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Pneumatic lectures
NONLINEAR PHENOMENA IN HYDRAULIC SYSTEMS Satoru Hayashi Professor Emeritus, Tohoku University, 981-3202, Sendai, Japan HZK00631@nifty.ne.jp ABSTRACT Hydraulic systems include various non-linearities in static and dynamic characteristics of their components. Consequently, a variety of nonlinear phenomena occur in the systems. This paper deals with intrinsic nonlinear dynamic behaviors of hydraulic systems. KEYWORDS Hydraulics, Nonlinear phenomena, Hard self- excitation, Micro-stick-slip, Chaos INTRODUCTION Hydraulic systems consist of various elements: pumps, actuators, control valves, accumulators, restrictors, pipelines and the like, which include many types of nonlinearity, such as pressure-flow characteristics in control valves, dry friction acting on actuators and moving parts of valves, collision of valves against valve seats. As a result, various types of nonlinear phenomena arise caused by these non-linearities. It is a marked feature of nonlinear systems that global behaviors are sometimes quite different from local behaviors. In such cases, results of linear analysis are unavailable to estimate global nature of the system. This paper focuses on the nonlinear phenomena occurring in hydraulic systems, especially, “hard self- excitation” [8] whose global stability drastically changes from local one on the basis of the author’s studies in the past [1]-[7]. HARD SELF-EXCITATION IN ASYMMET- RICALLY UNDER-LAPPED SPOOL VALVE [1],[2] Spool valves are classified into three types, over-lap valves, zero-lap valves and under-lap valves on the basis of the relation of the land-width to the port-width. They are used properly according to their applications. Usually in spool valves, the supply side lap is equated to the exhaust side lap, but the lap of the exhaust side is often taken smaller than that of the supply side by error in measurement in working or for stability purpose. This type of spool valve is called ”asymmetrically under-lapped spool valve”. Abnormal oscillations so- called “hard self-excitation” are excited in hydraulic servo-systems using this type of spool valve shown in Fig. 1 [1]. “Hard self-excitation” is a kind of a self-excited oscillation that occurs around a stable equilibrium point by disturbances beyond a critical value and it is distinguished from an ordinary self-excited oscillation which occur around a unstable equilibrium point and is called “soft self-excitation”. This situation is demonstrated in Fig. 2, which shows the relation between soft self-excitation and hard self-excitation by bifurcation maps of amplitude and phase plane trajectories of oscillations, where λ is a related system parameter. Fig. 1 Servo-system using asym- metrically lapped spool valve Fig. 2 Types of self-excitation, bifurcation maps and phase trajectories Fig. 3 shows responses of the cylinder of a hydraulic system shown in Fig. 1 for different magnitudes of step inputs given to a spool shaft of the system resting at the neutral position, whose asymmetry lap ratio is λ(= ε e /ε s ) = 0.047 (ε s =0.75mm) and the supply pressure is P s = 9.5MPa. As shown here, the transient oscillatory responses (a), (b) and (c) settle down to an initial equilibrium position for relatively small inputs. This shows the neutral position is locally stable. However, the response (d) for larger inputs beyond a critical valve develops into a finite amplitude oscillation. This fact shows that the phenomenon is a typical “hard self-excitation”[1]. Fig. 4 indicates a local stability map of the neutral position of the system, which is calculated from the following stability criterion Eq. (1) [2]. [ ] >+ ′ ′ + κκ 020 2 V aMAABbMbB V (1) and A is the cross-sectional area of the actuator, B the damping coefficient, C x the leakage coefficient, M the load mass, Q the flow rate of the valve and κ the bulk modulus of oil. The curve in Fig. 4 shows the critical supply pressure against asymmetry ratio Λ(=1−λ). According to the map, the system using a symmetrical lapped valve λ=1 (ε s = ε e ) is locally stable for the supply pressure P s =5.9MPa. But for the system using a spool valve with asymmetry lap ratio λ=0.047, the neutral position is stable. Equivalent asymmetry ratio (Λ=1−λ) is gradually increases according to the increase of the spool amplitude after the valve begins to move by input disturbances, even though the system is stable at the neutral position. The pressure-flow coefficient b in Eq. (1) drastically increases as shown in Fig. 5. On the other hand, the flow-gain a changes little. As a result, the system becomes unstable and the oscillation is excited. This is the mechanism of the “hard self- excitation”. Taking into consideration this hard self- excitation, the self-excited region is enlarged more than locally unstable region that is between a solid line and a dashed line as shown in Fig. 6. Fig. 3 Responses of hydraulic servo- system with asymmetrical spool valve for different magnitude of step inputs , 2 1 0 ,2 0 2 0 1 , 0 where VVV d C e Cbb P Q P Q b x Q a ==++= ′ ∂ ∂ = ∂ ∂ −= ∂ ∂ = Fig. 4 Local stability map by asymmetri- cal lap ratio 21 0 , PPP P Q b L L −= ∂ ∂ = Fig. 5 Pressure-flow coefficient NEW DEVELOPMENTS IN PNEUMATICS Dr. Kurt Stoll Festo AG & Co., Ruiterstr. 