DE102019205089B3 - Controlling a multi-axis robot - Google Patents

Abstract

A method according to the invention for controlling a multi-axis robot (10), which has at least three swivel joints (G3-G6), whose axes of rotation (q4-q6) intersect at a common root point (HWP), for traversing a predetermined circular arc (C) with a Robot-fixed reference (TCP), with a start pose (SP) of the robot-fixed reference being specified, comprises the steps: - Rotation (S20) of the specified starting pose (SP) into a modified starting pose (SP ') such that the root point is on a perpendicular ( L) lies through a center point (M) of the specified circular arc on a plane (E) in which the specified circular arc lies; - Approach (S40) the modified starting pose with the robot-fixed reference in such a way that the root point lies on the perpendicular; and- traversing (S50) the predetermined circular arc with the robot-fixed reference starting from this modified starting pose solely by adjusting one or more of these three axes of rotation (q4-q6).

Description

The present invention relates to a method and system for controlling a multi-axis robot and a computer program product for performing the method.

Robots are often said to have robotic references, especially theirs TCP or a robot-guided tool (point), circular arcs, ie (full) circles or circle segments.

The DE 10 2016 203 361 A1 relates to an industrial robot having a robot arm with a plurality of links which are connected by means of a plurality of joints and are mounted such that they can be adjusted relative to one another by the plurality of links, and comprising a supply line which runs along at least two of the plurality of links of the robot arm over at least one of the plurality of links and outside of the Robot arm is arranged, and having a protective sleeve, which is arranged on one of the links, namely at least partially or completely surrounding at least one of the links over its circumference, wherein the protective sleeve has an outer jacket wall which is formed, a storage surface for a section to form the supply line.

In the DE 10 2010 010 920 A1 describes a method for calibrating a robot which the manufacturer has equipped with an operating program, under the regime of which his tool center point is guided on a trajectory defined by a plurality of support points.

The DE 196 01 857 A1 relates to a device for position detection with movably connected links and with sensors that detect relative movements of the links against each other.

The DE 10 2013 205 008 B4 describes a device for achieving advantageous kinematic properties on program-controlled, rotationally symmetrical tools that can be pivoted about two axes, preferably welding and cutting torches, which are in their basic position with their direction of action parallel to the direction of gravity and with a proximal link on the side of an industrial robot facing away from the frame or is attached to a robot-like guiding machine and consists of rigid orientation links, each with two intersecting axes of rotation, these links are connected serially one after the other and with the adjacent axes of rotation and a drive is arranged at the junction of two links, which program-controlled the angular position of the two with each other connected orientation members and the distant orientation member carries a tool with a torch holder, the number of orientation members being at least three and the axes of all drives and the tool intersect in the TCP, at this point the tip of the tool is also arranged, each drive consists of a rotary motor and a reduction gear, the axes of rotation are not arranged coaxially with the axis of the assigned rotary motor, designed as hollow shafts and each orientation element consists of two elements, a proximal element and a distal element, an axis of rotation is associated with each of the elements and associated proximal and distal elements can be moved relative to one another by small amounts by perpendicular to the plane formed by the two axes of rotation are designed to be rotatable and translatory along the same axis, each with adjusting elements in their position relative to one another and fixable with counter elements in their position relative to one another.

The DE 10 2015 216 550 A1 relates to a robot gripper, comprising a gripper base body which has a connecting flange which is designed for fastening the rotary gripper to a tool flange of a robot arm, further comprising a base member which by means of a first swivel joint which is automatically adjustable by a first drive motor, around a first Axis of rotation is rotatably mounted on the gripper base body, and having a first gripper finger which is rotatably mounted with respect to the base member by means of a second swivel joint, which is automatically adjustable by a second drive motor, and has at least at least a second axis of rotation which is aligned parallel to the first axis of rotation a further gripper finger, the second swivel joint being designed for the individual adjustment of the first gripper finger by the second drive motor independently of the at least one further gripper finger.

The object of the present invention is to improve traversing a given circular arc with a robot-fixed reference.

This object is achieved by a method with the features of claim 1. Claims 7, 8 provide protection for a system or computer program product for carrying out a method described here. The subclaims relate to advantageous further developments.

According to an embodiment of the present invention, a multi-axis robot has at least three, in one embodiment successive and / or, in particular motor-actuated, rotary joints, the (virtual or kinematic) axes of rotation of which are, in particular, always or constructively conditionally cut at a common root point.

