Planetary Roller Screw

Comprehensive analysis of planetary roller screw

Definition and basic structure

Planetary Roller Screw (PRS) is a kind of precision transmission mechanism which converts rotational motion into linear motion through thread meshing. Its core consists of screw, nut, roller three parts, supplemented by internal gear ring, Cage, spring retaining ring and other auxiliary components.

Lead Screw: designed for thread angle 90 degrees of multi-head thread, as a power input shaft.

Roller: using single-head thread, tooth profile often processed into a spherical surface to enhance load capacity and reduce friction, the number is usually 6-12, evenly distributed around the screw.

Nut: with screw head matching the number of internal threads, responsible for the output of linear motion.

Cycle: similar to the planetary gear structure, the roller around the screw at the same time revolution and rotation, through the helix angle matching to ensure pure rolling.

II. Working principle

The working principle of a planetary roller screw is based on the analogy of a planetary gear system:

Power input: motor-driven screw rotation, forming a similar“Sun Gear” movement.

Roller movement: Roller (planetary gear) driven by the screw, both around the screw axis revolution, and around its axis rotation.

Straight-line output: the nut (center wheel) is fixed in the circumferential direction and moves along the axial straight line under the meshing effect of the rollers.

Different from the ball screw, it transfers load through line contact, the contact area is larger, and the impact resistance is significantly enhanced.

Performance characteristics

High load capacity: line contact design makes static load capacity up to 3 times the ball screw, dynamic load capacity is higher, life up to 15 times the ball screw.

High stiffness and impact resistance: multi-roller impact load distribution, stiffness improvement, suitable for high-speed heavy-duty scenarios (speed up to 14,000 rpm, acceleration up to 3G) .

Precision Control: lead accuracy up to ± 0.005 mm, support micron-level positioning, suitable for high-precision CNC machine tools and robot joints.

Environmental Adaptability: Can Be in extreme temperature (- 50 °C to + 150 °C) , dust, no lubrication and other harsh conditions stable work.

Low noise and long life: Roller synchronous movement to reduce vibration, low friction loss, long maintenance period.

Classification and form of structure

According to the relationship between the roller motion, planetary roller screw is divided into five categories:

Standard: the most widely used, suitable for high-load, high-speed scenarios.

Reverse type: through the small lead to achieve higher rated load, reduce the driving torque.

Cycle type: combined with high precision and low speed operation, suitable for precision positioning.

Bearing ring type: integrated bearing function, simplified installation structure.

Differential type: suitable for high speed and heavy load, with differential motion characteristics.

V. Areas of application

Industrial Automation: CNC machine tool feed system, mechanical press, improve processing accuracy and efficiency.

Robotics: Android linear joints (like Tesla Optimus' 14) for high-precision motion control.

Aerospace: aircraft landing gear (such as F-35B) , satellite antenna adjustment, high reliability and shock resistance requirements.

Medical Instruments: surgical robots, CT scanners, rely on high accuracy and low noise.

New Energy and vehicles: Alternative Hydraulic Drive, for electric vehicle ABS system, underground oil production equipment.

Comparison with ball screw

Characteristics, planetary roller screw, ball screw

Load transfer unit, line contact (threaded roller) point contact (ball)

High load capacity (3-5 times lower than ball screw)

Long Life (15 times shorter than ball screw)

Strong impact resistance (multi-roller load distribution) weak

Wide range of leads (smaller leads can be designed) limited

High cost and processing difficulty (high technical barriers, dependence on imports) lower (higher degree of localization)

Applicable scenarios, heavy load, high speed, harsh environment, light load, high precision, conventional environment

Market status and major manufacturers

Market size: $1.27 billion global market in 2022, projected to 2028 to $1.6 billion (Cagr 5%) .

Competitive Pattern: European and n Enterprises leading, Switzerland Rollvis (market share of nearly 40%) , Germany Bosch Rexroth, Japan NSK monopoly high-end market.

Localization progress: Domestic Enterprises (such as Qinchuan Machine Tool, Nanjing process) gradually break through technical barriers, but industrialization is still in the early stage, mainly used in the field of national defense.

Viii. Technological challenges and future trends

Manufacturing barriers: high-precision grinding process (screw thread accuracy to micron level) , material heat treatment (commonly used 42CrMo and GCR15 steel) .

Homemade alternative: Breakthrough Precision Processing Equipment (such as thread grinder) rely on imported bottlenecks, reduce production costs.

Innovation Direction: develop self-lubricating, high temperature resistant coating technology, expand the application in new energy and Android fields.

Conclusion

Planetary roller screw with high load, long life, strong impact resistance and other characteristics, has become the core component of high-end transmission field. Despite high technical barriers and a foreign-dominated market, its application potential will continue to be unlocked as domestic substitution accelerates and downstream demand (e.g. , Android, Aerospace) grows. In the future, continuous breakthroughs in materials, processing technology and structural design are needed to enhance the international competitiveness of domestic products.