Field of the Invention

This invention relates to an apparatus for con¬ trolling the ink level in an ink fountain used in a printing press such as the viscous ink in art offset litho- graphic press.

Background of the Invention

The ink consumption in a modern, high -speed print¬ ing press is very large and as a result, ink is frequently pumped to the press in pipes installed for that purpose. Most offset printing inks are quite viscous, and are comparable to very thick molasses in this respect. As a result, ink neither flows readily, nor seeks its own level quickly. When the valve in the ink line is opened to introduce additional viscous ink into an ink fountain used in a printing press, the new ink takes a long time to level out.

Ink generally is considered an active substance in the sense that the ink sets when allowed to stand and dries when exposed to air. In addition, ink is sticky and readily adheres to all commonly used materials. These properties pose a difficulty in sensing ink level since the ink has a tendency to accumulate or build up on any sensing member or component with which the ink comes into contact.

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Typically, the ink fountain or reservoir in an offset printing press is constructed in the form of a trough such as shown in U. S. Patent 3,848,529 to Gegen- hei er et al, which is assigned to the same assignee of this invention. The ink trough is formed by a flat blade which forms a nip with a fountain roller. A feature of such reservoir is that the surface of the ink contained therein is not flat, but usually undulates while the pres is in operation at a frequency in the range from 0.25 to once a second. This undulation is produced by a ratchet action of a fountain roller and makes it difficult to sense the ink level.

Ink fountains in many printing presses are commonly equipped with ink agitators which improve ink distribution, prevent the formation of surface skin and improve feeding of the ink to the nip between the flat blade and the fountain roller. The main element of an in agitator may be in the form of a conically shaped roller which is caused to rotate while traveling to and fro the length of the ink fountain. Such roller is illustrated i the aforementioned Gegenheimer et al patent. The presenc of an agitator produces a wave in the ink of a height which may be of the order of an inch or even more. When the ink is so disturbed, its surface quivers and undulate so as to make it difficult to sense ink level.

The space above the ink fountain must be kept relatively clear to allow room for the operator of the printing press to clean the fountain or to enable ink to be fed manually for occasions when special or spot colors are necessary. As a result, the sensing of ink level mus be done in such manner that the area or space over the in fountain is not unreasonably obstructed.

When multi-color printing presses having many ink fountains are involved, a plurality of ink level con- trol systems are employed. On any particular printing operation, however, it may not be necessary to use all of the ink fountains. As a result, some of the unused

fountains may not have any ink and the ink level control must be able to sense such condition to avoid system malf nctioning.

A large number of automatic ink level sensor designs have been proposed. Ink level sensors may use floating, tactile, capacitance, pneumatic or ultrasonic techniques. U.S. Patent 3,025,793 describes an ink level control for a newspaper press utilizing a float operated ink feed valve. Although such an approach is workable in newspaper presses, which utilize relatively thin or low viscosity inks, the float concept is not feasible in commercial presses requiring thicker inks. A major diffi¬ culty encountered with a floating device resides in the accumulation of ink on the float, eventually rendering it inoperable. The float also tends to take up a large amount of space, particularly when such float is directly connect¬ ed to operate an ink flow control valve.

The U.S. Patent 3,373,052 and the previously mentioned Gegenhei er et al patent are examples of ink level controls wherein a tactile type sensor detects the ink level by touching the ink. Such sensor does not cir¬ cumvent the difficulties due to ink activity and, as a result, the sensor tactile element must be periodically cleaned for reliable operation. In the aforementioned Gegenheimer et al patent, a tactile sensor is employed to monitor the height of the wave of ink generated by an agitator, thereby overcoming the difficulty posed by the waves in measuring the ink level. Gegenheimer et al also discloses the use of an adjustable timer to limit the duration of ink feed to over¬ come the difficulty posed by the high ink viscosity which prevents an even ink level from being quickly established when the ink valve is opened. In one form for such timer, adjustable feed pulses are applied through a relay to actuate the ink valve. The width of the feed pulses and the intervals between the pulses can be selected.