In one embodiment, the robot has a robot arm, this robot arm having at least, in one embodiment exactly, six rotary joints in succession in one embodiment and / or the three axes of rotation that intersect at the common root point, axes of rotation of a robot hand, in particular a central hand , of the robot arm. In one embodiment, the robot is this robot arm and / or an industrial robot. The common root point is thus in one embodiment a wrist point of a robot, in particular a central hand of the robot (arm).

Since such robots occur very frequently and, on the other hand, often their (basic) axes, which (proximally) approach the three axes of rotation that intersect at the common root point, or which guide them or the robot hand, in particular have hysteresis due to weight and / or gearbox , The present invention can be used here with particular advantage.

According to an embodiment of the present invention, an arc is specified, in particular, which the robot is to travel with a robot-fixed reference, in an embodiment by a corresponding program, in particular a corresponding program command, for example “(S) CIRC auxiliary point, target point” or the like .

As explained in the introduction, a circular arc can have 360 ° or more than 360 ° or less than 360 °. One version of the robot-fixed reference is a tool center point ( TCP ) of the robot or a point of a robot-guided tool.

According to one embodiment of the present invention, a starting pose of the robot-fixed reference is specified on the circular arc, in one embodiment the circular arc by means of or based on this predetermined starting pose and / or the starting pose by moving to the starting pose with the robot-fixed reference and saving this starting pose or teaching of the starting pose is or is given. The starting pose can determine, in particular, a start of the circular arc.

In one embodiment, a pose has a one-, two- or preferably three-dimensional position and / or a one-, two- or preferably three-dimensional orientation (the robot-fixed reference), in particular it can consist of or define or be defined thereby.

• - Verdrehen bzw. Umorientieren der vorgegebenen Startpose in eine modifizierte Startpose derart bzw. mit der Maßgabe, dass der Wurzelpunkt auf einem Lot durch einen Mittelpunkt des vorgegebenen Kreisbogens auf eine(r) Ebene liegt, in der der vogegebene Kreisbogen liegt (wenn die roboterfeste Referenz die (solcherart modifizierte) Startpose aufweist bzw. einnimmt;
• - Anfahren der modifizierten Startpose mit der roboterfesten Referenz derart, dass (dann bzw. bei der modifizierten Startpose) der Wurzelpunkt auf dem Lot liegt; und
• - Abfahren des vorgegebenen Kreisbogens mit der roboterfesten Referenz ausgehend von dieser modifizierten Startpose alleine durch Verstellen einer oder mehrerer dieser drei Drehachsen, vorzugsweise nur einer dieser drei Drehachsen.

According to an embodiment of the present invention, a method for controlling the robot to travel the predetermined circular arc with the robot-fixed reference has the steps:

• - Twisting or reorienting the given starting pose into a modified starting pose in such a way or with the proviso that the root point on a plumb line lies through a center point of the given circular arc on a plane in which the given circular arc lies (if the robot-fixed reference which has (thus modified) starting pose;
• - Approaching the modified starting pose with the robot-fixed reference in such a way that (then or in the modified starting pose) the root point lies on the plumb line; and
• - traversing the predetermined circular arc with the robot-fixed reference, starting from this modified starting pose, simply by adjusting one or more of these three axes of rotation, preferably only one of these three axes of rotation.

In one version, the specified and modified start pose have the same (Cartesian or start) position (the robot-fixed reference) or differ only or possibly in the orientation or angular position (the robot-fixed reference (in this (start) position)) .

An embodiment of the present invention is therefore based on the idea of abandoning the orientation of the (robot-fixed reference in the) predetermined starting pose or modifying it in such a way that the circular arc, starting from this modified starting pose, simply by adjusting one or more of the three axes of rotation which intersect in the common root point, preferably only one, in particular the closest or proximal, of these three axes of rotation, or can be traversed, in an embodiment without the root point (by adjusting the further or basic axes of the robot (arm) s ) to move. Accordingly, the position of the root point (on the plumb line) remains constant when the arc is traversed.

Thus, in one embodiment, these further or basic axes of the robot (arm) and in a further development also one or two of these axes of rotation, which intersect at the common root point, do not have to be moved when or for traversing the predetermined circular arc, In one embodiment, a hysteresis-related path deviation, which can arise in particular as a result of gravitational forces, gear elasticities and / or opposite or reversing movements of these axes, can be advantageously reduced.

