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Basics of CMM(Coordinate Measuring Machine)

What is CMM?

CMM(Coordinate Measuring Machine) is an advanced measurement machine works for measure complex and large component. CMM is a device for measuring the physical characteristics of an object. The machine is controlled by a computer or an operator.

CMM consists of 3-axis namely X-axis, Y-axis, Z-axis. Measurement is done by the prob attached to a third moving axis. This prob could be mechanical, optical, laser or white light.

So, the machine who takes reading in 6 DOF(Degree of freedom) known as CMM.

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Components of CMM

The 3 main component of CMM are-

  1. Machine itself (includes its 3-axis)
  2. Probing System
  3. Controllers & Softwares

Working Principle of CMM

CMM record X, Y, Z coordinates of the object and generate point which analysis by regression algorithm. This points are collected by Prob via direct computer control.

Main Parts of CMM

  • Air Bearing
  • Scales & Encoders
  • Prob system
  • Servo motors
  • Joystick
  • Machine control system
  • Software
crysta plus mitutoyo cmm

This is Mitutoyo’s manual floating bridge type CMM coordinate measuring machines designed to achieve very high accuracy in a wide range of applications.The model type is CRYSTA-PLUS M is the intelligent alternative to the complex, cost-intensive measuring equipment with conventional  multi-point measuring devices.

Pros of CMM

  • Single Setup
  • Accuracy
  • Improved Productivity
  • Reduced Setup Time

Probs of CMM

CMM probes are available in three main forms:

  1. Touch-Trigger probes
  2. Displacement Measuring CMM probes
  3. Proximity or Non-contact Probes

Read more about Prob of CMM

Types of CMM


There are four basic types of stationary CMM:

  • Bridge.
  • Cantilever.
  • Horizontal Arm.
  • Gantry.

Read More about Types of CMM



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Basics of Gear Metrology

Gears are transmitted power and motion in industries and machines, mainly used for torque multiplication.

Gear also increase or decrease the speed of any system.

gear train
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This is widely used in machine tools, transmission, automobile-like mechanical motion devices.

The purpose of a gear wheel is to transmit rotary motion and force. A gear wheel with accurately machined teeth round its edge.

colorful gears
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A shaft passes through its center and the gear may be geared to the shaft. Gears are used in groups of two or more, which is known as a gear train.   

Types of Gears

Bevel gears

These gears have teeth cut one cone instead of a cylinder blank. Bevel gears are used in pairs to transmit rotary motion and torque.

Which are 90 degrees to each other.  

By Diego Delso, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=18836416
By Diego Delso, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=18836416

Worm and Worm Wheel

A gear which has one tooth is known as Worm, this tooth in the form of a screw thread. A worm wheel meshes with the worm .

By Arthur Clarke at English Wikipedia - Transferred from en.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2851216
By Arthur Clarke at English Wikipedia – Transferred from en.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2851216

Helical Gear

Helical gear used for very quiet and smooth running at high rotational Velocities.

helical gear
By Arthur Clarke at English Wikipedia – Transferred from en.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2738668

Spiral Bevel Gears

These gears used where necessary to transmit quietly and smoothly a large torque through a right angle at high velocities.

spiral bevel gear
By Myriam Thyes – Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4078185

Rack and Pinion

Rack and Pinion are used for converting rotary motion to linear motion.

rack and pinion
By OSHA Directorate of Technical Support and Emergency Management – Point of Contact Between a Rack and Pinion. The original uploader was Brian0918 at English Wikipedia., Public Domain, https://commons.wikimedia.org/w/index.php?curid=186765

Spur Gears

This type of gear is widely used today. A spur gear, transmit a positive motion between two shafts lying parallel to each other.  

Every gear rotates about its axis. So, all parameter have to be inspected about the axis of rotation.

spur gear
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Tooth gear Measurement  

  1. Gear tooth Vernier
  2. Flange Micrometer
  3. Gear rolling Tester

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Feeler gauge| Types of Feeler gauge| Use of Feeler Gauge| Size of feeler gauge

What is feeler gauge?

