Brushless Servo Motors Speed Pharmaceutical Dispensing
Modular Design And Efficient, High-Torque Servo Motors Write The Prescription For Success
Lines at your local pharmacy will be a thing of the past, if ScriptPro has anything to say about it. The company, based out of Mission, Kansas, has developed automated prescription dispensing systems that can handle everything from tablets and capsules to packages of ointments, offering complete labeling and traceability, along with 99.7% counting accuracy. Leveraging high-efficiency, high-torque servo motors from MICROMO, the ScriptPro family of dispensing robots is fast, robust, compact, and efficient enough to operate off of a single wall plug.
Designing For Performance
The average pharmacy dispenses many hundreds of prescriptions, creating customer delays and presenting constant staffing challenges. In an effort to streamline the process, ScriptPro has built a line of machines designed to store and automatically dispense everything from pills to unit-of-use medications like ointments and lotions. The base model, the SP 200, consists of a cabinet enclosing an array of 200 specially designed pill cells with dispensing chutes. A gantry arm fitted with a gripper can hold and convey a variety of pill vials to any of the cells in seconds. At the cell, a singulation system feeds pills into the chute, where an LED-based sensor counts each pill as it drops into the vial. The use of separate cells for each medication eliminates the risk of cross-contamination and a barcode/scanner system ensures accuracy of dispensing and labeling; a final check by the pharmacist provides quality control.
When the ScriptPro design team set out to design the SP 200, the goal was to offer a machine that required no pharmacy modifications beyond simply replacing the existing shelves with the unit. The engineers focused on developing a cell array and robot with a footprint that matched that of a typical pharmacy shelving system. Equally as important was making the unit wall plug compatible. That meant focusing on efficiency throughout the design. Reliability and robustness were the final requirements, allowing ScriptPro to confidently offer 24/7 customer service.
For starters, the engineering team minimized the number of motors required for the machine. Instead of designing a pill dispensing system with a motor for each cell, they left the cells passive. The entire machine in fact uses only four: two to power the gantry, one to control the gripper that holds the pill vial, and one to power the pill singulation and dispensing process. “Basically the only moving parts are on the gantry system,” says Bradley Lockard, software engineer at ScriptPro.
Dispensing the pills is powered by a flat, plastic gear about 3 inches in diameter that lies at the bottom of each cell. The gripper that holds the vial is on a pivot arm. When the vial is held up to the dispensing chute, a 1 inch servo motor-driven gear on the pivot arm simultaneously interfaces with the plastic gear. In one motion the gripper positions the vial and triggers dispensing process. As the plastic gear turns, it conveys the pills into a singulation funnel that ends in the dispensing chute. An LED-based sensor counts each pill as it passes, stopping at the right quantity number with 99.7% accuracy. A separate actuator uses the motion of the pivot arm to open the cell door.
Powering the dispensing gear requires a surprising amount of torque. Primarily consisting of a small amount of active ingredients held together by inert binders, pills can be quite heavy in bulk. “We actually have some fairly large, chalky pills that are just really hard to move around,” says Lockard. “We like to have a nice torquey motor for them but we were kind of worried about the length of the motor because we have to have an encoder.” The encoder is crucial to maintaining accuracy numbers, so it was essential that the motor fit. “We were able to find a nice small motor that had plenty of torque. We also made the decision to go with brushed instead of brushless [motors] because the brushed had much bigger lifespans. The gearbox is large enough that the motor lasts a long time. I haven't heard of those motors really ever going bad.”
In the best spirit of design, the ScriptPro team has not only extended the SP 200 design to a family of dispensing machines (the SP 100 and SP 50, with 100 cells and 50 cells, respectively), but they've also spun the concept into several other modules that can be combined to meet various needs.
Batch loading provides an answer for pharmacies that require higher output. An automatic handling system pre-counts standard numbers of pills into holding tanks that are then dumped into pill vials on demand. One servo motor powers the dispensing process and the other transfers pills into the vial. "Because the automatic handling system was designed as an add-on to the SP 200 family, it had to remain compact", Lockard says. That sent them looking for more motors.
“Luckily we were able to get a servo motor from MICROMO with a small enough form factor that we can have two of the motors inside this small device that we can fit into an existing machine,” says Lockard. "It wasn’t just size that was a factor", he notes. "Power consumption was also a concern. Our biggest systems can have up to 14 of the automated systems along with the rest of the robot running, so we need to have fairly efficient motors to be doing all of this motion at the same time.”
For non-tablet and capsule prescriptions like bottles of fluid or tubes of ointment, the SP Unit Dispenser (SPUD) delivers unit-of-use packages to an automated handling system via a system of conveyors. This machine can be combined with the base dispensing unit to provide comprehensive capabilities.
To serve the biggest mail-order pharmacies, ScriptPro integrates all of the capabilities into an industrial unit for high volume operation, the Industrial Control Center model (ICC). "When one of the motors in the machine’s gripper unit needed to be a different size from the standard design, it wasn’t a hardship", Lockard says. “We actually found a motor that had a whole lot of the same characteristics and just a slightly different form factor that worked for us, so we were able to use all the rest of the same basic pieces.”
Indeed, modular design pays off big in production, reducing design requirements and minimizing dollars tied up in inventory. The ScriptPro design team kept this philosophy in mind when working on an alternative to the collator, a pick-and-place vial-handling module in which a motor and screw-lead design move vials to one of 14 different locations. “We like to use the same parts as often as we can,” says Lockard. “One of the motors that we used to move part of our mechanism in the screw drive was actually the same one that we use in the x-y gantry system. It was nice because we could just buy the same motor with a little bit different head and have it in two fairly different applications in our system.”
Efficiency, size, speed, and reliability; careful attention to design combined with quality components from MICROMO have made ScriptPro the choice in pharmacy automation.