1. Advanced Mechatronics
Instructor: Professor I. Charles Ume
Hall effect Sensors
Variable Reluctance Sensor
Ultrasonic Sensors (Sonic Distance Sensors)
Photo Interrupt
Pressure Sensors
Accelerometers

2. Hall Effect Sensor Sensing a Shaft Speed
Developed by Edwin Hall in 1879; and hence the name Hall effect
Used to:
provide noncontact means to detect and measure magnetic field
Hall Effect Sensor Sensing a Shaft Speed

3. Depiction principle of the Hall Effect
How they work
Presence of magnetic field deflects electrons flowing through conductive material
As electrons move to one end of conductive material:
Potential is developed in direction perpendicular to gross current flow
Potential indicates strength of magnetic field
Depiction principle of the Hall Effect

4. Applications IC Engine Electronic Ignition Systems
Used to determine position of cam shaft
Brushless DC Motor Control
Sensors determine position of permanent magnet rotor
Assembly Lines
To determine shaft position and velocity
As contactless limit switches
Current Sensing ICs
Electrically isolated alternative to shunt resistors

5. Hall Effect Sensor Types
Linear Hall Effect Sensors
Output is proportional to magnetic field strength
Hall Effect Digital Switches
Presence of magnetic field above threshold turns switch on
Presence of magnetic field below threshold turns switch off
Hall Effect Digital Latches
North field turns latch on
South field turns latch off

6. Packaging and Manufacturers
ICs
Analog Devices:
AD22151G from Analog Devices
Allegro MicroSystems, Inc.
Wide range of linear, latching and switching sensors
Great sampling policy
Many, many more
Packaged units
Honeywell
SOT23
SIP
Hall Effect Sensor Module

7. Implementation and Words of Warning
Sensors may be affected by temperature variation.
Some sensors incorporate circuitry to reduce this error.
Sensors may be directional:
Care must be taken with respect to orientations of sensor and magnet
Some Hall Effect sensors detect presence of ferromagnetic materials, not magnetic fields

8. Variable Reluctance Sensors
Used to measure speed and/or position of moving metallic object
Sense change of magnetic reluctance (analogous to electrical resistance) near sensing element
Require conditioning circuitry to yield a useful signal (e.g. LM1815 from National Semi.)
Industrial Variable Reluctance Sensor

9. How Variable Reluctance Sensors Work
Magnet in sensor creates magnetic field
As ferrous object moves by sensor
Resulting change in magnetic flux induces emf in pickup coil
Typical Configuration
Variable Reluctance Sensor Construction

10. Typical Application Shaft velocity sensor for ABS/traction control
Crank and cam shaft position sensors
Installed on CV axle
Sensor Schematic

11. Emf is proportional to rate of change of magnetic flux.
Interfacing Concerns
Emf is proportional to rate of change of
magnetic flux.
Dictates ferrous material must be moving for sensor to generate signal.
Output voltage is dependent on velocity of toothed wheel
Performance may be reduced at slow speeds

12. Ultrasonic Transducer
Ultrasonic transducer (piezoelectric transducer) is device that converts electrical energy into ultrasound
Upon receiving sound echo (pressure wave) back from surface, ultrasound transducer will turn sound waves into electrical energy which can be measured and displayed
Ultrasound are sound waves above normal range of human hearing (greater than 20K hertz).

13. Since piezoelectric crystal generates voltage when force is applied to it, same crystal can be used as an ultrasonic generator and detector
Some systems use separate transmitter and receiver components while others combine both in single piezoelectric transceiver
Alternative methods for creating and detecting ultrasound include magnetostriction and capacitive actuation.
Pulse echo sensor
Transmit-Receive sensor

14. Sound is transmitted through propagation of pressure in air
Speed of sound in air is normally 331 m/sec at 0oC and 343 m/sec at 20oC for dry air
Digital signal processor embedded in sensor calculates distance between sensor and object

15. Range of sensor varies between 5 cm to 20 m
X = vsound . t
Where:
Vsound is known
t = 0.5 (time of flight)
X is distance between sensor head and object
Range of sensor varies between 5 cm to 20 m
Sensor is not appropriate for very short distance measurements
Frequency response (distance measurement update rate) varies with distance measured
In general, it is about 100 Hz

