APPARATUS AND METHOD FOR DETECTING FAULTS IN CAN END SEALANT DEPOSITING MACHINE

Abstract: The present invention detects sealant deposit faults by detection of a quantity related to sealant flow within the valve chamber of the needle valve employed in the sealant depositing machine. A proximity detector (120) indicates to an electronic controller (100) when a can end (30) is in position for depositing the sealant. The electronic controller preferably monitors the pressure within the valve chamber (26) during at least one predetermined interval of time during the open and close operation of the needle valve (27). Upon detection of a pressure abnormality during one of these predetermined intervals of time, the electronic controller generates a reject signal which enables the transport mechanism to remove that particular can end from the stream of can ends going to the next station and place it in a reject pile (38). The monitoring takes place during an initial opening period of the needle valve, and during a time when the sealant flow is relatively steady. The rate of flow of sealant into the controllable valve may also be measured directly or measured from the pressure difference measured on opposite sides of a flow restrictor (117).

Description: APPARATUS AND METHOD FOR DETECTING FAULTS IN CAN END SEALANT DEPOSITING MACHINE Technical Field of the Invention The technical field of this invention is process control in a can end sealant depositing machine, and more particularly the detection of defects in the sealant deposit. Background of the Invention This invention is useful in the construction of metal cans. Metal cans are employed for numerous uses in packaging. Metal cans are typically constructed of either steel or aluminum. The typical construction of a steel can employs three parts. First steel sheet metal is rolled into a cylinder. This cylinder is then joined with a circular bottom and top, each of which is hereinafter referred to as a can end. The typical construction of aluminum cans employs two parts. The first part is a one piece cylinder and bottom. The second part is a can end similar to those employed in steel cans. In the case of both steel and aluminum cans, a similar technique is employed to attach the can ends to the base structure. The perimeter edge of the can end is typically rolled over the edge of the base cylinder and crimped there. In order to achieve a better seal at this junction, it is conventional to employ a sealant deposited in an annular pattern at the perimeter of the can end. This sealant forms a bond between the can end and the base cylinder when the can end is crimped onto the cylinder. The deposition of this sealant on the surface of the can end is typically accomplished by a special purpose machine. These machines are highly developed and operate at great speeds. In the typical installation can ends are fed sequentially from a source to a station where the deposition takes place. At this depositing station, the can end is spun about its axis of symmetry. A needle valve is employed in conjunction with a source of pressurized sealant. The needle valve is opened, and sealant is thereby sprayed onto the spinning can end. It is typical for the needle valve to be opened during more than one revolution of the can end, in some cases 2 1/2 revolutions of the can end, in order to provide a more even sealant layer. Once the deposit of sealant has taken place the needle valve is closed. Thereafter the spinning of the can end is stopped, and this can end is moved away from the depositing station. A transport mechanism typically is employed to move this can end to a collection station where the can ends are collected prior to assembly with the other parts of the can. In the meanwhile, another can end from the source of can ends is brought to the depositing station, and then spun in preparation for its receiving a sealant deposit. These can end sealant depositing machines are highly specialized mechanisms which operate at a very great rates. A typical machine of this type will deposit sealant on more than 100 can ends per minute. Because this technology is relatively old and highly refined, the incidence of defective can end deposits is very low. In a typical machine of this type the instance of defective deposits is less than (sometimes much less than) 1 per thousand of all can ends processed. While this seems to be a relatively low rate of defects, even this level of defects can cause problems. Such cans are often used for foodstuffs, which are subject to contamination, or for materials which will be stored under pressure. In addition, in some cases the material packaged within the can is chemically active and can attack an imperfect seal. The crimping process for attaching the can ends to the base can body can also make it difficult to detect the sealant defect. This crimping process typically forms a reasonable seal without the aid of the sealant, at least for a short period of time. Thus it has been known, for example, for a pressurized can to appear normal when leaving the packaging factory, only to fail and cause the pressurized contents to leak during shipping. In such cases it is typically required that the entire lot be discarded, in order to ensure that no other defective cans are shipped to the ultimate consumer. This is particularly the case in which the packaged material is foodstuff. There are several known scenarios which an result in a defective deposit of sealant. In the most serious defect, the needle valve fails to open, typically because it is clogged by some portion of the sealant. In such a case, no sealant is deposited on the can end and therefore there is no sealant at this joint in the can. In another type of failure, the needle valve becomes partially clogged, and in this case insufficient sealant is deposited on the can end. Insufficient deposit of sealant may also occur if a bubble in the sealant reaches the valve during the deposit on a particular can end. This causes there to be a period during which no sealant is deposited on the can end, resulting in insufficient sealant. There have been previous attempts to detect defects in sealant deposits on these can ends. Known prior techniques involve inspection of the deposited sealant on the can end. A first type of system uses an infrared light source and infrared sensor. The infrared light source is directed to the deposited annular strip of sealant. The sensor detects the infrared light reflected from the sealant strip and the adjacent uncoated can end. The presence of a skip or void in the sealant deposit is detected as a function of the contrast ratio between the deposited sealant and the bare can end. Such systems are sensitive to the alignment of the light source and sensor. In addition, variation in the color of the sealant or in the reflectivity of can end can adversely effect the accuracy of the measurement. This type of system is further limited by being capable of detecting only gross voids or skips and not being able to differentiate between a light and a heavy coating of sealant. A second type system employs machine vision. An image of the coated can end is formed after the can end leaves the sealant deposit station. This image is digitized and the digitized image is compared with an image from a defect free standard can end. The system typically compares the reflectance ratios of the sample and the standard. This method is dependent upon a fairly consistent color value of the sealant and a fairly consistent reflectance of the can end. This method can detect gross defects such as skips and voids and has the additional capability to determine the physical dimensions of the can end. These prior attempts to detect sealant deposit faults have not been completely successful. The typical machine vision system requires very close tolerances in the placement of the illumination and the visual sensor. The same is true for infrared detection systems. Because the sealant deposit typically takes place in a rather dirty environment, the illumination sources and sensors of these prior art systems must be constantly cleaned. This maintenance of the detection system reduces the amount of time available for depositing sealant on can ends. The sensors used in the known prior art systems are typically very expensive. In addition, such prior art systems require a great deal of computer processing power, which further adds to the expense of the fault detection system. Therefore, there is a need in the art for some manner of detecting defects in can end sealant deposit which is both inexpensive and requires little maintenance. Summary of the Invention The present invention operates by detection of a quantity related to the rate of flow of sealant through the controlled valve employed in the sealant depositing machine. In the preferred embodiment this quantity is the pressure within the valve chamber of the needle valve. A proximity detector indicates to an electronic controller when a can end is in position for depositing the sealant. This enables the electronic controller to correlate particular readings with a particular can end. The electronic controller monitors the quantity related to the rate of flow of sealant during at least one predetermined interval of time during the open and close operation of the needle valve. Upon detection of an abnormality during one of these predetermined intervals of time, the electronic controller generates a reject signal which enables the transport mechanism to remove that particular can end from the stream of can ends going to the next station and place it in a reject pile. In accordance with the preferred embodiment of the present invention, the quantity related to the rate of flow of sealant is the pressure within the valve chamber of the needle valve. The pressure is monitored during an interval when it is expected to be at a relatively stable level. During this interval the valve pressure is relatively steady and slightly below the static pressure, while the sealant is steadily deposited on the can end. During this interval the electronic controller computes the average