Mechanical Design Elements

Mechanical Engineers:Brian LomickaJelani Williams

Industrial Engineer:Rohan Gulati

Agenda:1. System Overview

a. Customer Needsb. Requirementsc. Specifications

2. Headgear system:a. Review of Frame Selection

i. Selection Matrixb. Review of Eye Camera Mount Design

i. Selection Matrixii. Concept Pictures

iii. Technical Drawingsiv. Structural Analysisv. Prototype

c. Review of Scene Camera Mount Designi. Selection Matrix

ii. Concept Picturesiii. Technical Drawings

3. Camera Selection

4. Review of EOG/EEG selectiona. Concept Justification

5. Review of Enclosure Designa. Enclosure Layout Drawingb. Initial Conceptc. Initial Structural Analysis

6. Risks and Contingencies

7. Bill of Materials

System Overview:

The mechanical portion of this project consists of two systems: the Headgear and the Enclosure. The Headgear has two subsystems, the mount for the scene camera, and the mount for the eye camera. Additionally the responsibility of selecting electrodes and mounting solutions for the EOG and EEG signals were delegated to the mechanical team.

Mechanical Systems

Headgear Enclosure EOG/EEG

Scene Camera Mount

Eye Camera Mount

EOG Electrodes

and Mounting

EEG Electrodes

and Mounting Figure 1: Block Diagram of Mechanical Systems

The Headgear system consists of a frame that has been designed to fit a variety of head and face shapes. These will be purchased, as there are many different styles readily available. The Headgear will carry the various systems needed for video eye tracking.

In order to have meaningful video eye tracking, two cameras are required: one to view the eye itself, the other to view the scene the eye is looking at. Mounts for each camera will be constructed and attached to the Headgear.

The enclosure will contain all the electronics that are required to run our system. It will be wearable and comfortable for the expected duration of the test.

The EOG and EEG electrodes are required to record bio-potential signals. Solutions for attaching the electrodes to the test subject were developed.

Customer Needs:

Customer Need # Importance Description

MechanicalCN1 1 Minimze camera movement/vibrationCN2 1 Minimize eye camera intrustion into FOVCN3 1 Adaptable to right or left eyeCN4 2 Headset wearable with glassesCN5 1 EOG - 2 points - Clinical StandardCN6 1 Must be portableCN7 1 EOG electrode mounting all in one pieceCN8 2 Headset a small form factor (lightweight, unintrusive)

CN9 1 Moniter one eye only - scalable to 2 eyes in futureCN10 1 Robust Design

Figure 2: Mechanical Customer Needs

Requirements:

Requirement #Corresponding Customer Need

Description Comments/Status

R1 CN1, CN2, CN10, CN12 Need to have appropriate number of channels Two for EOG and Eight for EEG

R2 CN3Need a camera pointed at the eye. Centered on eye. Must be black and white.

Camera ordered. Prototype of mount built

R3 CN3 Need to provide adjustability to eye camera Prototype built

R4 CN4Need a camera pointed at the scene. Centered on eye. Must be able to change lenses. 70*+ FOV.

Camera ordered.

R5 CN4 Need to provide adjustability to scene cameraNeed adjustability in order to acquire the

scene of interest

R6 CN6Must find a way to securely lock down the camera to minimize the motion

Eye Camera - Prototype built

R7 CN7 Provide adjustability to camera locationCan position the camera to minimize

effect on FOVEye Camera - Prottype built

R8 CN8Provide a way to clip the camera, and electrode connection point to either eye

Camera mount prototype made.

