Crossed Roller Bearings: The Optimal Solution for Robotics

What are Crossed Roller Bearings?

A crossed roller bearing is an ultra-precise slewing unit engineered to support complex mechanical loads in extremely restricted installation spaces.

Internal Geometric Structure

Unlike conventional ball bearings that utilize a single rolling path, a crossed roller bearing features cylindrical rollers arranged at strict 90-degree alternating angles within a V-groove raceway. Each individual roller is kept separate from its neighbors by a precision plastic spacer or retainer. This orthogonal layout ensures that half of the rollers bear loads in one orientation while the remaining alternate rollers handle forces perpendicularly.

Handling Multi-Directional Forces Simultaneously

Because of this unique 90-degree crossing configuration, a single crossed roller bearing can simultaneously manage heavy radial loads, axial thrust forces from both directions, and massive overturning moments (tilting forces). In traditional mechanical designs, engineers are typically forced to combine multiple angular contact ball bearings or tapered roller bearings in paired arrangements to achieve comparable multi-load capabilities. The crossed roller architecture condenses this entire multi-part assembly into a single, highly stable, integrated ring structure.

Key Components and Materials

Crossed roller bearings are manufactured using premium vacuum-degassed bearing steels that undergo advanced metallurgical heat treatment. This process ensures exceptional core toughness, uniform microstructures, and superior resistance to rolling contact fatigue. Precision plastic spacers or cages separate each roller, preventing roller-to-roller contact and reducing internal friction while maintaining proper roller orientation.

Why Crossed Roller Bearings Are Ideal for Robots?

Robotic joints undergo frequent directional reversals, high-acceleration cycles, and heavy cantilevered payload shifts, making unique mechanical properties a necessity.

Superior Structural Rigidity and Zero Backlash

Industrial and collaborative robots require absolute positional repeatability at the tool center point. Any structural deflection or internal slack within the joint assembly results in positioning errors. Crossed roller bearings provide exceptional stiffness because their line-contact cylindrical rollers distribute mechanical stress evenly across the raceway, minimizing deformation under heavy loads. Furthermore, many variants are factory-preloaded to completely eliminate internal clearance, ensuring zero backlash during movement.

This rigidity is particularly critical in applications such as spot welding, where robotic arms must maintain precise positioning under fluctuating loads, or in assembly operations where component insertion tolerances are measured in microns.

Space-Saving and Lightweight Architecture

Modern robots must minimize overall arm weight to maximize payload capacity, dynamic speed, and energy efficiency. Conventional bearing setups require bulky housings and multiple independent mounting pieces. In contrast, the thin-section, low-profile layout of crossed roller bearings allows mechanical designers to significantly shrink joint housing sizes, keeping robotic arms streamlined, sleek, and highly agile.

The compact cross-section also contributes to lower overall robot weight, enabling higher acceleration and deceleration rates, reduced energy consumption, and extended servo motor life.

Smooth Multi-Axis Rotation and Low Friction

The integration of precision spacers between rolling elements prevents roller skewing and edge-loading phenomena, drastically cutting down internal rotational friction. This smooth movement enables robotic joints to execute subtle, micro-step adjustments without stick-slip behavior, which is vital for electronics assembly, precision dispensing, and delicate medical procedures.

Additionally, lower friction translates to reduced heat generation, which helps maintain stable joint temperatures and prevents thermal expansion that could compromise positioning accuracy over long operation cycles.

High Durability and Long Service Life

Robots are designed for continuous, 24/7 operation in demanding industrial environments. Crossed roller bearings are built to withstand millions of operating cycles without significant degradation in performance. The use of premium bearing steels and advanced heat treatment ensures exceptional wear resistance and fatigue life, reducing maintenance frequency and unplanned downtime.