pressure level. This average pressure level is compared with upper and lower limits. If the average pressure is outside the range of the upper and lower limits then a pressure anomaly is detected and the can end is rejected. These upper and lower limit pressures may be initially set empirically. These empirical limits are set based upon observation of the expected levels during normal operation of that particular type of sealant depositing machine. It is expected that this set of limit pressures will be adaptively adjusted during operation of the sealant depositing machine, in order to take into account operator initiated changes in the base pressure. It is known in the art that the valves in such machines typically undergo some wear causing their openings to increase in diameter. Thus it is necessary for the operator of the sealant depositing machine to monitor and periodically adjust the pressure of the sealant. The pressure must be slightly reduced to compensate for the wearing of the valve opening. Otherwise, as the valve opening wears greater and greater amounts of sealant will be deposited on the can end. In the preferred embodiment the limit pressures for a pressure anomaly are adjusted based upon a weighted average of the pressure levels measured for a predetermined number of prior valve openings. Adjusting the limit pressure based upon such a calculation from the measured average pressures of prior valve openings enables the defect detector to compensate for these changes in pressure. In a further aspect of the preferred embodiment of the present invention the electronic controller compares the average pressure during an initial interval with a limit pressure. This initial interval corresponds to a time when the pressure in the valve chamber drops upon the initial opening of the valve and then recovers. A pressure anomaly is detected when this initial interval average pressure is greater than (that is not as far below the static pressure level as) a pressure limit. As in the previous case this limit pressure may be initially empirically determined from observation of the pressure during normal operation of the sealant depositing machine. However, in the preferred embodiment this limit pressure is adjusted based upon a weighted average of the pressure averages measured for a predetermined number of prior valve openings. In accordance with a further embodiment of the present invention the quantity measured is the rate of flow of sealant is the through the controlled valve employed. This rate of flow may be measured directly via a flow sensor. Alternatively, this rate of flow may be measured by detecting the pressure differential on either side of a calibrated orifice. This differential pressure is then converted into the rate of flow of sealant. In the further embodiment, the electronic controller checks for flow abnormalities during the steady state interval and during the initial valve opening interval. The test for flow abnormality in this further embodiment is made relative to average flow rates for the respective intervals in analogy to the pressure sensor embodiment discussed above. In addition, it is also considered advantageous to provide adaptively adjusted flow limits in a manner similar to the adaptively adjusted pressure limits discussed above. Brief Description of the Drawings These and other aspects of the present invention will become clear from the following description of the invention taken in conjunction with the drawings in which: FIGURE 1 illustrates schematically the arrangement of the relevant mechanical parts of the sealant depositing machine and the electronic controller in the preferred embodiment of the present invention; FIGURE 2 illustrates in schematic form the electrical connections of the preferred embodiment of the present invention, and in particular the connections of the electronic controller; FIGURE 3 illustrates an example of a typical normal pressure curve, illustrating the time intervals and the respective pressure limits; FIGURE 4 illustrates a pressure curve during which the valve is partially clogged; FIGURE 5 illustrates a pressure curve during which the steady state pressure is improper resulting in insufficient sealant deposit; FIGURE 6 illustrates a flow chart for control of the computer controller illustrated in Figures 1 and 2 for practicing the present invention; FIGURE 7 illustrates schematically the arrangement of the relevant mechanical parts of the sealant depositing machine and the electronic controller in an alternative embodiment of the present invention; and FIGURE 8 illustrates schematically the arrangement of the relevant mechanical parts of the sealant depositing machine and the electronic controller in a further alternative embodiment of the present invention. Detailed Description of the Preferred Embodiments Figure 1 illustrates in schematic form the mechanical parts of the preferred embodiment of the present invention. In the embodiment of Figure 1, the measured quantity related to the rate of flow of sealant through the controlled valve is the pressure within the valve chamber. Figure 1 illustrates sealant depositing machine 10 including the controller for detection of sealant defects. It should be understood that some of the structures illustrated in Figure 1 are constructed in accordance with the prior art and other of the structures illustrated in Figure 1 are constructed in accordance with the present invention. The following description of the operation of sealant depositing machine 10 will make it clear which is which. Sealant depositing machine 10 is constructed to deposit a sealant compound on can ends 30. Can ends 30 are withdrawn from a supply of can ends 32 and moved to a depositing position 34. At depositing position 34 they are rotted via motor 40. A source of pressure 20 operates on a liquid sealant within tank 22 which is further attached to valve assembly 24. Valve assembly 24 includes valve chamber 26 and needle valve 27. In accordance with the prior art, the sealant depositing machine momentarily opens needle valve 27 while can end 30 is being spun by motor 40. A portion of the sealant from sealant tank is thus deposited in an annular strip on can end 30. In accordance with the prior art, needle valve 27 is typically open during approximately 2 1/2 revolutions of can end 30 via motor 40. Sealant depositing machine 10 then closes needle valve 26. Thereafter can end 30 is forwarded from the depositing position 34 to ultimately rest in pile 36. In accordance with the prior art, the operation of conveying can ends 30 to depositing position 34 and hence to the accumulation pile 36, together with the timing of spinning motor 40 and the opening of needle valve 27 are simultaneously controlled via the sealant depositing machine operating system. This operating system could be a complex mechanical cam mechanism, an electrical mechanism or a hydraulic or pneumatic mechanism. The exact nature of this part of the operation of sealant depositing machine 10 is in accordance with the prior art and is not relevant to the present invention. In accordance with the preferred embodiment of the present invention, sealant depositing machine 10 includes computer controller 100, pressure detector 110, proximity sensor 120, reject apparatus 130, keyboard 140 and display 150. Computer controller 100 receives a signal from pressure sensor 110 indicating the pressure within valve chamber 26. Computer controller 100 further receives a signal from proximity sensor 120. Proximity sensor 120 generates a signal indicating that a can end 30 has reached sealant depositing position 34. Computer controller 100 employs this signal to determine the start of a measurement process during which computer controller 100 monitors the pressure sensed by pressure sensor 110. In a manner that will be more fully described below, computer controller 110 monitors the pressure within valve chamber 26 sensed by pressure sensor 100 during one or more predetermined intervals of time while needle valve 27 is open. If computer controller 100 detects a pressure anomaly during any of these intervals, computer controller 100 actuates reject apparatus 130. Reject apparatus 130 operates to displace can end 30 from the line leading to accumulation pile 36 to reject pile 38. Computer controller 100 presents a signal to reject apparatus 130 at the proper time to ensure that the can end 30 shunted to reject pile 38 is the same can end 30 which was at the sealant position 34 when the pressure anomaly was detected. Interface between computer controller 100 and the operator of sealant depositing machine 10 is via keyboard 140 and display 150. Figure 2 illustrates in schematic diagram form, greater details of the computer controller 100. Computer controller 100 includes central processing unit 101, input buffer 102, input buffer 103, keyboard buffer 104, random access memory 105, read-only memory 106, output driver 107 and display driver 108. Central processing unit 101 provides the major processing and control function of computer controller 100. In accordance with the preferred embodiment of the present invention, central processing unit 101 is embodied by an Intel 8088 microprocessor, or the equivalent. Pressure sensor 110 is connected to computer controller 100 via input buffer 102. In accordance with the preferred embodiment of the present invention pressure sensor 110 is a BM1000 precision miniature pressure transducer manufactured by Kulite Semiconductor Products. This pressure transducer consists of a thin stainless steel diaphragm which is flexed based upon the difference between the pressure on one surface and a standard pressure on the opposite surface. A set of piezoresistive elements are bonded on this stainless steel diaphragm. In a typical configuration, these piezoresistive elements are formed as a Wheatstone bridge. Flexure in the stainless steel diaphragm results in differing resistance for these piezoresistive elements. The relative resistance of these piezoresistive elements provides the indication of pressure. Input buffer 102 includes a biasing circuit for