Shin-Etsu Handotai Co. Ltd.
In our system active laser triangulation is achieved by using the reflection of a laser line off the object onto a single CCD camera frame. The geometrical relationships of position and orientation is known between the camera and the laser light source. Using this information the illuminated points can be triangulated. For the Nugget Geometry Acquisition (NGA) phase, the laser line is scanned across the nugget by moving the nugget across the field of view by the manipulator/gripper at a constant velocity. For the crucible Surface Geometry Acquisition (SGA) phase, the laser line is scanned across the nugget field using a one dimensional galvanometer mirror scanner. Hence a full map of exposed surfaces is achieved.
The end effector for the Adept One robot will pick up a high percentage of the nuggets and place them into the desired crucible location. The design consists of a closely packed triad of deep 20mm diameter suction cups mounted on a two degree of freedom gimbaled wrist. This wrist is attached to a JR3 six axis force/torque sensor that is connected to the Adept One. The suction cups are connected to a vacuum source. The vacuum can be released with a valve controlled by the master control computer. Nuggets smaller than 60 grams are placed within a bin that the manipulator can grasp and pour into the center of the crucible; these nuggets need not be precisely placed.
The manipulator brings the nugget from the scanning station to the crucible with a high speed slew motion. Then the nugget is brought into contact with the wall. In order to maintain a safe force level while moving the nugget along the wall, the system will switch out of position control to a different control algorithm Possible control algorithms include:
Compliant Position Control: The manipulator will be very compliant in the direction normal to the wall surface, and stiffer in those directions parallel to the wall surface. Position control will be used. The manipulator is directed to move to a position beneath the surface of the wall. The springiness of the control scheme will cause the arm to exert a constant force against the wall (as it attempts to move the nugget into the crucible wall.)
Hybrid Control: The manipulator will use standard position control in the directions parallel to the wall surface, and it will use force control in the direction normal to the wall surface. This algorithm involves more active monitoring of the wrist sensor. The following figure depicts a block diagram representation of a hybrid control system.
The blocks labelled F and P are selection matrices which effectively split up the control signal into force and position components. The force sensor allows for explicit force control which is more responsive than compliant position control, but raises stability issues.
Key Technical Issues for the Factory System Design:
The factory design must provide for easy crucible transport to and from the robot packing area and for complete operator safety and ergonomics. The design must accommodate robot access to all edges of a 36 inch crucible, to the small nugget holding device, and to the large nugget loading area. The operator must be able to sort the nuggets and transport them to the robot loading area without ever entering the robot's workspace while the robot is operation. There must be a precise placement of the crucible relative to the robot to coordinate the vision and controls systems.
- Operating Cost
- Investment Cost
- Operator Ergonomics
- Operator Safety
- System Reliability
- Implementation Time
- Packing Rate
Research is being performed to determine any additional requirements that the actual factory system will have beyond those of the laboratory system. The primary difference between the two systems is the crucible size, which is an 18 inch diameter for the lab and a 36 inch diameter for the factory. Also, there is a higher budget for the factory system, so better equipment could be utilized. The crucible could be packed using one very large robot, using two smaller robots, or using one smaller robot and a turntable. Another possibility is to use one robot to load a portion of several crucibles. For one large robot, commercially available SCARA, gantry, and inverted articulated arm robots with a workspace of at least 42 inches in the x and y directions are being investigated. The robot(s) chosen must have good reliability and speed capability and must be rated for a clean room environment.
Other areas currently being investigated are optimal nugget sorting weight, number of operators needed for each robot, and cycle times for packing the 36 inch crucible robotically.
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