Investigations of a Robotic Test Bed With Viscoelastic Liquid Cooled Actuators

Kim, D.; Ahn, Junhyeok; Campbell, Orion; Paine, Nicholas; Sentis, Luis

doi:10.1109/tmech.2018.2872176

Cited by 17 publications

(18 citation statements)

References 36 publications

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“…DRACO is our newest humanoid lower body, having 10 viscoelastic liquid-cooled actuators (Kim et al, 2018) on its hips and legs. Each limb has five actuators: hip yaw, roll, pitch, knee pitch, and ankle pitch.…”

Section: Resultsmentioning

confidence: 99%

Dynamic locomotion for passive-ankle biped robots and humanoids using whole-body locomotion control

Kim

Jorgensen

Lee

et al. 2020

The International Journal of Robotics Research

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Whole-body control (WBC) is a generic task-oriented control method for feedback control of loco-manipulation behaviors in humanoid robots. The combination of WBC and model-based walking controllers has been widely utilized in various humanoid robots. However, to date, the WBC method has not been employed for unsupported passive-ankle dynamic locomotion. As such, in this article, we devise a new WBC, dubbed the whole-body locomotion controller (WBLC), that can achieve experimental dynamic walking on unsupported passive-ankle biped robots. A key aspect of WBLC is the relaxation of contact constraints such that the control commands produce reduced jerk when switching foot contacts. To achieve robust dynamic locomotion, we conduct an in-depth analysis of uncertainty for our dynamic walking algorithm called the time-to-velocity-reversal (TVR) planner. The uncertainty study is fundamental as it allows us to improve the control algorithms and mechanical structure of our robot to fulfill the tolerated uncertainty. In addition, we conduct extensive experimentation for: (1) unsupported dynamic balancing (i.e., in-place stepping) with a six-degree-of-freedom biped, Mercury; (2) unsupported directional walking with Mercury; (3) walking over an irregular and slippery terrain with Mercury; and 4) in-place walking with our newly designed ten-DoF viscoelastic liquid-cooled biped, DRACO. Overall, the main contributions of this work are on: (a) achieving various modalities of unsupported dynamic locomotion of passive-ankle bipeds using a WBLC controller and a TVR planner; (b) conducting an uncertainty analysis to improve the mechanical structure and the controllers of Mercury; and (c) devising a whole-body control strategy that reduces movement jerk during walking.

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Section: Resultsmentioning

confidence: 99%

Dynamic locomotion for passive-ankle biped robots and humanoids using whole-body locomotion control

Kim

Jorgensen

Lee

et al. 2020

The International Journal of Robotics Research

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“…The liquid cooling system increases the maximum allowable continuous current by a factor of 2.5. For more detailed information, readers are referred to our previous work [1].…”

Section: B Viscoelastic Liquid Cooled Actuatorsmentioning

confidence: 99%

“…DRACO is actuated by Viscoelastic Liquid Cooled Actuators (VLCAs) which include viscoelastic elements in the drivetrain in order to improve joint position controllability as reported in [1]. Liquid cooled Reaction Force Sensing Series Elastic Actuators (RFSEA) are used for the hip and knee joints, reducing actuation weight while increasing energy efficiency, torque density, impact resistance and position/force controllability.…”

Section: Introductionmentioning

confidence: 99%

Control of a High Performance Bipedal Robot using Viscoelastic Liquid Cooled Actuators

Ahn

Kim

Bang

et al. 2019

2019 IEEE-RAS 19th International Conference on Humanoid Robots (Humanoids)

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This paper describes the control, and evaluation of a new human-scaled biped robot with liquid cooled viscoelastic actuators (VLCA). Based on the lessons learned from previous work from our team on VLCA [1], we present a new system design embodying a Reaction Force Sensing Series Elastic Actuator (RFSEA) and a Force Sensing Series Elastic Actuator (FSEA). These designs are aimed at reducing the size and weight of the robot's actuation system while inheriting the advantages of our designs such as energy efficiency, torque density, impact resistance and position/force controllability. The system design takes into consideration human-inspired kinematics and rangeof-motion (ROM), while relying on foot placement to balance. In terms of actuator control, we perform a stability analysis on a Disturbance Observer (DOB) designed for force control. We then evaluate various position control algorithms both in the time and frequency domains for our VLCA actuators. Having the low level baseline established, we first perform a controller evaluation on the legs using Operational Space Control (OSC) [2]. Finally, we move on to evaluating the full bipedal robot by accomplishing unsupported dynamic walking by means of the algorithms to appear in [3].

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“…Motor current could also be used to estimate motor torque, however, the torque provided by the motor alone is too small to fulfill the application requirement. The harmonic drive is often adopted to play the role in amplifying the motor's output torque [18,19]. As a consequence, it is essential to model the nonlinearities of harmonic drive in order to obtain more accurate torque estimation of SVAs.…”

Section: Introductionmentioning

confidence: 99%

Improvement of Torque Estimation for Series Viscoelastic Actuator Based on Dual Extended Kalman Filter

et al. 2021

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Adding damping such as viscoelastic element in series elastic actuators (SEA) can improve the force control bandwidth of the system and suppression of high frequency oscillations induced by the environment. Thanks to such advantages, series viscoelastic actuators (SVA) have recently gained increasing research interests from the community of robotic device design. Due to the inconvenience of mounting torque sensors, employing the viscoelastic elements to directly estimate the output torque is of great significance regarding the real-world applications of SVA. However, the nonlinearity and time-varying properties of viscoelastic materials would degrade the torque estimation accuracy. In such a case, it is paramount to simultaneously estimate the output torque state and viscoelastic model coefficients in order to enhance the torque estimation accuracy. To this end, this paper first completed the design of a rubber-based SVA device and used the Zenner linear viscoelastic model to model the viscoelastic element of the rubber. Subsequently, this paper proposed a dual extended Kalman filter- (DEFK) based torque estimation method to estimate the output torque and viscoelastic model coefficients simultaneously. The noisy observations of two Kalman filters were provided by motor current-based estimated torque. Moreover, the dynamic friction of harmonic drive of the designed SVA was modeled and compensated to enhance the reliability of current-based torque estimation. Finally, a number of experiments were carried out on SVA, and the experimental results confirmed the DEFK effectiveness of improving torque estimation accuracy compared to only-used rubber and only-used motor current torque estimation methods. Thus, the proposed method could be considered as an effective alternative approach of torque estimation for SVA.

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Investigations of a Robotic Test Bed With Viscoelastic Liquid Cooled Actuators

Cited by 17 publications

References 36 publications

Dynamic locomotion for passive-ankle biped robots and humanoids using whole-body locomotion control

Dynamic locomotion for passive-ankle biped robots and humanoids using whole-body locomotion control

Control of a High Performance Bipedal Robot using Viscoelastic Liquid Cooled Actuators

Improvement of Torque Estimation for Series Viscoelastic Actuator Based on Dual Extended Kalman Filter

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