12 PID Ping Pong Ball Levitation - Vernier Software & Technology

Project 12CHALLENGE DESIGN REQUIREMENTSNote: Do not attempt the Challenge until you have completed the Project Design Requirements.Add a Vernier Motion Detector to the top of the tube. Then modify your VI created in the Project tolevitate the ping-pong ball at an exact distance of 30 cm away from the Motion Detector usingProportional-Integral-Derivative (PID) control. Your device should raise the ball to this position asquickly as possible with a minimum of oscillation. You should create Waveform Charts on the frontpanel for the motor voltage, desired position of the ball, and actual position of the ball. Display boththe desired and the actual position of the ball on the same Waveform Chart.ADDITIONAL MATERIALSVernier Motion Detectorrod clampCHALLENGE SETUPConnect a Motion Detector to the levitation device1. Position the Motion Detector about 5 cm above the top of the tube using a rod clamp. The goldcircular sensor should be centered exactly above the tube opening and pointing downward.Tip: The Motion Detector has a pivoting head to aid in positioning the sensor. Simply rotate thedetector head away from the detector body.2. Set the sensitivity switch on the Motion Detector (if it has one) to the short-range (cart) setting.The sensitivity switch is located under the pivoting detector head.3. Connect the Motion Detector to the DIG port on the interface.CHALLENGE BACKGROUND INFORMATIONIn the Challenge, you are asked to levitate the ping-pong ball at an exact distance away from theMotion Detector. When using a front panel control, as in the Project, the user can raise the ball tothe desired position fairly quickly by increasing the voltage to the fan for more lift and thendecreasing the voltage to maintain that lift. However, in this Challenge, the program needs a methodof control in the absence of a human operator.A Proportional-Integral-Derivative (PID) controller uses the weighted sum of three error terms toquickly and smoothly adjust the ball to the desired position. The proportional term takes intoconsideration how far away the ping-pong ball is from the desired position. As the difference growsor shrinks, the influence of the proportional term grows or shrinks. The main problem withproportional control alone is that the ball will tend to oscillate up and down. You could increase thevoltage to the fan at a very slow rate to avoid oscillating the ball, but your goal is to get the ball toits desired position as quickly as possible. Addition of the integral term will accelerate the balltowards the desired position; but since the integral term is accelerating the process, it can cause theball to overshoot and even fly out of the tube. A derivative term is added to reduce the amount ofovershoot. This equation can be shown as:deV t G Kpe t Kie t dt KdVbiasdt where V(t) is the voltage, G is the gain, K p is the proportional constant, e(t) is the error, K i is theP12 - 4Engineering Projects with NI LabVIEW and Vernier

Vernier Lab Safety Instructions DisclaimerTHIS IS AN EVALUATION COPY OF THE VERNIER STUDENT LAB.This copy does not include:• Safety information• Essential instructor background information• Directions for preparing solutions• Important tips for successfully doing these labsThe complete Engineering Projects with NI LabVIEW and Vernier manual includes12 projects as well as essential teacher information. The full lab book is available for purchaseat: http://www.vernier.com/cmat/epv.htmlVernier Software & Technology13979 S.W. Millikan Way • Beaverton, OR 97005-2886Toll Free (888) 837-6437 • (503) 277-2299 • FAX (503) 277-2440info@vernier.com • www.vernier.com