Abstract:
A method and apparatus for selectively applying, a material to a target moving along a path is disclosed. The apparatus includes at least one detector for identifying an upstream position of the target; a dispenser spaced downstream from the detector by an offset distance, the dispenser configured for selectively releasing material to contact the target; a velocity sensor for creating a velocity signal proportional to a velocity of the target; and a controller for selectively varying the offset distance in response to the velocity signal.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the transfer of material between objects in relative motion, and more particularly to a control system for regulating the application of a solid or liquid material to a moving target. 
     BACKGROUND OF THE INVENTION 
     The application of liquid or solid material to a target in relative motion includes applying ink, paint, or adhesives to a substrate; applying cleaning fluids, or applying decorative edible materials such as icing, sugar, or batter. 
     Traditionally the application of the material to a target is signaled to commence by an electrical impulse from a sensor (e.g., a photoelectric “eye”). The impulse from the sensor is transmitted to a dispenser. These devices are generally divided into two main categories: (i) those that actuate the dispenser after a time delay to locate the point of application on the target (time delay systems) and (ii) those that utilize velocity or location information from an external sensor to control the moment of application (velocity/position sensor systems). 
     Time delay systems can be operator adjusted to position the point of application on the target. Velocity/position sensor systems can be used over a relatively wide range of conditions compared to the time delay systems, but the velocity/position sensor systems require a somewhat more complex control method utilizing velocity (or position) information from the external sensor. 
     In the velocity/position sensor systems, the greatest difficulties arise because of the need to compensate for the time delay between the instant that a control unit or sensor actuates the dispenser, by transmitting a signal to it, and the instant that the material released by the dispenser actually contacts the target. The delay between the instant that the control unit issues an initiate or open command and the instant that the material makes contact with the target is often referred to as “delivery delay”. Delivery Delay can be reduced, but not eliminated, thus always resulting in some placement error. Accuracy in placement of the application material is at least partially dependent upon the delivery delay. The placement error resulting from delivery delay increases as the relative target speed increases. 
     Most velocity/position sensor systems can compensate for delivery delay under steady-state velocity conditions. Thus, if the targets are moving at a constant velocity, the effects of delivery delay can be reduced by using mathematical calculations to “factor in” the dispenser delay interval and material time-of-flight, and advance the moment of activation of the dispenser by an amount which approximates the delay interval. 
     One approach for compensating for delivery delay entails decreasing the size of the photo detection area of a photoeye. This approach requires that calculations be done much more frequently to account for variations in the conveyor speed. Thus, there would be a need for more frequent inputs to the control logic which controls the dispenser. 
     Delivery delay is not well compensated by the prior art devices which rely on the simple mathematical model of geometry. Because the timing of prior devices is based on a tachometer measurement of conveyor speed, delivery delay could only be done to the nearest range cell, the smallest unit measured. At higher conveyor speeds, the range cells must be made larger to avoid exceeding the computational bandwidth of the control unit, resulting in a potentially noticeable error in the placement of a bead under conditions of changing conveyor speed. Because an operator-adjustable multiplier is used, the dispensed material tends to fall between two range cells. Since microprocessors in the controllers had other tasks, any appreciable change in conveyor speed would introduce an error in bead position. Adjustments could only be made once per item, therefore, long bead applications would vary greatly from its desired position due to changes in conveyor speed. 
     Therefore, the need exists for a method and apparatus for selectively applying material to a target, wherein delivery delay is inherently accommodated. A need also exists for a system that can adjust to varying target speeds. The need exists for a simple technique to accurately place material on a moving target wherein the target speed may have some variation and the target size may be variable and relatively small. 
     SUMMARY OF THE INVENTION 
     The present invention includes an apparatus for selectively applying a material to a target moving along a path and includes a detector for identifying position of the target along the path; a dispenser spaced from the detector by an offset distance, the dispenser configured for selectively releasing material to contact the target; a velocity sensor for creating a velocity signal proportional to a velocity of the target; and a controller for selectively varying the offset distance in response to the velocity signal. 
     In a particular embodiment, an actuator moves the detector in a direction opposite to the direction of conveyor travel as the conveyor speed increases and moves the detector in the same direction as the conveyor travel as the conveyor speed is decreases. In a further configuration, multiple position detectors may be employed to provide further control signals in the application of the material. 
     The present invention addresses at least three separate sources of delivery delay in a typical application system: 
     1. Valve motion delay, resulting from the moving elements of the valve changing position at finite speed. For example, if mechanical solenoids are employed, the magnetic fields generated within the solenoids require appreciable amounts of time to build up when the valve is energized or decay when the valve is de-energized; 
     2. Time of flight delay resulting from the finite speed at which the material is propelled across the distance between the valve/nozzle assembly and the target location; and 
     3. Column inertia resulting from the mass of the column of delivery material resident in a delivery material supply, and the viscosity of the material. Because of these physical properties, the column requires some finite amount of time to get moving when the open command is sent to the valve. This delay is influenced by the delivery pressure and temperature. 
