机械原理(双语)试卷2答案.pdf

1 机械原理 双语 课程试卷 2 答案 机械原理 双语 课程试卷 2 答案 一 Checkpoint mark your answer on the answer sheet by True or False 20 points 2 points each 1 The links within a mechanism can have determined relative motions if and only if the DOF of the mechanism is greater than zero and equal to the number of the driving links T 2 During the group dividing of mechanism if the DOF of the group is zero then the group is called Assur group F 3 Any three independent links in general plane motion must have three instant centres the three instant centres may lie on a common straight line F 4 If a mechanism comply with the Grashof s criterion then the mechanism must have a crank F 5 A rotor is statically balanced if it has been dynamically balanced T 6 In the velocity polygon The vector connecting the any two points except point p represents relative velocity between them and the direction is opposite to the velocity symbol T 7 The analysis with dynamic static is analysis of the mechanism force with exception of the inertia force applying into the case of low velocity mechanism F 8 In a crank rocker mechanism the rocker DC reaches its two limiting positions DC1 and DC2 if the crank AB is a driver then the limiting positions are called dead points F 9 The pressure angle remains the same at all points on the tooth profiles of the rack ak a which is also called the normal pressure angle T 10 The transmission ratio of worm gearing worm is driver can be calculated by the formula i12 d2 d1 F 二 Calculate the degree of freedom of the mechanism shown in Fig 10 points solution A passive DOF B compound hinge n 9 PL 12 PH 2 B 2 F 3n 2PL PH 3 points 3 9 2 12 2 1 7 points 三 For the plate cam mechanism with translating inline roller follower as shown in Fig the cam contour is circle the radius r 100mm the radius of roller rR 10mm OC 20mm the cam rotates at anticlockwise 1 Draw out the pitch curve of the cam mechanism 2 Find out the radius of prime circle rp 3 Find out the lift of follower h 4 For the position shown indicate pressure angle 5 For the position shown indicate displacement s 20 points solution 1 the pitch curve of the cam mechanism As shown in Fig dotted circle 2 points 2 rp r OC rT 90mm 2 points 3 h 2 OC 40mm 2 points 4 As shown in Fig 2 points 5 As shown in Fig 2 points C O 3 四 Design an offset slider crank mechanism by graphic method The offset e is 16mm The coefficient K of travel speed variation is to be 1 2 The working stroke H of the slider is to be 50mm solution 1800 k 1 k 1 1800 1 2 1 1 2 1 16 40 3 points 3 points Select uL 2 Design the offset slider crank mechanism by graphic method 8 points 8 points then LBC LAB AC1 x ul 36 LBC LAB AC2 x ul 86 LAB 25mm LBC 61mm 4 points 4 points 五 A pair of standard spur involute gears has a module of 10mm pressure angle 200 transmission ratio i12 2 the numbers of teeth z1 30 1 Find out reference diameters d1 d2 2 Tooth thickness s and spacewidth e 3 Find out reference centre distance a 3 If working centre distance a a 1 find out working pressure angle 15 points solution 1 i12 2 Z2 Z1x2 80 d1 m Z1 300mm d2 m Z2 600mm 4 points 4 points 2 P m 31 4mm S e m 2 15 7mm 4 points 4 points 3 a d1 d2 2 450mm 3 points 3 points 4 acos a cos 450cos200 451cos 20 30 4 points 4 points P A C2C1 e 4 六 The numbers of teeth of the gears in the gear train shown in Fig are given as Z1 20 Z2 40 Z2 20 Z3 30and Z4 80 Calculate the train ratio i lH 15 points solution 1 Dividing the gear train gear train with fixed axes gear1 gear2 planetary gear train gear 2 gear3 carrier H gear4 5 points 5 points 2 Calculate the train ratio i lH gear train with fixed axes i12 n1 n2 z2 z1 2 n