Denso SMT7 - Page 31

Chapter 2 Engineering Design of Servo Mechanism
15
Therefore, from equation (1)
dr
nL
f
≧



2
7
10 (mm)
where
L = Max. stroke + Nut length/2 + Shaft end allowance
= 700 + 50 + 100 = 850 (mm)
f = 15.1
dr = 14.4 (mm)
dm  n value
Allowable speed is also regulated by dm
 n value which shows peripheral speed (dm: center circle
dia. of steel ball mm n: speed rpm).
Generally
For precision (Accuracy grade C7 or higher) dm
 n  70,000
For general industry (Accuracy grade C10) dm
 n  50,000
Therefore,
dm
n
≦
70000
= 23.3 (mm)
Primary selection: Shaft dia. 20 (mm)
Lead 20 (mm)
4) Life forecast
(When accelerating
)
a
1 
V
t
mas
1
1
025.
4 (m / sec )
2
F
1



()()WWgWWa
AL AL1



0016098604 245.. .9 (N)
N
1
 
n
2
3000
2
1500 (rpm)
t
a


2
14
tt 0.75 (sec)
(At constant speed
)
F
2





(). ..WWg
12
001 60 98 59 (N)
N
2
 3000 (rpm)
t
b


2
25
tt0.65 (sec)
(When decelerating
)
F
3






()()WWg WWa
12 123
234 (N)
N
3
 1500 (rpm)
t
c


2
35
tt0.75 (sec)
············ Equation (2)