How to Design Assembly Instructions
Authors: Hinrichsen Sven , Bläsing Dominic 
Published: April 2022

Manual assembly of products that consist of many components in different constellations is a serious challenge for each employee in an assembly system. Each appearing new product to be assembled requires an immediate adaptation of familiar assembling habits to actual demands of the order. The higher the complexity of the assembly task, the higher is the resulting entropy and the more uncertainty has to be coped with. For the employee this implies to be more attentive, to recognize and process more information, to meet more decisions and invest more cognitive capacity in the control of behavior. Generally, a high level of task complexity leads high mental workload (Young et al., 2015). As a consequence excessive load can affect selective attention, leading to an increase of lapses and errors and performance degradation. An ergonomic preventive strategy that can help to make the experienced complexity manageable for the employees, consists of a better design of instructions or informational displays. These instructions aim to select and present information on the assembly process in such a way that the sensory reception, the cognitive processing of this information and the response selection and control lead to more effective (error prevention) and more efficient (short execution time) performance. However, often there is a discrepancy between intended and realized effects. Hollnagel (1997) offers two explanations for these discrepancies: Employees do not have a proper understanding of their work and additionally, designer´s conceptualizations of the internal model of users are far from perfect. In practice, this can lead to a disagreement between designer and operators, whether information is useful or not. This paper discusses some important principles for the design of assembly instructions. The design hints are classified in terms of content, information provision and the medium that is used for presentation. Important content requirements for assembly instructions relate to relevance, actuality, clarity, accentuation, and completeness. Requirements for the provision of information include, in particular, the type of information presented on a display, the structuring of information, constellation of representation codes, and the design of the information dependent on operator experience. With regard to the medium, assembly instructions can be provided via analog or digital interfaces. Concerning the last topic (analog: paper-based instructions vs. digital: information assistance system based instructions) results from laboratory studies are discussed in the paper. Finally, some guidelines for the design of an information management system and a framework for continuous improvement of such instructions are presented. The goal must be to implement end-to-end digital process chains – starting with the client´s order via product data and ending with output of assembly instructions at individual workstations. To this goal, the organizational prerequisites are to be shaped, for example by further developing competencies of members of the industrial engineering of the company. Additionally, with participation of users, a continuous improvement process should be established to regularly evaluate and optimize existing assembly instruction standards.