DRIVING SAFETY

Logistics Insight Asia, 1/11/2009

With advanced sensing technology, you can improve warehouse safety and increase productivity. RICHARD UNGERBUEHLER explains how.

Leading businesses know that safety is not incompatible with efficiency – instead, it can improve efficiency and enhance productivity. These companies use safety as a competitive advantage. Since the majority of serious industrial utility vehicle accidents involve stability incidents and vehicular collisions with pedestrians, new safety system solutions will integrate technologies addressing both problems with intelligent presence detection, vehicle tracking, and pedestrian tracking that can provide both improved safety and increased productivity.

With the possibility of improving efficiency, a strong business case can be made for investing in safety systems and technology to eliminate hazards and prevent accidents.

A wide spectrum of technologies can be used to detect industrial utility vehicles. These can be functionally categorized as follows:

• Presence Detection
• Presence & Distance Detection
• Presence & Identification
• Location and Tracking

Presence Detection
Presence detection sensors indicate that a vehicle is within the detection distance or zone of the sensor. In most cases, there is some ability to configure or engineer the detection distance. Inductive or capacitive proximity sensors and photoelectric sensors, all of which are familiar to automation engineers, fall into this category.

Proximity sensors detect the presence of a large metal mass like a truck within their detection range – usually less than one to two meters. This short detection range makes this type of sensor most applicable for detection at “chokepoints” such as dock doors. Photodetector sensors are also used for this purpose; Wickham Fork-Alert and Alert Safety Products are among the companies that off er safety products for the warehouse based on this technology.

Fork-Alert employs an invisible infrared light beacon mounted on the top of the vehicle. An infrared receiver can detect the infrared light up to 25 meters away and trigger warning lights or audible alarms for pedestrians and other drivers. Alert Safety Products combines the light source and the detector in a single unit that is mounted on a wall or post. Strips of reflective tape are applied to both sides of forklifts so the vehicles can be detected when traveling by the sensor.

Microwave sensors work similarly and can shape the detection zone to match an area of interest. For example, products from Door-Man and Alert Safety Products offer warehouse intersection warning products using microwave sensors. Four sensors and a warning light are hung above an intersection with microwave sensors aimed in all four directions. A vehicle approaching the intersection is detected and triggers the appropriate warning light.

Presence & Distance Detection
The next class of sensors not only detects a target but can accurately measure the distance from the sensor to the object. The principal technologies here are ultrasonic range sensors and laser time of flight sensors. Ultrasonic sensors emit high-frequency sound waves which are too high for the human ear to hear. When waves are reflected back from a solid object, the sensor can determine the distance from a few centimeters up to 10 meters.

Laser systems can measure distances with higher accuracy and longer ranges. Found typically in high-end safety systems on automated guided vehicles, these sensors measure distances very accurately with time-of-flight calculations on the reflected laser light. For instance, a commercial safety laser scanner from Germany’s Sick can be programmed for different scanning areas and distances and configured to have both warning and emergency stop thresholds.

Presence & Identification
RFID technology has received extensive press for inventory tracking applications in warehouses. Typical applications use passive RFID with inexpensive tags that can be read (detected and identifi ed) by an RFID reader, but the read distance is small – usually less than a meter. Longer read distances of up to tens of meters are possible with active RFID systems. These systems detect and identify a tagged entity within the proximity of the RFID reader. This capability has been employed widely for security and access control applications.

Location & Tracking Systems
The latest technology for tracking vehicles in warehouses is machine vision for optical RTLS (real-time location systems). Machine vision (image processing) has been used widely in industrial automation for high speed package sortation, automated product inspection, and robotic guidance for the past 20 years.

This technology has recently been adapted to provide accurate and reliable tracking of industrial vehicles inside buildings. With the Sky-Trax Indoor Position Sensing (IPS) technology, vehicles are tracked in real time to accuracy of 5-20 cm. Important to many safety applications, IPS systems determine the instantaneous speed and orientation (heading or direction of travel) of each tracked vehicle.

The system (Figure 1) employs a small imaging sensor mounted on each vehicle that views upward toward the ceiling, where an array of encoded position markers is visible. The imaging sensor includes image processing intelligence to capture and analyze pictures of the ceiling several times per second. From ceiling scene analysis, X and Y positions as well as the angular direction of the vehicle are determined. Its velocity is calculated from location changes noted from frame to frame, and position data are transmitted wirelessly to a computer which collects data on the location and status of all vehicles in real time.

TOWARDS INTELLIGENT SAFETY
An Intelligent Safety System (ISS) includes a direct means for alerting drivers and pedestrians when hazards hazards exist and a direct means of automatically limiting speed. The ISS will utilize data collected from on-board sensors and facility monitoring systems to:

• Accurately track the location, direction, and speed of all vehicles

• Accurately track the location and movement of all pedestrians

• Know the status of each vehicle (driver ID, load, current task, impact events, etc.)

Given an abundance of real-time data, ISS intelligence will predict collision hazards and initiate action to warn or eliminate hazards. ISS will have communication and control links with drivers for hazard alerting, with trucks for automatic speed limiting, and with facility safety systems for intersection control and other intelligent warning systems.

Figure 2 illustrates a simplistic ISS. Safety zones are defined and configured in ISS software; for example, safe, caution, and danger zones are designated for intersections with the green, yellow, and red shading in the illustration. As Truck A approaches the intersection from a safe zone, ISS, which controls the intersection traffic lights, gives a green light to Truck A and to pedestrians, even though Truck B and Truck C are in the intersection’s caution zones. That’s because with knowledge of the exact location, direction of travel, and speed of vehicles and pedestrians, ISS determines that Truck C is moving away from the intersection and presents no danger to vehicles A or B, or to the pedestrians. Likewise, Truck B’s orientation and speed indicate that it is putting away a load and not entering the intersection.

An unintelligent intersection safety signal system would illuminate caution or stop signals for Truck A based on the proximity of Truck B and Truck C. Importantly, ISS preserves productivity – Truck A will not be slowed – while establishing a safer workplace.

CREATING COMPETITIVE ADVANTAGE
Technology will continue to offer the ability to reduce or eliminate vehicle stability accidents, multiple vehicle collisions, and vehicle/pedestrian collisions, using new sensors and intelligent, automated safety solutions. As this progress is increasingly recognized by industry leaders, regulatory agencies, and safety researchers, it is expected that industrial vehicle manufacturers will incorporate the new safety technology into their products, and that marketleading companies will take advantage of the new capabilities.

Everyone is in favor of increased safety, especially when it enhances productivity and the bottom line. Technology cannot replace the basics of safety – strong management commitment, good operations design, training, and accountability. But when safety is introduced into a safety conscious culture, technology will provide the tools for transforming safety into a competitive advantage.