Tzyh Jong Tarn

Integrated task scheduling and action planning/control for robotic systems based on a max-plus algebra model

Presents a paradigm for task scheduling and action planning/control of a robotic system. Based on the proposed max-plus algebra model, a robotic task involving both discrete and continuous actions can be scheduled, planned and controlled in a perceptive reference frame. Therefore, task scheduling, which usually deals with discrete type of events, as well as action planning, which usually deals with continuous events, can be treated systematically in a unified framework. More importantly, the unique feature of this approach is that interactions between discrete and continuous events can be considered in the same framework. As a result the efficiency, robustness and reliability of the task schedule and action plan can increase significantly. A typical assembly task in a dual-robot manufacturing work-cell is used to illustrate the proposed approach. The experimental results clearly demonstrate the advantages of the proposed approach.

New integrability conditions for differential constraints

Abstract This paper discusses differential-form-based integrability conditions for dynamic constraints using the Frobenius theorem. The conditions can be used for the classification of holonomic and nonholonomic constraints. Some of the previous conditions used for this purpose are only sufficient. The conditions presented here are both necessary and sufficient. The papers main interest is on differential constraints for under-actuated mechanical systems. Different from many discussions in classical mechanics that deal with mostly on kinematics constraints, the constraints discussed here are from the Lagrange equations, which correspond to unactuated part of the system dynamics.

Visualization of dual-arm robot motion space under kinematic constraints

This article presents a technique for determining and visual izing the geometric motion capabilities of dual-arm robotic systems when the arms work on an object in a closed kine matic chain configuration, taking account of robot arms base placements, object dimensions, object holding and contact constraints, and space occupancy conflicts of the two arms links. The constrained and object orientation restricted motion space in general can be visualized as a complex 3D object with hidden unreachable holes or cavities of varying shapes. An automated visualization methodology is presented together with its graphical implementation, illustrated by an example. The methodology is an inverse computer vision technique in the sense that it creates rather than recognizes visual forms.

Progress in theoretical quantum computing

Computing is perhaps one of the most distinguished features that differentiate humans from animals. Aside from counting numbers using fingers and toes, abacus was the first great computing machine of human civilization. Over thousands of years, the development of mechanical computing machines had been slow. A breakthrough came with the invention of vacuum tube. Later inventions of transistors and VLSIs have led to the birth of modern electronic computers. Modern electronic computers have completely transformed the life of the human race. Quantum computers are a new type of computing machine which works on the principles of the microscopic world, quantum mechanics. There have been intensive worldwide efforts in physically building such machines. To build such a machine, the system must be able to provide a sequence of two-level quantum sub-systems that serve as quantum bits, or qubits for short. Secondly, the quantum system should be initializable to some desired states. Thirdly, it should be robust against environmental disturbance which is translated into a long coherence time in the terminology of physics. Fourthly, the system should accommodate at least a set of basic universal gates so that any unitary operations performed in a quantum computer can be constructed from them. Finally, we should be able to measure the quantum system to read out the results of the computation. These five conditions are usually called the Divincenzo criteria. There have been several good candidate systems for quantum computers, and the progress has been steady over the years. However, we are still years away from a practical quantum computer. Quantum computers are no longer an extravagant superfluity, but the sword of Damocles hanging high above the security systems of the world. No one dares to be dropped behind in the race. Ever since its birth, computer scientists have been playing an important role in the development of quantum computers. With the monumental work of Shor, Grover and others, the study of quantum computers has become the world’s research frontier. In this issue we present ten invited articles that focus on part of the endeavor of researchers in basic quantum computing theories. These articles cover a rich range of subjects that include: entanglement that is unique to quantum systems in that it appears simultaneously in more than two places; decoherence suppression; quantum fixed point search algorithm; quantum codes; controlled teleportation; quantum programming language; duality quantum computing; quantum probabilistic cloning and its applications in quantum computation; high dimensional Bell inequalities and quantum automata. Because of the vast scope of quantum computing, and also the short period of time taken in organizing this special issue, there are still other topics that are not covered in this special issue. We are looking forward to reviewing more research in this area in the future.

