# Implementation and Evaluation of Dynamic Task Allocation for Human-Robot Collaboration in Assembly
## 2 Materials and Methods
### Study Design and Evaluation Methodology
#### 2.3.3 Procedure of User Study  
The study was conducted with a total of 20 subjects. The composition of the subjects regarding demographics, background experience, and technical affinity is presented in Section 3. For anonymization purposes, all subjects were assigned with identification numbers (IDs), which are exclusively used during the evaluation. Subsequently, the subjects were randomly divided into four user groups, in which the duration of the process delay differs (no delay, 30, 60, and 90 s delay). Furthermore, the order of the task allocation modes (manual, static-asymmetric, static, and dynamic) was randomly selected for all subjects, whereby care was taken to ensure that each mode came first, second, third, and last, respectively, with equal frequency. This was performed to reduce the influence of learning effects. After an initial pilot test, individual appointments were arranged with all 20 subjects, spread over a period of two weeks. The study was conducted by a study coordinator with the assistance of a supporting person in order to quickly perform disassembly and reset of the initial situation between the individual runs.  
The study procedure for all subjects, with a duration of about 1.5 h each, is shown in Figure 16 and described in the following: First, an introduction to the context and the course of the study was given by the study coordinator. Here, it was explicitly pointed out that the study coordinator was not the person responsible for the development of the overall system or the study design to ensure honest and critical feedback from the subjects. In addition, the voluntary nature of participation was emphasized and a consent form for participating in the study was signed by the subject. This was followed by a short familiarization phase with the user interface, in which the main areas for visualization and information provision as well as the button for confirming completed process steps were shown. Moreover, subjects were instructed to carefully follow the assigned tasks and assembly instructions displayed on the screen, and to confirm each task upon completion.  
After that, the assembly process was performed in the first task allocation mode according to the random, subject-dependent order. Within each task allocation mode, the assembly was performed first with one and then with three components (in the manual and static-asymmetric mode, only one component and three components, respectively, were assembled). An exemplary illustration of a complete process flow of collaborative assembly execution is shown in Appendix B. By starting the assembly process execution, automatic data logging of the process times and final task assignments takes place. Depending on the duration of the delay, the screws initially available in the assembly station were deliberately too few, so that the subject had to collect the screws needed from the warehouse during the assembly process either once (30 s delay), twice (60 s delay), or twice with an extended pause, instructed by the study coordinator (90 s delay). After completing the assembly runs in the respective mode, the subject was asked to complete the short questionnaire (see Appendix C.1). Meanwhile, the study support person restored the initial state of the experimental setup.  
The other three task allocation modes were performed in the same way. In total, six assembly runs were carried out by each subject. After completing all assembly runs, the final questionnaire (see Appendix C.2) was filled out by the subject.