Whether it is industrial robots and collaborative robots participating in quality inspection and goods handling on production lines, service robots providing guidance and navigation for people in shopping malls, or humanoid robots performing on the Spring Festival Gala stage, behind every smooth and precise movement lies the precise operation of joints.

The performance of joints directly determines the precision, speed and flexibility of a robot's movement. Among different types of robots, due to the differences in working environments and task requirements, there are also variations in joint configurations and the key components adopted. Among them, the common shape design mostly adopts a modular approach, integrating the motor, reducer, driver, encoder and other sensors into one unit to form a power output unit.

From the perspective of the composition of joint components, it is overall composed of an absolute value encoder at the motor end, a multi-turn absolute value encoder at the output end, a frameless torque motor, a harmonic reducer, a brake retainer, a servo driver and a torque sensor.

Among them, the encoder is equivalent to a precise "Angle feedback system" of the machine. It can monitor the position of the robot's joints in real time and feed this information back to the control system.

In the eRob series of joint module products, absolute value encoders with a repeat positioning accuracy of ±7 arcseconds and an absolute positioning accuracy of ±15 arcseconds are built-in at both the motor end and the output end of the reducer, forming a full closed-loop position control to prevent the backlash, wear and manufacturing errors of the reducer from affecting the positioning accuracy of the robot joint. This is also currently the harmonic robot joint with the highest precision and the fastest response speed.

Take medical robots as an example. Medical robots are mostly used for surgeries inside the human body. Therefore, they have extremely strict requirements for the repeat positioning accuracy of core components, power consumption and heat generation, safety protection, and torque control.

In humanoid robots, self-developed encoders can achieve more precise control of joint positions, ensuring that the robot can accurately reach the target position during operations such as material handling and parts assembly, thereby enhancing production efficiency and product quality. This can be applied in scenarios such as parts assembly on automotive parts production lines.

At present, the "torso" and "limbs" of humanoid robots mainly have the following three transmission methods: harmonic reducers, planetary reducers and planetary roller screws. Planetary roller lead screws complete linear drives, and rotary movements are accomplished by the joint drive of harmonic reducers or planetary reducers as transmission components.

Planetary reducers have strong load-bearing capacity, can withstand large torques and loads, and have relatively low costs. When applied on a large scale, they can reduce the overall equipment cost. However, at the same time, the single-stage transmission reduction ratio of planetary reducers is relatively small, making them more suitable for heavy-load working conditions and motion structures with relatively low precision requirements.

One of the major advantages of planetary reducers lies in the fact that China has a complete industrial chain foundation, and the related processing equipment has a huge stock in the domestic mechanical processing industry. In addition, the planetary reducer has a simple structure and flexible design modification methods. Its gears can be easily integrated with other components of the joint in one design.

However, for humanoid robots, their structure is complex and they have more than 40 joints. This requires that the joints not only have a sufficiently high power density but also be strictly controlled in terms of volume and weight to fit the compact shape of the humanoid robot. Therefore, the performance of planetary reducers in this aspect may be slightly insufficient. On the contrary, harmonic reducers have demonstrated their significant advantages. Harmonic reducers can achieve a larger transmission ratio within the same space, and through higher transmission accuracy and smaller backlash, they enable robots to perform precise operation tasks.

The enterprise focuses on the joints of harmonic reducer solutions, which are small in size and light in weight, coinciding with the lightweight structure requirements of humanoid robots. Moreover, the transmission accuracy of harmonic is extremely high and the single-stage transmission ratio is large, which can ensure that the joint movement of the robot achieves extremely high precision.

Of course, the current harmonic scheme still has its limitations. On the one hand, harmonic reducers are constrained by high thresholds for processing equipment, large capital investment, strict processing technology requirements, and more critical technical challenges such as materials, heat treatment, and tooth profile design. This requires enterprises to invest a significant amount of capital and human resources in research and development and technological accumulation. On the other hand, in the current situation where the mass production of humanoid robots is difficult to advance, the harmonic reducer, as a core component, is also facing the contradiction of being unable to reduce costs and being restricted in large-scale application in the short term.

The different performances of harmonic and planetary transmission methods in terms of lifespan, shock resistance, noise and failure forms determine that it is difficult for the market to define which transmission method is better in the short term. The harmonic and planetary reducer joints will exist in parallel for a long time. According to the final requirements of the humanoid robot as a whole, choosing the appropriate transmission method in different requirement scenarios remains the optimal solution.

In terms of size, the eRob joint module has a minimum module diameter of only 70mm and a maximum allowable torque of 70Nm, with a maximum module diameter of 170mm and a maximum allowable torque of 1180Nm. Compared with other joint modules of the same load capacity on the market, it has the smallest volume. This feature of achieving high torque output in a small size has significant advantages in practical applications.

For instance, in the logistics and warehousing scenario, users will choose the joints of the smallest modules to drive robots in a limited environment, meeting the flexible operation requirements within the narrow warehouse space. In surgical robots, a smaller joint volume can reduce the distance between multiple surgical robotic arms, and various surgical instruments can be performed through smaller incisions. In addition, smaller joint volumes also provide the possibility for the external dimensions of humanoid robots to continuously approach the real human body dimensions.

For downstream customers, by building standardized and multi-model joint modules, it helps enterprises quickly complete the assembly of robots, saving a large amount of human and time costs consumed in the selection, design, procurement and assembly of hundreds of mechanical and electronic components, allowing robot companies to truly focus on the development of robot complete machines and applications.

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