THE POWERED EASEL

Kyle Madison, Neil Wasylewski, Brent Ruthenberg Biomechanics Laboratory, Mechanical Engineering Department Michigan Technological University Houghton, MI USA, 49931

ABSTRACT

The Powered Easel (Figure 1), offers an expanded sense of freedom to a very important segment of our society. The device is designed to be used by individuals who have minimal mobility of their upper extremities. The drawing surface is moved with the use of a joystick. The joystick controls two small DC motors that in turn drive a set of power screws. Although the design was undertaken specifically for one quadriplegic, complete drawings have been released for interested groups or individuals. This design produces a cost effective solution to what would otherwise be a completely custom designed and fabricated unit. This alternative is obtainable because it utilizes some flexibility in manufacturing, simple machining, and is made of readily available parts. This project would be an ideal high school shop project, providing students the opportunity to contribute their talents to the community.

Figure 1: The Powered Easel

BACKGROUND

This project was initiated in order to assist a young artist. The specific individual became a quadriplegic a few years ago as a result of a diving accident. Before receiving the electric easel, this talented artist would draw over a very small area with a pencil in his mouth, wait for someone to move the paper and then continue drawing. Due to this dependence, even the simplest of drawings could take many hours to complete. Therefore, a device that would allow this individual to maneuver the drawing surface independently, could improve the quality of his life and those that help to care for him. The Powered Easel, through the use of its joystick controller, allows for easy adjustment of the drawing surface. A chin operated joystick control was chosen due to its similarity to the motion controls used on most motorized wheel chairs. Therefore, a certain amount of familiarity would exist and most users could adjust to the controls very quickly. Also, by using switch components easily obtained from any electronics store, an inexpensive high amperage joystick design was incorporated.

STATEMENT OF THE PROBLEM

A portable easel composed of inexpensive components needed to be designed and built. This device needed to have an adjustable, tilting drawing surface and adjustable joystick controller so that the easel could accommodate the user where ever it was set up.

DESIGN

For this particular case the frame was made of galvanized pipe and utilizes adjustable fittings, which allow easy assembly and re-sizing. Due to a lack of upper mobility, this adjustability is important to assure proper drawing alignment. To further assist in this vertical alignment, the easel drawing surface incorporated rough adjustments by the use of tear drop fasteners (also known as key holes). This adds four vertical positions that the drawing surface can be mounted on, relative to the X-Y table. Since this particular design of the easel was built for an individual who likes to draw outside, several other factors became important. The easel needed to be small enough so that it could fit through a standard entry door. It needed to be heavy enough so that it would not fall over when the wind was blowing hard. Finally, it needed to be portable, so wheels and carrying handles were included in the design. The drawing board and X-Y table are easily removable at the hinges, and can be reinstalled to any other frame, tabletop or bench with little trouble. Since linear motion was desired, power screws were chosen as the method used to transmit the power to the drawing board. Large power screws were used, much larger than were necessary due to system loading. This was purely an economic design decision. The one inch diameter screw chosen, and the large pillow block bearings used to constrain the screw, were far less expensive than the smaller components actually needed. The X-Y table sub-assembly involved the most synthesis. Once a piggy-back configuration was chosen for the two power screws (Figure 2), it was necessary to choose some type of mechanism that could be used to provide the linear motion needed. Linear slides are preferable but they are generally too expensive for a project of this type. Therefore, it was decided to use v-track and v-track rollers to guide the X-Y table sub-assembly components driven by the power screws.

Figure 2: Piggy Back Power Screw Configuration

After the v-track roller system was established, and the desired motion had been attained, the next logical step was to determine how to deliver power to the power screws. Due to the nature of the design, large loads would not likely be experienced so very low torque, inexpensive motors could be used. This also makes it possible to use small rechargeable motors (i.e., cordless drills/screwdrivers). The stall current of the motors selected is approximately 5 amps with normal operation requiring between 1 and 2 amps (at 12 V DC). In order to purchase a joystick controller that can handle currents of this magnitude an industrial grade joystick, costing between $200 and $300, would need to be bought. It was believed, that a much cheaper joystick could be designed using mini-lever switches. As shown in Figure 3, all of the components of the joystick are easily obtainable and are not too expensive. The plastic housing box and the mini-lever switches are standard electrical components and can be purchased at most electronic stores.

Figure 3: Joystick Components

As can be seen in Figure 2, one of the two power screws in X-Y table sub-assembly directs the movement of the drawing surface in either the X or Y direction. The lower power screw moves the drawing surface in the X direction and the upper power screw moves the drawing surface in the Y direction. A schematic of the Y-axis control system is provided in Figure 4. The joystick assembly, which is composed primarily of four mini-lever switches and a switch activator attached to the joystick handle, controls the current and polarity to the motor. When the switch activator is moved in the positive Y direction of Figure 4, by moving the joystick handle in the negative Y direction of Figure 4, the mini-lever switch completes the circuit from the battery to the motor. The motor is wired so that this polarity turns the power screw clockwise and the nut then moves down. The two limit switches are attached to a member supporting the motor and the power screw pillow blocks. When the nut engages the lower limit switch the circuit is broken and power to the motor is removed. Similarly when the lower mini-lever switch is triggered, the nut moves upward until it contacts the upper limit switch. The lever switches on the left and right sides of the joystick box control the X-axis movement in the same fashion.

Figure 4: Easel Schematic for Y-axis Controls

DEVELOPMENT

Other models of the powered easel are in the design stage. One of which is light and small enough to fit into a brief case. The idea behind the small portable powered easel is that it can easily be set up on a desktop or tabletop using a three legged frame similar to a non-powered artists easel. Another design incorporates three axis movement (X,Y,Z) instead of just two axis movement (X,Y), and includes powered tilt adjustment about the sagittal axis. The drawing board on this three axis powered easel is made out of Plexiglas so that the user can see through it. The drawing board is controlled with puff and sip controls instead of a joystick. There is also a sonar safety switch on the z axis and tilt adjustments. The current design is a relatively low cost solution that can be used as an inexpensive means to accomplish the intended task. This project has been completed with the intentions that anyone that wants to build a similar device will be provided with the information needed to guide them through building one. This would be a project that a high school shop class could easily complete, providing the students and the school with a great opportunity to give back to their community.

EVALUATION AND DISCUSSION

On February 23, 1995 the completed easel was delivered to the intended user. The powered easel has greatly increased the artist's productivity and has allowed him to complete his drawings by himself which boosts his sense of satisfaction. There have been no reported problems with regards to the operation and durability of the easel. While the easel was still in the lab where it was built it took a considerable amount of constant use, and after a few minor adjustments, it weathered this wear very well.

ACKNOWLEGMENTS

The author would like to thank Dr. John Beard for undertaking and delegating projects of this type to his research assistants, and for his continued support and guidance. The author would also like to thank Bishop-Wisecarver Corp. of Pittsburg, CA for the donation of the v-track and v-track rollers, these were the most expensive components of the powered easel.

Kyle Madison 2107 Woodmar Apt. E Houghton MI, 49931 USA (906) 487-4142 email: kvmadiso@mtu.edu

Questions, or requests for free copies of the plans should be directed to:

Dr. John Beard Mechanical Engineering Department Michigan Technological University 1400 Townsend Drive Houghton, MI 49931 USA (906) 487-3110 email: jebeard@mtu.edu