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.”

FASTRACK Linear Encoder System from Renishaw

Renishaw’s new FASTRACK linear encoder scale system brings high accuracy, stainless steel construction and quick, easy installation to large, sectional machines used in flat-panel display and photovoltaic manufacturing applications, as well as large CMMs that require removal of the scale for transit. Also ideal for linear motors with aluminum substrates, and applications where thermal expansion of the scale must be independent of the machine structure, or those involving dissimilar axis materials, the track-mounted scale can run across gaps up to 25 mm wide, while providing ± 5 µm/m accuracy.

The FASTRACK system consists of two miniature guide rails that secure low-profile scales (8 x 0.2 mm cross-section) while allowing them to freely expand at their own thermal expansion rate with almost zero hysteresis. The scale can be installed, removed and reinstalled as many times as required, and damaged scales can be pulled out of the guide rails and quickly replaced, even where access is limited, reducing machine downtime.

FASTRACK is available on reels for cut-to-length flexibility at the point of installation, allowing machine builders to minimize stock and lead-times. Generous tolerance makes measuring and cutting quick and easy. Easily installed, the self-adhesive guide rails feature integral pre-aligned sacrificial spacers which are removed after the rails are fitted to the axis. The scale is then fed in from either end and locked to the substrate at a single datum point anywhere along the axis using cyanoacrylate glue or a clamp.

Part of a modular solution, FASTRACK can be used with either the RTLC stainless steel incremental scale and super-compact TONiC readhead, or Renishaw’s new RESOLUTE linear absolute encoder and RTLA absolute scale. The encoders in both set-ups feature advanced optoelectronics with resolutions to 1 nm, low sub-divisional error (SDE) and very low jitter for smooth velocity control and rock-solid positional stability. For TONiC RTLC incremental scale installations, limit magnets and a reference mark selector are fitted to the FASTRACK and secured with a bolted clamp rather than using glue. The RTLC scale features multiple INTRAC reference marks at regular spacing.

The FASTRACK system is backed by Renishaw’s global sales and support network and, like the TONiC and RESOLUTE encoder systems, it is compliant with the WEEE and RoHS environmental standards.

Renishaw
www.renishaw.com/encoders