Abstract:
A method for controlling the retention time of a casting retained in a mold comprises providing a vibratory shakeout conveyor having a conveying surface, placing the mold on the conveyor; and imparting a vibratory force to the conveyor at a predetermined angle to the conveying surface whereby the predetermined angle determines the retention time of said casting in said mold. A plurality of sensors for detecting mold position and media breakdown may also be employed to detect appropriate mold retention time.

Description:
FIELD OF THE INVENTION 
   The present invention is related generally to a system and method for advancing an article on a vibratory conveyor and more specifically to a system and method for controlling the retention time of an article being conveyed by selective and directional application of a vibratory force to a conveyor as a function of at least one sensed variable. 
   BACKGROUND OF THE INVENTION 
   There are known in the art a plurality of commercially available vibratory conveyor systems for controlling the speed and direction of articles or materials being conveyed thereby. Many prior art systems vary conveying speed and direction by changing either the direction or magnitude of a force applied to a conveyor trough that is resiliently mounted on a suspension system to permit vibratory motion to be imparted thereto. Alternative prior art conveying systems employ a wide variety mechanical systems to elevate or decline an end of the vibratory conveyor, thereby changing the angle of inclination of the entire conveyor trough to speed up or slow down the progress of an article along the conveyor. 
   One exemplary prior art system of this nature is U.S. Pat. No. 5,615,763 to Schieber, assigned to Carrier Vibrating Equipment, Inc., of Louisville, Ky., herein incorporated by reference. Generally speaking, this systems varies the vibratory force being applied to a resiliently mounted conveyor trough by securing to the trough a plurality of shafts having a plurality of eccentric weights mounted thereto. The shafts, and consequently the eccentric weights, are capable of rotation, typically through the action of driven pulleys or the like such that the rotating shafts and eccentric weights impart a vibratory force to the conveyor trough. 
   The angle of the vibrating force acting on the conveyor in such systems is determined by the relative position of the eccentric weights on the rotating shafts. The relative position, or phase angle relationship between eccentric weights may be maintained and controlled by various mechanical control and positioning systems or alternatively, by utilizing an electronic control system to monitor and adjust the phase angle relationships between various rotating masses. 
   Prior art vibratory conveyor systems are incapable of monitoring an article being conveyed to adjust the speed and direction of conveyance to impart a desired amount of vibratory force to an article before its discharge from the conveyor. The ability to monitor an article&#39;s position or progress along the conveyor can be very beneficial for certain products and manufacturing processes that require the input of a particular amount of force over a given time period for proper production. For example, some casting and molding processes utilize vibratory force to separate a casting or part from its mold and concomitant media. In many prior art systems, foundries utilize vibratory shakeout devices to mechanically separate sand or other surrounding media used in the casting process from the casting itself. 
   In operation, prior art vibratory shakeout devices have attempted to control the time a casting is retained in its mold by changing the elevation of one end of the shakeout to change the angle of inclination of the conveyor trough. Longer casting retention times are typically required for more complete media removal whereas short retention times are desirable for more fragile castings since a shorter retention time typically requires that less vibratory force is imparted through the conveyor trough to the fragile casting. Increasing the angle of inclination of a shakeout typically increases the retention time of a casting in the mold and, conversely, decreasing shakeout inclination usually decreases mold retention time. 
   Many prior art shakeout systems utilizing angle of inclination type control systems are relatively unreliable since they typically employ complex mechanical systems such as air bellows or hydraulic cylinders to elevate an end of the shakeout. These mechanical systems are inherently unreliable, particularly in the harsh industrial environment of a foundry or other molding facility. Furthermore, many prior art systems offer only a limited range of process control since the angle of inclination can only be raised a few degrees before the ability to convey the casting forward along the conveyor trough ceases unless a tremendous amount of vibratory force is applied. Additionally, variations in casting speed are difficult to effect with these prior art systems. 
   SUMMARY OF THE INVENTION 
   The present invention provides a system and method for controlling the retention time of an article on a vibratory conveyor that modifies the angle of the vibratory force imparted to the conveyor as a function of the desired retention time or alternatively, as a function of article position on the conveyor or another sensed variable that is indicative of article progress. The present invention provides an electronically adjustable system for controlling conveyor retention time that permits an article being conveyed to be monitored such that a desired result is achieved prior to the article being discharged from said conveyor. For example, the present invention may be employed to monitor casting retention in a mold and adjust or modify that retention time based on a desired retention time or alternatively based on other sensed variables such as article position, relative amount of media removal, or both. 
   The invention comprises a vibratory shakeout conveyor that may utilize an electronic control system to modify the relative angle of the vibratory force applied to the conveying surface responsive to a desired retention time, either as input by an operator or responsive to a sensed variable such as casting position or media removal. A plurality of sensors may be employed, both to monitor and adjust the resultant angle of vibration and also to monitor the progress of the article being conveyed and its condition or status relative to a desired status prior to advancing the article. 
