Delta Tau Geo MACRO, User Manual And Reference Manual

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Geo MACRO Drive User Manual
70 Setting Up Primary Feedback
1/4096 of a line, so there are 4096 unique states per line, or 1024 states per hardware count.
For historical reasons, PMAC expects the position it reads for its servo feedback software to have units of
1/32 of a count. That is, it considers the least significant bit (LSB) of whatever it reads for position
feedback to have a magnitude of 1/32 of a count for the purposes of its software scaling calculations. We
call the resulting software units software counts and any software parameter that uses counts from the
servo feedback (e.g., jog speed in counts/msec, axis scale factor in counts/engineering-unit) is using these
software counts. In most cases, such as digital quadrature feedback, these software counts are equivalent
to hardware counts.
However, with the added resolution produced by the Geo Drive interpolator option, software counts and
hardware counts are no longer the same. The LSB produced by the interpolator (through the encoder
conversion table processing) is 1/1024 of a hardware count, but PMAC software considers it 1/32 of a
software count. Therefore, with the Geo drive, a software count is 1/32 the size of a hardware count.
The following equations express the relationships between the different units when using the Geo Drive:
1 line = 4 hardware counts = 128 software counts = 4096 states (LSBs)
¼-line = 1 hardware count = 32 software counts = 1024 states (LSBs)
1/128-line = 1/32-hardware count = 1 software count = 32 states (LSBs)
1/4096-line = 1/1024-hardware count = 1/32-software count = 1 state (LSB)
Note that these are all just naming conventions. Even the position data that is fractional in terms of
software counts is real. The servo loop can see it and react to it, and the trajectory generator can
command to it.
Four hardware counts per line
128 whole software counts and 3 bits
of fractional counts (1024) states per line)
One HW count
The Interpolator can accept a voltage-source (1Vp-p) signal from the encoder. The maximum sine-cycle
frequency input is approximately 8 MHz (1,400,000 SIN cycles/sec), which gives a maximum speed of
about 5.734 billion steps per second.
When used with a 1000 line sinusoidal rotary encoder, there will be 4,096,000 discrete states per
revolution (128,000 software counts). The maximum calculated electrical speed of this encoder would be
1,400 RPS or 84,000 RPM, which exceeds the maximum physical speed of most encoders.
Example 1:
A 4-pole rotary brushless motor has a sinusoidal encoder with 2000 lines. It directly drives a screw with a
5-mm pitch. The encoder is used for both commutation and servo feedback. The user first needs to set
MS<node>, MI101=6 and/or MS<node>, MI102=6 for sinusoidal encoder. If needed the direction decode
can also be reversed with MS<node>, MI910 equal to 3 (CW) or 7 (CCW)