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. 2019 May 7:13:17.
doi: 10.3389/fnbot.2019.00017. eCollection 2019.

Development, Analysis, and Control of Series Elastic Actuator-Driven Robot Leg

Chan Lee  1 , Sehoon Oh  1
Affiliations

Development, Analysis, and Control of Series Elastic Actuator-Driven Robot Leg

Chan Lee et al. Front Neurorobot. .

Abstract

The mass-spring system-like behavior is a powerful analysis tool to simplify human running/locomotion and is also known as the Spring Loaded Inverted Pendulum (SLIP) model. Beyond being just an analysis tool, the SLIP model is utilized as a template for implementing human-like locomotion by using the articulated robot. Since the dynamics of the articulated robot exhibits complicated behavior when projected into the operational space of the SLIP template, various considerations are required, from the robot's mechanical design to its control and analysis. Hence, the required technologies are the realization of pure mass-spring behavior during the interaction with the ground and the robust position control capability in the operational space of the robot. This paper develops a robot leg driven by the Series Elastic Actuator (SEA), which is a suitable actuator system for interacting with the environment, such as the ground. A robust hybrid control method is developed for the SEA-driven robot leg to achieve the required technologies. Furthermore, the developed robot leg has biarticular coordination, which is a human-inspired design that can effectively transmit the actuator torque to the operational space. This paper also employs Rotating Workspace (RW), which specializes in the control of the biarticulated robots. Various experiments are conducted to verify the performance of the developed robot leg with the control methodology.

Keywords: biarticular actuator coordinate; impedance control; leg force control; rotating workspace; series elastic actuator.

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Figures

Figure 1
Figure 1
Developed series elastic actuator-driven biarticular robot leg including force controller.
Figure 2
Figure 2
Representative biarticular muscles in the human lower extremity.
Figure 3
Figure 3
Various configurations of a two link robot. (A) series configuration, (B) biarticular configuration (wire/belt-driven), (C) biarticular configuration (linkage-driven).
Figure 4
Figure 4
Details of the developed SEA-driven biarticular robot leg: top view, front view and specifications of the robot.
Figure 5
Figure 5
Developed transmission force sensing type series elastic actuator (TFSEA).
Figure 6
Figure 6
Free body diagram of the SEA. The black-colored arrows indicate motor, load position and spring deflections, and the red-colored arrows denote motor, spring forces and friction force.
Figure 7
Figure 7
Block diagram of SEA dynamics with Disturbance Observer-based robust torque control.
Figure 8
Figure 8
Large force bandwidth characteristics of torque-controlled SEA.
Figure 9
Figure 9
Frequency responses of the proposed force control of the TFSEA. (A) force control with free load condition, and (B) with locked-load condition.
Figure 10
Figure 10
Basic configuration of a two-link system with two types of actuator coordination. (A) conventional serial actuator coordinates, and (B) biarticular actuator coordinates.
Figure 11
Figure 11
Organization and classification of contents in section 2.3. (A) Desired SLIP dynamics to realize human-like locomotion. (B) Hybrid Control strategy to achieve SLIP dynamics. (C) Rotating Workspace coordination for Hybrid Control. (D) Joint space control for better control performance.
Figure 12
Figure 12
Overall control structure of the Robust RWHC for biarticular robot.
Figure 13
Figure 13
HC in the RW for biarticular robot leg.
Figure 14
Figure 14
Robust HC in the RW for biarticular robot leg. The final form of the controller consists of inertia decoupling, gravity control and inertia control.
Figure 15
Figure 15
Experimental setups. Dynamic experiment: fixed body and freely moving leg. Static experiment: fixed body and leg with load cell.
Figure 16
Figure 16
System identification procedure of the robot leg by utilizing the force, position measurement and position control capabilities of SEA.
Figure 17
Figure 17
Gravity coefficient identification result. (A): relationship between θm and τm.g, and (B): Relationship between θb and τb.g.
Figure 18
Figure 18
Verification of Static with various robot postures. (A) robot leg postures, and (B) end point force tracking performance.
Figure 19
Figure 19
Performance verification of the proposed decoupling control. (A) excitation signal on monoarticular actuator, and (B) excitation signal on biarticular actuator.
Figure 20
Figure 20
Dynamic response of the end point with different impedance setting. (A) various stiffness settings, and (B) various damping settings.
Figure 21
Figure 21
Robustness and tracking performance verification of Rotating Workspace Hybrid Control.
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