven gear to drive the carriage along a rack gear disposed on the floor of the housing. Yet other alternative embodiments use more than one spring in any of the above-described configurations or combinations of these configurations.  
         [0024]    In FIG. 1, the optical carriage is shown in what might be considered a “home” position, ready to start a scan. If the scan is to be performed in a fast-preview mode or the like, motorized drive mechanism  102  would preferably be set in a neutral, or free, setting. If motorized drive mechanism  102  employs a stepper motor, the stepper motor may be set in such a neutral setting by shorting the coils of the stepper motor as detailed below in the description of FIG. 4. Shorting the coils on a stepper motor releases the motor and reduces the electromagnetic resistance produced by the motor when freewheeling. Setting drive motor  107  to a neutral setting enables relatively low-resistance to exist in motorized drive mechanism  102  and tension in loaded biasable drive  103  preferably overcomes any remaining resistance and the inertia of carriage  101 , pulling optical carriage  101  down carriage rod  104  at a rapid speed, facilitating a fast-preview or other low-resolution, high-speed scan.  
         [0025]    To return optical carriage  101  to the home position and reload biasable drive  103 , motorized drive mechanism  102  is preferably re-engaged and carriage  101  is preferably pulled back to the home position. In a standard, or high-resolution scanning mode, biasable drive  103  is not the main carriage-driving mechanism. Although biasable drive  103  may still exert force on carriage  101 , motorized drive mechanism  102  is preferably used to perform higher-resolution, lower-velocity, high-accuracy scans in a standard scanning mode, or the like. Alternatively, biasable drive  103  may be disengaged from carriage  101  for normal-speed or low-speed scanning functionality performed employing motorized drive  102 .  
         [0026]    Advantageously, the load of a spiral spool-type spring, such as shown in FIG. 1, has a force curve that is relatively easy to manipulate, particularly the beginning loading and the unloaded state of the spring at the end position for carriage  101 . Advantageously, most springs provide slightly stronger force upon initial release. In accordance with the present invention this provides additional force to initially overcome inertia of carriage  101  and any resistance presented by motorized drive mechanism  102 , and provide a relatively flat level of pulling force once the carriage starts moving.  
         [0027]    With a motorized drive mechanism that uses a stepper motor, being an open loop system, the position of the carriage  101  is determined based on a number of motor steps during a normal or low-speed scan. However, when biasable drive  103  is employed for a fast-preview scan or the like, the position of carriage  101  is preferably tracked, particularly if the force of biasable drive  103  varies and thus the speed of carriage  101  varies along the translation path. Linear encoder  114 , disposed along carriage rod  104  or some other location along the length the translation path of carriage  101  may be employed. Linear encoder  114  may take the form of a clear strip of plastic disposed next to carriage rod  104 . Encoder  114  preferably has grating lines printed onto it at a very high-resolution, and a photo diode or the like disposed on scanner carriage  101  picks up high/low, high/low or dark/light, dark/light regions along the strip and returns this information to control circuitry, software and/or firmware for scanner  100  to derive the position of carriage  101 . Alternatively, an optical wheel encoder on spiral spring spool  110 , on pulley  105 , in motor  107  or in transmission  108  may be employed.  
         [0028]    Regardless, a mechanism preferably enables control electronics, software and/or firmware for scanner  100  to track the velocity carriage  101  is traveling and/or the position of carriage  101  at any point in time. This tracking is desirable for control of exposure and for mapping the location of the scan lines made so that an image can be properly rastered.  
         [0029]    In some embodiments of the present invention, the encoder of a servo-motor based-motorized drive mechanism may be used to establish velocity and/or location of carriage  101 , thereby requiring no extra components beyond additional electronics and/or logic to track the higher velocity of carriage  101  afforded by the present invention in a high-speed, low-resolution scan mode.  
