As the invisible support point of the joint transmission chain, choosing the wrong bearing is like planting a time bomb. This article will dissect the four most "deadly" hidden pitfalls in robot bearing selection and provide a hardcore checklist to help engineers avoid mistakes, ensuring the designed lifespan of robots is not "compromised".

Pitfall 1: The Trap of Micro-Motion "Eroding" Precision

Case Study: After 3 months of operation, the repeat positioning accuracy of the J5 joint (near the end effector) of a collaborative robot dropped sharply from ±0.05mm to ±0.25mm. Disassembly revealed uniform fine pitting on the raceway of the "standard" deep groove ball bearing at the output end of the harmonic reducer—a typical symptom of micro-motion wear!
Cause: Underestimating the micro-vibrations and oscillating torques from the reducer output, which caused unavoidable "creeping" between the rolling elements and raceways inside the bearing.
Core Pain Points:

• For high-precision joints (e.g., robot end effectors, wrist/ankle joints of humanoid robots), resistance to micro-motion wear is critical under low-speed and high-rigidity requirements.
• Although deep groove ball bearings are commonly used, their uncontrollable clearance becomes a precision killer under high-frequency vibrations and oscillating torques.

Countermeasures:

• "Zero-Tolerance" Clearance: Preloaded crossed roller bearings (e.g., RB series) must be used at the output ends of harmonic and RV reducers. The crossed arrangement of rollers enables simultaneous engagement with the inner and outer rings, inherently resisting overturning and achieving zero clearance.
• Angular Contact Pairs "Lock" Precision: For high-speed positions (e.g., forearm rotation), use back-to-back paired angular contact bearings (e.g., 70xx CTYNSUL P4) with a contact angle of 15°-25°. Precision preloading (5-10N is critical) eliminates axial clearance.
• Wall Thickness Limit Challenge: When space is limited, select ultra-thin-walled crossed roller bearings with flanges (e.g., MR series, wall thickness < 3mm), but the rigidity of the mounting surface must be maximized!
• Key Indicator for Lifespan Calculation: The equivalent static load Po=Xo⋅Fr+Yo⋅Fa must be less than the bearing's C0 value, with additional consideration of the overturning moment conversion factor (refer to the manufacturer's manual).

Pitfall 2: Cage Fracture

Case Study: During the 15th day of field testing for a quadruped robot's knee joint, an abnormal noise suddenly occurred. Disassembly showed that the nylon cage of the ceramic ball bearing had shattered into pieces! Spectrum analysis revealed that the instantaneous angular acceleration during impact exceeded 150 rad/s² (equivalent to 15g impact), far exceeding the limit of ordinary nylon cages.
Core Pain Points:

• Instantaneous high-g impact loads on the joints of legged robots and heavy-duty humanoid robots are common.
• Lightweight structures leave minimal buffer space for bearings, making ordinary stamped steel or nylon cages unable to withstand the load.

Countermeasures:

• Add "Armor": Full-complement cylindrical roller bearings (e.g., NJ, NUP series) are the first choice for impact resistance. Without cage restrictions, the full arrangement of rollers significantly increases rigidity (e.g., NJ206 for connecting rod joints, with a maximum impact acceleration > 30g).
• Strengthen the "Frame": For high-speed applications, select reinforced stamped steel cages (suffixed with J or M); solid brass cages (suffixed with MA) offer the highest strength but are heavier.
• Ceramic Ball Advantage: For high-frequency vibration scenarios (e.g., joints directly driven by servo motors), use Si