Independent Handling

Mobile Robotic Drive Units Use Distributed Intelligence to Provide Pick-Pack-and-Ship Solution

How do you turn material handling into material empowerment, allowing them to walk and talk on their own with limited central control? Kiva Systems in Woburn, Mass., builds mobile robotic drive units with distributed intelligence to provide a pick-pack-and-ship solution that increases worker productivity as much as threefold, says Pete Mansfield, engineering fellow hardware systems at Kiva. "The complete system is designed to remove the need for inventory workers to walk or drive around a facility to locate and pick inventory," he explains. "Instead the items come to them."

Along with Raffaello D'Andrea and Peter Wurman, CEO Mick Mountz founded the company in 2003, after working at online grocer Webvan, where fulfillment troubles contributed to its checkout in 2001. D'Andrea was the leader behind Cornell University's championship robotic soccer team, and Wurman was co-director of North Carolina State University's e-commerce program.

Now with approximately 120 employees—almost half of which comprise an engineering and technical staff or electrical, mechanical, quality and computer systems/software/firmware engineers—Kiva builds its mobile robotic drive units as part of a larger integrated material handling solution. "There are currently two drive unit versions differentiated from a marketing perspective by their payload capacity—1,000 lb and 3,000 lb," says Mansfield. "The drive units perform the task of moving inventory stored on mobile shelving—pods—between storage locations and the inventory worker who requires access to the storage location."

Kiva Systems
Zappos.com employs a Kiva Mobile Fulfillment System in its Shepherdsville, Ky. Order-fulfillment operation. The installation includes a dozen operator stations serviced by approximately 70 robotic drive units and more than 3,000 inventory storage pods. Operator stations are seen along the left side of the floor with orange drive units carrying blue inventory-laden pods.

The drive units are autonomous and battery-powered with onboard computing capacity to handle local movement control functions, explains Mansfield. "They operate anywhere within a grid pattern of cells defined on each level of the storage-facility floor and can move between levels on automated lifts," he says. "The drive units view simple adhesive-backed markers placed on the floor in each cell to periodically verify their global location but otherwise stay on course using dead reckoning."

Each drive unit is represented as an autonomous agent in a central control system where path planning and negotiation for grid cell occupancy is handled. Regenerative braking helps to conserve battery power. Battery charging is accomplished via Kiva-designed docking stations employing rapid charging technology from PosiCharge. Drive units sense a need to charge, negotiate charger availability with other drive units and automatically dock with a charger when it's their turn.

"The drive units employ a carefully architected distributed control hierarchy that brings together machine vision, angular position, proximity, angular rate and other sensing to control the drive unit motors during mobility and lifting," explains Mansfield. "The motors are brushless dc for high torque and long life." And Kiva's design employs embedded control. "All internal electronic systems including power supply/distribution and motor driver/control boards are Kiva's proprietary designs," he says.

Kiva uses a Freescale processor with Analog Devices' DSP and rate gyro in its controller board design, and wireless communication on each drive unit is accomplished with off-the-shelf miniPCI radio modules, explains Mansfield.

"Because our drive units are autonomous and there can be hundreds of these at a given site, it would be inconvenient to physically plug into each one for downloading firmware updates," he says. "Instead, we have developed a process for performing updates over-the-air via the wireless communications link. When firmware containing new features is available, it may be downloaded to each drive unit in the system in a matter of minutes requiring little downtime for an individual unit."

Kiva's central management control system relies on an Extricom 802.11-based wireless link for communicating with drive units. "A wireless network is installed as part of our system and allows the central planning software to communicate tasks to the drive units and for drive units to report status," explains Mansfield. Kiva uses HP servers for supporting the central control system. Each operator station features HP station controller computers with ELO touchscreens and Symbol barcode scanners.

Several levels of safety also are built into each Kiva system. "Drive units have onboard obstacle sensing to avoid objects that may have fallen in their path," explains Mansfield. "The area where drive units operate is considered 'inside the machine' and is off-limits to people while the system is running. Human interaction is limited to perimeter zones where an inventory article may be placed onto or retrieved from an inventory pod."

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