Glossary

D

de-Encoder

see Digital Encoder Technology

Deviation in Image Field Scaling

see gain error

Digital Encoder Technology

SCANLAB offers galvanometer scanners equipped with analog position detectors, as well as versions with digital encoders.

Digital encoder products include the field-proven de-Encoders and the further-enhanced se-Encoders (SCANLAB encoders).

de-Encoders

Special care has been taken to ensure that these digital encoders enhance positioning precision without compromising dynamics or mechanical dimensions. They offer highest dynamic performance with XY-stage precision, as well as comprehensive position feedback and diagnostics. They are particularly suitable for applications that demand the highest possible precision and throughput.

de-Encoders enable a positioning resolution of 19-20 bits, exceptionally low dither (electronic noise), best linearity and lowest drift .

se-Encoders

Position detectors with se-Encoders (based on interferometric sensing) ensure outstanding resolution along with lowest drift and dither .

SCANLAB's patented, ultra-low-inertia design makes systems equipped with these se-Encoders (e.g. intelliSCAN_se10) among the fastest, most accurate scan heads on the market – even starting with apertures of 10 mm and up.

Dither

Dither is positioning noise of the scan mirrors in the time range of a few milliseconds.

Independently of their activated motion, scan mirrors oscillate irregularly across a broad frequency spectrum from roughly 200 Hz to 20 kHz. The excursion magnitude is specified as the standard deviation σ (or RMS ) of the scanner's optical angle . The resulting maximal amplitude can be approximated as 3σ.

In high-speed vector applications, dither effects during laser marking can produce irregular waves and spikes. At lower vector speeds, oscillations get concealed by overlapping laser pulses, but a slight broadening of marking occurs. This same broadening is also visible when a line is rewritten. Likewise, jump-and-shoot applications with short single pulses are susceptible to dither -induced imprecision. For long or repetitive pulses, dither broadens the effective beam or working diameter.

Systems with low dither

Special tunings (micro-machining) are available for applications requiring low dither amplitudes. The lowest dither is achieved using systems with digital encoders (se and de systems).

Drift

Drift  is alteration of the image field over a long time period (from five minutes up to several hours).

At long time scales, mechanical and electronic effects occur that influence the image field. The sum of these effects is called drift . Because a large portion of these deviations is attributable to ambient temperature changes, those are evaluated separately. Drift values specified by SCANLAB are always valid for each scan axis individually.

The following specifications apply:

• Long-term drift : The temperature-independent drift component is specified for different time regimes:
  - 8 hours, after 30-minute warm-up
  - 24 hours, after 3-hour warm-up
  Prerequisites here are constant ambient temperature and steady work load of the scan system.

• Temperature drift : Ambient temperature fluctuations are specified in accordance with the magnitude of temperature change.

Temperature and long-term drift specifications consist of error values for offset and gain:

• Offset: Shifting of the image field specified as an angle per temperature change (offset error ).

• Gain: Deviation in image field scaling specified as percent deviation per temperature change (gain error ).

Systems with low drift

For drift -sensitive applications, systems with digital encoders (also see digital encoder technology ) can be advantageous.
Be careful to maintain constant environmental conditions.

Dynamic

see Tuning