机械原理英文版2Camdesign

ε?
Cam Design
Size ofcase of Over large size roller
Cam Design
Sizing the cam
R f min
Sharp point

R
p
s 2v 2 a R p s
Determine For the fall s(θ) ? 180<=θ<270
270 h 270 1 s 1 cos( ) 1 cos 2 2 4
180<=θ<270
Ideal case： μ=90；
Engineering case : μ>40;
压力角β=90-μ；
Pressure angle in cam
Pressure angle By convention, the pressure angle is used for cams Definition The angle φ between the direction of motion of the follower and the direction of the axis of transmission. Φ=0 no slip velocity Φ=90 no motion of the follower
2
R
p
s v 2
2

3/2
Cam Design
Sizing the cam
Cam Design
Sizing the cam
Cam Design
Sizing the cam
Radius of curvature
Can not follow a concave cam
Cam Design
Eccentricity
1)
2)
Sizing the cam
ds b dt
ds ds d ds dt d dt d b b
3) Pressure angle
tan
b
2 s Rp 2


2 s Rp 2
Cam Design--1
Cam and mushroom follower
Analyzing Method
e base circle
偏心
s0 =initial position
近休止
s 0 r0 e 2
2
Cam Design--2
Cam and roller follower
For B point
project (due day Oct.14)
A) Computer design cam surface curve and roller follower where the diameter of roller is rb=8mm, the displacement is given by
1)rise 2)dwell 3)
For the rise pp237
Review
3)
0<=θ<90
?
s 270 h 270 1 ) 1 cos 2 1 cos( 2 4
h 1 s 1 cos( ) 1 cos 2 2 4
Cam Design-3
Cam and flat-face follower
Instant center P
Analyzing Method
then
No base cycle, but instant center
Cam Design-4
Cam and oscillating follower
Analyzing Method
90 180 270
θ
Rigid shock unacepptable 2)
1 s h sin( 2 ) 2
0<=θ<90 ?
270 1 270 s h sin(2 ) 2
180<=θ<270
Cam Design
Analyzing Method
For normal line
“-” 内包络；“+”外包络
review • Example4
Instant center
Cam and follower 1
3
2
1. Follower will have its instant center at Infinity along a line perpendicular to the direction of follow 2. Slide pair: line perpendicular to contact surface
Where β=90, h=20, r0=30
B) Check pressure angle
Requirement of Cam CAD project :
• • • • • • Objective SVAJ curve Formula for designing cam surface curve Diagram of pitch curve and cam surface curve Pressure check for cam surface curve Matlab code
Cam Design
Review
Step1: biases cycle with radius e Step 2: prime cycle with radius r0 Step3: uniformly dividing angle and drawing tangent line Step4: drawing s Step5: drawing roller Step6: drawing envelope
1, Finish home work on time 2, Drawing tool for machinery course
Cam Design
Follower motion is expressed as
Review
s
1)S=kθ
Determine
0<=θ<90
s(θ) ? 180<=θ<270 o
Pitch curve
理论轮廓
Cam surface 实际轮廓
Key points for Cam CAD design
1)Give out the coordinate of cam surface curve (x,y); known: cam size, displacement function 2) Drawing the diagram of Cam surface curve in Matlab by using function plot(x,y) or polar(sita,r) 3) Check the pressure angle for designed cam surface curve
1 s h sin( 2 ) 2
S=20
homework
1) Graphical design cam surface curve with flat face follower, the displacement is given by
1)rise 2)dwell 3)
where
0~360
design
Initial angle
review
• Transmission angle μ (传动角）
– Definition：the angle between the output link and the coupler (force) – Pressure angle: the angle between the velocity direction of output link and the coupler (force)
arctan

2 s Rp 2
Cam Design
Overturning moment
Pressure angle is zero for all position
Sizing the cam
d is the key size
Keep cam as small
as possible
In 90 degrees in 90 degrees in 90 degrees in 90 degrees
270 1 270 s h sin(2 ) 2 4) dwell s=0
r0=30
Where β=90, h=20,
Cam CAD Design
1 s h sin( 2 ) 2
S=20
In 90 degrees in 90 degrees in 90 degrees in 90 degrees
270 1 270 s h sin(2 ) 2 4)dwell s=0
ε ↑ RP ↑ →θ↓
CAM SIZE↑
Cam Design
Prime circle radius
Sizing the cam
PP209
Cam Design
Sizing the cam
1）ε=0 2）ε≠0
The pressure angle on the rise will be reduced The pressure angle on the fall will be increased Create a smoother running cam