In human-robot collaboration, humans and robots work closely together in a manufacturing process. To ensure proper and eficient execution of the manufacturing process while considering human safety and damages to the robot and the work product, advanced planning of the collaborative manufacturing process is important. Goal models can be used already in the early phases to specify and analyze human-robot collaborations. However, as model-based development along other established software engineering practices do not belong to the core of roboticists training, guidance is needed for the creation and usage of goal models for human-robot collaborations. In this paper, we investigate diferent ways how goal modeling can be used to specify human-robot collaborations to determine a set of best practices and recommendations in the future. To do so, we compare the results of two teams, who - after initial training on goal models - applied goal modeling to specify the same human-robot collaboration system. The outcome shows that multiple useful ways of using goal modeling for human-robot collaborations exist, that need to be considered in the future.
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been successfully applied to human-robot collaboration (e.g., [
For all modeling languages, but particularly for modeling used in early development phases, there exists a multitude of ways how the modeling language can be used, and the model creator can develop their own style. Therefore, in this paper, we take a look at diferent ways of developing iStar goal models for human-robot collaborations using a concrete case system. Comparing the diferent modeling approaches and their outcomes shall allow us in the future to define guidelines for developing goal models for human-robot collaborations.
The paper is structured as follows: Section 2 discusses related work, followed by Section 3.1, which describes the study setup along with the case example used. Section 3.2 then presents the results along with Section 3.3 which presents the major findings. This is later evaluated and discussed in Section 4. This section also concludes the paper.
Approaches for modeling human-robot collaboration often focus on the human behavior
inside the collaboration, which is challenging to sketch, and, therefore, often times needs the
combination of modeling approaches from diferent perspectives [
Furthermore, these behavior focused approaches typically can be applied at the later stages of
development. In the very early stages, the exact behavior is unknown and rather a proof concept
is needed or narrowing down the expected behavior of human and robot in the collaboration to
be precisely specified later on. An abstract modeling language for the early phases that already
allows analyses is goal modeling [
In previous work, we have shown that GRL goal models are an adequate means for modeling
human-robot collaborations in requirements engineering [13], particularly concerning safety
aspects [
The goal of this study is to investigate diferent uses of iStar to model human-robot collaborations. This shall later on serve as foundation for defining best practices and guidelines.
To do so, we recruited robotics students from a sixth semester elective requirements engineering course. As part of the course’s curriculum, iStar and GRL were taught. In addition, our extensions for modeling collaborative systems, particularly, human robot collaborations were presented to the students, and also used for the tasks.
The course was split into two groups, which were given the opportunity to create an iStar model for a human-robot collaboration system for extra credit. As a case example, a collaborative assembly station was chosen. The existing case system could be observed by the students, and the responsible engineers were available to answer detailed questions.
3.2.1. Goal Model 1 3.2.2. Goal Model 2
Overall Workspace
C_WS shal be a safe environment
AND Have adjustable height
Lockable wheels
Resources need to be in working conditions
Information and safety layer
AND C_WS shal be higher than the H_WS and
R_WS
Attach projector at appropriate location +
Output toy cars
+
Has CE markings and fol ows EU regulations
Picking parts for
assembly ?
Altering gripper strength based on the part material
Fol ow the same calculated path
Assisting Human Operator in assembly
AND Placing parts for assembly Path planning
AND Place parts in the right order and location
Comply VDI/VDE safety
standard ? Holding parts for assembly in col aboration slow down while handling large or sharp objects Camera System 1 Camera 2B Projecting the tasks for cobot and operator
Camera Systems Camera 2A
Projecting and monitoring the workspace
The important aspects of the assembly process include the two main actors—the human and the cobot—the monitoring system, and safety. All these aspects are featured in both goal models, but not in the same way.
When discussing safety, Figure 1 represents it within each sub-actor, showcasing how the human and the cobot must individually maintain safety aspects. On the other hand, Figure 2 shows safety as a separate actor, encompassing all the safety aspects of both the human and the cobot. With regard to the monitoring system, both goal models include it as a separate actor that features cameras for monitoring and a projector for displaying instructions. Despite using diferent labels, the representation of the monitoring system remains consistent in both models.
The main focus of the assembly process is the collaboration between the human and the cobot. Figure 1 illustrates this collaboration through tasks within the individual actors and their communication via the monitoring system ‘Ulixes A600’. On the other hand, figure 2 shows the same with the use of a separate actor. The tasks within this actor are either dependent on or influence tasks from the ‘human operator’ and ‘cobot’ actors.
