Kinematics of pantograph device

[zoom1]

I need to obtain the forward and inverse kinematics of a pantograph device. It is easy when only the one side of the pantograph is considered; So, it becomes a 2DOF planar elbow mechanism, which is easy to solve. However, there is symmetry on pantograph, so I kinda need to combine two planar elbow mechanism, but it confuses me since it's a closed loop mechanism.

This is the depiction of the mechanism;
http://i.imgur.com/M3ANKre.png

Q1 and Q3 are controlled with the motors and Q2 and Q4 rotates accordingly.
How am I supposed to approach this mechanism ?

 

[Chestermiller]

The key to a pantograph is that each cell forms a rhombus, and the diagonals of a rhombus are always perpendicular. So you are dealing with right triangles.

Chet