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Transcript
San José State University
Department of Mechanical and Aerospace Engineering
ME 106
Fudamentals of
Mechatronics
Course Reader
Spring, 2011
BJ Furman
iii
TABLE OF CONTENTS
Page no.
ACKNOWLEDGMENTS .............................................................................................iv
Introduction to ME 106 .................................................................................................v
1 Analog Electronics .....................................................................................................1.0
Ohm’s Law, current, resistance, voltage .....................................................................___
Signal sources ..............................................................................................................___
Signal conditioning .....................................................................................................___
Operational amplifiers .................................................................................................___
Transistors ...................................................................................................................___
MOSFET’s ..................................................................................................................___
Controlling power .......................................................................................................___
2 Sensors and Transducers ..........................................................................................2.0
Sensor and transducer fundamentals ...........................................................................___
Position ........................................................................................................................___
Pressure .......................................................................................................................___
Acceleration ................................................................................................................___
Force and torque ..........................................................................................................___
3 Actuators ....................................................................................................................3.0
Motors .........................................................................................................................___
Piezoelectric actuators .................................................................................................___
Shape memory actuators .............................................................................................___
Drive systems ..............................................................................................................___
4 Digital Electronics......................................................................................................4.0
Basic logic functions ...................................................................................................___
Important digital logic IC’s .........................................................................................___
BJ Furman
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iv
5 Microprocessor System Fundamentals ....................................................................5.0
Coding schemes...........................................................................................................___
System layout ..............................................................................................................___
6 Programming in C for Microprocessor Control .....................................................6.0
Program structure ........................................................................................................___
Variables, arithmetic, and logic operations .................................................................___
Communicating to ports ..............................................................................................___
Functions .....................................................................................................................___
M68HC11 basics .........................................................................................................___
Appendix A: Laboratory Experiments ........................................................................A.0
Introduction to the Mechatronic Engineering Lab ......................................................___
RC filters .....................................................................................................................___
Electronic scale ...........................................................................................................___
Light controlled relay ..................................................................................................___
Electronic level ............................................................................................................___
Printer carriage motion control....................................................................................___
DC motor speed control ..............................................................................................___
Digital counter .............................................................................................................___
Introduction to C programming on the M68HC11 ......................................................___
Reading and writing to ports (AD and DA conversion) ..............................................___
Analog interfacing and stepper motor control .............................................................___
Stepper motor speed control ........................................................................................___
Appendix B: Pin-outs of Common Components .........................................................B.0
Appendix C: Additional Information on Actuators ..................................................C.0
Appendix D: Drive Components...................................................................................D.0
BJ Furman
ME 106 Reader rev. 1.0
January 6, 2011
v
Acknowledgments
The authors would like to thank the other members of the Mechatronic Curriculum
Development Team: Tai-Ran Hsu, Ji Wang, Peter Reischl, Addisu Tesfaye, and Fred Barez,
for their contribution in large and small parts in initiating, implementing, and developing the
Mechatronics curriculum stem in the Department of Mechanical and Aerospace Engineering
at San José State University.
We also acknowledge significant contributions by the Advisory Committee in their ongoing
support of the development of mechatronics at San José State University. Of special note is
Mr. Ed Muns of the Hewlett-Packard Corporation who facilitated a generous donation of HP
Test and Measurement equipment for the Mechatronic Engineering Laboratory, and Mr.
David Brown whose financial support enabled us to establish the David Brown Graduate
Fellowship in Mechatronics.
We also recognize the help of our student assistants: Joe Christman, Doug Sprock, Marvin
Lam, Mike Kearny, and Jeff Fontana in the development of the Mechatronic Engineering
Laboratory and the laboratory experiments; our administrative assistant, Dorothy Lush, and
our technicians, Lou Schallberger and Tom Ng.
Financial support from the National Science Foundation is specially acknowledged.
BJ Furman
ME 106 Reader rev. 1.0
January 6, 2011
6
Introduction
If you look around, you’ll notice that many of the devices you use in the course of a day are
mechatronic, that is, they integrate mechanical and electronic functions in a synergistic way.
In fact, it is difficult to avoid mechatronic devices! Microwave ovens, automatic teller
machines, washing and drying machines, dishwashers, cameras, camcorders, VCR’s, CD
players, automobiles… These are all mechatronic devices. And not only consumer products,
but industrial processes, such as a semiconductor fab, also are highly mechatronic in nature.
The overarching philosophy in mechatronics is that enhanced performance, flexibility, and
reliability can be obtained in a product or process through the integration of mechanics and
electronics under the control of software.
