Rockwell Automation 8510 AC Spindle Drive System User Manual - Manual (Page 9)

Introduction
Chapter 1
1-5
High Resolution Velocity Control
Optimum velocity control and smoothness is provided by a 14 bit A/D
converter for the command, and a multi-pole resolver with 16 bit resolution
for velocity feedback. For C axis operation in Servo Mode, the input can
be rescaled to achieve full 14 bit resolution over both the rapid traverse and
the feed speed ranges. An optional 16 bit parallel digital input can be used
to provide a 4 digit BCD or 16 bit binary digital speed command input
when operating in Spindle Mode.
High Response Control Loops
To provide the dynamic response required by state of the art machine tools,
the 8510 delivers up to a 50 Hz velocity loop bandwidth. For improved
response, feedback is sampled every 0.4 ms, and Servo Mode command is
sampled every 0.8 ms.
Spindle Orient
The spindle orient function can be provided by a CNC that can close a
position loop around the spindle drive or by a spindle orient capability that
is part of the spindle drive itself. With the 8510, spindle orient using either
an optical encoder or a high resolution magnetic feedback device is a
standard feature. The user provided feedback device must be mounted with
a direct 1:1 ratio to the spindle shaft that is to be oriented. If an optical
encoder is used, the resolution is 360/(4 x encoder lines) degrees.
A special high resolution magnetic feedback device is available. This
consists of a fine pitch, very accurate ring gear that must be mounted
directly to the spindle shaft and a sensor that picks up signals as each gear
tooth passes. The ring gears are available with between 225 and 500 teeth
(pitch diameters of 90 mm to 200 mm (3.5 to 7.9 in.)). Within the 8510
drive, each tooth is resolved into 1000 parts giving resolutions of 225,000
to 500,000 parts per revolution. With the 500 tooth gear, absolute accuracy
of 0.015 degrees can be achieved with precision mounting of the gear to
the spindle.
Orient is to a single preset orient position or, with the optional 16 bit digital
command input, an external 4 digit BCD or 16 bit binary orient position
command can be given. After reaching orient position, the drive can be
programmed to hold the spindle in that position or to remove motor torque
and allow free movement of the spindle.