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Sideloaders—a case study in the port industry
Apphed Ergonomws, 4.3, 163-167
Side loaders-a case study in
the port industry N.M. Hartwell Birkbeck College This report is an evaluation of a vehicle used in the port industry for handling containers. The vehicle is a self-loading lorry which both transports and stacks the containers w i t h i n the port. Three aspects of the evaluation are discussed in the operating context: internal and external visibility, and the cab layouts. It is concluded that the vehicle has a restricted view to the rear, although with care this can be catered for. The design and position of the cab, however, can demand extreme and uncomfortable postures on the part of the driver. Certain anoma lies in the cab control and display layouts are also briefly discussed, with a view to standardisation and a reduction of the driver's work-load. The main problem is seen as one of the integration of the driver/operator w i t h a machine with t w o discrete functions. The visibility and posture problem areas are considered to stem from the compromises dictated by the nature of this dualfunction vehicle. Imperial units are retained since containers are specified by the ISO on the basis of American measures.
There has been a major revolution in the cargo handhng field over the past decade due to the world-wide introduction of the system of containers. The advent of th~s system has posed many problems to the various port operators due to the cost and dwerslty of the mechamcal handling methods avaflableo My work is part of an evaluauon of just one of these systems, sideloader operations. The sldeloader has been developed from early vehicles used for handhng steel or umber where the use of a forkhit truck would be inappropriate. A typical general purpose sldeloader is shown m Fig 1. The container handhng vehicles differ only m size and m the addmon of a large hftmg frame. The vehicle is basically a self-loading lorry of large proportions. The machine's funcuons are as follows The driver stops abreast of the container to be hfted and lowers a set of stabfl~ser jacks~ He then traverses the mast assembly across the bodywork to the right-hand side and lowers the large hftmg frame on to the container. The majo~ skill reqmrement for the driver is to ahgn this frame accurately relatwe to the box so that the four locking pros, or tw~stlocks, can be engaged. The container is then hfted and the mast and load are traversed back across the bodywork to be placed on the loading platform. The mactune is then driven off to the unloa&ng point.
Th~s report Is based on a paper read at the 1973 Annual Conference of the Ergonomics Research Society titled An ergonomic evaluation of the container handling sldeloader. The work was financed by the Social Science Research Councd and was comm=ss=oned by the National Ports Councd.
Fig 1. General purpose sldeloader
The Port Typical container ports use sideloaders as a link m the mechamcal handhng system. Ships are unloaded using large gantry cranes and the containers are then stored to await chspatch by road or rail. The drwer of the sldeloader undertakes a shuttle service between the quayslde, &spatch and storage areas and serves the dual thnctlons of both rapld transport and mechamcal handhng of its 20-30 ton load. Since these mactunes cost up to £50 000, any defects
Applied Ergonomics September 1973
163
in the ergonomic layout or design which adversly affect the driver can soon be seen an the repair bills. The ports are by no means uniform in layout, surfacing, hghtmg or traffic and tlus can place hmltataons on certain types of operauon. Machines whxch work well under optmaum condmons may become increasingly ineffective as these conditmns deteriorate. Poor working condmons and bad weather can affect the best design of machinery and the cost of a poor layout can be measured m terms of accidental damage occurnng m the storage areas and m the increased cycle times needed. The container berth must also be designed to cater for the hm~tatlons of the machines themselves and the hazards of operatmg the system ~tself, such as the chstoruon of the roadways by the heavy ground loadmgs of the containers. Off spillage ~s a common event and this can make the roadways very shppery at trmes. There ~s also the problem of the safe integration of road and dockside traffic wathln the dispatch areas. All of these points are included to glve a rough p~cture of the dock environment and the problem areas where ergonomics can make a contrlbut~on. Driver training and the most efficient design of both cab and machine can help, but cannot be expected to cure all of the problems inherent In the use of machines for container handhng.
The S t u d y Bearing this m mind, two models of s]deloader were chosen for the analysls, handtmg 20 and 40ft containers respectively. These machines differ from the design above m that they both have a cab wbach can be traversed across the front of the machine. Apart from the hard data m terms of photographs and measurements, the fieldwork was fairly straightforward. The drivers and maintenance workers were interviewed at three ports using the critical incidents techmque to try to hnk these me,dents to actual accidents and the machine's desagn. Perhaps the best source of comparatwe data is ]n the work of one of my colleagues, Mr Wdkmson, who has just wntten a s]mdar report on a compeutive machine, the straddle carrier (Wdkmson, 1972), and some of the methods developed m his study have been incorporated m my own report. Apart from this, there ~s httle duectly comparatwe data avadable m this field, except for some unpubhshed work by the British Rad Department of Ergonomics.