82, D-73734 Esslingen, Germany ABSTRACT This paper dealt with the new developments of pneumatics in the following areas: • Pneumatic components • Industry segment specialized applications • Best before-sales and after-sales services KEYWORDS: Developments, Pneumatic drive, Servo control, Field-bus, valve terminal, modular systems, dynamic simulation, database INTRODUCTION Pneumatics were first utilised at the beginning of the fifties. Fig. 1 shows a device built in 1955, which was fitted with single-acting aluminium die cast cylinders. A typical pneumatic system of that time was used in this device; it consisted of cylinders and manually operated valves. An operator played the roll of a “logic controller”. Fig. 1 An early pneumatic system Fig. 2 A purely pneumatic sequence controller with 12 inputs and 12 outputs Over the past 50 years, with the rapid developments in science and technologies, especially in automation, mechanical, electronic and computer technologies, pneumatics has been experiencing a quick expansion and development. Take automation sequence controllers as an example, the first pneumatic control systems functioned via valves that were actuated by driven camshafts. In the seventies many purely pneumatically actuated sequence controllers such as the QUICKSTEPPER (Fig. 2), which consisted of several pneumatic logic elements, were used in applications. How is pneumatics applied in today’s modern world? I would like to focus on the new developments in pneumatics in the following areas: • Pneumatic components • Industry segment specialized applications • Best before and after-sales services NEW DEVELOPMENTS IN PNEUMATIC COMPONENTS o The combination of different techniques The combining of pneumatics with electronics and of pneumatics with mechanics became an obvious trend over the last 10 years. Behind this trend is the fact that more and more pneumatic drives, sensors and valves are used in a modern automatic machine. This means more inputs and outputs are required in the control system. A purely pneumatic control system is no longer suitable to meet present demands. So in most machines today, PLCs or IPCs are used as sequence controllers together with a large number of electro-pneumatic converters, or solenoid valves. As a result, the pneumatic suppliers are faced with demands to improve the performance and to expand the functions of pneumatic components. A pneumatic valve should be easy to install and fast switching. A pneumatic drive should be able to move faster and more precisely. Sometimes an electro-pneumatic proportional valve is required to convert a continuous electronic signal into pneumatic signal. All this resulted in the combination of pneumatics, electronics and mechanics. By combining pneumatics with mechanics, customers will not only save engineering time with regard to designing and testing, but also receive an optimised solution because the product they receive is proven and tested by the pneumatics manufacturer. Fig. 3 shows a swivelling/linear unit, in which a linear cylinder is combined with a rotary drive to get independent linear and rotational movements. Fig. 3 A swivelling/linear unit Fig. 4 shows pneumatic units used in an assembling system. This includes a linear and rotary cylinder combined with a high precision guide unit. Excellent precision and rigidity can be achieved with this combination of components. The “valve terminal” concept was introduced at the beginning of the nineties. In recent years valve terminals have been widely used. The origin of such a product is to meet the demands of the larger scale control system. In a valve terminal, the valves and electronic I/Os are integrated in accordance with specific user interfaces (Fig. 5). Customers can order a valve terminal according to the specification of their application. They will get a complete factory Fig.4 Pneumatic units with several precision mechanical parts pre-assembled and pre-tested unit. They can link the valve terminal to a PLC or IPC via the