EXAM 1 CH 1-6 Flashcards
Kinematics
study of motion without regard to forces
Kinetics
Study of forces on system of motion
Mechanism
Device that transforms motion to some desirable pattern and typically develops very low forces and transmits little power as opposed to a machine that has high forces and power
James Watt
People
Grandfather of Kinematics
Euler(equation/theorem)
People
General displacement of a rigid body with one point fixed is a rotation about an axis
e^(ipi) + 1 = 0
Robert Willis
people
Mechanism Synthesis
Franz Reuleaux - Alexander Kennedy
people
Translated Franz Reuleaux’s famous kinematic text
Archimedes - Eureka
people
Applied geometry to the study of the lever
Iterations
Optimization
Binary link
One with two nodes
nodes are the points where the links meet
Ternary link
one with three nodes
Quaternary link
one with four nodes
Form-closed
The geometric form holds the pair together
Force-closed
Some external force holds the pair together
Kinematic chains
An assemblage of links and joints interconnected in a way to provide a controlled output motion in response to a supplied intput motion.
Half joint
The half joint removes only 1 DOF from the system (because a half joint has 2 DOF)
Gruebler’s Equation
M = 3L - 2J - 3G
* M is mobility (DOF)
* L is the # of links
* J is the # of joints
* G is the # of ground links
How many DOF
a) Mechanism
b) Structure
c) Preloaded structure
a) Mechanism +1 DOF
b) Structure 0 DOF
c) Preloaded structure -1 DOF
The Grashof Condition
S+L<=P+Q
* S = Length of shortest link
* L = length of the longest link
* P = length of one remaining link
* Q = length of the other remaining link
Function Generation
Input vs output motion
Path Generation
Control of a point along a path
Motion Generation
Control of a line in a plane
Limiting Conditions
- Toggle positions
- Stationary positions - where a rocker stops and changes directions.
*Transition angle - Angle that the linkages form to transmit force.
*90 is best but not possible, 40 is too low
Position Synthesis
Determines the ratio of the linkages to get the job done (linkages can be scalled up or down without loss of motion)
Dyad
A two bar chain added to a four bar mechanism to turn it into a sixbar
a) Cusp
b) Crunode
a) A sharp point on a curve (means there is a instantaneous zero velocity position)
b) A double point where the curve crosses itself.
a) Forward Stroke
b) Return Stroke
a) Usually requires force
b) Usually very low forces or external forces helped you
Cognate
A linkage, of different geometry, which generates the same coupler curve
Dwell
Zero output motion for some nonzero input motion
Global or absolute coordinate system
A coordinate system that doesnt change with the motion of the desired object.
Local coordinate system
This coordinate system moves with the subject.
Inertia reference frame
A system which itself has no acceleration
Pose
Position of a point in the link and the orientation of a line on the link
Translation
All points on the body have the same displacement
Curvilinear
Moving in a curve
Rectilinear
Moving in a straigth line
Rotation
Different points in the body undergo different displacements and this is a displacement difference between any two points chosen.
Complex motion
Sum of translation and rotation components
Eular’s Theorem
The general displacement of a rigid body with one point fixed is a rotation about some axis.
Chasles’ Theorem
Any displacement of a rigid body is equivlent to the sum of a translation of any one point on that body and a rotation of the body about an axis through that point.
Tranmission angle
Angle between the output link and the coupler
(can be done between any two links)
Circuit
All possible orientations of the links that can be realized without disconnecting joints.
Branch
A continuous series of positions of the mechanism on a circuit into a series of branches
Circuit defect
Needs to be disassembled to reach a position
Branch defect
Needs A circuit change to reach a position
Velocity
The rate of change of position with respect to time. It is always in a direction perpendicular to the radius of rotation and is tangent to the path of motion.
Absolute velocity
This is refecenced to the global coordinate axes.
Velocity difference
The speed of two point in the same body.
Relative velocity
The speed of two points in different bodies.
Instant center of velocity
A point common to two bodies in plane motion, which point has the same instantaneous velocity in each body
of IC = (1/2) # of bodies * (# of bodies - 1)
Kennedy’s Rule
Any three bodies in plane motion will have exactly three instant centers and they will be in the same straight line.
Axis of slip
tangent to the slider motion and is the line along which all sliding occurs between links.
Axis of transmission
It is perpendicular to the axis of slip and pass through the slider joint. (the only line along which we cna transmit motion or force across the slider joint, except for friction.)
CAD
Computer Aided Design
FEM
Finite Element Method
FEA
Finite Element Analysis
SI
Systemes Inernationale
GFBM
Geared Five Bar Mechanism
MEMS
Micro-Electromechanical System
BR
Bearing Ratio
DC
Direct Current
AC
Alternating Current
TDC
Top dead center
BDC
Bottom dead center
PM
Permanent Magnet
LNCS
Local nonrotating coordinate system
LRCS
Local rotating coordinate system
Roberts
(straight line)Triple rocker
DOF
Degrees of Freedom
