Design of Human-Centered Collaborative Assembly Workstations for the Improvement of Operators’ Physical Ergonomics and Production Efficiency: A Case Study
Abstract
:1. Introduction
2. Materials and Methods
- a)
- Analysis of the current situation in terms of physical ergonomics;
- b)
- Evaluation of the potentials for collaborative robotics;
- c)
- Workstation re-design for physical ergonomics and production efficiency enhancement.
2.1. Analysis of the Current Situation in Terms of Physical Ergonomics
2.2. Evaluation of the Potential for Collaborative Robotics
2.3. Workstation Re-Design for Physical Ergonomics and Production Efficiency Enhancement
3. Test Case Study Description
4. Results
4.1. Analysis of the Current Situation in Terms of Physical Ergonomics
4.1.1. The OCRA Analysis Results
4.1.2. The RULA Analysis Results
4.2. Evaluation of the Potential for Collaborative Robotics
4.3. Workstation Re-Design for Physical Ergonomics and Production Efficiency Enhancement
4.4. Collaborative Workstation Assessment
4.4.1. Manual Handling Improvements
4.4.2. Postural Improvements
4.4.3. Production Efficiency Improvements
5. Discussion and Conclusions
- Physical ergonomic assessment:
- 2.
- Ergonomic improvements:
- 3.
- Cycle time:
- 4.
- Future research directions:
Author Contributions
Acknowledgments
Conflicts of Interest
Appendix A
Appendix A.1. NIOSH Lifting Equation
Appendix A.2. OCRA Check List
Appendix A.3. RULA Method
Appendix A.4. RULA Evaluation of the Current Assembly Process
A—Arm and Wrist Analysis | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Upper Arm Posture Scores | Lower Arm Posture Scores | Wrist Posture Scores | Wrist Twist Posture Scores | Look-Up Posture Index in Table A | Find row in Table C | |||||||
Task nr. | Left | Right | Left | Right | Left | Right | Left | Right | Left | Right | Left | Right |
1 | 4 | 3 | 3 | 1 | 2 | 3 | 2 | 2 | 5 | 4 | 5 | 4 |
2 | 1 | 1 | 2 | 2 | 3 | 2 | 2 | 2 | 3 | 2 | 3 | 2 |
3 | 1 | 2 | 2 | 3 | 1 | 3 | 2 | 2 | 3 | 4 | 3 | 4 |
4 | 3 | 3 | 2 | 2 | 3 | 4 | 2 | 2 | 4 | 5 | 4 | 5 |
5 | 3 | 4 | 1 | 2 | 3 | 3 | 2 | 2 | 4 | 5 | 4 | 5 |
6 | 2 | 2 | 2 | 1 | 2 | 2 | 2 | 1 | 3 | 3 | 3 | 3 |
7 | 3 | 6 | 1 | 1 | 3 | 4 | 2 | 1 | 4 | 8 | 4 | 8 |
8 | 2 | 2 | 2 | 1 | 3 | 2 | 2 | 1 | 4 | 3 | 4 | 3 |
9 | 4 | 4 | 1 | 2 | 3 | 3 | 2 | 2 | 5 | 5 | 5 | 5 |
10 | 3 | 3 | 2 | 2 | 3 | 4 | 2 | 2 | 4 | 5 | 4 | 5 |
11 | 2 | 2 | 2 | 1 | 2 | 2 | 2 | 1 | 3 | 3 | 3 | 3 |
12 | 3 | 5 | 2 | 2 | 3 | 3 | 2 | 1 | 4 | 6 | 4 | 6 |
13 | 3 | 6 | 1 | 1 | 3 | 3 | 2 | 1 | 4 | 7 | 4 | 7 |
14 | 2 | 6 | 1 | 2 | 3 | 4 | 2 | 1 | 4 | 9 | 4 | 9 |
15 | 2 | 6 | 1 | 2 | 3 | 4 | 2 | 1 | 4 | 9 | 4 | 9 |
16 | 2 | 6 | 1 | 2 | 3 | 3 | 2 | 2 | 4 | 9 | 4 | 9 |
17 | 1 | 6 | 2 | 1 | 3 | 4 | 2 | 2 | 3 | 9 | 3 | 9 |
18 | 2 | 2 | 1 | 1 | 2 | 2 | 2 | 1 | 3 | 3 | 3 | 3 |
19 | 3 | 3 | 2 | 3 | 3 | 4 | 2 | 2 | 4 | 5 | 4 | 5 |
B—Neck, Trunk, and Leg Analysis | |||||
---|---|---|---|---|---|
Task nr. | Neck Posture Scores | Trunk Posture Scores | Leg Posture Scores | Lookup Posture Index in Table B | Find Column in Table C |
1 | 3 | 3 | 1 | 4 | 4 |
2 | 3 | 1 | 1 | 3 | 3 |
3 | 4 | 3 | 1 | 6 | 6 |
4 | 4 | 3 | 1 | 6 | 6 |
5 | 4 | 3 | 1 | 6 | 6 |
6 | 4 | 3 | 1 | 6 | 6 |
7 | 4 | 4 | 1 | 7 | 7 |
