Experimental Physics and
Industrial Control System

Hi,
I ran into the following issue using the Parker PC6K device support with 
a Gemini GT6K controller:

The Parker command reference states that the s curve parameter AA 
("average acceleration") and the acceleration parameter A have to 
fulfill the following relation:

1/2*A <= AA < A

The PC6K device support always sets AA = 1/2*A to achieve the smoothest 
possible move. In some rare circumstances the values send with the 
commands do not fulfill the above relation. This seems to be caused by 
limited floating point precision in combination with rounding. The bug 
results in the motor controller ignoring the move command.

Please see the attached test case for details. A patch can be found here:

https://github.com/mark0n/motorRecord/commit/c09f92074f08a67dd319bda07e59464dbbe9912a

Please include this patch into the next revision of motor record.

Thanks,

Martin

-- 
Martin Konrad
Control System Engineer
Facility for Rare Isotope Beams
Michigan State University
640 South Shaw Lane
East Lansing, MI 48824-1321, USA
Tel. 517-908-7253
Email: [email protected]

#include <stdio.h>
#define NINT(f) (long)((f)>0 ? (f)+0.5 : (f)-0.5)       /* Nearest integer. */

double halfdouble(double dval) {
  int intval = NINT(dval);
  printf("%dA%d\t\t", 1, intval);
  printf("%dAA%ld\n", 1, NINT(dval/2.0));
}

double halfint(double dval) {
  int intval = NINT(dval);
  printf("%dA%d\t\t", 1, intval);
  printf("%dAA%d\n", 1, (intval % 2) ? intval / 2 + 1: intval / 2);
}

main() {
  halfdouble(767.9);
  halfdouble(768.9); /* the "half" value computed here is smaller than half the input! this is not allowed for PC6K controllers! */
  halfdouble(769.9);
  printf("\n");
  halfdouble(768.0);
  halfdouble(769.0);
  halfdouble(770.0);
  printf("\n");
  halfdouble(768.1);
  halfdouble(769.1);
  halfdouble(770.1);
  printf("\n*****\n\n");
  halfint(767.9);
  halfint(768.9); /* this implementation (hopefully) does it right: the "half" value is always half the input or greater */
  halfint(769.9);
  printf("\n");
  halfint(768.0);
  halfint(769.0);
  halfint(770.0);
  printf("\n");
  halfint(768.1);
  halfint(769.1);
  halfint(770.1);
}

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