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Applied Ergonomics 34 (2003) 265271Aspects to improve cabin comfort of wheel loaders and excavatorsaccording to operatorsL.F.M. Kuijt-Eversa,*, F. Krausea, P. Vinka,baTNO Work and Employment, P.O. Box 718, Hoofddorp 2130 AS, The NetherlandsbIndustrial Design, TU Delft, The NetherlandsReceived 19 April 2002; received in revised form 25 November 2002; accepted 29 December 2002AbstractComfort plays an increasingly important role in interior design of earth moving equipment. Although research has beenconducted on vehicle interiors of wheel loaders and excavators, hardly any information is known about the operators opinion. Inthis study a questionnaire was completed by machine operators to get their opinion about aspects which need to be improved inorder to design a more comfortable vehicle interior. The results show that almost half of the operators rate the comfort of their cabinaverage or poor. According to the operators, cab comfort of wheel loaders can be increased by improving seat comfort. Besidesimproving seat comfort, cabin comfort of excavators can be improved by changing the cab design (including dimensions, ingress/egress), view, reliability, and climate control.r 2003 Elsevier Science Ltd. All rights reserved.Keywords: Cabin comfort; Operators opinion; Earth moving equipment1. IntroductionComfort plays an increasingly important role invehicle design. As machine operators of earth movingequipment often spend long hours in their vehiclesometimes even more than 8h a daycomfort is amajor issue in interior design of these machines.Operating earth-moving machinery is not a physicallyheavy job and can be sustained for long periods.Nevertheless, operating such a machine appears to bea risk factor for musculoskeletal disorders, especiallywhen the task is not interrupted by other workingactivities or breaks. Zimmerman et al. (1997) showedthat the main problems of earth-moving machineryoperators concern physical complaints in the neck/shoulder and low back region, general fatigue andfeelings of discomfort. This might be attributed to acombination of static load during prolonged sittingfrequently in awkward posturesexposure to wholebody vibrations, and handling and steering the machine(Zimmerman et al., 1997; Tola et al., 1988; de Loozeet al., 2000).A comfortable well-designed vehicle interior mayreduce awkward postures and provide an environmentthat stimulates optimal operator performance. Based ona literature review about musculoskeletal disorders andtheir risk factors, Zimmerman et al. (1997) made fourrecommendations for reducing work-related musculos-keletaldisordersamongoperators:minimizingofmagnitude and frequency of vibration reaching theoperator; locating controls optimally to minimize reachdistances, trunk flexion and trunk rotation; providingmaximum operator visibility from an upright supportedseated posture; and taking regular breaks to minimizethe effects of sustained postures. Improvements of cabcomfort are very often based on reducing the riskfactorsforwork-relatedmusculoskeletaldisorders(Zimmerman et al., 1997; Attebrant et al., 1997). Onlya few studies have mentioned aspects which operatorswish to see improved. Nakada (1997) describes thedesirability ranking for dump trucks and wheel loadersgiven by product creators, designers, design engineers,operators and young people. Nakada, (1997) shows thatmuch design attention has been paid to instrumentpanel/monitors and meters and the operator seat.*Corresponding author. Tel.: +31-23-55-49-938; fax:+31-23-55-49-305.E-mail address: l.kuijtarbeid.tno.nl (L.F.M. Kuijt-Evers).0003-6870/03/$-see front matter r 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S0003-6870(03)00032-2Unfortunately,theoperatorsopinionscannotbedistinguished in Nakadas study (1997).However, in order to design a comfortable vehicleinterior, the opinion of the operators is important asthey are the end-users of the machines. Their userexperience may be of great help designing a morecomfortable vehicle interior. The aim of the currentstudy is to find aspects mentioned by wheel loader andexcavator operators, which can be used to improve thecomfort of vehicle interiors in the future. In this articlewe describe the results of a questionnaire given to 273machine operators. They were asked their opinion abouttheir current machine, their future demands and aspectsthey considered important to work well with themachine. This allowed us to identify aspects that needimprovement in machine design.2. Method2.1. SubjectsA convenience sample was obtained through ap-proaching operators visiting Bauma (the worlds largestexhibition for construction equipment). Most of theparticipants were wheel loader operators (n 61) andexcavator operators (n 212). The others (n 65) wereoperators of several construction machines (e.g., mobilecranes, dozers, tower cranes, off-road trucks). Only theresults for wheel loader and excavator operators arepresented in this article, as they account for 18% and62.7% of the total number of respondents respectively.Figs. 1 and 2 show a typical wheel loader and excavator.2.2. QuestionnaireData were collected by