US3656495A

US3656495A - Fluidic devices

Info

Publication number: US3656495A
Authority: US
Inventors: Carl Anders Noren
Original assignee: Atlas Copco AB
Current assignee: Atlas Copco AB
Priority date: 1968-08-26
Filing date: 1969-08-19
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18
Also published as: SE327340B; DE1943137B2; DE1943137A1; GB1274276A; JPS4813158B1

Abstract

A fluidic device without moving parts consists of a housing having a verturi shaped main passage which has one or more secondary passages branched-off from the minimum section of the venturi and which form an acute angle with the outlet portion of the main passage. The cross section area of the venturi increases suddenly downstream of the branch-off point.

Description

United States Patent Noren I Apr. 18, 1972,

[54] FLUIDIC DEVICES [72] Inventor:

Sweden [73] Assignee: Atlas Copco Aktiebolag, Necka, Sweden [22] Filed: Aug. 19, 1969 [21] Appl. No.: 851,195

[30] Foreign'Application Priority Data 4 Aug. 26, 1968 Sweden ..11434/68 52 vs. C] ..,.....1'37/s1.s [51] Int. Cl. ..Fl5c U118 [58] Field ofSearch..... ..137/81.5

[56] References Cited UNITED STATES PATENTS 3,182,674 5/1965 Horton ..l37/81.5 3,194,253 7/1965 Havee ..137/8l.5

Carl Anders Noren, Fasanvagen, Ektorp,

3,212,515 10/1965 Zisfein et al. ..l37/8l.5 3,170,476 2/1965 Reilly ...l37/81.5 3,204,405 9/1965 Warren et a1. l37/81.5 X 3,232,095 2/1966 Symnoski et al ..l37/81.5 X 3,258,023 6/1966 Bowles ..137/81.5 3,285,262 11/1966 Ernst et a1 ..137/81.5 3,457,935 7/1969 Kantola ..l37/81.5 3,468,328 9/1969 Metzger ..137/8 1.5 3,500,846 3/1970 Wood ..137/81.5 3,509,897 5/1970 Abler ..l37/81.5

Primary Examiner-Samuel Scott Attorney-Munson and Fiddler [57] ABSTRACT A fluidic device without moving parts consists of a housing having a verturi shaped main passage which has one or more secondary passages branched-oif from the minimum section of the venturi and which form an acute angle with the outlet portion of the main passage. The cross section area of the venturi increases suddenly downstream of the branch-off point.

9 Claims, 15 Drawing Figures PATENTEDAPR 18 1972 SHEET- 20F 4 Ana MS NTOR. r )1.

PATENTEUAPR 18 I972 SHEET 3 BF 4 I VEN'I'UR.

Cal"! And rs A mm FLUIDIC DEVICES This invention relates to fluidic devices without movable parts, and particularly to a type of fluidic devices in which a fluid flowing into a main passage in the device flows out chiefly through a main outlet portion and in which a pressure is produced in one or more secondary passages, communicating with the main passage which pressure is lower than the pressure which prevails in the outlet end, of the main outlet portion if the outflow of fluid through said main outlet portion is not restricted to any considerable degree, for instance by blocking of the remote end of a conduit connected to said main outlet portion. In the latter case, the fluid instead flows out through the secondary passage or passages.

Hydraulic or pneumatic fluid operating means are often used for controlling machines, measuring instruments, various operating cycles, or the like. This is particularly the case when a plant contains fluid driven operating components or in cases where the working fluid is used as a signal transmitting medium in a control system or parts thereof.

The control signals appearing in a fluid control system are produced by governing fluid control means forming parts of the system, which governing means are themselves controlled in one way or the other. Said governing fluid control means controls the supply or escape of fluid in control signal transmitting conduits connected to the input or output ports, respectively, of fluidic control devices. Since, according to the law of Bernouilli a certain relation exists between the pressure and the flow velocity of a fluid, the produced signals may be sensed as pressure or flow velocity changes in the control signal transmitting conduits and in the signal ports of the controlled fluid means connected thereto.