desired interface, such as multipin or fieldbus. They can even order a valve terminal with a PLC already integrated. In this way, application engineers can easily divide their control systems into a couple of sub-systems. They obtain the sub-systems from the suppliers with guaranteed functionalities. That is to say, what the customers get are not only the components, but also the whole solution, a solution that suits their application. Fig. 5 A valve terminal, the combination of pneumatics and electronics A valve terminal equipped with fieldbus connection makes it possible for the pneumatic system to be integrated as a part of a factory network. Another example of combination and integration is shown as Fig. 6, a pneumatic unit with the combination of a cylinder, sensors, speed control valves and direction control valve. Where the interfaces to the sensor and direction valve could be fieldbus or individual connections. Fig. 7 is a multi controlled positioning system, a pneumatic servo-positioning axis is combined with an electrically driven axis. In this system, we can see that both the guided pneumatic linear cylinder DGPL and the guided electrical axis DGEL have the same mechanical interfaces. This makes it much easier for customers to design their machines. Fig. 6 Cylinder, solenoid valve, speed control valves and sensors in an integrated unit Fig.7 Pneumatic and electrical drives with the same mechanical interface o Compact performance In many applications, a pneumatic control valve is to be mounted together with some moving parts of the machine. In this case, the valve should be as light and as small as possible. On the other hand, in order to shorten machine cycle time, the control valves should be installed as close to the cylinder as possible. Fig. 8 provides a direct comparison of a solenoid valve made in 1961 with one made in 1997, both valves have the same flow rate (400 l/min) but the new generation of solenoid valve is only 10 mm in width, while the old type is 40 mm. Fig.8 In comparison, valves of 1961 and 1997, the same flow rate, but a quarter of the width o More intelligence is integrated into products. Faster movement is often desired on a machine. It is not difficult to get a cylinder to move faster. But it is more difficult to stop a fast moving cylinder properly (without vibrations or shocks). Fig. 9 shows a soft-stop cylinder, in which a displacement sensor, a 5/3 dynamic proportional valve and a smart controller are included. With such a system, the time taken for the cylinder to travel from one end position to the other can be reduced by 30%. In addition, 2 freely selectable intermediate position settings are possible. Fig.9 Fast speed and soft stop Fig. 10 shows a pneumatic servo positioning system. A digital smart controller is employed in such a system. Fig.10 Smart pneumatic positioning axes The controller is robust and suitable for industrial applications. Built-in intelligence enables it to find the optimised control parameters. The user needs only to input the essential application data, such as the load, stroke, diameter and so on. Or even more simply, in the case of the SPC11 controller, just to push a “teach-in” button. o Cutting costs with the modular product concept In a modern highly automated machine, the control system often has many functions. One solution is to make such products, in which all the necessary functions are integrated, but this may incur high manufacturing costs. Fig. 11 A modular valve terminal with 26 solenoid valves and various electronic interfaces A very elegant way is to use a modular product concept. The benefit of a modular product for customers is that they can order the products in modules which exactly meet their requirements. They only pay for the functions they need. A modular valve terminal is shown in Fig. 11. Customers can configure or select the number and the size of the valves, the quantity of the electronic I/Os and so on. Fig. 12 and Fig. 13 show modular vacuum components and modular air service unit respectively. Fig.12 A modular vacuum system with freely combinable suction cup holder, angle compensator, filter and suction cup o Innovation, the new driving principle A new single-acting pneumatic drive - fluidic muscle - is shown in Fig. 14. It can output 10 times more force than a standard cylinder of equivalent diameter. Fig. 14 shows some applications of such a drive. Fig. 13 A modular air service unit with manual on-off valve, compressed air filter and regulator, lubricator, soft-start valve, distributor and pressure switch Fig. 14 Fluidic muscle and some typical applications It is well known that with a pneumatic