chapter 7 state university of new york at …nsf-pad.bme.uconn.edu/1993/chapter_7.pdf · the goal...

CHAPTER 7STATE UNIVERSITY OF NEW YORK AT

BUFFALOSchool of Engineering and Applied Sciences

Department of Mechanical and Aerospace Engineering335 Jarvis Hall

Buffalo, New York 14260

Principal Investigator:

Joseph C. Mollendorf, Ph.D., (716) 645-2509

82 NSF 1993 Engineering Senior Design Projects to Aid the Disabled

Wheelchair Seat Lift: Device to Increase Accessibilityof Wheelchair Users

Student Designers: Alan BZatter, Bradley Malta, Jennifer PiatekClient Coordinators: Dr. Pendergast, Dr. Mollendorf

Supervising Professor: Dr. Joseph C. MollendorfMechanical and Aerospace Engineering

SUNY/Buflalo, Bufialo NY 24260

INTRODUCTIONPeople restricted to wheelchairs can experience limitedaccess and difficulty of transfer due to the fixed heightof their wheelchair. At the same time, people desire tobe self-sufficient, and this fixed height restriction in-creases their dependence on others. because of thelow height of a standard wheelchair, transfer betweenthe wheelchair and other surfaces, such as chairs andbeds, is difficult. Additionally, the environment is of-ten unsuitable to their needs. Many standard surfacesand storage spaces, both inside and outside theirhome, are beyond their reach.

SUMMARY OF IMPACTThe goal of this project was to design and build a self-contained wheelchair seat-lifting device. The focus ofour project involved creating a device that is safe,marketable, and practical.

Safety concerns revolved around the strength of thematerials, including choosing materials strong enoughto support the weight of a person, yet light enough tomake the device portable. Simplicity and low cost arekey in assuring marketability, as well as in the device’saesthetics. Making the seat lift easily removable anduniversal to any standard adult size wheelchair wouldadd the appeal. Furthermore, this device must notrequire any modifications to the existing wheelchair.

The device must involve a simple and practical design,and preferably a self-contained mechanism. The maindifficulty arises in finding a motor that producesenough power to lift the person, especially at lowheights, and be small enough to fit under the seat.

TECHNICAL DESCRIPTIONDesign options considered included: a four-post de-sign, an inflatable bladder design, a hydraulic design,and a scissor arm mechanism. The four-post design isdesirable because it could raise a person from a posi-

tion in which the two platforms are initially flush. Un-fortunately, such a configuration requires all fourposts to be powered and all four motors to be preciselysynchronized to avoid binding.

The bladder design consisted of an off-the-shelf,pneumatically powered, inflatable device, that elimi-nates the’need for a rigid and complex transmission.This design, however, does not supply the necessarystability, and is therefore an unacceptable designchoice.

Another design consideration invovles incorporatingfour hydraulic pistons mounted at the four comers ofthe seat. Since a piston’s maximum compression gen-erally equals one half its full extension, this design hasa limited initial height.

The final design consists of two platforms containing apair of scissor arms. The arms are attached, at theirends, to a bearing mechanism that slides along trackson the inside surface of the platforms. The “sliders”inside the lower tracks ride along screws with oppos-ing threads. Turning the threaded rods causes thesliders to move toward each other, the scissor arms toseparate, and the seat to raise. Screw gears provide alarge mechanical advantage, lowering the initial re-quired torque, and making a low initial height possi-ble. This design meets all of the project objectives andwas selected for use in the wheelchair seat lift.

The method of power and motor location are impor-tant considerations for the wheelchair seat lift. It isnecessary to power both threaded rods to avoid bind-ing in the mechanism, wherein one side moves fasterthan the other, causing a torque about a vertical axis.Since employing two motors requires precise syn-chronization, one motor with a transmission is chosenas the power source for simplicity in this project.

The ideal location for the motor is between the twoplatforms. However, since a low initial height is de-

Chapter 7: State University of New York at Buffalo 83

sired, which happens to be, with the scissor design,where the torque is very large. To avoid this problem,two self-contained but separate units are designed,instead of one, consisting of: the seat-lifting mecha-nism as one unit, motor, gear reduction unit, and

power source. The latter is located beneath the exist-ing seat of the wheelchair, with the output shaft of thegear reduction connected to the threaded rods by asystem of pulleys and timing belts.

