Project Proposal

Introduction

The following page represents the formal proposal for the accessible syringe device. It contains information and justification on the various concepts chosen, as well as a preliminary list of materials that were to be used on the prototype. The report contains the following sections:

• Executive Summary
• Technical Description of Proposed Device
  • Key Subproblems
    • Bottle Loading
    • Bottle Mixing
    • Syringe Loading
    • Syringe Dosing
    • User Interface
    • Bottle-Syringe Interface
  • Integrated Solution
• Economic Justification
• Conclusion

Executive Summary

In response to the National Student Design Competition sponsored by the RERC-AMI, this proposal outlines the design of a solution to the issue of accessibility in syringe dosing. Although a variety of assistive devices for syringe dosing exist on the market today, they fall short one or more aspects with respect to the needs of people with low vision, hard of hearing, low tactile sensation, or impaired motor control in one or more aspects. By combining an intuitive and simple interface with a sophisticated robotic system, our syringe dosing system surpasses the competition and maximizes the number of people who can operate it. All aspects of the user interface have been designed to make the process as error free and effortless as possible.

Our solution provides a means for dosing a syringe that is universally easy to use, regardless of the abilities of the client. Here are some additional highlights to our design:

• Economical operating costs - Uses standard 1 cc syringes and 10 mL medicine bottles eliminating the need for expensive proprietary needles and storage vessels.
• Ease of use - In a few steps, the user can load the syringe, bottle and input the dose. The device takes care of mixing and dosing automatically.
• Reliable Dosing - Accurate and precise dosing mechanism ensures the correct amount is drawn every time.

The accessible syringe dosing device will assist people who already use injectable medications to dose syringes with greater accuracy and less effort. It will also open the door for people with disabilities who previously could not dose a syringe themselves to do so in their own homes, decreasing dependence on others to assist them with their medication. The syringe dosing device provides an economical, easy to install, and easy to use solution for loading syringes with medication, thereby improving health care delivery, reducing health care costs, and ultimately improving the quality of life for its users.

Technical Description of Proposed Device

The intent of this project is to attempt to emulate the actions that a human would take to dose a syringe. Consequently, the problem does not lend itself naturally to functional decomposition; breaking down the problem into a sequence of steps allows each step in the process to be addressed as its own subproblem. The process of dosing the syringe is shown in the following diagram:

Figure 1: Functional Diagram Showing Subfunctions

Key Subproblems

From this diagram, six key subproblems were extracted and addressed separately. Of course, some consideration was taken to guarantee that the solutions to these subproblems were compatible with each other. All in all, however, each subproblem was addressed separately in order to allow for the best solution to each critical component of the dosing process.

The following six subproblems were isolated: bottle loading, bottle mixing, syringe loading, bottle/syringe interface, syringe dosing, and the user interface. Each subproblem will be addressed in the following sections.

Bottle Loading

The first step in the dosing process is to load the bottles into the device. This task is complicated by the fact that a user of this device could have a number of disabilities, including blindness and muscle tremors. Both of these disabilities would make it difficult to accurately and correctly load a bottle. As such, the process was designed to be as forgiving as possible. In other words, if the user could get the bottle to a very general location, the device would then guide the bottle to its final and correct location. The solution to this problem is shown below:

Figure 2: Bottle Loading Concept

The concept incorporates a hinged door that would drop from the device at approximately a 45 degree angle. The door would be approximately twice as wide (about 3 inches) than the bottle itself, and it would be concavely curved in order to funnel the bottle to the center of the door. The angle of the door would then enable the bottle to slide down into its proper position. Therefore, instead of having to place the bottle into a definitive location, the user can drop the bottle anywhere on the door, and the angle and shape of the door will allow the bottle to always slide into the proper position. If the bottle is positioned correctly, the door will shut completely, locking in place through the use of a spring-loaded latch. Correct orientation of the bottle is ensured by the form of the bottle being molded into the back of the cylinder into which the door is closing. For example, if the bottle is upside down, the door will not close. There will also be a switch located at the door that will act as a safety feedback loop. If the door is not closed properly, the switch will remain open, signaling to the microcontroller that the dosing process cannot continue. This design ensures that the bottle is loaded correctly without the user having to be perfectly precise in placement.

