Design of an Adaptive Controller for Cylindrical Plunge Grinding Process

In modern competitive manufacturing industry, machining processes are expected to deliver products with high accuracy and good surface integrity. Cylindrical plunge grinding process, which is a final operation in precision machining, suffers from occurrence of chatter vibrations which limits the ability of the grinding process to achieve the desired surface finish. Further, such vibrations lead to rapid tool wear, noise and frequent machine tool breakages, which increase the production costs. There is therefore a need to increase the control of the machining processes to achieve shorter production cycle times, reduced operator intervention and increased flexibility. In this paper, an Adaptive Neural Fuzzy Inference System (ANFIS) based controller for optimization of the cylindrical grinding process is developed. The proposed controller was tested through experiments and it was seen to be effective in reducing the machining vibration amplitudes from a 10-1 µm to a 10-2 µm range

IMECE2005-82073 A NEW DYNAMIC STATE SPACE MODEL FOR THE CYLINDRICAL GRINDING PROCESS

ABSTRACT A new dynamic state space model is proposed for the inprocess estimation and prediction of part qualities in the plunge cylindrical grinding process. A through review on various grinding models in literature reveals a hidden dynamic relationship among the grinding conditions, the grinding power, the surface roughness, and the part size due to the machine dynamics and the wheel wear, based on which a nonlinear state space equation is derived. After the model parameters are determined according to the reported values in literature, several simulations are run to verify that the model makes good physical sense. Since some of the output variables, such as the actual part size, may or may not be measured in industry applications, the observability is tested for different sets of outputs in order to see how each set of on-line sensors affects the observability of the model. The proposed model opens a new way of estimating the part qualities such as the surface roughness and the actual part size based on application of the state estimation algorithm to the measured outputs such as the grinding power. In addition, a long term prediction of the part qualities in batch grinding processes would be realized by simulation of the proposed model. Possible applications to monitoring and control of grinding processes are discussed along with several technical challenges lying ahead

Modelling of grinding mechanics : a review

Grinding is one of the most widely used material removal methods at the end of many process chains. Grinding force is related to almost all grinding parameters, which has a great influence on material removal rate, dimensional and shape accuracy, surface and subsurface integrity, thermodynamics, dynamics, wheel durability, and machining system deformation. Considering that grinding force is related to almost all grinding parameters, grinding force can be used to detect grinding wheel wear, energy calculation, chatter suppression, force control and grinding process simulation. Accurate prediction of grinding forces is important for optimizing grinding parameters and the structure of grinding machines and fixtures. Although there are substantial research papers on grinding mechanics, a comprehensive review on the modeling of grinding mechanics is still absent from the literature. To fill this gap, this work reviews and introduces theoretical methods and applications of mechanics in grinding from the aspects of modeling principles, limitations and possible future trendencies

Kraftsensorlose Manipulator Kraftsteuerung zur Abtastung unbekannter, harter Oberflächen

Die vorliegende Arbeit zeigt ein Verfahren zur kraftgesteuerten Kontaktierung unbekannter harter Freiformflächen mit einem Standard–6DOF-Industriemanipulator (z.B. Manutec R2). Die bisher entwickelten Verfahren auf dem Gebiet der Manipulatorkraftregelung waren auf teure, fragile, mehrdimensionale Kraft-/Momentensensoren am Manipulator-Endeffektor angewiesen, die bei dem in dieser Arbeit entwickelten Ansatz der sensorlosen Kraft-/Geschwindigkeitsregelung überflüssig werden. Die Einstellung der gewünschten Kontaktkraft zu der unbekannten Umgebung erfolgt ausschließlich über eine robuste, beobachtergestützte Regelung der Motorströme der Gelenkantriebe. In freien Bewegungsphasen garantierte eine kaskadierte Kraft-/Geschwindigkeitsregelung vordefinierte Heranfahrgeschwindigkeiten an die unbekannte Kontaktoberfläche. Hierdurch eröffnen sich vollkommen neue Einsatzszenarien für die kraftkontrollierte Kontaktierung und Bearbeitung unbekannter Oberflächen oder Werkstücke beliebiger Härte und Steifigkeit

