Comparison of low-complexity controllers in varying time-delay systems

Abstract : Motivated by the recent developments in networked control systems and control over wireless, this paper presents a comparison of five control algorithms that are based on PID, IMC and fuzzy gain scheduling techniques and discusses their performance in varying time-delay systems. The low complexity of the proposed algorithms makes their use attractive in resource-constrained environments such as wireless sensor and actuator networks. The control system consists of a controller, a simple process and an output delay in the feedback loop. Three different delay models are considered in this framework; constant, random, and correlated random delay. In addition to presenting modifications to the control algorithms to better fit the varying time-delay systems a delay-robust tuning method is proposed, and the performance of various controllers is evaluated using simulation. The results show the benefits of adapting the controller parameters based on delay measurement if its amplitude is significant with respect to the time-constant of the process. Nevertheless, the PID algorithm used in the study also performs well in all scenarios, and this is achieved by its careful tuning

A review of friction models in interacting joints for durability design.

This paper presents a comprehensive review of friction modelling to provide an understanding of design for durability within interacting systems. Friction is a complex phenomenon and occurs at the interface of two components in relative motion. Over the last several decades, the effects of friction and its modelling techniques have been of significant interests in terms of industrial applications. There is however a need to develop a unified mathematical model for friction to inform design for durability within the context of varying operational conditions. Classical dynamic mechanisms model for the design of control systems has not incorporated friction phenomena due to non-linearity behaviour. Therefore, the tribological performance concurrently with the joint dynamics of a manipulator joint applied in hazardous environments needs to be fully analysed. Previously the dynamics and impact models used in mechanical joints with clearance have also been examined. The inclusion of reliability and durability during the design phase is very important for manipulators which are deployed in harsh environmental and operational conditions. The revolute joint is susceptible to failures such as in heavy manipulators these revolute joints can be represented by lubricated conformal sliding surfaces. The presence of pollutants such as debris and corrosive constituents has the potential to alter the contacting surfaces, would in turn affect the performance of revolute joints, and puts both reliability and durability of the systems at greater risks of failure. Key literature is identified and a review on the latest developments of the science of friction modelling is presented here. This review is based on a large volume of knowledge. Gaps in the relevant field have been identified to capitalise on for future developments. Therefore, this review will bring significant benefits to researchers, academics and industrial professionals

Electroless nickel plating: PCB process modelling and estimation

The process of electroless nickel plating in printed circuit boards (PCB) industries by plating-through-hole (PTH) was discussed. In the technology, the product quality is controlled through the process chemistry using an automatic control system stabilizing the nickel concentration and pH-index continuously. The current densities of the electrochemical reactions were represented as a two-directional process in a model, which was mainly the anodic reaction model for oxidation and cathodic reaction model for others. To prevent unstable situations, a piecewise constant pH-trajectory was aimed while the nickel concentration level was aimed for keeping the level constant

Model for electroless nickel plating of through holes board process:Model accuracy testing

Model for the electroless nickel plating of through holes board process developed earlier is tested in this paper on independent (from calibration) data and shown to be adequate and thus capable to be applied for monitoring of the board and bath parameters usually analysed in laboratory with a delay of 6-10 hours

Current control of piezoelectric actuators with power loss compensation

This paper introduces a feedforward charge control method, which controls the displacement by the amount of current fed to the actuator. The method includes estimation and compensation of the power losses occurring in the actuator. Power losses are estimated with an experimentally created dynamic model, that does not include the load and self heating effects. Even though the method is based on feedforward control, the amount of current is controlled in closed loop, using a precise current measurement and a PID controller. Experiments with a piezo bender show promising results; the hysteresis was nearly reduced to one part in twenty and drift to one part in ten, in comparison to open-loop voltage control. The proposed method can predict the power losses quite accurately and can therefore be utilized not only for the control but also for power estimation in applications where power consumption is critical.Peer reviewe

Electroless nickel plating: Bath control

in this paper, bath control is proposed for the electroless nickel plating through holes board process. The main parameters of the product (board) - thickness of the plating film and phosphorous content - are stabilized at constant levels using optimal tracking control. The set point for control is calculated from the model in dependence on the current state of the process. The pH-index and nickel percentage are stabilised at time-variable set points using simple feed-forward PI-control that is robust to the loading perturbation. Copyright © 2005 IFAC

Position control of a 3 DOF piezohydraulic parallel micromanipulator

This paper focuses on the open-loop and closed-loop position control of a tripod-like joint-free parallel micromanipulator that is composed of three piezohydraulic actuation systems. The micromanipulator is controlled in open-loop using a general inverse kinematics model presented earlier for a tripod manipulator having ball and pin joints. Open-loop control is sufficient in many applications but when high accuracy and high speed are required, closed-loop control must be applied. The closedloop control of the micromanipulator is organized in multiple levels. The first level compensates non-linearities of the actuation systems and the second level controls the position of the end-effector. Level three is a supervisory level and level four tackles automatic operations. Level two, i.e. the position feedback controller, consists essentially of two single input/single output (SISO) proportional-integral (PI) controllers and an incremental form of the inverse kinematics model. The experimental results show that the position feedback control efficiently eliminates drift and vibration of the end-effector.Peer reviewe