Simulate taking USB cable in and out
Try 

sudo kextunload -b "com.apple.driver.usb.AppleUSBEHCIPCI"; sleep 5; sudo kextload -b "com.apple.driver.usb.AppleUSBEHCIPCI"


Works on my system, just tested it. I had to run the command 3 times though because for 2 times my usb camera didn't reconnect correctly, no idea why that happened.

Or similar to this with the full path

sudo kextunload /System/Library/Extensions/IOUSBMassStorageClass.kext
sudo kextload /System/Library/Extensions/IOUSBMassStorageClass.kext


Oh well, this work