1. technology and computing

Mechatronic systems
Mechatronic systems
What is mechatronics?
mechanics
•
Introduction to mechatronics
•
Sensors and actuators used in mechatronics systems
•
Applications of MEMS
Key Elements of Mechatronics
electronics
mechatronics
Mechatronics - the synergistic integration of mechanical
engineering, with electronics and intelligent computer control in the
design and manufacturing of industrial products and processes.
Historical Development
Definition of Mechatronic Systems
A typical mechatronics system
A typical mechatronics system consists of a
sensing unit, a controller, and an actuating unit.
A sensing unit can be as simple as a single
sensor or can consist of additional components
such as filters, amplifiers, modulators, and other
signal conditioners.
Sensor is a device that when exposed to a
physical phenomenon (temperature, force,
displacement, etc.) produces a proportional
output signal (electrical, mechanical, magnetic).
The controller accepts the information from
the sensing unit, makes decisions based on the
control algorithm, and outputs commands to the
actuating unit.
The actuating unit consists of an actuator
and optionally a power supply and a coupling
mechanism.
Actuators accepts a control command
(mostly in the form of an electrical signal) and
produces a change in the physical system by
generating force, motion, heat, flow, etc.
1
Definition of Mechatronic Systems
General scheme of a (classical) mechanical-electronic system
A classical mechanical-electronic system is resulted from adding available sensors, actuators,
and analog or digital controllers to mechanical components. The limits of this approach were
given by the lack of suitable sensors and actuators, the unsatisfactory life time under rough
operating conditions (acceleration, temperature, contamination), the large space
requirements, the required cables, and relatively slow data processing.
Ways of integration within mechatronic systems
The Integration of Components (hardware integration)
results from designing the mechatronic system as an overall
system and imbedding the sensors, actuators, and
microcomputers into the mechanical process.
This spatial integration may be limited to the process and
sensor, or to the process and actuator.
Microcomputers can be integrated with the actuator, the
process or sensor, or can be arranged at several places.
Integrated sensors and microcomputers lead to smart
sensors, and integrated actuators and microcomputers lead
to smart actuators.
The Integration of Information Processing (software
integration) is mostly based on advanced control functions.
Besides a basic feedforward and feedback control, an
additional influence may take place through the process
knowledge and corresponding online information processing.
This means a processing of available signals at higher levels,
including the solution of tasks like supervision with fault
diagnosis, optimization, and general process management.
Classification of mechatronic systems
The Automobile as a Mechatronic System
Mechatronic systems are classified as:
1.
conventional mechatronic systems,
2.
microelectromechanical-micromechatronic systems (MEMS),
3.
nanoelectromechanical-nanomechatronic systems (NEMS).
The operational principles and basic foundations
of conventional mechatronic systems and MEMS
are the same, while NEMS can be studied using
different concepts and theories.
In particular, the designer applies the classical
mechanics and electromagnetics to study
conventional mechatronic systems and MEMS.
Quantum theory and nanoelectromechanics are
applied for NEMS.
MEMS products not only contain a micromachined components but typically include
electronic signal conditioning circuits, self-testing and calibration, and are packaged with all
the required I/O ports and terminals. MEMS products represent completely autonomous
miniaturized systems, which are capable of performing specified sensing and actuation
functions in themselves or acts as subsystems in larger products.
Classification of sensors
Sensor is a device that when exposed to a physical
phenomenon (temperature, force, displacement, etc.)
produces a proportional output signal (electrical,
mechanical, magnetic).
Type of Sensors with respect to
principle of operation:
• Resistive
• Capacitive
• Inductive
• Ultrasonic
• Piezoelectric
• Piezoresistive
• Light
• ...
Type of Sensors for Various
Measurement Objectives:
• Linear/Rotational sensors
• Acceleration sensors
• Force, torque, and pressure sensor
• Flow sensors
• Temperature sensors
• Proximity sensors
• Light sensors
• Smart material sensors
• Micro- and nano-sensors
Classification of sensors
Sensors can also be classified as passive or active.
In passive sensors, the power required to produce the output is provided by
the sensed physical phenomenon itself (such as a thermometer) whereas the
active sensors require external power source (such as a strain gauge).
Furthermore, sensors are classified as analog or digital based on the type of
output signal. Analog sensors produce continuous signals that are
proportional to the sensed parameter and typically require analog-to-digital
conversion before feeding to the digital controller. Digital sensors on the other
hand produce digital outputs that can be directly interfaced with the digital
controller.
