A Study Regarding the Development Trends - incdmtm

International Conference 

2ND International Conference on Innovations, Recent Trends and Challenges 

in Mechatronics, Mechanical Engineering and New High-Tech Products 

Development 

MECAHITECH‘10 

Bucharest, 23-24 September 2010 

Pneumatic Distributors - A Study 

Regarding the Development Trends 

Mihai Avram, Constantin Bucşan 

Politehnica University of Bucharest, 

Splaiul Independentei 313 , 77206 Bucuresti, 

mavram02@yahoo.com 

ABSTRACT 

The paper analyzes the important future development of pneumatics. There are 

identified and motivated the main trends and perspectives of the domain, as follows: the 

miniaturization and modularization of the equipment, the direct integration of the interface 

electronics within the equipment, the optional interface for connecting the equipment to the 

system data bus, the development of some modulated pulses command techniques for the 

on/off type distributors in order to obtain a proportional flow control, the use of some new 

type of unconventional actuators within the distributing equipment structure, the development 

of environmental friendly structures etc. 

INTRODUCTION 

Nowadays the pneumatic actuating systems are used in a large number of 

applications, due to the undoubted qualities of this type of actuators: stamina, simplicity in 

construction, productivity, high reliability, lower costs and non-pollutant energy. 

The actual stage and the development trends situates pneumatics beyond the top 

technologies. The future high development of pneumatics is analyzed using pertinent 

arguments in [1]. There are identified and analyzed the principle trends of the domain. The 

success rests in the results of some fascinating researches on limiting the negative effects of 

the working fluid low viscosity and high compressibility. These two properties are the 

principle obstacles in the way of building accurate pneumatic positioning systems. 

Most pneumatic actuating systems incorporate one or more classic or proportional 

distributors. The classic distributors lead the compressed air to certain tracks according to 

the external commands. So, it is possible to invert the moving direction of the load carried by 

the system motor and in some cases, to stop this moving. Additionally the proportional 

distributors control the flowrate and thereby the speed of the actuated load. As an example, 

figure 1 shows the functional scheme of a pneumatic positioning system [2]. There are three 

distributors: two proportional ones, DP 1 and DP 2 and a classic one, DC. 

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Figure 1: The functional scheme of a pneumatic positioning system 

PNEUMATIC DISTRIBUTING EQUIPMENT – TRENDS AND PERSPECTIVES 

The performances of a pneumatic actuating system depend on the performances of 

every equipment within its structure. In many cases the distributing equipment represents 

"the heart" of the pneumatic actuating system and highly influences the static and dynamic 

performances of the whole system. That's the reason why this paper takes regard to such 

equipment. An analysis of the evolution of the distributing equipment emphasizes the 

following trends: 

• a sustained attention to increase the reliability, the functional accuracy and the static 

and dynamic performances; 

• decreasing the price of the equipment; 

• promoting the low power consumption equipment; 

• miniaturizing and modularizing the equipment; 

• the integration of the interface electronics within the equipment; 

• the use of optional interfaces to connect the equipment to the data bus of the system; 

• the development of control techniques using modulated pulses to control the on/off 

distributors in order to obtain the proportional flowrate control; 

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• using new types of unconventional actuators within the equipment structure; 

• promoting environment friendly solutions. 

There is a large constructive variety of distributing equipment, differenced by: the type of 

the mobile element (sliding valve, valve), the type of the mobile element movement 

(translation, rotation), the number of the steady functional positions, the number of orifices, 

the type of the control, the presence of the preferred position. The most used types are those 

with cylindrical sliding valve. 

Well known companies in the field of pneumatics as Festo and SMC offer such 

distributors with acceptable static and dynamic performances. In order to improve this 

performances the research is focused on minimizing the weight of the mobile element, 

because it is the parameter that determines the response time of the equipment and its 

frequency response. 

As mentioned, there is a large demand of distributing equipment and also a large offer. 

Beyond the working performances the decisive element is the price of the equipment and the 

costs of working and maintenance. 