One difficulty in the construction of fluid control systems is that the produced control signals do not affect the controlled fluid control means in the desired way since the pressure amplitude or the pressure amplitude intervals of the signals do not correspond completely or partly to the pressure interval in which the controlled fluid control means works most favourably or at all functions.

One object of the present invention, therefore, is to provide in a fluid control system means for transformation of the pres-.

sure amplitude of control signals from one level to another lower level.

Another object of the present invention is to provide in a fluid control system means for transformation of the pressure changes of control signals within a certain interval into pressure changes within another interval on a lower level including positive or negative pressures as well as both positive and negative pressures.

A third object of the present invention is to make possible in a fluid control system the utilization of a comparatively'long signal transmitting conduit which is continously supplied with fluid at the end which is adjacent the controlled fluid control means and which conduit at the other end is provided with a signal emitter which produces signals by controlling the outflow velocity of the fluid from the signal transmitting conduit.

A fourth object of the present invention is to make possible, in a fluid control system, the utilization for signal transmission of a comparatively long conduit or hose connected to a binary signal emitter disposed externally of the control system, which emitter may be a device which registers the attainment of a certain end position or the like and which permits or blocks a flow through the conduit or hose of fluid such as air, which is continuously supplied from a built in fluid source in the control system so that separate supply of signal transmitting fluid to the signal emitter may be eliminated.

A fifth object of the present invention is to make possible, in a system for pneumatic measuring or control of dimensions and tolerances, the utilization of a device according to the invention as an element for accomodation of signals or as an amplifier element between a controlled means of some kind and a signal transmitting conduit or hose which conduit or hose is continuously supplied with air from a built in source of air in the measuring system, said measuring signals being produced by externally disposed emitters of conventional type, such as measuring points or gauges.

The signals in a fluid control system maybe transmitted according to various principles. According to one principle, which may be characterized as hydrostatic, thesignal transmitting fluid is constantly at rest. The signals then comprise pressure changes which are transmitted in the fluid without any noticable flow therein. In connection with the present invention hydrostatic signal transmitting may be disregarded. Accordingto another principle, the signal transmission comprises a conduit with a flowing fluid. The occuring phenomena are then of a dynamic character and the signal transmission may be said to be hydrodynamic. v

A fluid control means may be either pressure controlled or flow controlled. A pressure controlled fluid control means is a means which, within the control range, has no consumption of control fluid. In this case, pressure signals through a control signal port affect a control chamber which may comprise the closed volume above a piston or a membrane, the interior of a bellow or a Bourdon tube, etc. A pressure increase produces a displacement of a piston rod connected to the piston or other corresponding element, which displacement in turn may be used to control a power flow. A flow controlled fluid control means, on the other hand, consumes control fluid within the whole normal control range. As an example of such devices may be mentioned fluid control means with flappers or fluid amplifiers of the non-moving part type. However, hybride forms also exist, i.e. means which are pressure controlled within certain parts and flow controlled within other parts of the control range.

A principal object of the present fluidic device is to produce a device which may be utilized in connection with flow controlled fluid control means and particularly in connection with fluid amplifiersJThe invention may, however, also be utilized in connection with pressure controlled fluid control means if the signal transmission is of hydrodynamic character.

The fluidic device according to the invention comprises a housing, a main passage and one or more secondary passages branched off from the main passage formed in the housing, said main passage being substantially of venturi shape and having an inlet portion and an outlet portion and an intermediate minimum cross section area portion, and said secondary passage or passages being branched off from the main passage at the minimum cross section area portion. The invention is principally characterized by the fact that the secondary passage forms an acute angle with said outlet portion of the main passage, and that the cross section area of the outlet portion increases suddenly at the point where the wall of the secondary passage intersects the wall of the outlet passage, so that a fluid flow or jet through the main passage leaves the wall of the main passage at the point where the secondary passage is branched off and shortly afterwards adheres to or reattaches said wall of the outlet portion.

On the accompanying drawings some embodiments of fluidic devices according to the invention and systems built with such devices are illustrated by way of example.

