High-precision transmission control makes mechanical transmission widely used There are three basic ways to transmit power: mechanical transmission, electric transmission and fluid power transmission (including pneumatic transmission and hydraulic transmission). Generally, it is necessary to correctly select the appropriate transmission mode according to the basic characteristics of each transmission mode.
Electric transmission is the use of electrical equipment and adjustment of electrical parameters to transmit power and control. Its main advantages are convenient energy transmission, rapid signal transmission, high degree of standardization, easy to realize automation, etc. Its disadvantage is that the motion stability is poor, and it is easy to be affected by external load, and the inertia is large, and the starting and commutation are slow, and the cost is higher, and it is greatly affected by environmental factors such as temperature, humidity, vibration, corrosion. In order to improve its transmission performance, it is often used in combination with mechanical (electromechanical transmission), pneumatic or hydraulic transmission in some occasions.
Pneumatic transmission uses compressed air as the working medium for energy transmission and control. Its advantages are simple structure, low cost, easy to realize stepless speed regulation, small resistance loss, fire and explosion proof, and good adaptability to the working environment. Its disadvantage is that because the air is easy to compress, the load has a greater influence on the transmission characteristics, and the working pressure is low, and it is only suitable for low-power transmission.
Hydraulic transmission uses liquid as the working medium for energy conversion, transmission and control. Its advantages are that the power/mass ratio and the force/mass ratio are large, the control is flexible, the response speed is fast, the stepless speed regulation can be realized, the control is convenient and easy to realize automation, the hydraulic components are easy to generalize, standardized, and have a long service life. Its disadvantage is that the liquid leakage as the working medium leads to pollution, and the compressibility of the liquid, the influence of temperature and the elastic deformation of the pipeline lead to the difficulty to achieve a strict transmission ratio, the transmission efficiency is low, the hydraulic component manufacturing precision is high and the price is expensive, and the working fault is difficult to deal with in the closed system.
According to the difference in transmission principle, mechanical transmission can be divided into three categories: friction transmission, meshing transmission and push transmission. Wherein, friction transmission comprises belt drive, rope drive, etc.; meshing drive comprises gear/gear mechanism transmission (cylindrical tooth, bevel tooth, planetary tooth, etc.), worm drive, spiral drive, chain drive, synchronous belt drive, etc.; thrust drive comprises cam/ratchet/sheave mechanism, connecting rod mechanism, etc.
Humanoid robot application scenarios naturally require flexible motion performance As the most intuitive product performance, the motion performance of humanoid robots is the primary concern of consumers. Although the specific application scenarios of humanoid robots in the future are not yet clear, general-purpose robots that can liberate humans from boring, dirty or dangerous environments are regarded by many as the ultimate goal of the field of robotics. From robotic arms on assembly lines to delivery drones roaming the air, specialized robots have revolutionized industries over the past few decades, bringing great convenience to people's lives, but multi-functional general-purpose robots are still nowhere to be found. Based on this, the downstream application scenarios for humanoid robot products naturally include the potential demand for "being able to move as flexibly as humans".
In fact, the development of humanoid robots is also moving towards the pursuit of more flexible and agile movement performance, and the industrial robots used to replace specific links in specific production lines are generally four-axis SCARA or six-axis robots, that is, there are 4 or 6 degrees of freedom, and the Optimus engineering prototype shown by Tesla has 28 degrees of freedom on the body of the joints and 11 degrees of freedom on the hands, while the real human body has 27 degrees of freedom on the hands alone, and the whole body has more than 200 degrees of freedom The current humanoid robots are still beyond the reach of flexibility in terms of flexibility. In terms of athletic agility, we see Boston Dynamics' Atlas, for example, being hydraulically powered and capable of extreme sports such as parkour and 360° backflips, with agility that can move significantly closer to humans.
The movement performance required by the humanoid robot should be large and light, low energy consumption, fast response, and its motion core is concentrated in the lower body. Boston Dynamics' Atlas demonstrated incredible athleticism and could even be said to set the industry standard for humanoid robots. Similar to the brain control muscle in the human body, for the complex humanoid robot system, the complex control algorithm is embodied through the actuator, wherein the "brain" is the control algorithm, and the "muscle" is the actuator, and both are indispensable if you want to achieve excellent athletic ability. We're only talking about actuators here.
A powerful actuator should meet the following criteria:
(1) It has a high output self-weight ratio, that is, the same force is output, and the lighter the weight of the actuator, the better;
(2) It has a low output cost, that is, the same force is output, and the less energy consumption the actuator needs, the better;
(3) It has a high force response speed, that is, the actuator can quickly output force according to demand, and the lower the response delay, the better. Generally speaking, consider that the strength of the lower limbs of a person is much greater than the strength of the upper limbs.
The use of hydraulic drives can make humanoid robots move strongly, but they are difficult to commercialize due to their high cost.
In terms of hydraulic drives, Boston Dynamics is currently at the forefront of its effectiveness and influence, as well as other hydraulic actuator systems jointly developed by Moog and IIT. Boston Dynamics Atlas uses a high-power hydraulic drive that can output considerable force with very low losses, the weight of the actuator is low, and a single power source can be extended to multiple hydraulic actuators, which is itself a low-to-medium speed actuator and also meets the output speed of humanoid robots.