A lower price may be achieved in more ways, as follows: 

- using standard parts in the construction of the equipment, when possible; 

- using adequate manufacturing and assembly technologies, often advanced 

technologies, especially in the case of proportional equipment; 

- using new materials that are cheaper, lighter, with superior mechanical properties, 

more machinable and accessible. 

The miniaturizing of the equipment is another challenge for the manufacturers. The 

goal is to reduce the sizes and the weight, to use less materials and energy and to reduce 

the cost of working and maintenance. The weight of the mobile element is also reduced and 

the dynamic performances increase. 

In the last decade the most influential trend was to build compact distributing 

equipment, with a high level of aggregation of the component parts in a reduced volume. 

Some examples are the equipment for textile industry, the automatic manufacturing and 

assembly lines, the robotized systems, the equipment for electronic components 

manufacturing. The miniaturizing of the electronic and optoelectronic components brought 

forward the design and manufacturing of micromechanical devices, micro-systems and 

miniaturized pneumatic equipment. The goals are to reduce the actuating power, to integrate 

in certain technologies and to develop more efficient equipment. For the integration process 

it is essential to build mixed pneumatic and electronic systems, where every technology 

participate with its specific characteristics. There were built low sizes pneumatic motors and 

the sizes of the distributing equipment were significantly reduced according to the reduced 

flowrates needed. The miniaturization requested an adequate design of the distributing 

section of the equipment, the optimization of the actuator and the use of new materials. 

The miniaturization process was initiated by building some basic pneumatic equipment 

(motors, distributing equipment) that were used to build pneumatic mini-systems. These 

equipment are similar to the conventional ones and have the same working principle. In 

many cases it was sufficient to reduce the scale of the equipment. One example is shown in 

figure 2, a. It is a Festo distributor of the MH1 type. Figure 2, b shows an "island" of such 

distributors, mounted on the PB base and having a common P power input orifice. The 

electric power signals are transmitted through the C connector, reducing the volume of the 

equipment. The equipment has the following characteristics: 

- length: 10 mm; 

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- nominal flowrate: 10...14 l/min; 

- power voltage: 5/12/24 V; 

- switching time: 8, 5 or 4 ms; 

- pressure range: -0,9...8 bar. 

Figure 2: a) The Festo MH1 distributor 

b) An "island" of distributors Figure 3: The "Airbox" module 

The "Airbox" module shown in figure 3 is an autonomous system including two very compact 

mini-distributors. 

The miniaturizing trend led to the development of more reduced dimensions 

distributing equipment, known as micro-distributors or micro-pneumatic distributors. While 

the classic distributors (with usual sizes) control flowrates in the range of 10.000...10 dm 3 /min 

(ANR - atmosphere normal reference conditions: 20 o C temperature, 65% humidity and 1013 

mbar pressure), the micro-distributors control flowrates lower than 1 dm 3 /min (ANR). All 

micro-distributors are based on a mobile element with membranes that close or open the 

flowing area. The mobile element is controlled with specific actuators as: electromechanical, 

piezoelectric, electrostatic, thermal, shape memory, electrolytic, etc. 

The difference between mini and micro - pneumatics is not neat set out. The two 

concepts use first to measure the possibilities of miniaturizing in pneumatics. 

The manufacturers already use silicon - the material used for microprocessors and AI - in 

order to miniaturize pneumatic equipments. There were built silicon chips with etched 

structure capable to direct the air flow. This distributors have virtually null intake power, their 

response time is much lower than 1 ms, and they are made of silicon. This means that it is 

possible to build the electronic circuits on the same substrate. This concept work, as showed 

by the developed prototypes. The input voltage must be 150 V, but the intake power is 

virtually null, the mobile element being moved by the force of the electrostatic field. 

Figure 4 shows a micro-distributor with electrostatic actuation [3]. 

The upper side of the distributor is a SiO 2 membrane covered with a thin layer of 

chrome acting as a mobile electrode. The body of the distributor is made of silicon and a 

passing orifice is etched on it. The membrane stays in the proffered upper position due to 

internal stresses. When a control voltage is applied to the poly-silicon electrodes the 

membrane is pushed down and the flow is stopped. 

