Luzius Brodbeck

Morphological Evolution of Physical Robots through Model-Free Phenotype Development

Artificial evolution of physical systems is a stochastic optimization method in which physical machines are iteratively adapted to a target function. The key for a meaningful design optimization is the capability to build variations of physical machines through the course of the evolutionary process. The optimization in turn no longer relies on complex physics models that are prone to the reality gap, a mismatch between simulated and real-world behavior. We report model-free development and evaluation of phenotypes in the artificial evolution of physical systems, in which a mother robot autonomously designs and assembles locomotion agents. The locomotion agents are automatically placed in the testing environment and their locomotion behavior is analyzed in the real world. This feedback is used for the design of the next iteration. Through experiments with a total of 500 autonomously built locomotion agents, this article shows diversification of morphology and behavior of physical robots for the improvement of functionality with limited resources.

Robotic body extension based on Hot Melt Adhesives

The capability of extending body structures is one of the most significant challenges in the robotics research and it has been partially explored in self-reconfigurable robotics. By using such a capability, a robot is able to adaptively change its structure from, for example, a wheel like body shape to a legged one to deal with complexity in the environment. Despite their expectations, the existing mechanisms for extending body structures are still highly complex and the flexibility in self-reconfiguration is still very limited. In order to account for the problems, this paper investigates a novel approach to robotic body extension by employing an unconventional material called Hot Melt Adhesives (HMAs). Because of its thermo-plastic and thermo-adhesive characteristics, this material can be used for additive fabrication based on a simple robotic manipulator while the established structures can be integrated into the robots own body to accomplish a task which could not have been achieved otherwise. This paper first investigates the HMA material properties and its handling techniques, then evaluates performances of the proposed robotic body extension approach through a case study of a “water scooping” task.

Active sensing system with in situ adjustable sensor morphology.

Background Despite the widespread use of sensors in engineering systems like robots and automation systems, the common paradigm is to have fixed sensor morphology tailored to fulfill a specific application. On the other hand, robotic systems are expected to operate in ever more uncertain environments. In order to cope with the challenge, it is worthy of note that biological systems show the importance of suitable sensor morphology and active sensing capability to handle different kinds of sensing tasks with particular requirements. Methodology This paper presents a robotics active sensing system which is able to adjust its sensor morphology in situ in order to sense different physical quantities with desirable sensing characteristics. The approach taken is to use thermoplastic adhesive material, i.e. Hot Melt Adhesive (HMA). It will be shown that the thermoplastic and thermoadhesive nature of HMA enables the system to repeatedly fabricate, attach and detach mechanical structures with a variety of shape and size to the robot end effector for sensing purposes. Via active sensing capability, the robotic system utilizes the structure to physically probe an unknown target object with suitable motion and transduce the arising physical stimuli into information usable by a camera as its only built-in sensor. Conclusions/Significance The efficacy of the proposed system is verified based on two results. Firstly, it is confirmed that suitable sensor morphology and active sensing capability enables the system to sense different physical quantities, i.e. softness and temperature, with desirable sensing characteristics. Secondly, given tasks of discriminating two visually indistinguishable objects with respect to softness and temperature, it is confirmed that the proposed robotic system is able to autonomously accomplish them. The way the results motivate new research directions which focus on in situ adjustment of sensor morphology will also be discussed.

Enhanced robotic body extension with modular units

The adaptation of robots to changing tasks has been explored in modular self-reconfigurable robot research, where the robot structure is altered by adapting the connectivity of its constituent modules. As these modules are generally complex and large, an upper bound is imposed on the resolution of the built structures. Inspired by growth of plants or animals, robotic body extension (RBE) based on hot melt adhesives allows a robot to additively fabricate and assemble tools, and integrate them into its own body. This enables the robot to achieve tasks which it could not achieve otherwise. The RBE tools are constructed from hot melt adhesives and therefore generally small and only passive. In this paper, we seek to show physical extension of a robotic system in the order of magnitude of the robot, with actuation of integrated body parts, while maintaining the ability of RBE to construct parts with high resolution. Therefore, we present an enhancement of RBE based on hot melt adhesives with modular units, combining the flexibility of RBE with the advantages of simple modular units. We explain the concept of this new approach and demonstrate with two simple unit types, one fully passive and the other containing a single motor, how the physical range of a robot arm can be extended and additional actuation can be added to the robot body.

