Mission Statement:

Develop a product using contact charging technology to help electric wheelchair users to power their wheelchairs more easily without the aid of a caregiver.

Problem Statement and Background:

With this project our team is mainly looking into creating a product that will enable the wheelchair user to charge his chair without the help of anyone else in a very convenient manner.  Their power chairs are charged through an adapter box that converts the AC outlet current to DC current. The DC current then charges the battery of the power chair through a cable connection that goes from the adapter box to the armrest plug port.

A wheelchair battery takes around 8 hours to fully charge, so often the chair is left charging overnight while the user sleeps. Typically the battery has a potential range of 10 to 20 miles which corresponds to approximately 2 to 3 hours of continuous working time. When we visited Rancho Los Amigos Rehabilitation center in Los Angeles Downey, CA, to get more information on the standard power chair adapters, Andy Lin, MS, ATP, a rehabilitation engineer at the facility and one of our project mentors, told us that many times the battery would run out of power at inconvenient times and the user would have to stop in the hallway near an outlet to charge the batteries. This problem was also confirmed through surveying several power wheelchair users at Rancho as well as a number of physical therapists.

Another problem regarding charging is that in order to do so without the help of a caregiver, the user must plug the charging unit into the wall and a port by the armrest of their chair. However, this may require fine motor control in the upper extremities which individuals who use power chairs do not have. For users who are accompanied by a caregiver at all times, charging is actually not a huge problem since it is very easy for the caregiver to plug in the chair. Yet, there are power chair users who live alone or simply don’t have a caregiver that can tend to them at all times. For these cases our product will provide a new horizon of independence.

Solutions Considered:

Our initial design was to build an induction based charged station placed on the floor. The charging box would contain a power inverter and coils for one end of the induction circuit. This circuit would then be completed via another set of coils and a control unit that would be attached to a plate placed under the power chair. The second set of coils would then be connected to the chair battery and hence charge the vehicle. With the base and receiver installed, the power chair user would be able to drive over the charging station and the charging would automatically start. However we had to abandon the induction design for several reasons:

• There is inherent charging efficiency loss for induction, but this is not the case for contact charging.
• Manufacturing an inductive charger requires expensive manufacturing process and expensive parts such as voltage controllers and coils. A contact charger is very easy to manufacture since it is a simpler mechanism and there are no expensive materials.
• Electro-magnetic interference was an issue was considered with inductive charging which could have caused problems with the electronics of the power chair and potential medical equipment like pacemakers that could be on the user. With contact charging this is not a problem.
• Perfect alignment of the coils was very important for inductive charging which would have forced us to over complicate the product by attaching rail guides. Contact charging is much more flexible as we can adjust the size of the plates that rods have to contact with.

Final Design:

By abandoning the induction solution, we had to find an alternative method that would connect the charging box and the power chair. Thus, two other ideas were decided on: Contact charging, and “Magsafe” connection charging which uses magnets to connect a charging cable to a port. These two are not completely separate ideas as we plan on using contact charging methods as a stepping stone to design a Magsafe adapter charging mechanism.

For contact charging, a box is used as a raised platform to hold up two conductive rods. These conductive rods are attached to the DC cable coming from the adapter box which is split into to two and soldered separately to the conductive rods. We would then be completing the circuit through a base plate that has two conductive plates (see Figure 4) attached to it that would complete the circuit when in contact with the rods sticking up from the charging box (see Figure 2). In order to switch to Magsafe adapters we will be using magnets at the receiving plate portion to catch the male ends protruding from the box.

Our initial prototype is made of plywood and wire with XLR cable heads to connect to the adapter and wheelchair. The dimensions are 9” square at the base and 9”x7” on top, and 2.5” height, plus the height of the contact wires, which should fit well under a standard wheelchair. This prototype is meant to prove our concept; any alignment aids or electrical safety measures have not yet been implemented, which will be added in later iterations. Also the final version will be built out of a stronger material such as acrylic or carbon fiber.

Human Factor Considerations on Design

The initial design with induction charging had very few ways it could be used out of its purpose and was very danger-free. With our product the most important human factor is that, we are assuming that the power chair user will be able to move his chair over the charging station. The alignment will be somewhat of a problem and if getting the conductive ends meet with the receiving plates under the chair is proving to be a huge problem for the user, implementation of rail guides as additional attachments to our product will be considered.