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Figure 4: The scheme of a micro-distributor with electrostatic actuation 

The experimental models have flow areas in the range of 10x10 µm to 100x100 µm, 

the membrane dimensions are in the range of 80...1000 µm and the thickness is in the range 

of 20...120 µm. The blocking voltage is 68 V and the working voltage is 120 V. The 

equipment is nonsensitive to electromagnetic fields and supports mechanical shocks due to 

the very low weight of the mobile element. Another advantage consist in the possibility to 

build more distributors on one substrate. 

Figure 5 shows the construction of a thermal controlled micro-distributor developed by 

IFAS and FhG - ISIT from Itzehoe, Germany [4]. 

Figure 5: The IFAS and FhG - ISIT 

thermal controlled micro-distributor 

Figure 6: The dynamic characteristic 

A pre-tensioned nickel bridge is warmed and suspended, allowing the control of a 

nozzle. Due to the used physical principle the needed input power is less than 1 W to 

modulate pressures up to 10 bar. The distributor may be of the two or three ways type and it 

has a proportional working mode. The main advantage of this distributor is the relative long 

stroke: 40 µm. Even if the distributor is thermal controlled it has excellent dynamic 

performances as shown in figure 6. The response time for a 90% step input signal is about 

16 ms. The maximum flowrate of the thermal controlled distributor is ten times larger than the 

maximum flowrate of the electrostatic distributor, due to the longer stroke. The thermal 

controlled distributor may be used as a pilot, with no need for an amplifier. 

The control interfaces for such equipment are designed as cards or modules. A 

modern development trend is to integrate the electronic interface directly within the 

equipment, that becomes a mechatronic structure controlling the pneumatic parameter 

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through an electric control signal. There are yet unsolved problems in connection with the 

environment and especially with the temperature, that decisively influences the working of 

the electronic components within optimum parameters. Figure 7 shows a proportional 

distributor manufactured by Norgren, having direct actuation and position control for the 

mobile element using a microprocessor integrated within the equipment. 

Figure 7: The Norgren proportional distributor 

The characteristics of the equipment are the following: 

- the digital micro-controller assures a high stability and a superior dynamics for the 

mobile element of the equipment; 

- linear characteristic and minimum hysteresis; 

- very good sensitivity; 

- high flowrate range; 

- very good sealing; 

- zero cover; 

- low pressure loss; 

- PC configurable using the V24 interface; 

- the control signal: 4...20 mA; ±5 V; 0...10 V. 

The pneumatic equipment manufacturers offer an optional interface to connect directly to 

the data bus. Figure 8 shows such an equipment using integrated digital electronics and 

environment monitoring functions. The bus module transmits the digital commands for 

automations. Other distributor modules and I/O modules are connected to a circuit that is 

independent of the bus protocol. This allows the diagnose to the distributor or coil level. 

Power, transmitting or configuring errors may be detected at the system level. Power, output 

and input errors may be detected at the distributor or coil level. In the case of distributors with 

feedback functions a variation of the signal larger than the permitted one will produce an 

error message. The error is easily eliminated by replacing the components or by stopping the 

process. 

Beside the analogical proportional pneumatic distributors, there were developed 

proportional distributors with discrete working. Using adequate control techniques based on 

the modulation of the electromagnet power pulses, this distributors assures the control of the 

average flowrate, while the control of the instantaneous flowrate is not possible. These are, 

in fact, electric actuated 3/2 micro-distributors with preferential position, with a mobile 

element that is not a slider but often a valve. The actuation is performed by a classic 

electromagnet and the working is of the type "all or nothing". In this case the mobile element 

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opens and shuts the inner circuit with a high frequency (≈ 200 Hz), allowing the control of the 

average flowrate. The main advantages of this distributors are the following: high response 

speed, acceptable price (the construction is simple and does not need special manufacturing 

and assembly conditions), the elimination of hysteresis and its unwanted effects, a very good 

repeatability. An actuating system that integrates such equipment may be controlled by a 

digital microprocessor, which simplifies the control system structure. 

