High-precision laser interferometer feedback systems

High-precision laser interferometer feedback systems Product scope Product scope 2 In today’s semiconductor and electronics marketplace, many manufacturing equipment suppliers are having to adopt ‘more for less’ strategies to retain a competitive edge. This has resulted from the continual drive to accommodate smaller feature sizes, increase throughput and reliability whilst simultaneously decreasing equipment footprints and costs. These requirements impact on every component integrated into the final system. For providers of position encoders this means ongoing OEM demand for higher system resolution,...

Experts in interferometry Renishaw began manufacturing the world leading ML10 interferometer based calibration system in the late-1980s, and has recently introduced the next generation solution, the XL-80. ML10 calibration laser HS10 laser scale The success of the ML10, combined with Renishaw’s unsurpassed reputation in the field of metrology, led the machine tool and aerospace industries to request a Renishaw laser system suitable for positional feedback applications. Consequently, during 1994, utilising the field proven technology of the ML10, the HS10 laser scale was released. This robust...

High-precision laser interferometer feedback systems Introduction to the RLE Introduction to the RLE 4 The RLE system is a unique, advanced homodyne laser interferometer system specifically designed for position feedback applications. Each RLE system consists of an RLU laser unit and one or two RLD10 detector heads, the model of which is dependent upon the requirements of the specific application. The system provides the user with subnanometre resolution capability at velocities of up to 2 m/sec (80 inch/sec) for axis lengths of up to 4 m (160 inches). To maximise application flexibility, all...

RLD detector units RLE system benefits Most RLD10 detector units contain the fringe detection scheme, interferometer optic and integrated laser beam steerer(s). Six different RLD detector heads are available based on four variants. The unique fibre optic launch based architecture allows the RLE to provide interferometer system performance with the ease of use normally associated with glass or tape scale based encoder systems. • Single pass interferometer - Uses an external retroreflector target optic for linear applications with axis lengths to 4 m. Available with 0º or 90º beam launch orientation....

21st century homodyne interferometry High-precision laser interferometer feedback systems 6 21st century homodyne interferometry Unique fringe detection system Every RLE interferometer system comprises a combination of RLU laser unit and RLD detector head(s). The RLD detector head contains the interferometer (single pass, double pass or differential), laser beam steerer and fringe detection scheme. Figure 1 shows a schematic of a double pass interferometer RLD detector head. The unique fringe detection scheme includes a multi-channel integrated photodetector. This advanced approach to homodyne...

RLE performance summary The technology applied within the RLE system provides a versatile, easy to use interferometer system for position feedback applications with axis lengths to 4 m. As previously shown, a distinct advantage of the homodyne technique is the fact that the fringe detection system produces ‘industry standard’ analogue sine and cosine signals in real-time. These low noise analogue signals are made directly available to the user and may be interpolated within the motion control system or using the Renishaw RPI20 (see page 9) to produce sub-nanometre resolutions. For applications...

High-precision laser interferometer feedback systems RLE system accessories RLE system accessories 8 Accessories Mirrors mounts To complete an RLE interferometer system requires only one additional, external target optical component fitted to the motion system. (When using the differential interferometer, optics are required on the motion system and a fixed reference point e.g. column/tool.) To enable mirrors to be mounted and aligned on the motion system, Renishaw can also provide adjustable mounts for use with mirrors up to 350 mm in length with 25 mm x 25 mm cross section. In applications...

Renishaw’s RLE laser interferometer systems directly produce 1 Vpp sine/cosine signals with periods of 316 nm and 158 nm from single and double pass interferometers respectively. These sinusoidal signals can be interpolated to provide ultra-high resolution positional feedback. Although sine/cosine interpolation is available within a number of proprietary control systems, the analogue bandwidth of these systems is often designed for tape and glass scale based encoders. These scale systems produce relatively coarse signal periods and the sinusoidal frequencies for any given velocity are considerably...

High-precision laser interferometer feedback systems REE series interpolators REE series interpolators 10 The REE range of interpolators produce high-resolution digital quadrature signals from analogue 1 Vpp sine and cosine signals supplied by the position encoder. The resolution of the digital output quadrature is a function of the distance represented by one 360º cycle of the input analogue signals, and the interpolation factor. When REE interpolators are used with the RLE laser interferometer, the following resolutions can be obtained: Each interpolator module includes reference mark circuitry,...

The Renishaw RCU10 quadrature compensation system provides significant improvements in process accuracy and repeatability by addressing environmental error sources associated with the feedback system, the workpiece and the machine structure; all in real time. To achieve this, the RCU10 compensator is located directly within the position feedback loop. Taking readings from the encoder and environmental sensors, the position feedback is then modified to remove associated errors before the signals are supplied to the motion control. The system can be used with any linear encoder that produces differential...