Hardware
The hardware decisions in this project were made with a morfological chart. Each possible solution was given scores on several points, the solutions with the highest scores were chosen. These solutions and the scores can be found here. The hardware for this project was designed to be able to transfer carriers between Turtlebots. These were used to make sure the gripper could be designed to be great at securing 1 shape, instead of having to be able to pick up a multitude of different components. These carriers could contain any number of different components of products.
Since the Turtlebot’s stability will be heavily influenced when holding carriers, some changes were made. To make sure the storage could be placed as close to the ground as possible, the camera was removed from its original position and put in the lowest section of the Turtlebot. Custom wood plates were made, which matched the hole pattern of the Turtlebot. Using these plates, the storage could be placed much lower.
The gripper was designed to passively secure the carrier. This means there are no actuators involved in closing it. From a safety standpoint this is much better, since there will be no motor continuing to apply force when something gets stuck between the fingers of the gripper.
When no carrier is held by one of the grippers, it remains open because of a spring. If a carrier has to be transferred, the two Turtlebots involved will drive against each other, with the carrier pushing against the moveable plate of the gripper. The force of the spring will be overcome, causing the fingers of the gripper to close. When the carrier is securely held, a spring-tensioned, servo-operated mechanical latch will lock the gripper. Consecutively, the latch on the other Turtlebot will be unlocked, completing the transfer. The gripper has been tested, the video can be found here.
To make the alignment of two Turtlebots as easy as possible, each storage is able to rotate on its own. This was achieved by placing the multiple grippers on a Lazy Susan bearing. Rotation of the storage is actuated by a Nema 14 stepper motor, which is also put on the bearing. A gear is put onto the shaft of the Nema 14, which connects with a larger gear located in the middle of the supporting plate. With this construction, the entire storage can rotate 360 degrees. To make sure the electric wiring does not become tangled, a slip ring is used that connects the wires through the supporting plate to the power supply and/or Arduino.
The system is controlled by an Arduino UNO. Power for this is supplied by the Turtlebot’s battery.