PATENT ABSTRACT
A pneumatic control head for controlling the supply of a product into a container via a filling head. A manifold has a pilot air duct. A start valve outputs main air to the pilot air duct when actuated by a mechanical switch. A pilot valve activates a cylinder using the main air in response to air pressure in the pilot air duct. A filling head source valve routs either sensing air or blow down air to a filling head output in response to the condition of a blow down valve actuated by a mechanical switch. An overpressure valve exhausts the pilot air duct in response to the sensing air having a pressure higher than normal. The switches each includes a ball bearing captured by a collar. An external cam pushes the ball bearing into the collar, causing the ball bearing to actuate the respective valve. Duct connections to valves are implemented by a single machined plate with a depression that overlaps the duct aperture and valve opening. An o-ring fits into a groove surrounding the depression and valve opening and provides a seal between the plate and the manifold.

PATENT DESCRIPTION
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to liquid product filling heads, more particularly, to a pneumatic control unit for automatically shutting off a liquid product filling head filling a container upon sensing that the container is full. 
     2. Description of the Related Art 
     There are a number of automatic container filling machines in the art wherein a sensing tube extends into a container to be filled and when the lower end of the tube is blocked by the product in the container, back pressure through the tube actuates a control device to stop the flow of product into the container. In particular, U.S. Pat. No. 5,161,586 discloses a pneumatic control unit that responds to a sensed back pressure to shut off liquid to the filling container. The shortcomings of the disclosed design are discussed in detail below relative to the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a pneumatic control unit for a liquid filling head that is easier and less expensive to manufacture and that is easier to maintain than pneumatic control units of the prior art. 
     The present invention is a pneumatic control head for controlling the supply of a product into a container via a filling head with a sensing tube that extends into the container. The control head has a manifold with several air inputs. A main air input receives main air at an operating pressure, typically at about 60 psi. A blow down air input receives blow down air for cleaning the filling head as needed. A filling head output connects to the sensing tube. A cylinder for operating the filling head attaches to the manifold. 
     The majority of the control unit is built in a manifold. The manifold has a pilot air duct for conducting pilot air at a pressure near that of the main air operating pressure. A start valve takes in the main air and outputs it to the pilot air duct when actuated by a mechanical switch. The switch includes a ball bearing captured by a collar whereby the switch is actuated when the ball bearing is pressed into the collar. 
     A pilot valve in the manifold takes in the main air and allows it into a cylinder air duct to activate the cylinder in response to air pressure in the pilot air duct. Optionally, there is a no container switch that exhausts air from the pilot air duct in the event that there is no container under the filling head. 
     A flow regulator mounted to the manifold receives sensing air and outputs regulated sensing air at a sensing pressure. Optionally, a sensing air shut off valve precedes the flow regulator. The sensing air shut off valve is controlled by the main air to the cylinder so that if the cylinder is not actuated, there is no sensing air to cause the filling product to bubble. 
     The regulated sensing air passes through a filling head source valve to a filling head output. Normally the filling head source valve routs the regulated sensing air to the filling head output. The filling head source valve routs blow-down air to the filling head output in response to main air from a blow down valve. The blow down valve takes in the main air and outputs it to a switch the filling head source valve when actuated by a mechanical switch. The switch is of the same design as that of the start valve. 
     An overpressure valve mounted to the manifold exhausts the pilot air duct in response to the regulated sensing air having a pressure higher than normal. When the product fills the container to the point that the product nearly contacts the sensing tube, a back pressure is created that causes the overpressure sensor valve to trip. 
     Physically, the control unit includes a manifold within which are cut holes for valves and channels for ducts. A top plate houses the flow regulator and provides a mount for the overpressure sensor valve. 
     The start and blow down valve switches are improvements over those of the control units of the prior art. Each switch is a ball bearing captured by a collar. An external cam pushes the ball bearing into the collar, causing the ball bearing to push the start valve. Friction is reduced because the ball bearing rotates within the collar as the cam slides by. The improvement includes significantly fewer moving parts that substantially reduces both the initial manufacturing and the periodic maintenance costs. 
     Another improvement over the prior art is the means by which two of the ducts are routed to their respective valves. The pilot and filling head source valves fit into openings in the manifold. The appropriate duct exits at an aperture adjacent to the valve. A single machined plate has a depression that overlaps the aperture and the valve opening. An o-ring fits into a groove surrounding the depression and valve opening. The o-ring provides a seal between the plate and the manifold when installed. 
