Concept Selection

Introduction

After concepts for the various subproblems were generated, the group compared the concepts to eachother and determined which concept would be persued for the project. In some cases, the group used a rating system to score each of the concepts and chose to go with the concept that was rated the highest. In other cases, the group simply discussed the pros and cons of each concept and decided on the final concept by group concensus. This document contains the following sections:

• Description of Competitive Concepts
  • Bottle Loading
  • Bottle Mixing
  • Syringe Loading
  • Syringe Dosing
  • User Interface
• Economic Analysis
• Justification of Final Design(s)
  • Bottle Containment and Mixing
  • Bottle Loading
  • Syringe Loading
  • Syringe Dosing
  • User Interface
• Final Design Concept Sketch
• Preliminary Bill of Materials

Description of Competitive Concepts

Bottle Loading

In order for the user to obtain a properly dosed syringe, the first step is to securely load the bottle. The design should be easily accessible to the user, both while loading the bottle and later unloading it.

Claw

One possible concept would grip the bottle by a spring-loaded claw that holds the bottle at the neck. As the bottle is inserted into the device the bottom will physically activate the mechanism. Once the bottle is pushed all the way down, the pivot will then swing into place, holding the bottle at the neck. Then to release the pivot, a release button could be pressed which would cause the pivot to return to its normal position, popping the bottle out so it can be removed easily.

Flexible Clips

Another solution would involve the bottle being held in place by clips that would wrap around the lower half of the bottle and the neck of the bottle. The bottle would snap into these form-retaining clips. Since the clip that goes around the neck would have a smaller diameter, it would help ensure that the bottle is inserted correctly.

Molded Form

Similar to the clip design, a form fit method consists of a bottle-shaped molding which would require the user to force the bottle into the molding. The molding would be composed of a material which would allow for strong gripping of the bottle, preventing slipping. There would be finger grooves in the foam on the sides of the bottle that would allow the user to remove it.

Spring Loaded Latch

Another possible concept would require a person to place the bottle with the cap pointed down into the device. As the bottle is pushed further into the device, it will activate a switch, resulting in a spring loaded latch encircling the neck of the bottle, holding it firmly in place.

Bottle Caddy

The next idea is an external foam caddy which would require the bottle to be inserted into the caddy, and then the caddy being inserted into the device. This figure demonstrates how the caddy incorporates the form fit method described above. The caddy would ensure that the bottle is inserted correctly.

Enclosure with Hinged Door

The final, promising concept incorporates a hinged door that would drop from the device at approximately a 45 degree angle. The door would be curved in the shape of the bottle. To load the bottle into the open door, the user drops the bottle into the door, and the angle and shape of the door allows the bottle to slide into the proper position. If the bottle is placed correctly, the door will shut completely, locking in place through the use of a spring-loaded latch. Correct placement is ensured by the form of the bottle being molded into the back of the cylinder into which the door is closing. If the bottle is upside down, the door will not close.

Bottle Mixing

Any design should have some ability to mix the bottles in order to prepare the insulin properly for injection. A capability to lower the bottles is a possible advantage because the bottles may need to be lowered in order to access the syringe.

Rotating Drum

The first concept 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 clear and cloudy insulin without having to perform any manual action.

Parallel Orientation with Mixing Oscillation

Another possibility is a device that would store two insulin bottles side by side. The two adjacent bottles will be positioned with the caps facing downward. The mold could oscillate translationally, either horizontally or vertically, in order to sufficiently mix the insulin. The vertical movement could also be used to connect the bottle to the syringe in order to allow dosing. The translational motion is convenient because it again allows for switching bottles for mixed dosing without the user having to perform any manual action.

Parallel Orientation with Bottle Rotation

A similar concept would again position the bottles side by side with the caps facing downward. Located in-between the two bottles would be a wheel positioned horizontally, maintaining contact with the sides of both bottles. As the wheel was driven by a motor, the bottles would spin in place, properly mixing the insulin. Translational movement of the bottle mold could again be used to switch bottles for mixed dosing without the user having to perform any manual action.

