As has been suggested, 3-Space sensor devices are mounted in Linux as /dev/ttyACMx, where x is 0,1,2,3... depending on how many USB devices you have connected that use a serial interface.
It has been suggested that you can change permissions to 666 (chmod 666 /dev/ttyACMx). This will work, but the next time you log in, you'll have to set the permissions again.
A more permanent fix is to make sure your user is in the dialout group. At least this works for me in Ubuntu 16.04. I used the user management gui tool to add myself and others to dialout, but you can also do it from the command line. A logout is required for the change to take effect.