AMCI SD4840EK, Руководство пользователя

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SD4840EK User Manual
M
OVE
P
ROFILES
21
Definition of Acceleration Types (continued)
What is jerk? (continued)
In order to keep the Acceleration Jerk parameter value that is programmed into the SD4840EK below sixteen
bits, the SD4840EK’s Acceleration Jerk parameter does not have units of steps/sec
3
. The Acceleration Jerk
parameter equals ({100 * jerk in steps/sec
3
} / acceleration in steps/sec
2
). This translates to the jerk property
in steps/sec
3
equalling ({Acceleration Jerk parameter/100} * acceleration in steps/sec
2
). With the range of
values for the Acceleration Jerk parameter being 1 to 5,000, the jerk value ranges from 0.01
a
to 50
a
where
“
a
” is the acceleration value in steps/sec
2
. For example, if the acceleration is programmed to 20,000 steps/
sec
2
, then the value of the jerk property used by the module can be programmed to be between 200 steps/sec
3
(0.01*20,000) and 1,000,000 steps/sec
3
(50*20,000).
Constant Acceleration
When the Acceleration Jerk parameter equals zero, the axis accelerates (or decelerates) at a constant rate until
the programmed speed is reached. This offers the fastest acceleration, but consideration must be given to
insure the smoothest transition from rest to the acceleration phase of the move. The smoothest transition
occurs when the configured Starting Speed is equal to the square root of the programmed Acceleration value.
Note that other values will work correctly, but you may notice a quick change in velocity at the beginning or
end of the acceleration phase.
Figure R2.1 Constant Acceleration
Additional information, including example move calculations, can be found in section 3,
Calculating Move
Profiles
starting on page 39.
S-Curve Accelerations
When the Acceleration Jerk parameter value is in the range of 1 to 5,000, the SD4840EK uses this value to
accelerate and decelerate the rate of acceleration. This is known as S-Curve acceleration because of the shape
of the speed curve that results from the variable acceleration.
When using S-Curve accelerations, the starting speed does not have to be equal to the square root of the pro-
grammed acceleration value. The S-Curve acceleration will provide smooth transitions at the beginning and
end of the acceleration phase.
Trapezoidal S-Curve Acceleration
When the Acceleration Jerk parameter is set high, Trapezoidal S-Curve acceleration usually results. The
acceleration value quickly increases (accelerates) until it reaches the value of the Acceleration Parameter. At
this point, the acceleration remains constant until the SD4840EK begins to apply the jerk property value to
decrease the acceleration value until it equals zero when the programmed maximum speed is reached. Figure
R2.2 shows a trapezoidal curve when the Acceleration Jerk setting results in the acceleration being constant
for half of the acceleration time. With this setting, the Trapezoidal S-Curve acceleration only requires 33%
more time to achieve the same velocity as a Constant Acceleration move.
Figure R2.2 Trapezoidal S-Curve Acceleration
SPEED
AC
C
E
L
E
RA
T
IO
N
TIME TIME
t t
Programmed
Speed
SP
EE
D
AC
CEL
ERA
T
IO
N
TIME TIME
4/3t 4/3t
1/4 1/4 1/2 1/2
1/4 1/4
Programmed
Speed