In one embodiment, the predefined starting pose is at an angle around a reference axis rotated into the modified starting pose, this angle and / or this reference axis being determined in this way or with the stipulation, in particular that the root point lies on the plumb line when the robot-fixed reference has or assumes the (such modified) starting pose. In one embodiment, this rotation of the predefined into the modified starting pose is determined in such a way or with the proviso that the (start) position of the starting pose is not changed, but the root point lies on the plumb line. As a result, the reorientation can be determined and / or carried out particularly simply and / or precisely in one embodiment.

In one embodiment, a target pose of the robot-fixed reference and / or an auxiliary point lying on the circular arc, in particular a position of the auxiliary point, is specified for the circular arc, in one embodiment the circular arc by means of or based on this predetermined target pose and / or (the predetermined position) of the auxiliary point and / or the target pose by moving to the target pose with the robot-fixed reference and storing this target pose or teaching the target pose and / or the auxiliary point, in particular its position, by moving to the auxiliary point with the robot-fixed reference and storing its position, in particular pose, or teaching the auxiliary point. The target pose can, in particular, determine an end of the circular arc. Likewise, the circular arc can also end before or after the target pose, in particular by additionally specifying a circular angle or a circular arc length.

The circular arc can hereby be specified in a simple, reliable and / or precise embodiment. Additionally or alternatively, in this way, in one embodiment, robot controllers known per se can advantageously be used (further) which have the possibility of specifying an arc of a circle in this way.

• - Verdrehen bzw. Umorientierung der vorgegebenen Zielpose in eine modifizierte Zielpose derart bzw. mit der Maßgabe, dass der Wurzelpunkt (weiterhin) auf dem Lot liegt (wenn die roboterfeste Referenz die (solcherart modifizierte) Zielpose aufweist bzw. einnimmt); und
• - Anfahren der modifizierten Zielpose mit der roboterfesten Referenz auf dem vorgegebenen Kreisbogen, wobei in einer Ausführung der Hilfspunkt (weiterhin) auf dem Kreisbogen liegt.

In one embodiment, the method has the following steps:

• - Twisting or reorienting the specified target pose into a modified target pose in such a way or with the proviso that the root point (still) lies on the plumb line (if the robot-fixed reference has or assumes the (such modified) target pose); and
• - Approaching the modified target pose with the robot-fixed reference on the specified circular arc, in one embodiment the auxiliary point (still) lying on the circular arc.

In one embodiment, the specified and modified target pose have the same (Cartesian or target) position of the robot-fixed reference or differ only or, if appropriate, in the orientation or angular position of the robot-fixed reference (in this (target) position).

An embodiment of the present invention is based on the idea of also abandoning the orientation of the (robot-fixed reference in the) predetermined target pose or modifying it in such a way that the circular arc, starting from the modified starting pose and through the modified target pose, simply by adjusting one or more of the three axes of rotation that intersect at the common root point, preferably only one, in particular closest to the base or proximal, of these three axes of rotation, in an embodiment without the root point (by adjusting the further or basic axes of the robot (arm ) s) to move.

In one embodiment, the predetermined target pose is rotated by an angle about a reference axis into the modified target pose, this angle and / or this reference axis being determined in this way or with the proviso that, in particular, the root point (still) lies on the plumb line, if the robot-fixed reference has or assumes the (such modified) target pose. As a result, this reorientation can be determined and / or carried out particularly simply and / or precisely in one embodiment.

In one embodiment, when the modified target pose is approached on the specified circular arc, the orientation of the robot-fixed reference, in one embodiment continuously, in particular circular (arc length), is converted from the orientation in the modified starting pose to the orientation in the modified target pose.

As a result, the predetermined circular arc can advantageously be traversed.

The inventive modification of the start and, if applicable, the target pose allows the execution of the arc to be increased in precision in one embodiment. The present invention can therefore be used with particular advantage when cutting, in particular circular, holes, in particular along the predetermined circular arc. Correspondingly, in one embodiment, a hole is cut into a workpiece when the circular arc is moved by means of a tool, the robot guiding the tool or workpiece and, in one embodiment, cutting along the predetermined circular arc.

