Fig.2. 6 blades Iris mechanism kinematic structure.(concept design)
Figure2. shows the kinematic structure of the Iris mechanism. Blue circle line is the outer actuation ring, black lines are the links, and O2 is the center of the rotation. Since the blade is connected to the RBO4 link, we can decide the shape and angle of the blade after finishing the kinematic analysis of the linkage mechanism.
Fig.3. kinematic for 1-blade(left) and four-bar linkage system of the one blade(right)
In order to do the kinematic analysis of the Iris mechanism, I focused on only one blade because other blades have the same kinematic structure and characteristics. If we draw imaginary links such as RO2A and RO2O4, we can know that this is the four-bar mechanism which is described as Fig.3. Based on the concept design which is Fig.2., design specifications such as length of links(a,b,c, and d) and fixed joint angle(theta2) are determined and described below.
In the four-bar mechanism system, the closed-loop equation for the position analysis is
Where theta3 and theta4 are unknown variables of the mechanism and theta2 joint variable is rotated by the outer actuation ring. Theta 3 and theta4 are determined by the other given elements using the above closed-loop equations(eq.3. and eq.4.) and the below plot shows the x and y position of the joint B by changing the theta2.
Fig.4. movable area
Fig.5. linkage position at θ2=190°(left) and θ2=200°(right)
Figure 4 shows the reasonable theta 2 angles to move the blades. As shown in Fig.5, the linkage position is significantly changed when theta2 is around 195°.
In addition, since y position of point B is decreased after theta2 is 280°, the expected range of motion of the theta 2 is from 200° to 280°. The below figure 6 shows the motion of the one blade as theta2 rotates in the expected range of motion.
Fig6. Simulation from θ2=200° to θ2=280°
By differentiating equation 1, the unknown velocity parameters (w3 and w4) can be determined.
Since point A is the fixed joint, theta 1 is constant, which means that w1 is zero. The w2 is arbitrary given as 1 rad/sec in order to find the w3 and w4. the angular velocity of A and B by changing the theta2 is shown in Fig.7.
Fig.7. Angular velocity of A and B
