HELP NEEDED

Hello everybody

I have bought an actuator (LINAK PLC LA12)

Datasheet is here :

http://www.linak-us.com/pdf/english/la12_plc_eng.pdf

STRIPPED ACTUATOR:
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
piston.

MICROCONTROLLER (Keil MCB167-NET)
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
piston.

INTERFACE:
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
circuit.

SOFTWARE FOR MICROCONTROLLER:
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?

Thanks,

John

 

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:
http://www.tcnj.edu/~rgraham/PID/popelish.html

 

Thank you very much. )

If you have more info please let me know

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