Abstract:
A bulk density sampling method and device whereby formed product is flowed through a vertically disposed passage of pre-determined size. The passage is temporarily obstructed to collect and weigh a known volume of product upon which to base a calculation of bulk density and the generation of a control signal for regulating a multi-tasking processor to constantly monitor, control, and display speed, head gap position, temperature, feed rate and target moisture.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to machines for extruding food products, for example, from corn meal, and more particularly relates to a method and means for controlling such a machine with improved bulk density sampler techniques for selective sampling of extruded material flowing in a material processing stream. 
     2. The Prior Art 
     The prior art is exemplified by machines of the type manufactured and sold by the assignee of the present application, one exemplification of which is disclosed in U.S. Pat. No. 5,143,738 issued Sep. 1, 1992 and entitled “Computerized Food Product Extrusion Machine and Method.” 
     Bulk density sampler arrangements occur in the prior art. For example, reference is made to U.S. Pat. No. 5,563,384 issued Oct. 8, 1996 wherein a receptacle of known volume is intermittently interposed into and out of a stream of flowing material to gather a supply of the formed extruded material. After the receptacle is withdrawn from the product stream, special instrumentalities must be provided to measure the weight of the gathered formed product. First, the receptacle is weighed when it is empty and it is weighed again when it is full. Means are provided to restore the sample product into product stream. 
     Additionally, the mechanism must be provided with a housing for protection of the sampling assembly and receptacle from the product stream and other debris which may be present in the operating environment. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention contemplates the utilization of a method and means of controlling a food extruder wherein raw material is extruded to make formed product. The formed product is discharged and flowed into a material processing stream. 
     At one point in the stream the formed product flows through a permanent stationary confined calibrated passage of prescribed known volumetric size. One end of the calibrated passage is selectively obstructed so that formed product will be collected and accumulate in the confined passage. Sensing means are utilized to sense when a quantum of accumulated formed product has been collected in the calibrated passage equal to the pre-determined known volume, whereupon the collected known volume of formed product is weighed to generate a control signal which is a function of the of the bulk density of the collected formed product. 
     The control signal is then fed to a programmable logic computer (PLC) which controls the operation of the extruder to constantly monitor, control and display speed, head gap position, temperature, feed rate and target moisture. 
     The end of the permanent stationary collection passage is simply cleared of the temporary obstruction so that the formed product accumulated within the passage, as well as the formed product continuously flowing through the product stream, may proceed downstream without further incident in the material processing stream. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view, with parts broken away, and with schematic wiring control circuitry added, and showing a food extruder for producing cellular food product, but having a bulk density arrangement provided in accordance with the principles of the present invention, and capable of practicing the method of this invention. 
     FIG. 2 is a fragmentary front elevational view of the bulk density measuring mechanism provided in accordance with the principles of the present invention. 
     FIG. 3 is a side elevational view of the mechanism of FIG.  2 . 
     FIG. 4 is a top plan view of the mechanism of FIG.  2 . 
     FIG. 5 is a rear elevational view of the mechanism of FIG.  2 . 
     FIG. 6 is a top plan view, in section, of the food extruder and bulk density measuring mechanism taken generally in the plane of line V—V of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 of the drawings, there is shown an exemplary form of a food extruder  10  of the type wherein raw material is extruded to make formed product. The extruder  10  has a number of basic components which together with one another provide the environment in which the specific improvements of the present disclosure find their greatest utility. 
     First of all, raw material, such as corn grain, is stored or fed in a hopper, for example, a vibrating stainless steel hopper  12 , from which the raw material is transferred to a positive auger metering feeder  11 , at which time the raw material is humidified under the control of a moisture control system  13  regulated by computer means having a programmable logic controller  14  (PLC). 
     From the metering feeder  11 , the raw material is conveyed via a mixer screw, sometimes referred to as a pre-blender, into an extruder unit. In the extruder unit, the raw material is processed by being extruded through an adjustable head gap, also under the control of the PLC  14 . The PLC  14  adjusts the temperature at the point of extrusion and, automatically brings the head gap into precise position for maximizing product quality. With digital read out to thousandths of an inch, consistent quality product is assured. A resultant formed product, or cellular food product, exits the extruder unit via an outlet. 
     The PLC preferably utilizes a code which directs the execution of sampling bulk density in a random manner to obtain optimum statistical process control. 
     Vibrator means provided on the hopper  12  assist in moving grain to the conduit having an outlet in which is situated a moisture probe comprising one or more dielectric sensors by means of which the moisture content of the grain is measured. A water delivery system in the moisture control system  13  adds water to the grain to bring the moisture content thereof up to an optimum required level for accomplishing quality extrusion. 
     In operation the moisture control system  13 , or the probe of that system, generates an analog moisture content signal which is sent to the PLC  14  in which the signal is compared with the preselected desired moisture content. A differential signal resulting from the comparison is digitized and is used to control the delivery of water to the metering feeder. 
     The positive auger metering feeder  11  comprises a helical screw that is driven at infinitely adjustable variable speeds, and which is also under the control of the PLC  14 . The amount of water flow delivered by the water delivery system is controlled in proportion to the quantum of grain transported out from the hopper  12  to the extruder  10  so that the formed product has the requisite characteristics of shape, form and density. 