Figure 7.1. Seat-Lift Device.

Design calculations included geometric, force, kine-matic, and strength of materials analyses. Geometricanalysis is performed to design the mechanism with alow initial height, while still maintaining stability in itsfinal configuration. These computations yielded thelink length, final base size, and the final scissor linkangle.

A force analysis is performed to compute the torque,T, and rotational speed, o, needed to power themechanism. The device is designed for a 200 poundperson and a safety factor of 1.5, resulting in a designload of 300 pounds; these loads provide a verticalforce of 75 pounds at each link.


The resultant torque is calculated on the drive screwsusing the horizontal force, F, at the bottom of eacharm. The pertinent formulas for these calculations are:

F, = (weight) cot @

T,ower = F d, @@m - ‘)’ 2 @a, + pl)

where dm, 1, and u are the mean diameter, lead (pitchfor a single thread), and coefficient of friction of thescrew, respectively, and 4) is the link angle.

During the lowering process, the required torque islower, since the person’s weight aids in the process.Also, a self-locking condition is used in the design.This condition occurs when the force component fromthe weight of the person cannot overcome the fric-tional force component such that:

p>tanh

where 3L is the lead angle of the screw. If this conditionis imposed, the mechanism lowers when a net motortorque is applied on the drive screw. This eliminatesthe need for a locking mechanism and only requires areversal of the electronic signal to the motor, produc-ing a negative torque, to lower the person.

The kinematic analysis is necessary to determine theangular speed of the screw to raise the person in agiven time. The velocity formula from the analysis is:

v, = 2v, cot@

and integrated with respect to the link angle to findthe total time to raise a person.

The strength of materials analyses included calcula-tions of bending, shear stress, and buckling of the scis-sor arms. It also included analysis of the stress on thepins and the torsional stress on the threaded rods. Thefollowing table summaries these results.

Table 7.1. Stress Analysis

Pin Shear 10.261

Arm Buckling 12.815I

Critical Load (lo3 lbs)I I I

Total project cost was $650.

Chapter 7: State University of New York at Buffalo 8.5


Adjustable Hold Walker: A Device to Maintain aPerson Attached to a Walker

Student Designer: Edgar MaldonadoSupervising Professor: Dr. Joseph C. Mollendorf

Mechanical and Aerospace EngineeringSlINY/Buffalo, Buffalo NY 14260

INTRODUCTIONThe main objective of this project was to redesign adevice that holds a person’s body to a walker. Thisholding device is being redesigned for Matthew Stein,a disabled teenager with limited muscle coordination.Previously, another student implemented a magnet asthe holding device. A plate was strapped aroundMatthew and the plate was held to the walker by amagnet. This holding device, however, created amagnetic field that affected a recently implanted mi-crochip that controls a pump inside Matthew’s body.

SUMMARY OF IMPACTWhen using the walker, Matthew must wear a bodyjacket to keep his upper body straight. In addition,Matthew’s father (Dr. Stein) wanted the body jacket tosolely maintain Matthew in a standing position whenusing the walker. Dr. Stein pointed out that Matthew,being a teenager, is still in a growing process and itwould be a good idea to make the holding deviceheight adjustable.

An important aspect of the project is to restrict newimplementations to fit the original design. The newholding device should not be placed in a differentposition from the original. This would ensure thecenter of gravity of the walker to remain the same.

TECHNICAL DESCRIPTIONThe adjustable walker consists of two parts. The firstconsists of an envelope type metal case designed sothat a plate can slide into it. In the original design, af-ter the magnet was removed, a limited space of 4 by 2inches is left for new implementations. The envelopemust fit in the limited space. The second part was tomold a metal plate to the outer shape of the bodyjacket so that it can be permanently attached. Weldinga small bead between the plate that slides into the en-velope and the plate molded to the body jacket willlink the body jacket to the holding device (envelope).

Choosing the material was no problem. Mild steelwas chosen due to its low cost, high strength and easein machining. Weight presented no problem since allparts are relatively small, and all the weight will becarried by the walker, thus it will not be an inconven-ience to Matthew. The steel was to be coated with cor-rosive resistant paint to prevent it from rusting.