A Feeler gauge is used to measure the clearance between two parallel flat faces for example piston and cylinder. As the name suggests, feeler gauge called as to measure neither tide nor freely.

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feeler gauge

Feeler gauges are used for measurement of clearances.

It is a tool that measures air or narrow gap widths between two surfaces in engines and machinery.

Size of Feeler gauge

Feeler gauge available in no. of the blade like 10,13,20 and 28. With a step of 0.05 and 0.10 mm.

The thickness of the blades are in fractions of mm and inches, usually ranging from 0.03 mm to 1mm.

leaf of feeler gauge

Parts of Feeler gauge

The feeler gauge has two major parts, a  body or block which acts like a protective case or shealth and a large number of blades of different thickness.

The body is the base that holds the blades together. Feeler gauges are made entirely of steel so that they are corrosion free and the blades do not rust easily.

In machinery and engine service, it is important to predict accurate measurement of gaps for smooth performance and to avoid any faulty operations.

It is extensively and mostly used for measuring the gap between an engine cylinder and piston.

When there is extra gap even after a blade is inserted then the blades of the feeler gauge can be used in various combinations as per the requirement, that is different blades having different thickness can be stacked together and used.

How to use Feeler gauge?

The working of feeler gauge is easy. The blades are kept on the vacant gap that needs to be measured, initially one blade of standard thickness is kept, then if there are extra gaps other blades are adjusted and joined together and used.

Ensure that the blades can be easily pushed to and fro and are not tight nor free to move.

In order to have a problem-free measurement, the blades should be free of dirt and grease.

Feeler gauge look like same to Radius gauge.

To maintain the blades for longer lifetime apply motor oil after every use.


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Do you know How to Measure strain?

We all know about stress and stain and and its relation. But have you ever know about the measurement of Strain. please comment your valuable response.

The strain gauge is fundamental of many type of sensors like pressure sensors, load cells, torque sensors etc.

The most common form of strain gauge is the electrical resistance strain gauge.

The gauges are formed by either a length of wire arranged in an axial grid pattern or by etching a thin metal foil into the desired shape.

By Izantux – WikiCommons, CC0, https://commons.wikimedia.org/w/index.php?curid=14933147

Most strain gauges are foil types.

Foil Strain gauge

Unmounted_strain_gauge
By Pleriche – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=61871859

Foil stain gauges are available in a wide choice of shapes and sizes to suit a variety of applications.

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They operate by simple principle i.e. As the foil is subjected to stress, the resistance of foil changes in defined way.

Normally, wire gauges are used for high temperature applications and foil gauges are used for routine applications.

Some important parameter about Foil gauges are

  • High stability
  • Good proportionality
  • Easy manufacturing
  • Low output voltage(requires amplification)

A strain gauge’s conductors are very thin if it made of round wire, about 1/1000 inch in diameter.

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What is Transducer? and it’s classification

We know that the generalized measuring system consists of three functional elements(transducer is first stage):

  1. primary detector-transducer stage,
  2. intermediate modifying stage, and
  3. the output or terminating stage.

 Each stage performs certain functions so that the value of the physical variable to be measured (measurand) is displayed as output

What is Transducer?

A transducer is a device that converts one form of energy into another form.

signal process of transducer
By Brews ohare – Own work;… Uses File:EAR.jpg and File:Sexy-Red-Lips Happy-Girl.jpg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19048816

 The transducer, which may be electrical, mechanical, optical, magnetic, piezoelectric, etc., converts the sensed information into a more convenient form.

The detecting or sensing element of a measuring system first makes contact with the quantity to be measured, and the sensed information is immediately transduced into an analogous form.

Classification of Transducers

Analog and Digital Transducers

 In the case of analogue transducers, the input quantity is converted into an analogue output, which is a continuous function of time.

pressure transducer
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LVDT, strain gauge, thermocouple, and thermistor are some examples of analogue transducers.

 If a transducer converts the input quantity into an electrical signal that is in the form of pulses, as output, it is called a digital transducer.

These pulses are not continuous functions of time but are discrete in nature. Examples are shaft encoders, linear displacement transducers.

