# Development of a Small CNC Machining Center for Physical Implementation and a Digital Twin
## 4 Materials and Methods
### Physical Implementation of the System  
The physical implementation of the open-control architecture CNC equipment (built by the authors) is illustrated in Figure 13a-c.  
The notations in Figure 11a-c represent the following:  
1. The Y-axis incremental encoder;
2. Y-axis DC servo motor (Dunkermotoren);
3. X-axis DC servo motor (Dunkermotoren);
4. X-axis incremental encoder;
5. Z-axis DC servo motor (Pololu);
6. Main spindle unit;
7. Support structure (frame);
8. Z-axis ball screw transmission unit;
9. Workpiece fixing system;
10. Y-axis ball screw transmission unit;  
Figure 12: Circular interpolation: (**a**) imposed and actual trajectories (resistant torque 2%); (**b**) imposed and actual trajectories (resistant torque 2%)—scaled.  
The system was realized in a modular form and consisted of the following modules:  
- A supporting structure composed of extruded aluminum profiles;  
- Kinematic feed kinematic chains on the X-, Y-, and Z-axes, structured as closed-loop motion control systems. The drive equipment was the DC servo motor, and the feedback device was the incremental encoder. For the X- and Y-axes, Dunkermotoren GR63x25 servo motors (Dunkermotoren GmbH, Bonndorf, Germany)were employed, while a Pololu servo motor (Pololu, Las Vegas, USA) was utilized for the Z-axis. THK LM Guide Actuator (THK Co., Ltd., Tokyo, Japan) KR ball screw-nut type THK LM Guide Actuator KR were used as transmission devices on all three axes.  
- Main kinematic chain (main spindle drive unit) achieved through the integration of a Proxxon mini drilling machine, comprising a drive system powered by a single-phase AC motor with manual speed adjustment capability and a chuck-type tool clamping  
Figure 13: Circular interpolation: (**a**) main view; (**b**) side view; (**c**) view from above.  
system for the cutting tool. This system enabled the manual clamping and replacement of cutting tools, including cylindrical mill, center drill, twist drill, and tapping drill types. The working unit provided the primary cutting motion for the CNC system.
* Command and control module achieved through the implementation of two Arduino MEGA development boards, each equipped with an 8-bit AVR ATMega 2560 microcontroller (Microchip Technology, Chandler, AZ, USA). The Arduino boards were responsible for issuing commands to the drive modules of the three axes (as reference inputs for the automatic motion control systems) and to the main spindle module. The term \"control\" in this context refers to the implementation of PID-type automatic control algorithms on each motion axis. The utilization of these command-and-control systems guaranteed the system's open-architecture nature, facilitating the implementation of flexible control algorithms and the straightforward modification of control parameters. The command-and-control module incorporated Pololu Dual VNH5019 boards (drivers, Pololu, Las Vegas, USA), which facilitated the power supply for DC servo motors, with voltages ranging from 5.5-24 V and currents ranging from 12-24 A. Each of these two drivers was capable of powering up to two DC servo motors and was compatible with Arduino MEGA boards (Arduino S.R.L., Monza, Italy).  
It is imperative to reiterate that the two Arduino MEGA boards facilitated the coordination and control of all three drive modules, as well as the main spindle module.