Patent Application
20060093382
The invention relates generally to systems and methods for rendering printable material, and more specifically to the use of optical motion sensors to accurately track printable material.
Various techniques are in use that allow for the rendering of printed material by automated printing, scanning, copying, transmission, and generation devices. Instruments such as, for example, typewriters, thermal printers, inkjet printers, printing presses, laser printers, plotters, and typesetting machines, can all generate printed substrates consisting of, for example, text and/or images. Scanners, copiers, and facsimile machines can be used to generate and/or transmit electronic versions of printed substrates. The printed substrate used may be monochromatic or multi-color depending on the requirements of an end-user. For maximum utility, printed text and/or images should be located accurately on a printed substrate to ensure desirable characteristics such as readability, attractiveness, and overall clarity.
Accurate positioning of a substrate is generally a desired characteristic of instruments such as printers, scanners, copiers, and facsimile machines. Accurate positioning of the substrate may employ mechanical positioning systems using, for example, cogged wheels in contact with the substrate. However, many mechanical solutions are not accurate enough for images requiring fine detail and correspondingly fine positioning of the substrate. Also, the precision of these mechanical systems may not allow for reproducibility if multiple copies of printed material are desired.
Instruments that use drive motors, wheels, or rollers in contact with a substrate may infer the position of the substrate from movement of the drive motors, wheels, or rollers. For example, one prior art solution uses a shaft encoder coupled to a drive motor shaft. Rotation of the drive shaft is used to approximate the movement of a substrate with which the shaft is in contact. However, any variances in the diameter of the drive shaft result in inaccurate approximations of the substrate movement. If the drive shaft is of smaller than nominal diameter, it will advance the substrate less than desired for a given amount of shaft angular rotation. Additionally, if the drive shaft rotates about a center with an eccentric error, the approximated substrate movement may have a periodic error that may be large or small depending on the magnitude of the eccentricity.
Inkjet printers that use shaft encoders are particularly susceptible to image distortions and errors caused by substrate movement. Ideally, the substrate is advanced exactly the distance needed to match the inkjet nozzle pattern produced during a previous pass of the printing head. If the distance advanced is correct, seamless printed material is produced. However, if the method used to approximate the movement of the substrate is not accurate, inaccuracies in the printed material will result. If the substrate is not advanced enough, the inkjet printing head will produce a dark band across the substrate where there is overlap with the previous printing pass. If the paper is advanced too far, there will be a gap between printing passes where the printing head did not deposit ink. Also, cumulative printing errors can result in distortion of images. For example, a printed circle may appear elliptical due to accumulated error in the approximation of the printing substrate advancement.
Solutions are needed that accurately and precisely track the movement of a substrate. Accurate tracking of substrate movement may ensure that printed material is rendered with the desired quality characteristics. Accurate substrate tracking may also ensure that, for example, printed text and/or images are located in the desired location on a printing substrate. Also, precision tracking may provide for reproducible duplication of printed material in, for example, a copier or scanner.
The present disclosure is directed to systems and methods which accurately allow a printed substrate to be rendered. One embodiment comprises a method for accurately tracking the position of a substrate that provides a substrate and advances the substrate towards a printing mechanism a predetermined distance. The actual distance advanced by the substrate is then measured by a motion sensor, and the position of the substrate may then be adjusted if the actual distance advanced does not equal the predetermined distance. The difference between the actual distance advanced and the predetermined distance can be used to calibrate a system. Both optic and magnetic motion sensors are disclosed.
In one embodiment, a system for accurate rendering is achieved by using a substrate, a roller in close contact with the substrate, and an optical motion sensor that tracks the motion of the roller. The roller is patterned to allow the optical motion sensor to more easily track the motion of the roller. The optical motion sensor of the embodiment consists of a light source and a sensor. In other embodiments, more than one roller may be used in combination with more than one optical motion sensor.