FIG. 1 is a diagrammatic perspective view of a fluidic device according to the invention having a mainpassage and a secondary passage formed in a housing having a cover which is illustrated in lifted up position.

FIG. 2a, b, and c are plan views of devices according to F IG. 1 with the cover taken away.

FIG. 3 is a perspective view of an embodiment of the fluidic device having two secondary passages.

FIG. 4a and b illustrates in longitudinal section and end view a rotosymrnetrical fluidic device according to the invention having a number of secondary passages.

FIG. 5 is a perspective Roentgen view of a fluidic device with five main and secondary passages.

FIG. 6 illustrates a system in which a fluidic device according to the invention forms a part and FIG. 7a and b are diagrammes illustrating the pressure variations in the systems.

FIG. 8 illustrates a conventional well known fluidic device.

FIGS. 9 and 10 illustrate two apparatus in which the invention forms a part and FIG. 11 is a diagram.

The fluidic device according to FIG. 1 consist of a housing 1 in which passages with rectangular cross section are formed and which has a flat cover 2 which covers the passages and is secured to the housing. The passages comprise a main passage and secondary passage. The main passage is substantially of venturi shape with a converging inlet portion 3, a diverging outlet portion 4, forming the main outlet, and an intermediate minimum cross section area portion 5. From the last mentioned portion a secondary passage 6 is branched off, which at the point where it is branched off forms an acute angle 7 with the main outlet portion 4. The angle 7 may vary according to prevailing conditions and is usually between 20 and 60, but it may preferably be about 45. At the branch-off point of the secondary passage the main passage, cross section area increases discontinuously so that the down-stream portion 8 of a wall, from which the secondary passage extends, is withdrawn a short distance relative to the up-stream portion 9 of said wall. A step is consequently formed in said wall. The diverging walls of the main outlet portion form an angle of 10 to the diffuser angle.

A fluid flowing through the fluidic device increases its velocity in the inlet portion and simultaneously the static pressure of the fluid decreases since the cross section area decreases unto the minimum cross section area portion. In this portion the flow velocity is at its maximum and consequently the static pressure is minimum. The pressure then decreases as the flow velocity is reduced when the fluid flows through the outlet portion or the secondary passage.

if the outlet portion 4 opens without restriction into a surrounding space with a certain pressure, which is usually the atmospheric pressure, then a reduced pressure prevails in the minimum cross section area portion. Since the secondary passage is branched off from the main passage at this point said reduced pressure is spreading into the secondary passage. if the fluid is permitted to flow freely into the ambient atmosphere from the outlet portion ofthe main passage then the flow velocity within certain limits is defined by the pressure at which the fluid enters the fluidic device, i.e. the pressure in the fluid source from which fluid flows into the main passage. If this admission pressure is increased then the flow velocity increases until the pressure drop in the main passage becomes critical which, however, does usually never occur in devices of this type. If the pressure fluid source is a signal emitter or if a signal emitter is situated in the fluid supply conduit which produces pressure signals, then pressure signals are obtained in the secondary passage which may be utilized in certain applications.

Since according to the law of Bernouilli a certain relation exists between pressure and flow velocity it would be proper also in connection with flow controlled fluid control means to talk of control signal pressure thereby meaning the static pressure which prevails in the fluid flow utilized for control. This is also proper, since manufacturers of fluid control means often define the relationship between the control signal and the output signal as a relation between control signal pressure and output signal pressure irrespective of whether the device is pressure or flow controlled.

In the related fluidic device the relation between input signal pressure in the main passage inlet and output signal pressure in the secondary passage may consequently be described as a falling or decreasing function of the increasing pressure ofthe input signal.

If on the other hand the pressure ofthe fluid source remains constant and the flow through the main passage outlet is restricted, an increase of the pressure in the minimum cross section area portion and a corresponding increase of the pressure in the secondary passage is achieved due to the decrease of flow velocity in the main outlet. These pressures will reach their maximum values when the main passage outlet is completely blocked.

A signal emitter which directly or by means of a fluid conduit is connected to the main passage outlet port ofthe related fluidic device and consists of a means which more or less permits or completely blocks the fluid flow coming from the said outlet, may consequently be utilized to generate pressure signals in said secondary passage. This possibility will be utilized in several applications.

