proceedingsedge.rit.edu/content/p07009/public/deliverables/technical... · web viewslotted...

Multi-Disciplinary Engineering Design ConferenceKate Gleason College of Engineering

Rochester Institute of TechnologyRochester, New York 14623

Project Number: P07009

WARFARIN AUTOMATIC HOME MEDICATION DISPENSER

Alan Strandburg RIT ME

Chris AbramoRIT ME

Gordon YeungRIT ME

Nicholas Columbare RIT EE

Ntongho AminRIT EE

Albert LamRIT CE

ABSTRACTThe focus of this project was to develop and create a prototype automated home medication dispenser that administers a month supply of Warfarin in varying dosage combinations. The device communicates with the physician via a computer interface, is equipped with operating checks and alerts, is easily refilled by the pharmacist, can relay the patient’s usage information, and is easy to use. This prototype unit is intended to be used to attract potential investors, therefore it was designed to be robust and spill proof due to frequent travel.

INTRODUCTIONWarfarin is an anticoagulant used for blood clotting medical conditions. Dosages of Warfarin are taken daily and need frequent adjustments to maintain effectiveness. For the first few months of the regimen, adjustments are made based on weekly or bi-weekly blood test results. This requires frequent coordination with the physician, patient, and pharmacist.

Frequent coordination between the physician, patient, and pharmacist is time consuming, inconvenient, and poses a risk to the patient’s health by increasing the chances of error or a missed dose. Since patients taking Warfarin require frequent dosage changes, there exists an opportunity to develop a real-time adaptive system.

Previous iterations of this project concept have been developed to create a generic automated medicine dispenser. The focus of such projects entailed the dispensing of an array of different medications. In contrast, our project concentrated on one medication but of varying dosages.

DESIGN REQUIREMENTS

ME Requirements: Enable one pill to be moved from a bulk

compartment to delivery compartment at a time.

Contain one month supply of Warfarin. Enclosed and latched with tamper evident

indicator. Deliver correct dose without error. Rapid delivery of dose after dose button push. Quickly demonstrable. Loading of device done easily and quickly. Spill-proof. Large / easily visible buttons for dose

retrieval and information. Clearly labeled bins. Reasonably quiet. Easy to use latching cup handle.

EE Requirements: Backlit color screen with large characters for

messages. Rapid delivery of dose after dose button push. Quickly demonstrable. Alert for service when pill supply is low. Delivery compartment with removable dose

cup needs to be in place prior to dispensing. Audio/visual alarm to alert patient that it is

time to take medication.

© 2007 Rochester Institute of Technology

Proceedings of the Multi-Disciplinary Engineering Design Conference

CE Requirements: Remote dose programming through

interactive software interface. Programmable messages from programmer to

dispenser. Rapid delivery of dose after dose button push. Update dosing information by physician. Quickly demonstrable. Alert for service when pill supply low. Audio/visual alarm to alert patient that it is

time to take medication. System to alert designated care-provider if

medication dose not taken. Track dose, with data available to physician

through user interface.

CONCEPT SELECTION

Each team member developed concepts individually to meet dispensing design requirements. The main focus was on the dispensing mechanism because other requirements were dependent on this design aspect. Each concept was explored in a Pugh matrix and evaluated for practicality. Some of the concepts were refined and optimized to produce a few hybrid designs. After completing concept selection two designs utilizing solenoids were chosen. After a deep dive into available solenoid technology it was discovered that a solenoid which met all of our requirements did not exist. The violent nature of solenoid actuation was our primary concern. This led to the decision to use hobby servos in place of the solenoids. The use of hobby servos dictated which configuration would be used within the final design.

FINAL DESIGN

Slotted Stainless Steel Tubes

It was decided early on that the pills were to be stacked in order to make individual pill dispensing more achievable. The tubes provided the dispensing mechanism with a pill in a consistent orientation while minimizing the risk of jamming and potential damage to the pills. In order to get the most consistent pill orientation when stacking, the inner diameter of the tubes needed to be as close as possible to the outer diameter of the pills.