     The present invention accommodates changes in the conveyor speed and reduced spacing between targets. The present device also offers the advantages of: 
     1. employing physical geometry to accomplish what is previously accomplished by means of computational power as through a microprocessor in a control unit; 
     2. compensating for acceleration of target items at rates far higher than can be achieved by present methods based on digital control techniques; and 
     3. controlling the deposition of material with position resolution considerably greater than can be achieved through prior devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a first embodiment of the present invention. 
     FIG. 2 is a schematic of a second embodiment. 
     FIG. 3 is a schematic of a third embodiment of the invention. 
     FIG. 4 is a fourth configuration of a portion of a detection assembly, employing a two-dimensional array of staggered detectors. 
     FIG. 5 illustrates a fifth embodiment having an array of individual optical fibers. 
     FIG. 6 illustrates a sixth embodiment having an “aperture mask” to “space-modulate” the image plane. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first embodiment of the present invention for selectively applying material  6  from a reservoir  4  to a target  8  in relative motion. As shown in FIG. 1, the present invention includes a conveyor assembly  20 , a detector assembly  40 , a dispenser assembly  60 , a velocity sensor  80 , and a controller  100 . Generally, the dispenser assembly  60 , velocity sensor  80  and the controller  100  are disposed at a fixed location along the conveyor assembly  20 , and the detector assembly  40  is moveable along the conveyor assembly. 
     Conveyor Assembly 
     The conveyor assembly  20  translates the target  8  along a predetermined path, and preferably passes the target within an operable distance of the dispenser assembly  60 . The conveyor assembly  20  includes a conveyor  22  that may be any of a variety of configurations such as a belt, rollers or rack system. The conveyor assembly  20  also includes a drive  24  for translating the conveyor  22 . The drive  24  may include drive rollers, a winding drum, hooks, or a pulley mechanism. It understood the conveyor  22  may travel along a straight path or a curvilinear path. 
     Detector Assembly 
     The detector assembly  40  is used to identify a position  41  of the target  8  at a given time and location. The detector assembly  40  includes a source  42  and a detector  44  spaced from the source. The position  41  monitored by detector  44  is located at an offset distance OD from the dispenser assembly  60 . 
     The offset distance OD is shown as a distance extending from the dispenser assembly  60  downstream to the detector assembly  40 . The offset distance OD may vary from being substantially coincident with the dispenser assembly to several inches or even feet from the dispenser assembly, depending upon the shape of the target  8 , the material  6  and the speed of conveyor  22  (target). It is understood the offset distance OD may also be located to extend from the dispenser assembly  60  upstream to the detector assembly  40 . 
     The detector  44  is a sensor which may be a photodetector, a photo electric cell, a photo conductive cell or a photo voltaic cell. However, it is understood, the detector  44  may be sensitive to any desired portion of the electromagnetic spectrum. 
     The source  42  may be a light source such as a light emitting diode, a laser, an infrared source or a visible light source. It is understood the source  42  and detector  44  are compatible. Although the detector assembly  40  is described in terms of a source  42  and a detector  44 , it is understood that in some operating environments, the detector can monitor an ambient condition and create a signal in response to a change in the ambient condition resulting from passage of the target  8 . The detector assembly  40  may thus function with the detector  44  alone. 
     At least, the detector  44  of the detector assembly  40  is connected to an actuator  50  for selectively varying the location of the  10  detector  44  along the path of the conveyor  22  that is varying the offset distance. In a preferred embodiment, the detector assembly  40  is connected to actuators  50  for movement along the path in the upstream and downstream direction. The actuators  50  may be any of a variety of mechanisms such a screws, levers, pistons or cams. Further, the actuators  50  may be mechanically, hydraulically or pneumatically driven, and configured as a linear actuator. 
     In a preferred configuration, both the source  42  and the detector  44  are equipped with actuators  50 . However, it is understood the detector assembly  40  may be selectively translated to varying the offset distance OD by a single actuator  50 . The actuators  50  are linear actuators individually driven by respective drivers  52 . The actuators  50  are configured to selectively move the source  42  and the detector  44  in either the upstream or downstream direction with respect to the conveyor travel. 
     In a preferred configuration, the actuator  50  translates at least the detector  44  less than approximately  24  inches along the path. However, this value may be substantially varied as dictated by the desired operating parameters. 
