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Note for Kinematics of Machinery - KM By Dhanen Thiran

  • Kinematics of Machinery - KM
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SRMTRPEC DEPARTMENT OF MECHANICAL ENGINEERING SRM TRP ENGINEERING COLLEGE (SRM GROUP) (An ISO 9001:2018 Certified Institution) Irungalur, Trichy-621105 DEPARTMENT OF MECHANICAL ENGINEERING Unit 1- BASICS OF MECHANISMS 1 Define sliding pair or sliding connectors and what type of kinematic pair exists between human shoulder and arm.  Sliding connectors are used when one slider is to drive another slider. Usually the two sliders operate in the same plane but in different directions.  Spherical pair is exists between human shoulder and arm. 2 Compare machine and structure. S.No 1 2 3 4 3 Machine Structure Relative motion exists between its No relative motion exists between its parts. members. It transforms available energy into It does not convert the available energy into useful work work Links are meant to transmit motion Members are meant for carrying loads and force. having action. Examples: Scooter, Car, Bus. Examples: Roof trusses, bridges. Define kutzbach criteria for a mechanism.  Kutzbach’s criterion for determining the number of degrees of freedom or movability (n) of a plane mechanism is n=3(l-1)-2j-h  n-Degree of freedom, l-Number of links, h-Higher pair joint, j-Lower pair joint. 4 Write short note on complete and incomplete constraints in lower and higher pairs.  A pair having surface contact or area contact between the two elements while in motion is called as lower pair. The relative motion in lower pair is only turning or sliding.  When the two elements of the pair have a line or point contact when relative motion takes place and the motion between the two elements is partly turning and partly sliding, then the pair is known as higher pair. 5 State types of kinematic pairs and the types of constrained motion. Types of kinematic pairs  When two links are in contact with each other it is known as a pair. If the pair makes constrain motion it is known as kinematic pair.  Based on the nature of relative motion between the links. Sliding pair, Turning pair, Cylindrical pair, Rolling pair, Spherical pair, Screw pair.  Based on nature of contact between the links Lower pair, Higher Pair TWO MARKS ME8492-KINEMATICS OF MACHINARY

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SRMTRPEC DEPARTMENT OF MECHANICAL ENGINEERING  Based on the nature of mechanical constraint Closed pair, Unclosed pair Types of constrained motion  Completely constrained motion, incompletely constrained motion, successfully constrained motion. 6 When a linkage becomes mechanism?  If one of the links of a kinematic chain is fixed, then the chain is known as mechanism. If a mechanism uses four links, then it is known as simple mechanism and if the mechanism uses more than four links, then it is known as compound mechanism. 7 Define transmission angle of a four bar mechanism.  The angle between the coupler link and driven link. The worst value of transmission angle is less than 45° 8 Define Grashoff’s law  It states that in a planar four bar mechanism, the sum of shortest link length and longest link length is not greater than the sum of remaining two links length, if there is to be continuous relative motion between two members. (s+l)<=(p+q) s= length of the shorter length, l= length of the longest link 9 What is Mechanical advantage?  It is defined as the ratio of output torque to the input torque also defined as the ratio of load to effort. M.A ideal = TB / TA TB =driven (resisting torque), TA =driving torque 10 Differentiate a kinematic chain from a mechanism. S.No 1 2 3 TWO MARKS Kinematic Chain It is a combination of kinematic pairs. The relative motion between the links is completely or successfully constrained or locked. Types: Four chain, Slider crank chain, Double slider crank chain, etc. Mechanism If any one of the link in the kinematic chain is fixed then the kinematic chain is said to be a mechanism. The relative motion between the links is completely or successfully constrained. Types: Simple mechanism, Compound mechanism. ME8492-KINEMATICS OF MACHINARY

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SRMTRPEC DEPARTMENT OF MECHANICAL ENGINEERING Unit 2- KINEMATICS OF LINKAGE MECHANISMS 1 Define Instantaneous centre  The combined motion of rotation and translation of the link may be assumed to be a motion of pure rotation about some centre.  Total number of Instantaneous centre N=n(n-1) / 2 2 What is Coriolis component of acceleration and When coriolis component of acceleration occurs?  Coriolis component of acceleration occurs when a point on one link is sliding along another rotating link, such as in quick return mechanism.  Whenever a coincident point exists in a mechanism, we have to consider Coriolis component of acceleration. 3 Write the relation between the number of instantaneous centres and the number of links in a mechanism?  First of all determine the number of instantaneous centre.  Locate the fixed and permanent centre by inspection.  On the circle diagram, join the point by solid lines to show that centers are already found. 4 What is a relative pole, with respect to velocity analysis?  A pole of a moving link is the centre of its rotation with respect to a fixed link. However, if the rotation of the link is considered relative to another moving link, the pole is known as relative pole.  The relative pole can be formed by fixing the link of reference and observing the motion of the other link in the reverse direction. 5 What are the different methods used for finding the velocity?  The two important methods for determining the velocity are.  Graphical methods. Instantaneous centre method and Relative velocity method  Analytical method 6 Describe configuration diagram  Configuration diagram is a line sketch of a given mechanism drawn to a suitable scale. The configuration diagram forms the basis for the construction of both velocity and acceleration diagrams. 7 Define rubbing velocity of that point. What will be the expression for rubbing velocity at a pin joint?  The links in a mechanism are mostly connected by means of pin joints. The rubbing velocity is defined as the algebraic sum between the angular velocities of the two links TWO MARKS ME8492-KINEMATICS OF MACHINARY

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SRMTRPEC DEPARTMENT OF MECHANICAL ENGINEERING which are connected by pin joints, multiplied by the radius of the pin  Rubbing velocity of pin = ( ωA + ωB ) * r (links moves in Opposite direction)  Rubbing velocity of pin = ( ωA - ωB ) * r (links moves in Same direction) 8 Define Velocity ratio theorem.  The magnitude of the velocities of the points on a link is directly proportional to their distance from the instantaneous centre. The direction of their velocities is perpendicular to the line joining them with the instantaneous centre 9 Explain the radial component of acceleration  Radial component of acceleration is perpendicular to the velocity of the particle at the given instant.  The magnitude is given by arBA= ω2 . AB = v2BA/AB 10 What is the objective of Kinematic analysis?  The objective of Kinematic analysis is to determine the Kinematic quantities such as displacement, velocity and acceleration of the element in a mechanism TWO MARKS ME8492-KINEMATICS OF MACHINARY

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