We present a distributed controller for the center of mass of a modular robot. This is useful for locomotion of a modular robot over uneven and unknown terrain. By controlling the center of mass, a robot can prevent itself from falling over. We present a distributed and decentralized algorithm that computes the mass properties of the robot. Additionally, each module also computes the mass properties of the modules that are directly or indirectly connected to each of its connectors. With this information, each module can independently steer the center of mass towards a desired position by adjusting its joint positions. We present simulation results that show the feasibility of the approach

This paper presents the design of an experimental system for assembly applications in space. The prototypical application is the assembly of mechanical trusses. The system used an air-hockey table to simulate a frictionless two-dimensional space. Assembly robots fly on the surface finding, gathering and assembling the relevant parts to perform the construction. The system design involved building the FIMER Robots, the test bed, the sensing system for position and velocity feedback and the control scheme. This paper describes the hardware and software used in the various sub-systems and includes calibrations and measurements and the results of experiments

Docking between independent groups of self-reconfigurable robotic modules enables the merger of two or more independent self-reconfigurable robots. This ability allows independent reconfigurable robots in the same environment to join together to complete a task that would otherwise not be possible with the individual robots prior to merging. The challenges for this task include: (1) coordinate and align two independent self-reconfigurable robots using the docking guidance system available only at the connectors of the docking modules; (2) overcome the inevitable errors in the alignment by a novel and coordinated movements from both docking ends; (3) ensure the secure connection at the end of docking; (4) switch configuration and let modules to discover the changes and new connections so that the two docked robots will move as a single coherent robot. We have developed methods for overcome these challenging problems and accomplished for the first time an actual docking between two independent CONRO robots each with multiple modules.

This paper presents an experimental system for assembly in space. A weightless and frictionless environment is approximated using an air-hockey table where robots and structural components can float on the surface. The robots use fan propulsion to dock with components and assemble them together to make 2D structures. This system is designed to implement three key technologies for space self-assembly: 1) intelligent components with universal connectors, 2) a set of self-reconfigurable robots that fetch and assemble components, and 3) a distributed method for controlling the robotic-assembly process. An overview of the system's design and experimental results is presented.

This paper describes two contributions for chain typed self-reconfigurable robots: a very illustrative self-reconfiguration task changing from "I" shape to "T" shape, and a sensor-based distributed control method for automatic planning and execution of self-reconfiguration. In the "I-to-T" task, a snake robot is to reconfigure itself into a tripod by docking the tail to a target module in the body, releasing a portion of the connected mass as a new leg, and switching to a new gait automatically. We first accomplished this task using predetermined instructions for individual modules without considering sensor inputs. We then developed a sensor-based approach using our hormone-inspired distributed control to allow the robot to dynamically accept the point of connection at run-time, align the tail and the target using sensors, and select appropriate actions based on modules' location in the configuration. Compared to the standard inverse kinematics, this new control approach is sensor-based and can endure the limited computational resources and uncertainties in the connections. It can be applied to self-reconfigurations that are not designed by the programmers but triggered by the environment.

The topology of a self-reconfigurable robot can change at anytime. This can be as a result of the failure of some modules of the robot, joining new modules to the robot, displacement of some modules from one location to another caused by the self-reconfiguration task or any combination of these cases. Considering that the process of selecting relevant behaviors to accomplish a given task is based on the current topology of the self-reconfigurable robot, modules must be able to detect and respond to any changes to the robot topology. When changes to the topology of the robot are detected, modules can investigate new ways of accomplishing the given task. This paper presents a distributed solution, FEATURE algorithm, to the problem of autonomous discovery and functional response to topology change. The result is experimentally verified and demonstrated on the CONRO self-reconfigurable robots.

This paper describes a new docking system, called Compliant-And-Self-Tightening (CAST), developed as an effective and efficient connector for joining and releasing modules of self-reconfigurable or metamorphic robotic systems. CAST has been successfully implemented in CONRO where its highly compliant and passive features have allowed a considerable ease of execution of a variety of docking algorithms, while using no additional energy for docking and negligible amount of energy for undocking. Development of CAST was motivated by observing the difficulty of implementation of an earlier less compliant docking system designed by the authors for CONRO.

Self-assembly systems in space are arguably within the reach of today's technology based on the research and development of self-reconfigurable robots on earth. This paper presents an approach to self-assembly in space by developing: (1) a novel design for intelligent and reconfigurable components; (2) the free-flying "intelligent fiber/rope" "match-maker" robots with self-reconfigurable and self-adjustable tethering for autonomous docking; and (3) a totally distributed control method for planning, executing, and monitoring the assembly process. These approaches are partially evaluated by a set of experimental and simulation results to simulate the dynamics and control of free-flying objects in zero-gravity environment.

In this paper we examine locomotion in the context of self-reconfigurable robots. Self-reconfigurable robots are robots built from many connected modules. A self-reconfigurable robot can change its shape and configuration by changing the way these modules are connected. The focus of this paper is to understand how several locomotion gaits can be represented in such a robot and how the robot can select one of these gaits depending on its configuration. We implement a control system based on role based control in a physical self-reconfigurable robot built from seven modules. In several experiments we successfully demonstrate that when the robot is manually reconfigured from a chain to a quadruped configuration the robot changes gait from a sidewinder snake gait to a quadruped walking gait. We conclude that role based control is a promising central method for controlling locomotion of self-reconfigurable robots.

