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BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to hopper containers for dispensing viscous liquid or granular materials and, more particularly, to safety door systems for hopper containers as may be used in such applications as pavement construction or repair or in agricultural uses. 
   2. Description of the Prior Art 
   Containers that hold and dispense viscous liquid or granular materials for use in pavement construction or repair or agricultural applications are well known in the art. Such containers may be called hopper bodies and be used in stationary or mobile equipment. Some hopper bodies typically include one or more rotating implements in the interior of the hopper for stirring, agitating or facilitating the dispensing of the material from the hopper, usually from an opening disposed in the lower portion of the hopper. For example, hopper bodies used in asphalt pavement repair vehicles are described in U.S. Pat. No. 5,988,935, issued Nov. 23, 1999 and assigned to the assignee of the present invention. This patent is hereby incorporated by reference into this specification in its entirety. 
   The hopper bodies of asphalt pavement repair vehicles may be large enough to contain up to four cubic yards, or more, of material. The material may be heated to prepare it for use and agitated by a paddle shaft mechanism to maintain a uniform consistency and temperature. Further, during dispensing of the material, an auger used as a screw conveyor may be used to facilitate the dispensing process. Both the paddle shaft and the screw conveyor may be rotating mechanisms powered by hydraulic motors, for example. In some situations of use, the material in the hopper body may become too viscous or tend to clog the rotating mechanisms during a mixing or dispensing operation. In these or similar situations, operating personnel may be tempted to climb inside the hopper body to attempt to clear a blockage or to manually assist the paddle shaft or screw conveyor in stirring or conveying the material. This is an extremely dangerous activity because it exposes the operating personnel to the risk of serious injury by the rotating implements within the hopper body. 
   What is needed is a system or method for ensuring that operating personnel are prevented from entering the hopper body while the rotating equipment is operating. Further, even if a worker enters the hopper body for some reason, a system or method is needed for stopping the operation of the rotating machinery or any other moving device within the hopper body to minimize the risk of injury to the person. 
   SUMMARY OF THE INVENTION 
   Accordingly there is disclosed a safety door system for a hopper body containing a rotating implement powered by a hydraulic control system. The hopper body for transporting liquid or granular material, which has a V-shaped floor to facilitate dispensing the material, further includes the rotating implement for dispensing the liquid or granular materials from an opening in the hopper body and/or for agitating the liquid or granular materials. A safety door, provided for covering and preventing access into the hopper body during use, is hinged along a first edge to a corresponding first side of the hopper body and moveable between a closed and an open position when a hydraulic actuating cylinder, coupled between a second edge of the safety door and a corresponding second side of the hopper body, opens the safety door when the hydraulic actuating cylinder extends its length and closes the door when the hydraulic actuating cylinder retracts its length. An interlock device coupled between the hydraulic actuating cylinder and the hydraulic control system prevents the rotating implement within the hopper body from rotating whenever the safety door is not in its closed position. 