8 | 4 | 3 | 1 | 6 | 6 |
9 | 3 | 2 | 1 | 3 | 3 |
10 | 4 | 3 | 1 | 6 | 6 |
11 | 4 | 3 | 1 | 6 | 6 |
12 | 4 | 3 | 1 | 6 | 6 |
13 | 4 | 4 | 1 | 7 | 7 |
14 | 4 | 4 | 1 | 7 | 7 |
15 | 4 | 4 | 1 | 7 | 7 |
16 | 4 | 4 | 1 | 7 | 7 |
17 | 4 | 3 | 1 | 6 | 6 |
18 | 3 | 2 | 1 | 3 | 3 |
19 | 4 | 3 | 1 | 6 | 6 |
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Category | Process Critical Issue (PCI) | Weight (Wi) | Score (Sij) |
---|---|---|---|
Safety and ergonomics | PCI 1: Are there physical ergonomic problems related to: —lifting/lowering or carrying of objects OR —repetitive tasks of the upper limbs characterized by repeated work cycles OR —static or awkward working postures? | 3 | 0–3 |
PCI 2: Are there occupational risks for the operator’s safety which are not properly managed OR occupational risk for operator’s health which are not properly managed? (not yet considered in the previous point) | 3 | 0–3 | |
PCI 3: Is there high work monotonousness OR very low requirements in terms of task qualification of the manual work? | 3 | 0–3 | |
Product and Process Quality | PCI 4: Are there not-constant/satisfactory product quality OR unsuitable process quality levels according to the nominal values (i.e., characterized by high variability/low standardization)? | 2 | 0–3 |
Economics | PCI 5: Is there an inefficient use of time and/or resources without a real advancement of production, which means tasks which cannot generate value to the final costumers (not value-added activities) OR Is there low/not satisfactory process productivity and/or production efficiency? | 1 | 0–3 |
(*) Score meaning: 0—Improvements are not required for that activity / the problem does not exists 1—The achievable improvements could be moderate for that activity 2—The achievable improvements could be good for that activity 3—Improvements could be very significant for that activity |
Possible HRI Workstation Layouts | Nr. of robots R = 1 | Nr. of robots R = n > 1 | |||
---|---|---|---|---|---|
Nr. of kind of workpieces P = 1 | Nr. of kind of workpieces P = m > 1 | Nr. of kind of workpieces P = 1 | Nr. of kind of workpieces P = m > 1 | ||
Nr. of workers W = 1 | Nr of working area A = 1 | RPWA-1111 | RPWA-1m11 | RPWA-n111 | RPWA-nm11 |
| | | | ||
Nr of working areas A = s > 1 | RPWA-111s | RPWA-1m1s | RPWA-n11s | RPWA-nm1s | |
| | | | ||
Nr. of workers W = q > 1 | Nr of working areas A = 1 | RPWA-11p1 | RPWA-1mq1 | RPWA-n1q1 | RPWA-nmq1 |
| | | | ||
Nr of working areas A = s > 1 | RPWA-11qs | RPWA-1mqs | RPWA-n1qs | RPWA-nmqs | |
| | | |
Nr. | Task | Average Task Time (s) |
---|---|---|
1 | Taking 1st wire harness | 2 |
2 | Positioning 1st wire harness | 1 |
3 | Taking 2nd wire harness | 3 |
4 | Positioning 2nd wire harness | 3 |
5 | Adjusting 1st and 2nd wire harness | 2 |
6 | Taking taping pistol | 2 |
7 | Performing 1st taping | 1 |
8 | Depositing taping pistol | 1 |
9 | Taking 3rd wire harness | 3 |
10 | Positioning 3rd wire harness | 5 |
11 | Taking taping pistol | 2 |
12 | Performing 2nd taping | 10 |
13 | Performing 3rd taping | |
14 | Performing 4th taping | |
15 | Performing 5th taping | |
16 | Performing 6th taping | |
17 | Performing 7th taping | |
18 | Depositing taping pistol | 1 |
