Analysis of Existing Design

8/12/2019 Analysis of Existing Design

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CHAPTER III

ANALYSIS OF THE EXISTING DESIGN

This chapter deals with the detailed ergonomic evaluation of the worksystem which

consists of existing crane cabin design, human operators and the work environment.

The study proceeds with first getting an overview of the worksystem and then goes

into the detail study of each component of the worksystem. First, a reconnaissance

study of the work system was done to get a acquainted with the worksystem: people,

machine, place, processes and their interactions.

3.1Reconnaissance Study of the Cabin Worksystem

The information obtained from the initial survey of the worksystem is shown

diagrammatically in figure 3.1. The centre of the worksystem is man, i.e. crane

operator, as show in figure 3.1. A single crane operator drives one crane. The

intermediate circle of machine represents the crane cabin and includes all the machine

components with which man interacts. The controls crane operator interacts with are

as listed below.

One control for Longitudinal Travel (LT) of the crane, on left hand side.

One control for Main hook Cross Travel (MCT), on left hand side.

One control for Auxiliary hook Cross Travel (ACT), on left hand side.

One control for Main hook Hoisting (MH) on right hand side.

One control for Auxiliary hook Hoisting (AH) on right hand side.

One cabin motion switch on right hand side.

One alarm bell on right hand side.

One tong rotation switch on left hand side.

Walky Talky on left hand side

The signalling or information providing devices are listed as below

An array of indication cum reset switches on right hand side.

LCD touch screen on front right side.

An annunciation panel on the right side at height.


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The Walky Talky, LCD touch screen and Indication cum reset switches are of dual

nature as they provide information and also crane operator manually interacts with

them.

Fig 3.1 Diagrammatic representation of worksystem of BAF EOT crane cabin.

The intermediate circle of the worksystem (figure 3.1) represents the machine, i.e.

crane cabin with all its components. The further study is about the machine

component of the worksystem. The different sub components of crane viz. controls

and indicators are studied for their location, distances and how crane operator

interacts with them.

Man

Main Hoist

ControlAuxiliary

Hoist

Control

Cabin

Motion

Switch

Array of

Indicator

cum Reset

Switches

Longitudinal

Travel

Control

Auxiliary

Cross

Travel

Control

Walky

Talky

LCD Touch

Screen

Bell

Switch

Crane

Cabin

Environment

Annunciation

Panel

Tong

Rotation

Switch

Main Cross

Travel

Control

Confined

SpaceHigh

Elevation Poor

Lighting


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The outermost circle represents the workenvironment. All the four cranes in BAF are

at highest elevation of 18 meters among all the cranes in CRM complex. The cabin

space is very confined with not enough space for easy movement or easy ingress and

egress to the chair. There is only standing space of any extra person in the crane

cabin. The lighting at the workzone is inadequate for the visual requirement of the

task.

There are 21 crane operators in BAF, who are equally distributed among the 3 shifts

of a day. In each shift 6 crane operators run the cranes with one crane operator on a

weekly off. The activities performed by crane operators are already mentioned in

section 1.1.2. The complexity of the crane cabin worksystem is clearly apparent from

the above discussion. Each of the crane operators was personally interviewed with a

questionnaire covering workspace, visibility, chair design, ease of use of controls,

placement of controls and ingress and egress to the cabin. The results of the interview

are generalised as mean and shown in table 3.1

Table 3.1 Generalised result of assessment of BAF crane cabins by crane operators

Name of the cranesParameters Crane-3A Crane-3 Crane-4 Crane-5

Structure of cabin 7.45 4.55 4.45 4.36

Space inside the cabin 7.64 4.36 4.27 4.73

Chair design 4.64 4.09 4.55 4.18

Ease of use of controls 4.27 5.09 5.36 4.45Placement of controls 5.64 6.18 6.27 6.00

