Endless Axes
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Contents
Endless Axes
Introduction
Axes that can theoretically move endlessly in ether direction are supported in the softMC system. The limits of such axes are actually the range of the double-floating point format (-1.79769e+308,1.79769e+308) which practically gives endless axes operation.
Drive Limitations
However, the drive-controller communication uses much smaller range its position data is transferred using 32-bits data so the limits of internal drive position units are:
[-2 ^{ 31 },+2 ^{ 31 }-1]. This is visible on properties: CCFB, CCMD, and CEXT. They are all integer type, 32-bit variables and as such have limited values.
softMC Position Variables
The system automatically extends range position variables (pcmd,pfb,pext) to [mindouble,maxdouble] by counting the number of cycles of 32-bit range. Each time the position feedback (or external) passes 31 bit limit internal counter of revolutions (count_rev) is increased (decreased). So the position property values: PFB, PCMD , PEXT do not exhibit any discontinuities.
Detecting 32-bit Limit Exceeded
Detecting the 32 bit limit is done by checking the current and the previous value of the feedback position obtained from the drive.
- If the XOR operation on the most-significant bits of the current and the previous feedback value is 1
- we increase(decrease) the revolution counter by 1 and then compute the PFB:
- pfb = pfac*(cfb + 2 ^{ 32 }*count_rev)
- If the XOR operation on the most-significant bits of the current and the previous feedback value is 1
The revolution counter (count_rev) can be reset by:
- accessing position factor, e.g., "PFAC = PFAC" or any other assignment
- calling user function: MOT_RESET_ROLLOVER or MOT_RESET_EXROLLOVER