WO2004076075A1 - Flow detection in liquid application systems - Google Patents

Abstract

Method and apparatus for detecting normal and abnormal flow conditions in a liquid flow device such as a spray nozzle are provided. Flow conditions are detected by using a sensor disposed external the flow device. The sensor, such as a piezoelectric accelerometer, detects mechanical radiant energy produced by liquid flow. Various circuits are optionally provided to carry out various functions such as detecting normal and abnormal flow conditions, issuing alarm and warning signals, detecting gun on delay, gun off delay, gun on duration, valve events such as open and close, and so on. A last valid averaged sample technique is provided to improve accuracy, as well as a de-bounce feature. Various noise filtering techniques are also described.

Description

FLOW DETECTION IN LIQUID APPLICATION SYSTEMS

Related Application

This application claims the benefit of United States Provisional patent applications serial nos. 60/450,481 filed on February 27, 2003 for SPRAY MONITORING SYSTEM FOR LIQUID SPRAY APPLICATIONS, and 60/453,926 filed on March 12, 2003 for PIEZOELECTRIC

FILM BASED VIBRATION SENSING SPRAY MONITOR, the entire disclosures of which are fully incorporated herein by reference.

Technical Field Of The Invention The invention relates generally to apparatus and methods for applying liquid and liquefiable material onto a surface. More particularly, the invention relates to detecting abnormal flow conditions including substantially no-flow conditions within the liquid application device.

Background of the Invention

Many articles are sprayed or coated with liquid coating materials such as liquid paint, adhesives, conformal coatings, food products and so on. The liquid application operations are performed by use of liquid application devices such as liquid spray guns, liquid dispensing guns and so on. A typical application device includes a nozzle assembly having an orifice through which the liquid material is ejected in a pattern. A typical nozzle assembly may include a nozzle body or cap, a nozzle tip with the orifice therein, and a nut or other device that is used to attach the nozzle assembly to the gun body. A valve mechanism is also commonly used within the nozzle assembly, with the valve mechanism being open and closed in response to a signal from an operator or controller. For example, a controller may issue a trigger signal that indicates whether the valve should be open or closed. A nozzle may be of a multi-piece construction or an integral device. In many gun designs, the nozzle assembly is designed to atomize the liquid to improve the quality of the film or coating applied to an article. Electrostatic energy may also be used to electrostatically charge the liquid pattern. There are many different types of guns and nozzles and the present invention is not limited to any particular type or configuration or application technology, including but not limited to spraying, dispensing, electrostatic, non- electrostatic, air assisted and so on.

In many liquid coating material applications, it is impossible for the operator to visually observe the performance of the gun, such as the pattern shape or even whether the gun is ejecting material at all. Nozzles can become clogged which can severely reduce or even interrupt the flow of liquid. Nozzles can also become worn, resulting in abnormally high flow rates with substantially reduced atomization. Moreover, it may be difficult to visually inspect an article to verify that the article was properly coated. Any of these factors can contribute to poorly coated or even uncoated articles being passed by, leading to rework, recalls and so on. Various efforts have been made to detect abnormal flow conditions such as due, for example, to a clogged nozzle. To our knowledge, such systems have typically relied on attempts to detect or monitor pressure of the liquid within the internal flow path. This has been accomplished, for example, by placing a flow restrictor and pressure sensor within the nozzle assembly or elsewhere in the flow path. Flow restrictors are oftentimes undesirable and also require modification of the gun. Pressure based methods further suffer from the fact that system pressure can vary significantly during a liquid application operation, particularly when a plurality of guns are connected to a common source. Pressure changes can thus occur due to various guns turning on and off at random times, as well as pumps turning on and off at random times (resulting, for example, in significant momentary pressure drops or surges known as pump wink.) Pressure based monitoring systems thus must be carefully timed as to when the data is deemed valid so that false readings due to pump wink and other pressure affecting phenomena are not misinterpreted as abnormal flow due to a clogged or worn nozzle.