     Other objects of the present invention will become apparent in light of the following drawings and detailed description of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and object of the present invention, reference is made to the accompanying drawings, wherein: 
     FIG. 1 is an front perspective view of the pneumatic control unit of the present invention; 
     FIG. 2 is a rear perspective view of the pneumatic control unit of the present invention; 
     FIG. 3 is a side view of an assembly of the control unit of the present invention and a filling head; 
     FIG. 4 is a schematic diagram of the control unit of the present invention; 
     FIG. 5 is an exploded view of the start switch mechanism of the control unit of FIG. 1; and 
     FIG. 6 is an exploded view of the pilot valve at the rear of the control unit of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The pneumatic control unit  10  of the present invention, shown in FIGS. 1-3 and schematically in FIG. 4, has three inlets for external air supplies. The main air inlet  12  accepts the main control air, typically at a pressure of about 60 psi. The sensing air inlet  14  accepts the sensing air, typically at a pressure of about 5 psi This pressure is chosen to be low to avoid bubbling the liquid  95  in the top of a container  97  being filled while being high enough to reliably build a back pressure when the liquid  95  fills the container  97 . The blow down air inlet  16  accepts the blow down air at a pressure typically in the range of about 20-40 psi. The purpose of the blow down air is to clean the filling head  96  as needed, so the pressure is set accordingly for the thickness of the filling liquid. 
     The air cylinder  20  for operating the filling head extends from the bottom of the control unit  10 . The air cylinder piston  90  extends downwardly under controlled air pressure to open the filling head  94 . 
     Refer now to FIG.  4 . The start switch  22  mechanically actuates a start valve  24 . The start valve  24  receives the main air and is normally closed, blocking the main air from the pilot air duct  46 . When actuated, the start valve  24  opens, permitting the main air into the pilot air duct  46 . The air in the pilot air duct  46  is referred to as the pilot air. The high pressure pilot air is routed into a no container safety valve  36  of well-known design. Essentially, when there is no container to fill, a mechanical switch  18  actuates the no container safety valve  36 , which exhausts the pilot air from the pilot air duct  46 , as at  37 , preventing it from causing the actuation of the air cylinder  20 . A flow restrictor  30  prevents an excess of main air pressure from exceeding the capacity of the no container safety valve  36 . 
     The pilot air is routed to a pilot valve  32  and to an overpressure sensor valve  34 . When the start switch  22  is actuated, the pilot air actuates the pilot valve  32  thereby permitting the main air into a cylinder air duct  33 , actuating the air cylinder  20 . Preferably, the pilot valve  32  has a compensating orifice which opens into a passageway into the pilot air chamber of the pilot valve  32 . When the pilot valve  32  is actuated, a portion of the main air passes through the compensating orifice into the pilot air chamber to help hold the pilot valve  32  actuated in order to compensate for any pilot system leaks. For example, some air is bled out of the pilot air duct  46  through a small bleed orifice in the overpressure sensor valve  34 , as described below. A drop in the pilot air pressure will deactuate the pilot valve  32 . Once closing begins, the air from the cylinder air duct  33  is exhausted through the pilot valve exhaust port  38 . In this way the pilot valve  32  reacts quickly to a drop in pilot pressure to stop the liquid filling operation. 
     The overpressure sensor valve  34  quickly triggers the shut off of the liquid filling operation in response to back pressure from the container  97  being filled. The sensing air is applied to a diaphragm and is allowed to escape through a bleed orifice  49 . When the pressure on the diaphragm increases such that the diaphragm flexes, the flexing diaphragm covers the bleed orifice  49 , causing a build up of pressure which triggers the valve  34  to open. When the overpressure sensor valve  34  opens, the pilot air is exhausted out through the valve  34 , as at  48 , causing the air cylinder piston  90  to retract, halting the liquid filling operation. 
     The sensing air inlet  14  provides the sensing air control signal to the overpressure sensor valve  34 . Optionally, the sensing air is routed through a sensing air shutoff valve  40  that is controlled by the main air to the cylinder  20 . By shutting off the sensing air when the fill is complete, bubbling of the filling liquid by the sensing air is avoided. 
     A flow regulator  42  permits accurate regulation of the pressure of the sensing air, providing a means to adjust the control unit  10  for the height of the liquid fill. If the flow regulator  42  is of a variable type, two or more control units  10  may be employed in a mass production filling machine by adjusting the sensing air to fill all containers to the same height. 
     The sensing air from the flow regulator  42  passes through a filling head source valve  44  to a filling head output  43 . The normal state of the filling head source valve  44  routs the sensing air to the filling head output  43 . The switched state of the filling head source valve  44  routs blow-down air to the filling head output  43 , as described below. 
     The filling head output  43  is connected, via a hose  96 , to a sensing tube  93  at the end of the filling head  92 . The sensing air easily passes out of the sensing tube opening  94  until the filling liquid  95  contacts or nearly contacts the opening  94 . When this occurs, a back pressure is created that causes the overpressure sensor valve  34  to trip, shutting off the filling operation. 
     The blow down operation clears the sensing tube  93 . A blow down switch  26  mechanically actuates the blow down valve  28 , allowing main air into a filling head source control duct  45 , which directs the filling head source valve  44  to rout the blow down air from the blow down air inlet  16  to the filling head output  43 . The blow down-operation is momentary, that is, it only operates as long as the blow down switch  26  is activated. When the blow down switch is not actuated, the main air is exhausted from the filling head source control duct  45  by the blow down valve  28 , as at  41 . 
