Renishaw Helps Achieve High Accuracy Grinding for Giant Wind Turbine Bearings

KMT Lidköping (www.kmtgroup.com/lidkoping/) has unveiled its new hard-turning VTG4000 (Vertical Turning Grinding) machine that uses a combination of Renishaw SiGNUM optical angle and linear encoders to achieve the required accuracy, and Renishaw magnetic encoders placed on the exposed axes of the cutting heads.

“Our largest machine used to accommodate parts up to 600 mm diameter, but the VTG4000 can handle diameters in excess of 4000 mm, the size of the largest wind turbine bearings. This is hard turning and grinding which can be very demanding, and the positioning accuracy is very important, with a direct effect on the quality of the finished bearings. A standard size machine, using ballscrews on the axes, will manage to maintain a 3 µm form deviation, yet despite the considerable difference in relative size, the VTG4000 has been proven to achieve an exceptional form deviation of less than 1 µm, with feed resolution in 0.1 µm steps,” said Eive Johansson, Lidköping’s VTG Chief Designer.

“At the heart of a Lidköping machine are the linear slides. The combination of hydrostatic guideways, air seals and linear motors create a stiff, accurate and maintenance-free system. To achieve dynamic stiffness we need high gain and the gain is linked to the quality of the encoder scales. It also makes a big difference that the angle encoders have the scale integrated directly onto the ring,” he added.

Mr. Johansson first saw the Renishaw SiGNUM encoders during the EMO 2007 exhibition in Hannover, and then followed a period of rigorous testing by the company. As he explained: “The choice of Renishaw was easy; we compared different scales assembled on our reference slide and bought the one with the best performance. It was important that the linear encoders could be supplied in a continuous length of at least 4.5 m and SiGNUM is the easiest way to achieve this. The Renishaw encoders also give more resistance to dirt. We have now fitted Renishaw encoders to all four linear slides and as expected, we have had no problems!”

“The rotary table has the same design principle, with hydrostatic radial and axial bearings, air seals and torque motors for the drive. The same analysis was done, and the Renishaw SiGNUM angle encoders were chosen,” he added.

The Renishaw encoders have an integral patented set-up LED that speeds installation and eliminates the need for separate set-up equipment/complex external, or oscilloscopes.

“One of the best features of the Renishaw encoders is how easy they are to set-up,” Mr. Johansson said. “With the scale attached and the readhead approximately located the indicator lights make it very easy to see how well the two elements are aligned and then make the final adjustments.”

Rexroth CKK Ball Screw Actuators Raise Performance for Wind Turbine Builders

Wind turbine technology is an established sustainable, green technology. Many consider it a technology that will help define the energy future. But wind energy also depends, to a great extent, on more traditional manufacturing techniques, such as welding – vitally important for creating the massive towers.

One of the leaders in creating welding solutions for the energy industry – as well as many other applications – is Rexburg, ID-based machine builder AMET Inc. (www.ametinc.com). Recently, AMET called upon the Linear Motion and Assembly Technology specialists of Bosch Rexroth to help them create a new generation of custom welding systems for the increasingly important wind energy industry.

The design of AMET welding equipment – and the role of linear motion technologies – is largely dictated by the techniques required to create massive wind turbine towers that can be around 90 meters high (close to 300 feet). During a weld, while the bulk of the equipment remains stationary, the weld head constantly moves small distances along at least 2 axes, both along and across the seam. A linear control actuator mounted at the end of a horizontal arm determines the motion of the weld head.

AMET’s goal was to create a cost-effective, dependable welding system that could perform accurate longitudinal and circumferential submerged arc welding. One of the most important challenges, however, was to assure smooth and precise (within 1/100th of an inch) control of the weld head, to avoid improper welds that would need to be redone and ultimately result in wasted time and materials. And this precise control had to be maintained within a very demanding environment. “The tremendous amount of particulates, especially flux dust, generated by this form of welding can really cause problems for this machine’s finer controls, particularly with systems such as linear actuators,” said Craig Dees, AMET Engineering Manager.

AMET also wanted linear motion elements that offered good strength (dynamic loads in excess of 20,000 Newton) with light weight and compact size. Yet another challenge was to support smooth weld head acceleration of up to 3 meters per second squared (3m/s2), for a travel speed of 1.5 meters per minute.

To meet these needs, AMET turned to a familiar source for linear motion: Northwest Motion, Inc. (www.nwmotion.com), a distributor of Rexroth linear motion products. Rexroth precision-ground, hardened steel guide rails were to be specified for the guide rail that carries the suspended weld head for outside welding. With the CKK Compact Modules, however, AMET put Rexroth linear motion systems in a particularly crucial role.

The compact CKK design, light in weight but durable and strong, makes machine assembly smoother and easier. “We knew that other linear motion solutions couldn’t give us the reliability and protection against contamination and pitting that the CKK modules could,” Dees says.

Another important feature leading to better and faster machine production is the fact that CKK 20-145 modules are complete, prepackaged systems, with dual ball rails and a ball screw drive integrated into the module. This simplifies design, saves space, and removes the costs and effort of machining, assembly, bearing alignment and other application engineering tasks.

Download the complete case study from the Bosch Rexroth Case Studies & Technical Papers web page.

Bosch Rexroth
www.boschrexroth-us.com