Week 9 – 10 Jul: Actuator Algorithm

Before we can code anything to control the actuators in our lifting system, we first need to derive an algorithm for the process. As of now, we are not sure which actuator will take longer to fully extend as we have not completed our real-life motion study, so two key assumptions will be made:

1.  500mm actuators take longer to extend as they are longer in length.
2. The first actuator (closer to support tower) of double actuator configuration will take longer to extend as it will likely bear more weight.

 

Here is Seet Ynn’s draft summary for the actuator algorithm (if simplified to up and down motion, and forward and backward motion of arm is ignored):

1. Press UP button, then all 4 actuators extend
2. While length limit of 2x 300mm double actuator is reached, 2x 500mm actuator will continue to extend.
3. When reach lifting arm height of 2.75m, first actuator of double actuator configuration will stop extension and second actuator of double actuator configuration will continue to extend.
4. When reach lifting arm height of 2.8m, second actuator of double actuator configuration will stop extension.
5. When the lifting arm stops moving, SMRT technicians can proceed with unit replacement.

 

Here is Seet Ynn’s draft, in full, with thinking process:

1. Press UP button, then all 4 actuators extend (2x 300mm double actuator in parallel between support tower and first arm, 2x 500mm double actuator).
   1. The 2x 300mm double parallel actuators have to extend together as they both handle the movement of the first arm. If only one of the actuators extend, this will cause the first arm to be bent sideways and cause unintended strain on the first arm.
   2. The 2x 500mm double actuator configuration must extend with the 2x 300 double actuator to increase the rate at which the arm lifts, especially since the 2x 500mm double actuator will take longer to extend.
2. While length limit of 2x 300mm double actuator is reached, 2x 300mm double actuator will stop extension and 2x 500mm actuator will continue to extend.
   1. 2x 300mm double actuator cannot extend beyond length limit to prevent damage to the actuator and programmable logic controller.
   2. 2x 500mm double actuator will continue to extend to increase height of lifting arm.
3. When reach lifting arm height of 2.75m, first actuator of double actuator configuration will stop extension and second actuator of double actuator configuration will continue to extend.
   1. Lifting arm height of 2.75m is chosen, as the targeted height of the lifting arm (excluding clamp system) for it to be within the working space is about 2.8m. A vertical clearance of 5cm and slower motion should be sufficient to ensure safety and good condition of the parts.
   2. Movement of a single actuator to ensure greater precision when the unit is inside the train and close to the small working place. This will better ensure the safety of workers who may have to adjust the unit in the working space to better align it to its lock. This greater precision is also important to prevent the unit from being scuffed up against the LED screen behind the working space, and vice versa.
   3. Since first actuator is slower than the second actuator, first actuator will be stopped and locked so the lifting arm will be slowed down but not too slow
4. When reach lifting arm height of 2.8m, second actuator of double actuator configuration will stop extension.
   1. Any future extension of the double actuator configuration at this point may cause the unit to hit the top of the working space or be too high to slot into lock, even with our highly mobile double ball joint configuration
5. When the lifting arm stops moving, SMRT technicians can proceed with unit replacement.
   1. Safety first!!