Crossed roller bearings are special-type bearings with a split inner ring and a rotating outer ring. After inserting rollers and a spacing retainer into the split inner or outer ring, they are fixed together with a crossed roller ring to prevent separation, making installation simple. Due to the cross-arrangement of rollers, a single set of crossed roller rings can withstand loads in all directions, with rigidity increased by 3-4 times compared to traditional models. Meanwhile, the split structure of the inner or outer ring allows adjustment of bearing clearance, enabling high-precision rotational motion even under preload. This unique structure makes it commonly used as a joint bearing in industrial robots.

Cylindrical roller bearings feature a parallel arrangement of rollers inside, with a spacing retainer or separator installed between rollers to prevent tilting or mutual friction, effectively avoiding an increase in rotational torque.

Crossed roller bearings are equipped with a rotatable table, a machine tool accessory used for clamping workpieces and achieving rotation and indexing positioning, commonly referred to as a turntable or fourth axis. Turntables are classified into general-purpose and precision types based on functionality.

Fatigue Life under Cyclic Loading

The fatigue life of crossed roller bearings refers to the number of stress or strain cycles required for material fatigue failure under cyclic loading, often measured in working hours for actual components. The fatigue life before the occurrence of engineering cracks (macro-visible or detectable cracks, approximately 0.2-1.0mm in length) is called crack initiation life, while the life from engineering crack propagation to complete fracture is called crack propagation life. Total life is the sum of both. For materials, fatigue life is the number of stress cycles before fatigue failure, typically measured in working hours for components. Under given repeated loads, it is the number of stress or strain cycles required for material damage, generally divided into crack initiation life and crack propagation life. It is widely accepted that the stress range is the main factor affecting fatigue life: a larger range shortens life, and vice versa.

Clearance of Crossed Roller Bearings

Bearing clearance refers to the movement amount when one ring (inner or outer) is fixed, and the unfixed ring moves radially or axially before the bearing is installed on a shaft or housing. It is divided into radial clearance and axial clearance according to the movement direction.

As a new-type bearing, crossed roller bearings have unique structural features and advantages. Although their theoretical research and production technology are quite mature abroad, domestic research on such bearings remains limited. In bearing design and application, load-carrying capacity and life are critical considerations, making the study of crossed roller bearing mechanisms of great academic and practical value. This paper introduces the material, characteristics, and domestic research status of crossed roller bearings in detail and prospects their future research directions.

Key Research Contents

1. Contact Mechanics Analysis
   Based on rigidity assumptions and classic Hertz theory, the contact problem between rollers and the inner/outer rings of crossed roller bearings was studied. The influence formula of interference fit between the inner ring and shaft (as well as the outer ring and housing) on clearance was determined. Stress calculation formulas for contact rings and important formulas for stress distribution on line-contact elliptical cylindrical surfaces were derived.

2. Load Distribution Model

   • Static Analysis: A model for static radial load and eccentric axial load was established, analyzing the influence of external radial/axial loads, moment loads, and the number of rollers on load distribution.
   • Dynamic Analysis: A dynamic radial load model was developed to obtain load distribution laws under varying rotational speeds, external loads, and radial clearances.

3. Fatigue Life Calculation
   According to bearing load distribution theory and classic contact theory, formulas for rated dynamic and static loads of crossed roller bearings were derived. Based on the Lundberg-Palmgren fatigue life theory, a fatigue life calculation model was established. Combined with engineering-oriented life models, the influence of structural and load parameters on bearing fatigue life was analyzed.

4. Structural Optimization
   Using optimization design theory, an objective function for bearing life optimization was proposed, with boundary conditions determined by theoretical and practical applications. A program was developed using the Matlab genetic optimization algorithm toolbox, and a human-computer interaction interface was created via Matlab's GUI module. This allows ordinary engineers to use the optimization program without mastering Matlab, facilitating practical design and improving bearing life through optimization results.

Conclusion

This paper studies the load distribution, fatigue life, and structural optimization of crossed roller bearings, with results of significant theoretical and engineering application value.