Journal of Forest Engineering • 7
A Self-Leveling and Swiveling
Forestry Machine Cab
Sten Gellerstedt
日常生活用品Swedish University of Agricultural Sciences
Garpenberg, Sweden
ABSTRACT
A radical, new innovation with regards to for-estry machines is the design of a cab suspended from an arched column connected to a swiveling socket. The purpo of the design is to reduce the amount of skewed and twisted work postures, which are often frequent among operators of logging ma-chines. The ability to sit straight is what most opera-tors point out to be the most desirable feature of the lf-leveling and swiveling cab. The low noi level is also appreciated, as is the ability to swivel the cab around on its vertical axis. The swiveling ability of the cab gives better visibility and also helps reduce t
he amount of head rotations. Furthermore, jarring motions and extreme swing due to uneven terrain are much less bothersome than in a conventional cab design. Vibration levels at the operator's at in the lf-leveling cab are equal to tho measured in conventional rigid cabs. This new cab design pro-vides comfort to the operator and improves the operator's ability to work at a sustained high effi-ciency. A follow-up study conducted over veral years shows that the productivity of a harvester incread by 5 to 10% after a change from a rigid to a lf-leveling and swiveling cab.
Keywords:Cab-design, ergonomics, work posture, pro-ductivity, vibrations. BACKGROUND AND PURPOSE
This article describes the design and ergonomic studies of a lf-leveling and swiveling cab manu-factured by the Swedish company Pendo AB. De-tails are provided of a time-study, a follow-up of machine productivity, and the options of the opera-tors who have ud the new design. Additional studies are prented that describe entering and exiting the cab, cab size, work posture, visibility, vibrations on the operator's at, noi, and the extent of cab usage.
Operators of forestry machines are expod to an array of fatigue-causing factors: cab vibrations, jar-ring motions due to uneven terrain, uncomfortable work positions, and the constant twisting and t
urn-ing of the head, neck, and cervical regions. Results of a health investigation of 1174 forest machine operators in Sweden indicated a prevailing average overload syndrome of 50%, mainly characterized by neck/shoulder complaints [3]. The pursuit of suitable technical solutions to the problems has been in the works for a number of years. Some of the solutions are cabs with better visibility, chairs with cushioned vibration, lf-leveling chairs, the mounting of a bogie on both front and rear axles, split rear axles, wider tires, pendulum arms for all tires, a swiveling cab, the passive cushion of shock waves in the hydraulic system, an actively cushion-ing and leveling cab, and a suspended, lf-leveling and swiveling cab.
Within forestry, a lf-leveling and swiveling cab is a radical new innovation for the alleviation of skewed and twisted work positions. In this design the cab is suspended from an arched column that is in turn connected to a swiveling socket (Figure 1). The cab can swivel around on its vertical axis from 0° to 270° and remains vertical in terrain with a 15°slope or less. The cab's swiveling ability is control-led by the operator and is parated from the move-ments of the crane. This gives the operator the means with which to adjust the cab for optimum visibility at all times. The arched column has a vibration-reducing and shock-absorbing joint posi-tioned at the at of the beam supporting the cab (at eye level behind the operator), the purpo of which is to keep the cab on a h
orizontal position sideways. Above this joint is a U-shaped cab carrier beam with one shock absorbing joint at each side of the cab working to keep the cab in a horizontal position lengthwi. The stiffness of the absorbing joints can be manually adjusted from within the cab.
To reduce the amount of vertical vibrations, at-tempts have been made to u rubber bellows at the cab connection sites and hang the U-shaped cab carrier beam in an absorbing joint (Figure 2). The cab is intended to be mounted on new or ud forestry machines. Approximately 90 cabs of this type have been produced up to mid 1997. Of the there are currently 80 mounted on harvesters and 10 on forwarders, mostly on older and renovated ma-chines. The cost for a lf-leveling cab ranges be-tween US$15,000 and $23,000.
The author is Rearch Manager, Department of Opera-tional Efficiency.
8 • Journal of Forest Engineering
Figure 1.The lf-leveling and swiveling cab suspended from an arched column attached to a swiveling socket.
Figure 2.Sideways view of lf-leveling cab: 1) Swiveling socket; 2) Sideways cushioning (y-axis);
3) Lengthwi cushioning (x-axis); 4) Horizontal cushioning (z-axis); 5) Sidebeam.