16. Ultrasonic sensors work on principle similar to radar or sonar
Piezoelectric crystals have property of changing size when voltage is applied
Applying alternating current (AC) across them causes them to oscillate at very high frequencies
Producing very high frequency sound waves
Ultrasonic sensors work on principle similar to radar or sonar
Radar and Sonar evaluate attributes of target
Interpreting echoes from radio or sound waves respectively

17. Medical: Medical ultrasonic transducers (probes):
Applications
Medical:
Medical ultrasonic transducers (probes):
Come in variety of different shapes and sizes for use in making pictures of different parts of body
Transducer may be:
Passed over surface of body or
Inserted into body opening such as rectum or woman’s reproductive organ
Clinicians who perform ultrasound-guided procedures often use probe positioning system to hold the ultrasonic transducer.

18. Technology can be used for measuring:
wind speed and direction (anemometer),
speed through air or water
fullness of tank
amount of liquid in tank
sensor measures distance to surface of fluid.
Other applications include:
in robots for obstacle avoidance
burglar alarms
non-destructive testing, and etc

19. Laser Ultrasound System
Nd:YAG pulsed laser:
Repetition rate: 20 Hz
Pulse Width: 10 ns
Pulse Energy: mJ/pulse
Beam Diameter: 6 mm
Positioning Stage:
Resolution: 50 μm
Electro-Magnetic Acoustic Transducer (EMAT):
Bandwidth: 200 kHz-2.5 MHz
Data Acquisition Card:
Resolution: 14 bit
Sampling Rate: 125 MHz
Control
Box
Nd:YAG
Laser
EMAT and
Preamp
Positioning
Axis-lead screw
Data Acquisition
and User Interface

20. Automated Weld Inspection System
System consists of laser, beam delivery subsystem, stepper motor driven linear screw, electromagnetic acoustic transducer (EMAT), data acquisition card, computer software, and control unit
Generated ultrasounds traveling through weld seams are received by EMAT
System resolution not yet determined, but has been used to detect 0.4 mm void
Used system to inspect 180 mm long weld bead at 1 mm increment in 26 secs
Type of defects: Lack of penetration; Blow hole; and Short leg
Laser
Beam Delivery
EMAT
Linear Screw
Sample
Preamp
Incident Laser Beam
Mirror 1
Mirror 2
Mirror 3
Lens

21. Identifications of Solder Bump Defects in Chip Packages
Examples of Emerging Microelectronic Packages:
3-D Packaging: Stacked Die
Chip Scale Package
Flip Chip
Quad Flat Package (QFP)
Total Bumps: 560
Amkor Super BGA
Ball Grid Array (BGA)

22. Optical Micrographs of Good and Bad Solder Bump Cross Sections
Good Solder Bump
Head-in-Pillow defects
Two medium size voids near the interface
Poor wetting, an intermittent connection

23. Optical micrographs of Good and Bad Solder Bump Cross Sections
Pad crater with crack initiating at the trace
Crack initiates at the edge of the pad
Inspection of solder bumps is crucial process in
microelectronics manufacturing industry.