Robust Control of Diesel Drivelines

The original contribution of this thesis is to provide insight into research of non-traditional control techniques for automotive power train applications, culminating in experimental evidence of much improved performance and reduced commissioning costs. This includes much work on the technique of Observer Based Robust Control (OBRC) which, before the research documented in this thesis commenced, was only in its infancy with some promise being shown through the simulation of electric drive applications (Dodds, 2007). The thesis, therefore, contributes to the process of bringing this new control technique nearer maturity. OBRC is based on an observer designed to provide information enabling effective control of an automotive power train application and its performance assessment. Comparison with traditional and other robust control techniques is included. The observer in OBRC is is designed to estimate the equivalent disturbance input, referred to the control input to a plant. This represents plant modelling errors as well as external disturbances. The equivalent disturbance estimate is applied to the real plant input to cancel its effect, thereby reducing the control problem to that of controlling the known real-time model of the plant employed in the observer. One of the disadvantages of conventional robust control methods, such as those based on sliding mode control, is that relatively high gain control loops are closed around the uncertain plant. This increases the risk of instability due to the dynamic elements, such as sensor lags, that are not included in the assumed plant model. The initial reason for investigating OBRC is that the high gain loops are applied to the known plant model in the observer and that the stability of these loops, taken in isolation, can therefore be guaranteed. It was found that the observer gains are limited only by the finite sampling frequency of the digital processor. In theory, infinite observer gains would yield ideal robustness. However, in practice only finite gains are possible. The aforementioned application of the equivalent disturbance estimate to the real plant input effectively transfers the high gain loops from the plant model in the observer to the real plant. This meant that closed loop stability could not be guaranteed under all circumstances. In view of this, it was decided that sliding mode control should not be excluded from the set of controllers for comparison. Since the control chatter associated with basic sliding mode control has to be eliminated for the vehicle application, polynomial control (a continuous version of the discrete RST controller) with robust pole assignment is included. This polynomial control can be regarded as equivalent to the sliding mode control with a boundary layer, but without the uncertainty associated with the choice of the boundary layer width. Two more controllers, based on the Internal Model Control (IMC) and H-infinity, are included for comparison on the basis that their design methodologies do not demand high gains. The various control techniques are demonstrated and compared via their application to Diesel Drivelines for commercial road vehicles. One of the operational problems with conventional PI engine speed controllers is the need for time consuming initial controller tuning. This requires different sets of gains for each gear selection, including idle (i.e., neutral) and later retuning to compensate for changes in the driveline characteristics with component aging. A major advantage of OBRC in this application is the elimination of the tuning procedure. Of particular interest is the fact that the order of the system is increased by two when a gear is engaged due to a vibration mode created by the finite torsional compliance of the propeller shaft and other driveline components. Since this driven mechanical load can be represented by its inverse dynamic model in a feedback path whose output acts at the same point as the control variable, the OBRC compensates for this automatically without the need for any parametric changes. The simulations and experimental work were carried out on the DAF 12 litre diesel engine. The comparative study was carried out, not only with respect to the main application of Diesel Drivelines, but also using academic examples that are even more demanding of the controllers’ capabilities. A key parameter in an engine configuration is the saturation limit on the injected fuel rate, which is highly dependent on the engine capacity from 10 litres to 16 litres. One example was introduced with a saturation block and the abilities of the various controllers under this constraint were assessed. The H-infinity controller could not handle such a saturation constraint, which is common practice in automotive applications and therefore this had to deemed unsuitable. The remaining controllers were able to operate with fuel rate saturation. The overall conclusion is that the controllers based on OBRC, polynomial control and IMC are capable of a similar performance with appropriate controller parameter settings. However all are subject to the trade-off between the conflicting requirements of short response times and robustness