Electric Screw Jack – Structure Diagram & Working Principle
Electric Screw Jack – Structure Diagram & Working Principle
An electric screw jack (worm gear screw lift) converts motor rotation into linear motion for lifting, lowering, and positioning heavy loads.
✅ Core structure composition and working principle
1. Electric motor
As a power source, DC or AC reduction motors are usually used to output low-speed high torque, directly
connected to the worm shaft to drive the transmission system.
2. Worm and worm gear pair
Worm: A spiral steel shaft driven to rotate by an electric motor.
Worm gear: a gear that meshes with the worm and is fixed at the bottom of the screw, converting
rotational motion into torque transmission.
The transmission ratio is usually 20:1 to 100:1, achieving a large reduction ratio and increasing
output torque.Screw and nut
3. Screw rod: a precision steel rod with trapezoidal threads, installed vertically, and connected to a lifting
head at the upper end.
Nut: It engages with the thread of the screw, is fixed inside the housing, and moves along the axial
direction of the screw with the rotation of the worm gear, pushing the screw up or down.
This structure achieves efficient conversion from rotation to linear motion, with a transmission efficiency
of approximately 20-30%.
4. Shell and protective structure
Fully enclosed cast iron or aluminum alloy casing to protect internal transmission components.
Internally filled with lithium based grease to reduce friction and wear.
External permanent dust cover or retractable sheath to prevent dust and water vapor from entering.
Limit and braking device
5. Upper and lower limit switches: prevent damage to the screw rod due to overtravel.
Electromagnetic brake: automatically locks when power is off, ensuring self-locking safety, and does not
slide even when power is off.
Workflow: Motor → Worm gear rotation → Worm gear rotation → Nut fixation → Linear lifting of screw
rod to achieve lifting of heavy objects.
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