Software for the synchronization of axes - Kollmorgen

SOCAPEL SA SOFTWARE FOR SYNCHRONIZATION OF AXES 024.8068.A8.10 SYNCHRONIZATION PRECISIONConverting the speed of the master shaft into a slave-shaft speed is achieved using the carrymethod (see paragraph 8.5.2) : VMUS may momentarily be approximate, due to the digitizingprocess and the complexity of the conversion factors (±1 bit), but there will be noaccumulative error.Sum of VMUS's = constant . sum of VMAST's.Two axes can therefore be slaved together for several days at a time, without moving bymore than one position bit.During synchronizing or desynchronizing, VMUS and VGES are added. VGES is most oftenfixed by parameters, and is therefore independent of VMAST. Thus VIREF is neitherproportional to nor independent of VMAST.Special case :If an IRG RATE dependent on VMAST is selected, VGES will be proportional to VMAST butthe conversion carries will not be processed.Sum of VGES = approx. constant . sum of VMAST.Similarly, any modulated acceleration values will not be converted exactly : their degree ofinternal precision will diminish with size. For this reason, if the slave appears to be "waiting"for the master, synchronizing is achieved by setting :VIREF = C . VMAST - C1 . VMASTC = approximately C1, whence VIREF = approximately 0.The above discussion on speed control showed how VGES can be approximate, but that theSUM of the individual VGES values is CONTROLLED, and for this reason the relativepositions of the axes after or before synchronizing will be EXACT, without cumulative error.If the master shaft is an ST1, the fiber-optic transmission system imposes a common timebase for both master and slave, hence there will be no relative-positioning error between thetwo. There is only an absolute error (± 100 ppm) due to a quartz crystal in the transmissionsystem.Two independent ST1's would operate on such a time-base (error of 100 ppm). If theyreceived the same references at the same time, they would reproduce a maximum error of0.2 revolutions after 1000 revolutions.81