You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to a step in the construction of interior walls. After the wall of a building has been constructed, it is common to cover the wooden members or “studs” with dry wall (also known as sheet rock or wallboard). After the dry wall is in place, the joints formed where two pieces of drywall abut are typically filled in before the wall is painted or wall papered. Failure to do so results in visible discontinuities in the finished wall. Filling in these joints is usually a four step process.  
           [0002]    The first step involves applying a layer of thick paste called mastic or joint compound. Once the joint compound is applied, and while it is still wet, tape is applied over the wet mastic and pressed into the joint. This taping step is the second step but is often combined with the first step through the use of a taping tool.  
           [0003]    Numerous taping tools have been developed which apply a layer of compound to one side of tape supplied from a roll and press the tape and compound into the joint. This is accomplished in one sweeping motion of the taping tool. Prior art taping tools will be discussed in more detail below.  
           [0004]    The third step is to apply a second layer of compound over the tape. This compound acts to blend the tape into the wall by covering the edges of the tape and any remaining groove in the joint. Though some of the prior art applicators try to combine this step with the first two, it has been found that allowing the first layer of compound to dry thoroughly before applying the second is advantageous for several reasons. First, the compound shrinks as it dries. Allowing the first layer to dry thoroughly permits completion of the shrinking process so that the resulting crevice can be filled in completely. Second, it is often desirable to use a thinner, finishing compound for the second layer. Having an applicator with multiple supply hoppers with different compounds in each hopper either increases the weight of the tool, or decreases the supply of the compound. In either case the tool becomes more complicated and cumbersome.  
           [0005]    The fourth step is optional but widely practiced. A third, wider layer of compound is applied over the second layer after the second layer has dried thoroughly and been sanded. This third layer is thinner than the second and is feathered into the walls resulting in an even finish which makes the abutment of the two wall boards virtually invisible when painted or papered. Because the second layer of compound is the thickest, it is common to allow the second layer to dry for at least one day, more often two days, before the third layer is applied.  
           [0006]    The four steps just described were originally performed by hand and were all time consuming and labor intensive. This led to numerous developments in the art to reduce the time and effort required to finish walls. Despite these efforts, little progress has been made.  
           [0007]    U.S. Pat. No. 3,116,195 to Lathrop et. al. issued Dec. 31, 1963 generally relates to an applicator which applies tape coated on one side with compound to a joint. The applicator receives the compound from a supply hopper by means of an internal combustion engine powering a positive displacement pump. Despite the obvious carbon monoxide gas dangers associated with operating a gasoline engine indoors, the positive displacement pump relies on a relief valve to open in order to divert extra compound back into the supply hopper via a bypass line if excess pressures develop. As positive displacement pumps have the capacity to generate tremendous pressures, it is unwise to rely on a mechanical valve, which is in constant contact with a thick cement-like paste, to open in order to prevent casualties.  
           [0008]    U.S. Pat. No. 4,080,240 issued Mar. 21, 1978 to Dysart, relates to a similar taping tool with a different pump. Dysart relates to a pneumatic pump having two tanks containing compound and floating pistons resting on the surface of the compound. A compressor supplies high pressure air to the top of the tanks, above the pistons. This places downward pressure on the pistons and pushes the compound through a supply line to the applicator. Though this may appear to be safer than using an internal combustion engine indoors, there are possible dangers associated with high pressure air. For instance, in order to refill the containers, the pistons usually have to be removed. As it is generally difficult to remove a sealed piston from a cylinder, Dysart uses a high pressure line from the compressor to the bottom of the cylinders. Valves are used to align the high pressure air through these lines in order to blow the cylinders to the top of the tanks for easier removal. There are obvious potential dangers inherent in this system. Not only is valve alignment crucial to operation in either mode, it is dangerous to use high pressure air to deliver a potential projectile to an operator.  
           [0009]    A popular system used today is a commercially available taping tool known as a “Bazooka”. Variations of this tool are available from a number of manufacturers. These tools use a hollow, telescoping, cylindrical handle with an actuator and a piston. The handle is filled with compound and the operator pushes on the actuator section of the handle to push the compound to the head of the tool where the taping mechanism is affixed. The taping mechanism receives the compound and applies it to the wall-side of the tape as the tape is being applied to the joint.  
           [0010]    A tool known as a “finish box” is commonly used to apply the second and third layers of compound after the first has dried. A similar cylindrical handle with a piston is used in conjunction with a box-type head. The compound in the handle is either pushed through the cylinder manually or is forced through by compressed air pushing on a piston. The compound is delivered to a hollow, box-shaped head. The back wall of the head is attached such that it can slide into the head like a rectangular piston. This wall is also attached to the handle so that the operator can apply force to the sliding wall by pushing on the handle. The opposing wall of the head has a slot through which a layer of the compounded passes and a scraper blade trailing the slot which applies the compound to the wall with uniform thickness. In operation, the piston in the handle presses on the compound stored in the handle, thereby keeping the box head full of compound. The operator, pushing on the handle puts pressure on the rear, piston-like wall of the box, squeezing the compound through the slot which is then smoothly applied to the wall as it passes under the blade.  