means of a questionnairewhich was completed during an interview. The ques-tionnaire was divided into three parts: (1) characteristicsof the population, (2) evaluation of the current machinebeing operated, and (3) future demands on earth movingmachinery. In the first part we asked the operators age,years of experience as operator, the kind of machinerybeing operated and its age. In the second part of thequestionnaire, operators evaluated their machine byrating overall comfort and their opinion of specific partsof the machine on a four-point scale (very good, good,average, poor). Finally, two open questions asked aboutthe operators future demands: what improvementswould make the machine more comfortable and whataspects are the most important to work well with themachine.Fig. 1. Excavator.L.F.M. Kuijt-Evers et al. / Applied Ergonomics 34 (2003) 2652712662.3. Data analysisData were sorted by machine type, after which theresponses of wheel loader operators and excavatoroperatorswereseparatelyanalyzed.Withinthesegroups, operators of older machinery (X4 years old)were separated from operators of newer machinery (o4years old). In addition, the categories very good andgood were combined (very good/good) and thecategoriesaverageandpoorwerecombined(average/poor).Frequencytablesweremadeoftheoperatorsopinions about overall machine comfort and abouttheir opinions about specific parts of their machines.Chi-square was calculated between age of machine andoverall comfort and between age of machine and theoperators opinion of specific parts of the machine. Weassumed that if fewer than 80% of the operators rated apart of the machine good/very good, improvement ofthis part could contribute to a more comfortable vehicleinterior. In part three of the questionnaire, the operatorsindicated aspects to improve machine comfort andaspects they found necessary to work well with themachine. We classified these aspects into categories andcalculated the percentage responses.3. Results3.1. Characteristics of the populationBoth the wheel loader operators (mean age: 36.579.4years) and the excavator operators (mean age: 36.379.3years) who participated in this study, were experiencedwith a mean of 12.3 (78.1) and 13.4 (79.2) years ofservice, respectively. Half of the operators operatemachines less than 4 years old (53% of the wheel loaderand 50% of the excavator operators; see Fig. 3).3.2. Evaluation of current machine57.4% of wheel loader operators and 55.9% of theexcavator operators rated the overall cabin comfortgood/very good. Fig. 4 shows that operators of newermachinery (o4 years old) rated the overall cab comfortas good/very good more often than operators of olderFig. 2. Wheel loader.Age of machinesPercentage of machines per category0102030405060ExcavatorsWheel loadersMachines (%)less than 4 years old4 years or moreFig. 3. The participants machines are divided into two categories:machines o4 years old and machines =4 years old.L.F.M. Kuijt-Evers et al. / Applied Ergonomics 34 (2003) 265271267machines (X4 years old). This was found both amongwheel loaders (w21 8:5; po0:04) and among excava-tors (w21 23:0; po0:001). Seventy-eight percent of theoperators driving wheel loaders less than 4 years old,rated the comfort of their machine as good/very good.With excavator operators this figure was 81%. Theseresults show that during recent years the experienced cabcomfort of excavators and wheel loaders has improved.Fig. 5 illustrates the opinion of the operators aboutspecific parts of the machines less than 4 years old. Asseen in Table 1, fewer aspects of wheel loaders are ratedaverage/poor by more than 20% of the operators,than excavators. Common aspects which can contributeto increase of cab comfort are dashboard and displays,adjustabilityofseatsandcontrols,vibrationanddamping, noise reduction, and seat comfort. Excavatoroperators would also like to see improvement of climateGeneral opinion about comfort of the cabPercentage of operators rating good/very good020406080100ExcavatorsWheel loadersOperators (%)less than 4 years old4 years or moreFig. 4. Percentage of operators rating their machines good andvery good on cab comfort.Excavators less than 4 years old Percentage operators rating good and very good 020406080100020406080100Seat comfortAdjustablility of seat and controlsWay controls workPedalsDashboard and displaysViewClimate controlCab dimension/interior spaceMachines appearanceNoise reductionVibration and dampingOperators (%)GoodVery goodGoodVery goodWheel loaders less than 4 years old Percentage operators rating good and very goodSeat comfortAdjustablility of seat and controlsWay controls workPedalsDashboard and displaysViewClimate controlCab dimension/interior spaceMachines appearanceNoise reductionVibration and dampingOperators (%)Fig. 5. Opinion of excavator and wheel loader operators about specific parts of the machines.L.F.M. Kuijt-Evers et al. / Applied Ergonomics 34 (2003) 265271268control, improved machine appearance, and better cabdimensions (including interior space, ingress/egress),view, and reliability.3.3. Future demandsThe participants generated 467 items desired toimprove the machines comfort. We classified