Seilgetriebene Lösung für dexter Hand - Der Schlüsselweg und die ideale Wahl für hochdexter und menschenähnliche Manipulationen

This article aims to analyze the core reasons why the cable - drive concept has become the mainstream and shown remarkable potential in the field of dexterous hands of modern humanoid robots. First, the strategic position of the dexterous hand in the humanoid robot system is defined, and the technological challenges it faces are identified. In the process, an evaluation system is established, with the human hand as the ultimate reference model. Subsequently, the focus is placed on the core advantages of the cable - drive concept compared to traditional drive systems, including breakthroughs in dynamic optimization, spatial arrangement, bionics, and the application of new materials. Through the analysis of industry - leading examples such as Tesla Optimus and the practice of Jiuzhangzhu Company in the fields of intelligent prosthetics and industrial dexterous hands, the technical feasibility and market prospects of the cable - drive concept are verified. Finally, the market for disabled users is considered to explore how the technology can evolve from an assistive tool to a partner for an enabling life and to uncover deeper humanistic values and market opportunities.

1. Technical Requirements and Ultimate Challenges of the Dexterous Hand

In the pursuit of general intelligence by humanoid robots, the dexterous hand plays a crucial role. It is not only the main medium for the robot to interact with the physical world but also the core component for performing fine manipulations and complex tasks.

The human hand's motion system consists of 22 degrees of freedom (excluding the internal and external rotation of the forearm). Each of the five fingers has 4 degrees of freedom (20 in total), and the wrist has 2 degrees of freedom. These degrees of freedom are distributed among the metacarpophalangeal joints (MCP), the proximal interphalangeal joints (PIP), and the distal interphalangeal joints (DIP). The dexterous hand must replicate this complex structure to achieve the fine manipulation capabilities of the human hand, such as 13 basic functions like hanging, carrying, touching, pressing, hitting, dynamic manipulation, spherical grasping, tip - grasping, cylindrical grasping, pulling, two - tip grasping, multi - tip grasping, and lateral grasping.

To fulfill this role and perform these movements, the design of the dexterous hand must meet a series of strict technical requirements:

High Number of Degrees of Freedom: The motion capacity of the human hand with multiple joints and fingers must be replicated to enable the grasping and manipulation of objects of different shapes, sizes, and materials. New materials are used to mimic the soft palm, and by increasing the contact area during grasping, the grasping stability is enhanced, and energy consumption is further reduced to improve the energy - efficiency ratio.

Lightweight Design: Since the hand is at the end of the robot arm, its weight and moment of inertia directly affect the energy consumption, speed, and stability of the overall movement.

Fast Response: The dexterous hand must have a reaction time in the millisecond range to enable dynamic grasping, fast responses, and seamless human - robot interaction. Through motion solutions and algorithm compensation, the repeatability and consistency of movements are ensured.

However, the only ultimate reference model for the success of the dexterous hand is the human hand, which has been perfected over millions of years. Therefore, we must establish a multi - dimensional evaluation system whose criteria are not only based on technical parameters but also comprehensively consider "human - like" characteristics:

Function and Performance: It is not only about indicators such as force, speed, and accuracy but also about whether the hand can perform a series of complex "in - hand manipulations" such as opening bottle caps, using tools, and tying shoelaces.

Size and Bionics: The size should match that of the human hand so that the hand can work seamlessly in an environment designed for humans. Its movement form and grasping posture should be biologically natural.

Influence on the Whole Body: How the design of the dexterous hand affects the dynamic properties, energy consumption, and control complexity of the entire humanoid robot is the key to evaluating its quality.

Functional Representation in Structure: The human hand combines the three functions of motion, support, and sensation. Therefore, the design of the dexterous hand must not only consider the drive but also integrate a rich sensor array (force, position, temperature, etc.) to enable a closed - loop of perception and control.

In the current discussion, there is a widespread view that the humanoid - dexterous hand performs worse than specialized three - jaw chucks or parallel grippers in certain situations. This view confuses the fundamental difference between general - purpose devices and special - purpose devices. For example, the human hand is not as efficient as a torque wrench when tightening screws with high torque, but this does not diminish the versatility and value of the human hand. In this example, the three - jaw chuck is a special - purpose tool on the industrial automated production line, which focuses on maximum efficiency for a single task; the dexterous hand, on the other hand, is a general - purpose tool aiming to achieve adaptability and versatility in an unstructured environment. This is essentially a matter of "every thing has its strengths and weaknesses" and not a debate about whether the technical direction of the dexterous hand is correct or not. The application goal and scope of the dexterous hand are to achieve general functionality in a human - robot environment based on sufficient performance and cost - effectiveness.

2. Core Advantages of the Cable - Drive Concept: The Perfect Combination of Technical Feasibility and Bionics

In the search for a "human - like" dexterous hand, the choice of the drive concept is the crucial starting point for the overall performance of the system. Traditional gear drives, linkage or point - plunger concepts, etc., have already had mature applications in industrial robot arms and other scenarios. However, when constructing a dexterous hand with a high number of degrees of freedom and miniaturization, they actually reach the limits of size, weight, and structural complexity. At the same time, the cable - drive concept, with its lightweight design and flexible arrangement, offers new possibilities for the realization of the dexterous hand. It should be noted that different drive systems are not mutually exclusive - in the body parts and large joints of the humanoid robot, the traditional drive still has important value; in the "hand", which requires high finger mobility and integration, the cable - drive concept shows a rather unique adaptability.

