Method and a device for optimizing a programmed movement path for an industrial robot

#This application is the national phase under 35 U.S.C. §371 of PCT/EP2008/065873 filed 19 Nov. 2008.

#The present invention relates to a device and a method for optimizing a programmed movement path for an industrial robot. The invention is suitable for any types of robot automated processes in which the tool orientation is of less importance, such as laser welding, laser cutting, water jet cutting, arc welding, and milling.

#An industrial robot is generally used for industrial automation. The robot is programmed to follow a movement path while the robot carries out work during a work cycle. The robot program has information about what the robot should do and in which order tasks should be executed along the path. The robot program has information about all target points on the movement path. The robot programming could be done online manually by teaching the robot positions and orientations of target points on the movement path. The robot program could also be created by an offline programming and simulation tool running on an external computer, such as a PC. Typically, the robot target is a position target, which means that the target comprises a Cartesian value (x, y, z) defining the position of the tool and information about what orientation the tool should have at the target. The information on the tool orientation can be described in different forms, for example, as quartions, a rotation matrix, or as roll, pitch and yaw angles. If the target points are position targets it requires some calculations for transforming the position targets to joint values for the axes of the robot. This transformation is done by a kinematic model of the robot. In order to transform values from the Cartesian space to joint space inverse kinematics is used.

#The invention will now be explained more closely by the description of different embodiments of the invention and with reference to the appended figures.

#FIG. 1 shows an example of an industrial robot holding a tool carrying out work along a movement path.

#FIG. 2 shows an example of a tolerance interval for the orientation of the tool in a target point.

#FIG. 1 shows an example of an industrial robot 1 holding a tool 3 and carrying out work along a movement path 5 including a plurality of programmed target points 7. The target points can be programmed on-line by teaching the robot the target points or off-line using an off-line programming and simulation tool. The robot program includes information on the positions and orientations of the tool in the target points. The robot 1 is a typical six-axis robot and comprises a base 9 arranged to be attached to the ground. The ground is, for example, a floor, a wall, or a roof of a building. The robot further comprises a first arm 10, which is rotatable relative to the base 9 around a first axis. In the top end of the first arm 10, a second robot arm 11 is mounted rotatable relative to the first arm about a second axis. In the outer end of the second arm 11, a third arm 12 is mounted rotatable relative to the second arm about a third axis. In this example, the third arm 11 comprises two parts and the outer part is rotatable relative to the inner part about a fourth axis. The third arm 12 supports in its outer end a so-called robot hand 13, which is rotatable around a fifth axis. The robot also comprises a tool attachment, which is rotatable relative to the robot hand about a sixth axis. For this type of robot, the performance of the first, second and third axes are poorer than for the other axes. In particular, movements about the first axis should be avoided due to poor performance of the first axis.

#In some applications the orientation of the tool is not important. For example, the angle of the tool 3 with respect to a target point 7 can be varied within a cone 16 around the tool as shown in FIG. 2. The angle α of the cone defines a tolerance interval for the orientation of the tool in the target point. Further in many applications, such as laser jet cutting and laser welding, the rotation of the tool about its symmetrical axis can be arbitrary. According to the invention, the robot path is optimized by optimizing the orientation of the tool within a given tolerance interval. The optimization is made with regard to minimizing the cycle time and thereby to reduce production cost.

#FIG. 3 shows a device 20 for optimizing a programmed movement path according to an embodiment of the invention. The device 20 is a computer, for example a PC, including a user interface 22, such as a display screen, a keyboard and a mouth. The device 20 comprises hardware necessary for processing data such as a central processing unit (CPU), data storage, and communication means for communicating with external equipment, for example with a robot controller. The device 20 also comprises software for carrying out the method according to the invention. The device 20 comprises a computing unit 24 configured to receive tolerance intervals for the orientation of the tool at target points on the programmed movement path. The tolerance intervals are, for example, input by a user through the user interface 22. The device 20 also comprises data storage 26 for storing a programmed movement path including information on tool positions and tool orientations a at the target points of the path. The computing unit 24 is also configured to store received tolerance intervals for the target points in the data storage 26.