senior-mechanical-engineering-laboratory-at-clemson-university-experiments-learning-objectives-and-assessment

2006-1012: SENIOR MECHANICAL ENGINEERING LABORATORY ATCLEMSON UNIVERSITY - EXPERIMENTS, LEARNING OBJECTIVES, AND ASSESSMENT John Chastain, Clemson University Harvin Smith, Clemson Univer

2006-1012: SENIOR MECHANICAL ENGINEERING LABORATORY AT

CLEMSON UNIVERSITY - EXPERIMENTS, LEARNING OBJECTIVES, AND

ASSESSMENT

John Chastain, Clemson University

Harvin Smith, Clemson University

Mason Morehead, Clemson University

David Moline, Clemson University

John Wagner, Clemson University

© American Society for Engineering Education, 2006

Senior Mechanical Engineering Laboratory at Clemson University – Experiments, Learning Objectives, and Assessment

Abstract

The senior undergraduate laboratory in the Department of Mechanical Engineering at Clemson

University is the fourth and final course in the laboratory sequence In this one hour course,

engineering principles are reinforced through open ended, student conducted, multifaceted

mechanical and thermal/fluid system experiments The students work in a collaborative manner

to develop mathematical models, create test plans, apply measurement techniques, perform data

analysis, and write comprehensive technical reports In this paper, an overview of the three

experimental systems and accompanying student learning objectives will be presented The first

experiment features the modeling, testing, and analysis of a single degree-of-freedom system

subject to excitation from a rotating unbalanced mass The student teams are tasked to

analytically and experimentally investigate the system and design a dynamic vibration absorber

In the second experiment, microprocessor programming and control is explored through software

kernel creation and stepper motors A vertical positioning system with human/machine interface,

representative of a passenger elevator with drive motor and operator panel, is created using a

scale bench top platform The third experiment allows students to characterize and regulate the

thermal behavior in electronic equipment through the application of thermistors, fans, and heat

sinks One common thread to all experiments is the close collaboration among student team

members Finally, to improve the overall course quality, a supplemental assessment tool has been

introduced to gather student feedback regarding the experiments

1 Introduction

The senior laboratory in the Department of Mechanical Engineering at Clemson University (ME

424: Mechanical Engineering Laboratory IV) presents students with an opportunity to integrate

their course work and laboratory experiences together in the pursuit of open ended experiments

The course’s catalog description states “Mechanical engineering principles and phenomena are

reinforced through open ended, student designed and conducted experiments The laboratory

experiments require utilization of measurement techniques, data analysis, and report writing.”

The previous three mechanical engineering laboratories are ME 221, ME 322, and ME 323

which are described in the undergraduate catalog as follows:

ME 221: Mechanical Engineering Laboratory I 1(0,3) Discovery of mechanical

engineering principles and phenomena Introduction to laboratory safety practices,

instrumentation, calibration techniques, data analysis, and report writing

ME 322: Mechanical Engineering Laboratory II 2(1,3) Mechanical engineering

principles and phenomena are reinforced through student conducted experiments

Presentation of fundamentals of instrumentation, calibration techniques, data analysis,

and report writing in the context of laboratory experiments P

ME 323: Mechanical Engineering Laboratory III 2(1,3) Continuation of ME 322

Mechanical engineering principles and phenomena will be reinforced through student

conducted experiments Presentation of fundamentals of instrumentation, calibration

techniques, data analysis, and report writing in the context of laboratory experiments

A brief literature review will now be presented on mechanical engineering laboratories Schmaltz

et al.1 reported on the senior mechanical engineering capstone laboratory at Western Kentucky

University that focuses on students undertaking mechanical, materials, and thermal/fluid

experiments Important activities are the definition of requirements, design of methods and

equipment, execution of test plan, analysis of results, and reporting To ensure topical coverage,

a design of experiments plan was created to implement, assess, and adjust the laboratory

experience Layton et al.2 discussed the need to identify the learning objectives for each

laboratory in the mechanical engineering laboratory sequence at Rose-Hulman Institute of

Technology The senior level mechanical engineering laboratory at the University of Tennessee -

Chattanooga was reviewed by Knight and McDonald3 The authors emphasized the need to find

a balance between mechanical and thermal systems; an overview of the various laboratory and

design projects was also presented Lyon et al.4 reviewed the mechanical engineering senior

controls laboratory at Purdue University and offered insight into resolving common laboratory

course problems For an international perspective, Ohadi et al.5 presented the four undergraduate

mechanical engineering laboratories that have been developed at the Petroleum Institute (Abu