In addition to the flow conditions upstream and downstream the main passage, the pressures in the minimum cross section area portion and the secondary passage is affected by the flow condition in the secondary passage itself. If fluid flow through said passage is possible then a secondary flow is obtained at reduced pressures in the minimum cross section area portion towards the main passage. Said secondary flow mixes with the main flow through the main passage. This results in a pressure in the minimum cross section area portion which is higher than the pressure obtained therein if the secondary passage had been completely blocked. When the pressure in the minimum cross section area portion exceeds the pressure of the ambient atmosphere or the surrounding space, due to the outflow through the main outlet portion being restricted, then the fluid flows out through the secondary passage if the outlet port of said passage is not blocked. This is utilized in connection with some applications of the present invention. It is then desirable to use the fluid flow which is fed into the inlet portion of the fluidic device with as small losses as possible. The secondary passage, therefore, has been given such a shape that it presents a minor flow resistance to the fluid flowing out through the secondary passage. This, among other things, is obtained by giving the fluidic device such a shape that the fluid flow direction is changed as little as possible from the incoming fluid flow direction when the fluid flows out through the secondary passage. The angle between the inner portion of the secondary passage and the main passage outlet portion must consequently be an acute angle. However, it is not possible to make said angle too small since this reduces the ability of the fluidic device to produce a pressure below atmospheric pressure in the minimum cross section area portion and in the secondary passage. The inlet port to said secondary passage has to be isolated from the main passage so that the fluid flow through the main passage does not hit directly on said inlet port, since in such a case a part of the fluid flow might be driven out through the secondary passage due to its kinetic energy in spite of the fact that the outflow through the main outlet portion is not obstructed. For this reason a step has been provided in one

wall

8, 9 of the main passage at the port leading to the secondary passage which step increases the isolating effect. This step is indicated at 10 in FIGS. 2ac. These figures show the fluid flow through the fluidic device 1 at different degrees of throttling of the main outlet portion 4.

The step functions in such a manner that a fluid flow or jet moving through the main outlet portion 4, FIG. 2a, detaches from the

side wall

9,8 at the port leading to the secondary passage and reattaches to said side wall at a distance downstream of said port. This separation of the flow or jet from the wall helps to reduce the pressure in the secondary passage under the flow conditions illustrated in FIG. 2a, and consequently also raises the level which a back pressure produced by throttling of the main outlet portion must exceed in order that a flow of fluid out through the secondary passage may occur. This feature of the fluidic device according to the invention is one of the most important.

It has been mentioned hereinabove that pressure or flow signals in the discharge part of the secondary passage may be produced by controlling the supply of fluid to the fluidic device, on one hand by increasing or decreasing the pressure of the source of fluid supply and on the other hand by controlling the discharge of fluid from the main passage outlet by means of some kind of valving or throttling device.

Both methods may be utilized simultaneously in order to combine signals from two signal emitters.

The dimensions of the passages in the fluidic device may vary within wide limits. For many purposes, however, it is preferred to carry out the main passage with rectangular cross section with a height in the minimum cross section area portion which is 1-10 times the width of the passage in said portion. Suitable dimensions may be a height perpendicular to the common plane of the main passage and the secondary passage of 0.5-1.0 millimetres and a width of 0.1-0.2 millimetres in said minimum cross section area portion.

In the embodiment of FIG. 3 the fluidic device 11 is provided with two opposite

secondary passages

12 and 13 which are intended to simultaneously control two fluid control means. The main passage has, similar to the embodiment of FIG. 1, an inlet portion 3 and an outlet portion 4. The cover 2 of FIG. 1 has been left out in FIG. 3.

The fluidic device illustrated in FIG. 4a and b is rotosymmetrical and has a number of secondary passages, say, five passages indicated by the

reference numerals

15, 16, 17, 18, and 19 and serving to control a corresponding number of fluid control means. 20 indicates the'main passage inlet portion and 21 the main passage outlet portion. 22 is the minimum cross section area portion and 23 indicates one of the steps in the wall where the secondary passage 15 is branched off.

