College of Engineering Technology and Computer Science
Department of civil & Environmental Engineering
MEEN 3210 – MECHANISM DESIGN
Dr. L. Onyebueke
Project #1
Group Member 1: Chinonso Chimezie
Group Member 2: Mohammed Alghamdi
Group Member 3: Said Alamri
Group Member 4: Donald Toohey
Date Submitted: 10/14/15
Term: Fall 2015
Table of Contents
Cover Page 1
Table of Contents 2
Introduction 2
Explanations of Design Decisions 2
Problem-Solving Methodology, Methods of Analysis, and Synthesis 3
Engineering Principles used in the Design 7
Failure Theories and Design Criteria, Design Equations and Sample Calculation 7
Safety Aspects of the Project and the Designer’s Response to Potential Safety Problems 8
Creative thinking; Decision Making 9
Optimization 10
Computer Simulation 11
Identification of Group Work and Individual Work 14
Discussion and Interpretation of results 14
References 15
Introduction
In this report, an analysis of a construction lift is presented along with a discussion of potential safety aspects and the interpretation of results. Construction lifts are an important product on construction sites. It makes it easier to transport bricks from one floor to another thus increasing the efficiency for construction cost and labor. The designs of these types of lifts are crucial for the safety of operation. The important part of the design of this lift is to design the motion for the carriage of the lift.
In this report, the technical specifications of lift are provided. In subsequent sections analysis of the lift design is carried out and then discussion about the safety of lift is presented.
Explanations of Design Decisions
The feasibility study of our project was based on a four bar linkage and six-bar quick return linkage mechanisms. The four-bar linkage is the simplest pin jointed mechanism for single degree of freedom controlled motion. It could generate many different motion depends on the links length, and it is the most common device used in machinery. Whereas the six bar mechanism is more complex mechanism and needed for a difference in average velocity between their forward and return strokes.
The decision of choosing a design was made in order to include what has been studied in this course. Therefore, four bar linkages and a six bar quick return mechanism was chosen to have a mechanism that could make a full revolution and transport a body 90 degrees. After a careful consideration the group members have finally decided to design a mechanism to handle brick transport. It was difficult at first to choose a design since everyone liked different design, so each member in the group asked to sketch their desire design and the best one was selected.
Problem-Solving Methodology, Methods of Analysis, and
Synthesis
Initially the analysis of the problem revealed that the bricks not only transferred from one belt to the next but that these belts were perpendicular and had a vertical difference of one meter. After the establishment of what motion was needed, research on existing systems lead to several robotic forms. However, it was decided that these robots did not meet the criteria for the design.
In designing the mechanisms, position synthesis was used to create a direction and size of motion from the starting position to the final position. The geometric positioning of the bricks were set in a horizontal tray and lowered along the vertical plane. Then they were rotated on a horizontal plane so that the bricks would be positioned such that the longitudinal axis of the brick continued to stay perpendicular to the direction of the next conveyor belt motion. Finally the bricks are transferred to the next conveyor belt by ejecting them onto the belt.
The vertical belt was design as a quick return linkage so that the downward motion was slower than the return motion, shown in Figure 1. This motion was intentionally designed so that the bricks would stay in a continuous downward assisted motion versus allowing them to fall. The brick were to be stabilized so that when transferred to the next tray it is at a slower motion so that the bricks do not bounce off the tray they are being transferred to.
![]()
Figure 1 - Vertical Synthesis
The vertical distance from top of the first belt to top of the second belt was designed at one meter. However, the vertical distance the tray moves was increased to 44” so that the tray could continue to move down and out of the way so that the horizontal tray could catch the brick and rotate. When the brick lands on the middle tray the motor for the horizontal tray is turned on for a brief second and stops momentarily so that the next tray can pick up the brick, then the horizontal motor is again engaged so that the tray returns home. The last mechanism is also on a time delay and will continue to run until it returns to the home position. This mechanism does not hold the brick which allows the brick to be ejected onto the next belt. Another reason the distance was increased was so that when the brick is lifted off the second tray the brick is ejected with a low elevation above the last belt. Both link syntheses were completed at the same time because they are simply a four bar linkage mechanism, shown in Figure 2.
![]()
Figure 2 - Horizontal Transport and Vertical Lift
The calculations used are shown in the figures above but are placed here below to show mathematical formulas and values used
Mechanism 1
The vertical tray must be a preloaded structure so that the tray stay horizontal to the ground, therefore DOF =0
L= 7 J1=9 J0=0
Vertical tray must move a minimum of 44”
Link 4 and 2 are grounded perpendicular to the movement of the tray.
Link 4 = 44”/2 = 22”
Link 1 = 6” (distance between ground link 4 and 2)
Time Ratio 1:2
To get the link to travel slowly down and quickly return, set the inside angle such that it is 240°, by finding an angle 45° off the direction of movement and then offsetting or dividing the 120° evenly across the new angle. Therefore to find the angle setting for the motion set the angle to the left of the direction of motion and the find the time ratio with respect to 180°.
