Chapter 8 Acceleration in Mechanisms

Transcription

1 Chapter 8 Acceleration in Mechanisms 1

2 Acceleration Diagram for a Link

3 Example The crank of a slider crank mechanism rotates cw at a constant speed of 300 rpm. The crank is 150 mm & the ConRod is 600 mm long. Determine: 1. Linear velocity & acceleration of midpoint of ConRod 2. Angular velocity & angular acceleration of ConRod, at a crank angle of 45 from IDC.

4 4 Example 8.2 An engine mechanism is shown in Fig The crank CB = 100 mm and the connecting rod BA = 300 mm with center of gravity G, 100 mm from B. In the position shown, the crankshaft has a speed of 75 rad/s and an angular acceleration of 1200 rad/s 2. Find 1. velocity of G and angular velocity of AB 2. acceleration of G and angular acceleration of AB.

5 Example 8.3 In the mechanism shown in Fig. 8.7, the slider C is moving to the right with a velocity of 1 m/s and an acceleration of 2.5 m/s 2. The dimensions of various links are AB = 3 m inclined at 45 with the vertical and BC = 1.5 m inclined at 45 with the horizontal. Determine: 1. magnitude of vertical and horizontal component of the acceleration of point B 2. angular acceleration of the links AB and BC. 5

6 Example 8.4 PQRS is a four bar chain with link PS fixed. The lengths of the links are PQ = 62.5 mm ; QR = 175 mm ; RS = mm ; and PS = 200 mm. The crank PQ rotates at 10 rad/s cw. Draw the velocity and acceleration diagram when angle QPS = 60 and Q and R lie on the same side of PS. Find the angular velocity and angular acceleration of links QR and RS. 6

7 Example 8.5 The dimensions & configuration of the four bar mechanism, shown in Fig. 8.10, are as follows: P 1 A = 300 mm; P 2 B = 360 mm; AB = 360 mm, and P 1 P 2 = 600 mm. The angle AP 1 P 2 = 60. The crank P 1 A has an angular velocity of 10 rad/s and an angular acceleration of 30 rad/s 2, both cw. Determine the angular velocities and angular accelerations of P 2 B, and AB and the velocity and acceleration of the joint B. 7

8 Example 8.6 In the mechanism, as shown in Fig. 8.12, crank OA rotates at 20 rpm ccw and gives motion to the sliding blocks B and D. The dimensions of the various links are OA = 300 mm; AB = 1200 mm; BC = 450 mm and CD = 450 mm. For the given configuration, determine: 1. velocities of sliding at B and D 2. Angular velocity of CD 3. linear acceleration of D 4. angular acceleration of CD 8

9 Example 8.6 9

10 Example Find out the acceleration of the slider D and the angular acceleration of link CD for the engine mechanism shown in Fig The crank OA rotates uniformly at 180 rpm in cw direction. The various lengths are: OA = 150 mm; AB = 450 mm; PB = 240 mm; BC = 210 mm; CD = 660 mm.

11 11 Example 8.7

12 Example 8.8 In the toggle mechanism shown in Fig. 8.16, slider D is constrained to move on a horizontal path. The crank OA is rotating in the CCW direction at a speed of 180 rpm increasing at the rate of 50 rad/s 2. The dimensions of the various links are as follows: OA = 180 mm; CB = 240 mm; AB = 360 mm; and BD = 540 mm. For the given configuration, find 1. Velocity of slider D and angular velocity of BD 2. Acceleration of slider D and angular acceleration of BD 12

13 13 Example 8.8

14 Example 8.9 The mechanism of a warping machine, as shown in Fig. 8.18, has the dimensions as follows: O1A = 100 mm; AC = 700 mm; BC = 200 mm; BD = 150 mm; O 2 D = 200 mm; O 2 E = 400 mm ; O 3 C = 200 mm. The crank O 1 A rotates at a uniform speed of 100 rad/s. For the given configuration, determine: 1. linear velocity of point E on the bell crank lever 2. acceleration of points E and B 3. angular acceleration of the bell crank lever. 14

15 Example

16 16 Example 8.10 A pump is driven from an engine crankshaft by the mechanism as shown in Fig The pump piston shown at F is 250 mm in diameter and the crank speed is 100 rpm. The dimensions of various links are as follows: OA = 150 mm ; AB = 600 mm ; BC = 350 mm ; CD = 150 mm; and DE = 500 mm. Determine for the position shown : 1. The velocity of the cross-head E 2. The rubbing velocity of the pins A and B which are 50 mm diameter 3. The torque required at the crank shaft to overcome a pressure of 0.35 N/mm2 4. The acceleration of the cross-head E.