A computational method to geometric measure of biological particles and application to DNA microarray spot size estimation.

Geometric measures (volume, area and length) of biological particles are of fundamental interest for biological studies. Many times, the measures are at micro-/nano-scale, and based on images of the biological particles. This paper proposes a computational method to geometric measure of biological particles. The method has been applied to DNA microarray spot size estimation. Compared with existing algorithms for microarray spot size estimation, the proposed method is computational efficient and also provides confidence probability on the measure. The contributions of this paper include a generic computational method to geometric measure of biological particles and application to DNA microarray spot size estimation.

Sensor‐referenced multiple robot cooperation for material handling

In this paper, a new cooperation control scheme for multiple robot material handling is presented. First, the event‐based planning and control method is introduced, which lays down the foundation for sensor‐referenced cooperation of multiple robot systems. The key step is the development of event‐based action reference. Based on the real‐time sensory information, the event‐based action reference drives the system to achieve the best possible coordination. The event‐based cooperation control scheme can easily be implemented in a distributed computer system. A real‐time control and computing architecture is proposed to implement this scheme in a parallel computation. The new multiple robot cooperation scheme has been experimentally implemented and tested on two 6‐DOF PUMA 560 robots. The experimental results have demonstrated the advantages of the scheme.

Intelligent task scheduling, planning, and control for manufacturing work cells

This paper presents a novel approach for solving the challenging problem in intelligent control of manufacturing systems, i.e. the integration of low-level system sensing and simple control with high-level system behavior and perception. The proposed Max-Plus Algebra model combined with event-based planning and control provides a mechanism to efficiently integrate task scheduling, sensing, planning and real-time execution so that task scheduling, which usually deals with discrete types of events, as well as action planning, which usually deals with continuous events, can be treated systematically in a unified analytical model. More importantly, the unique feature of this approach is that interactions between discrete and continuous events can be considered in a unified framework. This feature allows the manufacturing system to intelligently cope with unexpected events and uncertainties so that the efficiency and reliability of the task schedule and action plan can increase significantly. A robotic manufacturing system is used to illustrate the proposed approach. The experimental results clearly demonstrate the advantages of the proposed approach.

A Linear Filter for Discrete Systems with Correlated Measurement Noise

This paper introduces an optimal linear filter for discrete systems with correlated measurement noise by generalized least square method which is novel in its structure, its derivation and its simplicity. The equations reduce to the standard Kaiman filter equations when the measurement noise is independent. The new filter avoids the increased order and other complexities of previously proposed methods particularly those based on augmented state and differencing approaches.

Geometric characterization of multi-input lower-triangular forms

This paper is concerned with the problem as to whether a multi-input nonlinear system is equivalent to the so-called low-triangular form. Two elemental forms of multi-input lower-triangular systems are proposed. Then, using the theory of singular distributions, the necessary and sufficient conditions under which multi-input nonlinear systems are locally feedback equivalent to these two lower-triangular systems are established. Furthermore, algorithms are provided to describe how to realize these equivalent transformations via state feedbacks and coordinate conversions.

Complementary data fusion in guidance and control of robot compliant motion

This paper is devoted to the control problem of a robot manipulator for a class of constrained motions in an unknown environment. To accomplish a task in the presence of uncertainties, we propose a new guidance and control strategy based on multisensor fusion. Three different sensors-robot joint encoders, a wrist force-torque sensor and a vision system--are utilized for our task. First of all, a sensor-based hybrid position/force control scheme is proposed for an unknown contact surface. Secondly, a new multisensor fusion scheme is utilized to handle an uncalibrated workcell, wherein the surface on which there is a path to be followed by a robot is assumed to be unknown but visible by the vision system and the precise position and orientation of camera(s) with respect to the base frame of the robot is also assumed to be unknown. Our work is related with areas such as visual servoing, multisensor fusion and robot control for constrained motion. The main features of the proposed approach are: (1) multi-sensor fusion is used both for two disparate sensors (i.e. force- torque and visual sensors) and for complementary observed data rather than redundant ones as in traditional way; (2) visual servoing is realized on the tangent space of the unknown surface; (3) calibration of the camera with respect to the robot is not needed.