Due to the customer’s dislike of using a free floating internal spring, an external spring design needed to be developed. In order to accommodate an external spring arrangement the tubes needed to be slotted to provide a track for the pill following mechanism to work.

Initially polycarbonate tubes were selected as the material to be used, but after machining the required slots it was found that they were not rigid enough and a more rigid material was needed. The design required a material that was rigid, corrosion resistant, machinable, and was manufactured in seamless tubing to the required inner diameter as dictated by the pill’s diameter. There was also a constraint on the outer diameter of the tubes due to clearance conflicts with the follower assembly. Stainless steel tubes were determined to satisfy all of these requirements.

Stainless Steel Pill Plates

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Proceedings of the KGCOE Multi-Disciplinary Engineering Design Conference

The pill plates were machined from stainless steel and polished to a mirror finish to minimize the effects of friction. Since the pill plates and the servo plate are critical contact components that will undergo many cycles in their lifetime. The material selection was based primarily on durability and the reduction of sliding friction.

Micro-Servos

Originally, our design utilized standard size servo-motors that used a pulling motion to dispense the pills. This design required a separate mounting platform which not only introduced several clearance and alignment liabilities but also required more operating space.

When it was discovered that micro-servos had enough torque to be able to perform the same task without additional parts, the design was revised to make the unit more compact and efficient. Instead of having the servo motors use a pulling motion, they would now push. By pushing the pills out, the need for a separate mounting platform was eliminated and instead was merged with the pill servo plate. Overall, the micro-servos drastically reduced the size, the complexity, the machining time, and the cost of the unit.

To control the micro servos, a 1-2ms pulse with a 20 ms duty cycle was required to set the motor position. In the original design, all of the servos had their control driven by one MOSFET pulsed by a microcontroller on the evaluation board. This MOSFET would then turn on and off a 5V pull up creating the necessary control pulse to position the motors; conveniently all of the motors require the same signal. To select an individual servo a separate

set of MOSFETS, one for each motor, would then be selectively turned on and off disconnecting the ground of the motor. In theory this design worked well but without being able to attain electrical information of the inner-workings of the servos a few assumptions were made.

These assumptions led to failure in the hardware application. Though all of the control signals could be driven by a single MOSFET, the use of individual MOSFET’s to remove the ground from the motor did not work as well as predicted. It was predicted that the motors would be unable to move without the ground connection. It was soon found that though without a ground and with a control signal, the servos did not move properly but they chattered and moved slowly which was an unacceptable operating state. This caused a very late change in the design.

The solution was to either disconnect the 5V itself from the motors using relays or by selectively applying the control signal. The relays were determined to be too space consuming to be contained within the dispensing unit and would require a great deal of additional wiring. This left the option of selectively applying the control signal which could be accomplished using a SV203 controller (special thanks to Dr. Phillips for suggesting it). This controller had an embedded PIC microcontroller, which with a proper serial signal from the evaluation board, was able to send up to eight individual control pulses. Using this controller the motors were successfully actuated.

The spare serial port on the evaluation board was intended to be used with the SV203 controller. This turned out to be problematic because the output out of this port was inverted. After fervently attempting to change this using the software a simple hardware solution was proposed. A simple DDM74SL04 digital inverter was implemented to correct the signal. This inverter was an inexpensive solution and allowed for successful servo actuation.

Power

Copyright © 2005 by Rochester Institute of Technology


The device is battery powered, by a 4-cell rechargeable lithium ion battery which supplies 7.2V at 5200mah. The device can also be powered using 120V wall power which supplies 15Vdc through an adapter. The voltage from the battery (7.2V) and the voltage from the adapter are regulated to 5Vdc using a LM1084IS-5 voltage regulator. Switching between wall power and battery power is done using a solid state relay. When the wall power is connected to the device, the battery is disconnected from the system and the battery is being recharged. The system then receives its power from the wall power. The battery is recharged using a MAX745 chip from Maxim-IC which is a switch-mode lithium ion battery charger. The MAX745 chip regulates the voltage and provides a constant regulated charging current of 4A.

