Self-adaptive tensioning system and tensioning method for main motor of punching machine

The invention provides a punching machine main motor self-adaption tensioning system which comprises a tensioning device and a tensioning oil way, the tensioning device comprises an oil cylinder, the tensioning oil way comprises an oil tank, an oil pump, a reversing valve, an overflow valve, a one-way valve and a pressure gauge, a port A of the reversing valve is connected with a rod cavity of the oil cylinder, and a port B of the reversing valve is connected with a port C of the oil cylinder. A port B of the reversing valve is connected with a rodless cavity of the oil cylinder after passing through the one-way valve, a port P of the reversing valve is divided into two branches, one branch is connected with an oil tank after passing through the overflow valve, the other branch is connected with an oil pump, and a port T of the reversing valve is connected with the oil tank and used for oil return. And the pressure gauge is connected with a rodless cavity of the oil cylinder and is used for detecting the pres