The envelope needed angular mobility to make sureMatthew would be placed in an upright position whenthe “arm” attached to the holder device was eitherlowered or raised. Four hinges were made to connectthe envelope to the “arm”. Two hinges were weldedto the arm and two at the bottom of the envelope. Apin through the hinges allowed the envelope to rotate.The pin carries most of Matthew’s weight. The selec-tion of the size of the pin is based on a safety factor ofthree.

Another hinge pin connection is needed to maintainthe envelope rigid once the desired angle is obtained.It was agreed that the envelope should be maintainedrigid by friction. Two smaller hinges were made andwelded to the back of the envelope. The hinges werecarefully placed to allow maximum rotation of the en-velope. A pin (factor safety of two) goes through thehinges and holes made in two plates which maintainthe envelope rigid. These two plates had slots to spe-cifically allow a quarter of an inch screw to go throughthem. The slots allow the screw to slide from side toside, and therefore permited the envelope to be ad-justed to the right angle. The screw, when tight, com-presses the two plates against a section of the “arm”preventing the envelope from moving.

The plate that slides into the envelope must be pre-vented from sliding out. Matthew has limited musclecoordination and could accidentally detach himselffrom the holding device. To prevent this from hap-pening a hand retractable pull ring plunger is imple-mented to the envelope. It allows easy access andquickness to secure or detach Matthew to or from thewalker.


A plate is molded to the outer shape of the body jacketand held in place with five screws. A second thin gal-vanized plate is molded to the inner shape of the bodyjacket to distribute the load due to the screws througha larger area. This is done to prevent the head of thescrews from perforating the body jacket.

The final design is achieved according to the originalplan without any unpleasant surprises. The cost ofparts was about $30. This does not include the cost ofthe mild steel used.

Figure 7.2. Adjustable Hold Walker.


Wheelchair-Mounted Camera Control Mechanism: ADevice Used to Facilitate the Use of a Standard

Automatic Camera for a Wheelchair Bound IndividualStudent Designers: Kenneth J. Chesnin and Eon H. Verrall

Client Coordinator: Eon H. VerrallSupervising Professor: Dr. Joseph C. Mollendotf

Department of Mechanical and Aerospace EngineeringSUNY/Buffalo, Buffnlo NY 14260

INTRODUCTIONRaymond Holcomb, a wheelchair bound individual,wants to operate a camera. Raymond has minimal useof his limbs; only his hands function effectively. Themain objective of this project is to build a device thatwill allow people in Raymond’s predicament to oper-ate a standard, automatic camera.

SUMMARY OF IMPACTThe wheelchair-mounted camera control mechanism(see Figure 7.3) is a device that attaches to a standard,powered wheelchair, allowing Raymond to operate acamera using only his hands. Raymond is able to ad-just the camera to his eye position and take the desiredphotograph. The device lowers out of the way whenhe is not taking photographs and does not add to thewidth of a standard powered wheelchair, so as not toimpede the mobility of the wheelchair. The device issimple enough for someone to easily attach and detachit from the wheelchair, it is easily assembled, and itutilizes accessible or easily manufactured parts.

TECHNICAL DESCRIPTIONThe wheelchair-mounted camera control mechanismis adjustable with four degrees of freedom. Using ahand-held control system, the user is able to adjust thecamera to his eye position and take the desired photo-graph.

The lifting mechanism employed in the device utilizespart of a standard camera tripod. The tripod employsa hand-cranked rack and pinion gear that is modifiedto accommodate a motor, and allows for adjustment tothe user’s eye level. The device employs an X-Y posi-tioning mechanism that utilizes slide tubes, roller as-semblies, and power screw to adjust the camera to theusers’ eye position. The device also tilts the camera,allowing for different angled photographs. A solenoidswitch allows the user to shoot the picture under re-mote control. All the motors utilized in the device op-erate on a 12 or 24 volt power source that is alreadypresent on a standard, powered wheelchair.

Total project cost is about $400, including the camera.

