US3862414A

US3862414A - Material dispenser control circuit with false trigger prevention

Info

Publication number: US3862414A
Application number: US434034A
Authority: US
Inventors: Harvey R Algeri
Original assignee: Nordson Corp
Current assignee: Nordson Corp
Priority date: 1974-01-17
Filing date: 1974-01-17
Publication date: 1975-01-21
Anticipated expiration: 1992-01-21
Also published as: FR2258659A1; GB1474640A; JPS50102061A; CA1017030A; DE2502257C2; FR2258659B1; JPS5819531B2; DE2502257A1

Abstract

A control system for turning on and off apparatus which discharges material onto objects moving on a conveyor past an article sensing and material dispensing station. An article sensor, including an incandescent lamp and a phototransducer spaced on opposite sides of a conveyor, senses movement of an article beneath a material dispensing valve as the article interrupts a light beam projecting across the conveyor from the lamp to the phototransducer. A threshold detecting circuit, including an operational amplifier and a single-shot, responds to the change in light intensity on the phototransducer occasioned by interruption of the light beam to energize a solenoid which controls operation of the material dispensing valve. A power supply including a full-wave rectifier and a smoothing capacitor provide power for the circuit components. A switch in the energization path of the solenoid, which is opened when the main ON/OFF power switch located between the rectifier and a conventional 60Hz source is opened, prevents discharge of energy from the smoothing capacitor to the solenoid to actuate the dispensing valve when the threshold detector faslely cycles as the incident light on the photocell decreases when the lamp is de-energized by open-circuiting the ON/OFF switch. A capacitor connected between the phototransducer input line to the operational amplifier and the power supply alters the potential of the reference input to the operational amplifier such that the signal output from the phototransducer to the operational amplifier temporarily existing after the ON/OFF switch has been closed and prior to build-up of the incandescent lamp intensity to its normal level does not falsely trigger the operational amplifier and in turn cycle the solenoid and material dispensing valve.

Description

United States Patent 1 Algeri [111 3,862,414 5] Jan. 21, 1975 MATERIAL DISPENSER CONTROL CIRCUIT WITII FALSE TRIGGER PREVENTION [75] Inventor: Harvey R. Algeri, North Olmstead,

Ohio

[73] Assignee: Nordson Corporation, Amherst,

Ohio

[22] Filed: Jan. 17, 1974 [21] Appl. N0.: 434,034

[52] US. Cl. 250/206, 250/223 [51] Int. Cl. I-IOIj 39/12 [58] Field of Search 250/206, 214, 222, 223;

Primary ExaminerJames W. Lawrence Assistant Examiner--D. C. Nelms Attorney, Agent, or Firm-Wood, Herron & Evans 1 1 ABSTRACT A control system for turning on and off apparatus which discharges material onto objects moving on a conveyor past an article sensing and material dispensing station. An article sensor, including an incandescent lamp and a phototransducer spaced on opposite sides of a conveyor, senses movement of an article beneath a material dispensing valve as the article interrupts a light beam projecting across the conveyor from the lamp to the phototransducer. A threshold detecting circuit, including an operational amplifier and a single-shot, responds to the change in light intensity on the phototransducer occasioned by interruption of the light beam to energize a solenoid which controls operation of the material dispensing valve. A power supply including a full-wave rectifier and a smoothing capacitor provide power for the circuit components. A switch in the energization path of the solenoid, which is opened when the main ON/OFF power switch located between the rectifier and a conventional 60Hz source is opened, prevents discharge of energy from the smoothing capacitor to the solenoid to actuate the dispensing valve when the threshold detector faslely cycles as the incident light on the photocell decreases when the lamp is de-energized by open-circuiting the ON/OFF switch. A capacitor connected between the phototransducer input line to the operational amplifier and the power supply alters the potential of the reference input to the operational amplifier such that the signal output from the phototransducer to the operational amplifier temporarily existing after the ON/OFF switch has been closed and prior to build-up of the incandescent lamp intensity to its normal level does not falsely trigger the operational amplifier and in turn cycle the solenoid and material dispensing valve.

7 Claims, 1 Drawing Figure LIGHT K M l 77 Patented Jan. 21, 1975 I I I I l l i I M DARK g K afim M I LIGHTI MATERIAL SOURCE MATERIAL DISPENSER CONTROL CIRCUIT WITH FALSE TRIGGER PREVENTION This invention relates to control circuits for material dispensing apparatus of the type wherein a moving article interrupts a light beam from an incandescent lamp to cause the control circuit to actuate the material dispenser, and more particularly to acontrol circuit of such type incorporating means to prevent false triggering of the control circuit and operation of the dispenser when the control circuit is turned on and/or turned off.

In many automated manufacturing operations, articles move on a conveyor past a station in which material is dispensed to the moving article. For example, in automated paint spraying operations, articles suspended from a moving conveyor are provided with a coating of paint as they pass through a paint spray coating station. In other automated production lines, adhesive is applied to, for example, a flap of a box which subsequently will be folded to adhere it in place, as the box passes through a glue application station. In either type operation, material is dispensed to an object as it passes through a material dispensing station. Obviously, if such material dispensing operation is to be automated, article sensing means must be provided to sense when the article is located proximate the material dispenser.

One common form of article sensing means is predicated on the sensing of the interruption of a light beam by an article moving on a conveyor. In arrangements of this type, a source of light and a phototransducer are positioned on opposite sides of the path of the moving objects such that as the objects move down the production line they interrupt the light beam proximate the material dispensing apparatus. Interruption of the light beam causes the phototransducer, which previously had been incident with a relatively high level light intensity from the light source, to now be incident with relatively low intensity light. This change in received light intensity by the phototransducer is detected by a suitable control circuit causing actuation of the material dispenser.

