Abstract
An efficient motor-control system for stable walking of the lightweight humanoid robot KONDO KHR-3HV on inclined surfaces is investigated. The motor-control system is based on the angular velocity of the pitch motion of the robot, which is detected by a gyro sensor attached to the robot torso and referred to as the angular-pitch velocity. The robot gait is analyzed for different downslopes with and without the motor-feedback control. A novel method of frequency-domain analysis of the angular-pitch velocity is proposed for explaining the reasons behind the instabilities of dynamic humanoid-robot walking on inclined surfaces. The results show, that a nonlinear nature of the motor torque, due to a force induced by the slope, gives rise to harmonics of the fundamental walking frequency of 1.73 Hz. These harmonics are the origin of the unstable robot walking. Additionally, the feedback-gain parameters KA and KH affect the amplitudes of the harmonics, which give rise to vibrations at a higher surface inclination. Increased surface friction allows a reduction of the feedback gain, which reduces this specific contribution to the harmonics and thus stabilizes the robot. To improve the walking stability on inclined surfaces, it is found that the damped natural frequency of the motor-control system must be kept lower than the fundamental walking frequency.
Highlights
Robots are important means to sustain as well as to develop a comfortable society [1,2,3,4,5,6]
That additional oscillatory patterns appear appear in waveforms,which whichbecome becomemore more obvious obvious as as φφ increases
We have investigated the origin of the robot-posture instability, which occurs during walking on inclined surfaces
Summary
Robots are important means to sustain as well as to develop a comfortable society [1,2,3,4,5,6]. The intensive utilization of robots has already been realized to reduce the necessity of human efforts for different purposes such as agricultural automation [1,2], inspection and maintenance [3,4], or rescue operations [5,6,7]. Humanoid robots are being developed to support human beings in various other tasks [6,8,9,10]. In an environment, where human beings act and dwell, it is especially practical and useful to develop robots of the humanoid type for supporting these human beings. Recent robotics challenges [11] have showcased humanoid robots for various tasks, which are difficult to be performed by human beings, e.g., as underground surveying, operations in mineralogical sites, or inspection of nuclear power plants. One of the very fundamental and widely used control techniques is based on the Zero Moment Point (ZMP) [18,19], where the projection of the Center of Mass (COM) of the robot has to be kept always within the support
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