   In another embodiment there is disclosed a method of limiting access to a hopper body of a mobile pavement repair system during its use, the hopper body having an open top and a V-shaped floor, for transporting liquid or granular materials, and a rotating implement disposed within the hopper body and powered by a hydraulic motor in a hydraulic control system. The method comprises the steps of: covering the open top of the hopper body with a safety door, hinged along a first edge to a corresponding first side of the hopper body and operable between a closed and an open position; opening and closing the safety door using a hydraulic actuating cylinder, the hydraulic actuating cylinder coupling the safety door from a second edge thereof to a corresponding second side of the hopper body, wherein the hydraulic actuating cylinder extends its length to open the safety door and retracts its length to close the safety door; and preventing the rotating implement from rotating, whenever the safety door is not in its closed position, under the control of an interlock device coupled between the hydraulic actuating cylinder and the hydraulic motor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a hopper body system for storing and dispensing liquid or granular materials equipped with one embodiment of a safety door system according to the present invention; 
       FIG. 2A  illustrates an end view of the hopper body of the embodiment of  FIG. 1  shown with the safety doors in a fully closed position; 
       FIG. 2B  illustrates an end view of the hopper body of the embodiment of  FIG. 1  shown with the safety doors in a partially opened position; 
       FIG. 2C  illustrates an end view of the hopper body of the embodiment of  FIG. 1  shown with the safety doors in a more fully opened position; 
       FIG. 3  illustrates a portion of the control apparatus for operating the safety door system of the embodiment of  FIG. 1  according to the present invention; and 
       FIG. 4  illustrates a side cross-sectional view along a vertical centerline of the hopper body of the embodiment of  FIG. 1  showing one configuration of rotating implements that may be used in the hopper body. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , there is illustrated a hopper body system  10 , e.g., for storing and dispensing viscous liquid or granular materials equipped with one embodiment of a safety door system according to the present invention. A hopper body  12 , which includes a powered implement (See, e.g.,  FIG. 4 ) that rotates or moves in other directions, includes a safety door  14  for covering an open top of the hopper body  12 . The powered or rotating implement may, for example be a conveyor of the belt type or auger type. The hopper body  12  is typically rectangular in shape, may be fabricated of welded steel panels, or other suitable materials considering the materials to be transported or stored. In some applications the hopper body may be round or conform to some other shape. Mobile versions of the hopper body  12  may be adapted for mounting upon the chassis of a truck, or upon a trailer that could be towed by a truck or other vehicle. Stationary versions of the hopper body may be supported on a suitable frame, which typically elevates the hopper body for positioning a mobile unit below the hopper body when dispensing material from the hopper body into the mobile unit. 
   The safety door  14  shown in  FIG. 1  may be fabricated of sheet metal or synthetic materials and configured as a pair of bifold doors as will be described herein below. A first bifold door of the safety door  14  includes first and second door panels  16 ,  18 , which are hinged together along the joint  24 . A second bifold door of the safety door  14  includes third and fourth door panels  20 ,  22 , which are hinged along the joint  26 . In the illustrative example, the pair of bifold doors ( 16 ,  18  and  20 ,  22 ), when closed, meet along a junction  32 . The first panel  16  of the first bifold door  16 ,  18  is attached along a first edge thereof to a corresponding first side of the hopper  12  via a hinge (not shown) disposed along an axis indicated by a first tie pin  28 . The fourth panel  22  of the second bifold door  20 ,  22  is attached along a second edge thereof to a corresponding second side of the hopper  12  via a hinge (not shown) disposed along an axis indicated by a second tie pin  30 . The tie pins  28 ,  30 , which are aligned with the hinge axes and protrude from the end of the hopper body  12 , may be provided for securing a tarpaulin or for temporarily suspending lamps or other tools. 
   Although the illustrated embodiment of the safety door  14  is configured as a pair of bifold door panels, to cover a relatively large hopper body having a width of approximately six feet and a length of, e.g., six to twelve feet, a safety door  14  of the present invention could also be configured as a single panel door, or a pair of half-size door panels, etc., to cover a hopper of smaller dimensions or a different shape, without departing from the principles of the present invention. It is contemplated that different specific applications will suggest, to persons skilled in the art, variations in the door panel configuration and construction that is selected. 
   In one embodiment, the hopper body  12  may be configured for holding, transporting and dispensing asphalt mix paving materials, as disclosed in U.S. Pat. No. 5,988,935 and assigned to the assignee of the present invention, for repairing pavement damage such as potholes. The hopper body  12  may thus include mechanisms for heating the asphalt mix materials to an appropriate temperature and viscosity and structural features for insulating the walls of the hopper body  12  to retain the heat within the material inside the hopper body  12 . In other applications of a hopper body  12 , e.g., for holding, transporting and dispensing various materials used in road or building construction or agricultural materials for seeding or soil conditioning, the hopper body  12  may be equipped with other apparatus suited to the specific application. In such examples, a safety door system according to the present invention would serve the same purpose—the protection of operating personnel from serious risk of injury during operation or servicing of the hopper body system  10 . Further, as mentioned previously, it is contemplated that the safety door system lends itself as well to stationary as to mobile applications. 