In article sensing control circuits of the foregoing type wherein interruption of a light beam by a moving article causes material to be dispensed, a problem has resulted in that material is dispensed as an incident to turning on and turning off the photosensing circuitry. Specifically, the problem involves the false triggering of the photosensing dispenser control circuit during turnon and turn-off when in fact no article is present on the conveyor to receive the dispensed material, with the result that dispensed material is undesirably placed on the conveyor itself rather than on an article interrupting a light beam which is normally the case.

The false triggering which results during turn-on is atrributable to the fact that, for practical reasons, the light source is usually an incandescent lamp which takes a finite time after turn-on to reach its relatively high normal intensity level. While the intensity of the light beam is building up as the filament of incandescent lamp heats, but before it reaches its normal relatively high intensity level, the phototransducer is incident with a relatively low level light intensity from the lamp. The phototransducer interprets this relatively low level of incident light during lamp warm-up following turn-on in the same manner as it does when the normal, relatively high intensity level light beam is interrupted by a moving article on the conveyor, and as a consequence, falsely activates the material dispenser to dispense material when in fact no article is on the conveyor. Dispensing of material when an article is not on 5 the conveyor causes the dispensed material to be deposited on the conveyor itself which, for obvious reasons, is undesirable.

In accordance with certain principles of this invention the foregoing problem involving false triggering of the photosensing dispenser control circuit following initial turn-on is obviated by altering, for a brief period following turn-on and while the incandescent lamp filament heats up, a reference voltage against which the phototransducer output is compared to determine whether or not the light beam has been interrupted, whereby the normal relationship of phototransducer output and reference voltage associated with a noninterrupted beam of relatively high intensity from a fully heated filament is maintained even though the beam has in fact not yet reached its normal, relatively high intensity level. For example, in a preferred form of the invention the reference voltage is temporaily increased to avoid false triggering since the phototransducer output is such that it would normally increase when incident with less light, as occurs when a normal intensity light beam is interrupted by an article. In this way the increased output of the phototransducer temporarily occurring after turn-on does not exceed the reference voltage which has been temporaily increased during turn-on in accordance with this invention.

In a preferred form of the invention, temporary alteration of the reference voltage against which the phototransducer output is compared to avoid false triggering during turn-on is achieved by interconnecting a capacitor between the reference voltage terminal and the circuit power supply. Immediately following turn-on and prior to the time the capacitor has an opportunity to fully charge, there is a negligible voltage drop across the capacitor with the result that the reference terminal is at the same voltage as the power supply, namely, at an artificially high voltage, which voltage exceeds the temporarily high voltage output from the phototransducer immediately following lamp energization. As the capacitor charges following turn-on, the voltage of the reference terminal decreases. However, the rate of the decrease is selected such that during the transition period when the lamp intensity is building up the phototransducer output at all times will be less than the reference voltage, thereby avoiding false triggering. Thus, by utilization of a capacitor connected to the reference terminal the problem of false triggering upon turn-on has been eliminated. Further, since the capacitor is not in the phototransducer circuit itself, but rather in the reference voltage circuit, the response of the phototransducer is not slowed down by capacitive delay effects.

False triggering, resulting in the undesired discharge of material in the absence of an article on the conveyor, is also a problem during turn-off of the photosensing control circuitry.

Specifically, as a consequence of turn-off, the incandescent lamp is de-energized causing the intensity of light incident on a phototransducer to drop. This decrease in light intensity on the phototransducer, insofar as the phototransducer is concerned, is interpreted as an interruption of the light beam by an article moving on the conveyor, with the result that the control circuit is cycled.

Under normal conditions, that is, when the light beam is interrupted by an article moving on the conveyor and the control circuit cycled, an electronic switch, such as a transistor in series with the valve actuator, for example, a solenoid, is placed in a conductive condition, allowing current to flow from the power supply to the solenoid, energizing the solenoid, in turn actuating the material dispenser. Since the power supply for the solenoid includes a smoothing capacitor to remove the ripple from the full-wave rectified output of the typical bridge rectifier circuit fed with conventional 60Hz a.c. power, the power supply is capable of storing sufficient energy in capacitive form to energize the solenoid when the circuit is falsely cycled due to the decreased light intensity on the phototransducer present when the circuit is de-energized. Thus, the combination of capacitively stored energy and the decreasing light intensity incident on the phototransducer when the circuit is turned off, causes the solenoid to become energized, dispensing material when in fact an article is not present on the conveyor.

Accordingly, it has been a further objective of this invention to obviate the false triggering and consequence undesired dispensing of material occasioned by turning off a photosensing control circuit. In accordance with certain additional principles of this invention, this objective has been accomplished by connecting an auxiliary switch in the energization path of the solenoid, which switch is operated jointly with the ON/- OFF switch of the control circuit. When the ON/OFF switch for the control circuit is placed in an open circuit to de-energize the control circuit, the auxiliary switch in the energization path of the solenoid is placed in open-circuit condition, preventing energization of the solenoid with capacitively stored energy, which would otherwise tend to occur when the control circuit is cycled by the decreased light incident on the phototransducer occasioned by de-energization of the incandescent lamp upon turn-off. In an alternative form of the invention the auxiliary switch, instead of being connected in the energization path of the solenoid, is connected across the smoothing capacitor and placed in a closed-circuit condition simultaneously with the opencircuiting of the main ON/OFF switch. When so placed and operated, the auxiliary switch discharges the capacitor through a path other than the solenoid when the control circuit is turned off and cycled by the reduced light incident on the phototransducer caused by de-energization of the incandescent lamp. Thus, the mere addition of an auxiliary switch, in either the energization path of the solenoid or to discharge the smoothing capacitor, eliminates energization of the solenoid by capacitively stored energy which would otherwise tend to result when the control circuit is cycled as a consequence of the reduced light incident on a phototransducer, when the incandescent lamp is deenergized by open-circuiting of the main ON/OFF switch.