In one embodiment, a position of the root point on the plumb line is determined for rotating the predetermined starting pose into the modified starting pose, in one embodiment based on a radius the predetermined circular arc and / or a, in particular constant, distance between the root point and the robot-fixed reference, in particular in such a way or with the proviso that the sum I ² + r ^{2 of} the square I ^{2 of} the distance I between the root point and the center point arranged on the plumb line and of the square r ^{2 of} the radius r of the predetermined circular arc is equal to the square d ^{2 of} the distance d between the root point and the robot-fixed reference (with the predetermined starting pose), and / or, in particular based on this position of the root point on the perpendicular, a rotation of the vector determined from the predetermined starting pose to the root point (in this predetermined starting pose) in the vector from the modified starting pose to the root point arranged on the plumb line as a rotation of the predetermined starting pose in the modified starting pose.

Additionally or alternatively, in an embodiment for rotating the predetermined target pose into the modified target pose, in particular based on this position of the root point on the plumb line, the vector is rotated from the predetermined target pose to the root point (with this predetermined target pose) into the vector from the modified one Target pose to the root point arranged on the plummet is determined as a rotation of the predetermined target pose into the modified target pose.

In one embodiment, the predetermined auxiliary point (still) lies on the circular arc traversed according to the invention or the circular arc is traversed in this way.

• - Mittel zum Verdrehen bzw. Umorientieren der vorgegebenen Startpose in eine modifizierte Startpose derart, dass der Wurzelpunkt auf einem Lot durch einen Mittelpunkt des vorgegebenen Kreisbogens auf einer Ebene liegt, in der der vorgegebene Kreisbogen liegt;
• - Mittel zum Anfahren der modifizierten Startpose mit der roboterfesten Referenz derart, dass der Wurzelpunkt auf dem Lot liegt; und
• - Mittel zum Abfahren des vorgegebenen Kreisbogens mit der roboterfesten Referenz ausgehend von dieser modifizierten Startpose alleine durch Verstellen einer oder mehrerer dieser drei Drehachsen.

According to an embodiment of the present invention, a system, in particular hardware and / or software, in particular program technology, is set up to carry out a method described here and / or has:

• - Means for rotating or reorienting the predetermined starting pose into a modified starting pose such that the root point lies on a plumb line through a center point of the predetermined circular arc on a plane in which the predetermined circular arc lies;
• - Means for approaching the modified starting pose with the robot-fixed reference such that the root point lies on the perpendicular; and
• - Means for traversing the predetermined circular arc with the robot-fixed reference, starting from this modified starting pose, simply by adjusting one or more of these three axes of rotation.

• - Mittel zum Vorgeben einer Zielpose der roboterfesten Referenz und/oder eines Hilfspunkt, der auf dem Kreisbogen liegt, für den Kreisbogen;
• - Mittel zum Verdrehen der bzw. einer vorgegebenen Zielpose in eine modifizierte Zielpose derart, dass der Wurzelpunkt auf dem Lot liegt;
• - Mittel zum Anfahren der modifizierten Zielpose mit der roboterfesten Referenz auf dem vorgegebenen Kreisbogen.
• - Mittel zum, insbesondere kontinuierlichen, Überführen der Orientierung der roboterfesten Referenz beim Anfahren der modifizierten Zielpose auf dem vorgegebenen Kreisbogen von der Orientierung in der modifizierten Startpose in die Orientierung in der modifizierten Zielpose; und/oder
• - Mittel zum Schneiden eines Loches in ein Werkstück beim Abfahren des Kreisbogens mittels eines Werkzeugs, wobei der Roboter das Werkzeug oder Werkstück führt.

In one embodiment, the system or its means have:

• - Means for specifying a target pose of the robot-fixed reference and / or an auxiliary point lying on the circular arc for the circular arc;
• - Means for rotating the or a predetermined target pose into a modified target pose such that the root point lies on the plumb line;
• - Means for approaching the modified target pose with the robot-fixed reference on the specified circular arc.
• - Means for, in particular continuously, converting the orientation of the robot-fixed reference when approaching the modified target pose on the predetermined circular arc from the orientation in the modified starting pose to the orientation in the modified target pose; and or
• - Means for cutting a hole in a workpiece when traversing the circular arc using a tool, the robot guiding the tool or workpiece.

