Autonomous speed adaptation by a muscle-driven hind leg robot modeled on a cat without intervention from brain

Abstract

This study aims to design a nervous system model to drive the realistic muscle-driven legs for the locomotion of a quadruped robot. We evaluate our proposed nervous system model with a hind leg simulated model and robot. We apply a two-level central pattern generator for each leg, which generates locomotion rhythms and reproduces cat-like leg trajectories by driving different sets of the muscles at any timing during one cycle of moving the leg. The central pattern generator receives sensory feedback from leg loading. A cat simulated model and a robot with two hind legs, each with three joints driven by six muscle models, are controlled by our nervous system model. Even though their hind legs are forced backward at a wide range of speeds, they can adapt to the speed variation by autonomously adjusting its stride and cyclic duration without changing any parameters or receiving any descending inputs. In addition to the autonomous speed adaptation, the cat hind leg robot switched from a trot-like gait to a gallop-like gait while speeding up. These features can be observed in existing animal locomotion tests. These results demonstrate that our nervous system is useful as a valid and practical legged locomotion controller.

Development of a Pneumatically Actuated Quadruped Robot Using Soft–Rigid Hybrid Rotary Joints

“…In addition, the maximum output torque of the rotary joint used for the quadruped robot depended on its maximum operating pressure of 250 kPa, which was determined from the material selection and the fabrication approach. In contrast, the maximum pressures of pneumatically actuated robots were 110 kPa in [20], 152 kPa in [14], 170 kPa in [15] and 400 kPa in [30,31]. How to improve the airtightness and durability of the bellows muscle used in this paper is worth investigating.…”

“…It is worth mentioning that pneumatic actuating systems composed of an air compressor, regulators and solenoid valves are normally heavy and bulky. Like most pneumatically actuated robots [27][28][29][30][31][32], in this work, the pneumatic actuation system was off-board, and the robot was tethered to make the robot lightweight. Though pneumatic robots without an external power source have recently been developed, as reported in the references [14,15], lightweight mini air compressors and valves bring in additional challenges, including a small volume of compressed gas, a low flow rate, a limited operating pressure and imprecise pressure control.…”

“…In addition, despite the actuation delay and the decrease in the actuator accuracy, the quadruped robots with antagonistic pneumatic actuators developed by Tsujita [28,29] achieved stable locomotion for walking and trotting patterns by adopting an oscillator network controller and adjusting the stiffness at the trunk. The quadruped robots built by Fukuoka [30,31] can adapt to speed variations and stabilize their running pace using a neuromorphic locomotion controller with leg-loading feedback. However, human assistance was needed during the experiments to prevent the robots from falling over.…”

Force analysis of a soft-rigid hybrid pneumatic actuator and its application in a bipedal inchworm robot

“…For example, the soft-rigid hybrid quadruped robot in refs. [41, 42] adapted to speed variation by adjusting its stride and cyclic duration, but the robot needs human assistance during walking. Further, with the rigid exoskeleton providing structural support and the soft pneumatic joints providing actuation and inherent compliance to external forces, soft-rigid hybrid-legged robots, including bipedal robots [43, 44], quadruped robots [45, 47], and hexapod robots [48], with simple gaits were proposed.…”

Design and locomotion analysis of a close-chain leg-wheel mobile platform

“…Because of the spring-U joints, it has self-adaptive ability to climb the obstacle and slope. By studying the muscular system of catamount's leg, another three novel robotic leg was designed (Park et al, 2014;Wu et al, 2021aWu et al, , 2021bFukuoka et al, 2021). They all have three joints (hip, knee and ankle), but the first one and the second turned the muscles into linkages and springs so that the leg became a close-chain mechanism driven by a crank motor and can run in a high speed; the third one turned the muscles into actuators (pneumatic) to drive the leg, which was controlled to realize autonomous speed adaptation.…”