theseaspects into 15 categories (see Table 2). Fig. 6 showswhich features should be improved according to theoperators. Seat comfort, climate control and accessoriesare often mentioned for both wheel loaders (20%, 12%,15%, resp.) and excavators (21%, 19%, 12%, resp.).Excavator operators also mention cab design (includingdimensions, ingress/egress; 19%).The aspects considered most important to work wellwith the machine are summarized in Table 3. Machineperformance is by far the most important issue if welook at the averages. Other aspects like view andreliability play less important roles.Table 2Classification of aspects mentioned by operatorsCategoriesExamplesTCO (total cost of ownership)Costs of machine (procurement,service costs, rest value)Machine performancePerformance, hydraulics, gearServiceabilityCleaning of the machine,manufacturer serviceReliabilityReliabilitySeat comfortSeat pan, lumbar support, armrests, curvature of back supportAdjustability of seat and controlsAdjustability of seat height,adjustability of controlsOperabilityJoystick, steering wheel,interaction joystick and beamViewView of work, dead angles,position of mirrorsDashboard and displaysUsability of dashboard/controls,readability, absent information,position of displaysClimate controlTemperature, dust filters,ventilation, blower positionDesign/dimensions/ingress andegressDesign and dimensions of cabinand machine, position of steps,grab railsNoise and vibrationNoise, vibration, dampingAccessoriesRadio, fridge, storage space, cupholderSafety and stabilityFeelings of safety, stability ofmachineEnvironmentNoise outside the machine,exhaust fumesTable 1Aspects rated average or poor by more than 20% of the operators for both wheel loaders and excavators less than 4 years oldWheel loadersExcavatorsAspectOperators (%)AspectOperators (%)Dashboard and displays32.0Seat comfort*29.5Adjustability of seat and controls31.2Vibration and damping*27.0Vibration and damping*28.1Dashboard and displays26.0Noise reduction28.1Climate control*24.1Seat comfort24.9Machines appearance24.0Cab dimensions, interior space, ingress and egress*22.3Noise reduction*21.9View21.9Adjustability of seat and controls*21.0Reliability20.9Aspects marked by* are rated by significantly more operators of newer machinery (less than 4 years old) as good or very good compared tomachines older machinery (4 years or more).Fig. 6. Aspects which need improvement according to excavator andwheel loader operators.L.F.M. Kuijt-Evers et al. / Applied Ergonomics 34 (2003) 2652712694. DiscussionThe aim of the current study was to find aspectsmentioned by wheel loader and excavator operatorswhich can be used to improve the comfort of vehicleinteriors in future. In order to find these aspects, weasked questions about three issues.*about comfort of specific aspects of the cab (rating ona four-point scale);*about aspects necessary to improve the cab comfort(open question);*about aspects important to work well with themachine (open question).Excavator and wheel loader operators mentionedimproved seat comfort, climate control and accessoriesas ways to increase cab comfort. Excavator operatorsalsomentionedcabdesign(includingdimensions,ingress/egress).Theseaspectswerealsoratedasaverage/poor by more than 20% of the operators(except accessories because this was not an item in thesecond part of the questionnaire). Other aspects whichcan be taken into account with cab design are thosewhich operators mention as most important aspects towork well with the machine. Especially when theseaspects are also rated as average/poor by more than20% of the operators, they need special attention.Improving these aspects have priority in designing amore comfortable cab.In our study, we collected our data among visitors tothe Bauma exhibition in 2001. The advantage of thiscollection method is that it is possible to reach a largegroup of operators within a short period of time, at thesame time getting a large response, which wouldnormally be very difficult. A disadvantage might bethat the vast majority of respondents were Germanwhich could mean that the results have a limited validityamong operators in other countries. The Germanoperators may have other ideas about cab comfort thanoperators, who work in other countries. The demands ofthe operators on their machine depend on the workingenvironment (e.g., climate, landscape, dust) and theirtasks (e.g., driving off road, driving on the main road),which can be different between countries. Besides, theoperators based their opinion on their current machine.It is possible that in Germany certain brands areoverrepresented compared to other countries and thatthe operators opinion might vary according to thebrand. The most common brands would thereforeinfluence the results of our study as many operatorsuse one of these machines (Excavators: brand A 22.6%,brand B 22.2%; Wheel loaders: brand A 21.3%, brand B18%, brand C 11.5%).Since we used a short questionnaire to collect thedata, no detailed information could be asked. The goalof our study was to get a global view on the operatorsopinion. The open questions gave the operators theopportunity to think open-minded which may rendervaluable