The need exists therefore to provide methods and apparatus for detecting abnormal flow conditions during liquid material applications. Summary Of The Invention

The invention contemplates in one aspect method and apparatus for detecting or monitoring liquid flow conditions in a liquid application device. Such flow conditions may be normal or abnormal depending on the condition of the liquid application equipment. An abnormal flow condition is broadly understood as any flow condition that is higher or lower than a selectable limit. In one embodiment, the detected flow condition is the presence or absence of desired flow through a nozzle assembly that is associated with the liquid application equipment such as, for example, a spray gun or dispensing gun. For example, an abnormal flow condition may be the complete absence or attenuation of flow through a totally or partially clogged nozzle assembly. The invention will find application in other flow elements wherein liquid flow causes mechanical radiant energy that can be detected.

In accordance with another aspect of the invention, normal and abnormal flow conditions are detected by positioning a sensor external the nozzle assembly. This permits detection of the flow conditions without requiring any modification of the nozzle assembly or the internal flow path in the application device, and without any intrusion into the flow path, h one embodiment, the external sensor detects mechanical radiant energy produced by liquid flow through the nozzle assembly, such as vibration transmitted through the nozzle assembly. In an exemplary embodiment, an accelerometer assembly is disposed in intimate contact on an outer surface of a nozzle assembly so as to detect vibration caused by atomization of liquid within the nozzle assembly. The absence of vibration energy is detected as an abnormal flow condition, thus indicating a clogged or worn nozzle that may be resulting in poor or unacceptable coatings.

In accordance with another aspect of the invention, a sensor circuit includes several optional functions that relate to detecting vibration energy produced by liquid flow in a nozzle assembly. The sensor circuit may optionally be used to determine gun on delay, gun off delay, gun on duration, and flow/no flow or low flow conditions. The sensor circuit may also optionally include a band pass filter to reduce noise effects from other vibration causing elements in the liquid application system, such as for example, pumps and other guns. The sensor circuit may further optionally include a de-bounce function in which an abnormal flow alarm or indication is made after a predetermined number of abnormal flow conditions have been detected. The sensor circuit may also optionally determine average signals from the sensor, and may select and store the last detected signal from the sensor just prior to the gun trigger signal turning off the spraying operation.

The invention further contemplates the methods embodied in the use of such apparatus as set forth above, as well as a method for detecting normal and abnormal flow conditions in a liquid application device, comprising the steps of producing a control signal that controls flow of material through the device, detecting mechanical radiant energy produced by flow of liquid through the device, the radiant energy being transmitted through the device, and determining normal and abnormal flow conditions based on the detected radiant energy as a function of the control signal, hi some applications, use of the control signal as part of the flow condition determining step may be optional. These and other aspects and advantages of the present invention will be readily appreciated and understood from the following detailed description of the invention in view of the accompanying drawings.

Brief Description Of The Drawings Fig. 1 is a schematic representation of a material application system that incorporates the invention; and

Fig. 2 is a spray nozzle with a sensor mounted exteriorly thereof, shown in longitudinal cross-section;

Fig. 3 is a functional block diagram of a conditioning circuit and an analytical circuit suitable for use with the present invention; Fig. 4 is a detailed schematic diagram of an exemplary conditioning circuit suitable for use with the present invention;

Fig. 5 is an exemplary Bode plot for an exemplary band pass filter circuit suitable for use with the present invention; Fig. 6 is a scope trace of a typical sensor output signal after converting the signal from ac to RMS dc; and

Fig. 7 is a timing diagram showing an exemplary data sampling technique suitable for use with the invention.

Detailed Description Of The Invention

1. INTRODUCTION

The present invention provides among other things as described herein methods and apparatus for detecting liquid flow through a device. Although the illustrated embodiments herein show particular application to a liquid spraying device such as a spray gun, those skilled in the art should appreciate that the invention will find application in many different types of liquid application systems. Such systems include but are not limited to electrostatic and non- electrostatic systems, air assisted atomization and pressure atomization systems, as well as liquid application systems that do not necessarily atomize the liquid, and liquid application systems that are manually operated or electronically controlled automatically. It is important to note that the term "liquid" as used herein is intended to be interpreted in its broadest sense to include not only homogenous liquids but also any liquefiable material such as suspensions, slurries, epoxies and so.

