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HA0364T Rev C Aug 2022
Chapter 6
Position Err Limit
parameter set in the
Advanced - Control Loop Settings
tab, the axis
is not stopped if it moves outside the specified tracking window.
This function is useful for processes that rely on the motor's correct tracking of a set
trajectory within a specific range. The tracking window may also be used as an early
warning for performance problems that do not yet qualify as motion error.
The size of the tracking window (i.e. the maximum allowable position error while
remaining within the tracking window) is specified in the
Tracking Window
field, in the
range 0 to 65535. If the position error of the axis exceeds this value, the Tracking
Indicator status bit (bit 13) is set to 0 in the Status Register. When the position error
returns to within the window boundary, the status bit is set to 1 - see the
APTServer
helpfile
for details on accessing the status register.
Position Profiling
To prevent the motor from stalling, it must be ramped up gradually to its maximum
velocity. Certain limits to velocity and acceleration result from the torque and speed
limits of the motor, and the inertia and friction of the parts it drives.
The system incorporates a trajectory generator, which performs calculations to
determine the instantaneous position, velocity and acceleration of each axis at any
given moment. During a motion profile, these values will change continuously. Once
the move is complete, these parameters will then remain unchanged until the next
move begins.
The specific move profile created by the system depends on several factors, such as
the profile mode and profile parameters presently selected, and other conditions such
as whether a motion stop has been requested.
Profile Mode
– This field is used to set the profile mode to either
Trapezoidal
or
S-
curve.
In either case, the velocity and acceleration of the profile are specified using
the
Velocity Profile
parameters on the
Moves/Jogs tab.
The
Trapezoidal
profile is a standard, symmetrical acceleration/deceleration motion
curve, in which the start velocity is always zero.
In a typical trapezoidal velocity profile, (see Fig. 6.7.), the stage is ramped at
acceleration ‘
a’
to a maximum velocity ‘
v’
. As the destination is approached, the stage
is decelerated at ‘
a’
so that the final position is approached slowly in a controlled
manner
.