     The majority of the control unit  10  is formed in a manifold  50 , preferably a block of aluminum. Holes are drilled and channels are cut in the manifold  50  to accommodate the valves and to form the passages between those valves, all in a manner well-known in the art. 
     A top plate  51  is mounted to the top of the manifold  50 . The top plate  51  provides a housing for the flow regulator  42  and a connection to the manifold  50  for the overpressure sensor valve  34 . The flow regulator control knob  52  extends vertically from the top of the top plate  51 . The sensing air shutoff valve  40  extends rearwardly from the top plate  51 . It receives its connection to the pilot air duct  33  by a hose  53  from the manifold  50 . The output  43  of the filling head source valve  44  is located on the bottom of the manifold  50  and is connected to the filling head  92  by a hose  96 . 
     The start valve  24  and blow down valve  28  are located on the same side of the manifold  50 . In the prior art, the start switch  22  and blow down switch  26  are rather complicated mechanisms. The appropriate valve is actuated by a leaf spring that is pushed by a pivoting arm. At the free end of the arm is a roller that is pushed by an external cam. The reason for the roller is so that friction is kept to a minimum as the external cam slides by. The various moving parts require regular maintenance to keep operating properly. 
     The present invention replaces each roller/arm mechanism with a simple ball bearing  57  inside a collar  58 . As can be seen in FIG. 5, the front surface  56  of the manifold  50  is covered by a front plate  59 . The front plate  59  includes a clearance hole  60  for the collar  58 . The collar  58  is a short tube with a flange  62  at the inner end. The inside diameter of the tube is slightly larger than the ball bearing  57  so that the ball bearing  57  slides easily within the tube. An internal lip  64  at the outer end of the collar  58  as an inside diameter slightly smaller than the ball bearing  57  so that the ball bearing  57  is retained in the collar  58  when installed. The plate  59  is typically removably secured by screws  65  sandwiching the collar  58  by the flange  62  between the manifold front surface  56  and the front plate  59 . The ball bearing  54  extends outwardly from the collar  58  at least the length of travel of the start valve  24 . As the control unit  10  moves past the start cam, the cam pushes the ball bearing  57  into the collar  58 , causing the ball bearing  57  to push the start valve  24 , initiating the fill operation. Friction is reduced between the start switch  22  and the cam because the ball bearing  57  rotates within the collar  58  as the cam slides by. The blow down  26  switch is implemented in the same way. 
     The ball bearing design is an improvement over the design of the prior art. The numerous moving parts, including the roller, the arm, and the leaf spring, are replace by a single moving part, the ball bearing  57 . The reduction in the number of parts substantially reduces both the initial manufacturing cost and the periodic maintenance cost of the control unit  10 . 
     The rear of the control unit  10  is shown in FIGS. 2 and 6. As can be seen, the filling head source valve  44  fits into a cylindrical opening  70  in the manifold  50  leaving the actuator  72  free. The filling head source control duct  45  exits at an aperture  74  in the rear wall  76  and must be routed to the filling head source valve  44 . The pilot valve  32  and the pilot air duct  46  have the same arrangement. In the prior art, a gasket with a groove fits over the rear wall of the manifold such that one end of the groove is positioned over the valve and the other end of the groove is positioned over the aperture. A metal plate is placed over the gasket and secured to the rear wall. The groove provides the connecting duct and the gasket prevents leaks. Since the rear of the control unit of the prior art has two valves and an air inlet, there are a number of components, including three plates, three gaskets, and a handful of screws, making the manifold relatively costly to manufacture and assemble. 
     The present invention replaces the piecemeal design of the prior art with the design of FIG.  6 . The multiple plates and gaskets are replaced by a single machined plate  78  and o-rings  80 . A depression  82  that overlaps both the aperture  74  and part of the valve opening  70  is machined in the surface  84  of the plate  78 . The shape of the depression  82  is unimportant, as long as it overlaps both the aperture  74  and the valve opening  70 . In the present embodiment, the depression  82  is cylindrical for ease in machining. A groove  86  surrounding the depression  82  and valve opening  70  is machined in the plate surface  84 . An o-ring  80  seats in the groove  86  and provides a seal between the plate  78  and the manifold rear wall  76  when the plate  78  is secured to the rear wall  76 , typically by screws  88 . In the present embodiment, the groove  86  is eccentric because of the dimensions of the plate  78  and manifold  50 . However, the shape of the groove  86  is unimportant as long as it provides a seat for the o-ring  80  as required. Since there are actually two valves and ducts that need to be connected, the control unit  10  of the present invention has two depressions  82 , two grooves  86 , and two  0 -rings  80 , one each for the pilot valve and the filling head source valve  44 . 
     Thus it has been shown and described a pneumatic control unit which satisfies the objects set forth above. 
     Since certain changes may be made in the present disclosure without departing from the scope of the present invention, it is intended that all matter described in the foregoing specification and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.