无传感器液压系统的压力实时监测和控制————英语论文解读.pdf

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1、.1/6 Real-Time Pressure Monitoring and Control of a Hydraulic System without Sensor Tianshu Peng1,Craig Struthers2,and Peng Wen2 1 Computing Centre of Gansu Provincial Department of Science&Tech-nology Lanzhou,Gansu Province 730030,China pts22yahoo 2 Faculty of Engineering and Surveying University o

2、f Southern Queensland Toowoomba,QLD 4350,Australia Abstract.In a traditional hydraulic system,a pressure sensor is used to im-plementfeedback control.However,there are many industrial cases where applicationshave required a pressure feedback but the media is so corrosive and/ordangerous,the sensor b

3、ecomes prohibitively expensive.This research proposesthe control of a pumping system which can achieve the desired pressure withouta pressure sensor.Along with the control system itself,a user friendly interfaceis developed to operate over the Ethernet.Keywords:system reliability,Modbus Protocol,pre

4、ssure transducer,Ether-netnetwork and WEB server interfaces.1 Introduction There are a greater number of pumps which are utilized in almost all aspects of industryand engineering,and range widely from feeds to reac-tors,distillation columns inchemical engineering and pump storm water in civil and en

5、vironmental engineering.There is an almost endless assortment of pumping equipment available ranging insize,type and material of con-struction 6,8.Research contributing to advancementsin pumping technol-ogy can potentially create immense benefits for a large proportionof the en-gineering and industr

6、y sectors.Currently,within the industrial field there appears to be a deficiency in productsdesigned specifically for the control of pumping systems.This is particularly evidentin the application of constant pressure in a hydraulics system.The current industrystandard is to perform this process with

7、 multiple units and a pressure transmitter feedback.Fig.1 demonstrates how pressure control in a hydraulic pumping system iscurrently achieved.Note in particu-lar the use of a pressure transmitter in conjunctionwith a controller and a Variable Speed Drive.The research was chosen in order to find a p

8、ractical solution to achieving pressurefeedback in pumping applications with highly corrosive or danger-ous mediums.Atpresent,this particular aspect of the pumping industry does.2/6 not appear to be adequatelyaddressed.Although pressure transmitters are available for mediums that areconsidered dange

9、rous and corrosive the cost of this component is highly prohibitive.Fig.1.Illustration of existing Pressure Control System Furthermore,replacement or calibration of the pressure transmitter compo-nent can bedifficult and again not cost effective under such severe condi-tions.Research into current in

10、itiatives reveals that the main developments in sensorlesspump control are being undertaken predominantly within the medical field such asartificial hearts and blood pumps.The objective being to remove the invasive pressuretransmitter component from within the hu-man body 7,9.This research proposes

11、to develop a pumping controller able to maintain constantpressure within the hydraulics system without utilizing a pressure transmitter andcontroller.The main purpose of this undertaking is to ensure that the controller willhave no physical contact with the medium.Thus re-moving the pressure transmi

12、ttercomponent of pump pressure control in order to achieve the reduction of a component.In completing thefunctionality,a real-time monitoring,configuration and controlsystem software package is also being developed.2 Methodology This research proposes to remove the pressure transducer component of p

13、ump pressurecontrol in order to achieve an efficient process 5.Fig.2 rep-resents the proposedpressure control system whereby all the pressure control is performed within theVariable Speed Drive itself,the WEB server is simply a remote user inter-face.Fig.2.Illustration of proposed Pressure Control S

14、ystem 2.1 System Configuration The culmination of some specified equipment that will be listed in next sec-tion resultedin the final test product as can be seen from Fig.3.The outlet of.3/6 the pumpfeeds into the tank creating a closed loop system.The pressure transmitter has thenbeen connected back

15、 into the VSD and the VSD is then monitored for pressure,speedand motor current readings.Fig.4 shows pho-tos of the actual test equipment used.Fig.3.Closed Loop Testing System PI Diagram Fig.4.This Photograph is of Closed Loop Testing system and Testing Sys-tems Pump,PressureTransmitter and VSD 2.2

16、System Components Following is the components that have been utilized for this project.Each item hasbeen carefully chosen for its suitability for the purpose of the re-search.A pumping system essentially consists a supply or suction side,a pump with adriver and a discharge or delivery side 8.A centr

