Pneumatic Inverted Pendulum

Construction

Mechanical structure

Compressed air comes from air compressor and goes in the proportional valve. Coming out from the proportional valve, there are two branches of air flow (one is compressor air, the other one is exhausted air) which connect to the air cylinder (pneumatic actuator). The pneumatic actuator connects to a cart (the aluminum box) where the pendulum is attached, and underneath the cart lies the carrier, which guides the cart along straight line. The rotational encoder is inside the cart, and its shaft is fastened throught the cart. The pendulum is attached to the shaft and is able to rotate 360 degrees. At the back side of the cart, a linear encoder is attached. For more detail please refer to VIDEO 1.

 

Note: the flow control valve is unused.

Control circuit board

 

Arduino is used as the data acquisition board and control unit. Signals from the linear encoder and rotational encoder are acquired into the Arduino, and then an output voltage is calculated, which will then control the proportional valve through a Digital Analog Converter and Operational Amplifier. The circuit schematic diagram is shown below:

 

Note that the “black green red yellow” in linear encoder diagram are just merely the color of wires. You might have different ones, but after watching VIDEO 3, it should be clear on how to use a linear encoder–the connection and programming are similar to rotational encoder. The operational amplifier should be connected to the +12 and -12 power supplies (not depicted). As noted above, if using separate power supplies, they must share a common ground.

Arduino

Visit arduino.cc to learn more.

Rotational encoder

The rotational encoder used in this project is S1-1250-250-I-N-D (more detail available in TABLE 1).

This encoder has 1250 counts per 360 degree (2*pi radians). Therefore, we have:

 

1250/(2*pi) = angle_count/alphaWhich gives us:

 

 

alpha = 0.00503*angle_count (unit: radian)And the angular velocity could be estimated via

 

 

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