Additionally, various aspects of the invention are described and illustrated herein as embodied in combination in the exemplary embodiments. These various aspects however may be realized in many alternative embodiments, either alone or in various combinations and sub- combinations thereof. Still further, various alternative embodiments as to the various aspects and features of the invention, such as alternative materials, structures, configurations, methods, devices and so on may be described herein, but such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether known or later developed. Those skilled in the art may readily adopt one or more of the aspects of the invention into additional embodiments within the scope of the present invention even if such embodiments are not expressly disclosed herein. Additionally, even though some features and aspects of the invention may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless so expressly stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present invention however, such values and ranges are not to be construed in a limiting sense and are only intended to be critical values if so expressly stated.

The invention builds on our realization that liquid flow in a device, such as a spray nozzle of a liquid spray gun to name one example, may be sufficiently turbulent to produce mechanical radiant energy that is transmitted as longitudinal pressure waves in a material medium. These longitudinal pressure waves cause vibrations in the spray nozzle. Thus, the term mechanical radiant energy includes vibrations as one example and it is within the scope of this invention to sense such vibrations and relate them to a liquid flow condition.

In addition, this mechanical radiant energy could be manifested as sound waves which may be but need not be within an audible range of humans. Therefore, it is also within the scope of this invention to sense such sound waves with a sound wave sensing device and relate them with a liquid flow condition. Due to inherent ambient noise such as sound waves that transmit through air, however, the exemplary embodiments of the invention are directed to detecting such mechanical radiant energy transmitted through a material medium such as a gun body part (for example, a spray nozzle) as vibrations rather than as sound waves. Regardless of the form of the mechanical radiant energy sensed, the present invention is not limited in use to any particular liquid flow device such as a liquid spray nozzle. 2. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

With reference to Fig. 1, a material application system 10 in accordance with an exemplary embodiment of the invention is illustrated in a simplified schematic form. The system

10 includes a liquid application device 12, such as a liquid spray gun. A suitable gun is a model A7A available from Nordson Corporation, Westlake, Ohio, however, any liquid application device may be used and need not be limited to spray and dispensing guns.

The application device 12 typically includes a nozzle assembly 14 having a nozzle tip 16 that defines an outlet or orifice 18 through which liquid material is ejected, sprayed or dispensed.

Although the exemplary embodiment illustrates the invention in use with a spray nozzle assembly 14, those skilled in the art should appreciate that the invention can be applied to any liquid carrying device in which liquid flow therein produces detectable mechanical radiant •energy. hi accordance with one aspect of the invention, a sensor 20 is provided that detects mechanical radiant energy resulting from fluid flow within the nozzle assembly 14 and produces a corresponding output signal 22. The output signal 22 typically will be an AC electrical output signal, although other signal formats may be used such as optical, RF, TR and so on depending on the design of the selected sensor 20 and related circuitry. In accordance with this aspect of the invention then, a sensor 20 is disposed with respect to the application device 12 (in this case on the nozzle assembly 14) so as to be able to detect mechanical radiant energy caused by the turbulent flow of liquid within the nozzle assembly 14. Such turbulence may arise from the liquid being under pressure as it is being forced out the orifice 18, as well as the composition of the liquid, and furthermore some devices 12 include turbulence plates to increase such turbulence.

The sensor 20 detects mechanical radiant energy, such as for example vibrations, transmitted through the nozzle assembly, and produces the output signal 22 in relation thereto. The sensor 20 preferably although not necessarily is mounted on a surface of the nozzle assembly 14. The sensor 20 may be positioned anywhere that it is able to detect the mechanical radiant energy of interest. Thus, the sensor 20 can be disposed off of the nozzle 14 or the device 12 provided that there is adequate coupling of the mechanical energy to the sensor 20. For example, the sensor 20 in one embodiment is a thin film piezoelectric accelerometer, model ACH-01 available from Measurement Specialties Incorporated, Norristown, PA. Such a device includes a housing that is mounted with a suitable adhesive to the surface of interest, such that the vibration sensitive element itself is not directly in contact with the mounting surface.