In the perspective Roentgen view of FIG. 5 five planar fluidic devices of the same type as shown in FIG. 1 are provided in a housing 24 and each fluidic device has one secondary passage. A common conduit 25 provides fluid to the inlet portions 3 of the fluidic devices. The five secondary passages 6 open at the back of the housing 24 and the main outlet portions 4 open at the front side. The secondary passages are connected to conduits or hoses 26-30.

The most common method to adapt a too strong pressure signal to the level which can be accepted by the controlled fluid control means is to use some kind of throttling, which may be fixed or adjustable, and in which the flowing fluid is subjected to a pressure drop so that the signal pressure is reduced to a suitable level. However, this causes a certain loss of power which may sometimes results in a not desired time delay of the signal. If, instead, a fluidic device according to the invention is used, a smaller loss of signal power is obtained which results in a quicker signal transmission. In the system illustrated in FIG. 6 a fluidic device 1 according to the invention is connected between a controlled fluid control means 31 and a signal transmitting conduit 32 in which a signal carrying fluid flows towards the fluidic device 1 from a signal emitter 33. The controlled fluid control means 31 may, for instance, comprise a flow control apparatus which is controlled by letting the control signals influence the deflection of a membrane to which a valve spindle is secured. The signal emitter 33 may comprise an adjustable throttle valve which is mechanically actuated by any suitable machine element so that the flow of signal carrying fluid into the conduit 32 is increased or reduced.

By means of an adjustable throttling device 34 the flow velocity of the fluid may be adjusted, so that the control signals appearing in the secondary passage 6 which affect the controlled fluid control means 31 reach suitable pressure levels.

Let us now assume that a fluid control means of the same type as shown in FIG. 6 is directly connected via a fluid flow conduit to a signal emitter having the same characteristics as the one in FIG. 6. This signal emitter emits pressure signals which may consist of a constant pressure level on which pressure variations are superimposed. This is shown in FIG. 7a where the curve 35 shows the pressure variations of the signals as a timefunction. It is also assumed that the controlled fluid control means 31 has its functionally most favourable control range when the control signals vary between the pressure levels a and b in FIG. 70. It is obvious that the fluid control means in this case does not function properly, or does not function at all, due to the fact that the control signals completely fall outside the pressure range in which optimum performance of the fluid control means is achieved.

Now, if a fluidic device as above described is introduced in the system together with an adjustable throttle device 34 according to FIG. 6, then the output signals occuring in the secondary passage 6 due to the input signals from the signal transmitting conduit 32 may be adjusted so that they vary within the desired range a and b if the design of the fluidic device 1 is suitable. If the setting of the throttling device is changed so that its flow area is increased then the flow velocity in the main passage of the fluidic device is also increased which means that the pressure variations in the outlet portion of the secondary passage which are'utilized for controlling the fluid control means will vary between other lower pressure levels, for. instance within an interval which includes positive as well as negative pressures, or an interval of negative pressures only according to curve 37 in FIG. 7a. It must be pointed out that should the fluid control means 31 be a control means which is controlled by fluid flow rather than fluid pressure, then the flow velocity in the secondary passage of the fluidic device will affect the pressure conditions in said passage.

Sometimes there is no requirement that the output signal pressure in the conduit 6 should rise when the pressure in the signal transmitting conduit 32 rises and it may only be desirable that the output signal from the secondary passage of the fluidic device 1 should vary between two levels. This may be the case when the effect of the output signals on the controlled means is defined by the frequency by which alternate pressure increases and pressure decreases in the fluid control stream occur. There is then greater freedom to choose a suitable geometric design of the fluidic device. By means of the variable throttling device 34 the variation range for the output signal may be adjusted to that said range covers the desired interval.

In other cases, however, it is a sufficient requirement that the input signal pressure to the controlled fluid control means 31 always is below a certain level, the overamplification limit, i.e. the level which must not be surpassed if the apparatus is to function satisfactorily. Also in this case the designer has greater freedom to choose a suitable geometry of the fluidic device 1.