Space between front window and

chair 6.36 5.45 6.00 5.82

Inclination of front window 6.45 4.27 4.73 4.73

Total window area 7.09 4.73 4.91 5.27

Floor window area 6.91 4.09 4.73 5.09

Placement of walky-talky 4.91 3.64 3.73 4.27

Placement of touch screen 5.09 4.91 4.36 4.27

Placement of annunciation panel 6.82 6.36 6.09 5.64

Placement of AC and fan 7.27 7.18 7.09 7.18

Placement of switches 5.55 5.91 5.55 5.64Placement of indicators 5.64 5.27 5.82 5.55

Left side visibility 6.18 4.36 4.45 4.73

Right side visibility 6.91 4.82 4.00 4.55

Front visibility 7.45 5.73 5.64 6.18

Bottom visibility 6.64 4.55 4.73 4.36

Speed of the crane 7.55 4.45 4.36 2.45

Pathway to crane cabin 5.82 4.55 4.73 5.27

Total= 6.61 5.23 5.29 5.24


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The cranes 3, 4 and 5 are older cranes which were designed by the companys own

design department and are operational since the commissioning of the CRM. The

crane 3A was also designed and installed by companys design department but was

installed much later. Few improvements are made in crane 3A over the rest with

respect to the work requirements of the crane operator. The width of the crane has

been increased by 250 mm and it reduces the feeling of congestion inside the cabin. A

larger floor window area is provided. The analysis of the crane operators feed back

gives the idea of features that eases the work of crane operators. Features like

structure of the cabin, space inside the cabin, total window area, floor window area,

visibility and speed of the crane reduces the stress and increases the productivity of

crane operators. The chair installed in the crane cabin is the seat of a car. The car seat

is designed for reclining sitting posture, while crane operators adopt forward bending

posture during work. It increases the stress in the lumbar portion of the body byreducing the angle between the thigh and trunk. The crane operators assessment

clearly shows that the car seat provided as a chair in BAF crane cabin is totally

unsuited for the work requirements of the crane operators.

The basic understanding of the components and their interactions with man gives one

the complete understanding of the worksystem. This leads to the further study of the

central component of the worksystem, man. For this an anthropometric study of the

crane operators was carried out.

3.2 Anthropometric Study of Crane Operators

Knowledge of the anthropometric characteristics of the human is the pre-requisite for

a good understanding of the fit between the man and machine and the biomechanical

design of any work system. An anthropometric study was carried out for the total

population of crane operators in the BAF. In this study 24 body dimensions were

measured out of which 19 are static and 4 are dynamic dimensions. The sample size

of 30 people where taken which consisted of 21 crane associates and 9 ground

associates, who were formerly crane associates. The measurements were done in a

standard setup of straight sitting posture on an ergonomic adjustable chair. After the

measurement of all the relevant dimensions the 5th

percentile, 95th

percentile, mean,

standard deviation and range of each of the parameter was calculated. The results of


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the anthropometric study are showing in table 3.1. The relevance of each dimension

with respect to various ergonomic characteristics of the worksystem is also

mentioned.

Table 3.1 Anthropometric Study Results

Parameters MeanStd.Dev

5th%ile

95th%ile Range Relevance for Design

Sitting Height 829.80 31.32 778.44 881.16 102.72 Head Rest height

Sitting shoulder height 561.83 25.46 520.07 603.59 83.52 Back Rest height

Eye height 729.93 27.16 685.39 774.48 89.09 Placement of Indicators

Sitting Elbow height 215.60 23.84 176.50 254.70 78.20 Hand rest

Poplitieal height 428.47 23.41 390.07 466.86 76.79 Seat Height

Knee height 520.50 25.05 479.42 561.58 82.16 Clearance over knee

Thigh height 552.67 25.50 510.84 594.49 83.65 Thigh ClearanceBack-to-Poplitiealdepth 483.70 27.28 438.96 528.44 89.48 Seat Length

