外文翻译--控制移动液压起重机(编辑修改稿)

外文翻译--控制移动液压起重机(编辑修改稿)内容摘要：

is tool position control. 3 LABORATORY FACILITIES As the focus of this thesis is on developing control strategies that can be implemented on mercial machinery, much emphasis will be placed on experimental results. Experimental results will be obtained from two systems. The first, a simple one degree of freedom crane,was designed as an experimental platform. The second is a real crane which was donated to the University by H248。 jbjerg Maskinfabrik (HMF) a Danish crane manufacturer. Refer to Figure 1. Figure 1 Experimental Systems in Laboratory. Left: One DOF crane model. Right: Real Mobile Hydraulic Crane As there are currently no mercially available separate meterin/separate meterout valves,two separate valves will be used instead. A sample circuit of one cylinder is shown in Figure 2. The control algorithms which control the valves, will be programmed on a Digital Signal Processor (DSP)/Pentium dual processor system. The DSP will run the control code and the Pentium will do diagnostics and provide a graphical user interface. Figure 2 Separate Meter In / Separate Meter Out Setup 4 CURRENT WORK Flow Control by Direct Actuation of the Spool Most flow control valves on the market today work with a pressure pensator (Andersen。 Ayres 1997). The pressure pensator keeps a constant pressure drop across the main spool of the valve, which keeps the flow constant. However, the addition of a pressure pensator makes the valve more plicated than a simple single spool valve. Another way of doing flow control is to measure the pressure drop across the valve and adjust the spool position to account for this (Back233。 Feigel 1990). This is not a new idea but has not been implemented mercially because of the high cost of pressure transducers and micro controllers. However, with the current drop in cost of micro controllers and pressure transducers this idea is now mercially feasible. The concept is very simple, spool position is calculated from the Bernoulli equation using the pressure drop across the spool and a reference flow. Even though this is a simple equation, it is not easy to implement. The accuracy of the flow control is dependent on the precision of the position sensors and of the pressure on the pressure or the position signals can cause stability problems. Filtering the noise,introduces delays in the control which can also affect stability. In addition the Bernoulli equation is not followed exactly over the entire operating range of the valve, so it may be necessary to store the valve characteristics as a data table or develop a more plex equation. Cylinder Control Strategy To control a hydraulic cylinder, the strategy has to be able to handle four different situations depending on the directions of the load and the velocity of the cylinder. Refer to Figure 3 The control strategies that have appeared in the literature are usually quite plex and depend on measurements of the cylinder position and velocity (Elfving,Palmberg 1997。 Mattila。 Virvalo 1997). They are also based on rather plex control algorithms. It is the goal of this thesis to start with a control strategy which is based on simple PI controllers and makes no demands for position and velocity of the cylinder. The performance of this system will be lower than a plex control strategy, but it may be easier to implement mercially because it has no need for special sensors and is easier to understand for the average engineer. Figure 3 Different Situations in Crane Operation Another feature which needs to be acknowledged when designing a control strategy, is thetype of valve used. Mobile hydraulic valves demand low leakage and since most mobilevalves are spool valves, they usually have large overlaps. In addition, to make the cost of thevalve acceptable to industry, the actuation stage on the spool is usually quite slow. This bination of large overlap and slow actuation makes it hard to implement many of the strategies that have been presented. Pressure control especially bees difficult when there is an overlap and a slow actuator. One example of a new strategy which is simple and robust is described as follows. Flow control is implemented on the inlet si。