Control of 3D printer nozzle temperature
The hot end of a 3D printer can be seen in the schematic in Figure 1. The nozzle is heated using a heating element, while a thermocouple is used to record the temperature. The hot end uses two cooling fans: the hot end fan and the layer cooling fan, where the blue lines indicate cold air and red lines indicate hot air. A controller is used to maintain the temperature at a constant 200°C.
Figure 1: Schematic of 3D printer hot end
For the system shown in Figure 1, the layer cooling fan suddenly turns on and the thermocouple temperature drops to 190°C.
Part 1: Using a block diagram, sketch out the interactions between the controller, process, and sensor. Define the following:
1. Set point
2. Process variable
3. Control variable
Figure 2: Schematic showing heating cycle of hot end
(Figure 2 shows a schematic of the thermocouple data as the 3D printer hot end is heated from roomtemperature to 200°C). CHECK ATTACHED FILE FOR FIGURE
As the temperature hits 200°C, it overshoots to 205°C before returning to a relatively steady of 200°C +/- 1°C. The system uses a PID controller, where the values are set at:
• Kp = 21.33
• Ki = 1.13
• Kd =98.22
• For the system above, explain why the thermocouple overshoots?
• Sketch the expected temperature time profile (i.e. the graph in Fig. 2) from room temperature to 200°C for the following 3 scenarios:
1. Kp is halved, the other two values are unchanged
2. Ki is doubled, the other two values are unchanged
3. Kd is halved, the other two values are unchanged
• If a full PID controller was not available, which controller would be more suitable for the system described in figure 2: PI or PD. Explain your answer.