11

MAV Design Aspects Using MEMS

151

The role of these actuators can be considered as key area of discussion as they

will be playing a vital role in generating the aerodynamic effects if placed at leading

edge. On the other hand, check-valve actuators are mounted in the wings in such

a way that during downstroke they are closed and are open during upstrokes. The

power is spent during downstroke and saved during upstroke [3] which is more or

less a recovery stroke.

Astrongfeedbackcontrollingsystemcanbeadopted,anditwillbeveryinteresting

to maintain desired aerodynamic forces and even to improve the flight performance

of the MAV in different conditions. The mechanical wings in an MAV cannot move

their wings like biological flapping flexible wings due to lack of muscles, feathers

and wing structures. Hence the role of active flow controls and their design will be

a key area to focus while designing a bio-mimicking MAV. The biggest challenge in

Active Flow Control is to develop a control system to handle the complex problems

of aeroelasticity due to structural deformation. This problem in a bio-mimicked MAV

will be more complicated if the designed wing structure is containing more number of

actuators and sensors. Apart from aeroelasticity, there are other practical challenges

for MAV in real time due to wind gust, low weight, aerosols, mist, landing and

takeoff.

Another important consideration of MAV flight is related with its wing kinematic

motion and its flight mode control during transition periods. A good MAV model

needs to take care of rotation of the wing over the longitudinal axis of the body during

upstroke and downstroke [5]. These problems can be solved by using a controlled

DC motor connected with wings along with a controlled gearing system. By varying

the DC voltages the angular speed and wing movement can be controlled according

to the desired levels of aerodynamic wing movements.

Process Development of Micromachining

Designing of MEMS involve various processing steps and a broad classification of

these steps are given below.

1.

DefinevarioussetofmechanicalstructureswhichareusefulinMEMSinProcess

Evaluation Vehicle (PEV).

2.

Write down the Process flow chart to realise the structures.

3.

Optimise the Unit Processes independently according to their Fab capabilities.

4.

Define Process Control Monitoring (PCM) Limits.

5.

Design a set of Masks of each MEMS structure according to unit processes.

Depend on process flow, the number of Masks varies up to 10 levels.

6.

Realise the PEV and evaluate the performance of the structures and devices.

7.

Evaluate which MEMS structures have good performance and good yield.

8.

Second Iteration of PEV as mentioned in step 1 and repeat the whole cycle up

to step 7.

The process has to continue until good working MEMS based MAV is realized.