ScriptPro’s automated drug dispenser uses servo motors to position a vial at a particular pill cell and dispenses the required number of pills into the vial. One of the four motors, from MicroMo Electronics, Clearwater, Fla. (micromo.com) appears to the left of the orange vial. It drives a 3-in. dia. plastic gear at the base of the cell to dispense pills, one at a time, so they can be counted as they drop into the vial.

An automated drug dispenser handles everything from tablets, capsules, and ointment packages, and up to 200 different drugs. The SP200 from ScriptPro Inc, Mission, Kan., (scriptpro.com) labels filled prescriptions for traceability, and does so with 99.7% accuracy.

The base model, the SP 200, includes of a cabinet that holds an array of 200 pill cells with dispensing chutes. A gantry arm and griper can move a variety of empty pill vials to any of the cells in seconds. At the cell, pills are fed into a chute one at a time so an LED-based sensor can count each one as it drops into the vial. Using a separate cell for each medication eliminates the risk of cross-contamination while a barcode and scanner ensures dispensing and labeling accuracy. A final check by the pharmacist provides quality control.

A design goal was to offer a machine that required no modifications to pharmacies beyond removing store shelves to clear space for the unit. The design team focused on a cell array and robot with a footprint that matched typical pharmacy shelves, and only needed power from a standard wall outlet.

The team also minimized the number of motors. Instead of a motor at each cell, the cells were kept passive. The entire machine uses only four motors: two power the gantry, one controls the gripper that holds vials, and one powers the pill counting and dispensing. “The only moving parts are on the gantry,” says ScriptPro software engineer Bradley Locker.

Despite the size of the SP 200, it needs only four motors to dispense up to 200 different prescriptions, and power comes from a standard wall outlet.

A 3-in. diameter plastic gear at the bottom of each cell assists dispensing the pills. The vial gripper mounts to a pivot arm. Holding the vial to the dispensing chute lets a 1 in. servo-motor-driven gear on the pivot arm meshes with the 3-in. gear. In one motion the gripper positions the vial and triggers dispensing. As the gears turn, they convey pills to a funnel and dispensing chute. A separate mechanism uses the motion of the pivot arm to open the cell door.

Locker says pills in bulk can be quite heavy, so powering the dispenser requires a surprising amount of torque. “Some fairly large, chalky pills are hard to move,” he says. “We wanted a high-torque motor for them, but were concerned about its length because it must also carry an encoder.” The encoder is crucial for accuracy. “We found a small motor with plenty of torque and a gearbox large enough so the motor lasts a long time.”

Turning the gear at the bottom of this cell shifts pills into a counting funnel before they drop into a dispensing chute on the right.

The ScriptPro team extended the SP 200 design to two more machines (recent units have 50 and 100 cells) but spun the concept into several other modules that can be combined to meet various needs. Batch loading provides an answer for pharmacies that need higher output. A handler recounts pills into holding tanks. Pills are then dropped into vials as needed. “The handler is an add-on to the SP 200 family, so the handler has to be compact,” says Locker. That sent the team looking for more motors. “We found a MicroMo motor small enough to fit two inside this small handler that then fits into an existing machine,” says Locker.