2
Classification of sensors
Classification of sensors
Resistive and capacitive sensors
Inductive sensors
Resistive sensors
Measurement objectives:
 position/displacement
 angle
Capacitive sensors
The LVDT (Linear/Rotational Voltage Differential Transformer) is
a tube with a plunger, the displacement of the plunger being the
variable to be measured.
The tube is wrapped with at least two coils, an excitation coil and
a pickup coil. An AC current (typically 1 kHz) is passed through
the excitation coil, and an AC signal is detected from the pickup
coil and compared in magnitude and in phase (0 or 180°) to the
excitation current.
Measurement objectives:
 position/displacement
 force and pressure
Classification of sensors
Measurement objectives:
 position/displacement
 angle
Classification of sensors
Inductive sensors
Principle of operation of LVDT
Inductive sensors
Principle of operation of LVDT
Support electronics are needed for the demodulation, which is called synchronous
detection. The plunger carries a ferromagnetic slug, which enhances the magnetic
coupling from the excitation coil to the pickup coil. Depending on the position of the slug
within the pickup coil, the detected signal may be zero (when the ferrite slug is centered in
the pickup coil), or increasing in amplitude in one or the other phase, depending on
displacement of the slug.
Classification of sensors
Classification of sensors
Inductive sensors
Ultrasonic sensors
Hall Effect sensors
The Hall effect is the production of a voltage difference (the Hall voltage) across an
electrical conductor, transverse to an electric current in the conductor and a magnetic
field perpendicular to the current.
Ultrasonic sensors use the time-of-flight of a pulse of ultrasonic sound
through air or liquid to measure distance.
Measurement objectives:
 detection of a moving part,
 indexing of rotational or
translational motion
Measurement objectives:
 distance
 depth
3
Classification of sensors
The Ultrasonic Flowmeter
The ultrasonic flowmeter measures the velocity of any liquid or gas through a pipe
using ultrasonic transducers. The results get slightly affected by temperature, density or
viscosity of the flowing medium. Maintenance is inexpensive because there are no
moving parts. Some may be able to measure liquid level as well. With the level
measurement and pipe size, flow rate and total discharge can be calculated.
Classification of sensors
Piezoelectric and piezoresistive sensors
Piezoelectric sensors utilize a mass in direct contact with the piezoelectric component or
crystal. When a varying motion is applied to the sensor, the crystal experiences a varying
force excitation (F = ma), causing a proportional electric charge q to be developed across it.
Piezoresistive sensors are based on resistance properties of electrical conductors. If a
conductor is stretched or compressed, its resistance alters due to dimensional changes,
and the changes in the fundamental property of material called piezoresistance.
Classification of sensors
Classification of sensors
Tensometers
The tensometer is a device used to evaluate the Young's modulus (how much it
stretches under strain) of a material and other tensile properties of materials, such as
tensile strength. It is usually loaded with a sample between 2 grips that are either
adjusted manually or automatically to apply force to the specimen.
Most tensometers use two or four active gauges
arranged in a Wheatstone bridge. Extra precision
resistors are used, as part of the circuit, in series
with the input to control the sensitivity, for
balancing, and for offsetting temperature effects.
Classification of actuators
Actuators are basically the muscle behind a mechatronics system that accepts a
control command (mostly in the form of an electrical signal) and produces a change in
the physical system by generating force, motion, heat, flow, etc. Normally, the actuators
are used in conjunction with the power supply and a coupling mechanism. The power
unit provides either AC or DC power at the rated voltage and current.
The coupling mechanism acts as the interface between the actuator and the physical
system. Typical mechanisms include rack and pinion, gear drive, belt drive, lead screw
and nut, piston, and linkages.
Smart Material Sensors
Optic fibers can be used to sense strain, liquid
level, force, and temperature with very high
resolution. The relative change in the transmitted
intensity or spectrum is proportional to the change
in the sensed parameter.
Typical applications:
 damage sensors,
 vibration sensors,
 cure-monitoring sensors.
Classification of actuators
Electrical switches are the choice of actuators for most of the on-off type control
action. Switching devices such as diodes, transistors, triacs, MOSFET, and relays
accept a low energy level command signal from the controller and switch on or off
electrical devices such as motors, valves, and heating elements.
For example, in a MOSFET switch the gate terminal receives the low energy control
signal from the controller that makes or breaks the connection between the power
supply and the actuator load.
Actuators can be classified based on the type of energy:
 Electrical
 Electromechanical
 Electromagnetic
 Hydraulic
 Pneumatic
The new generations of actuators include smart material actuators,
microactuators, and nanoactuators.
4
Classification of actuators
The most common electromechanical actuator is a motor that converts electrical
energy to mechanical motion. Motors are the principal means of converting electrical
energy into mechanical energy in industry. Broadly they can be classified as DC
motors, AC motors, and stepper motors.
