In today's era of rapid technological advancements, humanoid robots have become the focal point of global attention. From Tesla's Optimus to Xiaomi's Iron Man, and UBTech's WalkerX, renowned companies have been launching humanoid robot products, sparking waves of discussions. At the 2024 World Artificial Intelligence Conference, 25 humanoid robots made a collective appearance, capturing people's imaginations. Their presence not only showcased the charm of technology but also inspired people to imagine the future possibilities in our daily lives.
Among the many key technologies of humanoid robots, the harmonic reducers, as a core component, is undeniably crucial. Reducers can mainly be categorized into harmonic reducers, planetary reducers, and RV reducers. Among these, the harmonic reducers have become the mainstream choice for humanoid robots due to its unique advantages. They feature small size, light weight, high precision, large transmission ratio, and strong load capacity, fulfilling the movement demands of humanoid robots that are limited by space and weight, achieving high-precision and high-torque movements.
Imagine the joints of a humanoid robot are like human joints, requiring flexible and precise movements. The harmonic reducers act as the "unsung hero" in these joints, converting the high-speed rotation of the motor into low-speed, high-torque output. This provides stable and powerful support for the robotic joints, allowing the robot to perform complex and precise actions such as shaking hands, dancing, operating tools, and more. In essence, without the exceptional performance of the harmonic reducers, many functions of humanoid robots would be difficult to realize.
Although small, the harmonic reducers contain immense energy and play a critical role in the motion control of humanoid robots. So, how does it work?
The harmonic reducers mainly consist of four basic components: a wave generator, a flex spline (flexible gear), a flex bearing, and a rigid spline (rigid gear). Their operating principle is based on the planetary gear transmission principle, using the wave generator to produce controllable elastic deformation in the flex spline, which then engages with the rigid spline to transmit motion and power. When the wave generator is inserted into the flex spline, the flex spline is expanded into an elliptical shape because the wave generator's length is slightly larger than the inner diameter of the flex spline.
In the long axis direction of the ellipse, the teeth of the flex spline fully engage with those of the rigid spline, while in the short axis direction, the two are completely disengaged. As the wave generator continuously rotates, the deformation of the flex spline continuously changes, along with its engagement state with the rigid spline, from engaging, meshing, disengaging, to re-engaging, repeatedly. This enables the slow rotation of the flex spline relative to the rigid spline in the direction opposite to the wave generator.
This unique operating mode endows the harmonic reducers with numerous notable features. Its structure is relatively simple, consisting of only three main components, with the input and output shafts being coaxial. This not only reduces the number of parts but also makes installation more convenient. Its small size and light weight mean that compared to conventional reducers, the harmonic gear reducers' volume can be reduced by 2/3, and their weight can be halved while delivering the same output torque. This is a significant advantage for humanoid robots that face strict space and weight constraints.
The harmonic reducers offer a large transmission ratio, with a single-stage harmonic gear transmission ratio ranging from 70 to 500, and in some devices, even up to 1000. Multi-stage transmission ratios can exceed 30000, meeting the diverse speed and torque requirements of humanoid robots. They also offer high motion precision, with transmission errors being only about 1/4 of ordinary cylindrical gear transmissions at the same gear precision level.
By slightly altering the wave generators' radius to increase the flex splines' deformation, backlash can be minimized, or even achieve zero backlash engagement, making them suitable for reverse motion, thus ensuring the precision of humanoid robot actions. Moreover, harmonic reducers can transmit motion in confined spaces, utilizing the flexibility of the flex splines to achieve unique functions unmatched by other transmission systems.
In summary, due to these outstanding features, the harmonic reducers have found their niche in humanoid robots, primarily applied in light load areas such as the forearms, wrists, and hands. These areas demand high requirements for volume and flexibility, and the harmonic reducers' small size, light weight, high transmission ratio, and high precision enable them to fully leverage their advantages, aiding robots in performing various agile and precise movements.
For instance, when a robot shakes hands with a human, the wrist's harmonic reducer can accurately control the force and angle, making the handshake natural and smooth; when the robot operates small tools, the hand's harmonic reducer ensures the accuracy and stability of the actions, completing delicate operational tasks.