A significant advantage of the present invention is that it permits detection of flow conditions completely exterior of the flow device. This is a non-intrusive sensing technique that avoids if so desired any need to modify the liquid application device, or any portion of the internal flow path of the liquid being applied. Furthermore, although the exemplary embodiments illustrate the use of a vibration sensor 20, other mechanical radiant energy sensors may be used in the alternative. One example would be a microphone that could be used to detect sound waves transmitted through air. The vibration sensor 20 is preferred as there is usually substantial ambient noise that would need to be filtered out from the sensor signal in order to detect the signal component that related to the liquid flow.

Those skilled in the art will appreciate that numerous noise cancelling techniques may be used as required. For example, the exemplary embodiments herein use time domain noise filtering. Alternatively or in addition one could use frequency domain filtering. For example, if there is a known source of noise in the sensor output within specific frequency ranges, suitable processing, particularly digital, may be used to filter such noise. For example, fast Fourier transform filtering through use of digital signal processing (DSP) is one option. Another option would be to use differential noise cancellation in which a second sensor may be appropriately positioned relative to the primary sensor 20 so as to detect noise components that are present in the sensor 20 output. By subtracting the two sensor outputs from each other, the noise is substantially filtered leaving a stronger signal to noise ratio in the filtered sensor output. Many other noise filtering and cancellation techniques, analog and digital, are available.

The sensor 20 thus produces an output signal 22 that corresponds to the liquid flow characteristics inside the flow device 14 of interest, in this case a spray nozzle. The presence of detected mechanical radiant energy corresponds to a normal flow condition if the output signal 22 meets predeterminable criteria, and the absence of such mechanical radiant energy would correspond to an abnormal flow condition such as might arise, for example, from a worn or clogged nozzle.

The invention further contemplates various optional output signal conditioning and analytical functions that may be used to more fully realize the benefits of using the sensor 20. A conditioning circuit 24 may be used to carry out one or more functions such as a preamplifier to strengthen the sensor output signal, and a band pass filter function to reduce low frequency noise that may be present in the sensor 20 signal. Still further a line driver function may be used to allow the sensor signal to be coupled over a long cable distance to a processing circuit. Such coupling may be necessary, for example, to meet various fire safety regulations.

The output 110 of the conditioning circuit 24, or if appropriate the output of the sensor 20, may be input to an analytical sensor circuit 26. The analytical circuit 26 may be used to carry out one or more functions for interpreting the sensor 20 output signal 22. For example, the analytical circuit 26 may be used to detect any one or more of the gun on delay time, gun off delay time, gun on duration time, actuation of the internal control valve of the nozzle assembly

14, normal and abnormal flow conditions and generate various alerts and alarms if so desired.

The analytical circuit 26 may also perform a calibration function as will be described hereinafter.

Typical liquid application systems, especially spray guns, are controlled by means of a device controller 28. This controller 28 may perform a wide variety of functions, one of which is to produce a flow control signal 30 that is sent to the application device 12, usually in the form of a trigger signal. The trigger signal controls operation of a spray on/off valve in the device 12. This is one example of a convenient signal that may be used by the analytical circuit 26, as represented by the additional signal line input thereto in Fig. 1. For manual spray guns, a corresponding trigger signal may be generated in response to actuation of the gun trigger and supplied to the analytical circuit 26. It is important to note that use of the control signal 30 is not required in all embodiments of the invention.

It will further be noted that the various circuits 24, 26 and 28 may be realized in a wide variety of ways well known to those skilled in the art. The circuits may be digital, analog or a combination thereof. They may include programmable controllers such as microprocessor based systems as well as circuits built from discrete components, programmable logic controllers, state machines and so on. The invention is not limited in any manner to the design and implementation of the various circuits described herein. Furthermore, the circuits may be combined into a single circuit arrangement, or may be realized as separate circuits.

