Abstract: A tensioning device of a coil winding machine which provides back tension to a wire fed from a wire supply source to a coil winding position through a main tension pulley and a back tension lever which is urged in the back tension applying direction by a spring and is swingably supported. The tensioning device comprises a first back tension spring having one end connected with the back tension lever, a second back tension spring having one end connected to a fixed position of the device, the spring constant of the second back tension spring being smaller than that of the first back tension spring, and means for connecting the first and second back tension springs. A control member is further provided, which fixes the connecting means so that in a first operating mode only the first back tension spring acts on the back tension lever and in a second operating mode the first and second back tension springs operate in series to control the back tension lever.

Abstract: A magnetic tensioning device comprises a main tension pulley to which a braking torque is applied, an absorbing lever for absorbing fluctuation in tension and a second tension pulley mounted at one end of the absorbing lever. Adequate tensioning is obtained by means of the main and second tension pulleys. The braking torque is generated by a permanent magnet and a magnetizable disc opposed to each other. When tension is received at the absorbing lever, it displaces and the distance between the magnet and the magnetizable disc is changed according to the displacement of the lever to generate a correcting braking torque.