Fluidic Timer

Abstract

Back pressure from a vane and nozzle assembly continuously supplies a timing chamber with a pressure which is substantially independent of the supply pressure variations at the vane and nozzle assembly input maintaining a predetermined chamber volume and pressure thereby. When an input signal is provided to an input chamber, a valve blocks the vane and nozzle back pressure from the timing chamber and the predetermined volume of the timing chamber is vented, with the volume decreasing in response to timing chamber pressure drop, until an output signal from the fluidic timer is triggered. When the input signal is removed from the input chamber, vane and nozzle back pressure is restored to the timing chamber and it is reset to the predetermined volume and pressure level.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to timing apparatus which delay an output signal until substantially complete venting of a timing chamber is accomplished and particularly to fluidic timing apparatus which are insensitive to supply pressure variations and provide a variable volume timing chamber to compensate by volume change for pressure changes in the timing chamber.

2. Description of the Prior Art

In the prior art devices heretofore known, a constant volume timing chamber is discharged through an orifice in a time interval dependent upon fluidic capacitance and resistance. This method gives an RC discharge time which is logarithmic and therefore difficult to adjust accurately since a small variation in orifice resistance can cause large variations in volume chamber discharge times. This result is caused by the timing chamber varying in pressure during the discharge cycle.

Furthermore the prior art timing chambers are directly charged by supply pressure to the supply pressure level and therefore have initial pressure levels which vary along with the normally encountered supply pressure variations. This causes discharge time errors. To alleviate this problem a pressure regulator is placed in the supply pressure line leading to the timing chamber. However, there is no feedback of the timing chamber pressure to the regulator and any change in the regulator condition due to wear or low supply pressures is not compensated and still results in discharge time errors.

Some fluidic timers, presently available, utilize a variable volume timing chamber. This chamber, however, is reset for discharge from a timing chamber volume initially at ambient pressure level rather than from some constant positive pressure level and thus has a starting pressure which is dependent upon ambient pressure which varies with location altitude. This timing chamber is discharged by having the input pressure signal directly change the timing chamber volume by compression. There is no feedback between the input signal and the timing chamber. Discharge time is dependent upon the pressure level of the input signal and discharge time errors result from the normal input signal variations.

The Applicant's invention solves all these and other problems as well as providing advantages that will become obvious upon reading the specification.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a fluidic timer having a main body with a pressure inlet and venting port. A diaphragm is mounted within this body to form a timing chamber whose volume is changed by the diaphragm deflecting into the timing chamber in response to venting of the timing chamber during a timing cycle. The timing chamber is pressurized to a predetermined volume and pressure by connecting a pressure source of substantially constant pressure level to the inlet of the timing chamber and venting the timing chamber at a rate less than the rate of the source. Switching means responds to an input signal to decouple the supply pressure from the timing chamber. The timing chamber is maintained in a vented condition and as the timing chamber vents, the diaphragm moves within it to change the timing chamber volume, thereby compensating the decreasing pressure of the timing chamber. When the timing chamber is substantially vented, the output means produces a signal indicating completion of the timing cycle.

Since the timing chamber volume is changed as the timing chamber vents, compensation for decreasing timing chamber pressure is accomplished to provide a more accurate and repeatable timing cycle. This timing cycle may be more linearily varied by changing the area of the venting port. This eliminates the problems of logarithmic RC discharge associated with constant volume chambers.

Further in accordance with the invention, a vane and nozzle assembly is used as the pressure source of the timing chamber. Back pressure from this assembly is connected to the inlet of the timing chamber. A feedback signal is provided by coupling the diaphragm to the vane of the vane and nozzle assembly. This assures that the reset volume and pressure are repeatably returned to the same values, providing accurate and repeatable timing signals. The high gain and feedback of the vane and nozzle assembly eliminate errors due to supply pressure variations.

Further in accordance with the invention the output means includes a permanent magnet mounted to the diaphragm and an output vane and nozzle assembly mounted externally to the timing chamber. The permanent magnet exerts a force on the vane of the output vane and nozzle whenever the timing chamber is substantially evacuated thereby restricting the associated nozzle and producing an output signal thereby. This allows the timing chamber to be mechanically isolated from the output means.

