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ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators
Topic: Hall Effect Rotary Encoders
Prepared by: Mike Tyger
Dept. of Electrical and Computer EngineeringUtah State University
3/06/2009
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11/11/2013 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
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Outline
Reference List Explore Further Major applications Overview Basic working principle Typical Application Major Specifications Limitations
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11/11/2013 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
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Reference list Sensors, Understanding Integrated Hall Effect
Rotary Encoders,www.sensorsmag.com/sensors/article/articleDetail.js
p?id=383802. EDN, Rotary encoder mates with digital
potentiometer ,www.edn.com/article/CA278837.html
EDN, Automotive Hall-effect rotary-position sensoruses novel flux-concentrator technology www.edn.com/article/CA6492443.html
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11/11/2013 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
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To explore further
(survival pointers of web references etc) http://www.austriamicrosystems.com/eng/Products/Magnetic-
Encoders/Rotary-Encoders Leading manufacturer of hall effect rotary encoders. Data sheets for
complete product line http://www.everightsensors.com/index.shtml
Manufacturer of rotary encoders
http://en.wikipedia.org/wiki/Hall_effect
In depth discussion of the Hall effect
http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.everightsensors.com/index.shtmlhttp://en.wikipedia.org/wiki/Hall_effecthttp://en.wikipedia.org/wiki/Hall_effecthttp://www.everightsensors.com/index.shtmlhttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encodershttp://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encoders -
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Major Applications Measure:
Angular Velocity Angular Position Magnetic Field Strength
11/11/2013 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
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Overview - General
11/11/2013 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
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Voltage output of Hall sensor varies with thestrength and pole of the magnetic field.
http://www.sensorsmag.com/sensors/data/articlestandard//sensors/442006/383802/i1_t.jpg
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Overview Angular position
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Multiple Hall sensors in an array are used to accuratelydetermine angular position
http://www.sensorsmag.com/sensors/data/articlestandard//sensors/442006/383802/i2_t.jpg
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Advantages Small Lightweight Low power Non-Contact Long life
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Advantages High degree of accuracy Simplified manufacturing compared to
optical encoder
Programmable zero-position
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Principle Field Strength
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The 4 Hall sensors in the array each measure a different magneticfield strength as the magnet rotates on the axis.
http://www.sensorsmag.com/sensors/data/articlestandard//sensors/442006/383802/i10_t.jpg
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Principle Sine and Cosine Signals
11/11/2013 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
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The output of each sensoris a Sine or Cosine wave
= peak amplitude = magnet rotationalangle relative to thesensor
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Principle Differential Signals
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Differential amplificationof signals from oppositesensors in the array
results in a sine and acosine wave which can
be interpreted by theCORDIC algorithm
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Principle CORDIC Algorithm
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A CORDIC (coordinate rotation digitalcomputer) transforms the differentialsignal into angle and magnitude
A= measured angle = magnet rotational angle relative tothe sensor = peak amplitude
The final equation shows that themagnetic field amplitude can beeliminated from the calculation, resultingin the elimination of the effects of straymagnetic fields.
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Principle 360 Measurement
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The output of the CORDIC can accurately determine the angular position of the magnet relative to the sensors.
http://www.sensorsmag.com/sensors/data/articlestandard//sensors/442006/383802/i7_t.jpg
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11/11/2013 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
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Design Issues Resolution Accuracy Phase Error Offset Errors ADC nonlinearities Magnet nonlinearities
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Resolution and Accuracy
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Resolution Resolution is the smallest angle step that can be
measured by the sensor. Angle changes smaller thanthe resolution will not be read. Resolution is mainlydetermined by the resolution of the ADC and thecalculation depth of the CORDIC.
Accuracy Accuracy is the deviation between the indicated angle
and the actual angle.
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Typical Application
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http://news.thomasnet.com/images/medium/499/499091.jpg
Rotary encoder in industrial housing
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Major Specifications 360 contactless angular position encoding User programmable zero position High speed: up to 30,000rpm Direct measurement of magnetic field strength allows exact
determination of vertical magnet distance Wide magnetic field input range: 20 ~ 80mT Wide temperature range: -40C to 125C
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Limitations Highly susceptible to stray magnetic fields
Requires precise assembly Possible need for magnetic shielding
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Limitations Sensors must be placed very accurately around
the centerline of the rotational axis. Multiple sensors are typically contained in a single
package Sensor must be very accurately placed on PCB Small tolerances of sensor PCB mounting fixtures
can increase cost
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Other Considerations Robustness
The non-contact nature of a magnetic encodermakes it fairly robust. The CORDIC can be used toeliminate the effect of stray magnetic fields
Hall effect sensors are used in a wide variety ofapplications
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Other Considerations The ratio of sensor accuracy to sensor cost is
very good for a hall effect rotary encoder
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