Dhabi) with discussion of the experiments and corresponding educational objectives Finally, in

a slightly different context, Ghone et al6 discussed the creation of a multi-disciplinary

mechatronics laboratory at Clemson which features student created open-ended experiments The

focus on real world inspired laboratory experiments was well received by students and offered

opportunities to work with common manufacturing instrumentation and control systems

The bench top laboratory experiments have been custom created at Clemson University and

duplicated to support four self contained work stations The students are placed in teams of three

to four members Typically, six sections are offered each semester; three teaching assistants

(TAs) are responsible for two three hour sections Mechanical engineering students completing

the program at Clemson indicate that the top three near-term professional career plans are to

pursue (in descending order) design positions, manufacturing positions, and graduate school

opportunities7 The senior level laboratory should satisfy three key items: (i) accepted ABET

(Accreditation Board for Engineering and Technology) syllabus, (ii) general learning goals

collectively established by the faculty, and (iii) student career needs Consequently, students

should learn how to use common instrumentation, sensors, actuators, and data acquisition

systems that complement analytical and numerical solutions to investigate engineering problems

Although the mechanical engineering program graduates may take different post-graduation

pathways, the laboratory experience is one of the key signatures of an undergraduate program

The general laboratory assignment philosophy is to create “open ended” experiments which

encourage student excitement, creativity, and thoroughness in their solution The teams must

demonstrate a rigorous laboratory methodology which emphasizes, if appropriate, analytical

modeling, numerical simulations, instrumentation configuration, equipment calibration, test plan,

data acquisition, real time control, experimental testing, uncertainty/statistical analysis, and

written communication Further, the students should draw on their past academic courses and

laboratory experiences to synthesize theoretical concepts and laboratory techniques For instance,

mathematical models can be derived, or computer software packages may be applied to predict

the system behavior to evaluate control algorithms, explore various design scenarios, and to

compare with the experimental test results Similarly, an uncertainty analysis should accompany

each laboratory to identify/quantify errors within the measurement systems and methods Finally,

the teaching assistants have been instructed to encourage students to work through their

questions and not offer immediate answers

In this paper, an overview of the Clemson University Department of Mechanical Engineering

Senior Educational Laboratory is presented in terms of experiments and assessment methods

The paper’s objective is to document and share the laboratory experiments so that a dialog may

be initiated within the academic community The manuscript is organized as follows Section 2

presents three experiments that have been completed by students during the sixteen week course

Section 3 discusses laboratory assessment with the summary contained in Section 4

2 Laboratory Experiments

A series of custom laboratory experiments have been fabricated and implemented at Clemson

University that emphasize different aspects of the undergraduate mechanical engineering

curriculum In general, the program thrust areas are design, dynamic systems, engineering

mechanics, and thermal/fluid systems Although commercial turn-key experimental systems can

be procured and offered, student feedback indicates that these experiments are generally too

passive and uninspiring The experiments that will be discussed have the general themes of: (i)

modeling and frequency analysis of vibration systems, (ii) sensor integration and

micro-processor programming for position control, and (iii) thermal analysis of electronic systems with

design tradeoffs in cooling strategies Some of the goals for these experiments include an open

design architecture for student insight, “hands on” activities, reconfigurability to allow system

modifications, ease of maintenance, robustness to survive many semesters, and basis for

open-ended engineering problems

2.1 Rotating Unbalance Vibration System

The first experiment investigates the vibration of a single degree-of-freedom horizontal mass

with minimal damping and structural stiffness The apparatus, shown in Figure 1, is subjected to

a variable speed rotating unbalanced mass for harmonic force inputs This experiment is intended

to mimic structures that support rotating machinery In such structures, the machinery can cause

unwanted oscillations and damage when running at or near the structure’s natural frequency

The goal of this experiment is for students to analyze the system’s oscillatory behavior in both

free and forced response scenarios This system has integrated sensors and pc workstation data

acquisition to allow students to observe the resulting oscillatory behavior for analysis in the time

and frequency domains (FFT) The students are challenged to complete two primary tasks: derive

and experimentally validate a dynamic system model, and design a method to dampen plant

oscillations at the natural frequency The learning objectives include: (i) gain an understanding of

experimental sensor wiring and calibration, (ii) perform vibration analysis with respect to single

degree-of-freedom systems, (iii) design a vibration absorber, (iv) validate a mathematical model

using simulation and experimental methods, and (v) explore fundamental vibration concepts

Figure 1: Laboratory one features a horizontal mass-spring system with servo-motor exciter to

induce oscillations; note accelerometer and four strain gauges mounted on the beam

As shown in Figure 2, the experimental apparatus is equipped with a single axis accelerometer

