How to send via formOutput the automatically set date(today)

Hey guys,
I'm new to bonity and have trouble with a date picker. I have a form with a date picker, which is set to read-only because I want to just set the date automatically.

So at this time my value of the date picker is set to "formInput.bvar_ManuskriptEinsendenInput.eingereichtAm", which is of course wrong, because I dont want the client to choose the date. "eingereichtAm" is my date-variable:

business variables do not retrieve the values from the formOutput

I use several business variables to store values chosen by user interaction from UI forms.
After each task I want to use a business variable to store the user selection for a certain type and at the end of the process the last form is supposed to display the selected data from each tasks.