Problem with "Serial to USB Adapter"

Dear All,

I have several computers have must be connected with "Digital Scale"
and "Barcode Printer", and both devices must be connected by using
RS232 comm port.
Since a computer merely have 1 comm port, hence I use "Serial to USB
Adapter" as additional comm port.
So the problem with lack of comm port is solved, but another problem
comes.
The problem now is sometimes the connection between "barcode Printer"
and computer is broken due to "Serial To USB", and I have to plug off
the USB and plug in again to the USB Port.

Pls someone give idea how to solve this problem?

Thanks

Robert Lie