外文翻譯--改善電磁閥和液力偶合器的控制-文庫吧在線文庫
【正文】 e before that. The time between measurements is critical. A too short sampling time can result in excessive equipment cycling, while a too long sampling time can result in overshoot and instability [8]. The constants Kc,Tj Td are originally determined theoretically according to the wellknown ZIEGLERNICHOLS method [6]. These values serve as a starting point from where further fine tuning was done experimentally. The effect of each of these constants on the controller’s performance has been described by SMITH [3] and can be summarised as follows [7]: A small value of Kc produces large overshoot but gives good stability, while larger values of Kc reduce the overshoot but increase equipment cycling. Small values of Tj eliminate constant errors quickly, but result in rapid cycling of control equipment. In turn, large values of Tj cause constant errors to occur. A small value of Td causes large overshoot, while a large value of Td increases the reaction time, which results in increased stability. Although the valve can only be switched on or off, it is still possible to control the switching as if it were a linearly varying valve by controlling the time for which it is switched on or off. By applying Eq. (2), △ T is converted to a duty cycle, which is defined as follows: Duty cycle = max 100[%]ontt ? [2] where: ont time for which the valve is switched on ( max0 ontt?? ) [s] maxt time between each sample which also represents maximum time for which the valve can be switched on during one interval (tmax = sT )[s]. In fact the conversion may be done in several ways ranging from a simple proportional relationship between △ T and time of valve operation to a rather plex one where rates of torque/oil flow change are taken into account. Development and/or selection of the concept may be governed by several factors of which simplicity of the control software and limitations of the hardware are the two most obvious ones. For this specific application, the valve may not be switched more than 5 times per second or 5 Hz. The optimum length of the maximum duty cycle (tmax) may be determined by trial and error according to specified criteria or by dynamic simulation. Conveyor Simulations Verifying the Performance of the Developed Concept: The concept has been tested and verified by means of conveyor dynamic simulations. The first set of simulations utilised a puter model of a conveyor which was a subject of a detailed design investigation by Dynamika Materials Handing two years ago. The conveyor was supplied with drain couplings working in conjunction with a three way valve. Detailed information about the system and the conveyor may be found in [9]. The coupling characteristics utilised are similar to that presented in [11] as it is a representative of drain fluid couplings used in South Africa. The torque based starting strategy was analysed in significant detail. Acceptable performance results were obtained by adjusting the duty cycles and control settings. This led to further exploration of a velocity based starting strategy. To plete the investigation, the simulations were extende
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