Further in accordance with the invention an adjustable spring is located against the diaphragm to balance the timing chamber pressure exerted on the diaphragm. By adjusting the spring force a different timing chamber pressure is needed to balance it and the timing chamber pressure may be varied thereby. This increases the range of timer discharge times by providing a second timing adjustment for chamber pressure in addition to the venting area.

The primary object of the invention, therefore, is to provide an accurate fluidic timer which is substantially insensitive to supply pressure variations.

Another object of the invention is to provide an accurate fluidic timer having a repeatable starting pressure and volume.

Another object of the invention is to provide a fluidic timer whose output signal is mechanically isolated from its timing chamber.

Another object of this invention is to provide an accurate fluidic timer whose timing chamber changes volumes in response to venting during the timing cycle to compensate for pressure changes therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view of the fluidic timer taken along section 1--1 of FIG. 2.

FIG. 2 is a top view of the fluidic timer of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1 and 2, a timer assembly 10 has an upper body 12 and a lower body 14 with an input signal diaphragm 22 and a timing diaphragm 48 mounted therebetween in a manner that is well known to those familiar with the art. The diaphragm 22 and upper body 12 form an input signal chamber 18 which communicates with an input signal inlet 16. The diaphragm 22 and the lower body 14 form a vent chamber 20 and a switch chamber 36 having a pneumatically balanced switch 26 therein. A back pressure passageway 30 communicates with the switch chamber 36 and a back pressure chamber 33 of a nozzle 32. The nozzle 32 has an orifice 28 therein. The nozzle 32 is pressurized through a supply pressure inlet 24.

The diaphragm 48 and lower body 14 form a timing chamber 40 which communicates with the switch chamber 36 through a communicating passageway 38. The timing chamber 40 has a vent orifice 54 with a timing adjustment screw 52 mounted therein. The adjustment screw 52 has a tapered end extending through the orifice 54 to variably restrict it thereby. A vent passage 51 communicates with an orifice chamber 53 for venting the flow of air exiting through orifice 54. Connected to the diaphragm 48 so as to move with it is a feedback stem 46 which can be in mechanical contact with a vane 34 mounted to the upper body 12 by screws 50. The diaphragm 48 has a permanent magnet 42 bonded to one side. The opposite side of the diaphragm 48 has a spring 44 retained between spring adjustment screw 45, which is threaded into the upper body 12, and a spring holder 43 bonded to the diaphragm 48 on a side opposite the magnet 42.

The lower body 14 has an output nozzle 62 formed therein communicating with the supply inlet 24 by way of an orifice 66 and a back pressure chamber 68. The back pressure chamber 68 communicates with an output passage 64 which provides the output signal from the timer 10. Also connected to the lower body 14 by screws 60 is a vane 58, extending over the nozzle 62. The vane 58 acts as a magnet coupler since it is composed of ferromagnetic material and is in close proximity to the lower body 14.

In operation, with no input signal supplied to inlet 16 the supply inlet 24 is connected to a source of pneumatic pressure such as an air supply for a fluidic system. The air is communicated to back pressure chambers 33 and 68 through orifices 28 and 66, respectively, and vented through respective nozzles 32, 62. The spacing between the nozzles 32, 62 and their respective vanes 34, 58 determine the magnitude of pressure buildup in the chambers 33, 68. The back pressure of chamber 33 is communicated through passageway 30 to the switch chamber 36, wherein floats the fluidic switch 26. Chamber 36 communicates with chamber 20 on one side of the switch 26 and with passageway 38 on the other side of the switch 26. The chamber 20 is continuously vented by way of an outlet 21. From passageway 38 the back pressure of chamber 33 is communicated to timing chamber 40 wherein a pressure build-up is initiated due to the orifice 54 being unable to vent the chamber 40 at the same rate as the input to the chamber 40 supplied by passageway 38. As pressure builds up in chamber 40, the diaphragm 48 begins to roll toward the upper body 12 increasing the volume of chamber 40, compressing the spring 44 and moving the vane 34 away from the nozzle 32. As the restriction of nozzle 32 by the vane 34 is decreased, the back pressure in chamber 33 decreases, due to increased venting from nozzle 32, and consequently the pressure in chamber 40 decreases. The above described action continues until an equilibrium position is achieved wherein the pressure in chamber 40 exerted on diaphragm 48 balances the force of spring 44 on diaphragm 48. This balancing pressure results at a definite clearance between nozzle 32 and vane 34. Since the diaphragm 48 is coupled to the vane 34 through stem 46, this balancing pressure will occur at a specific diaphragm location ensuring not only a repeatable equilibrium pressure but also a repeatable volume of chamber 40.