   Superimposed over the outline drawing of the hopper body  12  in  FIG. 1  is a schematic pictorial diagram of the portion of the hydraulic control system  40  involved in the operation of the safety door system of the present invention. Structures of the hydraulic control system  40  in  FIG. 1  are not necessarily shown in their actual locations. The double lines in the drawing represent hydraulic fluid (oil) lines and the single lines represent electrical conductors. The hydraulic oil stored in an oil tank  42  is circulated in the direction of the arrows by pump  44  through oil line  48 , a stack valve  58 , an oil return line  50  and the various other lines as will be described. Returning oil, except for oil diverted by the solenoid-operated safety dump valve  110  (which flows along path  54  to return to the oil tank  42 ), is filtered by filter  46  and follows oil return line  50  back to the oil tank  42 . Oil return from the safety dump valve  110  is unfiltered in order to remove any restriction to the flow of oil, which may impair the response of the safety door system to the opening of the safety doors  14 . Control of the flow of oil to various parts of the safety door system is provided by the stack valve  58 . 
   The stack valve  58  is a system of valves and oil distribution ports, typically configured as a single, composite structure having a plurality of valves and ports, for controlling the flow of oil to operate the various components, including powered implements, connected in the hydraulic system. In the illustrative example the valves are operated by hand levers, coupled to the stack valve  58  by operating rods (not shown) typically moveable between ON and OFF, or FORWARD and REVERSE positions. In some applications the levers may include an intermediate ‘NEUTRAL’ position. In other applications, the levers might be replaced by electric solenoids connected to control rods and operated from a remote position with respect to the device(s) being controlled. 
   Continuing with  FIG. 1 , the stack valve  58  in the illustrated embodiment includes a control lever  60  for operating a screw conveyor motor  70 , a control lever  62  for operating an agitator motor  80 , and a control lever  64  for operating the safety door  14 . The control lever  64  is moveable between a ‘CLOSED’ position, indicated by the letter “C”(Ref. No. 66) and an OPEN position indicated by the letter “O.” The levers  60 ,  62  in the illustrated embodiment are operable between FORWARD, NEUTRAL, and REVERSE positions. In some applications the three positions may be LOW, OFF, and HIGH speeds, for example. Hydraulically operated conveyor motor  70 , connected to the stack valve  58  via oil supply line  72  and oil return line  74 , functions to rotate a screw conveyor (auger) in the hopper body. Hydraulically operated (paddle shaft) agitator motor  80 , connected to the stack valve  58  via oil supply line  76  and oil return line  78 , functions to rotate a paddle shaft and thereby control the rotation of the agitating paddles. The screw conveyor and paddle shaft will be described further in the description for  FIG. 4 . 
   Before continuing with  FIG. 1 , several other types of hydraulic system components used in the safety door system of the present invention will be described. These components include: an unloader valve ( 92 ,  96 ,  102 , and  106 ); a check valve ( 94 ,  98 ,  104 , and  108 ); a normally open dump safety valve ( 110 ); and a proximity switch ( 170 ). 
   An unloader valve ( 92 ,  96 ,  102 , and  106 ) is normally open to allow oil to flow through it, if there is any flow at all in the line in which it is installed. In the illustrated embodiment, the unloader valves are installed in bypass lines of a pilot control circuit that is controlled by a dump safety valve  110 . If the dump safety valve  110  opens under a condition in which oil must be diverted from a normal function and returned to the oil supply reservoir (oil tank  42 ), the unloader valve acts to unload the pilot control oil supply circuit to the component being supplied. This action prevents the operation of the component supplied by the protected oil line. 
