Nonconventional control of the flexible pole-cart balancingproblem: Experimental results

Emerging techniques of intelligent or learning control seem attractive for applications in manufacturing and robotics. It is however important to understand the capabilities of such control systems. In the past the inverted pendulum has been used as a test case, however, this problem is not sufficiently testing. This research therefore concentrates on the control of the inverted pendulum with additional degrees of freedom as a testing demonstrator problem for learning control system experimentation. A flexible pole is used in place of a rigid one. The transverse displacement of the flexible pole has distributed elasticity and therefore infinite degrees of freedom. The dynamics of this new system are more complex as the system needs additional parameters to be defined due to the pole's elastic deflection. This problem also has many of the significant features associated with flexible robots with lightweight links as applied in manufacturing. Novel neural network and fuzzy control systems are presented that control such a system in real time in one of its modes of vibration. A fuzzy-genetic approach is also demonstrated that allows the creation of fuzzy control systems without the use of extensive knowledge.     

Nonlinear control with end-point acceleration feedback for a two-link flexible manipulator: Experimental results

Experimental results for end-point positioning of multi-link flexible manipulators through end-point acceleration feedback are presented in this article. The advocated controllers are implemented on a two-link flexible arm developed at the Control/Robotics Research Laboratory at Polytechnic University. The advocated approach in this article is based on a two-stage control design. The first stage is a nonlinear (1) feedback linearizing controller corresponding to the rigid body motion of the manipulator. Because this scheme does not utilize any feedback from the end-point motion, significant vibrations are induced at the end effector. To this effect, and to enhance the robustness of the closed-loop dynamics to parameter variations, the inner loop is augmented with an outer loop based on a linear output LQR design that utilizes an end-point acceleration feedback. The forearm of the manipulator is significantly more flexible as compared with the upper arm. Experimental and simulation results validate the fact that the end-effector performance is significantly better with the proposed (1) feedback linearizing control as compared with the linear independent joint PD control. In addition, the nonlinear control offers other advantages in terms of smaller and smoother actuator torques and reducing the effects of nonlinearities. Close conformation between simulation and experimental results validates the accuracy of the model.     

A practical approach for robust control of flexible structures

This paper deals with the robust control of linear single-input, single-output (SISO) systems. First, general concepts of the frequency-domain approach are presented. We then focus on the particular problem of flexible structure and control. A new method is proposed which combines the advantages of hyperstability and small gain approaches. Finally, an application of an industrial sight system prototype is detailed.     

Active control of flexible systems by a mathematical programming approach

A class of control problems for a damped distributed parameter system governed by a system of partial differential equations with side constraints (equality and/or inequality) is considered. The proposed approach approximates each control force of the system by a Fourier-type series. In contrast to standard linear optimal control approaches, the method used here is based on the mathematical programming approach, in which the necessary condition of optimality is derived as a system of linear algebraic equations. The proposed approach is easy to apply to a large class of control problems. A vibrating beam excited by an initial disturbance is studied numerically in which the effectiveness of the control and the amount of force spent in the process are investigated in relation to the reduction to the dynamic response.     

Optimal design for robust control of uncertain flexible joint manipulators: a fuzzy dynamical system approach

A novel fuzzy dynamical system approach to the control design of flexible joint manipulators with mismatched uncertainty is proposed. Uncertainties of the system are assumed to lie within prescribed fuzzy sets. The desired system performance includes a deterministic phase and a fuzzy phase. First, by creatively implanting a fictitious control, a robust control scheme is constructed to render the system uniformly bounded and uniformly ultimately bounded. Both the manipulator modelling and control scheme are deterministic and not IF-THEN heuristic rules-based. Next, a fuzzy-based performance index is proposed. An optimal design problem for a control design parameter is formulated as a constrained optimisation problem. The global solution to this problem can be obtained from solving two quartic equations. The fuzzy dynamical system approach is systematic and is able to assure the deterministic performance as well as to minimise the fuzzy performance index.     

