Sunscreen Tester. Evaluation copy

Transcription

1 Sunscreen Tester Project 18 Skin cancer is the most common form of cancer for young adults. Wearing sunscreen can protect your skin from the sun s harmful ultraviolet (UV) radiation. The effectiveness of a sunscreen is measured by its sun protection factor (SPF). The SPF indicates the amount of time you can remain in the sun before getting a burn. For example, a person wearing a sunscreen labeled SPF- 10 can remain in the sun ten times longer than a person wearing no sunscreen. SPF ratings are approximate values, however, because most sunburns also depend on your skin type, the amount of sunscreen you applied, and the type of activity you are doing. In this project, your challenge is to build a sensor-controlled robot to test the effectiveness of various sunscreens. Your robot should be fairly rugged, since you will be using it outdoors. You will use a Vernier UVB Sensor and a Vernier NXT Sensor Adapter connected to your LEGO NXT to measure UV levels and determine the best sunscreen. One idea described here is to build a mobile robot to move back and forth under a plastic-wrapped canopy. The canopy can be built from LEGO beams or bricks, and a thin layer of assorted sunscreens can be applied to different sections of the plastic wrap. After the robot travels the length of the canopy, testing each sunscreen, it will position itself under the most effective sunscreen. Note: This lab is best done in summer months when the sun is high in the sky and UV levels are high. You should not do this project if the UVB readings in the direct sun are less than a few hundred mw/m 2. OBJECTIVES Evaluation copy In this project, you will Build a robotic device to test samples of sunscreen. Use the NXT to measure UVB levels. Use sensor data to select the most effective sunscreen. STEM with Vernier and LEGO MINDSTORMS NXT 18-1

2 Project 18 DIFFICULTY LEVEL Construction Intermediate Programming Intermediate MATERIALS computer LEGO NXT Intelligent Brick MINDSTORMS Edu NXT v2.0 software Vernier NXT Sensor Adapter Vernier UVB Sensor LEGO MINDSTORMS NXT Educational Set assorted sunscreens plastic wrap DESIGN REQUIREMENTS In this project, you will design and build a mobile robotic device for testing assorted sunscreens during summer months, when the sun is high and UVB readings are substantial. You must build a plastic-wrapped canopy just tall enough for the robot and sensor to travel beneath. Your program should move the robot to each sample and then read and store UVB levels in a text file. It should determine the sample that allows the lowest level of UVB penetration (most effective sunscreen) and then position the robot under that sample. Because SPF values above 15 tend to cut out most of the UVB light, try to use the lowest SPF sunscreens you can find. For best results, use sunscreens with SPF factors of 2, 4 and other low factors. You are strongly encouraged to use the Engineering Design Method when creating your device (see Appendix G). However, construction and programming instructions for one possible solution follow. CONSTRUCTION These directions were created using LEGO Digital Designer (LDD), a CAD-like software program for LEGO components. This program allows you to view the following building instructions interactively on your computer. A free download of LDD is available from The Sunscreen Tester LDD file is provided on the accompanying CD. The base for this robotic device is a basic Four-Wheel Cart. (See Appendix E for detailed building instructions. The 4Wheel Cart LDD file is also provided on the accompanying CD.) The building instructions below are for a UVB Sensor Holder subassembly that will be added to the basic cart STEM with Vernier and LEGO MINDSTORMS NXT

3 Sunscreen Tester UVB Holder Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 STEM with Vernier and LEGO MINDSTORMS NXT 18-3

4 Project 18 Step 7 Step 8 Step 9 Step 10 Step 11 Step STEM with Vernier and LEGO MINDSTORMS NXT

5 Sunscreen Tester Step 13 Step 14 Step 15 Step 16 Step 17 Step 18 Step 19 Step 20 Step 21 STEM with Vernier and LEGO MINDSTORMS NXT 18-5

6 Project 18 Step 22 Step 23 Step 24 Step STEM with Vernier and LEGO MINDSTORMS NXT

7 Sunscreen Tester Attach the UVB Sensor Holder between the two motors on the Basic Cart; then position a Vernier UVB Sensor between the four axles. The UVB Sensor should be pointing directly up. Secure the UVB Sensor in place by wrapping two rubber bands from your MINDSTORMS NXT Educational Set around the upper and lower pair of axles. Connect the UVB Sensor to the Vernier NXT Adapter; then connect the Adapter to Port 1 on the NXT. Your robot will travel back and forth under a plastic-wrapped canopy built from additional LEGO pieces. An example is shown below. Sunscreen Canopy Step 1 Step 2 STEM with Vernier and LEGO MINDSTORMS NXT 18-7