1. Remote Drive Design and Dynamic Optimization

One of the greatest advantages of the cable - drive concept is that it supports indirect remote transmission. This means that the drive units (actuators) such as motors and gearboxes, which have high requirements for spatial arrangement, can be removed from the smaller execution space and instead installed at a remote location with relatively more space. This "remote drive design" offers advantages in terms of dynamics:

Figure: Schematic diagram of the cable - drive concept

Concentrating the mass near the center of motion of the robot can significantly reduce the inertia at the end of the arm during movement. This allows the arm to move faster, reduces the overall energy consumption of the robot, and improves the dynamic response ability. Studies have shown that the movement speed of the fingers of an optimized cable - driven hand can be in the range of 30 milliseconds, and the reaction delay of the motor can be reduced to 18 milliseconds. Although the flexibility of the cable may pose challenges in control, it has great speed potential under low load.

2. Space - Saving Design and Enabling a Design with a High Number of Degrees of Freedom

Within the limited space of the size of a human hand, more than 20 degrees of freedom must be integrated. The cable - drive concept significantly simplifies the mechanical structure at the finger end by replacing rigid gears and linkages with flexible "cables". One or more cables can cross multiple joints to enable coupled movement or independent control. This makes it possible to realize complex multi - joint movements in a high - density space and paves the way for the design of a human - like dexterous hand with over 20 degrees of freedom.

3. Replication of Human Tendons and Enabling Flexible and Natural Movements

The structure of the cable - drive concept is very similar to the "skin - muscle - skeleton" system of humans. On the one hand, cable - drive control enables flexible motion transmission, which is the fundamental characteristic compared to traditional rigid drive systems. This bionic design is not only more natural in appearance but also brings "flexibility (compliance)" in function. On the other hand, the filling material between the motion mechanism and the surface can absorb part of the impact energy due to its elasticity when the dexterous hand comes into contact with an object, thus preventing a rigid collision from damaging the motor or the object. This internal flexibility is crucial for safe interaction with humans or sensitive objects in an unstructured environment.

4. Key Material Breakthrough: The Power of Ultra - High - Molecular - Weight Polyethylene Fibers (UHMWPE)

The long - term reliability of the cable - drive concept was once its main drawback, but the discovery of new materials has fundamentally changed this situation. High - performance fibers such as Ultra - High - Molecular - Weight Polyethylene (UHMWPE) (e.g., Dyneema® or Spectra®) form the solid foundation for the technical application of the cable - drive concept.

Figure: Advantages of the Ultra - High - Molecular - Weight Polyethylene fiber material

High Strength and Lightweight Design: The specific strength of UHMWPE fibers is more than 15 times higher than that of high - quality steel, and the density is only 0.97 g/cm³. This reduces the overall weight of the dexterous hand by 30% - 40% and the moment of inertia by 45%, which improves the grasping speed and mobility and makes it the ideal material choice for realizing a lightweight design and high - load transmission.

Excellent Abrasion and Fatigue Resistance: This material has excellent abrasion resistance, corrosion resistance, and resistance to kink fatigue. After 2 million cycles of tensile stress, it still retains over 95% of its strength, which is a significant advantage compared to traditional polyester fibers, which lose 30% of their performance after 1 million cycles. This ensures that the fiber retains high strength even after millions of motion cycles and meets the high - frequency usage requirements of the robot hand.

Dealing with Creep: Although creep (the irreversible elongation under long - term load) was once the main problem of UHMWPE fibers and could potentially affect the long - term accuracy of the system, its influence has been reduced to an acceptable level through advanced weaving techniques, pre - tensioning techniques, and compensation in the control algorithms. Solving the creep problem remains an important research area for improving long - term reliability.

Overall, the cable - drive concept can approximate the size of the human hand. In terms of performance, although it may not be as powerful as a heavy - duty gear - drive system in maximum torque output, its combined advantages in terms of speed, mobility, and lightweight design make it more suitable for the application fields of general dexterous hands.

3. Industry Applications and Existing Case Studies for Verification

Theoretical superiority must ultimately withstand the test of practice. The cable - drive concept has already proven its value in several leading fields and is gradually becoming the mainstream choice in the industry.

The Market - Leading Product Defines the Technical Direction: Tesla Optimus

Tesla has used a hybrid drive structure of "planetary gear + spindle + cable - drive" in the dexterous hand of its second - generation humanoid robot Optimus Gen 3. The motor and the gearbox are also integrated in the forearm. The spindle converts the rotational motion into linear motion, and finally, the cable - drive transmits the force to each finger joint.

The external arrangement of the drive increases the number of degrees of freedom, the spindle improves the accuracy and load capacity compared to a worm, and the cable - drive increases the mobility compared to a torsion spring. This design gives the dexterous hand 22 degrees of freedom, which is close to that of the human hand.