Lecture 1 - Department of Mechanical Engineering

Transcription

Fluid Power Controls Laboratory (Copyright – Perry Li, 2004-2015)
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Lecture 1
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Introductions
Course overview / Syllabus
Fluid Power Introduction
Fluid Power Fundamentals
Least Squares Fitting
M..E., University of Minnesota (updated 12.2013)
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ME4232 Course Overview
Instructor:
Prof. Perry Li
Offices: ME309
Email: [email protected]
Tel: 612-626-7815
Format:
• One 110 minutes lecture per week
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Office Hour: M: 11-12 ??
Or: Find me in office (ME309)
Or: Email me questions
Or: make appointment
Friday 11:15am-1:10 pm.
(one or two industry speakers)
Two 2 hour lab sessions
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Read handouts and do pre-labs before hand
Typewritten lab report
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• TAs:
• Sangyoon Lee (PhD candidate, hydraulic transformers)
• Mohsen Saadat (PhD candidate, compressed air energy storage)
• Everett Wentzel (PhD, fluid flow)
• Introducing your neighbors: (2 + 8 mins)
• Groups of 2
• Name;
• Where they are from;
• One interesting thing about him/her
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Objectives
• Introduce fluid power component, circuits, and systems
• Functions, modeling and analysis
• Provide hands on experience in designing, analyzing and
implementing control systems for real and physical systems;
• Consolidate concepts in Systems Dynamics/Control (ME3281)
• modeling, control and other dynamical systems
Course syllabus, lab assignments, notes, etc. on course webpage (subject
to change without notice)
http://www.me.umn.edu/courses/me4232/
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Expected Outcome
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Familiarity with common hydraulic components, their use, symbols, and
mathematical models
Ability to formulate / analyze math models for simple hydraulic circuits
Comfortable with commercial hydraulic catalogs
Ability to identify single input single output (SISO) dynamical systems
Ability to design, analyze and implement simple control systems
Appreciation of advantages and disadvantages of various types of controllers
Ability to relate control systems analysis with actual performance
Intuitive and mathematical appreciation of dynamical system concepts (e.g.
stability, instability, resonance)
Appreciation of un-modeled real world effects
Become very familiar with using Matlab for analysis and plotting.
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Learning Activities
• Lab assignments (experiments and lab reports) [60%]
• Hydraulic work bench [1/2 semester]
Labs 60%
• Electro-hydraulic control setup [1/2 semester]
• Experiments and analysis of real physical systems Exam 30%
Participation 10 %
• Understanding from models and analysis
• Ask questions! Design your own extra experiments
• Assumptions versus real world unmodeled effects
• Simulink modeling of hydraulic components
• Work in groups
Physical
Diagram
Conceptual
model
Mathematical
analysis
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Participation
• Active learning in lab and in lecture
• Doing and experimenting
• Teaching = learning
• Engagement – ask/answer questions/discussion
• Attendance to lectures
• Download / print out slides ahead of time
• Take notes
• Lab attendance policy (tentative):
• Pre-lab due first 5 mins of session (else no points)
• Get approval (1 week in advanced) if you cannot make a lab due to
reasons such as conflicts with job interviews [should be rare!]
• Coordinate w/ TAs to attend other sessions
• If not possible, make-up during slack sessions.
• Unexcused absence or 30 mins late for session = zero points for lab report
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Course Conduct
1. Observe safety at all times
2. Learning (preliminary data) before data taking
3. Lab reports should be type written, succinct, but self-contained. Page
limits are sometimes imposed. They should contain your observations
(use well labeled graphs!) as well as explanations, and if appropriate,
mathematical analysis.
4. The exercises on the lab sheets are base line exercises. You are
encouraged to formulate additional questions and to test them using
the lab setup.
How much you learn depends on how willing you are to ask and answer
additional questions.
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Course Conduct
5. Cheating will be properly dealt with. Your lab reports and your
modeling exercises should be your own work, and reflect your
understanding of the problem. No copying allowed. However, you are
encouraged to work together to figure things out..
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Pre-labs and Lab Report
• Pre-labs are due at beginning of lab session (~10% of grade)
• Lab reports are due 1 week after the lab is completed
• Turn in at the beginning of session (1st 5 mins)
• Grades for late report: normal grade * 0.8n where n = # of weeks late
• Opportunity to resubmit report for lab 2.
Lab report guideline:
• http://www.me.umn.edu/courses/me4232/lab_handouts.shtml
I-M-R-D format:
- Introduction: focus on question / hypothesis for lab
- Method: Brief explanation how the question can be answered
