This paper analyzes and develops new approaches for handling and shaping collections of microscale objects such as particles or cells. While traditional dielectrophoretic manipulation approaches are based on creating an energy trap, this work employs a distributed manipulation philosophy: shaping the energy field to model the point-wise forces and hence the characteristics of the field. This method offers a better perspective on the behavior, exact shape, position, and orientation of the collection of objects under manipulation. Furthermore, this research showcases devices that artificially generate planar quadratic and squeezing force fields by setting the potential at each point in space. These devices enable the positioning of particles and collections of particles to a predefined shape and orientation. Finally, we demonstrate a novel approach to distributed manipulation. We construct a 3-D potential force field by setting the boundary conditions of the differential equation describing the dynamics of a natural medium (the voltage profile in our case). This approach is illustrated by constructing cylindrical and ellipsoidal potential force fields for use in particle and cell manipulation.

Actuation redundancy is common in cooperative mobility and cooperative manipulation systems. In this paper we present an extension to a previously developed method in order to characterize and exploit redundancy. Our idea is based on the introduction of a virtual linkage in the system to be able to determine the null hyperplane in the actuation force space. We then exploit the null directions to optimize critical design limits. We first demonstrate the development of this approach with a 3-robot cooperative mobility system and then we apply the approach to analyze actuation redundancy in a manipulation system.

The contribution of this paper is the introduction of the event-condition-action (ECA) paradigm for the design of modular logic controllers that are reconfigurable. ECA rules have been used extensively to specify the behavior of active database and expert systems and are recognized as a highly reconfigurable tool to design reactive behavior. This paper develops a method to design modular logic controllers whose dynamics are governed by ECA rules, with the ultimate goal of producing reconfigurable control. Modularity, integrability, and diagnosability measures that have in the past been used to measure the reconfigurability of manufacturing systems are used to assess the reconfigurability of the developed controllers. For the modularity measure, criteria found in computer science to evaluate the modularity of object-oriented programs are adapted to evaluate the modularity of modular logic controllers. The results of this paper are that reconfigurability is highly dependent on the level of modularity of the logic control system, and that not all "modular" structures are reconfigurable. There are approaches, such as the one shown in this paper using ECA rules, that can greatly increase the modularity, integrability, and diagnosability of the logic control system, thus increasing its reconfigurability. Note to Practitioners-This paper has been motivated by the problem of designing reconfigurable modular logic controllers. Reconfiguration is important in manufacturing, but it has also been an issue in the software design domain. There are software systems that currently exist, such as active data bases or expert systems with very powerful reconfiguration capabilities enabled by event-condition-action (ECA) rules. This paper applies the ECA concept to the design of modular logic controllers. This paper begins by describing what an ECA logic system is and then focuses on how ECA logic systems can be implemented with modular control approaches. To this end, two designs are considered. First, modular finite state machines are used to construct ECA logic systems, and a theoretical framework is built using this approach. Three qualitative measures for reconfigurability (modularity, integrability, and diagnosability) are presented and the controllers are evaluated using these measures. Second, an implementation using the IEC 61499 function block standard is presented as it is a widely understood and accepted standard for modular control applications. Future work entails theoretical analysis using modular verification techniques that exploit a controller structure

This paper presents one approach to design logic control systems using event-condition-action (ECA) rules implemented with IEC 61499 function blocks (FBs). ECA rules have been used extensively to specify the behavior of active database and expert systems and are recognized as a highly reconfigurable tool to design reactive behavior. Recent results have shown how the use of ECA rules can greatly increase the modularity, integrability, and diagnosability of the logic control system thus increasing its reconfigurability. This paper proposes a FB architecture such that the behavior of the control system follows the ECA paradigm.

PROFINET is the industrial Ethernet standard devised by PROFIBUS International for "Ethernet on the plant floor". PROFINET allows to implement a comprehensive communications solution on Ethernet which includes peer-to-peer communication between controllers, distributed I/O, machine safety, motion control and data acquisition. In this paper an analysis is conducted on the peer-to-peer interlocking performance based on PROFINET specification. Tests were performed to determine the performance of the peer-to-peer communication mechanism, to evaluate the impact of switches on the system, and to measure the impact of data size on peer-to-peer communication performance. The paper summarizes the test results.

The improvement in Ethernet based technologies has resulted in its use in real-time applications on the factory floor. Manufacturers, vendors and end users of automation devices are aiming at the economical and technical benefits of Ethernet based communication. Many Ethernet based protocols have been developed due to the promotion by several companies and organizations. There has been a considerable amount of research on whether these Ethernet based systems are able to fulfill the real-time requirements. To this end, this paper presents an evaluation of EtherNet/IP and its applicability for peer-to-peer communications on the factory floor.

