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Systems Design

Table of Contents 1 Team Vision for System-Level Design Phase 2 Action Items for Systems Design 3 Functional Decomposition 4 Engineering Requirements (Metrics & Specifications) 5 Benchmarking 5.1 Vision 5.2 Commercially Available Devices 5.3 Current State of Technology 6 Morphological Chart and Concept Selection 7 Concept Development 7.1 Selection Criteria 8 Risk Assessment 9 Air Muscles Concept 10 Gyroscopes Concept 10.1 Feasibility of Concept 11 Bowden Cable Concept 11.1 Feasibility of Concept 12 Magnetic Braking Concept 12.1 Proof of concept 12.2 Feasibility of Concept 13 Control System 14 Electrical System 15 Feasibility: Prototyping, Analysis, Simulation 15.1 Displacement System Model 15.2 Velocity System Model 15.3 Acceleration System Model 15.4 Force System Model 15.5 G-Force System Model 15.6 Sensors 15.7 Documentation 16 Plans for next phase 16.1 Key Goals for Next Phase 16.2 Key Questions for Next Phase 16.2.1 Is the Magnetic Braking idea feasible? 16.2.2 Are flex sensors feasible for our application? 16.2.3 Is our designed electric system feasible? 16.2.4 What type of elastic material will be able to house all of the necessary components without hindering actuator or sensor function? 16.2.5 How is the tremor force distributed along the hand?

Team Vision for System-Level Design Phase

During this phase, it is intended for the feasibility of all the main contributors to be further researched and various concepts to be tested and selected for an extended feasibility analysis. The Team has come up with a functional decomposition diagrams to identify the main functions of the system and to define the scope of the project. The target is to have a better understanding of the systems’ plausibility and definition. Furthermore, the phase should help in narrowing down the scope and the selection of the concepts based on the benchmarking researched for the different products in the industry. The left open topics that needs to be addressed in this phase would be to define the type of actuators that needs to be used and the concepts/approaches needed to achieve the goals laid out in project definition.

Action Items for Systems Design

Functional Decomposition

Engineering Requirements (Metrics & Specifications)

Link to document here

Benchmarking

Vision

Many devices has already been released to help mitigate tremors when it comes to certain functions, such as: drinking coffee, buttoning a shirt, holding spoons and utensils, using a dish, tip-resistant bottles and drinking soup. These technologies are available commercially and can be obtained relatively easy.

Commercially Available Devices

Therefore, Benchmarking of our product was more directed toward a wearable technology

Current State of Technology

Morphological Chart and Concept Selection

Link to document here

Concept Development

Selection Criteria

1. High level of comfort for user.
2. Ease to take off and put on device.
3. Ease to fasten the device.
4. Overall projected price of the device.
5. Feasibility to create a working prototype by the end of MSD II.
6. Battery life of the device.
7. Overall surface area of the device.
8. Responsiveness to tremors.
9. Effectiveness to mitigate tremors.
10. Overall safety of the device.
11. Weight of the device.
12. Level of fatigue user would experience while wearing device.

A list of the concepts in the chart can be seen here.

By using this Pugh chart we were able to determine the features of the designs that had the most promise, and eliminate other features that provide unsuitable. It was discovered that the actuation process was the most crucial to the design, while it was agreed that a device that fit with either elastic or ratchet straps would be the most secure. Micro-controllers were the ideal processing method, accelerometers and flex sensors were picked for sensors. a battery that could be removed to be recharged seemed to make more sense than finding a way to do some method of power harvesting.

Since actuation method is the Achilles Heel of this project, many methods are being looked into for feasibility.