24. Intelligent Laser Ultrasound Inspection System
Laser Beam Delivery:
High-quality fiber face polish with fiber injection optics
Stable laser injection optical mount
Rugged, rubber/metal fiber jacketing
Variable excitation spot ( mm2)
Excitation standoff distance > 50 mm
Fiber-coupled sensor head
16 mm aperture
3 μm minimum spot diameter
Variable standoff distance via autofocus system
DVT SmartImage Sensor
PC programmable stand-alone image processing sensor
Fiducial coordinates sent to PC through serial port
640 x 480 pixel resolution, 8–bit grayscale CCD
1/10 th pixel software resolution, 5 mm viewing window
Possible sub-micron resolution
Model: New Wave Research Polaris II
Wavelength: 1064 nm or 532nm with SHG
Repetition Rate:1~20 Hz variable
Pulse Width: 4-5 ns
Pulse Energy: 45mJ/pulse, optical attenuator adjustable B A C D
Typical Data Acquisition Parameters
Sampling rate: Bit res.
Trigger source: Laser output
Sample depth: 2048 samples (~ MHz)
Voltage Range: ±100 mV (~ ±5 nm)
Signal Averaging: 4–128 avgs. E
High stiffness, preloaded bearings
Integral X/Y table designed with wide base to increase stiffness
Higher bidirectional repeatability (< ±6 μm,)
Larger mounting surface (326 x 326 mm)
Larger travel (200 x 200 mm) F
Stiff, pre-loaded linear motion components
Linear encoder measurement (1μm res.)
High precision (±10 μm) G
Polytec Laser Doppler Vibrometer
Heterodyne interferometer capable of displacement measurements
50 nm/Volt analog output
150 nm full scale output (peak to peak)
Operating Frequency Range: 50 kHz to 25 MHz
Lower cutoff frequency: 25 kHz (-3 dB), rolloff 40 dB/dec H
Vibrometer Autofocus System
Hands free autofocus system to increase repeatability and throughput
Customizable focusing algorithms for different kinds of chip package
Remote operable
Serial interface with MATLAB for fully automated testing
Average refocus time: 3 sec I

25. Laser Ultrasound Inspection (LUI) System
3 US Patents Have Been Issued & 2 Pending

26. Photo Interrupt Uses emitter and detector photo diode pair
With no obstruction detector is high
When an object blocks the light the detector is low
Advantages
Simple to interface
Inexpensive
Reliable

27. Photo Interrupt Types Wide variety of packages and orientations Types
Logic (digital ±5 volts)
Transistor/diode (analog)
Manufacturers
Fairchild
Honeywell

28. Photo Interrupt Applications
Encoder wheel for angular measurements.
Computer mouse with a ball

29. Photo Interrupt Applications
Detect holes or slots for positioning of liner slides
Elevators
Detect the location of products on and assembly line

30. Pressure Sensors Used to detect pressure of fluids or gasses.
Technologies (many)
Strain gage
Piezoresistive
Microelectromechanical systems (MEMS)
Each sensor has a pressure range that it works in.
Most have analog outputs that need amplification
Some have built-in amplifiers for direct connection into microcontroller

31. Pressure Sensors Types
Differential Pressure
Difference between two or more pressures introduced as inputs to the sensing unit
2 input
Absolute/Gage Pressure
The pressure relative to perfect vacuum pressure or set pressure (like pressure at sea level)
1 input

32. Pressure Sensors Applications
Measure pressure of gas or fluids
Measure altitude
For plains or weather balloons
Measure flow
pressure sensors in conjunction with the venturi effect to measure flow
Measure depth of water
When measuring liquids, most sensors are not rated to have unclean liquids contact the sensor components. A small amount of air in the tube right before the sensor will create a barrier from the liquid.

33. Accelerometers Used to measure acceleration
Common SI units meters/second2 (m/s2) or popularly in terms of g-force (1 g is earth’s gravity)
At rest an acceleration will measure 1 g in the vertical direction
They can come in 1, 2 or 3 axis configurations
With 3 axis it gives a vector of the accelerations direction (after accounting for gravity)

34. Accelerometers
Because of earth’s gravity, the sensor will read 1 to 0 g as the sensor is rotated from being vertical to horizontal.
This can be used to measure angle the of tilt
Each sensor has a range that it works in.
Most have analog outputs that need amplification
Some have built-in amplifiers for direct connection into microcontroller

35. Accelerometers How they work
Mechanically the accelerometer behaves as a mass-damper-spring system
Many use Microelectromechanical systems (MEMS). Which use very small cantilever beams with masses on them
Under the influence of gravity or acceleration, the proof mass deflects from its neutral position.
This deflection is measured in an analog or digital manner
Commonly the capacitance between a set of fixed beams and a set of beams attached to the proof mass is measured.
Integrating piezoresistors in the springs to detect spring deformation is another method

36. Accelerometers Applications
Can be used to sense orientation, vibration and shocks.
Used in electronics like the Wii and iPhone for user input.
Acceleration integrated once gives velocity, integrated a second time gives position.
The integration process is not precise and introduces error into the velocity and position.