Classification of actuators
The stepper motor is a discrete (incremental) positioning device that moves
one step at a time for each pulse command input. Since they accept direct
digital commands and produce a mechanical motion, the stepper motors are
used widely in industrial control applications.
Principle of operation
The winding-1 is between the top and bottom stator pole, and the
winding-2 is between the left and right motor poles. The rotor is a
permanent magnet with six poles resulting in a single step angle of
30 degrees. With appropriate excitation of winding-1, the top
stator pole becomes a north pole and the bottom stator pole
becomes a south pole. This attracts the rotor into the position as
shown.
Now if the winding-1 is de-energized and winding-2 is energized,
the rotor will turn 30 degrees. With appropriate choice of current
flow through winding-2, the rotor can be rotated either clockwise or
counterclockwise. By exciting the two windings in sequence, the
motor can be made to rotate at a desired speed continuously.
Classification of actuators
The solenoid is the most common electromagnetic actuator. A DC solenoid actuator
consists of a soft iron core enclosed within a current carrying coil. When the coil is
energized, a magnetic field is established that provides the force to push or pull the iron
core. AC solenoid devices are also encountered, such as AC excitation relay. A solenoid
operated directional control valve is shown in Figure.
Classification of actuators
Hydraulic and pneumatic actuators are normally either rotary motors or linear
piston/cylinder or control valves. They are ideally suited for generating very large forces
coupled with large motion. Pneumatic actuators use air under pressure that is most
suitable for low to medium force, short stroke, and highspeed applications. Hydraulic
actuators use pressurized oil that is incompressible. They can produce very large forces
coupled with large motion in a cost-effective manner. The disadvantage with the hydraulic
actuators is that they are more complex and need more maintenance.
Normally, due to the spring force, the soft iron core
is pushed to the extreme left position as shown.
When the solenoid is excited, the soft iron core will
move to the right extreme position thus providing
the electromagnetic actuation.
Another type of electromagnetic actuator
is the electromagnet.
Electromagnets are used extensively in
applications that require large forces.
Classification of actuators
In electrostatic motors, electrostatic force is dominant, unlike the conventional motors that
are based on magnetic forces. For smaller micromechanical systems the electrostatic forces
are well suited as an actuating force.
In the electrostatic motor the rotor is an annular disk with uniform permitivity and conductivity.
In operation, a voltage is applied to the two conducting parallel plates separated by an
insulation layer. The rotor rotates with a constant velocity between the two coplanar
concentric arrays of stator electrodes.
Classification of actuators
Magnetostrictive material is an alloy that generates mechanical strains in response to applied
magnetic fields. The magnetostrictive rod actuator is surrounded by a magnetic coil. When
the coil is excited, the rod elongates in proportion to the intensity of the magnetic field
established.
The piezoelectric actuators are essentially piezocrystals with top and bottom conducting
films. When an electric voltage is applied across the two conducting films, the crystal
expands in the transverse direction as shown by the dotted lines. When the voltage polarity
is reversed, the crystal contracts thereby providing bidirectional actuation.
5
Classification of actuators
Unlike the bidirectional actuation of piezoelectric actuators, the electrostriction effect
is a second-order effect, i.e., it responds to an electric field with unidirectional
expansion regardless of polarity.
Electrostrictive actuators are made of a lead-magnesium-niobate (PMN) ceramic
material. PMN is a non-poled ceramic with displacement proportional to the square of
the applied voltage. PMN unit cells are centro-symmetric at zero volts. An electrical
field separates the positively and negatively charged ions, changing the dimensions of
the cell and resulting in an expansion. Electrostrictive actuators are operated above
the Curie temperature which is typically very low when compared to Piezo materials.
Classification of actuators
Shape Memory Alloys (SMA) are alloys of nickel and titanium that undergo phase
transformation when subjected to a thermal field. The SMAs are also known as NITINOL for
Nickel Titanium Naval Ordnance Laboratory. When cooled below a critical temperature,
their crystal structure enters martensitic phase. In this state the alloy is plastic and can
easily be manipulated. When the alloy is heated above the critical temperature (in the range
of 50–80 deg. C), the phase changes to austenitic phase. Here the alloy resumes the shape
that it formally had at the higher temperature.