Turning now to Fig. 2, in an exemplary embodiment of a liquid application device in the form of a spray gun head 40 and nozzle assembly 42 is shown. Note that in Fig. 2, reference numeral 42 corresponds to the same element as numeral 14 in Fig. 1, and reference numeral 46 corresponds to the same element as numeral 16 in Fig. 1. This spray gun head and nozzle functions may be but need not be substantially as described in the following United States Patents: 3,702,107 issued to Rood et al., the entire disclosure of which is fully incorporated herein by reference. The gun head 40 is mounted on a gun body (not shown) which supplies liquid material to the head. Operation of the spray gun is not important to an understanding of the present invention and reference may be made to the referenced patents for additional detail. All that is needed to understand for the exemplary embodiment is that liquid material under pressure enters the gun head 40, passes into a nozzle cap 44 and exits through a nozzle tip 46 having an orifice 18 therein. A nut 48 is used to secure the nozzle cap 44 onto the gun head 40. The present invention may be used with a wide variety of gun and nozzle designs, as well as with other fluid carrying devices. Due to the constricted flow through the orifice 18, a substantial turbulence is produced inside the nozzle cap 44 under normal flow conditions. This turbulence produces mechanical radiant energy that is transmitted through the structure of the nozzle cap 44 and also may transmit through the gun head 40. This mechanical energy, most notably in the form of vibrations, is further transmitted in and through the nut 48. For convenience, but certainly not the only option, the sensor 20 is mounted against the nut 48. hi this embodiment, the sensor is realized in the form of a thin film piezoelectric accelerometer 50 that is embedded in an epoxy fill 52 within a housing 54. The housing 54 is securely mounted on the nut 48 using a set screw or bolt 56. The mounting of the sensor is done in a close coupled manner so as to provide sufficient mechanical acoustic coupling between the sensor 50 and the nut 48 so as to minimize attenuation of the mechanical radiant energy produced by the liquid. Suitable alternative mounting arrangements will be readily apparent to those skilled in the art and are determined in large measure by the structure of the particular flow device being monitored.

In the exemplary embodiment, liquid flow is controlled by opening and closing a valve that is realized in the form of a ball valve element 60 that engages a valve seat 62 to close the valve. A valve stem 64 under the control of an actuator (not shown) pulls the ball 60 away from the seat to open the valve and permit flow through the nozzle. Many alternative valve arrangements and designs may be used. The noteworthy point is that the valve actuation may be controlled by the flow control signal 30 (Fig. 1) to the actuator. With reference next to Fig. 3, many of the advantages of the present invention can be realized with conventional electronic circuit designs. The sensor output signal by itself contains enough information to determine flow conditions within the flow device 12. Therefore, the various circuits described herein, although preferred, are not required and are optional depending on a specific application. The sensor 20 output signal 22 is input to a preamplifier circuit which may be conventional in design to provide gain. A fixed gain circuit may be used when the invention will be used with similar fluid application devices. However, the quality and signal to noise ratio of the sensor output 22 is a function of a number of factors including the pressure of the liquid, the characteristics of the liquid, the quality of the coupling between the sensor and the flow device, and so on. Consequently, in some applications it will be advantageous to utilize a variable gain preamplifier circuit so that the gain can be adjusted to provide the best signal to noise ratio of the conditioned signal.

The preamplifier is designed as a conventional circuit so as to boost the signal strength so that the conditioned signal can be transmitted down a long cable if needed for fire protection regulations. The preamplifier 100 may be designed as a high input impedance amplifier to minimize the load on the sensor 20 and noise effects. The conditioning circuit also provides bias current for sensor excitation (+V in Fig. 4).

The preamplifier output 102 is input to a band pass filter 104. The band pass filter 104 may be conventional in design and based on the particular application for the invention. For example, for the exemplary embodiment herein we have discovered that liquid paint under normal flow and atomization conditions produces a strong vibration frequency at around 10 kHz.

Therefore, the band pass filter in this example is designed to pass signals in that frequency range.

