linear encoder

ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators

Topic: Linear Optical Encoder Specific by: HeidenhainPrepared by:Josh Grange

Email: [email protected]/11/2010

*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*Outline Reference listTo explore furtherMajor applicationsBasic working principle illustratedA typical sample configuration in applicationMajor specificationsLimitationsTypes of ScalesHow to ChooseCostWhere to Buy

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*Reference list

Heidenhain. (2010). Brochures: Length Measurement - Heidenhain. Retrieved February 20, 2010, from Heidenhain: http://www.heidenhain.com/en_US/services_and_documentation/documentation_information/brochures/


*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*To explore further http://www.heidenhain.com

Other Brand:http://www.farrandoptical.com

http://www.mitsubishi.com


*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*Major applications CNC Machine PositioningDigital Readouts for PositionMeasuring and Production equipment in the semiconductor industryPCB assembly machinesHigh accuracy machine toolsPrecision Machining for Lathes and MillsMeasuring Instruments


Working PrincipleHeidenhain encoders with optical scanning incorporate measuring standards of periodic structures known as graduations. These graduations are applied to a carrier substrate of glass or steel (Heidenhain, 2010).Schematic representation of an incremental graduation with distance-coded reference marks.*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*(Heidenhain, 2010)(Heidenhain, 2010)(Heidenhain, 2010)

(Heidenhain, 2010)


Working PrincipleFollowing illustration is: Photoelectric scanning in accordance with the imaging scanning principle with steel scale and single-field scanning (Heidenhain, 2010).

Heidenhain encoders operate using the principle of photoelectric scanning . Photoelectric scanning of a measuring standard is contact-free, and as such free of wear.

Heidenhain typically uses two types of scanning principles with linear encoders (Heidenhain, 2010):The imaging scanning principle for grating periods from 10m to 200 m.The interferential scanning principle for very fine graduations with grating periods of 4 m and smaller.*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*(Heidenhain, 2010)


Working PrincipleFollowing illustration is: Photoelectric scanning in accordance with the interferential scanning principle and single-field scanning.

The interferential scanning principle exploits the diffraction and interference of light on a fine graduation to produce signal used to measure displacement.*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*(Heidenhain, 2010)


Sample Configuration12 Horizontal Mill (Base)12 Gray Mill*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*Linear Scale


Sample ConfigurationIn the previous slide the two pictures gave an example of a Heidenhain linear encoder scale in application. This scale ran 60 in the x direction of the machine and was used to keep linear measurements within one ten thousandths of an inch. In the following picture are the drives used to manipulate and read the encoder signals and the reader head.*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*


Major Specifications*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*The accuracy of the linear measurement is mainly determined by:

The quality of the graduation

The quality of the scanning process

The quality of the signal processing electronics

The error from the scale guide way relative to the scanning unit or head

Specifications:

Temperature Range: -20 C to +70 C

The tapes have different Coefficients of Thermal Expansion that need to be considered

Max Value for Vibration: 55 Hz to 2000 Hz

Scanning Frequency: 98 kHz (max pulse count)

Traversing Speed: .75 m/min to 7.6 m/min


Limitations and Considerations*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*Some of the following are limitations or considerations to the linear encoders:Needs a clean or sealed environment

Do not use force to insert head such as a striking blow to align or seat

Should be mounted as close to the working plane as possible

Need to be mounted on solid part of machine or moving surface

Susceptible to continuous vibrationsScales and Reader Head should be mounted away from heat and fluctuating temperature

Subject to thermal expansion

Best application in a controlled environment

Length of scale must be considered in which type of reader head and scale material is desired


Types of ScalesDiadurDiadur precision graduations are composed of an extremely thin layer of chromium on a substrate-usually of glass or glass ceramic. The accuracy of the graduation structure lies within the micron and submicron (Heidenhain, 2010).AurodurAurodur graduations consists of highly reflective gold lines and matte etched gaps. Aurodur graduations are usually on steel carriers (Heidenhain, 2010).*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*MetallurWith its special optical composition of reflective gold layers, Metallur graduations show a virtually planar structure. They are therefore particularly tolerant to contamination (Heidenhain, 2010).


Types of Scales*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*SupradurGraduations manufactured with the Supradur process act optically like three-dimensional phase gratings, but they have a planar structure and are therefore particularly insensitive to contamination (Heidenhain, 2010).Phase GratingsSpecial manufacturing processes make it possible to produce three-dimensional graduation structures, possessing special optical characteristics. The structure widths are in the range of a few microns down to quarters of a micron (Heidenhain, 2010).MagnodurThin magnetically active layers in the micron range are structured for very fine, magnetized graduations (Heidenhain, 2010).


How to Choose Length of TravelAccuracySpeed of TravelArea for Placement of Reader HeadLocation of ScaleVibrationTemperatureCleanlinessSignal Type

*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*(Heidenhain, 2010)


Location of ScalesConsiderations for Choosing*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*(Heidenhain, 2010)


CostLengthAccuracyEnclosedExposedConnection TypeScale MaterialReader TypeCost on Linear Glass/Tape Scales: $2,000 - $10,000*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*(Heidenhain, 2010)


$2,000 Includes:Glass Scale up to 1 meterAccuracy of up to 2 micronOne continuous piece*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*(Heidenhain, 2010)


$10,000 Includes:Tape Scale up to 15 metersAccuracy of up to 5 micronAluminum Extrusions with one continuous tape scaleSealedPositive air displacement*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*(Heidenhain, 2010)


Where to Buy*ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuatorsSlide-*Heidenhain Sales Dept.Address: 333 East state Parkway Schaumburg, IL 60173-5337Phone: 800-233-0388Email: [email protected]


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