Risk Assessment

Link to Risk Document here

Due to the many muscles and bones in the wrist, normal range of motion is limited to 70° for extension, 75° for flexion, and 20° for radial and 35° for ulnar movement. If the wrist was to be forcibly moved past these stop points by our device, the most likely result would be straining of muscles or fracturing of bones depending on the force exerted. (http://www.eatonhand.com/nor/nor002.htm)

Air Muscles Concept

Reasons air muscles were eliminated:

1. Need for a constant source of air/ compression
2. Amount of air muscles needed
3. Constant hissing may be an annoyance
4. Requires a filter which can increase maintenance costs
5. Pneumatics aren’t great for fine motor movements and accuracy

Gyroscopes Concept

Feasibility of Concept

Gyroscope Feasibility

Bowden Cable Concept

Feasibility of Concept

Bowden Cable Feasibility

Magnetic Braking Concept

This system would use cables attached to the users hand to resist the movement of the tremor. As the patients hand tremors, the cables will pass through brake pads which will clamp and resist the cables movement, resisting the tremor but not entirely locking the arm.

Proof of concept

Feasibility of Concept

Magnet Force Feasibility 1

Magnet Force Feasibility 2

Control System

In the overview:

The microcontroller will receive an event to begin mitigation, will begin to fire the actuators at some default level, and then monitor the effect on the system using the sensors.

In the microcontroller:

microcontroller senses tremor occurance, sends an actuator response and then senses the effect of the sensor, if the tremor still is occuring stop resisting the tremor, but if it continues, tune the tremor to maintain mitigation. repeat until tremor ceases.

Electrical System

Components:

Microcontroller: receives data, processes, and makes decisions on the actions to take based on the data it receives.

Accelerometer: measures acceleration in at least one axis

Flex Sensor: measures deflection of a plane

Battery: supplies electrical power to the system

Regulator: takes raw battery power and controls its voltage level and current supply

Fuse: Protects the circuit and the patient from high current draw

Actuators: electromechanical devices that the system uses to actively control the tremors.

VCC: rail voltage to power electronics

GND: common ground

External System:

External Charger: pre-existing charging system for charging spare batteries

Battery: supplies electrical power to the system

Feasibility: Prototyping, Analysis, Simulation

Displacement System Model

Velocity System Model

Acceleration System Model

Force System Model

G-Force System Model

Sensors

Sensor selection is driven by the axis of motion and type of motion we are interested in capturing. Three things are desirable for this: that we know the tremor has begun, its frequency and intensity, and which axis they are occurring on.

Feasibility of Sensors:

1. Accelerometer: capture the acceleration of a point in at least one axis.

2. Flex Sensors: measure the bend of a plane. The bend of the plane is related to the change in resistance over the sensor. Full details on the device can be seen in the following document.

Documentation

Forces Feasibility

Accelerometer Feasibility

Flex Sensor Feasibility

Plans for next phase

Key Goals for Next Phase

1. Prove out Magnetic Rail idea.
2. Start building test fixture for Magnetic Rail idea.
3. Purchase or borrow flex sensors for testing.
4. Build a basic electrical prototype.
5. Purchase or borrow Bowden Cables for testing.
6. Purchase or borrow Gyroscope for testing.
7. Start looking into different types of elastic for device and run strength calculations.

Key Questions for Next Phase

Is the Magnetic Braking idea feasible?

1. Will be proved out with a test fixture.
2. What friction force will the Magnetic Braking create?
3. Is the friction force from the Magnetic Braking enough to mitigate our ideal tremor?

Are flex sensors feasible for our application?

1. Will purchase a few flex sensors for testing.
2. What is the acquisition time for flex sensors?
3. Is the flex sensor acquisition time fast enough to detect desired movements?
4. What are the desired movements we want to use the flex sensors for?

Is our designed electric system feasible?

1. Electrical prototype will be built to prove out or electrical design.
2. Components for electrical prototype will be purchased.

What type of elastic material will be able to house all of the necessary components without hindering actuator or sensor function?

1. Where does our glove need to be elastic?
2. Where does our glove need to rigid?
3. How elastic?
4. How rigid?

How is the tremor force distributed along the hand?

1. What is the force along each point along the hand?
2. what is the ideal point to add regulative forces to compensate tremor forces?

Link to Gantt Chart here

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