Revolving Bottle

Our final two concepts are variations on the same general idea. The common thread between the two is that the bottles will be dropped into separate holes of a cylinder shape with the caps facing downward. The mixing of the bottles would be carried out by rotating the cylinders, thus rotating the bottles contained within. The rotation could be used to switch bottles for mixed dosing without the user having to perform any manual action.

The variation on this concept changes the method for mixing the bottles. Instead of the cylinder moving and the bottles remaining stationary in their holes, the bottles would be rotated inside the cylinders by a motor-driven belt.

Syringe Loading

For the design of the mechanism to hold and secure the syringe during the process of needle insertion and syringe dosing, several concepts were generated. The following is a presentation of the feasible approaches to securing the syringe.

Form Fit Approaches

Clip

Several semi-circular clips secure the syringe by attaching the barrel of the syringe at various points. At the end of the clips, angled tabs help to guide the syringe into the correct position. The clips would be composed of some flexible material such as thin metal or plastic. They would attach to the syringe base either by an adhesive or by a counter-sunk fastener securing the clip at the center.

Drop-in Cylinder

Instead of having the user insert the syringe from the side, the user would drop the syringe into a molded cylinder. The opening of the cylinder would be tapered to help guide the user's movement until the syringe could be safely released and fall into place.

Self-Closing Latch

The syringe would be loaded in a manner similar to that of the clips, however the securing mechanism would be different. As the syringe is inserted, the barrel makes contact with a lever arm in the center of the mechanism. As the lever arm rotates about a fixed axis, the other part of the lever arm swings into place, securing the syringe.

Molded Form

A block of material is either molded or milled such that it contains a cavity that conforms to the shape of the syringe, specifically to that of the barrel and the wings at the end of the barrel near the plunger. After the syringe in loaded, the tight fit of the mold keeps the syringe from moving.

Force Fit Approaches

Spring loaded latch

A mechanism inspired by the rings found in a three ring binder is used to hold the syringe in place. Due to some spring-like action, the clasp wants to naturally be in the closed position. When the syringe is loaded, the clasp is forced open through a mechanism initiated by the user or the device. When the syringe is in the proper location, a mechanism restraining the tension of the clasp is released and the clasp snaps shut to secure the syringe.

Spring Loaded Ball Bearings

A form would be made with a cross-section resembling a half-pipe. Embedded in the side of the form would be a series of pairs of spring-loaded ball bearings secured in the surface of the form by some retaining crown. When the syringe is loaded, the barrel of the syringe pushes the ball bearings below the surface of the form, allowing the syringe to be fully seated in the form. After the syringe has moved past the ball bearings, they shift back out and apply compression on the syringe barrel, holding it in place.

Undersized Form

Similar to the molded form described under Form Fit, a piece of material would be molded or milled such that it loosely conforms to the shape of the syringe. The inside of the shaped form would be lined with some compressible material similar to foam rubber. Once the syringe has been inserted, the foam rubber conforms to the shape of the syringe, holding it in place through compression and friction.

Syringe Dosing

Screw

A rotational motor drives a screw gear that actuates the plunger.

Linear Motor

A linear motor is effectively a rotational motor that has been unwound.

Belt

A rotational motor drives a belt to which the plunger is attached.

Winch

Rotational motor(s) drive winches. One winch drives the plunger forward, and the other winch drives it backward.

Rack and Pinion

A rotational motor drives a pinion connected to a rack that actuates the plunger.

Rotational Motors

AC Servo

Alternating current driven motor. Servo motors do not require feedback loops from encoders or other means because they have internal feedback mechanisms.

DC Servo

Direct current driven motor. Servo motors do not require feedback loops from encoders or other means because they have internal feedback mechanisms.

Stepper Motor

Motor rotates shaft in incremental steps with DC pulses.

User Interface

The user must input the number of insulin units injected into the syringe. Thus, an interface must be designed that not only accomplishes this objective, but is accessible to individuals with blindness, deafness, neuropathy, and tremors.

A voice-recognition system could be implemented to allow hands-free entry of the dosage. Voice-recognition hardware and software would be programmed to respond to specific voice commands to initiate the dosing process and to specify the dose amount. Another interface concept would utilize a ten-digit (0-9) keypad. The surface of the keys would have the Braille equivalent of the number to assist the blind. In addition, the size and spacing of the buttons would be considered to efficiently accommodate blindness, tremors, and other disabilities.