17、ifugal pump alter-natively is knownas a pressure generator because its rotating element trans-fers the energy to the fluid 2,8.Not withstanding the fact that the centrifu-gal pump is one of the most widely usedpumps for transferring liquids,it al-so has excellent ability to control pressure,is quiet

18、in comparison to other pumps,has relatively low operating and maintenance costs,takes up minimal floor space and can create a uniform,non pulsating flow 2,3.For these reasons above,the type of pump chosen is a Centrifugal pump with a RadialFlow Impeller driven by a suitably sized Squirrel cage induc

19、-tion motor.This form of pump consists of a shaft mounted impellers rotating unidi-rectionallywithin a casing.The velocity head is converted into pressure head by the Volutewhich directs the liquid from the outer perimeter of the impel-ler to the pump discharge1.A VSD alters the speed of an electric

20、 motor by means of modulating the power tothat motor.The VSD maintains constant pressure in a conventional pumping systemby receiving a signal from a pressure transmitter,and cor-responding the motor outputrelative to the feedback from the transmitter 4.VSDs provide a number of advantagesover tradit

21、ional methods ofconstant pressure control which have been takeninto consideration as part of this re-search.Most significantly,a VSD allows for rapidadjustment of small varia-tions which greatly enhances its value 5.The WEB server chosen for this project is a device which has a primary role ofconver

22、ting from Ethernet to serial.With recent technological advanc-es it is now possibleto interact with these devices from a remote location us-ing a WEB browser overan Ethernet network 11.A Lantronix Din Rail mounted Serial to Ethernet convertor/Web server was selected.The unit can be programmed to per

23、form calculations and con-.4/6 trol functions forthe VSD system as well as be able be configured as an HMI from the VSD system to the real world.2.3 Programming and Implementation The VSD has a user programming software which was developed by PDL calledVysta.The VSD has 30 registers that can be used

24、 for a userapplication written inVysta.The PDL Microdrive Elite Series are primarily motor con-trollers.Thereforeany programming that is done in Vysta must not interfere with their ability to controlthe motor 10.Programming of the VSD involved utilising three softwares written and suppliedby PDL Ele

25、ctronics.The first software used was Vysta which is the actual programminglanguage that provides the platform to write the control applications.The next software that is used is PDL Drivelink Version 2.7.This soft-ware is utilizedto download the compiled Vysta program into the VSD.This was required

26、to bedone throughout the project during the various testing stages.The last software that is required to be used is PDL Drivecome Version 3.It wasused to set up variables used in the Vysta programs that have been written to achievethe end result of the project.In order to develop the user interface,

27、various types of WEB servers were investigated.A Lantronix unit was chosen.It is 24 volt DC powered and has the ability tocommunicate from Ethernet to RS-232,RS-422 or RS 485 all within the one unit.Theadded benefit of using this type of device is that any person within an organizationwho has access

28、 to their LAN or WAN can view and adjust parameters without thecost of further software other than windows explorer.3 Test and Evaluation A program was written in Vysta which ramped the speed of the drive up and then heldit at maximum speed and then ramped it down again.This was done repetitively so

29、that a pressure,speed and motor current relationship in an open head and a closedhead system could be obtained.3.1Open Head System Tests Fig.5 illustrates the motor current and pressure variance in an open head system whenthe speed of the pump is varied from 0%to 100%and vice ver-sa.It shows that th

30、emotor current at 3.75amps at full speed results in a pres-sure of approximately 155Kpa.This indicates that the motor current is line-arly proportional to both speed andpressure in the Open Head System.Fig.5.Plot of Pressure and Motor Current with speed being varied for 0%-100%with the pumpoutlet va

31、lve fully open 3.2 Closed Head System Tests.5/6 Fig.6 shows that the motor current drops down to approximately 3 amps whilst thepressure increases up to 200 Kpa or thereabouts.This data indi-cates that there arepressure limitations within the system.These limitations are that once the pressure ofapp

32、roximately 165 Kpa is reached,then the mo-tor current begins to decrease untilsuch time that a minimum current of ap-proximately 3 Amps is reached and maintained.This current of 3 Amps will be held at this level as long as the motor pressureis greater than the 165 Kpa.Fig.6.Plot of Pressure and Moto