Results Th~s report can be considered an three secuons internal and external ws]bdlty, and the cab layouts. Vlslbd]ty cnterm, both internal and external, are important, tor ]t is when a driver cannot see what he is doing that accidents can occur. The records of such accadents, if kept, provide a rough and ready mdlcatmn of some of the problem areas that may warrant special attention. The study of vlslbdlty Is just one of the ways of studying the design of vehicles, but with some far reaching consequences.
External v i s i b i l i t y This ]s the vlslbthty of objects m the vacm]ty of the machine, but not pa~t of it.
164
AppliedErgonomics September 1973
The cntenon by wtuch external visibility is measured here is one of a human figure who maght be m the vicinity of the machine. The machines differ in design and type and it ~s pomtless to discuss wsibdlty w~thout any quahfications as to the uses to which the machines are put. S~deloaders have two dastmct phases m thelr operating cycle, those of transport and stacking. In the transport mode, the driver needs only to take account of the external VlS]bthty. This is necessary for the negotmtmn of any obstacles and for drlwng both within the container stack and on the quaysldeo To do this, as on any road vehicle, the driver needs to be able to gauge the clearances reqmred for his vehicle's passage, and the minimum spaces reqmred for turning. In these respects, sldeloaders generally have an acceptable design, due to the forward mounting of the cab. The fixed cab machines are at a shght disadvantage when loaded, however, as the driver's vaew to the nght is then restricted by the bulk of the machine's load, When the driver attempts to reverse a sldeloader, he has a much more restricted field of view, which ]s dlustrated m Fig 2. Thas Vlslbd]ty map shows the 20ft container handhng sadeloader with a traversing cab and the shaded areas to the rear represent the bhndspots. The double hatched area shows the arc m whach a man or object under 6ft (2 m) tall would be mvaslble to the drwer m the cab at posmon A, w~th the vetucle unloaded. Once loaded, the bhndspot expands to cover the whole of the shaded area to the rear. There xs no outer hmlt to these bhndspots and within their area objects as large as containers may be invisible at umes. One instance as noted where a driver reversed into a small van and pushed it for some 10 yd (10m) before he was made to stop.
Cab position The driver can Improve his view to the rear to some extent by traversing the cab from A to B and leaning out of the window to see down both sides of the vehicle,
5 ft
t
Veh,cle and drwer facing [ ] Areas vlsJble at all times [ ] Dr,vet unhkely to s.ee any thm 9 less than 6ft tall .~ in th,s area [ ] Driver unlikely, to ~.~ ~A ~/~
see anything Jess than Oft toll ~n this area when dn~r,th a2Oft
i
Fig 2. S,deloader vlsibd,ty map (cab traversed to right-hand side)
although this is not ergonomlcally commendable. The drivers interviewed nevertheless preferred to keep the cab on the nght (posmon A). Th~s ~s so that they can accurately ahgn the machine next to the container to be hfted and closely observe the loading operations. What they lose by not moving the cab is to some extent compensated for by the fact that once they revert to the dnvmg role, they have a stable vantage point. This ~s as against the problems that they would otherwise encounter from driving a machane with both left and right hand drive. The reader may v~suahse th~s by considering the transient problems inherent m crossing the Channel and adapting from the British to the Continental traffic system. The driver of a fixed cab sideloader has none of these problems, although he ~s relatwely further away from the right-hand loachng s~de of the machine, and he must therefore exercise greater skill m al~gmng has machine pnor to hftmg. The v~sthlhty map for such a machine (w~th the cab at pos~uon C) ~s essentially the reverse of the one shown, and from posmon C the vaew to the right ~s severely hm~ted when loaded. Th~s calls for even greater skill when the dnver has to approach a stack, lorry or railway wagon to deposit has load. These problems call for s~mple palhauves 1 The bhndspot to the rear can be catered for m the ports concerned by keeping to a circular flow of traffic from the storage areas to the quaymde and back. Thas would at least avoid the need for frequent reversing, 2 The lanes ms, de the storage park must be straight and well marshalled to allow for the bhndspot which occurs to one side when the machine ~s loaded. Th~s would avoid the accidents which happen where s~deloaders have struck containers on their bhnd side,
t
/
,-1
I
,,l.