Back-to-Knee depth 562.27 26.56 518.71 605.82 87.10 Clearance ahead knee

Hip breadth 345.97 25.86 303.55 388.38 84.83 Seat Width

Shoulder breadth 419.40 21.61 383.96 454.84 70.88 Back Rest Breadth

Elbow-to-Elbowbreadth 451.73 34.81 394.65 508.81 114.16

Distance between Handrest

Knee-to-Knee breadth 430.77 51.08 347.00 514.54 167.54 Seat Width in fore

Distance betwn bothfeet 354.80 78.86 225.47 484.13 258.67 Footrest placement

Chest width 284.40 22.56 247.41 321.39 73.99 Backrest Feature Design

Thigh width 158.73 11.08 140.56 176.90 36.34 Seat Feature Design

Knee width 99.73 7.29 87.78 111.69 23.92 Seat Feature Design

Max. Forward reach 732.00 43.59 660.52 803.48 142.96 Workspace design

Max. Side reach 705.53 36.67 645.39 765.67 120.28 Workspace design

Easy. Forward reach 463.73 23.97 424.43 503.04 78.61 Workspace design

Easy. Side reach 449.63 23.59 410.94 488.32 77.38 Workspace design

Back-to-Crotch depth 289.80 31.00 238.96 340.64 101.67 Seat Feature Design

Palm length 185.63 10.69 168.11 203.16 35.05 Workspace design

The following column charts (figure 3.2 to 3.23) show the distribution of data

points for each parameter. They also give us an understanding of the number

of data points in various ranges. The red line at the top is for the 95 thpercentile

dimension of the population. The blue line in the middle is for the mean of the

population. And the green line below the blue line is for the 5thpercentile of

the population. This information is of vital importance while designing for a

human population as a definite range has to be decided for which the design

will be applicable.


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Sitting Height

700

720

740

760

780

800

820

840

860

880

900

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample

Height(mm)

Sitting Height

95th Percentile

Mean

5th Percentile

Fig 3.2 Column chart showing distribution of Sitting Height.

Shoulder Height

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample

Height(mm)

Shoulder height

5th Percentile

Mean

95th Oercentile

Fig 3.3 Column chart showing data point distribution of Shoulder Height.


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Sitting Eye Height

600

620

640

660

680

700

720

740

760

780

800

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Samples

Height(mm)

Eye height

5th Percentile

95th Percentile

Mean

Fig 3.4 Column chart showing data point distribution of Sitting Eye Height.

Sitting Elbow Height

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample

Height(mm)

Sitting Elow Height

5th Percentile

95th Percentile

Mean

Fig 3.5 Column chart showing data point distribution of Sitting Elbow Height.


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Poplitieal Height

0

50

100

150

200

250

300

350

400

450

500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample

Height(mm)

Poplitieal height

95th Percentile

5th Percentile

Mean

Fig 3.6 Column chart showing data point distribution of Poplitieal Height.

Knee Height

420

440

460

480

500

520

540

560

580

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample

Height(mm)

Knee Height

5th Percentile

95th Percentile

Mean

Fig 3.7: Column chart showing data point distribution of Knee Height.


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Thigh Height

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample

Height(mm)

Series1

Mean

5th Percentile

95th Percentile

Fig 3.8 Column chart showing data point distribution of Sitting Thigh Height.

Back-Poplitieal Depth

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample

Depth(mm)

Back Poplitieal Depth

Mean

85th Percentile

5th Percentile

Fig 3.9 Column chart showing data point distribution of Back to Poplitieal

Depth.


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Back-Knee Depth

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample

Depth(mm)

Back to Knee Depth

Mean

95th Percentile

5th Percentile

Fig 3.10 Column chart showing data point distribution of Back to Knee Depth.

Hip Breadth

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30Sample

Breadth(mm)

Hip Breadth

Mean

95th Percentile

5th Percentile

Fig 3.11 Column chart showing data point distribution of Sitting Hip Breadth.


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Shoulder Breadth

0

50

100

150

200

250

300

350

400

450

500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Samples

Breadth(mm)

Shoulder Breadth

Mean

95th Percentile

5th Percentile

Fig 3.12 Column chart showing data point distribution of Shoulder Breadth.