A finite-element approach to control the end-point motion of a single-link flexible robot

A structural finite-element technique based on Bernoulli-Euler beam theory is presented which will permit the finding of the torques (or forces) that are necessary to apply at one end of a flexible link to produce a desired motion at the other end. This technique is suitable for the open loop control of the tip motion. It may also provide a good control law for feedback control. The finite-element method is used to discretize the equations of motion. This method has a major advantage in the fact that different material properties and boundary conditions like hubs, tip loads, changes in cross sections, etc., can be handled in a very simple and straightforward manner. The resulting differential equations are integrated via the frequency domain. This allows for the expansion of the desired end motion into its harmonic components and helps to visualize the complex wave propagation nature of the problem. The performance of the proposed technique is illustrated in the solution of a practical example. Results point out the potential that this technique has in the study of the dynamics and control not only of flexible robots, but also of any other flexible mechanisms like those used in biomechanics, where high precision at the tip of very light flexible arms is required.     

Towards a unified approach to encodability and separation results for process calculi

We present a unified approach to evaluate the relative expressive power of process calculi. In particular, we identify a small set of criteria (that have already been somehow presented in the literature) that an encoding should satisfy to be considered a valid means for language comparison. We argue that the combination of such criteria is a valid proposal by noting that: (i) several well-known encodings appeared in the literature satisfy them; (ii) this notion is not trivial, because some known encodings do not satisfy all the criteria we have proposed; (iii) several well-known separation results can be formulated in terms of our criteria; and (iv) some widely believed (but never formally proved) separation results can be proved by using the criteria we propose. Moreover, the criteria defined induce general proof-techniques for separation results that can be easily instantiated to cover known case-studies.     

A class of high level languages for process control

An abstract notational system can serve as a model for the investigation of high level programming languages that explicitly support the monitoring and control of parallel events, provide data types at the bit level and allow real-time interaction between user and process. Run-time mechanisms that support the execution of programs in the notational system chosen on specific hardware can also be identified. A software tools environment can be designed to provide high level languages and runtime support for process control in a way that encourages portability among different hardware configurations.     

工业过程中液位的区间控制

液位的定位控制是造成物流频繁变化的主要因素之一。在工业过程中,充分利用液位所具有的容量特性对物流流量的缓冲作用,尽可能地对设备或容器的液位实行区间控制,能够大大提高生产装置的平稳运行水平和产品质量。模型预测控制是一种行之有效的方法,在吸收稳定装置的实际应用中取得了非常好的效果。     

EVAC: a virtual environment for control of remote imaginginstrumentation

The objective of this project, called the Experimentalist's Virtual Acquisition Console (EVAC), was to demonstrate a prototype system for using virtual environments that would allow a researcher access the hardware in a remote experimental laboratory over high-speed networks, in order to control remote instrumentation. We wanted to give the researcher tools that would not only allow for complete control of the imaging system but also provide the potential for collaboration with researchers at distant sites. We targeted three imaging instruments, all located at the Beckman Institute for Advanced and Technology: a magnetic resonance imaging system, a transmission electron microscope and a scanning tunneling microscope. Our goal was not to control all three instruments simultaneously but rather to demonstrate that our unified virtual environment interface could be adapted to these widely different imaging devices. In building this demonstration, we faced many problems commonly encountered in developing a remote interface to a new instrument. These included the lack of any standard interface to the devices, the necessity of dealing with proprietary software, and the problem of developing a distributed model so that the instruments could be controlled over the network. The EVAC project has illustrated the potential of a virtual laboratory over a high-speed network     

Evolving the process of a virtual composer

In this paper we present a genetic programming system that evolves the music composition process rather than the musical product. We model the composition process using a Turing-complete virtual register machine, which renders musical pieces. These are evaluated using a series of fitness tests, which judge their statistical similarity against a corpus of Bach keyboard exercises. We explore the space of parameters for the system, looking specifically at population size, single-versus multi-track pieces and virtual machine instruction set design. Results demonstrate that the methodology succeeds in creating pieces of music that converge towards the properties of the chosen corpus. The output pieces exhibit certain musical qualities (repetition and variation) not specifically targeted by our fitness tests, emerging solely based on the statistical similarities.