A self-reconfigurable robot can be viewed as a network of many autonomous modules. Driven by their local information, the modules can initiate tasks that may conflict with each other at the global level. How the modules negotiate and select a coherent task among many competing tasks is thus a critical problem for the control of self-reconfigurable robots. This paper presents a distributed algorithm called DISTINCT to solve this challenging problem and show that it can be successfully applied to the CONRO self-reconfigurable robots. A discussion how to apply DISTINCT to other types of distributed systems such as sensor network, swarm robots, or multi-agent systems is also given.

How do multiple robots self-organize into global patterns based on local communications and interactions? This paper describes a theoretical and simulation model called "Digital Hormone Model" (DHM) for such a self-organization task. The model is inspired by two facts: complex biological patterns are results of self-organization of homogenous cells regulated by hormone-like chemical signals, and distributed controls can enable self-reconfigurable robots to performance locomotion and reconfiguration. The DHM is an integration and generalization of reaction-diffusion model and stochastic cellular automata. The movements of robots (or cells) in DHM are computed not by the Turing's differential equations, nor the Metropolis rule, but by stochastic rules that are based on the concentration of hormones in the neighboring space. Experimental results have shown that this model can produce results that match and predict the actual findings in the biological experiments of feather bud formation among uniform skin cells. Furthermore, an extension of this model may be directly applicable to self-organization in multirobot systems using simulated hormone-like signals.

Presents a biologically inspired approach to two basic problems in modular self-reconfigurable robots: adaptive communication in self-reconfigurable and dynamic networks, and distributed collaboration between the physically coupled modules to accomplish global effects such as locomotion and reconfiguration. Inspired by the biological concept of hormone, the paper develops the adaptive communication (AC) protocol that enables modules continuously to discover changes in their local topology, and the adaptive distributed control (ADC) protocol that allows modules to use hormone-like messages in collaborating their actions to accomplish locomotion and self-reconfiguration. These protocols are implemented and evaluated, and experiments in the CONRO self-reconfigurable robot and in a Newtonian simulation environment have shown that the protocols are robust and scaleable when configurations change dynamically and unexpectedly, and they can support online reconfiguration, module-level behavior shifting, and locomotion. The paper also discusses the implication of the hormone-inspired approach for distributed multiple robots and self-reconfigurable systems in general.

A Conro reconfigurable robot is formed by joining set of self-contained modules in a particular configuration; the actions of the robot are the result of the coordinated actions of its modules. These actions can be controlled using a master-slave approach only if the master can map the particular configuration of the robot to one that it already knows how to control. We discuss how to describe this configuration using graphs, how to discover a robot configuration and how to identify it as a particular known configuration. The methodology used is very general and can be applied easily to other modular robots. Experimental results for Conro quadrupeds and snakes are presented.

Metamorphic robots with shape-changing capabilities provide a powerful and flexible approach to complex tasks in unstructured environments. However, due to their dynamic topology and decentralized configuration, metamorphic robots demand control mechanisms that go beyond those used by conventional robots. This paper builds on our previous results of hormone-based control, and develops a novel distributed control algorithm called CELL that can select, synchronize, and execute gaits and other reconfiguration actions without assuming any global configuration knowledge. This algorithm is flexible enough to deal with changes of configuration, and can resolve conflicts between locally selected actions and manage multiple active hormones for producing coherent global effects.

Self-reconfigurable robots are modular robots that can dynamically and intelligently reconfigure their shape and size to accomplish difficult missions. To build such robots, however, a number of technical challenges must be overcome. One critical problem is the design and implementation of the reconnectable joints (also called connectors), which allows modules to autonomously connect and disconnect from one another. Such a mechanism must be power efficient, reliable, and compact (the mechanism must fit into a tight space). This paper gives an overview of the CONRO self-reconfigurable robots, and focuses on the reconnectable joints of the CONRO modules. The paper identifies a set of desired features and operation constraints for the joints, and describes our current design for the connectors.

Docking is a crucial action for self-reconfigurable robots because it supports almost all practical advantages of such robots. In addition to the classic docking challenges found in other applications, such as reliable dock/latch mechanics, effective guiding systems, and intelligent control protocols, docking in self-reconfigurable robots is also subject to some unique constraints. These constraints include the kinematics constraints imposed on the docking modules by other modules in the configuration, communication limitations between the docking and relevant modules, and the demand for distributed control software because of the dynamics of configuration. To solve these challenging problems, this paper reports a set of solutions developed in the CONRO reconfigurable robot project. The paper presents a three-stage docking process, six different alignment protocols, distributed inverse kinematics, and other techniques such as dynamic lubrication that are essential for successful docking in CONRO-like robots. These solutions enable CONRO robots to perform autonomous and distributed reconfigurations in a laboratory environment, and they also suggest important considerations for docking in self-reconfiguration in general.

