Method and arrangement for measuring the position of an end head of a roll

A method for determining a position of an end head used in rolls of packing paper, cellulose, or board relative to a grab transporting the end head, when the end head is attached to the grab, comprising:

• transporting a detector along a circular curve assumed to be intersected by a circular curve defined by an edge of an end head;
• measuring an angle position of the detector on the circular curve of its transport path;
• detecting intersection points between the circular curve traveled by the detector and the edge of the end head;
• calculating a position of a center point of the end head on the basis of:
• a) a radius of the circular curve traveled by the detector and the position of the center point of the circular curve traveled by the detector,
• b) a position of a tool point of the grab,
• c) an assumed radius of the end head, and
• d) positions of the detected intersection points;
• and
• calculating a position of the center point of the end head in the set of coordinates of the grab.

An apparatus for determining a position of an end head used in rolls of packing paper, cellulose, or board relative to a grab transporting the end head, when the end head is attached to the grab, comprising:

• a grab comprising a body, elements for gripping an end head, and a predefined tool point;
• a measuring arm rotatable on a rotation shaft fitted to the body;
• a measuring device, operable for determining an angle of rotation of the measuring arm around the rotation shaft;
• and
• a detector attached to the measuring arm, operable for detecting passage of an edge of the end head over the detector.