The fitting of an intermittent horn for reversing movements would be of some use m exastmg layouts to warn other drivers and stray people who may not be aware of the fact that the dnver cannot see them. Marrors would only be of use ff they could be mounted where it is ~mposslble to break them. The visibility map pertalmng to the larger model sldeloader stuched is not presented here as It Is somewhat comphcated by the fact that its view to the rear ~s obscurred by the bodywork, sance tts cab ~s mounted at ground level and the loading platform extends over the dnver's head.
Internal visibility This is the vlsiblhty from the driver's seat of the van,us operating parts of the machine, mduchng the load. The external vlsibfllty of the slddoader xs a measure of the vasual profile m the horizontal plane. At most ports, the containers are stacked up to three h~gh and the internal vlslbthty ts therefore also compnsed of the visual profile m the vertical plane. Dunng the loading and unloading operations the driver has to integrate these two profiles to achaeve a three-chmens~onal image of the operauon of his machine° It xs essenual for the efficient handling of containers that the dnver can accurately place has hftmg frame on top of the container to be hfted and that he can see the insertion of the tw~stlocks rot, the four container corner posts. If he is to do this repeatedly and accurately, there must be no sen,us difficulty or discomfort inherent m the task as thas may lead to fatigue and subsequent damage to either the machine or the containers. Slddoaders do present such chfficultles and dascomforts to the driver as can be shown by Fig 3. Thas dmgram shows the front view of the smaller sldeloader studied, m the process of lifting a container. From thas picture It may be apprecmted that the drwer m pos~taon A can accurately see the engagement of the tWlstlocks when hftlng a container from the ground or from a lorry trader or railway wagon. The higher that the containers are stacked however, the hagher becomes the angle through whach the driver must turn his head in order to observe the lifting frame.
\
The larger model sldeloader stuched has its cab at ground level or posmon B on the chagram. From this posit]on the driver ~s at a defimte chsadvantage, since for two or three-hagh stacking he must look upwards at angles approaching the vertical.
lZ
I
JJ J JJJJJJJJJ Fig 3. Front view of s~deloader
W~th both of these machines it ~s possible to traverse the cab to posmon C where the cab is to be found on fixed cab sldeloaders. From this posmon the extreme angles required are considerably reduce& Thas is, however, at the cost of an extra operation In the work-cycle or the extra difficulty m approaching the container stack w~th the critical clearance on the bhnd side.
Driver posture It is not so much the VlSlbdlty m the verUcal plane which results m complaints of backache from the drivers, but the combmauon of having to look both upwards and
Apphed Ergonomics
September 1973
165
to the rear at the same time, due to the forward position of the cab. Before a dnver can hft a container he must observe the engagement of both pairs o f twlsflocks, both fore and rear. Due to the constraints of the window pillars and the mast assembly this means that he must lean out o f the cab window to l o o k along the side of the vehicle to see the rearmost pair. This movement ~s accentuated m the case o f 40ft containers winch are handled by the larger machine with its low slung cab. The c o m b m a t m n of three Ingh staclong with 40ft boxes is to be avoided where possible, unless it ~s possible to pre-select drivers on the basis of neck flexabthty. This situation is further complicated by the tack of a swivel seat on the larger machine, as well as the restrlctmn of cab width which prevents the driver from turning 90 ° to the right where he could accomodate these movements more comfortably. Within the present cabs, the best solution would be one of provl&ng a seat with a lower backrest. This would allow the driver's shoulderblades to turn more freely and thereby distribute the neck torsion more evenly down the spree.
The
cab
®®Q I
/
layouts
While the visibility of the controls and &splays within the cab is of great importance to the driver of a sldeloader, there are so many different layouts at present m use that it ~s necessary to hmlt these considerations to the study of just two &fferent cabs for the purpose of brevity and clarity.
L _ _¢ ......
