So I´m back and have good and bad news ^^
At first: The Animation works now 
So what was the problem? To be honest, I absolutly don´t have any clue…
I can just tell what I changed to make it work now.
- I downloaded the human.obj-files from this post, where bruno asked for them
Can someone send me here the hearthling models to animate? - Next I searched the skeleton-files in the stonehearth main-mod.
- Imported both files in blender and clicking the “prepare skeleton”-button, the helper bones
appeared at the right positions (!) in the model and the green light turned on - I prepared the relations for all parts and exported a meta-file for later animations
- Smashing the “prepare animation”-button the second green light turned on and the model is
positioned in the middle of the grid. - Preparing the animation and exporting it as (animation) json-file.
And now it works 
But then there is another problem right behind the next corner…
When the crafting process ends, the worker gets stuck in an loop between “Idle” and “Crafting item XY”.
As you can see, she puts her shovel away and in the next second she has it in her hands again.
The only way to end this is to cancel the crafting process, but then you won´t get the product and get the ressources back.
Did anyone encounter a similar problem?
I tried already to change the “effort”- and “work_unit”-values in the recipe, tried to change the length of the animation from 110 frames to 120 or 30 frames (so that it´s a multiple of 30). This steps didn´t work.
And a second question I have in relation with this topic is how to change the “drop_effect” in the workshop.json so that she doesn´t drop the ressources in front of the oven?
As always I may ask you for help or ideas and hints that could sign me in the right direction for a solution. 