Coordinate measuring machine pdf


 

Position. • Actual size is obtained by probing the surface at discrete measuring points. Every pt is expressed in terms of its x,y,z coordinates. Functions of CMM. CMM. 3D coordinate measuring machines from Mitutoyo: The new dimension of quality assurance. Today's manufacturing demands more accuracy, speed. CMM. 3D coordinate measuring machines from Mitutoyo: the new dimension of quality assurance. Today's manufacturing demands more accuracy, speed.

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Coordinate Measuring Machine Pdf

PDF | 25+ minutes read | Coordinate measuring machines in various branches of industry within last years became very common. Measuring machines can be. PDF | Traditional touch trigger probes are widely used on most commercial coordinate measuring machines (CMMs). However, the CMMs with these probes . PDF | In this research work, a comparative study between the precision obtained with a touch probe (TP) and that obtained with a scanning.

Machine body[ edit ] The first CMM was developed by the Ferranti Company of Scotland in the s [1] as the result of a direct need to measure precision components in their military products, although this machine only had 2 axes. Leitz Germany subsequently produced a fixed machine structure with moving table. This moves freely along the granite table with one leg often referred to as the inside leg following a guide rail attached to one side of the granite table. The opposite leg often outside leg simply rests on the granite table following the vertical surface contour. Air bearings are the chosen method for ensuring friction free travel. 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 movement of the bridge or gantry along the granite table forms one axis of the XY plane. The bridge of the gantry contains a carriage which traverses between the inside and outside legs and forms the other X or Y horizontal axis. 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. Optional rotary tables can be used to enhance the approachability of the measuring probe to complicated workpieces. The rotary table as a fourth drive axis does not enhance the measuring dimensions, which remain 3D, but it does provide a degree of flexibility. Some touch probes are themselves powered rotary devices with the probe tip able to swivel vertically through 90 degrees and through a full degree rotation.

This moves freely along the granite table with one leg following a guide rail attached to one side of the granite table.

ASME | Journal of Mechanical Design | ASME DC

The opposite leg simply rests on the granite table following the vertical surface contour. Air bearings are the chosen method for ensuring friction free travel. 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 movement of the bridge along the granite table forms one axis of the XY plane. The bridge of the gantry contains a carriage which traverses between the inside and outside legs and forms the other X or Y horizontal axis.

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.

Some touch probes are themselves powered rotary devices with the probe tip able to swivel vertically through 90 degrees and through a full degree rotation. A very common probe was made by soldering a hard ball to the end of a shaft.

This was ideal for measuring a whole range of flat, cylindrical or spherical surfaces. These probes were physically held against the workpiece with the position in space being read from a 3-Axis digital readout DRO or in more advanced systems, being logged into a computer by means of a footswitch or similar device. New probing systems[ edit ] 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.

The next generation of scanning, known as noncontact scanning, which includes high speed laser single point triangulation, [3] laser line scanning, [4] and white light scanning, [5] is advancing very quickly. This method uses either laser beams or white light that are projected against the surface of the part.

Many thousands of points can then be taken and used not only to check size and position, but to create a 3D image of the part as well.

This "point-cloud data" can then be transferred to CAD software to create a working 3D model of the part. These optical scanners are often used on soft or delicate parts or to facilitate reverse engineering. Micrometrology probes Probing systems for microscale metrology applications are another emerging area. However, current optical technologies cannot be scaled small enough to measure deep, narrow feature, and optical resolution is limited by the wavelength of light.

X-ray imaging provides a picture of the feature but no traceable metrology information. Fringe projection systems, theodolite triangulation systems or laser distant and triangulation systems are not called measuring machines, but the measuring result is the same: a space point.

Laser probes are used to detect the distance between the surface and the reference point on the end of the kinematic chain i.

Coordinate Measuring Machines

This can use an interferometrical function, focus variation , light deflection or a beam shadowing principle. Portable CMMs with articulated arms have six or seven axes that are equipped with rotary encoders, instead of linear axes. Portable arms are lightweight typically less than 20 pounds and can be carried and used nearly anywhere.

However, optical CMMs are increasingly being used in the industry. Designed with compact linear or matrix array cameras like the Microsoft Kinect , optical CMMs are smaller than portable CMMs with arms, feature no wires, and enable users to easily take 3D measurements of all types of objects located almost anywhere. Certain nonrepetitive applications such as reverse engineering , rapid prototyping , and large-scale inspection of parts of all sizes are ideally suited for portable CMMs.

The benefits of portable CMMs are multifold. Air bearings are the chosen method for ensuring friction free travel. 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 movement of the bridge or gantry along the granite table forms one axis of the XY plane. The bridge of the gantry contains a carriage which traverses between the inside and outside legs and forms the other X or Y horizontal axis.

Coordinate Measuring Machine (CMM)

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. Optional rotary tables can be used to enhance the approachability of the measuring probe to complicated workpieces.

The rotary table as a fourth drive axis does not enhance the measuring dimensions, which remain 3D, but it does provide a degree of flexibility.

Some touch probes are themselves powered rotary devices with the probe tip able to swivel vertically through 90 degrees and through a full degree rotation. As well as the traditional three axis machines as pictured above , CMMs are now also available in a variety of other forms. These include CMM arms that use angular measurements taken at the joints of the arm to calculate the position of the stylus tip.

Because CMM arms imitate the flexibility of a human arm they are also often able to reach the insides of complex parts that could not be probed using a standard three axis machine. In the early days of coordinate measurement CMM , mechanical probes were fitted into a special holder on the end of the quill.

A very common probe was made by soldering a hard ball to the end of a shaft. This was ideal for measuring a whole range of flat face, cylindrical or spherical surfaces. Other probes were ground to specific shapes, for example a quadrant, to enable measurement of special features.

These probes were physically held against the workpiece with the position in space being read from a 3-Axis digital readout DRO or, in more advanced systems, being logged into a computer by means of a footswitch or similar device.

Measurements taken by this contact method were often unreliable as machines were moved by hand and each machine operator applied different amounts of pressure on the probe or adopted differing techniques for the measurement.

Coordinate-measuring machine

A further development was the addition of motors for driving each axis. Operators no longer had to physically touch the machine but could drive each axis using a handbox with joysticks in much the same way as with modern remote controlled cars.

Measurement accuracy and precision improved dramatically with the invention of the electronic touch trigger probe. The pioneer of this new probe device was David McMurtry who subsequently formed what is now Renishaw plc.

As the probe touched the surface of the component the stylus deflected and simultaneously sent the X. Y,Z coordinate information to the computer. Measurement errors caused by individual operators became fewer and the stage was set for the introduction of CNC operations and the coming of age of CMMs.

Optical probes are lens-CCD-systems, which are moved like the mechanical ones, and are aimed at the point of interest, instead of touching the material. The captured image of the surface will be enclosed in the borders of a measuring window, until the residue is adequate to contrast between black and white zones. The dividing curve can be calculated to a point, which is the wanted measuring point in space.

The horizontal information on the CCD is 2D XY and the vertical position is the position of the complete probing system on the stand Z-drive or other device component. 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.

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