Screw jack, also known as helix transmission equipment, methodically change its rotation into linear motion. Some crew jacks serve for the weight lifting (such as press and lifting jack), some for the movement transmission(the shafts that connect platens). Some for the adjustment of relative location of parts.
There are two kinds of structures of screw jack----trapezoidal sliding friction structure and ball rolling friction structure. For trapezoidal screw jack, with the easy manufacturing, low cost and self-locking function, it has large a friction resistance torque and low transmission efficiency (30%~40%).For ball screw jack, with its complication in structure and high cost, it cannot be self-locking, but the biggest advantage of that is the small friction resistance torque, the high transmission efficiency(92%~98%), its accuracy and stiffness. With the reversible and flexible motion, the long useful life makes it widely used in mechatronic systems.
1. Components: turbine, screw, worm, bearing and so on.
2. The operating principle: Driven by external force, worm shaft drives the turbine at a certain speed ratio, and the internal thread of the turbine pushes the screw to make a linear motion.
The transmission form of the screw jack is based on the combination of the relative movement of the lead screw and the nut. There are two types of basic transmission forms.
1.The nut do rotation while the screw moves. Under such condition, nut plays a supporting role, eliminates the additional axial shift which generated by the screw bearing. This form features a higher transmission with an easy structure.
2. Screw do rotation while nut moves.Under such condition, nut do anti-rotation,so there would be a guide needed.This form features a compact structure and a high stiffness of the screw, which suitable for the large stroke lifting.
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