外文翻譯--改善電磁閥和液力偶合器的控制(文件)
【正文】 ff. 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 extended to conveyors of greater length and higher installed power. Some of the graphs presented in this paper refer to an km long overland conveyor with head and tail drives [10]. Although the actual system operates with scoop couplings, in these simulations the conveyor was modeled with drain couplings operating in conjunction with solenoid valves. Results of the Conveyor Dynamic Simulations Torque was ramped at a rate of Nm/s which is suitable for a km long conveyor with steel cord belting (2100 Nm should be reached in 15 sec). The resulting ramp is too steep for the coupling during the initial stages, specifically during the initial 6 seconds of pump operation. Consequently, the control system es into action with an approximate delay of 12 seconds. Two problems are apparent : Initial low torque delivery does not allow instant acceleration of the conveyor. This is possible to rectify by adjustments in the software as is the case for the simulations, it can be noted that the velocity ramp and controlling action starts some 8 seconds after the motors and 6 seconds after the coupling’s pumps were energized. The rate at which oil is discharged from the coupling is limited and may be in
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