Reference no: EM131141718

Laboratory Exercise: Ball in Tube -PID Control

Procedure-

There are two different relationships in this portion of the lab. One involves the laser and the ball's position. The other involves the PWM output of the fan and the height of the ball in the tube.

In each case, the input or (x) variable can be manipulated and the output or (y) variable observed. This lab involves determining the linearity for each of the relationships.

The procedure involves going from the low value to high value in small increments and from high to low in small increments. If the output value saturates (goes to 100%), all remaining input values may be skipped.

1. Collect values of output (y) for laser input vs values of input (x) of ball height (from yardstick). To do this, set the mode to PWM (auto) and adjust output % from 0 to 100 in increments of 10. Then repeat from 100 to 0 in increments of 10.

2. Collect values of output (y), ball height vs values of input (x) or PWM %.

PWM % represents a number for the percent of time the pulse to the motor is on. To do this, set the mode to manual and adjust the output % in 1% intervals starting at 10%. There will be a point at which the ball takes off. This threshold will then allow the ball to reach the top without further adjustment. Then move from high values to low values. You will see a relationship that is different when the ball is at the top and the percent is lowered.

3. Graph of Laser Output vs Ball Position:

You may want to use the graph at the end of the lab report or generate the graph automatically using XLS (in scatter x-y mode).

4. Graph of Ball Height vs PWM%:

You may want to use the graph at the end of the lab report or generate the graph automatically using XLS (in scatter x-y mode).

Questions:

1. Are these two relationships linear?

2. Is linearity necessary to have an automatic operation?

5. Use the system in auto (PID PWM) to control the height of the ball. Set the set-point to a height and observe the ball's movement. Move the Setpoint (PID) from a low value such as 20% to a higher value such as 60%. Describe movement of the ball as it moves to 60% height.

6. Now switch to manual (Manual PWM) and try to control the height to the same height as in the auto mode. Describe the movement of the ball in this mode. Is it harder to control to a set height?

7. Switch the system back to auto and hold your hand over the tube so as to cause a restriction (but letting some air through). What happens when controlling the ball to a set height?

If you hold your hands on the vents for a much longer time, what results are observed? Do not hold your hand near the fan at the bottom of the tube!!!

8. Do the same procedure of holding your hands on the vents with the system in manual. What happens to the ball's position when controlling the ball to a set height?

9. Now vary the set-point from a high percent to a lower percent while in auto mode. This is the reverse of the step function above. Move the set-point from 60% to 20% and observe and record the graph for the negative step function.

10. Vary the set-point by a great amount while in auto. Set the set-point at 10% and then enter a step to 90%. Record the results. Are these results different than those previously recorded? If they are greatly different, reduce the step to a lesser percent to determine at what point the results seem to be more like the step function from 20 6o 60%.

11. Reverse the process and set the step to 10% from 90%. This is the reverse step. Record the results.

Please type your responses to the sections below. The provided descriptions of each section, as well as this text, should be removed after your own writing is complete.

1. Objective

What is the purpose of the experiment?

2. Procedure

Write an explanation of the theory or procedure behind the exercise. Do not re-list the procedure as given in the laboratory manual or give a step-by-step account of the steps you took.

3. Results and Calculations

Give the experimental data in tabular or graphical form. Show samples of calculations. If applicable, include relevant MATLAB results such as graphs of output and command screen history. These can be attached as an appendix if needed.

4. Discussion

Discuss the results or your exercise and show how the objectives were met. Comment on how the results correlate with theoretical values. What are some causes of error in the results?

5. Conclusions

Briefly reiterate the key points of the above sections. Was the experiment considered a success? What (if anything) could have been done differently or better? What are some lessons learned?

6. Questions

Answer any questions that were asked in the exercise.