   The present invention may incorporate at least one electric motor that is capable of being electronically controlled, for example by a variable frequency drive, responsive to an resultant angle of vibration or speed input supplied thereto. The motor speed is readily adjusted to modify the relative speed of a rotating shaft or shafts, thereby changing the resultant angle of vibratory force being applied to said conveyor. Other objects, features, and advantages of the present invention will become apparent upon an examination of the detailed description of the preferred embodiment taken in conjunction with the drawing Figures. 

   
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       FIG. 1  is a block diagram of a vibratory conveyor and control system in accordance with one embodiment of the present invention. 
       FIG. 2  is a block diagram of a vibratory conveyor and control system in accordance with one embodiment of the present invention. 
       FIG. 3  is a block diagram of a vibratory conveyor and control system in accordance with one embodiment of the present invention. 
       FIG. 4  is a block diagram of a vibratory conveyor and control system in accordance with one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Referring now to the drawing Figures, and in accordance with a preferred constructed embodiment of the invention, a system  10  and method for controlling the retention time of an article comprises a vibratory conveyor  20  including a trough or conveying surface  21  which is mounted on a stationary base  22  by a plurality of isolating springs  24  or equivalent resilient mounting means. A plurality of shafts  30 ,  32 , and  34  are mounted for rotational motion within a frame  40 . Each shaft further includes at least one eccentric weight  36  positioned at a point between the ends thereof that rotates with its respective shaft. In one embodiment of the present invention an exemplary system  10  may employ a plurality of eccentric weights  36  centrally positioned on shaft  32  while the outboard shafts  30  and  34  may employ just a single eccentric weight  36 . Each shaft further includes a pulley  38  mounted thereon that is driven by a belt  42  that is in turn driven by a pair of motors  44  and  46  respectively, each having associated pulleys  48  secured to their output shafts. 
   In an exemplary embodiment of the present invention as shown in  FIG. 1  rotating motor  44  drives shaft  30  through belt  42 . Belt  50  is coupled to shaft  30  to drive shaft  34  such that both shafts  30  and  34  are synchronously rotated by operation of motor  44 . In effect shaft  34  operates as a slave to shaft  30 . Additionally, motor  46  drives middle shaft  32  via pulley  48  and belt  42 , preferably in a rotational direction opposite to that of shafts  30  and  34 . 
   The system  10  thus far described comprises an eccentric weight vibratory conveyor  20  capable of altering the direction of the resultant force acting on conveyor  20  due to the centrifugal forces imparted thereto by the rotating eccentric weights  36 . The direction of the resultant force acting on conveyor  20  is dependent upon the relative phase angle between the positions of the rotating eccentric weights  36 . Accordingly, by varying that relative position or relative phase angle between the shafts and therefore the weights  36 , the direction or angle of resultant vibratory force acting on conveyor  20  is varied so that the conveying rate and direction of material placed on conveyor  20  can be altered. 
   The system  10  may further comprise a plurality of proximity sensors or switches  60  positioned proximate shafts  32  and  34  capable of sensing the position of the respective shafts by sensing a flag or other detectable element located thereon, as is well known to one of ordinary skill in the art. Sensors  60  provide an output  62  responsive to a sensed shaft position that is operatively connected to a controller  70 . Controller  70  may comprise a conventional microcontroller having a processor, an associated data memory and a plurality of inputs and outputs that may be operatively coupled to external devices as discussed further herein below. 
   Controller  70  calculates an actual value of relative phase angle Ø 1  between shafts  32  and  34  by comparing the shaft position signal inputs  62 . A manually operated user input  72 , which may comprise a known in the art potentiometer, thumbwheel switch, or alternatively a numerical keypad having an output representative of a user&#39;s selection, may be adjusted to provide a desired speed and direction signal to controller  70 . It should be noted that user input  72  may be either a desired relative phase angle setting or alternatively a speed and direction setting. In the case of the latter, controller  70  may be suitably programmed to mathematically convert a desired speed and direction setting supplied by user input  72  to a desired phase angle either by use of a look up table or a suitable mathematical formula, as is well known to one of ordinary skill in the art. 
   The controller  70  provides an output signal  73  representative of a desired motor  46  speed to a variable frequency drive  80  or equivalent electronic motor controller, thereby altering the speed of motor  46  to change the relative phase angle between shafts  30 ,  34 , and shaft  32 . The signal  73  sent to variable frequency drive  80  is continuously adjusted by controller  70  to maintain a desired relative phase angle thereby advancing an item positioned on vibratory conveyor  20  as desired. 
   In an alternative embodiment of the invention, a plurality of photo-eyes, motion detection, or infra-red sensors  74  or equivalent sensors are positioned at a plurality of locations along vibratory conveyor  20  to sense the progress and position of an article placed thereon. The sensors  74  include associated outputs  76  operatively connected to a plurality of inputs of controller  70 . Sensors  74  are positioned at various points along the path of articles being conveyed to monitor the advancement of the articles or alternatively the amount of media breakdown which has occurred in a mold containing a casting, which in turn may be used to vary relative phase angle Ø and alter conveying speed and/or direction as discussed in detail herein below. 
