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Development of electric-hydraulic control system for

large-sized mining shovel

Manabu Tamura, Nobuaki Matoba*1), Kiyoshi Takahashi*2)*1) Construction Machinary Laboratory , Takasago Research & Development Center

Mitsubishi Heavy Industries, Ltd. 2-1-1 Shinhama, Arai- Cho, Takasago, Hyogo Pref 676 JAPAN*2) Construction Machinary Department , Kobe Shipyard

Mitsubishi Heavy Industries, Ltd. 1-1-1 Wadamisaki- Cho, Hyogo- Ku, Kobe, Hyogo Pref 652JAPAN

ABSTRACTThe world-largest class hydlaulic mining shovel has recently been developed by Surface MiningEquipment for Coal Tecnology Research Association(SMEC). To operate with huge weight and inertia, anewly-developed electric-hydraulic control system aided microcomputer processing is adopted,resulting in superior controllability, greater production and better fuel consumption. This paper introducethe abstruct of the shovel which is fully used higher electronics control technologies.

1. PrefaceOur company participated in Surface Mining

Equipment of Coal Technology ResearchAssociation (SMEC) and jointly developed theworld-largest class hydraulic mining shovel.SMEC was established in March, 1983, by 11companies of the related industries fordevelopment of surface coal mining equipment

(large-sized mining shovel and large-sizedwheel loaders) that contributes to rationalization ofcoal mining overseas and to constant supply ofcoal in line with the energy policy of our countryfor development of alternate petroleum energy.For development of the large-sized shovel, 7companies joined in the project and our companytook part in developing the upper structure exceptattachments, we made efforts for its developmentin close co operation with the collaborators forcomponent development. This paper is to introducean overview of the machine developed and thenewly applied electric-hydraulic control R&D

projects.

2. Intent of developmentThe hydraulic excavators introduced to our

country 25 years ago have made a remarkabledevelopment since then, and having beensupported by advanced hydraulic technology andneed of larger machines, even 100-ton classmachines appeared in Japan in '70s. Their highversatility was valued and are widely used inengineering works including urbanengineeringworks and darn construction. In themining industry, too, they are partly applied todevelopment drilling and loading. This is becausethat high self-supporting capability without high

pressure power supply, bucket handling with highdegree of freedom and high maneuverability

(gradability and swingability at spot) are valuedby the surface mining industry who digs down

ground surface and excavates sloped coal seam. Inoverseas surface mines, the trend toward larger-sized dump trucks has been used and those of 120

-200 ton carrying capacity are increasing

gradually. This machine developed was intended tocombine in function with dump trucks of this class,and adopted the bucket capacity of 15-30 m3, themachine weight of 420 ton and the engine outputof twin 900 kW taking account of loadingcompatibility (loading weight and cycle time,required loading time and geometric dimensions)and workability on bench of 15-18 m high.Table 1 shows its basic specification.

Tablet basic specification

Fluid Power. Edited by T. Maeda. (C) 1993 E & FN Spon. ISBN 0419191003.

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As seen above, this machine is significantlylarger in weight and output than the existing largestdomestic machines requiring new design of all ofthe components. It required the design forrealizing more than 10 years of service life ofmajor components, the research of manufacturingtechnology, the design of larger capacity engineand hydraulic equipment. In addition to the

problems of strength and functions of structures,hydraulic equipment, etc., larger sizing ofhydraulic equipment is said commonly thatreliability would be deteriorated in a geometricseries and that there would exist the limit of largesizing. From the standpoint of reducing thenumber of items of components and parts, thismachine adopted the large-sized hydraulicequipment of large capacity arranged in parallel tosatisfy the capacity. Further, to give attention torotational motion of the shovel on vertical andhorizontal surfaces, the inertia force becomes 5times of the existing largest machine (160 t), and aconsiderable difficulty was assumed to arise forattaining controllability and responsibility at thetransition period similar to small and medium-sized machines. Deterioration of controllabilitywould spoil the work efficiency and thecomfortability particularly required for large-sized machines owing to dull movement,oscillation of machine body when controllingheavy cargo lifting and shock at each action end.

To realize efficient operation of such a system,easier handling and energy saving, it is essential toadopt highly advanced control technology.

Figurel R & D themes of electronic control system

3. Design philosophy of electronicControl System

If the tremendous inertia force would besubjugated to attain speed controllability wideenough from slow speed to fast, or if a bucketcould be freely controlled only by hands and feetof operators, it contributes of improvement of

productivity. And, on working condition variable atany time, if any measure would be obtained toeffectively operate a system multiply combinedand to effectively utilize inertia and kinetic energystored in a machine while its shovel action, thisalso contributes to improvement of productivity. Inthe case of this machine having many acomponent, if it has not the functions to instantlydo operation spread over anywhere and tomomentarily transmit its result to others, thecontrollability expected as mentioned above cannotbe realized. From the viewpoint of above, theelectronic control system integrating amicrocomputer in the control system was adoptedfor improvement of controllability, energy saving,and low fuel consumption.

