Re: sine wave encoder outputs

Hi, The main advantage of a sine/cosine encoder is the absence of
servo "dithering" when stopped. Unless it is an extremely accurate
(read expensive) encoder, any scheme to increase resolution is
unsatisfactory for the following reasons:

1) Encoders have a cyclic amplitude modulation; a sine/cosine
amplitude of +/- 1 volt may be +/- 1.2 volts when the encoder is
turned 180 degrees.

2) Any resolution enhancing scheme depends on a 90 degrees
relationship between the two channels. This cannot be gauranteed.

3) The waveform more than likely is a "quasi-sinewave". This means it
actual waveform will be somewhere between a sinewave and a triangle
wave.

4) Even if the encoder is perfect, the circuitry necessary to extract
additional resolution is complex and expensive.

Apart from the "non-dithering" advantage, the expense of
interpolation is better spent on a higher resolution digital encoder.
If anyone is interested, I can post a circuit I designed that
extracts an analog voltage proportional to position between encoder
counts.

Mariss

--- In CAD_CAM_EDM_DRO@egroups.com, "Elliot Burke" <elliot@h...>
wrote:

> Does anyone know a way to convert (4 phase)sine wave encoder output

to allow

> interpolation of the phases?
> It should be possible to greatly multiply the pulse resolution by
> interpolation. The encoder has a spec of 10° precision of the

quadrature

> phases, so that limits accuracy for large interpolations.
>
> Elliot Burke