Mechanical Design Elements

Mechanical Engineers:

Brian Lomicka

Jelani Williams

Industrial Engineer:

Rohan Gulati

Agenda:

  1. System Overview
  2. Customer Needs
  3. Requirements
  4. Specifications
  1. Headgear system:
  2. Review of Frame Selection
  3. Selection Matrix
  4. Review of Eye Camera MountDesign
  5. Selection Matrix
  6. Concept Pictures
  7. Technical Drawings
  8. Structural Analysis
  9. Prototype
  10. Review of Scene Camera MountDesign
  11. Selection Matrix
  12. Concept Pictures
  13. Technical Drawings
  1. Camera Selection
  1. Review of EOG/EEG selection
  2. Concept Justification
  1. Review of Enclosure Design
  2. Enclosure Layout Drawing
  3. Initial Concept
  4. Initial Structural Analysis
  1. Risks and Contingencies
  1. 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.

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:

Figure 2: Mechanical Customer Needs

Requirements:

Figure 3: Mechanical Requirements

Specifications:

Figure 4: Mechanical Specifications

Headgear

Figure 5: Head Total Concept

Frame

Selection Matrix

Three styles of frames were analyzed:

  1. Half-Frame Safety Glasses
  2. Full Frame Safety Glasses
  3. 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 face
  2. Bulk – How large the frame is
  3. Camera Mounting – How easy it will be to mount the camera’s
  4. 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.

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.

Figure 7: Eye Camera MountConcept 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 MountConcept

Figure 9: Eye Camera MountConcept 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 in

L2 = 2.5 in

D = .25 in

δa = .0625 in

Find:P = ?

Assumptions:

Neglect Shear effects

Aluminum Alloy 6061 – E = 10000 ksi; G =3770 ksi

Schematic:

`Solution:

Use Castigliano’s Theorem:

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.

Figure 10: Scene Camera MountSelection 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 MountConcept

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 MountSub frame

Figure 13: Scene Camera MountConcept 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 attached
  2. 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: 2.8lbs

Density of Steel: 0.283lbs/inch^3

The 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 Date
Design 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