intrunk lifting system - ltu.edu a rough ... at this time, the cable would be released and the chair...
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InTrunk Lifting system
Midterm Report
Senior Design Projects 2 BME 4013
Department of Biomedical Engineering
Lawrence Technological University
LTU Team Members:
Brendon Clover, Fatmah ALhaji
UDM Team Members:
Elliot Fernandez, Martha Dunbar, Evan Gage, Daniel Modes
Faculty Advisors:
Dr. Mansoor Nasir, Lawrence Technological University
Dr. Darrell Kleinke, Dr. Molly McClelland, University of Detroit Mercy
Major Changes in Project`s Design
This semester, we have worked with three iterations of our design, which will be further detailed below. Coming into January, we were working with the design we presented at the end of last semester, a rough sketch of which is below.
Figure 1: Rampwinch design presented at the end of the fall semester
Doing further analysis independently over the Winter break, each group member found something wrong with this design. One issue we identified was that a ramp, while helpful in moving the wheelchair to the lip of the trunk without causing damage to the car, would ultimately cause resistance in lifting. Furthermore, any ramp design that we could think of that would limit this effect was rigid, heavy, and complex, and would take up so much space in the trunk that the wheelchair would not be able to fit inside. In addition to this problem, we realized that the downward force of the winch’s cable would be too much for the trunk to handle, and would cause the trunk to close unless additional support was added. About halfway through the fall semester, the team members from University of DetroitMercy (referred to as U of D or UDM) purchased the back half of a car which is the same make, model, and year as the one belonging to our client. They attached a mock winch which mimicked the size and weight of a winch, and found that the panels on the interior of the trunk were not strong enough to support the weight of winch, which would more than likely result in failure of the system. We then resolved to move the winch into the back of the trunk and place a pulley on the hatch, but thought this was too risky, as the downward force exerted by the cable could also cause failure. For these reasons, we changed our design to the one below.
Figure 2: Wincharm concept drawing
In this design, the winch was moved to the back of the trunk, as we had previously discussed doing, but without the pulley attached to the trunk’s hatch. We replaced this with a telescoping arm, labeled “7” in the image above. To operate the device in this design, one would first open the trunk and manually extend the arm and roll out the ramp. the tow cable would then be pulled out and attached to the wheelchair, and the winch would be activated. The chair would be pulled up to to the end of the arm, and the arm would retract, bringing the chair over the sliding plate inside the trunk. At this time, the cable would be released and the chair would be set down into the trunk. In order to remove the chair, the process would be reversed with a few slight changes. When the trunk is open and the arm is extended, a pin would be used to lock the arm so it did not retract. This causes the chair to be pulled out the trunk, where it is then lowered onto the ramp and released.
While planning this design, we had difficulty finding a material and design that would work well for the telescoping arm. Anything that we thought of or found would either be too weak, heavy, or expensive to work for our purposes. The difficulty of this component ultimately resulted in us scrapping the design, which led us to our current and final design, a schematic of which is below.
Figure 3: Platform design, retracted
Figure 4: Platform design, extended
This design, which is the one we are moving forward with, is a complete redesign from what we previously had. In this iteration, the goal is simplicity and a minimal number of separate components. At its core, the mechanism is composed of two pair of sliders and two pairs of hinges. One pair of sliders is attached to the inside of the trunk and allows the system to move in
and out of the trunk. A short beam is attached to this with a hinge, and the beam has another hinge on the other end, which connects to another slider. The platform which the wheelchair rests on is connected to these sliders so it can extend from the trunk. More detailed photos of the prototype are below.
Figure 5: Prototype with same labels as Figures 3 and 4
Figure 6: Prototype with same labels as Figures 3 and 4
The prototype in the images above is not made of the same materials as the final product will be. We plan to use a lightweight aluminum such as 6061 or 7005. 6061 is generally more cost efficient and will get the job done effectively, but 7005 is more lightweight and has a very comparable strength. The sliders and rails (which are labeled 2 and 3 in the images above) were salvaged from a dismantled project at UDM, and therefore came to us at no cost. These components will be used in the final mechanism, as will the hinges, which were also from the dismantled project. The platform, marked by the number 4, will be made of aluminum and will have a shape similar to the one below in Figure 7. This shape will allow it to have the lowest possible weight while being strong enough to hold the chair, and it also allows for the chair to be attached.