These and other advantages, features and objectives of the invention will become more readily apparent from a detailed description of the invention in which the single figure is a diagrammatic view, partially in perspective, of a material dispensing system incorporating the control circuit of this invention.

General Description The control circuit of this invention can be used in a variety of applications wherein it is desired to control a device in response to interruption of a light beam. However, for the purposes of clarity and ease of understanding, the control circuit of this invention is described in connection with a preferred environment in which it is utilized to control the application of glue to cartons moving on an endless belt conveyor, which cartons interrupt a light beam to effect dispensing as they move beneath a glue dispensing valve.

With reference to the FIGURE depicting the preferred embodiment, an endless conveying belt 10 is included, the upper section of which is driven in the direction of arrow 11 by suitable motor means (not shown) which are drivingly connected to one or both of the rolls [2, 12 over which the belt trains. Disposed above the belt 10 at a suitable point along its length is a material dispensing valve 13 connected via conduit 14 to a source of material (e.g., glue) to be dispensed 15. The source of material 15 is preferably pressurized to facilitate flow through the conduit 14 and dispensing valve 13 when the valve is switched from a closed condition to an open condition. The valve 13 is provided with a movable flow control member (not shown) positionable between a closed position in which material is not dispensed and an open position in which material is dispensed. Movement of the valve flow control member between its open and closed positions is accomplished by an electromechanical actuator 16, the mechanical output of which is connected via suitable means shown schematically by dotted line 17. To control the electromechanical actuator 16, and hence the dispensing of glue from valve 13, a control circuit 22, to be described in detail hereafter, is provided. Control circuit 22 includes, among other things, a source of light 24 and a phototransducer 25 located on opposite sides of the conveyor belt 10 such that a beam of light 26 emanating from the lamp 24, which is incident on the phototransducer 25, is interrupted by a moving article 20, such as a box having a flap to which glue is to be applied, when it arrives beneath valve 13.

In operation, when the leading edge of the box 20 moving on the conveyor belt 10 in the direction of arrow 1] interrupts the light beam 26, the phototransducer 25, which is normally incident with light from the lamp 24 at a relatively high intensity, is incident with ambient light only which is at a much lower intensity level than existed prior to interruption of the beam. The change in level of intensity of light incident on the phototransducer 25 causes the control circuit 22 to energize the electromechanical actuator 16, preferably for a predetermined interval, such as one second. Energization of the electromechanical actuator 16 causes movement of its mechanical output 17, in turn switching the flow control member of the dispensing valve 13 from a closed condition to an open condition which, for the duration of the predetermined energization interval of the electromechanical actuator 16, causes adhesive to be dispensed from the valve for application to the flap of the box 20.

Detailed Description The lamp 24, which directs a beam of light 26 across reasonably intense source of light to overcome ambient lighting effects, a lamp of the incandescent type. A 6.3- volt, No. 12 incandescent lamp marketed by General Electric Company has been found satisfactory in applications wherethe distance between lamp and phototransducer, which is dictated by the width of the belt measured in a direction transverse to its length, is approximately 15 inches, and the ambient lighting conditions are equivalent to those generally found in manufacturing plants. The phototransducer 25 is preferably of the type having a resistance which varies as a function of incident light. In practice, it has been found that a phototransducer is satisfactory having a resistance in the meg-ohm range when in a dark" condition, i.e., at low incident light intensity when the beam 26 is interrupted, and a resistance in the range of 2k-5k ohms when in a light condition, i.e., when incident with an uninterrupted beam of light of relatively high intensity from the lamp 24. A suitable phototransducer is marketed by Clairex Electronics, Inc., designated Model No. CL603A.

The lamp 24 is energized from a step-down transformer 28 which has its primary winding 28A connected to a conventional l-volt 60Hz. a.c. power supply 30 via lines 31 and 32. An ON/OFF switch 33 is connected in line 32 between the a.c. power supply 30 and the secondary winding 28A of transformer 28. Transformer 28 has a secondary winding 288 which is connected to the lamp 24 via

lines

35 and 36. The transformer 28 steps down the l20-volt a.c. power from supply 30 to 6.3-volt a.c. for energization of the lamp 24.

The remaining components of the control circuit 22, including the phototransducer 25, a threshold detector 37 incorporating a photocell trigger amplifier 38 and a single-shot 40, and an electronic switch for controlling current flow through the electromechanical actuator 16, are powered by a transformer 42, full-wave rectifier 44, smoothing capacitor 46 and voltage regulator 49. Transformer 42 includes a primary winding 42A which is connected across the conventional a.c. power supply 30 through the ON/OFF switch 33 via lines 31 and 32. The secondary winding 42B of the transformer 42 is connected to the input of the full-wave rectifier 44. The transformer 42 steps/down the l20-volt a.c. power from the supply 30 to 28 volts a.c. for input to the fullwave rectifier 44. The full-wave rectifier 44 is a conventional bridge-type rectifier which provides full-wave rectification for the a.c. power input from the stepdown transformer 42. To remove the ripple in the fullwave rectified power output from the rectifying bridge 44, the smoothing capacitor 46 is connected to the rectifier output, providing across line 48 and grounded line 47 substantially ripple-free unidirectional, or d.c., power.

The voltage regulator 49 is of the conventional series regulating type for providing 26-volt d.c. regulated power on regulator output line 50, and l5-volt d.c. regulated power on regulator output line 52. As those skilled in the art understand, a voltage regulator of the series-type includes a variable impedance 49A, which in this case is a Darlington transistor circuit, in series between regulator input line 48 and regulator output line 50. A voltage comparator in the form of a transistor 49B alters the impedance of series transistor circuit 49A as the result of a comparison between a reference voltage established by a Zener diode 49C and the regulated output voltage on line 50 as reflected by the output 49D of a voltage divider 49E responsive to the volt age on regulator output line 50. The regulated output voltage on line 52, which is approximately 11 volts below that on regulated output line 50, is provided by a voltage dropping transistor 49F connected between

lines

50 and 52. Resistor 49G combines to provide bias for transistor 49F and to provide current limiting for Zener diode 49C. A capacitor 49H connected between regulated voltage line 50 and ground line 47 provides additional smoothing of the regulated output from the regulator 49.

