Abstract
In this paper, a novel mechatronic design philosophy is introduced to develop a compact modular rotary elastic joint for a humanoid manipulator. The designed elastic joint is mainly composed of a brushless direct current (DC) motor, harmonic reducer, customized torsional spring, and fail-safe brake. The customized spring considerably reduces the volume of the elastic joint and facilitates the construction of a humanoid manipulator which employs this joint. The large central hole along the joint axis brings convenience for cabling and the fail-safe brake can guarantee safety when the power is off. In order to reduce the computational burden on the central controller and simplify system maintenance, an expandable electrical system, which has a double-layer control structure, is introduced. Furthermore, a robust position controller for the elastic joint is proposed and interpreted in detail. Vibration of the elastic joint is suppressed by means of resonance ratio control (RRC). In this method, the ratio between the resonant and anti-resonant frequency can be arbitrarily designated according to the feedback of the nominal spring torsion. Instead of using an expensive torque sensor, the spring torque can be obtained by calculating the product of spring stiffness and deformation, due to the high linearity of the customized spring. In addition, to improve the system robustness, a motor-side disturbance observer (DOb) and an arm-side DOb are employed to estimate and compensate for external disturbances and system uncertainties, such as model variation, friction, and unknown external load. Validity of the DOb-based RRC is demonstrated in the simulation results. Experimental results show the performance of the modular elastic joint and the viability of the proposed controller further.
Highlights
Robots, especially those working in industrial environments, have been generally designed according to the principle “rigidity by design, safety by sensors and control”
The final assembly of the elastic joint consists of a brushless direct current (DC) motor, harmonic reducer, customized torsional spring, bearings, magnetic encoders, fail-safe brake, etc
It is easy to understand that the elasticity of the joint mainly answers for the delay and the disturbance observer (DOb)-based resonance ratio control (RRC) for achieving vibration suppression will further pull down the system bandwidth
Summary
Especially those working in industrial environments, have been generally designed according to the principle “rigidity by design, safety by sensors and control”. Jin et al [18] designed an adaptive tracking controller using a time-delay estimation technique While his approach was to achieve accurate motor-side position before the elastic element and let the arm side show passive compliant behaviors. In order to solve this problem, Petit et al [23] proposed a model-free damping control approach, which utilized the joint elasticities to convert kinetic energy into elastic energy to achieve vibration suppression. This control approach was employed mainly to deal with the vibration introduced by disturbances.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
