A.3.6 Impact Of An Angle Error Within The Error Limits Of Vector Length Monitoring On The Speed Signal - Festo CAMC-G-S3 Manual

A Technical appendix
A.3.6 Impact of an angle error within the error limits of
vector length monitoring on the speed signal
Assume the following case: There is an error in an encoder signal e
error, for example. However, the error is small enough for vector length monitoring to not respond.
If the axle moves at a constant speed / the shaft turns at a constant rotational speed, then the error
will lead to "fluctuations" in the currently measured speed. However, the speed averaged over an en­
coder period corresponds to the actual movement speed.
Fig. A.7 Error curves on the speed signal (CH1) at a reduction of the signal amplitude of ex by 10%.
This also produces a speed ripple of 10%.
The measurement took place on an external drive of the shaft with a constant rotational
speed.
Normally, position encoder 1 is also analysed in the basic unit and used for rotational speed adjust­
ment. The basic unit now adjusts the current speed to the fluctuations. At low frequencies beneath the
critical frequency of the rotational speed control circuit, at least the supposed fluctuation is com­
pensated, the axle does not travel at a constant speed, but the actual rotational speed fluctuates and
the angle and speed signal now are "OK"
The option of detection of speed errors in safety functions, such as SLS or SSR, is therefore dependent
on multiple factors:
a) If, in addition, a second measuring system is used at the downforce, the fluctuation is detected
safely.
The speed fluctuation is detected correctly using the second measuring system, the safety module
detects an excessively high current rotational speed and switches to the safe status.
b) Only one encoder system with a high number of periods per revolution is used:
Even at low speeds, there is a relatively high frequency, which is not compensated. The rotational
speed fluctuation is detected by the safety module, and it switches to the safe status.
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or e , which could be an amplitude
x y
Festo – GDCP-CAMC-G-S3-EN – 1406NH – English