As humanoid robots accelerate into practical applications such as industrial collaboration, domestic services, and emergency inspections, dynamic body protection, gait optimization, and human-machine safety interaction have become critical pain points in industrialization. Impact sensors, serving as the "impact perception nerves" of robots, rely on sensing principles like piezoelectricity and MEMS to accurately capture instantaneous impact forces and acceleration changes. Distributed across key areas such as the feet, joints, torso, and arms, they establish a comprehensive perception system ranging from gait regulation to collision avoidance and self-protection, making them indispensable core components for humanoid robots to achieve human-like movement and safe operation.
Impact sensors are primarily divided into piezoelectric and MEMS accelerometer types, tailored for robots' varied impact conditions. Piezoelectric sensors feature microsecond-level response and ultra-wide frequency response, capable of capturing instantaneous impact pulses of 0.1~2ms, commonly used for high-speed collision detection in the head and fingertips. MEMS miniature impact sensors are compact in size and highly resistant to overload, withstanding up to 10,000 times gravity impact, and boast lower mass production costs. They are widely deployed in the ankles, soles, and torso for routine landing impact monitoring. These two types of sensors complement each other, covering the full measurement range from micro-contact forces of a few grams to thousandfold gravity impact from falls.
Foot-to-ground monitoring is the most fundamental application of impact sensors. When a robot walks or trots, the instantaneous impact at heel strike can reach 50~200g, and uneven terrain further amplifies the force, easily causing long-term fatigue damage to reducers and servo joints. Impact sensors embedded in the foot and lower leg collect real-time ground impact waveforms and peak data. The main control system dynamically adjusts stride length and landing cushioning force based on feedback to achieve a compliant landing. When encountering steps or uneven surfaces, sudden changes in impact values trigger gait correction logic, enabling the robot to autonomously slow down and adjust its center of gravity, significantly reducing hard impact damage to mechanical structures and extending the overall lifespan of the machine.
Fall prevention is the core safety value of impact sensors and a critical prerequisite for the mass production of humanoid robots. When a robot unexpectedly loses balance and falls, the body's acceleration instantly exceeds the threshold of normal movement. The sensor captures abnormal impact signals within 0.5ms, triggering a three-tiered protection mechanism: prioritizing the outward extension of arms to form a buffer support, then cutting off the high-power joint motor output to prevent gears and servos from damage due to instantaneous impact, and finally fine-tuning the body posture at the moment of landing to prioritize the protection of vulnerable areas such as the head and precision components. Test data shows that the fall protection system based on impact sensing can reduce peak impact force upon landing by nearly 70%, significantly lowering repair costs from falls.
In human-machine collaboration and environmental collision scenarios, impact sensors establish a dual safety defense for both personnel and equipment. When service robots interact closely with humans or industrial humanoid robots perform collaborative assembly tasks, micro-sensors deployed on the torso and arms distinguish between flexible contact and rigid impact: minor contact below safety thresholds is identified as human-machine interaction, allowing the robot to maintain its original motion; if the impact exceeds limits, the system immediately halts operation and retracts the robotic arm to prevent collisions that could harm personnel or damage equipment. Meanwhile, the sensors fully record impact amplitude and occurrence location, enabling data review and optimization of motion algorithms in later stages to continuously enhance the robot's compliant control capabilities.
In addition, impact sensors are also used for end-effector operation monitoring and overall structural health diagnostics. When a robot holds a tool to strike during assembly, the sensor monitors the consistency of the operational impact in real time and automatically adjusts the output force. During long-term operation, abnormal joint impact data can warn of potential bearing and linkage fatigue issues, enabling proactive maintenance scheduling.
As humanoid robots evolve toward lightweight, high-dynamic, and low-cost designs, impact sensors are advancing toward miniaturization, multi-axis integration, and low power consumption. In the future, with the maturation of flexible thin-film sensing technology, large-area electronic skin integration for impact sensing will become mainstream, further narrowing the perception gap between robots and humans and laying a robust sensing foundation for the large-scale commercial deployment of humanoid robots.