Terminating Devices

Meter Indicators

Meter indicators can be categorized as follows:

  1. Simple D’Arsonval type to measure current or voltage
  2. Volt–Ohm milliammeters or multimeters
  3. Vacuum tube voltmeters

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Simple D’Arsonval Type to Measure Current or Voltage

 It essentially consists of components like a permanent

magnet, coil, hairsprings, pointer, and scale. The coil assembly is mounted on a shaft, which in turn is hinged on a hair spring.

 To concentrate the magnetic fields, initially, the iron core is placed inside the coil.

 The curved pole pieces are then attached to the magnet to ascertain if the torque increases as the current increases.

This means that electromagnetic energy is used to move the meter.

Volt-Ohm Milliammetersor Multimeters 

The typical volt–ohm milliammeter employs switching provisions for connecting multipliers, shunt resistors, and rectifier circuits.

The current flowing through the resistor can easily be determined by switching over to the ohm-meter function, wherein the leads can be connected to the unknown resistance that causes the meter movement.

The advantage is that direct measurement is possible since the current flow indication is calibrated in terms of resistance

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Vacuum Tube Voltmeters

The vacuum tube voltmeter, popularly known as VTVM, is basically used to measure voltage.

To control the grid of the tube, proper multiplier resistors are employed through which the AC or DC input is given to the meter.

The input resistance of a VTVM is usually very high, when compared to that of a simple meter, due to high grid circuit resistance. This minimizes the loading of the signal source.

Cathode Ray Oscilloscope

 A CRO is a voltage-sensitive device that is used to view, measure, and analyse waveforms.

Its advantage is that a beam of electrons with low inertia strikes the fluorescent screen, generating an image that can rapidly change with varying voltage inputs to the system.

 The cathode ray tube (CRT) is the basic functional unit of CRO. The electron gun assembly comprises a heater, a cathode, a control grid, and accelerating anodes. When a cathode is heated, electrons are generated.

The accelerating anodes, which are positively charged, provide the necessary striking velocity to the emitted electron stream.

The electron beam, after gaining necessary acceleration, passes through horizontal and vertical deflection plates, which provide the basic movements in the X and Y directions.

XY Plotters

The XY plotters generate Cartesian graphs, which are obtained by two DC inputs, in X and in the Y-axis. It consists of two self-balancing potentiometers, one to control the position of the paper and others to control the position of the pen.

 In XY plotters, the output is generated by plotting one emf as a function of the other emf.

 Further, the emf, which is the output signal of transducers, may be a value of displacement, force, pressure, strain, or any other parameter.

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Metrology Terminologies

Measurement is a Natural part of everyday life. We express daily needs in size & weights, water and electricity are also metered.

A number of blood samples, active sub-stain in medicine also needs to be precise.

I think it is Impossible to describe anything without measuring it.

measurement tools
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Room temperature, body weight, sunshine,chest width and so on..

Almost every company are concerned with Quality management in the process of Introducing their work

First, we try to understand what is Metrology!

What is Metrology?

Metrology word derived from the Greek words Metro(means Measurement) and Logy(means Science).

Metrology includes all aspects with reference to measurements, whatever their level of accuracy.

Terminologies

Some technical terms are difficult to understand, so the following terminology is quite helpful for further studies

Accuracy

Accuracy is the closeness between a test result and accepted value.

Bias

Bias is the difference between the expected value and the accepted reference value.

Calibration

Calibration is the set of operations that establish under specified conditions, the relationship between values of quantities indicated by a measuring instrument or values represented by a material measure and the corresponding values realized by standards.

Drift

Drift is slow to change of a metrological characteristic of measuring instrument.

Magnification

The output result from a measuring device to be magnified many times to make it more readable, called Magnification.

Precision

Precision is the closeness of agreement between independent test results obtained under stipulated conditions.

Resolution

The smallest change of the measured quantity which changes the indication of a measuring instrument is called Resolution.

Traceability

Traceability means a measured result can be related to references.

Read more, about Units of Metrology

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