Chapter 7: State Universiw of New York at Buffalo 89

Figure 7.3. Wheelchair-Mounted Camera Control Mechanism.


Low Noise Cast Cutter: A Device to Eliminate Fear inPatients

Student Designer: Eric j. SchatzSupervising Professor: Dr. Joseph C. Mollendorf

Mechanical and Aerospace EngineeringSUNY/Buflalo, Buffalo NY 14260

INTRODUCTIONThe main objective of this project was to fabricate acast cutter that would eliminate the fear a patient ex-periences when having a cast removed. This is espe-cially true in children with disabilities. The fear is aresult of the noise emission from current cast cutters.The saw blade of the cast cutter merely oscillates so asnot to cut skin. This oscillation is achieved in the cur-rent cast cutter by a motor and a four-bar-linkage. Thenumber of moving parts in the current cast cutterprove to be the source of the noise. So, logically, a newcast cutter must be fabricated with less moving parts.

SUMMARY OF IMPACTA quiet cast cutter is essential to eliminate the fear ex-perienced by the patient, because possibly with thisfear comes violence (kicking, swinging, screaming).This violence puts the patient and practitioner at anincreased risk of injury. The new cast cutter shouldclosely match the current cast cutter in size, shape,weight, and cost (usual retail is about $700).

TECHNICAL DESCRIPTIONThe main goal here is to decrease the number of mov-ing parts, which will in turn, eliminate some of thenoise produced. Instead of utilizing a four-bar-linkageto create an oscillation, a DC permanent magnet motorconnected to an AC input voltage is used. This con-figuration is modeled as a second order differentialequation (below) with a sinusoidal input and negligi-ble damping effects.

Id28 P .- = Tsino,,t = -dt2 Odr

smci)d,.t

By tuning the input power and the inertia of the rotorof the motor, the oscillation characteristics (that is,stroke size and speed) of the new cast cutter can bematched to the current cast cutter. The current castcutter operates with a stroke size of eight degrees ineach direction and a stroke speed of about 17,000 oscil-lations per minute. Solving for the inertia in terms ofthese values yields an unobtainable inertia.

For design considerations, it is important to determinewhether the cast cutter’s cutting ability is a function ofthe stroke speed or the input power. Upon experi-mentation, the cutting ability depended more on thepower than the speed. This fact enabled a lower oscil-lation speed to be used in the design. This designchange increased the required inertia to realistic levels.

A 24 VDC motor, with the proper rotor inertia, is usedin the project. A transformer is used to step down thealternating voltage from 120 to 24 VAC. Also, sincethe motor will not be rotating, the motor cannot dissi-pate heat as effectively. So, the cutter is equipped witha cooling fan. The design requires that the motor betransformed into something that looks like the currentcast cutter. This was done by attaching a hand-unitonto one end of the motor and running a shaft (rigidlyconnected to the motor rotor) through the hand-unit toa saw blade at the other end (see Figure 7.4). The newcast cutter matches the current one in size and weight.Even though the new one does not have as much ex-cess power as the current one, it effectively cuts theprimary casting materials (fiberglass and plaster ban-dage) .

Total project cost was about $200.

Chapter 7: State Universitv of New York at Buffalo 91

I I

Figure 7.4. Cast Cutter and Power Pack.


Cause Switch and Effect Devices: Mechanized Toysused for Therapeutic Purposes

Student Designer: C.E. GreenTherapist: Christina Robach, Children’s Hospital of Buflalo

Supervising Professor: Dr. Joseph C. MollendorfMechanical and Aerospace Engineering Department

SUNY/Buffalo, Buffalo NY 14260

INTRODUCTIONThe cause switch and effect devices project is a thera-peutic appliance used to teach mentally disabled chil-dren the concept of cause and effect. An existingFisher-Price piano cause switch is modified in thisproject so that there are only two large keys. When thechild presses one of the two keys (the left or the right),a corresponding effect device is activated. Currentlythe only effect device is a modified tape player. Sinceeach child has a different degree of disability, this loneeffect device does not interest all children.

The purpose of this project was to create another effectdevice to work in conjunction with the piano. Acommercially available toy was selected to be modi-fied. The Disney cartoon-music box is mechanized,and used with the existing cause switch. This particu-lar toy was selected because it was both visually andaurally stimulating, as well as compact and transport-able.