Also, a two-button interface in which one button scrolled through increasing dose amounts while the other decremented the amount could be used. Again, Braille could indicate the functionality of each button, while simply an up and down arrow would suffice for those visually enabled.

Finally, a rotary dial could be used to scroll through each discrete dose amount in the design range. For both the rotary dial and ten-digit keypad input, a visual and audio output must be dually provided to accommodate both the deaf and blind, respectively. Options for visual output include 7-segment LED displays, LED matrix displays, or a liquid crystal display (LCD). Audio options include the output from a voice-recognition system or an audio controller that converts the dose amount into an audio output using a speaker.

Economic Analysis

Production Quantities

There are approximately 16 million people in the United States that are afflicted with diabetes. Of these, approximately 7.5% have Type I diabetes, which means that they are insulin dependant. This leaves a general market of 1.2 million people who require daily doses of insulin. However, our product is geared towards those who are disabled or afflicted with long-term symptoms of diabetes such as blindness and tremors. We assume that a majority of these people are in older age brackets, and, therefore, we would say about a quarter of the 1.2 million Type I diabetics would have an immediate interest in our product. As a result, we have set a production quantity goal of 300,000 units.

Production Processes

At present, we anticipate very few production processes. The outer casing and bottle drum will both be produced through injection molding. We will most likely require some machining in order to produce a metallic frame on which we can mount the bottle drum. In order to assemble the electronic parts, some circuit board printing and soldering will be necessary. Finally, the individual parts of the device will need to be hand assembled.

Development Costs

It is estimated that the number of man-hours required next semester will be 6 hours a week per team member. The salary rate for these five engineers will be $20 an hour.

16 weeks x (30 hours / week) x ($20 / hour) = $9600

There will also be costs associated with acquiring material for prototyping. We anticipate the cost of prototyping to be no more than $1000. This money can be broken down as follows:

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 $30 an hour, we will need $600 to properly test our device in order to confirm that our device is truly compatible with our customer base.

Total Development Cost = $9600 + $1000 + $600 = $11200

Please note that the above equation assumes that you have to pay for the engineers to develop the product. In our situation, the labor was free!

Justification of Final Design(s)

Bottle Containment and Mixing

The drum concept was selected as the final concept for bottle containment. This concept was chosen because of the versatility of the design. This design made it easy for the user to load the bottle, which fulfills one of the main needs of our customers. This concept also allows for thorough mixing of the insulin. Furthermore, this concept has capability to switch between two insulin types with the same motion that it uses to mix the insulin, limiting the degrees of freedom of the device, making the device less complicated, and thus less prone to breakdown. The molding concepts were rejected because they require the user to insert the bottle into a precise mold which would be hard to do if they have Parkinson's disease or are blind. It was determined that both of the revolver concepts would not provide adequate mixing of the insulin in the bottles and as such would be dangerous to the user.

Bottle Loading

The spring-loaded door was chosen as the final concept for loading the bottle. The concept was chosen because it incorporates an easy method for loading the bottle, allowing those who are blind or have tremors to avoid having to make precise movements when loading the bottle. The shape and angle of the door allows the bottle to settle into the correct position. This design also allowed for an easy way to ensure the bottle is loaded correctly. This is an important factor because it may be difficult for those that are blind or have limited sensation in their hands to determine if they are loading the bottle upside down. Other concepts had their downfalls. The caddy was rejected because having a removable piece of the device may result in the piece being lost, resulting in loss of function of the device. It was determined that the clip design may be an unstable way of holding the bottle because the clips may become worn-out from the constant use. It may also prove difficult to load the bottle into such a precise location. The spring-loaded pivot seemed to also be an insecure mechanism for holding the device.

These two concepts were then combined to form our final concept for bottle loading, mixing, and switching. As a result, the drum will have two doors that open away from the device and remain open at a 45 degree angle; however, only one door could be open at anytime. The back of the cylinder chamber will be the shape of the bottle to ensure the bottle is loaded correctly. The door will lock using a spring-loaded mechanism which will require a release in order to be reopened. The drum will be rotated most likely by using a servo motor, and as such will be isolated to only 180 degrees of movement, but will allow for precise alignment of the bottles. Other possibilities for drum rotation could be a stepper motor or a rack and pinion system.

