Embedded Files
Complete Device Annotated and Described Below
Linear Actuator
The final design of this project is a device built around a Mjunit 200 mm stroke belt-driven linear actuator (Figure 2). The linear actuator is powered by a 2.8A NEMA 23 Stepper Motor and a microstepper driver that allows it to operate anywhere from fine, slow speed motion to fast, full-stroke motion up to 1000 mm/s.
Slide Platform
Mounted to the carriage of the linear actuator is a slide platform (Figure 3) with a recessed slot to securely hold microscope slides during the smear motion. This slot additionally features a round boss with a FlexForce A301 force sensor attached to control the pressure of the smear.
Figure 1. CAD of Final Design
Linear Actuator and Slide Platform
Smearing Mechanism
Figure 3: Slide Platform
Figure 2. Belt-driven Linear Actuator
The magazine (Figure 5) itself was fabricated from acrylic and contains two slits slightly larger than an individual blade in the back and front of the bottom-most blade. The two side walls of the magazine were toleranced so they act as linear bearings, ensuring the blades move straight and smoothly out of the magazine.
An Actuonix PQ12-R linear servo (Figure 13) behind the magazine pushes the bottom blade from the back slit out through the front slit 15 mm. The push blade attached to the end of the servo shaft was made of half a PerfectSmear blade due to its lightweight, rigidity, and smooth surface.
The rollers were created using a 3D-printed rubbery material known as TangoPlus that provide friction against the blades. The bottom roller is connected to a pulley system powered by a RobotGeek continuous rotation servo with 4.5 kg*cm of stall torque, while the top roller is spring-loaded to provide constant friction between the blade and the rollers.
Additionally, the entire assembly is mounted to the end of the Mjunit linear actuator and connected to a powerful LewanSoul LD-25MG 180° servo capable of 25 kg·cm of torque. To dispose of soiled blades, the servo pans or rotates 45° outboard where the rollers then eject the blade into a bio-waste container and the entire assembly rotates back to the original
Drying Unit
The drying unit (Figure 9) consists of a 12V fan that is mounted 30 mm above the microscope slide as it passes below it. Drying time was experimentally determined to be 2 minutes and was set to be the default duration.
Smearing Mechanism
The smearing assembly consists of an acrylic magazine loaded with 72 Diamond PerfectSmear™ polystyrene blades (Figure 4) that loads into a dispensing mechanism that pushes each blade out one by one. The mechanism consists of a push-plate that initiates the dispensing motion and a motor-driven roller meshed with a spring-loaded roller that rolls the blades out with a constant grip. The assembly is mounted on a platform connected to a servo motor that allows the spent smearing blades to be ejected into a sharps container for disposal.
Figure 4: PerfectSmear Figure 5: Magazine Figure 6: Linear Servo Pusher
Drying Unit
Figure 7. Smearing Unit Position on Device Figure 8. Annotated Smearing Unit
Electronics
Figure 9: Drying Unit
Electronics
The blood smear device is controlled by a Beaglebone Black (BBB) Wireless microcontroller board to drive all the motors with pulse width modulation. The BBB runs on Debian Linux with Python coding in all the routines. Connected to the BBB is a 7” LCD screen which the user can use to select different hematocrit levels with preset smearing speeds. The graphical user interface (GUI) also has prompts for operators to load slides and dispense blood.
To reduce the wiring and potential electrical hazards, the team created a PCB. The PCB was created using the software of ExpressPCB and ordered through the same company. Figure 10 shows a schematic of the PCB. The final product with all wire neatly placed within the electronics box is shown in Figure 11.
Figure 10: PCB Schematic Figure 11: Electronics Enclosure
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