1 The structure and working principle of NMT cross roller bearing

The NMT cross roller bearing is a precision bearing composed of three major components: a split inner ring or outer ring, cylindrical rollers, and spacer retainers. Its most notable feature lies in the fact that the cylindrical rollers are arranged alternately at a 90° angle along the raceway. The bearing direction of adjacent rollers is perpendicular, and the V-shaped integrated raceway forms four-directional bearing contact surfaces.

 

With this structure, it is possible to simultaneously bear radial loads, axial loads in both directions, and moment loads from all directions. During operation, the cylindrical rollers roll along the raceway in line contact, and the contact stress is uniformly distributed, thus achieving high rigidity and precision.

 

The two major characteristics of this bearing structure are as follows:

 

Split rings: The inner ring is split or the outer ring is split, and the assembly is achieved by applying preload with locking bolts to eliminate the clearance, thereby achieving a zero clearance preload state. This effectively suppresses the inclination during joint load application.

 

Line contact bearing: The rollers and raceways have full-length line contact, which results in an effective bearing contact area on the same cross-sectional height that is more than four times higher compared to shafts with point contact. The elastic deformation is significantly reduced.

 

The NMT cross roller bearing is made of high-quality bearing steel, undergoes ultra-precision grinding on the track, and the rollers are strictly graded and selected, thereby suppressing vibration, heat generation, and noise during high-speed operation. It comes in various configurations, including integral (non-split) types and types with mounting holes, allowing for selection based on the application requirements.

 

2 Core performance advantages of NMT cross roller bearing

Firstly, "single set bearing, multi-directional load bearing". With one set of cross roller bearing, it can simultaneously bear radial loads, axial loads in both directions, and moment loads, eliminating the need for multiple bearing sets to be stacked in robotic wrists or positioners. The structure is significantly simplified, and a compact layout is achieved.

 

Secondly, "simplification to the limit and high rigidity". The cross roller bearing's axial cross-sectional height is reduced by 1/2 to 1/3 compared to the combined bearing (stacked configuration of multiple bearings). At the same time, the rigidity is increased by 3 to 4 times compared to the traditional bearing. This characteristic of "small cross-sectional height but high rigidity" is most suitable for joint parts with limited space, such as collaborative robots and humanoid robots.

 

Thirdly, "high rotational accuracy and low friction torque". NMT strictly manages the roundness and waviness of the raceway and introduces online dynamic balance correction technology to achieve extremely low vibration during high-speed rotation. Operation in the negative preload (zero clearance or slight tightening) state is possible, with extremely small fluctuations in friction torque, providing stable rotational accuracy.

 

Fourthly, "long-term precision maintenance". NMT strictly manages the crowned curve of the rollers and the surface integrity of the raceway, effectively flattening the stress peaks in the rolling contact area. As a result, even after experiencing millions of switching loads, the rotational accuracy of the shaft support remains stable from the initial state, and the gap does not gradually expand.

 

The fifth point is "Ease of assembly and pressure management". The NMT cross-roller shaft support incorporates a positioning and pressure setting structure on the outer ring. By utilizing the height difference between the end faces of the inner and outer rings, an elastic compression amount that can be calculated is formed, and it is transformed into a stable axial pressure during bolt tightening. This enables assembly workers without extensive adjustment experience to obtain consistent pressure effects and ensures the consistency of joint performance in mass production robots.

 

The sixth point is "Versatile customization support". In the standard models of NMT cross-roller shaft supports, the interface for exchanging lubricating grease according to different working conditions is ensured in advance. The seal structure also offers multiple options of non-contact labyrinth type and contact rubber seal, and it is suitable for a wide range of environments from clean assembly workshops to casting and grinding workshops.

 

3 Main industrial application scenarios of NMT cross-roller shaft supports

3.1 Joint parts of industrial robots

 

It is widely adopted in the body, shoulder, and wrist joints of 6-axis industrial robots, as well as collaborative robots, humanoid robots, etc. The main shaft support at the output end of the RV reducer and the ultra-thin type that is integrated into the inner ring of the high-torque reducer are important components that determine the "lower limit of motion" of the robot.

 

3.2 Precision rotary tables for work machinery

 

Used in machining centers' rotary tables and extraction devices of work machinery. In precision processing where high rotary accuracy and rigidity are required, the NMT cross-roller shaft support provides stable processing accuracy.

 

3.3 Medical machines and optical machines

 

Suitable for the rotary parts of machines requiring high precision and rigidity, such as medical robots, surgical support arms, precision measurement machines, and IC manufacturing devices. Especially in optical inspection robots, the slight vibration of the shaft support directly affects the image resolution, and the low vibration characteristic of NMT plays a significant role.

