Classic Rocker
Team 7: Mechanized Legless Rocker
Project Proposal
NSF Project for Ohio University
Project Coordinator: Dr. Brooke Hallowell
Advising Professor: Dr. John Enderle
Tom Dabrowski
Adam Rauwerdink
Sarah Philo
I. Executive Summary
The self-rocking Classic Rocker will provide the Passionworks Studio with an additional way to inspire its artists with disabilities. A self-rocking legless rocker will provide the artists with a comfortable area where they can develop new ideas for their work. Having a legless rocker with integrated audio components can create an inspiring atmosphere for the artists, helping them to relax and enjoy themselves. Innovation is a key component to artistry, and being surrounded with innovative devices can further help the development of ideas.
The Classic Rocker will also provide a new experience for those who cannot use a rocking chair on their own. Creating a self-propelled legless rocking chair for adults is a unique idea, not only because of the fact that it moves without any force from the user, but also because its rocking motion can be controlled by the user. Allowing the user to have control over whether or not he or she will rock allows a certain freedom of decision to those who often depend upon others for help in their daily routines.
When fabricating the classic rocker there are many factors to consider. Protecting and pleasing those who will use the rocker is the main concern, and so safety from electrical and or device malfunction is of the utmost importance. The safety goals of the project are to ensure that the electricity flowing to the device will stay isolated and the device will rock without tipping or without moving too quickly. The controls will be simple, and the overall design will be affordable, easy to move, and easy to use.
II. Statement of Need
The Passionworks Studio provides a setting for artists with disabilities to pursue their interests. It is important for the Passionworks artists to have a setting that promotes the creative process. Passionworks has an entire room devoted to the process of aiding the artists in enhancing their creativity. The Classic Rocker will be housed in this multisensory stimulation room. The legless rocker provides the residents with an enjoyable experience while they develop new artistic ideas.
An electronically controlled rocking chair with a self-rocking motion is requested for the Passionworks facility. Activation of the rocking motion must be through a simple switch that a person who is mentally disabled would be capable of controlling. Further, caretakers must have master control over the user switch through a switch not accessible to an artist in the chair.
In addition, a speaker system for providing sensory stimulation to the chair occupant is requested. Like the rocking motion this is to be controllable by the user.
Competing Products and Previous Projects
A proper starting point for any major project is to first examine the existing market for products that are currently available. Improving upon the existing available designs allows for the creation of a product that more consumers will be interested in. The following list compiles marketed self-propelled rocking chairs available to the public, previously completed projects National Science Foundation funded projects, and current patents that have been issued for self-rocking devices.
Electric and Mechanical Assistive Technologies Motorized Rocking Chair: To date, this product is the only self-propelled rocker available to the public. The chair is equipped with variable rocking speed and can be programmed to shut off automatically. This item was created for those who have special physical needs. The price of the device is not listed anywhere on the product website.
Figure 1 : EMAT Motorized Rocking Chair.
National Science Foundation Project – 1989 - “The Mechanical Rocking System”: This project was completed at Rensselaer Polytechnic Institute for a child who has cerebral palsy. The mechanized rocking chair allows for the movement of the user without any physical exertion being required. A simple motor and cam system are used to induce a rocking motion, and the total cost of the project came to $455.
Figure 2 : NSF Project – 1989, Rensselaer Polytechnic Institute.
In addition to these self-rocking devices, there are numerous patents that have been granted for the use of self-rocking mechanisms or self-rocking chairs. The patents include:
· 6,899,393 – “Linkage mechanism for a motion chair”
· 6,695,799 – “Relaxation apparatus” (Oscillatory motion in a recliner)
· 6,412,867 – “Automatic two speed musical rocking chair” (Infant rocker)
· 6,318,803 – “Chair executing oscillatory motion”
· 6,152,529 – “Motor driven rocking chair”
These patented devices all relate to the classic rocker project because they involve the use of mechanisms to initiate a rocking motion.
