ME8501- Metrology and Measurments - Unit-3 Two marks

Subject Name: Metrology and Measurments

Subject Code: ME8501

B.E. Mechanical Engineering - semester 05

Anna University Regulation 2017 Mechanical 5th sem ME8501(Metrology and Measurments) 2 marks for 3rd unit is provided below. ME8501 all units 2 marks, Metrology and Measurments all units notes , syllabus are listed down for students to utilize it for scoring maximum marks with our study materials.

1.Why is laser preferred in engineering metrology?

Answer

It is used in engineering metrology because of its properties such as a high Precision, high accuracy, rapid non-contact gauging of soft,delicate or hot moving points.

2.list out the different methods of dimensional measurements using laser.

Answer

1. Laser telemetric system. 2. Laser Triangulation sensors. 3. Two frequency laser interference.

3.what are the characteristics of laser?

Answer

1. Monochromatic light source 2. Directional possibility 3. Coherent light rays.

4.What is crust and trough?

Answer

The light is a form of energy being propagated by electromagnetic waves which is a sine curve. The high point of the wave is called crust and the low point is called trough.

5.What is wavelength?

Answer

The distance between two crust or two rough is called the wavelength.

6.why is monochromatic light used in interferometry instead of white light?

Answer

Monochromatic light is used to suit radiations other than light. A most unusual feature of the interferometer is its high tolerance to large misalignments of its optical elements.

7.State the principle of interferometry.

Answer

Two light rays from the same monochromatic light source can be combined to give a bright or dark surface by changing the phase difference between them. The brightness or darkness can then be a measure of displacement.

8.What is the advantage of using laser beam interferometry?

Answer

Laser provides a source of coherence and truly monochromatic light. The property of clearance enables it to be projected in a narrow pencil of beam without any scatter.

9.Write the application of laser interferometry

Answer

1. Laser measurement 2. Angular measurement

10.What is interferometer? Name the different types of interferometer.

Answer

Interferometer is an optical instrument used for measuring flatness and determining the length of slip gauges by direct reference to the wavelength of light. Types. 1. NPL flatness interferometer. 2. Michelson interferometer. 3. Laser interferometer. 4. Zesis gauge block interferometer.

11.What do you mean by alignment test on machine tools?

Answer

The alignment test is carried out to check the grade of Manufacturing accuracy of the machine tool.

12. List the various geometrical checks made on machine tools.

Answer

a. Straightness of guide ways and slide ways of machine tool. b. Flatness of machine tables and slide ways. c. Parallelism, equidistance and alignment of the slide ways. d. True running and alignment of shaft and spindle. e. The pitch error or lead of lead screw. f. Pitch errors of gears.

13.Distinguish between geometrical test and practical test on a machine tool.

Answer

The alignment test is carried out to check the grade of manufacturing accuracy of the machine tool. Performance test consists of checking the accuracy of the finished component. Alignment test consists of checking the relationship between various machine elements when the machine tool is idle. Performance test consists of preparing the actual test job on the machine and checking the accuracy of the job produced.

14.Differentiate between straightness and flatness.

Answer

Straightness is defined as a line where all elements of a line are collinear but flatness is the minimum distance between two planes within which all points on a surface lie.

15.State any two applications of laser in machine tool metrology.

Answer

This testing is more suitable for aircraft production, shipbuilding etc. Where a number of components are spaced long distance apart, they have to be checked for predetermined straight line. Other uses of laser equipment are testing of flatness of machined surfaces, checking squareness with the help of an optical square etc.

16.What is CMM?

Answer

It is a three dimensional measuring instruments for various components. These machines have precise movement is X-Y-Z coordinates which can be easily controlled and measured. Each slide in three directions is equipped with a precision linear measurement transducer which gives the digital display and it senses the positive and negative direction.

17.Mention any four types of CMM.

Answer

1. Cantilever type. 2. Bridge type. 3. Horizontal boring type. 4. Vertical boring type.

18.Define straightness of axes.

Answer

Straightness is a condition where an element of a surface or an axis is a straight line. Straightness of axes is defined as the deviation from a straight line in two orthogonal planes for each axis movement and six measurements to be considered. Straight lines of x-axis are measured in y and z direction, y-axis in x and z direction, z-axis in x and y directions.

19.Define position accuracy.

Answer

It is defined as the difference between positions read out of a machine along an individual axis and value of a reference length measuring system. Three parameters are needed for position accuracy. Position accuracy of x-axis, y-axis and z-axis are measured.

20.Define axial slip of machine tool.