An extendible reconfigurable robot based on hot melt adhesives

The ability to physically enlarge one’s own body structures plays an important role in robustness and adaptability of biological systems. It is, however, a significant challenge for robotic systems to autonomously extend their bodies. To address this challenge, this paper presents an approach using hot melt adhesives (HMAs) to assemble and integrate extensions into the robotic body. HMAs are thermoplastics with temperature dependent adhesiveness and bonding strength. We exploit this property of HMAs to connect passive external objects to the robot’s own body structures, and investigate the characteristics of the approach. In a set of elementary configurations, we analyze to which extent a robot can self-reconfigure using the proposed method. We found that the extension limit depends on the mechanical properties of the extension, and the reconfiguration algorithm. A five-axis robot manipulator equipped with specialized HMA handling devices is employed to demonstrate these findings in four experiments. It is shown that the robot can construct and integrate extensions into its own body, which allow it to solve tasks that it could not achieve in its initial configuration.

Automatic real-world assembly of machine-designed structures

Several approaches have been presented which allow robots to build structures to adapt themselves or their environments. To autonomously build these structures, a design must be made, from which instructions for the fabrication process can be derived. For a constrained fabrication process, e.g. considering the limited range of a robot, this transfer can be cumbersome. We present a local building process based on a sequence of two distinct operations, which implicitly encodes the shape of a structure. Given this encoding, the structure can readily be built with a real-world robotic system. We show automatic design of structures reaching out of the robots range and fulfilling stability and strength constraints using an evolutionary design algorithm. The final design can then be built with a robotic arm from wooden cubes and hot melt adhesives. We demonstrate the whole process including the construction of a structure from more than thirty cubes with our real-world setup. We expect that automatic design and construction can further improve the physical adaptability of robotic systems.

Robotic Invention: Challenges and Perspectives for Model-Free Design Optimization of Dynamic Locomotion Robots

To improve a robot’s performance at a given task, or to respond to changing requirements, shape adaptation can be beneficial. To efficiently explore complex behaviors, diverse morphologies must be generated and implemented. For continuous and autonomous design optimization, the robot has furthermore to be able to assess its own performance and in turn generate and implement adapted morphological designs. Here, we present the morphological adaptation of physical robotic agents to a locomotion task. The robots are automatically assembled by a robotic manipulator from elementary modules and the assembly process of each agent is encoded in a genotype. The genotypes of a robot population are optimized using an evolutionary algorithm based on real-world performance feedback. In the experiments, 500 genotypes were evaluated. To develop rich behavioral diversity, shape variations are beneficial. Analysis of the results highlights the influence of the fabrication constraints on shape diversity, which impose limitations especially for larger structures.

The Solving by Building Approach Based on Thermoplastic Adhesives

While, in nature, changes of morphology such as body shape, size, and strength play essential roles in animals’ adaptability in a variety of environment, our robotic systems today still severely suffer from the lack of flexibility in morphology which is one of the most significant bottlenecks for their autonomy and adaptability. With the ability to autonomously modify own body shapes or mechanical structures in surroundings, robotic systems could achieve a variety of tasks in flexible and simple manners. For this reason, we have been investigating technological solutions based on a class of unconventional material, the so-called Thermoplastic Adhesives (TPAs), with which the robots are able to construct their own body parts as well as connecting and disconnecting various mechanical structures. Based on our technological exploration so far, in this paper, we introduce the concept of “solving-by-building” approach, in which we consider how autonomous construction of mechanical parts can help robots to improve performances or to “solve” problems in given tasks. Unlike the conventional adaptive systems that can only learn motor control policies, the ability to change mechanical structures can potentially deal with a significantly more variety of problems. By introducing some of the recent case studies in our laboratory, we discuss the challenges and perspectives of the solving-by-building approach based on TPAs.

Flexible Self-reconfigurable Robots Based on Thermoplastic Adhesives

The paper introduces a concept of flexible self-reconfiguration that makes use of thermoplastic adhesives (TPAs) in robotic systems. TPAs are polymer based materials that exhibit several interesting mechanical properties beneficial for self-reconfiguration. For example, thermoplasticity enables robots to flexibly fabricate a number of different mechanical structures, while temperature-dependent adhesion allows systems to make robust connection and disconnection. This paper introduces robotic self-reconfiguration by using three TPA handling processes, i.e. structure formation, connection and disconnection. These processes are then examined in a few practical application scenarios, i.e. pick and place operations of a variety of objects, autonomous body extension of robotic manipulators, and robots climbing on uneven surfaces. And finally we discusses challenges and perspectives of this approach.