     Dispenser Assembly 
     The dispenser assembly  60  controls the transfer of the material  6  from the reservoir  4  to the target  8 . The dispenser assembly  60  is operably connected to the controller  100 . The specific dispenser assembly  60  is at least partially dictated by the material to be transferred. The dispenser assembly  60  includes a transfer line  62  extending from the reservoir  4  to a valve-nozzle assembly  70 . Generally, the reservoir  4  presents the material to the valve-nozzle assembly  70  under a predetermined pressure. However, it is understood a pressure generator may be disposed intermediate the reservoir  4  and valve-nozzle assembly  70 . The valve-nozzle assembly  70  is controlled to selectively release the material  6 . The valve-nozzle assembly  70  includes a nozzle  72  for providing a particular pattern of the material  6  as it contacts the target  8 . The valve-nozzle-assembly  70  also includes a valve  74  for selectively releasing material through the nozzle  72 . 
     Velocity Sensor 
     The velocity sensor  80  provides a signal corresponding to the velocity of the target  8  along the conveyor  22 . Generally, the velocity is attributed to the target  8  at the location of the velocity sensor  80 . The velocity sensor  80  may be any of a variety of systems. Its selection is at least partially dictated by cost considerations. 
     In a preferred configuration, the velocity sensor  80  includes an idler wheel  82  connected to the conveyor assembly  20  and a speed or position transducer  84  connected to the idler wheel. The transducer  84  is preferably a tachometer generator. The tachometer generator produces an analog voltage having an amplitude which represents the instantaneous speed of the conveyor  22 , and hence target  8  at the particular location along the conveyor. The analog voltage is converted to a pulse train by a linear voltage controlled oscillator circuit  86 . The pulses generated by the linear voltage controlled oscillator circuit  86  correspond to fixed intervals of distance along the conveyor  22 . These distance intervals represent the smallest quanta of motion to which the controller  100  can detect or respond. The velocity of the conveyor  22  is thus measured and a signal corresponding to the velocity of the conveyor, and hence target is generated. 
     The Controller 
     The controller  100  is operably connected to the velocity sensor  80 , the detector assembly  40  and the dispenser assembly  60  for selectively responding to and/or actuating the respective component. The controller  100  directs the dispenser assembly  60  to permit passage of material through the nozzle  72 . The controller  100  may also calculate velocity of the target  8  from the velocity sensor signal. Further, the controller  100  may recognize the position of the target  8  at the detector location from the signal generated by the detector assembly  40 . The controller  100  may be a dedicated computer or a control system. Alternatively, the controller  100  may be an integrated circuit component embedded in a larger control system. 
     FIG. 2 represents a second configuration of the invention, where two detector assemblies  40 ,  40 ′ are employed, wherein a first upstream detector assembly  40  is used to provide a “valve open signal” and a second downstream detector  40 ′ assembly is located downstream of the first detector assembly  40  to provide a “valve closed signal.” 
     In addition to the components set forth in the description of FIG. 1, the apparatus of FIG. 2 further includes first and second actuators  50 ,  50 ′. These components are similar to the ones described in the first embodiment, such that the first actuator  50  is operably connected to the upstream detector assembly  40  and the second actuator  50 ′ is connected to the downstream detector assembly  40 ′. 
     The use of two detector assemblies in the second embodiment allows the dedication of a respective detector assembly  40  to a specific function. Specifically, the upstream detector assembly  40  generates a commencement signal and the downstream detector assembly  40 ′ generates a termination signal. That is, the upstream detector assembly  40  signals for material flow through valve-nozzle assembly  70  and the downstream detector assembly signals  40 ′ for stopping material flow through the valve-nozzle assembly. 
     FIG. 3 shows a third embodiment having a first detector array  92  and a second detector array  94 . Corresponding first and second source or emitter arrays  42  are shown. The arrays  92 ,  94  have a longitudinal axis that preferably extends parallel to the direction of conveyor travel. The first and the second detector arrays may be transistor arrays. Similar to the previous embodiments, the detectors  92 ,  94  are translatable along the conveyor  22  in the direction of conveyor travel and opposed to the direction of conveyor travel by corresponding actuators. In this embodiment, the arrays  92 ,  94  are used to more finely define distances to more precisely deliver material from the valve-nozzle assembly  70  to the target  8 . 
     FIG. 4 shows a fourth configuration of a detector assembly  40  for use in the present invention. The fourth configuration of the detector assembly  40  includes a two dimensional array of detectors  44 . As shown in FIG. 4, the detector  44  includes a plurality of rows R and columns C formed by individual detectors. Resolution of the detector assembly  40  is determined by the distance or spacing between adjacent detectors. Therefore, resolution of the detector assembly  40  along the travel direction of the conveyor  22  is determined by the individual detectors in a given row R. 
     In the embodiment of FIG. 4, the detectors are evenly spaced within each row R and the rows are offset along the travel direction of the conveyor  22 . That is, the otherwise blank space between two adjacent detectors in a given row R is “occupied” by a detector in one of the remaining rows. The range of detection along the array having offset rows is substantially continuous. The “staggered center” orientation of the rows R thus improves the resolution in the along the axis of target motion. 