Bottle Mixing

Loading the bottle(s) is merely the first step of the process. It is important to keep in mind that many diabetics can require the use of 2 different kinds of insulin and as such, can have two different bottles that they may draw insulin from. In some cases, they may need to mix the two types of insulin into a single dose. Therefore, the ability to load two bottles into the device and mechanically move the bottles to choose the proper type of insulin is required. Also, some types of insulin (generally long-acting) require the bottle to be mixed prior to dosing so that the consistency of the insulin is even throughout. Furthermore, it is recommended that the mixing of the bottles be gentle, for shaking the bottle violently or excessively can cause a breakdown in the chemical makeup. In order to maximize efficiency and minimize cost, it proved beneficial to combine the movements of both bottle selection and bottle mixing into one motor-controlled motion. The following concept fulfilled these requirements:

Figure 3: Bottle Mixing Concept

This design is a molded form fit drum which would hold the two different kinds of insulin. The insulin bottles would be stored in a fashion where the bottom of the bottles would be placed towards the center of the drum and the caps would be facing the outside of the drum. This drum will have 180 degrees of rotation which would allow it to mix the insulin before dosing. The motion will also allow for the user to switch between two types of insulin without having to perform any manual action.

This concept was chosen because of the versatility of the design. This design allows the user to have two bottles loaded simultaneously, removing the need to switch bottles when performing a mixed dose. This concept also allows for a thorough, yet gentle mixing of the insulin. Most importantly, this concept has the capability to switch between the two insulin bottles with the same motion that it uses to mix the insulin, limiting the degrees of freedom of the device, making the device less complicated, less prone to breakdown, and more cost effective.

Although not shown, there will be an axis through the center of the drum on which the drum will rotate. The drum will be rotated by the use of a DC motor. The drum may only be physically allowed to turn 180 degrees. As such, the DC motor can be rotated clockwise until it hits a mechanical stop signifying it is in the proper location. By reversing the current, the drum will spin 180 degrees in the opposite direction until hitting another mechanical stop. This will guarantee proper placement of the bottles and still allow the bottles to be mixed. The current sent to the DC Motor will be controlled by the microcontroller.

Syringe Loading

Now that the bottles are properly loaded and mixed, it is necessary to load the syringe. Again, the users of this device may have disabilities that can make accurate placement difficult. Therefore, it was hoped that a guide could be developed to help the user place the syringe in the correct location. Also taken into account was the fact that the syringe will change in length as it is dosed. The following concept was conceived:

Figure 4: Syringe Loading Concept (Top View)

Figure 5: Syringe Loading Concept (Side View)

As shown, there are multiple guides incorporated into this design. The first tapered guide, shown from the top in Figure 4, will help guide the syringe into the proper place laterally. The vertical placement is ensured by keeping the wings of the syringe flush with the base as it is moved back into the device. Finally, the plunger of the syringe is guided into a separate location by a tapered piece. The syringe is then held in place by two clips, spaced at the top and bottom of the syringe cylinder. The area in between allows space for the user's hand to push the syringe in its proper place. This is an entirely external load. This allows for easy access of the user, for the syringe to move up and down, and for the syringe to be removed easily after dosing.

Syringe Dosing

In order to dose the syringe with the user-input insulin volume, a mechanism controlled by the microcontroller is required. In its simplest form, the syringe plunger will be actuated by a drive mechanism controlled by a motor.