Elbow-to-Elbow Breadth

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Samples

Breadth(mm)

Elbow to Elbow Breadth

Mean

95th Percentile

5th Percentile

Fig 3.13 Column chart showing data point distribution of Elbow to Elbow Breadth.


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Chest Width

0

50

100

150

200

250

300

350

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Samples

Width(mm)

Chest Width

Mean

95th Percentile

5th Percentile

Fig 3.16 Column chart showing data point distribution of Chest Width.

Thigh Height

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample

Height(mm)

Series1

Mean

5th Percentile

95th Percentile

Fig 3.17 Column chart showing data point distribution of Thigh Width.


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Knee Width

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Samples

Width(mm)

Knee Width

Mean

95th Percevtile

5th Percentile

Fig 3.18 Column chart showing data point distribution of Knee Width.

Max Forward Reach

0

100

200

300

400

500

600

700

800

900

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Samples

Reach(mm)

Max Forward Reach

Mean

95th Percentile

5th Percentile

Fig 3.19 Column chart showing data point distribution of Maximum Forward

Reach.


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Max Side Reach

0

100

200

300

400

500

600

700

800

900

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30Samples

Reach(mm)

Max Side Reach

Mean

95th Percentile

5th Percentile

Fig 3.20 Column chart showing data point distribution of Maximum Side

Reach.

Easy Forward Reach

380

400

420

440

460

480

500

520

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Samples

Reach(mm)

Easy Forward Reach

Mean

95th Percentile

5th Percentile

Fig 3.21 Column chart showing data point distribution of Easy Forward

Reach.


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Easy Side Reach

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Samples

Reachinmm Easy Side Reach

Mean

95th Percentile

5th Percentile

Fig 3.22 Column chart showing data point distribution of Easy Side Reach.

Back to Crotch Depth

0

50

100

150

200

250

300

350

400

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Samples

Depthinmm Back to

Crotch Depth

95thPercentile

50thPercentile

5th Percentile

Fig 3.23 Column chart showing data point distribution of Back to Crotch

Depth.


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3.3Study of Component Layout

The layout of all the components in the crane cabin of BAF was studied and their

distances measured. The distances of the control are measured from the elbow

reference point. The layout of controls on arm controller is shown in figure 3.42. The

controls are numbered in the figure, while their names are mentioned in table 3.2

Fig 3.24 Controls and their placement.

Two distances are measured for the controllers. The forward distance is measured

from the seat reference point. Seat reference point is the point of intersection of

centreline of seat pan and back rest. The offset distance is measure from the elbow

reference point to the right or left direction. Elbow reference point is the point the

elbow touches on arm rest while in straight sitting posture with arms close to body.

The direct length is the distance measured along the line joining the elbow reference

point and the control. The distances of controls and components is shown table 3.2

The heights are measured with respect to seat reference point and are show in the

same table 3.2


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Table 3.3 The distances of controls and other components

Control

Name Control

Number

Forward

Distance

(mm)

Offset*

(mm)

Direct Length

(mm)

LT #1 295 85 307

MCT #2 165 200 259

ACT #3 45 200 205

MH #4 295 85 307

AH #5 295 200 307

Length Height

Hand

Rest 75 55

Foot Rest 125 365

Floor 615

The layout of the components is a distinct characteristic of any worksystem and

determines the ease of human machine interaction. The fit between the human

machine interface is studied to know the conformance of machine with the

biomechanical limitations and capabilities of human.

3.4 Misfit in Human Machine Interface

On comparison of results of the anthropometric study with the component placement

data of the crane cabin clearly identifies the misfit of the crane operator population

with the exiting work system. The misfit is measured as the difference between the

ideal position of the control or the component and the existing position. The misfit

data is shown in table 3.3. In table 3.3 the dimensions mentioned in brackets their

placement distances. For the control positions of Longitudinal Travel, Main Hoist and

Auxiliary Hoist, 50

th

percentile of population have 45 mm of misfit while 95

th

percentof population have misfit of 84 mm. Similarly for 95

thpercentile of population has

136 mm of misfit for Main Cross Travel and 256 mm for Auxiliary Cross Travel. The

ACT control has the largest misfit values for direct distance of 510.67 for 5the

percentile population and 589.28 for 95th

percentile population. When the operator sits

50 mm ahead of the seat reference point the misfits for all the controls increases. The

largest increase in misfit is for 3rd

controller which gets behind the operator by 5 mm.