Finally, there are several non-mechanized legless rocking chairs available for purchase by consumers from many different retailers dealing, at least in part, with home décor. Such retailers include Wal-Mart® and Target®. The available chairs come in a range of qualities, from base qualities with cheaper fabrics and frame constructions, to those of greater quality, perhaps spill-resistant fabrics, and also with better, sturdier frames.
Figure 3 : Legless rocker example available at various retailers.
Technical Specifications
Mechanical:
Weight of Users: 80-190 lbs.
Chair Dimensions:
Height: 34 in
Width: 21 in
Length: 31 in
Chair Weight: 45 lbs
Rocking Speed: 30 Hz
Rocking Forces: -mg(R-h) sin(θ) = mh2
Maximum Rocking Angles: ±15°
Electrical:
Power Supply: 12 VDC Output
Audio input: Compact Disc
Speakers: Two; 3”
Rocking Mechanism: Electric motor or electric actuator
Switches:
User Controlled: Rocking motion, audio output
Caretaker Controlled: Chair power, audio power, audio volume
Environment:
Operating temperature: 40 to 100°F
Storage temperature: 0 to 120°F
Power:
AC 120V @ 60 Hz
III. Project Description
Objective:
This chair will provide a mechanized self-rocking motion for use by persons with physical limitations. 120 VAC power will come from a wall socket and enter a power supply which will convert the power to the 12 VDC needed by the CD player and possibly the actuator or motor. To initiate the rocking motion, the caretaker will have to plug in the chair and then turn on a master power switch, which controls power to all aspects of the chair, and individual switches for power to the rocking mechanism and CD player. The caretaker will also be able to select a desired audio track and set the proper volume. The actual initiation of motion or sound will be dependent on the user. A set of interchangeable, simple-to-use switches will attach to a control station which will be positioned for maximum ease of use. After the user depresses the appropriate switch, the actuator or motor assembly will receive power and be put into motion. Non-modifiable internal systems will control the speed and range of motion to ensure a safe rocking experience. Sound output, once triggered, will be from two speakers implanted into the chair. A powered amplifier will be used to provide a higher quality of sound.
Methods:
Mechanical:
At this time, two major mechanisms for providing the desired rocking motion are being considered. The first is a linear actuator. The current models of these devices that best suit the project needs are electronically controlled mechanical devices. Actuators are also available in hydraulic and pneumatic form but these would require the installation of a hydraulic pump or compressor, respectively. The addition of hydraulics would negatively impact the simplicity and reliability of the rocking mechanism. A hydraulic or pneumatic system would be potentially much louder as well. Electronic actuators come in a variety of stroke lengths, speeds, and load strengths. The model that is chosen will depend on the chosen attachment point on the back of the chair. A higher attachment point would require less force to induce motion because the moment at this point would be greater, but it would have the trade off of requiring a much greater speed and longer stroke length. The stroke speed is a limiting factor of actuators, so an attachment point that is lower on the chair back would most likely be used. A lower point of attachment will require shorter stroke length and less speed, but it will require greater load strength.
Fig. 4 – Linear Actuator Mechanized Chair
The second method of mechanization being considered is an electric motor. The motor would be connected to a linkage system that would provide the required motion. The speed of the motor and the properties of the linkage system would determine the chair rocking frequency and amplitude. An electric motor would have the benefit of a more easily controllable speed in comparison to an actuator. A major obstacle of using the electric motor would be the requirement for isolation of the moving parts of the motor linkage assembly. A linear actuator has a simple moving piston that provides little chance of personal injury. A rotating system of linkage bars would provide ample opportunity for someone to get his/her body or clothing caught.
