Did some research on usb and it seems you just can't open and close it like a com port it seems that there is a extra chip needed for doing so
you could do
[com port] [usb port]
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put here the relais --------
and switch the
+ from the usb cable
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Usb device
so you would need
1 USB cable A--> B (for PC --> the print)
1 USB female A-connecter (for on the print so the USB device can be putted in here)
1 USB female B-connector (for on the print so the PC can be connected)
1 Print (just in a 1 by 1 frame arround 6x6 maybe 10x10)
1 RS232 cable
1 Relais
this all together should switch any usb device