An Energy Efficient Two-Stage Supply Pressure …downloads.hindawi.com/journals/mpe/2018/2161937.pdf9.9. Design of Two-Stage Supply Pressure Hydraulic System. DuringtheDTRoperation,loadforceofactuatorchanges

Research ArticleAn Energy Efficient Two-Stage Supply Pressure HydraulicSystem for the Downhole Traction Robot

Delei Fang Jianzhong Shang Junhong Yang ZhuoWang Yong Xue andWeiWu

College of Mechatronic Engineering and Automation National University of Defense Technology Changsha 410073 China

Correspondence should be addressed to Jianzhong Shang jz shang nudt163com

Received 12 December 2017 Revised 3 May 2018 Accepted 20 May 2018 Published 11 June 2018

Academic Editor Anna M Gil-Lafuente

Copyright copy 2018 Delei Fang et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The efficiency of hydraulic drive system has become one of the significant issues in mobile robot In this paper an energy efficienttwo-stage supply pressure hydraulic system is proposed to solve the energy waste in the one-stage supply pressure system of thedownhole traction robotThis novel two-stage hydraulic system canmatch different pressure requirements of actuator by changingthe modes of supply pressure which is helpful to reduce the energy loss and improve the efficiency for traction robot Based onthe robot working principle the load characteristics in different actuators are obtained and the shortage in traditional hydraulicsystem is analyzed The novel hydraulic system which consists of a high-pressure source and a low-pressure source is designedincluding the system structure and energy supply method According to the energy flow process energy loss models of the systemand components are established to analyze energy-saving principle of the novel hydraulic system The feasibility and efficiency oftwo-stage supply pressure system are verified by simulating the operating process of telescopic mechanism Finally the simulationshows that control precision of the novel system can reach 35 mm and the efficiency is increased to 5953 which can providetheoretical reference for design of hydraulic drive system in traction robot and the efficiency improvement of multiactuator mobilerobot

1 Introduction

With the development of information technology sensationtechnology and control technology mobile robots havebeen dramatically improved which can be widely used inmilitary industry and civil service [1ndash3] As a kind of mobilerobots downhole traction robots have been applied to thedevelopment in petroleum field in recent years Also theyplay an important role in well drilling logging and otherborehole operations [4 5] In order to raise load capacitymore and more traction robots are using hydraulic systemHowever most traditional systems have the shortcomings oflow drive efficiency and large heat release which severelyaffect the reliability and durability in the robot operation[6ndash8]

Traction robot works in the complex environment withhigh temperature and high pressure While if the energyconsumption is large in the narrow pipe there will be lots ofproblems

(1)Thehigh energy loss requires the system to have higherpower so the high power motor and pump should be chosenwhich inevitably leads to the increase of weight and volumeof motor and pump

(2) When the robot performs lower power action it willinevitably result in a lot of pressure drop loss which dissipatesin the form of heat

(3) As the energy loss increases the system becomesmoreheated the power of the cooling system should be larger andvolume andweight of the cooling system increases whichwillalso affect the compact structure of the robot

(4) If the heat is not dissipated timely it will affect thenormal operation of relevant machine components whichinevitably affect robot working safety

Therefore improving the drive efficiency of hydraulicsystem has become one of the most essential techniques todevelop downhole traction robot

So far the research of downhole traction robot hasbeen focused on mechanical design trajectory planning

HindawiMathematical Problems in EngineeringVolume 2018 Article ID 2161937 9 pageshttpsdoiorg10115520182161937

2 Mathematical Problems in Engineering

and stability control However there are few studies on theefficiency of hydraulic drive systems We can refer to theresearch on efficiency of mobile robot hydraulic power unitin recent years [9ndash11]

Helmut Kogler proposes a new type of hydraulic buckconverter consisting of high frequency switch valves elon-gated tubes and accumulators which can enhance the systemefficiency bymatching output pressure with the requirementsof actuator However the thin pipe which is used as aninertial device is too long to be placed in the limited spaceof robot In addition the pressure wave in the elongatedpipe affects the converters ability to adjust the pressure andreduces the energy utilization [12ndash14] Kyoung Kwan Ahndesigns a device to achieve energy recovery and releasewhich consists of a flywheel hydraulic motor and a largecapacity accumulator [15 16] Due to the limitation of volumeand weight this method is mainly applied in excavatorsvehicles and other large equipment which is not available fortraction robot Now there are also applications of two-stagepower supply applied to hydraulic press and hydraulic liftmachinery whose idea of saving energy is to reuse excessiveenergy When the machine operates the extra potentialenergy is stored in the accumulator When the machineruns again the extra potential energy is released from theaccumulator to improve the power system energy efficiencyHowever thismethod does not solve the problemof excessiveenergy output primarily [17 18]

Beside the devices which are attached to the system toimprove the efficiency some special control method is devel-oped to reduce energy loss [19 20] A R Plummer and DN Johnston put forward a variable pressure control methodcalled VPVC (variable supply pressure valve-controlled)Themethod can predict the load and adjust the speed of motorwhich canmake system pressure match the pressure requiredfor the actuator This method can reduce throttling loss atcontrol valve However the system pressure only matches themaximum pressure of the actuators in operation For otheractuators there is still much energy loss due to excessiveinput pressure Monika Ivantysynova proposed removingproportional control valve and control motor speed to adjustoutput flow rate which can directly dominate the movementof hydraulic cylinder So thismethod achieves high efficiencydue to the elimination of throttling loss caused by excess flow[21ndash24] However this method requires that each actuatormust be configured with one pump and one motor resultingin a large hydraulic system which is not suitable for smallmobile robots

In view of the traction robot characteristics of com-plex dynamic performance in multiactuators and compactmechanical structure the previous energy-saving methodsare not applicable to downhole traction robot hydraulicsystem In this paper a novel two-stage supply pressurehydraulic system is proposed which can make system pres-surematch the requirement of actuator reduce throttling lossin servo valve and improve the efficiency of the hydraulicsystem of downhole traction robot Based on the tractionrobot working principle the loads of all actuators are ana-lyzed Then mechanism structure and operating principle oftwo-stage supply pressure hydraulic system are presented

According to the energy flow process in the robot energyloss models in traditional system and the novel system areestablished which can be used to analyze the energy-savingreason in the novel system relative to the traditional oneFinally telescopic mechanism is selected as an example toanalyze efficiency of two-stage supply pressure system Andoperating process in the novel system is simulated which canbe used to prove feasibility and energy-saving in two-stagesupply pressure system The novel pressure supply method isdifferent from the existing application mainly in the modeof energy supply and energy-saving idea The purpose ofthis paper is to provide reference and guidance for practicaldesign for traction robot hydraulic system and mathematicalanalysis on drive efficiency for multiactuator mobile robot