(~
____
)
F=g 4. Cab of 20ft s=deloader
The side views of the cabs o f the two machines studied are given m Figs 4 and 5. The main comment which can be made ~s that despite the ~dentlcal functmns of the two machines, the layouts are completely different. Neither possesses any clear advantage over the other due to several factors. Fig 4 shows the cab of the smaller machine. This ' m o d e r n ' design is marred by the following details 1. The driver's foot-space to the right IS obstructed by the large cab heater on the floor, makang it ~mposslble to use the svavel seat properly. 2 The chals and warning hghts are distributed around the cab with httle thought to VlSlbthty. 3. The gear levers (seen here end-on) are m o u n t e d so close to the fascm under the steering wheel that the drivers scrape their knuckles when changing gear. Fig 5 shows the cab o f the larger mactune which is m o u n t e d at ground level. While this cab has a clear chsplay console and a gate-type gear lever, it is spoilt by the lack o f a swivel seat. It must be remembered that the dr~ver of this machine has to handle 40ft containers and has therefore to look twice as far to the rear from inside the cab The main complaint is that despite the identical functmns of both machines, and their simultaneous use at some ports, the order of the bank of controls to the drivers' right is reversed, Those levers operated by the n.ght hand on one machine become those operated by the left hand on the other and vice versa. This potentially hazardous situation is mitigated by the provlsmn of an interlock system which stops the driver from actwatmg the wrong lever at the wrong time, but the crmclsm still remains. The manufactureres have released a third model with yet another control layout, so the plea for a standardlsed control layout remains unanswered
166
Apphed Ergonomics September 1973
_l
I i I I I
F=g 5. Cab of 40ft s=deloader On this machine, however, and across all o f their range of products, they have introduced an ergonomlc innovation in control knob design. Tins departure from the standard ball or tuhp shaped knobs is shown m Fig 6 and ~s commendable as a new approach. The operation of this lever is one o f fingertip-pull - palm-push, and it still allows the identifying symbol to be presented at a good angle for the driver's Vision
Other points
[:
There are many other salient points which could be made in this evaluation, such as the poor position o f the headlights on the larger model sideloader or the noise, vibration and ventilation. The one 1tern which Is worth including here is that of the twlstlock indicator display. This display is a square of four lights which, together with two operating buttons, is to be found on most pieces of container handling eqmpment. It indicates the state of the twlstlocks on the lifting frame. On many of the machines studied it would only indicate whether the individual twistlock was in the locked or unlocked position, and therefore whether it was safe to lift or not. Beanng m mind the difficulty that a driver may have m seeing the insertion of the twistlock pros into the contmner corner posts, and the fact that at most times he can only see three out of the four twIstlocks, it is imperative that this display should really Inform the driver that it IS safe to hft. The system described only tells the driver m point of fact if a tWlstlock has jammed and cannot lock, not whether it Is m or outside of the container In its locked position. This satuation has resulted m drivers trying to hft containers with the front pair of twistlocks only, resulting in considerable damage to both container and machine. This IS not entirely the manufacturer's fault, as they can supply a system which Indicates that the twlstlocks are inserted in the container and therefore that it is safe to hft. This sytem is preferable to most other systems, both electrical and mechanical, since it allows the driver to complete the hftmg operation with the m u u m u m of physical effort In turning round inside the cab. The provision of more displays and analogues reside the cab of the sldeloader would reduce the criticisms that can be made of the driver posture, although m the context of the docks such sophisticated devices are easily and frequently damaged.
Conclusions It is unfortunate that this study could not have been more comprehensive, or for that matter, that the experimental recommendations made have not been put on trial. The study was commissioned, however, as an evaluation of the sideloader, and the National Ports Council has largely an advisory role with regard to the port operators in this country. The one factor emerging from the study IS that there IS a basic confhct for the designer of integrating within the one machine the functions of transport and mechanical handling. The sldeloader IS a mixture of a forward travelling vehicle and a sideways facing loader and stacker. The problem is not one of engmeenng, but one of where to put the driver with respect to these two functions. In the case of these machines a compromise has been made and this has resulted In a machine which, while well adapted to the dnving and
Fig 6. New control knobs
manoeuvenng role (except while reversing), IS less well adapted to the lifting and stacl~ng role. This may help to explain why these machines have been accepted in ports where the driving conditions are not perfect and other machines have proved Inoperable. The vlsibihty considerations are not an outnght condemnation of the sldeloader, since they are in part due to the principles of loachng from the side and to the bulk of the containers themselves. They are at best hmltatlons of the system which must be taken into account in the design and layout of the port Itself. The criticisms of the cab layouts stand, nevertheless, bearing in mind the cost of the cab relative to the overall cost of the maclune. The ergonomlc moral to be drawn, If any, is that a machine built to serve two distinct functions will necessitate a compromise at some point in the design. Whether this is an inevitable consequence of the uses to which the machine is put, or due to the concept of a machine with dual functions, is a point for further discussion.
