50
HA0302T Rev A Feb 2016
Chapter 5
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 gen erator, which performs calculations to
determine the instantaneous position, velocity and acceleration of each axis at an y
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. 5.7.), the sta ge is rampe d 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
.
Fig. 5.7 Graph of a trapezoidal velocity profile
The
S-curve
profile is a trapezoidal curve with an additional 'Jerk' parameter, which
limits the rate of change of acceleration and smooths out the contours of the motion
profile.
Jerk Setting
– This parameter is specified in mm/s
3
and accepts values in the range
0 to 46566139. It is used to specify the maximum rate of change in acceleration in a
single cycle of the basic trapezoidal curve.
velocity
maximum
velocity (v)
time
acceleration (slope) a