Distributed manipulation using passive air flows generally produces multiple equilibria. In this paper, a straight stationary barrier is considered in a manipulation problem using passive air flows. Such a system simplifies equilibrium analysis but raises problems on contact modes, rolling or sliding. Coulomb's friction model is employed to solve contact modes when an object sits on a straight barrier. This paper illustrates the relationship between contact modes and the location of a flow sink with respect to location of the straight barrier. Although the friction coefficient is poorly estimated, numerical prediction of contact modes quite well agrees with experimental results

A team of small, low-cost robots instead of a single large, complex robot is useful in operations such as search and rescue, urban exploration etc. However, the performance of such a team is limited due to the restricted mobility of the team members. This paper presents the results obtained toward the goal of enhancing mobility of a team of mobile robots by physical cooperation among the robots with the focus on the development of the low level system components. Recognizing that small robots need to overcome discrete obstacles, we develop specific analytical maneuvers to negotiate each obstacle where a maneuver is built from a sequence of fundamental cooperative behaviors. We have developed a 2-robot hardware system based on our idea of cooperative mobility improvement and guided by the results from the static analysis. We have demonstrated the implementation of basic cooperative behaviors, such as cooperative lift, and by implementing the decentralized control architecture we have demonstrated gap crossing maneuver with the hardware. We have analytically proved that robot dynamics can be used to reduce the friction requirements in the lift behavior and have demonstrated, with simulations, implementation of this idea for the cooperative lifting behavior

Planar quadratic potential fields are useful for distributed manipulation because they are readily analyzable and naturally produce predictable equilibria. This generally simplifies implementation since feedback and control may not be necessary. Traditionally, to dynamically produce moving fields for complex manipulation tasks, these fields had to be realized by highly capable but redundant actuator arrays. This paper suggests a new method: using simpler devices to generate basic component fields, and superposing these fields to produce desired fields with similar degrees of freedom. This approach is particularly useful for naturally produced force fields which do not allow the dynamic moving and changing of a field but allow for superposition and thus can be spatially combined to produce the desired net behaviors. A vector representation of these fields is developed and applied to two problems: How to place the fields in space to span the maximum possible configuration space, and how to generate an optimal solution to generate a desired field by a superposition of a fixed field arrangement with minimal effort from each field. Finally, we experimentally validated these methods using airflow fields based on phenomenological and time superposition

Distributed manipulation systems induce motions on objects through the application of forces at many points of contact. Current forms of distributed manipulation include multiple mobile robots, vibrating plates, actively controlled arrays of air jets, and planar micro- and macro-mechanical arrays of actuators. The authors have presented a new form of distributed manipulation using passive airflow fields. This paper lays out infrastructure for manipulation algorithms using logarithmic potential fields applicable to passive airflow distributed manipulators. It uses a line-integral form of the lifted force equations, and provides a numerical approach to check the uniqueness of the robust pivot point for given objects in a logarithmic potential field. The numerical method is proved analytically to require a finite resolution to find all robust pivot points. It also proposes a squeeze-like sequential manipulation algorithm to bring an object with a unique robust pivot point to a unique final pose using airflow fields without sensors. The algorithm has been verified by experiments which are conducted for three different starting orientations, and end up with a unique final pose at the end of the manipulation sequence

Planar quadratic potential fields are useful for distributed manipulation because they are readily analyzable and naturally produce predictable equilibria. This generally simplifies implementation, since feedback and control may not be necessary. Traditionally, to dynamically produce moving fields for complex manipulation tasks, these fields had to be realized by highly capable, but redundant, actuator arrays. This paper suggests a new method: using simpler devices to generate basic component fields, and superposing these fields to produce desired fields with similar degrees of freedom. This approach is particularly useful for naturally produced force fields which do not allow the dynamic moving and changing of a field, but allow for superposition, and thus, can be spatially combined to produce the desired net behaviors. A vector representation of these fields is developed and applied to two problems: how to place the fields in space to span the maximum possible configuration space; and how to generate an optimal solution to generate a desired field by a superposition of a fixed field arrangement with minimal effort from each field. We experimentally validated these methods using airflow fields based on phenomenological and time superposition. Finally, we use superposition to simplify trajectory following, by blending proportions of two fields over time and by superimposing a set of component fields, each responsible for compensating a particular dynamic term

Distributed manipulation systems induce motions on objects through the application of many external forces. Many of these systems are abstracted as planar programmable force fields. Quadratic potential fields form a class of such fields that lend themselves to analytical study and exhibit useful stability properties. This paper introduces a new methodology to build quadratic potential fields with simple devices using the naturally existing phenomena of airflow, which is an improvement to the traditional use of the complicated programmable actuator arrays. It also provides a basis for the exploitation, in distributed manipulation, of natural phenomena like airflow, which require rigorous analysis and display stability difficulties. A demonstration and verification of the theoretical results for the special case of the elliptic field with airflows is also presented.

