Optical RTLS: One Innovation, Many Solutions

Optical RTLS: One Innovation, Many Solutions

By Richard H. Ungerbuehler, Sky-Trax Inc.

A single innovation can enable solutions to a wide range of practical problems. Optical RTLS™, a new technology utilizing optical sensors as the basis for real-time location systems, is helping to transform indoor logistics by solving many of its most difficult problems.

The Global Positioning System (GPS) has been a notable modern example of a single innovation enabling many solutions. GPS has brought about sweeping changes in recreation, surveying, automotive, travel, and logistics industries. For example, real-time tracking of transport ships and overland freight carriers using GPS has improved global supply chain visibility and allowed tighter control of shipments than was possible before GPS’ development. Unfortunately, GPS has not been suitable for indoor use due to radio wave reflection and absorption by building structure and contents. This has left indoor utility vehicles – especially five million indoor forklift trucks - without an equivalent tracking capability.

A broad variety of technologies and integrated solutions based on mechanical, ultrasonic, radio and optical methods, aim toward solving the problem of determining the real-time location of objects inside buildings. Any technology that hopes to meet the needs of an indoor position determination system must offer five critical features: reliable wide-area coverage in a broad variety of facilities; adaptability to dynamically changing environments, highly accurate position and heading data that is visible in real-time, operation on board a wide variety of vehicles, and cost effectiveness.

One Innovation

In 2004, Sky-Trax Inc. developed a position and orientation determination system based on machine vision technology and utilizing fixed-position optical markers installed in the ceiling, away from the facility floor. A US patent granted to Sky-Trax in December 2010 protects the Optical Real-Time Location System technology.

The Sky-Trax Optical RTLS system determines the X-Y location and orientation of any object to which a specialized optical sensor attaches. Offering out-of-the-box precision of a few inches for positioning, and a few degrees for heading, the system is suitable for tracking utility and material handling vehicles inside any size industrial or commercial building. It uniquely offers all five capabilities necessary for a complete indoor position determination solution.

How it works

Optical RTLS applies machine vision technology in a fashion similar to celestial navigation. Position markers bearing two-dimension barcodes uniquely identify ceiling positions and serve as “constellations”. Markers constructed of lightweight materials and placed in known locations above the operating area affix to building structure.

The electro-optic sensor contains a digital camera, signal processing electronics, and dedicated data processor, and is mounted on the vehicle and powered by the vehicle power source. The sensor aims toward the ceiling and captures multiple images per second as the vehicle moves beneath the array of position markers, which typically cover all vehicle operation areas of the facility. The sensor decodes each marker visible within the camera’s field of view and geometrically analyzes the image, producing inch-accurate position data. The resulting data maps to the facility floor, providing real-time position, heading and vehicle velocity using facility coordinates.

A basic implementation of Optical RTLS places a moving map display on board a vehicle to show location in much the same way that a dashboard mounted automotive navigation system does. This can assist the driver to know “Where am I?”

A low bandwidth data stream from optical sensors transmits over standard wireless data networks to a control computer. A data controller time-stamps and stores data received from all sensor-equipped vehicles. Since Optical RTLS accurately tracks vehicles, the precise tracking of materials is also possible. An industry standard database provides customer access to the data to allow connection to host computer systems such as inventory control and labor management systems. Sky-Trax software generates statistical reports, produces video-like vehicle tracking displays, and graphically presents data for a variety of operating analysis purposes.

Many Solutions

By providing high-resolution location data and operating reliably inside many types of buildings and on a variety of vehicles, Optical RTLS has enabled new solutions to long-standing problems. For example, many logistics operations would benefit from tracking utility vehicles and freight, locating vehicle drivers, automating data collection, warning of impending inter-vehicle collisions, guiding automated vehicles, and managing mixed fleets of driven and automated utility vehicles.

Tracking Utility Vehicles

The Optical RTLS system data controller receives inch-accurate position indications from each vehicle several times per second, allowing real-time monitoring of vehicle location. Graphic depictions created by the controller show the location and identity of each vehicle, answering the question “Where is Vehicle X?”

Tracking People

A driver’s location can be determined by associating the driver with his/her vehicle. For example, a real-time display may key on driver identity instead of truck identity, answering the question “Where is Driver X?”

Tracking Materials

Inch-accurate vehicle tracking enables materials tracking in ways not previously possible. The position of a unit load on a vehicle carriage is relative to the vehicle body and the position of the optical sensor. Therefore, load position and orientation are determined from a calculation of vehicle and sensor position and orientation.

Three-dimensional tracking capability is possible by adding a fork height sensor to the transport vehicle and integrating its data with position sensor data. An inventory control system may command a transport vehicle to acquire a load at an exact three-dimensional location and orientation, and deposit it at another rigidly defined location.

For convenience, the geographic coordinates determined by the Optical RTLS system translate into facility ocations. For example, a load deposited at a location 361.2 feet south, 196.1 feet west, a height of 4.1 feet, and a heading of 92 degrees (relative to a facility reference) may translate to “Aisle J, position 214, second tier, east facing”. Asset tracking information is typically integrated with the facility WMS to allow bidirectional data exchange in the format of the host system. This type of Optical RTLS application provides the answer to “Where is pallet X?”

The use, value and results of the functions of warehouse management, labor management, and enterprise resource planning systems are more accurate, timely and provide larger cost savings using Optical RTLS.