MAX745

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Audio

An audio alarm was included in the required deliverables. The evaluation board included a headphone jack that could provide an audio output which seemed like the most logical signaling method. The maximum output of the headphone jack was 900 mV rms across a 100 Ω resistor. Rather than trying to match this output impedance and obtain the required power, a LM386 audio amplifier chip was selected to create a gain of 20 on the signal line. This amplifier, when powered up from the rectifier on the PCB, created a noise frequency of 3.47 kHz. To resolve this problem a high pass filter was placed on the power line. The filter was developed using the following equation

Where the desired RC was found to be 46.1 µf·Ω, a C=4.7µf and R=10 Ω. This filter successfully removed the noise off of the input and thus cleaning the ouput signal.

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Pill Slide

To deliver the pills from the tube to the medicine cup, a reliable conduit was required. It was recommended that there be a sweeping mechanism to ensure 100% pill delivery but the benefit of adding a separate motor was not enough to justify the cost or spatial compromise. There was also a concern that in the event that the motor failed, pill dispensing could not be achieved.

Ultimately, our design relies on the absolute certainty of gravity to transport the pills. A pill slide was constructed to catch and guide the pills into the cup. The pill slide design consisted of two slide angles. The primary slide angle is the angle at which all the pills would slide at whereas the secondary slide angle allows pills from the outermost tubes to be moved towards the center of the unit and into the cup. Both angles were analyzed and tested to ensure that the pills would not become stuck after they are ejected from the pill plates.

Pill Follower Assembly

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This assembly was developed in order to meet the customer requirement of being spill proof. The spring provides sufficient force in order to prevent the pills from disorienting when the unit is inverted. The design is a self-contained unit independent of the base unit. The assembly is threaded at the bottom for easy removal and installation.

The assembly consists of a top and bottom aluminum hub both of which get epoxied into either end of a polycarbonate tube. The polycarbonate tube retains the spring which applies a force onto the plunger made from nylon 6/6. The plunger has a small pin that is pressed into it perpendicular to the primary axis and on center, which directs the assembly down the slots of the tubes. Refer to the diagram for additional clarification.

Handle with Sensor Switch

The customer provided an example of the handle desired in order to accommodate arthritic hands. It was

required that there be a means of checking for the cup or handle’s presence prior to dispensing and also that the handle be secured. This requirement led to several cup detection schemes but was ultimately integrated into a single mechanism. The final mechanism provides stability and security of the handle through a locking grab catch while also detecting its presence with an integrated micro-switch.

Fully Vented One-Piece Housing

The unit’s outer housing was designed to be easily removed for maintenance and cleaning. Four screws are the only fasteners connecting the outer housing to the unit. The electronics that are mounted on the inside of the housing have been placed into harnesses to facilitate removal. Portions of the housing have also been slotted to offer ample convective cooling to the electronics.

Pill Loading Device

Loading of the device needed to be quick and reliable. The original loading design used a generic funnel that was attached onto the stainless steel tubes, but it proved to be too inconsistent and burdensome. The final design incorporated the funnel with a solid polycarbonate tube attached to it. The pills are poured into the funnel where they are stacked within the polycarbonate tube. At the bottom of the polycarbonate tube there is a release pin preventing the



pills from falling out. The release pin is attached to a structure that slides over the polycarbonate tube. Using the slots in the stainless steel tubes as a guide the loading structure slides down the polycarbonate tube and down the stainless steel tubes. This allows the pills to enter into the tubes in a smooth, well-controlled manner. Once the loading structure has reached its maximum travel the release pin is pulled out and the pills descend the remaining few millimeters into place, maintaining consistent pill orientation.

Friction Hinges

Friction hinges were used in order to support the weight of the lid. The friction hinges allow the cover to be rotated and held open at various positions. It also ensures safe internal access to the unit by preventing the lid from violently dropping closed.

Powder Coated Components

The outer housing and some internal sheet metal components were powder coated to give them a durable, corrosion free finish. Matte white was chosen for the color as this most replicates most household appliances. The powder coating will offer excellent protection against the rigors of travel as well as make the unit easy to clean. As an added benefit, the finish offers aesthetic qualities that signify work that was of high quality and excellent craftsmanship.