The pressure conditions in an important special case are illustrated in FIG. 7b. The pressure in the signal transmitting conduit 32 varies or changes between two levels a and b, the latter being equal to the ambient atmosphere and said variations or changes are illustrated by the curve 38. However, it is required that the control signal changes between 12 and c according to the curve 39 FIG. 7b, i.e. that the control signal is always a pressure below atmospheric. In such a case the throttling device 34 in FIG. 6 may be dispensed with.

In a control system, most of the signal emitters are usually placed adjacent to the operating devices and other components of the system are brought together on a board or in a control box. In order to avoid the necessity of providing separate conduits for the supply of fluid to the emitters, signal transmitting conduits may be used in which the signal carrying fluid flows from the controlled fluid control means to the signal emitters. The signals are then produced, as mentioned hereinabove, by letting a signal emitter control the flow velocity of the fluid through a signal transmitting conduit. Such an arrangement is particularly advantageous when the number of signal emitters is large.

A conventional way to produce signal transmission is illustrated in FIG. 8. 40 is a signal emitter which according to any principle is mechanically or electrically actuated by a working member 41. The actuation affects the flow velocity in the signal transmitting conduit 42 which is supplied with fluid over a throttling device 43 from a fluid source 44. The pressure in the control signal conduit 6 of the controlled fluid control means 45 consequently changes according to the flow velocity in the signal transmitting conduit. The throttling device 43 is dimensioned so that the pressure in the control signal conduit 6 changes within a pressure interval which is defined by the input characteristics of the controlled fluid control means 45. With a fixed throttling device area an increase of the length of the signal transmitting conduit results in an increased back pressure for the fluid flow in the signal transmitting conduit 42. The pressure in the control signal conduit 6 then varies within a higher interval than is the case with a shorter length of signal transmitting conduit. In order to change the back pressure to the value which exists in connection with the short signal transmitting conduit and consequently in order to restore or bring back the pressure variations of the signals to the interval which may be accepted by the controlled fluid control means the flow velocity of the fluid may be reduced by increasing the degree of throttling in the throttling device 43, i.e. by reducing the flow area of said throttling device. However, this results in a condition in which it takes longer time to empty or fill the signal transmitting conduit 42, hence involving longer time to reach eqvilibrium between the flow conditions in all parts of the system. In other words, the speed of translation or propagation of the signals in the signal transmitting conduit is reduced. Since very long signal transmitting conduits require a considerable throttling of the flow velocity of the fluid, the resulting time lag in the signal transmission may be so large that this principle for signal transmission can not be used for practical purposes.

The throttling of the supply of fluid has a particularly disadvantagous influence ifthe controlled fluid control means 45 is ofthe flow control type such as a fluid amplifier.

The fluidic device according to the invention makes it possible to utilize much larger lengths of signal transmitting conduits than what is possible with an arrangement according to FIG. 8. Due to the fact that a local pressure drop is produced in the minimum cross section area portion of the fluidic device 1, a greater flow velocity may be permitted in the signal transmitting conduit without the back pressure from the transmitting conduit causing changes in the signal pressure to values above the range which can be accepted by the controlled fluid control means. Since the fluidic device 1 has been designed so that it presents a minimum flow resistance, a large portion of the input pressure is recovered in the outlet portion, and this helps to reduce the time lag.

In the system illustrated in FIG. 9 the fluidic device 1 according to the invention is connected to a monostable wall attachment amplifier 46. When no control signal is present in the control inlet 47 ofthe fluid amplifier, the powerjet coming from the inlet nozzle 48, which in most applications is an air jet, selects to move out of the fluid amplifier through the outlet passage 49. The vent passage 50 always connects the interior of the fluid amplifier with the ambient atmosphere or a surrounding space with other pressure. If a control fluid is led through the signal inlet 47 with a gradually increasing pressure, the control signal pressure, then the power jet, changes outlet passage when the said pressure has reached a certain level. This means that the fluid control means is actuated so that fluid now flows out through the outlet passage 51 and no outflow occurs through the outlet 49. Usually the switch-on pressure level is between -10 ofthe pressure (the pressure above the ambient pressure) which prevails in a supply conduit 52. The fluid amplifier remains in actuated condition until the control signal pressure has been reduced below another level which is slightly lower than the switch-on pressure level. When this occurs the fluid jet switches back from the outlet 51 to the outlet 49 i.e. the apparatus is switched off.

