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BLDC Overcurrent

Discussion in 'Electronic Design' started by [email protected], Jan 29, 2008.

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    I am currently working on automatic door that uses a BLDC motor. I am
    using the current of the motor to determine if an obstacle is in the
    way of the sliding doors. The problem is to determine when it is a
    real obstacle or a cold start (stiffness of the gears and door). The
    method I am using is to store a value and compare with the next 50
    readings and check if it is a greater rate of change by checking if
    the current value has exceed a constant threshold with comparison to
    the stored value. The only problem is that the sensitivity of the
    system decreases (i.e. a higher force is needed to stop the door) and
    the threshold is not dynamic so if door size changes, I would not know
    if the threshold is correct.

    I tried using speed by setting the PWM to 0 to stop the door and
    compare the speed between the cold start and an obstacle detection but
    there isn't much speed differences.

    The microcontroller code that I inherited, the person calculates the
    acceleration and deceleration using the following equation:

    m = max_speed - min_speed/size of door*10/slope; Slope varies between
    10-100 and the size of door is the amount of halls sensor counts.

    Any help will be useful.

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