Force control of a jumping musculoskeletal robot with pneumatic artificial muscles

Hong

Int. J. Control Autom. Syst.

2021

We propose a bipedal walking and impact reduction algorithm for a bipedal robot with pneumatically driven knees. The proposed algorithm is meaningful in that unlike in the existing studies on fully pneumatically driven robots and their control, it can overcome the low control performance of pneumatic actuators while utilizing the high compliance of pneumatic actuators through the high control performance of other joints in robots that apply pneumatic actuators only to the knee joint. Our algorithm takes advantage of whole-body control to overcome the low control performance of pneumatic systems and utilizes pneumatic compliance by simultaneously controlling the force and stiffness of the pneumatic actuators. Since a pneumatic actuator outputs a force, a force and torque converter is added to the general whole-body control framework, and a torque limit is considered as a function of the joint angle. In addition, a mechanism for selecting the stiffness of the knee is added. In particular, a force control method based on maintaining the minimum stiffness is applied to reduce the impact force when the ground conditions suddenly change. The pneumatics and the robot system were accurately modeled in a simulation, and the proposed algorithm was applied in the simulation to realize bipedal walking and to confirm the impact reduction effect in the event of a sudden ground condition change.

Section: Introductionmentioning

confidence: 99%

Bipedal Walking and Impact Reduction Algorithm for a Robot with Pneumatically Driven Knees

Hong

Int. J. Control Autom. Syst.

2021

“…For multiarticulate musculoskeletal lower-limb robots, control of both the reaction force from the ground and the jumping force has been conducted considering muscle elasticity [6][7][8]. Similar to upperlimb robots, two joints with biarticular muscles have been considered.…”

Section: Introductionmentioning

confidence: 99%

“…The stiffness of the biarticular muscle and muscle model of the lower limb as a passive spring were studied in [6]. In [7], antagonistic muscles spanned different joints, and in [8], a model with antagonistic biarticular muscles that spanned the same joints was derived. However, none of these studies have addressed instability in the musculoskeletal system.…”

Section: Introductionmentioning

confidence: 99%

Stability Analysis of Multi-Serial-Link Mechanism Driven by Antagonistic Multiarticular Artificial Muscles

Ishikawa

Nabae

Endo

et al. 2021

Preprint

Artificial multi-joint musculoskeletal systems consisting of serially connected links driven by monoarticular and multiarticular muscles, which are often inspired by vertebrates, enable robots to elicit dynamic, elegant, and flexible movements. However, serial links driven by multiarticular muscles can cause unstable motion (e.g., buckling). The stability of musculoskeletal mechanisms driven by antagonistic multi-joint muscles depends on the muscle configuration, origin/insertion of muscles, spring constants of muscles, contracting force of muscles, and other factors. We analyze the stability of a multi-serial-link mechanism driven by antagonistic multi-joint muscles aiming to prevent buckling and other undesired motions. First, we theoretically derive the potential energy of the system and the stable condition at the target point. Then, we validate the method through dynamic simulations and experiments. We confirm that we can construct a stable multiarticulate musculoskeletal system using the proposed formulation and conditions.

“…A human being can hop or leap over a wide ditch, but for a biped robot to perform the same task requires high power actuators 23 with the added difficulty of impact during the landing phase. 24 Controlling the biped robot during landing phase of jumping is a tedious task. Also, going for high power actuators which are heavy poses safety issues.…”

Section: Introductionmentioning

confidence: 99%

Generating real-time trajectories for a planar biped robot crossing a wide ditch with landing uncertainties

Janardhanan¹,

Kumar²

2018

Robotica

SUMMARYDitch crossing is one of the essential capabilities required for a biped robot in disaster management and search and rescue operations. Present work focuses on crossing a wide ditch with landing uncertainties by an under-actuated planar biped robot with five degrees of freedom. We consider a ditch as wide for a robot when the ankle to ankle stretch required to cross it is at least equal to the leg length of the robot. Since locomotion in uncertain environments requires real-time planning, in this paper, we present a new approach for generating real-time joint trajectories using control constraints not explicitly dependent on time, considering impact, dynamic balance, and friction. As part of the approach, we introduce a novel concept called the point of feasibility for bringing the biped robot to complete rest at the end of ditch crossing. We present a study on the influence of initial posture on landing impact and net energy consumption. Through simulations, we found the best initial postures to efficiently cross a wide ditch of width 1.05 m, with less impact and without singularities. Finally, we demonstrate the advantage of the proposed approach to cross a wide ditch when the surface friction is not same on both sides of the ditch.