References
Wilkinson, B. 1972, Driver's comparative visibility from straddle carriers. National Ports Councd Bulletin, No 3, Win ter.
Applied Ergonom=cs September 1973
167
Side loaders-a case study in
the port industry N.M. Hartwell Birkbeck College This report is an evaluation of a vehicle used in the port industry for handling containers. The vehicle is a self-loading lorry which both transports and stacks the containers w i t h i n the port. Three aspects of the evaluation are discussed in the operating context: internal and external visibility, and the cab layouts. It is concluded that the vehicle has a restricted view to the rear, although with care this can be catered for. The design and position of the cab, however, can demand extreme and uncomfortable postures on the part of the driver. Certain anoma lies in the cab control and display layouts are also briefly discussed, with a view to standardisation and a reduction of the driver's work-load. The main problem is seen as one of the integration of the driver/operator w i t h a machine with t w o discrete functions. The visibility and posture problem areas are considered to stem from the compromises dictated by the nature of this dualfunction vehicle. Imperial units are retained since containers are specified by the ISO on the basis of American measures.
There has been a major revolution in the cargo handhng field over the past decade due to the world-wide introduction of the system of containers. The advent of th~s system has posed many problems to the various port operators due to the cost and dwerslty of the mechamcal handling methods avaflableo My work is part of an evaluauon of just one of these systems, sideloader operations. The sldeloader has been developed from early vehicles used for handhng steel or umber where the use of a forkhit truck would be inappropriate. A typical general purpose sldeloader is shown m Fig 1. The container handhng vehicles differ only m size and m the addmon of a large hftmg frame. The vehicle is basically a self-loading lorry of large proportions. The machine's funcuons are as follows The driver stops abreast of the container to be hfted and lowers a set of stabfl~ser jacks~ He then traverses the mast assembly across the bodywork to the right-hand side and lowers the large hftmg frame on to the container. The majo~ skill reqmrement for the driver is to ahgn this frame accurately relatwe to the box so that the four locking pros, or tw~stlocks, can be engaged. The container is then hfted and the mast and load are traversed back across the bodywork to be placed on the loading platform. The mactune is then driven off to the unloa&ng point.
Th~s report Is based on a paper read at the 1973 Annual Conference of the Ergonomics Research Society titled An ergonomic evaluation of the container handling sldeloader. The work was financed by the Social Science Research Councd and was comm=ss=oned by the National Ports Councd.
Fig 1. General purpose sldeloader
The Port Typical container ports use sideloaders as a link m the mechamcal handhng system. Ships are unloaded using large gantry cranes and the containers are then stored to await chspatch by road or rail. The drwer of the sldeloader undertakes a shuttle service between the quayslde, &spatch and storage areas and serves the dual thnctlons of both rapld transport and mechamcal handhng of its 20-30 ton load. Since these mactunes cost up to £50 000, any defects
Applied Ergonomics September 1973
163
in the ergonomic layout or design which adversly affect the driver can soon be seen an the repair bills. The ports are by no means uniform in layout, surfacing, hghtmg or traffic and tlus can place hmltataons on certain types of operauon. Machines whxch work well under optmaum condmons may become increasingly ineffective as these conditmns deteriorate. Poor working condmons and bad weather can affect the best design of machinery and the cost of a poor layout can be measured m terms of accidental damage occurnng m the storage areas and m the increased cycle times needed. The container berth must also be designed to cater for the hm~tatlons of the machines themselves and the hazards of operatmg the system ~tself, such as the chstoruon of the roadways by the heavy ground loadmgs of the containers. Off spillage ~s a common event and this can make the roadways very shppery at trmes. There ~s also the problem of the safe integration of road and dockside traffic wathln the dispatch areas. All of these points are included to glve a rough p~cture of the dock environment and the problem areas where ergonomics can make a contrlbut~on. Driver training and the most efficient design of both cab and machine can help, but cannot be expected to cure all of the problems inherent In the use of machines for container handhng.
The S t u d y Bearing this m mind, two models of s]deloader were chosen for the analysls, handtmg 20 and 40ft containers respectively. These machines differ from the design above m that they both have a cab wbach can be traversed across the front of the machine. Apart from the hard data m terms of photographs and measurements, the fieldwork was fairly straightforward. The drivers and maintenance workers were interviewed at three ports using the critical incidents techmque to try to hnk these me,dents to actual accidents and the machine's desagn. Perhaps the best source of comparatwe data is ]n the work of one of my colleagues, Mr Wdkmson, who has just wntten a s]mdar report on a compeutive machine, the straddle carrier (Wdkmson, 1972), and some of the methods developed m his study have been incorporated m my own report. Apart from this, there ~s httle duectly comparatwe data avadable m this field, except for some unpubhshed work by the British Rad Department of Ergonomics.