2 Mechanism and Design of Two-Stage SupplyPressure Hydraulic System

21 Working Principle of Downhole Traction Robot Figure 1shows downhole traction robot (or DTR for short) based onthe single-directional locking mechanism which consists oftwo locking mechanisms and one telescopic mechanism[25]Locking function and horizontal motion are realized sepa-rately by the asymmetric hydraulic actuators and hydraulicsystem of the traction is shown in Figure 2 DTR traditionallyadopts the supply mode of one-stage supply pressure whichis that a pump is driven by a motor to supply pressure forall hydraulic actuators At present the energy supply for thedriving motor is realized by cable which is connected to theground

As shown in Figure 1 DTR assembles drill bits and otherunderground equipment on the right end which is selectedas the forward direction In the initial state as shown inFigure 1(a) the locking arm shrinks and the DTR remainsstatic In the working step 1 which is shown in Figure 1(b)pressed oil enters small cavity (or the cavity with rod) oflocking actuator 2 Pressed oil drives piston rod to movewhich pushes locking arm and locking wheel to lock the pipeThe pressed oil enters big cavity (or the cavity with no rod)of telescopic actuator and pushes bit for drilling operationAs telescopic piston moves one stroke locking mechanism 1begins to lock the hole and locking mechanism 2 shrinks theholeThe pressed oil enters small cavity of telescopic actuatorand the rear part of DTR is dragged forward as shown inFigure 1(c) After movement is accomplished DTR is backto the state in Figure 1(a) So DTR can realize motion byrepeating motions from Figures 1(a)ndash1(c)

As shown in Figure 2 traditional hydraulic system ofDTR is a one-stage supply pressure system (or OSP forshort) In order to ensure that all actuators work properly themaximum pressure required in all actuators must be selectedas system output pressure However each actuator requiresdifferent pressures in different operating modes Also atdifferent times the pressure required in one actuator variesgreatly

The clamping force is mainly related to the frictionforce of pipe which is a complicated physical quantity anddifficult to measure The clamping data is obtained through

Mathematical Problems in Engineering 3

telescopic mechanism

locking mechanism 2 locking mechanism 1

pipelocking wheel locking arm

(a)

(b)

(c)

Figure 1 Schematic diagram of traction robot motion

M

telescopic actuator

locking actuator 1

locking actuator 2

servovalve

servo valve 2

servo valve 1

filter

filter

motor

relief valve

pump

F

F1

F2

1

2

Figure 2 Diagram of downhole traction robot hydraulic system

simulation based on ADAMS and AMESim In fact duringoperation the forces will fluctuate To simplify simulationresearch all the forces are rounded into integers As shownin Figure 3 the load forces of all actuators under drillingoperation mode are depicted The load force of telescopicactuator is the most severe which can vary from -300N to6500N while load range of supporting actuator 1 is -600N to1500N and load range of supporting actuator 2 is -300N to3000N

According to the above analysis to make sure the robotcan operate output pressure in traditional OSP hydraulicsystem must match the maximum load 6500N which hasexceeded the pressure requirement of other actuators There-fore to meet the needs of small load in other actuatorsthe redundant output pressure for actuator should be lost inthrottling form at the corresponding servo valve The lost

energy is converted into heat not only reducing the energyefficiency of hydraulic system but also affecting the reliabilityof DTR

22 Design of Two-Stage Supply Pressure Hydraulic SystemDuring the DTR operation load force of actuator changesdramatically and the duration of peak value is relativelyshort Combined with the above traction features a novelenergy efficient two-stage supply pressure hydraulic systemis presented in this paper which is abbreviated as TSPTSP hydraulic system has a low-pressure source and aninstantaneous high-pressure source including a switch valveand a small accumulator As shown in Figure 4 the low-pressure pump is responsible for low-pressure supply of threeactuators and the high-pressure pump is used to chargeenergy for accumulatorThe low-pressure pump is connected


X Time [s]

Y F

orec

[N]

telescopic actuatorlocking actuator 2locking actuator 1

Figure 3 Load curves on actuators under drilling mode

directly to the motor while the high-pressure pump isconnected with themotor through the clutchWhen receivedsignal that the accumulator pressure arrives presets pressurevalue the control system issues instruction to separate thehigh-pressure pump from motor Otherwise the controlsystem sends instructions to connect the high-pressure pumpwith the motor to replenish energy to accumulator

According to the working principle traction robot move-ment is driven by three actuators Because of low-pressurerequirement the two supporting actuators can be drivenby low-pressure source To meet the high-pressure demandtelescopic actuator is offered pressure by low-pressure sourceand a small auxiliary high-pressure accumulator When theload on telescopic mechanism is small telescopic actuator issupplied by the low-pressure source When the load becomesso large that the low-pressure source cannot meet telescopicactuator is transformed into high-pressure supply mode byopening switch valve

When DTR is operating normally the load force has avery short peak value and the pressures of two supportingactuators both are far less than the peak load value So drivingthree actuators by the OSP system leads to a large numberof throttling losses inevitably TSP system can offer differentactuators different pressures according to the different loadforces Therefore the TSP method can reduce throttling lossresulting from redundant pressure of OSP in a long timewhich can increase energy efficiency of fluid power systemin the robot

3 Energy Loss Analysis of TwoHydraulic Systems

In the research on traction robot and pipeline robot manyscholars focus on structural design and stability design andthere is little research on energy consumption of powersystem Therefore the establishment and analysis of math-ematical model for energy-saving will provide theoreticalreference for the research on mobile robot power system

Energy loss models are established to explain the reasonwhy efficiency of TSP system is higher than that of OSPsystem In order to research the different effects of two

hydraulic systems on robot efficiency we do not considertransmission energy loss between motor and pump andoutput energy loss of pump The energy loss in the switchvalve is ignored because of large opening andminute pressuredrop In the two types of hydraulic system robot performs thesame amount of work and actuators need the same power

31 Energy Loss Models of Systems The balance equation ofpower in OSP system is expressed as

119875119894119899 = 119875119901119894 + 119875V119886 + 119875119888119910 + 119875119900119906119905 (1)

where 119875119894119899 is the total input power 119875119901119894 is the power loss inthe fluid pipe 119875V119886 is the power loss in the servo valve 119875119888119910 isthe power loss of hydraulic cylinder 119875119900119906119905 is the total outputpower

For OSP by assuming that T is the operating time thetotal energy transmission loss of hydraulic system during aperiod is expressed as

119864119889119890 = int1198790(119875119901119894 + 119875V119886 + 119875119888119910) 119889119905 (2)

Similarly power loss for TSP system is expressed as

1198751015840119894119899 = 119875(1)119901119894 + 119875(2)119901119894 + 119875(2)119886119888 + 1198751015840V119886 + 1198751015840119888119910 + 1198751015840119900119906119905 (3)

where 1198751015840119894119899 is the total input power 1198751015840119900119906119905 is the total outputpower and 1198751015840V119886 is the power loss in servo valve 1198751015840119888119910 is thepower loss of hydraulic cylinder In high-pressure supplycircuit 119875(2)119901119894 is the power loss in the fluid pipe and 119875(2)119886119888 is thepower loss in the accumulator In low-pressure supply circuitthe power loss in the fluid pipe is 119875(1)119901119894