the Wheatstone bridge, a sensing circuit for sensing the voltage between opposite corners of the bridge, and an analog to digital converter core converting the sensed current signal into digital number which can be manipulated by central processing unit 101. Proximity sensor 120 generates a signal upon detection that a can end 30 has arrived at the sealant depositing station 34. In the preferred embodiment, proximity sensor 120 is connected to the feed mechanism of sealant depositing machine 10 for providing this signal. The exact time that this proximity signal is generated is not critical except for two factors. Firstly, it must be reliably received prior to the time that needle valve 27 is open for depositing sealant on that particular can end 30. Secondly, the time from the receipt of this proximity signal until the opening of needle valve 27 must be relatively constant. This is because this proximity signal permits computer controller 100 to set the predetermined intervals for monitoring the pressure from pressure sensor 110. Input buffer 103 receives the signal from proximity sensor 120 and forms a signal capable of being read by central processing unit 101. This could be in the nature of an interrupt signal to central processing unit 101, in which case central processing unit 101 then performs a priority function based upon this interrupt signal. In the alternative, input buffer 103 can set or reset a register which is periodically read by central processing unit 101. In this event, central processing unit 101 must be programmed to read this register sufficiently often in order to ensure that there is not a great variation in the length of time between detection of the proximity signal and the opening of needle valve 27. Keyboard 140 enables operator control of computer controller 100. Keyboard 140 enables the operator of sealant depositing machine 10 to control the mode of operation of computer controller 100. Keyboard 140 also enables the operator to enter constants required for the operation of computer control 100. Keyboard buffer 104 receives signals from keyboard 140 and converts these signals into the type of signals recognizable by central processing unit 101. Central processing unit 101 is bidirectionally coupled to a memory unit including random access memory 105 and read only memory 106. Read only memory 106 is a permanent type memory which stores the program for control of central processing unit 101 and any constants needed in its normal operation. Read only memory 106 may be formed of semiconductor manufactured read only memory, which is permanently fixed upon manufacture. In the alternative, particularly for installations where relatively few computer controllers would have the same program, read only memory 106 can be formed of programmable read only memory. Programmable read only memory is programmed electrically prior to installation in computer controller 100. Other than the manner in which the program is fixed within read only memory 106, these two forms of memory operate the same. The amount of read only memory required depends primarily upon the complexity of the program executed by central processing unit 101. Random access memory 105 is preferably formed of so called static random access memory. This memory can be read and rewritten repeatedly by electrical signals from central processing unit 101. In accordance with the preferred embodiment of the present invention, random access memory 105 includes 192 kilobytes of memory. Computer controller 100 is connected to output driver 107, which in turn is connected to reject apparatus 130. Central processing unit 101 sends a signal to output driver 107 which indicates that a can end 30 has been rejected. Output driver 107 then produces the necessary signal for reject apparatus 130 in order to reject that particular can end 30. As mentioned above, the time of generation of this reject signal is selected so that the occurrence of a pressure anomaly during sealant deposit on a particular can end 30 leads to that same can end 30 being rejected via reject apparatus 130. This would involve generation of the reject signal at a predetermined time after the detection of the pressure anomaly. This predetermined time corresponds to the length of time necessary for sealant depositing machine 10 to transport a particular can end 30 from depositing station 34 to the vicinity of reject apparatus 130. Computer controller 100 is connected to display driver 108, which in turn is connected to display 150. Central processing unit 101 sends signals to display driver 108 corresponding to messages to be communicated to the operator. Display driver 108 then produces the necessary signals for causing display 150 to form the required display. It is convention in small computers such as computer controller 100 to employ a video signal for driving a cathode ray tube display. Display driver 108 and display 150 enable computer controller 100 to communicate with the operator for requesting instructions, acknowledging input commands and the like. Figure 3 illustrates the pressure versus time curve during normal operation of needle valve 27. In accordance with the preferred embodiment of the present invention, the pressure versus time curve is divided into a plurality of zones for monitoring. Time t 0 corresponds to the time of receipt of the proximity signal. As noted above, this proximity signal must be selected to lead the time at which the needle valve 27 opens. First zone 310 (hereinafter referred to as zone I) begins at time t 17 substantially coincident with the opening of the needle valve 27, and ends at time t 2 . During zone I the pressure curve shows a substantial drop in pressure from the supply pressure (noted as 0.0) and thereafter a recovery to much nearer the supply pressure. This drop in pressure and recovery corresponds to the initial opening of needle valve 27. During zone I the sealant initially begins to flow reducing the pressure, followed by an approach to the steady state condition in which the pressure recovers. It has been found that the average pressure 315 during zone I must be below a certain upper limit pressure 313 to ensure proper deposition of the sealant on the can end 30. One of the functions of computer controller 100 is to measure the average pressure 315 in zone I and compare it to the upper limit pressure 313. The second time zone 320 (hereinafter referred to as zone II) begins at time t 2 and ends at time t 3 . Zone II is a transition zone from the initial opening of the valve to the steady state conditions. During this transition within zone II the pressure reaches a peak which is generally still less than the static pressure of the source and then drops to at or near a steady state pressure. It has been found that the nature of the pressure versus time curve during zone II is not sufficiently consistent in order to enable control based upon the pressure during this zone. Therefore, in accordance with the preferred embodiment of the present invention, computer controller 100 does not compare the pressure measured during zone II with any limit pressures. The third zone 330 (hereinafter referred to as zone III) begins at time t 3 and ends at time t . The pressure during zone III is generally a steady state pressure. At this time the pressure within valve housing 24 is generally a relatively steady amount less than the static pressure provided by pressure source 20. It is believed that the major portion of the sealant deposited by the sealant depositing machine occurs during zone III. One of the functions of computer controller 100 is to measure the average pressure 335 in zone III and compare it to an upper limit pressure 333 and a lower limit pressure 337. A pressure anomaly is detected when the average pressure 335 is not between upper limit pressure 333 and lower limit pressure 337. Fourth time interval 340 (hereinafter referred to as zone IV) begins after time t 4 and continues until the next proximity signal corresponding to the next cycle. Needle valve 27 is closed during zone IV. During zone IV the pressure recovers from the steady state pressure of zone III and returns to the static pressure provided by pressure source 20. During this interval the pressure may in fact include an overshoot beyond the static pressure with a relaxation then toward the static pressure. It has been found that the pressure during zone IV is not sufficiently consistent in order to enable control based upon the pressure measurements this zone. Therefore, the preferred embodiment of the present invention does not compare the pressure measured during zone IV with any limit pressures. Figure 4 illustrates a pressure time curve of an instance in which the needle valve 27 initially opens, but is later clogged. Note that during zone I the pressure initially drops below the static pressure provided by pressure source 20, however the average pressure 315 in zone I does not fall below the upper limit pressure 313. Thereafter, the pressure rebounds to above the static pressure and then recovers to near the static pressure. Note that the average pressure 335 during zone III is not between the upper limit pressure 333 and the lower limit pressure 337. Computer controller 100 would reject the can end 30 corresponding to this pressure versus time curve. Figure 5 illustrates the case in which needle valve 27 for some reasons fail to open at all during the sealant depositing interval. In this case, the pressure versus time curve remains relatively stationary near the nominal pressure of pressure source 20. The average pressure 315 during zone I and the average pressure during zone III are the same as the static pressure provided by pressure source 20. Computer controller 100 would reject the can end 30 having the corresponding pressure versus time curve illustrated in Figure 5. The specification of the times t 0 , t 1 t 2 , t 3 and t 4 forming the boundaries of zones I, II, III and IV are made empirically for each type of sealant depositing machine 10. This empirical determination of the zone boundaries is made by observation of the pressure versus time