mechatronic system design

1Mechatronic systems

Introduction to mechatronics Sensors and actuators used in mechatronics systems Applications of MEMS

Mechatronic systems

What is mechatronics?

mechanics 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.

Key Elements of Mechatronics

Historical Development Definition of Mechatronic SystemsA 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.

2Definition of Mechatronic SystemsGeneral 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 systemsThe 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

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 MEMSare 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.

The Automobile as a Mechatronic System

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 for VariousMeasurement 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

Type of Sensors with respect toprinciple of operation: Resistive Capacitive Inductive Ultrasonic Piezoelectric Piezoresistive Light ...


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.

3Classification of sensorsResistive and capacitive sensors

Resistive sensors

Capacitive sensors

Measurement objectives: position/displacement angle

Measurement objectives: position/displacement force and pressure


The LVDT (Linear/Rotational Voltage Differential Transformer) is a tube with a plunger, the displacement of the plunger being thevariable 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.

Inductive sensors

Measurement objectives: position/displacement angle


Principle of operation of LVDT

Inductive sensors

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.


Principle of operation of LVDT

Inductive 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.

Inductive sensors

Measurement objectives: detection of a moving part, indexing of rotational or

translational motion


Ultrasonic sensors use the time-of-flight of a pulse of ultrasonic sound through air or liquid to measure distance.

Ultrasonic sensors

Measurement objectives: distance depth

4Classification of sensors

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.

The Ultrasonic Flowmeter


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.

Piezoelectric and piezoresistive sensors


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.

Tensometers

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 sensorsSmart 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

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.

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.


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 relaysaccept 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.

5Classification 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.


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.


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.

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 actuatorsHydraulic 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.

Classification of actuatorsIn 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.


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.

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.

6Classification of actuatorsUnlike 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 actuatorsShape 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 5080 deg. C), the phase changes to austenitic phase. Here the alloy resumes the shape that it formally had at the higher temperature.

Typical Wing and Flap

Hinge less shape memory alloy Flap

Electromechanical Actuator

Applications of MEMS

Measurements of acceleration with micromechanical and convective accelerometers

Construction and principle of operation of micromechanical rate gyroscope

Applications of BioMEMS (Implantable Blood Pressure Sensor)

Types of accelerometers

Applications of accelerometers

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)

Micromechanical accelerometerADXL202 accelerometer

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)

7Micromechanical accelerometer

Differential capacitive sensor

A Simplified Diagram of the ADXL202 Sensor at Rest.

CS1 = CS2

The ADXL202 Sensor Momentarily Responding to an Externally Applied Acceleration

CS1 < CS2

Principle of operation

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.

Micromechanical accelerometer


The actual structure of the sensor consists of 46 unit cells and a common beam.



Functional Block Diagram



( ) tUdxtu COUT cos00

=

( ) tUtu Ccos01 =( ) tUtu Ccos02 =

00 == OUTvx

d0 rest position between platesx displacement of central plate from rest position

ttVdXvtXx CSOUTS coscoscos 00

00 ==




Synchronous demodulator

Hd() ( )tu0( )tui )(tup( )tuSYNC

0 S g 2CS 2C 2C+S

( ) ( ) ( )

+++= tttUdXtu SCSCSp 2cos2

12cos21cos

220

0

0

up(t) signal spectrum

( ) ( )thtUdXtu dSo = cos2

20

0

0

( ) ttUdXtu CSi coscos00

0 =( ) tUtu CSYNC cos0=

|Up()|Hd()



YXFILTg CR ,

1=

Principle of operationSetting the Bandwidth Using CX and CY

YXFILTg CRf

,21

=

8Micromechanical accelerometerPrinciple of operation

Direct Conversion Modulator

[ ]=M

RT SET1252

Duty Cycle Decoding:0 g = 50% Duty CycleScale factor is 12.5% Duty Cycle Change per gA(g) = (T1/T2 0.5)/12.5%

DCM modulator circuit

tuPWLu

prU

Waveforms

K

Upr1 > Upr2T1(uPWL1) > T1(uPWL2)

tu

1PWLu

1prU

2PWLu

2prU

2T

)( 11 PWLuT

)( 21 PWLuT


Functional Block Diagram of ADXL202 sensor


Micromechanical accelerometerUsing 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).

Micromechanical accelerometerUsing the ADXL202 Duty Cycle Output

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, animproved 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 fallingedges of the Y output (Tc and Td) are recorded.

By definition:T1x = Tb Ta = Tb (if the counter is zero at Ta)T1y = Td TcT2x = 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 accelerometerCalibrating 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 turn-on 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 accelerometers 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 +1gLet 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%/gOffset (0g point) = B + [A B]/2g = 43.5%

Micromechanical accelerometerCalibrating the ADXL202 sensor

Calibration algorithm in C:mesure_x_y();//set initial valuesxmin = 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 scalefor one axis equals:

Sensitivity = [max min]/2gOffset = min + [max min]/2g

9Micromechanical accelerometerUsing 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 earths surface.

When the accelerometer is oriented so both its X and Y axes are parallel to the earths 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:

Pitch = ASIN (Ax/1g)Roll = ASIN (Ay/1g)

Convective accelerometerConvection refers to the movement of molecules within liquids or gases.

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 fluidmovement. 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.