For TSP the total energy transmission loss of hydraulicsystem is expressed as

1198641015840119889119890 = int11987910119875(1)119901119894 119889119905 + int1198792

0(119875(2)119901119894 + 119875(2)119886119888 ) 119889119905 + int119879

01198751015840V119886119889119905

+ int11987901198751015840119888119910119889119905

(4)

where T1 is the time of low-pressure energy supply andT2 is the time of high-pressure energy supply To analyzethe specific energy loss difference between the two systemspaper establishes energy loss in fluid pipe energy loss inaccumulator and energy loss in actuator including the servovalve and the cylinder

32 Energy Loss in Fluid Pipe Because the pressure in the twosystems is different it is necessary to analyze whether the lossin fluid pipe is also different It is assumed that dimensionsof all pipes are the same The loss pressure along pipe isexpressed as

Δ119901 = 120582 1198972 120588V2

119889 (5)

where 120582 is pipe friction coefficient 120588 is fluid density ] isthe liquid velocity in pipe l is pipe length and d is the innerdiameter of pipe


M

downhole traction robot

sensors

servo valve+cylinder 1clutch

accumulatorswitch valve control system

high-pressuresource

servo valve+cylinder 2

servo valve+cylinder

low-pressuresource

Figure 4 Schematic diagram of two-stage supply pressure system

When flow rate through the pipe is q the relationshipbetween flow rate and liquid velocity can be obtained

V = 119902119878 = 4120587 1199021198892 (6)

By combining (5) and (6) the pipe power loss is expressedas

119875119901119894 = Δ119901119901119894 sdot 119902119901119894 = 120582 8120587211990211990111989431198895 119897119901119894120588

119875(1)119901119894 = Δ119901(1)119901119894 sdot 119902(1)119901119894 = 120582 81205872[119902(1)119901119894 ]31198895 119897(1)119901119894 120588

119875(2)119901119894 = Δ119901(2)119901119894 sdot 119902(2)119901119894 = 120582 81205872[119902(2)119901119894 ]31198895 119897(2)119901119894 120588

(7)

where 119902119901119894 is flow rate in the OSP 119902(1)119901119894 is the flow rate inthe low-pressure circuit of the TSP 119902(2)119901119894 is the flow rate in thehigh-pressure circuit 119897119901119894 is pipe length of the OSP 119897(1)119901119894 is thelength of the low-pressure circuit and 119897(2)119901119894 is the length of thehigh-pressure circuit

During one cycle the difference of pipe power loss inOSPand TSP is expressed as

Δ119864119901119894 = int1198790119875119901119894119889119905 minus int1198791

0119875(1)119901119894 119889119905 minus int1198792

0119875(2)119901119894 119889119905 (8)

Obviously when actuator operates the same motion therequired flow rates are identical in the both systems And119897119901119894 and 119897(1)119901119894 have the same length combining (7) and (8) theenergy loss dissipation is obtained

Δ119864119901119894 = 120582 812058812058721198895 (119897119901119894 minus 119897(2)119901119894 )int1198792

0119902(2)3119901119894 119889119905 (9)

Assuming that 119897119901119894 and 119897(2)119901119894 are the same length the valueof (9) is zero Therefore pipe power loss in the two systemswill be the same despite the different system pressures

33 Energy Loss in Accumulator It is also essential to ana-lyze power loss in accumulator as the accumulator is theimportant component in TSP When gas is compressed heatis generated and the energy is lost which is irreversible in thesystem The energy loss in accumulators is expressed as

Δ119864119886119888 = int11987900119875(1)119888 119889119905 minus int1198792

0119875(2)119889 119889119905

= int11987900119901(1)119888 (119905) 119902(1)119888 (119905) 119889119905minus int11987920119901(2)119889 (119905) 119902(2)119889 (119905) 119889119905

(10)

int11987900119902(1)119888 (119905) 119889119905 = int1198792

0119902(2)119889 (119905) 119889119905 (11)

where 119902(1)119888 is the flow rate streaming into the accumulator119902(2)119889

is the flow rate issuing from the accumulator 119901(1)119888 isthe pressure in energy storage 119901(2)

119889is the pressure in energy

releasing state and 1198790 is the energy recharging time

34 Energy Loss in Actuator As shown in Figure 5 theactuator includes servo valve and hydraulic cylinder Theenergy loss in actuator is the main loss in hydraulic systemThe reason is that input pressure provided in hydraulic systemis greater than the pressure required by the load which causesredundant pressure to be wasted in the form of throttling lossat servo valve Therefore reducing throttling loss is the mainreason that TSP system is more efficient than OSP system

The mathematic model of power loss in actuator isobtained The balance equation of power is expressed asfollows

1198751198941198990 = 119875V119886119905 + 119875V119886119887 + 119875119888119910 + 119875119900119906119905 (12)119875V119886 = 119875V119886119905 + 119875V119886119887 (13)

where 1198751198941198990 is the input power 119875V119886119905 is the throttling loss atthe inlet and 119875V119886119887 is the throttling loss at the outlet

There is a force equilibrium equation in cylinder

1199011119860 119894119899 minus 1199012119860119900119906119905 = 119865119897119900119886119889 + 11989811990910158401015840 (14)


Table 1 Simulation parameters in hydraulic system

parameter valueThe diameter of cylinder piston (m) 0024The diameter of cylinder rod (m) 0012The length of the stroke (m) 01The servo valve natural frequency (Hz) 100The switch valve natural frequency (Hz) 50The maximal flow rate of low-pressure pump (Lmin) 60The maximal flow rate of high-pressure pump (Lmin) 10The maximal pressure of the low-pressure pump (MPa) 75The maximal pressure of the high-pressure pump (MPa) 21The gas precharge pressure (MPa) 18The polytropic index 12The accumulator volume (L) 02

loadF

x

in0P

vatP

outP

valP

vabP

in0P

valP

vatPvabP

cyPm

Figure 5 Schematic diagram of power flow in actuator

where 119865119897119900119886119889 is the load force 119898 is the total mass 119909 is thepiston displacement 119860 119894119899 is the area of cylinder piston 119860119900119906119905is the area in cavity of no rod 1199011 is the pressure of fillingchamber and 1199012 is the pressure of returning chamber

At servo valve port the fluid flow equation is obtained

119902119894119899 = 119860 1198941198991199091015840 = 1198621198891198600radic2 (119901119894119899 minus 1199011)120588119902119900119906119905 = 1198601199001199061199051199091015840 = 1198621198891198600radic21199012120588