In other embodiments, a substrate is advanced by an advancement mechanism towards a printing mechanism. A ball roller is placed in contact with the substrate so that movement of the substrate results in movement of the roller. An optical motion sensor is used to track the motion of the roller. In some embodiments, more than one motion sensor may be used to track the motion of the ball roller in more than one plane of movement.
In still another embodiment, a substrate is advanced towards a scanning head by an advancement mechanism. A two-axis roller system is included with one roller being used to track the movement of the substrate in one plane, while a second roller is being used to track the movement of the substrate in another plane. In some embodiments, a third roller may be used in a three-plane system.
Other embodiments of the invention may use magnetic detectors such as magnetometers to detect magnetic materials and magnets embedded in or attached to the surface of a roller in contact with an advancing substrate. Electromagnets may also be incorporated into the roller.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
Substrate 102 may comprise printed material such as, for example, text, pictures, images, paintings, handwriting, photographs, etc. In one embodiment, substrate 102 is paper and/or paper products such as, for example, cardboard, construction paper, photo paper. In other embodiments, substrate 102 is plastic, polymer, or cellulose products such as, for example, transparency films, photographic film, x-ray films. In yet other embodiments, substrate 102 is metal such as, for example, aluminum, steel, or metal alloys. Other substrates utilizing compounds comprised substantially of carbon, minerals, and other flexible and non-flexible materials capable of hosting printed text and/or images are used with some embodiments.
Intermediate roller 103 is in constant contact with substrate 102 such that the surface of intermediate roller 103 moves at the same speed as does substrate 102. The surface of intermediate roller 103 may be selected to provide optimal friction with substrate 102 and thereby will move at the same speed as substrate 102. Intermediate roller 103 is a grit wheel in certain embodiments with excellent traction and repeatability, and may be driven if desired. In one embodiment shown intermediate roller 103 is not driven, but is allowed to move freely according to the movement of substrate 102. Intermediate roller 103 is constructed having a pattern recognizable by optical means. Such a pattern may be drawn on the roller or created using different colored materials. A pattern may also be generated by etching the surface of intermediate roller 103 or by adding ridges or raised portions.
Motion sensor 104 is comprised of light source 105 and sensor 106. Motion sensor 104 may be similar to that described in U.S. Pat. No. 5,149,980 granted to Ertel et al. Motion sensor 104 infers motion of substrate 102 by monitoring motion of intermediate roller 103. The surface of intermediate roller 103 may be selected in some embodiments to provide an optimum signal to sensor 106. Such a surface may include a patterned or quasi-patterned surface. Light source 105 may be monochromatic, such as a laser light source, or may be chromatic light from a light bulb or other broad-spectrum source. Light source 105 may, if desired, be a light-emitting diode (LED). Light source frequency can vary and is selected to produce optimum signal strength and tracking correlation to sensor 106. Sensor 106, in one embodiment, can be a photovoltaic sensor that produces electric current in response to photon stimulation by a light source. Sensor 106 is positioned to receive reflected light from light source 105 via the surface of intermediate roller 103. In some embodiments, variations in the signal strength generated by sensor 106 may be correlated to motion of intermediate roller 103.
Process 402 provides a roller in contact with the provided substrate. The surface of the roller is constructed to provide optimum contact with the substrate. The roller provided may be a roller as discussed herein, and a plurality of rollers are provided in some embodiments.
Process 403 advances the substrate towards the printing mechanism. In other embodiments, the substrate is advanced towards a scanning or other imaging mechanism. Substrate advancement may be effected by the process of step 402 or by additional rollers.
Process 404 measures the actual distance moved by the substrate by measuring the rotation of the roller using an optical motion sensor as discussed above. In some embodiments, the measured movement of the roller is compared to a predetermined rotation and the substrate position is adjusted until the measured roller rotation equals the predetermined rotation. In other embodiments, the printing mechanism is adjusted to compensate for any difference between the measured substrate position and the predetermined substrate position.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