   A check valve ( 94 ,  98 ,  104 , and  108 ) is a one-way poppet valve that allows oil to flow through the oil line in one direction only. The check valve closes if the oil pressure in the line reverses direction. It is used, in the present invention, to maintain oil flow in one direction only—toward the oil tank and away from the pump. 
   A normally open dump safety valve ( 110 ) is held closed by the action of an energized solenoid coil. When installed in a bypass circuit, a closed dump safety valve prevents the operation of the bypass circuit. When the solenoid drops out, i.e, releases, the dump safety valve opens and allows the oil supply to flow from the unloader valves through the bypass circuit to return to the reservoir. 
   A proximity switch ( 170 ) is used to sense the change in the proximity of a nearby movable component to a sensing element in the switch. In one configuration of the present invention a set of contacts in the proximity switch, closed when the nearby component is in proximity, open with the loss of proximity. These contacts, when connected in the operating circuit of a solenoid coil in the dump safety valve, cause the solenoid coil to release when the proximity is lost. Release of the solenoid coil opens the dump safety valve, which opens the unloader valves and diverts the oil supply for the conveyor and agitator motors back to the oil tank. 
   Continuing with  FIG. 1 , a bypass circuit (See the enlarged view of the bypass circuit  190  shown in  FIG. 3 ) in the hydraulic control system  40  is controlled by a normally open dump safety valve  110 . The bypass circuit includes bypass oil lines that divert the pilot control oil for both the conveyor motor  70  and the agitator motor  80  back to the oil tank  42  whenever the safety door  14  begins to open. The bypass circuit for the conveyor motor  70  includes two branch circuits: a first oil line  82 , an unloader valve  96  connected between the stack valve  58  and a first branch of a tee fitting  90 , which is connected to a first entry branch of the dump safety valve  110 ; and a second oil line  84 , an unloader valve  92  connected between the stack valve  58  and a second branch of a tee fitting  90 , which is connected to the first entry port of the dump safety valve  110 . Similarly, the bypass circuit for the agitator motor  80  includes two branch circuits: a third oil line  86 , an unloader valve  106  connected between the stack valve  58  and a first branch of a tee fitting  100 , which is connected a second entry port of the dump safety valve  110 ; and a fourth oil line  88 , an unloader valve  102  connected between the stack valve  58  and a second branch of a tee fitting  100 , which is connected to the second entry port of the dump safety valve  110 . Persons skilled in the art will realize that not every hydraulic circuit in a machine that may be used in a hopper body will require an associated bypass circuit—only those circuits that may pose a hazard to persons in the proximity thereto or which may require bypass circuits for other operational reasons. 
   In one embodiment of a stack valve  58  as used in the present invention, the unloader valves  92 ,  96 ,  102  and  196  are installed in respective auxiliary option ports of the stack valve  58 . Thus, pilot control oil line  84  is associated in the stack valve  58  with oil line  74  and pilot control oil line  82  is associated with oil line  72 . Similarly, pilot control oil line  88  is associated in the stack valve  58  with oil line  78  and pilot control oil line  86  is associated with oil line  76 . Further, an outlet port of the dump safety valve  110  is connected to a return oil line  54 , which returns oil diverted by the dump safety valve  110  to the oil tank  42 . Electric current for operating the solenoid coil  112  of the dump safety valve  110  is connected to the solenoid coil  112  via terminals  114 ,  116 , as will be described herein below. 
   Included in the pictorial schematic of the hydraulic control system  40  in  FIG. 1  are hydraulic actuating cylinders and associated components for opening and closing the door panels and providing the safety interlock functions of the door safety system of the present invention. As used in the illustrative embodiment, a hydraulic actuating cylinder is a linear actuator having a sealed tubular cylinder and a movable rod protruding from one end that may be extended from or retracted within the one end of the tubular cylinder. As oil is pumped into one end or the other end of the tubular cylinder, the movable rod, attached to a piston at the end of the rod inside the tubular cylinder, extends or retracts the overall length of the hydraulic actuating cylinder. 