Because of the ubiquitous nature of mechatronics, the mechanical engineer must understand
the fundamentals of mechanics, electronics, and software in order to be successful in today’s
world. By and large, most undergraduate mechanical engineering programs do a good job
teaching the fundamentals of mechanics, but fall short in giving students the necessary
understanding of electronics, computer interfacing, and how these are integrated in
mechatronic systems. This text attempts to give the student enough of a foundation in analog
and digital electronics, sensors and transducers, actuators, and microprocessor interfacing, so
he or she can begin to function effectively as an engineer in an increasingly mechatronic
world.
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7
1 Analog Electronics
What is voltage? What is current? What is resistance? Technically speaking, voltage is the
electric potential difference between two points in a circuit, current is the flow of charge in a
conductor, and resistance is determined by dividing the voltage between two points on a
conductor by the current flowing through the conductor. Operationally speaking, we can liken
voltage to pressure in hydraulic systems, current to fluid flow rate, and resistance to a flow
restriction, such as an orifice.
Ohm’s law states a relationship between voltage, V, current, I, and resistance, R, in
electrical systems:
V=I•R
(1.1)
If any two of the three quantities are known, the third may be determined. This simple
relationship is fundamental and broadly applicable in analyzing any electronic circuit. For
example, if V = 10 V and R = 100 Ω, what is I through the resistor?
Figure 1.1
Ohm’s law example
Resistors in Parallel
When resistors in a circuit are arranged in parallel, the total resistance of the circuit is
always less than any of the individual resistors, because there are additional paths for current
to flow through. Figure 1.2 shows a circuit with resistors arranged in parallel. The equivalent
resistance of this arrangement is,
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Req = 1/(1/R1 + …
(1.2)
Resistors in parallel
Figure 1.2
Resistors in parallel. The total resistance of the circuit is always less than any
of the individual resistors, because there are additional paths for current to
flow through.
Resistors in Series
When resistors in a circuit are arranged in series, the total resistance of the circuit is always
greater than any of the individual resistors. Figure 1.3 shows a circuit with resistors arranged
in series.
Figure 1.3 shows a circuit with resistors arranged in parallel. The equivalent resistance of
this arrangement is,
Req = R1 + R2 + … + Rn
(1.3)
Resistors in Series
Figure 1.3
Resistors in series. The total resistance of the circuit is always greater than any
of the individual resistors.
The Voltage Divider
Suppose a voltage source and two resistors are arranged as shown in Figure 1.4. What is the
output voltage, Vout? If you apply Ohm’s law, you will find out that
Vout = Vin[R2 /(R1 +R2)]
BJ Furman
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Voltage divider circuit
Figure 1.4
The voltage divider circuit.
This circuit is called a voltage divider, because a fraction of the source voltage appears across
R2. In fact, the larger the resistance of R2, the larger is the share of the input voltage across it.
Suppose R1 = R2 , what is Vout? What if R1 = 10R2, what is Vout? What if R1 = 0.1R2, what
is Vout?
The Current Divider
Suppose a current source and two resistors are arranged as shown in Figure 1.5. The input
current is divided between the two resistors, and the path of least resistance gets the largest
current. Again, using Ohm’s law, and noting that the voltage across both resistors is the same,
Iout = Iin[R1 /(R1 +R2)]
(1.5)
current divider circuit
Figure 1.5
The current divider circuit.
What about Thevenins’ Theorem, Kirchhoff’s voltage and current laws???
Believe it or not, armed with Ohm’s law and the concepts of voltage and current division,
you are ready to tackle most of the electrical analysis you’ll need to do in any mechatronics
project. Of course there is much more to learn about in terms of specific components and
their behavior, but if you can rigorously apply these fundamental concepts, you will do well.
BJ Furman
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10
Practice Problem - The Wheatstone Bridge
The arrangement of resistors in the circuit shown in Figure 1.6 is called a Wheatstone Bridge.
It’s a very useful circuit as you will find out later. Find Vout in terms of Vin and the resistors.
(Hint: do you see any voltage dividers in this circuit?)
Wheatstone bridge circuit
Figure 1.6
The Wheatstone Bridge circuit.
Signal Sources
Mechatronic systems use sensors to determine the state of the system so appropriate action
can be taken at the right time to accomplish the desired function. For example, the airbag
deployment system in an automobile uses an accelerometer to measure the rate of change of
the velocity of the vehicle. If the decceleration is above a prescribed level, say from a
collision, the system inflates the airbags, and hopefully prevents serious injury of the
passengers inside. The voltage output from the accelerometer represents the acceleration of
the vehicle to the controller, which decides if it is large enough to inflate the airbags. We say
the acclerometer functions as a signal source. A signal source is differentiated from other
electrical sources, such as the car’s battery for example, in that for signal sources, we are
primarily interested in the information carried by the signal or voltage they output. Most
signal sources output relatively low-level voltages, which in turn need to be conditioned to be
of use to the system they are connected to. It is important therefore to understand the
limitation of signal sources, so that we can handle them properly.
