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    coordinate measuring machine

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    1 : Coordinate measuring machine
    2 : introduction A coordinate measuring machine is a 3D device for measuring the physical geometrical characteristics of an object. This machine may be manually controlled by an operator or it may be computer controlled. Measurements are defined by a probe attached to the third moving axis of this machine. Probes may be mechanical, optical, laser, or white light, amongst others.
    3 : description The typical 3 "bridge" CMM is composed of three axes, an X, Y and Z. These axes are orthogonal to each other in a typical three dimensional coordinate system. Each axis has a scale system that indicates the location of that axis. The machine will read the input from the touch probe, as directed by the operator or programmer. The machine then uses the X,Y,Z coordinates of each of these points to determine size and position with micrometre precision typically.
    4 : A coordinate measuring machine (CMM) is also a device used in manufacturing and assembly processes to test a part or assembly against the design intent. By precisely recording the X, Y, and Z coordinates of the target, points are generated which can then be analyzed via regression algorithms for the construction of features. These points are collected by using a probe that is positioned manually by an operator or automatically via Direct Computer Control (DCC). DCC CMMs can be programmed to repeatedly measure identical parts, thus a CMM is a specialized form of industrial robot.
    5 : Types of cmm The various types of CMM are: Cantilever type Bridge type Horizontal bore type Vertical bore type Floating bridge type Spherical co-ordinate measuring
    6 : Technical details PARTS Coordinate-measuring machines include three main components: 1.The main structure which include three axes of motion 2.Probing system 3.Data collection and reduction system - typically includes a machine controller, desktop computer and application software.
    7 : Main sructure Main structure of CMM is made of cast iron, contains a granite table, housings and slider of bridge carrying probhead. It is mainly manufactured by electronica, mitoyota and COSMOS. It contains 3 digit no. which shows the max. dimension measured by it along X,Y,Z axis respectively in multiples of 100mm.
    8 : Probe specifications It is international standard to use probhead manufactured by RENISHAW only. It has function of half and full rotation about X and Z axis respectively. A clamp is provided to lock the probhead.
    9 : In probe, the bolt type structure is fixed called module, which provides recess for prob. Actually, prob consist of two parts, one is extension and other is styli. Ruby diamond is attach to styli for contact measurement. It has spring inside it for shock absorption. Extension extends length of styli to longer ranges.
    10 : Software specifications On average, most CMM’s in many industries runs on DELCAM software. Program which needs to be installed in computer to operate CMM is POWER INSPECTOR.
    11 : Cmm reference sphere The calibration sphere is used to perform calibration of your probe system. Standard sizes are: Ø25.4 mm (1.000") with ?-16 thread mount for surface plate inserts (M10 Optional). Ø12.7 mm (0.500") with M6 thread mount for surface plate inserts. It is fixated into the recess provided in granite table.
    12 : Other requirements Robotic arm of CMM is air controlled , so air separator should connected to it. CMM should placed in constant temp. room. Nearly 17 Celsius. Proper calibration must needed, otherwise observations give wrong results.
    13 : USES They are often used for: 1.Dimensional measurement 2.Pr DMIS standard 3. Measures critical jobs which can’t be measured by simple measuring devices. 4. 3D- comparison between two similar jobs.
    14 : Function of air seperator In these, compressed air is forced through a series of very small holes in a flat bearing surface to provide a smooth but controlled air cushion on which the CMM can move in a frictionless manner. The third axis of movement (Z axis) is provided by the addition of a vertical quill or spindle which moves up and down through the center of the carriage. The touch probe forms the sensing device on the end of the quill. The movement of the X, Y and Z axes fully describes the measuring envelope
    15 : New standard in cmm NEW PROBING SYSTEM There are newer models that have probes that drag along the surface of the part taking points at specified intervals, known as scanning probes. This method of CMM inspection is often more accurate than the conventional touch-probe method and most times faster as well. Ex- point triangulation, laser line scanning, and white light scanning.
    16 : American IQ metrology is now providing silicon nitride other than ruby for contact measurement. Newest CMM have capability to measure up to range of 1 meter. Fully Automatic Helmel Phoenix is the latest no-air functioned CMM.
    17 : Portable cmm Portable CMMs are different from "traditional CMMs" in that they most commonly take the form of an articulated arm. These arms have six or seven rotary axes with rotary encoders, instead of linear axes. Portable arms are lightweight (typically less than 20 pounds) and can be carried and used nearly anywhere. The inherent trade-offs of a portable CMM are manual operation (always requires a human to use it), and overall accuracy is somewhat to much less accurate than a bridge type CMM. Certain non-repetitive applications such as reverse engineering, rapid prototyping, and large-scale inspection of low-volume parts are ideally suited for portable CMMs.

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