Vishal Parikh, Peter Bohlen, Andrew Pappa, Ben Wiener (University of North Carolina-Chapel Hill)
ABSTRACT:
We developed a device that was designed to provide individuals in wheelchairs with a controlled, multi-dimensional movement. Because our clients have various disabilities such as cerebral palsy and autism, they are unable to experience movement without physical input from another individual. The goal of our project was to design and construct a device that would allow our clients to experience angular movement. To meet the requirements of our project the device needed to be safe and efficient. Additionally, the control system of the device needed to be user friendly so that any individual could safely control the device. The motion of the device is controlled by linear actuators which determine the tilt of the platform. By using this device our clients are able to experience and enjoy novel movement.
BACKGROUND:
Our clients are students at a local middle school who have a variety of disabilities, mainly autism and cerebral palsy. Autism is a developmental neurological disorder associated with impaired social interaction, communication, and restricted and repetitive behavior [1]. This prevents our clients from communicating with other individuals. Cerebral palsy is a neurological disorder which is caused by an injury to the brain during childbirth, and causes limited mobility [2]. The individuals at the middle school we are working with do not have control over their extremities and lack other motor controls. For example, some of the individuals are unable to fully extend their wrist and elbow to reach for objects placed in front of them. Due to these disabilities, they require aid in order to experience the sensation of movement. To experience these sensations, the individuals at the middle school enjoy being rocked in their wheelchair by their instructor. Because of this, the goal of our device was to design a device that can fit in the classroom, produce a safe form of movement, and be easily controlled. To make our device acceptable it needed to provide the user with front to back and side to side tilting movements. There are products which accomplish these tasks, however, they are very expensive and some are quite large. In addition, a majority of them are limited to rocking forward and backwards [3].
Project Goals
The goal of the project was to design a device that provided unique movement for individuals in wheelchairs. Since there are no devices that can provide the breadth of movement the children enjoy, a compact device needed to be designed that can not only provide the students with these sensations, but also do so in a safe and reliable manner. In order to ensure the client’s safety, the device had to be universal for all wheelchairs, as well as provide the teacher with control over the device so as not to harm the client or induce seizures.
METHODOLOGY
Our device had to be compact in size and design, as well as stable and safe. Our device consisted of three main components: the base, the platform, and the control system. Our device was arranged with the base resting on the ground, the platform above and the control system in between. The control system uses linear actuators to control the movement of the platform. The device had a width of 36”, a length of 40” and an overall height of 12.5”, these size constraints were due to the limited space available in the classroom.
This picture illustrates the key components that make up the device.
The Base
The base is made out of ¾” reinforced plywood and is 36”x40”. This wide base of support prevents the device from tipping over during use. Several components were attached to the base, with the first being metal supports. These were arranged in a geometric rectangle around the central pivot, and were used to add strength and sturdiness to the device. A central support is used to support the weight of the client when on the platform and is located at the geometric center of the platform. At the top of the central support is a ball and socket joint, which allows for the attachment of the platform to the base. The ball and socket joint provides a wide range of movement for the platform. Additionally, in specific locations along the perimeter of the base are connection points for springs to attach. These springs connect from the base to the platform and arse used to reduce the forces on the actuators.
This picture shows the base of the device. Located in the center is the central support, and on the sides are the springs.
Control System
The control system consists of two linear actuators, the power source for the actuators, and the controller. The actuators are attached with ball and socket joints to the platform, and are screwed in to the base. With the central pivot at the origin, the actuators were placed along the positive X and Y axes of the base. The linear actuators are able to extend or retract, so using the concept that three points create a plane, the device is able to tilt in various directions, while still remaining sturdy. This creates a variety of planar movements. The distance between the actuators and the central pivot determines the angular velocity of tilt. The closer the actuator is to the central axis, the higher the angular velocity. In the device, the actuators are located 4.5” away from the origin. This was the ideal distance to provide the desired incline of the platform, in addition to providing the required force. These actuators are able to withstand 400 lbs of force and move at a speed of 0.59”/sec. Furthermore, these actuators have a stroke of 2” which allows for approximately 12.5 degrees of angular movement front to back and side to side. The actuators are connected to a control box for manual control and the extension/retraction of the actuators is controlled by a joystick.