Rubber Feet

Rubber feet were mounted on the bottom of the unit to offer stability when the handle is inserted or removed. The rubber feet also help to make it easier for the unit to be picked up since it’s raised off the surface and allows access to the on/off switch. The feet also insulate the unit and allow air to enter through the slots in the base plate.

Aluminum Components

The majority of our unit was built using aluminum. Aluminum was selected early in the design process because it is easily machined, lightweight, and has exceptional thermal properties. Using aluminum compared to steel cut our machining time in half. The material is significantly lighter than steel and has a fairly low specific heat so that it can conduct and dissipate heat very quickly and effectively.

Plexiglas Cover and Cover Plate

These covers prevent spilled or dropped pills from entering into irretrievable areas. Both plates also provide protection to internal electrical components. The Plexiglas cover has holes drilled in it to facilitate air circulation. In the event of a dropped pill, the cover plate is angled such that the pill will fall into the slide and consequently into the cup.

SOFTWARE FUNCTIONALITY

The objective of the software environment is to provide a controlled way to demonstrate the potential of the automatic dispenser concept. A PC (currently an IBM/Lenovo ThinkPad A31p) hosts a web server where the doctor, pharmacist, patient, and caregiver can access an appropriate web page to control or view the status of the machine. Some of the web pages contain server side scripting, using PHP4, in order to store configuration parameters and send commands via the RS-232 port.

Demonstration modes are made available via the web interface in order to force the machine to dispense pills without the need to wait for the specified dispense time. The first demo mode dispenses pills continuously until one of the stacks is empty. This can be used to demonstrate the effect of dispensing over many days. The second demo mode starts a short countdown and then forces the machine to dispense once. The audio and visual alerts are used in this mode. This can be used to demonstrate the patient's use case for one day without the need to wait for a dispense time.

The doctor's interface can adjust the dosing schedule and the dispense time. It can also store information about the patient, caregiver, and pharmacy. This information can be used in the future to create a patient database for the doctor's reference, or to make the machine display personalized messages.

The patient, caregiver, and pharmacist interfaces can be used to view the settings made by the doctor, but not modify them. The pharmacist has the added ability to reset the internal pill counter. This is used when the pharmacist is refilling the machine.

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The web interface also allows the user to configure the machine parameters. Internal machine variables such as dispense time, motor actuation time, audio volume, and even the motor pulse widths can be set so that the source code does not have to be modified in order to make minor operating adjustments.



CALCULATIONS

There were four main areas of focus when determining validation of design components. These areas were the following:

Servo Load (Torque required) Spring Constant Slide Angle

In order to determine the required torque needed by the servo motors, the friction acting on the pills and the servo plates was calculated by analyzing the above parameters. Research was done to make an accurate assumption of the pill’s coefficient of friction. It was assumed that the pills properties were similar to that of paper. Therefore a coefficient of friction of 0.4 for paper on steel was used. In addition to the weight of the pills, the normal force was determined by the weight of the follower and the force from the spring. In order to determine the total frictional force acting on the pill plates, a coefficient of friction of 0.61 for steel on aluminum was used. The normal acting forces on the pill plates were its own weight, the weight of the pill, the weight of the follower, and the spring force exerted on the pills by the spring.

A total friction force was calculated and a minimum torque of 1.238 oz-in would be needed to operate the unit. The maximum torque output of the motors is 20.8 oz-in.

The required spring constant was governed by the weight and travel of the pill stack as well as the crush force of the pills. For the given spring travel, the spring force could not exceed the crush force of the pills. The spring force could not be less than the weight of the pill stack in order to maintain proper pill orientation when the unit is inverted.

The weight of a pill is 0.00216 N and has a height of 3.7mm. By using both these values, a critical spring constant was found to be 2.9165N/m = 0.00333 lbs/in. Given this parameter and a constraining outer diameter, a spring was chosen to have a spring constant of at least 1.7513 N/m = 0.01 lbs/in.

