Team Vision for System-Level Design PhaseDuring 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
Engineering Requirements (Metrics & Specifications)
Link to document here
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
- High level of comfort for user.
- Ease to take off and put on device.
- Ease to fasten the device.
- Overall projected price of the device.
- Feasibility to create a working prototype by the end of MSD II.
- Battery life of the device.
- Overall surface area of the device.
- Responsiveness to tremors.
- Effectiveness to mitigate tremors.
- Overall safety of the device.
- Weight of the device.
- 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.
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:
- Need for a constant source of air/ compression
- Amount of air muscles needed
- Constant hissing may be an annoyance
- Requires a filter which can increase maintenance costs
- Pneumatics aren’t great for fine motor movements and accuracy
Feasibility of ConceptGyroscope Feasibility
Bowden Cable Concept
Feasibility of ConceptBowden Cable Feasibility
Magnetic Braking ConceptThis 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
Control SystemIn 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.
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 Charger: pre-existing charging system for charging spare batteries
Battery: supplies electrical power to the system
Feasibility: Prototyping, Analysis, Simulation
Displacement System Model
Plot 1 : Modelling a displacement model at 4 Hz with uncertainties propagate through. The plot aids in making the decision of providing 3D plots since error can be left out of plots.
Velocity System Model
Acceleration System Model
Force System Model
Plot 5 : Modelling the Max force model from 4 - 8 Hz over one period of time, s. These calculations assumed a 240 lb human.
Plot 6 : Modelling the Min force model from 4 - 8 Hz over one period of time, s. These calculations assumed a 160 lb human.
G-Force System Model
Plot 7 : Modelling the Max G-force model from 4 - 8 Hz over one period of time, s. These calculations assumed a 240 lb human.
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.
Plans for next phase
Key Goals for Next Phase
- Prove out Magnetic Rail idea.
- Start building test fixture for Magnetic Rail idea.
- Purchase or borrow flex sensors for testing.
- Build a basic electrical prototype.
- Purchase or borrow Bowden Cables for testing.
- Purchase or borrow Gyroscope for testing.
- Start looking into different types of elastic for device and run strength calculations.
Key Questions for Next Phase
Is the Magnetic Braking idea feasible?
- Will be proved out with a test fixture.
- What friction force will the Magnetic Braking create?
- Is the friction force from the Magnetic Braking enough to mitigate our ideal tremor?
Are flex sensors feasible for our application?
- Will purchase a few flex sensors for testing.
- What is the acquisition time for flex sensors?
- Is the flex sensor acquisition time fast enough to detect desired movements?
- What are the desired movements we want to use the flex sensors for?
Is our designed electric system feasible?
- Electrical prototype will be built to prove out or electrical design.
- 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?
- Where does our glove need to be elastic?
- Where does our glove need to rigid?
- How elastic?
- How rigid?
How is the tremor force distributed along the hand?
- What is the force along each point along the hand?
- what is the ideal point to add regulative forces to compensate tremor forces?
Link to Gantt Chart here