           [0011]    Though this method of application is effective, it is laborious and time-consuming. The operator must maintain considerable force on the handle to keep a steady flow of compound exiting the box. Furthermore, having the supply of compound stored in the handle of the tool makes the tool heavy. Finally, the supply of compound in the handle is only enough to apply compound to two or three joints. Once the handle is empty, the operator has to refill the tool by pumping compound into the handle. The amount of time the operator spends refilling the applicator can become significant.  
           [0012]    There have been few attempts at improving the steps of the drywall process which occur after the first layer of compound and tape have been applied. Most attempts have tried to combine all of the steps into one applicator. An example is U.S. Pat. No. 5,545,287 issued Aug. 13, 1996 to Carlson, which relates generally to a device to be attached to a Bazooka that redirects the excess compound, which gets squeezed out the sides of the tape, onto the outside surface of the tape to fill in the remaining crack.  
           [0013]    Another example is U.S. Pat. No. 5,013,389 issued May 7, 1991 to Retti which relates generally to a device that attempts to accomplish all steps at once. The device uses multiple compound supply lines from a backpack tank worn by the operator to apply the various coats of the compound to either side of the tape. In order to overcome the problems with drying, Retti suggests a formula for a quick drying compound to be used. However, even a quick drying compound generally cannot dry within the fraction of a second between its application and the application of the next layer.  
           [0014]    These and other attempts to combine all of the above steps into one typically fail for lack of sufficient drying time. This is evidenced by the standard practice in the industry of waiting at least one day between applications. Two days are preferred in humid climates. Additionally, these tools require that the same compound consistency be used for all of the applied layers.  
           [0015]    There is a need for a tool which is designed to apply compound of any desired consistency to the outer side of tape, which has already been applied to a joint using a Bazooka or similar device, and has an ample supply of compound which is delivered from a hopper to the wall without requiring excessive lifting, pushing, or other physical exertion by the operator.  
         BRIEF SUMMARY OF THE INVENTION  
         [0016]    Advantageously, this invention generally provides a tool for applying compound over a layer of compound and tape which has already been applied to a wallboard joint and allowed to dry.  
           [0017]    It is another characteristic of this invention to provide a tool light enough for applying wallboard compound without substantially tiring the operator.  
           [0018]    This invention is also beneficial in that it provides a tool for applying wallboard compound which generally does not require excess physical exertion by the operator in order to exude the compound from the tool.  
           [0019]    It is another advantage that the invention generally provides a tool for applying wallboard compound which receives a substantially continuous supply of compound from a hopper with an electrically-powered pump.  
           [0020]    It is also a characteristic that the invention provides a system for applying wallboard compound which is generally safe to operate under normal operating conditions and practices.  
           [0021]    The instant invention comprises an applicator for drywall compound having a hopper with a supply of compound which is pumped to an applicator head designed to allow application of the compound without requiring the operator to exert force on the tool to dispense the compound. The tool can be broadly described as having three parts: a pump, a handle, and an applicator head.  
           [0022]    The pump is preferably an electric, positive-displacement rotor/stator pump such as those commercially available from PETE&#39;S Equipment of Auburn, Wash., which are able to pump thick compounds. These pumps are designed for pumping coating compound to a dual supply spray nozzle which also receives compressed air. The compressed air mixes with the compound and blasts it onto the receiving surface. However, these pumps have been modified for use with the present invention by not attaching a spray nozzle with a compressed air line.  
           [0023]    The handle comprises a tube of sufficient diameter to concentrically house or form a section of the compound supply line and allow for a comfortable grip by the operator, preferably between ½and 2 inches, more preferably on the order of ¾to 1 inch in diameter. Additionally, the handle preferably includes an on/off switch and a flow regulator knob for remote control of the pumping speed.  
           [0024]    The on/off switch is preferably a button switch which is normally off such that whenever the operator releases the button, the pump shuts off. The switch may be electrically connected to the control box of the pump motor but is preferably a remote control switch.  
           [0025]    The flow regulator knob is preferably an analog dial knob which controls a variable resistor in the pump motor circuit such that any of a continuous range of pumping speeds may be selected. Like the on/off switch, the regulator knob may be electrically connected to the control box of the pump motor but is preferably a remote control knob.  
           [0026]    The applicator head comprises a thin, hollow box of a rigid material, preferably brushed aluminum, with a ball joint connecting the rear face of the box with the handle. The ball joint preferably has a passage extending through it to allow passage of the compound into the box. More preferably, the ball joint has a quick release mechanism to allow a variety of applicators to be attached to the handle for applications such as corners and the like.  