A static control system architecture cannot meet the demand for continually introducing new parts into manufacturing systems while maintaining high quality and throughput for existing parts; a reconfigurable control infrastructure is needed. Control authority in the factory is typically allocated to three levels: the machine, cell, and system. The machine controllers must be reconfigurable to process different parts, the cell controllers must be reconfigurable to adapt to different part flows, and the system level controller must be reconfigurable to adapt to new parts in the system. In this paper, we describe the reconfigurable control infrastructure that we have developed at the University of Michigan's reconfigurable factory testbed. We then show through example how this infrastructure enables the real-time reconfiguration of the controllers at the machine and cell levels to adapt to quality problems and unexpected faults

Distributed manipulation systems induce motions on objects through the application of many external forces. Many of these systems are abstracted as planar programmable force fields. Quadratic potential fields, which belong to such a class of fields, lend themselves to analytical study and exhibit useful stability properties. This paper introduces a new methodology to build Quadratic fields with simple devices using the naturally existing phenomena of airflow which is an improvement to the traditional use of the complicated programmable actuator arrays. It also provides a basis for the exploitation, in distributed manipulation, of natural phenomena like airflow, which require rigorous analysis and display stability difficulties. A demonstration and verification of the theoretical results for the special case of the elliptic field with air flows is also presented.

Distributed manipulation systems induce motions on objects through the application of forces at many points of contact. Current forms of distributed manipulation include multiple mobile robots, vibrating plates, actively controlled arrays of air jets, and planar micro and macro-mechanical arrays of actuators. The authors have presented a new form of distributed manipulation using passive air flow fields, which has been experimentally demonstrated along with a computational method to locate equilibria. This paper presents a numerical approach to check the uniqueness of the pivot point of lifted logarithmic potentials. For objects with a unique pivot point, a squeeze-like sequential manipulation using air flow which brings the object to a unique final pose is presented and verified with experiments.

A team of small low cost robots instead of one big, complex robot is useful in operations such as search and rescue, urban exploration etc. However, the performance of such a team is limited due to restricted mobility of the team members. We propose to overcome the mobility restrictions by physical cooperation among the team members. We carry out a feasibility analysis of a particular behavior of two robots cooperating to cross a gap. We simulate the dynamic equations describing the motion, which leads to the relaxation of the requirements derived from the static analysis. A decentralized control architecture is designed which avoids continuous communication between the robots thus rendering the cooperation to be simple and low cost.

Distributed manipulation systems induce motions on objects through the application of forces at many points of contact. Current forms of distributed manipulation include multiple mobile robots, vibrating plates, actively controlled arrays of air jets, and planar micro and macro-mechanical arrays of actuators. The authors have presented a new form of distributed manipulation using passive air flow fields, which has been experimentally demonstrated and a computational method to locate equilibria. This paper presents a methodology for guaranteeing the existence of the equilibria and its synthetic usage for efficient manipulation of objects using passive air flow fields.

Distributed manipulation systems induce motions on objects through the application of many external forces. An actuator array performs distributed manipulation using a planar array of many stationary elements, which cooperate to manipulate larger objects through the generation of a programmable force field. This paper defines and studies a class of manipulation force fields called quadratic potential fields. Methodology is developed to decompose these fields into simpler components and superimpose them both vectorially and geometrically, simplifying the design of manipulation strategies. Application to trajectory following is also presented.

Many distributed manipulation systems are capable of generating planar force fields which act over the entire surface of an object to manipulate it to a stable equilibrium within the field. Passive air flow fields, previously introduced by the authors generate force fields through the linear superposition of logarithmically varying radial potential fields. The main advantage of these fields Is that they are realizable through very simple actuation. However, they do not lend themselves to analytical prediction of net forces or equilibria. The paper presents an efficient means of numerically computing the net force and moment exerted by such fields on objects composed of multiple simple shapes, as well as efficient means of finding equilibrium points on these fields.