19 | Storing the wire harnesses | 4 |
Total assembly time (s) | 40 |
HRI Physical Assistance | Key Question | Answer | Motivation |
---|---|---|---|
Manual handling of heavy objects | Is there manual lifting or lowering of heavy objects during the assembly cycle? | NO | The cables are very light (weight << 3kg). The taping pistol weight is less than 3 kg and is supported. |
(Note: it is possible to consider a “heavy object” a weight ≥ 3 kg [18].) | |||
Repetitive upper limb task | Are there one or more repetitive tasks of the upper limbs during the assembly cycle? | YES | The operator performs the same assembly all the day. The average assembly cycle is 40s. In that time, the operator performs 19 tasks. This means that the total amount of daily manual tasks performed by an operator is about 10,945 per shift (it is supposed a shift duration of 8 hours and an effective working time of 80%). |
(Note: it is possible to consider a “repetitive task” an activity with a total duration of one hour or more per shift and characterized by repeated work cycles or tasks during which the same working actions are repeated for more than 50% of the cycle time [19].) | |||
Awkward working postures | Are there awkward working postures during the assembly cycle? | YES | According to a first visual ispection, there are different human body districts which do not maintain a suitable posture during the work. The operator performs the same assembly all day. |
(Note: the awkward working postures are related to neck, trunk, and/or upper limbs and repeated for a significant part of the working time [23].) |
Multiplier | Right Part Value | Left Part Value | Motivation | |
---|---|---|---|---|
Recovery multiplier | 1.33 | The shift (8h) is interspersed with a break (1h). As a result, the operator works for 4 hours without a recovery period. | ||
Constant of frequency (dynamic actions) | 4 | 4 | The movements of the arms are rapid (~40 action/min), interruptions are infrequent and uneven. | |
Constant of frequency (static actions) | 4.5 | 4.5 | The operator is handling the taping pistol and the cables for all the assembly cycle (there is a pinch for more than the 80% of the time for both the right and the left hands). | |
Force multiplier | 0 | 0 | According to the operator interviews, the assembly tasks do not require the use of force (Borg scale values lower than 3). | |
Posture and movements multiplier | Shoulder | 6 | 1 | The movements and related postures were studied according to the guidelines provided in the check list. |
Elbow | 2 | 6 | ||
Wrist | 0 | 0 | ||
Hand | 8 | 8 | ||
Stereotype | 0 | 0 | No stereotype. | |
Additional factors score | 0 | 0 | No additional factors. | |
Multiplier for net duration | 0.95 | The total net duration of the repetitive tasks was estimated to 361–420 min/shift, which takes into account the unplanned interruptions that may occur. | ||
Final Check-list values | 15.8 | 15.8 | Medium red | |
Final risk estimation | Medium | Medium |
Nr. | Task | Left Value | Right value |
---|---|---|---|
1 | Taking 1st wire harness | 5 | 4 |
2 | Positioning 1st wire harness | 3 | 3 |
3 | Taking 2nd wire harness | 5 | 6 |
4 | Positioning 2nd wire harness | 6 | 7 |
