ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Hall Effect Rotary Encoders

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Hall Effect Rotary Encoders Prepared by: Mike Tyger Dept. of Electrical and Computer Engineering Utah State University 3/06/2009

2. Outline • Reference List • Explore Further • Major applications • Overview • Basic working principle • Typical Application • Major Specifications • Limitations ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list • Sensors, ‘Understanding Integrated Hall Effect Rotary Encoders’, www.sensorsmag.com/sensors/article/articleDetail.jsp?id=383802. • EDN, ‘Rotary encoder mates with digital potentiometer’, www.edn.com/article/CA278837.html • EDN, ‘Automotive Hall-effect rotary-position sensor uses novel flux-concentrator technology ’ www.edn.com/article/CA6492443.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. 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 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Major Applications • Measure: • Angular Velocity • Angular Position • Magnetic Field Strength ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. Overview • A linear Hall sensor generates a DC output voltage proportional to the strength of an applied magnetic field. • The output of a Hall sensor is a sine wave with a with a frequency of one cycle per revolution when the sensor is placed near a rotating diametrically magnetized magnet. • Multiple Hall sensors can be used for accurate angle measurements. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Overview - General Voltage output of Hall sensor varies with the strength and pole of the magnetic field. http://www.sensorsmag.com/sensors/data/articlestandard//sensors/442006/383802/i1_t.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Overview – Angular position Multiple Hall sensors in an array are used to accurately determine angular position http://www.sensorsmag.com/sensors/data/articlestandard//sensors/442006/383802/i2_t.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Advantages • Small • Lightweight • Low power • Non-Contact • Long life ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Advantages • High degree of accuracy • Simplified manufacturing – compared to optical encoder • Programmable zero-position ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Principle – Field Strength http://www.sensorsmag.com/sensors/data/articlestandard//sensors/442006/383802/i10_t.jpg The4 Hall sensors in the array each measure a different magnetic field strength as the magnet rotates on the axis. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Principle – Sine and Cosine Signals The output of each sensor is a Sine or Cosine wave â = peak amplitude α = magnet rotational angle relative to the sensor ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Principle – Differential Signals Differential amplification of signals from opposite sensors in the array results in a sine and a cosine wave which can be interpreted by the CORDIC algorithm ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Principle – CORDIC Algorithm A CORDIC (coordinate rotation digital computer) transforms the differential signal into angle and magnitude A= measured angle α = magnet rotational angle relative to the sensor â = peak amplitude The final equation shows that the magnetic field amplitude can be eliminated from the calculation, resulting in the elimination of the effects of stray magnetic fields. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Principle – 360º Measurement http://www.sensorsmag.com/sensors/data/articlestandard//sensors/442006/383802/i7_t.jpg The output of the CORDIC can accurately determine the angular position of the magnet relative to the sensors. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Design Issues • Resolution • Accuracy • Phase Error • Offset Errors • ADC nonlinearities • Magnet nonlinearities ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Resolution and Accuracy • Resolution • Resolution is the smallest angle step that can be measured by the sensor. Angle changes smaller than the resolution will not be read. Resolution is mainly determined by the resolution of the ADC and the calculation depth of the CORDIC. • Accuracy • Accuracy is the deviation between the indicated angle and the actual angle. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Phase and Offset Errors • Phase Errors • The Hall sensor signals must be phase-shifted by exactly 90°, propagation delays in the sensors can result in significant error. • Offset Errors • Offset errors occur primarily in the Hall element and are due to poor transistor matching of the components in the analog signal path. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Nonlinearities • ADC nonlinearities • A High-performance ADC is required since ADC nonlinearity cannot be compensated for. • Magnet nonlinearities • The Hall elements of the array must be in the linear range of the magnetic field. This range is larger for larger diameter magnets but the field distribution curve is more shallow, resulting in a smaller differential signal. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Typical Application Rotary encoder in industrial housing http://news.thomasnet.com/images/medium/499/499091.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. 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: -40°C to 125°C ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

22. Limitations • Highly susceptible to stray magnetic fields • Requires precise assembly • Possible need for magnetic shielding ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

23. 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 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

24. Other Considerations • Robustness • The non-contact nature of a magnetic encoder makes it fairly robust. The CORDIC can be used to eliminate the effect of stray magnetic fields • Hall effect sensors are used in a wide variety of applications ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

25. Other Considerations • The ratio of sensor accuracy to sensor cost is very good for a hall effect rotary encoder ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators