机械原理(双语)试卷2

《机械原理（双语）》课程试卷2

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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 ( )

2. During the group dividing of mechanism, if the DOF of the group is zero, then the group is called Assur group ( )

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. ( )

4.If a mechanism comply with the Grashof’s criterion , then the mechanism must have a crank. ( )

5. A rotor is statically balanced if it has been dynamically balanced. ( )

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 ( )

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. ( ) 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 . ( ) 9. The pressure angle remains the same at all points on the tooth profiles of the rack (a k=a), which is also called the normal pressure angle. ( ) 10. The transmission ratio of worm gearing (worm is driver) can be calculated by the formula i12=d2/d1 ( )

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二. Calculate the degree of freedom of the mechanism as shown in Fig

(10 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 r R =10mm, OC=20mm, the cam rotates at anticlockwise .

2). Find out the radius of prime circle r p =?

3). Find out the lift of follower h=?

(20 points)

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四. Design an offset slider-crank mechanism by

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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 (15 points)

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五. A pair of standard spur involute gears has a module of 10mm, pressure angle α=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 α’ (15 points)