PROPNEU – AN INTELLIGENT SOFTWARE TOOL

Hong Zhou, Ph. D.Festo AG & Co.

Ruiterstr. 82, D-73734 Esslingen, GermanyEmail: ZOU@FESTO.COM

ABSTRACT

This paper deals with a software tool – Propneu. Inpractice, the design of a pneumatic system often startswith knowing the required performance of the system. Adesign engineer then needs to know which componentscan generate this required performance. Propneu helpshim to do it. After a pneumatic system is composed,Propneu can then predict the dynamic behavior andoptimize the settings of the components.

KEYWORDS Dynamic simulation, componentselection, parameter optimization, database

INTRODUCTION

With the rapid development of automation industry, itbecomes very important to rapidly design automationsystems with:

• shortest machine cycle time• optimum machine functions• minimal machine costs• compact machine space

To meet these demands, the selection of pneumaticcomponents used must be optimized.

Traditionally, the design of a pneumatic automationsystem was mainly based on the experience of a designengineer. Or components were selected based on the ruleof thumb that pneumatic cylinders, valves and pipingshould all have the same connection size. This methodoften resulted in over-dimensioning, sometimes evenunder-dimensioning.

Over- dimensioning a pneumatic system results in bigmachine components, increased costs and airconsumption. With under- dimensioning, the positioningtime of cylinders will be too long.

An efficient way to avoid these problems is by simulation,that is, to predict the behaviors of the pneumatic systemwithout the need of actually connecting components.

Today more and more simulation tools are therefore putinto use.

Many simulation tools require the user to design thecomplete system. Simulation takes place only after all thecomponents of the system have been selected. Suchsoftware tools are helpful for users to find out theperformances of his system before the machine is actuallyset up.

However in practice, the design of a pneumatic systemoften starts with knowing the required performances ofthe system. For instance, in order to reach a givenmachine cycle time, the pneumatic sub-system must finishits actions within a required period of time. The designengineer then would like to know which components cangenerate this required performance. For these cases wetherefore need a software tool which not only simulatesthe system but also helps the design engineer to select theright components.

And that’s exactly what the software tool Propneu does!

Propneu makes it possible to select pneumaticcomponents while having only limited information aboutthe application.

Propneu uses a mathematical model composed ofdynamic differential equations and static equations is setup. It uses a database which contains the technical data ofthe pneumatic components.

Two factors are taken into account when deriving themodel: the model should be accurate enough to describe areal system and at the same time the calculating timeshould be as short as possible.

Just a little example: the system consists of:a double-acting cylinder with 25 mm piston diameter, 500 mmlength, controlled by a one-way flow control valve typeGRLA-1/8-RS-B and a JMYH-5/2-M5-L-LED solenoidvalve. The mass load is 10 kg, 6 bar pressure supply. Theflow control valve is adjusted so that the positioning timeis 1.06 s. With a 240 MHz PC, simulating and calculatingthis system takes only 0.06 seconds! Compared with

common simulation software, Propneu is thus more than20 times faster.

THE INTERFACES FOR PARAMETERINPUT

There are essential variables in the mathematical modelthat define the application. These variables should beinput by the user. Several user friendly configurationwindows have been created to enter these data.

Fig. 1 shows the first window, in which a user can inputparameters such as:

Fig. 1 The first parameter window of Propneu

• The desired positioning time• The decision whether a one-way flow control valve is

to be included in the circuit (Fig. 2)• The direction of the movement

(cylinder is extending or retracting)• The required stroke length• The angle of installation• The number of simultaneously moving cylinders.

This allows the user to design a circuit, in which asolenoid valve controls more than one cylinder.

• The system pressure• The tubing lengths• The moving mass• The external force load• The additional friction:

The friction caused by the mechanical parts installedby the user, while cylinder friction is already takeninto account.

