# Using a Cable-Driven Parallel Robot with Applications in 3D Concrete Printing
## 1 Introduction
Some application projects of cable robots had extremely large operating spaces of up to hundreds of meters. The SkyCam system developed by [PERSON] in 1980 [8] was widely used for live broadcasts. The camera in a SkyCam was suspended by four cables; its speed can be up to 44.8 km/h, and high-speed photography was possible with SkyCam on a large scale. This structure controls the robot to move the camera by tracking any target in the stadium with a high velocity; the installation time has also been shortened as the points on the stadium dome can be used as cable ties. In 1999, a feed support system in a 500-m aperture spherical radio telescope (FAST) was developed by [PERSON] et al. in China [9]; this system consisted of six cables placed on six columns and connected to a feed cabin as the moving platform, where the position of the feed cabin was controlled by the six cables. The authors analyzed the static and dynamic problem of the cable suspension model with random wind load. In a nonlinear static model, the value and orientation of the tensions can be obtained by the equilibrium equation to specify the position of the moving points. In a dynamic analysis, the finite element was used to solve the dynamic equation. In this paper, we propose an automatic concrete 3D printing system based on the CDPR configuration. Part 1 is a synthesis of related studies on large 3D printing, with studies on the materials and additives for automatic concrete extrusion structures. The analyzed  
Figure 1: Structure of the cable-driven parallel robot (CDPR). synthesized method is used to propose research issues, such as the design and calculation of a 3D concrete printing system with a cable robot, problems in calculating and designing the cable robot configuration, and investigating the workspace of the CDPR based on the pseudo-static equilibrium problem when the robot moves at a low speed, thereby calculating the tension forces according to the printed trajectories and calculating the matching variable values, which are the length of the cable with the impact tension forces and cable deflection, forming the cable robot control signal according to the given trajectory. The main contribution of this study is to propose a flexible 3D concrete printing system on the basis of CDPR with two efficient algorithms used to calculate the workspace, check the trajectory in the workspace for each specific configuration of the CDPR, and calculate the cable tension that satisfies the conditions of a quasi-static equilibrium condition, forces limit, load variation, and cable sagging, thereby calculating the control differences as to the length of the cables according to each given path. The mechanical structure of the CDPR is designed and analyzed in Section 2, and the quasi-static workspace is determined with a linear programming algorithm, taking to account the change of payload when printing. Section 3 shows the process of optimizing the tensions of the cables with the dual simplex algorithm. The results of this process and the kinematic problem are used to solve the cable sagging problem, to specify the value of the length of the cables, with the offset sagging values, in Section 4. Section 5 presents the mechanical design of the 3D concrete printing system based on CDPR; the structures of the cable winch and concrete extruder are designed and calculated to be suitable for the specification of this system. Section 6 shows the experimental result of this system. Parameter calculations are used to control the system to perform the printing trajectory.