17 17 Example 8.10

18 Example 8.11 Fig shows the mechanism of a radial valve gear. The crank OA turns uniformly at 150 rpm and is pinned at A to rod AB. The point C in the rod is guided in the circular path with D as center and DC as radius. The dimensions of various links are: OA = 150 mm; AB = 550 mm; AC = 450 mm; DC = 500 mm; BE = 350 mm. Determine velocity and acceleration of the ram E for the given position of the mechanism. 18

19 19 Example 8.11

20 Example 8.12 The dimensions of the Andreau differential stroke engine mechanism, as shown in Fig. 8.24, are as follows: AB = 80 mm; CD = 40 mm; BE = DE = 150 mm; and EP = 200 mm. The links AB and CD are geared together. The speed of the smaller wheel is 1140 rpm. Determine the velocity and acceleration of the piston P for the given configuration. 20

21 21 Example 8.12

22 Coriolis Acceleration Frame OXY is fixed and frame Oxy rotates with angular velocity. Position vector r P for particle P is the same in both frames but rate of change depends on choice of frame. Absolute velocity of particle P is v P r OXY r r Oxy

23 Coriolis Acceleration v P r v v P P r F Oxy Absolute acceleration for particle P is a P r 2 a a P P F r r Oxy r r Oxy r Oxy Utilizing the conceptual point P on the slab, r Absolute acceleration for particle P a a a 2 r a P c P P ap a 2 P r F F Oxy ac 2 v Oxy P F

24 Coriolis Acceleration Collar P slides at constant relative velocity u along rod OB. Rod is rotating at a constant angular velocity w. point A on rod corresponds to instantaneous position of P. Absolute acceleration of the collar is a a P A P F a a c a A a P F r a r 0 Oxy c 2v a 2u P F 2 r a r c A

25 Coriolis Component of Acceleration When a point on one link is sliding along another rotating link, then Coriolis component of acceleration must be calculated.

26 26 Example 8.13 The figure shows a mechanism of a crank & slotted lever quick return motion. If the crank rotates ccw at 120 rpm, determine the velocity & acceleration of the ram D. Also determine the angular acceleration of the slotted lever. Crank AB = 150 mm; Slotted arm, OC = 700 mm and link CD = 200 mm.

27 27 Example 8.13

28 28 Example 8.14 The driving crank AB of the quickreturn mechanism, as shown in Fig. 8.30, revolves at a uniform speed of 200 rpm. Find the velocity and acceleration of the tool-box R, in the position shown, when the crank makes an angle of 60 with the vertical line of centers PA. What is the acceleration of sliding of the block at B along the slotted lever PQ?

29 29 Example 8.14

30 30 Example 8.15 In a Whitworth quick return motion, as shown in Fig OA is a crank rotating at 30 rpm in a cw direction. The dimensions of various links are: OA = 150 mm; OC = 100 mm; CD = 125 mm; and DR = 500 mm. Determine the acceleration of the sliding block R and the angular acceleration of the slotted lever CA.

31 31 Example 8.15

32 32 Example 8.15

33 Example The kinematic diagram of one of the cylinders of a rotary engine is shown in Fig The crank OA which is vertical and fixed, is 50 mm long. The length of the connecting rod AB is 125 mm. The line of the stroke OB is inclined at 50 to the vertical. The cylinders are rotating at a uniform speed of 300 rpm, in a cw direction, about the fixed center O. Determine: 1. Acceleration of the piston inside the cylinder 2. angular acceleration of connecting rod

34 34 Example 8.16

35 35 Example 8.16

36 Example 8.17 In a swiveling joint mechanism, as shown in Fig. 8.36, the driving crank OA is rotating cw at 100 rpm. The lengths of various links are: OA = 50 mm ; AB = 350 mm; AD = DB ; DE = EF = 250 mm and CB = 125 mm. The horizontal distance between the fixed points O and C is 300 mm and the vertical distance between F and C is 250 mm. For the given configuration, determine: 1. Velocity of the slider block F 2. Angular velocity of the link DE 3. Velocity of sliding of the link DE in the swivel block 4. Acceleration of sliding of the link DE in the trunnion 36

37 Example

38 Example