1. Industry Pain Points: The Rigidity Dilemma and Space Paradox of Robot Joints

In today's robot joint design, bearing selection has moved far beyond simple support functionality to become a fundamental variable defining overall machine performance. Next-generation intelligent equipment such as collaborative robots, humanoid robots and medical manipulators place nearly contradictory demands on joints—slender enough to free design space yet rigid enough to handle combined loads; large hollow passages for cables and tubes yet extremely high rotational accuracy and long life.

 

Traditional ball bearings carry loads through point contact. Under heavy loads or moments, local deformation occurs, leading to end-effector jitter. Conventional multi-bearing combinations can分散 loads, but axial space is significantly occupied and cumulative assembly errors further degrade rotational accuracy. Imported crossed roller bearings offer excellent performance but have long procurement cycles and high prices, while domestic products commonly suffer from insufficient roller crowning control, poor rolling consistency and weak cage strength.

 

At the interface between robot reducers and joint housings, bearing rigidity directly affects overall torsional stiffness and positioning accuracy. Many automation engineers have experienced this: newly assembled robots have perfect accuracy, but after thousands of hours of operation, trajectory drift begins, eventually forcing speed reduction. The root cause often lies in early bearing micro-wear and clearance amplification effects.

 

For applications requiring extreme space efficiency, ultra-high rigidity and full-lifecycle precision retention, specialised crossed roller bearings with single-bearing multi-directional load capacity, thin cross-sections, high rigidity, hollow design for cable routing and long-term precision stability are urgently needed.

 

2. Product Core Positioning: One Bearing, All Directions of Force

The core structure of NMT crossed roller bearings features cylindrical rollers arranged at 90° perpendicularly in V-shaped raceways. Unlike the point contact of ball bearings, rollers form line contact with raceways, allowing stress to disperse evenly across raceway surfaces like flowing water. This orthogonal dense arrangement enables a single bearing to simultaneously resist radial forces, axial forces and tilting moments—equivalent to integrating the functionality of two angular contact bearings into the width of a single bearing, while significantly saving axial space.

 

By arranging cylindrical rollers at 90° staggered on a compact rolling circumference, NMT achieves simultaneous load carrying of multi-directional loads within minimal section height. Robot wrists or positioners no longer need to stack multiple bearings to分散 loads. Even when a robotic arm extends at full speed and makes an emergency stop, the joint maintains geometric stability with no unwanted vibration transmitted to the end-effector. Compared to conventional types, NMT crossed roller bearings deliver 3-4 times higher rigidity.

 

Through strict control of roller crowning profiles and raceway surface integrity, NMT effectively reduces stress peaks in rolling contact areas. Spacers or separators between rollers prevent tilting or mutual friction, effectively avoiding abnormal increases in rotational torque. Even after millions of alternating load cycles, bearing rotational accuracy remains stable and clearances do not gradually increase.

 

True precision motion cannot exist without strict management of "clearance." NMT implements negative clearance preload during crossed roller bearing manufacturing—through precision matching of inner and outer rings, rollers operate with zero clearance or even slight interference. This preload, based on precise calculation of raceway profiles and roller crowning, ensures friction torque fluctuations are controlled within an extremely narrow range throughout the entire rotation cycle. For industrial robots that need to repeatedly perform welding or assembly at the same point, this means every positioning action reproduces the same posture without random angular drift.

 

The ultra-thin cross-section design minimises inner and outer ring dimensions, approaching the极限 of miniaturisation. The central hollow passage allows cables and tubes to pass straight through. The axial space saved can be allocated to cables, air tubes or even force sensors, enabling robot bodies to maintain high rigidity while possessing more powerful end-integration capabilities.

 

3. Structural Classification & Functional Advantages

(1) RB Series – Outer Ring Split Type

 

Outer ring split with integrated inner ring design, suitable for applications requiring high inner ring rotational accuracy. Rollers are arranged perpendicularly in V-shaped raceways separated by spacers. The split structure allows precise clearance adjustment, enabling high-accuracy rotational motion even under preload. Suitable for collaborative robot wrists, medical manipulators and other applications with extreme precision requirements.

 

(2) RE Series – Inner Ring Split Type

 

Inner ring split with integrated outer ring design, suitable for applications requiring high outer ring rotational accuracy. Main dimensions are the same as RB series, catering to different rotational accuracy requirements.

 

(3) RU Series – Integrated Inner and Outer Ring Type

 

Both inner and outer rings are integrated structures with pre-machined mounting holes, eliminating the need for fixing flanges and support housings. Installation has minimal impact on performance, providing stable rotational accuracy and torque. The high-rigidity integrated design with optimised mounting hole layout effectively reduces deformation caused by installation bolts, further enhancing rotational stability and precision, suitable for applications where both outer and inner rings rotate.

 

(4) RA Series – Ultra-Thin Compact Type

 

A new type derived from RB series design, with inner and outer ring thickness reduced to the极限. Most suitable for applications requiring lightweight and compact design, such as collaborative robots, humanoid robot wrists and ankles, precision alignment platforms and more.

 

Quick-Change Robot Special Design: NMT's crossed roller bearings for quick-change robots integrate high-hardness locating tapers on inner and outer rings. Through precision grinding, these tapers form self-centring rigid connections with matching taper holes on robot interfaces. Even after thousands of quick-change cycles, bearing installation positions remain repeatable to micron-level accuracy without incremental compensation of tightening torque. This design, which transfers positioning functionality from the housing to the bearing itself, enables modular robots to maintain joint rigidity while achieving true plug-and-play flexibility.

