Marek Pawelczyk

Analogue active noise control

Abstract The aim of this article is to present in details all the stages of an analogue active noise control system. As the exemplary plant, an active personal hearing protection device is considered. In the introductory section the plant is presented and the state of the art is reported. In subsequent section, first a way of identification of a continuous-time model of the plant is described and performance limitations are analysed. Then, the procedure for designing optimal controller is proposed. It starts from analysing properties of the plant and choosing a suitable controller structure. Next, coefficients of the controller are found following the design premises. These coefficients serve as initial parameters in the optimisation process. For this process the performance index and appropriate constraints are built. Next, details on implementation of the controller using a chip with switched capacitors are given. Attenuation results of various noises are presented. Finally, cost of the hardware is evaluated. The methodology presented in this article can be considered as a detailed procedure for designing and practically realising cheap and easily tuneable controllers providing good noise attenuation and satisfying several constraints related to frequency band, stability margin, etc.

Fuzzy Control for Semi-Active Vehicle Suspension

In this paper semi-active control of the suspension of an all-terrain vehicle is considered. A seven degree of freedom suspension model is presented first. A fuzzy approach for controller synthesis is then proposed. Expert knowledge is stored in the form of IF-THEN rules. The Takagi-Sugeno inference system is employed, with triangle membership functions. The fuzzy system output is the damper coefficient. In contrary to many other control algorithms, the presented fuzzy algorithm does not require inverse modelling of the magnetorheological damper. Instead, some scaling parameters are set. They can be chosen experimentally, or a bio-inspired strategy can be applied. The fuzzy control is then compared with the Skyhook control in simulations, in terms of road holding and driving comfort indicators. Obtained results are similar. However, lack of necessity to use an MR inverse model allows the fuzzy system to provide successful performance in case of different operating conditions, what is an important benefit.

Active reduction of device multi-tonal noise by controlling vibration of multiple walls of the device casing.

The aim of this paper is to verify the idea of active reduction of device and machinery noise by controlling the vibration of their casing. The Active Structural Acoustic Control (ASAC) technology known from the literature for reducing noise propagating through a single wall is going to be applied to multiple walls of the casing, thus globally protecting the user and environment from excessive noise generated by the machine or the device. Based on previous research by the authors, pairs of vibration actuators and sensors are installed on the walls in order to provide highest sound insulation efficiency. Two adaptive control strategies are investigated - feedfoward and Internal Model Control feedback, both with the adaptive Leaky Normalised Filtered-x Least Mean Square (FxLMS) algorithm used to update control filter parameters. The control systems are experimentally verified by using a laboratory set-up, in presence of a multi-tonal primary disturbance. Obtained results are reported, discussed, and conclusions for future research are drawn.

Model of the air stream ratio for an electromagnetic mill control system

The paper presents a model of the air stream ratio in the dry grinding and classification circuit with the electromagnetic mill. The concept of the grinding system is described along with indirect measurement methodology. Model structure and identification problems are discussed and a supervisory control algorithm based on the model is derived.

Analog Active Control of Acoustic Noise at a Virtual Location

In this brief, an analog virtual microphone control system in application to noise reduction for a phone is designed. It aims at generating a zone of quiet at a virtual microphone location corresponding to the eardrum. Such location is different than the real microphone location. The idea of the control system is based on the assumption that the primary acoustic noise is the same at these two locations. The first constraint is formulated to guarantee a sufficient stability margin. Another constraint protects against excessive noise reinforcement for any frequency. Controller parameters are found by solving the optimization problem. Due to its high nonlinearity the exhaustive search method is used. It follows a preliminary analysis of the solution space. Additionally, a feedforward filter compensating for influence of the control system on the transmitted speech is designed. The overall control system is implemented using chips with switched capacitors, what makes the tuning and maintenance easy. The system is verified by means of simulations and real-world experiments. It is shown that road noise is satisfactorily reduced. Both measurement results and subjective impressions confirm that the system meets the requirements.

