To voxelize the STL files, binvox(https://www.patrickmin.com/binvox/) is recommended here.
modify the path in file 'from_binvox_to_vxc.py' to your local directory. Then, run
python from_binvox_to_vxc.py
to generate vxc file format in order to be opened in VoxCad(https://www.creativemachineslab.com/voxcad.html)