# Analysis of a Novel Automatic Control Approach for the Free Forging Hammer
## 3 System Structure and Dynamic Performance Analysis  
### Configuration of an Automatic Free Forging Hammer  
Figure 5 shows the configuration of a free forging hammer controlled by the proposed automatic control system. Main control valve 3, which controls the oil inlet and outlet of the upper cavity of forging hammer cylinder 2, is a three ways, three positions slide valve with a cone seal. A servo control system, composed of servo valve 6, servo cylinder 4, and displacement sensor 5, is used to control the operation of servo cylinder 4. Floating valve 3 is driven by servo cylinder 4 at different speeds and different displacements, thereby realizing different operations of the forging hammerhead. The main components of the proposed control system are arranged from top to bottom along the vertical direction, as shown in Figure 5b. Servo cylinder 4 and main control valve 3 are rigidly connected, and the rod tail of the cylinder and the head of the valve core are fixed by bolts to ensure the stability and accuracy of displacement/force transmission. A buffer area is arranged between main control valve 3 and main working cylinder 2, thereby preventing the main control valve from being damaged by excessive pressure in the upper chamber during the return stroke. In addition, sensors 5 and 8 are installed on the bracket drawn out from the top of the operating room, and the installation position is isolated from the hammer body, which reduces the impact of vibration and shock on the measurement accuracy during the forging process. Main control valve 3 is composed of pilot valve 1, slave valve 2, valve body 3, etc., as shown in Figure 6. The force and displacement output from slave valve 2 directly drive the floating valve to control operations of the hammerhead. When pilot spool 1 is moved to the right by the drive of the servo cylinder, the valve port of pilot spool 1 to cavity A opens, and the pressure oil enters cavity A from port P, pushing slave valve 2 to the right. As spool valve 2 reaches the set place of pilot spool 1, the valve port closes and slave valve 2 stops moving. The displacement and speed of slave valve 2 follow pilot valve 1, and at the same time, the right end of slave valve 2 outputs a certain displacement and force to drive the floating valve, thereby connecting the upper chamber of the main working cylinder with the fuel tank. The main working cylinder drains and the hammerhead returns under the pressure of the accumulator. Similarly, when the servo cylinder drives pilot spool 1 to the left, chamber A in the valve body discharges oil and the pressure decreases. Slave valve 2, driven by the floating valve, moves to the left simultaneously with the floating valve, leading to a connection between the upper chamber and accumulators. Then, the piston of the main working cylinder realizes the downward strike under the action of hydraulic differential power and the dead weight of the hammerhead. Since the forging frequency and forging efficiency are both realized by the main control valve, the dynamic performance of it is a key factor in determining the performance of the entire system. However, the response performance of the main control valve is determined by the dynamic characteristics of the servo cylinder. Therefore, three servo cylinders with different structures are studied in this paper, as shown in Figure 7. Figure 7a is the principle diagram of a single-acting cylinder. When hydraulic oil enters the servo cylinder chamber from port B, piston 3 moves down and drives main control valve 1 down. Then, the upper chamber of the main cylinder drains and the hammerhead returns. As oil discharges from port B, floating valve 1, driven by the pressure oil  
Figure 5: (a) Configuration of the proposed free forging hammer; (b) sectional view of the proposed hammer. Figure 6: Schematic diagram of the main control valve. at the bottom, moves up and pushes piston 3 back. Meanwhile, recovery accumulators connect to the upper chamber of the main cylinder and the hammerhead strikes downward.