P15044: Intelligent Mobility Cane
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Subsystems Design

Table of Contents

This node contains information pertaining to the subsystem design's for P15044's Intelligent Mobility Cane. Included are Test Plans, test results, preliminary budgets, and associated information.

Team Updates from Systems Design Review

Summary

Requirements Updates

All requirements highlighted in yellow have been updated since the Systems Design Review.
P15044, Updated Engineering Requirements

P15044, Updated Engineering Requirements

Function-Requirement Mapping

P15044, Function Requirement Mapping

P15044, Function Requirement Mapping

Subsystem Decomposition

P15044, System Decomposition

P15044, System Decomposition

Based off of Proof of Concept testing and the System Decomposition as shown above, the team determined that the critical subsystem decompositions to show were those of the feedback and detection systems.

P15044, Feedback Subsystem Decomposition

P15044, Feedback Subsystem Decomposition

P15044, Detection Subsystem Decomposition

P15044, Detection Subsystem Decomposition

Electrical Testing

Ultrasonic Transducer Testing

The majority of electrical subsystem testing performed during this phase concerned finding an ultrasonic sensor that would fit the team's budgetary constraints while still conforming to the Engineering Requirements for detection. After analyzing the Engineering Requirements, two common ultrasonic sensors were determined and tested: the HC-SR04, a common proximity sensor used by hobbyists, and the MB1010, a proximity sensor often used for robotics applications. As per the Function-Requirement Mapping, the ultrasonic sensors were tested for beam angle width, dowel/pipe detection, sheet detection, and range information.

HC-SR04

P15044, HC-SR04 Time of Flight for Dowel/Pipe-Like Objects

P15044, HC-SR04 Time of Flight for Dowel/Pipe-Like Objects

While testing the HC-SR04, it was hard to determine the output of the sensor, and as the graph shows, results were not predictable or representative of the datasheet. Such deviance was seen in other trials performed by the team; in addition it is well documented by other users that while the sensor does not perceive an object in front of it, oftentimes 'garbage' data is output. With such a low tolerance for false positives, such issues are a concerned for the team.

MB1010

P15044, MB1010 Time of Flight for Sheets

P15044, MB1010 Time of Flight for Sheets

P15044, MB1010 Time of Flight for Dowel/Pipe-Like Objects

P15044, MB1010 Time of Flight for Dowel/Pipe-Like Objects

While testing the MB1010, it was relatively easy to determine the output of the sensor as it is an analog signal that did not further analysis to determine whether the results were accurate as were needed with the HC-SR04. Also, as the charts above relay, all of the trials for distance sensing with different objects followed the same trend as dictated by the sensor's datasheet. In addition, there was no significant deviation in the results using different types of common building materials such as metal and wood.

Conclusions

From our preliminary testing, we were able to get results from the MB1010 throughout our entire range, and even past our maximum detection distance. This sensor provided a relatively linear response, which is desirable for ease of processing. On the other hand, the HC-SR04 was difficult to setup, difficult to interpret the data, and incredibly inaccurate. These results, as shown in the following spreadsheets, indicate that the MB1010 is the ideal ultrasonic sensor for detecting objects. These results sheets also detail bulk purchasing costs - while the HC-SR04 is cheaper, the MB1010 provides all of the desired functionality within budget.

IR Testing

GP2Y0A02YK0F

P15044, GP2Y0A02YK0F Time of Flight for Sheets

P15044, GP2Y0A02YK0F Time of Flight for Sheets

P15044, GP2Y0A02YK0F Time of Flight for Dowel/Pipe-Like Objects

P15044, GP2Y0A02YK0F Time of Flight for Dowel/Pipe-Like Objects

While testing the GP2Y0A02YK0F IR transducer, it was evident that the range was not sufficient for our requirements, as the reliability of the analog voltage output decreased greatly after 5 ft; since we are planning on using IR to detect drop-offs, and placing the sensor array near the handle of the cane, our sensor will need at least 3ft of range (or dead zone) that can compensate for the length of the cane. Since our maximum sensing range is 6 ft past the tip of the cane, we will want an IR transducer that can cover at least 9 ft. We decided to purchase a GP2Y0A710K0F IR transducer to complete further IR testing, as the range of that sensor (3 - 16 ft) more appropriately adheres to our range requirements. However, as our output results matched the datasheet quite accurately for larger objects, we determined that the GP2Y0A02YK0F transducer would be adequate enough for use for preliminary software deployment and data acquisition tests, as the output response for the GP2Y0A02YK0F and GP2Y0A710K0F transducers have the same characteristic over different ranges.

