Delta Tau Acc-51E, Руководство пользователя

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Accessory 51E
Principle of Operation 17
The following equations express the relationships between the different units when using the Acc-51:
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
One encoder line
32 software counts per HW count
(128 software counts states per line)
1024 states per HW count
(4096 states per line)
One HW count
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 commutation uses the hardware counter. There are 8000 hardware counts per revolution, and 2
commutation cycles per revolution of the 4-pole motor. Therefore, Ix70 will be set to 2, and Ix71 will be
set to 8000. Ix83 will contain the address of the hardware counter’s phase capture register.
For the servo, we use the interpolated results of the conversion table. There are 128 software counts per
line, or 256,000 software counts per revolution. With each revolution corresponding to 5 mm on the
screw, there are 51,200 software counts per millimeter. The measurement resolution, at 4096 states per
line, is 1/8,192,000 of a revolution, or 1/1,638,400 of a millimeter (~0.6 nanometers/state).
Example 2:
A linear brushless motor has a commutation cycle of 60.96 mm (2.4 inches). It has a linear scale with a
20-micron line pitch. The scale is used for both commutation and servo feedback.
The commutation uses the hardware counter. There are 200 hardware counts per millimeter (5 microns
per count), so 12,192 hardware counts per commutation cycle. Ix70 should be set to 1, and Ix71 should
be set to 12,192.
The servo uses the interpolated results of the conversion table. With 128 software counts per line, and 50
lines per millimeter, there are 6400 software counts per millimeter (or 162,560 software counts per inch).
The measurement resolution, at 4096 states per line, is 204,800 states per mm (~5 nanometers/state).