ERGONOMIC AND LEGAL PERSPECTIVES
CHAPTER 1 CHAPTER 1 1
3. Remove new roll and place on floor
4. Roll new roll across the floor to the wrapping machine (dis- 5. Insert spindle into new roll and lift assembly into machine.
6. Secure new roll in feed mechanism and splice leader to rem- location.
tance up to 13 f t [4.0 m]).
nant of old roll.
Posture Analysis
Due to the low height of plastic roll on the wrapping machine and the low storage height of boxes on the pallet, elements # 1 , 3 , 4,5, and 6 were performed with the worker’s trunk bent forward.
As shown in Table 11-3,87% of the work cycle was performed with the trunk in severe flexion (forward bending more than 45O). In addition, mild forward flexion of both shoulders was required when performing some of the low reaches.
Methods for Evaluating Postural Work Load
Observed
Table 11 -3. Results of posture analyses on case study iob (Keyserling et al. 1993)
% of postures
Trunk
Stand, neutral Stand, mild flexion Stand, severe flexion Obscured view Neck
Neutral Mild flexion Severe flexion Twisting Obscured view Left shoulder Neutral Mild elevation Severe elevation Obscured view Right shoulder Neutral Mild elevation Severe elevation Obscured view
Pre-change
13 0 87 0
75 24 0 3 0 31 68
< 1 0
21 79
<1 0
ycle
Post-change
72 23 2 3 58 38
<1
< 1 3 88 10 0 3 89 8 0 3
Time in post1 Pre-change
9.5 0.0 70.5 0.0
17.0 5.7 0.0 1.4 0.0 10.9 23.8 0.3 0.0 10.7 51.8 0.3 0.0
Note: Lower body posture was not considered during this case study.
e (seconds) Post-change
30.6 8.4 3.1 7.0 22.4 9.6 0.7 1.5 7.0 113.0 16.0 0.0 6.8 46.6 4.6 0.0 6.9
ERGONOMIC CHANGES
ic stresses on this job:
Three significant changes were implemented to reduce ergonom- 1. The location of the film roll on the machine was raised from
15 in. (38 cm) to 31.1 in. (79 cm). See Figure 11-6.
2. The pallet used for storing film rolls was positioned on a 22.8- in. (58-cm) “backsaver” rack. See Figure 11-7.
3. A lift cart was provided for raising, lowering, and transport- ing rolls. Not only did this eliminate the need to stoop while rolling the roll across the floor from the storage pallet to the
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Ergonomics in Manufacturing
Film roll (in place on machine)
31.1 in. (79 cm)
Figure 17-6 Location of film roll on wrapping machine after ergonomic changes.
Raising spindle location reduced awkward trunk posture during roll change operations.
machine, but it also eliminated the need to manually lift and lower a heavy load-66 lb (30 kg), including spindle.
P OST-CHANGE ANALYSIS
Workstation Layout and Work Elements
The effort of the worker to reach to low locations was ameliorat- ed by raising the height of the film roll on the machine and placing storage pallets on racks. firthermore, with the addition of the lift cart, the following sequence of tasks was used to perform a roll change:
1. Cut film and use lift cart to remove old roll and spindle from 2. Use cart to transfer used roll to storage location; place used 3. Push cart to pallet holding boxes of new rolls.
4. Remove new roll from box and place on cart.
machine.
roll on storage pallet.
Methods for Evaluating Postural Work Load
22.8 in.
(58 cm)
film film
film film
film film
Backsaver
Figure 1 1-7 Location of film roll on machine after ergonomic changes. Placement of the pallet on a "backsaver" rack raises rolls off the floor, reducing awkward trunk posture.
5. Push cart to wrapping machine.
6. Insert spindle in new roll, use cart to lower assembly into 7. Secure new roll in feed mechanism and splice leader to rem-
machine.
nant of old roll.
Posture Analysis
As a result of changes to workstation layout and equipment, it was no longer necessary for the worker to position the trunk in severe flexion. As shown in Table 11-3, the new configuration al- lowed the worker to maintain a neutral posture for 72% of the work cycle. Mild trunk flexion was required during 23% of the cycle and a twistedbent posture was required for only 2% of the cycle. The time spent with the left and right shoulders in an elevated posture was also decreased as a result of reduced reach requirements.
Case Review
A posture analysis of this job revealed that roll changing required prolonged usage of awkward trunk postures. This information was used to develop changes in workstation layout and equipment to re- duce the duration and severity of awkward trunk postures. firther- more, the new lift cart significantly reduced the amount of lifting and carrying required to perform a roll change. Both of these chang-
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Ergonomics in Manufacturing
es reduced worker exposure to risk factors associated with occupa- tional low-back pain. There was also a slight reduction in awkward shoulder postures as a result of the layout changes.
SUMMARY
Awkward working posture occurs when there is a mismatch be- tween a worker’s body size and job requirements. When awkward postures are used repetitively or for extended periods, undesired outcomes may occur, including fatigue, discomfort, injury, and re- duced productivity.
Ergonomists have developed a number of job analysis method- ologies to evaluate awkward postures. Some of these methods (for example, posture checklists and OWAS) are easy to use and do not require special equipment. These methods can be used as part of a rapid screening program to identify jobs where postural demands are excessive. When the rapid screening methods identify a job with excessive postural stress, it is necessary to perform a detailed analysis to determine the root causes of awkward posture. This analysis provides the essential information for developing practi- cal and effective workplace interventions for controlling awkward posture.
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