This is just a FYI as I had just managed to get my own Acer 320U scanner up and running in Win8.1 x64. This driver also works in Win7 to Win10!
The same drivers work for the following abandoned Acer/BenQ scanner models:
310U/620U
320U/340U/620U+/640U
620UT+/640UT
1240UT/5100U
640BT/640BU...