Results Th~s report can be considered an three secuons internal and external ws]bdlty, and the cab layouts. Vlslbd]ty cnterm, both internal and external, are important, tor ]t is when a driver cannot see what he is doing that accidents can occur. The records of such accadents, if kept, provide a rough and ready mdlcatmn of some of the problem areas that may warrant special attention. The study of vlslbdlty Is just one of the ways of studying the design of vehicles, but with some far reaching consequences.
External v i s i b i l i t y This ]s the vlslbthty of objects m the vacm]ty of the machine, but not pa~t of it.
164
AppliedErgonomics September 1973
The cntenon by wtuch external visibility is measured here is one of a human figure who maght be m the vicinity of the machine. The machines differ in design and type and it ~s pomtless to discuss wsibdlty w~thout any quahfications as to the uses to which the machines are put. S~deloaders have two dastmct phases m thelr operating cycle, those of transport and stacking. In the transport mode, the driver needs only to take account of the external VlS]bthty. This is necessary for the negotmtmn of any obstacles and for drlwng both within the container stack and on the quaysldeo To do this, as on any road vehicle, the driver needs to be able to gauge the clearances reqmred for his vehicle's passage, and the minimum spaces reqmred for turning. In these respects, sldeloaders generally have an acceptable design, due to the forward mounting of the cab. The fixed cab machines are at a shght disadvantage when loaded, however, as the driver's vaew to the nght is then restricted by the bulk of the machine's load, When the driver attempts to reverse a sldeloader, he has a much more restricted field of view, which ]s dlustrated m Fig 2. Thas Vlslbd]ty map shows the 20ft container handhng sadeloader with a traversing cab and the shaded areas to the rear represent the bhndspots. The double hatched area shows the arc m whach a man or object under 6ft (2 m) tall would be mvaslble to the drwer m the cab at posmon A, w~th the vetucle unloaded. Once loaded, the bhndspot expands to cover the whole of the shaded area to the rear. There xs no outer hmlt to these bhndspots and within their area objects as large as containers may be invisible at umes. One instance as noted where a driver reversed into a small van and pushed it for some 10 yd (10m) before he was made to stop.
Cab position The driver can Improve his view to the rear to some extent by traversing the cab from A to B and leaning out of the window to see down both sides of the vehicle,
5 ft
t
Veh,cle and drwer facing [ ] Areas vlsJble at all times [ ] Dr,vet unhkely to s.ee any thm 9 less than 6ft tall .~ in th,s area [ ] Driver unlikely, to ~.~ ~A ~/~
see anything Jess than Oft toll ~n this area when dn~r,th a2Oft
i
Fig 2. S,deloader vlsibd,ty map (cab traversed to right-hand side)
although this is not ergonomlcally commendable. The drivers interviewed nevertheless preferred to keep the cab on the nght (posmon A). Th~s ~s so that they can accurately ahgn the machine next to the container to be hfted and closely observe the loading operations. What they lose by not moving the cab is to some extent compensated for by the fact that once they revert to the dnvmg role, they have a stable vantage point. This ~s as against the problems that they would otherwise encounter from driving a machane with both left and right hand drive. The reader may v~suahse th~s by considering the transient problems inherent m crossing the Channel and adapting from the British to the Continental traffic system. The driver of a fixed cab sideloader has none of these problems, although he ~s relatwely further away from the right-hand loachng s~de of the machine, and he must therefore exercise greater skill m al~gmng has machine pnor to hftmg. The v~sthlhty map for such a machine (w~th the cab at pos~uon C) ~s essentially the reverse of the one shown, and from posmon C the vaew to the right ~s severely hm~ted when loaded. Th~s calls for even greater skill when the dnver has to approach a stack, lorry or railway wagon to deposit has load. These problems call for s~mple palhauves 1 The bhndspot to the rear can be catered for m the ports concerned by keeping to a circular flow of traffic from the storage areas to the quaymde and back. Thas would at least avoid the need for frequent reversing, 2 The lanes ms, de the storage park must be straight and well marshalled to allow for the bhndspot which occurs to one side when the machine ~s loaded. Th~s would avoid the accidents which happen where s~deloaders have struck containers on their bhnd side,
t
/
,-1
I
,,l.
