Completing the OCRA checklist using the ViveLab Ergo software for ergonomic evaluation
There are several methods for ergonomic evaluation worldwide that are based on estimates after visual inspection, including RULA, OWAS, EAWS, APSA, NPW and OCRA. These ergonomic analysis methods are excellent tools for mapping workplace shortcomings and critical areas, as well as for proposing and implementing corrective measures in order to improve working conditions. However, since these methods have until recently been based exclusively on inspection with the naked eye, followed by estimation and manual evaluation, they have had three major disadvantages:
• In the case of larger production plants corrective measures may have been delayed for an unforeseeable period due to the inaccuracy of the visual inspection and the slowness of the ergonomic evaluation that was carried out manually.
• The results depended on the subjective judgement of the ergonomics expert
• Visual inspection may have left some shortcomings unnoticed
Today, however, both survey and evaluation of the results are assisted by digital solutions thanks to the Xsens motion capture equipment and the ViveLab Ergo software for ergonomic analysis. The Xsens sensory equipment captures body postures and movement objectively and replaces lengthy monitoring that has been requiring a lot of concentration and still remained inaccurate sometimes. TheViveLab Ergo software evaluates the captured motion file in the blink of an eye.The ergonomic analysis report that can be exported from the software accelerates the completion of the OCRA checklist as well. In this blog post we are going to explain the steps of the procedure and to reveal the benefits of this method.
ViveLab Ergo in a nutshell
The movement of the workers at the production line is recorded with Xsens motion capture sensory equipment. The recorded digital motion file is imported into the ViveLab Ergo 3D software and analyzed with the help of the implemented ergonomic analysis methods, such as RULA, OWAS, NASA-OBI, ISO 11226, EN 1005-4, reachability zone and spaghetti diagram. The software evaluates postures and checks whether the load on each body part exceeds the acceptable limit. A detailed report of the analysis results can be exported from the software in a few minutes.
All those skills that the most experienced and qualified professionals should have in assessing workstations from ergonomic point of view have been implemented in the software. The chance of mistakes due to carelessness or lack of attention is eliminated this way.
Since the motion is captured by Xsens sensory equipment and the analysis of the motion files is carried out by the ViveLab Ergo software, neither the survey nor the evaluation of results depend on the capabilities, skills and judgment of the person who carries out the procedure. We always get the same, accurate and objective results.
How can we extract OCRA data from the software?
The ergonomic standards and methods for posture analysis have all been devised to prevent musculoskeletal disorders. Their evaluation methodology and testing aspects are very similar. OCRA (Occupational Repetitive Actions) examines the load on the upper limbs during repetitive work. The RULA, EN 1005-4: 2005 + A1:2009 and ISO 11226: 2000 methods test (along with other body parts) the upper body load similarly to the OCRA method. These latter three more comprehensive methods are implemented in the ViveLab Ergo software and a detailed report of these methods can be easily compiled to provide the information needed to complete the OCRA checklist.
Let's have a look at an example
In order to determine the frequency score OCRA considers static and dynamic positions as well. To this purpose the ISO 11226: 2000 and EN 1005-4: 2005 + A1: 2009standards can be used that are both implemented in ViveLab Ergo. The ISO 11226:2000 analysis lists all static positions with holding times longer than 4seconds. Figure2 shows that during the 22-second work cycle the worker was forced to hold the trunk in an axially twisted position for 5s 300ms. During this 5s 300ms time interval the average axial rotation angle was 21 °. From the holding times of critical postures that are listed according to ISO 11226: 2000 and from the length of the work cycle the time percentage when critical static postures are taken throughout the workflow can be calculated.
The EN1005-4: 2005 + A1: 2009 analysis, that is implemented in the ViveLab Ergo software, lists all critical body movements that are exceeding the allowable frequency of holding a particular body part at certain angle. Figure3 shows, for example, that during a 22-second work cycle the trunk had to be rotated axially 5 times and lateral flexion of the trunk occurred 8 times. These objective values can be used to calculate the OCRA frequency sub-score.
The OCRA partial score that is related to posture can also be calculated using the ISO 11226:2000 and EN 1005-4: 2005 + A1: 2009 methods. In this regard the RULA analysis can be of great help as well. The RULA analysis results show the percentage of time when relevant body parts had to be held in a certain angle range during the work cycle. For example, Figure4shows the analysis results for the left arm and left wrist. In 26.1% of the duration of the work cycle the left arm was forced to be held at an angle greater than 90 °. The left shoulder had to be lifted during 34.8% of the work cycle. The employee had to keep his left wrist at an angle greater than 15 ° during 30.4% of the work cycle and it had to be tilted to the left or right in 60.9%of the time. Based on these data the OCRA score can be easily calculated.
Why is it worth using ViveLab Ergo?
It is clear from the examples above that the reports generated by the ViveLab Ergo software make it possible to examine objectively and extremely quickly those data that are considered in the different posture related units of the OCRA analysis.
When using the ViveLab Ergo method, it is not necessary to have an ergonomics expert on-site to record the movements of the employee. It is enough to have a technician who puts on the motion capture suit and starts the recording. This can replace the lengthy, tiring and subjective visual inspection that requires deep concentration.
Without the help of the ViveLab Ergo software it can take from three up to five years for a team of experts to analyze 2000 workstations. During this time the workforce pool and the environment can undergo dramatic changes. By the time the experts finish the survey of the production plant, they may have to start it from the beginning again. As the number of trained ergonomics experts is very limited, it is unlikely that many of the experts can work simultaneously on the same task for months or years. Consequently we can hardly count on multiplying the number of experts working on our project. Using the ViveLab Ergo software the same task can be accomplished by a team of three technicians in four months. The time needed can be significantly reduced to as little as one month employing more technicians and using more than one Xsens motion capture suits. Considering that the training of a technician can be completed within one or two days, it is possible to multiply the number of members in the survey team and to reduce the time that is needed to carry out the survey.
For further information, have a look at our pdf document and read how ViveLab Ergo can support OCRA evaluation!