Electromechanical Actuator
Typical Wing and Flap
Hinge less shape memory alloy Flap
Applications of MEMS
Types of accelerometers
Measurements of acceleration with micromechanical and
convective accelerometers
 Construction and principle of operation of micromechanical rate
gyroscope
 Applications of BioMEMS (Implantable Blood Pressure Sensor)
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Applications of accelerometers
Micromechanical accelerometer
ADXL202 accelerometer
‰ Measure vibration on cars, machines, buildings,
process control systems and safety installations
‰ Used for machinery health monitoring of rotating
equipment such as pumps, fans, rollers, compressors
‰ Human activities - walking, running, skipping
‰ Construction work – drilling, excavating, demolition
‰ Moving loads on bridges
‰ Vehicle collisions
‰ Air blast pressure
‰ Loss of support because of ground failure
‰ Earthquake
‰ In an Inertial Navigation System (INS) is used to
continuously calculate via dead reckoning the position,
orientation, and velocity (direction and speed of
movement) of a moving object without the need for
external references (GPS signal)
The ADXL202 is a complete acceleration measurement system on a single monolithic IC.
It contains a polysilicon surfacemicromachined sensor and signal conditioning circuitry
which implements a force-balance control loop. The ADXL202 is capable of measuring
both positive and negative acceleration to a maximum level of ±2 g.
Sensor package – CLCC (Ceramic Leadless Chip Carrier)
6
Micromechanical accelerometer
Micromechanical accelerometer
Principle of operation
Principle of operation
Differential capacitive sensor
Differential capacitive sensor
The differential capacitor sensor consists of independent fixed plates and central plates attached
to the main beam that moves in response to an applied acceleration. The two capacitors are
series connected, forming a capacitive divider with a common movable central plate.
A Simplified Diagram of the ADXL202
Sensor at Rest.
CS1 = CS2
The actual structure of the sensor consists of 46 unit cells and a common beam.
The ADXL202 Sensor Momentarily Responding
to an Externally Applied Acceleration
CS1 < CS2
Micromechanical accelerometer
Micromechanical accelerometer
Principle of operation
Principle of operation
Differential capacitive sensor
Functional Block Diagram
u1 (t ) = U 0 cos ωC t
u2 (t ) = −U 0 cos ωC t
uOUT (t ) =
x
U 0 cos ωC t
d0
d0 – rest position between plates
x – displacement of central plate from rest position
x = 0 ⇒ vOUT = 0
x = X 0 cos ωS t ⇒ vOUT =
Micromechanical accelerometer
ui (t )
×
u p (t )
uSYNC (t )
Principle of operation
Synchronous demodulator
Setting the Bandwidth Using CX and CY
X0
U 0 cosω S t ⋅ cosωC t
d0
uSYNC (t ) = U 0 cos ωC t
ui (t ) =
u0 (t )
u p (t ) =
1
1
X0 2

U 0  cos ω S t + cos(2ωC − ω S )t + cos(2ωC + ω S )t 
2d 0
2
2


uo (t ) =
up(t) signal spectrum
|Up(ω)|
Micromechanical accelerometer
Principle of operation
Hd(ω)
X0
V0 cos ωS t ⋅ cos ωC t
d0
ωg =
fg =
1
RFILT C X ,Y
1
2π ⋅ RFILT C X ,Y
X0 2
U 0 cos ω S t ∗ hd (t )
2d 0
Hd(ω)
ω
0
ωS
ωg
2ωC–ωS 2ωC 2ωC+ωS
7
Micromechanical accelerometer
Micromechanical accelerometer
Principle of operation
Principle of operation
Direct Conversion Modulator
DCM modulator circuit
U pr
K
Functional Block Diagram of ADXL202 sensor
Waveforms
u PWL
ut
U pr1
U pr 2
ut
T2
u PWL1
Duty Cycle Decoding:
0 g = 50% Duty Cycle
Scale factor is 12.5% Duty Cycle Change per g
A(g) = (T1/T2 – 0.5)/12.5%
T2 =
RSET [Ω]
125MΩ
T1 (u PWL1 )
u PWL 2
T1 (u PWL2 )
Upr1 > Upr2
T1(uPWL1) > T1(uPWL2)
Micromechanical accelerometer
Micromechanical accelerometer
Using the ADXL202 Duty Cycle Output
Using the ADXL202 Duty Cycle Output
The most direct way to decode the duty cycle output is shown in Figure 1. A counter is
started at the rising edge of the X output (Ta = 0). The count at the falling edge (Tb) is
recorded, and the timer is stopped at the next rising edge of the X output (Tc). This
process is then repeated for the Y output (Td, Te, and Tf).
Since the duty cycle modulator (DCM) uses the same triangle wave reference for the X
and Y channels, the midpoints of the T1 of each period must be coincident. Therefore, an
improved PWM decode technique can be used to speed up the data acquisition time.