Figure 1 shows the R&D themes tasked by thisdevelopment project. To classify them broadly, forenergy saving are 1) effective use of engine power,2) HST swing control, and 3) regenerative energycontrol, and for improvement of controllability are4) optimum power distribution and 5) semi-automatic control of implements. Still moresimplification and parts standardization to replacethe conventional system to incorporate a linkageinto each implement for locus and attitude controlof a bucket, the electronic control was applied todo these functions, thereby, its structure issimplified and strength and reliability areimproved. Further, to make the most of thecharacteristics of mechatronic control, the systemis simplified and the parts are standardized bymaking various hydraulic valves all in commonand by dealing with variation of control bysoftware.

4. CompositionThe mining shovel is composed, as shown on

Figure 1, of the undercarriage equipped withcrawler independently driven to both right and leftand the upper structure installed on it via the swingbearing. On the upper structure, operator's cab,engine, power transmission, and other devices ofauxiliary functions are arranged at its rear end.Counterweight is fixed. At the front of the upperstructure, implement to dig and load are installedby pin connection.

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Figure2 Schematic diagram of control and driving system

Figure3 Basic hydraulic diagram

Figured Sectional drawing of electric hydraulic transformer

4.1 Arrangement of major componentsFigure 2 shows the schematic diagram when

viewing mainly of control and driving system.When the operator starts the engines and handlesthe joysticks, electric signals of what, to whichdirection and by what a speed are transferred to themain controller. These signals are operatedaccording to various control programs betweenengine pump and valve controller, sent to eachequipment as pulse signals and converted toelectric hydraulic for driving them for necessaryamount.

4.2 Hydraulic circuitAs shown on Figure 3, engine output is

transferred to speed up gear and converted tohydraulic energy by hydraulic pumps fitted atoutput shaft. Pressure oil from hydraulic pumps of2 systems at both sides is transferred to hydraulicvalves here it is distributed to cylinders andhydraulic motors. Hydraulic valves for hydrauliccylinder control are combination valves combiningspool valves and poppet valves and are applied to

proper use for respective purposes. All hydraulicvalves are equipped with electric-hydraulictransformers by stepping motor system. As shownon Figure 4, turning angle of stepping motor ischanged to pilot spool displacement by action ofeccentric cam to control pilot pressure, and by thisaction, main valve is controlled. Pressure oil fromhydraulic pump is connected in parallel to each ofhydraulic valves. This is to cope with sequentialoperation proper to the shovel, which is driven inorder of action and pump priority for operation the

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operator requires.

Hydraulic swing pumps mounted on engines of

both sides are directly connected to hydraulicmotors to form HST circuit. Command for

operation from the operator is given to electric-

hydraulic transformer for control of cam plate of

pumps, and pump discharge becomes inlet flow torotate output shaft. Return oil from each actuator is

returned to hydraulic oil tank through high

efficiency filters and hydraulic oil cooling circuit.

Figure 5 Schematic diagram of electronic control system

(a) Common RAM

(b) Distributed Common RAM

Figure 6 Decentralized common RAM method

4.3 Electronic control systemFigure 5 shows an outline of the electronic

control system. This system employs the

hierarchized and decentralized system to controlvarious components including engines, hydraulic

pumps and hydraulic valves with high speed andhigh accuracy. At the lowermost layers, componentcontrollers are installed to directly controlcomponents, and above it, system controllers arearranged for multiple control of componentcontrollers. These system controllers are groupedinto 10 systems for usage of each component andcontrolled by main controller of the uppermostlayer. To connect controllers arranged at various

parts of machine body and to realize mutualtransfer of control signals, this system adopted theoptical fiber signal transfer control system of highspeed and high reliability expanded from thecommon RAM (Random Access Memory) system.The common RAM system is the system, as shownat the upper part of Figure 6, to connect multiplecontrollers or processors and one RAM by a bus orserial line for data transfer between controllers viaRAM. The decentralized common RAM system isthe system having a separate transfer line and acommunication controller that bus is divided basedon this common RAM, and RAM is provided pereach divided bus for mutually copying of data ofRAM. The decentralized common RAM system isshown on Figure 6, and an outline specification ofthe communication controller on Table 2.

Table 2 Specification of Communication Controller

It also has the operation management system to

detect status of each component and to centrally

display them on monitor in operator's cab, and

processor to process signal from various sensorsare mounted in 2 sets of engine pump control units.

