Abstract:
Apparatus and method for separating lightweight waste from product with cyclic pulses of air. An air separator includes a blower duct directing air upward through product conveyed on a foraminous conveyor. A pair of counter-rotating vanes in the blower duct cyclically open and close to establish a pulsating air flow in the center of the duct across the width of the conveyor. The pulsating air flow lifts lightweight waste from the product and blows it through a vertical duct above the conveyor to waste separation chambers for separation and disposal.

Description:
BACKGROUND 
       [0001]    The invention relates generally to separating waste material from product and more particularly to apparatus and methods for separating lightweight waste from heavier product with blasts of air. 
         [0002]    Air separators are used in the processing of many raw materials to separate lightweight debris and other materials from a product. Some examples include winnowing chaff from grain, separating coal into fines, shelling nuts, and separating loose shell and appendages from peeled shrimp meats. In the shrimp-processing industry, for example, machine-peeled shrimp are conveyed on a foraminous conveyor belt from a peeler to a cooker or packaging station. Although most of the shells, heads, and other appendages that are removed in the peeler are also washed away, some bits adhere to the peeled shrimp meats. The shrimp meats are conveyed through an air separator, which blows air up from a blower duct through the meats on the conveyor to lift the lighter shell and appendage peelings from the shrimp meats. The air flow carries the waste peelings away in a waste conveyor duct above the conveyor to a waste separation chamber in which the waste materials settle and are collected for disposal. 
         [0003]    Conventional air separators have blowers, or fans, that produce a constant air flow whose speed may be modulated or unmodulated. A rotating paddle, or vane, in the blower duct of some air separators is used to modulate the air speed to produce a pulsating air flow. The speed of the air varies between a minimum speed when the vane is closed to block the duct and a maximum speed when the vane is open. With air-flow modulation, smaller and less noisy blowers can be used to achieve higher maximum speeds than with a constant, unmodulated flow. The higher air speeds improve the separation of the peelings from the meats. 
         [0004]    One of the problems with conventional air separators, especially those for use with wet and slimy product like shrimp, is that the waste peelings can stick to the walls of the waste conveyor duct, necessitating frequent cleaning to keep the duct clear for effective separation. 
       SUMMARY 
       [0005]    One version of an air separator embodying features of the invention for separating lightweight waste from product comprises a first duct having an exit proximate the underside of a conveyor conveying product in a conveying direction and a pair of vanes spanning the first duct. The vanes counter-rotate back and forth on parallel axes between a closed position blocking air flow through the first duct and an open position forming between the vanes a centrally disposed gap across the first duct to direct a pulsating air flow centrally through the first duct and the conveyor to blow lightweight waste upward from the product. 
         [0006]    Another version of an air separator embodying features of the invention comprises a blower assembly disposed below the carryway of a foraminous conveyor belt conveying product in a conveying direction. The blower assembly includes a blower and a blower duct directing air from the blower upward through the foraminous conveyor belt. Two vanes extend laterally across the width of the blower duct on laterally disposed axes of rotation perpendicular to the conveying direction. The blower assembly also includes means for cyclically rotating the vanes on the axes of rotation between a closed position blocking the blower duct and an open position directing air in the blower duct between the vanes to produce a pulsating air flow through the foraminous conveyor belt. 
         [0007]    In another aspect of the invention, a method for separating lightweight waste from product conveyed on a foraminous conveyor belt comprises: (a) directing an air flow through a duct and the underside of a foraminous conveyor belt conveying product in a conveying direction; (b) confining the majority of the air flow to a central portion of the duct uniformly across the width of the foraminous conveyor belt; and (c) cyclically pulsing the air flow between a maximum speed and a minimum speed to blow lightweight waste upward away from the product conveyed on the foraminous conveyor belt. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These features and aspects of the invention, as well as its advantages, are better understood by referring to the following description, appended claims, and accompanying drawings, in which: 
           [0009]      FIG. 1  is a perspective view of an air separator embodying features of the invention; 
           [0010]      FIG. 2  is a perspective view of the blower assembly of the air separator viewed from the opposite side of  FIG. 1 ; 
           [0011]      FIG. 3  is a side elevation view, partly cut away, of the air separator of  FIG. 1 ; 
           [0012]      FIG. 4  is a perspective view from below of the flow modulation vanes in the top of the blower duct of the air separator of  FIG. 1 ; 
           [0013]      FIG. 5  is a perspective view of one version of a vane drive mechanism in the air separator of  FIG. 1 ; 
           [0014]      FIGS. 6A-6D  are side elevation views of the blower duct showing the cyclic operation of the vanes of  FIG. 4 ; 
           [0015]      FIG. 7  is a side elevation view of another version of a vane drive mechanism using a variable speed motor drive for the vanes; and 
           [0016]      FIG. 8  is a block diagram of a control system for the air separator of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    One version of an air separator embodying features of the invention is shown in  FIGS. 1-3 . The air separator  10  comprises a lower blower assembly  12  and an upper waste separation assembly  14  on opposite sides of a carryway portion  15  of a conveyor, such as a conveyor belt  16 . The two assemblies are mounted in a frame  18  that also supports the conveyor. In this example, the conveyor belt  16  is trained around drive sprockets (not shown) on a drive shaft  20  and an idle shaft  21  and around idle rollers  22  in a lower return run. The belt is driven by a drive motor  24  and a gear box  25  coupled to the drive shaft  20 . The belt travels up an inclined section  26  to the upper horizontal carryway  15 . The belt is laden with product conveyed along the upper carryway in a conveying direction  30 . The conveyor belt  16  is a foraminous belt with many openings  31  ( FIG. 4 ) extending through the belt&#39;s thickness. The openings are large enough to allow fluids to drain through the belt and for air to pass upward through the belt into the product. Each opening is small enough to prevent products from falling through. Side rails  32  flank the belt on opposite sides to confine product to the belt. 
