Research → Mechatronic systems → Pneumatically actuated inverted wedge



The balancing mechanism of an inverted wedge system has fairly similar characteristics as an inverted pendulum system. In this control task, the objective is to design a controller for achieving a motion of the cylinder slider such that the frame of the wedge has horizontal position during the time. The controlled system should have zero steady state error in angle of the frame and satisfactory disturbance rejection properties. Movement of the slider is realized by pneumatics. Energy of compressed air can steer the slider of the cylinder left and right in order to keep the wedge in balance. The control system has one control input, which is the force proportional to the pressure difference between two cylinder chambers. There are two measured outputs of the system, which are the frame angle q and the slider position x. In a broader sense, this balancing mechanism can be considered as a two degrees- of-freedom planar robot controlled by a single control input. Because it is an under-actuated system with a non-minimum phase characteristic and nonlinear actuator dynamics, this experimental model offers great possibilities to learn design in a mechatronic way.

Below figures illustrate the photo of the experimental setup (see experimental system description) and the schematic diagram of the pneumatically actuated inverted wedge.

  1. Frame
  2. Rodless cylinder
  3. Rotational potentiometer for q
  4. Rotational potentiometer for x
  5. Electronic reference card
  6. Pressure transducer
  7. Proportional valve
  8. Pressure valve & filter
  9. Air supply valve
  10. Electronic interface
  11. Control computer

Photography of inverted wedge

Schematic diagram of control system


The control algorithm is realized based on developed model of the inverted wedge system and linear quadratic regulator (LQR) optimal design. During the wedge balancing a state feedback controller should be appropriate to keep the wedge in horizontal position. The control algorithm is implemented digitally using a computer program with the sampling period T=0.01 s. Below figure illustrates the experimental results of the control system. The disturbances to the system were given by flicking the frame with fingertips.

Experimental results of inverted wedge balancing using state feedback controller


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