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Leadscrew
The load has to be reflected back to the motor shaft. The leadscrew inertia has to be included (can
use the formula for inertia of a cylinder). If preloading is used the torque must be included since it
may be significant.
Typical Efficiencies
Type
Ball-nut
Acme with plastic nut
Acme with metal nut
Application Notes
Speed:
Load
Torques: T
Friction
Torques:
Inertia:
Where:
Efficiency
0.90
0.65
0.40
Page 10
W
=
V
P
M
L
1
F
1
F
=
L +
L
2π pe 2π
1
µW cos o + W sin o
T
=
F
2π pe
)
(
2
J
= W
1
1
T
g
2πp
e
W
=
motor speed (rpm)
M
V
=
linear load speed (in/min)
L
p
=
lead screw pitch (revs/in)
e
=
lead screw efficiency
T
=
load torque at motor shaft (lb-in)
L
T
=
friction torque (lb-in)
F
F
=
load force (lb)
L
F
=
preload force (lb)
PF
J
=
total system inertia (lb-in-s
T
J
=
motor inertia (lb-in-s
M
J
=
lead screw inertia (lb-in-s
LS
W
=
load weight (lb)
F
=
frictional force (lb)
F
µ
=
coefficient of friction
g
=
gravitational constant (386 in/s
Coefficient of Friction
Material
Steel on steel
Steel on steel (lubricated
Teflon on steel
Ball bushing
PF
x 0.2
p
+ J
+ J
LS
M
)
2
)
2
)
2
)
2
Coefficient
0.580
0.150
0.040
0.003
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Troubleshooting
