Method of positioning a metal sheet for a sheetmetal working machine

A method of positioning a metal sheet which is initially flat between a pair of linear tools in which the metal sheet is manipulated by a movable gripping member of a manipulator robot controlled by a programmer according to a working program for positioning successive lines of working of the metal sheet in correspondence with the tools, the gripping member being movable along at least two axes, a first of which is parallel to the tools and a second of which is perpendicular to the tools, and which is rotatable at least about a third axis movable with the gripping member and normal to a plane in which the sheet lies, comprising the steps of:

• a) establishing a preliminary, physically-detectable, virtual working line on the metal sheet;
• b) providing the programmer with a spatial and an angular coordinate of a theoretical engagement point at which the gripping member is to engage the metal sheet;
• c) gripping and moving the metal sheet to a position sensor and detecting the virtual working line;
• d) detecting an angular position error of the metal sheet about the third axis;
• e) rotating the gripping member about the third axis to bring the virtual working line into parallel with the tools and thus correcting the angular position error;
• f) detecting a first position error of the virtual working line and correspondingly of the actual engagement point of the gripping member relative to the theoretical engagement point in the direction of the second axis;
• g) rotating the gripping member and the metal sheet about the third axis through a predetermined angle to bring a first actual working line into coincidence with the tools;
• h) translating the gripping member and the metal sheet along the first axis by a distance which corresponds to the product of the first position error and the sine of the predetermined angle in a direction such as to return the theoretical engagement point to a correct centered position relative to the tools;
• i) gripping the metal sheet between the tools and releasing the gripping member from the metal sheet;
• j) comparing the coordinates of the theoretical engagement point with those of the actual engagement point of the gripping member and deriving therefrom a second position error;
• k) moving the gripping member according to the first and second position error to bring the gripping member to the theoretical engagement point;
• l) carrying out the working program starting with the formation of the first actual working line.

A method of bending a metal sheet which is initially flat between a pair of linear tools in which the metal sheet is manipulated by a movable gripping member of a manipulator robot controlled by a programmer according to a working program for positioning successive lines of working of the metal sheet in correspondence with the tools, comprising the steps of:

• a) establishing a preliminary, physically-detectable, virtual working line on the metal sheet:
• b) providing the programmer with a spatial and an angular coordinate of a theoretical engagement point at which the gripping member is to engage the metal sheet;
• c) gripping and moving the metal sheet so that the virtual working line is brought into parallel with the tools;
• d) comparing the position of the actual engagement point of the gripping member with that of its theoretical engagement point when the virtual working line is in parallel with the tools, thereby deriving and storing a first position error;
• e) rotating the gripping member and the metal sheet by a predetermined angle so as to bring a first actual working line into coincidence with the tools;
• f) comparing the position of the actual engagement point of the gripping member with that of its theoretical engagement point, thereby deriving and storing a second position error;
• and
• g) carrying out the working program with starting with the first working line, while correcting the working program according to the first and second error.