Figure 1: A linear encoder. Source: Gurley Precision InstrumentsA linear encoder is a positional feedback device that consists of a sensor (readhead) and scale that work in conjunction to sense and feedback linear position. The readhead senses and reports linear position change over a measured distance and feedbacks that change to a digital readout or control system. Linear encoders are available in two types: absolute and incremental.

The focus of this article will be on Gurley Precision Instruments’ family of linear encoders including:

• LA18 linear absolute encoder
• LR18 linear incremental encoder
• P20/P40 plunger-type incremental encoders

Figure 2: In addition to linear encoders, Gurley Precision Instruments offers a full line of rotary encoders

The LA18 series linear absolute encoders offer resolutions down to 0.1 micron (in SSI output format) over measuring lengths up to 3 m. It is an enclosed linear encoder, with the glass scale mounted into an aluminum extrusion with rubber sealing flaps for superior protection against FOD during operation. It is designed for long life in high-performance applications such as surgical robotics, CMMs and industrial printers, where accurate position is required upon power-up.

The LR18 linear incremental encoders are also enclosed and mechanically similar to the LA18 series. The LR18 offers resolutions down to 50 nm over measuring lengths up to 3 m. The unit is offered with two output types: analog (11 uA or 1 V pk:pk) or RS-422 differential line driver. It is also designed for long life in high-performance applications such as DNA analyzing equipment, sonic welders and PET scanning equipment.

The P20/P40 plunger-type incremental encoder operates in the same manner as the LR18 and offers resolutions down to 0.5 microns. The P20/P40 is ideal for applications where space is limited, but high performance is still needed for applications such as precision X-Y stages or QC test fixturing.

Rated for a minimum of 100,000 operating hours, all three linear encoder offerings incorporate ball-bearings for smooth operation and greater resistance to side loads, and an internal ASIC for reliable electronic interpolation.

The same technologies used to make encoder scales have been used in a number of other applications as well. Reticles, optical calibration pieces and logo projectors are just some of the industries that take advantage of these patterning technologies.

Figure 3: Gurley Precision Instruments Optics & Optographics capabilities. Source: Gurley Precision Instruments

Typically, a vacuum deposited metal such as chromium is etched away in a photolithographic process to create the lines and spaces the encoder readhead will “read.” In recent years, the sizes of the features that can be patterned accurately have continued to decrease, with feature sizes in the hundreds of nanometers now available from higher end manufacturers. Traditional contact photolithography is still used for most applications with features greater than 5 um, but laser systems, stepper systems and e-beam systems can be used to mass produce features less than 1 um in size with amazing accuracy and failure rates measured in parts per million.

For information regarding encoders, please contact Chris Guiry – c.guiry@gurley.com. For information regarding Optics, please contact Simon Miner – s.miner@gurley.com, or visit the Gurley Precision Instruments’ website.