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For 50th

percentile of population the misfit with foot rest is 63 mm and with floor is

187 mm. While the LCD touch screen is at an offset of 190 mm from the 50 th

percentile population eye height and beyond the maximum forward reach of 100

percent of the population. All the indicators were located behind the operator, which

were totally out of field of vision while working.

Table 3.4 Misfit for BAF crane associates with their workspace.

Parameters Mean 5th percentile 95th percentile

Offset of Touch screen from Eye Height 190.07 234.61 145.52

Armrest misfit 5.60 33.50 44.70

Leg-footrest misfit 63.47 25.07 101.86

Leg-Floor misfit 186.53 224.93 148.14Offset of arm-rest on sides 51.63 80.17 23.09

Person is sitting with his back supported by backrest

Ideal position for Control 339.98 300.67 379.28

Misfit for 1st/4

th/5

thcontrol 44.98 5.67 84.28

Misfit for 2nd

control 174.98 135.67 214.28

Misfit for 3rd

control 294.98 255.67 334.28

Misfit for 1st/4

th/5

thcontrol direct 29.98 9.33 69.28

Misfit for 2nd

control direct 79.98 40.67 119.28

Misfit for 3rdcontrol direct 549.98 510.67 589.28

Person Sitting 50 mm ahead of Back Rest

Misfit for 1st/4

th/5

thcontrol 94.98 55.67 134.28

Misfit for 2nd

control 224.98 185.67 264.28

Misfit for 3rd

control 344.98 305.67 384.28

The misfit between man and machine results in many problems like awkward postures

adopted, the stress induced do to awkward postures, the decrease in human efficiency.

The further study was about the various postures human operator was required to

adopt while working and the time durations for which the postures were occupied.

3.5 Postures Adopted while Working

The real time observation of the crane operator while working was carried out to

identify the postures adopted by the crane operators. From this study 7 main postures


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were identified which were adopted by crane operators. These postures were dictated

by the geometry of the work space and the limited window areas.

Fig 3.25 Seven Different Postures Occupied by Crane Operators

85 mm

#1 Sitting

Straight andLooking ahead

#2 Bending

Forward &Looking down

#3 Bending

Right & Lookingdown-right

#4 Bending Left

& Lookingdown-left

#5 Looking Up #6 Stretching out for

Walky-Talky/Mouse

#7 Reclining on

the chair with

back supported

Hip

Reference

Point

295 mm365

mm

990 mm

200 mm

85 mm

200 mm


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3.6 Posture Duration

A systematic time study was done to find out the time duration for which each of the

postures are held. Following is the result of the posture time study, which shows the

result in form of percentage of total working time a posture is occupied and the

minutes the posture was in work period of 1 hour.

Table 3.5 Posture duration

No. Name

% of total

time Minutes/Hour

1 Sitting Upright 14 8.4

2 Forward Bending Looking Down 64 38.6

3 Bending Right & Looking down-right 7 4.2

4 Bending Left & Looking down-left 7 4.2

5 Looking Up 1 0.6

6 Stretching out for Walky-Talky/Mouse 1 0.67 Reclining on the chair with back supported 6 3.6

The posture Forward Bending and Looking Down is occupied for the maximum

amount of time that is 64 percent of working time which is 38.6 minutes in 1 hour of

working. Followed by this posture are Straight Back Sitting and Looking Forward

which is occupied for 14 percent of total working time i.e. 8.4 minutes in 1 hour or

working. Bending on Sides and Looking Down on Sides is occupied for 7 percent oftotal working time i.e. 4.2 minutes in 1 hour of working. While Reclining Back on

Chair is occupied for just 6 percent of time which is just 3.6 minutes in 1 hour ofworking. This posture is classified as Low Level Static Posture. Low Level means

postures which exert low level of loads on muscles, while static means that loads are

maintained on muscles for a significant period of time without any or much motion in

muscles. Such postures pose great risk on muscular health and ability of the muscles

to perform its work properly over a period of time. If proper work period is not

allowed between the work periods there will be accumulation of fatigue which can

result in injury and loss of work functions of the muscles. From the following study of

work rest cycle studies the amount of total loading of muscles during a day of work.