curves of a number of instances of independently verified proper sealant deposit. In general, the region of this pressure versus time curve having the minimum pressure (zone I) and the region having the steady pressure (zone III) are relatively easy to determine. In an alternative embodiment some of these times are set empirically relative to time t,, while time t 1 is determined by computer controller 100. In accordance with the present invention time t 1 should be the time when needle valve 27 is opened. In this alternative embodiment computer controller 100 determines the earliest time the measured pressure falls below a predetermined threshold. This earliest time is then taken to be the time t 1 . The times t 2 , t 3 and t 4 are determined based upon time t,. In a further refinement of this embodiment, the threshold for defining time t, is determined based upon a weighted average of the earliest time the measured pressure drops below the predetermined threshold for the present can end 30 and a predetermined set of previous can ends 30. Figure 6 illustrates a flow chart for control of central processing unit 101 within computer controller 100 for practicing the present invention. In accordance with the preferred embodiment of the present invention program 200 illustrated in Figure 6 is stored within read only memory 106 of computer controller 100. Central processing unit 101 is responsive to this program to activate the reject apparatus 130 whenever a pressure anomaly is detected. Program 200 illustrated in Figure 6 is not intended to represent the exact detailed steps necessary for computer 100 to control the process of the present invention. Instead Figure 6 illustrates the general overall outline of the required program. One skilled in the art of computer programming would be enabled to produce the exact program required from this illustration taken in conjunction with the description of the invention, once the particular central processing unit 101 together with its corresponding instruction set is selected. Furthermore, program 200 illustrated in Figure 6 is merely an example of one program for practicing the invention. The invention is not limited to the details of program 200 illustrated in Figure 6. Program 200 is begun via start block 201. Program 200 first tests to determine whether or not the proximity signal has been received from proximity sensor 120 (decision block 202). If this proximity signal has not been received then program 200 causes central processing unit 101 to return to decision block 202 to continue to seek this signal. Central processing unit 101 remains in this loop until the proximity signal is detected, indicating that control can commence. Upon detection of the proximity signal, program 200 causes central processing unit 101 to start a real time clock (processing block 203) . This real time clock is employed to determine times t,, t 2 , t 3 and t 4 , and thereby determine the boundaries of zones I, II, III and IV. Program 200 then tests to determine whether or not the interval t 1 has passed since the beginning of the clock (decision block 204) . If this interval has not yet expired then program 200 repeats processing block 204 until this time has expired. Thus computer controller 100 waits until the beginning of zone I before performing any measurements. Upon the start of zone I, program 200 causes central processing unit 101 to store the pressure data received from pressure sensor 110. In accordance with the preferred embodiment of the present invention, input buffer 102 repetitively samples the analog output of pressure sensor 110 in synchronism with the rate of operation of central processing unit 101. Input buffer 102 converts each such sampled analog value into a digital number capable of manipulation by central processing unit 101. During the time interval of zone I, central processing unit 101 causes each of these digitized, sampled pressures to be stored within random access memory 105. These stored pressures are later employed by central processing unit 101 in detection of pressure anomalies. Program 200 next tests to determine whether or not the time t 2 has elapsed, indicating the end of zone I (decision block 206) . If this interval has not expired, then control returns to processing block 205 to again sample and store the detected pressure. Central processing unit 101 remains in this loop, receiving and storing the measured pressure, until the end of zone I. Program 200 next tests to determine whether or not the time interval t 3 has expired, indicating the beginning of zone III (decision block 107) . In accordance with the preferred embodiment of the present invention, computer controller 100 is not sensitive to the pressure during zone II. Therefore, computer controller 100 is idle during this interval. If the time t 3 has not yet elapsed, then program 200 repeats decision block 207 until this time has expired. Thereafter during zone III, central processing unit 101 receives and stores the sampled, digitized pressure data from input buffer 102 (processing block 208) in the same manner as previously described. This pressure data is stored in other portions of random access memory 105 for later use in determining the presence of a pressure anomaly. Program 200 next tests to determine whether or not the time interval t 4 has elapsed, indicating the end of zone III (decision block 209) . In the event that this interval t 4 has not expired then control returns to processing block 208 to receive and store the next pressure sample from input buffer 102. Program 200 remains within this loop until the end of zone III, as determined by the expiration of the time interval t 4 . At the end of zone III computer controller 100 has stored all the pressure data used for detection of defective sealant deposits. Program 200 next analyzes the sampled pressure data stored within random access memory 105 to determine the presence or absence of a pressure anomaly. In general, the detection of a pressure anomaly during either zone I or zone III causes computer controller 100 to reject the corresponding can end 30. Program 200 next computes the average pressure during zone I (processing block 210) . This average pressure AP ZI is then compared with an upper limit pressure for zone I 313 (decision block 211) . This test determines whether: AP 2I < H_- where H zl is the upper limit pressure 313 for zone I. In the event that this test fails, then a pressure anomaly is detected. In this event, program 200 goes to a reject routine which will be further described below. In the event that the calculated average pressure AP ZI passes this test, then program 200 tests to determine if the pressure limit for zone I is to be automatically updated (decision block 212) . Computer controller 100 preferably permits operator selection of whether or not to automatically update the pressure upper limit H zl . This operator selection is communicated to computer controller 100 via keyboard 140. If this pressure limit is to be automatically updated, then the pressure upper limit H_ r is updated (processing block 213) . The value H 2l is generally initially empirically determined initially. This initial value for H zl may be permanently stored within read only memory 106 or it may be input via keyboard 130. The automatic limit determination is preferably made based upon a smoothed.measure of the mean of the average pressure AP rI of a sample of can ends 30 and a smoothed measure of the range of pressures for the sample. In accordance with the preferred embodiment of the present invention this sample is less than all previous can ends 30. Typically the present invention would employ a sample of the last 5 can ends 30 per each 100 can ends. The smoothed mean SM zTj - is computed as follows: SM ZIj = (100% - SF) x MP ZI + SF x SM zIj . 1 where: SF is a smoothing factor between 0% and 100%; MP 2l is the mean of the average pressures AP ZI for the elements of the sample; SM ZIJ - is the smoothed mean to be computed; and SM jj -.., is the prior smoothed mean. This algorithm is known as exponential averaging. The greatest weight is given to the last measured value while prior measured values are reduced in weight by a factor of SF for each prior generation. The smoothed range SR ZI - is computed as follows: SR ZIj = (100% - SF) X R zl + SF x SR^ j .,, where: SF is the smoothing factor; R zl is the range calculated from the difference between the highest average pressure AP ZI and the lowest average pressure AP z1 within the sample within zone I; S ^ j is the smoothed range to be computed; and SR z , j _., is the prior smooth range. The updated upper limit pressure H zl for zone I is then computed as: H zl = S z ι + (SR Z , X LFH ZI + L0H ZI ) where: LF H ZI is an empirically determined limit factor upper constant for zone I between 0 and 2; and LOH z1 is an empirically determined limit offset upper constant for zone I. Program 200 next computes the average pressure AP ziπ during zone III (processing block 214) . This process involves recall of each of the pressure samples stored during zone III from random access memory 105 and computation of the average pressure AP zUI . Program 200 next tests to determine whether or not this average pressure AP ZI u is within a predetermined upper limit pressure 333 and a predetermined lower limit pressure 337 (processing block 215) . This test determines if: L ZII I < AP ZIII < H ZIπ where: AP ZIII is the computed average pressure during zone III; L J - UJ is the lower limit pressure 337; and H ziπ is the upper limit pressure 333. As previously described the lower limit pressure L...