An Adaptive Data-Driven Iterative Feedforward Tuning Approach Based on Fast Recursive Algorithm: With Application to A Linear Motor

The feedforward control can effectively improve the servo performance in applications with high requirements of velocity and acceleration. The iterative feedforward tuning method (IFFT) enables the possibility of both removing the need for prior knowledge of the system plant in model-based feedforward and improving the extrapolation capability for varying tasks of iterative learning control. However, most of IFFT methods require to set the number of basis functions in advance, which is inconvenient to the system design. To tackle this problem, an adaptive data-driven IFFT based on fast recursive algorithm (IFFT-FRA) is developed in this paper. Explicitly, based on FRA the proposed approach can adaptively tune the feedforward structure, which significantly increases the intelligence of the approach. Additionally, a data-based iterative tuning procedure is introduced to achieve the unbiased estimation of parameters optimization in presence of noise. Comparative experiments on a linear motor confirms the effectiveness of the proposed approach

Design and Analysis of Long-Stroke Planar Switched Reluctance Motor for Positioning Applications

This paper presents the design, control, and experimental performance evaluation of a long-stroke planar switched reluctance motor (PSRM) for positioning applications. Based on comprehensive consideration of the electromagnetic and mechanical characteristics of the PSRM, a motor design is first developed to reduce the force ripple and deformation. A control scheme with LuGre friction compensation is then proposed to improve the positioning accuracy of the PSRM. Furthermore, this control scheme is proven to ensure the stable motion of the PSRM system. Additionally, the response speed and steady-state error of the PSRM system with this control scheme are theoretically analyzed. Finally, the experimental results are presented and analyzed. The effectiveness of the precision long-stroke motion of the PSRM and its promise for use in precision positioning applications are verified experimentally

Mechatronics Methods for Mitigating Undesirable Effects of Pre-motion Friction in Nanopositioning Stages with Mechanical Bearings

Nanopositioning (NP) stages are used to for precise positioning in a wide range of nanotech processes, ranging from substrate patterning to micro additive manufacturing. They are often used for point-to-point (P2P) motions, where the stage is commanded to travel to and settle within a pre-specified window of the target position, and for tracking motions, where the stage is commanded to follow a reference trajectory. The settling time, in-position stability and tracking accuracy of NP stages directly affects productivity and quality of the associated processes or manufactured products. NP stages can be constructed using flexure, fluidic, magnetic or mechanical bearings (i.e., sliding and, especially, rolling-element bearings). Of these choices, mechanical bearings are the most cost-effective, and are currently the only commercially viable option for a growing number of NP applications that must be performed in high vacuum environments. However, mechanical-bearing-guided NP stages experience nonlinear pre-motion (i.e., pre-sliding/pre-rolling) friction which adversely affects their precision and speed. Control-based compensation methods, commonly used to address this problem, often suffer from poor robustness and limited practicality due to the complexity and extreme variability of friction dynamics at the micro scale. Therefore, this dissertation proposes three novel mechatronics methods, featuring a combination of mechanical design and control strategy, as more effective and robust solutions to mitigate the undesirable effects of pre-motion friction. The first approach is vibration assisted nanopositioning (VAN), which utilizes high frequency vibration (i.e., dither) to mitigate the low speed (slow settling) of mechanical-bearing-guided NP stages during P2P motions. VAN allows the use of dither to mitigate pre-motion friction while maintaining nanometer-level positioning precision. P2P positioning experiments on an in-house built VAN stage demonstrates up to 66% reductions in the settling time, compared to a conventional mechanical bearing NP stage. A major shortcoming of VAN is that it increases the cost of NP stages. To address this limitation, a friction isolator (FI) is proposed as a simple and more cost-effective method for mitigating pre-motion friction. The idea of FI is to connect the mechanical bearing to the NP stage using a joint that is very compliant in the motion direction, thus effectively isolating the stage from bearing friction. P2P positioning tests on a NP stage equipped with FI prototypes demonstrate up to 84% reductions in the settling time. The introduction of FI also enables accurate and robust reductions of motion errors during circular tracking tests, using feedforward compensation with a simple friction model. One pitfall of FI is that it causes increased error of the stage during in position. Therefore, a semi-active isolator (SAI) is proposed to mitigate the slow settling problem using the FI, while maintaining the benefits of friction on in-position stability. The proposed SAI, which connects the bearing and NP stage, is equipped with solenoids to switch its stiffness from low, during settling, to high once the stage gets into position. P2P experiments demonstrate up to 81% improvements in the settling time without sacrificing in-position stability. The proposed mechatronics methods are compared and FI stands out as a result of its simplicity, cost-effectiveness and robust performance. Therefore, the influence of design parameters on the effectiveness of FI are investigated to provide design guidelines. It is recommended that the FI should be designed with the smallest stiffness in the motion direction, while satisfying other requirements such as in-position stability and off-axis rigidity.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/155296/1/terrydx_1.pd

Gas Bearings: Modelling, Design and Applications

This book focuses on the modelling and the design process of gas bearings, on the experimental validation of such models, and on their applications. In particular, recent developments about foil bearings, aerostatic bearings, porous bearings, and non-contact precision positioning systems are shown

Model-Guided Data-Driven Optimization and Control for Internal Combustion Engine Systems

The incorporation of electronic components into modern Internal Combustion, IC, engine systems have facilitated the reduction of fuel consumption and emission from IC engine operations. As more mechanical functions are being replaced by electric or electronic devices, the IC engine systems are becoming more complex in structure. Sophisticated control strategies are called in to help the engine systems meet the drivability demands and to comply with the emission regulations. Different model-based or data-driven algorithms have been applied to the optimization and control of IC engine systems. For the conventional model-based algorithms, the accuracy of the applied system models has a crucial impact on the quality of the feedback system performance. With computable analytic solutions and a good estimation of the real physical processes, the model-based control embedded systems are able to achieve good transient performances. However, the analytic solutions of some nonlinear models are difficult to obtain. Even if the solutions are available, because of the presence of unavoidable modeling uncertainties, the model-based controllers are designed conservatively

Positioning Control System for a Large Range 2D Platform with Submicrometre Accuracy for Metrological and Manufacturing Applications

The importance of nanotechnology in the world of Science and Technology has rapidly increased over recent decades, demanding positioning systems capable of providing accurate positioning in large working ranges. In this line of research, a nanopositioning platform, the NanoPla, has been developed at the University of Zaragoza. The NanoPla has a large working range of 50 mm × 50 mm and submicrometre accuracy. The NanoPla actuators are four Halbach linear motors and it implements planar motion. In addition, a 2D plane mirror laser interferometer system works as positioning sensor. One of the targets of the NanoPla is to implement commercial devices when possible. Therefore, a commercial control hardware designed for generic three phase motors has been selected to control and drive the Halbach linear motors.This thesis develops 2D positioning control strategy for large range accurate positioning systems and implements it in the NanoPla. The developed control system coordinates the performance of the four Halbach linear motors and integrates the 2D laser system positioning feedback. In order to improve the positioning accuracy, a self calibration procedure for the characterisation of the geometrical errors of the 2D laser system is proposed. The contributors to the final NanoPla positioning errors are analysed and the final positioning uncertainty (k=2) of the 2D control system is calculated to be ±0.5 µm. The resultant uncertainty is much lower than the NanoPla required positioning accuracy, broadening its applicability scope.<br /