# Natural Virtual Reality User Interface to Define Assembly Sequences for Digital Human Models
## 1 Introduction  
The goal of Model Based System Engineering (MBSE) is to consider all system-relevant parameters within the virtual product creation. Shortening the product development process and thus saving money is motivation for a holistic model mapping. Once the product to be developed and additionally dependent subsystems have been developed, later dependencies and interactions can be predicted. In particular, advanced systems engineering (ASE) emphasizes the protection of the user and postulates the protection of human factors in the early phases of product development. The evaluation of human factors is not new. Aspects such as user experience and usability are, for example, required as sales arguments. Still, it is often the case that human factors are usually only tested on real prototypes in late phases of product development. In this phase, significant changes to the product are hardly possible, and it is therefore necessary to efficiently integrate the assurance of human factors into the early virtual product development process. One of the central challenges is to involve human beings already in the early stages of the product development process to design suitable assembly stations and ensure consistent product quality [1]. Therefore, companies use digital human models (DHMs), which are digital representations of human beings. They are used to design secure and efficient workplaces and processes [2]. Such DHMs are often integrated into computer-aided software systems (JACK by Siemens PLM (Siemens PLM 2016), RAMSIS by Human Solutions [3] as well as the HUMAN from Dassault Systemes [4]). The use of DHM software improves the communication possibilities within companies [5]. The reason why many companies do not use DHMs is the high cost of training engineers to use them for ergonomic analysis. Thus, the complexity of the software keeps small and middle-sized enterprises away from using DHMs. The report \"Digital ergonomics 2025\" [6] describes the results of a survey with experts about trends of digital human models until 2025. The experts recognized six impediments of DHM software systems, of which three address the aspect of usability of such software systems: the high complexity of the software systems, the high amount of time to conduct virtual simulations, and the high operating costs, especially to train the employees. There are already DHM software systems that attempt to address these impediments and put a focus on optimized usability. For example, the digital human model \"Intelligently Moving Manikin\" (IMMA) [7] provides collision-free path and movement planning, which enables users to analyze assembly processes and conduct more precise and efficient ergonomic assessments. They increase the usability by decreasing configuration effort to use manikin families. A manikin family is a group of manikins \"intended to accommodate the population based on a certain confidence level.\" [8]. Such manikin families include data about anthropometrics and the gender of the population of different regions of the world. One way to reduce the complexity of using DHM software is to make use of the possibility of working with DHMs in a virtual environment intuitively [6]. Due to today's democratization of VR technology, it is possible to integrate VR technologies like HMDs into the daily workplace at a low cost [9]. VR offers the possibility of representing 3D models on a one-to-one scale [10]. This representation already integrates the human perspective into the product development process [11]. Users are thus able to experience the environment and investigate construction models in design reviews [12]. Software companies like MiddleVR [13] or IC.IDO [14] provide software tools, which allow the use of DHMs in a VR-application. However, this type of software only allows for conducting ergonomic assessments in two ways. The first is using motion capture systems. This method allows the recording of body movements and mapping to a digital human model, which is then used to simulate the ergonomics.