- J and the upper limit pressure H ZIII are generally empirically determined initially. If the average pressure AP ziπ is not within these limits then program 200 enters a reject routine which will be fully described below. In the event that the calculated average pressure AP ziπ during zone III is between the lower limit pressure L ZIII and the upper limit pressure H ziπ then program 200 tests to determine if these upper and lower limit pressures are to be automatically updated (decision block 216) . Computer controller 100 preferably permits operator selection of whether or not to automatically update the upper limit pressure H zlll and the lower limit pressure ___-„. This operator selection is communicated to computer controller 100 via keyboard 140. If these limit pressures are to be automatically updated, then program 200 updates these values (processing block 217). As in the case of H zl , the upper limit pressure H zln and the lower limit pressure L zUI are generally empirically determined initially. These initial values may be permanently stored within read only memory 106 or may be input via keyboard 130. The automatic limit determination of the upper limit pressure H ziπ and the lower limit pressure L ziπ is preferably made based upon a smoothed measure of the mean of the average pressure AP ZIII of a sample of can ends 30 and a smoothed measure of the range of pressures for the sample. As previously described, this sample is preferably less than all previous can ends 30. The smoothed mean SM ZIIIJ - is computed as follows: SM z j = (100% - SF) X MP ziπ + SF X SM ziπj . 1 where: SF is the smoothing factor; MP ZIII is the mean of the average pressures AP ziπ - is the smoothed mean to be computed; and SM z m j -ι is the prior smoothed mean. The smoothed range SR ZIIIJ - is computed as follows: SR ziπj = (100% - SF) X R ZIII + SF X SR^.^.., where: SF is the smoothing factor; R zUI is the range calculated from the difference between the highest average pressure AP zm and the lowest average pressure AP ZIII within the sample within zone I; SR ZIIIJ - is the smoothed range to be computed; and SR^^-.., is the prior smoothed range. The updated upper limit pressure H zm and the updated lower limit pressure L zUI for zone III are then computed as follows: H z_π = SM zπι + (SR zIπ x LFH ZIII + L0H ziπ ) L 2 iπ = SM ZIII - (SR ziπ x LFL zπι + L0L ziπ ) where: LFH zπι is an empirically determined limit factor upper constant for zone III between 0 and 2; L0H ziπ is an empirically determined limit offset upper constant for zone III; LFL ziπ is an empirically determined limit factor lower constant for zone III between 0 and 2; and LOL ZIII is an empirically determined limit offset lower constant for zone III. Program 200 then returns to decision block 202 to await the next detection of the proximity signal for the next can end 30. In the event that a pressure anomaly has been detected in accordance with the previous description, program 200 executes a reject routine. Firstly, program 200 tests to determine whether or not it is time to generate the reject signal to reject that particular can end 30 (decision block 218) . As previously described, there is a fixed time interval from the time that a particular can end 30 reaches depositing station 34 and the time at which it is opposite reject apparatus 130. Computer controller 100 waits until this interval has expired before rejecting the can end 30. Once this time interval has expired, the can end is rejected (processing block 219) by triggering reject apparatus 130 via output driver 107. This serves to displace that particular can end 30 into the reject pile 38. An alternative embodiment determines the time t 1 by computer controller 100. The time t., should be the time when needle valve 27 is opened. In this alternative embodiment computer controller 100 determines the earliest time after receipt of the proximity signal that the measured pressure falls below a predetermined threshold. This earliest time is then taken to be the time t The length of time for zones I, II, III and IV are set as before. Thus the times t 2 , t 3 and t 4 are defined in relation to time t,. In order to achieve this alternative embodiment, a small modification of program 200 illustrated in Figure 6 is required. Processing block 203 and decision block 204 are replaced. Program 200 tests to determine if the last measured pressure P, is less than a starting threshold pressure H start . If this is not the case, this test is repeated until it is true. Once this test is satisfied, indicating the start of zone I, then the clock is started. Decision blocks 206, 207 and 209 are modified to determine the respective times t 2 , t 3 and t 4 relative to the thus determined time t 1 rather than to the time t 0 when the proximity signal is received. In a further refinement of this embodiment, the time t 1 is determined based upon a weighted average of the earliest time the measured pressure drops below the predetermined threshold for the current can end 30 and of previous can ends 30. Thus the time t., is set as follows: t = (100% - SF) x t th + SF x V} _ where: SF is the smoothing factor; t, j is the smoothed time t, computed for the current can end; t th is the time the measured pressure fell below the pressure threshold H start ; and t jj .., is the prior smoothed time t,. Program 200 illustrated in Figure 6 represents only a single processing task which may be one of several processing tasks performed simultaneously by central processing unit 101. The technique of programming multiple simultaneous tasks is known in the prior art and forms no part of the present invention. It is contemplated that central processing unit 101 will be enabled to perform these other tasks during the intervals of program 200 during which central processing unit 101 is described as idle. In particular, it is possible that the receipt of a new proximity signal may come prior to the time for rejection of a can end. Thus the process for two can ends 30 on the same sealant deposition machine 10 may overlap. Furthermore, it is contemplated that computer controller 100 will be programmed to service operator inputs via keyboard 140 and outputs to the operator via display 150 during the control process. Lastly, a single computer controller 100 may have the processing and memory capacity to service two sealant deposition machines 10 simultaneously. In such a case, two control processes such as illustrated in Figure 6 will occur simultaneously. Because program 200 is intended for real time control, the order and arrangement of the various steps may be different from that shown in Figure 6. Such differences may be necessary in order to accommodate the particular timing requirements of a particular installation. For example, the reject determination based upon the average pressure AP ZI may take place during the time of zone II when no other processing takes place. The prior embodiment discussed above in conjunction with Figures 1 to 6 measures the pressure within valve chamber 26 as a surrogate to measuring the flow through controllable valve 24. In many instances this is an advantageous technique. The controllable valves 24 often have unused ports suitable for receiving a pressure sensor, thus retrofitting this invention into an existing sealant depositing machine 10 is relatively easy. Pressure sensors are relatively stable and easy to calibrate in this application. There are some installations in which this embodiment is unsuitable. If a single source of pressurized sealant is employed for more than one controllable valve, the apparatus illustrated in Figure 1 is difficult to use. In particular, the previously described embodiment requires a relatively stable pressure measure during intervals when the controllable valve is closed for calibration purposes. When a single source of pressurized sealant feeds more than one controllable valve 24, it is typical for the valves to be opened out of phase. Particularly for the case of three or more valves supplied by the same source of pressurized sealant, the base pressure may be so unstable that this technique is unreliable. In such cases it is better to measure another quantity related to the rate of flow of sealant. Figures 7 and 8 illustrate alternative embodiments of the present invention. Figure 7 illustrates sealant depositing machine 13 in which the pressure sensor 110 has been replaced by a flow sensor 111 in the sealant line between sealant tank 22 and controllable valve 24. The output of flow sensor 111 is supplied to computer controller 100 in the same manner as supply of the output of pressure sensor 110 is supplied to computer controller 100 in Figure 1. Figure 8 illustrates sealant depositing machine 17 in which the pressure sensor 110 has been replaced by a first pressure sensor 113, a flow restrictor 117 having an orifice with predetermined dimensions, and a second pressure sensor 115 in the sealant line between sealant tank 22 and controllable valve 24. The outputs of pressure sensors 113 and 115 are supplied to computer controller 100 in the same manner as supply of the output of pressure sensor 110 is supplied to computer controller 100 in Figure 1. Computer controller 100 is programmed to compute the rate of sealant flow into controllable valve 24 from the pressure difference on opposite sides of flow restrictor 117 as measured by pressure sensors 113 and 115, the known dimensions of the orifice of flow restrictor 117 and the known properties of the sealant in accordance with principles known in the art. Computer controller 100 employs the flow rate either measured by flow sensor 111 (Figure 7) or computed from the pressures measured by pressure sensors 113 and 115 in a manner similar to the prior embodiment. During zone I the flow rate initial increases to a peak and then returns to a lower value. During zone I the computer controller 100 computes the average flow rate and compares it to a predetermined lower limit flow rate LR ZI . The predetermined lower limit flow rate of LR ZI can be automatically adjusted based upon previous average flow rates during zone I, in a manner analogous to the adjustment of H zl previously described. Likewise the average flow rate during zone III must be between a predetermined lower limit flow rate LR z πι nα ^ predetermined upper limit flow rate HR ziπ . The predetermined lower limit flow rate LR z τ U and the predetermined upper limit flow rate HR ZIII can be automatically adjusted based upon previous average flow rates during zone III, in a manner analogous to the adjustment of L z and H ziπ previously described.