Figure 8: Pneumatic equipment with integrated digital electronics 

Some control techniques [5] are based on mixing up the outputs of more microdistributors 

of the same type, grouped in "batteries", and especially on controlling the 

opening and shutting time of the distributor flowing area. The used control methods may be 

classified as follows: 

a. flowrate control methods based on coupling more distributors: the PNM method 

(“Pulse Number Modulation”) and the PCM method (“Pulse Cod Modulation”); 

b. flowrate control methods using modulated control signals: the PFM method 

(“Pulse Frequency Modulation”) and the PWM method (“Pulse Width Modulation”); 

c. mixed flowrate control methods. 

Beside the consecrated actuators (the classic electromagnet and the proportional 

one) there were developed another types of unconventional actuators, as: piezoelectric 

actuators, magneto-strictive actuators, actuators without mobile elements (with electroviscous 

or magnetic fluids). 

Piezoelectric actuators are the most interesting. Figure 9 shows two, a linear one (figure 9,a) 

and a bimorph actuator (figure 9,b). 

Figure 9: Micro-distributors with piezoelectric actuators 

In the first case (figure 9,a), when the actuator is not commanded, the position of the 

beam 3 determines the valve S 1 to close the orifice (1), and so the orifice (2) is connected to 

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the orifice (3). When the control voltage is applied to the actuator 2, the length of the actuator 

increases (the elongation is about 5 … 10 µm, according to the applied voltage), the 

generated force determines the buckling of the beam and the valve S 2 closes the orifice (3), 

while the valve S 1 opens the orifice (1) which is now connected to the orifice (2). In this case 

the beam 3 works as a mechanical amplifier of the actuator displacement. 

In the second case (figure 9,b), the beam 2 consist of at least two piezoelectric 

segments, bonded with each other, or both bonded on a metallic segment. When the control 

voltage is applied to the piezoelectric segments, the free end of the beam moves 

proportionally with the voltage value. 

The proportionality factor depend on the sizes of the segments and on the used 

materials. This actuators have the advantage that produce a displacement of tenths of a 

millimeter, but the developed forces are very small (of about 0,5 N). 

The problem of the environment pollution was first connected to the industrial areas. 

The next step was to analyze the technologies and so the notion "clean technology" was 

born. The actual approach is to analyze the product along its hole life cycle, starting with the 

manufacture of the materials, design, manufacture, transport and operation, and finishing 

with the possibilities of recycling or return to nature in a non-polluting form. This are also 

valid for pneumatic equipment. 

CONCLUSIONS 

The development of the pneumatic distributors domain was imposed by demands of 

automation technologies. Pneumatics was one of the main innovation factors in fluid power 

domain. The trends of miniaturization, increase of dynamic performances, piezoelectric 

technologies, and the use of the connection to the data bus, appeared in pneumatics earlier 

then in hydraulics. A recent trend in distributors development is the use of reduced sizes 

micro-distributors, with low energy consumption, made of silicon using etching technologies. 

The on/off distributors can reach similar performances as the analogical equipment using 

modulated pulses control, and this is why they are interesting for the designers. 

REFERENCES 

[1] Vogel, G., Mühlberger, E., L’univers fascinant de la pneumatique, HOPE Internationa 

Communication, 2003 : 

[2] Avram M., Bucsan C., Pneutronic Positioning Unit - Part 1: Design and Working Principle, 

Romanian Review of Precision Mechanics, Optics and Mecatronics 2009 (19), No.36; 

pag.7…10; 

[3] Haji Babaei, J., A New Bistabile Microvalve Using SIO 2 Beam as Movable Part, Proc. Of 

Int. Conf. On New Actuators, Bremen, 1994, pag.34...37; 

[4] Günther, Götz; Quenzer, Hans-Joachim: Entwicklung eines pneumatischen Mikroventils. 

O+P “Ölhydraulik und Pneumatik” 44 (2000) Nr. 9; 

[5] Avram, M., AcŃionări hidraulice şi pneumatice – Echipamente şi sisteme clasice şi 

mecatronice, Editura Universitară, Bucureşti, 2005. 

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