New innovation of magnetic scales used in digital height masters and digital read out systems


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New innovation of magnetic scales used in digital height masters and digital read out systems

  1. 1. Journal of Management Research and Development (JMRD), ISSN 2248 – 937X (Print) ISSN Journal of Management Research and Development (JMRD),ISSN – 9390(Online), Volume 1, Number 1, January - December (2011) 2248 2248 – 937X (Print)ISSN 2248 – 9390(Online), Volume 1, Number 1 JMRDJanuary - December (2011), pp. 58-62 © PRJ PUBLICATION© PRJ Publication, NEW INNOVATION OF MAGNETIC SCALES USED IN DIGITAL HEIGHT MASTERS AND DIGITAL READ OUT SYSTEMS K. Kalaiarasu, Research Scholar Sathyabama University, Chennai, India, E-mail:, Dr.N.Kalyanaraman,HOD, Dept. of Management, D.G. Vaishnav College, Chennai, E-mail: profnkr@gmail.comABSTRACTGenerally usage of scales in digital read out systems and Height master will plays a majorrole due to its unique functions. The scales using those instruments ensure the specifiedaccuracy and resolution of particular applications. Developments and technical revolutionsof these magnetic scales is playing a major role in the engineering industry where the need ofdigital read out systems for conventional machines and Digital Height Masters in thestandards room’s New developments of magnetic scales has its own advantages overmetallic and glass scales which is mostly used in wide range of applications in theengineering industries..Key Words : Magnetic scales, Digital read out systems, System Accuracy, Reader Head.1. INTRODUCTIONThe new linear magnetic scale which measures the displacement of the product very preciselyand To ensure the specified accuracies of a magnetic scale, selection and right type of scaleplays a major role. For the past four decades in digital read out systems and digital heightmasters, people were using steel scales as well glass scales both has its own advantages andlimitations too. The new development of magnetic scales in the recent past and the usage inboth above instruments leads very good results which has eliminates most of the limitations.Over the period a large number of machines and applications have come in the engineeringindustries where glass cannot suit the requirements. Even using steel scale also has not solvedthe purpose and not fulfilled by the end-users. To fulfill such demand a new technology hasemerged over the steel and metallic scales in the current industries. These scales are based onmagnetic and can satisfy the above needs. They are becoming more and more popular due totheir unique features and cost to benefit ratio.Limitations of Glass ScalesGlass scales have been very popular for measuring length, dimensions of a part, distancetravelled etc. In a Machine tool, profile projector ,Metrology equipment’s usage of these glassscales and Magnetic scales is inevitable nowadays.Eariler days large number of machines andapplications have come up with glass scales which was having more limitations such as, 58
  2. 2. Journal of Management Research and Development (JMRD), ISSN 2248 – 937X (Print) ISSN2248 – 9390(Online), Volume 1, Number 1, January - December (2011) 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 RoughnessAverage (Ra) or Mean Arithmetic Deviation, which is used to assess the coarseness of thesurface 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 maximumroughness 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 particularlyvaluable where components are subjected to high stresses. Any large peak-to-valley heightsmay be areas likely to suffer from crack propagation. These finishes are not falls in thiscategory.2. CONSTRUCTION OF MAGNETIC SCALES Magnetic scale consists of the magnetic tape which is also called as magnetic band, whichto 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. Themagnetic scales I glued firmly with a double sided tape in the groove and thin of 0.15 mmthick, stainless steel strip is inserted over the magnetic tape in the aluminum section throughthe 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 throughwater, through oil, through wood, paper and dirt. The strip is coated with magnetic materialpower such as Barium Ferrite mix. This material directly cannot used in the strip , due to itsbreaking nature. So they do glue in the magnetic strip and they will magnetize the same. The 59
