## 4 Mixed Reality for Human-Robot Interaction
### Mixed Reality-Enhanced Robotic Tele-Welding
#### 4.4.2 Mixed Reality-Enhanced Robot-Assisted Welding
However, the operator does not have sufficient visual feedback to check the status of the robot during operation. [PERSON] et al. [164] developed an MR-based human-robot collaborative welding system (Figure 9). The collaborative tele-welding platform combines the strengths of humans and robots to perform weaving gas tungsten arc welding (GTAW) tasks. The welder can monitor the welding process through an MR display without the need to be physically present. Welding experiments indicated collaborative tele-welding provides better welding results compared to welding performed by humans or robots independently. Figure 8: The projection-based MR remotely controlled robotic welding system for transferring welder skills and human-level dynamics to the welding robot. (**a**) Overview of the welding station and virtual station. (**b**) Replica of a welding torch used in the MR welding station. Reprinted with permission from Ref. [163]. 2017, Elsevier. MR-based robot-assisted remote welding platforms were developed in [165] to provide the welders with more natural and immersive human-robot interaction (HRI). However, in these systems, the users rely on visual feedback for movement control and have no haptic effects to completely prevent accidental collisions between the robot and the workpiece when the operator controls the robot for welding from a distance. Hence, they are still limited. A visual and haptic robot programming system based on mixed reality and force feedback was developed in [166]. However, the system was not suitable for real-time remote welding operations and was inefficient in unstructured and dynamic welding situations. Haptic feedback provides the welders with additional scene modality and increases the sense of presence in the remote environment, thereby improving the ability to perform complex tasks [167]. In contrast, it can be difficult to implement effectively. The primary advantage of integrating haptic effects is to enhance both the performance of tele-welding tasks and the operator's perception. Current remote robotic welding systems fail to fully utilize the potential improvements in performance offered by various forms of haptic feedback. The rapid advancement of MR-enhanced teleoperation has facilitated the merging of MR and virtual fixtures, aiming to enhance task performance and user perception. This integration effectively addresses the deficiencies in existing telerobotic welding systems. By creating an immersive and interactive MR environment, virtual workpieces can be generated in the user's space. When combined with Virtual Fixture (VF) technology, this environment provides users with force feedback and guidance, improving the precision of robot movements and preventing accidental collisions [168,169]. The main limitation of existing studies on tele-welding lies in the insufficient incorporation of MR technology and virtual fixtures into remote-controlled robotic welding systems. This lack of integration hampers the elimination of potentially harmful collisions in the tele-welding process and prevents welding robots from achieving human-level dynamics for intricate Gas Metal Arc Welding (GMAW) tasks. Additionally, there has been no effort to simplify operations to assist inexperienced welders in performing welding tasks quickly, addressing the issues of time-consuming training and the shortage of qualified personnel. Figure 9: Overview of MR-based telerobotic system for remote welding tasks. (**a**) System configuration of MR-based human-robot collaborative welding platform. (**b**) Telerobotic welding site. (**c**) The MR scene displayed to the operator is augmented by a real-time on-site welding stream. Reprinted with permission from Ref. [164]. 2019, Elsevier. An exception is [107], which introduces an integrated approach utilizing MR and haptic feedback for intuitive and immersive teleoperation of robotic welding systems.