In addition, the band pass filter 104 may be designed to attenuate low frequency noise. For example, operation of the spray gun and surrounding equipment can inject low frequency vibration into the system. The output 106 of the band pass filter 104 is input to a line driver 108. The line driver

108 can be designed as a conventional buffer circuit for driving a lengthy cable. The output 110 of the line driver 108 is input to the analytical circuit 26.

Fig. 4 provides an exemplary embodiment of the conditioning circuit 24. Each of the functional blocks of Fig. 3 is identified by dashed boxes. Again, these circuit concepts are conventional and subject to many iterations and variations depending on the particular application system. Fig. 5 is a Bode plot of amplitude versus frequency (logarithmic scale) of an exemplary band pass filter 104. Note that the frequency response is fairly flat in the region 104a from about 3 KHz to about 80 KHz, with an upper roll off around 100 KHz. Further note the attenuation in the region 104b from about 10 Hz to about 1 KHz. This attenuation removes noise present in the sensor output 22 that is not related to vibration from the liquid material flow condition. For example, it can remove 60 Hz noise, low frequency equipment vibration, pump wink fluctuations and so on. Again, the particular frequency response may be selected based on the overall system design, and in some cases the band pass filter, the preamplifier and/or the line driver circuit may be omitted.

With reference again to Fig. 3, the conditioning circuit 26 may be realized in many different forms and configurations. In the exemplary embodiment the circuit is microprocessor based but such a design is not required. Moreover, the conditioning circuit 24, the analytical circuit 26 and the control circuit 28 (Fig. 1) may be combined into a single circuit, or incorporated into another control circuit, or may be separately provided in different sub- combinations. A detailed schematic of the analytical circuit is not necessary to understand and practice the present invention since microprocessor based control systems are well known and readily available to execute the functions described herein.

The output 110 from the line driver 108 may first be input to an intrinsic safety barrier circuit 120 for applications requiring such protection. The basic characteristics of the sensor 20 output signal is at this point still an ac signal 122. This signal 122 is input to an AC to DC converter circuit 124 using a Root Mean Square (RMS) method which may be of conventional design well known to those skilled in the art. The output 126 of the converter 124 is a DC signal with some noise riding on top of the DC. Typical wave forms are illustrated in Fig. 6 for normal flow conditions. In Fig. 6, trace A is the trigger signal (30) used to control flow of liquid through the nozzle. Trace B is the sensor output 22 as conditioned and after conversion from AC to DC and scaling (output 129 of Fig. 3 is represented in an exemplary manner in Fig. 6). Note that the waveform follows the general shape of the trigger signal except for time delays. The rising edge Al of the trigger signal corresponds in this example to a gun on command, and the falling edge

A2 corresponds to a gun off command. In the sensor output trace B, note that there is a leading pulse or spike Bl, which corresponds to the ball valve element being pulled away from the valve seat. This action causes vibrational noise either from the valve actuation itself or the initial flow of liquid or both possibly. In any event there is a similar pulse B2 when the valve is closed, and this may be the result of the ball element contacting the valve seat. Between Bl and B2 note that the DC value of the sensor signal substantially increased due to detecting the mechanical radiant energy of the flowing liquid. When the valve is closed (gun off) note that the DC signal level as at Cl and C2 is low. Further note that there is a distinct time delay between the trigger on time Al and the time Bl that the valve actually opens and flow begins. This is a well known phenomena and referred to commonly as gun on delay. Likewise, there is a delay from the trigger off time A2 and the time that flow stops B2, commonly known as gun off time. The time period between Bl and B2 is generally known as gun on duration which corresponds to the actual time period that liquid is being sprayed or dispensed from the gun. It will be readily appreciated that the sensor output 22 thus in and of itself contains enough information to determine gun on duration and flow condition characteristics. A worn or clogged nozzle, for example, would be noted in that the signal strength between Bl and B2 would be detectably attenuated.