R9 CN11Need to enclose all circuitry together into a backpack carrying device

R10 CN13Need to be structurally sound, so that cables are securely locked into place

R11 CN13Need to find a way to ensure ease of use for everyone

Figure 3: Mechanical Requirements

Specifications:

Engr. Spec. # Importance Specification

(description) Unit of Measure Marginal Value Ideal Value

ES1 Scene Cam Range of Rotation Vertical deg 60 90ES2 Scene Cam Range of Rotation Horizontal deg 60 90ES3 Scene Cam Resolution lines 360 GreaterES4 Scene Cam Size in x in x in 1 x 1 x 1 SmallerES5 Scene Cam Field of View deg 70 90ES6 Eye Cam Range of Motion Back-Forth in - 0.375ES7 Eye Cam Centered on eye inch off center ±0.125 0ES8 Eye Cam Range of Rotational deg - 135ES9 Eye Cam Resolution lines 240 GreaterES10 Eye Cam Size in x in x in .6 x .6 x .625 SmallerES11 Camera's Allowable Camera Movement durring light activityin 0.03125 0ES12 Camera's Allowable Camera Movement durring heavy activityin 0.0625 0ES13 Frame Able to withstand being dropped ft (height) 4 6ES14 Frame Adjustabe bridge location for glasses in 0.5 0.75ES15 Frame Lightweight lbs 5 3ES16 Battery Life min 45 60ES17 Backpack Hold's all equipment in x in x in 15x12x3 12x10x3

Figure 4: Mechanical Specifications

Headgear

Figure 5: Head Total Concept

Frame

Selection Matrix

Three styles of frames were analyzed:1. Half-Frame Safety Glasses2. Full Frame Safety Glasses3. Goggles

Half Frame glasses consist of an upper frame, but there is no lower frame around the lens itself.

Full Frame glasses consist of a frame that extends all the way around the lens.

Goggles consist of a full frame that is pressed firmly against the face.

The selection criteria were:

1. Weight – how much the frame weights on the face2. Bulk – How large the frame is3. Camera Mounting – How easy it will be to mount the camera’s4. Wearable with Glasses – How much work is required to make the frames

wearable with glasses.5. Rigidity – How rigid the frames will be once the lenses are removed or

cut.

The three concepts were rated according to the criteria, and a half-frame was selected.

Frame ConceptsA B C

Segment Half-Frame Full Frame Goggles

Selection Criteria Weight Rating Notes Wtd Rating Notes Wtd Rating Notes WtdWeight 15% 10 1.50 10 1.50 5 0.75Bulk 30% 10 3.00 8 2.40 3 0.90

Camera Mounting 30% 7 2.10 7 2.10 10 3.00Wearable with Glasses 5% 5 0.25 3 0.15 10 0.50

Rigidity 20% 5 1.00 7 1.40 8 1.60Total Score 7.85 7.55 6.75

Rank 3 2 1Continue? Yes No No

Figure 6: Frame Concept Selection Matrix

Eye Camera Mount

Selection Matrix

Three different concepts for the Eye Camera Mount were analyzed.

1. Bent Arm – An arm extends from a mounting point near the temple and bends 90o to locate the camera in from of the eye.

2. Under-eye Arm – An arm extends out from a mounting point directly under the eye, locating the camera in front of the eye.

3. Over-eye Arm – An arm extends out from a mounting point directly over the eye, locating the camera in from of the eye.

The selection criteria were:

1. Ease of Implementation – How easy is the concept to implement (includes mounting points and required adjustability).

2. Bulk – How large and heavy the concept is.3. Field of View Limitation – How much of the concept intrudes into the test

subjects field of view.

The three concepts were rated according to the criteria, and the bent arm was selected.

Eye Cam Mouting ConceptsA B C

Bent Arm Under-Eye Arm Over-Eye ArmSegment

Selection Criteria Weight Rating Notes Wtd Rating Notes Wtd Rating Notes WtdEase of Implementation 30% 10 3.00 8 2.40 8 2.40

Bulk 20% 6 1.20 8 1.60 8 1.60FOV Limitation 50% 8 4.00 6 3.00 2 1.00

Total Score 8.20 7.00 5.00Rank 1 2 3

Continue? Yes No NoFigure 7: Eye Camera Mount Concept Selection Matrix

Concept Pictures and Technical Drawings

The final concept for the eye camera mount meet’s all the customer’s requirements for adjustability, field of view limitation, and stability.