The electromechanical actuator 16, which preferably takes the form of a solenoid valve having a movable armature shown schematically by dotted line 17, is connected between a grounded line 54 and the regulated voltage line 50 via a switch 55, a resistor 56, and an electronic switch 53. Resistor 56 provides a current limiting function should the solenoid l6 become shortcircuited. The electronic switch 53, which preferably takes the form of a transistor, facilitates energization of the solenoid 16 when the threshold detector 37 provides an output thereto on line 57 in response to interruption of the light beam 26 in the manner to be described. A diode 58 is connected in series with a Zener diode 59, both of which are connected across the solenoid 16 to protect the transistor switch 53. Zener diode 59 performs the additional function of not slowing down the response of the solenoid to controlled current flow through the transistor switch 53, which would otherwise tend to occur by reason of utilization of diode 58.

The switch 55, which is also in series with the energization path of solenoid l6 and the electronic switch 53, is operated jointly with the ON/OFF switch 33. Switch 55, when the ON/OFF switch 33 is transferred from a closed-circuit to an open-circuit condition, prevents energy capacitively stored in smoothing capacitors 46 and 49H from being discharged through the solenoid 16 when the electronic switch 53 is placed in a conductive state by the detector 37 which occurs, in a manner to be described, as a consequence of de-energization of the lamp 24 when ON/OFF switch 33 is opened, causing the phototransducer 26 to go dark. Were switch 55 omitted, when the control circuit 22 is de-energized by opening switch 33, the solenoid 16 would be momentarily energized, resulting in unwanted dispensing of adhesive from valve 13.

Specifically, when the ON/OFF switch 33 is switched to an open-circuit condition, power is removed from the lamp 24, which lamp then ceases to irradiate the phototransducer 25. Since the detector 37 operates to activate the electronic switch 53 for energizing the solenoid 16 when the phototransducer 25 goes dark," which normally occurs when the beam 26 is interrupted by an article 20 on the conveyor 10, de-energization of the lamp 24 as a consequence of removing power from the control circuit via switch 33 is interpreted by the detector 37 as an interruption of the light beam, which detector then responds to provide an output on line 57 to render electronic switch 53 conductive. Even though ON/OFF switch 33 is open, since energy is capacitively stored in smoothing capacitors 46 and 49H, sufficient energy is available for cycling the detector 37 and solenoid 16 when the lamp 24 ceases to be illuminated upon opening of ON/OFF switch 33.

Inclusion of the switch 55, which is actuated jointly with switch 33, eliminates energization of the solenoid 16 when the ON/OFF switch 33 is opened and the lamp 24 darkened, simulating interruption of the beam 26 by an article on the conveyor. Specifically, energy capacitively stored in the smoothing capacitors 46 and 49H is prevented from flowing to the solenoid 16, when the electronic switch 53 is falsely cycled by deenergization of the lamp 24 occasioned by opening ON/OFF switch 33, which deenergization of the lamp 24, as indicated, simulates interruption of the light beam 26 by an article 20 on the conveyor 10.

While the switch 55 has been shown connected in series between line 50 and current limiting resistor 56, those skilled in the art will understand that switch 55 could be connected anywhere in the energization path of the solenoid 16 between line 50 and grounded line 54. Alternatively, instead of placing switch 55 in the energization path of the solenoid 16 between

lines

50 and 54, the energy capacitively stored in smoothing capacitor 46 could be by-passed with respect to the solenoid 16 when the detector is falsely cycled by deenergization of the lamp 24 when the switch 33 is opencircuited. Specifically, the switch 55 could be replaced by two

switches

55 and 55" placed in series with resistors R and R, respectively, across the smoothing capacitors 46 and 49H, respectively, as shown in dotted lines. With

switches

55 and 55" placed across smoothing capacitors 46 and 49H, rather than a switch 55 in series with the solenoid 16, when the ON/OFF switch 33 is placed in an open-circuit condition the

switches

55 and 55" would be placed in a closed-circuit condition to discharge the capacitors 46 and 49H to ground via resistors R and R". Thus, when the detector 37 is falsely cycled to actuate the electronic switch 53 and place it in a conductive condition as a consequence of lamp 24 being de-energized by opening of ON/OFF switch 33, energy capacitively stored in capacitors 46 and 491-1 will not be discharged through the solenoid 16 to operate valve 14, but rather will be discharged to ground 47 via resistors R and R.

The phototransducer trigger amplifier 38, which forms the first stage of the threshold detector 37, principally includes an operational amplifier 60 having a reference voltage input terminal 60A, a sampling votage input terminal 608, and an output terminal 60C. So long as the reference voltage input to terminal 60A exceeds the signal input to sample terminal 608, the output at terminal 60C is at a relatively high level. However, should the sample voltage input to terminal 60B become more positive than the reference voltage input to terminal 60A, the output at terminal 60C is reduced to a relatively low level. An operational amplifier found to operate satisfactorily is marketed by Fairchild Semiconductor Company, designated Model UA741 described at pages 107-1 13 of Fairchild Linear Integrated Circuits Data Catalog, November 1971 edition.

The reference terminal 60A of the amplifier 60 is connected to the midpoint of a voltage divider consisting of resistors 62 and 63 connected between ground line 54 and the regulated -volt d.c. line 52, providing a 7% volt d.c. reference level. The sampling terminal 608 of the operational amplifier 60 is connected to a voltage divider which includes a resistor 68 constituting one section of the voltage divider, and a resistor 69 connected in parallel with the phototransducer 26 which collectively constitute the other portion of the voltage divider.

