me 2220_sp15_lec01 - intro to kinematics
TRANSCRIPT
Prof. Albert Espinoza
Polytechnic University of Puerto Rico
Mechanical Engineering Department
Spring 2015
Professor Info
Albert Espinoza, MSME
Office: L-455
Office Hours: MW (11:00 AM-2:00 PM)
email: [email protected]
Cell: (281) 798-9737
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Title: Design of Machinery, 5th (2011)
Authors: R.L. Norton
ISBN-13: 9780077421717
Textbook
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This course introduces students to the application of fundamental
concepts of kinematics and kinetics to the analysis and design of
mechanisms in mechanical systems. The course focuses to the design
of linkages, cams, and gears using analytical, graphical, and computer-
aided techniques.
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Course Description
Course Content (Tentative)
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Topic Time (Hrs.)
Introduction. Kinematics Fundamentals 6
Position Analysis 6
Velocity Analysis 6
Acceleration Analysis 6
Dynamic Force Analysis 8
Introduction to Cam Design 4
Introduction to Gears and Gear Trains 6
Tests (2 in-class & final exam) 6
TOTAL 48
1. Partial exams (2) : 60%
2. Project : 20%
3. Final exam (Comprehensive) : 20%
Grading Policy:
A (90-100), B (80-89), C (70-79), D (69-60), and F (0-59)
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Test attendance is mandatory.
No section-switching.
There will be no make-up tests, no show = zero.
Evaluation
After taking this course, the students should be able to:
1. Recognize, illustrate, identify , and calculate the mobility for different types of mechanisms such as the standard four-bar linkage, slider-crank mechanism, five- and six-bar linkage, cam-follower, and gear train systems, among others.
2. Analyze the kinematic and kinetic behavior of mechanisms using CAD software and analytical methods.
3. Develop a translating cam-follower mechanism (given the follower position diagram).
4. Analyze the kinematic behavior of stationary and planetary gear trains (given a gear’s diagram).
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Objectives
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Basic Concepts
Mechanism
System of elements arranged to transmit
motion in a predetermined fashion
Machine:
Collection of components that will do work
Typically designed to provide significant
forces and transmit significant power
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Basic Concepts
Arbitrary distinction, need to consider both in the design of machines
Kinematics
The study of motion without regard to forces
Design desired motions of mechanical components
Kinetics
The study of forces on systems in motion
Provides information for further stress analysis and strength-based design
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Basic Concepts
Key topics for machine design
Analysis
Given a mechanism configuration and input motion, determine their kinematic
output characteristic (trajectories, velocities and accelerations)
Synthesis (Design)
Given output (desired) conditions, find the necessary mechanism configuration
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Degrees of Freedom (aka Mobility)
Number of independent parameters (measurements) which are needed to
uniquely define its position in space at any instant of time
Example: Pencil in a plane
3 DOF (two lengths, one angle)
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
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Types of Motion
All points on the body describe parallel (curvilinear or rectilinear) paths
Pure Translation
A reference line drawn on the body changes its linear position but does not change its angular orientation
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Types of Motion
Body possesses one point (center of rotation) that has no motion with respect
to "stationary" frame of reference.
Pure Rotation
A reference line drawn on the body through the center changes only its angular orientation.
Points on the body (i.e., different from center of rotation) describe arcs about that center.
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Types of Motion
Simultaneous combination of rotation and translation
Complex Motion
Any reference line drawn on the body will change both its linear position and its angular orientation.
Points on the body will travel nonparallel paths, and there will be, at every instant, a center of rotation, which will continuously change location
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Links, Joints and Kinematic Chains
“Rigid” body (at least initially assumed) with at least two nodes (i.e., attachment points)
Link
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
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Links, Joints and Kinematic Chains
Link Types
Crank
Makes complete revolution, pivoted to
ground (2)
Rocker
Oscillatory rotation, pivoted to ground (4)
Coupler
Connecting rod, complex motion (3)
Ground (aka Frame)
Fixed (nonmoving) with respect to reference
frame (could be moving)
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Links, Joints and Kinematic Chains
Connection between two or more links (at their nodes), which allows some motion, or potential motion, between the connected links.
Joint
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
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Links, Joints and Kinematic Chains
Joint – classified by the type of contact (line, point, or surface)
Lower Pair Joints
Contact between joined links occurs at every point of a surface segment
Higher Pair Joints
Contact between joined links occurs at isolated points or along line segments
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012) 20
Links, Joints and Kinematic Chains
Six Possible Lower Pairs (1, 2, 3 DOF)
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
Building blocks for more complex joints 21
Links, Joints and Kinematic Chains
Joint – classified by the number of degrees of freedom allowed at the joint
1 DOF (rotation or slide) – Full Joint
Ex: Pin Joint, Slider Joint
2 DOFs (roll + slide) – Half Joint
Ex: roll-slide joint, gears, cams
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012) 22
Links, Joints and Kinematic Chains
Joint – classified by the type of physical closure of the joint.
Form Closed
Force Closed
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
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Links, Joints and Kinematic Chains
Joint – classified by the number of links joined (order of the joint).
Order = # Links-1
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
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Links, Joints and Kinematic Chains
Full/Lower Order Joints
Pins (Revolutes)
Sliders (Prismatic)
Allow 1 DOF 25
Links, Joints and Kinematic Chains
Half/Higher Order Joints
Cams
Gears
Allow 2 DOFs 26
Links, Joints and Kinematic Chains
Kinematic Chain
A mechanism is a chain with at least one grounded link
• Open mechanism – at least one link connected to only one other link
• Closed mechanism – each link connected to two or more links
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
Assemblage of links and joints, interconnected to provide controlled output 27
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Kinematic Diagrams
Source: Design of Machinery (4th), R.L. Norton, McGraw-Hill (2012)
Schematic diagrams showing links and joints 29
Kinematic Diagrams
Key Steps
1. Identify the Frame (“ground”), link 1
2. Identify all other links (Label 2, 3, 4, 5, etc.)
3. Identify the joints (Label A, B, C, D, etc.)
4. Identify any other point of interest (load applied, output) (Label X, Y, Z,
etc.)
5. Draw the diagram (using binary, ternary links, prismatic, rotational
joints, etc.)
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Kinematic Diagrams
Example
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Kinematic Diagrams
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Example
Kinematic Diagrams
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Example
Kinematic Diagrams
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Example
Kinematic Diagrams
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Example
Kinematic Diagrams
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Example
Kinematic Diagrams
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Example
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