USEFUL FORMULAE FOR SCREW JACK
OR LINEAR ACTUATOR CALCULATIONS
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Lifting Screw Lead
Lifting Screw lead (mm) = Screw Pitch (mm) * Number of Starts on Lifting Screw
Calculation of Linear Speed for a Screw Jack or Linear Actuator
Metric Units
Linear Speed (mm/min) = |
RPM of Input Shaft * Lifting Screw Lead (mm) |
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Gear Ration |
or alternatively
Linear Speed (mm/min) = |
RPM of Input Shaft |
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Turns of Worm for 1mm Raise |
Imperial Units
Linear Speed (in/min) = |
RPM of Worm Shaft * Lifting Screw Lead (in) |
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Gear Ration |
or alternatively
Linear Speed (in/min) = |
RPM of Worm Shaft |
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Turns of Worm for 1" Raise |
Calculation of Input Torque for a Screw Jack or Linear Actuator
Metric Units
Input Torque (Nm)= |
Load (kN) * Lifting Screw Lead (mm) |
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2 * Π * Actuator Efficiency * Actuator Gear Ratio |
r alternatively
Input Torque (Nm)= |
Input Power (kW) * 9550 |
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Input Speed (rpm) |
Imperial Units
Linear Speed (lbf .in) = |
Load (lbf) * Lifting Screw Lead (in) |
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2 * Π * Actuator Efficiency * Actuator Gear ratio |
or alternatively
Linear Speed (ibf .in) = |
Input Power (HP) * 63000 |
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Input Speed (rpm) |
Calculation of Input Power for a Screw Jack or Linear Actuator
Metric Units
Input Power (kW)= |
Load (kN) * Lifting Screw Lead (mm) * Input Speed (rpm) |
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60000 * actuator Efficiciency * Actuator Gear Ratio |
or alternatively
Input Power (kW) = |
Load (kN) * Raise rate (mm / min) |
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60000 * Actuator Efficiency |
Imperial Units
Input Power (HP) = |
Load (lbf) * Lifting Screw Lead (in) * Input Speed (rpm) |
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3.96 x 105 * Actuator Efficiency * Actuator Gear ratio |
or alternatively
Input Power (HP) = |
Load (lbf) * Raise Rate (in /min) |
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3.96 x 105 * Actuator Efficiency |
General Power Calculations
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Mertic |
Imperial |
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Lifting Motion |
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Linear Motion |
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Rotary Motion |
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Symbol |
Quantity |
Metric Units |
Imperial Units |
P |
Power |
kW |
HP |
T |
Torque |
Nm |
lbf.in |
F R |
Resistance due to Friction |
N |
lbf |
m |
Mass |
kg |
- |
W |
Weight |
- |
lb |
g |
Gravitational Acceleration |
9.81 ms -2 |
32.185 ft –2 |
v |
Velocity |
ms –1 |
Ft/min |
η |
Efficiency |
decimals |
decimals |
μ |
Coefficient of Friction |
decimals |
decimals |
n |
Rotational Speed |
rpm |
rpm |