Under normal conditions, that is, when the lamp 24 is energized and the beam 24 incident on phototransducer 25, providing the phototransducer with a resistance of 2k-5k ohms, the line 70 input to sampling terminal 60B is at approximately 2 volts. Under such conditions of lamp energization and beam continuity, the 7 /2 volt reference signal input to operational amplifier terminal 60A is more positive than the normal 2-volt phototransducer signal level input to operational amplifier terminal 608, with the result that the output from the operational amplifier on line 60C is at a relatively high value. However, should the light beam 26 from source 24 incident on phototransducer 25 be interrupted by, for example, passage of an article on the conveyor 10 between the lamp and phototransducer, or light beam interruption simulated by de-energization of the lamp, the resistance of the phototransducer 25 shifts to a value exceeding 1 meg-ohm, providing on line 70 to the operational amplifier sampling terminal 60B a voltage of approximately 14 volts. Under these input conditions wherein the voltage of sampling terminal 60B exceeds the voltage of reference terminal 60A, the output on line 60C shifts from a relatively high level to a relatively low level.

A diode and resistor 76 series-connected between ground line 54 and the regulated 15-volt d.c. line 52, in combination with a capacitor 77 connected between operational amplifier line 60C and the junction of diode 75 and resistor 76, function to differentiate the downshift in signal level at terminal 60C which accompanies interruption of the light beam 26, providing on line 78 a negative-going voltage spike each time the light beam is interrupted by passage of an article between the lamp and phototransducer, or each time light beam interruption is simulated as when, for example, the lamp 24 is de-energized by open-circuiting the switch 33.

The single-shot circuit 40, preferably is a linear integrated circuit connected in a monostable mode of operation, having an input terminal 40A, is responsive to the differentiated output from the operational amplifier 60 present on line 78. Each time a negative-going spike is input to the single-shot 40 on line 78, a positive pulse of selectively variable duration is output from the single-shot on line 79. The duration of the positive pulse output from the single-shot on line 79 as a consequence of each negative-going spike input thereto on line 78 can be varied by varying the magnitude of a control signal level input to the single-shot via a potentiometer 80 connected between a control terminal 40B of the single-shot and a source of positive potential. Preferably the adjustment is such that the duration of the output pulse on line 79 is approximately in the range of 0.01 to 1.0 seconds.

The positive pulse output on line 79 from the singleshot 40 each time a negative-going spike is input to the single-shot on line 40A from the operational amplifier 60 which, as noted, occurs each time the light incident on the phototransducer 25 decreases, as occurs, for example, when the light beam 26 is interrupted by an article moving on a conveyor or the lamp 24 is deenergized by opening switch 33, is input to the base of transistor switch 53 by a coupling resistor 82. The transistor switch 53 which is normally non-conducting, that is, is not conducting absent a positive pulse input thereto from the single-shot 40, is rendered conductive by the positive pulse output from the single-shot. Conduction of transistor switch 53 completes a portion of the energization path between ground line 54 and the regulated voltage line 50 for the solenoid 16, the other portion of the path being completed by switch 55 which is closed when the control circuit is energized by placement of switch 33 in the closed condition. Conduction of transistor switch 53 in response to a positive pulse input from the single shot 40, assuming switch 55 is also closed, causes the solenoid 16 to be energized for the duration of the single-shot output pulse. Energization of the solenoid 16, in a manner heretofore described, actuates valve 13 to dispense adhesive from the source 15 to the article positioned therebeneath.

When ON/OFF switch 33 is switched to an open circuit condition, lamp 24 is de-energized causing the level of light incident on phototransducer 25 to decrease. As a consequence, the voltage input to terminal 608 of the operational amplifier on line 70 shifts from its normal level of approximately 2 volts to approximately 14 volts, in turn producing a negative-going spike input at terminal A of the single-shot 40 which in turn provides a positive pulse on line 57 to the electronic switch 53. Thus, the operational amplifier 60 and the single-shot 40 are falsely cycled when the lamp 24 is de-energized by opening switch 33, producing an output from detector 37 to switch 53 similar to that which occurs when the enregized lamp 24 has its beam 26 interrupted by an article in the conveyor.

The switching of transistor switch 53 to a conductive state in response to the false cycling of the operational amplifier 60 and single-shot 40 when the lamp 24 is deenergized would, were it not for the opening of switch 55 concurrently with the opening of ON/OFF switch 33, cause the energization of solenoid 16, since energy capacitively stored in smoothing capacitors 46 and 49H would, even though the switch 33 has been opened, discharge through the solenoid 16 causing it to be energized and actuate the valve 13. Actuation of the solenoid l6, and hence the valve 13, in response to deenergizing the lamp 24 when the switch 33 is opened is avoided in accordance with principles of this invention by utilization of switch 55 in series in the energization path of solenoid 16, which switch 55 is open simultaneously with opening of switch 33, thereby preventing discharge of capacitively stored energy through the solenoid 16.

In accordance with an alternative form of this invention, energization of the solenoid 16 in response to false triggering of the operational amplifier 60 and singleshot 40 when the switch 33 is opened and the lamp 24 de-energized, is avoided by location of the

switches

55 and 55" across the capacitors 46 and 49H rather than placing a switch in series with the energization path of the solenoid 16. With the switches 55' and 55" such that they are normally open, but are closed when the main switch 33 is opened, energy capacitively stored in the capacitors 46 and 491-! will discharge through resistors R and R" to ground when the main switch 33 is opened.

