2. Journal of Management Research and Development (JMRD), ISSN 2248 – 937X (Print) ISSN
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a) The suitable in the dirty environment nearby machine areas. b)It is not water proof,
when glass scales undergo water and cutting oil while using in the systems, the
performance will reduce or breakdown will happen.c)Accuracy will change much
during vibrations.
One of the most commonly used roughness measurement parameter is the Roughness
Average (Ra) or Mean Arithmetic Deviation, which is used to assess the coarseness of the
surface such as those produced by Grinding, Turning, Milling or other Finishing operations.
Fig-1. Type of metallic and glass scales used in digital read out systems.
Rmax & Rz : For some surface it is sometimes desirable to specify the maximum
roughness height Rmax, or the peak-to-valley height, Rz, rather than use the mean height Ra.
The Rmax parameter measures the highest and lowest points of the profile and is particularly
valuable where components are subjected to high stresses. Any large peak-to-valley heights
may be areas likely to suffer from crack propagation. These finishes are not falls in this
category.
2. CONSTRUCTION OF MAGNETIC SCALES
Magnetic scale consists of the magnetic tape which is also called as magnetic band, which
to be magnetized with extruded plastic material section glued on stainless steel strip.Fig.2.
For ease of installation on machine tools, magnetic tape is pu in aluminum extrusion. The
magnetic scales I glued firmly with a double sided tape in the groove and thin of 0.15 mm
thick, stainless steel strip is inserted over the magnetic tape in the aluminum section through
the grooves provided accordingly. There are three basic elements on construction,
Magnetic Scale ,Magnetic Reader Head.,Magnetic Tape.
Fig.2. Type of Magnetic Strip used in Magnetic Scales
These Magnetic scales are based on magnetic principal that magnetism passes through
water, through oil, through wood, paper and dirt. The strip is coated with magnetic material
power such as Barium Ferrite mix. This material directly cannot used in the strip , due to its
breaking nature. So they do glue in the magnetic strip and they will magnetize the same. The
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process is carried by special purpose machines .Fig 2 is a type of magnetic strip used in
magnetic scales which has having unique advantages as follows,
• Magnetic Scales perform will under dirt conditions in shop floor. Coolant and Water
splash exists in machining area , will not affect the scales. Life of magnetic is more
over glass and metallic scales. Accuracy and other measurements will not affect under
vibrations.
2.1 Technical Aspects of Magnetic Scales
The steel backed up magnetic strip is magnetized with the help of a magnetizer for alternate
poles N-S-N-SN-S N-S of desired width 2mm to 10mm.The magnetic sensor is made to
move along the length of the strip at right angle to the poles. The sensor detect the changing
magnetic field and gives voltage signal output.
This voltage signal is further interpolated and the required pulse train output is
obtained along with direction signal. With the help of this pulse train O/P distance
measurement can be obtained. This is a magnetic linear encoder works. Air gap between the
sensor and the magnetic strip is decided depending upon the magnetic field strength and
sensitivity of the sensor. It is normally of the order of 0.5 to 2mm depending upon the pole
pitch, accuracy etc.
2.2 Applications of Magnetic Scales
• It can be used in Digital read out systems along with conventional milling machines.
• Ideal to use in Digital Height masters in the DRO.
• Magnetic Scales also used in conventional lathe DROs.
• Profile projectors, special purpose machines can be used.
3. Reader Head
Fig.3. Type of Magnetic Tape scale with Reader Head.
3.1. Technical Specifications of Magnetic scale:
• Measuring length upto 30 meter , • Electrical ouput 5V TTL quadrate, • Resolution 5
micron, 10 micron, 20 mic, 50 mic & 100 mic , Reference mark optional, • Accuracy + 2
counts per meter at 20°c , • Protection against dust & coolant, • Maximum permissible cable
length - 15 mtrs, • Speed of operation - 10 met/sec (32ft./sec) ,Line driver with
Complimentary output
This is the most important part of the measuring system. It consists of an Aluminum box in
which is housed the electronic including the magnetic sensor. At the bottom of the sensor is a
stainless steel plate to prevent any damage to the sensor due to foreign body and while
operations. From one side of a box a cable with carrying all signal and supply wires.[Ref
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4.Fig.3] This reader also will work in dirt and water even they made such a way to absorb
and work under vibration conditions.