- Results: - use graph, curve fitting, analysis ….. etc.
- Discussion: what results mean, what you have learned, ….. etc.
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What is fluid power?
• Uses “fluid” as a medium to transmit
power
• liquid = hydraulics
• gas = pneumatics
1N
Power source
(pump)
Transmission
(hoses, pipes
carrying fluid)
Control units
(valves)
100 N
weight
Actuator
(cylinder,
hydraulic
motor)
Bramah press (1795)
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http://www.nfpa.com/education/LearningResources-TVPrograms.aspx
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Metal Forging
Injection Molding Machines
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UMn Teleoperated Backhoe
UMn Human Power
Amplifier
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UMN Hydraulic Hybrid Vehicle
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Hydro-mechanical transmission with regeneration
Composite
Accumulator
Pump/Motor Units
Belt Drive
Diesel IC
Engine
Chain Wheel
Drive
Planetary
Differentials
Transmission
Clutch
Wheel
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Hydraulic Wind Turbine
Compressed Air Energy Storage
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Opportunities in Research Lab (F 2015)
• Hydraulic hybrid vehicle project
• Compressed air energy storage
• Human interactive control
• Summer “Research For Undergraduates Experiences” (REU)
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Local Perspectives
Local fluid power companies
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Components:
• Eaton Corporation, Eden Prairie
• Danfoss, Plymouth
• Continental Hydraulics, Salvage
• Parker Hannifin, Golden Valley
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Systems:
• MTS Systems, Eden Prairie
• Toro Company, Bloomington
Center for Compact and
Efficient Fluid Power
@ University of Minnesota
• Caterpillar Paving
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a NSF Funded Engineering Research Center
http://www.ccefp.org/
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Where Fluid Power is Used
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Automotive
Aerospace
Construction industry
Lawn and garden
Agriculture
Robotics
• Rescue
• Biomedical
• Mechanical testing
• components / materials
• structure
• Manufacturing
• steel
• injection molding
50% of ALL
industrial
products have
critical fluid
power components!
Nearly ALL
manufacturing
plants rely on
fluid power !
US$45 billions (2006) of
worldwide sales of
components alone!
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What is fluid power?
• Uses “fluid” as a medium to transmit
power
• liquid = hydraulics
• gas = pneumatics
1N
Power source
(pump)
Transmission
(hoses, pipes
carrying fluid)
Control units
(valves)
100 N
weight
Actuator
(cylinder,
hydraulic
motor)
Bramah press (1795)
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Advantages of Fluid Power
• Large force capacity
• 3000 psi *1 in2 = 3000 lb-f = 13kN
• Force = Pressure * area
• Pressure limited by material strength
• High power density
• can deliver large power using a small
package (< 1.0 lb/Hp)
• Force and speed can be controlled
• High efficiency (can be 90+%, depends)
• Possibility of precise control
Much better
than electro-mechanical
(electrical motors)
Force = B * i * l
B = magnetic flux
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Limited by size of
iron core or rare
earth magnets
• hydraulic fluid has high bulk modulus
• Flexibility (hoses can go around corner)
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Advantage of Fluid Power –
Torque/Force/Power density
• Both motors generate 1.6kNm (1200 ft-lb) at 400 rpm !
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Electric Motor (Moog 416)
Power density = 0.15 Hp/lb
Torque density = 3.7 lb-in/lb
Weight = 33lbs, Power = 5Hp, Torque = 123 lb-in
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Moog 416 Servo Motor
Volume = 19cm X 19cm X 20cm = 8 liters
Power density = 0.01 HP/in3
Torque density = 0.25lb-in/in3
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Sauer-Danfoss Orbital Motor
DS-36 Orbital Motor
Torque: 50Nm (500lb-in)
Power: 5.9kW (7.8Hp)
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Volume: 9 x 9 x 12 cm3
= 1 liter = 61 in3
Weight = 5.4 kg (12lb)
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Power density: 1.1kW/kg [0.65 Hp/lb]
Torque density: 9.26Nm/kg [42 lb-in/lb]
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Power (volume) density: 0.127Hp/in3
Torque (volume) density: 0.82lb-in/in3
120mm
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91mm
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Disadvantages of fluid power
• Leaks!
• Fire hazard (flash point approx. 220 F)
• Difficulty in precise control
Water hydraulics
• inherently nonlinear
• fluid compressibility
• control accuracy and efficiency
• Electrohydraulics
• Advanced control
• Prone to contamination (reliability)
• Efficiency (compared to purely mechanical)
• Poor efficiency using current control methods
• Noise
New
control
principles
noise cancellation, better hose design
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Challenges
• More accurate control
• Energy efficiency
• Noise and vibration
• Compact energy source
• Compact energy storage
• Leak-free
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Fluid Power Fundamental