With the knowledge of awkward postures adopted by the crane operators and the and

the time durations for each of the postures the further study was carried out to know

the total time duration an operator works in a day and the pattern of his work rest

cycle.


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3.7Work Rest Cycle

The extreme work rest cycle is observed during the night shift from 10 pm to 6 am

when the crane operators continuously work for 4 hours without a break. This results

in extreme stress levels among night shift crane operators. BAF is a process driven

system. The study shows that work rest cycle depends on many factors like

completion of heating cycles, work load, work scheduling, availability of operators

and cranes and shift. Our study show that on an average crane operator works for

3:08:11 hours in A shift, 3:26:44 hours in B shift and 4:00 hours in C shift. The data is

attached in appendix C.

Combining the above two studies of postures and work rest cycle we get the data of

how long a person occupies a posture in a shift, as shown in the table below.

Table 3.6 Total time a posture is occupied in a shift

No. Name

A shift

(minutes)

B shift

(minutes)

C shift

(minutes)

1 Straight Back Sitting 26.32 28.84 33.6

2 Forward Bending Looking Down 120.32 131.84 153.6

3 Bending Right & Looking down-right 13.16 14.42 16.8

4 Bending Left & Looking down-left 13.16 14.42 16.8

5 Looking Up 1.88 2.06 2.4

6 Stretching out for Walky-Talky/Mouse 1.88 2.06 2.4

7

7 Reclining on the chair with back

supported 11.28 12.36 14.4

This shows that forward being posture is occupied for over 120 minutes in A shift,

over 131 minutes in B shift and over 153 minutes in C shift. These time durations

exceed the recommended time limits for Low Level Static Postures.

The interaction between the workspace geometry, work organisation and human

results in postures adopted, duration the posture is adopted and work rest cycle.

Another type of interaction between the man and machine is with use of controls. The

further study deals with the interaction between human and control and studies the

frequency of operation, frequency of toggle and sequence of operation of the controls.


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3.8Control Operation Frequency and Sequence

This study shows the frequency of use of each control, the sequence of use of controls

and the duration of occupancy of hands with each of the controls. In table 3.6 shows

operation frequency data for the left hand side controls. Here the operation denotes thenumber of times the control was reached for operation and frequency denotes the

number of times a control was toggled. The time duration for each of the study is 1

hour. The mean frequency of controls use in one hour is 517 for LT, 347 for MCT, 179

for ACT, 20 for Walky-Talky, 401for MH, 243 for AH, 30 for Cabin cross travel and 3

for Bell. Percentage of time left hand is occupied with MT is 36, MCT 36, ACT is 21

and Walky-Talky is 6. Percentage of time right hand is occupied by MH is 43, AH is

24, Cabin Movement 28 and Bell is 4.

Table 3.7 Control operation frequency for left hand Side controls.

Study

Operation

LT

Operation

MCT

Operation

ACT

Operation

WT

1 107 90 71 10

2 100 125 84 24

3 97 95 30 27

4 41 34 16 0

Average 86.25 86 50.25 15.25

Table 3.8 Control toggle frequency for left hand Side controls.

Frequency Frequency Frequency

Study LT

Frequency

MCT ACT WT

1 508 369 247 17

2 372 513 287 27

3 481 248 82 34

4 706 258 102 0

Average 516.75 347 179.5 19.5

Table 3.7 clearly shows that Longitudinal Travel control is the most used

control followed by Main Cross Travel and Auxiliary Cross Travel in

respectively. So LT has to be placed in the most accessible and comfortable

position to enhance the ease of its use. Then priority wise MCT and ACT


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should be placed. Walky Talky is least frequently used and so the function of

leaving the controls to reach the walky talky should be eliminated by provision

for voice activated voice receiver.