Ideally, a sensor, such as the accelerometer, can be modeled as a dependent voltage source,
that is, a voltage source whose output depends on an input. As shown in Figure 1.7, the value
of the voltage output from the acclerometer depends on the acceleration, for example 10
mV/g (where g is the accleration of gravity, about 9.81 m/s2). The value 10 mV/g is called
the sensitivity of the accelerometer.
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In practice, however, a signal source will have limitations including low level signals, a finite
value of output impedance (opposition to current flow), noise, non-linear behavior, and offset
such as shown in Figure 1.8.
Ideal signal source model
Also include mV - g plot showing
input/output sensitivity
Figure 1.7
Model of an accelerometer as an ideal signal source. The source is a
dependent voltage source with a sensitivity of 10 mV/g
Practical signal source
model. Show offset,
noise, and saturation.
Figure 1.8
A practical signal source model for the accelerometer. The practical model
includes a noise source, finite output impedance, non-linearity, and offset.
Considering the acclelerometer, even at a 10 g input, the output will only be 0.1 V. In order to
fire the air bag, the detonation circuit may need a 5 V pulse, so the output would have to be
amplified 50 times.
A finite impedance means that there will be a limit to the amount of current that the source
can supply. For sensors such as the acclerometer, this current could be on the order of picoamps (10-12 amps)! Consider the Thevenin equivalent circuit for an accelerometer, such as
shown in Figure 1.9. The output impedance of the accelerometer is 10 MΩ. Suppose a
voltage measurement device with an input impedance, Rin, is connected at the output
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terminals of the accelerometer. If Rin is, say 10 kΩ, what will be the voltage measured? We
essentially have a voltage divider, with
Vout=Vin[104/107 + 104] = 0.001Vin
(1.6)
We will only measure a very small fraction of Vin if we record anything at all! The voltage
device has loaded the accelerometer. We will discuss how to handle impedance mismatches
such as this shortly.
Equivalent circuit for
accelerometer.
Figure 1.9
Equivalent circuit model for an accelerometer and voltage measurement
device. It is important to the effects of output and input impedance on the
level of the signal.
A sensitivity such as 10 mV/g begs to imply a linear relation between accleration and voltage
output, but there will always be some variation from exactly linear behavior in any sensor
with a nominally linear output relationship. We’ll take a closer look at linearity in the chapter
on sensors.
Power supply fluctuations, radiated electromagnetic waves from surrounding devices, etc.,
contribute to noise in the practical source. It’s obviously important to minimize noise, so that
the signal of interest can be discriminated above the noise. Filtering the signal is often what
can be done to attenuate noise. Finally, the accelerometer should nominally provide 0 V
output at 0 g input, but there may be some constant or time varying shift or offset of the
input-output curve from passing through a zero intercept.
Thus, a signal source can be modeled as a dependent voltage source with practical
limitations. Understanding the concepts of output and input impedance are important if a
signal source to avoid loading.
Practice Problem - Thermistor circuit
A thermistor is a device whose resistance changes with temperature. Figure 1.10 shows a
typical temperature vs. resistance graph for a thermistor. Consider the circuit using a
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thermistor shown in Figure 1.11. Sketch the output voltage, Vo of the circuit. At 0 ˚C, what is
the output impedance, looking into the terminals of Vo?
Resistance vs. temperature for a
thermistor
Figure 1.10 Resistance vs. temperature for a typical thermistor
Thermistor circuit
Figure 1.11 Thermistor circuit.
Dealing With Limitations of Practical Signal Sources
The limitation of low voltage level can be addressed through amplification.
Summary Concepts
Practice Problems
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2 Sensors and Transducers
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3 Actuators
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4 Digital Electronics
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5 Microcontroller Fundamentals
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6 Programming in C for Microcontrollers
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A-1
Appendix A: Laboratory Experiments
This appendix compiles the guidelines for the laboratory experiments in ME 106.
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A-2
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B-1
Appendix B: Excerpts From Selected Data Sheets
This appendix compiles excerpts from selected data sheets used in ME 106.
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B-2
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C-1
Appendix C: Motion Control Mechanics
This appendix compiles information relating to motor sizing and motion control mechanics
used in ME 106
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C-2
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D-1
Appendix D: Arduino-Related Information
This appendix compiles Arduino-related information used in ME 106
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D-2
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E-1
Appendix E: Lecture Notes
This appendix compiles the lecture notes used in ME 106
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