SUMMARY OF IMPACTThe toy was demonstrated in its original mode of op-eration to a number of people. All of the viewersfound the toy to be interesting. The toy should alsostimulate the disabled children and provide them theincentive to learn the basic principles of cause and ef-fect. A dual purpose for this therapeutic appliance isto assist physically disabled children, enabling them toplay with toys they could not otherwise operate.

TECHNICAL DESCRIPTIONOriginally the power for the music box was providedby a coiled spring, loaded via a wind-up knob locatedon the front of the unit. A gear train, originating fromthe music box, turned the cartoon scroll. RPM and

torque requirements needed to be calculated for de-sign considerations. A small motor with appropriateRPM and torque specifications is used to replace theoriginal spring mechanism.

The music box is modified by adjusting a speciallymade square steel part over its original shaft. Themotor’s shaft is fitted with a square-holed sleeve. Thissleeve matched the modified music box shaft.

The motor is fastened to a wooden platform, and thenplaced on the front of the toy where the originalwind-up knob is located. As to not detract from thetoy’s appearance, the motor and platform are enclosedby a thin metal housing. For safety reasons, all sharpedges are smoothed. This housing is decorated with aDisney-theme contact paper.

The new power system uses two 1.5-V, high capacity,rechargeable batteries. The electronic circuit designincorporates a specially made recharging system thatrequires minimal maintenance by the user. To re-charge the batteries, the toy needs only to be pluggedinto an electrical outlet for several hours.

A Plexiglas housing, with two separate compartments,contains the battery pack and the electronic circuit, re-spectively. The compartment containing the circuit issecured with screws on both sides of the lid. How-ever, the batteries may be accessed by adjusting the(removable) sliding lid. This housing is located on theback of the toy. The necessary wires to the motor runinside the toy such that no wires are exposed on theoutside of the toy. Again, the Disney contact paperdecorates the Plexiglas housing.

The total cost to modify and mechanize the cartoon-music box was approximately $80.


Figure 7.5. A Mechanized Toy used for Therapeutic Purposes.


Cause and Effect ToysStudent Designers: Julia Schafland ]oseph Mittnight

Client Coordinator: Children’s HospitalSupervising Professor: Dr. loseph C. Mollendorf

Mechanical and Aerospace EngineeringSUNY/Bufilo, Buffalo NY 14260

INTRODUCTIONThe main goal of this project is to alter two commer-cially purchased toys into cause and effect toys. Thesetoys are used by disabled children that have limitedmotions and have communication difficulties.

SUMMARY OF IMPACTMany little children have little or no reaction to stimulidue to physical and/or mental disabilities. Most ofthese children are unable to play with toys in the nor-mal fashion. The first part of this project involvedadapting a simple toy to produce an electrical outputthat could activate an effect toy. The toy chosen forthis part is the Disney “Play ‘N Pop” activity toy byMattel. The toy is recommended for children 9-36months old. It is felt that this was an appropriate agegroup for the project, considering the physical chal-lenges of the children.

The second part of the project involved motorizing atoy so that a physical input from the children wouldnot be needed. The toy would be activated from anelectrical input supplied from a cause switch like theone designed in the first part of the project. To morefully stimulate the children, auditory and visualstimulation is used. One of the motions of our effecttoy is also accompanied by a ringing bell.

TECHNICAL DESCRIPTIONThe first focus of our project is selecting the appropri-ate cause toy. A toy is desired that exercises variouslevels of ability and motion.

The original toy consisted of 5 mechanisms that oper-ate either by turning, pushing or switching, and theseactions triggered doors to open through springmechanisms. The spring mechanisms are discon-nected to keep the doors shut.

A simple electrical switch to activate the effect toy isutilized in the design. A micro-switch is used and ac-tivated when a roller is pressed down approximately 4millimeters. The internal levers of the toy proved to bevery useful in the design of the switching systems. Fortwo of the mechanisms, no lever modification wasnecessary. For two of the remaining three mecha-nisms, levers were not used and the switch was placedunderneath the mechanism itself. For the finalmechanism, there was not enough clearance for aswitch so a simple extension was used to increase theclearance of the lever.

