Engineering Solutions by Sainath Metrology Solutions llp

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• What is CMM Inspection ? 

A co-ordinate measuring machine ( CMM ) is a device that measures the geometry of physical objects by sensing discrete points of the object with a probe . Various types of probes are used in CMM's . We use ruby tip mechanical manually operated ( TESA Micro-hite 3D ), a Swiss made machine for our CMM inspections . 

The typical 3D bridge CMM allows probe movement along three axis X , Y & Z which are orthogonal to each other in three dimensional cartesian co - ordinate system . Each axis has a sensor that monitors the position of the probe on that axis typically with micrometer precision when the probe contacts ( or otherwise detects ) a particular location on the object , the machine samples the three position sensors , thus measuring the location of one point on the objects surface as well as the 3 - dimensional vector of the measurement taken . This process is repeated as necessary , moving the probe each time , to produce a "point cloud" which describes the surface areas of interest . 

A common use of CMM is in manufacturing and assembly process to test a part or assembly against the design intent . In such applications point clouds are generated which are analysed 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 CMM's can be programmed to repeatedly measure identical parts , thus an automated CMM is specialised from industrial robot . 

The accuracy of the co-ordinate measurement machines are typically given as an uncertainly factor as a function over distance . Far a CMM using a touch probe , this relates to the repeatability of the probe & the accuracy of the linear scales . 

Typical probe repeatability can result in measurements of within 0.001mm over the entire measurement volume . For 3 , 3 + 2 & 5 axis machines , probes are routinely calibrated using traceable standards & the machine movement is verified using gauges to ensure accuracy .

 What is Profile Projector / Optical comparator?

Profile projector often simply called as optical comparator is a device that applies the principles of optics to the inspection of manufactured parts . In a comparator the magnified silhouette of a part is projected upon the screen & the dimensions & geometry of the part are measured against prescribed limits . The idea of using a profile projector which was created by James Hartness & Russell W Porter came from mixing optics & measurement in a device . The use of the term comparator for metrological equipment had existed in other forms prior to Hartness & Russell E Porter came from mixing optics & measurement in a device . The use of the term comparator for metrological equipment , had existed in other forms prior to Hartness work , but they had remained in realms of pure science and highly specialised applied science . 

Profile projector also known as shadowgraph is an useful item in a small parts machine shop or production line for quality control inspection team . The profile projector magnifies the profile of the specimen and displays this on the built in projection screen . On this screen there is typically a grid that can be rotated 360º so the X - Y axis of the screen can be aligned with a straight  edge of the machined part to examine or measure . 

The projection screen displays the profile of the specimen and is magnified for better ease of calculating linear measurements . An edge of the specimen to examine may be lined up with the grid on the screen . From there , simple measurements may be taken for distances to other points . This is being done on a magnified profile of the specimen . It can be simpler as well as reduce errors by measuring on the magnified projection screen of a profile projector . 

The typical method for lighting is by diascopic illumination , which is lighting from behind . This type of lighting is also called transmitted illumination when the specimen is translucent & the light can pass through it . If the specimen is opaque , then the light will not go through it , bit will form a profile of the specimen measuring of the sample can be done on the projection screen . A profile projector may also have episcopic illumination which is light shining from above . This is useful in displaying bores on internal areas that may need to be measured . 

Advantages :

• Profile projector can reveal imperfection such as burrs , scratches , indentations or undesirable chamfers which both micrometers or callipers cant reveal .
• They're able to measure in 2-D space , unlike micrometers and callipers , which measure one dimension at a time , where comparators measure length & width simultaneously . 
• Optical comparators save time . Ease of use factors and ergonomic designs reduce the inspection time , retraining costs & operator fatigue , all while increasing throughput . 
•  Custom hard gauges are subject to wear and need frequent rectification , which takes them out of service and adds an additional cost . 
• Dimensioning techniques designed to give more leeway to parts in relation to their true functional purpose , such as profile tolerance and true position tolerating with bonuses , reduce the reject rate of good parts that might have passed had their tolerance been assigned differently . 

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A 3D model in engineering refers to a digital representation of an object or system created using computer-aided design (CAD) software or other similar tools. These models are three-dimensional, meaning they have width, height, and depth, allowing engineers to visualize and analyze objects or systems in a virtual space.

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