The operation of this type of fluid amplifier is, in other words, similar to an electric relay and has, as does the electric relay, a hysteresis range, i.e. an interval between a control signal pressure which must be exceeded for switching on of the amplifier or fluid control means and a lower control signal pressure below which the pressure must be reduced in order to switch off the fluid control means. In the system illustrated in FIG. 9 the reference numeral 53 indicates a binary signal emitter which is connected through a signal transmitting conduit 54 to a fluidic device 1 according to the invention. The emitter may be used, for instance, to indicate a certain position of a movable machine element 55 so that the signal emitter 53 is closed when the element 55 is in the position which is of interest and that the emitter by the action of a spring is completely open in other positions of the machine element.

The fluidic device 1 together with the signal transmitting conduit 54 connected thereto is supplied with fluid from the same fluid source 52 which supplies fluid to the fluid amplifier 46.

It is essential that the geometric design of the fluidic device 1 is made with due consideration to the properties of the complete system of fluid control means signal transmitting conduits, any fittings connected thereto, and the signal emitter, if the most speedy signal transmission is to be obtained. If this is of subordinate importance and it is instead desired to have possibilities to connect signal transmitting conduits up to a certain maximum length to the fluidic device 1 and said device is designed according to this requirement then the same arrangement may be used for all different lengths of signal transmitting conduits below said maximum length. This applies to binary fluid control means controlled by a signal pressure which is positive relatively to the surroundings and produced by blocking of the fluid flow from a signal transmitting conduit by means of a binary signal emitter, as mentioned above.

FIG. 10 illustrates anoter application of the invention in which the described fluidic device 1 is utilized as an amplifier in a control system for checking dimensions. This system operates on air. Principally, nothing makes this system different from the application illustrated in FIG. 9 as regards the signal transmission. In FIG. 10 the signal emitter 56 consists of a measuring point of conventional design whereas the controlled fluid control means 57 may be a system built up by fluid amplifiers or control components with movable parts, U- tube gauges, etc. The fluid control means 57 produces output signals which may be discontinous or continuous and which give information of the dimensions of the checked detail. This information may indicate total measures or deviations from prescribed tolerances. I

A measuring point is principally a needle valve in which the valve spindle or needle is returned by a spring. The measuring points is mounted in a fixture 58 in which the detail 59 which is to be checked may be placed in such a manner that it comes into contact with the spindle of the measuring point and moves said spindle against the spring pressure. Various dimensions of the detail result in various degrees of axial displacement of the spindle which in turn results in various flow areas in the measuring point or needle valve. This has as a result that the flow velocity in the signal transmitting conduit 60 and consequently also the pressure in the signal inlet 61 of the controlled fluid control means 57 is defined by dimensions of the checked detail.

Naturally other types of pneumatic measuring devices may be used, such as hole gauges, ring gauges, and flat gauges.

One advantage in using the described

fluidic device

1, 11, 14 according to the invention as distinct from the conventional method with a throttling device, as illustrated in FIG. 8, is that it is possible to use much longer

signal transmitting conduits

32, 54, 60 and, furthermore, that the signal pressure variations are amplified or strengthened materially. The desolving power or degree of a measuring system is consequently increased. In the diagrams in FIG. 11 the signal pressure in the inlet of the controlled fluid control means 45, 57 is illustrated as a function of an axial displacement of a measuring point 56. The curve 62 applies to known conventional systems, for instance according to FIG. 8, i.e. a system in which a throttling device is used, whereas the curve 63 applies to a system according to FIG. 10. The latter curve has a more favourable form with regard to the disolving capacity.

