Sub-System Design

MSD P14041 Smart Walker IIApril 14, 2014

Critical Sub-Systems

Electrical:● Strain Gauges● Fall Detection

○ TI Chronos Watch■ Specifications■ Coding■ Preliminary Testing

Critical Sub-Systems

Computer:● Code● Algorithms● XML Data (for caregivers)

Critical Sub-Systems

Mechanical:● Clutch/Motor System

○ Clutch Issues■ Clutch Design

○ Motor Issues

Electrical: ez430 Chronos Hardware

Electrical: ez430 Chronos Software

Electrical: ez430 Chronos Acceleration

Electrical: Strain Gage

Mechanical: Clutch DesignClutch Design Issues: ● Price point for clutches that fulfill the need have been too high to be

reasonable for our budget, as well as too high to be feasible for a long term solution.

● Clutches in the price range required, do not meet requirements:○ i.e. Only 1 direction, does not meet size requirements, does not meet

torque requirements.● With these issues in mind, we a looking into designing our own clutch

mechanism.

Mechanical: Clutch DesignInitial Design Concept:

● Mounts to walker wheel axle● Opposite side mounts to output shaft on motor● Electro-magnet inside clutch receives signal● Connected to an “actuator” will drive arms to

engage hub, and connect the wheel side to the motor side.

● Removal of the signal retracts actuator allowing wheel to free spin

Potential Issues:● Designing and integrating electro-magnet may

be difficult. ● Friction between clutch arms and hub needs to

be strong enough to withstand applied force from rolling.

Mechanical: Clutch Design

Mechanical: Motors

Motor Issues:● Price point for motors is also out of our price range for the budget as well as for a feasible long

term solution● To obtain new lower profile motors with encoders is a minimum of $400/ea (After tax and

shipping)

Solution:● Continue to use the Pololu motors currently on the walker (Purchase New Set) ● Redesign housing to create a more “integrated” look● Relocate motors to “clear” the walkway reducing the risk of user hitting the motor housing with

their feet● Integrate clutch design into existing motors

The above will allow the Electrical and Computer side to move forward with the final decisions on motor controllers as well allow programming and writing of code to begin

Hardware Architecture

Concept Selection for MCU

Pugh Matrix for MCU

Software Architecture

Periodic Reports

Concerns for Design:How often are reports generated?

Mockup is daily, but can be changed based on needs of end user.How much should data be compressed for user readability?

Varies with data type.How will data be presented?

Feedback on mockups will determine modifications to report. How long does data need to be stored?

Limited by memory of system, dictated by the needs of the end user.

End user of report: Doctors

A survey of doctors with regards to these issues would be useful for design.

Report Example

Customer RequirementCustomer Req

# Priority Description Comments/Status

CR01 9Reduce/ Eliminate noise from motors while walker is in "manual mode"

This was added per Sub-System design review. Clutch system was initially thought to be for the purpose of disengagement of the motors to reduce wear and extend motor life. Customer clarified they were more concerned with the noise from the motors.

CR02 1Set up External Microphone Array to connect to PC and IR Thermal Camera for External Fall Detection/ User Location

This was initially thought to not be a requirement, but instead a "would be nice" customer request. Still need further clarification of exact deliverables associated with this.

CR03 9 System must be robust and able to withstand everyday useALL components need to be able to withstand further testing, use, and demonstrations

CR04 9 Conceal systems within the frame of the walker.Walker must look "Off the shelf." Components should not be obtrusive to the user

CR05 9 Motors must not resist the manual movement of the wheels.

CR06 9System must be capable of detecting a user's fall and executing a recovery routine.

Multiple redundant detection/alert systems working in tandem.

CR07 9System should be capable of determining presence of a user based on handle interaction.

Include sensor/strain gages on handles

Customer Requirement cont’dCR08 9

Unify software subsystems and bring them to an acceptable operational level.

CR09 3 Redesign motor and powertrain system.

CR10 9Software should compile necessary info into a readable file to be sent to customers

XML formatted and sent once-a-day regularly, and immediately in the event of a fall or medical emergency

CR11 9 SLAM CapableHandled by ASUS Xtion Pro Live and previously developed algorithms

CR12 3 System must be capable of predicting pressure sores.

CR13 3 System should be able to brake the wheels on user input. Manual cable breaks included in walker frame.

CR14 3 Make power system rechargeable and user friendly.

CR15 1 System should be light weight.

CR16 1 System should have minimal power loss when idling.Converter selected for high efficiency, redundancy will be required to make sure that there is no excess current draw during normal operation

CR17 9 Odometry handled via a combination of IMU and encoder feedbackEncoders coupled to wheel motors, IMU pre-packaged and readily interfaceable

CR18 9 System must be readily reprogrammableSystem must be capable of being accessible on both the hardware and software side

Engineering RequirementsEng Req

# Customer Req # Description Unit of Measure

Marginal Value Target Value Comments/Status Owners

ER01 CR01, CR05Reduce Motor Noise While in Manual Mode

dBClutch Design / New gearing; Currently being designed and

prototyped

Anthony, Noah

ER02 CR02 Microphone sensitivity dB 40 15 To be tested Kelsey, Trevor

ER03 CR02Microphone directional accuracy

m 1 0.1 To be tested Kelsey, Trevor

ER04CR01, CR03, CR05, CR09

Motor resistance on wheels Nm 0.25 0.01 Clutch Design/ New GearingNoah,

Anthony

ER05 CR14, CR16 Battery life Hours 4 12Power subsystem design

mostly completeKelsey, Trevor

ER06 CR06 Response time to fall s 60 30Handled primarily via ez430

Chronos and other redundant systems

Alex, Dan, Kelsey, Trevor

ER07 CR03, CR15 System mass kg 20 5Noah,

Anthony

ER08 CR13 Braking force N 10 20Manual brakes already installed

on systemNoah,

Anthony

Engineering Requirement Cont’dER09 CR07 Handle sensitivity kg 2 0.25

Handled via frame strain gauges

Noah, Anthony, Kelsey

ER10 CR04Conceal Walker Components

cm

Rubber Grommets on frame to protect wires; New seat back to

allow more room to hide components; New housing for

motors

Anthony, Noah

ER11 CR08 Unify software systems Packet lossCommunication between

various controllers and lower level systems

Alex, Dan

ER12 CR09Motor housing/ mount; Clutch

cmDesign to be less obtrusive;

measurement based on protrusion into walkway

Anthony, Noah

ER13 CR10 Human-readable XML reportReports

generated1/week 1/day

Special report generated on medical emergency

Alex, Dan

ER14 CR11SLAM-capable camera system

Camera resolution

Handled by ASUS Xtion Live Pro

Alex, Dan, Kelsey, Trevor

ER15 CR12Pressure Measurement in seat

lengthHandled by strain gages in

seat. Measures displacementKelsey, Noah,

Anthony

Engineering Requirement Cont’d

ER16 CR17Odometry error measurement

m 0.1 0.05Handled through

Arduino+Encoders+IMUKelsey, Trevor

ER17 CR18Accessibility to control systems

# of reprogrammabl

e hubs1 3

Microcontroller housing and design

Anthony, Noah, Alex, Dan, Trevor,

Kelsey