ADAPTLVE DEVICE DESIGN FOR A DISABLED PERSON TO OPERATE A PAPER SHREDDER

R. Kiser, K. Maersch Undergraduate students

and R.M.V. pidaparti

Associate Professor Department of Mechanical Engineering

Purdue University Indianapolis, IN

ABSTRACT

A design process was undertaken to develop a device that would enable a handicapped person to feed paper into a shredder. The device was designed to allow e person with limited motor skills to control the device using a head switch.

This manuscript contains the requirements for this design as well as the design concept, important calculations and evaluation on how well the requirements are met.

I. INTRODUCTION

The purpose of undertaking this project was to help Rob become gainfully employed. Rob is a seventeen year-old high school graduate who suffers from cerebml palsy, a muscle disorder that confines him to a wheelchair. Rob is unable to speak and communicates “yes” and “no” through eye motions.

Rob is currently employed at the Special Education Office (SEO) of the Indiana Department of Education stamping envelopes with the use of a adaptive stamping device and a head switch. An assistant works with Rob the entire time by placing and removing the envelopes that Rob stamps. The SE0 would like Rob to perform more task in the office and afford a higher degree of independence.

One of the tasks the SE0 would l i e Rob to perform is feeding paper into a paper shredder. For Rob to be able to perform this task, a device must be developed that will feed paper to a shredder. The operation of this device will be controlled by Rob. Limited assistance will be required to load the device and correct any malfunctions that may OCCUT.

II. REQUIREMENTS

The requirements for this design were obtained through meeting with Rob and the SEO, and they are as follows.

1) Variety of Paper: The adaptive device must be able to feed 8-1/2 x 11” standard paper, 8-1/2 x 14” legal paper, 11 x 15” greenbar paper and 12 x 14” heavy paper.

2) Continuous Operation: The adaptive device needs to run for 20-30 min. before reloading the paper.

3) Multiple Sheets: The adaptive device should feed several sheets at a time.,

4) Esthetics: The adaptive device must be suitable for an office type setting.

5) Operator Feedback A switch should let the operator know when the device is empty, so the operator can signal for assistance.

6) Signaling: A control switch must be implemented for the operator be able to shut off the feeder and indicate a problem. This switch must be compatible with operators ability.

7) Environment: The device should blend well with other office equipment.

8) Standard Parts: The device should be constructed in such a way that all replaceable parts are easy to obtain and replace.

9) Safety: The device should be safe to operate. The device should be safe from

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exposure to electrical wires, mechanical movement; and the outside of the device should be free of rough, sharp, or jagged edges.

10) Maintenance: The device should be easy to maintain.

11) Easy to use: The device should be easy to Operate.

III. CONCEPT DESIGN

Fig. 1 shows the preliminary conceptual design chosen for this application. The inclined paper feed design utilizes an inclined paper stack design. This allows gravity to provide the bulk d the force necessary to transport the paper to the shredder. The design also has rollers that are positioned at the top of the stack parallel to the top sheet. The rollers are offset from the top sheet approximately 1/2” and are spring cushioned. The paper retrieval plate has a cable attached at each end. The cable loops over a roller at the top of the unit and is attached to a shaft undemeath the top roller. An electric motor drives the shaft and the cable wraps around the rotating shaft lifting the paper retrieval plate. As the plate advances, sheets of paper fall from the top of the stack into the paper shredder. If a stack of perforated greenbar paper is encountered that does not fall, it encounters the rollers which then propel it from the paper supply stack.

LELECTRIC MXOR

The inclined plate design allows any type of paper to be used in the shredder, regardless of the varying weight. Use of the incline also allows gravity to be utilized to propel the paper from the supply stack into the shredder throat. The rollers at the top of the device are encountered by a thickness of perforated paper greater that 1 P . The rollers are spring loaded and will assist m propelling continuous stacks of this perforated ‘paper. The controls for this design will include a head switch which will start the device with one activation and stop the device with another activation. If the device is stopped, a signal will be sent to the assistant alerting them that the operator requires assistance.

IV. PARAMETRIC DESIGN AND CALCULATIONS:

The remainder of this section is the calculation and determination of the critical parameters needed to satisfy the requirements.