Boston Dynamics, through a large number of patents accumulated in hydraulic drives, has created a very compact hydraulic drive unit weighing 5kg and 5kW, which contains an electric pump, a reservoir, batteries, filters, electronics and a cooling system, and uses 28 hydraulic drives to complete a variety of explosive acrobatic moves. In the case of the old Atlas, the largest output joints were the knee and hip joints in the legs, which reached 890Nm and 840Nm respectively, at about 115 rpm. However, even with the many advantages of hydraulic drives, there are unavoidable drawbacks:
(1) The energy efficiency of the hydraulic system is not high;
(2) The number of system parts is large, and for the hydraulic actuator with ultra-high integration, conventional machining cutting can no longer meet the requirements, and 3D printing needs to be used;
(3) It is more complicated to achieve high response of hydraulic pressure, and the servo control of hydraulic pressure requires independent motors, servo pumps and force sensors.
Since its inception in 2014, 1X Technologies (NEO), a humanoid robot manufacturer led by OpenAI, has focused on developing humanoid robots with high flexibility and scalability. 1X Technologies' flagship product is EVE, a robot with two arms, two eyes, and a four-wheeled chassis that can perform a variety of tasks in a variety of environments, such as patrolling, surveillance, handling, and more. 1X Technologies is currently working on a bipedal robot called NEO, which is expected to be released in 2024. 1X's innovation for actuator systems lies in the development of gearless solutions. The company believes that the biggest difficulty in replicating the flexibility and efficiency of robots is the use of gearing, which while providing power, also adds weight, reduces natural power, and hinders agility. While a humanoid robot would have had an inertia equivalent to a 24kg foot load using conventional technology (a gear ratio of about 80:1), 1X's gearless system was able to reduce inertia to 0.5kg, and 1X has succeeded in developing a motor that can achieve about 80% of the human muscle density without the use of gears.
Zhiyuan Robot (Expedition A1) In August 2023, Zhiyuan Robotics released its first humanoid robot, Expedition A1, which is 175cm tall and weighs 55kg, and is humanoid as a whole. In terms of hardware design, the whole body has more than 49 degrees of freedom, and is equipped with harmonic integrated joints, linear actuators, brushless planetary servos, coreless motors and other actuators. These actuators give it the flexibility to do a variety of movements, just like a human joint. The robot is equipped with a Power Flow articulated motor with a peak torque of 350Nm, a weight of 1.6kg, and a water-cooled cycle. The legs are designed with recurved knees, which can help the robot have more operating space than the regular bent knee design, and are more suitable for work. The dexterous hand design has 12 active degrees of freedom and 5 passive degrees of freedom, and the drive is built-in. In addition, it is equipped with a vision-based fingertip sensor that can distinguish the color, shape, and material of the operating object. The Expedition A1 is not only footed, but also wheeled. The robot is dexterous and also supports autonomous replacement.
Unitree Technology (H1) In mid-August 2023, Unitree Technology released its first general humanoid robot product H1, which is designed with lightweight materials, with an overall weight of only 47kg, and the whole body has 19 degrees of freedom, with a light and stable walking posture, in order to adapt to the needs of large loads, high density and high power, Unitree specially designed the M107 joint motor with higher torque density for the H1 humanoid robot, with a peak torque of 360Nm, while the hip motor torque is 220Nm and the ankle joint 45Nm, and 75nm for arm joints. At present, the H1 humanoid robot can reach a walking speed of 1.5 m/s and a potential locomotion capacity of up to 5 m/s. In terms of battery life, the H1 humanoid robot is equipped with a 15Ah battery with a maximum voltage of 67.2V, which can meet the standard of continuous exercise endurance for 1 hour.
MindMinds (XR4) In August 2023, MindMinds released the humanoid bipedal robot XR4 (Seven Fairies) at the World Robot Conference. XR4 is a full-size, full-function universal humanoid bipedal robot empowered by MindMinds Cloud Brain for full-scene applications, with a height of 165cm, a weight of 65kg, a lightweight and high-strength carbon fiber composite material for the whole body, more than 60 intelligent flexible joints, a parallel drive structure and a high-torque density motor, and a peak torque of up to 600Nm.
Fourier Intelligence (GR-1) On July 6, 2023, Fourier Intelligence released the GR-1 general-purpose humanoid robot at the 2023 World Artificial Intelligence Conference, which uses a self-developed FSA high-performance all-in-one actuator with powerful and flexible motion performance. Different from traditional concept products, Fourier Intelligence said that the GR-1 general-purpose humanoid robot released this time has the ability to be commercialized. The GR-1 is 1.65 meters tall, weighs 55 kg, has 40 degrees of freedom throughout the body, has a maximum peak torque of 300Nm of joint module, can walk at a speed of 5km/h, and carries a weight of 50kg. The GR-1 uses electric drive technology to meet the robot's motion needs with a high degree of precision and flexibility.
Fourier said that compared with hydraulic drive, electric drive technology is more cost-effective, has the advantage of large-scale commercial mass production, and also has advantages in energy saving and resource utilization. On the GR-1 general humanoid robot, Fourier Intelligent has adopted the self-developed FSA high-performance integrated actuator series, which can ensure the flexibility of the GR-1 general humanoid robot in the process of action, and has strength, stability, load adaptability, safety and reliability in the landing commercial mission scenario.
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