Motion MMI-8S - Manual (Page 39)

APPENDIX B: DESCRIPTION OF HOMING AND ABORT LOOP PAGE 2/2
SUPER HOMING. In high resolution systems, two sensors are used. The first sensor, the home sensor, is mounted
to the motion platform in the typical configuration. The second sensor, the index sensor, is located as an index
detector on the motor shaft. The index can be either a disk with a tab or a long pin. During the homing operation, the
motor is stepped backwards until the first sensor is blocked. The motor, however, continues to rotate until the
second or index mark is detected. The system is now "homed to the step". TMG systems with Super-Homing use
two identical "PHOTO-LOGIC" sensors wire-ORed together so that both must be blocked before the home signal is
detected. The H or home command of the motion controller will operate with either single or double sensors.
ABORT LOOP FUNCTION. In TMG systems, the ABORT loop is used to remove all winding power to the motor during
an out-of-bounds condition. The ABORT feature can be used to provide hard-limits, emergency stop, door inter-
locks, and other safety features. As the ABR input, to the driver, must be LO (ground) for the driver to step; opening
the loop will stop (free) the motor regardless of the control logic. The diagram is typical of TMG "Fail-Safe, Hard-
Soft" limit loops.
NOTE: CONTRARY TO POPULAR PRACTICE, IT IS UNWISE AND UNSAFE TO SENSE LIMITS AND OTHER SAFETY
CONDITIONS THROUGH THE COMPUTER INPUTS PORTS.
All motion products, regardless of their final intended form, should initially incorporate home sensors and slip-
detection in order to prove correct positioning during product development, particularly during software de-bugging.
Typically, a test routine is established which passes slip-detection. Any detrimental modification or code flaw will be
flagged by this routine.