PMAC Product Guide Home Trigger Condition PMAC’s homing search moves utilize the hardware position capture feature built in to the DSPGATE IC. Because software action is not required to do the actual capture, it is incredibly fast and accurate (delay less than 100 nsec). This means that the capture is fully accurate regardless of motor speed, so there is no need to slow down the homing move to get an accurate capture. Homing Search Move Trajectory Vel Specify Flag Set In the basic setup of the motor, Ix25 specifies which set of flags (associated with one of the encoder counters) is used for that motor. It is important that the flag number match the position encoder number for the motor (e.g.
if using ENC1 as the position-loop feedback, use Flags1 -- HMFL1, +/-LIM1, FAULT1 -- for thw flags, and CHC1 as the encoder index channel) in order to make use of PMAC’s accurate hardware position capture feature. Software Capture Option If not using quadrature encoder feedback for the position loop, but still need to do a homing search move, set bit 16 of the position-loop feedback address parameter Ix03 to 1 to tell PMAC that it cannot use the hardware capture feature, so it must use a software capture technique. For example, if the address for Ix03 is $0724, Ix03 should be set to $10724 for the software capture of home position.
When software capture is used, there is a potential delay between the actual trigger and PMAC’s position capture of several milliseconds. This can lead to inaccuracies in the captured position; the speed of the motor at the time of the trigger must be kept low enough to achieve an accurate enough capture. A two- step procedure with a fast, inaccurate capture followed by a slow, accurate capture, is common ly used in these types of systems.
Trigger Signals and Edges Once the set of flags for the motor with Ix25 has been specified, use Encoder/Flag I-Variable 2 (I902, I907, etc.) to tell PMAC whether to use a flag, the index channel, or both, as the capture trigger, and which edge of the flag and/or the index channel to use. 58 Programming PMAC Trigger Home Complete=1 Occurs Home Search in Progress=0 Home Complete=0 Home Search In Progress=1 Net distance from Ix23 trigger position = Ix26 Time Ix21 Ix21 Ix21 Ix20 Desired Velocity Zero=1 In Position=1 (when FE in range) Note: Rate of acceleration limited by Ix19 - can override Ix21 Ix21 Ix21 Ix20 and Ix21 Ix20 Ix20 Ix 23 Ix21 Ix21 Ix20 Note:
Rate of acceleration limited by Ix19 - can override Ix20 and Ix21 Ix21 Ix 21 Ix20 Ix20