 

3.4 Aerospace and defense equipment

 

Used in azimuth drive devices of satellite antennas and missile launch frames, etc. For applications requiring high reliability and accuracy, the compact and high-rigidity design of NMT cross-roller shaft supports is utilized.

 

3.5 Semiconductor manufacturing devices

 

Used in the rotary parts of wafer transfer robots in a vacuum environment and the precision stages of exposure devices. In clean environments with low dust and vacuum suitability requirements, NMT shaft supports exhibit stable performance.

 

4 Selection of types, assembly, and daily operation guidelines

4.1 Points for structure selection

 

RB type (outer ring split type): Basic type. The outer ring is constructed in two pieces, and the inner ring is a monolithic type. It is suitable for applications where the rotational accuracy of the inner ring is required.

 

RE type (inner ring split type): The inner ring is constructed in a split type, and the outer ring is a monolithic type. It is suitable for applications where the rotational accuracy of the outer ring is required.

 

RU type/CRBH type (inner and outer rings integrated type): This is a high-rigidity type with an integrated structure for both inner and outer rings. The mounting holes are pre-arranged, eliminating the need for flanges or support seats, and providing stable rotational accuracy.

 

 

Ultra-thin type: High-speed wave reduction mechanism joints and other joints that require extreme thinness are suitable for applications where thinness is required to the limit.

 

Precision selection: General-purpose robot joints are at the P4-P5 level; high-speed wave reduction mechanisms and ultra-precision applications are selected at the P2 level.

 

4.2 Assembly Considerations

 

The cross-roller shaft seal is of a split structure, so when assembling, the following points should be noted:

 

Clean the cross-roller shaft seal before assembly, and use special tools to press the inner and outer rings straight and uniformly.

 

Do not strike the cross-roller shaft seal directly with a hammer.

 

The locking bolt is tightened uniformly to the specified torque. Due to the positioning and pressure structure of the NMT's position determination, the appropriate preload is automatically obtained.

 

In the case of a split structure, there is a plug in the hole for inserting the rollers, and the position of the plug should be configured so that it does not exceed the maximum load range during installation.

 

The inner and outer rings are securely fixed in the holding plate in the axial direction.

 

4.3 Lubrication Management Advice

 

The NMT cross-roller shaft seal has an interface suitable for exchanging lubricating grease according to different working conditions in its standard model.

 

For precision assembly robots, lubricating grease with moderate damping (viscous resistance) is recommended.

 

For high-speed picking robots, lubricating grease with low friction and high responsiveness is recommended.

 

For applications in humid environments or marine climates, specifications with anti-rust and anti-corrosion measures such as low-temperature sulfur infiltration treatment should be selected.

 

4.4 Daily Inspection Items

 

Monitor the operating noise and temperature of the cross-roller shaft seal regularly. In cases where abnormal sounds or temperature rise occur, confirm the lubrication status and the presence of foreign matter intrusion. The NMT cross-roller shaft seal, with its high rigidity and high sealing performance, can achieve a long service life of tens of thousands of hours under normal operating conditions.

 

5 Input Replacement Value and Supply Chain Advantage of NMT Cross-roller Shaft Seals

For industrial robots and precision machine manufacturers, high-precision cross-roller shaft seals are indispensable components. Previously, high-precision cross-roller shaft seals had to rely on overseas brands, and the lead time and high cost were issues.

 

The Japanese NMT cross-roller shaft seals are produced based on a precision manufacturing benchmark, and their rotational accuracy, rigidity, and fatigue life are on par with top overseas brands. You can adopt them with confidence for applications with strict requirements.

 

The dimensions conform to international standards, and direct replacement with existing equipment is possible, without the need for additional processing. The universal size is available in large quantities in stock, allowing for stable supply even for large orders, and reducing the burden on the company's inventory of components. The simplification of the distribution route helps to reduce procurement costs and optimize mechanical manufacturing budgets.

 

High-quality NMT cross-roller shaft seals ensure the rigidity and accuracy of the robot joint, suppress vibration and position deviation at the end, and reduce equipment sudden stops. This contributes to the improvement of the industrial robot supply chain and the alleviation of the risk of delayed delivery from overseas shaft seals.

 

NMT selects temperature-adaptive base materials, optimizes thermal stability structures, provides special lubrication for a wide temperature range, and offers special non-standard specifications. The main sizes are in stock, and the installation method conforms to industry standards, allowing for direct replacement with equivalent products.