RG4 optical linear encoder

The RG4 open, non-contact optical linear encoder system eliminates friction and wear whilst permitting reliable high speed, high resolution operation. The 40 µm scale pitch allows higher speeds and greater set-up tolerances. In addition, RG4 systems are able to read a wider variety of scale types.

Options

RG4 linear encoder readheads are available with 40 µm analogue signal period or digital resolutions from 5 µm to 50 nm. The RGH34 is a compact component readhead, whilst the RGH40 and RGH41 are fully housed. All systems feature a unique set-up LED, which lights green when optimum installation has been achieved. Reference mark and/or limit switch outputs are available on all models of readhead, with dual limits available with the RGH40 and RGH41. The reference mark provides a repeatable home or zero position, whilst the limit is used as an end of travel indicator.

Technical

An infra-red LED emits light onto the angled scale facets where it is directed back into the readhead through a transparent phase grating. This produces sinusoidal interference fringes at the detection plane within the readhead. RG4 essentially uses the same optical principles as RG2, however, the Infra red LED emits light which is reflected at 90° to the scale axis, rather than parallel to it. The optical scheme averages the contributions from many facets and effectively filters out signals not matching the scale period. This ensures signal stability even when the scale is contaminated or slightly damaged.

The operating principle of the RG4 range allows the use of a variety of scale types. The RGH41 and RGH34 readheads work with RGS40-S tape scale which can be cut to any user defined length and matches the thermal behaviour of the substrate. The lacquer coated scale requires none of the careful handling and cleaning most scales need and incorporates a self adhesive backing to ensure quick and easy installation. Low short-term errors are assured by the unique optical design, typically giving less than ±0.25 µm cyclic error (or sub-divisional error). The specified linearity of RGS40-S tape scale is only 1 µm in 60 mm and better than ±3 µm in any metre length.

The RGH40 and RGH34 readheads work with RGS40-G chrome on glass scale which is available in individual lengths up to 1 m. RGS40-G is ideally suited for applications where the scale does not need to be mastered to the substrate and is easy to install using datum clamp and mechanical clips or adhesive backing tape. The RGH40 and RGH34 also work with the 40 µm RESR angle encoder whilst all versatile RG4 readheads can read customer designed reflective etched scale for specialist OEM applications.