(15)

where 119862119889 is the metering coefficient and 1198600 is thesectional area of the orifice

Through formulas (14) and (15) the throttling loss powerin servo valve can be calculated

119875V119886119905 = (119901119894119899 minus 1199011) sdot 1199021= 119860311989411989911990910158401198603119894119899 + 1198603119900119906119905 (119901119894119899119860 119894119899 minus 119865119897119900119886119889 minus 119898119909

1015840) (16)

119875V119886119887 = 1199012 sdot 1199022 = 119860311990011990611990511990910158401198603119894119899 + 1198603119900119906119905 (119901119894119899119860 119894119899 minus 119865119897119900119886119889 minus 1198981199091015840) (17)

As shown in formulas (16) and (17) on the premiseother parameters are constant The two equations reveal therelationship between input pressure and throttling loss thatthe input pressure is higher and the throttling loss is larger

In TSP system the pressure of charging gas is not lowerthan the maximum load on actuators so the output pressureof accumulator is higher than the system pressure in OSPsystem By combining (14) (15) (16) and (17) saved energyat servo valve is expressed as follows

Δ119864V119886 = int11987910(1199010 minus 119901(1)0 )119860 1198941198991199091015840119889119905minus int11987920(119901(2)0 minus 1199010)119860 1198941198991199091015840119889119905

(18)

Based on the above analysis the energy saved in TSPsystem is got

Δ119864119889119890 = 119864119889119890 minus 1198641015840119889119890 = Δ119864V119886 minus Δ119864119886119888 (19)

4 Simulation and Discussion

In order to verify the feasibility and energy-saving of TSPhydraulic system simulation analyses of TSP system andOSP system are carried out based on AMESim Telescopicmechanism of traction robot is selected as the simulationobject the same load and displacement are used as thesimulation inputs in the two hydraulic systems Accordingto the robot motion characteristics and working principle ofhydraulic system the simulation parameters are set as shownin Table 1 In order tomeet the requirements of high-pressuresupply (the working time is from 02s to 04s) and linearoutput pressure the frequency of switch valve is set to 50Hz


X Time [s]

Y d

ispla

cem

ent [

m]

actual motiontarget motion

(a)

Y d

ispla

cem

ent [

m]

X Time [s]


(b)

Figure 6 Displacement tracking curve of the actuator driven by TSP system

The input displacement in simulation is the ideal sinu-soidal signal whose frequency is 1Hz and amplitude is 01mThe input load of hydraulic actuator is depicted in Figure 2The output displacement curve of telescopic mechanismunder TSP system is obtained as shown in Figure 6

As shown in Figure 6(a) TSP hydraulic system can drivethe actuator move according to the displacement planningthe control accuracy can reach 35 mm and the time delayis 005 s which can meet the movement requirements oftraction robot It can be seen from Figure 6(b) that pistonmovement fluctuates at themoment of high frequency switchvalve opening which is the moment when the accumulatorreleases the oil caused by the insufficient flow instanta-neously In order to avoid fluctuating some measures shouldbe taken such as before switch valve opens servo valveopening size should be adjusted in advance to stabilize inputpressure and flow

Then the output pressures of two systems are analyzedand pressure curves simulated are shown in Figure 7

It can be seen from the graph that system pressuresupplied by one-stage system is constant 16MPa The systempressure provided by two-stage system is variableThe outputpressure maintains at a low level in the most times andwhen the larger driving force is needed the output pressureis higher than that of one-stage systemTherefore in actuatoroperation especially the low driving force is needed OSPsystem produces a greater pressure loss at the inlet of servovalve than TSP system

In order to directly observe the energy consumptiondifference between two pressure supply systems outputpower curves are obtained as shown in Figure 8

It can be seen clearly from Figure 8 that the output powerof TSP system is lower than the output power of OSP systemin most working times Only in the moment when actuatorhas a high load force which represents accumulator startingto work is the output power of TSP system larger than theoutput power of OSP system While for the whole workingtime the high-pressure energy supply is very shortTherefore

X Time [s]

Y P

ress

ure [

bar]

two-stage

requirmentone-stage

Figure 7 Pressure curves of two pressure supply systems

the power loss in two-stage supply pressure system is muchlower than the power loss in one-stage supply pressuresystem

Based on the power curves and the previous formulasthe total energy consumption of the two systems can becalculated as shown in Figure 9

In Figure 9 the green dashed line describes the actualenergy required for telescopic actuator the red solid linedescribes the energy consumption in two-stage supply pres-sure system and the blue dotted line is the energy consump-tion in one-stage energy supply system As can be seen fromFigure 9 the actual energy required for telescopic actuatorin three periodic motions is 1193J When actuator operatesunder the OSP system the total energy consumed is 3461JWhen actuator operates under the TSP system the totalenergy consumed is 2004J Therefore the efficiency of OSPsystem is 3447while the efficiency of TSP system is 5953which is increased by 2506

At the same time the total energy consumption ofall hydraulic components in the two pressure systems is


two-stage

X Time [s]

Y P

ower

[W]

one-stage

Figure 8 Output power curves of two pressure supply systems

two-stage

X Time [s]

Y E

nerg

y [J

]

one-stage

requirement

Figure 9 Energy consumption curves in two systems

calculated and the bars chart of energy consumption is shownin Figure 10

As shown in Figure 10 under the same load conditionsif two-stage hydraulic system is adopted the throttling lossof the servo valve is much smaller than that of traditionalhydraulic system Because of the accumulator the addedenergy loss is 108J The loss is tiny relative to throttle loss Soreducing throttling loss is themain reasonwhy the novel two-stage supply pressure system is highly efficient

5 Conclusions

Based on the working principle of downhole traction robotthe load characteristics of three actuators are obtained Inview of the reason for the throttling loss in the one-stagesupply pressure hydraulic system a novel two-stage supplypressure hydraulic system is proposed which can improvedriving efficiency through different pressure supply modes

The energy loss model of traction robot hydraulic systemand the significant components were established and thespecific forms and mathematical expressions were obtainedwhich is helpful to analyze the energy-saving principle anddesign the component in the novel hydraulic system

10000

input energy

30002000

other loss

throttling loss

useful energy1193 1193

1797 476

227471

2004 3461

TSP system

OSP system

total energies in three periods [J]

accumulator loss 108

Figure 10 The bars chart of energy consumption in hydrauliccomponents

The feasibility of two-stage supply pressure hydraulicsystem is verified by simulation The results have shownthat the control accuracy can reach 35 mm and the timedelay is 005s which can meet the movement requirementsof downhole traction robot

Based on simulation data and formulas the power andenergy consumed in the two types of drive system wereobtained which has shown that the efficiency in two-stagesupply pressure system can be increased to 5953 Themain reason why two-stage system can improve efficiency isreducing the much throttling loss at servo valve

