Sagar Dattatray Joshi | EPFL Graph Search

Sagar Joshi is currently pursuing his PhD in robotics at Reconfigurable Robotics Lab (RRL), EPFL. He has received his Master of Technology (M.Tech.) in Mechanical Engineering from IIT Bombay. Sagar has previously worked on modelling and design of an ankle prosthesis with a biomimetic actuation structure. His current research focuses on pneumatic systems for soft robots, soft actuator design, and wearable robots.

Sensorless force and displacement estimation in soft actuators

Sagar Dattatray Joshi, Jamie Paik

Sensing forms an integral part of soft matter based robots due to their compliance, dependence on loading conditions, and virtually infinite degrees of freedom. Previous studies have developed several extrinsic sensors and embedded them into soft actuators for displacement and force estimation. What has not been investigated is whether soft robots themselves possess intrinsic sensing capabilities, especially in the case of pneumatically powered soft robots. Such an approach, that exploits the inherent properties of a system toward sensing is called sensorless estimation. Here, we introduce sensorless estimation for the first time in pneumatically powered soft actuators. Specifically, we show that the intrinsic properties of pressure and volume can be used to estimate the output force and displacement of soft actuators. On testing this approach with a bending actuator, we observed errors under 10% and 15% for force and displacement estimation respectively, with randomized and previously unseen test conditions. We also show that combining this approach with a conventional embedded sensor improves estimation accuracy due to sensing redundancy. By modelling soft actuators additionally as sensors, this work presents a new, readily implementable sensing modality that helps us better understand the highly complex behaviour of soft matter based robots.

ROYAL SOC CHEMISTRY2023

Design and dynamic analysis of soft pneumatic systems for wearable robots

Sagar Dattatray Joshi

There are many challenges in the development of pneumatically powered soft robots due to the non-linearities of the materials used, non-linear pneumatic flow, complex non-standard designs, and high compliance that leads to loading-specific mechanical behaviour. As a result, there is still a significant gap towards understanding these robots, as compared to standard well-known actuators such as motors, rigid pneumatic actuators, or voice-coils. This thesis develops a comprehensive system-wide understanding of soft wearable robots through investigation and quantification of their soft actuator mechanical outputs, dynamic performance, and biomechanical effects. Towards this goal, we explore methods for accurate and consistent experimental characterization, modelling of SPA pressure and flow dynamics, and musculoskeletal modelling and analysis of soft wearable robots. First, we present a novel experimental protocol and setup for recreating application-specific loading conditions, in order to accurately capture the mechanical behaviour of soft robots. This concept is based on emulating the physical constraints acting on the soft robot at its contact points, and measuring the mechanical outputs. Then, we analyse the dynamic behaviour of SPAs and its dependency on the PSS and loading conditions. Via simulations and experimental testing, we map a direct relationship between properties of the PSS and SPA, and dynamic performance metrics. Using these relations, we present design optimization of PSSs for simultaneously meeting requirements of performance, portability and additional user-defined metrics such as mass or volume. By further investigating the effect of loading conditions on SPA dynamic behaviour, we introduce a previously unknown property of SPAs, self-sensing, that allows estimation of force and displacement without dedicated sensors. Finally, we investigate the biomechanical effect of soft wearable devices via the design and modelling of a soft exosuit for the human torso. The research in this thesis can be broadly categorized into three sections: quantifying mechanical behaviour of soft robots, modelling pressure dynamics of soft pneumatic actuators, and evaluating biomechanical effect of soft exosuits.

EPFL2021

Flow Path Optimization for Soft Pneumatic Actuators: Towards Optimal Performance and Portability

Sagar Dattatray Joshi, Jamie Paik, Harshal Arun Sonar

Soft pneumatic actuators (SPAs) are highly desirable for interactive robotics applications owing to their unconventional properties like high compliance, safe human-machine interaction and adaptable design space. The SPA dynamic behaviour is governed by pneumatic supply systems (PSSs) consisting of source, valve, tubing and fittings. Although their functionality is well known, the inter-dependence of PSS components and their impact on the SPA behaviour has not been quantified, especially in the context of performance and portability. Using the metrics of maximum actuation frequency, air and energy consumption per actuation cycle, here we systematically investigate the effect of five parameters: SPA size, tubing diameter and length, source pressure and valve flow capacity. We model the SPA pressure dynamics model using first principles and define a large study set of 162 model parameter combinations based on commonly used SPAs and PSS components. We then simulate and experimentally measure the maximum actuation frequency in these parameter combinations, while additionally defining experimental protocols for flow characterization of PSS components and valve control strategy for maximizing actuation frequency. Results from experiments and simulations show good agreement, depicting the trends of how different parameters affect SPA performance. An interesting observation was that for a set of SPA size, tubing length and valve flow capacity, there exists a unique optimal tubing diameter that maximizes the actuation frequency. By further analyzing air and energy consumption, this work allows us to define and solve a multi-objective optimization problem to select and control PSS components to optimize SPA performance and portability simultaneously.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2021

Design and dynamic analysis of soft pneumatic systems for wearable robots

Sagar Dattatray Joshi

EPFL2021