   A first hydraulic actuating cylinder  120  (which will also be referred to as an ‘actuator  120 ’) is connected between a first pin  122  on the side of an upper portion of the hopper body and a second pin  124  on a first edge of the door panel  22 . As oil is pumped into the actuator  120  it increases in length and causes the door panel  22  to swing upward from the hopper body  12  about the hinge axis  30 . When door panel  22  pivots upward, the door panel  20 , which is hinged to the door panel  22  along the joint  26 , is lifted away from the hopper body  12 . The free edge of the bifold door  20 ,  22  slides along the upper rim of the hopper body  12  as it is opened. Similarly, a second hydraulic actuating cylinder  130  (which will also be referred to as an ‘actuator  130 ’) is connected between a third pin  132  on the side of an upper portion of the hopper body and a fourth pin  134  on a first edge of the door panel  16 . As oil is pumped into the actuator  130  it increases in length and causes the door panel  16  to swing upward from the hopper body  12  about the hinge axis  28 . When door panel  16  pivots upward, the door panel  18 , which is hinged to the door panel  16  along the joint  24 , is lifted away from the hopper body  12 . The free edge of the bifold door  16 ,  18  slides along the upper rim of the hopper body  12  as it is opened. 
   The actuators  120 ,  130  may be extended together via a common ‘open’ oil line  150  and retracted via a common ‘close’ oil line  160 , both of which are connected at a supply end of the respective oil lines  150 ,  160  to the stack valve  58 . The opposite end of the respective oil lines  150 ,  160  is connected to respective ‘tee’ fittings  152 ,  162  to feed both respective actuators  120 ,  130  simultaneously. During an extension cycle, oil flows via oil line  150 , tee fitting  152  where the paths diverge into oil line  154  to port  126  on a base end of the actuator  120  and into oil line  156  to port  136  on a base end of the actuator  130 . The extension cycle is activated by moving the door lever  64  to the ‘OPEN’ position denoted by the letter ‘O’ marked on the stack valve  58 . During a retraction cycle, oil flows via oil line  160 , tee fitting  162  where the paths diverge into oil line  164  to port  128  on the rod end of the actuator  120  and into oil line  166  to port  138  on the rod end of the actuator  130 . The retraction cycle is activated by moving the door lever  64  to the ‘CLOSE’ position denoted by the letter ‘C’ marked on the stack valve  58 . Thus, as oil is pumped into oil line  150  to extend the actuators  120 ,  130  the bifold doors  20 ,  22  and  16 ,  18  are opened. Similarly, as oil is pumped into oil line  160  to retract the actuators  120 ,  130  the bifold doors  20 ,  22  and  16 ,  18  are closed. 
   Installed near the first end of actuator  120  is a proximity switch  170 , installed in a port in the cylinder body of the actuator  120 . The proximity switch  170  includes a sensing element (not shown)coupled to a pair of normally closed (‘NC’) contacts (not shown). The sensing element, for example, may be a magnet (not shown) within the proximity switch and attached or otherwise coupled to one of the contacts. The rod portion of the actuator is terminated in an iron piston at the inside end of the rod. The magnet responds to the proximity of the piston within the actuator  120 . In the illustrative example, the proximity switch  170  is placed in the port of the actuator so that, when the rod portion is in the fully retracted or ‘rest’ position corresponding to the safety door it controls being in a fully closed condition, the contacts of the proximity switch  170  are held closed by the internal magnet. As the door lever  64  is moved to the OPEN position, the oil pressure in the cylinder portion of the actuator  120  increases and forces the piston and rod to move away from its rest (fully retracted) position. The movement of the piston and rod is sensed by the sensing element in the proximity switch  170 , causing the contacts in the proximity switch  170  to open. 
