Capstone Design Project: Automated Pill Counter
Background
Pharmacists are healthcare professionals that are required to regularly count highly controlled substances due to regulatory and safety reasons. More specifically, they are required to report the number of Schedule II pills in the entire pharmacy to the state every 10 days. This process, however, is time consuming, prone to human error, and detracts from patient care.
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MedFinder, a small Boston based start up, hopes to tackle this issue by developing a fully automated pill counting machine that can open a pill bottle, dump the contents, count the pills, refill the bottle, and close it with minimal human operation. Through the Mechanical Engineering Department at Northeastern University, I worked with 4 other engineering students to develop a prototype for this machine, with my focus on the lead screw mechanism that actuates bottle opening/closing and pill dumping
Objectives, Constraints, & Skills Applied
Objectives
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Design and prototype a machine that automates pill counting with minimal human operation
Constraints
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The machine must be able to account for the tamper proof lock on a pill bottle.
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The machine must be able to open and close the pill bottle without human operation
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The machine must be able to accurately count the pills​
Skills Applied
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SolidWorks 3D Modeling
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Electronics & Firmware Integration
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Motor Control
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Full Subsystem Ownership
Full Assembly Overview
Before discussing what I specifically worked on, we will first take a look at the system as a whole.
Functionality & Assembly Overview
The process begins by placing the bottle on the scale, so the claw mechanism can clamp onto it and lift it up to the cap clamp. This secondary clamp holds onto the cap while the claw mechanism provides and upwards force and torque to remove the cap from the tamper proof lock and hold it in place. It then moves out of the way so the claw mechanism can continue moving upward, where it eventually contacts a set of brackets that tip the whole claw into a funnel so the pills can dump. An optical sensor counts each pill and then they wait at the bottom for the claw to move back to its starting point. A rack and pinion then place the pills back in the bottle, and then the claw mechanism reengages with the cap clamp to place the cap back on the bottle.
Lead Screw Assembly
My main focus on this project was designing and managing the lead screw assembly, which controls the vertical movement of the claw mechanism and cap clamp and provides the general structure of the whole assembly. Both of these subassemblies are supported with 4 carriages each, and the structure also contains a variety of aligning and positioning features for the assembly process. The vertical movement for the claw mechanism is vital to not only apply the upwards force for uncapping, but also to dump the pills, and the upwards movement for the cap clamp is necessary to provide clearance for the latter action.
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Claw Mechanism
The claw works similar to a drill chuck, so that when an internal gear is spun, 4 silicon grips in each corner converge at the center to grip the contents. This was necessary to account for a variety of bottle sizes and shapes since the center of the bottle will always be coaxial with the center of the claw. The entire mechanism also spins about its center so that the bottle can be capped/uncapped and the pills can be agitated during dumping.
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Cap Clamp
The cap clamp is made up of a bilateral lead screw and 2 guide rails that clamp the edges of the bottle cap with 2 silicon grips. This holds the cap in place while the claw mechanism is spinning to cap/uncap the bottle. This also keep the cap in place while the machine is performing a variety of processes, such as dumping and counting.
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Dumping Linkage
The claw mechanism sits on a plate that is connected to a pair of 4 bar linkages, which are then connected to the lead screw and carriages. This mechanism supports the claw during the capping/uncapping and also actuates dumping when it contacts the stationary brackets. Once the direction of the lead screw reverses, the linkage tips back to its original position.
Optical Counter
The optical counter begins with a hopper mechanism, which uses a funnel and vibration motors to direct pills to fall one by one into a chute with beam break sensors that optically count pills. The pills are then held in an enclosure at the bottom attached to a rack an pinion. Once the claw mechanism positions the bottle back in its original location, the pills are brought the bottle and they fall back in.