For the second part of the project, a commerciallyavailable toy is modified into an effect toy. An effecttoy has large moving parts, but requires no direct in-teraction with the child; the toy is activated electroni-cally by a cause toy.

Operationally, two motors are placed on the toy, oneunder the base of the toy to turn the horizontal wheeland one on the side to turn the vertical wheel.

A box is used to hold the motor under the base of thetoy. The top and bottom of the box are built of woodfor ease of handling and strength, while the sides aremade of clear plastic. The box is also used to hold thebattery supply and the charging circuit. The effect toyis able to be plugged into any wall outlet to charge theeight rechargeable batteries that power the motors.

The motor for the vertical wheel is mounted next tothe toy in a tower. The tower is constructed in thesame manner as the box under the toy, and its onlypurpose is to hold the motor in place. Since the motorin the tower is in a small space, three holes are drilledinto the top of the tower to allow for cooling.

Total project cost was about $300.


Figure 7.6. Cause Switch and Effect Device Toy.


Appliance Elevator: Automated Shelving Unit forKitchen Counters

Student Designers: David Kretschmann, JeffFleischmann, Tony PovinelliSupervising Professor: Dr. Joseph C. Mollendorf

Mechanical and Aerospace EngineeringSUNY/Buffalo, B@alo NY 14260

INTRODUCTIONThe project goal consisted of the development of adevice that would accommodate the hidden storageand counter top level accessibility of kitchen appli-ances. The need for such a device was due to the exis-tence of physical disabilities that prevent people fromlifting or repeatedly moving heavy objects, and the in-crease in the number of kitchen appliances peopleOWn.

SUMMARY OF IMPACTThis device offers those people that have physical dis-abilities the freedom to store and retrieve their smallkitchen appliances with minimal effort and pain. Cur-rently, an individual must lift and carry an appliancefrom either a wall cabinet or a base counter cabinet.This shelving unit automatically transports severalappliances to and from storage to counter top level,where the appliance is then moved to the desired lo-cation on the counter top.

TECHNICAL DESCRIPTIONThe device is comprised of three subassemblies, thedrive mechanism, the shelves, and the main frame.When completely assembled they maximize the num-ber of appliances capable of being stored, whileminimizing the loss of existing counter space.

The first subassembly, the drive mechanism, is an 81inch long by 1 i ” diameter, 4 TPI, and semi-hardenedacme threaded shaft that is powered by an AC motor.A portion of the two ends of the threaded shaft wasmachined down to a diameter of one inch, to allow theconnection of two one-inch diameter thrust bearings.These bearings provided support for the shaft whileallowing smooth and uninhibited rotation. The pur-pose for the shaft is to convert its rotational motioninto the vertical translational motion of the shelves.

To aid the drive mechanism are two brass supportrods. These support rods prevent the shelves from

freely rotating down the shaft and forcing the conver-sion of rotational to translational motion.

The second subassembly, the shelves, are circular andoperate similarly to a “Lazy-Susan.” The actual storageshelf is a 20” diameter piece of wood that has a centerhole cut into it to allow passage of the threaded shaft.This shelf is attached to the top of a 12” diameterbearing, which provides it with independent rota-tional movement about the shaft. This gives the useraccess to the entire shelf, maximizing the number ofappliances. To the bottom of the bearing is attachedanother piece of wood with a 12” diameter. The finalpart of the shelves is the nut and flange. The nut ismade out of brass and is threaded on both the interiorand exterior. The interior thread is matched to fit onthe threaded shaft, and the exterior thread exists forthe mounting of the flange. The flange is five inches indiameter and contains four holes, where two of theholes are used for the attachment of the bottom circu-lar piece of wood, and the other two holes are for thetwo brass support rods.

The third subassembly is the main frame, whichhouses and supports the shelves and drive mecha-nism. The frame is designed to be a free standingstructure that is constructed out of wood allowing it tobe easily incorporated into the comer of an existingkitchen counter.

The frame consists of a 24” square top and bottomplate that are connected by four 2x4 wooden studs,braced by several wooden horizontal cross braces,much like the construction of a house wall. The totalheight of the frame is 79 inches. The bottom platesupports the threaded shaft of the drive mechanismand the top plate supports the motor and motormount.

