润色下面一段话：本文所研究的Dobot机器人如第二章图23所示带有吸盘的Dobot机械臂有五个旋转关节。其中第四个关节是被动关节由第二、三个关节的步进电机一起进行控制第五个关节为末端执行器。

The Dobot robot studied in this article is shown in Figure 2.3 of Chapter 2, and it has five rotating joints with a suction cup attached to its mechanical arm. Among them, the fourth joint is a passive joint that is controlled by the stepper motors of the second and third joints, and the fifth joint serves as the end effector.