Distributed manipulation systems induce motions on objects through the application of many external forces. An actuator array performs distributed manipulation using a planar array of many small stationary elements, which cooperate to manipulate larger objects through the generation of a programmable force field. The paper demonstrates a methodology to perform trajectory following to transport objects with specified position and orientation. Open-loop "elliptic" force fields transport objects by pulling them along the trajectory both in position and orientation. This is done in three stages: purely open loop, open loop with feed-forward compensation to correct for steady-state error on lines and around circular curves, and closed-loop with both feed-forward and small-signal linearized feedback. These approaches apply to arbitrary paths through linear and circular trajectory approximations. Results are verified through simulation.

Distributed manipulation systems induce motions on objects through the application of forces at many points of contact. Current forms of distributed manipulation include multiple mobile robots, vibrating plates, actively controlled arrays of air jets, and planar micro and macro-mechanical arrays of actuators. The paper presents a form of distributed manipulation using passive air flow fields, which has been experimentally demonstrated. Rather than directly actuating the flow at each point, potential flow assumptions allow a small number of simple point-generated fields to combine to form complex manipulation fields. The paper presents a methodology for efficiently computing equilibria of objects manipulated by arbitrary combinations of radially symmetric fields (such as potential flow fields).

Exact cellular decompositions are structures that globally encode the topology of a robot's free space, while locally describing the free space geometry. These structures have been widely used for path planning between two points, but can be used for mapping and coverage of robot free spaces. In this paper, we define exact cellular decompositions where critical points of Morse functions indicate the location of cell boundaries. Morse functions are those whose critical points are non-degenerate. Between critical points, the structure of a space is effectively the same, so simple control strategies to achieve tasks, such as coverage, are feasible within each cell. In this paper, we derive a general framework for defining decompositions in terms of critical points and then give examples, each corresponding to a different task. All of the results in this paper are derived in an m-dimensional Euclidean space, but the examples depicted in the figures are 2D and 3D for ease of presentation.

An actuator array performs distributed manipulation where an object being transported and manipulated rests on a large number of stationary supporting actuators. The authors have developed a macroscopic actuator array consisting of many motorized wheels. As opposed to a MEMS array, the analysis requires the explicit modeling of the discreteness in the system, including the set of supports, distribution of weight, and generation of traction forces. Using an open-loop wheel velocity field, discreteness causes undesirable behavior such as unstable rotational equilibria, suggesting the use of object feedback. Discrete distributed control algorithms are derived by inverting the dynamics of manipulation. These algorithms reduce the many-input-three-output control problem to a three-input-three-output control problem.

The modular distributed manipulator system (MDMS) is a macroscopic actuator array which can manipulate objects in the plane. The piecewise-constant dynamics of manipulation on the MDMS are developed based on an exact discrete representation of the system. The resulting dynamics are inverted enabling the calculation of an open-loop vectorfield which provides arbitrary uniform object dynamics. The vector field positions, and under certain assumptions, orients objects.

An actuator array is a form of distributed manipulation where an object being transported and manipulated rests on a large number of supporting actuators. On a discrete array employing an open-loop field, some size and shape objects may have unstable equilibria due to this discreteness. The functional relationship between object dimensions relative to array spacing and rotational stability is examined, and a map of this function is generated. The geometry behind this relationship is also examined, and analytical expressions for the boundaries between stable and unstable regions in the map are derived.

During the Summer of 1997, Nomad, a planetary-relevant mobile robot, was driven via satellite link for more than 125 miles in the Atacama Desert of Chile by novice operators in North America, demonstrating many technologies relevant to robotic exploration of the planets. An innovative "transforming" chassis was demonstrated which uses a simple linkage to change the footprint of the vehicle from a stowed to a deployed position. This linkage also enables both double Ackennan and point-turn steering. This paper presents details on the design of the transforming chassis including kinematic analysis used in low and high level control.

We are developing a materials handling system where many small simple actuators cooperate to transport and to manipulate large objects in the plane. A discrete set of cells, each comprising two actuators, are fixed in a planar array. By coordinating the actuators in the cells on which an object rests, an object can be transported and manipulated. In essence, this system is an improvement over traditional conveyor systems in that objects can be re-oriented, as well as conveyed. Such an array provides flexible materials handling in which many objects independently can be manipulated and transported at the same time. The array is coordinated in a distributed manner where each cell has its own controller and each controller communicates with its neighbors. Towards the goal of motion planning, in this paper we consider the dynamics of parcel transport and manipulation. The parcel dynamics are based on an exact discrete representation of the system, unlike other methods where a continuity assumption is made. Two types of contact models are considered.