Holger Schlegel

Increased Performance of a Hybrid Optimizer for Simulation Based Controller Parameterization

The controller parameterization is often carried out by applying basic empirical formulas within an integrated automatic design. Hence, the determined settings are often insufficient verified by the resulting system behavior. In this paper an approach for the controller parameterization by using methods of simulation based optimization is presented. This enables the user to define specific restrictions e.g. the complementary sensitivity function to influence the dynamic behavior of the control loop. A main criterion for practical offline as well as controller internal optimization methods is the execution time, which can be reduced by applying a hybrid optimization strategy. Thus, the paper presents a performance comparison between the straight global Particle-Swarm-Optimization (PSO) algorithm and the combination of the global PSO with the local optimization algorithm of Nelder-Mead (NM) to a hybrid optimizer (HO) based on examples.

Experimental and numerical modal analysis of a servo-screw press with coupled drives as a basis for increasing flexibility and dynamics

Abstract The development of electromechanical servo presses permits greater flexibility in process kinematics. When this feature is exploited in a targeted manner, the result of the forming process is largely determined by the dynamic properties of the forming machine. Here, attunement between control and mechanics is a central criterion for ensuring good motion dynamics, positioning accuracy and component quality. The increased motion dynamics during workpiece contact require a dynamic stability of the system technology in order to ensure process reliability. They affect the reactions of the machine structure as a result of the attendant process forces and inertial loads. The resulting oscillations affect the component quality and the operational strength of the machine. The effects of the slide guide, press mounting support, mass distribution and stiffness distribution are studied on the basis of a linearly elastic model of a servo-screw press and the results of an experimental modal analysis. The results of this study are intended to help shorten commissioning times and increase the productivity of servo-screw presses.

Analysis of a position control extension on the model of a servo-screw-press

Currently, the achievable feedback control performance for servo-screw-presses is limited by its elastic structure. A possible approach to compensate this limitation is the extension of the velocity controller. This structural extension has the potential to improve the controller performance significantly due to a better damping of low frequencies. In this paper, the extension of the control structure by a state space feedback in the velocity control loop is examined. Considering that, the velocity control extension is investigated at a test rig which consists of a servo axis and a two mass system. Furthermore, a simulation model for the test rig is designed. The results of the simulated and experimentally obtained results of the test rig are presented and evaluated in order to make a prediction for the transferability to the simplified model of the servo-screw-press.

Non Invasive Identification of Servo Drive Parameters

For the tuning of servo controllers as well as for monitoring functions, significant parameters of the controlled system are required. In contrast to identification methods with determined input signals, the paper focuses on the problem of identification with regular process movements (non invasive identification), leading to a lack of power density in some frequency ranges. A nonlinear Least Squares (LS) approach with single mass system and friction characteristic is investigated regarding the accomplishable accuracy and necessary constraints. The proposed method is applicable on industrial motion controllers and has been carried out with a multitude of input sequences. To verify the performance of the approach, achieved experimental results for the model parameters are exposed.

Influence analysis on the model comparison performance index for servo drive control

The paper deals with the proposed performance index of [1], which can assess command action performance of a servo drive in terms of the parameterization of the comparison model. By reversing a tuning rule, the comparison model can be parameterized without any a priori knowledge, with the drawback of low significance for some controller detuning directions. The performance index is examined further regarding practical online usage as in a running production process here. Signal sampling is considered in terms of sample time and quantization. Excitation independence as a basic goal for a performance index is also examined. For a more realistic picture the index is calculated with the monitored system operated under cascaded position control. The influence of position command signal sequences with different jerk and acceleration parameters are analyzed. In conclusion the limitations of the performance index are discussed and required future work is discussed.

Fault Detection and Fault-Tolerant Control when Using SMA Actuators in Soft Robotics

Nowadays, smart materials, such as Shape Memory Alloys (SMA) are examined as actuators for flexible, adapting shapes and structures of soft robotics. However, several limitations such as long response times, the possibility of unintended actuation as well as structural fatigue are still present and obstructive for their utilization. For applying these actuators in field of robotics, this results in a reduction of reliability (e.g. position accuracy as well as repeatability) and safety of the overall system. To encounter this, the paper presents a method for automatic fault detection for SMA. Also an approach of fault-tolerant control will be discussed. The methods aims to ensure the operability of the overall system, comprising multiple SMA actuators even in case of significantly changed system parameters or failure of single actuators.

Improved Controller Performance for Electromechanical Axes

The cascaded position control structure is state of the art in modern production machines and machine tools. Since an adequate controller performance of the electromechanical axes is still a key aspect for a resource efficient and high-quality production, this topic is addressed by the paper. An overall approach/framework to monitor and ensure an improved controller performance over time, comprising five tangible approaches is presented. All methodologies were developed in the department for control and feedback control technologies of the Technische Universitaet Chemnitz. They will be demonstrated and also be discussed based on experimental results.

Similarity Estimation for Assessing the Accuracy of a Non-Invasive Identification Method

In the paper, an approach for parameter identification during regular movements of servo axes is discussed. In contrast to the usual case, where test signals are applied to the process, there is no deterministic excitation present in this manner. Consequently, the accuracy of the identified parameter depends on the available excitation and needs to be assessed after the identification is completed. Considering that, several methods of error calculation and similarity measurement are presented in the paper and discussed for the specific use case of non-invasive parameter identification.

Analysis of a Position Control Extension on the Model of a Servo-Screw-Press

Currently, the achievable feedback control performance for servo-screw-presses is limited by its elastic structure. A possible approach to compensate this limitation is the extension of the velocity controller. This structural extension has the potential to improve the controller performance significantly due to a better damping of low frequencies. In this paper, the extension of the control structure by a state space feedback in the velocity control loop is examined. Considering that, the velocity control extension is investigated at a test rig which consists of a servo axis and a two mass system. Furthermore, a simulation model for the test rig is designed. The results of the simulated and experimentally obtained results of the test rig are presented and evaluated in order to make a prediction for the transferability to the simplified model of the servo-screw-press.

A Model Comparison Performance Index for Servo Drive Control

This paper describes an approach for monitoring closed loop speed control of electromechanical drives. The data of the closed loop is evaluated and concentrated to a performance index, giving a scalar value to measure setpoint change behavior. The method uses an order-reduced model as comparison basis to closed-loop signals, which is possible to implement on controller equipment. Parameterization of the comparison model is addressed even pointing out a provision without requiring a-priori knowledge. Influence of the main parameters is shown by means of simulation results. Following, experiments are carried out and compared to theoretical results. In conclusion usability and possible further improvement is discussed.