Claims: CLAIMS 1. In a machine for depositing sealant in a can end having a station for holding a can end, a pressurized source of sealant, a controllable valve controlled to open to deposit sealant on a can end at the station and to close to stop the deposit of sealant, the valve having a valve chamber connected to the source of pressurized sealant, and a transport mechanism for transporting can ends to and from the station, the improvement comprising: a proximity detector for generating a proximity signal whenever a can end is at the station for holding a can end; a sensor coupled to the controllable valve for detecting a quantity related to the rate of flow of sealant through the controllable valve; a controller connected to said proximity detector and said sensor for monitoring the quantity detected by said sensor during at least one predetermined time interval following said proximity signal, and for generating a reject signal upon detection of an irregularity in said quantity during any one of said predetermined time intervals; and a reject apparatus connected to the transport mechanism and said controller for removing a corresponding can end from the transport mechanism upon receipt of a reject signal. 2. The improvement claimed in claim 1, wherein: said sensor consists of a pressure sensor coupled to the controllable valve for detecting the pressure in the valve chamber. 3. The improvement claimed in claim 2, wherein: said at least one predetermined time interval following said proximity signal of said controller includes a initial valve opening time interval corresponding to an interval of initial pressure drop and recovery upon opening the valve. 4. The improvement claimed in claim 3, wherein: said initial valve opening time interval starts a predetermined time following receipt of said proximity signal and has a predetermined duration. 5. The improvement claimed in claim 3, wherein: said initial valve opening time interval starts when said pressure detected by said pressure sensor falls below a predetermined pressure threshold following receipt of said proximity signal and has a predetermined duration. 6. The improvement claimed in claim 3, wherein: said initial valve opening time interval starts when a weighted average of the earliest time said pressure detected by said pressure sensor falls below a predetermined pressure threshold for the current proximity signals and the earliest time said pressure detected by said pressure sensor falls below a predetermined pressure threshold for each of at least some previous proximity signals following receipt of said proximity signal has passed and has a predetermined duration. 7. The improvement claimed in claim 3, wherein: said controller further includes means for computing the average pressure during said initial valve opening time interval, and generating said reject signal if said computed average pressure during said initial valve opening time interval is greater than a predetermined pressure. 8. The improvement claimed in claim 7, wherein: said controller further includes means for computing a measure of central tendency of said computed average pressure during said initial valve opening time interval for at least some previous proximity signals corresponding to valve openings for previous can ends, and computing said predetermined pressure for the current proximity signal as the sum of said computed measure of central tendency of said computed average pressure during said initial valve opening time interval for previous proximity signals plus an offset pressure. 9. The improvement claimed in claim 8, wherein: said at least some previous proximity signals consists of a selected subset of each group of a predetermined number of previous proximity signals. 10. The improvement claimed in claim 9, wherein: said at least some previous proximity signals consists of the last five of each group of 100 previous proximity signals. 11. The improvement claimed in claim 9, wherein: said controller computes said measure of central tendency of said computed average pressure during said initial valve opening time interval for said selected subset of each group of a predetermined number of previous proximity signals in accordance with: SM j = (100% - SF) x MP + SF X SM j ., where: SM- is said measure of central tendency of said computed average pressure to be computed; SF is a smoothing factor between 0% and 100%; MP is the mean of the average pressures for said selected subset of the most recent group of a predetermined number of previous proximity signals; and SM, ., is the prior measure of central tendency of said computed average pressure. 12. The improvement claimed in claim 9, wherein: said controller further includes means for computing a measure of the range of said computed average pressure during said initial valve opening time interval for said selected subset of each group of a predetermined number of previous proximity signals, and computing said predetermined pressure for the current proximity signal as the sum of said computed measure of central tendency of said average pressure during said initial valve opening time interval for said selected subset of each group of a predetermined number of previous proximity signals, plus the product of said computed measure of the range of said computed average pressure during said initial valve opening time interval for said selected subset of each group of a predetermined number of previous proximity signals times a predetermined constant, plus said offset pressure. 13. The improvement claimed in claim 12, wherein: said controller computes said measure the range of said computed average pressure during said initial valve opening time interval for said selected subset of each group of a predetermined number of previous proximity signals in accordance with: S j = (100% - SF) X RP + SF X SR j ., where: SR j is said measure of range of said computed average pressure to be computed; SF is a smoothing factor between 0% and 100%; RP is the range of the average pressures for said selected subset of the most recent group of a predetermined number of previous proximity signals; and SR-.., is the prior measure of range of said computed average pressure. 14. The improvement claimed in claim 2, wherein: said at least one predetermined time interval following said proximity signal of said controller includes a steady state time interval corresponding to an interval of relatively steady pressure while sealant is being deposited prior to closing the valve. 15. The improvement claimed in claim 14, wherein: said steady state time interval starts a predetermined time following receipt of said proximity signal and has a predetermined duration. 16. The improvement claimed in claim 14, wherein: said steady state time interval starts a predetermined time after said pressure detected by said pressure sensor falls below a predetermined pressure threshold following receipt of said proximity signal and has a predetermined duration. 17. The improvement claimed in claim 14, wherein: said steady state time interval starts a predetermined time after a weighted average of the earliest time said pressure detected by said pressure sensor falls below a predetermined pressure threshold for the current proximity signals and the earliest time said pressure detected by said pressure sensor falls below a predetermined pressure threshold for each of at least some previous proximity signals following receipt of said proximity signal has passed and has a predetermined duration. 18. The improvement claimed in claim 14, wherein: said controller further includes means for computing the average pressure during said steady state time interval, and generating said reject signal if said computed average pressure during said steady state time interval is greater than a first predetermined pressure or less than a second predetermined pressure, said second predetermined pressure being less than said first predetermined pressure. 19. The improvement claimed in claim 18, wherein: said controller further includes means for computing a measure of the central tendency of said average pressure during said interval of steady state time for at least some previous proximity signals corresponding to valve openings for previous can ends, computing said first predetermined pressure for the current proximity signal as the sum of said computed measure of central tendency of said computed average pressure during said steady state time interval for said at least some previous proximity signals plus a first offset pressure, and computing said second predetermined pressure for the current proximity signal as the difference between said computed measure of central tendency of said computed average pressure during said steady state time interval for said at least some previous proximity signals minus a second offset pressure. 20. The improvement claimed in claim 19, wherein: said at least some previous proximity signals consists of a selected subset of each group of a predetermined number of previous proximity signals. 21. The improvement claimed in claim 20, wherein: said at least some previous proximity signals consists of the last five of each group of 100 previous proximity signals. 22. The improvement claimed in claim 20, wherein: said controller computes said measure of central tendency of said computed average pressure during said steady state time interval for said selected subset of each group of a predetermined number of previous proximity signals in accordance with: SM j = (100% - SF) X MP + SF X SM j ., where: SM- is said measure of central tendency of said computed average pressure to be computed; SF is a smoothing factor between 0% and 100%; MP is the mean of the average pressures for said selected subset of the most recent group of a predetermined number of previous proximity signals; and SM,., is the prior measure of central tendency of said computed average pressure. 