     

ESCCS柔性过程模型研究

高技术战争要求装备保障指挥控制系统具有高度的柔性。工作流过程模型是装备保障指挥控制系统的基础,模型描述能力的强弱是解决系统柔性问题的关键。通过将任务类型分为基本任务类型和扩展任务类型,提出柔性过程模型主要由基本任务要素、柔性任务要素以及这些要素间的连接方式构成。将装备保障指挥控制工作流中的任务分解为基本任务要素和柔性任务要素增强了系统的柔性。描述了扩展后的柔性过程模型及其特点。     

Self-organizing fuzzy controller for the molten steel level control of a twin-roll strip casting process

The twin-roll strip casting process is a steel-strip production method that combines continuous casting and hot rolling process in a single operation. The quality of strip casting process depends on many process parameters, such as molten steel level in the tundish, solidification position and roll gap. Their relationships are complex and the strip casting process has the properties of nonlinear uncertainty and time-varying characteristics. Hence, it is difficult to establish an accurate process model for designing a model-based controller to monitor the strip quality. In this paper, a model-free control strategy is employed to overcome this problem. The self-organizing fuzzy control (SOFC) strategy is developed to control the molten steel level of a strip casting process. It has on-line learning ability and the rule tables can be modified automatically and continuously for responding to the system’s nonlinear and time-varying behaviors. Since this model-free controller has simple control structure and small number of control parameters, it is easy to implement. Simulation results based on semi-experimental system dynamic model and parameters are executed to show the control performance of the proposed intelligent controller.     

Quality control for deep x-ray lithography (LIGA): a preliminary metrology study

The x-ray lithography process is time-consuming and costly. The use of process design rules is essential along with CAD designs that should fulfil the specifications of dimension and roughness. Parameters such as the material of mask membrane, the technique to produce the mask, the resist used (poly (methyl-methacrylate) [PMMA], epoxy based photoresist SU-8), the synchrotron power and synchrotron spectrum do have an effect on the final geometry of the fabricated parts. To evaluate these parts, high accuracy metrology is essential. KIT/IMT and NPL have two different co-ordinate measuring machines (CMMs) designed for millimetre scale geometry measurements to micrometer accuracy. Test structures of various sized holes and columns, made by deep x-ray lithography in PMMA and electroformed in metal, have been measured by these two different CMMs. A comparison of the measurements taken from these two micro-CMMs will be presented and discussed. The outcome of these preliminary results on the x-ray lithography process will be shortly described.     

Low-level flexible planning for mobile manipulators: a distributed perception approach

The paper proposes a method to improve flexibility of the motion planning process for mobile manipulators. The approach is based on the exploitation of perception data available only from simple proximity sensors distributed on the robot. Such data are used to correct pre-planned motions to cope with uncertainties and dynamic changes of the scene at execution time. The algorithm computes robot motion commands aimed at fulfilling the mission by combining two tasks at the same time, i.e. following the planned end-effector path and avoiding obstacles in the environment, by exploiting robot redundancy as well as handling priorities among tasks. Moreover, a technique to smoothly switch between the tasks is presented. To show the effectiveness of the method, four experimental case studies have been presented consisting in a place task executed by a mobile manipulator in an increasingly cluttered scene.     

Minimax program control for the approach process in a two-level hierarchical discrete dynamical system

We consider a dynamical system consisting of three objects whose dynamics is given by vector linear discrete recurrent equations. The system contains two levels of managerial decision making, basic and secondary, that have different operational criteria and are united by informational and managerial connections defined in advance. For the dynamical system in question, we propose a mathematical formalization in the form of solving a multistage problem of two-level hierarchical minimax program control over the approach process with incomplete information and give a general scheme for its solution.     