If , then
This means that will be to the right on the direction of the rotary motion and the opposite angle for this is
To find Link 2 and 3, if Link 3 = c, Link 2 = b, and therefore because Link 1 = 6” and Link 4 = 22”
Mechanism 2 & 3
These are both four bar links with a time ratio of 1:1, DOF = 1, and Link 4 needs to rotate 90°.
L= 4 J1=4
If Link 3 = 6.5
Link 4 =
If Link 2 = 3.5”
Link 1
Link 1 = 7.492”
Engineering Principles used in the Design
The engineering principle of this mechanism design is to design a mechanism to handle brick transport. In another word, a mechanism to pick up bricks from a moving transport belt and transfer them onto another belt moving at 90 degrees. In this design, we used a simple engineering principle of the basic knowledge for mechanical and engineering design. In order for us to achieve and design a mechanism that functions as we want it to, some calculations and rules needed to be followed. Three mechanisms needed to transport bricks from one belt to another belt, using Grashof conditions to build two four-bar linkage, for the four bar linkage to make a full revolution case (I) has to be followed , which states that shortest link (S) plus longest link (L) must be less than the sum of the other two links (P & Q).
The other mechanism is six-bar quick-return linkage. In the six-bar quick return mechanism angels α and β needed to be determined using the time ratio 1:2 and the equations are as followed:
Moreover, the degree of freedom (DOF), is equal to the number of independent parameters needed to uniquely define its position in space, was found using the links and joints that were calculated in the calculation section.
Failure Theories and Design Criteria, Design Equations and
Sample Calculation
One of the most perplexing problems we faced during with this project was the selection of design and develop a reboot design to withstand failure. We all came to a decision of choosing the brick transport as our topic for this project. To predict or estimate the mechanical failure and yield of machine parts and structural members we analyzed our design of the brick transport with the failure theories. The mechanical failures of the structural components in our design will be associated with excessive flexibility of our materials, which are the limitation in stress and strains of the materials over a period of time. Because our design incorporates motion and syncretized timing, functional failures become a high probability. A secondary failure can occur with the failure of some other piece of equipment. The durability of the joints and links are also susceptible to failure because of the motion and weight of the bricks. We identify the mechanism where the bricks lay while being transported as our area of overdesign and will need to be modified in the future.
In our concept design of the brick transport, designing a feasibly transporter to meet the design criteria and requirements provide to be our biggest challenged. The design criteria is to design a brick transport that will pick up bricks from a moving transport belt and deposit them onto another moving at 90° angle. The speed of the belt is 0.5m/sec with the width at 0.4m. The brick dimensions are 20 x 10 x 5 cm and weighs 2.5 kg. The maximum acceleration on the brick is 2g. The bricks lie flat on the belt with the distance between bricks being 20 cm in the direction of the motion and 10 cm along the longitudinal axis of the brick. The vertical distance between the two belts is 1 m.
In order to meet our requirement, we incorporated a four bar linkage with a six bar quick return linkage mechanisms. To determine the degree of freedom for the four bar linkage, Gruebler’s equation is used, which is DOF = 3(L – 1) – 2 + where L is the number links. is the number full joints and is the number of half joints. Using this equation, we get our DOF to be two degrees for the entire structure. For the six bar quick return linkage mechanisms, the rate of change of angular velocity with respect to time can be determine by using the equation
The beta angle, β, can also be found with this equation
The following equations below are used to find the retracted, extended, and F extend.
Since many arrangements of links chosen during our design of the brick transport will provide the same features, we had to synthesize the right one. We used two equation where is the ratio of our design and =. = 1:2. The second equation being α + β = 360. This can be incorporated in solving for angles α and β to give the output stage.
α =
β =
Safety Aspects of the Project and the Designer’s Response to Potential Safety Problems
The safety aspects to be considered for this lift are:
1. From the design perspective, the lift is built for the factor of safety of five. This makes the lift to take five times of the ultimate load in an uncertain condition. When the load reaches above this level, the lift will fail.
2. Construction lift for brick transportation is designed with the power electronics concept. Such that, when the load reaches the level beyond the factor of safety, the machine will automatically shut down because of the connection breakdown for the belt rotation power supply.
3. The maximum of one pair of bricks can be transferred using this machine.
4. Operational safety is ensured in a construction lift, by providing the emergency shutdown controls.
5. The maximum acceleration load considered for the design of lift is twice the gravitational force. This ensures the safety of lift during any free fall event scenario.
Technical Specification
In this section the given technical specifications for construction lift are presented.
Angle between lift belts, θ = 90
Brick transport rate, r = 1 brick/second
Belt speed, v =0.5 m/s
Belt width, b = 0.4 m.
