Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech II KINEMATICS OF MACHINES Previous Question Paper (December - 2018 - R15)
Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit.
Part A
What is ‘Inversion’ of a mechanism? Give one example.
Answer
The inversion of a mechanism is the method of obtaining different mechanisms by fixing different links in a kinematic chain. An example is the inversion of a four-bar chain, such as the beam engine (crank and lever mechanism).
Distinguish between Rigid Link, flexible link, and fluid link.
Answer
A rigid link does not undergo any deformation while transmitting motion (e.g., connecting rod). A flexible link is partially deformed in a manner not affecting the transmission of motion (e.g., belts or ropes). A fluid link transmits motion through fluid pressure (e.g., hydraulic press).
Write the approximate expressions for the displacement, velocity and acceleration of slider of a single slider crank mechanism with the usual notation.
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Draw the velocity diagram of a single slider crank mechanism by Klien’s construction and write the expressions for the velocity of crank, connecting rod, and piston in terms of the uniform angular speed of the crank.
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What is a Pantograph, and why is it used?
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Derive the condition for correct steering.
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Explain how do you draw the displacement diagram for a follower having a motion of uniform acceleration and retardation, the acceleration being twice the retardation?
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What is the difference between a tangent cam and circular arc cam with convex flanks?
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Draw and explain the different types of helical gears.
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Sketch a reverted gear train. Where is it used?
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Part B
Explain the different types of constrained motion for a kinetic chain.
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Determine the degrees of freedom of the mechanisms shown in figure 1.
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Draw and explain the working of the double-crank mechanism as an inversion of a four-bar chain.
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In a crank and slotted lever mechanism, the distance between fixed centers is 180 mm, and the crank length is 70 mm. If the length of the slotted lever is 450 mm, find the ratio of the times taken during the cutting and return strokes and also determine the effective stroke length.
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A sewing machine needle-bar mechanism shown in figure 2 has the following dimensions of links: O1A = 1.6 cm; O2B = 2.2 cm; Vertical distance between O1 and O2 = 4 cm; Horizontal distance between O1 and O2 = 1.3 cm; AB = 3.5 cm; BC = 1.6 cm; ‘D’ lies vertically below O1. If the crank O1A rotates clockwise uniformly at 150 rpm, find the velocity of the needle at the point ‘D’. Solve by the Instantaneous Center Method.
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In the mechanism shown in Figure 3, O1O2 = 210 mm; O1B = 300 mm; and O2A = 60 mm. The crank O2A rotates uniformly at 300 rpm ccw. Find the:
velocity
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acceleration of the slider
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linear acceleration of the point ‘B’.
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Derive the relation to show how a pantograph can be used as a copying mechanism.
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Show how the Hart mechanism satisfies the condition for exact straight line motion.
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Draw a neat diagram of the Davis steering gear, and prove that it exactly satisfies the condition for correct steering.
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In a cam having a speed of 300 rpm, the distance between the axes of Follower and Cam is 20 mm. Each of the angles of ascent and descent is 75 deg, and the angle of dwell between ascent and descent is 30 deg. Lift of the follower is 25 mm, and roller diameter is 37.5 mm. The outward stroke of the follower takes place with uniform and equal acceleration and retardation, and the inward stroke with SHM. Draw the profile of the Cam, and determine the maximum velocity and acceleration of the follower during ascent and descent.
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A symmetrical circular cam operates a flat-faced follower with a lift of 30 mm. The minimum radius of the cam is 50 mm, and the nose radius is 12 mm. The angle of lift is 80 deg. If the speed of the cam is 210 rpm, find the main dimensions of the cam, and the acceleration of the follower at:
the beginning of the lift
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the apex of the nose.
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The figure 4 shows a compound gear train. The power is transmitted from a motor shaft to output shaft. The motor shaft is connected to gear 1 whereas the output shaft is connected to gear 4. The gears 2 and 3 are mounted on the same shaft. The gear 1 meshes with gear 2 whereas gear 3 meshes with gear 4. The motor shaft is rotating at 1200 r.p.m. in the clockwise direction. Find the direction and speed of output shaft if the no. of teeth on gears 1, 2, 3 and 4 are 25, 50, 20, and 40.
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Describe the selection of gear box for an automobile.
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Two 20 degree pressure angle involute gears in mesh have a module of 10 mm. Addendum is 1 module. Large gear has 50 teeth and the pinion has 13 teeth. Does interference occur? If it occurs, to what value should the pressure angle be changed to eliminate interference?
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