Direct strain feedback control of flexible robot arms: newtheoretical and experimental results

This paper addresses control problems for flexible robot arms by using direct strain feedback. The purpose is to make clear why direct strain feedback can damp out vibration of flexible arms satisfactorily. We concentrate on one-link flexible robot arms whose dynamic models can be represented by linear partial differential equations with appropriate boundary conditions which have been well examined in a number of papers. A key contribution of this paper is the introduction of the concept of (strict) A-dependent operators, which allows us to prove rigorously the closed loop stability of direct strain feedback and the existence and uniqueness of nonstandard second order abstract differential equations in Hilbert spaces. Several control experiments are performed, verifying the main theoretical points of this paper, demonstrating satisfactory control results of direct strain feedback, and leading to potential application of this simple control method for flexible robot control     

Evaluating the reliability and impact of a quality assurance system for E-learning courseware

Assuring e-learning quality is of interest worldwide. This paper introduces the methods of e-learning courseware quality assurance (a quality certification system) adopted by the eLQSC (e-Learning Quality Service Centre) in Taiwan. A sequential/explanatory design with a mixed methodology was used to gather research data and conduct data analyses. Sixty-seven e-learning courseware applications were evaluated using the e-Learning Courseware Quality Checklist (eLCQC). Analyses of item difficulty, item discrimination and generalizability indicated that the eLCQC provides high-quality evaluations. After participating in the certification process, the e-learning producers reported having more confidence in enhancing e-learning courseware quality. The certification experience also helped the producers to change their previous design concepts about e-learning courseware and to develop new concepts; further, their increased confidence about courseware design also enhanced their confidence in marketing courseware.     

Trajectory following for a flexible probe with state/input constraints: An approach based on model predictive control

This paper describes the trajectory following algorithm developed for a bio-inspired flexible probe, the direction of which can be controlled by means of an offset between interlocked probe segments which make up its body. The control approach employs model predictive control (MPC) to explicitly consider input and state constraints which arise from the unique mechanism of motion of the probe. For the sake of fast computation, a tracking error model is modified so that the nonlinear kinematic model of the probe is linearized, and the model is used to convert the optimization problem into a well-known quadratic programming (QP) problem. The input and state constraints are also converted into an inequality to be integrated into the QP problem. Simulated results demonstrate that the linearized tracking error model and the MPC control strategy are appropriate, handling large perturbations robustly, while satisfying all constraints. Experimental results in a gelatine sample, carried out with a 12 mm outer diameter prototype, demonstrate satisfactory two-dimensional trajectory following performance (0.52 mm average tracking error, with 1.49 mm STD). The experimental results also show that, given the probe’s constraints, the proposed controller provides more robust performance against large insertion perturbations than previously published control strategies developed for the probe.     

The development of a fault-tolerant control approach and its implementation on a flexible arm robot

This article presents a robust sensor fault-tolerant control (FTC) scheme and its implementation on a flexible arm robot. Sensor faults affect the system's performance in the closed loop when the faulty sensor readings are used to generate the control input. In this article, the non-faulty sensors are used to reconstruct the faults on the potentially faulty sensors. The reconstruction is subtracted from the faulty sensors to generate a 'virtual sensor' which (instead of the normally used faulty sensor output) is then used to generate the control input. A design method is also presented in which the virtual sensor is made insensitive to any system uncertainties (which could corrupt the fault reconstruction) that cannot fit into the framework of the model used. Two fault conditions are tested: total failure and incipient faults. Then the scheme robustness is tested and evaluated through its implementation on two flexible arm systems, one with a flexible joint and the other with a flexible link. Excellent results have been obtained for both cases (joint and link); the FTC scheme produced system performance almost identical to the fault-free scenario, whilst providing an indication that a fault is present, even for simultaneous faults.