Analysis Workstation in Manufacturing Industry using Occupational Repetitive Action (OCRA) Index Method to Reduce Risk of Work-Related Musculoskeletal Disorder

. According to analysis of Global Burden of Disease (GDB) 2019 data, approximately 1.71 billion people have musculoskeletal disorder (MSDs) worldwide. It could cause constant pain and limitations in mobility, dexterity, and reducing people’s ability to work. Musculoskeletal disorders can be caused by repetitive and heavy work activities. On Hub 2/3 work station, production is carried out by machining processes using CNC machines, drilling machines and tapping machines with predetermined target outputs. In this process, there are repetitive actions which have risk of musculoskeletal disorders. By using the OCRA method and calculating the OCRA Index value, the operator 1 is in the red zone, then operator 2 and operator 3 are in the yellow zone which means the work conditions at workstations must be improved. The objective of this paper is to analyze Hub 2/3 workstations in order to minimize the risk of musculoskeletal disorders for each operator. The proposed improvement are given to fulfill the objectives of this paper. The results of the OCRA calculations with the assumption that all proposed improvements are applied are smaller than the previous calculations which means the risk of musculoskeletal disorders is reduced.


Introduction
According to analysis of Global Burden of Disease (GDB) 2019 data, approximately 1.71 billion people have musculoskeletal conditions or musculoskeletal disorder worldwide.It can cause constant pain and limitations in mobility, dexterity, and reducing people's ability to work [1].
Musculoskeletal disorders could occur due to work.In manufacturing industry, upper limb is very often used for work.Therefore, the research is focused on analyzing the upper limb work-related musculoskeletal disorders (UL-WMSD).UL-WMSD are caused by repetitive and/or forceful movements of the upper limbs performed for prolonged periods in the workplace, which put the joints, muscles, tendons, and other soft tissues under significant strain and can also affect the peripheral nerves [2].
The ergonomic workstation and work organization are necessary to prevent UL-WMSD.Ergonomics (or human factors) is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system [3].Ergonomics adopts a systems approach to designing effective work, and that requires consideration of relevant cognitive, physical, and organizational factors [4].
There are many methods to evaluate the risk of UL-WMSD.Rorecrance et al. [5] use strain index method and OCRA checklist to asses risk of cheese processing tasks.Gualtieri et al. [6] use Rapid Upper Limb Assessment and OCRA checklist to asses risk and design human-centered collaborative assembly workstations.
This paper use OCRA index to analyze and evaluate Hub 2/3 workstations because this methods used in international and have been adopted by International Standard (ISO).[7] The occupational repetitive actions (OCRA) index is the most precise method for analyzing and evaluating the risk of exposure to repetitive tasks.The OCRA index is a particularly useful tool for those involved in designing the content and duration of work cycles.The index will help them to monitor and manage not just productivity but also risk levels, the likelihood of occupational diseases and disorders, and therefore also costs [2].Likewise, Tiacci L et al.Use OCRA index for risk evaluation and balancing/sequencing decisions for mixed model stochastic.[8] This research focuses on mass production processes that produce fixed number of products every hour.The type of production process carried out is a machining process that uses CNC lathe 2-axis and multi drill machine.In this process the operator perform repetitive work for 8 hours lifting objects weighing 15 kg.
In order to reduce risk of UL-WMSD, redesign workstation or work condition are necessary after calculating the OCRA index.The design of workstation should be pay attention to the task, workplace, and work organization.The tasks should be designed in a way that extreme ranges of joint movement, prolonged static postures and/or repetitive movements, combined with external forces, are avoided.The workplace should be designed in such a way that working postures and their sequences can be optimized.The work should organize to make the task duration not too long, the frequency of movements and or force exertions should not too high and can be adjusted by the worker to his/her own individual capabilities, and there should be sufficient recovery periods.[9] 2 Methods This study uses quantitative and qualitative methods in obtaining the data.Some data obtained from the company such as process production data, duration of working hours and rest time, layout of Hub 2/3 workstation.Other data was obtained by observing the conditions of work environment, work attitude, and working posture of Hub 2/3 operators then assigning a score to the results.There are potential confounding variables that may have influenced the results of this study such as the posture of operator, the fitness and the strength of operator.
