Beckhoff TS5066, Manual

Page: 28 / 31

Example
TS5066 28 Version: 1.0
4 Example
4.1 Synchronisation of axes on different PCs
("distributed axes")
(Example and quick reference guide)
This quick reference guide describes the synchronisation of NC axes in receiver PCs with an axis connected
to a sending PC. The "master axis" data are cyclically transferred to the receivers via network variables.
Phase differences in the real-time clocks lead to beat effects, causing individual axis information to be read
twice or missed on the receiver side. If the information is used directly for operating the receiver axes, these
step changes in the position or velocity lead to jerky motion. Figure 1 shows (slightly offset in y) the set and
actual velocity of an NC axis directly operated in the position interface with the received values. The duration
and frequency of the beat effects depends on the phase difference of the systems used.
For minimising the beat effects on the receiver side the PLC function block FB_AxisSync is used below. It
uses internally the function blocks FB_TimeSync and FB_AxisExtrapolateValues.
The FB_TimeSync block initially determines the time difference between the beat effects. Subsequently a
correction time is calculated and used for extrapolating the received the information into the future or
calculating back into the past, in order to obtain equidistant corrected information without beat effects. The
step changes in the kinematic axis variables caused by the beat effect are corrected through small changes
across the complete interval between two beat effects.
Two techniques that differ in terms of detail are available for extrapolation of the set values. The first
technique only uses the set velocity for extrapolating the set position:
AxisOut.fPosSoll:=AxisIn.fP AxisIn.fVeloSoll * fTimeCorrection;
AxisOut.fVeloSoll:=AxisIn.fVeloSoll;
Furthermore, the set acceleration may also be used for extrapolating the set position and set velocity:
AxisOut.fPosSoll:=AxisIn.fP AxisIn.fVeloSoll*fTimeCor 0.5 * AxisIn.fAccSoll
*fTimeCorrection^2;
AxisOut.fVeloSoll:=AxisIn.fVe AxisIn.fAccSoll *fTimeCorrection;
The second method, i.e. extrapolation taking onto account acceleration, is used as standard. If no
adequately smooth acceleration value is available, application of the acceleration deactivated as described
under
FB_AxisExtrapolateValues [ } 17] .
The corrected axis information is made available as NCTOPLC_AXLESTRUCT.