A. Determination of the paper bin height:

Customer requirement number two specifies that the device operate continuously for 20-30 minutes without operator assistance. The esthetics requirement specifies that the device not be larger that a three foot cubic space. The speed of the motor and the space requirement dictate the supply of paper that is required for the device to operate within those parameters. A twenty-four inch (24”) supply of paper is selected for three reasons. Typically, the operator of the device only works one day per week for apj~oxhatdy two hours per work session. A two foot stack of paper seems a reasonable amount of scrap produced in a typical office setting. The amount also meets the spatial requirements placed on the device.

B. Determination of the drive shaft diameter:

The drive shaft diameter is arbitrarily chosen as three-eighths inches (3/8”) due to the availability of gears with that bore diameter.

Fig. 1. Conceptual Design.

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Fig. 2. Force diagram for the drive mechanism

C. Determination of the shafr speed requirement:

For the above customer requirements to be satisfied simultaneously we found that the lift speed must be 24 inches of paper in 30 min. The lift speed is,

V, = 24130 min = 0.8in / min . The speed of the shaft is found by

acknowledging that the lift speed is the linear velocity of the shaft. The angular speed of the shaft is,

0.68rmp. 0.8in lrev 0.8in lrev % = ~ ~ = ~ ~ =

D. Detem‘nution of the motor torque requirement.

Fig. 2. shows a freebody diagram of the drive mechanism of the device.

E. Determination of the maximum weight of the paper + paper tray (Wt):

A sample of paper 8.5” wide by 11” long by 1 15/16” thick was weighed at 5.0 lbs. Paper density is equal to:

m lb p = - - e = ’lb =0.0276- V, 181.16in3 in3

The paper bin is designed to accommodate paper up to 12” wide and 16” long.

Maximum volume of paper supply: V=12x16x24” = 4608 in3

W t

Fig. 3. Free Body Diagram for the Paper and Tray.

Maximum weight of paper supply:

W= 0.0271bl in3*4608 in3 = 127.2 lb Weight of the paper tray:

Volume of paper tray = 19.2~13.76~0.125” = 34.26 in3

Weight = ,036 lb/in3 x 34.26 in3 = 1.23 lb

Total weight = 127.212, + 1.23 lb = 128.4 lb

F. Determination of the weight in the cables:

Force Balance Equations:

J)? = 0 3 F,,, = W, sin(40) FX = 0 +Ft = W, ms(40) + Ff

(1) (2)

Ff =F- 0 (3)

Combining (1) and (3) into (2); T = 128.4 cos(40) + 0.2(128.4) sin(40) sin(40) = 109 Zb

G. Determination of the torque needed at the shafr:

From Fig. 3. the torque of the 3/8 in diameter s b i t is equal to the combined tension in the cables multiplied by the moment arm 3/16 in.

3 16

Torque = T - = 20.43 lb. in

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H. Determination of the gear ratio between the motor selected and the shjt.

Specifications: Motor speed = 1.0 RPM Shaft speed requirement =.68 RPM The required gear ratio = 1/68 = 1.47

J. Determinution of the gear teeth.

Select the number of teeth on the drive gear to be twelve. The number of follower gear teeth is then: 1.47(12) = 17.64 = 18

V. EVALUATION

The device is able to shred each of the specified sizes of paper. The device was designed to withstand the forces generated by the largest size paper, which has the largest density. The rollers at the top of the unit ensure that no paper fails to leave the paper stack. The rollers also allow the device to feed perforated greenbar paper. When a stack of greenbar paper thicker that one-half inch (112”) becomes incident on the rollers, its top sheet is peeled from the stack and the remaining sheets follow.

The device was designed with the motor rpm and gearing required to ensure that the device will operate continuously for the specified period of time.

The device will feed multiple sheets. Between 5-10 sheets of 8.5~11” paper fall at a time.

The device is suitable for a office setting. The device meets the dimensional, noise level, and power requirements. The device is approximately thirty inches (30”) by twenty- eight inches (28”). The device is powered by plugging it into a standard wall outlet.

A signal light is provided for the assistant when either the operator signals for assistance or the paper bin becomes empty.

The device will be safe to operate. All moving parts are guarded or covered and the device was designed to have no sharp edges.

of the motor are low, the wear of the associated parts will not be significant for the cycles the device will be subjected to.

VI. CONCLUSION

Currently, the preliminary design concept is being evaluated based on its ability to be manufactured and availability of parts. Several tests have been conducted on the feasibility of certain facets of the design. The electric motor size and gearing requirements have been calculated based on the specified operation time as shown earlier. The cable driven inclined plate has been tested and found to be Satisfactory for the application.

There is no foreseen maintenance required for the adaptive device. Since the rpm and torque

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