A number of prior art systems employ sensors

which avoid ink contact by using the capacitance principl In one approach, such as disclosed in the U.S. Patent 4,010,683, a plate is mounted above the ink fountain to form an electrical capacitor with the ink fountain blade. Since the permitivity of ink differs significantly from air, the capacitance will vary the ink level and thus pro vides a non-contacting method for detecting ink level. This sensor design has a disadvantage in that the sensor must be located within approximately an inch of the ink surface, thus obstructing access to the fountain.

A pneumatic ink level measuring system is avail able in the form of a vertical tube which is inserted int the ink fountain. The tube is connected to a source of air and the pressure in the tube is monitored to obtain a measure of ink level. This concept is satisfactory for low viscosity, inks but difficult to apply to highly vis¬ cous offset printing press inks.

Ultrasonic techniques for detecting the level o liquids are well known and have been applied to ink level controls in a limited liquid contacting manner. A genera description of ultrasonic techniques can be found in an article entitled "Ultrasonic Instruments for Level and Flow" in the September, 1974 issue of Instrumentation Technology. Ultrasonic systems for determining liquid level utilize one of two basic approaches. In a first liquid contacting type, a detector provides an on-off signal whe the liquid comes into contact with the ultrasonic sensor; see, for example, U.S. Patent 3,520,186 to Adams et al. The liquid level may interrupt ultrasonic waves or cause change in the dampening characteristics of an ultrasonic transducer when it is contacted by the liquid. Contact b the detector with ink, however, is not desirable.

In another type of ultrasonic level detector, a echo ranging principle is employed, such as described in the U.S. Patent 3,985,030 to Charlton. A pluse of ultra¬ sonic energy is directed to a transducer toward the liqui ϊUK

surface. A receiver listens for an acoustic echo and the time required for the echo to return provides a measure of the distance between the ultrasonic transducer and the liquid surface. In the Charlton patent, a loss of echoes is detected and used to override an automatic level indi¬ cator by registering a maximum liquid level depth.

Summary of the Invention

In an ink level control in accordance with the invention, the ink level is sensed remotely with an ultra- sonic pulse-echo technique. An accurate ink level control is provided capable of detecting ink level even in the presence of a quivering, undulating ink surface and an agitator- wave, while providing operational safeguards for reliable and fail-safe operation. As described with reference to one embodiment for an ink level control in accordance with the invention, an ultrasonic transducer is selected of a type capable of operating within normally encountered space restraints near the ink fountain of a printing press. The transducer can be remotely spaced from an ink fountain to enable ac¬ cess for cleaning, yet can be mounted within the available space and provide a reliable sensor of the ink surface as a result of acoustic pulses directed at the ink. Acoustic reflections from the ink are detected and processed to produce a measured ink level signal representative of the ink level in the fountain. An averaged or smoothed measur¬ ed ink level signal is compared with a reference represent¬ ative of a normally desired ink level in the fountain and the comparison used to provide an ink feed signal. The ink feed signal is thereupon converted to ink feed pulses separated by intervals of a predetermined duration. Various ink feed limitations are applied to assure the proper feed of ink in a manner whereby the ink fountain is prevented from overflow. With such controls an accurate, non-contacting ultrasonic ink level sensor can be

used to maintain the ink level at a desired level while preventing an excessive feed of ink to the fountain.

As further described with reference to a prefer red embodiment of the invention, an echo loss detection network is used to detect when echoes are not received. Such loss may arise from the passage of the agitator's in wave in the path of the ultrasonic beam. When an echo loss occurs, a simulated ink feed signal is produced to maintain normal operation of the ink level control. In th event the echo loss persists longer than a particular tim an alarm is generated.

