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Collision Avoidance and Distance Detection Systems

Application
Reducing the potential for collisions between overhead cranes, monorail systems and fixed objects/obstructions has been a challenge for the overhead material handling industry for many years. Until recently, it was only possible to minimize the resulting impact from such collisions using mechanical means such as bumpers or limit switches. With today's advances in electrical technology, it is now possible to prevent these collisions in a variety of operating environments.

Problem
In manual or automatic tank line systems, several overhead cranes often times operate on the same runway, servicing a series of process tanks. In one application involving the processing of aircraft components, two tank line cranes and one return crane operate over 22 tanks.

The two tank line cranes are required to meet the customers' throughput requirements. The return crane operating on a separate runway above the tank line cranes and shuttles transported load fixtures between the unload and load station. This system required critical positioning to ensure that the loads were properly positioned in the tanks and at the load and unload stations. Since the tank line cranes operate on the same runway and service the same tanks, crane to crane collision avoidance protection is necessary.

Solution
Three automated cranes were provided to meet the system requirements. Laser distance detection devices mounted on the bridge provide the crane horizontal positioning of +/- 1/2". The hoist motor encoder and the IMPULSE® Flux Vector Adjustable Frequency Hoist Control are used for vertical positioning. All of the cranes are equipped with Electromotive IMPULSE® AFD crane controls to maximize their performance and reduce wear and tear on mechanical components. Each crane is provided with a PLC for automatic operation and communication with the off board control. Six enclosed type conductor bars, running the length of the runway, provide power and communication to the cranes. The floor mounted MMI control station includes a PLC with necessary interface to the process control PC. In addition, the cranes are equipped with Electromotive System's ReFlx 120 "Plus" Crane Collision Avoidance System. When two cranes approach each other, a primary signal is sent by the collision avoidance system to the on board PLC to initiate a slow down of the bridge. As the two cranes continue to approach each other a second signal is created by the ReFlx system to bring the cranes to a complete stop prior to contact. As an additional measure of safety, a third distance sensor is provided to act as a back-up emergency stop in case the primary sensor fails.

Result
The automated tank line and return cranes created an efficient, safe material handling system. The automation portion allowed an operator to control the cranes from a floor mounted MMI control station. The process control PC provided automatic recipe selection and interface with the other area controllers. The addition of the IMPULSE® drives and ReFlx collision avoidance systems to the cranes reduced maintenance costs, and enhanced performance and safety of the entire system.

Electronic Technologies Employed by Magnetek for Collision Avoidance Systems
If the application requires collision avoidance between cranes, monorail carriers, and other obstructions, Electromotive Systems has the solution. Below are some of the technologies Electromotive Systems applies to collision avoidance for the overhead material handling marketplace.

ReFlx 120 and ReFlx 120 "Plus"
Intended for use with overhead crane bridges and trolleys to prevent collisions or limit their approach to adjacent bridges and trolleys. The systems are designed to be immune to most electrical noise including that which can be created by variable frequency crane controls and other parasitic interference affecting the reliability of RF-based systems. The range of this system is from 10 to 120 ft. It uses a two channel infrared sensor, which allows for a separate slowdown and stop command when used with Electromotive Systems IMPULSE crane controls.

Laser Based Distance Detection
Laser based distance detection and collision avoidance are primarily used in an automated environment where the distances between monorail carriers or cranes can be relatively great. The range of a laser based system (from 0 to over 1000 ft.) allows the ability to monitor distances between cranes, trolleys and monorail carriers, and when interfaced with a PLC, can be used to prevent collision between this equipment. Laser based systems also offer the advantage of precise position accuracy which is critical in an automated environment.

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