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Ele ctric cylin der s S RS A , SVS A a n d S L S A
Case “home switch is fixed on the machine
driven by the Ewellix cylinder”
In this case, depending on the servoamplifier definition (read
servoamplifier user manual to get corresponding informa-
tion), it might be necessary to make sure that the length of
cam detected by the home switch will be longer than the
stroke achieved by the cylinder for one motor revolution.
Once this precaution has been taken, the zero reference
definition opportunities offered by the servoamplifier are
enough to answer all possible cases.
NOTE
To define a zero reference which will always stay the same, even
when the cylinder is replaced by a new one, it is required to write
a program which makes the pushing cylinder meet a mechanical
stop and which defines the zero reference in relation to the
reached position.
4.4 How to check position
control behaviour – first
approach
WARNING
At the time of first cylinder commissioning, it’s advised as a first
approach to check that the position control operates correctly
without risk to generate a tracking error fault or overspeed fault
(see the servoamplifier manufacturer’s technical documentation
to get more details on these two faults). These faults might
generate heavy property damages (see explanation below).
Depending on the servoamplifier manufacturer, it’s possible
that tracking error fault or overspeed fault switch off torque
on the cylinder motor (read servoamplifier documentation for
more information). If this is the case and if this occurs when
the cylinder is at maximum speed, the cylinder will keep
moving because of the kinetic energy of the cylinders inter-
nal rotating parts. Consequently, it is very likely that the cyl-
inder will stop suddenly against its internal mechanical stop
or the machine’s mechanical stop. In both cases, this might
generate heavy property damage.
To avoid this from happening, it’s advisable to check the be-
haviour of the position control.
As a first step, please read the servoamplifier technical doc-
umentation to see if there’s an existing method or if specific
tools have been developed by the servoamplifier manufac-
turer to make this check.
Otherwise, use the following method which is a simplified
evaluation of position control behaviour.
Principle of evaluation method:
Position control behaviour is estimated through measure-
ments made with the servoamplifier scope tool (see servo-
amplifier technical documentation for more details) while the
cylinder is making forward and backward moves. The scope
tool allows the user to see a value evolution of the control
variables in the function of time. In this way it is, for example,
possible to see in one graph the evolution of cylinder speed
and the evolution of motor current in the function of time.
To make an estimation of position control behaviour, it’s re-
quired to see the speed set point, actual speed, tracking er-
ror and motor current of the cylinder (see servoamplifier
technical documentation to know the corresponding varia-
bles name). Depending on observations made on the shape
of acquired curves, it will be possible to estimate the risk of
generating a tracking error fault or over speed fault on a
scale ranging from zero to very high.
Detailed description of method:
• Put the cylinder into the final use conditions (cylinder has
to be installed inside a machine and has to be able to
achieve the work for which it has been designed) and de-
crease the maximum moving speed value (take maximum
speed equal to 1/10th of maximum speed defined for the
application) and acceleration/deceleration values (take
value equal to 1/10th of acceleration/deceleration values
defined for application).
• First, start a cylinder forward movement and then a back-
ward movement and make scope record at the same time.
Look at the acquired graph and compare it with the two
example graphs given below. Conclude about risk level to
generate tracking error fault and/or over speed fault.
• If the risk is low, increase speed value and acceleration/
deceleration values and remake measurements with the
scope tool during a forward-backward cylinder movement.
Remake an estimation of risk level to generate a fault. As
long as the risk stays low, repeat this step until to values of
speed, acceleration and deceleration defined for applica-
tion are reached.
• If the risk is becoming significant, do not keep increasing
speed and/or acceleration/deceleration but try to reduce
the speed overshoot value and/or tracking error value. To
do that, study the servoamplifier technical documentation
to identify actions to perform to reduce the risk level to
generate an over speed fault and/or tracking error fault.
DANGER
Customer should be sure that the commissioning steps
suggested in method described to the left can’t create any
problems.
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