This picture shows the top platform of the device. That various attachment points can be seen.
EVALUATION
The goals for our project were to create a safe and efficient device for clients using wheelchairs. The device must provide movement without overwhelming the clients or putting them at risk for injury. In addition, the device is controlled with a joystick, so that precise motor control is not necessary to generate movement with the controller. Most importantly, we wanted the device to be fun and effective for the users. After our product was tested at the middle school, we believed we had accomplished all of our goals; the students were very excited and enjoyed the device very much. In addition, there were no safety concerns during the testing and the device could be easily controlled with the joystick by any of the instructors present. Furthermore, the platform was able to withstand the weight of both the individual and the wheelchair. The safety straps on the platform successfully prevented the wheelchair from sliding during the movement of the platform. In addition, the user of the device felt safe and secure throughout the demonstration, and thoroughly enjoyed the experience. One of the instructors stated that “This was a real treat for us to watch, I really enjoyed watching [client] having fun, smiling and laughing, and pushing his buttons. It’s a good sensory activity for the kids since they are limited in their mobility. So it was a real treat, thank you”.
DISCUSSION AND CONCLUSION
We managed to create a device that will be implemented into the daily routines of the students at a local middle school. They will be able add a new dimension to the students sensations. All of the aspects of our device that we intended to implement were successfully applied to the device. Our original specifications for the device were:
- Compact size for storage
- Angular Movement in all directions
- Safe, secure and stable
- Easily controlled
- Provide easy access for user
The most difficult problems in designing the device were the safety concerns of the platform. The device needed to be able to support at least 200 pounds, which was the heaviest combined weight of any client and his/her wheelchair. This problem was solved by placing right angle iron along the perimeter of both the base and the platform, in addition to placing a strong central support in the middle of the platform to act as a load bearing support. Furthermore, the device needed to provide angular movement without tipping over, or causing the individual to feel unsafe. This was accomplished by using springs to counterbalance the weight of the clients when on the device and using actuators that produced the proper force to withstand the weight of the client. The actuators were able to provide the required force to tilt the platform while the springs made the movements of the platform smoother and more stable during movement.
Another concern was preventing sliding of the wheelchair during motion of the device. Wooden bumpers, located on three sides of the platform, as well as tie-downs were used to prevent the wheelchair from rolling off. Also, due to the device’s initial height of 12.5”, a ramp is used to allow the wheelchair to be pushed onto the platform.
Our device met all of the required goals made at the beginning of our project. The device is easy to use and the users enjoy their experience with the device. Due to the device being user friendly, there was no tutorial needed, and the instructors were quickly able to control the device in a safe manner.
ACKNOWLEDGEMENTS
We would like to thank Lowes Grove Middle school students and staff for their hospitality and providing us with the necessary feedback during this project. We thoroughly enjoyed working the middle school students and were glad to build this device for them. We would like to thank Progressive Automations for providing us with the linear actuators at a discounted price. In addition, Dr. Richard Goldberg and Mr. Kevin Caves provided us with the guidance needed to make this device a success. The funding for this project was given by the NSF grant # 0453339.
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Motion Simulator
REFERENCES
1. Autism Society. About Autism. Autism Society of America. Retrieved February 16, 2010 from
http://www.autism-society.org/site/PageServer?pagename=about_home
2. National Institute of Health. Cerebral Palsy Information Page. National Institute of Neurological Disorders and Stroke. Retrieved February 16, 2010 from http://www.ninds.nih.gov/disorders/cerebral_palsy/cerebral_palsy.htm
3. AbleData. Products. AbleData. Retrieved February 16, 2010 from http://www.abledata.com/abledata.cfm?pageid=19327&top=14546&trail=22,14341,14537
Vishal Parikh
4020 Chaumont Drive
Apex, NC 27539
919-434-1292