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LAUNCHXL-F28069M: Motion planning with absolute angle

Christian Jacobsen21
Prodigy 20 points

Part Number: LAUNCHXL-F28069M

Hello,

my setup is one BLDC motor with incremental encoder and a multiturn absolute encoder. The BLDC motor drives ab big gearwheel and the absolute encoder is connected to this gearwheel.

My task is to rotate the gear between two absolute angles. In detail drive in one direction to the first angle. After this break and rotate in opposite direction to the second angle and back again.

Another similar task is to drive from angle one to angle two with a fixed speed and from two to in with higher speed, always in the same direction.

For now i’m looking for labs 13b with InstaTAC and motion planning. But it looks like InstaSpin is using relative steps with the inc. encoder. Is it possible to use the inc. encoder for the electric angle of the motor and another external absolute encoder for the position controller? The absolute encoder is connected via a CAN-BUS interface to the Evaluation Board.

Greetings,
Christian Jacobsen

  • 0
    TI__Genius 17175 points
    Hi Christian,

    I'm writing to let you know that we've asked for help from Adam at LineStream in answering this question. He should reply back shortly.

    Sean
  • 0
    Guru 12800 points

    Christian,

    It should be possible to use the motor-mounted encoder for electrical angle and a different encoder for mechanical angle (used by position control).  We align the two in the lab for simplicity.  It would simply be a matter of replacing the source of "electrical angle" into SpinTAC Position Converter.  You would also need to modify the configuration of SpinTAC Position Converter such that it is aligned with the angle you are generating.  

    The default configuration expects that the "electrical angle" provided to SpinTAC Position Converter varies between 0 and 1, and that there are a number of rollovers from 1 to 0 within a single mechanical revolution equal to the number of pole pairs in the motor.  This configuration is established in the spintac_position.h file.

    This solution would allow you to use two different encoders, but the position control scheme will still be in relative position steps.  The entire SpinTAC suite is based on a relative position scheme, so you will need to translate between your absolute system and the relative system employed by SpinTAC.

  • 0 in reply to Adam D. Reynolds
    Prodigy 20 points
    Hallo. Thanks for your answer. I'll try it next week.
    This days I tried out the motion planning examples, which are really nice.
    One question to the position mode planning, is there an option for not breaking to zero speed after a state. I look for something like moving with constant speed for 50rev and next accelerate to a new speed without deacceleration.
    Or with other word. The first state need to accelerate to a desired speed. The second state is only to move the motor for 50revs without any ramp but with the endspeed of the first state. And the third state for example is a ramp to zero rpm in 10revs.

    With my absolute angle approach I need a state which moves from one angle to another with constant speed. The ramps should be outside of this sector.

    Christian Jacobsen
  • 0 in reply to Christian Jacobsen21
    Guru 12800 points

    Look into lab 13e.  This lab talks about how to use SpinTAC Position Move to emulate velocity control systems while in position control.

    The profile generator is designed to be as generic as possible, but that does limit the number of modes it can support.