         [0030]    Other manners of tracking the velocity and/or location of scanner carriage  101  may be employed in accordance with the present invention. For example, as shown in FIG. 4, scanner  400  that employs a stepper motor  401  may use stepper motor  401  as an encoder. When the coils of stepper motor  401  are shorted to place motorized drive mechanism  102  in neutral, every time the rotor of stepper motor  401  is turned one step, due to the carriage being moved by the biasable drive, a small current flows from the coil(s). This current may be carried to control circuitry  402  for scanner  400  by ribbon cable  403 , or other connection, linking stepper motor  401  and control circuitry  402 . An electronic circuit, that may be integrated into control circuitry  402  for stepper motor  401 , may be used to measure the current pulse, thus using stepper motor  401  as a location encoder.  
         [0031]    Turning to FIG. 2, an alternative latch mechanism  201  securing carriage  101  to motorized drive mechanism  102  may release to enable biasable drive  103  to pull carriage  101  in a fast-preview mode or the like. In some embodiments, the motorized drive mechanism  102  may remain connected to carriage  101  during high-speed scans using biasable drive  103 , although it is preferable that motorized drive mechanism  102  present relatively low-resistance when motorized drive mechanism  102  is in a neutral setting. Thus, a relatively permanent latch between carriage  101  and motorized drive mechanism  103  may be employed when motorized drive mechanism  102  presents relatively low-resistance or friction for travel of carriage  101  when in a neutral setting. In a preferred embodiment, if motorized drive mechanism  102  creates enough resistive force to significantly impede traversal of the optical carriage in a biased drive mode, latch mechanism  201  may be disengaged from motorized drive mechanism  102 , specifically from belt  106 . Thus optical carriage  101  may run along carriage rod  104 , alone, being pulled by biasable drive  103 . After a preview scan, where carriage  101  is at an “end” position, motorized drive mechanism  102  preferably moves latch  201  into position to engage carriage  101  and latch back onto the carriage, preferably with a positive connection, so motorized drive mechanism  102  may then pull carriage  101  back to home position for a subsequent scan, whether a high-resolution, slow-speed scan or a low-resolution, high-speed scan. Advantageously, this also loads biasable drive  103  for another high-speed scan. Latch  201  may employ a servo release and/or connection to provide the aforementioned positive connection and disconnection. Similarly, a latch or release mechanism may also be employed with the aforementioned screw-drive or wheel-geared rack drives to disengage the drive from the optical carriage or other types of drives where significant frictional forces are present when the motorized drive mechanism is in neutral.  
         [0032]    [0032]FIG. 3 is a flowchart of embodiment  300  of a present method for providing bias drive carriage movement in an optical image scanner for rapid scanning, such as for preview scanning. At step  301  a scanner carriage is biased, preferably by loading a spring drive or the like extending from the optical head carriage to a point beyond an end point of a scanning path. Alternatively, the spring drive may drive a gear drive associated with the carriage, as described above, or otherwise bias the carriage for movement. In step  301  loading is preferably carried out by biasing a scanner carriage drive, such as by loading a spring carriage drive using a motorized carriage drive, or the like. This may be accomplished by engaging the drive mechanism and moving the carriage from an end position of the scan-path to a home position of the scan-path, thereby loading the spring drive. The drive mechanism may be engaged by moving it out of a neutral setting to a drive setting or, in another embodiment, by engaging a latch mechanism disposed between the carriage and the motorized drive mechanism. At step  302  the carriage is released by releasing a latch between the carriage and the motorized carriage drive, or the carriage is otherwise released such as by placing the motorized drive mechanism in neutral, enabling the carriage to move along the scan-path in step  303  to scan an image of media disposed on a platen glass of the scanner. As the carriage reaches the end of the scan-path, the motorized drive mechanism re-engages the carriage at step  304 . In one embodiment, the motorized drive mechanism may move to the end position at step  304  to engage the latch between the carriage and motorized drive mechanism. In another embodiment, the motorized drive mechanism may be re-engaged by placing it out of a neutral setting into a drive setting. Regardless, the motorized drive mechanism preferably moves the carriage to the home position at box  305 . Preferably this re-biases the carriage by reloading the biasable or spring drive in accordance with step  301 . Alternatively, the motorized drive mechanism may load a biased drive mechanism during a low-speed, high-resolution scan, from the home position to the end position, thereby biasing the carriage for high-speed scanning on a return from the end potion to the home position.