5 | Adjusting 1st and 2nd wire harness | 6 | 7 |
6 | Taking taping pistol | 5 | 5 |
7 | Performing 1st taping | 6 | 7 |
8 | Depositing taping pistol | 6 | 5 |
9 | Taking 3rd wire harness | 4 | 4 |
10 | Positioning 3rd wire harness | 6 | 7 |
11 | Taking taping pistol | 5 | 5 |
12 | Performing 2nd taping | 6 | 7 |
13 | Performing 3rd taping | 6 | 7 |
14 | Performing 4th taping | 6 | 7 |
15 | Performing 5th taping | 6 | 7 |
16 | Performing 6th taping | 6 | 7 |
17 | Performing 7th taping | 5 | 7 |
18 | Depositing taping pistol | 3 | 3 |
19 | Storing the wire harnesses | 6 | 7 |
Max values (Overall values) | 6 | 7 |
Process Critical Issue | Score (Sij) | |||
---|---|---|---|---|
Task 1–4, 9–10 | Task 5 | Task 6–8, 11–18 | Task 19 | |
PCI 1 | 3 | 2 | 3 | 2 |
PCI 2 | 0 | 0 | 0 | 0 |
PCI 3 | 2 | 2 | 2 | 2 |
PCI 4 | 0 | 0 | 2 | 0 |
PCI 5 | 3 | 0 | 1 | 3 |
Potential value (Pvalj) | 18 | 12 | 20 | 15 |
Potential class | good | good | good | good |
Involved Body Part, Posture, and Movements | Involved Task | Possible Solutions |
---|---|---|
upper arm position and movements | tapings | Use of a collaborative robot as support for tapings |
wrist position and twist and movements | all tasks | Re-design of the worktable areas according to main anthropometric requirements [24] |
neck position | all tasks | Re-design of the worktable areas according to main anthropometric requirements [24] |
trunk position | all tasks | |
Involved work-related feature | Involved task | Possible Solutions |
activity rhythm | all tasks | Use of a collaborative robot as support for the reduction of manual frequency |
overload balance | all tasks | Use of a collaborative robot as support for the balance of the overload between left and right body sides |
Multiplier | Right Part Value | Left Part Value | Motivation | |
---|---|---|---|---|
Recovery multiplier | 1.33 | It was supposed that the shift (8h) is interspersed with a break (1h). As a result, the number of hours without recovery period is 4, which means a multiplier equal to 1.33 | ||
Constant of frequency (dynamic actions) | 3 (–25%) | 3 (–25%) | The movements of the arms are rapid (~40 action/min). There is the possibility of short interruptions. This means a multiplier equal to 3. | |
Constant of frequency (static actions) | 2.5 (–44%) | 2.5 (–44%) | The operator handles the taping pistol and the cables for more than half of the assembly cycle (there is a pinch for about the 70% of the time for both the right and the left hands). This means a multiplier equal to 2.5. | |
Force multiplier | 0 | 0 | According to the operator interviews, the assembly tasks do not require the use of force (Borg scale values lower than 3). | |
Posture and movements multiplier | Shoulder | 1 (–83%) | 0 (–100%) | The movements and related postures were studied according to guidelines provided in the check list. |
Elbow | 8 (+300%) | 6 | ||
Wrist | 0 | 0 | ||
Hand | 0 (–25%) | 0 (–25%) | ||
Stereotype | 0 | 0 | According to the definition, there is no stereotype | |
Additional factors score | 0 | 0 | According to the definition, there are no additional factors | |
Multiplier for net duration | 0.95 | It was supposed that some working interruptions sometimes occur. As a result, the total net duration of repetitive tasks is 361–420 min/shift, which means a multiplier equal to 0.95 | ||
