Pre-Landing Control for a Legged Robot Based on Tiptoe Proximity Sensor Feedback

Abstract

The moment a legged robot touches the ground, the tip of its toe can experience a significant impact force. It is preferable to keep the landing impact force small because it causes imbalance and damage to the frame, motors, gears, and other components of the robot legs. In this paper, we propose a control method to mitigate the landing impact force by preliminary motion based on the proximity information of the tiptoe before landing. A proximity sensor is mounted on the tiptoe to detect the ground before landing, and feedback control is applied according to the sensor output to reduce the impact force. In landing experiments using a one-legged robot equipped with a proximity sensor on a tiptoe, we evaluated the effects of changing the sensor offset distance and the feedback gains on impact force mitigation. The results show that the landing impact force was mitigated by reducing the relative velocity of the tiptoe and the ground using the proposed proximity feedback control.

Perspective of Proximity Sensors on Robots Using Cross-Thought

“…However, with optical reflective proximity sensors, these problems can be solved, the distance between the ground and the tiptoe can be measured accurately, and the mechanical leg can adjust its gesture accordingly in time to reduce the landing impact force. The schematic is showed in Figure 19 [20].…”

“…Fig. 20 Picture of feet proximity sensors [21]. In another article, proximity sensors are used on the soles of the robot's feet for real-time detection of ground conditions to help the robot walk in different ground conditions (terrain situation).…”

Smoothly Connected Preemptive Impact Reduction and Contact Impedance Control

“…Sato et al [11] proposed an impact reduction method using the virtual elastic force for legged robots. Their sensor was developed in such a manner that the virtual elastic force did not interfere with posture control after landing.…”

“…Preemptive impact reduction methods have recently been developed [11], [12]. These methods use proximity sensors mounted near the contact area and are based on impedance control.…”

“…In these methods, however, an impedance control strategy works for both impact reduction and contact force control, i.e., these tasks interfere with each other. Consequently, selecting parameters that consider overall performance [11] or switching between virtual and contact forces [12] is needed. The former introduces a tradeoff between impact reduction and contact force control performances, and the latter destabilizes the system as This work is licensed under a Creative Commons Attribution 4.0 License.…”