1、 翻译部分 英文原文 CONTROL OF MOBILE HYDRAULIC CRANES Marc E. MNZER Aalborg University Institute of Energy Technology, Pontoppidanstrde 101 DK-9220 Aalborg, Denmark The goal of the thesis described in this paper is to improve the control of mobile hydraulic cranes. The thesis is split into five parts: a req
2、uirements analysis, an analysis of the current systems and their problems, an analysis of different possibilities for system topologies, development of a new control system for the near future based on electro-hydraulic separate meter in / separate meter out valves, and finally an analysis of more a
3、dvanced and complex solutions which can be applied in the more distant future. The work of the thesis will be done in coop-eration with industry so the thesis will have more of an industrial focus than a purely theoretical focus. Key words: Mobile Hydraulic Cranes, Control Strategies, Separate Meter
4、-in/Separate Meter-out. 1 INTRODUCTION The goal of the thesis described in this paper is to improve the control of mobile hydraulic cranes. A mobile hydraulic crane can be thought of as a large flexible mechanical structure which is moved by some sort of control system. The control system takes its
5、input from a human operator and translates this command into the motion of actuators which move the mechanical structure. The definition of this control system is purposely left vague in order not to impose any con-straints on its design. The control system consists of actuators which move the mecha
6、nical structure, a means of controlling the actuators, a means of supplying power to the actuators,and a way of accepting inputs from the operator. It is this control system which is the target of this thesis. The goal is to analyze the requirements made on the control system and present guidelines
7、for the design of new control systems. The thesis will be split into five parts: 1.Analysis of the requirements of the control system, from the perspective of the opera-tor, the mechanical system, efficiency, stability, and safety requirements. 2.Analysis of current control systems and what their pr
8、oblems are. 3.Analysis of the different options for the control system: different types of actuators,different types of control strategies, and different ways of organizing components. 4.Presentation of a new type of control system, which is commercially implementable. A system that will meet the ne
9、eds of industry in the near future. 5.Analysis of more optimized systems, with higher performance, better efficiency, more flexible control, etc. This will be less commercially applicable but will be a starting point for more research. 2 SECTIONS OF THE THESIS 2.1Requirements Analysis of the Control
10、 System Before starting detailed work on developing new control systems, it is important to analyze what the exact demands are on the control system. The control system is influenced by many factors. For example: the mechanical structure it is controlling, the human operator, effi- ciency, stability
11、, and industry regulations. Industry regulations are the first requirements that have to be addressed. Things like hose rupture protection and runaway load protection make a lot of demands on the control system.After regulations, stability is the next most important requirement； without stability th
12、e con-trol system cant be used. Once stability has been assured, the performance requirements of the control system have to be set. They are determined by the mechanical structure of the crane and the human operator. The mechanical structure of a mobile hydraulic crane is a very large flexible struc
13、ture which has very low natural frequencies. To prevent oscillations it is necessary to keep the speed of the control system below this natural frequency or to develop a control system which can increase this frequency. The human operator also imposes limits on the control system. If the control sys
14、tem is too slow or too fast then it is impossible for a human operator to give it proper inputs. And finally, once the regulations have been met, sta-bility is assured, and the performance is at the right level, the power efficiency of the control system has to be optimized. 2.2Analysis of Current C
15、ontrol Systems Before designing a new control system it is good to analyze the current control systems to find out what their problems are. Current control systems are mainly hydraulic and can suffer from three main problems: 1.Instability 2.High cost 3.Inefficiency 2.2.1Instability Instability is a
16、 serious problem as it can cause injury to human operators or damage to equip-ment. When a system becomes unstable it usually starts to oscillate violently. To avoid insta-bility in current systems, the designers either sacrifice certain functions which are desirable,or add complexity and cost. For
17、example, in the crane shown in Figure 1, it would be desir-able to have control over the speed. But due to the safety system that cranes are required to have, standard speed control is not stable. To add speed control requires a more complex and more expensive mechanical system. The parameters of a
18、hydraulic system, such as temperature or load force, also affect stability.A system that is stable with one set of parameters might be unstable with another set. To ensure stability over the entire operating range of the system, performance must sometimes be sacrificed at one end of the parameter ra
19、nge. 2.2.2High cost Current systems are purely hydraulic-mechanical, so if the user wants a certain function, the user buys a certain hydraulic-mechanical component. Because most users have different requirements, there are many different variations of the same basic component. This means that many
20、specialized components must be manufactured rather than one standard product.This drives up the cost of components. 2.2.3Inefficiency One form of inefficiency in current systems is due to the link between the flows of the two ports of the cylinder. This is because most valves use a single spool to c
21、ontrol the flow in both ports. Because of this link, it is impossible to set the pressure levels in the two sides of the cylinder independently. Therefore, the outlet side will develop a back pressure which acts in opposition to the direction of travel, which increases the pressure required on the i
22、nlet side to maintain motion. Since the force generated by the actuator is proportional to the pressure dif- ference between the two sides, the actual pressures in the cylinder dont affect the action of the cylinder. For example, the action of the cylinder for 0psi/600 psi would be the same as 1000p
23、si/1600psi. However, in the second case, the power supply would have to supply much more power. This extra power is wasted. 2.3Different Options for Control Systems Current control systems use hydraulic actuators with directional/proportional valves to control the movement. However there are many di
24、fferent options for controlling a cylinder. Options range from new high performance electro-hydraulic valves, to separate meter in / separate meter out (SMISMO) valves, to hydraulic bus systems, to intelligent actuators with built in power supplies, to pump based control strategies. These systems al
25、l have advantages and dis-advantages which need to be analyzed if the most optimum solution is to be chosen. 2.4 Near Future Solution It is expected that even if it is proven that a completely new system topology is the optimum configuration, the crane manufacturers and component manufacturers will
26、not accept the new technology overnight. This will most likely take time, so an interim solution will be devel-oped. This solution will be made up of micro computer controlled Separate Meter In / Separate Meter Out (SMISMO) valves (Elfving,Palmberg 1997；Jansson,Palmberg, 1990； Mattila,Virvalo 1997).
27、 SMISMO valves will make it possible to implement new control strategies which are more efficient and stable. The micro computer will make it possible to introduce flexibility to valves. Variants can be programmed in software. This eliminates the need to manufacture hundreds of different variants. T
28、he crane manufacturer will be able to choose the exact functions he wants in his valve, while the component manufacturer will have to manu-facture only one valve. This will lower the cost, even though the performance will have increased. 2.5 Analysis of Higher Performance Solutions This analysis wil
29、l depend on the results of the analysis of different topologies. If it is shown that pump based control is to be the way of the future for example, then analysis will be per-formed in this area. Another area which will also be explored, is tool position control. 3 LABORATORY FACILITIES As the focus
30、of this thesis is on developing control strategies that can be implemented on commercial 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