Conflicts of Interest

The authors declare no conflicts of interest

Acknowledgments

The work reported in this paper was supported by theNational Natural Science Foundation of China (nos51675527 51675522)

References

[1] T Li S Ma B Li M Wang and Y Wang ldquoAxiomatic designmethod to design a screw drive in-pipe robot passing throughvaried curved pipesrdquo Science China Technological Sciences vol59 no 2 pp 191ndash202 2016

[2] L I Yujia Q Liu Y Chen and T Ren ldquoDesign and analysisof an active helical drive downhole tractionrdquo Chinese Journal ofMechanical Engineering vol 30 pp 1ndash10 2017

[3] T Li S Ma B Li M Wang and Y Wang ldquoFuzzy theory basedcontrol method for an in-pipe robot to move in variable resis-tance environmentrdquo Chinese Journal of Mechanical Engineeringvol 28 no 6 pp 1213ndash1221 2015


[4] I Ahmad O Akimov P Bond et al ldquoReliable technology fordrilling operations in a high-pressurehigh- temperature envi-ronmentrdquo in Proceedings of the SPEIADC Drilling Conferenceand Exhibition 2014 pp 500ndash515 March 2014

[5] F Frans A Cuauro E Chalco D Brink M Ghozali and NBounoua ldquoTractor production logging in long cased horizon-tal wells operational experience from the Al Shaheen fieldOffshore Qatarrdquo in Proceedings of the International PetroleumTechnology Conference 2014 - Innovation and CollaborationKeys to Affordable Energy IPTC 2014 pp 2745ndash2755 December2014

[6] T Sheiretov ldquoWireline tractors and mechanical services toolsComparative study of technical solutionsrdquo in Proceedings of theSPEICoTA Coiled Tubing andWell Intervention Conference andExhibition 2016 March 2016

[7] D Heddleston ldquoAn evaluation of well deployment aspectsaffecting well flow performance on horizontal production logresultsrdquo in Proceedings of the Coiled Tubing and Well Interven-tion Conference and Exhibition 2013 pp 571ndash579 March 2013

[8] Y Li Q Liu and W Li ldquoDevelopment of a novel oil andgas in-pipe robotrdquo International Journal of Mechatronics ampManufacturing Systems vol 8 article 102 2015

[9] X Ouyang S Ding B Fan P Y Li and H Yang ldquoDevelopmentof a novel compact hydraulic power unit for the exoskeletonrobotrdquoMechatronics vol 38 pp 68ndash75 2016

[10] H Yang and M Pan ldquoEngineering research in fluid power areviewrdquo Journal of Zhejiang University-SCIENCE A vol 16 no6 pp 427ndash442 2015

[11] G Altare and A Vacca ldquoA Design Solution for Efficient andCompact Electro-hydraulic Actuatorsrdquo in Proceedings of the2nd International Conference on Dynamics and Vibroacousticsof Machines DVM 2014 pp 8ndash16 September 2014

[12] H Kogler and R Scheidl ldquoLinear motion control with a low-power hydraulic switching converter - Part I Concept testrig simulationsrdquo Proceedings of the Institution of MechanicalEngineers Part I Journal of Systems and Control Engineeringvol 229 no 8 pp 677ndash684 2015

[13] H Kogler and R Scheidl ldquoEnergy efficient linear drive axisusing a hydraulic switching converterrdquo Journal of DynamicSystems Measurement and Control vol 138 no 9 2016

[14] H Kogler R Scheidl and M Ehrentraut ldquoA simulation modelof a hydraulic buck converter based on a mixed time frequencydomain iterationrdquo in Proceedings of the ASMEBATH 2013Symposium on Fluid Power andMotion Control FPMC 2013 pp1ndash6 October 2013

[15] H H Triet and K K Ahn ldquoComparison and assessmentof a hydraulic energy-saving system for hydrostatic drivesrdquoProceedings of the Institution of Mechanical Engineers Part IJournal of Systems and Control Engineering vol 225 no 1 pp21ndash34 2011

[16] T H Ho and K K Ahn ldquoModeling and simulation ofhydrostatic transmission systemwith energy regeneration usinghydraulic accumulatorrdquo Journal of Mechanical Science andTechnology vol 24 no 5 pp 1163ndash1175 2010

[17] H Yang D Hu and B Xu ldquoEnergy-saving technology ofvariable counterweight and its energy consumption analysesrdquoJournal of Mechanical Engineering vol 46 no 2 pp 132ndash1382010

[18] J Yao B Li and X Kong ldquoEnergy saving and control ofhydraulic press fast forging system based on the two-stagepressure sourcerdquo Journal of Mechanical Engineering vol 52 no10 pp 199ndash206 2016

[19] C Du A R Plummer and D N Johnston ldquoPerformanceanalysis of an energy-efficient variable supply pressure electro-hydraulic motion control systemrdquo Control Engineering Practicevol 48 pp 10ndash21 2016

[20] K Baghestan SM Rezaei H A Talebi andM Zareinejad ldquoAnenergy-saving nonlinear position control strategy for electro-hydraulic servo systemsrdquo ISA Transactions vol 59 pp 268ndash279 2015

[21] J Zimmerman and M Ivantysynova ldquoHybrid displacementcontrolled multi-actuator hydraulic systemsrdquo in Proceedings ofthe The twelfth scandinavian international conference on fluidpower SICFP11 pp 22ndash27 Tampere Finland 2011

[22] R Hippalgaonkar and M Ivantysynova ldquoA Series-ParallelHydraulic Hybrid Mini-Excavator with Displacement Con-trolled Actuatorsrdquo in Proceedings of the 13th Scandinavian Inter-national Conference on Fluid Power June 3-5 2013 LinkopingSweden pp 31ndash42 2013

[23] N Daher and M Ivantysynova ldquoEnergy analysis of an originalsteering technology that saves fuel and boosts efficiencyrdquo EnergyConversion and Management vol 86 pp 1059ndash1068 2014

[24] M Sprengel T Bleazard H Haria and M IvantysynovaldquoImplementation of a novel hydraulic hybrid powertrain in asports utility vehiclerdquo IFAC-PapersOnLine vol 28 no 15 pp187ndash194 2015

[25] J-W Qiao J-Z Shang X Chen Z-R Luo and X-P ZhangldquoUnilateral self-locking mechanism for inchworm in-piperobotrdquo Journal of Central SouthUniversity of Technology (EnglishEdition) vol 17 no 5 pp 1043ndash1048 2010

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and stability control However there are few studies on theefficiency of hydraulic drive systems We can refer to theresearch on efficiency of mobile robot hydraulic power unitin recent years [9ndash11]

