Other Members who have suffered this problem have found that one of two things usually helps.
First of all, reset the router.
If that doesn't work, then go to 'Settings', 'WiFi' and tell the iPad to forget the WiFi settings.
Then, when the iPad picks up the WiFi signal again, re-enter the settings.
See if either of these helps; if not, don't hesitate to get back to us.
Tim