(Crossbow CXL04LP1) attached to the vibrating mass, strain gages (Omega SG-7/1000-DY13),

and strain gauge amplifier (Omega Omni-Amp III) to experimentally determine acceleration and

position These sensors are connected to a real time data acquisition system (National

Instruments PCI6023 with SCB-68 terminal box) to observe and record the sensor signals To

begin the experiment, the student teams are tasked with integrating, calibrating, and validating

the system sensors, and developing a system model With signals for position and acceleration

available, the free response from an initial condition is analyzed to determine the system’s

natural frequency and damping ratio from the observed period and a log decrement analysis For

this experimental apparatus, the students will observe a very small damping ratio and must

evaluate whether it may be neglected in the analysis An FFT may be used to confirm the

(graphically determined) natural frequency The spring constant may be experimentally

determined using force (e.g., spring scale) and displacement (e.g., ruler) measurements Based on

the natural frequency and spring constant, the effective system mass can be analytically

computed This mathematical model will also serve students in designing the dynamic absorber

The system’s forced response can be obtained using the actuator on the vibrating mass This

actuator consists of a 600 RPM gear head motor (Jameco 253446CB) driving an unbalanced

shaft with an angular velocity perpendicular to the plane of oscillation The system will exhibit a

response peak when the actuator is rotating at the system’s natural frequency In the problem

description, this is the undesired characteristic that must be attenuated At this point, the concept

of an undamped vibration absorber is reviewed The modified apparatus now consists of the

original mass and spring combined with an absorber mass and spring The absorber assembly is

typically designed to have the same natural frequency as the forcing frequency From an

analytical perspective, the harmonic force from the actuator is counteracted with equal, and

Figure 2: Horizontal vibration experiment - (a) wiring diagram, and (b) construction schematic

opposite, force from the absorber’s springs Students are challenged to validate their conclusions

through mathematical simulation and experimental testing The vibration absorber design

requires knowledge of the absorber mass and stiffness of the spring steel supports shown in

Figure 3 Note that the spring stiffness depends on the length which the students may adjust

Finally, frequency domain analysis is reviewed to allow further tuning of the vibration absorber

to maximize attenuation The frequency domain analysis should show two peaks in the response,

one at each of the modal frequencies in the two degree-of-freedom system, with a minimum

response at the original natural frequency (e.g., best system design)

2.2 Human/Machine Interface Programming and Position Control

In this experiment, the students design a vertical positioning system which raises and lowers a

payload in a manner similar to a conventional elevator (note: one of the safest modes of personal

transportation) A real time control algorithm is designed for the human/machine interface (e.g.,

floor buttons and display) and to also regulate the elevator’s vertical position between two fixed

locations using sensory data The laboratory offers students an opportunity to create software for

a Basic Stamp II (BSII) microprocessor and to explore fundamental control concepts The

learning objectives for this assignment include: (i) the ability to program a microprocessor, (ii)

understanding the computer logic needed to complete given tasks and construct flow charts, (iii)

familiarization with breadboard wiring, stepper motors, and sensors, and (iv) understanding

system integration

Figure 3: Diagram of the vibration absorber in the horizontal mass-spring system experiment

The laboratory tasks can be divided into two parts: learning to program the microprocessor, and

implementing the control logic within a mechatronic system As shown in Figure 4a, a Basic

Stamp II experimentation board (BSEB) is the primary component for the laboratory As can be

observed, the board contains numerous items available for use in the experiment including a

digital display, input/output ports, input buttons, and a speaker In the first task, students

familiarize themselves with the experimental board and some of its capabilities They are given

the Basic Stamp manual which contains programming commands and numerous examples that

allow them to explore the microprocessor’s operation Specifically, the manual presents

input/output commands, board hardware descriptions, wiring diagrams to run the example

experiments, and notes on how to change the sample code to produce different result To

facilitate the eventual system integration task, the stepper motor, proximity sensors, and sound

generation activities are addressed individually and demonstrated First, the students create

computer code to drive the stepper motor and translate the elevator platform up/down The

students analyze example software code to gain insight into the required logic, and then

implement their own algorithm Next, students are provided a simple software example which

demonstrates the implementation of a single proximity sensor The teams can then expand on the

concept, or develop an alternative, to integrate multiple position sensors Finally, the students are

required to generate a tone (symbolic of the platform reaching the desired floor) using the tonal

generation sequence covered in the Basic Stamp manual Overall, students are encouraged to

synthesize the supplied information and produce algorithms that accomplish the requested tasks

Figure 4: Laboratory two - (a) experimental board wiring, and (b) stepper motor elevator concept