Helmut Kogler proposes a new type of hydraulic buckconverter consisting of high frequency switch valves elon-gated tubes and accumulators which can enhance the systemefficiency bymatching output pressure with the requirementsof actuator However the thin pipe which is used as aninertial device is too long to be placed in the limited spaceof robot In addition the pressure wave in the elongatedpipe affects the converters ability to adjust the pressure andreduces the energy utilization [12ndash14] Kyoung Kwan Ahndesigns a device to achieve energy recovery and releasewhich consists of a flywheel hydraulic motor and a largecapacity accumulator [15 16] Due to the limitation of volumeand weight this method is mainly applied in excavatorsvehicles and other large equipment which is not available fortraction robot Now there are also applications of two-stagepower supply applied to hydraulic press and hydraulic liftmachinery whose idea of saving energy is to reuse excessiveenergy When the machine operates the extra potentialenergy is stored in the accumulator When the machineruns again the extra potential energy is released from theaccumulator to improve the power system energy efficiencyHowever thismethod does not solve the problemof excessiveenergy output primarily [17 18]

Beside the devices which are attached to the system toimprove the efficiency some special control method is devel-oped to reduce energy loss [19 20] A R Plummer and DN Johnston put forward a variable pressure control methodcalled VPVC (variable supply pressure valve-controlled)Themethod can predict the load and adjust the speed of motorwhich canmake system pressure match the pressure requiredfor the actuator This method can reduce throttling loss atcontrol valve However the system pressure only matches themaximum pressure of the actuators in operation For otheractuators there is still much energy loss due to excessiveinput pressure Monika Ivantysynova proposed removingproportional control valve and control motor speed to adjustoutput flow rate which can directly dominate the movementof hydraulic cylinder So thismethod achieves high efficiencydue to the elimination of throttling loss caused by excess flow[21ndash24] However this method requires that each actuatormust be configured with one pump and one motor resultingin a large hydraulic system which is not suitable for smallmobile robots

In view of the traction robot characteristics of com-plex dynamic performance in multiactuators and compactmechanical structure the previous energy-saving methodsare not applicable to downhole traction robot hydraulicsystem In this paper a novel two-stage supply pressurehydraulic system is proposed which can make system pres-surematch the requirement of actuator reduce throttling lossin servo valve and improve the efficiency of the hydraulicsystem of downhole traction robot Based on the tractionrobot working principle the loads of all actuators are ana-lyzed Then mechanism structure and operating principle oftwo-stage supply pressure hydraulic system are presented

According to the energy flow process in the robot energyloss models in traditional system and the novel system areestablished which can be used to analyze the energy-savingreason in the novel system relative to the traditional oneFinally telescopic mechanism is selected as an example toanalyze efficiency of two-stage supply pressure system Andoperating process in the novel system is simulated which canbe used to prove feasibility and energy-saving in two-stagesupply pressure system The novel pressure supply method isdifferent from the existing application mainly in the modeof energy supply and energy-saving idea The purpose ofthis paper is to provide reference and guidance for practicaldesign for traction robot hydraulic system and mathematicalanalysis on drive efficiency for multiactuator mobile robot

2 Mechanism and Design of Two-Stage SupplyPressure Hydraulic System

21 Working Principle of Downhole Traction Robot Figure 1shows downhole traction robot (or DTR for short) based onthe single-directional locking mechanism which consists oftwo locking mechanisms and one telescopic mechanism[25]Locking function and horizontal motion are realized sepa-rately by the asymmetric hydraulic actuators and hydraulicsystem of the traction is shown in Figure 2 DTR traditionallyadopts the supply mode of one-stage supply pressure whichis that a pump is driven by a motor to supply pressure forall hydraulic actuators At present the energy supply for thedriving motor is realized by cable which is connected to theground

As shown in Figure 1 DTR assembles drill bits and otherunderground equipment on the right end which is selectedas the forward direction In the initial state as shown inFigure 1(a) the locking arm shrinks and the DTR remainsstatic In the working step 1 which is shown in Figure 1(b)pressed oil enters small cavity (or the cavity with rod) oflocking actuator 2 Pressed oil drives piston rod to movewhich pushes locking arm and locking wheel to lock the pipeThe pressed oil enters big cavity (or the cavity with no rod)of telescopic actuator and pushes bit for drilling operationAs telescopic piston moves one stroke locking mechanism 1begins to lock the hole and locking mechanism 2 shrinks theholeThe pressed oil enters small cavity of telescopic actuatorand the rear part of DTR is dragged forward as shown inFigure 1(c) After movement is accomplished DTR is backto the state in Figure 1(a) So DTR can realize motion byrepeating motions from Figures 1(a)ndash1(c)

As shown in Figure 2 traditional hydraulic system ofDTR is a one-stage supply pressure system (or OSP forshort) In order to ensure that all actuators work properly themaximum pressure required in all actuators must be selectedas system output pressure However each actuator requiresdifferent pressures in different operating modes Also atdifferent times the pressure required in one actuator variesgreatly

The clamping force is mainly related to the frictionforce of pipe which is a complicated physical quantity anddifficult to measure The clamping data is obtained through





(a)

(b)

(c)


M

telescopic actuator

locking actuator 1

locking actuator 2

servovalve

servo valve 2

servo valve 1

filter

filter

motor

relief valve

pump

F

F1

F2

1

2







X Time [s]

Y F

orec

[N]











119875119894119899 = 119875119901119894 + 119875V119886 + 119875119888119910 + 119875119900119906119905 (1)



119864119889119890 = int1198790(119875119901119894 + 119875V119886 + 119875119888119910) 119889119905 (2)


1198751015840119894119899 = 119875(1)119901119894 + 119875(2)119901119894 + 119875(2)119886119888 + 1198751015840V119886 + 1198751015840119888119910 + 1198751015840119900119906119905 (3)



1198641015840119889119890 = int11987910119875(1)119901119894 119889119905 + int1198792

0(119875(2)119901119894 + 119875(2)119886119888 ) 119889119905 + int119879

01198751015840V119886119889119905

+ int11987901198751015840119888119910119889119905

(4)



Δ119901 = 120582 1198972 120588V2

119889 (5)



M


sensors



high-pressuresource



low-pressuresource



V = 119902119878 = 4120587 1199021198892 (6)


119875119901119894 = Δ119901119901119894 sdot 119902119901119894 = 120582 8120587211990211990111989431198895 119897119901119894120588

119875(1)119901119894 = Δ119901(1)119901119894 sdot 119902(1)119901119894 = 120582 81205872[119902(1)119901119894 ]31198895 119897(1)119901119894 120588

119875(2)119901119894 = Δ119901(2)119901119894 sdot 119902(2)119901119894 = 120582 81205872[119902(2)119901119894 ]31198895 119897(2)119901119894 120588

(7)



Δ119864119901119894 = int1198790119875119901119894119889119905 minus int1198791

0119875(1)119901119894 119889119905 minus int1198792

0119875(2)119901119894 119889119905 (8)


Δ119864119901119894 = 120582 812058812058721198895 (119897119901119894 minus 119897(2)119901119894 )int1198792

0119902(2)3119901119894 119889119905 (9)



