四川理工学院试卷 A（ 至 学年第 学期）
课程名称： 机械原理（双语） 命题教师： 胡莲君 适用班级：
共 5 页
题号 得分 一 二 三 四 五 六 七 总分 评阅（统分）教师 注意事项：
1、 满分100分。要求卷面整洁、字迹工整、无错别字。
2、 考生必须将姓名、班级、学号完整、准确、清楚地填写在试卷规定的地方，否则视为废
卷。
3、 考生必须在签到单上签到，若出现遗漏，后果自负。
4、 如有答题纸，答案请全部写在答题纸上，否则不给分；考完请将试卷和答题卷分别一同
交回，否则不给分。
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
1
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
B: compound hinge n=9, PL=12, PH=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 α 5). For the position shown, indicate displacement s (10 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) O 3). h=2 OC=40mm (2 points) 4). As shown in Fig
C (2 points)
2
ω 5).As shown in Fig (2 points)
四. In the offset slider-crank mechanism shown in Fig, LAB=100mm, LBC=300mm, e=70mm. the crank AB rotates at a constant speed
ωAB=10rad/s, when φ=450, analyze the output motion (velocity, acceleration ) of point C by Graphical method of Difference Vector Equation (15 points)
solution:
ωAB B1. find VC
A φVC = VB + VCB
Values: ? ωABlAB ?
eCDirection: level ⊥AB ⊥CB (3 points)
Select uv=(1cm) / (0.5m/s), draw velocity polygon (3 points)
b p
c
Vc=pc/uv=2.4×0.5=1.2m/s (p c) (1 point) VCB=bc/uv=1.7×0.5=1.05 m/s(b c) ωBC= VCB/LBC=1050/300=3.5rad/s 2. find aC
αC= αB + αnCB + αtCB
Values: ? ω12lAB ω22lBC ?
Direction: level B→A C→B ⊥CB (4 points) Select ua=(1cm) / (5m/s2), draw acceleration polygon (3 points)
c’ n’ b’ P’
3
ac=p’c’/ua=1.5×5=7.5m/s2 (p’ c’) (1 point)
五. 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 (15 points)
C1 solution:
e A θ=1800(k-1)/(k+1)
=1800(1.2-1)/(1.2+1)
=16.40 (3 points)
Select uL=2, Design the offset slider-crank mechanism by graphic method (8 points)
then ：LBC-LAB=AC1. x ul=36
LBC+LAB=AC2 x ul=86 LAB=25mm LBC=61mm
(4 points)
θ C2 P
六. 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) solution:
1 i12=2 Z2= Z1x2=80
d1=m Z1=300mm，d2=m Z2=600mm， (4 points) 2.
P=πm=31.4mm
S=e=πm/2=15.7mm (4 points)
4
3. a=（d1+d2）/2=450mm (3 points) 4. acosα= a’cosα’
450cos200=451cosα’ α’=20.30 (4 points)
七. 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) 2. Calculate the train ratio i lH gear train with fixed axes : i12=n1/n2=-z2/z1=-2
n2=- n1/2 (1) (2 points) planetary gear train:
iH2'4n2'?nHn2'?nHn2'???1???Z4/Z2'??4 (4 points) n4?nH0?nHnH
(2 points)
n2'?n2 n2?5nH (2) (2 points)
n2?5nH??n1/2i1H?n1??10nH 5
精品课件!《机械原理》_机械原理(双语)试卷A卷答案