Journal of Forest Engineering • 9
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program BZ 7105, and at-recorder 4322. Studies [10, 11] ud the Brüel & Kjær 2512 and the at-plate 4322. This particular equipment measures ac-celeration in one direction at a time only. The time-weighted noi levels, dB(A), were measured with the Brüel & Kjær 2221 noi meter with the micro-phone placed just above the operator's breast pocket.The operator's head movements (cervical spine ro-tations) were measured with a Nodmeter (jointed aluminium levers with goniometers worn by the operator).
RESULTS WITH COMMENTS
Time study and production. One hypothesis was that the work element “crane out” would be faster to perform from the new cab. The work element “crane out” took an average of 6.8 conds to perform during thinning, using the lf-leveling cab on the single grip harvester FMG 250 Super E with the crane 170 E (Table 1). At a similar first thinning the work element “crane out” took 9.6 conds [7]. In that study the operators ud the conventional cab connected to the FMG 250 harvester and the crane 374E. Plea note that the 170 E crane is more pow-erful than the 373 E, which makes it difficult in determining what part the lf-leveling cab played in reducing the time for the work element “crane out”.拗口令
During the first ason (1992/1993), with the lf-leveling cab mounted to a FMG 250 harvester, the productivity per hour ro by as much as 25% . This increa was due to, at least, three known factors:1.Improved operator ability during the cour of the year, particulary for one inexperienced op-erator.
METHODS AND MATERIALS
Previous studies have been done of the lf-leveling cab mounted on a number of single grip harvesters such as the FMG 250 Super Eva [4],Timberjack 1270 [6], FMG 1870 [11] Hemek EGS [9],as well as the forwarder Kockums 85-35 [5, 10].In this study, the cab has, in most cas, been compared to conventional forestry machine cabs ud in thinning and forwarding operations during normal work shifts. Thinning was carried out using the current Scandinavian short-wood system (cut-to-length system). Harvester-teams were comprid of a harverster with three alternating operators who operated machines in three-hour shifts for 12 hours a day. Forwarding was studied during normal work as well as when driving along a test track.The program TWT [7] and a notebook computer was ud in the time study. The following work elements were noted: “drive forward”, “drive re-ver”, “crane out to the tree”, “processing the tree”and “others”. Operators, management and the manufacturer's reprentatives were all asked to answer a t of prepared questions. The “E
rgo-nomic Checklist for Forestry Machinery” [2] was ud while performing the ergonomic study. The production of an FMG 250 Super E harvester was monitored before and after the changeover to the lf-leveling cab by the management from ASSIDomän Skog &Trä, Örebro forest management district.
Studies [4, 5, 6] measured whole-body vibrations in the x, y, z-directions simultaneously (WBWT according to ISO 2631/1, time-constant 1 cond)and ud Brüel & Kjær 2231/s, vibration-unit 2522,
Table 1.Time study in thinning of a single grip harvester FMG 250 Super E with the mounted lf-leveling
cab. Work elements studied were: Driving ahead, Crane out to the tree, Felling and processing (from gripping of tree to the relea of the top).Operator
Mean diameter of No. of Driving Crane Crane Felling and Study the trees removed,stems cut ahead out out processing time number of stems/ha per (c)mean std .dev.(c)(min)before and after thinning
minute
车辆上牌(c)(c)115.4 cm, 2000/1200 1.312.67.2 4.62721215.4 cm, 2000/1200 1.510.87.1 3.621119116.4 cm, 800/500 1.89.6 6.4 3.918472
16.4 cm, 800/500
1.7
8.4
6.5
3.4
19.2
70
10 • Journal of Forest Engineering
2.The crane itlf was retrofitted with shock absorb-ers during the fall of 1993 which improved crane stability.
3.The change to the lf-levling cab. An estimate [8] is that the new cab accounted for an approximate 5 to 10% of the productivity increa. The esti-mate is bad on a two-year follow-up of the production of a FMG 250 Super E harvester. Enter and exit the cab. In order for the operator to have a safe exit he/she has to turn the lf-leveling cab in such a way that the door is aligned with the ladder. If not, the exit will become an unforgettable “free fall” or at best an awkward climb over ma-chine parts. A minor imposition occurs when an operator enters the cab. First, the step up into the cab is higher than usual and in a diagonal fashion. Second, the cab rocks back when the operator ts his/her foot in the cab. A later model of the cab, with vertical cushioning, can be lowered and positioned on the swiveling socket. This allows for a safer and more cure way to enter and exit the cab. Working position. The operator's work environ-ment and body posture in a lf-leveling cab is horizontal even when the terrain is at an incline up to 15°. The ability of the cab to swivel around its vertical axis allows the operator to position the cab so that the best possible view over the work area can be obtained. The operator is thus not expod to the same amount of fatigue-inducing factors such as the skewed and twisted work postures that occur in a regular cab. After a few months operators using the lf-leveling cab ud its swiveling ability 0.8 times per tree. After two years the same figure had in-cread to an average of 2.3 times per tree. The swiveling ability was ud while driving forward, getting in position to cut, and during felling and processing.
