## 2 Design of the Robotic Catheter System
### Design of the Master Robotic Device  
By encoding the operator's natural hand movements, the master device (Figure 2) communicates appropriate signals to the slave platform (typically at the patient's bedside) to perform the axial translation and radial movement of flexible tools during R-PCI. The bi-axial DOF design consists of an incremental encoder, rotary collector, encoder module, etc., as shown in Figure 2a,b. Incremental encoders provide excellent feedback regarding speed and distance by generating pulses corresponding to their axial displacement across the electromagnetic handle. The signals are transmitted to the encoder module, where they are aggregated, and the corresponding position command is sent to the slave robot platform. This includes forward commands that drive the slave robot to advance an endovascular tool and pull movements for tool retraction during procedures. Similarly, the encoder (EKT58 series, JADE Optoelectronic Company, Wuxi, China) has a resolution of 5000 cycles per revolution (CPR) and a measurement frequency of 100 KHz. It generates corresponding pulses from clockwise or anticlockwise twists of the rotary collector by an operator, which are converted into discrete angular values to enable precise rotational movement of an endovascular tool by the slave robot.  
In addition, the master device allows for simultaneous translational and rotational movements. Typically, this movement includes rotating on advance or retract operations generated by turning the rotary collector after moving the encoder along the handle or vice versa. This unique movement has been proven as a way interventionalists skillfully navigate guidewire or catheters through complex paths within the heart coronaries [14]. Furthermore, the clamp controller coordinates the slave's tool-grasping fixtures to maintain a fixed pose of the flexible tool, thus preventing tool slippage and potential risks from blood vessel puncture during procedures. The stroke length of the master device is 120 mm. However, to achieve an infinite translational motion, the remote switch (Figure 2a) triggers after a full stroke for either forward or backward drive of the cylindrical knob towards the starting position without corresponding movement at the slave side. On the other hand, when the remote switch turns off, a displacement of the cylindrical knob advances or retracts the tool further at the slave side. Hence, the realization of an infinite motion for a given intravascular procedure. The encoded motion information at the master side is transmitted to the slave device via a wireless network using a transmission control protocol/internet protocol (TCP/IP) address. Additionally, a 12-volt DC-powered rechargeable lithium-ion battery, as shown in Figure 2b, is used to power the master device. At the same time, a DC boost module ensures the realization of varying step-up and step-down voltage-to-current during a given procedure, thus offering high efficiency across input and output voltage ranges.  
Figure 2: The design and assembling of the master platform. (**a**) The master device’s outer casing and exterior components, and (**b**) the inner view and main components of the master robotic device.