cylinder it is very difficult to achieve slow movement without the stick-slip effect. To overcome this disadvantage electrically driven cylinders of the same size and with the same installation interfaces as standard pneumatic cylinders have been developed and applied in applications. Customers don’t need to make mechanical modifications to their machines. TRENDS REGARDING APPLICATIONS With regard to pneumatic applications, one of the most important tasks today is to develop more and more specialized products for the various industry segments. Fig. 15 Pneumatic components for the food and packing industry Fig. 15 shows cylinders and valves that have been specially developed for the food and packaging industry, where high corrosion resistance and ease of cleaning are essential. The electronics and handling and assembly industry also need pneumatic products that can meet special requirements. Fig 4 shows some precisely guided pneumatic drives with very high rigidity that are suitable for use in the handling and assembling industry. Fig. 16 shows some miniature precisely guided pneumatic actuators that suit the applications in the electronics industry. Fig. 16 Components for the electronics industry OPTIMUM SERVICES ARE DESIRED It is not enough nowadays just to offer customers a good pneumatic product. Customers need more and more help with their everyday tasks. This is because they get less and less time for designing, establishing and maintaining their machines. A very efficient way is to help the customer by providing new software tools. An electronic catalogue using the database principle makes it possible to access product information and drawings quickly and easily, via function searching, image searching and other searching methods (Fig. 17). Fig. 18 shows a software tool ProPneu, which differs from a normal dynamic simulation software tool. ProPneu can not only check an existing pneumatic system via dynamic simulation but also automatically select the components according to the performances required by the customer. The customer needs only provide Propneu with a limited amount of information concerning an application. The settings and parameters of the components, such as the setting of the pneumatic cushioning and the flow control valves, can be automatically optimised by Propneu, according to the criteria the user has selected. Propneu can also recommend the appropriate pneumatic components for a given task, e.g. to move a defined load in a required time and a certain distance vertically, horizontally or any inclined installation. Fig. 19 shows the software FluidDraw that assists customers in creating pneumatic circuits on a CAD system. If customers need to know whether their circuit sequences are correct, then FluidSim is the right simulation tool. Fig. 17 Fast product accessing via the electronic catalogue Fig. 18 ProPneu, an intelligent software for the selecting, simulating and optimising of a pneumatic system Fig. 19 Software for designing and simulating circuits for pneumatic sequences Fig. 20 3D CAD drawings on a Website More and more engineers use a CAD system for machine design, so, it is very helpful for them to get 2D or 3D CAD drawings of the pneumatic components they have selected. As shown in Fig. 20, they can now easily import a 2D or 3D CAD drawing via the Internet. REFERENCES [1] Arnold, G., Pneumatics and Hydraulics in the History of Energy Technology. O+P Vol, 18, 1969 [2] Stoll, Kurt, What is Pneumatics? Thesis, University of Stuttgart, 1958 [3] Pneumatic Tips, No. 51/1994, Festo Pneumatic, Esslingen [4] Pneumatic World, 2000, No. 1, 2 [5] Werner Deppert, Kurt Stoll, Cutting Costs with Pneumatics, 1988, ISBN 7-111-07456-4, in 14 Languages (including Chinese) [6] Stefan Hesse, 99 Examples of Pneumatic Applications, 2000 [7] Hong Zhou, A Smart Pneumatic Servo Positioning Axis and Its Applications, 3 rd JHPS, Proceedings of the Third JHPS International Symposium on Fluid Power, Yokohama, 1996 The Project Sponsored by ROC, SEM A RESEARCH AND APPLICATION ON A NEW FNN CONTROL STRATEGIES * Wang Sun’an and Du Haifeng Xi’an Jiaotong University, 710049, Xi’an, P.R. China sawang@xjtu.edu.cn ABSTRACT As the precise model of most practical mechatronics system cannot be obtained, the practice of typical control method is limited. Accordingly, numerous AI (Artificial Intelligence) control methods have been used widely. Fuzzy control and Neural Network control have been an important point in the developing process of the field. However, shortcomings exist in each of these methods. For example, the fuzzy control is unable to learn, and the physical meanings of learning result of