Operator head rotation (the cervical spine rota-tion) were measured and compared while using both the lf-leveling cab and conventional rigid cabs (Figure 3). By mounting the lf-leveling cab to the harvester Timberjack 1270 the number of head rotations beyond 22.5° had been reduced by 10 minutes per hour two weeks after delivery. As for the FMG 250 Super E, the number of head rotations beyond 22.5° was reduced by as much as 28 minutes per hour four months after the lf-leveling cab was introduced.
宝宝多大可以吃盐Cab. The inside size of the lf-leveling cab ad-heres to recommendations t forth in the “Ergo-nomic Checklist” [2] (Table 2). However, available leg and foot room is not sufficient for an operator of above medium height.
Table 2.The size of two different lf-leveling cabs and the rigid Timberjack 1270 cab compared to recommendations laid out in the "Ergonomic checklist for forestry machinery" [2].
Point of Measurement Self-leveling cab Self-leveling cab Standard cab Minimum values in on FMG 250 SuperE on Hemek EGS Timberjack 1270Ergonomic checklist Width [cm] (glass to11511812590
glass at shoulder level)
Height [cm] (floor to165164164160 ceiling in front of chair)
Length [cm] (glass to157143145130
glass at elbow level)
Journal of Forest Engineering • 11
Figure 3.Distribution of operator head rotation (cervical spine rotation) within different ctors when measured with a “nodmeter” [7]. The area in each ctor reprents the amount of time that the
head spent there. The top picture shows measurements of an operator performing a thinning from
a conventional rigid ca
丽江游b mounted to the FMG 250 E. The bottom picture shows measurements of
an operator performing the same type of thinning while in a lf-leveling cab mounted to a single
grip harvester FMG 250 Super E. The dark areas are restricted views.
12 • Journal of Forest Engineering
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the highest 70 dB(A) (Table 3).
Vibrations. The vibration levels prented in Ta-bles 4 and 5 show that there is no significant differ-ence between the lf-leveling cab and the conven-tional rigid cab regarding the vector sum of the three axes. Table 4 shows, however, that the vertical vibrations (z-axis) in the lf-leveling cab, witho
ut vertical cushioning, are higher compared to the rigid cab. Table 5 shows that the cushioning of the vertical vibrations reduced the vibration level.Ideally, vibrations should be measured during a standardized run on a widely accepted work and test track. There is, however, no such accepted stand-ard. Measurements of vibrations that are accounted for in this study have been made on a number of different machines, with different equipment and in different terrain types, temperatures, speeds, etc.
Visibility from the cab. The lf-leveling cab provides good visibility both upward and forward.Sun reflection in the windows is alleviated by turn-ing the cab slightly to one side. The same turn applies for the windshield-wiped part of the win-dow during rain or snow. Limbs, which have the potential to smear the windows, can be moved away by swiveling the cab. One problem, however,is that debris, snow, and ice tend to stick to the slanted window above the head of the operator. The operator's ability to e below branches in a spruce forest is not as good as in a conventional rigid cab.This is becau the lf-leveling cab sits higher than usual (160 cm above ground in a Timberjack 1270).This is not a problem in a pine forest where high operator level is advantageous.
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Noi. Noi levels in the lf-leveling cab are lower than in the two other types of cabs that were measured. The lowest measured noi level during a work shift in a lf-leveling cab was 62 dB(A) a
nd
Table 3. Noi levels in lf-leveling cabs as compared to standard cabs.Machine Self-leveling cab Standard cab Comments
[dB(A) Leq]
[dB(A) Leq]
FMG 250 Super E 6668–69FMG 1870 EGS 62–Engine is mounted far from cab
Timberjack 127063–6570–72Kockums 85-3566–70–Exhaust pipe very clo to cab Hemek EGS
67
–
Exhaust pipe clo to cab