Answer

It is used for checking the profiles of complex components such as turbine blades.

21.Define axial length measuring accuracy and volumetric length measuring accuracy.

Answer

(i)Axial length measuring accuracy: It is defined as difference between the reference length of gauges aligned with a machine axis and corresponding measurement results from the machine. (ii)Volumetric length measuring accuracy: It is defined as difference between the reference length of gauges, freely in space and corresponding measured results from the machine.

22.What are the benefits of using CMM?

Answer

Measurement of diameter, center distance, and length can be measured as follows. 1. Measurement of plane and spatial curves 2. Minimise CNC programme. 3. Data communications. 4. Digital input and output command 5. Interface to CAD software.

23.Give the advantages of coordinate measuring machines.

Answer

(i)Quicker inspection. (ii)Accurate measurements. (iii)Easier to position. (iv)More accurate. (v)No need of GO/NOGO gauges. (vi)Reduction of scrap and good part rejection.

24.Mention the disadvantages of CMM.

Answer

a. The table and probe may not be in perfect alignment. b. The stylus may have run out. c. The stylus moving in z-axis may have some perpendicularity errors. d. Stylus while moving in x and y direction may not be square to each other. e. There may be errors in digital system.

25.Mention the application of CMM.

Answer

1. CMM's to find application in automobile, machine tool, electronics, space and many other large companies. 2. It is best suited for the test and inspection of test equipment, gauges and tools. 3. For aircraft and space vehicles of hundred percent inspections is carried out by using CMM. 4. CMM can be used for determining the dimensional accuracy of components. 5. CMM can also be used for sorting the tasks to achieve the optimum pacing of components within tolerance limits.

26.State the applications of CMM in Reverse Engineering.

Answer

It is used for determining the shape and position, maximum metal condition. It is also best suited for ensuring the economic viability of NC machines by reducing their down time for inspection results.

27.Distinguish between coordinate and conventional metrology.

Answer

In co-ordinate metrology, the three dimensional measurements are carried out by using machines. In conventional metrology, it is not possible to carry out the three dimensional measurement.

28.How are past process metrology incorporated CNC machines?

Answer

The process of measuring the work pieces during machining and automatically updating the machine tool offsets in the control system to maintain the dimensional quality of the work piece machined without any manual intervention is called post process metrology. The post process metrology set up can reduce the cost and time of production.

29.List the equipments needed for computer aided inspection.

Answer

(1) It is designed for multi-touch software control (2) It uses an advanced probe toolbox, graphics-based "part View" constructions (3) It can be a quick annotate, industry-leading support for additional tolerance conventions (4) Feature detail graphics support for all current industry standard software methodologies for stage and camera calibration (5) It is for industry as a leading operating system platforms and (6) Additional windows are functionality based.

30.What are the advantages of computer aided inspection?

Answer

A big advantage of computer is its processing capability and presently data in a form with the use of computer systems. It becomes possible to prevent making defective parts rather than rejecting them at the end of the whole cycle.

31.List any four applications of computer aided impection.

Answer

Computer aided inspection is mainly applied following purposes. (i)Checking tool accuracy (ii)Checking tool wear (iii)Monitoring manufacturing process (iv)Assisting quality engineers and machinist.

32.What are the steps involved in producing software for engineering metrology?

Answer

a. Precise and detailed definition of geometrical form. b. Specification of the measurement procedure. c. Mathematical modeling of the measurement.

33.What is CNC CMM?

Answer

A computer numerical control system can be used with CMM to do calculations while measuring the complex parts. Error can be stored in memory while doing calculations. For automatic calibration of probe, determination of co-ordinate system, calculation, evaluation and recording etc., special software's are incorporated.

34.Write brief note about (i) Co-ordinate measuring machine equipped with a laser probe (ii) Virtual measuring system.

Answer

1.A CMM equipped with a laser probe can convert a part of physical model into a digitize file. Such a file can be compared with other file and can be manipulated by designers to improve the quality. Manufactures can verify thet each finished part measures exactly as designed. 2.Virtual measuring system uses a microscope system to examine an electronic replica of the surface texture of part. Such a system is non-contact 3-D surface measurement system and provide image of the surface. The images are processed on a PC using vertical scanning interferometry and vision analysis software is to produce 2D-profile, 3-D plots and counter plots. 3.It generates statistics for average roughness, average profile height, reduced peak height, cares roughness depth, reduced valley depth and a number of other parameters. It also determines the depth, spacing and angle of groove in a hard surface optical probe of a cylinder bore can be rotated 360° and it is vertically moved along the cylinder wall.

