**1. Introduction**

In recent decades, the use of industrial robots in the production and development of nano technological processes, industrial automation, chemically contaminated environments, medical & biological industrial, the calibration of measurement system, etc., are seriously in circulation. So the scientific research centers are conducting some research in this regard to meet customers' demands. To compete with international markets, parameters such as precision, high repeatability in production, control management, and emphasis on standards have proved to be necessary in the usage of robot in modern technology. This has caused the companies to

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move toward a practical system to produce the maximum production variety at minimum time with the lowest expenses and the highest quality. Thus, the industrial automation with the help of robots replaces human force in production and in assembly lines.

Today, robots are divided into several groups: Serial robots, Parallel robots, Synthetic robots, and Mobile robots [2, 5]. Synthetic robots are to incorporate the serial and parallel manipulators by connecting them in serial. The serial connections of serial and parallel manipulators can be categorized into the following four types: Parallel-Parallel, Serial-Parallel, Parallel-Serial, and Serial-Serial [8]. Characteristics such as precision, speed, stiffness, and a workspace without singularity points have differentiated the Parallel robot from the Serial robots [4, 5]. The Parallel manipulator robots are used in making flight simulators, helicopters, machinery tools, precise robots, etc. The reverse kinematics solution of these robots as compared with the simple Serial robots and direct kinematics solution is hard with complicated equations [3, 8]. In this paper, first, the geometric attributes of the Triangle-Star Robot are offered and then based on motion geometry and robotic workspace, the limitations and weaknesses are recognized and indexically represented. In addition, to removing the abovementioned shortcomings, a new Triangle-Star Robot with telescopic arms and two new robots with improved structures are represented. Finally, the kinematics analysis of the robots similar to Denavit–Hartenberg approach is carried out.
