Originally Published July 2000

Automated Cart Dispenses Medication

The lightweight unit incorporates a gantry robot.

Jodi Triplett

Wasted medication, prescription errors, and inefficient or inaccurate completion of charts can severely impair the effectiveness of healthcare facilities. Such mistakes also increase the cost of care, both for the facilities and their patients. Pearson Medication Technologies (PMT; Alexandria, LA) has developed a portable, automatic medication delivery cart to address these concerns. The Rx⁵ cart dispenses and charges for pills one at a time, eliminating the cost of unused medication. The cart also uses an automated system for drug orders to prevent prescription errors caused by illegible handwriting. Administration and documentation are also fully automated, diminishing the estimated two to three hours per shift that nurses spend to keep manual accounts of administered medications. With these advantages, the Rx⁵ cart will reportedly decrease the cost of distributing medication while reducing dispensing errors in healthcare institutions.

Pearson's automated cart, with robot inside, delivers and charges for pills one at a time.

The cart had several stringent design parameters, including specific weight, mobility, and power requirements. The most demanding component, however, was the pick-and-place mechanism used for pill dispensing.

Faster, Error-Free Medication Delivery

The medication cart as a whole was designed to be lightweight so that the nursing staff would be able to push it easily. Structurally, this meant that the robotic pick-and-place mechanism had to be very light. It also needed to be quick. "A nurse administers four to five pills a minute, and we thought it would be nice if our unit could do it faster and without mistakes," says PMT's chief design engineer Dennis Murdock. The pill picker required three-axis linear motion, a vacuum and bar code reader with 0.00003-in. positioning accuracy to cover the pill tray, and sufficient horizontal and vertical range to pick up a pill and transport it to the delivery elevator. Since the cart is mobile, all mechanisms had to run on dc current. PMT also specified a 10-year bearing life for the unit.

The three-axis gantry robot from Rexroth Star weighs just 35 lb and has a projected service life of more than 10 years.

These requirements proved to be too demanding for PMT to overcome alone. One initial unit designed by the company's engineers came equipped with off-the-shelf linear bearings, but it proved to be an expensive disappointment. The slow and noisy robot had a huge drive, weighed 50 to 60 lb, consumed 10 A, and cost $10,000. It was at this point that PMT turned to linear motion specialist Rexroth Star (Charlotte, NC) for help.

Pill Picker Requires Three-Axis Linear Motion

Rexroth Star provided PMT with a three-axis gantry robot. The integrated solution was based on the company's lightweight Super Structure elements. The 40 x 40-cm profiles and modular connectors enabled PMT engineers to build a rigid frame within a 36 x 24-in. footprint. Rexroth Star's Bail Rail systems with aluminum runner blocks were selected for their small size and light weight. The x-axis structure is a rectangular frame with a leadscrew on one side and aluminum channel with guide rollers on the other. A MiniCompact slide mounted on the runner block of the y-axis gantry provides the z-axis motion. The slide has a stainless-steel leadscrew with a self-lubricating acetal nut for smooth, low-friction operation.

The Rexroth Star robot weighs 35 lb, consumes 2 A, and costs approximately $3000. The latest version of the Rx⁵ delivers 12 pills a minute, and runs quietly. "We had it in a nursing home and the patients didn't even know it was running. You'd just hear the pills go plop," reports Murdock. The projected service life of the unit is more than 10 years.

The carts are currently targeted to debut in nursing homes in Louisiana, PMT's home state. For the national rollout, the company will offer a range of patient ID options to comply with varying state laws. A stationary model for hospitals is also being planned. All Rx⁵ carts will automatically deliver and charge for pills one at a time, and all will incorporate the compact, quiet Rexroth Star gantry robot.

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