FAQ No. FAQ02497
Question
What concepts are applied for countermeasures for noise for a Servo
System?
Answer
1. Countermeasures for Noise
The following four aspects are important when considering countermeasures
for noise.
1-1. Investigate Noise Sources
Devices that cause rapid changes in voltage or current are noise sources.
Generally the larger the signal power, the stronger the noise source
becomes.
List the noise sources that surround your Servo System.
1-2. Identify the Noise Transmission Path
Once you know the source, position, type, and characteristic of the noise,
you can narrow down the noise transmission paths. For each possible noise
transmission path, apply a countermeasure. Start with the most probable
path. You can narrow down the noise transmission path by seeing how
effective the countermeasure is.
Another method is to use shield boards connected to frame grounds to check
the effect of electromagnetic waves, electromagnetic induction, and
electrostatic coupling.
1-3. Noise Countermeasures Must Not Be Removed
until the End
Even if the countermeasure applied to a noise transmission path was
ineffective, do not remove the countermeasure. There may be several noise
transmission paths and the countermeasure that you applied may be blocking
the second largest noise path.
1-4. Noise Transmission Paths That Are Common in
Servo Systems
Leakage current from the motor electrostatic coupling to the frame ground
becomes large in Servo Systems and Inverters.
If the current is not absorbed very well, the frame ground potential will
become unstable. This increases cases where noise is transmitted to other
devices through the frame ground.
2. Actual Noise Countermeasures
Countermeasures for noise transmission paths as well as countermeasures
against leakage current are described below.
2-1. Countermeasures for Electrostatic Coupling
|
Countermeasure |
Purpose |
Precautions |
Wiring |
|
Move the signal lines
further apart. |
To reduce electrostatic
coupling |
Move them at least 10 cm
apart; 30 cm is sufficient. |
Refer to
Figure 1 below. |
|
Use a conductive shield
(e.g., storage panel, metal pipe, shield). |
To reduce electrostatic
coupling |
The conductor to be used as
a shield must be connected to the frame ground.
The ground must be on one end only. (No current flow can be allowed in
the shield.) |
Refer to
Figure 2 below. |
2-2. Countermeasures for
Conductive Coupling
|
Countermeasure |
Purpose |
Precautions |
Wiring |
|
Noise filter |
Attenuation of high
frequency components |
After a
noise filter is inserted, completely separate the lines to the control
line and the power line. |
Refer to
Figure 3 below. |
2-3. Countermeasures for Electromagnetic Induction
|
Countermeasure |
Purpose |
Precautions |
Wiring |
| Move the
signal lines further apart. |
To reduce
the magnetic field strength. |
Move them
at least 10 cm apart; 30 cm is sufficient. |
Refer to
Figure 1 below. |
| Twist the
signal line and return line together. |
To reduce
the area affected by a magnetic field. To mutually cancel out the
effect of magnetic fields. |
Keep the twists small (5 cm
or smaller).
Do not make the twists for the power line and the signal line at the
same pitch. |
Refer to
Figure 4 below. |
2-4. Countermeasure for Electromagnetic Waves
|
Countermeasure |
Purpose |
Precautions |
Wiring |
|
Noise filter |
Attenuation of high
frequency components |
Keep the wiring short in
areas in which noise is not attenuated by a noise filter. |
Refer to
Figure 5 below. |
Use a
conductive shield
|
To reduce
electrostatic coupling |
The conductor to be used as
a shield must be connected to the frame ground.
The ground must be on one end only. (No current flow can be allowed in
the shield.) |
Refer to
Figure 6 below. |
2-5. Countermeasure for Leakage Current
|
Countermeasure |
Purpose |
Precautions |
Wiring |
|
Noise filter |
To
attenuate the common-mode (between power and frame ground)
high-frequency component |
Use a noise
filter that can remove the common-mode noise (must be implemented even
if it is only for the Control device). |
Refer to Figure 7 below. |
Connect to
ground
with a thick line at
the shortest
possible distance. |
To let the
leakage current escape quickly, and to reduce voltage changes.
|
The wire diameter must be
at least 2 mm˛. Keep the wiring distance as short as possible.
Directly ground to 100 W or less. |
3. Other Noise
Countermeasures
If noise-related errors persist even after applying noise countermeasures,
try the following measures. They may be effective depending on the model
of Position Controller and Servo Driver.
3-1. The Positioning Point Is Offset When
Connected to Position Controller with a Pulse Output
Problem:
Noise is superimposed on the command pulse input signal, so the Driver
takes the noise as a command signal.
Countermeasures:
Separate the power source.
Use a dedicated power supply for the Controller's pulse output.
It is effective to separate the ground line as well.
Shield the pulse signal
If positioning is offset even after separating the power source, connect
both ends of the command pulse signal line shield (shielded twisted-pair
cable) to the frame ground.
Note: Make sure that the Controller
and the Driver are always grounded to 100 Ω or less. If the grounding is
ineffective, it will make the problems worse.
3-2. The Positioning Point Is Offset When
Connected to Connect to a Controller with an Analog Output
Problem:
Noise is superimposed on the feedback pulse (encoder signal), so the
Controller takes the noise as a feedback pulse.
Countermeasures:
Shield the feedback pulse signal.
Connect both ends (Controller and Driver) of the feedback pulse signal
shield (shielded twisted-pair shielded cable) to the frame ground.
Note: Make sure that the Controller
and the Driver are always grounded to 100 Ω or less. If the grounding is
ineffective, it will make the problems worse.
3-3. The Ground Is Bad
Problem:
If the ground to 100 Ω is bad, noise will be transmitted from ground. If
noise persists no matter what countermeasures are used, check the ground
potential.
Countermeasures:
Connect to a good ground at 100 Ω or less.
Improve the condition of the ground.
Separate the frame ground of high-power
devices and low-power devices.
Float the frame ground line of the Control
device and other applicable devices
Cut the shield of the shielded cable.
These countermeasures are for worst case
scenarios. If the Servo System is operating in an environment with serious
noise problems, it will not operate at full capacity.
Other Servomotor / Servo Driver
FAQs
 What models of Servomotors with decelerators are used with SMARTSTEP A-series Servo Drivers?
What kind of noise is generated when the Servo System is used? Also what kind of noise affects the operation of the Servo System?
Is there a Servo System that has full-closed control?
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