The ability to have a desired pattern of a fluid, for example an adhesive, on a substrate is a necessity for manufacturers engaged in a variety of industries, including the packaging and plastics industries. A typical process to obtain a pattern of a fluid on a substrate is found in the packaging industry, and employs a dispensing device in the form of an adhesive gun to apply adhesive onto a substrate being moved past the dispensing device, for example, by a conveyor. A fluid dispensing system monitors conveyor movement and movement of the substrate to provide the adhesive gun with dispensing command signals.
The quality of the adhesive dispensing process is a subject to many variables that include general environmental conditions, the physical state of the adhesive being dispensed, the physical condition of the dispensing device, and the stability of other system parameters. Changes in such variables often result in variations in the operation of the dispensing device that in turn can produce variations from the desired pattern of the adhesive fluid on the substrate.
There are known devices for detecting and monitoring the placement of the pattern of a liquid, such as an adhesive dispersed by a fluid dispensing system onto a moving substrate. Some systems attempt to monitor the presence and location of adhesive on the substrate by measuring delays between dispensing gun activation and deactivation signals and signals representing leading and trailing edges of the applied adhesive, calculating a correlation between those signals, and evaluating the correlation through a statistical processing method. While such systems can effectively monitor the quality of a pattern of a fluid, those systems are not capable of monitoring a pattern of a fluid without utilizing dispensing gun activation and deactivation signals generated by a fluid dispensing system. Thus, they require a sophisticated interface with the dispensing system. Such systems are further limited to fluid dispensing systems employing an adhesive gun and are not applicable to fluid dispensing systems using other types of dispensing devices, such as a gum box.
Other systems for testing or monitoring the quality of the pattern of an applied fluid sense an edge of an adhesive bead within a programmed window within which the edge of the bead is predicted to occur. Some of such systems require that the bead adhesive pattern that is programmed into the fluid dispersing system also be programmed into the monitoring system, while the motion of the conveyor for the substrate to which the fluid pattern is applied be monitored by a conveyor motion sensor coupled to the conveyor. Thus, these systems require both a highly skilled technician to perform the programming and the presence of a conveyor motion sensor.
Some other systems acquire a sample fluid pattern by sampling a pattern of the fluid, the quality of which is satisfactory and then evaluating subsequent patterns by comparing time delays for leading and trailing edges of the beads of the sampled pattern with corresponding time delays extracted from the subsequent pattern. While such systems simplify the acquisition of the reference pattern data, the use of time delays as a measure for sensing the edges of the beads for comparison with the reference pattern limits the application of such systems to the monitoring of patterns of a fluid on substrates that travel with a constant line speed with respect to the dispensing and sensing devices, and requires the selection of new reference data and the associated recalibration of the system with every speed change.
There is accordingly a need for a fluid pattern monitoring system that effectively and reliably detects and monitors the quality of a pattern of a fluid applied by a fluid dispensing system that is applicable to a variety of dispensing devices applying the fluid to substrates moving with variable speeds with respect to the fluid dispensing device, and which operates independently from the fluid dispensing system, and is relatively easy and efficient in setup, calibration and maintenance.