Microelectromechanical systems (MEMS) have caught the imagination of the robot community as well as the general public. The excitement and promise of small, fast, capable micromechanical technology for robotics lies in being able to make extremely small machines that may be used for a variety of purposes ranging from small systems for space exploration to the wilder shores of tiny, implantable medical devices. The promise of MEMS is most evidently realized in the development of a wide variety of sensors that may be used to enhance the functionality of existing, more conventional robots, but MEMS capabilities in actuators are on the horizon, leading to the possibility of new robotics devices and systems. The paper discusses MEMS devices, the processes of making them, and some of their robotic applications, and ends with some open problems and challenges.

The goal of the Conro project is to build deployable self-reconfigurable robots, i.e., small homogeneous modular robots that can be reconfigured into different shapes such as snakes or hexapods. In this paper we describe the mechanical design of the first generation of Conro modules: the philosophy of their design, their parts and functionality and derive two inequalities that relate the design parameters of a module. Each module is fully self-contained in every sense; it carries its own CPU, power supply, and actuators. The modules were designed to work in groups, as robots, and thus, they also support inter-module communication. We conclude the paper describing a Conro hexapod as an example of the robots that can be built using these modules.

Assembly of nanometer-scale objects by scanning probe microscope (SPM) as a promising approach for the fabrication of nanoelectromechanical systems (NEMS). This paper describes several techniques for positioning nanoparticles, linking them to form subassemblies, and moving entire subassemblies. These are first steps towards the hierarchical construction of complex nanoassemblies. Results of experiments conducted in ambient air and in liquid environments are presented. Nanomanipulation in liquids opens new research directions involving interactions with single biomolecules, and fine control of forces between tips, particles and surface substrates.

We present a new approach to compute quasi-static and dynamic equilibrium positions and orientations (if any) of 2D polygonal or curved parts placed on general shaped 2D force field configurations. On the theoretical side, the novelty of our approach is that it puts into practice a fundamental result of piecewise-linear topology-the simplicial approximation theorem-and suggests an implementation using tools and techniques borrowed from modern computational geometry.

Precise control of the structure of matter at the nanometer scale will have revolutionary implications for science and technology. Nanoelectromechanical systems (NEMS) will be extremely small and fast, and have applications that range from cell repair to ultrastrong materials. This paper describes the first steps towards the construction of NEMS by assembling nanometer-scale objects using a scanning probe microscope as a robot. Our research takes an interdisciplinary approach that combines knowledge of macrorobotics and computer science with the chemistry and physics of phenomena at the nanoscale. We present experimental results that show how to construct arbitrary patterns of gold nanoparticles on a mica or silicon substrate, and describe the underlying technology. We also discuss the next steps in our research, which are aimed at producing connected structures in the plane, and eventually three-dimensional nanostructures.

The microelectromechanical systems (MEMS) field is proceeding at a rapid rate in designing and developing new ever smaller, ever higher performance sensor and actuator devices in silicon. These devices need to be assembled along with more conventional small devices into complete systems. Currently there are no automation systems capable of meeting the exacting requirements of handling these small and often fragile (until encapsulated) MEMS devices. This paper describes the latest results of our ongoing research on sensorless MEMS manipulator arrays. We use CMOS VLSI technology to construct automatic handling devices that scale with the technology curves of CMOS VLSI, and may offer a solution to the micro assembly problem. The intelligent motion surface (IMS), itself a MEMS device, has been designed to meet this challenge. This paper also introduces the CILIA software, a high-level programmable simulation software available to the research community via the WWW. The CILIA software decouples the design of applications requiring the use of manipulator arrays from the actual devices used to implement them, therefore offering a level of abstraction for the application designer, who can implement a set of motion plans independent of the MEMS device actually being used. Also, the CILIA software can be used to simulate both macro and micro manipulator array devices.

This paper introduces the concept of using a dense array of individual manipulator mechanisms as a programmable intelligent motion surface (IMS). The individual robots in the array can be implemented in a variety of technologies with different sizes. Programmability is the common necessary characteristic for an IMS; the array, with groups of contiguous robots acting in unison, can be programmed to various configurations to have the effect of imparting force fields on objects being carried on its surface. The appropriate choice of force fields is shown to cause parts placed on the array to be moved in manners that are useful. These include such functions as translation, rotation, orientation alignment, spatial filtering and the feeding of parts. The use of the IMS is described for primitive assembly operations. Limitations of the approach, extensions and possibilities for future work, particularly in microelectromechanical system (MEMS) implementations, are discussed in detail in the paper. The practicability and the programming of such an IMS-based active assembly bench was explored in a simulated environment.

This paper describes the software and hardware architecture of a system designed as a research tool for experiments on programming the computer controlled assembly of mechanical objects. The software consists of a real-time control level and a background level in which an on-line interpreter permits interactive programming. The hardware consists of a manipulator with sensory feedback coupled to an IBM System/7. Additional facilities are available through a link to an IBM System/370 Model 145. The application of the system to sample assemblies is also discussed.