# Development of Automatic Electric Drive Drilling System for Core Drilling
## 3 Design and Development
### Hardware Systems  
The drilling system is illustrated in Figures 3 and 4. It consists of four hardware systems: a rotation system, hoisting system, circulation system, and drill string system. Rotation System: The rotation system is similar to the conventional top drive used for vertical drilling. The rotation system provides torque and speed through a servo motor. The servo motor of the rotation system was fixed to the frame, and the motor shaft was connected to the upper part of the torque sensor through coupling. The torque sensor measures the actual torque output of the servo motor. The lower part of the torque sensor was connected to the rotary spindle through the splines. Outside the torque sensor, the pressure sensor measures the WOB in real time. The rotary motor is a Delta ASDA-A2 series servo motor, and the communication mode is CANopen. The motor-rated power,  
Figure 2: Control loop diagram of the automatic electric drive drilling system. Hoisting System: To simulate drilling operations, the system was equipped with a hoisting system consisting of an actuating motor, reduction box, mounting frame, and gear shaft [33; 34; 35; 36]. The gear shaft of the system was located at the upper part of the base of the device, and the transmission mode was a rack-and-pinion transmission. The shaft is the absolute multiturn encoder at one end of the gear. The encoder measured the footage, bit position, and ROP. The other side of the gear shaft is related to the reducer, which is converted into a WOB through rack and pinion. The reducer is a DYNABOX reducer, a self-locking worm gear reducer with a reduction ratio of 90:1 and a mechanical efficiency of 62%. The servo motor is a three-phase synchronous AC motor with a rated power of 3.65 kW, a torque of 11.7 N-m, and a speed of 3000 rpm. There were two rotating bearings between the gear shaft and frame, and three pairs of ear plates were installed at the bottom of the frame to ensure that the rack was not offset when the frame went up and down. The servo motor can operate with a rated torque within the rated speed, and the communication mode is Powerlink communication. The high accuracy of the actuating motor is key to ensuring the required weight-on-bit (WOB) control. To address the system's vibrations challenge, a pinion and racks were used between the actuating motor and actuators to reduce the overall vibrations, thereby making the system sturdier. The differential equation of the system:  
\[J_{\Sigma}(\frac{n}{r})\frac{d^{2}x_{0}}{dt^{2}}+c*(\frac{n}{r})\frac{dx_{0}}{ dt}+K_{\Sigma}(\frac{n}{r})x_{0}=K_{\Sigma}\theta_{i} \tag{20}\]  
where \(n\) is the reduction ratio, and \(r\) is the radius of the gear indexing circle. Figure 4: Three sensors in the hoisting system and rotation system. Circulation System: This circulation system provides a large pump volume for mud circulation [31]. This device circulates the drilling fluid (water, water-based mud, or oil-based mud) from the top of the derrick to the drill bit. The circulation system consists of a water box, rotary spindle, core box, self-priming pump, frequency changer, and a mud pool. The rotary spindle was equipped with a pair of water outlets, and the water outlet was placed in a water box. Two waterproof rubber rings were placed in the water box to prevent the washing fluid and mud from entering the bearing pedestal. During drilling, mud was extracted from the mud pool by a self-priming pump to the water inlet of the water box, and the bit was cooled and lubricated using a rotary spindle. Simultaneously, the cuttings and mud generated during the drilling process settled in the core box, and mud returned to the mud pool from the core box. The maximum pump capacity of the self-priming pump for mud circulation was 50 L/min. The frequency changer prevents the pumps from overheating, and should change the pump volume by controlling the input voltage and current to realize the stepless adjustment of the pump volume.