         [0018]    As shown in  FIGS. 1-4  and  6 A-D, the lower blower assembly includes a centrifugal fan, or blower  34 , driven by a motor  36  such as a variable-speed motor. The blower housing  38  has a screen  40  to cover the air intake  42 . The blower  34  blows air out the blower housing into a vertical blower duct  44 . The duct may optionally be divided into two parallel sub-ducts  46 ,  47  by an airflow divider  48  that extends across the width of the vertical blower duct. 
         [0019]    A pair of elongated vanes  50 , or paddles, are mounted between side walls  52 ,  53  of the blower duct near its top exit end  54 . A shaft  56  runs the length of each vane  50  across the width of the blower duct  44 . The ends of the shaft are mounted in roller bearings  58  in each side wall  52 ,  53 . The shafts define axes of rotation  60 ,  61  ( FIG. 5 ) for the vanes that are parallel to each other and perpendicular to the conveying direction  30 . When the airflow divider is used, each vane is more or less aligned with one of the sub-ducts  46 ,  47 . The vanes are counter-rotated back and forth to cyclically open and close the duct. When the vanes are open, the air flow is centered across the width of the duct away from the two laterally extending duct walls  62 ,  63 . 
         [0020]    One means for cyclically rotating the vanes includes a pair of meshed gear sectors  64 ,  65  mounted to the ends of the vane shafts  56 ,  56 ′ and a crank arm  66  pivotally connected at one end to a pivot pin  68  on one of the gear sectors and to a cantilevered crank  70  at the other end. The crank is mounted to a shaft  72  extending from a gearbox  74 . The crank is radially offset from the shaft to follow a circular orbit about the shaft&#39;s axis. A motor  76  is coupled to the gearbox to rotate the shaft. The pivot pin  68  extends outward of the gear sectors  64 ,  65  through a curved slot  78  in a gear cover  80 . The orbital motion of the crank  70  causes the gear sector  65  to which it is attached to reciprocate rotationally back and forth about the shaft  56  and rotate the associated vane. The geared coupling with the other gear sector  64  causes the other vane to rotate in the opposite direction from the first vane. In other words, when one vane rotates clockwise, the other rotates counterclockwise, and vice versa. The range of rotation of the vanes can be adjusted by changing the length of the arm  66 . As shown in this example, the arm is made length-adjustable by a turnbuckle  82  forming a segment of the arm. A linear actuator could be used to replace the manually operated turnbuckle with an automatically operated length-adjustable segment of the arm. A sensor, such as an angle encoder  84 , mounted on one or the other of the vane shafts can be used to provide a signal indicating the angular position of the vanes. 
         [0021]    As shown in  FIG. 3 , the air blown through the foraminous conveyor belt uniformly across its width and through the conveyed product lifts lightweight waste material  86  into a waste conveyor duct  88 , which forms a vertical tunnel. The lightweight waste is conducted mainly up a central region of the waste conveyor duct by the centered pulses of air provided by the counter-rotating vanes. The top of the lower duct has a short tapered portion  90  between the vanes  50  and the underside of the conveyor belt  16  to make the exit opening of the lower duct match the entrance opening to the waste conveyor duct  88 . Opposite lateral walls  92 ,  93  of the waste conveyor duct taper inward to narrow the duct in the conveying direction with distance from the conveyor belt. The constricting cross section increases the air speed toward the top end  94  of the waste conveyor duct. An upper hood  96  of the waste separation assembly  14  has an airflow bifurcator  98  centered opposite the top end  94  of the waste conveyor duct to split the air flow and conduct the lightweight waste  86  in two directions  100 ,  101 : one in the conveying direction, the other opposite to the conveying direction. Waste separation chambers  102 ,  103  on opposite sides of the airflow bifurcator collect the lightweight waste. The sides of the chambers are perforated with many small openings  99  to allow the air, and not the waste, to escape. The waste conveyor duct  88  has a textured surface  104 , such as a quilted surface, to prevent moist waste from adhering. A tilted waste pan  106  in each waste separation chamber provides a slide along which the collected waste can slide into a trough  108  and out the chamber through a drain pipe. Fluid nozzles  110  ( FIG. 1 ) direct water onto the tops of the pans  106  to wash the collected waste particles into the trough. The water is supplied via a pipe network  112 . 
