Kimon Roufas

PolyBot: a modular reconfigurable robot

Modular, self-reconfigurable robots show the promise of great versatility, robustness and low cost. The paper presents examples and issues in realizing those promises. PolyBot is a modular, self-reconfigurable system that is being used to explore the hardware reality of a robot with a large number of interchangeable modules. PolyBot has demonstrated the versatility promise, by implementing locomotion over a variety of terrain and manipulation versatility with a variety of objects. PolyBot is the first robot to demonstrate sequentially two topologically distinct locomotion modes by self-reconfiguration. PolyBot has raised issues regarding software scalability and hardware dependency and as the design evolves the issues of low cost and robustness will be resolved while exploring the potential of modular, self-reconfigurable robots.

Modular Reconfigurable Robots in Space Applications

Robots used for tasks in space have strict requirements. Modular reconfigurable robots have a variety of attributes that are well suited to these conditions, including: serving as many different tools at once (saving weight), packing into compressed forms (saving space) and having high levels of redundancy (increasing robustness). In addition, self-reconfigurable systems can self-repair and adapt to changing or unanticipated conditions. This paper will describe such a self-reconfigurable modular robot: PolyBot. PolyBot has significant potential in the space manipulation and surface mobility class of applications for space.

Connecting and disconnecting for chain self-reconfiguration with PolyBot

Chain modular robots form systems with many degrees of freedom which are capable of being reconfigured to form arbitrary chain-based topologies. This reconfiguration requires the detaching of modules from one point in the system and reattaching at another. The internal errors in the system (especially with large numbers of modules) are such that accurate movement of chain ends, required for the attaching of modules, can be extremely difficult. A three-phase docking process is described that utilizes both open- and closed-loop techniques. This process has been shown to work with an early version. Issues raised during this testing have been addressed in a later version. Discussion of these issues, their solutions, and preliminary results of the testing the latest version are given.

Phase automata: a programming model of locomotion gaits for scalable chain-type modular robots

Modular reconfigurable robots have the potential for great versatility and robustness; however, programming locomotion gaits for hundreds of modules remains a challenge. In this paper we present a formal model for programming locomotion gaits in chain-type modular robots: phase automata. A phase automation is an event-driven state automation with an initial phase delay. The phase delay is normally a real value between 0 and 1. Phase automata are compact representation of locomotion gaits and capable of being embedded and distributed across modules. The concepts of phase automata have been implemented on both PCs and embedded micro-processors. An XML script language and programming interface for phase automata are being built. Locomotion gaits programmed using phase automata have been tested both in simulation with 100+ modules and in hardware with 50+ modules.

Six Degree of Freedom Sensing for Docking Using IR LED Emitters and Receivers

Six DOF offset sensing between two plates is important for automatic docking mechanisms. This paper presents an easy and inexpensive implementation of such a system using four commercial-off-the-shelf (COTS) infrared (IR) light emitting diode (LED) emitters and two COTS IR receivers on each of two docking plates. The angular intensity distribution of an emitter and the sensitivity distribution of a receiver allow for estimation of the angle and distance between them. Simple experiments have been conducted indicating that such a setup is able to give positional offset in any of 6 degrees of error (x, y, z, pitch, roll, and yaw) within a range. A theoretical framework is also established using least squares minimization. The theoretical framework is general and applies to other configurations of emitter and receiver parts and positioning.

Walk on the wild side [modular robot motion]

Designers of the PolyBot robot system solve the challenges of locomotion by mimicking locomotion in the animal world. PolyBot is a robot system made of many repeated simple modules. These modules can be connected together to form a variety of shapes to form a new system enabling a variety of functionalities.

Climbing with Snake-Like Robots

Abstract This paper presents an implementation of a long serial chain robot that can climb stairs in a “snake-biting-its-tail” loop form, climb up ramps using a travelling wave gait and by adding small spikes or cleats it can also climb near vertical porous materials. The gaits are controlled with a gait control table which is a simple but powerful way to coordinate the motion of many degrees of freedom. The gaits are implemented on Poly Bot G1v4, a self-sufficient modular reconfigurable robot with onboard power, computation, sensors and actuators.

Software architecture for modular self-reconfigurable robots

Modular, self-reconfigurable robots show the promise of great versatility, robustness and low cost. However, programming such robots for specific tasks, with hundreds of modules and each of which with multiple actuators and sensors, can be tedious and error-prone. The extreme versatility of the modular systems requires a new paradigm in programming. We present a software architecture for this type of robot, in particular the PolyBot, which has been developed through its third generation. The architecture, based on the properties of the PolyBot electro-mechanical design, features a multi-master/multi-slave structure in a multi-threaded environment, with three layers of communication protocols. The architecture is currently being implemented for Motorola PowerPC using vxWorks.

Scalable and reconfigurable configurations and locomotion gaits for chain-type modular reconfigurable robots

Modular reconfigurable robots have shown the promises of great versatility and robustness; however they also impose design challenges on mechanical, electronic and software scalability. In this paper, we present a class of configurations that are scalable mechanically and electronically. Moreover, there exists a predefined reconfiguration sequence between any of the three configurations, namely, snakes, centipedes, and multi-loops. Locomotion gaits for the three configurations are defined and created using Phase Automata, a generalization of gait tables. The system has been tested both in simulation of 100+ modules and in hardware of 50+ modules.

Sensor Computations in Modular Self Reconfigurable Robots

Sensors play important roles in automatic systems; smart systems have to be equipped with smart sensors. PolyBot, a modular self-reconfigurable robot developed at the Palo Alto Research Center, is designed with a rich set of sensors in each of its 5 cm-cubed modules. These include infra-red (IR), accelerometers, potentiometers, force, and touch sensors. These sensors are used: to determine the current state of the system and its environment; to obtain the six degree-of-freedom offset between two docking plates for automatic reconfiguration; to select the right gait for locomotion; and to trigger different behavior modes in response to different terrain conditions. Sensor computations are computational methods that, given raw sensor data, extract or deduce the state information about the system. This paper discusses two types of sensor computation, forward computation and inverse computation and focuses on two interesting sensor computations in PolyBot: IR 6 DOF ranging and accelerometer 2 DOF orientation.