The echo loss detector is particularly useful during field installation of the ink control when the ul¬ trasonic transducer is aligned at the ink surface. The echo loss detector is visually monitored by observing an alarm light energized by an activated echo loss detector. Accurate alignment of the transducer may then be achieved by angularly moving the transducer to determine its angu¬ lar operating range over which an echo can be obtained. The transducer is then fixed at a midway position of the operating range. This procedure, when carried out for transverse planes which are also normal to the ink surfac provides a convenient technique for using and field align ing of a narrow beam .ultrasonic transducer. In the described ink level control in accordanc with the invention, both high and low ink level reference signals are generated to define an acceptable range of in level within the ink fountain. The measured ink level si nal is compared with these reference signals to generate an alarm when the measured ink level falls outside this acceptable range. Enhanced protection is provided by in¬ hibiting the feeding of ink when the ink level drops belo its acceptable low level. This feature prevents ink spil when the fountain is opened for cleaning. It is, therefore, an object of the invention to provide an ink level control which overcomes the previous described disadvantages while enabling an accurate, reliabl

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control of the ink level in an ink fountain of a printing press.

These and other advantages and objects of the invention can be understood from the following description of an embodiment described in conjunction with the draw¬ ings.

Brief Description of Drawings

Fig. 1 is a schematic block diagram of an ink level control in accordance with the invention for use with a printing press; and

Fig. 2 is an electrical schematic of a simulated ink feed signal generator for use in an ink level control in accordance with the invention.

Detailed Description of Embodiment

With reference to Fig. 1, an ink level control

10 for a printing press (not shown) is described. An ink fountain 12 as generally described and shown in the Gegen¬ heimer et al Patent 3,848,529 is illustrated with a foun¬ tain blade 14 and an ink fountain roller 16 converging at a nip 18. The ink fountain 12 may be provided with an agitator 20 which is moved to and fro as described in the Gegenheimer et al patent with a suitable actuator 22. The fountain roller 16 is periodically actuated with a ratchet mechanism (not shown) . Ink 23 is supplied to the fountain 12 from a supply 24 through an automatically controlled ink feed valve 26 and conduit 28. Other ink feed supply elements such as a pump have been deleted for clarity. The ink surface 36 tends to distort from its normal level as shown at 37 depending upon the frequency of operation of the agitator 20, fountain roller 16 and the viscosity of the ink. A more or less permanent quivering and undulated bulge such as 39 extending over the length of the fountain 12 is often encountered.

An ink level sensor 30, in the form of an ultra sonic transducer, is disposed at a suitable distance from the ink fountain 12 to direct acoustic pulses along a bea axis 34 transversely onto the surface 36 of the ink 23. The transducer 30 is selected of a type capable of genera ing acoustic pulses and providing an echo signal represen ative of acoustic returns or echoes from the ink surface 36 within the available space of a printing press. The transducer 30 must be capable of operating within the available space above the fountain 12. Since the trans¬ ducer must operate in air, it tends to produce an undampe acoustic pulse followed by undesirable ringing effects an a greater spacing from the ink is needed to allow such trailing acoustic transients to die down. With the print ing press' space limitation, however, the increased spac¬ ing frequently is difficult to accommodate and a high fre quency transducer, capable of operating in the range of about 200 KHz is preferred. Such higher frequency trans¬ ducer 30 enables one to employ remote acoustic ink surfac sensing on printing presses with acceptable accuracies. The high frequency transducer, however, has a narrow beam of the order of about six degrees. Hence, the transducer 30 is also carefully aligned and positioned to sense the various ink surfaces encountered on printing presses. A control network 38 is provided to actuate transducer 30 and respond to the echo signal for control over the ink level in fountain 12. Ultrasonic transducer capable of generating and detecting acoustic pulses are well known and need not be further described. Transducer 30 is controlled with a transceiver

40 formed of a digital circuit as may be commonly pur¬ chased. The transceiver 40 responds to pulses, Tx, on line 41 from a timer 42 which may generate these at a hig rate of the order of 100 pulses per second. Each trans- mitter pulse causes the transceiver to deliver a large driving pulse on line 44 to transducer 30 which generates an acoustic pulse towards the ink surface 36. Acoustic

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returns from ink surface 36 are detected by transducer 30, amplified by transceiver 40 and made available as an echo signal for processing on an output line 46.

