Compliance, locomotion and local computation in (self-) reconfigurable modular robots

Simon Lukas Hauser
EPFL, 2019
Thèse EPFL

Résumé

Animals display an enormous versatility and a remarkable ability to adapt to changes in environment and terrain. Research in bio-inspired robotics strives to transfer these skills to robots, including legged systems. Even though animals seemingly effortlessly perform most of their activities on rough terrain, this feature seems to be particularly difficult to achieve in their robotic counterparts. We hypothesize that perturbations caused by e.g. rough terrain are not handled by the central nervous system, but rather by local modifications of the locomotion system such as legs and feet. Modifications can include changing mechanical properties such as spring and damping characteristics, as well as adjustments in the movement pattern of the locomotion. In this thesis, we isolate instances where a specific component, in our view, needs such modifications to fulfill different functionalities in a locomotion cycle. Further, we introduce the concept of mode-switches: a local computation is performed to induce these changes in functionalities by changing the dynamical response of the component. We then present one mode-switch method in hardware, jamming of granular media, that can switch the functionality of a foot between impact damping'' and propulsion force transmission'', and we show how this regularizes step sizes on rough terrain. We then present one mode-switch method in control, a force feedback strategy named tegotae''. This switches the functionality of leg movement between displacing the leg'' and displacing the body'', and we show how this informs the controller about which legs are bearing less weight and thus are more suited to be moved. We suggest that these methods can be applied to any legged structure and use modular robots to demonstrate these concepts. In parallel, we also improved our previously developed self-reconfigurable modular robot platform Roombots'' such that they perform a variety of tasks centered around adaptive and assistive furniture with up to 12 modules. This includes demonstrations of self-reconfiguration, mobile furniture, object manipulation, interaction capabilities and the development of a user interface. With these improvements, this platform can in the future also be used for further locomotion research where the shape-shifting ability could be of major importance.

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https://infoscience.epfl.ch/record/268520?ln=fr

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Simon Lukas Hauser
EPFL, 2019
Thèse EPFL

Résumé

Official source

https://infoscience.epfl.ch/record/268520?ln=fr

À propos de ce résultat

Concepts associés (26)

Concepts associés

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Publications associées (96)

Publications associées

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Perception, control and planning for (self-)reconfigurable modular robots

Mehmet Hasan Mutlu

Modular robots (MRs) consist of similar modules that can be configured into different shapes. MRs introduce a number of benefits over conventional robots specifically designed for a task. Self-reconfigurable modular robots (SRMRs) are a sub-category of MRs that can perform complex morphological changes by making use of autonomous attachments and detachments. This thesis is pointing out various aspects of MRs with particular interest in SRMRs (but not exclusively). First of all, designs of SRMRs are studied and improvements have been demonstrated in Roombots (RB), a SRMR designed in the Biorobotics Laboratory. The design improvements involve both electromechanical hardware, control and planning aspects. After all improvements, complex scenarios can be studied involving more than 10 modules adding up more than 30 DOF system. Such SRMRs are not intuitive for humans to operate. To overcome this issue, three different user interfaces (UIs) are proposed covering different aspects to simplify use of SRMRs. The first UI is used for conveying shape information to SRMRs using a tangible interaction interface as a proxy. The second one does not have any interaction medium and user directly control SRMRs via gestures that are tracked by external vision systems. The last UI shows possibility of assembling SRMRs in a virtual reality environment using a head mounted display and a hand gesture tracking system. All three of proposed UIs are novel and first of their kind for SRMRs. The final focus is locomotion with modular morphologies and presented in three major studies. Initially, one of the most simplest modular structures, a parallel chain structure, is studied to develop a goal driven neuro-visual locomotion model of a swimming lamprey robot. It is followed by a slightly more complex chain structure. A snake robot is simulated during different serpentine gaits to evaluate implications of different on-board camera placement strategies for such robots. In the last phase, the importance of compliance in legged locomotion is experimentally assessed for quadrupedal modular structures. Compliance of legs as well as a control scheme that acts as a compliant element is taken into consideration for a comparative evaluation. Locomotion is a fundamental part of all mobile robots. Three biologically inspired methods are offered to tackle locomotion of MRs that present performance improvements on multiple aspects as well as better understanding of certain concepts. Although the idea of modularity is widely used in industrial production and common daily items, MRs still don't find much use in daily lives. This thesis brings MRs one step closer to wide daily use by addressing such systems from multiple perspectives.