Δ119864119886119888 = int11987900119875(1)119888 119889119905 minus int1198792

0119875(2)119889 119889119905

= int11987900119901(1)119888 (119905) 119902(1)119888 (119905) 119889119905minus int11987920119901(2)119889 (119905) 119902(2)119889 (119905) 119889119905

(10)

int11987900119902(1)119888 (119905) 119889119905 = int1198792

0119902(2)119889 (119905) 119889119905 (11)







1198751198941198990 = 119875V119886119905 + 119875V119886119887 + 119875119888119910 + 119875119900119906119905 (12)119875V119886 = 119875V119886119905 + 119875V119886119887 (13)



1199011119860 119894119899 minus 1199012119860119900119906119905 = 119865119897119900119886119889 + 11989811990910158401015840 (14)




loadF

x

in0P

vatP

outP

valP

vabP

in0P

valP

vatPvabP

cyPm





(15)




1015840) (16)





(18)


Δ119864119889119890 = 119864119889119890 minus 1198641015840119889119890 = Δ119864V119886 minus Δ119864119886119888 (19)




X Time [s]

Y d

ispla

cem

ent [

m]


(a)

Y d

ispla

cem

ent [

m]

X Time [s]


(b)








X Time [s]

Y P

ress

ure [

bar]

two-stage

requirmentone-stage







two-stage

X Time [s]

Y P

ower

[W]

one-stage


two-stage

X Time [s]

Y E

nerg

y [J

]

one-stage

requirement




5 Conclusions



10000

input energy

30002000

other loss

throttling loss


1797 476

227471

2004 3461

TSP system

OSP system








Acknowledgments


References


































Journal of












Journal of







Volume 2018






Volume 2018












(a)

(b)

(c)


M

telescopic actuator

locking actuator 1

locking actuator 2

servovalve

servo valve 2

servo valve 1

filter

filter

motor

relief valve

pump

F

F1

F2

1

2







X Time [s]

Y F

orec

[N]











119875119894119899 = 119875119901119894 + 119875V119886 + 119875119888119910 + 119875119900119906119905 (1)



119864119889119890 = int1198790(119875119901119894 + 119875V119886 + 119875119888119910) 119889119905 (2)


1198751015840119894119899 = 119875(1)119901119894 + 119875(2)119901119894 + 119875(2)119886119888 + 1198751015840V119886 + 1198751015840119888119910 + 1198751015840119900119906119905 (3)



1198641015840119889119890 = int11987910119875(1)119901119894 119889119905 + int1198792

0(119875(2)119901119894 + 119875(2)119886119888 ) 119889119905 + int119879

01198751015840V119886119889119905

+ int11987901198751015840119888119910119889119905

(4)



Δ119901 = 120582 1198972 120588V2

119889 (5)



M


sensors



high-pressuresource



low-pressuresource



V = 119902119878 = 4120587 1199021198892 (6)


119875119901119894 = Δ119901119901119894 sdot 119902119901119894 = 120582 8120587211990211990111989431198895 119897119901119894120588

119875(1)119901119894 = Δ119901(1)119901119894 sdot 119902(1)119901119894 = 120582 81205872[119902(1)119901119894 ]31198895 119897(1)119901119894 120588

119875(2)119901119894 = Δ119901(2)119901119894 sdot 119902(2)119901119894 = 120582 81205872[119902(2)119901119894 ]31198895 119897(2)119901119894 120588

(7)



Δ119864119901119894 = int1198790119875119901119894119889119905 minus int1198791

0119875(1)119901119894 119889119905 minus int1198792

0119875(2)119901119894 119889119905 (8)


Δ119864119901119894 = 120582 812058812058721198895 (119897119901119894 minus 119897(2)119901119894 )int1198792

0119902(2)3119901119894 119889119905 (9)



Δ119864119886119888 = int11987900119875(1)119888 119889119905 minus int1198792

0119875(2)119889 119889119905

= int11987900119901(1)119888 (119905) 119902(1)119888 (119905) 119889119905minus int11987920119901(2)119889 (119905) 119902(2)119889 (119905) 119889119905

(10)

int11987900119902(1)119888 (119905) 119889119905 = int1198792

0119902(2)119889 (119905) 119889119905 (11)







1198751198941198990 = 119875V119886119905 + 119875V119886119887 + 119875119888119910 + 119875119900119906119905 (12)119875V119886 = 119875V119886119905 + 119875V119886119887 (13)



1199011119860 119894119899 minus 1199012119860119900119906119905 = 119865119897119900119886119889 + 11989811990910158401015840 (14)




loadF

x

in0P

vatP

outP

valP

vabP

in0P

valP

vatPvabP

cyPm





(15)




1015840) (16)





(18)


Δ119864119889119890 = 119864119889119890 minus 1198641015840119889119890 = Δ119864V119886 minus Δ119864119886119888 (19)




X Time [s]

Y d

ispla

cem

ent [

m]


(a)

Y d

ispla

cem

ent [

m]

X Time [s]


(b)








X Time [s]

Y P

ress

ure [

bar]

two-stage

requirmentone-stage







two-stage

X Time [s]

Y P

ower

[W]

one-stage


two-stage

X Time [s]

Y E

nerg

y [J

]

one-stage

requirement




5 Conclusions



10000

input energy

30002000

other loss

throttling loss


1797 476

227471

2004 3461

TSP system

OSP system








Acknowledgments


References


































Journal of












Journal of







Volume 2018






Volume 2018









X Time [s]

Y F

orec

[N]











119875119894119899 = 119875119901119894 + 119875V119886 + 119875119888119910 + 119875119900119906119905 (1)



119864119889119890 = int1198790(119875119901119894 + 119875V119886 + 119875119888119910) 119889119905 (2)


1198751015840119894119899 = 119875(1)119901119894 + 119875(2)119901119894 + 119875(2)119886119888 + 1198751015840V119886 + 1198751015840119888119910 + 1198751015840119900119906119905 (3)



1198641015840119889119890 = int11987910119875(1)119901119894 119889119905 + int1198792

0(119875(2)119901119894 + 119875(2)119886119888 ) 119889119905 + int119879

01198751015840V119886119889119905

+ int11987901198751015840119888119910119889119905

(4)



Δ119901 = 120582 1198972 120588V2

119889 (5)



M


sensors



high-pressuresource



low-pressuresource



V = 119902119878 = 4120587 1199021198892 (6)


119875119901119894 = Δ119901119901119894 sdot 119902119901119894 = 120582 8120587211990211990111989431198895 119897119901119894120588

119875(1)119901119894 = Δ119901(1)119901119894 sdot 119902(1)119901119894 = 120582 81205872[119902(1)119901119894 ]31198895 119897(1)119901119894 120588

119875(2)119901119894 = Δ119901(2)119901119894 sdot 119902(2)119901119894 = 120582 81205872[119902(2)119901119894 ]31198895 119897(2)119901119894 120588