The fitting of an intermittent horn for reversing movements would be of some use m exastmg layouts to warn other drivers and stray people who may not be aware of the fact that the dnver cannot see them. Marrors would only be of use ff they could be mounted where it is ~mposslble to break them. The visibility map pertalmng to the larger model sldeloader stuched is not presented here as It Is somewhat comphcated by the fact that its view to the rear ~s obscurred by the bodywork, sance tts cab ~s mounted at ground level and the loading platform extends over the dnver's head.
Internal visibility This is the vlsiblhty from the driver's seat of the van,us operating parts of the machine, mduchng the load. The external vlsibfllty of the slddoader xs a measure of the vasual profile m the horizontal plane. At most ports, the containers are stacked up to three h~gh and the internal vlslbthty ts therefore also compnsed of the visual profile m the vertical plane. Dunng the loading and unloading operations the driver has to integrate these two profiles to achaeve a three-chmens~onal image of the operauon of his machine° It xs essenual for the efficient handling of containers that the dnver can accurately place has hftmg frame on top of the container to be hfted and that he can see the insertion of the tw~stlocks rot, the four container corner posts. If he is to do this repeatedly and accurately, there must be no sen,us difficulty or discomfort inherent m the task as thas may lead to fatigue and subsequent damage to either the machine or the containers. Slddoaders do present such chfficultles and dascomforts to the driver as can be shown by Fig 3. Thas dmgram shows the front view of the smaller sldeloader studied, m the process of lifting a container. From thas picture It may be apprecmted that the drwer m pos~taon A can accurately see the engagement of the tWlstlocks when hftlng a container from the ground or from a lorry trader or railway wagon. The higher that the containers are stacked however, the hagher becomes the angle through whach the driver must turn his head in order to observe the lifting frame.
\
The larger model sldeloader stuched has its cab at ground level or posmon B on the chagram. From this posit]on the driver ~s at a defimte chsadvantage, since for two or three-hagh stacking he must look upwards at angles approaching the vertical.
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JJ J JJJJJJJJJ Fig 3. Front view of s~deloader
W~th both of these machines it ~s possible to traverse the cab to posmon C where the cab is to be found on fixed cab sldeloaders. From this posmon the extreme angles required are considerably reduce& Thas is, however, at the cost of an extra operation In the work-cycle or the extra difficulty m approaching the container stack w~th the critical clearance on the bhnd side.
Driver posture It is not so much the VlSlbdlty m the verUcal plane which results m complaints of backache from the drivers, but the combmauon of having to look both upwards and
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to the rear at the same time, due to the forward position of the cab. Before a dnver can hft a container he must observe the engagement of both pairs o f twlsflocks, both fore and rear. Due to the constraints of the window pillars and the mast assembly this means that he must lean out o f the cab window to l o o k along the side of the vehicle to see the rearmost pair. This movement ~s accentuated m the case o f 40ft containers winch are handled by the larger machine with its low slung cab. The c o m b m a t m n of three Ingh staclong with 40ft boxes is to be avoided where possible, unless it ~s possible to pre-select drivers on the basis of neck flexabthty. This situation is further complicated by the tack of a swivel seat on the larger machine, as well as the restrlctmn of cab width which prevents the driver from turning 90 ° to the right where he could accomodate these movements more comfortably. Within the present cabs, the best solution would be one of provl&ng a seat with a lower backrest. This would allow the driver's shoulderblades to turn more freely and thereby distribute the neck torsion more evenly down the spree.
The
cab
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/
layouts
While the visibility of the controls and &splays within the cab is of great importance to the driver of a sldeloader, there are so many different layouts at present m use that it ~s necessary to hmlt these considerations to the study of just two &fferent cabs for the purpose of brevity and clarity.
