# Sewer Cleaning Robot: A Visually Assisted Cleaning Robot for Sewers
## 2 Hardware System Design of SCR
### Hardware Mechanism Design  
The arm is mounted at the front of the mobile platform, comprising the arm body, linear actuators, and a rotational motor. It provides three degrees of freedom (DoF), with a working range that covers any position within 780 mm sewer. The two pitch DoF of the arm are driven by a 400 mm stroke linear actuator using a double linear actuator structure, which directly delivers substantial torque. This setup is ideal for operations in confined spaces, enhancing arm stability and force control while also reducing costs. Double actuators ensure more stable movement and better load distribution than a single actuator, reducing potential problems such as tilting or uneven force application. At the end of arm, a high-speed cutting motor is equipped with various interchangeable cutting tools, enabling operations like cutting, chipping, and grinding to efficiently handle obstacles such as tree roots and cement slabs, ensuring both the feasibility and stability of operational tasks. During the process of maneuvering the arm to target, two DoF are controlled by linear actuators and combined with the arm mechanical structure, facilitating the pitching motion. The relationship between linear actuator length and joint angle is illustrated in Figure 2. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Size & 1210 mm \\ Weight & 42 kg \\ Adaptable Pipe Radius & 280–780 mm \\ Operation Length Range & 50 m \\ Signal Type & 485/CAN \\ Operation Method & Joystick, Keyboard \\ Turning Limitation & Limited to minor deviations \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical specifications of SCR. Figure 1: The structure of SCR. The blue triangle \(\Delta a_{1}b_{1}c_{1}\) forms the principal triangle of the third DoF. In the initial state of the arm, the lifting arm angle \(\theta_{3}=0\). \(l_{1}\) denotes the length of the linear actuator. \(m_{1}\) and \(n_{1}\) represent the fixed lengths of the mechanical structure. When the lifting arm angle \(\theta_{3}\
eq 0\), based on the \(\Delta a_{1}b_{1}c_{1}\), the relationship is described by Equation (1). \[\cos(\varphi_{1}+\theta_{3})=\frac{{{l_{1}}^{2}-{m_{1}}^{2}-{n_{1}}^{2}}}{2{m_ {1}}{n_{1}}} \tag{1}\]  
\(\varphi_{1}+\theta_{3}\) represents the value of \(\Delta a_{1}b_{1}c_{1}\) when the end-effector pitch angle is \(\theta_{3}\); the length of the linear actuator \(l_{1}\) is given by Equation (2). \[l_{1}=\sqrt{2{m_{1}}{n_{1}}\cos(\varphi_{1}+\theta_{3})+{m_{1}}^{2}+{n_{1}}^{2}} \tag{2}\]  
The red \(\Delta a_{2}b_{2}c_{2}\) represents the principal triangle associated with the second DoF, which rotates around point \(a_{2}\). In Figure 2, the arm is depicted in initial state, where the lifting arm angle \(\theta_{2}=0\). \(l_{2}\) denotes the length of the linear actuator, while \(m_{2}\) and \(n_{2}\) represent fixed-length structural components of the mechanical arm. When the lifting arm angle \(\theta_{2}\
eq 0\), based on the \(\Delta a_{2}b_{2}c_{2}\), the relationship is described by Equation (3). \[\cos(\varphi_{2}+\theta_{2})=\frac{{{l_{2}}^{2}-{m_{2}}^{2}-{n_{2}}^{2}}}{2{m_ {2}}{n_{2}}} \tag{3}\]  
\(\varphi_{2}+\theta_{2}\) represents the magnitude of \(\theta_{2}\
eq 0\) when the mechanical arm pitch angle \(\angle c_{2}a_{2}b_{2}\). From Equation (3), the length of the linear actuator \(l_{2}\) is given by Equation (4), when the lifting angle of the arm is \(\theta_{2}\). \[l_{2}=\sqrt{2{m_{2}}{n_{2}}\cos(\varphi_{2}+\theta_{2})+{m_{2}}^{2}+{n_{2}}^{2}} \tag{4}\]  
According to the target pitch angle, the length of the linear actuator corresponding to the angle is calculated. Finally, the computer drives the controller to accurately reach the specified position. The SCR vision system comprises front and rear gimbals, each fitted with a pinhole monocular camera (FS-ZK350, 1920 \(\times\) 1080 pixels 25 fps) equipped with supplementary lighting.