Master Thesis - Hochschule Bonn-Rhein-Sieg

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4. Overall evading concept Master Thesis Björn Ostermann page 52 of 126 Speed control from part 1 10 Drive by Approach Acquire distance between robot and objects from Data Exchange Object Calculate speed from distance Set robot’s speed to new value Path planning 9 Drive by reachable space Acquire the reachable space from Data Exchange Object Transpose coordinates Select significant part of the map Calculate the shortest free path Obstacle in direct path Load evasion goal pose Set movement to direct drive mode Figure 32: Flowchart path planning control thread – part 2 processing the environmental data (see Figure 25) in path planning routines The first subpart is the speed control, which is dependant on the distance between the robot and dynamic objects intruding into the workspace. It can be activated by the user (button 10), who automatically activates the acquisition of the required distance data as well. The data is transmitted via the data exchange object. This subpart acquires the data and changes the robot’s current speed accordingly, using the algorithm described in chapter 5.4. The next subpart, which requires the most computational effort in this task, is the path planning. It is activated by the user (button 9) if the robot is meant to evade intruding objects. As above, the activation of this subpart automatically activates the respective subpart of the camera control thread as well. The space the robot is able to reach, calculated by the camera thread, is acquired from the data exchange object. Since the coordinates of this space are still in the camera’s coordinate system, they have to be transposed into the robot’s coordinate system (see chapter 5.5.2). After this step, the significant part of the workspace, the part in which the movement takes place, can be chosen by an algorithm (see chapter 5.5.4). Based on the data about this significant part, the current pose of the robot and the next goal pose, another algorithm (see chapter 5.5.5) calculates the shortest free path, divided into sub-goals connected by straight lines, from the current pose to the goal pose around the part 3
4. Overall evading concept Master Thesis Björn Ostermann page 53 of 126 detected dynamic objects (see flowchart in Figure 72). In this calculation a required safety margin (see chapter 6.3) is added to the objects. If this algorithm does not result in one straight line, a dynamic object is present between the current pose and the goal pose. In this case, the first sub-goal of the calculated free path is stored as the next pose to be reached and the robot’s movement mode is set to “direct drive” (see chapter 3.1). The “direct drive mode” is necessary, since the trajectory of a “point to point” motion is not straight (see chapter 3.1). As with the basic work routine, described in chapter 4.4.1, positions can not be approached as exactly as they can be programmed. This algorithm thus sets a point as approached if the robot’s tool centre point is within 3 cm of the given position. 4.4.3 Collision reset Although the robot control thread is trying to prevent the robot from colliding with objects, collisions may happen, since the robot is only moving at a slow speed and can thus be easily reached by persons. This causes safety problems, as described in chapter 2.3, which have to be avoided. The detection of collisions between the robot and intruding objects is handled in the camera control thread (see chapter 4.3.4), and passed on to the path planning thread, which deals with the problem by causing the robot to stop. For safety reasons after a collision is detected the robot is only allowed to “restart by voluntary actuation of a control device” [66]. Additionally the necessary information on the workspace below the robot is lost, as described in chapter 2.3, and has to be regained with the user’s help. Therefore a detected collision has to be manually reset by the user, after the user inspected the workplace. This user reset is handled in this part of the path planning thread (Figure 33, button 17). The reset of the collision status is stored and also transmitted to the data exchange object.
Page 1 and 2: Master Thesis ”Industrial jointed
Page 3 and 4: Statutory Declaration Master Thesis
Page 5 and 6: Contents Master Thesis Björn Oster
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Page 9 and 10: 1. Introduction Master Thesis Björ
Page 11 and 12: 2. Overview on human-robot Master T
Page 19 and 20: 3. Hard- and software Master Thesis
Page 33 and 34: 4. Overall evading concept Master T
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Page 59 and 60: 5. Algorithms Master Thesis Björn
Page 101 and 102: 6. Evaluating the safety Master The
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6. Evaluating the safety Master The
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7. Conclusion and Outlook Master Th
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7. Conclusion and Outlook Master Th
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8. Bibliography Master Thesis Björ
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8. Bibliography Master Thesis Björ
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9. List of Figures Master Thesis Bj
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9. List of Figures Master Thesis Bj
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