The output 126 of the converter circuit 124 may be input to an optional and conventional scaling amplifier 128 which is used, as required, to condition and scale the DC signal as appropriate so that it can be input to an analog to digital converter 130. The A/D converter 130 is used to transform the time variant signal into a pure digital output signal 131 for analysis by the microprocessor 132. The microprocessor 132 in this embodiment is programmed to obtain sample values of the sensor output signal, as conditioned by the conditioning circuit 24 and the converter circuit 124 and scaling amplifier 128. In an exemplary embodiment, the microprocessor 132 periodically samples the sensor signal amplitude as represented by the output of the A D converter 130. For example, every 100 milliseconds or so the microprocessor can be programmed to obtain samples. To reduce noise effects, the microprocessor 132 takes ten samples for example, ignores the highest and lowest values, and averages the remaining eight samples to provide an average sample value. During a typical gun on duration of two seconds or so, the microprocessor may obtain two or three or more valid averaged samples. Moreover, the microprocessor then uses the last valid averaged sample that was obtained prior to the trigger signal "off command to determine whether flow conditions are normal or abnormal (note in Fig. 3 the trigger signal 30 is shown as an input to the microprocessor 132). However, other or different samples may be used as required in a particular system. If the selected last averaged sample value is outside a predetermined range that is assigned for "normal" flow detected vibration, then the microprocessor has detected an abnormal flow condition. The microprocessor 132 can immediately issue a fault indication 134 (such as lighting a lamp or an audible signal for example) when such an occurrence is detected. A de- bounce feature may be incorporated by requiring a predetermined number or percentage of consecutive averaged samples to be outside the "normal" range before a fault indication 136 is effected such as an alarm, for example, which may be used to shut down the line to stop improper application of the liquid. Using this technique can eliminate transitory noise such as from the valve opening and from pump wink.

Selecting the range of values for the average samples may be done empirically and stored in the microprocessor memory. Alternatively, the microprocessor can be programmed to execute a calibration operation. During calibration, a known good nozzle is used with a known good or normal flow condition and product coating. The microprocessor takes the average samples and stores these samples or their average values or their high and low readings for example. The samples can be taken for example during a sampling time when normal flow is occurring so as to not have transient effects reflected in the calibration values. These calibrated values can then be used as a comparison of average samples taken during liquid application cycles. Fig. 7 illustrates the exemplary sampling feature of this embodiment. It should be noted that any sampling technique may be used but we have found this one is particularly useful with the exemplary spray gun lags. As shown in Fig. 7, the samples may be timed with the trigger signal 30. Average samples are taken during both the gun on time period and the gun off time period, particularly during calibration. As noted in the drawing, it is the last valid averaged sample (X and Y) that is used by the microprocessor to determine if the flow condition is "normal" or within a prescribed range of values for the sensor signal, or "abnormal" meaning outside the prescribed range of values. Note from Fig. 7 that calibration can be based on a selected number of spray cycles such as four. The prescribed range of values may be determined during calibration or can be determined by a separate evaluation. For example, the range of values may be set to 50% and 100% of the averaged readings across a prescribed number of cycles during calibration with normal flow conditions, steady state flow and so on. The exact limits will be determined for each particular system. With the exemplary sampling feature shown in Fig. 7 using signals 30 and 129 one can determine true gun on, gun off, and spray duration times. As can be seen in Fig. 6 the requested gun on time signal 30 does not match the actual gun on time or true spray duration. True spray duration is a key factor in dispensing liquid materials. It determines the actual amount that liquid is dispensed (flow rate X time). In the prior art, the true gun on and off times often are not known in many applications. For example, the gun lags can be caused by air hose length, spring k factor, air pressure, material pressure and so on. The present invention allows one to measure these times and display them for operator setup and/or present fault indications based on them.

The invention has been described with reference to the preferred embodiment. Modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMSHaving thus described the invention, we claim:

1. A liquid spray apparatus, comprising: a spray nozzle; a sensor for detecting mechanical radiant energy produced by flow of liquid through said nozzle and producing an output signal in response thereto; and a sensor circuit for receiving said signal and determining therefrom normal and abnormal flow conditions of liquid through said nozzle.

2. The apparatus of claim 1 wherein said sensor detects acoustic energy produced by liquid flow through said nozzle.

3. The apparatus of claim 1 wherein said sensor comprises a thin film piezoelectric accelerometer.

4. The apparatus of claim 1 wherein said sensor is disposed against an outer surface of said nozzle and responds to vibration energy transmitted through said nozzle.