The total cost was approximately $1000.


Figure 7.7. Automated Shelving Unit for Kitchen Counters


The Stove Top Stirrer: A Device to Facilitate theStirring of Food

Student Designers: Steven Brown and Lori ChaykaSupervising Professor: Dr. Joseph C. Mollendorf

Mechanical and Aerospace EngineeringSUW/Buflalo, Buflalo NY 14260

INTRODUCTIONKitchen remodeling has become a popular means ofassisting physically limited people. Modifications arealso performed on kitchen appliances to accommodatethe special needs of such people. Currently, however,there is no device to stir food on a stove top for thosewho find it difficult or even painful. The purpose ofthis project was to design and build such an appliance.

SUMMARY OF IMPACTThose who are limited physically usually experiencethe need to do as much as possible without the help ofothers. The stove top stirrer can aid such independ-ence.

Once mounted on a stove top, the device can be usedwith pots ranging in diameter from 5 to 10 inches. TheStove Top Stirrer produces enough torque to stir foodwith viscosities up to 1.48 Pa-s. With choices of low,medium, and high, the user is able to select howquickly he or she wants the food stirred. A timer isanother option incorporated in the design. The appli-ance will either stir constantly or in intervals, with anon time of 10 seconds and an off time of 20 or 50 sec-onds.

TECHNICAL DESCRIPTIONThe first task of the project involved choosing a motorfor the device. This decision is based on how muchtorque is required to stir a majority of food types. Themotor chosen is from a 200W Black & Decker Power-Pro-Mixer.

While testing the motor, the rotation was determinedto rotate too quickly for the intended device. To solvethis problem, a 1O:l speed reducer is used, and re-sulted in desirable rotation speeds. The speed reduceralso facilitated the decision of motor placement. Sincefood particles and heat could ruin the motor, the mo-tor is placed 8 inches to the left of the cooking area.

The speed reducer enabled the transfer of motor rota-tion in a 90” angle.

A magnet is used to hold the appliance to the stovetop. If the user chooses to mount the device on an ad-jacent counter top, the magnet can easily be removedand a block of appropriate height attached. Thismodification might be necessary for small stove tops.

Fastened to the magnet is an aluminum box. This boxhouses the speed and timer controls as well as theircircuitry. Attached to this box is a 9” PVC tube 3” indiameter. This tube contains the motor that is securelyattached 2f ” from the top of the tube. The heat pro-duced by the motor is also a design consideration. Thecover of the PVC tube has been modified to containfour slits. The motor is equipped with a fan and is lo-cated 1” from the top of the tube to allow air flowthrough the slits in the PVC cover. The back of thealuminum box is also furnished with slits to allowmaximum air circulation.

The motor is attached to the speed reducer throughseveral connections. The shaft of a beater, which camewith the mixer, has been secured onto its originalopening in the motor. The opposite end of this beaterhas been press fit into a + ” diameter stainless steelshaft. The other end of the latter shaft is connected tothe speed reducer by a coupler. This entire connectionis enclosed in a l$ ” diameter PVC tube. The speedreducer is enclosed in a Plexiglas box.

Also enclosed in the Plexiglas is the coupler attachingthe speed reducer to a vertical shaft leading to the restof the stirring mechanism. The actual stirring rods aremade of Teflon, a plastic that can resist the heat en-countered on a stove top. The rods are designed toallow large food particles to pass through, and not ac-cumulate in the device. There are three stirring rods,one of which is stationary. The remaining two allowfor the diameter adjustment. The diameter adjustmentis accomplished by the use of two spring plungers at-

Chanter 7: State Universitv of New York at Buffalo 99

tached to a stainless steel rod. Once the spring plung-ers are in one of the three possible positions the userreleases a lever and the pins drop securely into place.

For cleaning purposes, the entire stirring mechanism isdetachable by a pin connecting two vertical shafts near

the Plexiglas box. Detachment of the stirrers is alsonecessary to the removal of the pot.

Total project cost was $340.

Figure 7.0. Stove Top Stirrer.

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