Trigonometry in reverse kinematic of five bar robot: don't understand resolution of system

[AlexTheFrench]

Hi everybody,

I'm currently stuck trying to understand the inverse kinematic of a five bar robot, which looks to me like a trigonometry problem,

I've attach the picture of where my problem is, and you'll also find the full pdf of the article.

What I don't understand is for the resolution of the system { Xc=Xd-L5cosθ2
{ Yc= Yd-L5sinθ2

because we know Xd, Yd and L5 but we don't know θ2, so this looks to me like a system with 3 unknows, and I haven't seen any other way to find θ2,

Can you tell me if i'm wrong with the fact that I can't solve this system of equation, maybe i've miss something in the article..

Thanks a lot, Alex

 

[blamocur]

because we know Xd, Yd and L5 but we don't know θ2, so this looks to me like a system with 3 unknows, and I haven't seen any other way to find θ2,

I get the same impression. Looks like their inverse kinematics model works for controlling point $\mathbf C$, but not for point $\mathbf D$.