   The proximity switch  170  is positioned on the actuator  120  such that the contacts in the proximity switch  170  open when the piston has moved to extend the overall length of the actuator  120  by a predetermined amount, in a typical embodiment of approximately five percent (5%) or less of the overall, extended length of the actuator  120 . This predetermined amount is only an approximation—an initial setting subject to experimentation in the particular case—and may vary substantially with the geometry of the safety door, the hopper body, the actuator used and the tolerances thereof. In the illustrative embodiment, for example, the contacts open when the piston has moved approximately ⅜″ from its rest position. This corresponds with limiting the distance to about one to four inches (e.g., to prevent a person inserting an arm through the door opening) that the safety door is allowed to open before the powered implement(s) is disabled. The overall stroke of the actuator in the illustrative embodiment is 13 inches. In other applications, the location of the port for the proximity switch in the cylinder body of the actuator may be specified to the manufacturer to meet the requirements of a particular application. 
   It will also be understood that, while the proximity switch is installed in the hydraulic actuating cylinder that opens and closes the safety door in the illustrated embodiment, in other applications a proximity switch may be installed elsewhere. For example, a proximity switch may be installed on the rim of the hopper body (or the edge of a door panel) and configured to respond to a magnet on the edge of a door to be opened (or the rim of the hopper body). In such cases, the contacts in the proximity switch may be adjusted to open when the edge of a door panel and the rim of the hopper body become separated by a distance in the range of, for example, one to four inches. This predetermined distance is approximate and subject to the results of experimentation in the particular application. The determination of this distance may also be in consideration of bending or distortion of the door panel structure. It is understood that the amount the door panel is separated from the hopper body to cause interruption in the movement of the rotating or powered implement is limited to a range of separation, at a location along the periphery of the door panel where a person may most likely attempt to gain entry into the hopper body, that prevents the person, or an arm or leg of the person, from entering the hopper body or reaching into the hopper body to the vicinity of the rotating or powered implement. 
   The proximity switch  170  has at least two terminals or leads. In the illustrative embodiment proximity switch  170  has a first lead  172  connected to a first terminal  114  of the solenoid coil  112  of the dump safety valve  110  and a second lead  174  connected to a ground terminal  176 . Connected between the terminal  116  of the solenoid coil  112  and the positive terminal  188  of a battery  182  is a wire  184 , an ON/OFF switch  180  and a wire  186 . The battery may be the battery of the vehicle carrying the hopper body  12 , e.g., a 12 VDC battery. Accordingly, the solenoid coil  112  of the dump safety valve  110  would also be rated at the same voltage, 12VDC. Other voltages may be employed, of course, as long as the solenoid voltage rating is consistent with the available supply voltage. A fuse may be inserted in the wire  184 . The ON/OFF switch  180 , which serves to activate the door safety system of the present invention, may be part of a vehicle ignition switch or a stand alone switch. Thus, when the door lever  64  is in a CLOSED position, the safety door is closed, the ON/OFF switch  180  is closed, and the safety door system is activated. If the door lever  64  is moved from the CLOSED position to the OPEN position, the proximity switch senses the movement of the rod in the actuator  120  and opens the circuit of the solenoid  112  of the dump safety valve  110 , diverting the oil supply from the conveyor and agitator motors  70 ,  80  to stop the rotation of the rotating implements within the hopper body. 
   The movement of the bifold doors  16 ,  18  and  20 ,  22  is illustrated in  FIGS. 2A ,  2 B and  2 C described herein below, wherein the same reference numbers are used to identify the same structures as shown in  FIG. 1 . 
