Dave pravi: > On 4/9/2010 12:04 PM, Jon Elson wrote: > >> The problem with the homing report is the destruction of data. When the >> home position is found, the machine position count is set to zero (or >> whatever the HOME_OFFSET value is). So, the old home position is >> destroyed by that operation. To stay with the canonical encoder >> definition as it is, you would have to store the position JUST before >> the home operation completed. I think you could make a custom HAL >> component that recorded the machine position every servo cycle. >> Whenever it saw ENCODER_INDEX transition from true to false, it would >> save the value recorded from the previous cycle. This would be the >> position one millisecond (at the default SERVO_THREAD rate) before the >> home position was found. I think this would give you a pretty >> consistent way of checking for drift of the home position. On the first >> home whe EMC is started, it would show the distance traveled from where >> the machine was to the home position. On later homing operations, the >> value should be very close to zero, assuming the approach to the home >> switch is slow. (Maybe watching ENCODER_INDEX only works where the >> index pulse is being used, how does the position count get set for >> stepgen, for instance? I'm only familiar with servo-like interfaces.....) >> >> I think this will work if there's a signal that tells you the home >> operation is happening NOW, and doesn't require any change to EMC2 >> itself. You would monitor this with HalMeter or the show hal signals menu. >> >> Jon >> >> >> >> > Hi Jon, > > Slavko is running steppers so I believe he has a base thread running > also which should be plenty fast enough to catch the step count just > before hitting the home switch. :-) > And if not, then I would think that a base thread could be added to > increase the accuracy. > > Just has to be worked out. > > Dave > Dave you are right. It's stepper based. And base thread is set very conservative at 50uSec. Stepper's start buzzing if I set base period at 60uS and computer's fell lazy is I set BT at 20uSec. Latency of system is aprox 16uSec. I have no problem with dir/step timming as I use phase drive.
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