Stretching unit for clamping and stretching a tubular film, flow-wrapper and method for clamping and stretching a tubular film

A method for clamping and stretching a tubular film in a flow-wrapper utilizing a stretching unit, the stretching unit comprising:

• a gripping head;
• two coupling rods attached to a moving means;
• two gripping fingers, each of the two gripping fingers are attached to the gripping head and to one of the coupling rods;
• wherein the two gripping fingers are moved from a remote position to a clamping position by a relative linear movement between the gripping head and the moving means parallel to a center axis of the moving means;
• wherein, in a first step, the method comprises:
• moving the moving means of the stretching unit relative to the gripping head of the stretching unit in a first direction, towards the tubular film, and thereby moving the two gripping fingers from the remote position to an intermediate position;
• wherein in a second step, the method comprises:
• moving the gripping head relative to the moving means in a second direction, which is opposite to the first direction and thereby moving the two gripping fingers from the intermediate position to the clamping position and thereby clamping the tubular film;
• wherein the tubular film is stretched by a further movement of the gripping head in the second direction;
• wherein the gripping head is moved by an electric motor, a linear motor, or a linear servo motor and/or wherein the moving means is moved by a pneumatic cylinder;
• and
• wherein a driving force of the electric motor and/or the linear motor and/or the linear servo motor is controlled depending on material properties and/or a geometry of the tubular film.