Knowledge of ball screw

A ball screw is a precision mechanical linear actuator that translates rotational motion into linear motion (or vice versa) with high mechanical efficiency exceeding 90%. Consisting of a threaded screw shaft, nut assembly, recirculating balls, and return deflectors, it replaces sliding friction with rolling motion.

Figure 1: King Square Precision Ground Ball Screw Shaft and Single/Double Nut

1. Key Advantages of Ball Screw Systems

• High Mechanical Efficiency: Operates at 90% to 95% efficiency, reducing drive motor torque requirement to one-third of conventional trapezoidal lead screws.
• Zero Backlash and High Stiffness: Preloading eliminates axial play, providing micron-level positioning repeatability (±0.003 mm).
• No Stick-Slip Phenomenon: Smooth movement even at micro-feed increments (< 0.1 μm), preventing mechanical chatter and positioning overshoot.
• Long Service Life: Super-finished raceways hardened to HRC 58–62 deliver exceptional fatigue resistance.

Figure 2: Ball Recirculation System & Preload Configuration

2. Recirculation Circuit Mechanisms

• External Circulation (Return Pipe): Steel balls exit the raceway through a curved guide tube and return to the opposite end. Ideal for large lead angles and heavy loads.
• Internal Circulation (Deflector Button): Steel balls cross over the screw crest through compact floating deflectors embedded in the nut wall. Offers minimum outer nut diameter.
• End-Cap Circulation: Balls return through end caps mounted on both nut faces, designed for high-lead and high-speed linear feeding.

3. Accuracy Grades (ISO / JIS)