A means in the sense of the present invention can be designed in terms of hardware and / or software, in particular one that is data or signal-linked, preferably digital, processing, in particular microprocessor unit (CPU), graphics card (GPU), preferably data or signal connected to a memory and / or bus system ) or the like, and / or have one or more programs or program modules. The processing unit can be designed to process commands that are implemented as a program stored in a memory system, to acquire input signals from a data bus and / or to output signals to a data bus. A storage system can have one or more, in particular different, storage media, in particular optical, magnetic, solid-state and / or other non-volatile media. The program can be designed in such a way that it embodies or is capable of executing the methods described here, so that the processing unit can carry out the steps of such methods and can in particular control the robot. In one embodiment, a computer program product can have, in particular a non-volatile, storage medium for storing a program or with a program stored thereon, an execution of this program prompting a system or a controller, in particular a computer, to implement one described here Execute method or one or more of its steps.

In one embodiment, one or more, in particular all, steps of the method are carried out completely or partially automatically, in particular by the system or its means.

In one embodiment, the system has the robot.

• 1: eine vorgegebene Startpose einer roboterfesten Referenz eines Roboters;
• 2: ein Verfahren zum Steuern des Roboters zum Abfahren eines vorgegebenen Kreisbogens mit der roboterfesten Referenz nach einer Ausführung der vorliegenden Erfindung; und
• 3: eine modifizierte Start- und Zielpose der roboterfesten Referenz.

Further advantages and features result from the subclaims and the exemplary embodiments. Here shows, partly schematically:

• 1 : a predetermined starting pose of a robot-fixed reference of a robot;
• 2nd : a method for controlling the robot to travel a predetermined circular arc with the robot-fixed reference according to an embodiment of the present invention; and
• 3rd : a modified start and finish pose of the robot-fixed reference.

1 shows a six-axis articulated arm robot 10th with swivel joints G1-G6 , whose successive axes of rotation are indicated by (the joint coordinates) q1 - q6, and a control 20 to control the robot 10th according to an embodiment of the present invention.

A central hand 11 of the robot 10th has the three distal swivel joints G4-G6 whose axes of rotation q4 - q6 are at the common wrist point HWP to cut.

1 shows a given start pose SP a robot-proof reference TCP of the robot 10th marked by the dash-double-dotted coordinate axes ( X _SP , Y _SP ) is indicated.

In a first step S10 (see. 2nd ) become this starting pose SP as well as a target pose ZP , in the 1 through the dash-double-dotted coordinate axes ( X _ZP , Y _ZP ) is indicated, as well as an auxiliary point HP taught and an arc C. through starting pose SP , Auxiliary point HP and target pose ZP predetermined, for example by the commands
LIN S (start) P (unkt)
(S) CIRC H (ilfs) P (unkt), Z (iel) P (unkt)
or similar. In a variation, these are the starting pose SP , Auxiliary point HP and target pose ZP already specified or taught and are in step S10 from a store 21 the control 20 read.

Now in one step S20 the solder L through a center M of the given circular arc C. at the same level E determined in which the specified arc C. lies (cf. 3rd ).

Then in step S20 a modified position of the carpal point HWP ' determined in such a way that the carpal point on the plumb line L lies.

mit dem Radius r des Kreisbogens C und dem Abstand d zwischen der roboterfesten Referenz und dem Handwurzelpunkt ermittelt.For this purpose, in one embodiment, a distance I of the carpal point to the center point M on the lot L by solving the equation: $${\text{I.}}^{\mathrm{2nd}}+{\text{r}}^{\mathrm{2nd}}={\text{d}}^{\mathrm{2nd}}$$

with the radius r of the circular arc C. and the distance d determined between the robot-fixed reference and the wrist point.

This becomes step S20 the rotation α computes the vector of (the origin of) SP to HWP into the vector of (the origin of) SP to HWP ' turns. This rotation is in step S20 now the taught starting pose SP into the modified starting pose SP ' reoriented or twisted, the in 3rd through the dash-dotted coordinate axes ( X _{SP '} , Y _{SP '} ) is indicated.

Analogously, in one step S30 the rotation β computes the vector of (the origin of) ZP to HWP into the vector of (the origin of) ZP to HWP ' turns. This rotation is in step S30 the taught target pose ZP into the modified target pose ZP ' reoriented or twisted, the in 3rd through the dash-dotted coordinate axes ( X _{ZP '} , Y _{ZP '} ) is indicated.