The echo signal is applied to a gate 48 which is normally enabled by the level on line 50 from an inverter 52 coupled to the timing pulses Tx from timer 42. While pulses Tx are active, gate 48 is disabled. This prevents erroneous responses when transducer 30 generates an acous¬ tic pulse. If desired, a longer lasting inhibition of gate 48 may be obtained by replacing inverter 52 with a pulse network whose output pulse would last while an acoustic return from ink surface 36 could not occur; for example, an inhibiting pulse lasting for slightly less than the round trip transit time of the acoustic energy could be used. The disabling level on line 50 is also applied to reset a flip-flop 54.

When gate 48 is enabled and receives an echo signal from transceiver 40, flip-flop 54 is set to provide an echo signal on line 56 to an ink level signal generator 58. The latter is responsive to transmitter pulses Tx on line 41 and the echo signal from flip-flop 54 to measure the time therebetween and produce, on output line 60, an ink level signal representative of the actual ink level in fountain 12. Techniques for measuring the transit time of an acoustic pulse to a reflecting surface are well known in the art. Hence, the measurement of the distance between transducer 30 and ink surface 36 can be carried out with a variety of different ink level signal generators 58. The latter may be an analog or digital circuit capable of pro¬ viding a signal representative of the ink level.

Since transducer 30 provides an echo signal at a time which is a function of the spacing of transducer 30 from ink surface 36, the ink level signal is similarly re- lated. However, by placing transducer 30 a fixed known distance from ink fountain 12, the ink level signal on line 60 represents actual ink level in the fountain

referenced relative to, for example, the deepest level 5 at nip 18.

The ink level signal on line 60 is applied to comparator 62 together with a reference signal represent tive of an operating ink level 59.3 desired to be main¬ tained in fountain 12. This reference signal is obtaine on line 64 from a suitable network 66 and a resulting comparison is produced as an ink feed signal on output 6 of comparator 62 when the ink level, as measured, drops below the operating reference. The comparator 62 is of type which does not present an output as long as the measured ink level is above the operating level. When t ink feed signal occurs on output 68 of comparator 62 it enables a clock 70 which generates ink feed pulses 72 se arated by ink leveling intervals 74 on line 75. The ink pulses 72 are applied to an ink feed relay 76 coupled to operate valve 26 and enable ink to flow into fountain 12. Clock 70 has an interval control network 78 to control the duration of intervals 74 and a pulse width selection network 80 to regulate the widths of pulses 72. The pulse widths are selected to be long enough to keep with the printing press' utilization of ink, but not so long that the fountain would overflow.

The intervals 74 must be long enough to allow the ink to level out in between feeds to prevent an over flow, but short enough to keep up with the ink utilizati of the printing press.

The interval control network 78 sets the time between successive pulses 72. This interval is made sufficiently long to enable a change in the ink level to be registered in response to a previous ink supply pulse. The duration is a function of viscosity with more viscous inks requiring longer intervals.

For a practical application, the pulse widths may be of the order of 1 to 15 seconds separated by inte vals of 15 seconds for an ink having a viscosity of the order of 200 poise.

The ink level control 10 maintains ink in the fountain below maximum level 59.5 by applying a high ink level reference signal on line 82 from a reference source 84 to a comparator 86. The high ink level reference sig- nal represents the maximum acceptable ink level 59.5 in the fountain 12 and is compared with the measured ink level signal on line 60 to produce an alarm on comparator output 88 when the ink level exceeds the maximum level 59.5. From time to time an ink wave, such as caused by the action of the agitator 20, generates an acoustic re¬ turn which causes the measured ink level signal on line 60 to temporarily represent an ink level above the maximum level 59.5. In such case comparator 86 may produce an alarm signal on output 88. Since such alarm condition is of short duration, a timer 90 is employed to screen out momentary high ink level detections. Timer 90 is of a type whereby the high ink level alarm on line 88 must per¬ sist for a minimum time period to cause a high ihk level alarm on output 92 to activate a high level relay 93. The relay may be used to sound an audible alarm 94.