The OCRA index is produced by the ratio of the absolute number of actual technical actions (ATA) currently performed in a work shift to the corresponding number of recommended technical actions (RTA).In order to calculating RTA, there are risk factors or multiplier that must be considered such as force multiplier, posture multiplier, repetitive multiplier, additional multiplier, duration multiplier and recovery multiplier.
Force multiplier determined by interviewing workers about the force exerted by workers while doing their work.The interview results are then converted into values based on the Borg CR-10 scale so that FoM values can be determined by calculating the duration of each force issued.Table 1 proposes a model for applying the Borg scale to gather information about perceived physical exertion and Table 2 used to assign the force multiplier (FoM).Posture multiplier determined by observing the posture the operator forms while performing the job and determining the value by calculating the duration of the awkward posture performed.This method focuses on postures and movements of the arm with respect to the shoulder, movements involving the elbow, wrist postures and movements, and hand postures and movements.Figure 1 shows the postural involvement of the shoulder which categorized as awkward posture and the score of the posture are shown in Table 3. Figure 2 shows the postural involvement of the elbow which categorized as awkward posture and the score of the posture are shown in Table 4. Figure 3 shows the postural involvement of the wrist which categorized as awkward posture and the score of the posture are shown in Table 5.  Figure 4 shows the postural involvement of the hand and fingers which categorized as awkward posture and the score of the posture are shown in Table 6.Table 7 shows the elements required to go from the descriptive effort score to the corresponding PoM.This table will be used for each segment of the upper limb and separately for each limb.The most penalizing posture multiplier (PoM) is used, corresponding to the highest postural effort from among the scores for the hand, wrist, elbow, or shoulder of each limb.Repetitive multiplier can be determined by two different scenarios as shown in Table 8.Additional multiplier can be by observing the work station whether there are other factors that interfere with the work process such as the working environment (lighting, vibration, temperature, noise) which is not good.In addition, observations were made on the personal protective equipment whether it cause more difficult to work, risks workers exposure to cold from the ambient temperature or from tools or materials.Table 9 shows the elements used to assign the additional risk factor multiplier (AdM), based on the descriptive classifications presented.Duration multiplier determined by obtaining the total net duration value when performing repetitive actions, namely by subtracting the duration of one full shift with breaks, lunch, movements that are categorized as recovery periods and the total duration of movements that do not include repetitive movements.Table 10 provides the parameters for dealing with the duration multiplier (DuM).(3) N = number of repetitive tasks per shift J = generic (j-th) repetitive task performed by the upper limbs CF = RTA frequency (30) per minute under reference conditions FoMj; PoMj; ReMj; AdMj = multipliers, chosen in relation to the behavior of the force, posture, repetitiveness, and additional risk factors embedded in each j-th task under examination Dj = duration (in minutes) of each j-th repetitive task RcM= multiplier for the "lack of recovery period" risk factor (one only for jobs with 1 or more repetitive tasks) DuM= multiplier that takes into account the net duration of repetitive tasks (one only for jobs with 1 or more repetitive tasks) Furthermore, the final value of OCRA index are classified on Table 12 to determine the suggested action.The last step are analyze each risk factor to find potential improvement to redesign Hub 2/3 in order to reducing or minimize the risk of UL-WMSD for each operator.

Results and discussions
Data collection was carried out at Hub 2/3 workstations with 3 operators operating 5 machines.Operator 1 operates CNC Lathe machines 1,2 & 3. Operator 2 operates a drill machine and Operator 3 operates a tap machine.The data obtained from observations are cycle time data and technical actions carried out by each operator which are recorded with a camera and interview with the operator.
Table 13 show the data of technical action of left upper limb and right upper limb on Operator 1.

Actual Technical Actions (ATA) calculations
The data of technical action that has been obtained, then able to be processed to obtain the frequency value and ATA which shown in Table 14.

Factor multiplier of RTA
In the calculation of RTA required multiplier factor of force, posture, repetitive, additional, duration of repetitive action and recovery.