Detail for Projected Tests and Tasks
1 Current:
Lock system:
To attach the wheelchair to the platform of the lifting device we need a lock system which is useable by patients with hand deformations. The attachment system should be small, light, and safe. Our first design was an electromagnetic locking system which would have quick and easy operation that would accommodate the client's hand deformation. In order to use this lock, it would need to be wired to a power supply. The magnet itself would be attached to the platform, and the metal circle which it attached to would connect to the chair itself. We eventually realized, however, that the wires would be a concern, as we would have to rout them so they did not get in the way of (or pinched by) the mechanism, and that the additional power draw could slow the movement of the platform.
Weight Holding Force Power Requirements
Cost
1.25 lbs 100 lbs. 12V $40
Table 2: Specifications for magnet used in first design
Figure 8: Electromagnet for first design, Skylink MC201 (Source: http://www.skylinkhome.com/row/products/sdo/mc201.html)
Both teams agreed that having a wireless design is more beneficial when taking into consideration the weight of the lock system and the cost. The second electromagnetic lock design was the Wireless Smart Electromagnetic Lock(PML1101R), which is the compact structure
without transmitterreceiver and wiring. It has a remote control range of up to 10 meters.The following table is the design specification and figure.
Weight Holding Force Power System Cost
5.5 lbs. 550 lbs. 12V/500mA, 24V/250mA
$150
Table 3: Specifications for magnet used in second design
Figure 9: Electromagnet for second design, (PML1101R) (Source: http://www.pongee.com/msg/msg61.html )
There were two main limitations to this design. Firstly, although it is wirelessly controlled, there is a power source which means the wiring problem is not solved. We initially thought that the magnet had an internal battery, but it did not. Also, it is too expensive for the project budget we are working with. The idea behind the wireless can be applied to the first electromagnetic design since it is much cheaper than the second one. However, it required continuous power, and there is not enough space in the trunk for additional power sources since the client needs to have some free trunk space. We can not use the car power because the electromagnetic lock system needs 12V, and the client has an old car which cannot support this requirement. For this reason, we changed the lock system from an electromagnetic lock to a mechanical lock. There are several advantages of using mechanical lock including ease of operation and no required battery. Also, we can adjust any design to make it efficient for a patient with hand deformation. The proposed design is aircraft seat belt lock. It is easy to operate, cheap, and strong. The following figure is the aircraft seat belt.
Figure 10: Aircraft safety seat belt (Source: http://www.ebay.com/itm/AirplaneAirlineSeatBeltExtensionExtenderBlackColor712DaysArriveUSA/270475740829)
According to federal law, seatbelt strength enable it to withstand thousands of pounds. All belts we looked at are capable of supporting at least 4,000 lbs. They also have a low cost, at $10$30 depending on strap length and material. We plan to use only a short length of strap, no more than 6” connected to each end. The following figure describes the position of the seatbelt on wheelchair and plate fram of the lifting device.
Figure 11: Schematic of seat belt position into the device and wheelchair
The female end of the mechanism will be attached to the platform itself, and the male end will be secured to the wheelchair. Using a short amount of strap on each end will allow the chair to be placed less precisely while still keeping the wheelchair securely in place. In an effort to reduce weight, we plan to use one connection, but we will add another if we find that it is necessary.
Future Plans
Table 4: Testing plan for patient’s range of motion and biomechanics
The table above outlines our plan for testing the patient’s range of motion and biomechanics to ensure that our design will be compatible with her limitations. Lately, we have had a difficult time meeting with her because she has been sick. This has caused her to have many medical appointments which have limited her time. We plan to complete these tests in the week immediately following Spring Break.
List of items bought and their application:
Items Application Cost
Used car Test the lifting device Approximately $70
Table 5: Purchased items and their uses