           [0027]    The front face of the applicator has a leading edge and a trailing edge. The leading edge has rollers to allow the applicator to easily slide along the wall during application. The rollers also space the leading edge away from the wall to allow room for the compound to exit the applicator.  
           [0028]    The compound is applied through a thin, slot-like exit opening proximate the trailing edge and extending substantially the width of the box. As the compound contacts the wall, it must pass under a blade which runs along and defines the trailing edge of the applicator. The blade presses the compound to the wall and leaves a smooth, flat surface on the resulting layer of compound.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    [0029]FIG. 1 is a perspective view of the present invention being used by an operator wherein the pumping system is shown as an elevational view which is not to scale and has a cutaway of the pump; and,  
         [0030]    [0030]FIG. 2 is a side elevational view taken generally along lines  2 - 2  of FIG. 1.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    With reference to the drawings, and first to FIG. 1, there is shown a tool  10  made up of a pump system  20 , a handle  40 , and an applicator head  80 . All three components of tool  10  are in fluid connection with each other so that drywall compound  12  communicates between the compound supply hopper  22  of pump  20  and head  80 .  
         [0032]    Pump system  20  is a commercially available pump system, preferably of the type manufactured by PETE&#39;S Equipment of Auburn, Wash. The pump system  20  comprises a hopper  22 , a positive displacement pump  24 , and an electric motor  26  operably connected to pump  24  via a drive shaft  28 . A control panel  30  provides a circuit  31  feeding electricity to pump motor  26  and has an on/off switch  32 , and a pump speed selector  34 . Pump  24  has an inlet  36  and an outlet  38 . Inlet  36  is fluidly connected to hopper  22 , which could be provided in various sizes. Positive displacement of the compound  12  from hopper  22  through pump  24  to its outlet  38  is accomplished by rotary pump auger  25  connected to motor drive shaft  28 . The rotary action of auger  25  ensures an even, continuous flow of compound  12  to applicator head  80 .  
         [0033]    Handle  40  generally comprises a supply line  42  and a hollow housing  44  with ends  46   a  and  46   b.  Supply line  42  is fluidly connected to outlet  38  of pump  24  and delivers compound to applicator head  80 . Supply line  42  runs through, and is supported by, elongated, hollow housing  44 , which attaches to applicator head  80  via a ball and socket joint  50 .  
         [0034]    In a preferred embodiment, supply line  42  comprises a continuous flexible hose, preferably rubber, more preferably braided plastic or nylon, which attaches to outlet  38  of pump  24 . Line  42  enters housing  44  at its end  46   a  and runs through housing  44  and attaches to a fluid passage  56 , shown in FIG. 2, which extends through ball and socket joint  50  and is defined by a neck  57 . A collar  48  attached to end  46   a  tightly surrounds supply line  42 , holding it in place.  
         [0035]    In a more preferred embodiment, (not shown in the Figures), a tube extends through housing  44  and is attached to fluid passage  56  of ball  52  of ball and socket joint  50 . The tube is also attached to collar  48 . Supply line  42  therefore runs from outlet  38  of pump  24  to end  46   a  of housing  44  where it attaches to the tube. Preferably, supply line  42  attaches to the tube via swivel coupling  68  in order to prevent supply line  42  from becoming twisted during use.  
         [0036]    In an even more preferred embodiment, shown in FIG. 2, hollow housing  44  is attached at end  46   a  to supply line  42  via swivel coupling  68  in such a way as to form part of the fluid path from the hopper  22  to the applicator head  80 . In this embodiment, hollow housing  44  fills with compound and directs the compound from the supply line  42  to neck  57  which is threadably connected to end  46   b  of handle  40 .  
         [0037]    In yet another embodiment (not shown in the Figures), supply line  42  comprises a continuous flexible hose which attaches to outlet  38  of pump  24 . Line  42  enters housing  44  at its end  46   a  and runs partially through housing  44 , exiting through an opening in housing  44  near end  46   b  and attaches to a fluid passage in rear face  84  of applicator head  80 . In this embodiment, it is unnecessary for ball and socket joint  50  to have a fluid passage. Again, a collar  48  attached to end  46   a  tightly surrounds supply line  42 , holding it in place. It is also envisioned that supply line  42  run directly to a fluid passage in rear face  84  of applicator head  80  without entering handle  40 . In this embodiment, supply line  42  may or may not be attached to handle  40 .  
         [0038]    It is preferred that handle  40  have a remote on/off switch  58  which remotely opens and closes circuit  31  of control panel  30 . Though it is envisioned that this remote switch  58  be electrically connected to control panel  30  via a wire that runs along supply line  42 , it is preferred that remote on/off switch  58  be an infrared transmitter which is operably communicating with an infrared receiver  60  on control panel  30  and integrated into circuit  31 . It is preferred that switch  58  be a normally off switch which requires an operator to keep the switch depressed in order to close circuit  31 .  
