With restriction
Definition: |
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With restriction refers to an assembly process in which obstructions may occur due to poor visibility or insufficient space. |
Explanation:
With restriction sight: Restrictions to the line of sight to the positioning location by the object to be positioned do not necessarily result in awkward body posture. With relatively small components, it can be expected that an obscured positioning location may lead to assembly delays due to corrective movements. But this does not generally result in unfavorable body posture. However, when working with relatively large or heavy components, resticted visibility can lead to poor body posture - such as forward bending, rotation of the trunk or lateral bending, or lateral bending. A restricted line of sight is therefore taken into account when evaluating ergonomic risks. |
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With restriction space: Restricted space usually means that access to the positioning location is more difficult for the hand/finger performing the motion. In order to achieve accessibility, unfavorable joint positions of the arms (upper limbs) performing the motion are to be expected here. From an ergonomic point of view, joint positions are considered unfavorable if the average joint mobility exceeds 50%. This applies to the wrist, elbow, and shoulder joints. Restriction in terms of accessibility is therefore taken into account when evaluating strains on the upper limbs. |
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There are three application rules:
Rule M-B1:
Definition: |
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If there is an restriction in space or line of sight, its frequency is 1 in the corresponding column. |
Rule M-B2:
Definition: |
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In the case of restriction due to space and visibility, both types of restriction are evaluated with a frequency of 1. |
Rule M-B3:
Definition: |
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If when positioning a component, the positioning locations are hidden by the component itself, restriction due to visibility is analyzed. |
Without positioning aids
Definition: |
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Without positioning aids refers to an assembly process in which neither the component or sub-assembly, nor the positioning location, is equipped with positioning aids, such as stops, guides, etc. |
Explanation:
Without positioning aids: Missing positioning aids inevitably result in assembly interferences. |
 w/o positioning aid |
 with positioning aid |
With fixing of position
Definition: |
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With fixing of position refers to an assembly process in which a component or sub-assembly is not in a stable (final) position after initial positioning. |
Explanation:
With fixing of position: Fixing of position comprises all measures necessary to keep a part in a specific position until it has reached a stable position through a subsequent assembly process. |
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The component is fixed only by the subsequent positioning of screws.
Example: |
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Assemble bolt with lock washer and washer  Assembly steps: 1.Place base plate in stable position 2.Lay washer on base plate and hold it in place 3.Place the spring washer on the washer and hold it in place 4.Position bolt through washer and lock washer into thread and hold it in place 5.Engage thread 6.Turn on and tighten bolt |
Please note: |
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From an ergonomic perspective, holding a component in position until the subsequent assembly process (e.g. screwing, locking into place) can result in an actual static action. This means that the component must be controlled for a longer period (4 seconds or more). Depending on the weight of the component and the mode of grasping (e.g. thumb and index finger or powergrip), this may result in an increased ergonomic risk for the upper limbs. The assembly difficulty "With fixing of position" is therefore taken into account in the ergonomic evaluation. |
Fault assembly position possible
Definition: |
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Fault assembly position possible refers to an assembly process in which it is possible to assemble a component or sub-assembly in more than one way. One or more of the possible positions may be wrong (Poka Yoke). |
Explanation:
The design of the component or assembly allows for fitting in more than one way. This may make it necessary to rework individual components or assemblies, or it may represent a risk of improper functioning. To avoid this, components or assemblies should be designed in such a way that wrong assembly positions are impossible (see schematic diagram or, e.g., tabs on a plug with defined polarity). The assembly difficulty "Fault assembly position possible" has no bearing on the ergonomic risk evaluation. |
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A design that provides for several assembly positions simplifies the assembly process.