I'm looking into using Teknic SDSK servo motors with MachineKit. The SDSK models accept step and direction pulses like a stepper motor, so using hal_pru_generic's stepgen is straight forward. The major issue I see is attempting to use Teknic's precision homing routines, as it doesn't fit into MachineKit's limit switch routines. I'd really like to use their homing routine because it is accurate to less than 1/10,000 of an inch in my setup, which could be difficult to achieve using my own limit switch setup. It seems to me that in order to do so would require either a custom homing routine implemented in C++ (so a custom build of MachineKit). Any thoughts on this would be appreciated!
The Teknic motors have 3 control pins and 1 feedback pin: Control Pins: Enable - Used to enable/disable the motor and plays a part in initiating the precision homing (see below). Step - Same as for a stepper motor Direction - Same as for a stepper motor Feedback - They refer to this as the HLFB (high level feedback) pin. Can be set to a number of different options, but the relevant one for homing would be ASG (all systems go) Position, which is high when the motor is in the commanded position, low while moving. The precision homing sequence is initiated as follows: 1) Put the motor into homing mode by toggling the enable pin on (if it's already on, then turn it off, then back on). 2) Command the motor with step and direction to move the joint to a hard stop. 3) The motor will detect the hard stop and stop accepting step pulses until it is commanded to go the opposite direction. 4) After the hard stop is detected the motor will back off to a precise location a configured number of internal encoder counts away. 5) After a configured number of milliseconds (default is 10), the HLFB pin asserts indicating that homing is complete. The hard stop detection and precision homing is fantastic. After the first homing sequence, the motor will return to a very precise location as long as the hard stop stays within ~2mm. I can physically put a shim (less than 2mm thick) in front of the hard stop and it still goes to a precise location that properly ignores the shim (so wearing on the hard stop over time doesn't affect the precision of the homing sequence). So, does anyone have recommendations for how to perform this sequence properly in MachineKit? Preferably, I'd avoid needing a custom build of MachineKit, but if it's required to make homing a simple click of a button then I'll have to go that route. -- website: http://www.machinekit.io blog: http://blog.machinekit.io github: https://github.com/machinekit --- You received this message because you are subscribed to the Google Groups "Machinekit" group. To unsubscribe from this group and stop receiving emails from it, send an email to machinekit+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/machinekit/6b01a405-251f-4633-af72-abbcd6c78ab0%40googlegroups.com.