     In operation, the formed product is discharged continuously onto a take-away conveyor  16  to form a material processing stream. The take-away conveyor  16  is reversible and the machine as described has an automatic start-up. The PLC  14  prepares raw material, adjusts the head gap, feeds the raw material, controls the temperature and reverses the discharge belt of the take-away conveyor  16  so irregular product is caught in a waste bin  17 . When satisfactory product is achieved, the discharge belt of the take-away conveyor is engaged in the forward direction. 
     In the running operation of the machine, the PLC  14  constantly monitors, controls and displays the parameters of speed, head gap position, temperature, feed rate and target moisture. 
     In order to accomplish an efficient and effective control of the extruding machine  10 , it is necessary and essential that the PLC  14 , receive frequent and accurate reports of data which reflect operating conditions. Food manufacturing processes typically require continuous monitoring in order to produce an acceptable food product of high quality. Thus, in the manufacture of products formed by extrusion, for example, snack foods, pastas, cereals and pet food, a good indicator of the product quality is the final density of the formed product. 
     Frequent samples must be taken of the formed product in the material processing stream. Such samples must be measured and analyzed. The information developed can be utilized by the algorithm programmed into the PLC  14  to adjust and control the process. 
     In accordance with the principles of the present invention, we have discovered an entirely new and different concept of bulk density sampling which is particularly adaptable to a food extruding machine. Referring now to FIGS. 1-6 of the drawings, an exemplification of a bulk sampling device capable of practicing the steps of the method contemplated is shown. The extruding machine  10  has a take-away conveyor  16  which is intended to remove the formed product from the immediate locale of the extruding machine  10 . It does this by delivering the formed product in the form of a material processing stream to a transport conveyor  18  which carries the formed product in the material processing stream to a packaging, or shipping, point of utilization. 
     At a first point in the material processing stream downstream of the take-away conveyor  16  on the extruding machine  10 , a point preferably situated between the take-away conveyor  16  and the transport conveyor  18 , we contemplate gravitationally flowing the formed product material processing stream through a permanent, stationary, vertical, confined, collection passage of uniform cross-section and of a prescribed size in length. Thus, it is, in effect, a longitudinally extending tube can be considered as being calibrated to be of a pre-determined known volumetric size at any selectively chosen level. 
     While it is conceivable that such a passage could be of any known regular geometric cross-sectional configuration, there is illustrated in the drawings a volume collection cylinder  19  disposed to provide a uniform cylindrical passage extending on a vertical axis  20  which intersects the plane of the take-away conveyor  16  as well as the plane of the transport conveyor  18 . Accordingly, formed product in the material processing stream at the first point in the stream will fall gravitationally, and continuously, from the take-away conveyor  16  downwardly in the direction of the vertical axis  20 , through the volume cylinder  19  and onto the transport conveyor  18 . 
     In the non-sampling mode of operation of the bulk density sampling device, the formed product in the material processing stream freely passes through the bulk density sampler without any interruption in a normal manner of product delivery. 
     In order to achieve a sampling mode, there is provided a controlled slide gate  21  which is movably supported in slide runners  22  carried on a support frame  23  at the lower end of the volume collection cylinder  19 . The slide gate  21  is selectively actuated by an air cylinder  24  having an operating piston  26  coupled to the slide gate  21  as at  27 . Thus, the slide gate  21  can be moved horizontally, i.e., at right angles to the vertical axis  20 , from a first inoperative position laterally displaced from the volume collection cylinder  19 , to a second obstructing position extending across the bottom of the volume collection cylinder  19  and completely closing the vertical passage through the volume collection cylinder  19 . When so moved to the second obstructing position, formed product will be collected and will begin to accumulate in the volume cylinder  19 . 
     There is an upper support frame  28  connected to the extruder and such frame  28  has one or more load cells  30  which support the volume collection cylinder  19  and the lower support frame  23 , which, in turn carries the slide gate assembly. Adjustment rods for the frame  28  are shown at  32 . 
     A photo cell  31  is attached, or mounted, in such a manner as to determine when the collection cylinder  19  is full. In the present embodiment, the photo cell  31  is attached to the top of the collection cylinder  19 . The lower frame  23  together with the volume collection cylinder  19  and the air cylinder  24  are suspended in such a manner that the programmable logic controller (PLC)  14  takes a reading of the gross weight of such components as are supported by the load cells  30  while empty, and in a non-sampling mode, commonly referred to as a tare weight. 
     In the sampling mode, the slide gate  21  is actuated by the PLC  14 . When formed product is accumulating in the volume collection cylinder  19 , the electronic photo eye, or photo cell,  31  “watches” the top of the volume collection cylinder  19  to sense when it has been filled to a predetermined level. When a “full” condition is sensed, the take-away conveyor  16  is momentarily stopped so that it stops sending product for approximately three (3) seconds while the load cells  30  determine the final weight of the filled volume collection cylinder  19 . The tare weight is subtracted from the filled weight, thereby giving the net weight by means of which the bulk density of the formed product can be automatically calculated. On the basis of such calculation, a control signal is generated and the PLC  14  makes such adjustments as may be required to automatically regulate head gap position, feed rate and target moisture. 
     While minor modifications might be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as come within the scope of our contribution to the art.