Figure 8: Eye Camera Mount Concept

Figure 9: Eye Camera Mount Concept Mounting

Remove This Page and Insert Drawings for Eye Cam

Structural Analysis

Problem: Using a simplified model of the mount (L-shaped rod with one end fixed) determine the force required to cause a .0625” deflection (spec for marginal allowable movement for heavy activity)

Given: L1= 3.5 inL2 = 2.5 inD = .25 inδa = .0625 in

Find: P = ?

Assumptions:Neglect Shear effects Aluminum Alloy 6061 – E = 10000 ksi; G =3770 ksi

Schematic:

P

P

L1

L2

a

b

c Section ab

a

b

P

v1

M1

P

c

v2 M2

T1

b

x

x

Section bc

` Solution:

Use Castigliano’s Theorem:Section Reaction δ/δP Bounds Type

AB v1 = P 1 0-L2 Shear AB M1 = Px x 0-L2 Bending BC v2 = P 1 0-L1 Shear BC M2 = Px x 0-L1 Bending BC T1 = PL2 L2 0-L1 Torsion

Neglecting Shear effects:

With the camera weighting approximately 5oz. (aprox mass = .00971 slugs) and using the Force equation, F=m*a, the camera would have to decelerate/accelerate at a rate of 257.5 ft/s2 to cause this deflection. At this time this value is believed to be safe. Testing will be performed using an accelerometer attached to the camera to determine if the value is acceptable.

Prototype

A prototype of the eye camera mount will be available during the Design Review.

Scene Camera Mount

Selection Matrix

Three different concepts for the scene camera mount were analyzed:

1. Internal Ball Mount – The camera is mounted inside the ball of a ball mount, with the lens protruding from the mount.

2. External Ball Mount – The camera is mounted to a rod that extends into the ball of a ball mount.

3. Double Hinge – The camera is mounted to a double hinge, providing 2 degree’s of freedom for adjustment.(up/down, left/right)

The selection criteria were:

1. Ease of Implementation – How easy is the concept to implement (includes mounting points and required adjustability).

2. Bulk – How large and heavy the concept is.

The three concepts were rated according to the criteria and the external ball mount was selected.

Scene Cam Mouting ConceptsA B C

Internal Ball Mount External Ball Mount Double HingeSegment

Selection Criteria Weight Rating Notes Wtd Rating Notes Wtd Rating Notes WtdEase of Implementation 70% 7 4.90 9 6.30 5 3.50

Bulk 30% 2 0.60 8 2.40 7 2.10Total Score 5.50 8.70 5.60

RankContinue? No Yes No

Figure 10: Scene Camera Mount Selection Matrix

Concept Pictures and Technical Drawings

Final concept of the scene camera mount meets all of the customer’s requirements for adjustability and stability.

Figure 11: Scene Camera Mount Concept

Because of difficulty mounting to the shape of the selected frames a sub frame was designed to mount the scene camera mount to the frames.

Figure 12: Scene Camera Mount Sub frame

Figure 13: Scene Camera Mount Concept Mounting

Remove This Page and Insert Drawings for Scene Cam

EOG/EEG Selection

Concept Justification

EOG Electrodes:

It was decided to use standard disposable snap electrodes for this project. The advantages of these electrodes are:

1. User can remove the lead’s, while keeping electrodes attached2. Electrodes come pre-gelled, reducing test set-up time.3. Because electrodes are 1 time use, there are no sanitary issues if more than

one person is tested during the same experiment.

The only disadvantage to the disposable electrodes is that they are a consumable and will need to be re-ordered periodically. We are currently planning on proving 100 electrodes with the system, as well as information for ordering more.

Figure 14: EOG Disposable Electrodes. EL503 series will be used. EEG Electrodes:

For the EEG electrodes there are pre-made EEG caps readily available that suit our purposes perfectly. By purchasing the EEG cap we can focus our time elsewhere, where it is needed.