information. Open questions are less suitablefor data analysis, because we needed to categorizeanswers. Inevitably information is lost in this process,but the goal of obtaining a global view was neverthelessachieved.Our results show that seat comfort, climate control,accessories (for wheel loaders and excavators) and cabdesign (including dimensions, ingress/egress), view, andreliability (for excavators only) are the aspects whichcan improve cab comfort. All these aspects are ratedaverage/poor by more than 20% of the operators andthey are also mentioned as aspects which need improve-ment in order to increase cab comfort. In our opiniondesigners should give priority to these items whenredesigning cabs. It is interesting that operators didnot mention vibration as an aspect which can improvecomfort, as it was ranked high on the list of machineparts rated average/poor. Besides, whole body vibra-tion is a serious health hazard (Houtman et al., 2001). Itis possible that the operators did not mention vibrationbecause they may see vibration as an engine property oran inevitable consequence of working on earth movingequipment. Operators might have the idea that vibrationcannot be reduced by redesigning only the cab. It is,however,unclearwhyoperators did notmentionvibration.When comparing excavators and wheel loaders,improving seat comfort is an issue for both wheelloaders and excavators. Although seat comfort inexcavators has been improved during recent years (seeTable 1), improvements are still necessary. However,this is not easy as sitting comfort depends on many otherfactors more or less related to seat design: e.g.,adjustability of seat and controls, vibration and damp-ing, and view. For example, a bad view from the cabincan result in awkward body postures, which reducescomfort in spite of a comfortable seat.Beyond the common aspect seat comfort, manydifferences exist between wheel loaders and excavators.One difference we found between the excavator and theTable 3Aspects considered most important to work well with the machineaccording to wheel loader and excavator operatorsWheel loadersExcavatorsAspectResponses(%)AspectResponses(%)Machinesperformance40.3Machinesperformance37.0View12.5Reliability14.6Reliability11.8View11.5Operability11.1The aspects noted in more than 10% of the answers are presented.L.F.M. Kuijt-Evers et al. / Applied Ergonomics 34 (2003) 265271270wheel loader was that excavator cab design (includingdimensions and ingress/egress) needs improvement. Thisdifference may be explained by access and space. First,there is a difference in machine access with gripsgenerally quite wide apart and steps to the cabin farfrom optimal, being either too high or too narrow.Operators could experience this as a problem. Secondly,there is a fundamental difference between wheel loadersand excavators in the space available for the cab. Withthe present design, excavators have a limited widthavailable for the cab as it must be positioned betweenthe boom and the left machine side, leaving approxi-mately 1m for the cab.Anotherdifferenceisthatimprovingviewcanincrease the cab comfort of the excavator. View is avery important aspect to work well with the excavator.The boom of the excavator has a wide range of motionand the operator needs to see the bucket for the fullrange. A comfortable cab provides a clear view of theworkplaceandthebucket,withoutnecessitatingawkward postures.In the introduction, we stated that comfort plays animportant role in cab design. It is therefore interesting tofind that the operators did not mention comfort as oneof the most important aspects to work well with themachine. They mentioned aspects such as the machinesperformance, reliability, view and operability. It seemsthat operators think first about the basic requirementsneeded to perform their task and apparently do not seecomfort as one of them.If we compare our results with the results of Nakada,(1997), in both studies the operator seat is ranked asimportant. Instrument panel, monitors and meters arealso ranked as important in Nakadas study. In ourstudy vibration, dashboard and displays are high on thelist of parts rated as average/poor by more than 20%of the operators, but they are not seen as aspects thatcan improve cab comfort. Nakadas study did notmention vibration at all. A reason for this may be that inour study, experienced operators played a larger rolethan in Nakadas and because that study was focused oninterior design.An increase in cab comfort has been achieved duringrecent years. From Table 1 it seems that wheel loadershave made progress on fewer aspects than excavators.But in fact, the improvements of specific aspects ofwheelloaders(i.e.,machinesappearance,climatecontrol, and view) were of such a high level that theseaspects were rated as average/poor by fewer than20% of the operators and are therefore not mentioned inthis table. However, 27.7% of the excavator operatorsand 25.0% of the wheel loader operators of machineryless than 4 years old rate the cabins comfort average/poor. These results show that improvement of cabcomfort is still needed. In our study, we
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