Brick dimensions = 20x10x5 cm
Brick Mass, m = 2.5 kg
Maximum acceleration on the brick, a = 2g
Vertical distance between the two belts, d = 1m
Bricks are oriented with their longitudinal axis perpendicular with the direction of motion and they lie flat on the belt in pairs with distance between bricks 20 cm in the direction of motion and 10 cm along the longitudinal axis of the bricks.
Analysis
In this section, the lift design is carried out.
Brick volume, V = 20 x 10 x 5 = 1000 cm3
Weight of brick, W = mg
W = 2.5 x 9.81 = 24.53 N
Acceleration loading on carriage, N = 2g
Total load, P = 24.53 * 2 * 9.81 = 481.27 N
Load for pair of bricks, F = 2P = 2 * 481.27 = 962.54 N
Using the engineering stress theory, the cross section of the carriage can be designed for material yield stress.
Chosen material for carriage is aluminum.
Stress, σ = F/A
Yield stress of aluminum,
Considering factor of safety, FOS = 5, the allowable limit of stress can be calculated as
Therefore, the allowable cross section for the carriage, A = 962.54/43 = 23 mm2 . This is the minimum required cross section for the aluminum carriage to carry the bricks.
Creative Thinking; Decision Making
Various mechanism ideas began with developing a motion that would pick up the brick and maneuver the brick vertically one meter. The first design began with a mechanism that would travel an inverted “J” movement, but as a group the motion could not be attained with one mechanism using various shapes of linkages. Next the consideration for a barrel cam was developed and drawn up. However, the rotational motion of the parallelogram linkage traveling vertically interfered with the side of the barrel cam, shown in Figure 3. Then the idea to catch the brick as it came off the end of the conveyor into a tray was considered but consisted of one tray that had the potential of dropping the brick before reaching the next belt, shown in Figure 4. Finally we concluded that the design could consist of more than one mechanism and that the motion could be create with three different mechanisms.
![]()
Figure 3 - Barrel Cam with Vertical lift
![]()
Figure 4 - Vertical Lift
With the thought process to use three different mechanisms, one mechanism could move the brick vertically, another could rotate the bricks 90 degrees and the last mechanism could deliver the bricks to the belt. The first mechanism that transfers the bricks vertically could be created with a six bar linkage that was set up with a 2:1 ratio so that the movement would be slower on the travel downward, then quickly return to the top to retrieve the next brick. The second and third mechanism are simple four bar mechanisms with a 1:1 time ratio. The positioning of the trays would be on a trigger sensor that would turn the power on to the motors once the brick was set in position.
Optimization
Optimization is the process of maximizing a desired quantity or minimizing an undesired one. Usually, optimization theory is a body of mathematics dealing with the properties of maxima and minima and also showing how to find maxima and minima numerically. This is supported by the design equations and simple calculations provided earlier. We used different optimization methods in search of the best combination of design models using sets of model to get a clear and desired outcome. Evolution of past designs was our first attempt to improve upon existing designs. We encountered trial and error as we optimized the brick transport, as we recognized that our first feasible design was not necessarily the best. In hopes of finding an improved design, different design model were exercised for iterations.
Computer simulation
![]()
Figure 5 - Tray Up and Tray down
![]()
Figure 6 – Horizontal Motion
![]()
Figure 7 - Brick Transfer Exchange
![]()
Figure 8 - Brick Ejection
![]()
Figure 9 - Return to Home Position
Identification of Group Work an Individual Work
Chinonso Chimeze
Optimization
Failure Theories and Design Criteria, Design Equations and Sample Calculation
Mohammed Alghamdi
Introduction
Technical Specification
Safety Aspects and Analysis
Discussion and Interpretation of Results
Said Alamri
Brainstorming design ideas
Explanation of Design Decision
Engineering Principles
Donald Toohey
Brainstorming design ideas
Drawing mechanisms
Problem-Solving Methodology, Methods of Analysis, and Synthesis
Creative Thinking; Decision Making
Computer simulation
Discussion and Interpretation of Results
The design of the construction lift is crucial for transporting the bricks during the construction event. This is a cost effective method. However safe working conditions are to be ensured, otherwise it can lead to a catastrophic failure. In this work, the construction lift is designed for the factor of safety of five. The lift carriage is designed with aluminum which is a light weight material having good strength to weight ratio.
The lift carriage area is calculated for an acceleration loading of twice the gravitational force and the weight of the lift. This is the minimum strength required for the carriage. The area provided in the technical specification is higher than the minimum area and hence the lift carriage is operationally safe. Thus the design lift is safe for carrying the pair of bricks at the speed of 0.5m/s.
References
Norton, Robert L. Design of Machinery. 5th ed. New York City: McGraw Hill, 2012. Print.
2
abdlla19
sample.docx
0
