The Embodied-Intelligence Wave: Fastener Requirements for Humanoid Robot Joints and Actuators
Executive Summary
Humanoid robots are moving from the laboratory toward mass production. The dozens of degrees of freedom across joints and actuators demand fasteners that are highly integrated, highly precise and reliable under high vibration. Shoulder screws at joints must simultaneously carry connection, positioning and rotational support; high-strength anti-loosening screws at actuators must maintain preload under continuous vibration. Drawing on engineering practice, this article breaks down fastener requirements and selection logic for the key positions of humanoid robots.
Table of Contents
- Three Requirements Humanoid Robots Place on Fasteners
- Joints and Reducers: The Positioning Function of Shoulder Screws
- Actuators and Pulley Wheels: Selecting High-Strength Anti-Loosening Screws
- Rod-End Joint Bearings and Articulated Structures
- Lightweight Structural Parts: Thread Inserts and Lock Washers
- Selection Checklist and Engineering Advice
A humanoid robot is covered with core joints such as hip, knee, shoulder and ankle, together with dexterous actuators in the fingers and fingertips. These positions move frequently, vibrate continuously and are compact in space, so fasteners must be small and light yet remain reliable under high-frequency reciprocating motion. Unlike automobiles, robot connections emphasize precision retention and miniaturization rather than sheer clamping force.
Three Requirements Humanoid Robots Place on Fasteners
The design goals for humanoid-robot fasteners can be summarized in three points: high precision—joint locating surfaces must not develop clearance from loose connections; high anti-loosening—preload must not decay under continuous reciprocating vibration; and light weight—every connecting part directly affects whole-machine energy consumption and endurance. Engineering practice has spawned several product lines: shoulder screws for joint positioning, high-strength anti-loosening screws for load-bearing joints, thread inserts for light-alloy housings, and lock washers for vibrating positions.
| Position | Typical Fastener | Core Requirement | Common Material Class |
|---|---|---|---|
| Hip / knee / shoulder joint | Shoulder screws, lock washers | Positioning precision, vibration resistance, long life | Alloy steel 12.9/14.9 |
| Finger / fingertip actuator | High-strength anti-loosening screws | Miniaturization, anti-loosening, corrosion resistance | Titanium 10.9/12.9, high-strength aluminum 6.8 |
| Torso / arm frame | Thread inserts | Soft-material thread reinforcement, anti-stripping | Stainless-steel inserts |
| Sensor / housing cover | Micro screws, captive screws | Precision, removable, anti-drop | Stainless steel, titanium |
Joints and Reducers: The Positioning Function of Shoulder Screws
Shoulder screws (shoulder bolts) are key foundational parts in humanoid-robot joints and moving structures, simultaneously carrying connection, positioning and rotational support: the smooth shoulder acts as the locating shaft and rotational support surface of the hinge, while the threaded section clamps the joint structure. Because shoulder diameter and length precision directly determine joint clearance, these screws demand strict control of concentricity, end-runout and heat-treatment distortion. They are commonly used at knee and ankle joints, dexterous hands and actuator mounting positions.
Actuators and Pulley Wheels: Selecting High-Strength Anti-Loosening Screws
Fingertip actuators, drive pulleys and similar positions are compact and move frequently, requiring fasteners that stay strong and anti-loosening while miniaturizing. Engineering practice commonly uses 12.9-class and even 14.9-class alloy-steel high-strength anti-loosening screws, paired with special thread treatment and surface finish to save space while improving reliability and corrosion resistance. For weight-sensitive positions, 10.9/12.9-class titanium screws or 6.8-class high-strength aluminum screws are used, reducing weight while solving galvanic corrosion with magnesium-alloy joints.
Rod-End Joint Bearings and Articulated Structures
Rod-end joint bearings are the core articulated parts of linear actuators (ball-screw push rods) and link structures, used for flexible hinges that allow controlled multi-directional swinging; they are core components of robot biomimetic motion. The matching fasteners must bear alternating loads and swinging wear at the hinge point, requiring high strength, wear resistance and anti-loosening ability. They are usually used with shoulder screws and lock nuts to keep hinge clearance stable over the long term.
Lightweight Structural Parts: Thread Inserts and Lock Washers
Robot torso frames, arm skeletons and leg main load-bearing structures make heavy use of lightweight light alloys and composites, and direct tapping in these soft materials strips easily. Here thread inserts reinforce the threaded joints of lightweight structures, solving stripping, joint strength and service life. At core hip, knee and shoulder joints and precision sensor modules, lock washers are used, mainly carbon steel and stainless steel, with high-end applications shifting toward high-strength alloy steel and lightweight composites to meet high-frequency vibration, high precision and long-life demands.
Selection Checklist and Engineering Advice
- Joint positioning: shoulder screws selected by smooth-shaft fit precision and shear requirement, with heat-treatment distortion controlled.
- Load-bearing anti-loosening: 12.9/14.9-class alloy-steel high-strength anti-loosening screws with thread anti-loosening treatment.
- Weight-saving positions: 10.9/12.9-class titanium or 6.8-class high-strength aluminum screws, also avoiding galvanic corrosion.
- Light-alloy frames: thread inserts to reinforce threads and prevent stripping under repeated disassembly.
- Vibrating joints: high-strength lock washers, choosing carbon-steel/alloy-steel/composite solutions by vibration magnitude.
Humanoid-robot fasteners are essentially "a high-precision, high-reliability, lightweight connection system built inside a millimeter-scale space." The loosening or clearance of a single screw is amplified by multi-degree-of-freedom motion into a whole-machine precision problem.
Conclusion
Humanoid-robot fasteners sit at the intersection of three demanding curves: ever-higher joint density, rapid weight reduction, and hundreds of millions of reciprocating cycles. Unlike an automotive bolt that mostly sees quasi-static or low-cycle loading, a robot joint bolt experiences continuous micro-vibration, and its preload must not decay over the product lifetime. This is why shoulder screws are so widely used at reducers: they let a pin handle radial position while the screw handles axial clamp, separating the two functions that a plain bolt would be forced to combine. For actuators and pulley wheels, the combination of high strength, low preload scatter, and proven anti-loosening behavior matters more than absolute minimum cost. When frames move into magnesium or aluminum castings, direct tapping is ruled out and thread inserts become mandatory, because soft alloy threads strip long before a high-strength bolt reaches its design preload. Lock washers or pre-applied adhesive are then selected by the vibration mode of the specific joint. Procurement should treat these fasteners as precision components with torque–clamp-force data and batch certificates, not as commodity hardware.
For procurement and design engineers, the practical takeaway is to specify these fasteners with their mating interfaces—reducer bore, shoulder diameter, insert size—as a controlled set, and to require torque–clamp-force data and batch certificates rather than generic material certificates. Joints that survive a humanoid product's lifetime are designed, not catalog-picked.
Humanoid robots push fasteners from ordinary connectors into precision moving foundational parts: shoulder screws handle joint positioning and rotational support, high-strength anti-loosening screws carry actuator loads, thread inserts reinforce light-alloy frames, and lock washers guard high-frequency vibrating positions. On the material side, the combination of 12.9/14.9-class alloy steel, 10.9/12.9-class titanium and 6.8-class high-strength aluminum forms the system. YF Zhichengjia serves the embodied-intelligence industry with selection and customization of shoulder screws, high-strength anti-loosening screws, thread inserts and lock washers. See the technical document library or contact our technical engineers.