Another potential source of false cycling of the solenoid 16 occurs when the control circuit 22 is initially energized by closure of the switch 33. Specifically, when the switch 33 is closed, energizing the voltage regulator 49 and the lamp 24, power is available on

lines

50 and 52 on a virtually instantaneous basis energizing the operational amplifier 60 and single-shot 40 and the circuitry associated therewith. Likewise, power is instantaneously available for energizing the solenoid 16 should the transistor switch 53 be rendered conduc- 5 tive since switch 55 is closed simultaneously with the closure of switch 33. However, the lamp 24 at the moment of closure of the switch 33 is not instantaneously rendered operative to produce light at full light intensity, but rather the intensity of the lamp 24 increases gradually from zero intensity to its operating level over an interval of approximately 100 milliseconds. While the intensity of the lamp 24 is increasing following closure of switch 33, but prior to its reaching full intensity, the phototransducer 25 is incident with a level of light below normal, that is, with a level of light associated with interruption of the beam 26 by an article on the conveyor. Under such conditions, the resistance of the phototransducer 25 is in the meg-ohm region placing a signal on line 70 of a relatively high level which, initially following closure of the switch 33, is more positive than the 7% volt level which is normally present on line 64. Were the level of the signal on line 70 immediately following closure of switch 33 permitted to exceed the level of the reference signal normally present on line 64, the operational amplifier would be falsely triggered to provide at its terminal 60C a relatively low level signal associated with interruption of the full intensity light beam 26, which in turn would falsely trigger the single-shot 40, energize the electronic transistor switch 53, and complete the energization path for the solenoid 16 to cycle the solenoid and the valve 13.

However, and to avoid false triggering of the operational amplifier and single-shot immediately following energization of the lamp 24 by closure of the switch 33 when, at least initially, the lamp 24 has a relatively low intensity, a capacitor 66 is connected between the 15- volt d.c. regulator line 52 and the sample terminal 60A of the operational amplifier 60. When switch 33 is initially closed and capacitor 66 uncharged, the voltage of line 64 is very close to the l5-volt potential of line 52. Since the potential of line 64 under these circum stances exceeds that of line existing when the intensity of the lamp 24 is relatively low, the output of the operational amplifier at terminal 60C is at a relatively high level characteristic of that present when the full intensity lamp beam is not interrupted by an article on the conveyor. Following closure of the switch 33 and as the capacitor 66 begins to charge, the signal level on line 64 drops from the approximately 15-volt level'on line 52 to 7% volt reference level established by the voltage divider 62, 63 when the capacitor 66 is fully charged. The size of the capacitor 66 and resistors 62 and 63 should be selected such that the decreasing signal level on line 64 associated with the gradual charging of capacitor 66 following closure of switch 33 remains above the level of the phototransducer signal on line 70 following closure of switch 33 associated with the gradual decrease in resistance of the phototransducer 25 as the intensity of the lamp 24 gradually increases to its steady state level. Thus, the capacitor 66 avoids false triggering of the operational amplifier 60 and single-shot 40 which, via transistor switch 53, would cycle the solenoid l6 and the valve 13 when the switch 33 is closed and the incandescent lamp 24 has not reached its full intensity.

False triggering of the operational amplifier 60 and single-shot 40 upon closure of the switch 33 due to the fact that the lamp 24 does not reach its full intensity until lapse of a specified warm up time could have been avoided by connecting the capacitor 66 between the phototransducer input terminal 608 and ground line 54, rather than between the reference terminal 60A and positive line 52. By so doing, line 70 would be kept at an artificially low potential immediately following closure of switch 33 while the lamp intensity 24 is building up, with the result that reference line 64, which by virtue of

voltage divider

63, 63 is at 7 /2 volts, exceeds the signal level on line 70, preventing false triggering of the operational amplifier 60. However, had the capacitor 66 been connected between ground line 54 and terminal 608 of the operational amlifier 60, rather than as in the preferred embodiment wherein it is connected between the reference terminal 60A of the operational amplifier and the positive line 52, the response time of the phototransducer 25 to changes in incident light when the beam is broken by an article on the conveyor would have been deleteriously affected, which is not the case when the capacitor 66 is connected between the reference line 64 and the positive bus 52 as in the preferred embodiment of this invention.

Having described the invention, what is claimed is:

l. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption of a light beam occur ring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising:

a rectifier circuit connectable to an ac. source for providing rectified current,

a capacitor connected to said rectifier for smoothing said rectified current,

an electronic switch connected between said capacitor and said electromechanical actuator, said switch operable in response to a control signal to switch to a conductive condition to facilitiate energizing said electromechanical actuator for operat ing said valve to dispense material to said article,

a phototransducer,

a lamp energizable to direct a light beam to said phototransducer,

first switch means connecting said lamp and said rectifier to said a.c. source for selectively energizing said lamp and rectifier when actuated,

a detector circuit connected between said phototransducer and said electronic switch for providing, in response to a decrease in light incident on said phototransducer, a control signal to said electronic switch for switching it to said conductive condition to facilitate energizing said electromechanical actuator for operating said valve to dispense material to said article, and

second switch means connected in series with said electromechanical actuator and said electronic switch, said second switch means being jointly actuable with said first switch means to prevent energization of said electromechanical actuator by energy stored in said capacitor when said electronic switch is rendered conductive by a control signal produced by said detector when said first switch is dc-actuated and said lamp deenergized, reducing the light incident on said phototransducer,

2. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption ofa light beam occurring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising:

a phototransducer,

an incandescent lamp energizable to direct a light beam to said phototransducer, the intensity of said lamp increasing gradually from a level less than normal when initially energized and reaching normal intensity after a predetermined interval,

said phototransducer providing a normal output sig' nal of a first level when incident with light of normal intensity from said lamp and providing an output signal of second level when incident with light from said lamp of intensity less than normal,

first switch means connecting said lamp and said power supply for selectively energizing said lamp when actuated,

a reference voltage source providing a reference voltage,

an operational amplifier having an input terminal connected to said reference voltage source, said operational amplifier providing a control signal to said electronic switch to render it conductive to actuate said electromechanical actuator for operating said valve in a material dispensing mode in response to a predetermined voltage relationship existing across said input and reference terminals, which predetermined relationship exists when said phototransducer is at said second level and said reference terminal is at said reference level, and means connected to said reference terminal for altering, during said predetermined interval, the voltage level at said reference terminal to prevent, while the intensity of said lamp is gradually increasing to normal, said predetermined voltage relationship from existing across said input and reference terminals, which would otherwise result by reason of said phototransducer output being at said level due to said lamp not yet having reached normal intensity, whereby production of false control signals are avoided as an incident to energizing said lamp.

3. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption of a light beam occurring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising:

a capacitor connected to said rectifier for smoothing said rectified current,

an electronic switch connected between said capacitor and said electromechanical actuator, said switch operable in response to a control signal to switch to a conductive condition to facilitate energizing said electromechanical actuator for operating said valve to dispense material to said article,

a phototransducer,

an incandescent lamp energizable to .direct a light beam to said phototransducer, the intensity of said lamp increasing gradually from a level less than normal when initially energized and reaching normal intensity after a predetermined interval,

said phototransducer providing a normal output signal of a first level when incident with light of normal intensity from said lamp and providing an output signal of second level when incident with light from said lamp of intensity less than normal,

a reference voltage source providing a reference voltage,

an operational amplifier having an input terminal connected to said reference voltage source, said operational amplifier providing a control signal to said electronic switch to render it conductive to actuate said electromechanical actuator for operating said valve in a material dispensing mode in response to a predetermined voltage relationship existing across said input and reference terminals, which predetermined relationship exists when said phototransducer is at said second level and said reference terminal is at said reference level,

a capacitor connected to said rectifier for smoothing said rectified current, and

second switch means connected in series with said electromechanical actuator and said electronic switch, said second switch means being jointly actuable with said first switch means to prevent energization of said electromechanical actuator by energy stored in said capacitor when said electronic switch is rendered conductive by a control signal produced by said detector when said first switch is de-actuated and said lamp is de-energized, reducing the light incident on said phototransducer.

4. The circuit of claim 2 wherein said reference terminal voltage level altering means includes a capacitor connected between said power supply and said reference terminal for effectively short-circuiting said reference terminal to said power supply to vary said reference terminal input voltage in a manner compensating for transient effects on the phototransducer output signal when said lamp intensity is increasing to normal following lamp energization.

5. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption of a light beam occurring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising:

a phototransducer having a resistance which varies inversely with the intensity of light incident thereon,

said phototransducer providing a relatively low output signal when incident with light of normal intensity from said lamp and providing an output signal of relatively high potential when incident with light from said lamp of intensity less than normal,

a reference voltage source providing a reference voltage intermediate said relatively low and high potentials associated with normal and less than normal incident intensities on said phototransducer, respectively,

an operational amplifier having an input terminal connected to said reference voltage source, said operational amplifier providing a control signal to said electronic switch to render it conductive to actuate said electromechanical actuator for operating said valve in a material dispensing mode only when said voltage at said input terminal exceeds the voltage at said reference terminal,

a capacitor connected between said reference terminal and said power supply for increasing, during said predetermined interval, the voltage levelat said reference terminal to prevent, while the intensity of said lamp is gradually increasing to normal, the phototransducer output at said input terminal from exceeding the voltage at said reference terminal, which would otherwise result by reason of said phototransducer output being at said relatively high potential in excess of said reference potential due to said lamp not yet having reached normal intensity, whereby production of false control signals are avoided as an incident to energizing said lamp.

6. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption of a light beam occurring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising:

a rectifier circuit connectable to an ac. source for providing a rectified current,

a capacitor connected to said rectifier for smoothing said rectified current,

a phototransducer,

a lamp energizable to direct a light beam to said phototransducer,

means connected to said capacitor and jointly actuable with said first switch means to prevent energization of said electromechanical actuator by energy stored in said capacitor when said electronic switch is rendered conductive by a control signal produced by said detector when said first switch is deactuated and said lamp de-energized, reducing the light incident on said phototransducer.

7. The control circuit of claim 6 wherein said energization prevention means includes a normally open second switch adapted to be closed when said first switch is de-actuated, said second switch being connected to said capacitor for discharging said capacitor through a path excluding said electromechanical actuator when said second switch is closed coincident with deactuation of said first switch.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 52,414 DATED January 21, 1975 lNVENTOMS) Harvey R. Algeri It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' In the Specification:

Col. 1', Line 56, change "atrributable" to --attributable-- In the Claims: I

Col. 12 Line 42, insert "second" between the words "said" and "level".

Signed and Scaled this D seventh Day of 0ct0rber1975 [SEAL] 1 Arrest: I

RUTH MQSON c. MARSHALL DANN Arleslmg Ojjicer Commissioner of Parents and Trademarks

Claims

1. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption of a light beam occurring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising: a rectifier circuit connectable to an a.c. source for providing rectified current, a capacitor connected to said rectifier for smoothing said rectified current, an electronic switch connected between said capacitor and said electromechanical actuator, said switch operable in response to a control signal to switch to a conductive condition to facilitiate energizing said electromechanical actuator for operating said valve to dispense material to said article, a phototransducer, a lamp energizable to direct a light beam to said phototransducer, first switch means connecting said lamp and said rectifier to said a.c. source for selectively energizing said lamp and rectifier when actuated, a detector circuit connected between said phototranSducer and said electronic switch for providing, in response to a decrease in light incident on said phototransducer, a control signal to said electronic switch for switching it to said conductive condition to facilitate energizing said electromechanical actuator for operating said valve to dispense material to said article, and second switch means connected in series with said electromechanical actuator and said electronic switch, said second switch means being jointly actuable with said first switch means to prevent energization of said electromechanical actuator by energy stored in said capacitor when said electronic switch is rendered conductive by a control signal produced by said detector when said first switch is de-actuated and said lamp deenergized, reducing the light incident on said phototransducer.

2. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption of a light beam occurring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising: a phototransducer, an incandescent lamp energizable to direct a light beam to said phototransducer, the intensity of said lamp increasing gradually from a level less than normal when initially energized and reaching normal intensity after a predetermined interval, said phototransducer providing a normal output signal of a first level when incident with light of normal intensity from said lamp and providing an output signal of second level when incident with light from said lamp of intensity less than normal, first switch means connecting said lamp and said power supply for selectively energizing said lamp when actuated, a reference voltage source providing a reference voltage, an operational amplifier having an input terminal connected to said reference voltage source, said operational amplifier providing a control signal to said electronic switch to render it conductive to actuate said electromechanical actuator for operating said valve in a material dispensing mode in response to a predetermined voltage relationship existing across said input and reference terminals, which predetermined relationship exists when said phototransducer is at said second level and said reference terminal is at said reference level, and means connected to said reference terminal for altering, during said predetermined interval, the voltage level at said reference terminal to prevent, while the intensity of said lamp is gradually increasing to normal, said predetermined voltage relationship from existing across said input and reference terminals, which would otherwise result by reason of said phototransducer output being at said level due to said lamp not yet having reached normal intensity, whereby production of false control signals are avoided as an incident to energizing said lamp.

3. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption of a light beam occurring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising: a rectifier circuit connectable to an a.c. source for providing rectified current, a capacitor connected to said rectifier for smoothing said rectified current, an electronic switch connected between said capacitor and said electromechanical actuator, said switch operable in response to a control signal to switch to a conductive condition to facilitate energizing said electromechanical actuator for operating said valve to dispense material to said article, a phototransducer, an incandescent lamp energizable to direct a light beam to said phototransducer, the intensity of said lamp increasing gradually from a level less than normal when initially energized and reaching normal intensity after a predetermined interval, said phototransducer providing a normal output signal of a first level when incident with light of normal intensity from said lamp and providing an output signal of second level when incident with light from said lamp of intensity less than normal, first switch means connecting said lamp and said rectifier to said a.c. source for selectively energizing said lamp and rectifier when actuated, a reference voltage source providing a reference voltage, an operational amplifier having an input terminal connected to said reference voltage source, said operational amplifier providing a control signal to said electronic switch to render it conductive to actuate said electromechanical actuator for operating said valve in a material dispensing mode in response to a predetermined voltage relationship existing across said input and reference terminals, which predetermined relationship exists when said phototransducer is at said second level and said reference terminal is at said reference level, a capacitor connected to said rectifier for smoothing said rectified current, and second switch means connected in series with said electromechanical actuator and said electronic switch, said second switch means being jointly actuable with said first switch means to prevent energization of said electromechanical actuator by energy stored in said capacitor when said electronic switch is rendered conductive by a control signal produced by said detector when said first switch is de-actuated and said lamp is de-energized, reducing the light incident on said phototransducer.

5. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption of a light beam occurring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising: a phototransducer having a resistance which varies inversely with the intensity of light incident thereon, an incandescent lamp energizable to direct a light beam to said phototransducer, the intensity of said lamp increasing gradually from a level less than normal when initially energized and reaching normal intensity after a predetermined interval, said phototransducer providing a relatively low output signal when incident with light of normal intensity from said lamp and providing an output signal of relatively high potential when incident with light from said lamp of intensity less than normal, a reference voltage source providing a reference voltage intermediate said relatively low and high potentials associated with normal and less than normal incident intensities on said phototransducer, respectively, an operational amplifier having an input terminal connected to said reference voltage source, said operational amplifier providing a control signal to said electronic switch to render it conductive to actuate said electromechanical actuator for operating said valve in a material dispensing mode only when said voltage at said input terminal exceeds the voltage at said reference terminal, a capacitor connected between said reference terminal and said power supply for increasing, during said predetermined interval, the voltage level at said reference terminal to prevent, while the intensity of said lamp is gradually increasing to normal, the phototransducer output at said input terminal from exceeding the voltage at said reference terminal, which would otherwise result by reason of said phototransducer output being at said relatively high potential in excess of said referenCe potential due to said lamp not yet having reached normal intensity, whereby production of false control signals are avoided as an incident to energizing said lamp.

6. A control circuit for energizing an electromechanical actuator to operate a valve in a material dispensing mode in response to interruption of a light beam occurring in timed relation to movement of an article past a dispenser associated with said valve, said control circuit comprising: a rectifier circuit connectable to an a.c. source for providing a rectified current, a capacitor connected to said rectifier for smoothing said rectified current, an electronic switch connected between said capacitor and said electromechanical actuator, said switch operable in response to a control signal to switch to a conductive condition to facilitate energizing said electromechanical actuator for operating said valve to dispense material to said article, a phototransducer, a lamp energizable to direct a light beam to said phototransducer, first switch means connecting said lamp and said rectifier to said a.c. source for selectively energizing said lamp and rectifier when actuated, a detector circuit connected between said phototransducer and said electronic switch for providing, in response to a decrease in light incident on said phototransducer, a control signal to said electronic switch for switching it to said conductive condition to facilitate energizing said electromechanical actuator for operating said valve to dispense material to said article, and means connected to said capacitor and jointly actuable with said first switch means to prevent energization of said electromechanical actuator by energy stored in said capacitor when said electronic switch is rendered conductive by a control signal produced by said detector when said first switch is deactuated and said lamp de-energized, reducing the light incident on said phototransducer.

7. The control circuit of claim 6 wherein said energization prevention means includes a normally open second switch adapted to be closed when said first switch is de-actuated, said second switch being connected to said capacitor for discharging said capacitor through a path excluding said electromechanical actuator when said second switch is closed coincident with de-actuation of said first switch.