Connect with us


Discussion in 'Electronic Basics' started by jakob, Nov 2, 2003.

Scroll to continue with content
  1. jakob

    jakob Guest

    Hello everybody

    I have bought an actuator (LINAK PLC LA12)

    Datasheet is here :

    I have removed the circuit that regulates the piston. All that is left
    is the mechanical system between the permanent magnet DC-motor and the

    I have a microcontroller that is able to generate PWM-signals. The
    microcontroller also has an A/D-port, which I will use to gain
    feedback-information that is necessary to regulate the position of the

    Between the stripped actuator and the microcontroller, there will be
    an interface. This interface will consist of an amplifier and a
    H-bridge. The H-bridge will control the spin-direction of the motor
    based on a PWM-signal from the microcontroller. I have to build this

    I need to make a software algorithm that regulates the position of the
    piston according to a desired, pre-defined position P. The software
    sets up the right PWM-signal and sends it to the interface. The
    software receives information about the state of the actuator and
    corrects errors by adjusting the PWM-signal. The correction continues
    until the desired position has been acquired.

    How do I make the algorithm? And how do I make the interface?


  2. If the speed that you achieve a match between the specified position
    (the setpoint) and the actual position (process variable) is
    important, you may also need more feedback measurements. Motor
    current is a good representation of the force that accelerates the
    motor. The average (during a PWM cycle) motor voltage, minus an R*I
    resistive drop correction is a good indication of motor speed.

    The control concept is as follows. If the position is wrong, alter
    the speed to reduce the positional error. If the speed is wrong,
    alter the force to reduce the speed error.

    Each of these correction processes need a way to compare a goal
    (setpoint) with a measurement (process variable) and use the
    difference of these two (error) to produce a control output through
    some algorithm (the controller).

    The most common algorithm for this sort of thing is a Proportional,
    Integral, Derivative combination (PID controller), though other
    possibilities exist.

    If time is not much of a factor, you may be able to eliminate one of
    both of the inner slave control loops, and just control the PWM
    directly with the position control loop, but it will perform poorly
    compared with the three loop cascade.

    If you are not at all familiar with PID controllers, you have a lot to
    study. I wrote a non technical tutorial on the tuning of the three
    terms of a typical industrial process controller (same concept but
    usually operating on a slower time scale) That you can read at:
  3. Bamse

    Bamse Guest

    Thank you very much. :eek:)

    If you have more info please let me know

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day