【正文】 without stability the control system can’t 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 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 impossible limits on the control system. If the control system is too slow or too fast then it is impossible for a human operator to give it proper inputs. And finally, once the requlations have been met, stability is assured, and the performance is at the right level, the power efficiency of the control system has to be optimized. Analysis of Current Control SystemsBefore 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. Instability2. High cost3. Inefficiency InstabilityInstability is a serious problem as it can cause injury to human operators or damage to equipment. When a system bees unstable it usually starts to oscillate violently. To avoid instability in current systems, the designers either sacrifice certain functions which are desirable, or add plexity and cost. For example, in the crane shown in Figure 1, it would be desirable 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 plex and more expensive mechanical system. The parameters of a 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 of the parameter range. High cost湖南理工學院畢業(yè)設計（論文）33 Current systems are purely hydraulicmechanical, so if the user wants a certain function, the user buys a certain hydraulicmechanical ponent. Because most user have different requirements, there are many different variations of the same basic ponent. This means that many specialized ponents must be manufactured rather than one standard product. This drives up the cost of ponents. InefficiencyOne 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 control 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 inlet side to maintain motion. Since the force generated by the actuator is proportional to the pressure difference between the two sides, the actual pressures in the cylinder don’t affect the action of the cylinder. For example, the action of the cylinder for 0psi/600psi would be the same as 1000psi/1600psi. However, in the second case, the power supply would have to supply much more power. This extra power is wasted. Different Options for Control SystemsCurrent control systems use hydraulic actuators with directional/proportional valves to control the movement. However there are many different options for controlling a cylinder. Options range from new high performance electrohydraulic 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 all have advantages and disadvantages which need to be analyzed if the most optimum solution is to be chosen. Near Future Solution It is expected that even if it is proven that a pletely new system topology is the optimum configuration, the crane manufacturers and ponent manufacturers will not accept the new technology overnight. This will most likely take time, so an interim solution will be developed. This solution will be made up of micro puter controlled Separate Meter In / Separate Meter Out (SMISMO) valves (Elfving, Palmberg 1997。 Pneumatics, Oct, 2022.[19] Johnson P. Help Your Filters Save Money. Hydraulics amp。在李老師艱辛教導下，經(jīng)過這短短幾個月時間，我不僅學到了豐富的專業(yè)設計知識和技巧，更重要的是使我學到了科學研究的方法和態(tài)度。使之更加完善，符合實際工程機械的要求。通過對液壓系統(tǒng)的性能計算和校核使系統(tǒng)符合最初設計，能夠完成設計要求。??當系統(tǒng)產(chǎn)生的熱量 H 等于其散發(fā)出去的熱量時，系統(tǒng)達到平衡，此時： ＝H/KA??當六面體油箱長、寬、高比例為 1：1：1－1：2：3 且液面高度是油箱高度的 倍時，其散熱面積的近似計算公式為： A= 32V所以可以導出：湖南理工學院畢業(yè)設計（論文）27 ＝ ??（5－7）式中 V——油箱的有效容量?？砂聪率焦浪阆到y(tǒng)的發(fā)熱能量： H＝ （1－ ） ipN?（5－5）式中 H——系統(tǒng)產(chǎn)生的熱量；——液壓泵的輸入功率。如下所示湖南理工學院畢業(yè)設計（論文）25在油缸夾緊時，油液依次經(jīng)過單向閥，電磁換向閥，疊加式雙單向閥，疊加式雙單項節(jié)流閥。在油缸夾緊時，油液依次經(jīng)過單向閥，疊加式減壓閥，疊加式溢流閥，電磁換向閥，疊加式雙單向節(jié)流閥， 。回油管口要斜切45176。隔板高度為液面高度的2/3～3/4。 確定油箱容積油箱的作用是儲油，散發(fā)油的熱量，沉淀油中雜質，逸出油中的氣體。Ⅱ工位夾緊液壓缸兩根油管同時選用 141（外徑 14mm，壁厚 1mm）的 10 號冷拔無縫鋼管。 選擇閥類元件應注意的問題1)應盡量選用標準定型產(chǎn)品，除非不得已時才自行設計專用件；2)閥類元件的規(guī)格主要根據(jù)流經(jīng)該閥油液的最大壓力和最大流量選取。電動機與泵之間采用連軸器聯(lián)結。初算時按經(jīng)驗數(shù)據(jù)選?。汗苈泛唵?，管中流速不大時，取 ＝ ～；管路復雜而且管中流速較大或者有p調速元件時，取 ＝ ～。 在合成液壓系統(tǒng)時要注意以下幾點：防止油路間可能存在的相互干擾；系統(tǒng)應力求簡單，并將作用相同或者相近的回路合并，避免存在多余回路；系統(tǒng)要安全可靠，力求控制油路可靠；組成系統(tǒng)的元件要盡量少，并應盡量采用標準元件；組成系統(tǒng)時還要考慮節(jié)省能源，提高效率減少發(fā)熱，防止液壓沖擊；測壓點分布合理等。湖南理工學院畢業(yè)設計（論文）13根據(jù)液壓設備所處環(huán)境及對溫升的要求，還要考慮加熱、冷卻等措施。對長時間所需流量較小的情況，可增設蓄能器做輔助油源。節(jié)流調速系統(tǒng)一般用定量泵供油，在無其他輔助油源的情況下，液壓泵的供油量要大于系統(tǒng)的需油量，多余的油經(jīng)溢流閥流回油箱，溢流閥同時起到控制并穩(wěn)定油源壓力的作用。閉式系統(tǒng)中，液壓泵的吸油口直接與執(zhí)行元件的排油口相通，形成一個封閉的循環(huán)回路。 節(jié)流調速一般采用開式循環(huán)形式。此種調速回路效率也較高，速度穩(wěn)定性較好，但其結構比較復雜。其優(yōu)點是沒有溢流損失和節(jié)流損失，效率較高。相應的調整方式有節(jié)流調速、容積調速以及二者的結合—容積節(jié)流調速。??2 ?? ?????? ?得 D=（mm）按 GB/T23481980 ,取標準值： D=50（mm）又 d=，得 d=25（m