Main Body & Slider - Main chassis of attachment. Provides sturdy base for attaching the electronics and syringe to.
Rack & Pinion Gears - Converts rotational motion of the stepper motor into linear motion of the syringe plunger.
Rotary Encoder - Allows the position of the syringe plunger to be calculated, since the stepper motor can slip if the plunger reaches its maximum position.
Stepper Motor - Provides precise rotational input to the rack and pinion mechanism.
Battery Holder - Stores 4x AAA batteries to provide power to the electronics.
Arduino Pro Mini - Small microcontroller to provide user interface and control stepper motor.
LCD Screen - Display for user interface.
Slots & Clips - Quick and easy way to insert syringe into the attachment and keep it secure.
Not included in CAD model: Buttons and Potentiometer for user input Stepper motor driver board
Comments
Pros: - This design lets the user specify an exact volume to be delivered, by using the user interface to calibrate the attachment to the syringe and input their desired dosage. - The combination of the stepper motor, encoder and rack & pinion components allows the user to manually move the plunger in order to perform a calibration without the system losing track of the plunger's position, before the stepper motor can take over to deliver an accurate volume. - The syringe can be quickly inserted into the attachment with very little hassle due to the snap-fit design of the syringe holders, and it is guaranteed to be held secure by the slots designed to fit the shape of the syringe and plunger grips.
Cons: - Due to the relatively large size of the electronics compared to the syringe, the attachment has turned out to be larger than expected and so may prove to be cumbersome to use. - The arduino microcontroller may have difficulty with running a stepper motor, monitoring position using the encoder, taking user input, and providing a user interface through the LCD display.
Next Steps
Since the electronics will prove to be relatively disadvantageous for making a lightweight attachment due to their bulky size, a slightly different design will be used in the next steps to minimise the size of the attachment, giving a more ergonomic feel to its use. The new design will aim to provide increased accuracy to syringes that are inherently inaccurate due to their size, while using a similar method to the current technique of using a syringe in order to maintain the familiarity of their use.
By integrating a digital caliper style system into the current design for the syringe attachment and removing the existing electronics from the design, the attachment will be able to display the position of the plunger and let the user calibrate the electronics to any desired value. Possible methods of use from this design could be:
Setting the zero point to be the position at which the syringe is empty. This mimics the current method of using a syringe and lets the user take in an amount of liquid that is more than their desired volume, remove air bubbles, then set the position more accurately than is possible without the attachment
Filling the syringe, removing air bubbles, then setting the zero point at any position. This means multiple dosages of varying volumes can be made with one filling of the syringe, since the zero point can be set again after each dosage.