JNTU
JNTU B.Tech II KINEMATICS OF MACHINERY Previous Question Paper (July/August - 2021 - R15)
Answer any Five Questions. All Questions Carry Equal Marks.
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What are Grashoff and non-Grashoff kinematic chains?
Answer
A Grashoff kinematic chain is a four-bar mechanism in which at least one link is capable of performing a full 360-degree revolution relative to the adjacent links. This occurs when the sum of the shortest and longest link lengths is less than or equal to the sum of the remaining two link lengths (s + l ≤ p + q). If the sum of the shortest and longest links is strictly greater than the sum of the other two (s + l > p + q), the chain is classified as a non-Grashoff kinematic chain, where no link can complete a full rotation relative to another, resulting in a double-rocker mechanism.
What are the inversions of Grashoff kinematic chains? Explain and draw a neat free hand sketch of each inversion.
Answer
When the shortest link is fixed, the inversion is a double-crank mechanism, where both input and output links rotate fully. When a link adjacent to the shortest link is fixed, it becomes a crank-rocker mechanism, where the shortest link rotates fully while the opposite link oscillates. When the link opposite to the shortest link is fixed, it results in a double-rocker mechanism, where both links adjacent to the fixed link oscillate. Sketches should depict: 1) Double-crank: shortest link as ground, both side links rotating. 2) Crank-rocker: link adjacent to shortest as ground, shortest link rotating, opposite link rocking. 3) Double-rocker: link opposite to shortest as ground, both side links rocking.
What are the inversions of double slider crank chain? Draw neat free hand sketches of all the inversions.
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Explain about the inversions of crossed double slider crank chains with neat free hand diagrams.
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Draw the mechanism shown in figure to a suitable scale and list the number of instantaneous centers for this mechanism. Draw guillet circle and locate any 12 instantaneous centers for the mechanism.
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Using Klein’s construction complete the velocity and acceleration analysis of the slider crank mechanism with a crank radius 30 cm and connecting rod length 125 cm when crank is at 40 degrees from the inner dead centre position. Crank speed is 12 rad/s clockwise.
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State and prove the condition for tracing exact straight line by a mechanism.
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Draw neat diagram of paucellier mechanism and prove that a point on it traces exact straight line.
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Derive the relations for angular velocity and angular acceleration of a Hooke’s joint.
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Draw the cam profile for a roller follower cam with the following data. Follower rises through 24 mm during 150 degrees of cam rotation with SHM and dwells for next 30 degrees of cam rotation. Follower returns to initial position during next 90 degrees of cam rotation with acceleration and retardation having acceleration = 2/3 of retardation and dwells further. Minimum radius of cam is 30 mm and the follower is a radial follower.
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What is interference in gears in mesh?
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Two 20 degrees pressure angle involute profile spurs are in mesh and the gear ratio for this drive is 3.5. Addendum for both the wheels is 110 percentage of the module. Determine the minimum number of teeth required to avoid interference on both the wheels?
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