23. The improvement claimed in claim 20, wherein: said controller further includes means for computing a measure of the range of said computed average pressure during said steady state time interval for said selected subset of each group of a predetermined ' number of previous proximity signals, computing said first predetermined pressure for the current proximity signal as the sum of said computed measure of central tendency of said computed average pressure during said steady state time interval for said selected subset of each group of a predetermined number of previous proximity signals, plus the product of said computed measure of the range of said computed average pressure during said initial valve opening time interval for said selected subset of each group of a predetermined number of previous proximity signals times a predetermined constant, plus said first offset pressure, and computing said second predetermined pressure for the current proximity signal as the difference between said computed measure of central tendency of said computed average pressure during said steady state time interval for said selected subset of each group of a predetermined number of previous proximity signals minus the sum of the product of said computed measure of the range of said computed average pressure during said steady state time interval for said selected subset of each group of a predetermined number of previous proximity signals times a second predetermined constant, plus a second offset pressure. 24. The improvement claimed in claim 23, wherein: said controller computes said measure the range of said computed average pressure during said steady state time interval for said selected subset of each group of a predetermined number of previous proximity signals in accordance with: SR j = (100% - SF) X RP + SF X SR j ., where: S j is said measure of range of said computed average pressure to be computed; SF is a smoothing factor between 0% and 100%; RP is the range of the average pressures for said selected subset of the most recent group of a predetermined number of previous proximity signals; and SR,.., is the prior measure of range of said computed average pressure. 25. The improvement as claimed in claim 1, wherein: said sensor consists of a flow sensor coupled between the pressurized source of sealant and the controllable valve for detecting the rate of flow of sealant into the valve chamber. 26. The improvement claimed in claim 25, wherein: said flow sensor consists of a first pressure sensor, a flow restrictor having a predetermined orifice and a second pressure sensor coupled in tandem between the pressurized source of sealant and the controllable valve; and said controller is connected to said first and second pressure sensors and includes means for determining the rate of flow of sealant into said controllable valve based upon the difference between the pressures measured by said first and second pressure sensors, respectively, and the dimensions of said predetermination orifice. 27. The improvement claimed in claim 25, wherein: said at least one predetermined time interval following said proximity signal of said controller includes a initial valve opening time interval corresponding to an interval of initial sealant flow upon opening the valve. 28. The improved claimed in claim 27, wherein: said controller further includes means for computing the average sealant flow rate during said initial valve opening time interval, and generating said reject signal if said computed average sealant flow rate during said initial valve opening time interval is less than a predetermined flow rate. 29. The improvement claimed in claim 28, wherein: said controller further includes means for computing a measure of central tendency of said computed average sealant flow rate during said initial valve opening time interval for at least some previous proximity signals corresponding to valve openings for previous can ends, and computing said predetermined flow rate for the current proximity signal as the sum of said computed measure of central tendency of said computed average sealant flow rates during said initial valve opening time interval for previous proximity signals minus an offset flow rate. 30. The improvement claimed in claim 25, wherein: said at least one predetermined time interval following said proximity signal of said controller includes a steady state time interval corresponding to an interval of relatively steady sealant flow prior to closing the valve. 31. The improvement claimed in claim 30, wherein: said controller further includes means for computing the average sealant flow rate during said steady state time interval, and generating said reject signal if said computed average sealant flow rate during said steady state time interval is less than a first predetermined flow rate or greater than a second predetermined flow rate. 32. The improvement claimed in claim 31, wherein: said controller further includes means for computing a measure of central tendency of said computed average sealant flow rate during said steady state time interval for at least some previous proximity signals corresponding to valve openings for previous can ends, computing said first predetermined flow rate for the current proximity signal as the difference between said computed measure of central tendency of said computed average flow rate during said steady state time interval for said at least some previous proximity signals minus a first offset flow rate, and computing said second predetermined flow rate for the current proximity signal as the sum of said computed measure of central tendency of said computed average sealant flow rate during said steady state time interval for said at least some previous proximity signals plus a second offset flow rate. 33. In a machine for depositing sealant in a can end having a station for holding a can end, a pressurized source of sealant, a controllable valve controlled to open to deposit sealant on a can end at the station and to close to stop the deposit of sealant, the valve having a valve chamber connected to the source of pressurized sealant, and a transport mechanism for transporting can ends to and from the station, the improvement comprising: a proximity detector for generating a proximity signal whenever a can end is at the station for holding a can end; a sensor coupled to the controllable valve for detecting a quantity related to the rate of flow of sealant through the controllable valve; a controller connected to said proximity detector and said sensor for monitoring the quantity detected by said sensor during a initial valve opening time interval starting immediately following receipt of said proximity signal and having a first predetermined duration, and a steady state time interval starting a predetermined length of time following receipt of said proximity signal and having a second predetermined duration, said initial valve opening time interval corresponding to an interval of initial sealant flow upon opening the valve, and said steady state time interval corresponding to an interval of relatively steady sealant flow prior to closing the valve, and generating a reject signal upon detection of an irregularity in said quantity in either said initial valve opening time interval or in said steady state time interval; and a reject apparatus connected to the transport mechanism and said controller for removing a corresponding can end from the transport mechanism upon receipt of a reject signal. 34. The improvement claimed in claim 33, wherein: said sensor consists of a flow sensor coupled between the pressurized source of sealant and the controllable valve for detecting the rate of flow of sealant into the valve chamber. 35. The improvement claimed in claim 34, wherein: said flow sensor consists of a first pressure sensor, a flow restrictor having a predetermined orifice and a second pressure sensor coupled in tandem between the pressurized source of sealant and the controllable valve; and said controller is connected to said first and second pressure sensors and includes means for determining the rate of flow of sealant into said controllable valve based upon the difference between the pressures measured by said first and second pressure sensors, respectively, and the dimensions of said predetermination orifice. 36. The improvement claimed in claim 33, wherein: said sensor consists of a pressure sensor coupled to the controllable valve for detecting the pressure in the valve chamber. 37. The improvement claimed in claim 33, wherein: said controller further includes means for computing the average quantity related to the rate of flow of sealant during said initial valve opening time interval, computing the average quantity related to the rate of flow of sealant during said steady state time interval, and generating said reject signal if either said computed average quantity related to the rate of flow of sealant during said initial valve opening time interval is less than a first predetermined quantity, or said computed average quantity related to the rate of flow of sealant during said steady state time interval is less than a second predetermined quantity, or said computed average quantity related to the rate of flow of sealant during said steady state time interval is greater than a third predetermined quantity. 