During operations magnetic dust can get collected on the surface of the magnetic scale. It
is always better to remove it otherwise it may damage the reader head. After long use. In
order to avoid it this dust should be scrapped away. In the construction of magnetic scales
special wiper has provided which will remove the dust during displacement which ensures for
better accuracy and readings without error.
4. Technical Specifications of Digital Height Master with Magnetic Scale:
Fig.4. Type of 2D Height Masters used in the industry with Magnetic Scales
•Color Graphical 5.7” size LCD Display,•Animated user friendly GUI
• High Accuracy Optical dual scanning Head Measuring 4 4 4 System,• Motorized
Measuring Carriage,• 3 Point Air Cushion,• Integrated Rechargeable Battery Backup
Provided for Long ,• Operation Time,• RS 232 Data Output,• Online 2D Drawing Plot on
LCD screen and DXF export to PC,• Auxiliary incremental Probe input
5. Safety Factors while installing the magnetic scales in Digital Read out systems:
The place where the scale is to be installed should be thoroughly cleaned from oil, dust,
coolant etc. Appropriate reader head mounting bracket to be designed to fix the reader head
such that it can freely move on the magnetic scale. Scale should be mounted in such a way
that grating sticker on the extrusion should be opposite side. Scale mounting surface of the
machine bed is even within 0.1mm per meter, then mount the scale directly on the bed by
using Allen screws through the holes in the end brackets and the desired positions.
We have ensure the parallelism to full length scale with the dial indicator firmly mounted
on machine and by moving table .If the mounting surface is even then scale mounting blocks
for each need to be manufactured before the installation of each scale. The measuring length
of the scale will vary depend upon the applications. Nonmagnetic portion of the scale at each
end of the scale so that magnetic dust pushed by the wiper will off. Technical specification as
follows,
a. Resolutions with four edge detections : 5,10,20 microns
b. System Accuracy : +/- 10 to 20 microns
c. Repeat Accuracy : +/- 1 count
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d. Scanning Material : Alloy aluminum with statin less steel base.
Mounting bracket for slider location (Fig .3.) should be be decided that slider should move
over the scale for full traverse of the machine slide and equal gap should be maintain between
slider bottom throughout its travel .Generally manual feed is is desirable for better results and
for life of the scale. The slider has to fit with M4 Allen keys firmly. Gap between scale and
slider should be maintained with the help of shim. To achieve this gap put the plastic shim
between the reader head and the bottom. While mounting the reader head we have to ensure
that dimple on the reader head is facing lines sticker on the extrusion.
Providing proper cover to protect scale and sensor for the entire length of the scale to ensure
the reliability and performance of the system. This cover gives protection against oil, coolant,
and metal chips during operations. This cable must be kept out of the way of moving parts of
the machine. The we have to ensure that, it will never get pulled or pushed during machine
operaations.Cable should not bend below radius 60mm during routing. Cable should the
routed nearby inductive load to avoid the electrical noise interference.
5. CONCLUSION
Though there are various types of scales available in the industries, cost of these equipments
has to consider. The role and significance of magnetic scale is inevitable in the engineering
industries as a technology up gradation and quality aspects. The cost per component for this
process is negligible in case of mass production. Even life of glass scale and metallic scale is
very less compare to glass scale. Therefore, cost per product will be less New Technology in
the manufacturing process and and have a edge in the field of metrology.
REFERENCES
1. Hand book for dimensional measurements By T. Farrago.P.18-25, 67-69.
2. www.innovativedro.com
3. Methods on precision finishing by Otech precision GmbH.
4. Metrology and measurements, by Bewoor.P23,54, 36-39
5. www.machine-dro.co.uk
6. Hand book on magnetic materials by, K.H.J.Bushow.
7. Machine tools Practices, by James A.Harvey. P.11,13-15,21,24
8. Text book for manufacturing technology by R.K.Rajput.P.488, P.496.
9. www.givimisure.tradeindia.com
10. New Generation scales, By shah, Chapter 4, P.18-26.
11. Luigi Lugiato Everything You Need to Know About Quantum Optics
12. Roy Tennant Magnetic scales in Digital readout systems.P.4,P.6-8,P.45-52
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