Outline:
• Pressure  force or torque
• Flow  velocity
• Components (valves, actuators, pump/motors ….) relate them ……
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FP Fundamental: Pascal’s Law
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Pressure
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Force perpendicular to a surface to
area A is the same and is given by:
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F=P*A
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for all orientations for the surface
P = force / area
For a fluid at rest, the pressure is
the same in all directions
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Shearing Force
• Shearing force is tangential to a surface
• A fluid cannot produce any shearing unless it is in motion
F=0
Fluid at rest
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Application of Pascal’s Law
• Using Newton’s law for the control volume in the horizontal direction:
• Assume that fluid is stationary
• Total horizontal force =
Newton’s law !
P1 = P2
hose
F=0
Force = P1*A
Force = P2*A
P1
Area = A
P2
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Vertical direction?
• Fluid is at rest.
• Is
P 1 = P2 ?
P2
• Total downward vertical force
0 = -P1 A + P2 A + mass * g
h
since mass = density * h * A
P1 = P2 + density * g * h
P1
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How important is gravity?
• Fluid density = 900kg/m3
• for 1 meter: density * g = 9000 N / m2 = 9 kPa
• In Psi: 1000psi = 7000 kPa = 70 bar
• So, influence of gravity is
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9kPa / meter
0.09 bar / meter
1.3 psi / meter
0.4 psi / foot
• Typical hydraulic operating pressure = 100-5000psi, gravity is not
important.
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The Importance of Units
• Fluid power industry in the U.S. uses English units
• pressure - psi
• volume - gallons
• power - hp
• Fluid power industry outside the U.S. uses S.I. units:
• pressure - Pa = N/m2
(1 psi = 6895 Pa)
• volume - m3 = 1000 litres
(1 gallon = 3.8 litres)
• power - Watts
(1 Hp = 746 W)
• Conversions •
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Calculation in S.I., report in English if necessary
Appendix in textbook
Megaconverter (http://www.megaconverter.com)
Google (“what is 1 psi in Pa”)
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Units Blunder Sent Craft Into Martian Atmosphere:
NASA By Daniel Sorid, Staff Writer
posted: 05:43 pm ET
30 September 1999
NASA (SI)
versus
Lockheed Martin
(English)
A team of Lockheed Martin engineers sent NASA key maneuvering data for the $125
million Mars Climate Orbiter in non-standard units, probably since the craft was launched in
1998, according to a NASA official trying to explain the loss of the craft.
Miscalculations due to the use of English units instead of metric units apparently sent the
craft slowly off course -- 60 miles in all -- leading it on a suicide course through the Martian
atmosphere. But the space agency was quick to deflect blame from Lockheed Martin, which
had been controlling the day-to-day operations of the craft, saying that NASA should have
had safeguards to catch the error.
He did say, however, that NASA operates using metric units, "and has for a long time."
House Science Committee Chairman F. James Sensenbrenner, Jr., sounding stunned,
released a two-word statement after hearing the news about the miscommunication: "I'm
speechless.“ The origin of the mistake apparently dates back to the very first maneuverings
of the craft, which was launched on December 11, 1998.
A Lockheed Martin spokesperson confirmed that their engineers had been sending data in
English units. When asked whether the company was aware that NASA had been expecting
metric units, the spokesperson said, "Obviously not.“ "I don't think this is a matter of
Lockheed Martin making a mistake," the spokesperson added.
Thrusters used to help point the spacecraft had, over the course of months, been fired
incorrectly because data used to control the wheels were calculated in incorrect units. The
problem did not affect the craft's propulsion system, Gavin said.
Lockheed Martin, which was performing the calculations, was sending thruster data in
English units -- in this case, pounds -- while NASA's navigation team was expecting metric
units, Newtons. One pound is equal to 4.48 Newtons
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Two Most important variables in fluid power
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FP fundamental: Continuity Equation
• Mass is not destroyed
• Example: T - junction
 
dM CV d
   ( x, y, z )dxdydz   v  dA
dt
dt CV
CV
• If fluid is incompressible, then
• volume is conserved
• Q1+Q2+Q3=0
Q2
Q1
• What if fluid is compressible?
• What if control volume is changing?
Q3
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Continuity applied to a simple actuator
?????
v
• Flow is incompressible
A1
Vol2(t)
Vol1(t)
A2
Q1
t
v
Q=constant
Q2
(In/)Compressible
stopper!
v
v
Q1 or Q2
Q2 = constant???
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Momentum / Force Balance
• Newton’s law!
Friction: F2
Vol1(t)
A1
Q1
P1
v
Vol2(t)
A2
Load F1
Q2
P2
• What is the relationship between F1, F2, P1, P2 ?
• What assumptions are being made?

Lecture 1 - Department of Mechanical Engineering

Transcription

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