This demonstrates how the goal model from Team 1 (Figure 1) encompasses all safety and collaborative aspects within the respective actors, while the goal model from Team 2 (Figure 2) separates safety and collaboration into distinct actors. Regarding the elements used, both teams incorporate basic goals, tasks, decompositions, and resources. Additionally, Team 2 focuses more on contributions and soft goals. Regardless of the approach taken to create the goal models, both models represent the collaborative workspace for manufacturing toy cars, including the human, cobot, monitoring system, and workspace safety.
In conclusion, although the two teams used diferent approaches to goal modeling for specifying human-robot collaborations, both successfully represented the complete collaboration and met the intended specifications.
It is well known for modeling that diferent modelers will end up with diferent models by using diferent modeling elements, modeling at diferent levels of granularity, or preferring a diferent layout. In addition, giving the degrees of freedom, modelers might select a diferent focus of a model due to their intended purpose. In our case, we did make specific requirements regarding the purpose of the modeling, other than that the model should adequately specify the case example. Therefore, it is not surprising that both models look diferent, but it shows that for capturing the important parts of human-robot collaboration multiple aspects are relevant, which were covered in both models. However, depending on the particular intention, e.g., giving safety the visual importance of an actor, in contrast to showing how safety plays a vital role within all actors, these aspects can be treated very diferently.
For the future, it remains to investigate further approaches to modeling human-robot collaborations with goal models and to analyze the usefulness of the possible approaches for diferent purposes. It can particularly be questioned whether a view concept is needed, as human-robot collaboration deals with a set of very vital aspects that are of importance to completely understand the collaboration and appropriately specify the system. For instance, • the production or assembly process is needed as the main context constraint, limiting the solution space; • safety must be considered as vital factor to enable real-world application of human-robot collaborations; • the physical actors, i.e. the human and the robot, where both need to be given specific tasks aligning with each other; • the collaboration itself, as source of constraints for aligning the actions of the human and the robot; • monitoring, planning systems, the production systems, aside from the robot itself humanrobot collaborations rely on other technical systems needed.
Human-robot collaboration is an evolving field in industrial robotics, to allow for semiautomation of complex production processes. To ensure successful collaboration in terms of product quality and safety, advanced planning of the collaboration process is needed. Goal modeling can aid in the specification and analysis of human-robot collaborations already in the early phases. However, currently there is a lack of guidance for roboticists on how to create and use goal models for human-robot collaborations best.
In this paper, we reported a first study to shed light into the use of goal models for humanrobot collaborations. Two teams were tasked with creating iStar goal models for an existing human-robot collaboration system. The results substantiate the assumption that iStar goal modeling is applicable and useful in this scenario. Both groups yielded in completely diferent models, placing emphasis on diferent aspects. This, highlights the need for future research to identify the crucial points on what is most useful to investigate in early requirements engineering for human-robot collaborations. Furthermore, it might indicate that a view concept is needed to emphasize multiple aspects of human-robot collaboration.
In addition, since the approach was tailored to a specific human-robot collaboration use case and applied only to a particular group of engineering students, its generalizability cannot be assumed. Thus, for future work, it is important to explore more case studies involving a wider variety of robotic collaborations and diferent types of interactions. [8] R. E. Yagoda, M. D. Coovert, How to work and play with robots: an approach to modeling human-robot interaction, Computers in human behavior 28 (2012) 60–68. [9] E. Kindler, Model-based software engineering: The challenges of modelling behaviour, in: Proceedings of the Second International Workshop on Behaviour Modelling: Foundation and Applications, 2010, pp. 1–8. [10] A. Van Lamsweerde, Goal-oriented requirements engineering: A guided tour, in: Fifth ieee Int. Symp. on requirements engineering, IEEE, 2001, pp. 249–262. [11] A. M. Grubb, M. Chechik, Formal reasoning for analyzing goal models that evolve over time, Requirements Engineering 26 (2021) 423–457. [12] S. C. Akkaladevi, M. Plasch, A. Pichler, B. Rinner, Human robot collaboration to reach a common goal in an assembly process, in: STAIRS 2016, IOS Press, 2016, pp. 3–14. [13] J. Jesus Raja, M. Manjunath, M. Daun, Towards a goal-oriented approach for engineering digital twins of robotic systems., in: ENASE, 2024, pp. 466–473. [14] M. Manjunath, J. Jesus Raja, M. Daun, Early model-based safety analysis for collaborative robotic systems, IEEE Transactions on Automation Science and Engineering (2024). [15] M. Daun, J. Brings, L. Krajinski, V. Stenkova, T. Bandyszak, A grl-compliant istar extension for collaborative cyber-physical systems, Requirements Engineering 26 (2021) 325–370.