Optical Encoder

An encoder provides precise motion feedback to any positioning system. Examples are pick and place machines for PCB assembly, wafer handling in semiconductor industry, machining tools for precise manufacturing and microscopy stages.

These can be based on rotation stages, linear stages, and goniometer stages, all of which are supported by the METIRIO.

The integrated light source illuminates a scale comprising an incremental grating with 20 µm pitch and a track with reference marks for absolute positioning. The reflected light generates an interference pattern which is detected by the photodiode array within the readhead. A relative movement between the scale and the readhead leads to change of the light pattern hitting these photo diodes. During a continous relative movement the output voltage of these photo-diodes are analog sine and cosine signals. From these signals a relative position can be calculated using the formula given on Key Features of the METIRIO® encoder - SmarAct.

An optical encoder can achieve higher resolutions and accuracy than a capacitive or magnetic encoder thanks to its interference-based design. This makes it ideal for semiconductor applications, synchrotron research facilities and other industries that require precise motion control.

A quadrature-based optical encoder has two sensors slightly offset from each other.
Therefore, it outputs two signals (analog sine and cosine or digital A and B), shifted by 90° in phase.

By comparing which signal (A or B) leads the other, the system knows the direction of themovement.

In general, it is important to keep the scale of an optical encoder as clean as possible, and they are less suitable for environments where significant contamination is likely. As the encoder relies on the reflected signal, any (particle) contamination will lessen the amount of power delivered and can alter the detected interference pattern. Despite this, the MEITIO is engineered to maintain signal strength through a contaminated scale. Smart algorithms can also be applied to the raw quadrature signals to further increase resistance to changing signal quality.

The METIRIO can operate in temperatures from 0° to +80° C and is resistant to mechanical vibrations. Additionally, the read head, and A1 package are UHV (10^-11 mbar) compatible.

The METIRIO is compatible with any reflective scale with a 20 µm pitch. All housed variants contain the same read head and are therefore compatible with the same scales – uniquely, it can be used interchangeably with linear, rotary, and goniometer scales.

We offer scales made from glass, steel and aluminum and offer custom-made scales upon request. Our scale catalog is available upon request.

The easiest way is to place linear scales on the intended support surface and press it with the edge into another intended lateral contact surface. The reflective grid-side of the scale should face up to the encoder, while the dark side (or uncoated transparent side) should point downwards to the support surface.

For rotary scales it is important to place the scale concentric with an almost perfect radial run-out smaller than 50 µm.

You can apply any adhesive to the contact surfaces or along the edges, if black glass or coated glass is used. You can freely choose commercially available adhesives according to your demands.

The most convenient way is to use a version with D-sub connector that is used as industry standard. For UHV variants we offer a circular 14-pin connector.

The METIRIO will output the sine, cosine, and TTL reference signals from the read head. All housed varaints will output these same signals, according to the pinout which can be found in its respective datasheet.

With the ENCODER INTERFACE MODULE the analogue signal is digitized and compatible with the ABZ and BiSS-C protocol.

Most applications for encoders involve integrating them into a motion system, which will have a controller requiring a certain data protocol. If the system can read the analog signals, such as is the case with SmarAct Motion’s MCS2 controller, only a cable with the proper pinout is necessary. In other cases, the motion system will be compatible with a certain protocol such as BISS-C, or ABZ. These are digital protocols created from the analog signals by a device such as the Encoder Interface Module and will have resolution defined by the number of bits used to interpolate.

Smaract provides the ENCODER EVALUATION KIT that comprises, the encoder evlaution module that is connect via USB to any PC or laptp, and the encoder evluation software as well as a ready mounted and aligned measurement setup.