  3. 3. Journal of Management Research and Development (JMRD), ISSN 2248 – 937X (Print) ISSN2248 – 9390(Online), Volume 1, Number 1, January - December (2011)process is carried by special purpose machines .Fig 2 is a type of magnetic strip used inmagnetic 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 alternatepoles N-S-N-SN-S N-S of desired width 2mm to 10mm.The magnetic sensor is made tomove along the length of the strip at right angle to the poles. The sensor detect the changingmagnetic field and gives voltage signal output. This voltage signal is further interpolated and the required pulse train output isobtained along with direction signal. With the help of this pulse train O/P distancemeasurement can be obtained. This is a magnetic linear encoder works. Air gap between thesensor and the magnetic strip is decided depending upon the magnetic field strength andsensitivity of the sensor. It is normally of the order of 0.5 to 2mm depending upon the polepitch, 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 5micron, 10 micron, 20 mic, 50 mic & 100 mic , Reference mark optional, • Accuracy + 2counts per meter at 20°c , • Protection against dust & coolant, • Maximum permissible cablelength - 15 mtrs, • Speed of operation - 10 met/sec (32ft./sec) ,Line driver withComplimentary outputThis is the most important part of the measuring system. It consists of an Aluminum box inwhich is housed the electronic including the magnetic sensor. At the bottom of the sensor is astainless steel plate to prevent any damage to the sensor due to foreign body and whileoperations. From one side of a box a cable with carrying all signal and supply wires.[Ref 60
  4. 4. Journal of Management Research and Development (JMRD), ISSN 2248 – 937X (Print) ISSN2248 – 9390(Online), Volume 1, Number 1, January - December (2011)4.Fig.3] This reader also will work in dirt and water even they made such a way to absorband work under vibration conditions. During operations magnetic dust can get collected on the surface of the magnetic scale. Itis always better to remove it otherwise it may damage the reader head. After long use. Inorder to avoid it this dust should be scrapped away. In the construction of magnetic scalesspecial wiper has provided which will remove the dust during displacement which ensures forbetter 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,• MotorizedMeasuring Carriage,• 3 Point Air Cushion,• Integrated Rechargeable Battery BackupProvided for Long ,• Operation Time,• RS 232 Data Output,• Online 2D Drawing Plot onLCD 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 headsuch that it can freely move on the magnetic scale. Scale should be mounted in such a waythat grating sticker on the extrusion should be opposite side. Scale mounting surface of themachine bed is even within 0.1mm per meter, then mount the scale directly on the bed byusing 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 mountedon machine and by moving table .If the mounting surface is even then scale mounting blocksfor each need to be manufactured before the installation of each scale. The measuring lengthof the scale will vary depend upon the applications. Nonmagnetic portion of the scale at eachend of the scale so that magnetic dust pushed by the wiper will off. Technical specification asfollows, a. Resolutions with four edge detections : 5,10,20 microns b. System Accuracy : +/- 10 to 20 microns c. Repeat Accuracy : +/- 1 count 61
  5. 5. Journal of Management Research and Development (JMRD), ISSN 2248 – 937X (Print) ISSN2248 – 9390(Online), Volume 1, Number 1, January - December (2011) d. Scanning Material : Alloy aluminum with statin less steel base.Mounting bracket for slider location (Fig .3.) should be be decided that slider should moveover the scale for full traverse of the machine slide and equal gap should be maintain betweenslider bottom throughout its travel .Generally manual feed is is desirable for better results andfor life of the scale. The slider has to fit with M4 Allen keys firmly. Gap between scale andslider should be maintained with the help of shim. To achieve this gap put the plastic shimbetween the reader head and the bottom. While mounting the reader head we have to ensurethat 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 ensurethe 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 ofthe machine. The we have to ensure that, it will never get pulled or pushed during machineoperaations.Cable should not bend below radius 60mm during routing. Cable should therouted nearby inductive load to avoid the electrical noise interference. 5. CONCLUSIONThough there are various types of scales available in the industries, cost of these equipmentshas to consider. The role and significance of magnetic scale is inevitable in the engineeringindustries as a technology up gradation and quality aspects. The cost per component for thisprocess is negligible in case of mass production. Even life of glass scale and metallic scale isvery less compare to glass scale. Therefore, cost per product will be less New Technology inthe 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. 3. Methods on precision finishing by Otech precision GmbH. 4. Metrology and measurements, by Bewoor.P23,54, 36-39 5. 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. 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 62