35.Define machine vision.

Answer

Machine vision can be defined as the simulating the image recognition and analysis capabilities of the human system with electronic and electromechanical techniques.

36.What are the four basic types of machine vision system?

Answer

1. Image formation 2. Processing of image 3. Analyzing the image 4. Interpretation of image.

37.What do you mean by 'Gray Scale' analysis?

Answer

In these techniques, discrete areas or windows are formed around only the portions of the image to be inspected. For determining if brackets are present, high intensity lighting is positioned so that a bracket when the bracket is missing no shadow will be cash. When the bracket is present, a large number of darker pixels can be observed in the window due to the cast shadow than when a bracket is missing. A contrast threshold between dark and light pixel value area can be set. This type of discrete area analysis is a powerful tool used for the inspection of absence, correct part assembly, orientation, part, integrity, etc.

38.Describe the features of a flexible inspection system.

Answer

1. A powerful computer serves as a real time processor to handle part dimensional data and as a multi-programming system to perform such tasks as manufacturing process control. 2. The terminal provides interactive communication with personnel computer where programmes are stored. 3. Input devices microprocessor based gauges and other inspection devices are used in CMM.

39.Explain briefly the three important fields of machine vision system.

Answer

1. Inspection: It is the ability of an automated vision system to recognize well-defined pattern and if these pattern match are stored in the system, it makes machine vision ideal for inspection of raw materials, parts, assemblies etc. 2. Part identification: It is the ability of part recognition provides positive identifications of an object for decision-making purposes. 3. Guidance and control: Machine vision systems are used to provide a sensor feedback for real time guidance and control ranging from visual serving of industrial robots and weld seam tracking to calculate of geometric off sets for part processing and assembly operations.

40.Write the advantages of machine vision system.

Answer

(i) It reduces the tooling and fixture cash. (ii) It eliminates the need for precise part location. (iii)It integrates the automation of dimensional verification (iv) It detects defects.

41.Explain the application of machine vision system.

Answer

a. It can be used to replace, machining for applications such as welding, machining to maintain relationship between tool and work. b. Machine vision systems are used for a printed circuit board. c. These are used for weld seam tracking, robot guidance and control, inspection of microelectronic devices and tooling, on line inspection in machining operation, on-line inspection of a assembling, maintaining high speed packaging. d. It is for the recognition of object from its image. e. It achieves 100% accuracy.

42.Name the types of accuracy specifications used for CMM.

Answer

(i) Geometrical accuracies such as positioning accuracy, straightness and squareness. (ii) Total measuring accuracy in terms of axial length measuring accuracy. (iii)Volumetric length measuring accuracy and length measuring repeatability i.e., CMM has to be tested as complete system. (iv) Environmental effects have great influence for the accuracy testing, including parameters, vibrations and relative humidity and required.

43.Explain the types of co-ordinate measuring machine.

Answer

(i) Cantilever type: It is easy to load and unload but the mechanical error may occur due to sag or deflection. (ii) Bridge type: It is more difficult to load but the mechanical errors are less. (iii) Horizontal bore mill: It is used for large and heavy work pieces. (iv) Vertical bore mill: It is very slow to operate but it is highly accurate. (v) Spherical co-ordinate measuring machine: Both linear and rotary axes are incorporated. It can be used to measure various features of parts such as cane, cylinder, hemisphere etc.

44.List any four possible causes of error in CMM.

Answer

1.The table of CMM may not have perfect geometric form. 2. The probes may have a degree of run out. 3. Variation in temperature of CMM, specimen and measuring lab influence the uncertainty of measurements. 4. The smoke particle, a finger print, a dust particle and human hair may introduce the uncertainty in measurement.

45.What is laser micrometer?

Answer

It is used for checking the profiles of complex components such as turbine blades.

46.What are the advantages of laser interferometer?

Answer

1. It is ideally suited for measuring linear positioning, straightness in two planes. 2. Long covering range and high sensitivity. 3. Free from noise disturbances. (Light noise, electrical noise,air turbulence). 4. Use of single photo detector per measurment axis,sensitivity to optical alignment is less. 5. Non-contact measurement is possible.

47.What is the purpose of retro-reflectors in laser interferometers?

Answer

Retro-reflector is a device or surface that reflects light back to its source with a minimum scattering of light and also reflects the beam always parallel to the incident beam in these devices.

48.Name the comman source of light used for interferometer.

Answer

1. Mercury 198 2. Cad minus 3. Krypton 86 4. Helium 5. Hydrogen 6. Laser mixed radiations

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