Table of Contents
Subject Matter Expert Interview Notes
Dr. Mark Kempski
- Commented on our two point design that it was feasible
- Suggested simplifying electrical requirements by advancing mechanical efficiency
- Proposed a Scissor Jack style mechanism
- Encouraged us to speak with Dr. Walters, who is a mechanics expert
Dr. Wayne Walters
- Agreed with Dr. Kempski that the two point design is feasible, but could be simplified by adding mechanical advantage
- Proposed “4 - Bar” system could be designed to assist in translating linear force into rotational
- Pointed out Worm Drive system would increase efficiency in supplying and controlling force
- Expressed some actuators do not lock while there is no power supplied to them, and constant power supply would severely drain battery over time
Ms. Mary D'Amico
- Would like 25% of Megan’s weight on her legs. Primarily on the right leg.
- Create a “boot” for left foot to even out length distance with left. Design adjustable foot holders
- Make harness keep her centrally in place. Megan has Scoliosis and is “Wind Blown”
- Poor Vision make sure her head is “forced” forward
- Harness can be designed to go directly over her hip
- Do not lock her knees in place; prone to dislocation.
Prototyping, Engineering Analysis, Simulation
Original Concept Design Drawings
- THESE ARE NO LONGER DESIGNS IN USE******
See drawings section for drawings of current model. For old drawings, see the Detailed Design Documents depository, and find the file needed.
Concept 1 includes two typical linear actuators that are positioned on the back of the chair.
- Stabilizes chair so that back would not twist
- Two forces needed to lift
- Need a lot of space behind the chair, might need extended baseplate
- May need extra motor to keep back of chair in vertical position
The four bar design only needs one actuator, and uses a rectangular system to convert the linear force into rotational motion.
- Only need one actuator
- Converts linear motion into rotational motion
- Takes up lots of space between base and chair
- Very difficult to fit with current base of chair
The scissor jack concept only requires one motor and uses a scissor like motion to extend in a linear motion.
- Only needs one force input
- Very sturdy
- Very bulky
The double actuator with mechanical advantage uses two actuators to lift the chair, and some lever arms to keep the chair rotating around the correct parts.
- Works well with current base
- Two Actuators
- May be more difficult to implement
Lift Design Pugh Analysis
Before we could do a final pugh analysis, some stress, force, and center of gravity analysis needed to be done.
Along with these analyses, we need to have an idea of where the actuators will be placed.
FINAL PUGH ANALYSIS
After many changes on our design, we decided to determine if one single actuator in the center would be better than two actuators on the outsides. Our results are shown here.
Our results are as follows:
The concepts shown here for the top harness concepts are all existing harnesses on the market. The ideas are all pretty similar here, but the cross harness, and the body point chest harness seem to give the user the most mobility in the arms.
Like the top harnesses, all the bottom harnesses are all existing in the market. The Canyon harness, and windsurfing harness are all meant to take the force pulling outward from the front. This is not exactly what is needed in out application, so the bungee trampoline harness might be the best bet for our concept. With this, the forces are meant to be pulling from all different directions, which is ideal for this application.
After speaking with Matt McGarvey of Fonte Surgical, he suggested we come up with something simpler. Our harness would work, but it is unnecessary. Hence, we came up with a bar harness design.
Drawings, Schematics, Flow Charts, Simulations
The base frame could from the old chair could possibly be used in this application.
The Lever arm will be welded to existing base frame using perforated steel. Dimensions will be determined from stress calculations and actuator mount requirements.
The back frame will consist of round perforated steel tubing. The existing frame can be used with an additional welded bar for actuator mount.
The lifting mechanism will consist of a Transmotech actuator, and mounting hardware.
These stress simulations were simulated under a worst case scenario, where all of Megan's weight was on every point of the frame. As seen in the simulations, there is very little deformation in either model, and since just the box frame is cheaper to make, that's the idea that will likely be used in our design.
The speed of the actuators will be controlled by potentiometers.
This limit switch mechanism shows where limit switches will be put so that the lift will not raise higher or drop lower than a certain point.
The electrical schematic shows how the power from the batteries will be distributed through switches to either the drive motor, or the linear actuators. The variable resistors are the potentiometers that will be used to control the linear actuator speeds. The limit switches will show how the lifting and lowering will be turned off when the limits are reached.
Limit switches are NOT included in the electrical schematic, because they are internal to the actuator.
This electrical board layout was done just for concept. It is not necessary, but will help keep wiring inside base neater.
It looks as if there is a concern with the battery life. However, the motors and actuators will not be fully loaded, and they will never draw 3Ah.
After each of the iterations of design, the final design with new support system was finally achieved.
A video of the chair moving from sitting to standing can be found here. This video was done without the support system for clarity.
Bill of Material (BOM)
View the current BOM here.
The full MSD II schedule can be found here. Microsoft Project is needed to view this file.
View the up to date Test Plan here.
View the current FMEA here.
Design ReviewsView the Subsystem Design review presentation here.
View the Detailed Design wk 12 review presentation here.
View the Final week 15 review presentation here.