Fig. 5 – Electric Motor Mechanized Chair
The speed of both the electric motor and the linear actuator vary with the load placed on them. When the motor or actuator is attached low on the back of the chair a high force is required to control the rocking motion. With this high load on the device the speed decreases. Alternatively, when a high attachment point is chosen a much weaker force is required. The lesser load on the device allows it to function at a greater speed. This speed is important because it will directly affect the rocking frequency of the chair. The speed of an electric motor can be varied greatly through the use of variable resistors, gear box, or DC speed controller. An actuator would require a mechanical lever system in order to mechanically increase the lift speed. In either case the use of mechanical speed varying devices puts increased strain on the device.
Fig. 6 –Speed vs. Load linear actuator (Duff-Norton) Fig. 7 – Speed vs. load electric motor (Motortech.com)
Fig. 8 – Lift speed vs. Load for linear actuator (Firgelli Automations)
Electrical:
Fig. 9 – Electrical System Block Diagram
The electric source for this project will be influenced greatly by the power demands of the actuator or motor. A CD player requires low voltage and amperage which can easily be provided by a battery system. The amperage requirements for the linear actuators varies greatly with model and manufacturer. Some models require as much as 25+ amps which would require a large battery system, as seen in the figures below. For this reason the ideal power source would be 120V AC power from a wall socket. The actuators require 12 VDC electric feed therefore an electrical converter would be needed to perform this function. Pre-fabricated converters can be purchased for around $40 or a converter can be built from scratch. A power supply from a computer also performs this function for around $30-50.
Fig. 10 – Current vs. Load (Firgelli Automations)
Fig. 11 – Current vs. Load (Duff-Norton)
If a motor is used in the rocking mechanism, the speed can be controlled through the use of a variable resistor, a gear box, or a DC speed controller. A variable resistor has the problem of motor stalling when the load increases. The DC speed controller works by creating a pulse signal of the voltage input. These devices are available from numerous electric supply companies for around $16 or can be built. Motors are available in both 12 VDC and 120 VAC models.
Fig. 12 – DC speed controller circuit diagram
Project Constraints
There are many considerations to take into account when constructing the legless rocker. Safety of the consumer is the primary concern. Because the electronic components of the chair will be connected to a 120V power source, electrical wires and constituents need to be sufficiently isolated from any flammable material it will most likely be surrounded by. Additionally, because individuals will be in direct contact with the chair, it is imperative to ensure that electrical components are properly isolated so they do not shock the user. The second safety issue taken into consideration is rocking speed and angle. The rocker must not move so fast as to make the user uncomfortable or sick, nor should it rock to angles that make the user uneasy or allow the chair to tip over. Because the chair will be used by multiple persons in a recreational area, various disabilities need to be considered. Varying levels of mental capacity, muscle control, attention span and coordination abilities need to be considered, as well as seizures of varying intensity which are a symptom of cerebral palsy. Lastly, caretaker controls need to be out of reach of the client using the chair, and need to override any input from the user controls.
Environmental constraints revolve around mobility and maintenance. The chair needs to be easily moved around a room, but stable when in use. This means that the rocking mechanism cannot be directly attached to the ground, and that the chair itself should be relatively light. The rocker must also be easy to clean, and it must be able to endure moderate abuse and extended use.
Economic constraints involve working within a budget, and attempting to make the legless rocker as cost efficient as possible. A prefabricated chair will most likely be purchased and modified to fit the clients’ needs to avoid the cost of constructing one from scratch. The purchased rocker will need to have a substantial frame that will be able to support both the rocking mechanism and the audio components that will be attached to it. Because the legless rocker will be marketed to persons with special needs and their respective caretakers and/or families, the rocker should be as moderately priced as possible. The cost of therapies, caretakers, medications, special equipment, doctor appointments, etc. adds up quickly. In order to successfully market the chair, cost needs to be taken into consideration.
Budget
National Science Foundation / + $ 750Pre Fabricated Chair / - $30-100
Motor or Actuator / - $16-250
Switch / - $50-100
Speakers / - $40-100
Amplifier / - $30-50
Hardware / - $50
Power Supply / - $30-50
DC speed control / - $16
Estimated Total / $500
Error Analysis / Balance
IV. Conclusion