Brick Sorter #2

Second in the series of brick sorters is this machine, which sorts black, grey and white bricks and seperates big from small bricks. Bricks are thrown into the brick store, go down to the conveyor belt one by one, and are put into one out of six bins on a rotating platform.

Each time I create a brick sorter, I try to tackle at least one additional design challenge. In this case, I wanted to further expand on #1 by enabling sorter #2 to also sort bricks by size. Also, I tried to add a mechanism that would automatically align bricks before they get inserted into the brick chute. The color and size sorting worked quite reliable, but the brick alignment wasn't a great success. The robot was programmed in the original RIS 2.0 software, and it was designed in December 2006.

About the design

The brick store

The idea was to allow the user to throw a set of bricks into this part of the sorter, and to have the sorter align them correctly by itself. This covers two challenges:

• Ejecting bricks to the cenveyor belt one by one
• aligning big bricks straight forward

This part of the design was not very succesful. A well working solution to this first problem is found in the Hybrid Brick Sorter (brick sorter #6), and the second challenge has been attempted once more in brick sorter #4.

Detecting the color and size of a brick

Once the bricks have left the brick store, they move forward on two conveyor belts. A light sensor is used to read the color of brick that pass by. The longer the sensor sees the brick, the bigger the brick. The 'length' of this period is actually proportional to the amount of rotations the wheel hubs in the conveyor belts make. This amount of rotations is counted with a modified LEGO speed computer, acting as a rotation sensor. This sensor gives three 'Touch Sensor' ticks per rotation. Because the rotation sensor is connected to an axle which turns faster than the one that powers the conveyor belt, the sensor has a fairly good resolution.

Storing the bricks in different bins

Once the size and color of a brick is known, it is ready to be stored in one of the six bins on the rotating platform at the end of the sorter. A second light sensor detects when the brick has almost reached the platform. With the help of another rotation sensor, the platform turns the appropriate amount of degrees, ready to store a brick. This sensor is connected to the same sensor port on the RCX. This is possible, because only one sensor has to operate at the time. The unused sensor is always locked in a position that doesn't make the RCX detect a pulse. Every detected pulse is therefore one from the sensor currently in use.