A counter is started at the rising edge of the X output (Ta = 0). The count at the falling
edge of the X output (Tb) is recorded. Then the counts at the rising and falling
edges of the Y output (Tc and Td) are recorded.
By definition:
T1x = Tb – Ta = Tb (if the counter is zero at Ta)
T1y = Td – Tc
T2x = T2y = Te – Ta = Tg – Tf
Since the midpoints of the high states of the X
and Y duty cycle signals are coincident:
T2 = [Td – ((Td – Tc)/2)] – [(Tb – Ta)/2]
T2 = [Td – ((Td – Tc)/2)] – [Tb/2]
(if the counter is zero at Ta)
Micromechanical accelerometer
Calibrating the ADXL202 sensor
The initial value of the offset and scale factor for the ADXL202 will require calibration for
applications such as tilt measurement. The ADXL202 architecture has been designed so
that these calibrations take place in the software of the microcontroller used to decode
the duty cycle signal. Calibration factors can be stored in EEPROM or determined at turnon and saved in dynamic memory.
A calibration method depends on making measurements at +1 g and –1 g on each axis.
The sensitivity for one axis can be determined by the two measurements. To calibrate,
the accelerometer’s measurement axis is pointed directly at the earth. The 1g reading is
saved and the sensor is turned 180° to measure –1g. Using the two readings, the
sensitivity is:
Let A = Accelerometer output with axis oriented to +1g
Let B = Accelerometer output with axis oriented to –1g
then:
Sensitivity = [A – B]/2g
For example, if the +1 g reading (A) is 55% duty cycle and the –1 g reading (B) is 32%
duty cycle, then:
Sensitivity = [55% – 32%]/2 g = 11.5%/g
Offset (0g point) = B + [A – B]/2g = 43.5%
Micromechanical accelerometer
Calibrating the ADXL202 sensor
Calibration algorithm in C:
mesure_x_y();
//set initial values
xmin = x; xmax = x;
ymin = y; ymax = y;
done = FALSE;
while (!done) {
mesure_x_y();
If (x > xmax) xmax = x;
else if (x < xmin) xmin = x;
If (y > ymax) ymax = y;
else if (y < ymin) ymin = y;
}
//Stop calibration setting done to TRUE
After calibration the sensitivity and scale
for one axis equals:
Sensitivity = [max – min]/2g
Offset = min + [max – min]/2g
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Micromechanical accelerometer
Convective accelerometer
Convection – refers to the movement of molecules within liquids or gases.
Using the ADXL202 as a dual axis tilt sensor
An accelerometer uses the force of gravity as an input vector to determine
orientation of an object in space. An accelerometer is most sensitive to tilt
when its sensitive axis is perpendicular to the force of gravity, i.e., parallel to
the earth’s surface.
When the accelerometer is oriented so both its X and Y axes are parallel to
the earth’s surface it can be used as a two axis tilt sensor with a roll and a
pitch axis. Once the output signal from the accelerometer has been converted
to an acceleration that varies between –1g and +1g, the output tilt in degrees
is calculated as follows:
Natural convection, or free convection, occurs due to temperature differences which
affect the density, and thus relative buoyancy, of the fluid. Heavier (more dense)
components will fall while lighter (less dense) components rise, leading to bulk fluid
movement. Natural convection can only occur, therefore, in a gravitational field.
In forced convection, also called heat advection, fluid movement results from external
surface forces such as a fan or pump. Forced convection is typically used to increase the
rate of heat exchange.
Pitch = ASIN (Ax/1g)
Roll = ASIN (Ay/1g)
Convective accelerometer
Convective accelerometer
MXA2500A accelerometer
Priciple of operation of convective accelerometer
MXA2500A
The MEMSIC accelerometers are a complete dualaxis motion measurement
system on a monolithic CMOS IC. The principle of operation of the MEMSIC
devices is based on heat transfer by natural convection. The devices measure
internal changes in heat transfer caused by acceleration. The devices are
functionally equivalent to traditional proof-mass accelerometers.
The MEMSIC devices are capable of measuring accelerations with a full-scale
range from below ±1.0g to above ±100g. The devices can measure both dynamic
acceleration (e.g. vibration) and static acceleration (e.g. gravity).