Then in one step S40 the modified starting pose SP ' with the robot-proof reference TCP approached so that the wrist point is on the plumb line L lies, and in one step S50 based on this modified starting pose SP ' simply by adjusting the axis of rotation q4 with the position of the root of the hand constant (held) the modified target pose ZP ' with the robot-proof reference TCP on the given circular arc C. approached, for example by the commands
LIN SP '
(S) CIRC HP , ZP '
or similar. The orientation of the robot-fixed reference TCP continuously from the orientation in the modified starting pose SP ' in the orientation in the modified target pose ZP ' transferred.

On flange 12th the robot hand 11 For example, a cutting head, in particular a laser or water cutting head, 13 can be arranged to move the circular arc C. departing TCPs a hole in a workpiece W to cut (cf. 1 ).

Reference list

10th

robot

11

Robotic hand

12th

flange

13

robot-guided cutting head

20

Robot control

21

Storage

G1-G6

Swivel

q1-q3

Basic axes

q4-q6

Hand axes

L

Lot

l

Distance [M, HWP ']

r

Radius of the circular arc

d

Distance [SP, HWP] = [SP`, HWP '] = [ZP, HWP] = [ZP`, HWP']

M

Focus

E

level

C.

Circular arc

HP

Auxiliary point

HWP

Wrist point

HWP '

modified position of the carpal point

SP ⁽ ' ⁾

(modified) starting pose

TCP

robot-proof reference

W

workpiece

ZP ^(')

(modified) target pose

α, β

Twisting (reorientation)

Claims (8)

Method for controlling a multi-axis robot (10), which has at least three swivel joints (G3-G6) whose axes of rotation (q4-q6) intersect at a common root point (HWP), for traversing a predetermined circular arc (C) with a robot-fixed reference (TCP), a starting pose (SP) of the robot-fixed reference is specified, with the steps: - Rotating (S20) the specified starting pose (SP) into a modified starting pose (SP ') such that the root point lies on a plumb line (L) through a center point (M) of the specified circular arc on a plane (E) in which the predetermined arc lies; - Approaching (S40) the modified starting pose with the robot-fixed reference in such a way that the root point lies on the perpendicular; and - traversing (S50) the specified circular arc with the robot-fixed reference, starting from this modified starting pose, simply by adjusting one or more of these three axes of rotation (q4-q6), a target pose (ZP) of the robot-fixed reference is specified for the circular arc and the method has the steps: - Rotating (S30) the predetermined target pose (ZP) into a modified target pose (ZP ') such that the root point lies on the plumb line; and - Approach (S50) the modified target pose with the robot-fixed reference on the specified circular arc, wherein when approaching the modified target pose on the specified circular arc, the orientation of the robot-fixed reference is converted from the orientation in the modified starting pose to the orientation in the modified target pose. Procedure according to Claim 1 , characterized in that an auxiliary point (HP) is specified for the circular arc, which lies on the circular arc. Method according to one of the preceding claims, characterized in that when the modified target pose is approached on the predetermined circular arc, the orientation of the robot-fixed reference is continuously converted from the orientation in the modified starting pose to the orientation in the modified target pose. Method according to one of the preceding claims, characterized in that the robot has a robot arm, the robot arm having at least six rotary joints (G1-G6) and / or the three axes of rotation which intersect at a common root point, axes of rotation of a robot hand (11) of the robot arm. Procedure according to Claim 4 , characterized in that the robot arm has exactly six swivel joints (G1-G6) and / or that the robot arm has successive swivel joints (G1-G6) and / or that the three axes of rotation that intersect at a common root point are axes of rotation of a central hand ( 11) of the robot arm. Method according to one of the preceding claims, characterized in that a hole is cut into a workpiece (W) by means of a tool (13) when the circular arc is traversed, the robot guiding the tool or workpiece. System for controlling a multi-axis robot (10), which has at least three rotary joints whose axes of rotation (q4-q6) intersect at a common root point (HWP), for traversing a predetermined circular arc (C) with a robot-fixed reference (TCP), wherein a starting pose (SP) of the robot-fixed reference is specified, the system being used for the implementation of a method according to one of the preceding claims. Computer program product with a program code, which is stored on a medium readable by a computer, for carrying out a method according to one of the preceding Claims 1 - 6 .

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