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Ch17-I044963.fm Page 79 Monday, August 7, 2006 12:42 PM
12:42 PM
Monday, August 7, 2006
Page 79
Ch17-I044963.fm
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attempt to grasp the comer and judge whether it has successfully grasped it or not by using the infrared
sensors. Tn case of failure, the robot can be programmed to repeat the process from any point.
20
towel
A
16
G’s w dh [do]
Gripper B t 12
G it 8 B
4
0
corner seen by
54
54
72
36
36
CCD camera CCD camera 0 0 18 18 Rotation angle [deg] 72 90 90 At A At B
CCD camera
Rotationangle
[deg]
AtA
Figure 4: Method of finding the best angle for first corner grasping
FINDING & GRASPING OF THE SECOND CORNER USTNG TRACING METHOD
After gripper B has successfully gripped the first comer, gripper A will then release the towel and trace
the edge of the towel starting from beneath the first corner and stops after reaching the second corner.
The flow of this tracing process is shown in Figure 5. First, a possible corner of the towel is determined
within a range just below gripper A using the CCD camera as shown in Figure 6. The range is set at
100x80 dots, the topmost right point set at 10 dots below the tip of gripper A on screen. The distance
between gripper A and the possible corner which is the point furthest left is then calculated. Gripper A
will then start tracing the edge of the towel by smartly using the feedbacks from the infrared sensors as
shown in Figure 6. Force control of 20gf is applied to gripper A during this process. The reason why
gripper A will eventually find a corner next to the one being grasped is due to its movement pattern. As
you can see in Figure 6, the ideal feedback pattern is A. Feedback pattern B is received when the
gripper is gripping too deep. When this occurs, the gripper will move away from the towel until the
pattern returns to A. It is hard though to keep the pattern at A because there is a chance that the towel
will slip away from the gripper. Once the towel starts slipping away from the gripper, it is hard for the
robot to prevent the towel from slipping entirely. We thought about this problem and suggested that
during feedback pattern A, gripper A should move slightly to the right. By doing this, the feedback
pattern will eventually turn to B and then the gripper will move away from the towel as mentioned
earlier. By using this pattern, gripper A will be tracing along the edge of the towel and ensures it to
reach the comer next to the one being grasped, not the one across it.
Tracingfailed
| Gripper A to grip the edge of towel under the first comer | Gripper A
Gripper A
Gripper B
amount
(certain amount Gripper B
(certain
of gripping force
of gripping force
r>| Confirming whether the second comer is near eripper A or not I
applied) Infrared sensors’
applied)
Infrared
sensors'
j , No feedback patterns
feedback patterns
| Set a target point within the image processingarea|
Move down-right
A A ° ' | • Move down-right
I Infrared sensors
Infrared
Moveleft
_ _| Force control is applicdto gripper A while it traces the edge B B •*•! Move left
of the towel based on feedbacks from infrared sensors
To image processing
Image processing area C C | o j» | To imageprocessing
Image processing area
Tracing failed
•|Target point reached or infrared sensors feedback C| D D ogo| Tracing failed
• Towel detected
Towel detected
| Spread towel by gripping both comers|^
o Towel not detected
detected
Towel not
Figure 5: Flowchart on tracing process Figure 6: Edge tracing movement patterns
EXPERIMENTS
Experiments were conducted 20 times for each process during towel spreading using a 32cm x 32 cm