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3.1 Thermodynamical process in the suction circuit
Fig. 3 depicts physical constitution of suction system:
sealing, mainbody, and impeller. Under the drive of the centrifugal fan impeller at high rotary speed, external atmospheric air (state A) flows into the chamber through the sealing component (state B), airflow’s static pressure drops from P0 to P1 as a result of viscous friction dissipation and dynamic-static pressure conversion through the sealing device. Let the effective coverage area be S0, and adsorption force Fa can be approximately calculated as：
Fig. 3. Diagram of air state changes in suction circuit
Improving impeller’s efficiency means avoiding or restraining the energy losses such as local losses, traveling losses, boundary layer separation and frictional secondary flow, on the premise that the impeller’s capacity of doingwork is not affected, which requires a specific designmethodology suitable for SWCR robot.
3.2 Hydromechanical analysis
Hydromechanical analysis is committed to providing technical solutions, which deduces the relationship between Fa and impeller’s work through a detailed analysis of air flow’s state changes in suction cycle.
High-speed airflow is concentrated close to the wallsurface in the chamber, and converges in the center, then bends 90?upward to the inlet of the impeller. The rest part of the chamber is backflow zone with a little effect on adsorption characteristics.
That is important for impeller design, relatingimpeller’s aerodynamic performance to Fa. Its physical meaning is that effective negative pressure consists of two parts, one is static pressure rise of impeller, and the other is the part of dynamic pressure at the export which is effectively used.
4 Design of Impeller Specific for SWCR
Design method for SWCR-specific centrifugal impeller is on the basis of that for common centrifugal fans, while the unique characteristics of this method are as follows:
(1) 7-parameter method is presented, in which theparameters are inlet width B1, outlet width B2, inlet diameter D1, outlet diameter D2, inlet installation angle β1A, outlet installation angle β2A, blade number Z, and determine the geometry of impeller, see Fig. 4.
Fig. 4. 7-parameter geometric modeling of impeller
(2) Instead of goals of preconcerted flow rate and pressure ratio, the method aims at meeting the need of chamber vacuum that produces an appropriate adsorption force for SWCR to adhere and maneuver. Based on Eq. the method properly allocates impeller static pressure and uses outlet kinetic energy, and ultimately attains a high-efficiency impeller that creates adequate negative pressure in the sucker.
(3) Static pressure rise plays a major role in formation of Fa, so that the impeller with a higher static pressure ratio could obtain the same vacuum at the cost of lower power. In addition, high-static-pressure-ratio impeller has poor ability of doing work, which means that impeller needs a higher speed for the same power capability, but, high rotating speed may lead to excessive relative velocity inside the impeller, which lowers the efficiency. Therefore static pressure ratio should be selected by contrast. Moreover, when static pressure ratio is constant, with β2A increasing, the adaptability to flow rate change is enhanced, which means vacuum level can be approximately maintained when there is a sudden increase in flow rate, however, corresponding B2 gets smaller, and the internal flow velocity higher, which also brings energy loss, so β2A should also be selected after comparison.