38. The improvement claimed in claim 37, wherein: said controller further includes means for computing a measure of central tendency of said computed average quantity related to the rate of flow of sealant during said initial valve opening time interval for at lest some previous proximity signals corresponding to valve openings for previous can ends, computing a measure of the range of said computed average quantity related to the rate of flow of sealant during said initial valve opening time interval for said at least some previous proximity signals, computing said first predetermined quantity for the current proximity signal as the difference between said computed measure of central tendency of said average quantity related to the rate of flow of sealant during said initial valve opening time interval for said at least some previous proximity signals, minus the product of said computed measure of the range of said computed average quantity related to the rate of flow of sealant during said initial valve opening time interval for said at least some previous proximity signals times a first predetermined constant, minus a first offset quantity, computing a measure of the central tendency of said average quantity related to the rate of flow of sealant during said steady state interval of time for said at least some previous proximity signals, computing a measure of the range of said computed average quantity related to the rate of flow of sealant during said steady state time interval for said at least some previous proximity signals, computing said second predetermined quantity for the current proximity signal as the difference between said computed measure of central tendency of said computed average quantity related to the rate of flow of sealant during said steady state time interval for said at least some previous proximity signals, minus the sum of the product of said computed measure of the range of said computed average quantity related to the rate of flow of sealant during said initial valve opening time interval for said at least some previous proximity signals times a second predetermined constant, minus a second offset quantity, computing said third predetermined quantity for the current proximity signal as the sum of said computed measure of central tendency of said computed signals times a first predetermined constant, minus a first offset quantity, computing a measure of the central tendency of said average quantity related to the rate of flow of sealant during said steady state interval of time for said at least some previous proximity signals, computing a measure of the range of said computed average quantity related to the rate of flow of sealant during said steady state time interval for said at least some previous proximity signals, computing said second predetermined quantity for the current proximity signal as the difference between said computed measure of central tendency of said computed average quantity related to the rate of flow of sealant during said steady state time interval for said at least some previous proximity signals, minus the sum of the product of said computed measure of the range of said computed average quantity related to the flow of sealant during said initial valve opening time interval for said at least some previous proximity signals times a second predetermined constant, minus a second offset quantity, and computing said third predetermined quantity for the current proximity signal as the sum of said computed measure of central tendency of said computed average quantity related to the rate of flow of sealant during said steady state time interval for at least some previous proximity signals plus the product of said computed measure of the range of said computed average quantity related to the rate of flow of sealant during said steady state time interval for said at least some previous proximity signals times a third predetermined constant, plus a third offset quantity. 39. A method for detecting improper sealant deposit in a machine having a valve for depositing pressurized sealant in a can end at a station for holding a can end, the process comprising the steps of: detecting when a can end is at the station for holding a can end; measuring a quantity related to the rate of sealant flow through the controllable valve; monitoring the measured quantity related to the rate of sealant flow during at least one predetermined time interval following detecting a can at the station for holding a can end; and rejecting a can end upon detection of an irregularity in the measured quantity related to the rate of sealant flow during any one of said predetermined time intervals. 40. The method claimed in claim 39, wherein: said step of measuring the quantity related to sealant flow consists of measuring the flow of sealant into the valve chamber. 41. The improvement claimed in claim 40, wherein: said step of measuring the flow of sealant into the valve chamber consists of routing the sealant from the source of pressurized sealant to the controllable valve through a flow restrictor having a predetermined orifice, measuring the pressure prior to the flow restrictor, measuring the pressure after the flow restrictor, and determining the rate of flow of sealant into said controllable valve based upon the difference between the pressures measured prior to the flow restrictor and after the flow restrictor, respectively, and the dimensions of said predetermination orifice. 42. The method claimed in claim 39, wherein: said step of measuring the quantity related to sealant flow consists of measuring the pressure in the valve chamber. 43. The method claimed in claim 39, wherein: said at least one predetermined time interval following detecting a can end at the station for holding a can end includes a initial valve opening time interval corresponding to an interval of initial sealant flow upon opening the valve. 44. The method claimed in claim 43, further comprising the steps of: computing the average quantity related to sealant flow during said initial valve opening time interval; and said step of rejecting the can end includes rejecting the can end if said computed average quantity related to sealant flow during said initial valve opening time interval is less than a first predetermined quantity. 45. The method claimed in claim 44, further comprising the steps of: computing a measure of central tendency of said average quantity related to sealant flow during said initial valve opening time interval for some previous detections of a can end at the station for holding a can end; computing said first predetermined quantity for the current can end as the difference between said computed measure of central tendency of said average quantity related to sealant flow during said initial valve opening time interval for said some previous detections of a can end at the station for holding a can end minus a first offset quantity; 46. The method claimed in claim 39, wherein: said at least one predetermined time interval following said detection of a can end at the station for holding a can end includes a steady state time interval prior to closing the valve. 47. The method claimed in claim 46, further comprising the steps of: computing the average quantity related to sealant flow during said steady state time interval; and said step of rejecting the can end includes rejecting the can end if said computed average quantity related to sealant flow during said steady state time interval is less than a first predetermined quantity or greater than a second predetermined quantity. 48. The method claimed in claim 47, further comprising the steps of: computing a measure of central tendency of said average quantity related to sealant flow during said steady state time interval for some previous detections of a can end at the station for holding a can end; computing said first predetermined quantity for the current can end as the difference between said computed measure of central tendency of said average quantity related to sealant flow during said steady state time interval for said some previous detections of a can end at the station for holding a can end minus a first offset quantity; and computing said second predetermined quantity for the current can end as the sum of said computed measure of central tendency of said average quantity related to sealant flow during said steady state time interval for said some previous detections of a can end at the station for holding a can end plus a second offset quantity. 49. The method claimed in claim 39, wherein: said at least one predetermined time interval following detecting a can end at the station for holding a can end includes a initial valve opening time interval corresponding to an interval of initial flow upon opening the valve and a steady state time interval steady state interval prior to closing the valve. 50. The method claimed in claim 49, further comprising the steps of: computing the average quantity related to sealant flow during said initial valve opening time interval; and computing the average quantity related to sealant flow during said steady state time interval; and said ^ step of rejecting the can end includes rejecting the can end if either said computed average quantity related to sealant flow during said initial valve opening time interval is less than a first predetermined quantity, or said computed average quantity related to sealant flow during said steady state time interval is less than a second predetermined quantity, or said computed average quantity related to sealant flow during said steady state time interval is greater than a third predetermined quantity. 51. The method claimed in claim 50, further comprising the steps of: computing a measure of central tendency of said average quantity related to sealant flow during said initial valve opening time interval for some previous detections of a can end at the station for holding a can end; computing said first predetermined quantity for the current can end as the difference between said computed measure of central tendency of said average quantity related to sealant flow during said initial valve opening time interval for said some previous detections of a can end at the station for holding a can end minus a first offset quantity; computing a measure of the central tendency of said average quantity related to sealant flow during said steady state time interval for some previous detections of a can end at the station for holding a can end; computing said second predetermined quantity for the current can end as the difference between said computed measure of central tendency of said average quantity related to sealant flow during said steady state time interval for said some previous detections of a can end at the station for holding a can end minus a second offset quantity; and computing said third predetermined quantity for the current can end as the sum of said computed measure of central tendency of said average quantity related to sealant flow during said steady state time interval for said some previous detections of a can end at the station for holding a can end plus a third offset quantity.

Inventors: ALBERTSEN ALBERT, LEAT ANDREW F V, SCHMID FRANK L, ALBERTSEN, ALBERT, LEAT, ANDREW, F., V., SCHMID, FRANK, L.
Applicants: TECH S INC, TECH-S, INC.
Application year: 1990
Main classification: G06F15
IPC codes: B05B1, B05B12, B21D51