Planetary Roller Screw (standard type) is a transmission mechanism that combines helical motion and planetary motion to transform the rotary motion of the screw into the linear motion of the nut. Planetary Roller Screws have the characteristics of strong load carrying capacity, high rigidity, high precision, wear resistance, shock resistance and long life, etc., which are widely used in industry and defence and military fields:
Composition: planetary roller screws are mainly composed of screws, rollers, nuts, internal gear ring, cage and elastic retaining ring;
Motion mode: planetary roller screws in the work, the screw is usually used as the power input, only around its own axis of rotation; nut is usually connected with the load, only along its own axis of movement; roller in the nut and the planetary movement between the screw and the axial displacement of the nut relative to zero, and the nut together with the movement in the axial direction.
With the planetary roller screw in various industries continue to deepen, its application scenarios also come more and more, in order to adapt to different application environments and installation conditions, the structure of the form is also in constant development. Standard, cyclic, reverse, differential and other planetary roller screws are more widely used:
(1) Standard type: In general, the screw is the active member and the nut is the output member. It can achieve a large stroke, suitable for harsh environments, high load, high speed and other occasions, mainly used in precision machine tools, robots, military equipment and other fields, is currently the most widely used type;
(2) Inverted type: its structural form is similar to the standard type, the difference is that it does not have an internal gear ring, the straight teeth at both ends of the screw mesh with the gears at both ends of the roller, and the nut as the active part, the length of which is much larger than that of the standard type. Generally speaking, the nut of the inverted planetary roller screw is the active member, the screw is the output member, and there is no relative axial displacement between the roller and the screw, which is mainly used for small and medium-sized loads, small strokes and high-speed application scenarios, and its biggest advantage is that its nut can be used as a motor rotor to achieve the integrated design of the motor and the screw to form a compact one-piece electro-mechanical actuator;
(3) Recirculating type: Compared with the standard type, it removes the internal gear ring and adds the cam ring structure, whose function is similar to that of the ball screw's returner, in order to make the roller return to the initial position after rotating in the nut for one week. The structural characteristics of the recirculating planetary roller screw increase the number of threads involved in the engagement, so it has high stiffness and large load capacity, and is mainly used in applications requiring high stiffness, high load capacity, and high precision, such as medical equipment, optical precision instruments, and other fields. The disadvantage is that its cam ring structure will produce vibration impact, there is a noise problem;
(4) Differential type: Compared with the standard type, the internal gear ring is removed and there is no gear segment on the roller. The structural characteristics of differential planetary roller screw make it possible to obtain a smaller lead, which is suitable for applications with larger transmission ratios and higher load carrying capacity. However, during its movement, the threads will produce sliding phenomenon, which is prone to wear under heavy loads, leading to loss of accuracy, reduced reliability and other problems.
An inverted roller screw in a linear actuator
Planetary roller screw penetration is expected to increase, replacing part of the field of ball screws and hydraulic transmissions:
(1) Compared with the transmission of ball screws, planetary roller screws have a stronger carrying capacity, can be applied in complex and harsh working conditions, long life and other advantages, is expected to be applied in the field of machine tools, robotic electric cylinders and other scenarios;
(2) Based on the planetary roller screw precision transmission structure, to overcome the traditional hydraulic transmission device inherent environmental adaptability, low reliability, the use of poor maintenance and other shortcomings, is expected to replace part of the scene hydraulic transmission device.
Post time: Nov-02-2023
