# An Approach Based on VR to Design Industrial Human-Robot Collaborative Workstations
## 2 The Proposed Approach
### VR-Based Interaction Design
#### 2.2.3 HMI Testing  
Testing sessions are always a fundamental phase in the HMI design process [34]. In particular, user testing allows designers to understand HMI usability and to collect information about the UX. The latter is closely related to the context of use, especially for interfaces in a working complex scenario, such as in industry [35]. Anticipating the UX evaluation is fundamental especially when innovative workspaces are designed, such as the novel human-robot collaborative workstations. Within this context, VR offers a good solution for promptly assessing HMIs, considering the influence of the environment on interaction.  
The proposed approach allows to include HMI testing in the VR scenario phase and follow a traditional qualitative approach [36], involving a limited number of participants to collect main feedback [37]. Qualitative testing goal is the collection of information about the users' perception of the product (e.g., interface) in order to improve it and fix problems [36]. Indeed, the quality of the insights (e.g., users' comments, suggestions, behavior, facial expressions) that emerge from the analysis is more important than objective results (e.g., task time execution, number of errors). For these test type, participants could be end-users (i.e., operators that will be involved in the new workstation) or other people available similar to the end-users profile. The participants' profile choice depends also on the specific testing aspects and goals [33].  
These kind of tests are structured in three main phases: pre-test participant data collection, task execution, and post-test questionnaire. The pre-test data collection aims at gathering all the necessary information about participants (e.g., age, working role, expertise level). These can change according to the specific project and considering what is more useful for a better interpretation of the collected data. Moreover, pre-test time could be used also to have the consent form signed. The task-execution phase involves the participant carrying out the defined tasks. These must not be too general or too specific, but leave the participant sufficient freedom to behave as he/she would normally do in a real work situation. In this phase, one member of the design team takes on the role of moderator while the rest take on the role of observers. The moderator has to indicate one at a time the tasks to be performed, without affecting the performance and remaining as neutral as possible [36]. Instead, it is essential for observers to collect everything that may be an indication of the HMI usability level. These may include the participant comments and his/her behavior during the interaction with the HMI (e.g., repetitive errors, indecision, surprise expression). During the task performance, specific devices can be used to collect participant physiological parameters in order to evaluate the stress level during the interaction [38]. Regarding the post-test phase, many questionnaires for the participant satisfaction investigation exist. Most of these involve evaluating graphical interfaces. Among the most used in this area are the Net Promoter Score (NPS), the System Usability Scale (SUS), the Usability Evaluation [39], the Usability Metric for User Experience (UMUX), and UUMUX-LITE [40]. Furthermore, it is considered important that the post-test evaluation questionnaire also explores how much the VR scene has influenced the interaction with the HMI and the participant perception of it. In this regard, three main aspects to be investigated have been identified: the VR scene responsiveness, participant discomfort and quality of the sensorial stimulation, depending on the adopted tools (e.g., visual, auditory, haptic).