EPFL2019

Chargement

Despite great efforts in designing legged robots, we are still far from the adaptivity, efficiency and robustness with which animals can move. Observations from successful biomimetic designs highlight the significant role of clever morphological design in achieving such performance. In addition, the important role of the controller in improving the locomotion performance is undoubtable. In fact, there is a complex link between morphology and motor control of locomoting systems. In animals’ locomotion, there is a large number of evidence showing the effective link between their morphology and functionality. Motivated by biological observations, similar questions can be posed from a robotics perspective: “what are the relative and complementary roles of robot control and morphology (similar to animal’s brain and body) in the generated locomotor behavior?”, and more pragmatically, “how can we take lessons from these observations to reduce the current gap between robots’ locomotion performance and what is observed in their biological counterparts?”. These are the fundamental questions that have motivated studies in this thesis. While empirical studies are essential to address aforementioned questions, they require simplifying contexts to yield insightful predictions and examinable theories. Both theoretical and physical models (i.e. simulations and robots) can significantly contribute in providing such insights. While robot experiments are essential to evaluate and explore the involved biological concept, they are usually time-consuming and costly. Hence, it would be advantageous if one could exploit the power of theoretical models for development of ideas and hypotheses before their implementation on the real robot. In this thesis, we aim at leveraging the strength of theoretical models to study the above-mentioned questions, namely, the relative role of control and morphology in improving the robot locomotion functionalities. To provide useful theoretical models, we take a step-wise approach, where we start from model-free methods and proceed with advancing the locomotion control by incorporating dynamics models at different levels of complexity. In particular, we develop a pool of robot models, starting from a simplified massless leg to a detailed dynamics model of the leg, to a 2D quadruped with spine joint and eventually to a 3D detailed dynamics model of a quadruped. Along with developing dynamics model of the robot, we devise a set of control and optimization techniques with the main goal of improving locomotion performance. There are several performance criteria to consider (such as energy efficiency, maneuverability, adaptivity to unknown terrains) and a key question is how to build the control architecture to hold a proper trade-off between these partially contradicting criteria. We take advantage of the developed dynamic models in both (i) improving the controller performance and (ii) implementing analytical tools to evaluate and compare different locomotion performance criteria. The central outcome of this thesis is a bio-inspired modeling, control, and optimization framework for legged robot locomotion, which is evaluated on a set of robots with different morphologies. In all cases, we explore how the locomotion performance can be improved by introducing new control techniques or be influenced by the morphological aspects (such as joint configuration and mass distribution). In particular, we show the effect of using more detailed dynamics model to improve the predictive performance of the simulations both for analyzing morphological factors and for robustness of the controller to internal (e.g. change in the inertial parameters) and external (e.g. walking on rough terrains) perturbations. The framework is generic and is used to model, control and analyze locomotion gaits for three compliant quadruped robots (Locomorph, Cheetah-Cub and Bobcat robots) and a modular robot (Roombots).

EPFL2013

Chargement

Combining Reflexes and External Sensory Information in a Neuromusculoskeletal Model to Control a Quadruped Robot

Auke Ijspeert, Azhar Aulia Saputra

This article examines the importance of integrating locomotion and cognitive information for achieving dynamic locomotion from a viewpoint combining biology and ecological psychology. We present a mammalian neuromusculoskeletal model from external sensory information processing to muscle activation, which includes: 1) a visual-attention control mechanism for controlling attention to external inputs; 2) object recognition representing the primary motor cortex; 3) a motor control model that determines motor commands traveling down the corticospinal and reticulospinal tracts; 4) a central pattern generation model representing pattern generation in the spinal cord; and 5) a muscle reflex model representing the muscle model and its reflex mechanism. The proposed model is able to generate the locomotion of a quadruped robot in flat and natural terrain. The experiment also shows the importance of a postural reflex mechanism when experiencing a sudden obstacle. We show the reflex mechanism when a sudden obstacle is separately detected from both external (retina) and internal (touching afferent) sensory information. We present the biological rationale for supporting the proposed model. Finally, we discuss future contributions, trends, and the importance of the proposed research.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2021

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EPFL2013

Perception, control and planning for (self-)reconfigurable modular robots

Mehmet Hasan Mutlu

EPFL2019