Abstract
Legged robots imitating animals have become versatile and applicable in more application scenarios recent years. Most of their functions rely on powerful athletic abilities, which require the robots to have remarkable actuator capacities and controllable dynamic performance. In most experimental demonstrations, continuous hopping at a desired height is a basic required motion for legged robots to verify their athletic ability. However, recent legged robots have limited ability in balance of high torque output and actuator transparency and appropriate structure size at the same time. Therefore, in our research, we developed a parallel robot leg using a brushless direct current motor combined with a harmonic driver, without extra force or torque sensor feedback, which uses virtual model control (VMC) to realize active compliance on the leg, and a whole-leg control system with dynamics modeling and parameter optimization for continuous vertical hopping at a desired height. In our experiments, the robot was able to maintain stability during vertical hopping while following a variable reference height in various ground situations.
Highlights
The most prominent advantage of a legged robot is its outstanding ability of highly dynamic locomotion strategies such as running and jumping, imitating real legged animals in field situations [1]
In this paper, focusing on controllable vertical hopping, we describe the development of the parallel legged robot with a high-performance actuator, and use current–torque control on the actuator to implement virtual model control (VMC) on the leg; this approach does not require an extra torque sensor but can provide active compliance in jumping and landing
Because the system design used a harmonic driver as the motor reducer in the actuator, the system achieved successful dynamic motion control and impact mitigation during hopping
Summary
The most prominent advantage of a legged robot is its outstanding ability of highly dynamic locomotion strategies such as running and jumping, imitating real legged animals in field situations [1]. Most low-ratio or even direct-driven actuators can accurately control their output with high transparency, but they have limited output torque which can only be used in small-sized robot To overcome this conflict, MIT Cheetah series robot [4,5,6,7] used a high-torque-density brushless direct current (BLDC) motor with a large gap radius as its actuator [8,9]. MIT Cheetah series robot [4,5,6,7] used a high-torque-density brushless direct current (BLDC) motor with a large gap radius as its actuator [8,9] This type of actuator is typically a large-torque, low-speed motor that usually cooperates with a low-ratio gearbox to achieve high back-drivability. The balance of output ability, transparency, and structure size for a legged robot is still a crucial problem to be solved
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