 

General advantages summary: Orthogonally arranged cylindrical rollers with line-contact high rigidity, 3-4 times higher than ball bearings; single bearing handling radial, axial and tilting moment loads; ultra-thin cross-section design providing reliable support with minimal height; central hollow for cable routing; negative clearance preload eliminating clearance amplification effects, ensuring repeat positioning accuracy; strict control of roller crowning profiles and raceway surface integrity effectively reducing stress peaks; full-lifecycle precision retention capability; split structure allowing precise clearance adjustment; precision grades covering P5/P4/P2.

 

4. Two-Grade Material & Process Selection

Grade 1: Through-Hardened Bearing Steel (General Version)

 

Integral quenching and low-temperature stabilizing tempering achieve uniform raceway hardness and excellent roller wear resistance. Suitable for general industrial robot joints, automation turntables, precision testing equipment and other conventional conditions, with outstanding cost performance for mass production supporting.

 

Grade 2: Carburized Bearing Steel (Heavy-Duty Reinforced Version)

 

Inner rings, outer rings and rollers undergo deep carburizing quenching for hard wear-resistant surfaces with a tough impact-absorbing core. Applied to heavy-duty palletising robots, large six-axis robots, humanoid robot hips and other high-load applications, withstanding instantaneous peak loads with significantly extended service life under extreme conditions.

 

5. Japanese Precision Manufacturing Process

Vacuum degassing refining of high-purity special steel forging, controlling non-metallic inclusions to extremely low levels and eliminating fatigue crack initiation points;

 

Precision forging + gradient heat treatment, ensuring thin-section rings maintain stable geometric shapes after quenching, preventing warpage from residual stress release;

 

Staged stabilisation treatment precisely coordinated with ultra-precision grinding—thin-section rings are prone to residual stress release and distortion after grinding; NMT employs staged stabilisation treatment precisely coordinated with ultra-precision grinding to bring raceway roundness and roughness to demanding levels;

 

Precise roller crowning profile control—strictly controlling roller crowning curves and raceway surface integrity to effectively reduce stress peaks in rolling contact areas;

 

Raceway online dynamic balance correction—real-time measurement and compensation of workpiece imbalance during grinding, ensuring uniform mass distribution of finished rings and minimising periodic excitation forces at high speeds;

 

Negative clearance preload—through precision matching of inner and outer rings, rollers operate with zero clearance or even slight interference, based on precise calculation of raceway profiles and roller crowning, ensuring friction torque fluctuations are controlled within an extremely narrow range throughout the entire rotation cycle;

 

Group matching of rollers with micron-level dimensional tolerance control for uniform load distribution;

 

Superfinishing and mirror-grade polishing of raceways with stable surface roughness control for stable lubricating oil film formation;

 

Assembly in temperature-controlled dust-free workshops with precise preload and clearance control;

 

100% full inspection including torque, vibration, rotational accuracy and run-in tests, with complete data archived.

 

All dimensions comply with international standards for direct interchange with mainstream crossed roller bearings.

 

6. Precision Grades & Customisation Options

P5 Grade: General precision grade, suitable for most industrial robot joints and automation turntables;

 

P4 Grade: High precision grade, suitable for precision testing equipment, optical instruments and medical imaging equipment;

 

P2 Grade: Ultra-high precision grade, suitable for semiconductor equipment, aerospace-grade precision rotation mechanisms.

 

Customisation options: special clearance configurations, high/low temperature resistant materials, special grease adaptation, non-standard sizes, integrated locating taper design, contact/non-contact labyrinth seal options and more.

 

7. Wide Application Fields

Industrial Robots: Bases, shoulders, elbows, wrists, finger joints—high-rigidity compact support; robot reducer and joint housing interface;

Collaborative & Humanoid Robots: Wrists, ankles, hips—dual requirements of thin-section and rigidity;

Medical Equipment: Surgical robot bases, CT scanner slip ring systems, rehabilitation equipment rotary platforms;

Semiconductor Equipment: Wafer handling robots, vacuum transfer chambers, IC manufacturing equipment rotary platforms;

Precision Testing Equipment: Precision test turntables, optical telescopes, large radar antennas;

Laser Processing Equipment: Laser cutting machine turntables, LiDAR scanning mechanisms;

CNC Machine Tools: Machining centre rotary tables, indexing plates, precision rotary worktables;

Aerospace: Satellite antenna azimuth drives, missile launcher slewing devices;

General Machinery: DD motors, robotic rotating sections, precision alignment platforms.

 

8. Brand Supply & Customisation Service

NMT maintains sufficient spot inventory of mainstream crossed roller bearing specifications for urgent equipment repair and mass complete machine supporting with short lead time. Customisation services include P4/P2 high precision grades, special clearance, high/low temperature resistant materials, special grease, non-standard sizes, integrated locating taper design, contact/non-contact labyrinth seal options and more. Professional engineers provide targeted selection schemes based on equipment load spectrum, installation space, accuracy requirements and speed range to optimise bearing configuration and structural selection, improve overall machine rigidity, control end-effector jitter, extend precision retention cycles and cut the overall life cycle cost of equipment.

 

Crossed roller bearings are redefining the motion quality of robots. From the vacuum environment of wafer handling robots to the high-impact scenarios of heavy-duty palletising robots, NMT crossed roller bearings span vastly different engineering boundaries. As the robotics industry moves from "being able to move" to "being able to run"—whether it is millions of repeated welding actions on automotive body welding lines or the dynamic balance of humanoid robots in complex terrain—every stable revolution of the crossed roller bearing inside the joint is NMT's most silent fulfillment of "precision transmission."