A drive screw gear will actuate the plunger. Due to their high degree of accuracy, drive screws are the most common type of drive system used in linear motion control. Specifically, an acme drive screw, which consists of a rotating screw and translating nut, will be used. While they are less accurate than ball screws, they are quiet, low-cost, require less maintenance, have smoother motion, work well in vertical orientations, and provide resistance during and after movement. Since the device utilizes a vertical syringe orientation, ideally needs no maintenance, and requires precise accuracy, the acme drive screw is an appropriate choice.

In selecting a motor to drive the acme screw, two major factors were considered. These factors, ease of motor control via the microcontroller and accurate shaft position control, lent themselves most directly to the use of a stepper motor. Stepper motors are specifically designed to rotate the shaft by a precise amount for each current pulse received. This step resolution is very consistent and permits open-loop applications without sacrificing accuracy. Typically, motor stalls occur when the amount of torque necessary to drive the load at the desired speed is not generated. Unique to stepper motors is the fact that decreasing motor speed actually increases available torque output. In the context of normal motor operations, the dosing of the syringe is not a high-speed application, so enough torque will be available such that stalling should be avoided. However, if a feedback mechanism such as an encoder or potentiometer is desired later on, integration with a stepper will not be a problem. Finally, though servo motors not only match the accuracy of steppers but also have a built-in feedback mechanism, their high cost and complicated controls ruled out their use.

To control the stepper motor, an IC driver will be used. This driver will receive inputs from the microcontroller indicating how many motor steps are required for a specific dose. It will then output the proper current signals to control the motor.

Ultimately, the acme drive screw and stepper motor will allow bi-directional actuation of the plunger. In other words, the plunger will be able to be drawn both backwards and forward. This is an important ability for the removal of bubbles that may be generated in the dosing process. Since it will remain unclear until the device is tested whether slowly drawing the dose will eliminate bubbles, an alternate method must be in place in case this technique fails. This method would involve overdrawing a specific amount of insulin with each dosing. In theory, if any bubbles should form, they will float within this excess volume due to a lower density. With a bi-directionally actuated plunger, this excess volume with bubbles could then be injected back into the bottle before user injection.

Figure 6: Syringe Dosing Concept

User Interface

The user must input the number of insulin units to be injected into the syringe. Thus, an interface must be designed that not only accomplishes this objective but also is accessible to individuals with blindness, deafness, neuropathy, and/or tremors. In addition, the interface must both visually and audibly confirm the proper loading of the insulin bottles and syringe and, subsequently, the input dose volume.

First off, the inputs and outputs of the user interface will be universally controlled by a microcontroller. The desired dose will be input using a rotary dial. A rotary dial will allow rapid scrolling through the 100 discrete dosing amounts (0-100 units). When the user reaches the desired dose, a green pushbutton will be pressed to enter the dose. The microcontroller will be programmed to store this value and initiate a routine to send the appropriate control signals to the stepper motor to initiate dosing. Ultimately, a rotary dial condenses into a single button what a ten-digit keypad or up/down dosing buttons accomplish in several, without the need for Braille to indicate functionality.

Visually, the dose amount is displayed using 5x7 LED matrix displays. Not only is the use of such a display more cost-efficient than using a liquid crystal display (LCD), but it can also be directly interfaced with a microcontroller. Three 5x7 LED matrix displays will be cascaded to display the input dose volume. A built-in ASCII decoder on the display IC allows for the display of any alphanumeric character. The microcontroller will input the 7-bit ASCII code of the desired character to be displayed. Finally, such display features as brightness and blinking can be adjusted to further assist the visually impaired.

Audio output will be generated by a speech synthesizer, which will repeat the dose input back to the user. This synthesizer converts ASCII code for the dose amount from the microcontroller into sound to provide audio feedback to the visually impaired user.

Finally, one additional push-button and two LED's will be used to ease the interaction process. In addition to the green pushbutton previously specified, a red pushbutton will abort the process at any point and reset the system. Finally, a pair of green LED's will let the user know if the bottle and syringe are loaded properly and to begin dosing.

