The tsunami that hit Japan two years ago caused a tremendous amount of damage and loss of life. The resulting catastrophe at the Fukushima Daiichi nuclear power plant caused a 20-kilometer (12.4-mile) area around the plant to become uninhabitable. Radioactivity will be present in the area for many years to come. After the earthquake, all the nuclear power plants in Japan were taken offline and remain so today, pending new safety regulations that will take effect this year.
Since the Fukushima incident there has been a strong push by much of the Japanese population to promote traditional and alternative energy sources. One of the growing alternatives for electrical power generation is wind power. After the 2011 earthquake, it was noted that none of Japan’s commercial wind turbines failed -- even the Kamishu offshore wind farm that was directly hit by the tsunami.
Support-bracket attached to tower with rack rail in place.
Large wind generators are now present in most parts of the world. These wind generators require occasional maintenance and repair. Wind generators require periodic cleaning and painting of the wind turbine tower, as well as inspection and repair of the blades. The height of these towers can be as much as 300 feet, with blade diameters of about 200 feet. Obviously, climbing to this height for maintenance and repair is no easy task. It can also be very dangerous. In the US, the exterior of many of these tall wind turbines are maintained by employees using wire ropes. A Japanese company, Sakurai, has developed a new way to approach these giant wind generators.
Currently, maintenance personnel travel up the inside of the support tower in a cramped space and then rappel from the top down along the exterior of the tower. The new system attaches to the exterior of almost any tower. First, an exterior ladder is constructed and bolted to the tower frame. Then, a centralized steel rack system is installed. This system is installed one section at a time from the ground up, eliminating the need for a mobile crane. This feature is especially useful for wind turbines at sea.
To drive the basket/elevator up and down the rack, a motor and worm-drive gearbox are used. The output of the worm-drive gearbox is attached to a pinion gear. Because of the high reduction in the worm gear, the system is inherently self-locking. But to assist in braking, an Ogura spring-applied brake, model SNB-1.2K, is used on the worm gear through-shaft. As an additional safety precaution, an Ogura spring-applied brake, model RNB-10K, is mounted directly on the stopping disc/pinion to hold the elevator in place.
The Ogura spring-applied brake, model SNB-1.2K, has a static torque rating of around nine foot-pounds. The brake is mounted on the input shaft, on the opposite side of the worm gear reducer. The SNB brake is designed for both stopping and holding. When no current/voltage is applied to the brake, a series of springs push against an internal pressure plate, squeezing the friction disc between the inner pressure plate and the outer cover place. This frictional clamping force is transferred to the hub, which is mounted to the shaft of the reducer.
When the brake is required to release, voltage/current is applied to the coil, creating a magnetic field. This magnetic field pulls the pressure plate, compressing the springs, and releasing the clamping force to the friction disc by creating an air gap allowing the brake, hub, and friction disc to turn freely. The power off brake is considered engaged when no power is applied, which is why it is considered a safety brake.