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  Method and apparatus for direct image pick-up of granular speck pattern generated by reflecting light of laser beamUSPTO Application #: 20060293865Title: Method and apparatus for direct image pick-up of granular speck pattern generated by reflecting light of laser beam Abstract: A granular speck pattern is generated by a reflecting laser beam as an object to be measured is irradiated with a laser beam. This granular speck pattern is directly picked up as an image index by a line sensor. An A/D converter converts an analog signal supplied from the line sensor to a digital signal, and a processing unit calculates the amount of movement of the object on the basis of movement of a pixel interval of the granular speck pattern. A display device displays the amount of movement calculated by said processing unit. (end of abstract) Agent: Price Heneveld Cooper Dewitt & Litton, LLP - Grand Rapids, MI, US Inventors: Kenichiro Kobayashi, Hiroyuki Konno USPTO Applicaton #: 20060293865 - Class: 702127000 (USPTO) Related Patent Categories: Data Processing: Measuring, Calibrating, Or Testing, Measurement System The Patent Description & Claims data below is from USPTO Patent Application 20060293865. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a continuation of U.S. patent application Ser. No. 10/737,336 filed on Dec. 16, 2003 entitled METHOD AND APPARATUS FOR DIRECT IMAGE PICK-UP OF GRANULAR SPECK PATTERN GENERATED BY REFLECTING LIGHT OF LASER BEAM, which is a continuation of U.S. patent application Ser. No. 09/838,905 filed on Apr. 20, 2001 entitled METHOD AND APPARATUS TO MEASURE AMOUNT OF MOVEMENT USING GRANULAR SPECK PATTERN GENERATED BY REFLECTING LASER BEAM, now U.S. Pat. No. 6,847,910. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a method and an apparatus adapted to measure an amount by which an object to be measured has moved in plane and back-and-forth in non-contacting fashion at a high speed without a demand for particular index or mark substantially freely from conditions of said object such as temperature, color or material thereof. [0004] Irradiation of the object to be measured with a monochromatic laser beam having high directivity, high luminance and linearity generates a granular speck pattern upon its reflection. This granular speck pattern depends on a degree of roughness on the surface of the object irradiated with the laser beam. The granular speck pattern translates in proportion to expansion or extension as the object is heated or an external stress is exerted on the object. On the other hand, the granular speck pattern is reduced or magnified as the object moves back-and-forth. [0005] The present invention intends to pick up this granular speck pattern in a direct and optical manner as an index, to calculate a movement of the object with respect to said index and to display the calculated result as the amount of movement. [0006] 2. Description of the Related Art [0007] A non-contact method for such measurement is well known in which the object is irradiated with a laser beam vertically to the object and there are provided a pair of unidimensional sensors at an angle of 45.degree. about the normal line, respectively. [0008] Irradiation of the object with a laser beam results in generation of the granular speck pattern due to interference of scattering light. Output of the respective unidimensional sensors is used as a reference signal to observe movement of the granular speck pattern as the surface of the object is moved or distorted. Such movement is photoelectrically detected at two points and a differential movement between these two points is obtained to automatically eliminate a rigid body movement component. This so-called cross correlating method is used to determine a distortion. [0009] According to another method of prior art, a darkroom is used as the measurement environment and a granular speck pattern generated by the reflecting laser beam is projected on a screen in the form of frosted glass. This projected pattern is picked up by a digital camera or the like, then a granular speck is selectively extracted by a computer and the amount of movement of the object in a plane is determined on the basis of an amount by which a granular point thereof has moved. [0010] A high accuracy is required for the optical parts as well as the optical system mechanism in the case of the method as has been described above for calculating an amount of distortion or movement from interference fringes. [0011] In addition, when a correlative peak value and a reference signal value determined by the cross correlating method is lower than a threshold value, processing is inevitably complicated and becomes troublesome. The measurement environment in the form of a darkroom is essential for projection on the screen formed by frosted glass. SUMMARY OF THE INVENTION [0012] The present invention aims to eliminate the restriction by many requirements for the prior art concerning the construction and the measurement environment. To achieve this, the present invention aims to simplify the respective means in the method as well as the apparatus for measurement and to enlarge a range restricted depending on the type of the object to be measured. The method and the apparatus according to the present invention should be able to measure even the object moving at a high speed by substantially simplifying the image processing in comparison to the prior art. [0013] The object set forth above is achieved by the method and the apparatus according to the present invention in which a granular speck pattern is