Method and apparatus for controlling the braking system for an unwinder

In an apparatus for controlling a braking action of a roll of web material supported for rotation on an unwinding device including:

• means for continuously measuring line speed and rate of change thereof of said web downstream of said unwinding device and providing an output signal proportional to said line speed, means for continuously measuring rotational speed of said roll of web and providing an output signal proportional to said rotational speed, means receiving said output signals from said line speed and rotational speed measuring means and combining said signals to produce an output signal proportional to the diameter of said roll, means receiving said output signal proportional to said roll diameter and producing an output signal proportional to a predetermined desired web tension downstream of said roll, means receiving said output signal proportional to said line speed and producing an output signal proportional to the acceleration or deceleration of said roll, if any, means receiving said output signals from said line speed and rotational speed measuring means and from said acceleration or deceleration signal producing means and producing an output signal proportional to the energy in said roll, braking means for applying variable braking force to said roll, and brake control means receiving and combining of said output signals proportional to the roll diameter, desired web tension and the energy in said roll and producing an output signal to said braking means for causing said braking means to apply variable braking force to said roll substantially maintaining said predetermined tension in said web as it is being unwound during acceleration, deceleration and constant web speed conditions,
• wherein the improvement comprises:
• said means for producing an output signal proportional to the energy in said roll includes, means receiving said output signal proportional to the diameter of said roll and producing an output signal proportional to the cube of the diameter of said roll;
• means receiving said output signal proportional to the cube of the diameter and said output signal proportional to said acceleration or deceleration of said roll, if any, and for combining said signals proportional to the cube of the diameter and the acceleration or deceleration of said roll to produce an output signal proportional to the energy in said roll, said last named means including means for manual adjustment to modify said output signal thereof to correspond to the density and width of said roll.