Main Types of Crossed Roller Bearings for Robots

Different robotic joint locations impose distinct structural and mounting demands. To match these engineering criteria and streamline mechanical integration, BY Bearings provides several primary configurations corresponding to standard product series:

Bearing Configuration	Structural Characteristics & Design Logic	BY Bearing Series Reference	Typical Robotic Joint Application
Integrated Inner/Outer Ring (Solid Type)	Both inner and outer rings form solid, continuous circles featuring pre-drilled bolt mounting holes. Ideal for applications requiring maximum structural rigidity and simplified installation.	BRU Series (CRBF equivalent)	Joints where external mounting brackets are minimal, installation simplicity is required, and maximum overall structural rigidity is needed. Suitable for heavy-payload robotic arms and base rotation units.
Split Outer Ring Type	The outer ring is divided into two separate halves while the inner ring remains a solid continuous piece, secured with special retaining rings. This design allows for easier assembly of the bearing around the shaft.	BRB Series (RB style) & BRA Series (RA style)	Applications requiring high rotational accuracy of the inner shaft with simplified outer housing attachment and compact dimensions. Common in wrist joints and small-to-medium robotic arms.
Split Inner Ring Type	The inner ring is cut into two independent halves while the outer ring remains a solid continuous circle. Suitable for joint architectures where the outer ring is fixed.	BRE Series (RE style)	Joint architectures where the outer ring is fixed and the central shaft or inner ring mounting necessitates pre-assembled clamping. Often used in turntable and indexing mechanisms within robotic work cells.

Selection Guide by Robot Type

Robot Type	Recommended Bearing Series	Key Considerations
Industrial 6-Axis Arms (Heavy Payload)	BRU Series, BRB Series	High moment load capacity, maximum rigidity
Collaborative Robots (Cobots)	BRA Series, BRB Series	Ultra-compact, lightweight, smooth torque
SCARA Robots	BRB Series	High rotational accuracy, compact design
AGVs / Mobile Robots	BRU Series	Easy installation, integrated mounting holes
Medical/Surgical Robots	BRA Series	Ultra-slim design, low friction, smooth motion

Advantages of Crossed Roller Bearings in Robotic Applications

Integrating crossed roller bearings into robotic designs delivers clear performance and economic benefits:

• • Simplified Housing Layouts: Eliminating complex multi-bearing arrangements allows engineering teams to streamline housing castings and reduce total component part counts. This simplification also reduces machining complexity and lowers manufacturing costs.

• • Accelerated Assembly Cycles: Pre-drilled mounting holes and factory-optimized preloads enable technicians to mount units quickly without tedious shimming or manual clearance tuning. This reduces assembly time and minimizes the potential for installation errors.

• • Improved Energy Efficiency: Reduced internal rotational resistance lowers the torque demands placed on harmonic drives and servo motors, cutting overall power consumption. This is particularly important for battery-powered mobile robots and collaborative robots designed for energy efficiency.

• • Extended Operational Lifespan: Premium vacuum-degassed steels combined with advanced heat treatment ensure robotic joints maintain high precision over millions of continuous operating cycles. This translates to lower total cost of ownership and reduced lifecycle maintenance expenses.

Installation and Maintenance Best Practices

Pre-Installation Preparation

Before installing crossed roller bearings in robotic joints, ensure all mounting surfaces are clean and free from burrs, chips, or contaminants. Verify the dimensional accuracy of the housing bore and shaft to match the bearing specifications. The installation area should be clean, well-lit, and free from dust or debris.

Installation Procedure

Step 1: Handling and Inspection
Carefully remove the bearing from its packaging, taking care not to drop or impact the unit. Inspect for any visible damage during transit. For split-ring types, check the factory alignment marks and ensure proper orientation.

Step 2: Alignment
Position the bearing so that its mounting holes align with the corresponding holes on the housing or shaft. For solid-ring types (BRU Series), the bearing can be placed directly onto the mounting surface.

Step 3: Fastening
Insert the mounting screws evenly around the circumference, tightening them lightly by hand. Using a calibrated torque wrench, tighten bolts in a "star" or crosswise pattern in three progressive stages: 40% of final torque (light pre-tightening), 70% of final torque (intermediate tightening), and 100% of final torque (final tightening).

Step 4: Rotation Verification
After completing torque tightening, manually rotate the joint to verify smooth operation without binding or abnormal resistance. Check that the bearing rotates freely and uniformly.

Lubrication and Maintenance

Crossed roller bearings typically ship with an initial high-quality grease suitable for most robotics applications. Regular maintenance involves periodic relubrication through dedicated grease fittings based on operating conditions. For high-speed robotic applications, more frequent lubrication intervals may be required.