In the second part, the experiment board was mated with a stepper motor and integrated into the

experimental apparatus displayed in Figure 4b As shown, the stepper motor with attached

sheave raises/lowers a Plexiglas “elevator” which travels on two metal rods bolted to a sturdy

steel base The sheave is aligned so that when the platform is being lifted, the cord wrapping

around the sheave pulls directly upwards on the center of the platform Two adjustable proximity

sensors (Square D PJF112N) have been attached to one metal rod for position feedback

information In Figure 5a, a signal flow diagram has been constructed for the experiment which

assists the students in the proper configuration of the wiring The logic flow diagram for the

control system is presented in Figure 5b The creation of the software kernel that will execute

this procedure must be designed prior to code writing Beginning with the first logical bubble,

students must familiarize themselves with the I/O functions and BSEB initialization procedures

The students need to initialize the motor to start from rest so that the platform travels upward

until it engages the lower proximity sensor Next, the platform must stop and wait for the floor

destination to be selected using push buttons located on the experimental board These buttons

ground the corresponding I/O pin; the digital signal may now be read by the BSII chip Finally,

the algorithm must determine whether the desired floor destination is greater than, equal to, or

less than the current platform location The stepper motor is now engaged to move the platform

2.3 Electronic Cooling System with Design Tradeoffs

The third experiment requires students to characterize the thermal behavior within a typical

metal enclosure, and then control the temperature at specific locations The laboratory emulates

the problem of cooling electronics through the application of thermistors, fans, heat sinks, and air

flow distribution The increasing miniaturization of electronic circuits, such as microprocessors,

and greater heat generation necessitates a demand for active cooling strategies of these

components This laboratory utilizes the student’s knowledge in thermal/fluid science and

electrical/circuit design to model, control, and optimize a cooling system in a configuration

similar to a small electrical box as shown in Figure 6 The learning objectives for this experiment

include: (i) understanding how to gather temperature information through the use of thermistors

and data acquisition systems with sensor calibration, (ii) analyzing the heat transfer problem in

terms of conduction, convection, and radiation; developing a dynamic model, (iii) developing an

electric circuit for cooling operations and data acquisition, (iv) applying different cooling

strategies (e.g., fans, heat sinks, and vents) to facilitate heat transfer away from the heating

element, and (v) designing a configuration to lower the overall temperature in the enclosure

Figure 5: Vertical positioning system with integrated sensors - (a) signal flow diagram, and (b)

logic flow block diagram for Basic Stamp II microprocessor program

A steel enclosure houses the components used for the experiment The internal components can

be viewed and arranged through the enclosure’s quick-access cover, which is left closed during

data collection Internal heating is provided by a 400W 110VAC heating cartridge (McMaster

#3618K255) mounted in a 5cm*5cm*12.7cm aluminum block controlled by a variable AC

transformer (Chaun Hsin SRV-500) A temperature cutoff switch, set at 100°C, is also mounted

in the aluminum block to insure safe operating temperature of the experiment The temperatures

are measured through a series of thermistors (10KΩ) strategically mounted throughout the

enclosure and “mobile” thermistors that allow temperature measurements at various locations

(e.g., outside the box) The power for these sensors is supplied through a constant 5VDC power

source The thermistors are configured in a simple voltage divider circuit and the output is

collected using LabVIEW™ data acquisition software These voltages must be calibrated by the

student teams into units of temperature These temperatures can characterize the enclosure

temperatures before the teams implement a cooling strategy

To dissipate the heat generated by the electric cartridge, a variety of mechanical and electrical

solutions can be pursued including: (i) Different sizes and shapes of heat sinks (MK-518 and

G1M-001) can be tactically mounted to the heated aluminum block to facilitate convective

processes The heat transfer processes can be analytically modeled by students using foundations

learned in undergraduate thermal/fluid science classes (ii) Two electric 12VDC fans (Panasonic

FMB-08A12M) similar to those used in computers can be controlled to aid enclosure ventilation

Further, the fan blade rotation can be reversed to change the air flow direction (iii) Outside vents

located on the enclosure’s exterior can be opened/closed to allow more outside air to enter/exit

25.4cm

15.2cm

Variable transformer

Air vent

Cooling fan PCU

power supply

Cartridge heater

Aluminum housing

Mobile thermistors

Metal enclosure

To DAQ

Temp

cutoff switch

Figure 6: Thermal cooling system experiment – (a) benchtop photograph, and (b) schematic

Once the students identify their optimal cooling configuration using the above devices and a

general design methodology, the teams are required to compare the temperature reductions

obtained with the formulated analytical models A comprehensive report is written which fully

describes the cooling system design and heat transfer behaviors In addition to the above