Mechanical Basis Flashcards
(38 cards)
definition of machine
a device that can achieve predetermined mechanical motion and it consists of numbers of fixed and moving bodies. it is used to provide significant forces to transform and transmit significant energy and power
characteristics of machine
- design by mankind
- convert energy
- have relative and regular motion
definition of machinery
- machine have more than 3 features, mechanism have 2 characteristics. machinery is the term used to cover both mechanism and machine
definition of machine element and catagory
basic element of manufacture. 2 catagories are
- general purpose parts/element common
- special parts/element peculiar
definition of link
a rigid structure that joined by numbers of machine element is a basic element in kinematic analysis
types of link
frame, driving, driven
- frame : the fixed and stationery link in mechanism
- driving link : link that moves according to the movement rule
- driven link : remaining link movement that follow driving link
kinematic pairs
every link must be kept permanently in contact with other link by some kind of connection with motion relative to them, in order to transform and transmit motion
types of kinematic pairs
- revolute pair : pair that permits only relative rotation
- sliding pair : pair that allow only relative rectilinear translation
degree of freedom
F = 3N - 2Pl -Ph
definition of planar linkage
kinematic pairs in a mechanism are lower pairs
types of 4 bar linkage
- crank rocker mechanism
- double rocker mechanism
- double crank mechanism
match the diagram
- arrow keluar is rotating
- arrow dua masuk is swing
- arrow keluar dari dalam is crank and oscillating
- arrow dua keluar is translating
characteristics analysis of 4 bar linkages
- pressure and transmission angle
- dead point
- quick return characteristics
what is dead point
rocker CD is input link and crank AB is output link. when the AB and the coupler BC is overlapping collinear, AB1C1D, and extended collinear AB2C2D. at that instant y=0degree. those two limitating positions are called dead point
deadpoint flywheel
when the rocker serves as the driver, the linkage is being driven through a deadpoint with the inertia of flywheel, fixed with driven crank
characteristics of quick return
if the crank is rotating at a constant speed, the oscillating link moves forward slowly and return quickly
ΞΈ and K
- the crank angle between 2 limitating position
- the coefficient of travel speed variation for time ratio
basic structure of cam mechanism
- it has curved/grooved contour which is usually used for contiunous constant velocity rotation and some for oscillating reciprocal movement
classification of cam mechanism
- by the shape of the follower end : knife-edge, roller, flat-faced
- by the shape of the cam : translating, plate, cylindrical
- by the form of closure : force closure, form closure
working process of cam mechanism
- base circle
- offset
- total follower travel
- cam angle for rise
- cam angle for outer dwell
- cam angle for inner dwell
- cam angle for return
- dispalcement curve of the follower
follower motion curve
- at the beginning and the end of the rise, the acceleration is positive and negative infinity. any of which will produce infinite inertia force.
- although the inertial force would not be infinite, it will reach a considerable value which will result in the large amount of shock, called rigid impulsive and rigid jerk.
- those 2 will produce a large vibration, high stress level and serious wear. it is only applied to low operations
constant acceleration and deceleration motion
soft impulse/soft jerk. can be used for low/intermediate speed cams
soft impulse/soft jerk
in acceleration plot, the acceleration jumps and will result in the abrupt changes in inertia force. the inertial force will be finite, instead of infinite so it will cause finite impulse or jerk
fundamental law of gearing
in order to maintain a constant angular velocity ration, the shape of the teeth must be normal at the point of contact between 2 teeth always passes the fixed point