5. The apparatus of claim 1 wherein said sensor circuit comprises a band pass filter to reduce low frequency noise from said output signal.

6. The apparatus of claim 1 wherein said sensor circuit detects a low or no flow condition by detecting a change in said output signal corresponding to a reduction or absence of said mechanical radiant energy.

7. The apparatus of claim 1 wherein said sensor circuit executes a calibrate function by storing representative signals for normal and abnormal flow conditions.

8. The apparatus of claim 1 wherein said sensor circuit executes a de-bounce function by issuing an alarm signal after a predetermined number of detected abnormal flow conditions.

9. The apparatus of claim 1 wherein said sensor circuit uses a sample of said output signal that last occurred prior to a trigger off signal of the spray apparatus.

10. The apparatus of claim 9 wherein said sample comprises an average of a plurality of samples of said output signal.

11. The apparatus of claim 1 wherein said nozzle comprises a valve element that opens and closes an orifice of said nozzle by contacting a valve seat, said sensor circuit determining valve open delay, valve close delay and valve open duration as a function of detecting vibration caused by said valve element against said valve seat.

12. The apparatus of claim 11 wherein said sensor circuit determines said valve open delay, valve close delay and valve open duration as a function of said detected vibration relative to a trigger signal, wherein said trigger signal controls operation of said valve element.

13. A method for detecting normal and abnormal flow conditions in a liquid spray nozzle, comprising the steps of: producing a control signal that controls flow of material through said nozzle; detecting mechanical radiant energy produced by flow of liquid through said nozzle, said radiant energy being transmitted through said nozzle; determining normal and abnormal flow conditions based on said detected radiant energy as a function of said control signal.

14. The method of claim 13 comprising the step of converting said mechanical radiant energy into an electrical signal whereby a low or no flow condition is detected as a function of said electrical signal during a time period in which said control signal indicates flow should be present through said nozzle.

15. The method of claim 13 wherein said step of detecting said mechanical radiant energy is performed external the nozzle.

16. The method of claim 13 comprising the steps of determining on delay, off delay and on duration of flow through said nozzle as a function of said detected radiant energy and said control signal.

17. The method of claim 13 wherein said control signal is a trigger signal for actuating a valve in said nozzle.

18. A liquid spray gun, comprising: a nozzle with a valve element and valve seat disposed therein, said nozzle in fluid communication with a source of pressurized liquid to be sprayed out said nozzle; said nozzle being open and closed in response to a trigger signal; a vibration sensor that detects mechanical radiant energy produced by flow of liquid through said nozzle and producing an output signal that corresponds to said detected radiant energy; and a sensor circuit that determines an abnormal low flow condition through said nozzle as a function of said detected radiant energy.

19. The spray gun of claim 18 wherein said sensor comprises a thin film piezoelectric accelerometer.

20. The spray gun of claim 18 wherein said sensor is acoustically coupled with an outer surface of said nozzle.

21. The spray gun of said 18 wherein said sensor comprises an accelerometer.

22. A liquid application device, comprising: a fluid flow element; and a sensor responsive to mechanical radiant energy produced by flow of liquid through said element and producing a corresponding signal.

23. The device of claim 22 comprising a sensor circuit for receiving said signal and determining therefrom normal and abnormal flow conditions of liquid through said element.

24. The device of claim 23 wherein said sensor circuit receives a second signal related to control of liquid flow through said element, said determination of flow conditions being a function of said corresponding signal and said second signal.

25. The device of claim 24 wherein said device is a gun nozzle, said sensor comprises a piezoelectric sensor, said corresponding signal being an electrical signal having an RMS value related to said mechanical radiant energy.

26. The device of claim 25 wherein said sensor circuit determines gun on delay, gun off delay and gun on duration.

27. The device of claim 26 wherein said second signal is a trigger signal for a valve that controls flow of liquid through said gun nozzle.

28. The device of claim 22 wherein said mechanical radiant energy comprises vibrations.