Convective accelerometerMXA2500A accelerometer

The MEMSIC accelerometers are a complete dualaxis motion measurementsystem 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 accelerometerPriciple of operation of convective accelerometer

MXA2500A


MXA2500A

ax = 0 Utp1 = Utp2 Utp1 - Utp2 = 0


MXA2500A

ax > 0 Utp1 > Utp2 Utp1 - Utp2 > 0 i Utp1 - Utp2 ax

10


ax > 0 Utp1 > Utp2 Utp1 - Utp2 > 0 i Utp1 - Utp2 ax

MXA2500A

Convective accelerometerPriciple of operation of MXA2500A accelerometer

x

y

Functional block diagram

Measurement range:+/-1gSensitivity:500mV/g

FEATURES:

Resolution better than 2 milli-g

50,000 g shock survival rating

30 Hz bandwidth expandable to >160 Hz

2.70V to 5.25V single supply operation

Convective accelerometer

Functional block diagram

Priciple of operation of MXA2020A accelerometer

Measurement range:+/-1gSensitivity: 20%/g

x

y

Duty Cycle output

Duty Cycle Decoding:0 g = 50% Duty CycleScale factor is 20% Duty Cycle Change per gA(g) = (T1/T2 0.5) / 20%

Convective accelerometerThermal Accelerometer Sensitivity

Convective accelerometerThe real micromechanical structure of MXD2020A accelerometer

Mechanical gyroscopeConstruction 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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GyroscopeApplications of gyroscopes

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

Gyroscopes are devices which are usedto measure angular rotation rate.

Generations of gyroscopes

a) 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.

b) 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.

c) 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 gyroscopeMicromechanical angular rate sensor 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

ADXRS401

Micromechanical rate gyroscopePrinciple of operation of mechanical gyroscope

= GGG vac 2

When a particle or structure moves in a rotating reference frame, this structure will experience aCoriolis force

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 of the rotating reference frame.

sin= viv GGGa

v

Rotation (green), Precession (blue) andNutation in obliquity (red) of the Earth

cc amFGG =

Micromechanical rate gyroscopePriciple of operation of micromechanical angular rate sensor

v

az

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.

The structure is a two-fold, orthogonal spring-mass-damper system with stiffness ks and resonant frequency r,s for the sense mode, and stiffness kd and resonant frequency r,d for the drive mode.

If the structure is suspended by a spring with a stiffness of k, the displacement x due to the Coriolis force is expressed as

2,sr

c

s

c

s

c akam

kFx

GGGG ===mk

r =

12


Fdm drive force amplitudeQd quality factor of the drive mode.

tkFQty rdd

dmd sin)( =Displacement amplitude at the drive-mode resonance frequency rd

tk

FQtv rd

d

drdmdy cos)( ,=

The velocity at resonance is

2,

2,

2

sr

zys

sr

cs

vK

aKx

==

The module of the second-order mechanical transfer function of the embedded sense accelerometer is

( )t

tkFQKtx rd

sr

zdr

d

dmds

cos)( 2

,

, =( ) tt zmz = cos

ttkFQKtx rd

sr

zmdr

d

dmds

=

coscos)( 2,

,

Assuming a sinusoidal rotation signal


Synchronous demodulator

Hd() ( )tx0( )txi )(txp

0 g 2r,d 2r,d 2r,d+

( ) ( ) ( ) +++= tttXk

FQKtx drdrsr

zmdr

d

dmdsp

,,02

,

, 2cos212cos

21cos

2

xp(t) signal spcectrum

( ) tXtx drSYNC ,0 cos=

|Xp()|Hd()

Priciple of operation of micromechanical angular rate sensor

ttkFQKtx rd

sr

zmdr

d

dmdsi

=

coscos)( 2,

,

( )tx0 tzm cos


Measurement range = 75 /s

-75 /s

+75 /s

Micromechanical rate gyroscopeVibrating 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 drived) Single-gimbaled mass with torsional drive

Single-gimbaled structures have an advanta-ge 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.

Subscript d is drive modeSubscript s is sense mode

Micromechanical rate gyroscopeVibratory Gyroscope Design

The real micromechanical structure of the z-axis gyroscope

Micromechanical rate gyroscopeVibratory Gyroscope Design

The real micromechanical structure of ADXRS401 rate sensor

Parameters:Qd = 45, fr,d = 15kHz, Ypp = 10m

13


PCB layout and pin description

Vibratory Gyroscope Design

Applications of Bio-MEMSMicrofilter, micropomp

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-MEMSMicrovalve & TAS

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 inmicromachined channels (i.e., pumping and valving)without any moving parts has enabled the realization of complex micro total analysis systems (TAS).With multiple independently controlled flow channels,complex sample preparation, mixing, and testingprocedures can be established. The electricallycontrolled pumping and valving mechanism is eitherelectroosmotic flow or electrophoretic flow. Liquidchromatography (i.e., a method of separating liquidsbased 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-MEMSSurgical Microinstruments

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.

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).

Applications of Bio-MEMSImplantable Blood Pressure Sensors

Implantable Blood Pressure SensorIntracranial pressure monitoring system

The intracranial pressure monitoring (ICPM) system consists of an interrogator andsubcutaneously 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.

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Implantable Blood Pressure SensorIntracranial pressure monitoring system

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 SensorCommunication between modules

Interrogator 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.


Initially, there is no data link between the interrogator and the biodevice.

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.

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.

The communication protocol is based on a dialogue mode of operation, in which the biodevice carries out the interrogator initiated commands.


The application layer implements the command-response 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.

The ICPM system uses a simplified, three-layer model of communication.

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.

Implantable Blood Pressure SensorImplantable (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 miniature spiral inductor on SOG/HR-Si wafer

Schematic of a capacitive pressure sensor

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.

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Measured received relative signal strength as a function of frequency.

(a) Pick-up antenna at a height of 5 cm.(b) Pick-up antenna at a height of 10 cm.

Measured resonance frequency versus chip capacitor capacitance

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.

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