         [0039]    Similarly, it is preferred that handle  40  have a remote pump speed selector  62 , proximate switch  58 , which remotely controls the speed of pump motor  26  thereby allowing the operator to adjust the flow rate of compound  12  while the operator is using tool  10 . Again, it is preferred that remote pump speed selector  62  be an infrared transmitter which is operably communicating with receiver  60  to adjust the speed of motor  26 . However, it is also envisioned that selector  62  be electrically connected to circuit  31  via a wire running along supply line  42 .  
         [0040]    Applicator head  80  is essentially a thin, hollow box  82  of a rigid material, preferably aluminum, with a front face  86  and a rear face  84 . Inside box  82  is a reservoir  88  partially defined by front face  86  and rear face  84 . Socket  54  of ball and socket joint  50  is defined by rear face  84  of box  82  and is further defined by a support plate  53 . It is preferred that socket  54  have a quick release mechanism  55  such that head  80  can be quickly and easily removed from handle  40  for cleaning and so that differently shaped heads may be interchanged with head  80  for various applications such as applying compound to comers and tight places. Mechanism  55  may comprise a threaded shaft  55   a  having a rotary operating handle  55   b  at its outer end and received within a threaded sleeve  55   c.  Tightening threaded shaft within sleeve  55   c  by rotation of handle  55   b  engages the tip of shaft  55   c  within a mating seat  55   d  on ball support plate  53  to secure ball  52  to head  80 .  
         [0041]    Applicator head  80  is given stability relative to handle  40  with a biasing mechanism, preferably a band spring  70 . Band spring  70  is more preferably a curved, flat, enlongated metal band attached at one end to the handle and attached at the other end to the applicator head. Band spring  70  acts to substantially return head  80  to a normal position after head  80  is rotated around ball and socket joint  50 .  
         [0042]    Front face  86  of applicator  80  has a leading edge  90  and a trailing edge  92 . Leading edge  90  preferably has rollers  94  rotatably attached to box  82  and extending outwardly therefrom to allow applicator  80  to easily slide along a wall during application. Rollers  94  also act to space leading edge  90  away from wall  100  to allow room for compound  12  to exit applicator  80 .  
         [0043]    Trailing edge  92  is defined by a blade  96  which protrudes outwardly and extends across front face  86 . Front face  86  also defines a slot opening  98  leading into reservoir  88 .  
         [0044]    In operation, hopper  22  is filled with a drywall compound  12  of a desired consistency. The operator then ensures on/off switch  32  is turned on and picks up handle  40  of tool  10 . The operator elevates applicator head  80  using handle  40  such that trailing edge  92  of head  80  is at the top of a joint to which compound  12  is to be applied.  
         [0045]    The operator then depresses remote on/off switch  58  on handle  40 . An infrared signal  64  is sent by switch  58  to infrared receiver  60  on control panel  30 , closing circuit  31 , thereby providing electricity to actuate motor  26 .  
         [0046]    Motor  26  rotates, turning pump auger  25  of pump  24  via drive shaft  28 . Pump  24  draws compound  12  through inlet  36  and pushes compound  12  out outlet  38  and into supply line  42 . Compound  12  follows supply line  42  to swivel coupling  68 . Compound  12  travels through hollow housing  44  of handle  40  to ball and socket joint  50 . Compound  12  is pumped through fluid passage  56  of joint  50  and into reservoir  88  of head  80 . Pump  24  quickly fills reservoir  88  and compound  12  is pushed through slot opening  98  of front face  86 , thereby contacting wall  100 .  
         [0047]    The operator then runs applicator  80  down wall  100  such that compound  12  passes under and is spread evenly by blade  96  against wall  100 . At this point the operator may want to adjust the amount of compound  12  being applied to wall  100 . To do so, the operator adjusts remote pump speed selector  62  which sends an infrared signal  64  to infrared receiver  60  which increases or decreases the voltage to motor  26  through a known device, such as a variable resistor, in circuit  31 .  
         [0048]    The present invention having thus been described, other modifications, alterations or substitutions may present themselves to those skilled in the art, all of which are within the spirit and scope of the present invention. It is therefore intended that the present invention be limited in scope only by the claims attached below.

Summary:
An apparatus for the application of drywall compound onto a taped drywall joint. The applicator uses an electrically powered, positive displacement pump which supplies a continuous flow of compound from a hopper to the applicator head via a fluid path. Remote controls on the handle of the applicator allow the operator to turn the pump on or off and also to select the optimal pump speed. The hopper is large enough so that an operator can apply compound to a number of joints before having to stop and refill the apparatus with compound.