Propneu always executes a series of calculations,whenever the user changes the input data. Thecalculations have the following functions:

• Making a plausibility check of the input data• Checking whether the desired performance is reachable

at all. A warning message as in Fig. 3 will appear, e.g.if the desired positioning time is not obtainable.

• Calculating the required cylinder diameter. Thecylinder must output enough force to cope with massload, friction and external force loads, and must alsoprovide enough acceleration so that the desiredpositioning time can be reached.

Fig. 2 A pneumatic circuit with and without a one-way flowcontrol valve

Fig. 3 Warning when the desired positioningtime is not obtainable

After the user has input these data, Propneu displays thenext window for selecting a cylinder (or cylinder type).Of course, only cylinders that are suitable for theapplication are listed in the window (Fig. 4).

Fig. 4 The window for selecting a cylinder

After the user has selected a cylinder, Propneu givesrecommendations on the types of solenoid valve, the one-way flow control valve, the tubing diameters and fittingsthat should be used. Propneu then proposes an initialdesign of the pneumatic system. (see Fig. 5).

Fig. 5 The pneumatic circuit with the componentsrecommended by Propneu

If the user wants to check the dynamic behaviors of hissystem, he can click on the “Simulation” button, and thedynamic simulation is started. Information such aspositioning time, maximum and average speed, airconsumption, impact velocity and impact energy will thenbe displayed (Figs. 5, 6 and 7).

Fig. 6 The position and speed diagrams

Fig. 7 Acceleration and pressure diagrams

OPTIMIZATION OF THE AUTOMATIONSYSTEM

We should keep in mind that the Propneurecommendation is only one of all possible solutions. Ifthe user is not satisfied with the simulation results,Propneu will help him actively to optimize his automationsystem.

For instance, if the user wants to reduce the positioningtime of the system, it is sometimes difficult to determinewhich component creates the restriction affecting thecircuit. Propneu compares the flow rates of the individualcomponents and indicates the component that creates thebottleneck (see Fig. 8).

Fig. 8 Indication of critical flow rates

When a cylinder impacts on the end position, it isimportant to check the remaining kinetic energy. If theimpact energy is too high, the service life of the cylinderwill be reduced or serious damage may occur. Propneuchecks whether the permissible kinetic impact energy hasbeen exceeded by means of the following formula:

epermissiblJvmJ ≤⋅⋅= 2

21

whereJ the actual kinetic impact energym the moving massv the speed when the cylinder reaches its end

positionJpermissible the maximum permissible kinetic impact

energy of the cylinder

If the kinetic energy is larger than Jpermissible, Propneu willgive a warning and suggest the user either to reduce thecylinder speed or to select another cylinder (Fig. 9) e.g. acylinder with pneumatic end position cushioning orhydraulic shock absorbers.

When using pneumatic cushioning, Propneu optimizes thesetting of the adjustable end position cushioning so thatthe remaining kinetic energy of the cylinder is minimized.Propneu also automatically optimizes the setting of theflow control valves so that the positioning time is exactlyas the user wishes.

Sometimes the user may want to make the cylinder traveltime as short as possible, as long as the permissiblekinetic energy is not exceeded. Propneu finds themaximum permissible setting of the flow control valve bymeans of an optimization algorithm.

Fig. 9 Propneu gives recommendations if the kinetic energyat an end position is too high

With the help of the Propneu system, the user thus arrivesat the best solution for his individual application. Theresults appear in a simulation report including graphics,tables etc. as shown in Fig. 10.

Fig. 10 The simulation report of Propneu

REFERENCES

[1] Stoll, Kurt, What is Pneumatics? Thesis, Universityof Stuttgart, 1958

[2] Hong Zhou, Study of Electro-PneumaticProportional-Servo System and its Control Strategies,Doctoral Thesis, Zhejiang University, May 1988

[3]Werner Deppert, Kurt Stoll, Cutting Costswith Pneumatics, 1988, ISBN 7-111-07456-4, in 14 Languages (including Chinese)