Force Multiplier
The force multiplier obtained with the use of Borg CR-10 scale are shown in Table 15 and assign the multiplier on Table 16.

Awkward posture multiplier
For awkward posture multiplier, the posture and movement of operator are assessed and analyzed with Table 3,4,5 & 6.The results are shown in Table 17.

Repetitive multiplier
Table 18 show the technical action adapted to repetitive scenario to obtain repetitive multiplier.

Additional multiplier
According to the data obtained.There are no additional factors that affect the risk of UL-WMSD of the workers Operator 1, 2 & 3. Therefore, the additional multiplier value is 1.

Duration multiplier
According to the data obtained.Duration of shift-1 workstation Hub 2/3 area 540 minutes with detail description shown in Table 19.

Recovery multiplier
The distribution of recovery time during shift 1 working hours at Hub 2/3 workstations is shown in Figure 5.According to Figure 5, the number of hours without adequate recovery are 3.5 hours from 12.30 until 16.00.Therefore, the recovery multiplier is 0.65.

Recommended technical action (RTA) calculations
The overall calculation of the number of RTA is used to determine the recommended technical measures.The results are shown in

OCRA Index calculations
The final step in data processing on the OCRA Index is to calculate the value of the OCRA Index which is done by comparing the results of the value of the number of actual technical actions (ATA) and the overall value of the number of reference technical actions (RTA).The results are shown in Table 21.

Proposed Improvements
Proposed improvements are given to reduce the value of the OCRA index so as to reduce the risk of workers against UL-WMSD.

Proposed recovery time
The current workstation has 2 rest periods with numbers of hours without adequate recovery period for 3.5 h. Figure 6 show the proposed distribution of recovery time which has 3 rest periods with numbers of hours without adequate recovery period for 2.5 h.Therefore, the RcM value becomes 0.7.

Proposed install flexible hose in Machine5
In the process of operator 3, there are a posture gripping the air gun for 83.14% of the cycle time.by installing a flexible hose on Machine5 then this can be eliminated so that the ReM and PoM value decreased.

Proposed use of back support for operators
The work piece weight of 15.2 kg makes the Borg CR-10 score 7 when lifting & placing the work piece.By using back support for operator, the score will be reduced because back support can reduce low back injuries by 34% [10].

OCRA index after improvement
After improve workstation using OCRA index, the proposed improvement has been implemented and be shown in Table 22.

Conclusion
The results of the OCRA calculations were obtained 0.82 on left hand of operator 1 and 3.69 on right hand of operator 1, 0.70 on left hand of operator 2 and 2.30 on right hand of operator 2, 0.14 on left hand of operator 3 and 2.40 on right hand of operator 3. Therefore operator 1 is classified in the red zone, operator 2 and operator 3 are classified in the yellow zone which means the work conditions at workstations must be improved.After improvement, OCRA index were obtained 0.71 on left hand of operator 1 and 2.71 on right hand of operator 1, 0.61 on left hand of operator 2 and 1.73 on right hand of operator 2, 0.12 on left hand of operator 3 and 1.02 on right hand of operator 3. From these results it can be seen the OCRA index after improvement are lower than before improvement.It means the risk of musculoskeletal disorders for each operator on Hub 2/3 work station is reduced.In other words the Hub 2/3 work station is more ergonomic.
According on the results of the analysis, the longer operator perform works without adequate recovery, the longer operator sustain static postures, the higher force used to perform works, then the risk of musculoskeletal disorders for operator are higher.
After this research, there is a potential for future research to analyze work equipment such as checking tables, conveyor tables, raw material pallet and finished goods pallet using the Recommended Weight Limit method to maximize the value of force multiplier.
of ATA calculated from actual action performed by operator per shift.At any rate: [3] duration (in minutes) of task j Fj = average frequency of action per minute of task j ({number of technical action * 60} / total net cycle time duration)

Table 15 .
Assessment of Borg CR-10 Scale right upper limb of Operator 1

Table 16 .
Assessment of force multiplier of Operator 1

Table 17 .
Assessment of posture multiplier of right upper limb Operator 1 (choose the worse between shoulder, elbow, wrist and hand and fingers)

Table 22 .
OCRA Index after improvement