the Neural Network control are not clear. Combining the strong points of above two methods, a new control method of FNN (Fuzzy Neural Networks) is explored in this paper. Additionally, a problem concerning the traditional network learning is discussed and a solution to such a problem is obtained subsequently. The new control strategy does not depend on the classical model and the algorithm is simple. The results of the experiments applying the new strategies are discussed. Through different researches on control system, which model is unacquainted, the reasonableness, effectiveness and applying universality of the new control strategies is proved. INTRODUCTION The mechatronics system becomes more and more complicated. According to the Incompatibility Principle [1], the higher complicacy of the system is, the lower ability to describe becomes. So the typical control methods based on the precise model cannot meet the need. AI offers new strategies for the mechatronics control system. Since the AI Project was launched at MIT in 1957, it has achieved great success in many fields. It attracts more and more attention to AI and many AI methods have been put forward [2]. Fuzzy and NN (Neural Networks) are important aspects in AI, simulating different functions of the human brain. The former simulates the macroscopical functions, such as syllogisms, but the latter simulates the associatron, classification, memory by way of imitating the microcosmic structure. But the Fuzzy cannot learn and the NN cannot deduce. In addition, the Fuzzy can be understood and the learning results of the NN cannot [3]. The new AI method, FNN , which integrated the good qualities of the two methods, has been the hotspot in AI fields. Firstly, this paper will discuss a new object function of FNN learning and a problem in NN control system. Then a new FNN control structure will be put forward based on them. Finally, some conclusions will be acquired, supported by related experiments. THE OBJECT FUNCTION Object function is very important for the control system. ∫e 2 dt is usually taken as the Object function in time fields. The smaller the area, like figure 1, which surrounded by the phase track in the phase space is, the better performance of the system is. So the integrated object function can be defined as deedteJ ∫ + ∫ = & βδ 2 (1) where e is the error between the sysytem’s real output and the reference input. e & is the differential coefficient of e . ∫e 2 dt is the general object function, ∫ dee & is the area. δ and β are the weighted coefficients. Fig. 1 A example of phase space On second thoughts ( ) dtedt dt de dt de de dt de dee 2 && =∗∗== (2) dtedee ∫ ∫ = 2 && (3) The area surounded by the phase track is the integration of the error’s differential coefficient. So the error and its differential coefficient are synthetically considered in the new object. [...]... conditions dộfinies, par exemple, de dộbit Druck zum Schlieòen eines Bauteiles unter definierten Bedingungen, z.B des Volumenstromes 5.8.1.8 - done coalescing filter filtre (m) coalescent Coalescer-Filter (n, m) Filter in which retention of contaminants occurs due to the difference in wetting properties on a particular porous medium, leading to liquid particles in suspension combining into particles... 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The analysis on the override pressure of relief valve, (in Chinese) Machine tool and hydraulics 1989(6):21~23 [2] Backộ W, Zhu Wen Hydraulic resistance circuit systemology, (in Chinese) Beijing: China machinery press 1980 [3] Wu Genmao Vorgesteuertes Druckbegrenzungsventil DB10 Serie 30 Versuchsbericht V932 Mannesmann Rexroth GmbH 1984 [4] Rexroth Induetrieventile und Zubehửr RD00101/09.92, ss.165 ISO/TC... be seen that different will results in different characteristic of the control pressure p1 varying with the compensating force: >0 p1 increases with the increasing of the compensating force, this is under-compensated ; =0 p1 keeps constant, and does not change with the compensating force, right-compensated; . the pneumatic suppliers are faced with demands to improve the performance and to expand the functions of pneumatic components. A pneumatic valve should be easy to install and fast switching. A pneumatic drive. Vol, 18, 1969 [2] Stoll, Kurt, What is Pneumatics? Thesis, University of Stuttgart, 1958 [3] Pneumatic Tips, No. 51/1994, Festo Pneumatic, Esslingen [4] Pneumatic World, 2000, No. 1, 2 [5] Werner. developments in pneumatics in the following areas: • Pneumatic components • Industry segment specialized applications • Best before and after-sales services NEW DEVELOPMENTS IN PNEUMATIC COMPONENTS o