Syringe Loading

After rigorous deliberation between group members, the following concept was selected for securing the syringe during syringe movement and dosing. It is a hybrid concept created by combining the molded form fit with flexible clips.

The premise of the concept is as follows: The user grasps the syringe at the barrel with the needle pointing up and the needle cover oriented away from the device (needle cover not shown in drawing). The user places the syringe at the front of the form, with the syringe wings resting flush on the supporting surface. While keeping the wings flush with the surface, the syringe slides back along the surface into several clips that will help to hold the syringe in place. The v-shape of the surface assists the user in moving the syringe into the proper location. The wings of the syringe fit snuggly into a slot created by the lowest clip and the wing supporting surface, also helping to support the syringe from tilting out away from the device. As the user slides the syringe body into place, the plunger is also being positioned into a form, separate from that which holds the body of the syringe, which will be used to push and pull the syringe during syringe dosing and possibly during bubble removal.

Syringe Dosing

It appears the best method for plunger actuation is a drive screw gear. Drive screws are the most common type of drive system used in linear motor control, renown for their high degree of accuracy. There are three basic types of drives: leadscrews, ballscrews, and acme screws.

Leadscrews move with the object they are actuating. Ballscrews and acme screws consist of a rotating screw and translating nut. Ballscrews differ from acme screws in that ballscrews contain ball bearings in the nut. Although they are highly accurate in position, very efficient, and very reliable, ballscrews are high cost. Acme screws will probably be more appropriate for the plunger actuation. While they are less efficient (25-60 % vs. 90%) and less accurate than ballscrews, they are lower cost, require less maintenance, quieter, have smoother motion, work well in vertical orientations, and they provide resistance during and after movement.

Linear motors are primarily used for faster motions. While they are simpler in their generation of motion, they require feedback, usually from an encoder, to regulate their position. Linear motors will not be used primarily because of their high cost and because their reliability can be greatly affected by the presence of dirt and dust in the track.

The belt design will not be used in this design because of the unbalanced moment on the flywheel, as is evident in the concept description diagram. This will accentuate the usual problems encountered in belt drives: slippage, stretching, and a difficulty in carrying loads.

The winch concept invokes similar problems to the belt concept. In addition, there is increasing complexity/cost with the requirement of two motors or the coupling of motion to the two independent drives.

The rack and pinion is a cost effective design alternative to the drive screw design. Motion is generally less precise than with the screw drive.

Stepper motors are the best rotational motion source for syringe dosing. AC and DC servo motors are more expensive than stepper motors. Stepper motors are better at providing high torque at low speeds. The microcontroller provides a flexible means to control the motion. Unlike the servo motors, stepper motors can be operated in the open loop mode. The microcontroller also has the capability to incorporate feedback if needed.

User Interface

Of each subsystem in the device, the user interface offers the most latitude in design constraints. Because a microcontroller-based interface was initially decided upon, flexibility in the various dosing input and output components exists. Because the costs of such electrical components as push-buttons, switches, and LED's are relatively inexpensive, as well as universally accommodated by a microcontroller, subsequent changes in the interface itself would present little concern.

Nonetheless, the current interface solution consists of a rotary dial dosage input. A rotary dial allows rapid scrolling through the 100 discrete dosing (0-100 insulin units) amounts. The dial condenses into a single button what the ten-digit keypad and up/down accomplish in several, without the need for additional Braille to indicate functionality. Visually, the dose amount will be displayed using 5x7 LED matrix displays. Such displays are significantly cheaper than an LCD, and can display alphanumeric characteristics as well. Audio output will be generated by a speech synthesizer, which will repeat the dose input back to the user. Finally, a pair of push-buttons and LED's will be used to ease the interaction process. A green push-button will enter the dose after the rotary dial is used to select the amount, while a red push-button 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, respectively, and to begin dosing.

Final Design Concept Sketch

Preliminary Bill of Materials

*Assembly Labor Rate is $20/hr*

Assumptions