What is a Humanoid Robot?
In general, a humanoid robot refers to a bipedal robot designed to mimic the form and movements of a human, aiming for versatility. These robots possess a wide range of capabilities—from basic actions such as grasping and carrying objects to learning and performing various tasks. With the rapid advancement of AI technologies in recent years, some humanoid robots have also acquired sophisticated intelligence and natural conversational abilities. A key characteristic of humanoid robots is their humanlike structure, typically consisting of a head, torso, two arms, and two legs. This resemblance contributes to their social acceptability and facilitates easier integration into environments originally designed for humans. For this reason, humanoid robots are expected to find applications across a wide range of fields, including industry, healthcare and caregiving, disaster response, and entertainment. On the other hand, challenges related to safety and ethics have been pointed out as essential issues to address before humanoid robots can become widespread. Despite these challenges, the market potential for humanoid robots is projected to be extremely high, driving active investment and development efforts, particularly in the United States and China. As AI and sensor technologies continue to advance, humanoid robots are expected to play an increasingly significant role in human society in the years to come.
University Collaboration – Free Standard Gears for Humanoid Robot Research (Click Here)
KHK Gears supports academic research on humanoid robots by providing our standard gears free of charge. We welcome technical collaboration and information exchange on gear applications.
Gears Used in Humanoid Robots
The complex, humanlike movements of humanoid robots rely on the precision of their internal mechanical components and the accuracy of their control systems. Gears used mainly in the arms, legs and their joints—for purposes such as acceleration, deceleration, and torque amplification—include not only versatile spur gears, but also worm gears, which are compact and offer high reduction ratios along with self-locking capability; bevel gears, which transmit motion at right angles; hypoid gears, which provide high reduction ratios; and internal gears, which form part of planetary gear systems that generate high torque with coaxial input and output shafts. In addition, strain wave gearing, composed of multiple gears, is widely used in humanoid robots because it achieves both high reduction ratios and excellent positioning accuracy. To ensure precise robot motion, gears are sometimes ground to improve accuracy, and hardened by heat treatment in areas requiring high torque. Furthermore, minimizing backlash, which affects motion precision, is an essential consideration in gear design.
Role Allocation Between Actuators and Gears in Robots
Actuators (here defined as units composed of a motor, reduction gear, encoder, and various sensors) are the source of force generation in humanoid robots and correspond to muscles in the human body.
In humanoid robots, actuators are often used in major joints that require large torques, such as the knees, hip joints, and shoulders.
In these joints, actuators can be directly mounted at the joint, which offers the advantage of a simple and easy-to-handle mechanical structure; however, this configuration tends to concentrate mass and rotational inertia around the joint, which may be disadvantageous in terms of motion performance and responsiveness.
On the other hand, gears in humanoid robots play the role of transmitting power while adjusting mechanical characteristics such as torque and rotational speed.
Gears are commonly used in parts where lightweight design and space efficiency are particularly important, such as the fingers, wrists, and neck.
The advantages of using gears in these parts include high flexibility in layout, the ability to reduce the mass and inertia of distal segments by placing the motor closer to the torso, and the possibility of achieving a human-friendly design by adopting a low reduction ratio and low-stiffness configuration that allows external forces to be absorbed.
In summary, in humanoid robots, major joints that require high torque are directly driven by actuators, whereas in parts with strict requirements on weight reduction and layout constraints at the distal ends, power is transmitted using gears.
Gears Used in Humanoid Robot Speed Reducers
Humanoid robots employ various types of speed reducers, such as strain wave reducers, cycloidal reducers, and planetary gear reducers. Many of the gears used in these robots serve as key components within those reducers. In recent years, as part of efforts to achieve more compact designs and reduce design workload, these reducers are increasingly being integrated with motors and encoders into a single actuator unit.
The gear tooth profiles differ depending on the type of reducer. For example, in a cycloidal reducer, a non-involute tooth profile—specifically, a trochoidal-type profile—is used. In contrast, planetary gear reducers typically use standard involute tooth profiles for spur gears (used as sun and planet gears) and internal gears.
University Collaboration – Free Standard Gears for Humanoid Robot Research
KHK Gears supports academic research on humanoid robots by providing our standard gears free of charge. We welcome technical collaboration and information exchange on gear applications.