Grain Size Determination and Classification Using Adaptive Image Segmentation with Shape-Context Information for Indirect Mill Faults Detection

In this paper, the authors described methods of material granularity evaluation and a novel method of grain size determination with inline mill device diagnostics. The mill diagnostic can be carried out with vibration measurements, machine vision or infrared imaging. Milling process is an extremely energy- and cost-consuming process, thus diagnostics process should be performed with high efficiency. Method proposed in this paper is based on the online examination of the final product during the milling process using real-time digital images. Determination of the total number of the grain, size of each grain, also classification of the grains is main goal of proposed method. In the proposed method, the visible camera with lightning mounted at two assumed angles has been used, what increases the grain detection process. Proposed method uses an adaptive segmentation to match correctly the grains, the information about particles shape and context is used to optimize the grain classification process in the next step. Finally, during image processing, the simple rule-based method is used to obtain information about overall quality of the product and possible faults in the milling process based on the evaluated parameters.

Evaluation of copper ore granularity and flow rate using vibration measurements

The research presented in this paper aims at developing a vibration-based method for online measurement of granularity and flow of loose solids. This information is essential for control of industrial milling processes when specific product characteristics is desired. The vibration-measuring approach seems to be a candidate for a cheap and reliable technique among the not-so-many contactless online methods. Experiments were carried out using four granularity classes of milled copper ore and a dedicated test rig. Signal processing was performed in the frequency domain with an algorithm, which takes into account the needs of continuous, real-time measurements. As demonstrated in the paper, the proposed algorithm allows for estimation of grain size and flow rate of the particles that caused the vibrations.

RT/FPGA implementation of the IEEE 1451 standard in sensors for machine conditioning systems

IEEE 1451.4 standard introduced the full “plug and play” for sensors and actuators thanks to the Transducer Electronic Datasheet (TEDS). The only requirement for the measuring system is compatibility with 1451.4. The advantage of this standard among all series of IEEE 1451 is that the Network Capable Application Processor (NCAP) is not necessary. This caused the IEEE 1451.4 to become the most popular and widely available on the market. This paper presents the implementation of the IEEE 1451.4 standard in custom made vibration transducers, based on MEMS accelerometers. The transducers were calibrated and the results of calibration are stored in TEDS added to the sensor. Then the transducers with TEDS were utilized in an experimental machine conditioning system based on embedded RT/FPGA platform.

Active noise control without secondary path modelling — Varying-delay LMS approach

The Filtered-Reference LMS, also known as FxLMS algorithm, is one of the most commonly used adaptive algorithms for noise control systems. It is appreciated due to its simplicity, low computational complexity, and performance efficiency. For its convergence, responses of the acousto-electric secondary path and its model should not differ by more than pi/2 for any frequency contributing to the noise being controlled. Good amplitude matching is, in turn, responsible for convergence rate. Thus, without an acceptable model, the FXLMS algorithm is vulnerable to high excess mean square error or even divergence due to updating control filter parameters in improper direction. The literature presents several recipes, of heuristic or theoretic origin, to cope in circumstances of inaccurate secondary path modeling, or when the path is subject to change during control system operation and thus differs from the model. They usually require additional wideband random excitation to allow for on-line modeling during control system operation. Such excitation deteriorates, however, overall noise reduction results, and the acoustic impression perceived by the user is poor. This paper focuses on an active noise control approach, which requires no secondary path modelling. The convergence is guaranteed by switching sign of the algorithm step size and, in this way, the sign of the parameter update term. It is combined with on-line tunable delay of the reference signal to significantly improve convergence properties of the algorithm. Theoretical justification for this approach is shown for a tonal noise. Then, the method is extended for the case of a narrowband noise. Theoretical consideration is validated by simulations based on data acquired from a real application.

Modelling dynamics of strongly coupled air paths in pneumatic transport system for milling product

In the milling circuit with an electromagnetic mill, a pneumatic system is used to transport the material and to maintain several parameters of the process. The pneumatic system contains three air inlets with controllable flaps and each inlet stream serves a different purpose, however, they are strongly physically coupled through the rest of the installation. Thus, position of each control flap strongly and nonlinearly affects the operating point of each inlet stream. Dynamics of air velocity within the main inlet pipe with respect to the setpoint of the main flaps position has been identified for multiple operating points of the installation, and the estimated models were checked and assessed. The resultant models may then be used to tune controller parameters for subsequent operating points. Identification and verification of the derived models was performed on data measured at an experimental milling installation.