Figure 7: User Interface Concept

Bottle-Syringe Interface

The bottle-syringe interface subproblem was identified as being an important component of the device, but specifics on this part of the device were not fully developed. This was due to a couple of reasons:

This concept was largely dependent on other key subproblems, namely the bottle loading and the syringe loading mechanisms. Factors such as the size and weight of these components would guide steer the concept to either bring the syringe to the bottle or the bottle to the syringe.

Furthermore, the motion was a simple linear motion. To mate the syringe needle and the bottle, a linear motion in a single dimension over a fixed distance was required. Consequently, it was deemed that this would be a relatively simple solution, as there are many ways to drive a linear motion. More complex problems should take priority over this problem.

Integrated Solution

With concept solutions generated for the respective subproblems, these solutions are integrated into a complete system. As seen in Figure 8, the entire device is vertically oriented, with an approximate height of 18 inches and depth between 8 and 10 inches. This depth dimension will be adjusted as decisions are made regarding the position of the DC and stepper motor in the device housing.

The powering of the entire device will be accomplished using 120VAC from a standard electrical outlet. This voltage will need to be stepped-down in order to power the motors, interface, and microcontroller. A commercial power supply will be used to provide the DC voltages needed to power the various components. Filtering via decoupling capacitors will be used to provide the constant DC voltages required and to safeguard against voltage spikes and electromagnetic interference.

The device was ideally conceived for table-top use. In addition, weight estimates at this point do not exceed 20 pounds. Once a definitive housing material is selected as well as the possible addition of counter-weights to balance the device, this weight will be more easily predicted. However, the final weight will be approached with portability of the device kept in mind.

Figure 8: Integrated Solution

Economic Justification

This project was supplied a budget of $2000 by RERC-AMI. As such, the economic feasibility of this concept corresponds to the ability to purchase, build and test the proposed device for less than the designated budget. The following table lists a preliminary list of materials. While it is not complete, a large amount of money remains for additional purposes.

Table 1: Tentative Parts List

Any molding costs come from an estimate that polypropylene will have a cost of $1 per kg.

We will also need microcontroller evaluation and programming boards totaling $258 in cost. As such, the total prototyping cost is $600.22. We also anticipate the need to test our prototype on human subjects. We would like to bring in 20 individuals with at least one of the following disabilities: blindness, deafness, or body tremors. At an industry standard of $20 an hour, we will need $400 to properly test our device in order to confirm that our device is truly compatible with our customer base. Therefore, the current cost of prototyping is approximately $1000 right now, which is well under the allowed budget of $2000.

Note that the values above reflect projected values and may differ significantly from that which was used in constructing the actual prototype.

Conclusion

The process of dosing a syringe requires, among other faculties, considerable amount of manual dexterity and good vision to execute. Disabilities such as low vision or poor motor control can make this routine task cumbersome or impossible. Existing dosing devices fall short of meeting the needs of the hypothetical clients in that they either are not accessible enough to accommodate the disabilities of the clients or they require the use of expensive proprietary needles and medicine bottles. In most cases, these solutions are built entirely around dosing insulin and lack the flexibility to handle other types of medication. Our proposed device will go the distance where others have fallen short and provide accessible syringe dosing for our hypothetical clients, as well as others with disabilities other than those of our clients.

The syringe dosing device has been carefully designed at each step of the dosing process to be as forgiving as possible, accommodating all types of users. Loading a bottle into the device is as simple as loading a cassette tape into a stereo, and the specially designed syringe holding mechanism guides the user's actions to ensure that it is positioned correctly every time. The user interface for selecting the dose requires only a few button presses before the device is on its way dosing the syringe.

With respect to economic aspects, development costs of the product are estimated to be well within our budget. Once an initial prototype of the product is fabricated, we will be able to better identify the needs of the system, fine-tune parameter, and eventually streamline the device to bring the cost of parts and assembly to its absolute minimum.