Duration of activity: 09:00-17:00 and 19:00-22:00 --> 11 hours
Group members participating: Ole Rasmussen and Kasper Føns
1. Goal
The goal today is to continue work on the distributor platform and to construct a new Loader system.
2. Plan
Our plan is to work in parallel on the following
- To continue work on the distributor platform.
- To create a new system, the Loader, which will hold back Lego bricks until the distributor is in position to receive them
- To incorporate the loader with the rest of the LegoSorter systems
3. Loader
We wanted to build a small cargo unit for transferring Lego bricks from the sorters to the distributer. It should be able to hold one brick (axle or beam) back while waiting for the distributer to signal that it is ready to receive it.
3.1 Brick or no brick?
Our first problem is to detect if the loader has a brick to transfer or not. Our initial idea was to use an old RCX touch sensor, since these are easier to press then the newer NXT ones. The sensor should be situated in a gate that we could pull up and down just like the car tray. Figure 1 shows our first test where a beam is being driven forward using the conveyor belt from the BeamCounter. Notice that the beam is not pushing the switch down, and thus the touch sensor is unable to register it. We could therefore not use the touch sensor to detect if there is a brick or not.
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| Figure 1: Old touch sensor from Lego RCX where a Beam is being pushed against it. |
Our second and final solution was to use two RCX light sensors to detect the presence of a brick. We figured that we did not need the same light intensity as for the BeamCounter and incorporating the old type light sensor into normal bricks was much easier. We figured that we did not need a gate, as we could simply stop the conveyor belt when a brick was detected. The system on Figure 2 worked.
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| Figure 2: Two light sensors is used to detect Lego bricks in the Loader subsystem. |
3.2 Example run
Below is an example run of our Loader. Our software will drive the conveyor belt until a brick is detected. When detected it is written on the NXT LCD and the Loader waits 3 seconds to simulate the the distributor gets into place and signals it is ready. It then ejects the Lego brick (driving the belt for two seconds) and again waits. The process then repeats.
3.3 Incorporating Loader
At this point we were happy with the Loader subsystem. We then connected the Loader to the BeamCounter. Figure 3 shows our Loader connected to our BeamCounter and the distributor located just below the Loader, simulating that it is ready to receive a brick.
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| Figure 3: System overview with Loader, BeamCounter and Distributer. |
4. Distributor platform continued
We need to alter our distributor platform such that the distributor car only needs to drop off bricks in one direction. The current platform can only have trays in one position, but this implies that beams and axles needs to be dropped in different directions.
Our solution was to create a distributor platform that could fit a tray in either direction. We could then rotate one of the trays when we position the platform around it such that the car only needed to drop the bricks in one direction. Now that the platform was larger then the tray, we needed a new way to hold the tray in place. Our solution was a set of hooks that went down on the inside of the tray. See Figure 3. We used six hooks for each tray. Figure 4 shows the platform from above on both trays side by side.
Our solution was to create a distributor platform that could fit a tray in either direction. We could then rotate one of the trays when we position the platform around it such that the car only needed to drop the bricks in one direction. Now that the platform was larger then the tray, we needed a new way to hold the tray in place. Our solution was a set of hooks that went down on the inside of the tray. See Figure 3. We used six hooks for each tray. Figure 4 shows the platform from above on both trays side by side.
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| Figure 3: A set of six hooks holds the tray in place inside the distributor platform. Above two of them are shown, there are three one each side of the platform for a total of 12 hooks. |
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| Figure 4: Tray platform used on axles (left) and beams (right). Notice that only six hooks is used at a time. Also notice that the largest axles and beams both needs to be dropped vertically, meaning that the distributor car only needs to drop bricks in on direction. |
5. Conclusion
We have constructed the Loader subsystem. It was easy to construct and works perfectly. We have incorporated it into the BeamCounter subsystem, so that beams coming from the BeamCounter will travel to the Loader system.
We now have a distributor platform that only requires the car to drop bricks off in one direction. We need to change tray each time we shift from sorting axles to beams or vice versa.
6. Next lab
In the next lab session we should make the different subsystems communicate with each other over Bluetooth, transferring information about what brick is coming (from Sorter, to Loader and then to the Distributor). We also need to incorporate the AxleSorter into the system, as pointed out on Figure 3, and construct the distributor bridge that the distributor car controls and on which the car drives.
