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The compact and lightweight design of robotic joints imposes stringent requirements on bearings: they must deliver sufficient load capacity within confined spaces while maintaining smooth rotation with low friction. Featuring an ultra-small cross-sectional height and excellent radial and axial load-bearing capacity, thin-section deep groove ball bearings serve as core components for joint modules of collaborative and service robots. However, the market is flooded with a wide array of bearing models. How to select specifications that fit robots’ high-frequency reciprocating motion and high-precision positioning demands? Combining common industrial application scenarios, this article analyzes key technical parameters and recommends several practically validated thin-section deep groove ball bearing series, offering actionable references for engineers during model selection.

Special Bearing Requirements for Robotic Joints

Robotic joints are generally mounted at the output end of reducers or directly act as rotary supports. Their operating conditions mandate bearings to meet the following criteria:

1. Ultra-narrow cross-section: Internal joint space is limited, leaving no room for standard bearings. Thin-section series such as KA, KB and KC are required, whose radial cross-section is merely 30% to 50% that of standard bearings.
2. Lightweight construction: Every 1-gram reduction in moving component mass cuts motor load and energy consumption. Thin-section bearings achieve weight reduction via optimized steel ball quantities and cage structures.
3. Low friction torque: Robotic joints undergo frequent start-stop and reverse rotation; bearing friction torque directly governs joint response speed and positioning accuracy.
4. High rigidity with low vibration: Deformation under external loads must be controlled at the micrometer level, while operational vibration and noise shall stay below industry benchmarks (typically vibration acceleration ≤ 10 dB).

Technical Advantages of Lightweight Thin-Section Deep Groove Ball Bearings

Balanced Compact Structure & Load Capacity

By reducing inner and outer ring wall thickness and raising the proportion of steel ball diameter, thin-section deep groove ball bearings deliver rated dynamic load comparable to standard bearings of the same bore size within an ultra-narrow cross-section. Take a typical specification with a 20 mm bore, 32 mm outer diameter and 7 mm width (6804 ZZ) as an example: its dynamic load can exceed 3.5 kN, fully covering combined radial and axial load demands of small robotic joints.

Precision Clearance Control & Rotational Accuracy

Robotic joint bearings usually adopt C2 or C3 clearance to compensate for thermal expansion, with rotational accuracy maintained at P5 class or higher. Thin-section precision bearings adopt sorting and matching processes during production, limiting radial clearance to a range of 5–15 μm. Paired with high-performance greases (e.g., Shell Dolyma R or Klüber BEM 41-141), they sustain stable low-friction performance across temperatures from -20 °C to +120 °C.

Recommended Mainstream Series & Comparison

Below are three market-proven thin-section deep groove ball bearing series engineered for robotic joints with varying load levels and space constraints. Data is sourced from manufacturers’ official catalogs and third-party test reports.

1. KA Series (Open Thin-Section)Suitable for high-speed, light-load applications. A typical model KA10CP0 has a 25.4 mm bore, 31.75 mm outer diameter and 3.967 mm width, with a limiting speed up to 30,000 rpm and friction torque as low as 0.5 mN·m. This series from thin-section precision bearing suppliers adopts hybrid ceramic balls to further lower inertia.
2. KC Series (Sealed)Designed for joints requiring dustproof protection and long-term grease retention. The recommended model KC062XP0 features a 15.875 mm bore, 22.225 mm outer diameter and 3.967 mm width. Its double-sided contact seal prevents grease leakage, making it ideal for wrist joints of collaborative robots.
3. KBF Series (Four-Point Contact Thin-Section)Optimized for shoulder or base joints subjected to heavy axial forces and overturning moments. Model KBF5-20 (20 mm bore, 26 mm outer diameter, 5 mm width) features a 30° contact angle, boosting axial load capacity by 40% versus standard deep groove ball bearings.

Field installation feedback confirms that the KBF series delivers stable performance in joints bearing loads ≥ 500 N, with a service life exceeding 8,000 hours under continuous rotation. The clearance dispersion of mass-produced units is less than ±3 μm.

Model Selection Based on Load and Rotational Speed

Selection requires comprehensive evaluation of the robotic joint’s maximum load, rotational speed, operating temperature and installation envelope. Follow the steps below:

1. Confirm the bearing bore diameter (normally equal to the joint shaft journal diameter) and maximum outer diameter (restricted by the inner bore of the joint housing).
2. Calculate the equivalent dynamic load P, then cross-reference the rated dynamic load C from product catalogs to ensure the C/P ratio ≥ 2.0.
3. Verify the limiting speed n. For high-speed joints (>10,000 rpm), select the open KA series or cage-equipped ceramic ball variants.
4. Determine sealing type: opt for sealed KC series if the operating environment contains dust or splashing coolant.

For axes J1–J3 of typical 6-axis industrial robots, the KBF thin-section precision bearing series is recommended. Its four-point contact design withstands radial, axial and moment loads simultaneously, eliminating the need for additional angular contact ball bearings and simplifying joint structure. For small axes J4–J6, open KA series with thin oil lubrication satisfies precision requirements.

Conclusion

Lightweight thin-section deep groove ball bearings play an irreplaceable role in robotic joints. Three core indicators shall be prioritized during selection: cross-sectional dimensions, clearance class and friction characteristics. The KA, KC and KBF series each cater to distinct load and speed ranges. During prototype development, contact the technical team of thin-section precision bearing suppliers to obtain customized clearance and lubrication solutions tailored to actual assembly boundary conditions, maximizing joint service life and motion smoothness.