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Computer Aided Inspection | CIM Notes

Computer Aided Inspection | CIM Notes
Inspection or testing is an act of checking materials, parts, components or products at various stages of manufacturing detecting poor quality manufactured products for taking corrective action. Inspection is performed before, during and after manufacturing to ensure that the quality of the product is consistent with the accepted design standard. The design standards are defined by the product designer, and for mechanical components they relate to factors such as dimension, surface finish and appearance. The objective of any inspection process is either to take actual measurements of the values of the specified product characteristics or to check whether specific characteristics meet design standards. 

When inspection and testing is carried out manually, the sample size is often small compared to size of the population. In high production runs, this size may be very small which may result in slipping of defective parts. In principle, the only way to achieve 100% good quality is to use 100% inspection using which only good quality parts will pass through the inspection procedure. But when this is done manually, the problem of expenses involved and error associated with the procedure is of major concern. Automation of inspection offers an opportunity to overcome these problems. Automated inspection procedures are carried out by sensors that are controlled by computers.

Computer Aided Inspection
Computer Aided Inspection (CAI) is a new technology that enables one to develop a comparison of a physical part to a 3D CAD model. This process is faster, more complete, and more accurate than using a Coordinate Measuring Machine (CMM) or other more traditional methods. An automatic inspection method and apparatus using structured light and machine vision camera is used to inspect an object in conjunction with the geometric model of the object. Camera images of the object are analyzed by computer to produce the location of points on the object's surfaces in three dimensions. Point-cloud data is taken from a laser scanner or other 3-D scanning device. During a setup phase before object inspection, the points are analyzed with respect to the geometric model of the object. The software provides a graphical comparison of the manufactured part compared to the CAD model. Many points are eliminated to reduce data-taking and analysis time to a minimum and prevent extraneous reflections from producing errors. When similar objects are subsequently inspected, points from each surface of interest are spatially averaged to give high accuracy measurements of object dimensions. The inspection device uses several multiplexed sensors, each composed of a camera and a structured light source, to measure all sides of the object in a single pass.

Computers are used in many ways in inspection planning and execution also.

Computer controlled inspection equipment

Coordinate Measuring Machine (CMM) is a 3-dimensional measuring device that uses a contact probe to detect the surface of the object. The probe is generally a highly sensitive pressure sensing device that is triggered by any contact with a surface. The linear distances moved along the 3 axes are recorded, thus providing the x, y and z coordinates of the point. CMMs are classified as either vertical or horizontal, according to the orientation of the probe with respect to the measuring table.

Coordinate Measuring Machine (CMM)
Fig.  Coordinate Measuring Machine (CMM)

Computer aided inspection setup planning

Computer-Aided Inspection Planning (CAIP) is the integration bridge between CAD/CAM and Computer Aided Inspection (CAI). A CAIP system for On-Machine Measurement (OMM) is proposed to inspect the complicated mechanical parts efficiently during machining or after machining. The inspection planning consists of Global Inspection Planning (GIP) and Local Inspection Planning (LIP). In the GIP, the system creates the optimal inspection sequence of features in a given part by analyzing the various feature information. Feature groups are formed for effective planning, and special feature groups are determined for sequencing. The integrated process and inspection plan is generated based on the series of heuristic rules developed. The integrated inspection planning is able to determine optimum manufacturing sequence for inspection and machining processes. Finally, the results are simulated and analyzed to verify the effectiveness of the proposed CAIP.

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