The ink level in fountain 12 is normally kept at or above operating level 59.3. If, notwithstanding such control, the ink level drops below the operating level 59.3 and also below minimum level 59.2, the condition is identified as a malfunction with a minimum level control 95.

The measured ink level signal on line 60 and a low ink level reference signal on line 96, representative of minimum level 59.2 and generated by a source 98, are compared by a comparator 100. If the measured ink level drops below minimum 59.2, a low ink level alarm signal is produced on comparator output 102.

Since a low ink level alarm is construed as a malfunction of the system, such as may occur if the ink fountain is in an open unused condition, the comparator output 102 is applied to an inhibit input of comparator 62

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to inhibit it from generating an ink feed signal on line 68. Comparator output 102 is also applied to a relay 104 to operate such devices as appear necessary to respond to such low ink level condition since the low level may also be due to valve 26 being stuck or the ink supply being de pleted. Relay 104 may, for example, sound an audible alarm 106.

The use of ultrasonic transducer 30 provides th advantage of remote sensing of the ink level. However, from time to time the ink surface 36 is not level so that acoustic returns are reflected in the direction of arrow 35 instead of back onto transducer 30. As a result, an echo may be lost and no echo signal produced on line 56. In order to avoid a misinterpretation of such echo loss a an excessively low ink level, the loss of echo signal is detected with a network 110 and an appropriate ink level signal is simulated and provided on line 60.

Echo loss detector 110 includes a pulse network 112 which sets a flip-flop 114 in the event an echo signa fails to occur on line 56 within a certain time period following a transmitter pulse Tx. If an echo signal does occur, the setting pulse from pulse network 112 is ineffe tive since the echo signal on line 56 from flip-flop 54 i applied to maintain flip-flop.114 in its reset state. In the event no echo is detected, the reset level on line 56 to flip-flop 114 is not present and the output pulse on line 116 from pulse network 112 sets flip flop 114 to provide an echo loss signal on flip-flop outp 118. With the generation of an echo loss signal on line 118, an echo simulator circuit 120 is activated to provide a simulated ink level signal on line 122 represen ative of an ink level 59.4 between the operating level 59 and maximum level 59.5. The ink level signal is applied network 58 and appears on line 60 as long as echoes are lost.- As soon as an echo signal again is produced, flip- flop 114 is reset and the simulated ink level signal on

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In the event an echo loss condition persists for an excessive time period, a malfunction signal is produced with a timer 124 actuated by the echo loss signal on line 5 118. Timer 124 generates an alarm signal on line 126 for actuation of an appropriate alarm 128.

Fig. 2 illustrates an analog form of echo simu¬ lator 120 for generating a simulated ink level signal. The simulator operates with an ink level signal generator

10 58 of an analog type whereby the average voltage from flip-flop 54 (proportional to ink level) is stored in a capacitor 132.

When an echo loss signal occurs on line 118, it closes a transistor switch 134 having a simulated refer-

15 ence level signal from a source 136 coupled to a power electrode 138 such as the collector. The other- power electrode 140, the emitter, is coupled to capacitor 132 to clamp its voltage to the simulated reference level from source 136. Hence, as long as an echo loss condition per-

20 sists, a simulated ink level signal is provided on line 60. A particular advantage of capacitor 132 involves its smoothing effect upon the ink level signal. Such smoothing is desirable in view of the occasional loss or changes in the arrival time of an echo signal due to the

25 vibratory and disturbed nature of the ink surface 36. This smoothing is done over a time period sufficient to average a desired number of echo signals. A time constant associated with the charging _, of capacitor 132 may be of the order of about a third of a second.

30 The ink level control in accordance with the invention can be obtained with a digital network. For example, a microprocessor may be programmed to respond to the transceiver output 46 and transmitter pulses, Tx, to provide a digital echo signal. One method in which this

35 can be done is to enable an internal microprocessor clock to enter pulses into a register and terminate this when the transceiver generates an echo signal. The accumulated

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count in the register represents the two-way travel time of an ultrasonic pulse from transducer 30 to ink surface 36. The actual distance is directly proportional to the travel time and can be derived using a value of the speed of sound in air.

