Hybrid Control of Flowrate in Microextrusion-Based Direct-Write Additive Manufacturing

Flowrate control has been a continuous challenge in Direct-Write Additive Manufacturing (DW AM) due to capacitive energy storage in the system and lack of suitable flowrate sensors at the microscale, resulting in poor dimensional control of material addition. While a pressure sensor can be used for pressure-based feedback control, the system will become marginally stable if the material losses contact with the pressure sensor, and thus feedback is lost. In this paper, we design and implement a pressure-based hybrid controller with a state-dependent switching strategy that eliminates the stability problem due to a loss of pressure feedback, and thus enables the real time, stable control of flowrate in DW AM. The stability of the hybrid controller is assessed using phase portraits and Multiple Lyapunov-like Functions. The hybrid dynamical model and the hybrid controller are experimentally implemented and validated. Stability results indicate that the hybrid controller resolved the marginal stability issue, and is stable in the sense of Lyapunov. Moreover, the hybrid control scheme implementation in the case study demonstrated that the shape fidelity of the parts is appreciably enhanced compared to the open loop control case.