Product Evaluation (Sensors)

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3D Modeling and CAD Video

General Engineering has created a video that covers the fundamental concepts of 3D modeling for the semester-long design project: 3D Modeling and CAD Video. This video provides the fundamental principles behind the engineering design process and will help determine what solutions justify creating a 3D model. Material covered in the video will be on the lab 3 quiz. Viewing the video is a mandatory pre-lab assignment.

Objectives

A specified robot to evaluate has already been created for this lab using an EV3 robotics kit. The design will be evaluated for accuracy and precision by utilizing two different sets of code, the first without the use of sensors and the second with. The robot will be tested on one of the two provided mini-courses. The data from the product evaluation of both sets of code will be used to determine if the robot should or shouldn’t use sensors.

Product Evaluation

Product evaluation is a common task for an engineer and for companies. Sometimes the product evaluated will be a company's product, and sometimes companies will be evaluating a competitor's design. In either case, this evaluation will use a standard (an accepted value), determine an average, and calculate accuracy and precision.[1]

Professional engineers must be sure of standards. For the purpose of this lab, the EG1003 Standard will be 80% precision and accuracy. This means that the product has to achieve a percent accuracy and percent precision of 80 percent and it has to pass 80 percent of the tests that it undergoes.[1]

When taking measurements, the first step is to determine an average.

Average\left(A_p\right) = \frac{P_1+P_2+P_3+...+P_n}{N}\,

In this equation, Ap is the average, P1, P2, P3, ..., Pn are the results of the tests and N is the total number of tests performed.

The average is compared to the standard. Accuracy is a variable the must always be considered. The degree of accuracy required will allow the results to be verified. Engineers often work on projects that affect people's safety; it is critical that the solutions to the problems solved by technical professionals are accurate.

The comparison of the average to the standard is called accuracy, defined as Acc in the following equation:

Acc = \left|P_s - A_p\right|\,

In this equation, Ps is the standard value, and Ap is the value measured. Accuracy is always a positive number, so use the absolute value in case Ps is less than Ap.

Precision is the repeatability of a result, or how close the results are to each other, defined as Prec in the following equation:

Prec = \left|P_{high} - P_{low}\right|\,

In this equation, Prec is precision, Phigh is the highest data value and Plow is the lowest data value. Like accuracy, precision is always a positive number, so use an absolute value here as well.

A product test can be accurate but imprecise, or precise but inaccurate (Figure 1). The goal is always the combination of accuracy and precision. In order for engineers to make a recommendation based on experimental test data, it is important to determine how a product compares to a standard. Engineers need these benchmarks to determine the quality of a product.

Figure 1: Accuracy and precision.

By determining the percent accuracy of an experiment, and comparing this percentage to a standard, it can be determined, based on experimental evidence, if the product has passed or failed. The equation for percent accuracy is:

%Acc = \left ( 1 - \frac{ \left | P_s - A_p \right | }{P_s} \right ) \times 100%\,

In this equation, %Acc is the percent accuracy, Ps is the standard value, and Ap is the value measured.

Percent accuracy shows how precise a product is compared to the standard. The equation for percent precision is:

%Prec = 100e^{-BP}\,

In this equation, %Prec is the percent precision, B is the exponential decay factor, and P is the precision measured. Each individual test requires the use of a different exponential decay factor (B):

Distance Test: B = 0.0972
Angle of Deviation Test: B = 0.0323

Calculating percent accuracy and percent precision and then comparing those results to a standard determines the quality of the product.

Quality Improvement

Quality improvement is a process of analyzing a design and testing it either through physical modeling, computer simulation, or mathematical modeling. Quality improvement ensures that a product will perform as expected and allows improvements to be made to the design.

When deciding how to improve the design in this lab, keep these questions in mind:

  • Does the robot perform to standard?
    • If no, what can be done to improve its functionality?
    • If yes, what can be done to improve its performance beyond the standard?

Changes will be implemented after testing the initial code.

Reverse Engineering

Reverse engineering software involves reversing a program's machine code to obtain the original source code or determine the file structures the program uses. This needs to be done when source code is lost or is not available. For example, when a project is reactivated after being dormant for years to add new features to a product, the original design documentation may have disappeared. Also, when companies are writing a program that must interface to a second company's software, the second company may not have any incentive to cooperate by describing how the data in the files they use are organized, forcing the first company to deduce it on their own. Sometimes, this process is also under­taken as a way to improve the performance of a program, to fix a bug, or to find a virus. When the source code is obtained in this way for any of these reasons it is legal and necessary. Reverse engineering software in order to copy it constitutes a copy­right violation and is illegal.[2]

Hardware reverse engineering involves taking apart a device to see how it works. If a processor manufacturer wants to see how a competitor's processor works, the company can purchase the processor, disassemble it, and then make a new processor similar to it. In some countries, this process is illegal. Hardware reverse engineering is quite expensive and requires an expert in the field.[2]

Design Considerations

Carefully consider the desired results and what needs to be done to achieve it:

  • What made or will make the results inconsistent?
  • If the robot failed a test, why did it fail?