The distance value effectively represents the measured ink level by virtue of the known distance betwee the transducer and the bottom level 59.2 of the ink foun¬ tain. The distance value is thus converted to a measured ink signal within the microprocessor and stored in a suit able memory location. A suitable averaging technique may be employed to smooth out the effect of ink level surface variations. The number of travel time or distance measur ments to be averaged depends upon the travel speed of the agitator 20 and the size and frequency of the vibrations of the ink surface 36. In a pulse echo ink level control which generates of the order of about 100 echo pulses per second, the averaging of about 50 measured travel times can be used. The stored ink level signal is then compared with various previously stored digital values for the hig low and operating levels to provide an ink feed signal to the ink feed valve 26. An echo loss can be detected by comparison with a particularly low ink level reference value such as 59.1. The digital form of ink level contro 10 may thus take the form of a programmed microprocessor or with discrete digital circuits as may appear desirable For purposes of illustration, with the control as shown i Fig. 1, a digital form of the measured ink level signal such as developed either by generator 58, or its digital counterpart, is stored in a memory such as represented by storage network 57. This storage may be a location in a microprocessor memory or a particular output register for subsequent comparison with the reference signals. The stored ink level signal is retained until replaced as a result of a new measurement with ^" an echo signal.

When a loss of echo signals is sensed, such as

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with detector 110, the newly measured ink level will appear as an excessively low ink level and should not be used. Therefore, the output on line 118 is applied to network 57 to prevent replacement of the previously stored digital measured ink level signal, Such effect may, for example,, be obtained by blocking the input to register 57 with suitable logic gates, Hence _{ when an echo loss occurs _r a previously measured ink level signal is used to simulate the current ink levels. This condi- tion persists until an echo signal is again detected.

It may be preferred to simulate a digital ink level measurement of a known ink level to avoid maintain¬ ing an ink level signal which demands a feed of ink. In such case the detection of an echo loss on line 118 is used to replace the digital signal in storage network 57 with one representative of a predetermined ink level to avoid ink fountain overflows as may occur when the previ¬ ous ink level measurement sensed a low ink level. Such digital simulated predetermined ink level signal may be generated as soon as an echo loss is detected or may, for example, be obtained from a digital form of the simulated reference source 136 as shown in Fig. 2 such as can be stored in a memory location of a microprocessor.

In some cases it may be convenient to employ the signal on the output 126 from timer 124 directly to an in¬ hibit input 144 of clock 70. This would automatically inhibit the feed of ink in case of an extended period over which an echo loss may arise. In such case, care must be taken to avoid a momentary erroneous occurrence of an ink level signal indicating a need for ink feed as•soon as echoes are sensed again.

The echo loss detector 110 may be conveniently employed to align the ultrasonic transducer 30 onto ink surface 36. This is done by mounting transducer 30 for pivoting in transverse planes which are also normal to ink surface 36. The transducer ^' 30 is then pivoted until the echo is lost as observed by detecting a visual ala

energized by detector 110. The middle of the pivot range for each plane is then selected as the aligned position o transducer 30.

In the embodiment shown in Fig. 1 the described alignment procedure may also be carried out by observing a light source 53, such as an LED, driven by the reset output 55 of flip-flop 54. During normal operations the output 55 will be off most of the time and hence a very dim LED output is obtained as a sensing of the proper operation of the ink level control. When an echo is lost however, the reset output 55 will be continuously on and as a result the LED output significantly brighter. When operational functions of the flip-flop 54 and related seg ments of control 10 are porvided inside a microprocessor alignment of transducer 30 can be carried out by monitor¬ ing alarm 128.

Having thus described a printing press ink leve control in accordance with the invention, its advantages can be appreciated. The level of ink can be precisely controlled without direct contact with the ink and while the ink surface is disturbed by an agitator. Variations from the described embodiment may occur to one skilled in the art. For example, the echo loss simulator network ma be in digital form to accommodate a digital ink level sig nal generator. Also, a plurality of ink controls may be used. The scope of the invention, therefore, should be determined by the following claims.

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