This equilibrium position of the diaphragm 48 provides a gap between the magnet 42 and vane 58 of magnitude sufficient to make the magnetic force exerted on vane 58 by magnet 42 non-existant. The nozzle 62 is therefore substantially unrestricted and the back pressure in chamber 68 is substantially zero due to venting through nozzle 62.

The timer is now reset and ready for timing operation.

When an input signal, the delayed effect of which is desired, is inputed into the inlet 16, the chamber 18 is pressurized and the diaphragm 22 is driven toward the switch 26. This motion continues until the plate 17 bonded to diaphragm 22 contacts the switch 26 and causes it to restrict passageway 38 thus sealing chamber 40 from back pressure from chamber 33. The timing cycle is now initiated.

The chamber 40 maintains its venting through orifice 54. As the pressure of chamber 40 decreases the spring 44 moves the diaphragm 48 toward the lower body 14 to compensate for the decreased pressure by decreasing the volume of chamber 40. As the spring extends, the spring force decreases and therefore the balancing pressure decreases. This decrease is made negligible by providing limited spring extension and compression.

To assure a constant force over the diaphragm as it moves, the chamber retaining the spring 44 could be pressurized to a constant pressure by connecting it to the supply inlet 24 and allowing it to vent to the desired pressure level.

The diaphragm 48 moves toward the lower body 14 at a constant or substantially constant pressure until the magnet 42 magnetically couples with the vane 58. The magnetic force drives the vane 58 toward the nozzle 62. This restricts the venting of chamber 68 and it is pressurized to some predetermined value. This back pressure is communicated by passage 64 to whatever indicating or controlling equipment is desired. The timing cycle is now complete and the output signal has been delayed a certain time interval required to vent the chamber 40.

This venting time may be varied by the adjustment screw 52 changing the area of the venting orifice 54. Since the chamber is discharged with a changing volume compensating for pressure changes, the venting is substantially dependent upon the area of orifice 54 and is therefore substantially linear. This allows for more accurate adjustment of the timing cycle than is possible with constant volume discharge chambers.

The starting pressure and volume of the timing chamber 40 may be varied by varying the spring force of spring 44. This is accomplished by compressing or relieving the spring 44 through adjustment screw 45. The pressure of chamber 40 on diaphragm 48 must balance the force of spring 44. This requires a corresponding chamber 33 back pressure which results from the spacing between vane 34 and nozzle 33.

Certain improvements and modifications will become obvious to those skilled in the art upon reading this specification. It is my intention that such obvious improvements and modifications be incorporated in this application .

Claims

I claim:

1. A fluidic timing apparatus, comprising:

a timer body having a pressure inlet and a venting port;

a diaphragm connected to said timer body to form a variable volume timing chamber;

supply means, connected to the pressure inlet of said main body assembly, for pressurizing the timing chamber of said timer body to a predetermined pressure and volume;

switching means, connected between said supply means and the pressure inlet of said timer body, for decoupling said supply means from the timing chamber of said timer body in response to an input signal;

output means, coupled with the timing chamber of said timer body, for producing a signal upon substantial evacuation of the timing chamber of said timer body;

wherein said venting port includes means for adjusting the venting rate of the timing chamber of said timer body; and

including means for adjusting the timing chamber pressure of said timer body to a desired value.

2. A fluidic timing apparatus as set forth in claim 1 wherein said supply means includes a vane and nozzle with the vane coupled to said diaphragm by a stem to provide a feedback signal from the timing chamber to said supply means.

3. A fluidic timing apparatus set forth in claim 2 wherein said output means includes:

a permanent magnet located on said diaphragm; and

an output vane and nozzle, located externally of the timing chamber, to provide an output signal upon said permanent magnet magnetically coupling with the vane of said output vane and nozzle.

4. A fluidic timing apparatus as set forth in claim 3 wherein said timing chamber pressure adjusting means includes an adjustable spring connected to said diaphragm to require its force to be balanced by the pressure in the timing chamber.