generated by a reflecting laser beam as an object to be measured is irradiated with a laser beam. This granular speck pattern is easily and directly picked up as an image in a measurement environment like an ordinary office and the problem is solved on the basis of a quantitative relationship between the object and the granular speck pattern generated by the reflecting laser beam. [0014] The object set forth above is achieved, according to one aspect of the invention, by a method for measuring an amount at which an object to be measured has moved without demand for a particular index or mark in non-contacting fashion, said method comprising steps of irradiating an object to be measured with a laser beam, optically and directly picking up the granular speck pattern generated by the reflecting laser beam as an index, calculating the amount of movement on the basis of movement of the granular speck pattern with respect to said index and displaying a result of the calculation as a numerical value of the measured amount of movement. [0015] The object set forth above is achieved, according to another aspect of the invention, by an apparatus for measuring an amount at which an object to be measured has moved in a plane in non-contacting fashion, said apparatus comprising a laser projector adapted to generate a granular speck pattern corresponding to a rough surface of an object to be measured, a line sensor adapted to directly pick up said granular speck pattern as an index, an A/D converter adapted to convert an analog signal supplied from said line sensor to a digital signal, a processing unit adapted to calculate an amount of movement of said object on the basis of movement of the granular speck in said pattern with respect to a pixel interval of said granular speck pattern picked up by said line sensor and represented by said A/D converted signal and a display device adapted to display the amount of movement calculated by said processing unit. [0016] The present invention generally comprises four elements. A first element is to irradiate an object to be measured with a laser beam. A second element is to pick up a granular speck pattern generated by reflection of the laser beam with which the object is irradiated. A third element is to quantify movement of the object and the picked up granular speck pattern and to use this quantified movement for a specific machine or apparatus. A fourth element is to compare the picked up granular speck pattern with pixels of the line sensor to calculate an amount of movement and to display this as a substantial amount of movement. [0017] These elements will be now described in combination with one another. The object is irradiated with the laser beam to generate the granular speck pattern corresponding to the rough surface of said object. One array of random white and black images is continuously picked up by the line sensor as the object moves and a granular speck in said white and dark images is selectively recognized. This speck is followed in a time series fashion by the computer and the movement is processed in real time on the basis of the pixel interval in the line sensor. A numerical value of movement obtained in this manner is displayed. For an extremely large amount of movement, a granular speck lying within a picking up range of the line sensor is repeatedly selected as a new index immediately before the previously selected granular speck as the index deviates from the pick up range of the line sensor. In this way, movement of the object can be continuously measured. [0018] The measuring instrument achieving the present invention comprises a semiconductor laser projector, a line sensor provided with a shielding tube adapted to shield extraneous light and allowing only the granular speck pattern to pass therethrough, a video signal branching device adapted to branch the video signal picked up by the line sensor in two, a monitor device adapted to display the video signal picked up by the line sensor, an A/D (Analog/Digital) converter, a processing unit comprising a computer, and a display device adapted to display the amount of movement. [0019] Irradiating the surface of the object to be measured with a monochromatic laser beam of high linearity, luminance, directivity and coherence generates the granular speck pattern due to coherence of the laser beam exactly depending on the roughness of the surface irradiated with the laser beam. [0020] The granular speck pattern translates as the object contracts and the granular speck pattern is proportionally reduced or magnified as the object moves back-and-forth with respect to the measuring instrument. The granular speck pattern generated by the reflecting laser beam is exactly depending on the roughness of the surface irradiated with the laser beam. In other words, the same granular speck pattern is reproduced when the same position of the object is irradiated with the laser beam being the same in emission waveform as well as in beam diameter using same picking up element. [0021] This granular speck pattern is continuously picked up by the line sensor as the index, the analog signal supplied from the line sensor is converted by the A/D converter to the corresponding digital signal which is, in turn, input to the processing unit, in which an amount of movement of the granular speck pattern in plane is calculated or an amount of back-and-forth movement on the basis of a ratio of reduction or magnification, and a result of calculation is displayed as a substantial amount by which the object has moved. Continue reading... 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