8 Project 18 Step 3 Step 4 Step 6 Step 5 Step 7 Step STEM with Vernier and LEGO MINDSTORMS NXT

9 Sunscreen Tester Step 9 Step 10 Step 11 Step 12 Step 13 Step 14 STEM with Vernier and LEGO MINDSTORMS NXT 18-9

10 Project 18 Step 15 Step 16 Step 17 Step 18 Step 19 Step STEM with Vernier and LEGO MINDSTORMS NXT

11 Sunscreen Tester Step 21 Step 22 Step 23 Step 24 Step 25 Step 26 STEM with Vernier and LEGO MINDSTORMS NXT 18-11

12 Project 18 Step 27 Step 28 Step 29 Step 30 Step 31 Step STEM with Vernier and LEGO MINDSTORMS NXT

13 Sunscreen Tester Step 33 Position the canopy high enough so that the robot can travel freely beneath it. You can build a vertical support from additional LEGO pieces or support the canopy with a ring stand, as shown in the figure at left. STEM with Vernier and LEGO MINDSTORMS NXT 18-13

14 Project 18 PROGRAMMING The 18 Sunscreen.rbt program created with MINDSTORMS software is shown below. (This program can be found on the accompanying CD.) The Sunscreen Tester program operates under the premise that the best sunscreen will allow the lowest amount of UV light to pass through, consequently appearing to the robot as the shadiest spot. The first two blocks initialize the UV Min and Count Min variables that the program will be using to store the lowest UV reading and the motor s location at the lowest reading. The main loop in the center is the UVB data-collection cycle. The first part of the loop activates motors B and C to move the robot forward a preset distance based on the width of each sunscreen sample. Modify this distance to match the spacing of your samples. The robot then takes a UVB reading. The settings for the Vernier Sensor Block are shown in the figure below STEM with Vernier and LEGO MINDSTORMS NXT

15 Sunscreen Tester The third block in the loop displays the UVB value on the NXT screen, and the fourth block records the value to the 18 UV Data.log file. The settings for the Start Datalog block are shown below. Next the UV reading is compared to the variable UV Min. UV Min stores the lowest recorded reading. If UV Min is greater than the current reading, it means the current reading is now the lowest reading that has been taken thus far. In this case the true branch of the Switch block is executed. (Note that only the true branch of the Switch block is shown in the figure above because the Flat view checkbox is de-selected.) The blocks inside the true branch store this lowest reading in the UV Min variable. In addition, the location of where this lowest reading was taken is stored by reading the value of the built-in rotation sensor on motor B and storing this value in the Count Min variable. After the Switch block code has been called, the last block in the loop pauses the robot for 3 seconds to let you know the data point has been taken. The robot will execute this measurement loop 5 more times in order to sample 6 different sunscreens. Storing new minimum readings, and the location of these readings, as they occur. When the program exits the measurement loop, it closes the 18 UV Data.log file and then reads the value of the built-in rotation sensor on motor B. The program subtracts the stored motor location value of Count Min (the location of the lowest UVB reading) from the current motor location to determine the distance the robot needs to move in reverse. The program activates motors B and C to move the robot back to the location of the lowest UV reading or the shadiest spot. STEM with Vernier and LEGO MINDSTORMS NXT 18-15

16 Project 18 EXTENSIONS 1. Start the Data Logger by clicking the Switch to NXT Data Logging button in the upperleft corner. Upload the UV Data.log file to graph the data. What is the relationship between the sunscreen s SPF value and the amount of UVB the robot saw? 2. Rewrite the program so that the robot moves continuously under the sunscreen canopy. As the robot moves, it will play a tone to indicate the current value of UVB radiation passing through to the sensor. A high UVB value will result in a high-pitched tone, while a low value will result in a low-pitched tone STEM with Vernier and LEGO MINDSTORMS NXT

17 Vernier Lab Safety Instructions Disclaimer THIS 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 labs The complete STEM with Vernier and LEGO MINDSTORMS NXT lab manual includes 14 lab activities and four projects as well as essential teacher information. The full lab book is available for purchase at: Vernier Software & Technology S.W. Millikan Way Beaverton, OR Toll Free (888) (503) FAX (503)