Another issue that needs to be addressed is that since the charging base will be sitting on the floor, it has to be durable. If the power chair user inadvertently drives over the base or if anyone steps on or kicks the base, the electronic connections should be preserved well enough that they won’t be damaged. This problem is addressed by building the box out of a durable material, having good internal structure and damage testing the product once it is manufactured.

A problem that did not come up with the initial induction solution was exposed electrical connections. Since two electrically conductive ends will be sticking out of the box, even if the electrical current on them is low enough, these ends should be covered well enough that someone can’t inadvertently shock themselves. Furthermore, having open electrical ends at the ground level could be hazardous for children who might be around the product. An easy solution to this is to use an additional outlet switch to turn off the unit while not in use.

In terms of installation, it will be a one-time process when the receiver plate will be attached under the chair. Thus, we do not need to worry about installation as the only time the receiver plate will be removed is when the product would need a repair. The first installment however will need to be done by an able-bodied person. Yet, having the product installed just once should be very satisfying from the perspective of the caregiver since this is better than having the caregiver plug in the chair almost every single day to an outlet.

Outcome and Results:

Since our first prototype was very recently finished, we have yet to try our product on a real power chair. We have consulted with several electric wheelchair users and on our design and are currently putting the finishing touches on the wiring of our prototype. We have gotten many positive responses in terms of the main concept behind our project but a couple of design issues were raised. The main concern of the wheelchair users were the ease of alignment. After their response we started to consider placing the receiver plate under the footrest instead placing it straight under the wheel chair. This way, the base plate will be in the wheelchair user’s field of vision and the contact-alignment can easily be made by adjusting the angle and the height of the footrest. Our next step in development is testing our wiring to be sure it will not damage the circuitry of a real power wheelchair, after which our prototype will be ready to use.  After functionality is achieved, installment and user-friendliness will be addressed.

Cost:

For our final product we will have these materials that make up the direct material cost:

• A DC cable connecting the standard adapter to the charging base
• The charging base box that will be produced out of acrylic or Plexiglas
• Two conductive rods/Magsafe adapter ends
• A base receiver plate that will have
  • Two conductive copper plates
  • Two magnetic female ends
• Another electrical cable connecting the receiver plate to the power chair battery

In terms of manufacturing costs we have:

• soldering of the DC cable to the conductive rods
• assembly of the box
• soldering of the receiver plate to the chair battery cable

The contact charging box would be relatively simple to manufacture. It only requires assembly of the box and wires with some soldering of the wire heads. The Magsafe version of the box might have some more manufacturing costs associated with it, because the connecting heads would be smaller and require more parts. Our project is overall very simple to manufacture because it doesn’t require any programming, special electronics, or even moving parts.

Since there are no precedents in the market it is hard to have an estimate to how much the product would sell for. Also at this development phase of the project it is also hard to project a final expenditure. Our first proof of concept prototype cost us around $40 total in materials. A final design will use mostly the same materials except the wood will be replaced with plastic or carbon fiber, and there would be relatively little labor involved.

Based on our estimates, a final product can be produced for about $60, and could be sold for $80-$100. Although there is nothing else like this product on the market, we would like to keep the price low so that it can benefit as many people’s lives as possible. The components can be made very affordable as they are mostly just wires, connections, and the unit’s housing, so the bulk of costs will be in labor in manufacturing the unit.

Significance:

Running out of fuel in the middle of the road is one of the worst things that can happen to any driver and power chair users have this worry at the back of their minds every single day. However, with our product we believe we can make charging much less of a menial task. If our product could be installed at critical spots where the users spend a considerable amount of time in a day, their chairs will be charged without them even them realizing.

Furthermore, we hope that our system could be implemented by many different commercial venues. As it turns out, there is a dedicated community of wheelchair users who spend time in casinos. Our charging stations could be installed at various places in the community, such as in a mall or at a bus stop; power chair users could then easily charge the vehicle by driving onto the spot. However, this is example is only one of the many places our charging stations can be used. For home use, a power chair user can simply place the charging station on a spot where he spends the most time during a day like in front of their TV or computer and not worry about leaving the chair near an outlet during day at an inconvenient time. Our main goal is to enable all power chair users to charge their vehicle without the help of a caregiver.