EV3 Sensors

Sensor Basics

A sensor is something that measures some specific value and is used as an input. Different features can be measured by the EV3 sensors, such as light intensity, angle, or distance. The three sensors used in this lab are the light sensor, gyro sensor, and ultrasonic sensor.

Light Sensor

The light sensor (or “color sensor”) can measure reflected light intensity, color, and ambient light, and is useful for when the robot has the option to follow a line or use differences in color to perform different actions (such as stopping when reaching a different color). If measuring color, the sensor outputs a value (0-7) that corresponds to a specific color. Measuring reflected light outputs a value (0-100) depending on the intensity of the light that is reflected. The ambient light works the same way as the reflected light, except it just measures the surrounding light. The light sensor, as well as all other sensors, can be found in the yellow category of MINDSTORMS:

Light sensor.PNG

The type of value the sensor can measure can be changed by clicking the small box on the bottom left of the block:

Light sensor 2.PNG

Gyro Sensor

The gyro sensor can measure the exact degree it turns or the rate at which it is turning. For example, if the robot is set to turn 90 degrees using the gyro, the robot will keep trying to turn until 90 degrees is reached, regardless of any bumps in its way:

Gyro sensor.PNG


Ultrasonic Sensor

The ultrasonic sensor measures the distance between the robot and the closest object to it. It can measure distance in both centimeters and inches; the recommended range is 1 cm to 250 cm:

Ultrasonic.PNG

Switches and Loops

Switches and loops are used to tell the robot what actions to perform depending on the inputs taken from its surroundings, measured by the sensors.

Switch

A switch serves as an “if-else” statement: if the initial condition is true, the top action will occur, if false, the bottom action will occur. This block is used when the robot has to perform different actions depending on the situation it is in:

Switch example.PNG

Loop

A switch will only run the code once, so if repeated action is desired, a loop must be used to repeat the switch’s statement. A loop continuously runs the code inside of it until the end statement occurs. The end statement can be determined with a sensor, or hard-coded to a specific amount of time or rotations; the figure below shows an infinite loop:

Loop.PNG

Materials and Equipment

  • Mindstorms kit with pre-made robot
  • Computer with Mindstorms software
  • Mini-course with accuracy markings

Procedure

Problem Statement

Evaluate two types of code for a robot by creating a line of code without the use of sensors and then a separate line of code using sensors. For each trial, record distance from the wall and angle of deviation. Test the first code by running four trials per section of the mini-course as marked on the physical course, giving you a total of eight trials for the first code. Create a second code using switches and loops to incorporate the types of sensors found on the robot and features on the mini-course. Test again with four trials per section. The total amount of trials for the whole procedure is 16. Download the pre-made Datasheet and fill in the data for each trial.

Course Breakdown

The mini-course is divided into two sections: one flat straight section of four tiles and a second section consisting of a right turn and ramp. Both sections have a wall at the end. In the following schematic, Section 1 is marked in red and Section 2 is marked in blue:

Course diagram.PNG

Part 1: Hardcoding

Section 1: Red

  1. Start the Mindstorms EV3 software
  2. Click on the + in the top left corner to open up a blank program.
    Lab evalimprov ev3 2.png
  3. The screen should look like this. Your program begins with the Start block.
    Lab evalimprov ev3 3.png
  4. Place a Steering block from the Action palette next to the Start block. Set the Port to reflect both motors plugged into the brick; both ports have to be correct.
    Steering block.PNG
    Along the bottom of the Steering block, there are four options. On the left, there is a Mode Selector button, followed by three values for the input parameters picture above the value: from left to right, Power, Rotations, and Brake at End.
    Steering options.PNG
  5. Change the type of the Steering block to On for Seconds. This will change the Rotations input parameter to Seconds.
    Steering seconds.PNG
  6. Test different values of Power and Seconds to find the best settings to travel the first four tiles of the course and stop 5 cm from the wall. When the optimal settings are found, alert the TA and run the program. Run the program for a total of 4 trials. For each trial, record the distance between the robot and wall when the robot stops and the angle of deviation from the center line (draw in pencil a line from the tape to a point on the robot that started on the tape at the start of the trial and measure the angle with a protractor). Record the angle as though the straight line is 360 degrees.

Section 2: Blue

  1. Create the second half of the program to turn the robot and continue up the ramp, stopping 10 cm away from the wall. The robot must start facing the wall and 5 cm away, as though it had just completed the first section. Test different values of Power and Seconds/Rotations to find the best settings to travel the last 5 tiles of the course. A sample turning code is provided below:
    Turn hardcode.PNG
  2. Run the program and make adjustments to the program. Once the accurate settings are found, perform 4 trials for this section, to bring the total count to 8 trials. Again, take distance and angle measurements for each trial.

Part 2: Sensors

Section 1: Red

The first section of the course requires following a straight line. The following steps outline how to build a line-following code for the robot to stay on track.

