Team Vision for Detailed Design PhaseThe focus of this phase was getting caught up. Following our preliminary detailed design review we realized that our progress was behind. The primary focus of this phase was completing items that should have been completed prior to the previous phase as well as advancing the project to having the ability to confidently order all components so that assembly will begin at the start of the semester. Areas of notable progress include: accelerometer testing, A301 force sensor circuit built, system architecture simulated, and a proof of concept alternative to the A301 sensors. At this time, all major components for the system to analyze force and location for a user who does not utilize an assistive device have been ordered. Accelerometers and minor electrical components still need to be ordered.
Prototyping, Engineering Analysis, SimulationIterative activities to demonstrate feasibility, including assumptions you made in your analyses or simulations. Have you completed sufficient analysis to ensure that your design will satisfy requirements? Have you included all usage scenarios in your modeling?
Accelerometer EvaluationThanks to Dr. Puchades, the team was able to test out some functionalities of the MMR accelerometer before purchasing. Location calculation and typical output were two areas of interest.
- Location Calculation
A study was done into the feasibility of calculating location using an accelerometer. Previous research performed by Dr. Puchades indicated that over 100m of error was introduced in a short time frame. The setup of the experiment was to have two accelerometers measure for a short time while laying still. Once the data was exported, two methods of location calculation were used; Excel and MATLAB. The idea behind using two accelerometers is that if the location error given in both cases was constant, then this is representative of noise which can be filtered out of the system. The analysis of the data using Excel and a rectangular approximation found that the error in the location was not a constant noise value, each accelerometer reportedly traveled hundreds of meters in the course of a few minutes.
- Accelerometer Operating Procedure
The software that is included with the MMR accelerometer can provide a data output which can be plugged into Matlab. The software is very user friendly and does not need to be recreated for the usage in our device. For each patient, a normal walking pattern will need to be established so that machine learning can be utilized to create bins. These bins will be included in the profile of a patient. When the patient uses the accelerometers for extended use, the data will be filtered by the bins, abnormalities can be analyzed individually to diagnose and treat specific problems.
- Accelerometer Raw Data
- Accelerometer Test Results
Fabrication of a Capacitive Force SensorAn idea that came out of the last phase was to fabricate our own force sensors in order to simplify the force measurement process, add durability, and save money. A simple force sensor can be created by making a parallel plate capacitor with a rubbery dielectric between them. The capacitance will increase as the space between the plates decreases. In this phase a simple parallel plate capacitor was created to assess the feasibility of creating a similar device.
Capacitor Demo: https://youtu.be/pJu7p9NzeGE
The results are encouraging. Moving forward, Nick will take ownership of the homemade force sensors, working into the next semester to create a product to rival the A301.
PCB Layout for our A301 Op-Amp Circuitry
Drawings, Schematics, Flow Charts, Simulations
While initial testing of the A301 Resistive Pressure sensors indicated that a reference voltage of 3.7 would be the most effective, this schematic shows the reference at less than 3.3V. This was done to illustrate the Zero Pi's capacity to supply a reduced voltage to the pressure sensors, as may need be done with A301 sensors with more appropriate calibration.
Subsystem Wiring Instructions
Component Housing and Shoe Attachment
The below images show our concept for the housing for all components that will need to be attached to the individuals shoe. The only exception is the accelerometer which we are creating as an accessory to this main system, since it will only be used when gait analysis is desired. This housing will be made out of PLA plastic and 3D printed at the RIT construct. It will have a weight of 60.85 g (0.13 lbs) which will cost $1.83 to print. The total weight of the housing and all components will be about 0.45 lbs, so it will be lightweight and hopefully will have a negligible affect on the individuals natural gait.
Assistive Device Force Sensor Integration Concept
In terms of the assistive device attachment, our current solution is to create our own version of the rubber tips that are commonly found on the legs of assistive devices such a walkers, crutches, and canes, and create a slit for the force sensor to slide into. This will then be wired to a similar housing as shown above, which will be connected to the leg of the device. This is a preliminary design, our current focus is fully implementing the system to an individuals foot, but many of the same concepts can be applied to the device attachment.
Interfacing Sensors with Microcontroller and Networking
Bill of Material (BOM)
The total advertised capacity of the system is 6800mAh, but the system is only expected to need 450mA per hour (2.5mA per pressure sesnor; 100mA for accelerometer; 250mA estimated for Zero W; 100mA for RF Beacon). For eight hours, the battery needs to supply 3600mAh, and these batteries were chosen due to their optimal shape and capacity.
- Include a snapshot of your current risk assessment as well as a link to the live document.
Plans for next phase
Team Goal for next semester
- The team goal for the next phase is to assemble the components into a robust system. By the start of the next semester all components will be in our possession and we will piece them together. An important goal for next semester will be to establish a good line of communication with our industry experts who can give advice regarding design choices as well as offer test subjects.
- Include a snapshot of your current Gantt Chart as well as a link to the live document.
Individual Responsibilities to Achieve Team Goals
- Martine Bosch
- Continue research and development of silicone insert with different materials and molds (including 3D printed mold).
- Determine exact wiring for components in the housing and create holes for USB inputs as needed.
- Communicate with Construct on 3D printing procedures and confirm design is good to print.
- Continue design of assistive device insert and housing attachment.
- Nick Petreikis
- Create smaller scale version of capacitive force sensor and design corresponding circuitry (50 hours).
- Learn basic Python programming to lighten the burden on Hrishikesh (20 hours).
- Continue purchasing components (X hours).
- Matthew Devic
- Work with Hrishikesh to decide upon pinouts for the A/DC and the RPi for data communication and acquirement (8+ hours).
- Update PCB layout with A/DC usage and wiring (5 hours).
- Properly calibrate the A301 pressure sensors with the op-amp circuit once all parts arrive (8+ hours).
- Test and verify that power supply can last for 8 hours and be properly recharged through the Juicebox Zero with a micro USB wall adapter (5 hours).
- Work with Martine to ensure that proper ports are accessible or covered through the casing (2 hours).
- Patrick Mylott
- I will be leaving the team and working a co-op job.
- I wish the team the best of luck and my goal before the end of the semester is to leave the team in the best position possible for MSD2.
- John LeBrun
- Assist Nick with the possible implementation of a capacitive pressure sensor and associated circuitry (10 hours).
- Reaffirm the best reference voltage for the A301 pressure sensors, test the feasibility of using a lower weight sensor rather than the current 100lb version (3 hours).
- Construct the physical circuitry of the system & assist Hrishikesh with data interpretation (3, 10 hours).
- Confirm the practicality of single cell Lithium Ion Batteries by testing them in-system (5 hours)
- Continue on with the weekly State-of-the-Project emails.
- Hrishikesh Moholkar
- Client-Server Automation
- Improve Pressure data and location data
- Prepare the pressure point and location simulation using MATLAB
- Erik Brown
- Create list of summer tasks to be completed
- Work to complete all tasks in order to progress project for fall