   Referring to  FIG. 2A , there is illustrated an end view of the hopper body  12  with the bifold safety doors  16 ,  18  and  20 ,  22  of the embodiment of  FIG. 1  shown in a fully closed position. In this case, the actuators  120 ,  130  are de-energized and in their fully retracted position, the contacts of the proximity switch  170  are closed, the solenoid  112  is energized, and the dump safety valve  110  is also closed. In  FIG. 2B , there is illustrated an end view of the hopper body  12  with the bifold safety doors  16 ,  18  and  20 ,  22  of the embodiment of  FIG. 1  shown in a partially opened position corresponding to actuators  120 ,  130  having been partially filled with oil. In this case, the actuators  120 ,  130  are partially extended, the contacts of the proximity switch  170  are open, the solenoid is de-energized or released, the dump safety valve  110  is open, diverting oil away from the conveyor motor  70  and the agitator motor  80 , which stops the rotating implements. The outline of the rim of the hopper body  12  is shown in a broken line. In  FIG. 2C , there is illustrated an end view of the hopper body  12  with the bifold safety doors  16 ,  18  and  20 ,  22  of the embodiment of  FIG. 1  shown in a more fully opened position, with the actuators  120 ,  130  nearly fully extended. Here, the conditions of the door safety system are the same as in  FIG. 2B . 
   Referring to  FIG. 3 , there is illustrated an enlarged pictorial view of the bypass circuit  190  portion of the hydraulic system  40  for operating the safety door system of the embodiment of  FIG. 1  according to the present invention. Most of the structures of  FIG. 3  are illustrated in  FIG. 1  and like elements bear like reference numbers.  FIG. 3  also shows the oil lines  192 ,  194  coupling the respective conveyor and agitator bypass circuits to the dump safety valve  110 . A hydraulic flow control valve at port  128  on the actuator  120  is also shown in  FIG. 3 . The actual physical location of each of the structures of  FIG. 3 , as in  FIG. 1 , is not shown; rather,  FIG. 3  is intended to show the relationship of the components with each other. For example, the solenoid  112  that controls the safety dump valve  110  may be located remotely to the stack valve  58  or other structures (because it needs only electrical wiring connections and has no oil lines connecting to it), or, it may be part of the stack valve  58 . The latter configuration is preferred because it saves space and provides a neater installation with no increase in cost, in the illustrative application of  FIGS. 1 through 4 . 
   Referring to  FIG. 4 , there is illustrated a side cross-sectional view along a vertical centerline of the hopper body  12  of the embodiment of  FIG. 1  showing one configuration of powered or rotating implements that may be used in the hopper body. An auger configured as a screw conveyor  196  is supported in bearings  198 ,  200  in the end walls of the hopper body  12  and driven by conveyor motor  70 . A paddle shaft configured as an agitator  202  is supported in bearings  204 ,  206  in the end walls of the hopper body  12  above the screw conveyor  196  and driven by agitator motor  80 . Included in a lower portion of the hopper body  12  is an outlet opening  208  and a dispensing chute  210  from which viscous liquid or granular material such as an asphalt mix is dispensed from the hopper body by the screw conveyor  196  following agitation as necessary by the paddle shaft  202  during a pothole patching operation. In some embodiments, other powered implements such as conveyor belts, stirring rods, chopping or cutting blades, metering and dispensing apparatus, and the like, which may all be powered by hydraulic motors, may be used within the hopper body  12 . 
   While the invention has been shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications as described herein above without departing from the spirit thereof.

Summary:
Accordingly there is disclosed a safety door system, comprising a hopper body containing a powered implement powered by a hydraulic control system, for dispensing liquid or granular materials or for agitating the liquid or granular materials; a safety door for covering and preventing access into the hopper body during use; a hydraulic actuating cylinder operative to open the safety door; and an interlock device coupled between the hydraulic actuating cylinder and the hydraulic control system such that the powered implement within the hopper body is prevented from operating whenever the safety door is not in its closed position. 
     In another embodiment there is disclosed a method of limiting access to a hopper body of a mobile pavement repair system during its use, the hopper body having a powered implement within the hopper body and powered by a hydraulic motor. The method comprises the steps of covering the open top of the hopper body with a safety door; opening and closing the safety door using a hydraulic actuating cylinder; and preventing the powered implement from operating whenever the safety door is not in its closed position, under the control of an interlock device coupled between the hydraulic actuating cylinder and the hydraulic motor.