33、r Current with speed being varied for 0%-100%with the pumpoutlet valve fully closed 3.3 Fixed Speed Tests After conducting the initial Open and Closed Head Tests,it was determined that furthertests were required in order to better understand the relationships between systempressure,pump speed and mo

34、tor Amps.Fig.7.Plot of Pressure and Motor Current when speed is held at 30%,40%,50%and 60%Fig.8.Plot of Pressure and Motor Current when speed is held at 70%,80%,90%and 100%Numerous testing was undertaken,and it was found that as the centrifugal pumpdoes not start moving the fluid until 30%speed or g

35、reater that the re-sults from tests atthe lower speeds were irrelevant.It became evident that below 60%of motor speed itwould be virtually impossible to control the pressure in the pumping system by modelingthe motor current.From the results obtained thus far it is evident that the control algorithm

36、 that is requiredto control pressure in a pumping system without the use of a pressuretransmitter will require the system to operate around a known speed which can becalculated to approximately match the pressure required in the system.At this point,due to the test data revealing that the actual mot

37、or cur-rent decreases as the systempressure increases,the information can be used as a feedback which will be used tofinely adjust the speed of the pump to control more closely the required pressuresetpoint.3.4 Closed Loop System Tests with Pressure Transducer and Using ProposedAlgorithm The closed

38、loop control of a conventional system with the use of a pressure transmitteris achieved by utilising the internal PID capabilities of the VSD which has anoutput as shown in Fig.9.It can be seen that the pressure is controlled constantlyabout the required setpoint of 65 Kpa.From this data the best se

39、tpoint to use for theClosed Loop System using the Control Algo-rithm was to be 65 Kpa as it can be seenfrom the conventional system,con-trol is possible.It can also be shown in Fig.9.that control around the setpoint was.6/6 achieved,with the pressure fluctuating marginally.This was due largely to ha

40、ving to controlsystem pressure by crude means of manually turning the outlet valve on the pump foropen to closed and vice versa.Fig.9.Closed loop system Pressure-with pressure transmitter feedback 4 Conclusion This project presents a new method to implement the pressure control of a hydraulicsystem

41、without sensor,and developed a user friendly interface package to monitor,control and configure the system over Internet in re-al-time.A comparison is carriedout between conventional pressure control system and proposed control strategy.Based on the obtained data,we can see the proposed control stra

42、tegy works well,however theperformance is not better than the traditional one.Further work is requiredto improve the pro-posed strategy to achieve better accuracy and smootherresponse.References 1.Australian Pump Manufactures Association Ltd:Australian PumpTech-nical Handbook,3rd edn.APMA LTD,Canber

43、ra 2.Darby,R.:Chemical Engineering Fluid Mechanics,2nd edn.MarcelDek-ker Incorporated,New York 3.Davidson,G.:Centrifugal Pump:Parallel&Series Operation.University of PittsburghSchool of Engineering 4.Five Star Electric Motors:Using Variable Frequency Drives on Pump Systems.Five StarElectric Motors M

44、otors Controls Drives San Antonio 5.Hydraulic Institute,Europump&the U.S.Department of Energys Industrial TechnologiesProgram:Variable Speed Pumping A Guide to Successful Applications,6.Karassik,I.,Krutzsch,W.,Fraser,W.,Messina,J.:Pump Handbook,2nd edn.McGrawHill Book Company,New York 7.Minghua,F.,L

45、ongya,X.:Computer Modeling of Interactions of an Elec-tric Motor,CirculatorySystem,and Rotary Blood Pump.,vol.46.Lippincott Williams and Wilkins,Inc.8.Nelik,L.:Centrifugal and Rotary Pumps Fundamentals with Applica-tions.CRC Press,Boca Raton 9.Trinkl,J.,Mesana,T.,Havlik,P.,Mitsui,N.,Demunck,J.,Dion,I.,Can-delon,B.,Monties,J.:Control of Pulsatile Rotary Pumps Without Pressure Sensors.Compendex Database,vol.37 10.Vysta Virtual Automation Programming Platform Version 2.0 Help File:PDL Electronics.Napier,New Zealand 11.Web Enabling Your Serial Device:Lantronix,Irvine,California