Table 3.9 Sequence of Operation of controls for Left Hand Side Controls

Study

Sequence

LT-MCT

Sequence

LT-ACT

Sequence

MCT-

ACT

Sequence

MCT-LT

Sequence

ACT-LT

Sequence

ACT-

MCT

1 60 43 25 60 45 23

2 62 28 45 60 27 47

3 59 12 10 54 15 9

4 19 7 4 17 7 3

Average 50 22.5 21 47.75 23.5 20.5

Table 3.8 shows that control LT and MCT are used most frequently in

sequence of each other. So these two controls should be placed nearer to each

other to reduce the hand travel to move from one control to another control.

Control Operation Frequency

Walky Talky

ACT

MCT

LT

0

100

200

300

400

500

600

1 2 3 4

Controls

Frequency

Fig 3.26 Bar chart showing the frequency of use controllers and walky talky

on left hand side.


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Table 3.9 Control Operation Frequency for Right Hand Side controls.

Study

Operation

MH

Operation

AH

Operation

Cabin

Operation

Bell

Freq.

MH

Freq.

AH

Freq.

Cabin

Freq.

Bell

1 21 10 16 2 289 213 20 2

2 39 20 29 1 585 214 37 2

3 25 22 10 2 290 434 41 2

4 23 9 15 6 440 109 23 6Average 27 15.25 17.5 2.75 401 242.5 30.25 3

Control Operation Frequency

Bell, 3

Cabin, 30

MH, 401

AH, 242

0

50

100

150

200

250

300

350

400

450

1 2 3 4

Frequency

Fig 3.27 Bar chart showing the frequency of use controllers and switches on

right hand side.

3.9Pain Occurrence

For getting the data about perception of exertion and pain by the crane operators

during the working a modified Borg scale of range 1 to 10 was used. The reason forusing the modified Borg scale was the ease of understanding and relating to the

modified Borg scale of range 1-10 instead of the original Borg scale of 6-20. The

operators were asked to give feed back on their perceived pain after every hour or

continuous work. Hundred percent of crane operators suffer from pain in lower back,

neck, upper back, shoulders, arms, forearms, knee and legs. During the first working


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hour the lower back, neck and upper back pain starts and reaches to very high levels

after 2.5 hours of continuous working.

Table 3.10 Pain Perception Feed Back by Operators (on Modified Borg Scale

1-10).

Body Zones 1hour 2 hour 3 hour

Neck 10 10 9

Upper Back 6 7 7

Lower Back 9 10 10

Sholder 4 5 6

Arms 4 5 5

Fore Arms 4 5 5

Wrist 1 1 2

Fingers 0 0.5 0.5

Knee 3 6 6

Legs 4 6 6

Ankle 0 1 0

From the above data it can be seen that all operators start feeling maximum pain in

neck and very very severe pain in lower back just after working for 1 hour in crane

due to continuous looking down. Also significant pain is perceived in other parts of

body. By the third hour of continuous working the pain in neck seems to subside but

when this data is seen in conjunction with all other data, it becomes clear that the

increase in level of pain in other body parts and being working continuously with

maximum level of pain makes the operators perception of pain in neck subside. The

over all results show that operators continuously work for hours under sever working

conditions with maximum pain in lower back and neck region, sever to very severe

pain in upper back and with varied degrees of pain in other body parts.

This study clearly demonstrates that the existing crane cabin design do not provide

any comfort, convenience of use or safety from high risks of musco-skeletal disorder.

A new crane cabin designed on ergonomic principles is necessary to be provided to

relieve the crane operators of stress, pain and risk of any injury. The next chapter

proposes a new ergonomic crane cabin design as a solution to the problems of crane

operators.


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Date post:	03-Jun-2018
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Analysis of Existing Design

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