   Referring to drawing  FIGS. 2-4  there is shown a conveyor  20  onto which a mold and casting  1  has been positioned to enable the breakdown of the media  2  surrounding casting  1  through the application of vibratory force.  FIG. 2  depicts casting  1  at an initial point on the vibratory conveyor  20 . As casting  1  advances along vibratory conveyor  20  (from left to right in the  FIGS. 2-4 ) the resultant angle of vibration Ø 1  is set to permit the casting  1  to advance to a predetermined position along conveyor  20 . 
   At that predetermined position depicted in  FIG. 3 , the controller  70  increases the resultant angle of vibration to Ø 2  by altering output  73  to variable frequency drive  80  to slow the advancement of casting  1  and aid the breakdown of media  2 . As the media  2  breaks down the angle of vibration may be increased to a point whereby casting  1  ceases advancing completely but maximum vibratory force is being imparted to conveyor  20 . Once media  2  has broken down and substantially vibrated away from casting  1 , the resultant angle of vibration is then decreased to Ø 3  to effect the advancement and discharge of casting  1  from conveyor  20 , as shown in  FIG. 4 . 
   The requisite changes to the resultant angle of vibration Ø applied to conveyor  20  may be effected by a plurality of embodiments of the present invention. In one exemplary embodiment, a first sensor  74  is a motion detection sensor, for example a commercially available PIR sensor or its equivalent that is capable of detecting motion at a point or area in space and producing an output responsive thereto, coupled to an input of controller  70 . In its initial state, controller  70  advances casting  1  along conveyor  20  at predetermined angle Ø i  (and thus at a predetermined speed) until the casting reaches a point where sensor  74  detects the presence of casting  1  and sends an output to controller  70 . Once controller  70  senses the output from sensor  74  indicating the presence of casting  1  controller  70  then sends a new speed signal  73  to variable frequency drive  80  to alter the speed of motor  46  and increase the resultant angle of vibration to Ø 2  to stop the advancement of casting  1  and facilitate the breakdown of media  2 . 
   The controller  70  may, in one embodiment of the present invention, simply set the resultant angle of vibration to Ø 2  for a predetermined time period selected to permit media  2  to substantially breakdown, whereupon controller  70  then automatically provides a new speed signal  73  to variable frequency drive  80  to change the resultant angle of vibration to Ø 3  to discharge casting  1  from conveyor  20 . 
   In a yet further embodiment of the present invention, a second sensor  74 , for example a photo-eye or its equivalent is positioned at a point proximate the area of conveyor  20  where casting  1  stops advancing (at resultant angle of vibration Ø 2 ) to sense when media  2  has substantially broken down. Stated another way, second sensor  74  is capable of detecting the absence of media  2  proximate casting  1  and sends a signal to controller  70  indicating that casting  1  is ready to be discharged from conveyor  20 . Alternatively, second sensor  74  may comprises one of a plurality of commercially available digital cameras that are capable of detecting surface voids or imperfections in a viewing area. In this embodiment of the invention, the digital camera may readily determine the absence (or presence) of media  2  in a given are when casting  1  has reached a predetermined positioned and send an output indicative of a predetermined media breakdown to controller  70 . 
   In an additional embodiment of the present invention controller  70  operates vibratory conveyor  20  in a pulse mode wherein once casting  1  enters conveyor  20  the resultant angle of vibration Ø is alternately increased and decreased to impart a greater, then lesser vibration to casting  1 . In this fashion, articles placed on conveyor  20  are advanced in a pulsing fashion, which further facilitates the breakdown of media  2 . Pulse mode operation may further be enhanced by utilizing a plurality of sensors  74  to determine the presence or absence of media  2  around casting  1  at a predetermined point along conveyor  20 . When casting  1  reaches the predetermined point, if media  2  is not sufficiently removed therefrom, as detected by a photo-eye or infrared sensor  74 , controller  70  may send a speed signal  73  to variable frequency drive  80  to increase the resultant angle of vibration Ø such that casting  1  reverses direction on conveyor  20  for a predetermined time or, alternatively, until casting  1  is sensed by a second sensor  74  at a second point along conveyor  20 . At this point controller  70  once again initiates pulse mode operation to advance casting  1  while removing media  2  therefrom. This process may reiterate itself until media  2  has been substantially removed from casting  1  whereupon the casting is advanced out of conveyor  20 . 
   While the present invention has been shown and described herein in what are considered to be the preferred embodiments thereof, illustrating the results and advantages over the prior art obtained through the present invention, the invention is not limited to those specific embodiments. Thus, the forms of the invention shown and described herein are to be taken as illustrative only and other embodiments may be selected without departing from the scope of the present invention, as set forth in the claims appended hereto.