Information collected here is transferred mutually

with operation managing controllers in main

controller by the "RS 232C communication

system", a common low speed signal transfer

system. Operation managing controllers in main

controller are so designed to process failure

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diagnosis and operating information, transmit datato plasma display in cab, transfer diagnosisinformation to common RAM, inform operatingcondition to control system, and when failed, totake necessary action by control system.

5. Development itemsFor organic connection with the electronic

control system, preliminary testing of elementswas frequently conducted including checking ofreliability and durability.

5.1 Efficient use of engine powerThe power control system has been developed to

automatically control total power of multiple

pumps not to exceed engine power when load ischarged, and consists of the following.

(1) From product of hydraulic pump dischargerequired by control lever and pump discharge

pressure, engine load is predicted and converted torack displacement.This is added as feedforwardsignal to PID output of engines to enhanceresponse of rack against load charging and tocontrol variation of engine revolutions.

(2) Sum of PID output of engines andfeedforward signal are controlled not to exceedmaximum rack command by controlling swash

plate angle of pumps in order that maximum outputof engines and pump load are matched. Figure 7 isan example of performance measurement byvehicle using this control system. Variation ofengine revolutions when maximum load is chargedshowed about 100 rpm which means an extremely

good characteristics.

Figure7 Test data of engine revolution drop in sudden load rise to max

Figure8 Block diagram of swing control system

Figure9 Test data of HST swing control

Figure 10 Block diagram of energy regenerative control system

5.2 HST swing controlThe HST swing control system was completed

for smooth acceleration and deceleration at start

and stop of swing system, for relief preventive ofhigh pressure line and for regeneration of energystopped. Since simple pressure feedback cannot

attain pressure control, the control system asshown on Figure 8 was made up including positivefeedback of speed of hydraulic motors to it. Itsmeasurement using a vehicle proved good

performance as shown on Figure 9.

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5.3 Energy regenerative controlThe most important to contribute to energy

regeneration is when sequential operation isperformed from dumping position with bucketlifted to the next digging position. For thismachine, poppet type hydraulic valve is providedat return side of cylinder for use as regenerativevalve and discharge valve resulting in nil of energyloss, thus, this energy is utilized for other systemsto improve work performance of the machine.Figure 10 shows the block diagram of controlsystem. Fundamentals of control are bottompressure of cylinder, and when it is high,regeneration is controlled by actuating poppet typehydraulic valves to meet retraction of cylinder.

5.4 Optimum power distributionCooperative control of engines, hydraulic pumps

and hydraulic valves is performed by integratingrequired flow to each actuator of swing system andimplement system based on electric signals ofjoystick and by setting swash plate of hydraulicpumps and priority of travel indication of eachhydraulic valve, and priority control of hydraulicvalve each other is also performed.

5. 5 Semi-automatic control ofimplements

For improvement of controllability and easieroperation, complex operation of implement system

has been realized by handling one lever. Forinstance, it includes level crowding control,constant bucket angle control and origin returningcontrol after dump loading.

5.6 Operation managementThis system has the monitoring equipment in

operator's cab to display operating condition orfailure information. This monitoring board hasdisplays of vehicle operation, semi-automaticoperating condition, alarm to operator, productionand menu. Also, when further information isneeded for failure or for maintenance, otherdisplays are shown if menu numbr is properlyselected. The following are typical displays.

(1) Display of operating conditionEngine revolutions, oil temperature, and residual

oil are monitored and displayed by bar graphs, andautomatic lever lock when operator is not seated,condition of ladder and lift if up or down, positionof upper structure against undercarriage androtating condition of oil cooler fan are displayedby graphics.

(2) Display of alarmBased on information from various sensors,

result of failure diagnosis and failure condition aremonitored and displayed, and if serious, alarmsound is outputted.

(3) Displays of menu and further systeminformation

By manipulating keyboard, operating conditionof each component can be displayed. For example,as for hydraulic pumps, command values of swashplate angle, feedback value of cam plate angle,pump pressure, etc. are displayed. By thesedisplays, operating condition of each componentcan be seen obviously, and maintenance andservicing can be easily carried out. It also has themenu to display data of common RAM so thatoperating condition of electronic control systemcan be watched and failure of control system canbe detected.

6. ConclusionThis prottype machine so developed was shipped

to the surface coal mine in Queensland, Australia.It was re-assembled, adjusted, and tested in thefield, and engaged in exploded rock strippingoperation for about 2 years. It was tested ofdurability of each part of the machine, particularlythe control systems, for perfection of thetechnolQgy, and the maintenance techniques shallalso be established by degree. We confirmed theexcellent controllability initially aimed at. Theseprecious experiences of electric-hydrauliccontrol system's reliability or durability are nowapplied small-sized hydraulic excavators.