To determine if the spring could potentially cause pill damage a pill crush test was performed yielding the results listed in the table.

An average crush force for the Coumadin tablet was found to be 15 lbs. The force exerted by the chosen spring is 0.08 lbs., giving a factor of safety of 187.

NOTE: Warfarin is the generic equivalent of Coumadin and is manufactured as a different shape. For the purpose of our project, Coumadin tablets were used.

The required angle of the slide was critical to the design in order to ensure that the pills would consistently slide into the medication cup. In order to determine this critical slide angle a test was conducted measuring the average slide angle for a pill to begin its descent. The average angle was found to be 26.35º. The designed angle is 33.3º, giving a factor of safety

of 1.3.

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GENERAL OPERATION EVALUATION AND RECOMMENDATIONS

Mechanical

Overall, the mechanical design succeeded in performing the required functions. One area that could use some minor attention is the machinability of the stainless steel tubes. Stainless steel is typically a difficult material to machine especially when trying to hold critical tolerances. The ductility of the material allows it to deform easily. Due to the lack of an available manufactured seamless tubing that met the design requirements of a specific outer and inner diameter, rigidity, and corrosion resistance, stainless steel was the only remaining option. A suggested countermeasure would be to use extruded aluminum tube or aluminum round stock. With the latter, the material could be turned to the required outer diameter, drilled through with the appropriate inner diameter, and then slotted with relative ease and minimal complications. The difficult issue of slotting the tubes can be avoided if a design was developed that didn’t require a pill following device, or didn’t use a slotted tube configuration.

Electrical

Over the course of this project many new things have been learned. First and foremost that one should get as much information on items going into a design as possible. The lack of information on the servos led to assumptions which should have been tested more extensively. More electrical testing should have been done earlier in the project. This would have reduced the scrambling in the end. As of right now the unit is in working condition with battery power. Currently the wall power circuit is inoperable due to a short during testing that burned up a fuse and a relay. If these two components were replaced the wall power and the battery charging should become fully operational as they circuit were before assembly. The SV203 was intended to be used to drive the servos and it was initially operational but upon assembly of the unit a short occurred which rendered the controller inoperable. The unit was then retrofitted to have the control signal for the servos to be provided by the evaluation board, which was successfully accomplished thanks to the hard work of our CE. In the future it would be beneficial to create a more robust design on the front end of the project so that fewer assembly complications would arise later on. Wiring and wiring harnesses should not be taken lightly; though they are simple they can make or break a project. Thus the analysis and design of these should be determined as early as possible.



Computer Engineering

The RJ45 (ethernet) jack is currently used for file transfers to the evaluation board. Changes to the software or file system requires the machine housing to be removed. A request to expose the RJ45 jack should have been made during the housing design stage.

The laptop PC used for the web interface should have been acquired earlier. This would have given sufficient time to determine if it was operating correctly and make any needed repairs. The IBM A31p obtained had a hard drive that had an extremely slow read time, which significantly increased development and testing time.

There should have been more development time to get Dr. Berg's feedback on the software operation. There should also have been more focus on the serial communication aspect since it was a core part of the project. Work on text positioning and displaying pill images should have been postponed.

There should have been more time to work on interfacing with the motor control circuit. A lot of unexpected interfacing problems needed to be resolved, such as signal noise, grounding issues, and signal inversion.

The code might have been more readable if an object oriented programming language is used.It should have been noticed earlier that the machine's housing would block a portion of the display when viewing it at an angle, effectively reducing the viewable area of the display. This would have given an opportunity to design around this problem.

Future CE Work Font positioning (text centering, text

justification, word wrap, background color mixing).

Use the whole screen once the viewing angle block is resolved.

Change the serial communication to TCP/IP communication so that the machine can be controlled over the internet.

Resolve intellectual property issues (audio file, use of the madplay binary).

Resolve concurrency issues, such as simultaneous running of demos

Firmware updater to correct program errors when discovered.

Figure out the battery discharge curve and make the battery level indicator more accurate.

Make the code more portable – abstract the setting of hardware registers, abstract the display of messages to the user.

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