iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC20/36
The design tool also shows the position and speed
overshoot resulting from the selected filter instance.
Position overshoot (shown in AB edges and me-
chanical degrees of encoder rotation) is proportional
to the entered maximum acceleration and is typical-
ly noticed on stopping (deceleration). At low accel-
eration values and/or low encoder resolutions, posi-
tion overshoot may be less than one AB edge and
thus totally undetectable during encoder operation.
For example, the Maxon EC 90 flat 90W motor with
the 24V winding (order number 323772) has a rotor
inertia of 3,060 gcm2 and a stall torque of 4,670
mNm. Thus its no-load maximum acceleration in
radians per second2 is
TS 4670
m
10,000 15,261
JR 3060
Using this value for the maximum acceleration pa-
rameter in the design tool will then show the per-
formance of the iC-TW8 when used in an encoder
for feedback with this motor.
Speed overshoot is calculated as a percent of speed.
The actual amount of speed overshoot in RPM is
proportional to encoder speed. Speed overshoot is
typically noticed at the end of the acceleration ramp
(the beginning of the constant velocity portion of the
motion profile).
The graphs below show typical motion profile per-
formance and encoder lag of the iC-TW8 using lag
recovery filter mode instance 89 at 15,261 radians
per second2 maximum acceleration.
Performance graphs of encoder lag in AB edges and
response to a trapezoidal motion profile with con-
stant acceleration, velocity, and deceleration are
shown to allow observing the effect of the different
filter instances. Scroll to the right on small computer
screens to see the performance graphs.
A single parameter (maximum acceleration) is used
to generate the filter response graphs. Enter a value
in radians per second2 that represents the maximum
expected acceleration of the encoder. The design
tool calculates the equivalent acceleration in units of
kRPM (1000 RPM) per second and time to reach the
chosen maximum speed, which may be more easily
understood. The acceleration value is used only to
generate the performance graphs, it does not affect
the configuration of the iC-TW8. The motion profile
is generated by accelerating for 1000 ADC samples
at the entered acceleration, running at the attained
speed for 1000 ADC samples, and decelerating at
the entered acceleration for 1000 ADC samples.
The maximum acceleration ( m ) of a motor in radi-
ans per second2 may be calculated knowing its stall
torque ( ) in Newtons and its rotor inertia ( R ) in
J
TS
kilogram seconds2 using the formula
.
m TS JR
Figure 21: Typical Encoder Performance Graphs
Copyright © 2011–2013 iC-Haus
http://www.ichaus.com
ICHAUS [ IC-HAUS GMBH ]