Figure 15: EEG Cap and Accessories

Camera Selection

The camera selected for the Scene Camera is supercircuits.com PC213XS.

Figure 16: Scene Camera Selected

The camera selected for the Eye Camera is supercircuits.com PC206XP

Enclosure

Layout Drawing:

`Figure 17: Enclosure Front View

The Above Diagram describes the layout of the components inside the enclosure. The enclosure consists of a bio potentials board, three boards that are stacked to form one cluster of boards (the video board, the single board computer and the power board). The battery is located on the side of the enclosure. The top face of the enclosure is open and there is a connector board which houses the connection ports used to connect the peripherals with the Single board computer and the bio-potentials board. Ample spacing between the bio potentials board and the connector board has been given in order to run the necessary cables and the same goes for the space between the bio potentials board and the single board computer.

Figure 18: Enclosure Side View

Figure 19: Enclosure Top View

The above Diagram shows the side and top view of the enclosure. The enclosure will be fitted with foam on the outside of the box in order for reduce strain on the persons back and add a certain degree of comfort while using the system. In order to secure the enclosure to the person the enclosure will be fitted with a Harness connected directly to the enclosure. The harness will be a 2 point harness to secure the enclosure to the person with a tight fit to reduce enclosure movement during use.

Initial Concept:

Initial Structural Analysis:

In order to verify that the enclosure will not deform or sustain any damage in the event that it is dropped the following assumptions/ variables were used.Weight of enclosure: 2.8lbsDensity of Steel: 0.283lbs/inch^3The Deflection calculated as a result of a 4ft vertical drop was calculated to be 0.011 inches. Hence Enclosure will sustain such an impact protecting the components inside it. In addition the circuits will be mounted on a Backboard which further absorbs shock on impact.

Risks and Contingencies

Risk Item1 Level2 Owner Status and/or Contingency Plans Decision DateDesign and Dimensions of Enclosure will change due to components

High Rohan Over Estimate dimensions in order to fit all components Ongoing

Unknown circuit board layout High Brian/Jelani/ Rohan

Until board layout is known, in-depth analysis of heat transfer is not feasible. Preliminary board layout complete.

Ongoing

Time Management High All Balancing MSD work with Class work. Some team members have reduced schedules next quarter, while others are more busy.

Ongoing

Communication between team members and project area’s

Med All Set up a standard form to keep track of action items for the week. Meet once a week to review progress and get feedback

Done

Communication With Customer Med All Send e-mails detailing decisions. Create a packet of selected concepts and detailed drawings to review with customer and get feedback.

Ongoing

Comfort of Enclosure Design Med Rohan Waiting on enclosure specs, Once Bio-design is finished can be determined, foam padding will be used. Preliminary Spec’s complete.

Ongoing

Mechanical Parts Manufacturing Lead Time

Low Brian/Jelani Parts should be simple enough to manufacture ourselves/with help from advisors in ME shop. If we don’t have the skill set or tools an outside shop will be contacted. Set deadline early in quarter 2 to have parts made. Eye-camera mount manufacturing time ~10 hours.

Ongoing

Durability of Enclosure Low Jelani/Rohan Performing preliminary FEA analysis with ANSYS. If multiple boxes can be acquired will perform testing

Ongoing

Heat Dissipation and flow has not been evaluated

Low Rohan/Brian Experiments will be run on circuit boards to aid in heat transfer analysis. There is not enough information available right now to perform a meaningful analysis. Venting and/or fans will be added to enclosure as needed. Will perform Black Box thermo analysis assuming a low flow rate.

Ongoing

Heat Dissipation might cause glue between enclosure and foam padding to melt

Low Rohan Use a higher temperature glue.

Design of enclosure cannot be made to fit entire population of people

Low Rohan Using adjustable buckles and straps will allow for adjustment to fit 95% of people

Bill of Materials

Figure 20: Mechanical Bill of Materials