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Bài giảng Kinematics and dynamics of machines - Chapter 9: CAM mechanism (Part 1) - Phạm Huy Hoàng

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CHAPTER 9  
CAM MECHANISM  
Pham Huy Hoang  
I. Introduction  
1. Definition:  
A rotating or sliding piece in a  
mechanical linkage used especially in  
transforming rotary motion into linear  
motion or vice versa.  
follower  
Cam mechanism has 2 main parts: cam,  
follower. Sometimes, it includes a roller.  
roller  
cam  
The basic purpose of using the cam  
follower is converting the rotary motion of  
the cam to the translating or oscillatory  
motion of the follower  
2. Classification  
a. By type of mechanism  
Planar  
Spatial  
Translating/Sliding cam  
c. By motion of follower  
Oscillating follower  
Sliding/Translating follower  
d. By the contact between follower and cam surface  
(Follower Configuration)  
Form-closed cam  
Conjugate cam/double-disc cam  
Cylindrical cam  
We will concentrate on kinematic and force analyses, and the  
design of 5 types as follows  
3. Applications  
Cam mechanisms serve in the fuel-intake and exhaust  
systems of internal combustion engines  
Toys  
Tools  
Textile machines  
Textile machines  
Automatic feeding systems of machine tools  
Automatic feeding systems of machine tools  
Automatic feeding systems of machine tools  
Automatic feeding systems of machine tools  
Nomenclature and definitions  
Radius of Base circle (smallest profile curve)  
Profile angles (near dwell,  
rise, far dwell, fall)  
Nomenclature and definitions  
Timing angles  
(near dwell, rise, far  
dwell, fall)  
Nomenclature and definitions  
Timing angles (near  
dwell, rise, far dwell, fall)  
Nomenclature and definitions  
Cam profile  
Trace point  
Base  
circle  
Pitch profile  
Prime  
circle  
II. Kinematic and Force Analyses  
1. Kinematic analysis  
a. Direct method  
C
B
S
A
O
a. Direct method  
 
0  
Having S() or (), we can obtain  
using numerical method  
To do this  
differentiation, we  
need the -axis being  
evenly distributed.  
x dx  
Y f  
A
d  
M  
O1P H  
M
   
i  
xi  
M   
  
y
   
i  
xi  
A H M  
1. Kinematic analysis  
b. Indirect method/ Inverse method  
C
B
A
O
 
b. Indirect method/ Inverse method  
B
A
Si  
S0  
H
i
i  
O
H0  
b. Indirect method/ Inverse method  
B
A
i
A
0
S
i
H
i
S
0
i
-axis is distributed evenly  
H
0
O
b. Indirect method/ Inverse method  
C
B
A
I
O
 
b. Indirect method/ Inverse method  
I
i
l
A
i
i
A
0
l
-axis is distributed evenly  
i
0  
a
I
0
By doing this, -axis is  
distributed evenly  
I
i
l
i
a
A
i
A
0
l
i
I
0
0
0
O
a
Having evenly-distributed -axis, the numerical differentiation is  
more exactly and easily.  
2. Force analysis  
Pressure angle  
n
Pressure angle α : angle between the  
cam-follower contact force N12 and  
velocity vector vA2 of follower.  
12  
vA2  
N
Pressure angle α determines the  
relation between the cam-follower  
contact force N12 and the useful force  
(component of N12 in the direction of  
motion).  
t
t
The power of contact force on the  
motion of follower is:  
n
a. Pressure angle has effect on  
the size of cam mechanism  
n
vA2  
vA1  
S  
t
t
R0  
R
S
n
e
S e  
1  
tan  
2
2
S R e  
0
+/-: H ở left/right side of O  
a. Pressure angle has effect  
on motion of cam  
mechanism  
cos.cos  
1
N P  
P
cos()  
1
Self locking:  
N1  
N
F
Fms  
R
Cam may tend to  
jam a translating  
follower in its  
guide.  
Fms1  
In practice: pressure  
angle limits are:  
30o (translating  
followers),  
35o (oscillating  
followers).  
P
F
1
R
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