2-130 S Curve
S Curve The S Curve function of the PowerFlex family of drives allows control of
the “jerk” component of acceleration and deceleration through user
adjustment of the S Curve parameter. Jerk is the rate of change of
acceleration and controls the transition from steady state speed to
acceleration or deceleration and vice versa. By adjusting the percentage of S
Curve applied to the normal accel / decel ramps, the ramp takes the shape of
an “S”. This allows a smoother transition that produces less mechanical
stress and smoother control for light loads.
Linear Accel & Decel
Acceleration is defined as moving away from zero; deceleration is defined
as moving toward zero. The linear acc / dec ramp is active when the S
curve% is set to zero. The accel time and maximum frequency determine
the ramp rate for speed increases while decel time and maximum frequency
determine the ramp rate for speed decreases. Separate times can be set for
accel and decel. In addition, a second set of accel and decel times is
available. In this example Ta = 1.0 sec, Td = 2.0 sec and Maximum
Frequency is set to 60.0 Hz.
S-Curve Selection
S-curve is enabled by defining the time to extend the acceleration and
deceleration. The time is entered as a percentage of acceleration and
deceleration time. In this case acceleration time is 2.0 seconds. The line on
the left has s-curve set to 0%. The other lines show 25%, 50%, and 100%
S-curve. At 25% S-curve acceleration time is extended by 0.5 seconds (2.0
* 25%). Note that the linear portion of this line has the same slope as when
s-curve is set to zero.
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Seconds
Hz
-80.0
-60.0
-40.0
-20.0
0.0
20.0
40.0
60.0
80.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Seconds
Hz
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
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