American Crane & Equipment Corporation has received a patent for a diagnostic system for cranes working in environments requiring enhanced safety.
Cranes play an integral part in the day to day operation of the nuclear industry. Human or technical error in this field can have disastrous consequences, so the constant development and improvement of safety techniques is of paramount importance to the future of the industry.
In 2003, Jeffrey Griesemer, vice president of engineering and general manager, American Crane & Equipment Corporation, tasked the electrical engineering department to design a system to augment the single failure-proof mechanical design of the cask and refuel cranes that were scheduled to be rebuilt at a number of commercial nuclear facilities in the USA.
Oddvar Norheim, Glenn Malek, and Jeff Griesemer were awarded a US patent for the resulting SafWatch system on November 13 2007, having submitted the original application in 2004.
In July 2003, a prototype was built and tested, with a first generation production unit assembled in late August. In early 2005 a second generation SafWatch was designed and built to address limitations of the first unit, which offered improved performance for an increased range of applications.
American Crane now holds three patents, two for its SafLift system, a process for transporting canisters of spent nuclear fuel, and another for SafWatch, the system outlined here to monitor crane operation.
SafWatch has been provided for both new and existing American Crane installations and for those of other crane manufacturers. However, SafWatch has not been provided to date as a “kit” for an end user installation.
American Crane’s single failure-proof cranes are a requirement and result of compliance with NUREG 0554 – “Single Failure-Proof Cranes for Nuclear Power Plants”, ASME NOG-1-2004 “Rules for Construction of Overhead and Gantry Cranes” and operating experience.
The SafWatch first generation and second generation units are in use at five commercial and two government facilities with multiple installations at each facility. Each SafWatch installation is designed, tested, and documented.
The features provided by SafWatch are redundant to safety features provided by the latest closed loop vector frequency drives. The SafWatch monitoring functions are from both the high speed and low speed components. This provides the ability to monitor and compare the direction and speed of the motor, drum, and corresponding hook. Additionally operator control inputs are monitored and compared to actual motion. This redundancy provides a layered approach or “Defense in Depth” to failures in the control and or mechanical systems.
The unit can detect hoist overspeed in excess of 115% of critical and non critical lift speeds. Brakes are automatically applied when an overspeed fault is detected.
US Patent & Trademark Office said:
“A hoist system for critical loads incorporates improved safety technology to monitor various possible fault conditions. For example, a command-not-operated function causes braking of the hoist when an encoder detects one of a group of conditions including a lack of load movement when a movement command is issued by the operating system, failure of encoder feedback, or failure of a control circuit.”
It added: “An uncommanded motion function also causes braking of the hoist when an encoder detects one of a group of conditions including load movement without a movement command issued by the operating system, or reverse directional movement of the load from a directional movement command input by the operating system.”
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Oddvar Norheim is president and CEO of American Crane & Equipment Corporation. He has a BS in Mechanical Engineering from Bergen Technical College, Bergen, Norway. He has been employed with American Crane for over 34 years and has provided leadership, development and oversight for company projects.
Jeffrey Griesemer is the vice president of engineering and general manager. He has an AS and BS in electrical engineering technology from Penn State University. He has been employed with American Crane for over 21 years and has worked on or been manager of a diverse number of crane projects from nuclear and fossil fuel power plants to aerospace and automated systems.
Glenn Malek works in American Crane’s engineering department as an electrical engineer with an AS in electrical engineering technology from Penn State University. He has been employed with American Crane for over 22 years and has worked on or managed a number of crane systems for commercial and government facilities.
