Inverse kinematics and reflex based controller for body-limb coordination of a salamander-like robot walking on uneven terrain

Search and rescue (SAR) missions are being carried out by several types of robots. They include ground, marine and air vehicles depending on the terrain and mission to be tackled. A particular niche for SAR activities are shallow waters. They present high difficultly for conventional ground or marine robots because of the mix of water and ground. Such an environment is difficult to be accessed for a robot without some built-in amphibious capabilities. Our lab has experience in the design of amphibious salamander-like robots. In order to consider whether these robots would be suited for SAR missions in shallow waters, a key requirement is the ability to tackle rough terrains. In this paper we present a control framework for a highly redundant salamander-like robot. It involves bio-inspired spine control, inverse kinematics-based limb control, proper limb-spine coordination, reflex mechanisms and attitude control. The framework is validated in a simulation and on the real robot. In both cases, the robot is used in two different configurations: with and without its tail, in order to investigate how the tail (which is necessary for swimming) affects ground locomotion. With this exploration, we aim to set the precedent for improving the problem of dynamic locomotion of salamander-like robots over unperceived rough terrain. Our results confirm that the design of reflexes like stumbling and extension, combined with an attitude controller, allows for the improving of the performance of the robot in a generic rough terrain which includes stairs, holes and bumps with several levels of complexity adjusted according to the robot dimensions.

Legged locomotion with spinal undulations

Konstantinos Karakasiliotis

Legged locomotion with spinal undulations is a topic that has not received much attention yet in robotics, though, vertebrates depend on both their limbs and spine to move efficiently in their environments. In this thesis, my aim is to get more insights into the role and function of these two body parts as well as their coordination. Biology provides several answers to these questions. Salamanders and lizards are great biological paradigms for studying animal locomotion with limbs and flexible spine. Not only do they have a highly flexible spine and limbs that can sometimes vary in strength or even number, but they also demonstrate a rich repertoire of locomotor modes. They can walk on land, while they can swim and walk in water. This provides many more examples on the ways that limbs and spine function and coordinate. Biorobotics is a growing field of robotics that aims at answering questions that cannot be answered from animal observations. Those questions often deal with the development of a specific function of a body part. In my studies, I initially used a bio-inspired amphibious salamander-like robot Salamandra robotica II to extract basic principles of salamander locomotion. Although the improvements of the limb and tail designs enhanced the robot’s performance to a level that was surprisingly close to the salamander’s, several limitations were identified owing to the simplicity of the bio-inspired design. These limitations motivated me to design a new amphibious salamander-like robot, Pleurobot, which is capable of replicating the movements of salamanders with reasonable accuracy. A novel methodology was also used during this process which proved to be effective but simple at the same time. Three-dimensional kinematics of the salamander’s skeleton were recorded and used to guide the design process and optimization of the robot’s morphology and joints’ topology. The raw angular kinematics, extracted from X-ray biplanar videos of salamanders, were then used to drive the joints of Pleurobot, resulting in natural-looking and effective locomotion. The main contributions of this thesis are two-fold: i) biological data and robotic prototypes that improve our understanding on sprawling locomotion and ii) a successful methodology for robotic design for more animal-like robots and agile control

EPFL2013

Control of Bio-Inspired Sprawling Posture Quadruped Robots with an Actuated Spine

Tomislav Horvat

Sprawling posture robots are characterized by upper limb segments protruding horizontally from the body, resulting in lower body height and wider support on the ground. Combined with an actuated segmented spine and tail, such morphology resembles that of salamanders or crocodiles. Although bio-inspired salamander-like robots with simple rotational limbs have been created, not much research has been done on kinematically redundant bio-mimetic robots that can closely replicate kinematics of sprawling animal gaits. Being bio-mimetic could allow a robot to have some of the locomotion skills observed in those animals, expanding its potential applications in challenging scenarios. At the same time, the robot could be used to answer questions about the animal's locomotion. This thesis is focused on developing locomotion controllers for such robots. Due to their high number of degrees of freedom (DoF), the control is based on solving the limb and spine inverse kinematics to properly coordinate different body parts. It is demonstrated how active use of a spine improves the robot's walking and turning performance. Further performance improvement across a variety of gaits is achieved by using model predictive control (MPC) methods to dictate the motion of the robot's center of mass (CoM). The locomotion controller is reused on an another robot (OroBOT) with similar morphology, designed to mimic the kinematics of a fossil belonging to Orobates, an extinct early tetrapod. Being capable of generating different gaits and quantitatively measuring their characteristics, OroBOT was used to find the most probable way the animal moved. This is useful because understanding locomotion of extinct vertebrates helps to conceptualize major transitions in their evolution. To tackle field applications, e.g. in disaster response missions, a new generation of field-oriented sprawling posture robots was built. The robustness of their initial crocodile-inspired design was tested in the animal's natural habitat (Uganda, Africa) and subsequently enhanced with additional sensors, cameras and computer. The improvements to the software framework involved a smartphone user interface visualizing the robot's state and camera feed to improve the ease of use for the operator. Using force sensors, the locomotion controller is expanded with a set of reflex control modules. It is demonstrated how these modules improve the robot's performance on rough and unstructured terrain. The robot's design and its low profile allow it to traverse low passages. To also tackle narrow passages like pipes, an unconventional crawling gait is explored. While using it, the robot lies on the ground and pushes against the pipe walls to move the body. To achieve such a task, several new control and estimation modules were developed. By exploring these problems, this thesis illustrates fruitful interactions that can take place between robotics, biology and paleontology.

EPFL2018

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.