# Practical Control of a Cold Milling Machine using an Adaptive PID Controller
## 5 Field Test
### Field Test Results  
The filed test is made up of two parts. In the first part, we operate the machine manually. When the machine works in the middle of the pavement, we choose the 'AUTO' mode of the machine, and then, the control system begins to work. The milling rotor of the machine gradually cuts into 8 cm depth of the pavement within the first 40 s of Figures 12a, 13a and 14a; the milling rotor entails enough power to meet the needs of consumers during this process, which make the engine speed decreases in Figure 12a. The hydraulic driving system is in a closed state at this point; the pressure of the hydraulic driving system in Figure 14a is the system back pressure. As the milling rotor of the machine gradually cuts into the depth of setting, the machine is slow-moving under the action of the level component of forces, so the work speed of the milling machine in Figure 13a is not zero. Fluctuations are mainly caused by the driver operation in Figures 12a, 13a and 14a. If the operator drives too fast the load increases sharply because of hard and rough usage over pavement. The driver needs to stop and loses time in a stationary position while powering up or reworking. Fluctuations are caused by local downhill pavement and the uneven distribution of pavement material within 161 s to 200 s in Figures 12a, 13a and 14a. When the machine works on the downhill pavement, the work speed of the milling machine will increase under the gravity along the ramp as the tractive force. Then, the forces of milling rotor increase with the depth of cut and feed rate, the milling rotor entails enough power to meet the needs of consumers during this process, which makes the engine speed decrease as in Figure 12a. The pressure of the hydraulic driving system in Figure 13a did not change significantly during this process, because the level component of forces and the gravity along the ramp as the tractive force was counteracting. The testing results are given in Figures 12-14. In Figure 12a, the engine is overloaded and the maximum fluctuation of the engine speed is 419 rpm when the machine is not equipped with the controller. The maximum engine speed is 2103 rpm; the machine is underloaded in this condition. When the machine is operated manually, the machine is often overloaded or underloaded. If the engine works on this condition, the output power is not at its desirable value. During this work process, the load of the machine with the fixed transmission ratio of the ground drive system is adjusted by the engine. If the machine load increases, the engine speed will go down. The work speed changes with the engine speed, i.e., the decline of the engine speed leads to the decline of the work speed. As a result the work load descends. When the work speed is at the certain value, the work load and the engine torque is in balance. This adjustment is a passive adaptation to the machine load for the system without the proposed controller. Figure 11: The milled cement pavement. and if the machine is under load the controller will reduce the work speed. This adjustment of the controller makes the work load descend or ascend and makes the engine work almost at its rated speed. Although the work speed in Figure 12b presents some fluctuation when the machine meets the great impulse load, the engine speed is almost at 1950 rpm mostly during the machine work process and the engine output power has increased near to its rated value. This adjustment is active adaptation to the machine load in this case. Figure 13a shows that the average work-speed is 2.4 m/min when the machine is working without an adaptive controller and the work speed is adjusted manually or by the engine. Figure 13b shows that once the load of the machine changes, the controller will adjust the work speed. The average work speed is 2.766 m/min, which is 15.25% higher than that the machine without an adaptive controller. That is to say, the productivity of the machine increases 15.25%.