(7)



Δ119864119901119894 = int1198790119875119901119894119889119905 minus int1198791

0119875(1)119901119894 119889119905 minus int1198792

0119875(2)119901119894 119889119905 (8)


Δ119864119901119894 = 120582 812058812058721198895 (119897119901119894 minus 119897(2)119901119894 )int1198792

0119902(2)3119901119894 119889119905 (9)



Δ119864119886119888 = int11987900119875(1)119888 119889119905 minus int1198792

0119875(2)119889 119889119905

= int11987900119901(1)119888 (119905) 119902(1)119888 (119905) 119889119905minus int11987920119901(2)119889 (119905) 119902(2)119889 (119905) 119889119905

(10)

int11987900119902(1)119888 (119905) 119889119905 = int1198792

0119902(2)119889 (119905) 119889119905 (11)







1198751198941198990 = 119875V119886119905 + 119875V119886119887 + 119875119888119910 + 119875119900119906119905 (12)119875V119886 = 119875V119886119905 + 119875V119886119887 (13)



1199011119860 119894119899 minus 1199012119860119900119906119905 = 119865119897119900119886119889 + 11989811990910158401015840 (14)




loadF

x

in0P

vatP

outP

valP

vabP

in0P

valP

vatPvabP

cyPm





(15)




1015840) (16)





(18)


Δ119864119889119890 = 119864119889119890 minus 1198641015840119889119890 = Δ119864V119886 minus Δ119864119886119888 (19)




X Time [s]

Y d

ispla

cem

ent [

m]


(a)

Y d

ispla

cem

ent [

m]

X Time [s]


(b)








X Time [s]

Y P

ress

ure [

bar]

two-stage

requirmentone-stage







two-stage

X Time [s]

Y P

ower

[W]

one-stage


two-stage

X Time [s]

Y E

nerg

y [J

]

one-stage

requirement




5 Conclusions



10000

input energy

30002000

other loss

throttling loss


1797 476

227471

2004 3461

TSP system

OSP system








Acknowledgments


References


































Journal of












Journal of







Volume 2018






Volume 2018









M


sensors



high-pressuresource



low-pressuresource



V = 119902119878 = 4120587 1199021198892 (6)


119875119901119894 = Δ119901119901119894 sdot 119902119901119894 = 120582 8120587211990211990111989431198895 119897119901119894120588

119875(1)119901119894 = Δ119901(1)119901119894 sdot 119902(1)119901119894 = 120582 81205872[119902(1)119901119894 ]31198895 119897(1)119901119894 120588

119875(2)119901119894 = Δ119901(2)119901119894 sdot 119902(2)119901119894 = 120582 81205872[119902(2)119901119894 ]31198895 119897(2)119901119894 120588

(7)



Δ119864119901119894 = int1198790119875119901119894119889119905 minus int1198791

0119875(1)119901119894 119889119905 minus int1198792

0119875(2)119901119894 119889119905 (8)


Δ119864119901119894 = 120582 812058812058721198895 (119897119901119894 minus 119897(2)119901119894 )int1198792

0119902(2)3119901119894 119889119905 (9)



Δ119864119886119888 = int11987900119875(1)119888 119889119905 minus int1198792

0119875(2)119889 119889119905

= int11987900119901(1)119888 (119905) 119902(1)119888 (119905) 119889119905minus int11987920119901(2)119889 (119905) 119902(2)119889 (119905) 119889119905

(10)

int11987900119902(1)119888 (119905) 119889119905 = int1198792

0119902(2)119889 (119905) 119889119905 (11)







1198751198941198990 = 119875V119886119905 + 119875V119886119887 + 119875119888119910 + 119875119900119906119905 (12)119875V119886 = 119875V119886119905 + 119875V119886119887 (13)



1199011119860 119894119899 minus 1199012119860119900119906119905 = 119865119897119900119886119889 + 11989811990910158401015840 (14)




loadF

x

in0P

vatP

outP

valP

vabP

in0P

valP

vatPvabP

cyPm





(15)




1015840) (16)





(18)


Δ119864119889119890 = 119864119889119890 minus 1198641015840119889119890 = Δ119864V119886 minus Δ119864119886119888 (19)




X Time [s]

Y d

ispla

cem

ent [

m]


(a)

Y d

ispla

cem

ent [

m]

X Time [s]


(b)








X Time [s]

Y P

ress

ure [

bar]

two-stage

requirmentone-stage







two-stage

X Time [s]

Y P

ower

[W]

one-stage


two-stage

X Time [s]

Y E

nerg

y [J

]

one-stage

requirement




5 Conclusions



10000

input energy

30002000

other loss

throttling loss


1797 476

227471

2004 3461

TSP system

OSP system








Acknowledgments


References


































Journal of












Journal of







Volume 2018






Volume 2018











loadF

x

in0P

vatP

outP

valP

vabP

in0P

valP

vatPvabP

cyPm





(15)




1015840) (16)





(18)


Δ119864119889119890 = 119864119889119890 minus 1198641015840119889119890 = Δ119864V119886 minus Δ119864119886119888 (19)




X Time [s]

Y d

ispla

cem

ent [

m]


(a)

Y d

ispla

cem

ent [

m]

X Time [s]


(b)








X Time [s]

Y P

ress

ure [

bar]

two-stage

requirmentone-stage







two-stage

X Time [s]

Y P

ower

[W]

one-stage


two-stage

X Time [s]

Y E

nerg

y [J

]

one-stage

requirement




5 Conclusions



10000

input energy

30002000

other loss

throttling loss


1797 476

227471

2004 3461

TSP system

OSP system








Acknowledgments


References


































Journal of












Journal of







Volume 2018






Volume 2018









X Time [s]

Y d

ispla

cem

ent [

m]


(a)

Y d

ispla

cem

ent [

m]

X Time [s]


(b)








X Time [s]

Y P

ress

ure [

bar]

two-stage

requirmentone-stage







two-stage

X Time [s]

Y P

ower

[W]

one-stage


two-stage

X Time [s]

Y E

nerg

y [J

]

one-stage

requirement




5 Conclusions



10000

input energy

30002000

other loss

throttling loss


1797 476

227471

2004 3461

TSP system

OSP system








Acknowledgments


References


































Journal of












Journal of







Volume 2018






Volume 2018









two-stage

X Time [s]

Y P

ower

[W]

one-stage


two-stage

X Time [s]

Y E

nerg

y [J

]

one-stage

requirement




5 Conclusions



10000

input energy

30002000

other loss

throttling loss


1797 476

227471

2004 3461

TSP system

OSP system








Acknowledgments


References


































Journal of












Journal of







Volume 2018






Volume 2018






































Journal of












Journal of







Volume 2018






Volume 2018















Journal of












Journal of







Volume 2018






Volume 2018








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