ElmoMC SimplIQ Software Manual - Manual (Page 190)

SimplIQ Software Manual Sensors, I/O and Events
MAN-SIMSW (Ver. 1.4)
12-5
The following table summarizes some of the real-time properties:
Topic Comment
Capture probability High. An input pulse may slip away unnoticed only if the user
program is not running , the input is masked or the pulse is so
short that it does not pass through the input filters.
Deterministic delay Yes. Position logging and value setting are immediate and
yield accurate results regardless of speed. Position is flagged
within 100 microseconds. Motion management functions are
responded to at the next controller sampling time.
Use ƒ Homing (setting an absolute origin for the incremental
position sensors).
ƒ Motion management.
ƒ High-speed signaling.
Table 12-5: Real Time Properties
12.5 Homing and Capture
SimplIQ drives use incremental position sensors, which enable it to determine the
distance the motor has traveled since power on, but not where the position counting
started. The process of determining absolute position is called “homing.”
Homing the main position counter (PX) is typically used for:
ƒ
Absolute position control in single-feedback position-control mode.
ƒ Relative work in single-feedback position-control mode. For example, an axis in a
machine may be homed by a sensor for the edge of the product on which the machine
is working. The position referencing of the axis becomes relative to the product.
Homing the auxiliary position counter (PY) is typically used for:
ƒ
Absolute position control in dual-feedback position-control mode.
ƒ Relative work in dual-feedback position-control mode.
ƒ Fixing the origin of the external position command in single-feedback position-
control mode (refer to
section 10.2.1 ).
In the homing process, a trap is set for the event of reaching a desired position. The
motor travels until an expected event occurs. The event indicates that the motor is now in
a known absolute position, which, if set to the position counter at the time of the event,
makes the position reading of the drive absolute.
The expected event may be one of the limited switches (RLS or FLS), the home switch, the
encoder index or the digital inputs. However, the capture accuracy depends much more
on the homing event selection. If a Home or Index signal is selected as the captured
event, the captured position will not miss. If another digital input is selected, the sensing
delay for the switch is d=(0.004*TS+IF[N]) milliseconds, and VX*d/1000 counts may be
missed.