Position Control of a Servopneumatic Linear Actuator

The objective of this experiment is to familiarize students with and analyze a problem using an industry-relevant test setup: a servopneumatic linear actuator (SPLA).

The task is to control the position of the servopneumatic actuator.

To this end, a linear model of the servopneumatic drive is developed using a Bode plot generated during the experiment.
This model is used to design a linear controller that controls the position of the linear drive. 

A challenge in modeling the system is the nonlinear friction of the linear actuator.

Laboratory Director

Axel Dürrbaum, Engineer

Implementation/Description

Each group consists of 4–5 participants. During the lab experiment, each participant prepares a lab report describing all the steps taken and the results obtained.
The experiment lasts 3 1/2 hours.

Materials needed: ruler, pencil, set square

Experiment steps:

  1. Set up the experimental apparatus (PC, amplifier, sensors, actuators)
  2. Determining the friction force curve
  3. Recording the measurement curves for specific amplitudes/frequencies of a sinusoidal excitation
  4. Plotting a Bode plot
  5. Determining the parameters of the linear system model from the Bode plot
  6. Controller design for the linear system model using the MATLAB Control Toolbox
  7. Simulation of position control with a PID controller and a linear plant in MATLAB
  8. Experimental validation of the position control system
  9. Discussion of the results

Experimental Setup

The section of the experimental setup to be controlled is the "PneuPos1" pneumatic linear actuator from Festo Didactic.

The system is considered a single-input, single-output (SISO) system:

  • one input variable: servovalve control signal uv
  • one output variable: position of the linear actuator xk

To reduce nonlinear friction forces, a sinusoidal excitation is added to the control signal uv (dithering), so that the actuator does not get stuck due to static friction.