...

We can see the machinery inside is a combination of a few different mechanisms. 

...

1. Opening of the coin box door using a cam mechanism. The follower of the cam (the animal head) lifts the box door up and allows the arm to reach the coin. Then it will close when the arm is returning.
   
   
2. 4-links mechanism pushes the arm to reach it to the coin. There will be a crank attached to the shaft at point O, which drives link 2. The link 3 is the arm touching and dragging the coin. The link 4 will be a spring to help returning mechanism.
   
3. The arm return mechanism using spring need to design. I need to use a spring with enough stiffness. Thus it toggles the returning mechanism when the copular point (the end of the arm) reaches the coin.

First Prototype

The prototypeIn the first prototype, I tried to install a cam mechanism from Karakuri book shown under. However, because the cover of the box was too rigid, the cam was unable to lift up the cover clearly and folded. Thus, I just use the coin grabbing arm 

Mechanical Analysis
Final Prototype
Conclusion