Convective accelerometer
Convective accelerometer
Priciple of operation of convective accelerometer
Priciple of operation of convective accelerometer
MXA2500A
ax = 0 ⇒
Utp1 = Utp2 ⇒ Utp1 - Utp2 = 0
MXA2500A
ax > 0 ⇒
Utp1 > Utp2 ⇒ Utp1 - Utp2 > 0 i Utp1 - Utp2
ax
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Convective accelerometer
Convective accelerometer
Priciple of operation of convective accelerometer
Priciple of operation of MXA2500A accelerometer
MXA2500A
Functional block diagram
Measurement range:
+/-1g
Sensitivity:
500mV/g
y
FEATURES:
Resolution better than 2 milli-g
x
50,000 g shock survival rating
30 Hz bandwidth expandable
to >160 Hz
ax > 0 ⇒
Utp1 > Utp2 ⇒ Utp1 - Utp2 > 0 i Utp1 - Utp2
ax
2.70V to 5.25V single supply
operation
Convective accelerometer
Convective accelerometer
Priciple of operation of MXA2020A accelerometer
Thermal Accelerometer Sensitivity
Functional block diagram
Measurement range:
+/-1g
Sensitivity: 20%/g
Duty Cycle output
y
x
Duty Cycle Decoding:
0 g = 50% Duty Cycle
Scale factor is 20% Duty
Cycle Change per g
A(g) = (T1/T2 – 0.5) / 20%
Convective accelerometer
Mechanical gyroscope
The real micromechanical structure of MXD2020A accelerometer
Construction of mechanical gyroscope
A gyroscope is a device for measuring or
maintaining orientation, based on the principles of
angular momentum. The device is a spinning
rotor whose axle is free to take any orientation.
This orientation changes much less in response to
a given external torque than it would without the
large angular momentum associated with the
gyroscope's high rate of spin. Since external
torque is minimized by mounting the device in
gimbals, its orientation remains nearly fixed,
regardless of any motion of the platform on which
it is mounted.
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Gyroscope
Generations of gyroscopes
Applications of gyroscopes
Gyroscopes are devices which are used
to measure angular rotation rate.
Typical applications of gyroscopes are:
• gyrocompasses which complement or replace
magnetic compasses (in ships, aircraft and
spacecraft, vehicles in general)
• assistance in stability (bicycle, Hubble Space
Telescope, ships, vehicles in general)
• Gyroscopes can be used as part of an inertial
guidance system
• GPS navigation systems (extrapolation of trajectory)
• Cooperation with accelerometer in automotive airbag
systems
• Gyroscopic effects are used in toys like tops, yo-yos,
and Powerballs
Micromechanical rate gyroscope
a)
b)
c)
Traditional gyroscopes with spinning wheels employed in the present aerospace and
military industries are bulky , need lubricant and eventually wear out. Ring laser
gyroscopes are also expensive and heavy.
Bulk-micromachined gyroscopes have large mass and relatively large readout
capacitance or piezoresistive readout. Therefore, bulk-micromachined gyroscopes do
not incorporate on-chip readout electronics, but instead require wire bonding to
separate electronic readout chips ‘‘two-chip’’ solution.
Surface-micromachining gyroscopes have small mass and relatively small readout
capacitance. However, the sensors and readout electronics are usually integrated on a
single chip, to reduce parasitic capacitance.
Micromechanical rate gyroscope
Micromechanical angular rate sensor ADXRS401
ADXRS401
The CMOS compatibility of the fabrication process enables full integration of
the sensor with interface and signal conditioning circuitry on a single chip.
Micromechanical rate gyroscope
Micromechanical rate gyroscope
Principle of operation of mechanical gyroscope
Priciple of operation of micromechanical angular rate sensor
Rotation (green), Precession (blue) and
Nutation in obliquity (red) of the Earth
The suspensions provide appropriate elastic
stiffness and constraints such that the central
proof mass relative to the frame may only
move in the x direction sense mode while the
frame relative to the chip may only move in the
y direction drive mode.
When a particle or structure moves in a rotating
reference frame, this structure will experience a
G
G
Coriolis force
Fc = mac
where m = mass of the structure.
The corresponding Coriolis acceleration ac is
proportional to the velocity v of the moving
structure and the rotation rate Ω of the rotating
reference frame.
G
G
G
a c = 2v × Ω
v
Ωz
a
The structure is a two-fold, orthogonal springmass-damper system with stiffness ks and
resonant frequency ωr,s for the sense mode,
and stiffness kd and resonant frequency ωr,d for
the drive mode.
a
G G G
v × Ω = i v Ω sin α
If the structure is suspended by a spring with a
stiffness of k, the displacement x due to the
G
G
Coriolis force is expressed as
v
α
Ω
G
a
G F mac
= 2c
x= c =
ωr ,s
ks
ks
ωr =
k
m
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Micromechanical rate gyroscope
Micromechanical rate gyroscope
Priciple of operation of micromechanical angular rate sensor
Priciple of operation of micromechanical angular rate sensor
Displacement amplitude at the drivemode resonance frequency ωrd
y ( t ) = Qd
Fdm – drive force amplitude
Qd – quality factor of the drive mode.
