## 1 Introduction  
Today there is strong competition among industries toward factory-wide automation; manufacturers apply automation in their production line since they have a high interest in increasing the production rate without jeopardizing the quality and accuracy of the final product. Recently, robots have played major roles in automated production lines due to their superior capabilities. Although robots have been widely used to perform repetitive, non-critical tasks, such as handling, welding, and joining [1], recently researchers have developed specific studies with the aim of integrating them in a collaborative workspace. A collaborative workspace deals with the cooperation of humans and robots trying to accomplish a specific task. However, using collaborative robots, operator safety should not be put at risk in any aspect; this requires clear task definition and allocation for humans and robots in a collaborative work cell [2]. A safety design framework for human-robot collaboration in the absence of predefined regulations has been proposed by Reference [3]; authors have tried various strategies to design a safe workspace. Their suggested strategies have used different devices, such as safety fences, sources, light curtains, cameras, and robot speed and area restriction stop systems. The effectiveness of the safety design has been evaluated by risk assessment methods; however, still there is a gap between this strategy and safety regulations. A practical case study of human-robot collaboration has been presented in Reference [4]; using inverse kinematic theories, authors have made a control framework to define the robot trajectory completely for the case of the automotive homokinetic joint assembly process. Authors of References [5; 6] have focused on the speed and separation method, defined as one of the available ISO standards for collaborative robots, to increase operator safety in the shared workspace. Having used this standard, the safety of the operator in the manufacturing cell increased by determining the minimum protective distance between humans and robots. With respect to previous contributions in the field, the authors of Reference [7] have investigated the advantage of virtual reality technologies to simulate the assembly and maintenance process in a digital environment that allows the simulation of the human and robot interaction. They proved that these technologies appreciably reduce the time and cost of production development. In Reference [8], in aiming to design novel manufacturing systems, the authors considered the safety issues of the operators with the possibility of planning collision-free paths for multiple robots in a Virtual environment. In Reference [9], the needs of modern manufacturing industries that have led to cooperation between humans and industrial robots were discussed. In this study, the system, called Beware of the Robot (BOR), is used to train the operators in human-robot interaction, considering the safety issues for humans and enhancing production. In Reference [10], the authors explained the design method in hybrid reconfigurable system (H-RS) engineering, which maintains the design method and clarifies the concept. This method was utilized to develop a hybrid reconfigurable work cell for assembling a top-class car chassis. During human-robot collaboration, task allocation is one of the most challenging problems. Researchers of Reference [11] have used the task analysis method to define the necessary order in collaboration tasks in an assembly cell. Using this method, they reduced the chance of duty interference between an operator and the assistant robot. In the present research, the effectiveness of human-robot collaboration for the assembly of a brake disc is proven in a general framework by the analytic hierarchy process (AHP) approach. In the second step, the hierarchical task analysis (HTA) method is used to define and allocate human and robot tasks without their duty interference.