Robert N. K. Loh

Passive compliance versus active compliance in robot‐based automated assembly systems

Industrial robots have found great potential in applications to assembly‐line automation. Programmable robot‐based assembly systems are often needed, in particular for circumstances in which special assembly equipments is not available or well‐trained operators could not be employed economically. Robots with enough compliance can perform not only classic automation tasks, such as spot welding, cargo carrying, etc., but also can operate those tasks which demand the compliant motion capacity of robots. Therefore, the research on robot compliance is especially important for parts assembly by robots, where robot compliant motions and manipulations are essential requirements. This paper presents a number of important issues in robot compliance research, including the specification of robot end‐effector compliance; properties of a robot compliance matrix at its end‐effector; discussions on passive compliance and active compliance and their comparisons; and derivation of the compliance at the end‐effector required for tasks.

Modeling, parameters identification, and control of an electronic throttle control (ETC) system

The modeling, parameters identification, and linear and nonlinear feedback control designs of an electronic throttle control (ETC) system is considered. A commercially available ETC system made by Bosch is selected for our investigation. The unknown parameters identified are used in designing linear and nonlinear controllers. Simulations and extensive experiments were conducted. A real-time linear controller was implemented with the xPC Target. The ETC model is then extended to a separately excited nonlinear DC motor model. The nonlinear controller is designed using the input-output feedback linearization technique; the extension proves to be of solid theoretical value. The results presented in this paper can be considered as an interesting and important case study encompassing system modeling, parameters identification, linear and nonlinear controller designs, and real-time control. The techniques and methodology developed are applicable to similar and/or other types of systems.

Modeling, design and implementation of discrete sliding mode control for an engine idle speed control system

A nonlinear model for the idle speed control (ISC) system of a 4-cylinder, 2.4-litre DaimlerChrysler car engine has been developed in this paper based on analytical methods and actual operational data. Through nonlinear state transformation and local linearization, the system model is then changed into a suitable form for which different control techniques and schemes can be applied. A discrete sliding mode (DSM) controller has been designed based on a reachability condition proposed in this paper. The resulting DSM control system was implemented into the DaimlerChrysler engine. The experimental results show that DSM control system has superior performance characteristics on tracking the desired idle speed and rejecting the system disturbances when compared with the existing controller.

Control of Weapon Pointing Systems Based on Robotic Formulation

A robotic formulation and control of weapon pointing systems are investigated. Specifically, a complete mathematical model for a helicopter and tank gun-turret system has been developed based on robotic formulation and methodology. The resultant mathematical model will automatically take into account the interaxis dynamics and nonlinear coupling between the azimuth and elevation axes, thereby providing more insight into the physics of the gun-turret characteristics. One of the major advantages of the proposed approah is that modern robotic technology, known for its versatility and ability to meet stringent performance requirements, can be utilized in the design and implementation of a large class of modern weapon pointing and platform systems with superior performance capabilities.

Passive Compliance from Robot Limbs and its Usefulness in Robotic Automation

Robots have been traditionally used as positioning devices without muchregard to external forces experienced by the tool. This has limited furtherpotential applications of robots in automation. Most tasks that remain to beautomated require constrained robot motion and/or involve work done by therobot on the environment. Such tasks require both force and positioncontrol. The ability to control the end-effector compliance is critical tosuccessful force and position control tasks. Although the end-effectorcompliance can be actively controlled through the joint flexibilitiesprovided by the joint servos or by active force sensing, the usefulness ofhaving the minimum passive compliance in addition to active compliancecontrol can improve performance. In surface following, for example, it isnecessary to make the end-point of a robot have the right compliance toprevent jamming. The usefulness of passive compliance has been demonstratedby the use of compliance-devices on the robot end-effector such as theRemote Center Compliance. The natural compliance inherent in light weightand flexible robot structures, however, can be exploited to provide thenecessary passive compliance required.In this paper we present a novel framework for computing the end-effectorcompliance from the compliance offered by the limbs of a serial robot. Theemphasis is on the explanation of the passive end-effector complianceresulting from these structures, and particular attention is given to theuse of these results in the selection of the type of robot for a particulartask. We show examples of end-effector compliances as functions of jointconfigurations for the SCARA- and PUMA-type robots. The joint-configurationdependent end-effector compliance can be used to select the desired robotpose for the performance of a robotic task.

Rule-based control of slowly varying systems using compensator segmentation determined by simulated annealing

A novel compensator segmentation scheme for rule-based control of a linear system characterized by structured uncertainties is presented. It is assumed that the design of a segmented compensator becomes necessary because the parameter variation region is too wide to be handled by a single robust compensator. The segmentation scheme is based on the simulated annealing technique. Starting with an initial estimate of the number of segments, the offline segmentation scheme attempts to minimize it while assuring coverage of the entire parameter variation region. The information about the segment boundaries and the appropriate compensators is then utilized as the database of a rule-based switching controller. The results of simulation studies that demonstrate the performance of the proposed scheme are included. >

Design of one-step-ahead prediction observers for system parameter identification

A unifying one-step-ahead prediction observer (identifier) for system parameter estimation or identification of autoregressive moving average (ARMA) processes has been developed. Four specific algorithms can be derived from the unifying algorithm. The properties of the four algorithms developed will be investigated.

Observer-based nonlinear control of depth positioning of a spherical underwater robotic vehicle

The analysis and design of observer-based nonlinear control of depth positioning of a spherical underwater robotic vehicle (URV) is investigated. The observer is required for estimating accurately the unknown state variables in the full-state feedback control laws developed, whereby these control laws can be implemented with the unknown states replaced by their observer estimates. The input-output feedback linearization approach and design techniques are employed. Three approximation schemes for smoothing the signum function in the URV model are developed; these smoothing schemes are required for deriving the linearizing feedback control laws and the related results. Simulation results show that the introduction of observer-based nonlinear control would provide a robust method to stabilize and control the depth position of the URV.

Nonlinear controller and observer designs of a CMOS-MEMS nano-newton force sensor

This paper addresses the design and application of an observer-based nonlinear controller employing a CMOS-MEMS nano-Newton force sensor. The sensor is designed using AMI 0.5µm 3-Metal 2-Polysilicon CMOS technology capable of sensing an out-of-plane force perpendicular to the probe tip; it is suitable for biomedical applications that measures external force excitation of less than 100 Hz. Measurement errors occur when there are in-plane movements of the probe tip; these errors can be controlled by the actuators incorporated within the sensor. Observer-based controller is necessitated in real-world control applications where not all the state variables are accessible for on-line, real-time measurements, and/or where the measurements are corrupted by noise.

Crank-angle Domain Modeling and Optimal Tracking Control for Automotive Engine Idle Speed

ABSTRACT In this paper, a nonlinear model has been developed for the Idle Speed Control (ISC) system of a 2.4-litre. 4-cylinder DaimlerChrysler car engine based on experiment data and system identification techniques. TIle model developed is relatively simple. An optimal idle speed controller has been designed and implemented into the engine. Simulation and experimental results show that the optimal ISC system is effective in both tracking and regular ing the desired idle speed and rejecting the disturbances.