     As in the previous configurations, the detectors  44  are connected to actuators  50  for translation upstream and downstream of the travel direction of the conveyor  22 . 
     FIG. 5 shows a fifth embodiment of the detector assembly  40 , wherein the detector  44  includes an array of optical fibers  96 . Each fiber  96  has a first end fixed in an array that locates the fibers in a predetermined pattern. Light from the source  42  passes into the anchored ends of the fibers  96 . A signal generator is operably connected to the fibers  96  to produce a signal in response to the entering light. 
     FIG. 6 shows a sixth configuration of the detector assembly  40  wherein the detector includes an aperture mask  98  to space modulate the passage of a target  8 . Preferably, the aperture mask  98  includes a multitude of light transmissive apertures  99 . In a preferred construction, the light transmissive apertures  99  are evenly spaced in an array. The aperture mask  98  may include a series of linear apertures (slits) located optically intermediate the source  42  and one or more detectors  44 . As a target  8  moves across the field of view, the light from source  42  causes a shadow to sweep across the aperture mask  98 , such that the apertures  99  convert the shadow into a series of discrete steps of intensity change. Electronic circuitry converts these steps into an accurate representation of the location of the leading or trailing edge of the target  8 . 
     In Operation 
     The present system compensates for the initial open delay by adjusting the location of the detector assembly  40  with respect to the dispenser assembly  60 . The open delay can be accurately compensated by translating the detector assembly  40  to increase the offset distance OD as the speed of the conveyor  22  increases. Thus, the controller  100  causes the offset distance OD to increase (moves the detector assembly  40  opposite the conveyor travel) as conveyor speed increases. The controller  100  further reduces the offset distance OD (moves the detector assembly  40  with the conveyor travel) as the conveyor speed decreases. By coordinating variances of the offset distance OD in real time with changes in conveyor speed, the remaining primary error to be addressed would be changes in conveyor speed during actual time off light intervals (the fill flight time of the material from the nozzle  72  to the target  8 .) 
     In operation, the conveyor assembly  20  transports the target  8  along the conveyor  22 . Upon the target  8  passing the detector assembly  40 , the target is detected and a corresponding signal is sent to the controller  100 . 
     Both the source  42  and the detector  44  are operably connected to a corresponding linear actuators  50 . The linear actuators  50  are driven by their respective drive motors  52 . The linear actuators to move the source  42  and the detector  44  to the left, opposite the direction of conveyor motion, as conveyor speed increases and to the right as conveyor speed decreases. 
     Target velocity is determined by the velocity sensor  80 . A velocity signal is created and sent to the controller  100 . The controller  100  directs the actuator  50  to adjust the location of the detector assembly. 
     The configuration of FIG. 1, thereby adjusts for delivery delay for a single bead and for the “on” or “open” delay. The amount of translation of the detector assembly  40  is determined by the product of the conveyor speed and a constant of proportionality, K. As long as the detector assembly  40  is moved by a distance that is exactly equal to the constant K, multiplied by the speed of the conveyor, the resultant effect is to advance the moment of valve actuation by a fixed interval of time. 
     Referring to FIG. 2, the “off” or “close” delay is addressed by the downstream detector assembly  40 ′ which generates an “end” or “close” signal. The offset distance OD for the downstream detector assembly  40 ′ is provided by the corresponding actuator  50  in response to the target velocity and the corresponding proportionally constant K. 
     Each detector assembly  40  instantaneously sends a signal to the controller  100 . The controller  100  includes a “flip-flop” to combine the separate the signals from the respective detector assemblies  40 ,  40 ′ into a single dispenser assembly open/close loop. The controller  100  adjusts the offset distance of the upstream and the downstream detector assemblies via the actuator  50 . Thus, delivery delay is accommodated by purely mechanical system. Thus, the prior limitations of range cell resolution. 
     Further, the present configuration obviates the prior limitation of the control units measuring time only in terms of distance. That is, unlike the prior systems which converted a time interval (that of the “delivery delay”), to a distance interval and real time. Thus, prior delivery delay compensation could only be done to the nearest range cell. So at higher conveyor speeds, the range cells had to be made larger so as to avoid exceeding the available computation band width. Further, where prior systems may encounter a dither resulting from the rounding errors in relation to certain conveyor speeds, the prior invention removes the dither issue. In addition, the present system allows for real time compensation of the offset distance, and hence, conveyor speed changes. Similarly, any variance in the conveyor speed during a length of deposition of material, can be accounted for in the present system. 
     Other improvements, modifications and embodiments will become apparent to one of ordinary skill in the art upon review of this disclosure. Such improvements, modifications, and embodiments are considered to be within the scope of the invention as defined by the following claims.