Fdmω r ,d
cosω rd t
kd
x = Ks
Assuming a sinusoidal
rotation signal
Ω z (t ) = Ω zm cos ωΩ t
x ( t ) = K s Qd
×
xi (t )
The module of the second-order
mechanical transfer function of the
embedded sense accelerometer is
The velocity at resonance is
v y ( t ) = Qd
Synchronous demodulator
Fdm
sin ω rd t
kd
ac
ωr2,s
= Ks
2 vy Ωz
ω r2,s
Fdm ωr ,d Ω z (t )
cos ωrd t
ω r2,s
kd
x ( t ) = K s Qd
Fdm ωr ,d Ω zm
cos ω rd t cos ωΩ t
k d ω r2,s
x p (t )
Hd(ω)
x0 (t )
xSYNC (t ) = X 0 cosω r ,d t
x p (t ) = K sQd
xi ( t ) = K s Q d
Fdm ω r ,d Ω zm
cos ωrd t cos ωΩ t
k d ωr2,s
Fdm ω r ,d Ω zm
1
1


X 0  cosωΩ t + cos(2ω r ,d − ωΩ )t + cos(2ω r ,d + ωΩ )t 
2k d ω r2,s
2
2


xp(t) signal spcectrum
|Xp(ω)|
Hd(ω)
x0 (t )
ω
0
ωΩ
ωg
Micromechanical rate gyroscope
Micromechanical rate gyroscope
Priciple of operation of micromechanical angular rate sensor
Vibrating gyroscope topologies
a) Single spring mass with translational drive
shares the same flexure for both the drive
and sense modes
b) Dual mass spring with translational drive can
be arrangedto form tuning fork resonators to
reject translational vibration
c) Single-gimbaled mass with translational drive
d) Single-gimbaled mass with torsional drive
Single-gimbaled structures have an advantage of decoupling the drive and sense modes,
but may have poor linear acceleration
rejection and temperature performance.
a) Dual-gimbaled mass with translational drive is
employed to improve the linear acceleration
rejection and stability at the price of
increased structural complexity.
+75 °/s
-75 °/s
Measurement range = ±75 °/s
Subscript d is drive mode
Subscript s is sense mode
Micromechanical rate gyroscope
Micromechanical rate gyroscope
Vibratory Gyroscope Design
Vibratory Gyroscope Design
The real micromechanical structure of the z-axis gyroscope
Ω zm cosωΩ t
2ωr,d–ωΩ 2ωr,d 2ωr,d+ωΩ
The real micromechanical structure of ADXRS401 rate sensor
Parameters:
Qd = 45, fr,d = 15kHz, Ypp = 10µm
12
Micromechanical rate gyroscope
Applications of Bio-MEMS
Vibratory Gyroscope Design
Microfilter, micropomp
PCB layout and pin description
The process used to produce conventional
filters capable of screening micron-scale
objects results in an unacceptably broad
statistical distribution of the size of objects that
can pass. Micromachining and MEMS
technology has been used to realize
microfilters that are precisely and uniformly
machined, which greatly reduces the statistical
variation in objects that pass through.
An electrostatically driven micropump produced by
bonding multiple bulk micromachined silicon wafers
together. The bonding process creates a pumping cavity
with a deformable membrane and two oneway check
valves. The electrodes are fabricated inside a second
isolated cavity formed above the deformable pumping
membrane so that they are sealed away from the
conductive solutions being pumped.
Applications of Bio-MEMS
Microvalve & µTAS
Several different types of microvalves have been microfabricated,
including normally-open and normally-closed valves either for
controlling gasses or fluids.
In the microvalve, a small quantity of inert fluid is heated with an
integrated resistor until a phase change is induced that exerts a
tremendous force.
The ability to electrically control fluid flow in
micromachined channels (i.e., pumping and valving)
without any moving parts has enabled the realization of
complex micro total analysis systems (µTAS).
With multiple independently controlled flow channels,
complex sample preparation, mixing, and testing
procedures can be established. The electrically
controlled pumping and valving mechanism is either
electroosmotic flow or electrophoretic flow. Liquid
chromatography (i.e., a method of separating liquids
based on their different mobility in a long flow channel)
can be used to perform a precise chemical analysis in
microfabricated flow channels.
Applications of Bio-MEMS
Implantable Blood Pressure Sensors
Applications of Bio-MEMS
Surgical Microinstruments
MEMS technology can be used to add a variety of capabilities to surgical microinstruments
(e.g., microheaters, microsensors, fluid delivery, fluid extraction, feedback and control).