The above described embodiments of the invention and the applications thereof should only be considered as examples and the invention may be used in various different ways and modified within the scope of the following claims.

lclaim:

1. A monostable fluidic device comprising a housing, a main fluid conveying passage fed with fluid from a fluid source and one or more secondary signal transmitting passages, each branched off from the main passage and formed in the housand having an inlet portion, an outlet portion substantially in alignment with said inlet portion, and an intermediate minimum cross-section area portion, said secondary passage or passages being branched off from the main passage at said minimum cross-section area portion thereof, and forming an acute angle with said outlet portion of the main passage, said cross-section area of the outlet portion increasing abruptly at the point where the wall of the secondary passage intersects the wall of the outlet passage, so that a fluid flow through the main passage leaves the wall of the main passage at the point where the secondary passage is branched off and shortly thereafter adheres to said wall of the outlet portion, so that a change of fluid flow in the main passage results in a signal in the secondary passage.

2. A fluidic device according to claim 1, in which a number of secondary passages are branched off from said minimum cross section area portion of the main passage and each per se form an acute angle with said outlet portion of the main passage.

3. A fluidic system according to claim 1 comprising, a device which consists of a housing, a main fluid-conveying passage fed with fluid from a fluid source, and one or more secondary signal-transmitting passages branched off from the main passage formed in the housing and of means for controlling the flow of fluid through said main passage, said main passage being substantially of Venturi-shape and having an inlet portion, an outlet portion substantially in alignment therewith and an intermediate minimum cross section area portion, the said secondary passage or passages being branched off from the main passage at the minimum cross section area portion and said secondary passage forming an acute angle with said outlet portion of the main passage, said cross section area of the outlet portion increasing abruptly at the point where the wall of the secondary passage intersects the wall of the outlet passage, so that a fluid flow through the main passage leaves the wall of the main passage at the point where the secondary passage is branched off and shortly after adheres to said wall of the outlet portion so that a change of the fluid flow in the main passage produced by said controlling means results in a signal in the secondary passage.

4. A fluidic system according to claim 3 in which the walls of the inlet portion and the outlet portion and the minimum cross sect on area portion form a smooth continuous curve except for the port or ports to the secondary passage or passages, respectively.

5. A fluidic system according to claim 3, in which the abrupt increase of the main passage cross section area at the point of branch off of the secondary passage amounts to 10-50% of the area immediately upstream of said point.

6. A fluidic system according to claim 3, in which the angle between the center line of the main passage and the center line of the secondary passage at the point of branch off is between 20 and 60, preferably about 45.

7. A fluidic system according to claim 3, in which the controlling means is a signal transmitter such as a variable throttling device or valve connected through a conduit to the inlet portion of the main passage.

8. A fluidic system according to claim 3, in which the controlling means is a signal transmitter such as a variable throttling device or valve connected through a conduit to the outlet portion of the main passage.

9. A fluidic system according to claim 8, in which the controlling means consists of two throttling devices in conduits connected, one to the inlet and the other to the outlet passage of the main passage.

Claims

1. A monostable fluidic device comprising a housing, a main fluid conveying passage fed with fluid from a fluid source and one or more secondary signal transmitting passages, each branched off from the main passage and formed in the housing, said main passage being substantially of Venturi-shape and having an inlet portion, an outlet portion substantially in alignment with said inlet portion, and an intermediate minimum cross-section area portion, said secondary passage or passages being branched off frOm the main passage at said minimum cross-section area portion thereof, and forming an acute angle with said outlet portion of the main passage, said cross-section area of the outlet portion increasing abruptly at the point where the wall of the secondary passage intersects the wall of the outlet passage, so that a fluid flow through the main passage leaves the wall of the main passage at the point where the secondary passage is branched off and shortly thereafter adheres to said wall of the outlet portion, so that a change of fluid flow in the main passage results in a signal in the secondary passage.

4. A fluidic system according to claim 3 in which the walls of the inlet portion and the outlet portion and the minimum cross section area portion form a smooth continuous curve except for the port or ports to the secondary passage or passages, respectively.

6. A fluidic system according to claim 3, in which the angle between the center line of the main passage and the center line of the secondary passage at the point of branch off is between 20* and 60*, preferably about 45*.