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F=g 4. Cab of 20ft s=deloader
The side views of the cabs o f the two machines studied are given m Figs 4 and 5. The main comment which can be made ~s that despite the ~dentlcal functmns of the two machines, the layouts are completely different. Neither possesses any clear advantage over the other due to several factors. Fig 4 shows the cab of the smaller machine. This ' m o d e r n ' design is marred by the following details 1. The driver's foot-space to the right IS obstructed by the large cab heater on the floor, makang it ~mposslble to use the svavel seat properly. 2 The chals and warning hghts are distributed around the cab with httle thought to VlSlbthty. 3. The gear levers (seen here end-on) are m o u n t e d so close to the fascm under the steering wheel that the drivers scrape their knuckles when changing gear. Fig 5 shows the cab o f the larger mactune which is m o u n t e d at ground level. While this cab has a clear chsplay console and a gate-type gear lever, it is spoilt by the lack o f a swivel seat. It must be remembered that the dr~ver of this machine has to handle 40ft containers and has therefore to look twice as far to the rear from inside the cab The main complaint is that despite the identical functmns of both machines, and their simultaneous use at some ports, the order of the bank of controls to the drivers' right is reversed, Those levers operated by the n.ght hand on one machine become those operated by the left hand on the other and vice versa. This potentially hazardous situation is mitigated by the provlsmn of an interlock system which stops the driver from actwatmg the wrong lever at the wrong time, but the crmclsm still remains. The manufactureres have released a third model with yet another control layout, so the plea for a standardlsed control layout remains unanswered
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F=g 5. Cab of 40ft s=deloader On this machine, however, and across all o f their range of products, they have introduced an ergonomlc innovation in control knob design. Tins departure from the standard ball or tuhp shaped knobs is shown m Fig 6 and ~s commendable as a new approach. The operation of this lever is one o f fingertip-pull - palm-push, and it still allows the identifying symbol to be presented at a good angle for the driver's Vision
Other points
[:
There are many other salient points which could be made in this evaluation, such as the poor position o f the headlights on the larger model sideloader or the noise, vibration and ventilation. The one 1tern which Is worth including here is that of the twlstlock indicator display. This display is a square of four lights which, together with two operating buttons, is to be found on most pieces of container handling eqmpment. It indicates the state of the twlstlocks on the lifting frame. On many of the machines studied it would only indicate whether the individual twistlock was in the locked or unlocked position, and therefore whether it was safe to lift or not. Beanng m mind the difficulty that a driver may have m seeing the insertion of the twistlock pros into the contmner corner posts, and the fact that at most times he can only see three out of the four twIstlocks, it is imperative that this display should really Inform the driver that it IS safe to hft. The system described only tells the driver m point of fact if a tWlstlock has jammed and cannot lock, not whether it Is m or outside of the container In its locked position. This satuation has resulted m drivers trying to hft containers with the front pair of twistlocks only, resulting in considerable damage to both container and machine. This IS not entirely the manufacturer's fault, as they can supply a system which Indicates that the twlstlocks are inserted in the container and therefore that it is safe to hft. This sytem is preferable to most other systems, both electrical and mechanical, since it allows the driver to complete the hftmg operation with the m u u m u m of physical effort In turning round inside the cab. The provision of more displays and analogues reside the cab of the sldeloader would reduce the criticisms that can be made of the driver posture, although m the context of the docks such sophisticated devices are easily and frequently damaged.
Conclusions It is unfortunate that this study could not have been more comprehensive, or for that matter, that the experimental recommendations made have not been put on trial. The study was commissioned, however, as an evaluation of the sideloader, and the National Ports Council has largely an advisory role with regard to the port operators in this country. The one factor emerging from the study IS that there IS a basic confhct for the designer of integrating within the one machine the functions of transport and mechanical handling. The sldeloader IS a mixture of a forward travelling vehicle and a sideways facing loader and stacker. The problem is not one of engmeenng, but one of where to put the driver with respect to these two functions. In the case of these machines a compromise has been made and this has resulted In a machine which, while well adapted to the dnving and
Fig 6. New control knobs
manoeuvenng role (except while reversing), IS less well adapted to the lifting and stacl~ng role. This may help to explain why these machines have been accepted in ports where the driving conditions are not perfect and other machines have proved Inoperable. The vlsibihty considerations are not an outnght condemnation of the sldeloader, since they are in part due to the principles of loachng from the side and to the bulk of the containers themselves. They are at best hmltatlons of the system which must be taken into account in the design and layout of the port Itself. The criticisms of the cab layouts stand, nevertheless, bearing in mind the cost of the cab relative to the overall cost of the maclune. The ergonomlc moral to be drawn, If any, is that a machine built to serve two distinct functions will necessitate a compromise at some point in the design. Whether this is an inevitable consequence of the uses to which the machine is put, or due to the concept of a machine with dual functions, is a point for further discussion.
References
Wilkinson, B. 1972, Driver's comparative visibility from straddle carriers. National Ports Councd Bulletin, No 3, Win ter.
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