The present invention relates to an optical encoding device for the sensing of position and/or motion.
Optical encoders are used in a wide variety of contexts to determine position and/or movement of an object with respect to some reference. Optical encoding is often used in mechanical systems as an inexpensive and reliable way to measure and track motion among moving components. For instance, printers, scanners, photocopiers, fax machines, plotters, and other imaging systems often use optical encoders to track the movement of an image media, such as paper, as an image is printed on the media or an image is scanned from the media
Generally, an optical encoder includes some form of light emitter/detector pair working in tandem with a “codewheel” or a “codestrip”. Codewheels are generally circular and can be used for detecting rotational motion, such as the motion of a paper feeder drum in a printer or a copy machine. In contrast, codestrips generally take a linear form and can be used for detecting linear motion, such as the position and velocity of a print head of the printer. Such codewheels and codestrips generally incorporate a regular pattern of slots and bars depending on the form of optical encoder.
While optical encoders have proved to be a reliable technology, there still exists substantial industry pressure to simplify manufacturing operations and decrease costs while improve spatial resolution and other performance issues. Accordingly, new technology related to optical encoders is desirable.
In a first sense, an optical encoding apparatus for the detection of position and/or motion of a mechanical device includes a codescale having an alternating pattern of windows and bars, the windows and bars having a substantially equal width, an encoder housing having one or more portions, a light-emitting source embedded within the encoder housing, a light-detecting sensor embedded within the encoder housing, the light-detecting sensor having at least six light-detecting elements, wherein the encoder housing includes one or more optical elements configured to enable light generated by the light-emitting source to project the codescale's pattern of bars and windows onto the light-detecting sensor, and wherein the width of each light-detecting element is no more than ⅓ the width of the windows and bars projected onto the light-sensing detector.
In a second sense, an optical encoding apparatus for the detection of position and/or motion includes a codescale having an alternating pattern of windows and bars, the windows and bars having a substantially equal width, an encoder housing having one or more portions, a light-emitting source embedded within the encoder housing, a light-sensing means embedded within the encoder housing for use in the detection of codescale travel; and one or more optical elements configured to enable light generated by the light-emitting source to project the codescale's pattern of bars and windows onto the light-sensing means.
In a third sense, a method for detecting both a distance and direction traveled for a codescale in an optical encoding apparatus includes projecting a first pattern of windows and bars from the codescale onto a light-sensing detector having at least six light-detection elements, the projected windows and bars each having a first width and the light-detection elements each having a second width, the second width being less than ⅓ the first width, sampling the state of each light-detection element a first time, moving the codescale at least one second width, projecting a second pattern of windows and bars from the codescale onto the light-sensing detector, sampling the state of each light-detection element a second time and determining at least the direction of codescale travel using the sensed states of the first and second samplings.
The example embodiments are best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements.
In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparatus and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparatus are clearly within the scope of the present teachings.
In the following embodiments, the novel systems and apparatus of the present disclosure can improve the spatial resolution of optical encoders over previously known devices. By incorporating detectors that use a high number of detection elements for a given distance as compared to the distance of a window and bar of a respective codescale, spatial resolution can be increased with a minimum of expense.
Optical encoders are generally classified into two categories: transmission-based optical encoders and reflection-based optical encoders. The following disclosure is generally directed to reflection-based optical encoders. However, it should be appreciated that many of the various system, devices and processes described herein can apply to transmission-based encoders as well.
In operation, light emitted by the optical emitter 122 can be focused by the first lens 124, then transmitted to the codescale 193 along the light's path 150 at location 195. Should the codescale 193 be positioned such that a reflective slot/bar is present at location 195, the transmitted light can be reflected to the second lens 134, then focused by the second lens 134 onto the optical detector 132 where it can be detected. Should the codescale 193 be positioned such that a reflective slot/bar is not present at location 195, the transmitted light will be effectively blocked, and the optical detector 132 can detect the absence of light. Should the codescale 193 be configured and position such that a combination of reflective and non-reflective bars are simultaneously present at location 195, the codescale 193 can reflect light commensurate with the pattern of reflective and non-reflective bars such that the pattern is effectively projected onto the optical detector 132.
Generally, it should be appreciated that conventional optical encoders use either single-element detectors or detectors having a low number of optical detection elements. By way of example,
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However, as will be demonstrated below, the inventor of the disclosed methods and systems has devised a different approach to optical encoders where the cost tradeoffs differ substantially from conventional approaches.
While the exemplary detector 534 has eight detection elements of width W3 (=W1/4), it should be appreciated the concepts of
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While example embodiments are disclosed herein, one of ordinary skill in the art appreciates that many variations that are in accordance with the present teachings are possible and remain within the scope of the appended claims. The embodiments therefore are not to be restricted except within the scope of the appended claims.