Say you are the designer for a block manufacturing plant. You are faced with a problem: how do you get the blocks (picture 2) from points A, B, C, and D on the ground to points A, B, C, and D on top of the shelf (picture 1)? Roboarm 11 is designed especially for the job. The hand closes and picks up one block; the arm raises, turns around, lowers and places the block on the shelf. Then the arm raises and turns back around. The base of the arm advances down the line, and then the arm lowers to repeat the sequence.
The video shows the robot dropping the first block on the shelf and going over to pick up the second block, which is half of one sequence.
When you first start the NXT program, the NXT sends a message to the RCX to close the pneumatic hand (picture 1 in this section). Two of the RCX ports are used for the Pneumatic Control Unit (PCU), which opens and closes the hand. Picture 2 shows the air compressor, which is driven by a Power Function (PF) motor. Picture 3 shows the other side of the PCU. To close the hand, the motor connected to the valve in the PCU turns the valve to the "close" position. The motor is connected directly to the valve without any levers or gears. If the RCX keeps the motor on continuously it might strain it. But if the RCX turns the motor on and off very quickly, it will have no problem turning the valve. After switching the valve, the air compressor pumps a little more air into the tank to close the hand.
The NXT communicates with Bluetooth and the RCX by infrared messaging. However, the IR-Link Sensor allows the NXT to send infrared messages to the RCX. See my other project, Perimeter Guard System, section 2, for more information about the IR-Link sensor.
Now the NXT uses a linear actuator (picture 1) to directly convert the motor's rotary (spinning) motion into the powerful linear (back and forth) motion that is needed to raise the heavy arm at the shoulder joint. But even with the shoulder at its maximum upward position, the forearm is still too low to place the block on the shelf. So, the NXT sends another message to the RCX to raise the forearm slightly at the elbow joint shown in picture 2. The elbow joint is also powered by the RCX, using two RIS geared motors and a blue rotation sensor for strong, but precise positioning. Since those two motors don't need to move separately, they are both wired to the same port.
Now the NXT rotates the arm around approximately 180 degrees to position the block over the shelf. The turntable and worm gearing (shown here) is under a lot of stress and resistance from the heavy arm, so a huge amount of reinforcing is required to hold it all together.
To put the block on the shelf, the robot must first open the hand and then raise the forearm slightly more so that the arm doesn't knock the block off the shelf when it rotates back around. To do this, first the NXT sends a message to the RCX telling it to perform this particular action. The motor connected to the valve in the PCU turns the valve to the "open" position. Then the air compressor pumps a little more air into the tank to open the hand, and finally, the forearm raises at the elbow joint.
The arm rotates back around about 180 degrees and then lowers the forearm down to its original starting postion. This picture shows the IR-Link sensor in the back and the two touch sensors. The touch sensors are only pressed when the arm is in its starting position. The arm stops moving when they are pressed, so it can start the new motion sequence from the same position every time.
Once the position of the forearm and the turntable is reset, the arm can go pick up the next block to put on the shelf. Using the giant treads, the base of the whole arm drives to the left, positioning itself behind the next block, and the shoulder joint motor lowers the arm. Then the whole process starts over again.
When you download the program, the loop count will be set to four, which means Roboarm 11 will pick up four blocks. By changing the number of times the sequence loops on the repeat block's control panel, you can change how many blocks you want the arm to pick up. Make sure you have the RCX IR-Link NXT-G programming block and the Mini Block Library before you download the program.
Thank you. Please watch the video and comment!