Relubrication Guidelines:

• • Frequency: Establish a schedule based on duty cycle—more frequent for heavy loads or high speeds

• • Quantity: Avoid over-lubrication, as excessive grease increases frictional torque and heat generation

• • Type: Use the correct grease type for the specific temperature range and speed requirements

Condition Monitoring:

• • Watch for abnormal noise, vibration, or increased rotational resistance

• • Monitor temperature during operation for signs of lubrication issues or wear

• • Conduct regular seal inspections to prevent contamination ingress

Key Considerations When Choosing Crossed Roller Bearings for Robots

Selecting the correct bearing involves careful analysis of several critical operational and environmental parameters:

1. Load Profile Evaluation

Calculate maximum radial, axial, and moment loads encountered during peak acceleration and deceleration phases of the robot duty cycle. Consider both static loads (end-of-arm tooling, workpiece weight) and dynamic loads (inertia during rapid movements). Moment loads are particularly critical for wrist joints where tools exert off-axis forces.

2. Precision Class Demands

Establish whether the application requires normal commercial tolerances or ultra-high precision grades (such as P5, P4, or P2) to minimize runout. For semiconductor handling and medical robotics, P2-grade bearings are often required to achieve sub-micron positioning accuracy. For standard material handling robots, P4 or P5 grades may be sufficient.

3. Speed and Thermal Dynamics

Continuous high-speed maneuvers generate internal heat, requiring precise selection of lubricant types and internal clearance classes. Higher speeds necessitate thinner cross-sections, better heat dissipation, and specialized low-friction greases. Consider the maximum RPM and acceleration rates when selecting the bearing configuration.

4. Environmental Exposure

Robots operating in harsh factory environments, cleanrooms, or washdown areas require specialized integrated seals and corrosion-resistant coatings. For food-grade or pharmaceutical applications, consider bearings with food-grade lubricants and specialized sealing to prevent contamination.

Your Reliable Partner for Robotic Bearings: BY Bearings

BY Bearings (Luoyang Boying Bearing Co., Ltd.) specializes in the research, development, and manufacturing of high-precision crossed roller bearings and rotary table bearings for robotics.

Utilizing premium vacuum-degassed bearing steels processed through advanced metallurgical heat treatment methods, BY Bearings ensures exceptional core toughness and uniform microstructures. Every raceway is precision-ground on state-of-the-art CNC grinding centers, achieving sub-micron dimensional accuracy and superior surface finishes. The company offers comprehensive selection support, custom dimension tailoring, and rigorous factory testing for customers across the global robotics industry.

With precision grades available up to P2 and strict ISO 9001 quality control, BY Bearings delivers reliable solutions for industrial robotics, collaborative robots, medical equipment, semiconductor automation, and precision measuring instruments. Inner ring sizes range from Φ50mm to Φ1300mm, with customization options including special dimensions, preload levels, sealing configurations, and specialized lubrication.

Need the right crossed roller bearing for your robotics application? Contact BY Bearings today for technical consultation and find the optimal bearing solution for your specific requirements.

FAQs

Q1: Why are crossed roller bearings preferred over standard ball bearings in robotic joints?
Unlike standard ball bearings that generally require multiple units paired together to handle combined forces, a crossed roller bearing accommodates radial loads, axial loads, and overturning moments simultaneously within a significantly more compact and rigid footprint. This simplifies joint design and reduces overall robot weight.

Q2: Can crossed roller bearings be disassembled during robot assembly?
Solid-ring models (such as BRU Series) must never be disassembled because doing so disrupts factory-set internal clearances and roller orientation. Split-ring models (BRB, BRE, BRA Series) allow temporary separation during mounting, but the pieces must be carefully reassembled matching their original factory alignment marks.

Q3: How do these bearings eliminate backlash in robotic arms?
Manufacturers frequently build crossed roller bearings with a slight negative internal clearance (preload). This tight mechanical fit ensures that rolling elements remain in constant contact with the raceways under reversing loads, eliminating free play or backlash. This is essential for achieving repeatable positioning accuracy in robotic applications.

Q4: What maintenance is required for crossed roller bearings in industrial robots?
Routine maintenance involves periodic relubrication with high-grade synthetic grease through dedicated lubrication fittings, alongside routine checks for unusual vibration, noise, or temperature spikes. For robots operating in harsh environments, more frequent maintenance intervals may be necessary.

Q5: Does BY Bearings offer customized dimensions for unique robot designs?
Yes, BY Bearings provides comprehensive engineering support and custom dimension tailoring to accommodate specialized housing constraints and unique load requirements for robotic manufacturers worldwide. Customization options include special dimensions, precision grades, preload options, sealing configurations, and specialized lubrication.