In the ultrasonic cutting tool fabricated by
bulk micromachining, the piezoelectric
material is attached to the cutter to resonante
the tip of the tool at ultrasonic frequencies.
Only when activated will the device easily
and rapidly cut through even tough tissues.
In the scalpel driven by a piezoelectric
microactuator the piezoelectric stepper motor
allows the position the scalpel to be precisely
controlled. By integrating an ability to measure
the stresses experienced by the scalpel during
cutting, the actual cutting force can be
quantified and controlled.
Implantable Blood Pressure Sensor
Intracranial pressure monitoring system
The intracranial pressure monitoring (ICPM) system consists of an interrogator and
subcutaneously implanted biodevice that are connected via wireless electromagnetic link.
The interrogator is an external device that provides an external power source, creates a
communication link, and controls the biodevice. The biodevice can have intracranial pressure
as well as a temperature sensor.
13
Implantable Blood Pressure Sensor
Intracranial pressure monitoring system
Implantable Blood Pressure Sensor
Communication between modules
Interrogator
The innovative approach in ICPM system is that the electromagnetic induction is used to
both power the biodevice and provide for a communication link. The advantage of the
approach is that the biodevice is hermetically sealed before implanting it in a patient,
thus making the whole procedure potentially less hazardous to the patient. The
elimination of the battery to power the biodevice, avoids the problems related to safety
hazards, battery size, power, and duration.
Implantable Blood Pressure Sensor
Communication between modules
Biodevice
The electromagnetic field created by the interrogator serves as a wireless link for powering
and communicating to the biodevice. The communication link is established by powering
electromagnetic waveform for half-duplex communication.
Modulation of the electromagnetic waveform in the interrogator and demodulation in the
biodevice establish the communication link from the interrogator to the biodevice.
Modulation of the inductive load that powers the biodevice is used to create a communication
link from the biodevice to the interrogator.
Implantable Blood Pressure Sensor
Communication between modules
The ICPM system uses a simplified, three-layer model of communication.
The communication protocol is based
on a dialogue mode of operation, in
which the biodevice carries out the
interrogator initiated commands.
Initially, there is no data link between the interrogator and the biodevice.
The application layer implements the commandresponse mode of operation and implements the
dialogue between the interrogator and biodevice.
The data link layer performs the transfer of the
blocks of data and error checking and correction.
Physical layer transmits the bits of data over the
wireless communication link by modulating and
demodulating the electromagnetic waveform.
If the interrogator is within the power transmission range, the biodevice is powered, incepts the
carrier, and enters verification dialogue.
Upon the successful verification, the interrogator and biodevice enter the application state.
Typical operations in the application state include transmission of intracranial pressure data from
the biodevice to the interrogator and recalibration of the sensor.
A natural extension for the ICPM system is to add another communication layer to provide for
the remote ICP monitoring. Apparently, remote monitoring enables the patient to stay at home,
thus reducing the cost and offering the patient friendly home environment.
The application state is followed by the termination state in which the carrier is terminated. If, at
any state, the communication fails, the interrogator terminates the carrier.
Implantable Blood Pressure Sensor
Implantable Blood Pressure Sensor
Implantable (bio-MEMS) based capacitive pressure sensor
Implantable (bio-MEMS) based capacitive pressure sensor
Contact-less powering and telemetry
application in biosensors
The contact-less powering and telemetry
concept, including the miniature square spiral
inductor/antenna
circuit
intended
for
integration with a MEMS pressure sensor.
Schematic of a capacitive pressure sensor
Schematic of miniature spiral inductor
on SOG/HR-Si wafer
The pressure sensor is of the capacitive type and is located in the annular region of the
inductor. The inductor behaves both as an inductance as well as an antenna thereby allowing
the sensor to receive as well as radiate out energy.
In the receive mode, the inductance picks up energy and charges the MEMS pressure sensor
diaphragm capacitance.
In the transmit mode, the above inductance and capacitance form a parallel resonant circuit
and radiate energy through the inductor which now behaves as a planar spiral antenna.
14
Implantable Blood Pressure Sensor
Implantable (bio-MEMS) based capacitive pressure sensor
Measured resonance frequency versus
chip capacitor capacitance
(a)
(b)
Measured received relative signal
strength as a function of frequency.
Pick-up antenna at a height of 5 cm.
Pick-up antenna at a height of 10 cm.
For a fixed L = 153 nH and capacitance in
the range of 0.3 to 4.0 pF, the resonance
frequency falls within 670 to 230 MHz.
15