A magnetically levitated spindle was designed for fatigue testing of cylinders made of fiber reinforced plastic. In these fatigue tests, the speed of the cylinders is varied cyclically between 15,000 and 30,000 rpm until their mechanical failure occurs. Several eigenfrequencies have to be passed to reach the operational speed range. During long-term operation, the rotor of the spindle is prone to overheating due to various losses. One way of reducing the rotor temperature is to decrease the bias current of the radial active magnetic bearings. Since the bias current influences the dynamic behavior of the system, the control of the bearings has to be adapted as well. This article describes a controller design for the system with different bias currents to determine the smallest usable bias current. A detailed model of the plant is developed, which is then used to optimize the parameters of the utilized controller with a predefined structure using the weighted ∞ norm as the objective function. Since the rotor is highly gyroscopic, its eigenfrequencies change with the rotational speed. To ensure that the system meets certain robustness criteria at all rotational speeds, the parameters of the controller are simultaneously optimized for the plant model at different speeds. This approach leads to a controller which can be used in the entire speed range without the need for gain scheduling. The functionality of the controller and the influence of the bias current on the rotor temperature are investigated through measurements.
Modern industry benefits from the automation capabilities and flexibility of robots. Consequently, the performance depends on the individual task, robot and trajectory, while application periods of several years lead to a significant impact of the use phase on the resource efficiency. In this work, simulation models predicting a robot’s energy consumption are extended by an estimation of the reliability, enabling the consideration of maintenance to enhance the assessment of the application’s life cycle costs. Furthermore, a life cycle assessment yields the greenhouse gas emissions for the individual application. Potential benefits of the combination of motion simulation and cost analysis are highlighted by the application to an exemplary system. For the selected application, the consumed energy has a distinct impact on greenhouse gas emissions, while acquisition costs govern life cycle costs. Low cycle times result in reduced costs per workpiece, however, for short cycle times and higher payloads, the probability of required spare parts distinctly increases for two critical robotic joints. Hence, the analysis of energy consumption and reliability, in combination with maintenance, life cycle costing and life cycle assessment, can provide additional information to improve the resource efficiency.
Active control of flexible rotors is a challenging issue in modern industries. This paper focuses on the synthesis of a mixed sensitivity robust controller for a linear parameter-varying (LPV) system. The objective is to control rotor vibration, especially when the rotor is passing the first two bending critical speeds. In the formulation of the problem for the controller, weighting functions are proposed based on the relationship between the desired shape of the open-loop transfer function and sensitivity functions of the closed-loop system. Recent research has highlighted the efficiency of mixed sensitivity robust controllers in stabilizing a wide range of magnetic bearing systems. Here, the method is extended to control the vibration of a piezoelectric bearing system. The experimental rotor features two unbalance-exited resonances within its operating range. Experimental results demonstrate good performance of the vibration reduction and the effectiveness of the design method.
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