Final Check-list values | 13.9 | 11.4 | Yellow | |
Final risk estimation | light | light | ||
Reduction percentage | –12.0% | –28% |
Nr | Task | Final Value Left Side | Final Value Right Side |
---|---|---|---|
1 | Picking the 1st wire harness the box | 2 | 2 |
2 | Positioning the 1st wire harness into the frame | 3 | 3 |
3 | Picking the 2nd wire harness from the box | 2 | 2 |
4 | Positioning the 2nd wire harness into the frame | 2 | 2 |
5 | Adjusting the first cable group on the second cable group | 2 | 2 |
6 | Pushing the button (robot call) | 3 | 3 |
7 | Moving from Panel 1 to Panel 2 | 2 | 2 |
8 | Taking the previous final assembly from the frame | 3 | 3 |
9 | Storing the previous final assembly into the box | 3 | 3 |
10 | Moving from Panel 2 to Panel 1 | 2 | 2 |
11 | Picking the 3rd wire harness from the box | 2 | 3 |
12 | Positioning the 3rd wire harness into the frame | 3 | 3 |
13 | Pushing the button (robot call) | 3 | 3 |
14 | Moving from Panel 1 to Panel 2 | 2 | 2 |
Perform the same tasks (from 1 to 6) on Panel 2 and then come back to Panel 1 *** | |||
15 | Taking final assembly from the frame | 3 | 3 |
16 | Storing the final assembly into the box | 3 | 3 |
Max values (Overall values) | 3 | 3 |
RULA Analysis Results (Max Values for Each Posture) | |||||||
---|---|---|---|---|---|---|---|
Actual Workstation | Collaborative Workstation | Index Variation | |||||
Left Side | Right Side | Left Side | Right Side | Left Side | Right Side | ||
Arm and Wrist Analysis | Upper Arm Posture Scores | 4 | 6 | 2 | 2 | –2 | –4 |
Lower Arm Posture Scores | 3 | 3 | 2 | 2 | –1 | –1 | |
Wrist Posture Scores | 3 | 4 | 2 | 2 | –1 | –2 | |
Wrist Twist Posture Scores | 2 | 2 | 2 | 2 | 0 | 0 | |
Muscle Use Scores | 0 | 0 | 0 | 0 | 0 | 0 | |
Force/Load Scores | 0 | 0 | 0 | 0 | 0 | 0 | |
Neck, Trunk, and Leg Analysis | Neck Posture Scores | 4 | 3 | –1 | |||
Trunk Posture Scores | 4 | 2 | –2 | ||||
Leg Posture Scores | 1 | 1 | 0 | ||||
Muscle Use Scores | 0 | 0 | 0 | ||||
Force/Load Scores | 0 | 0 | 0 | ||||
Max values (overall values) | 6 | 7 | 3 | 3 | –3 | –4 | |
Improvements (reduction % of overall workstation values) | 50% | 57% |
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Share and Cite
Gualtieri, L.; Palomba, I.; Merati, F.A.; Rauch, E.; Vidoni, R. Design of Human-Centered Collaborative Assembly Workstations for the Improvement of Operators’ Physical Ergonomics and Production Efficiency: A Case Study. Sustainability 2020, 12, 3606. https://doi.org/10.3390/su12093606
Gualtieri L, Palomba I, Merati FA, Rauch E, Vidoni R. Design of Human-Centered Collaborative Assembly Workstations for the Improvement of Operators’ Physical Ergonomics and Production Efficiency: A Case Study. Sustainability. 2020; 12(9):3606. https://doi.org/10.3390/su12093606
Chicago/Turabian StyleGualtieri, Luca, Ilaria Palomba, Fabio Antonio Merati, Erwin Rauch, and Renato Vidoni. 2020. "Design of Human-Centered Collaborative Assembly Workstations for the Improvement of Operators’ Physical Ergonomics and Production Efficiency: A Case Study" Sustainability 12, no. 9: 3606. https://doi.org/10.3390/su12093606