Sensor Distancing

 MB1010 Beam Pattern Specifications

MB1010 Beam Pattern Specifications

 Isosceles Triangle Beam Angle Approximation

Isosceles Triangle Beam Angle Approximation

Due to the nature of sonar, it can be assumed that the beam of the ultrasonic sensor is approximately triangular in nature.In this case, the distance from the sensor in inches is the height of the triangle (h), and 2*sensor spread length at distance in inches is the base of the triangle(a). Using these relations, it is possible to find the hypotenuse (b), and the associated angles. The angle between the two hypotenuses is the relative resolution beam angle.This angle can be found by subtracting 2&#920; from 180. At maximum range, we need at minimum a detection arc of <5°, which was calculated using the information from the specifications for the UltraCane.

Driving Multiple Ultrasonic Sensors simultaneously with decreased interference

Case A
Distance from sensor (ft) Distance from sensor (in) Sensor spread length at distance (in) Length of the hypotenuse (in) Resolution beam angle (°)
1 12 6 13.41640786 53.13010235
2 24 8 25.29822128 36.86989765
3 36 8 36.87817783 25.05761542
4 48 8 48.66210024 18.92464442
Case B
Distance from sensor (ft) Distance from sensor (in) Sensor spread length at distance (in) Length of the hypotenuse (in) Resolution beam angle (°)
1 12 6 13.41640786 53.13010235
2 24 12 26.83281573 53.13010235
4 48 15 50.28916384 34.70804927
6 72 18 74.21590126 28.07248694
7 84 21 86.58521814 28.07248694
8 96 12 96.74709298 14.2500327
Case C
Distance from sensor (ft) Distance from sensor (in) Sensor spread length at distance (in) Length of the hypotenuse (in) Resolution beam angle (°)
1 12 6 13.41640786 53.13010235
2 24 12 26.83281573 53.13010235
3.5 42 21 46.95742753 53.13010235
4 48 24 53.66563146 53.13010235
6 72 27 76.89603371 41.11209044
8 96 36 102.5280449 41.11209044
10 120 27 123 25.36076698
12 144 6 144.1249458 4.771888061
 Sensor Distancing Calculations

Sensor Distancing Calculations

 Sensor Distancing Calculations

Sensor Distancing Calculations

 Sensor Distancing Calculations

Sensor Distancing Calculations

 Sensor Distancing Conclusions

Sensor Distancing Conclusions

Software Testing

The majority of the software testing completed during this phase was proof of concept for the drop-off algorithm. As the drop-off detection needs to take into account the user sweep angle of the mobility cane, it is the one type of detection that requires complex processing from the microcontroller unit.

P15044, Dropoff Algorithm Sweep

P15044, Dropoff Algorithm Sweep

P15044, Dropoff Algorithm Sweep

P15044, Dropoff Algorithm Sweep

P15044, Dropoff Algorithm Sweep

P15044, Dropoff Algorithm Sweep

Project Budgeting

P15044, Current Budgetary State

P15044, Current Budgetary State

At the present time, we are on track with our spending - the next large purchase that we foresee occurring is a purchase of infrared sensors to perform extensive drop-off detection testing.

Updates

The majority of the updates to our Risk Management Plan concern the addition of specific technical hazards that the team may have to address. For full coverage, both subsystem and overall system faults have been detailed in this document. There are hazards for the enclosure, processing, detection, and feedback systems.

Next Steps, Lessons Learned

Next Steps

Lessons Learned


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