Automating Data Collection

Automatic data collection devices mounted on the vehicle can provide automatic load identification. For example, a bar code reader or RFID reader mounted on a forklift load backrest can automatically scan a unit load label or interrogate a pallet RFID tag. The driver is now relieved of all data collection responsibilities because key transaction data - item identification, location identification, and time - are captured automatically. The driver receives instructions for load and location pickups and drop-offs via an on-board screen, and is responsible only to drive the vehicle and handle any exceptions. The Sky-Trax version of this system uses an imaging barcode reader to decode barcode labels affixed to a load, and is trademarked Total-Trax®. Sky-Trax partners Rush Tracking Systems (US) and Peacock Brothers (Australia) offer systems using Sky-Trax Optical RTLS for location identification and RFID readers for load identification.

Guiding Automated Vehicles

In addition to affording tracking capability, Optical RTLS technology provides the necessary capability for automated vehicle navigation, which requires very high-resolution location and orientation data. AGV’s need position and angular resolution one- to two orders of magnitude better than a forklift requires for tracking purposes. Having configurable design, optical RTLS installations provide this capability for AGV fleets or mixed fleets.

Automated vehicles can be classified into two groups: autonomous and directed. Autonomous vehicles typically follow predetermined paths, monitoring for obstructions along the path, and proceeding at their own pace to a predefined destination. Directed vehicles receive commands from a human or automated controller and may follow a predetermined path or a dynamically changing path. Optical RTLS permits this evolving class of AGV, termed Automated Directed Vehicle (ADV) to enjoy free roaming capability. ADV’s start at any location, proceed along any path directed by the controller, and arrive at any destination within the controlled space.

Warning of Collisions

To achieve an improved level of operational safety, all fleet vehicles may be equipped with position determination equipment and share location data over a wireless network. Motion trajectories calculated by the controller transmit instantaneous warnings to drivers if vehicles are moving along intersecting paths. Signals installed at dangerous intersections automatically display “Stop”, “Caution”, and “Go” commands to vehicles or pedestrians.

Managing and Directing Mixed Fleets

The new level of fleet control enabled by Optical RTLS allows automated and driven vehicles to operate together. Since each type of vehicle uses the same navigation system and shares the same control network, they may now coexist in shared space. Automated vehicles have knowledge of the instantaneous location of driven vehicles and vice versa. Drivers know the proximity of other vehicles, and AGV’s or ADV’s stop before approaching an impending collision with a driven vehicle.

Free roaming ADV capability and fleet directed control multiply the power of operating a mixed fleet. Automated vehicles and driven vehicles can jointly perform interleaving and optimize goods transport, allowing dynamic routing and flexible control of all fleet vehicles.

Measuring the Results

Increased visibility to inventory and vehicle movement gives managers the ability to analyze and manage operations with hard data that has not been previously available. They can capture statistics on vehicle utilization and driver productivity, pictorially visualize materials flow, study facility layout and vehicle flow, and consider changing storage strategies. Comprehensive statistics based on hourly, daily or monthly reporting periods are available for analysis from the controller. This visibility typically allows warehouse managers to reduce the number of vehicles and drivers required to maintain or even increase throughput.

Automated inventory tracking provides numerous other benefits. By eliminating the time spent manually scanning pallet and position labels, the drivers can move more pallets per hour while eliminating many scanning errors. The resulting 100% accuracy in inventory location has allowed warehouse operations to reduce or eliminate the time spent on inventory reconciliation while improving shipping performance for their customers.

Optical RTLS deployments have enabled productivity gains of 10% to 45% in warehouse and distribution center installations while improving pedestrian and driver safety. Investment payback has been short, and the source of new data priceless. By employing Optical RTLS technology, indoor material control systems can now function in ways that were only available to outdoor logistics operations.

Seeing the Future

As material handling operations continue to evolve, a vision of future indoor logistics may include lights-out storage facilities with free-roaming driverless transport vehicles. Forklift trucks will serve dual purposes as driven vehicles and automated-directed vehicles. Collaboration with utility vehicle suppliers to pre-install Optical RTLS on their products and integrate RTLS data with their on-board systems will make superior vehicle performance available to all material handling facilities. In the future, inventory accuracy and visibility will be 100%; shipping errors will not occur, no goods will be misplaced, and operational costs will fall.

Most technology required for the future vision, including vehicle control systems, mobile computing, and wireless networks, has been available for several years. The missing link found in a single innovation - an accurate position determination method - scalable to any size operation, broadly applicable, and adaptable to many types of vehicles and facilities.

The development and refinement of RTLS technologies is certain to continue. Optical RTLS, which offers reliable wide-area coverage in dynamic environments and produces high-resolution positioning and heading data at a reasonable cost, is an important part of the progress.

Company Summary

Sky-Trax is the leading provider of Optical Real-Time Location Systems for tracking goods, vehicles and guiding autonomous vehicles in any size facility. Sky-Trax revolutionary inch-accurate location tracking and automatic data collection systems are designed for indoor industrial vehicles, primarily in warehouses. Applications employing Sky-Trax Optical RTLS are economical and practical to deploy, allowing warehouse professionals to substantially increase safety and improve warehouse efficiency. The results are fewer safety incidents, much lower operating costs, improved inventory accuracy, and greater throughput. For more information, please visit www.Sky-Trax.com.

About the Author:


Richard Ungerbuehler joined DuPont in 1974, working as a research engineer at the Engineering Physics Laboratory. His area of concentration was automatic product inspection and optical instrumentation. He later served as technology consultant for auto-ID and led an international team that coordinated data collection applications for DuPont. He retired from DuPont in 1999 and co-founded Sky-Trax in 2004 with ex-DuPont colleagues Larry Mahan and Dave Emanuel. Richard holds a Bachelor of Science degree in Electronic Engineering Technology from Spring Garden College, Philadelphia, and he holds various meritorious awards and certifications from the United States Army Signal Corps. He enjoys family, friends, food, and a multitude of hobbies and interests.