         [0022]    The cyclic operation of the vanes  50  is illustrated in  FIGS. 6A-6D . In  FIG. 6A , the vanes are shown in a closed position. The two vanes  50  are aligned linearly across the blower duct to block the air flow and build up air pressure below the vanes. When the vanes are closed, the air flow through the belt decreases to a minimum speed of zero. The gear sectors  64 ,  65  are at one end of their range of rotation.  FIG. 6B  shows the vanes  50  at an intermediate position on their way from the closed position to the fully open position. In this intermediate position, the central gap  114  between the vanes directs the air flow centrally through the duct. The sudden release of the high-pressure air through the vanes creates a blast of high-speed air along a central region of the duct across its full width. The air continues to flow at a high speed as the gear sectors  64 ,  65  counter-rotate to the opposite end of their range in the fully open position shown in  FIG. 6C , in which the major axes of the cross sections of the vanes are parallel to each other and vertical. In the fully open position, the gap  114  is at its maximum length. At this midpoint in the cycle, the gear sectors start to counter-rotate in the opposite direction, as indicated by the change in sense of arrows  116  in  FIG. 6D  showing the vanes closing on their way back to the closed position of  FIG. 6A  to end the cycle and start another. As the vanes close, the air speed decreases from its maximum value. The cyclic opening and closing of the vanes establishes a cyclically pulsing air flow to lift lightweight waste from the conveyed product and blow it through the waste conveyor duct to the two waste separation chambers. Cycle frequencies of between about 60 cycles/minute and 200 cycles/minute have been found to work well with shrimp. Splitting the flow exiting the waste conveyor duct with the bifurcator decreases the maximum path length that any waste particle has to travel to the waste separation chambers. This allows a smaller and less noisy blower to be used. And the centralized air flow lessens the amount of waste that adheres to the walls of the waste conveyor duct. 
         [0023]    Another means for cyclically rotating the vanes is shown in  FIG. 7 . In this version, a bidirectional, variable-speed motor  118  drives a first gear wheel  120  meshed with a second gear wheel  121 . Each of the gear wheels is mounted to one of the shafts  56 ,  56 ′ of the vanes  50 . In this way the two vanes can counter-rotate together back and forth between the open and closed positions. The 360° gear wheels also permit the vanes to counter-rotate continuously without the reversal required when the gear sectors  64 ,  65  of  FIG. 5  are used. Of course, 360° gear wheels could replace the gear sectors in  FIG. 5 , and gear sectors could be used with the motor  118  in  FIG. 7 . A shaft encoder  122  can be mounted to the shaft of one of the vanes to provide angular-position feedback. 
         [0024]      FIG. 8  shows a control system for automatic control of the air separator. The control system includes a controller  123 , such as a programmable logic controller or a laptop, desktop, or workstation computer. A user interface  124  to the controller allows an operator to control and maintain the operation of the air separator. Some of the operating variables the operator can set via the user interface include the speed of the conveyor, the range of rotation of the vanes, the speed or cycle time of the vanes, and the speed of the blower. Based on the operator&#39;s settings, the controller outputs signals to the conveyor drive motor  24  to set the speed of the conveyor, the blower motor  36  to control the air flow, the vane motor  76 ,  118  to control the speed or cycle time or frequency of the vanes and also the range of rotation of the vanes in the case of the motor  118  of  FIG. 7 , and the range of rotation of the vanes when the adjustable-link portion of the crank arm  66  of  FIG. 5  is realized with a linear actuator  126  instead of a turnbuckle. The controller  123  may also receive sensor signals to provide closed-loop control of the air separator. Feedback signals from the shaft encoder  84 ,  122 , an airflow sensor  128 , such as an anemometer, and motor-speed sensors  130 , such as tachometers, may be used to operate the air separator in a closed-loop system. 
         [0025]    The air separator described is particularly useful in separating lightweight shrimp peelings, such as shell and head fragments, swimmerettes, and legs, from peeled shrimp meats. But it may also be used in the processing of nuts, grains, fruits and vegetables, and non-food products. Although the air separator has been described in detail by reference to a few versions, other versions are possible. So the claims are not meant to be limited to the details of the disclosed versions or applications.