  1. Click on the + in the top left corner to open up a blank program.
  2. Insert a blank Loop. Insert a Switch within the loop.
    Loop switch.PNG
  3. Set the input of the switch to a Light Sensor and the type to Reflected Light Intensity. Set the comparison to the “greater than” symbol and use Port View on the EV3 brick to measure the light intensity of the line. Set the value of the light intensity to the value displayed by Port View.
    Port view.PNG
  4. In the top half of the switch, insert two Move Motor blocks. Set one to stop and one to continuously moving. Duplicate this in the bottom half but switch the ports. This way one wheel will move while the other stays stationary, which will make the robot wiggle along the line:
    Lab sensorsev3 26.png
  5. Use the Ultrasonic Sensor to make the robot stop 5 cm away from the first wall. Set the end statement of the loop to be controlled by the ultrasonic sensor and set the type to Distance Centimeters for 5cm.
    Loop options.PNG

Section 2: Blue

The second section of the course requires turning to the right 90 degrees, advancing forward one tile, and turning another 90 degrees to prepare for going up the ramp. Each time the Gyro Sensor is used, it has to be reset in order to set the direction the robot is facing before turning as zero.

  1. Insert a Gyro Sensor block and set it to reset:
    Gyro sensor reset.PNG
  2. Insert a Wait block right after the gyro reset. Set it to 2 seconds.
    Gyro wait.PNG
  3. In order for the robot to continue turning until 90 degrees is reached, a Loop must be used to constantly run the robot until the gyro sensor reads 90 degrees. Insert a loop after the wait block and set the end condition to be activated by the gyro sensor using Measure and Angle. Change the comparison to Greater Than and the value of the angle to 90 degrees.
    Gyro code 1 revised.PNG
  4. Insert a Motor block into the loop. Select the port that when activated will turn the robot to the right. Change the Motor type to Rotations and .05 rotations. This translates to the robot moving in .05 rotation increments until the gyro sensor reads 90 degrees:
    Lab3 gyroturn revised.PNG
  5. After the loop, insert a Steering block for the robot to travel straight one tile. Use either rotations or time to move the robot and duplicate the first part of the program after the motor block.
    Gyro code complete revised.PNG
  6. Recreate the line following code to allow the robot to travel up the ramp. Test different values of power to overcome the ramp. The end statement should cause the robot to stop 10 cm away from the wall.
    Section 2 complete revised.PNG

Tabulation of Results

All raw data must be inputted into the Datasheet. From the datasheet, determine if the EG standards were met for accuracy and precision:

Hardcoding Accuracy %Acc Pass/Fail Precision %Prec Pass/Fail
Distance Test
Angle of Deviation Test

Retest with new design using the same table, record the data.

Sensors Coding Accuracy %Acc Pass/Fail Precision %Prec Pass/Fail
Distance Test
Angle of Deviation Test

The lab work is now complete. Please clean up the workstation. Return all unused materials to the TA. Refer to the Assignment section for the instructions needed to prepare the lab report.

Assignment

Individual Lab Report

Follow the lab report guidelines laid out in the page called Specifications for Writing Your Lab Reports in the Technical Communication section of this manual. The following discussion points should be addressed in the appropriate section of the lab report:

  • Discuss product evaluation and the need for it.
  • Discuss quality improvement and its importance.
  • Explain why reverse engineering is important.
  • Discuss a standard, an average, accuracy, and precision.
  • Describe loops and switches and how they are useful in coding.
  • Describe the light sensor, gyro sensor, and ultrasonic sensor used in the lab
  • Discuss the importance of %Prec and %Acc in determining product quality.
  • Discuss the EV3 kit and software used.
  • Describe Mindstorms programming for only the sensors coding portion.
  • Compare the final code with sensors and final code without sensors; determine which is better. Substantiate the decision with data, observations, and other facts collected.
  • Make a final evaluation of the product: should it go into production? Describe its accuracy and precision.
  • Assess the techniques used in the testing process.
  • Discuss better testing methods for the robot design.
  • Recommend if any design improvements should be made.

Remember: Lab notes are required to be taken. Experimental details are easily forgotten unless written down. EG Standard Note Paper can be downloaded and printed from the EG Website. Use the lab notes to write the Procedure section of the lab report. At the end of each lab a TA will scan the lab notes and upload them to the Lab Documents section of the EG Website. One point of extra credit is awarded if the lab notes are attached at the end of the lab report (use the Pictures button in the Illustrations group under the Insert tab in MS Word after your Conclusion). Keeping careful notes is an essential component of all scientific practice.

Team PowerPoint Presentation

Follow the presentation guidelines laid out in the page called EG1003 Lab Presentation Format in the Introduction to Technical Presentations section of this manual. When preparing the presentation, consider the following points:

  • Based on the test results, what is the product's marketability?
  • If determinations were negative, what improvements could be made?
  • Why is product evaluation important?
  • Discuss why quality improvement is important.
  • Discuss the importance of utilizing sensors.
  • ^ a b Oakes, W.C., L.L. Leone, and C.G. Gunn, Engineering Your Future, MI: Great Lakes Press, 2002.
  • ^ a b What Is website. TechTarget Network. Retrieved July 29th, 2003.