RELATED APPLICATIONS 
     This application is a continuation-in-part of copending application Ser. No. 09/255,954 filed Feb. 23, 1999 now pending. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the removal of surface portions of dead or living tissue, sometimes termed microdermal abrasion and more specifically relates to an improved apparatus and process for the abrasion of surface portions of human tissue by the controlled flow of abrasive particles. 
     BACKGROUND OF THE INVENTION 
     Apparatus for the microdermal abrasion of the surface of tissue (living or dead) is well known. In these processes, a stream of abrasive particles such as sand is applied to the surface of the tissue or skin through an opening in a hand held tool (termed a handpiece) which is sealed against the skin. The tool and the particle stream is controllably scanned over the area to be abraded. The abrading particles and the removed tissue are then collected by vacuum in the handpiece and are passed through and collected by a filter to prevent the escape of the abraded tissue and sand into the vacuum pump and ambient atmosphere. 
     The handpiece has taken many forms in the past but usually provides a first passage for conducting abrasive particles from a reservoir to the area to be treated and a second parallel channel for conducting the particles and abraded skin away from the area treated and into a disposal vessel. 
     A typical prior art apparatus is shown in U.S. Pat. No. 5,037,432. The hand-held head of this patent is a long tubular structure having an off-center hole which permits the application of an abrasive particle jet to an area to be treated, and the subsequent removal of the particles and abraded skin. The off-center outlet hole is arranged to be on the same axis as the input abrasive particle jet which then reaches the area to be treated at a 45° angle. The outlet jet channel facing the opening has a nozzle restriction. The abraded skin and used particles are then withdrawn through a parallel return vacuum channel which is connected to a vacuum pump through a filter. 
     The above described hand held tool has a number of drawbacks. Thus, because it is relatively long (longer than about 5 inches) it is difficult to manipulate easily over a curved surface area to be abraded, for example, the surface of a human face. Further, the vacuum pressure within the hand tool is not easily changed by the operator when a weaker or more forceful jet of abrasive particles is desired at particular locations on the surface area being abraded. Further, the handpiece is subject to clogging at the restricted outlet nozzle, requiring the operator frequently to stop the treatment and clear the nozzle. 
     The above described handpiece is provided with a removable and disposable tip or bell section which contains the output hole. Thus, the tip can be removed and disposed of and replaced by a new tip after the treatment of each individual. The tip is normally press-fit onto the body of the handpiece and is tightly sealed thereto to prevent accidental escape of abraded skin and loss of vacuum. Therefore, the tip is very difficult to remove and replace. 
     It would be very desirable to provide a handpiece for abrasion of living tissue which avoids the above problems. 
     The abrasive particles and tissue which are removed in prior art devices are collected in a filter placed between the handpiece outlet channel and the vacuum pump. Such a filtration system is shown in U.S. Pat. Nos. 5,100,412 and 5,207,234 in the name of Rosso. The filter shown therein is an inverted cup at the outlet opening of a waste receiving chamber. The outlet opening is connected to the vacuum pump line and contaminated particles and debris flow from the cup exterior toward its interior thus building up on the cup exterior. This filter tends to become quickly clogged and becomes more and more impervious to the flow of air therethrough. Consequently, the system must be frequently turned off and the filter must be cleaned sometimes during and frequently after each use. 
     It would be very desirable to provide a filtration system which does not require frequent cleaning or emptying. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention a novel apparatus and process is provided which avoids the problems with prior art devices as stated above, and which provides added improved operation as well. 
     In accordance with a first feature of the invention, a novel filtration system is provided in which a large area cylindrical filter is disposed coaxially within a large volume container with an annular air outlet chamber defined between the cylindrical filter and the container. The annular outlet channel is connected to the vacuum pump of the system. 
     In operation, abrasion particles and skin are conveyed from the outlet channel of the hand held instrument to the interior of the cylindrical filter and are then entrapped within the large surface area interior of the filter. Filtered air then passes through the filter and into the annular low pressure area surrounding the filter and then into the vacuum pump. Because of the large area of the filter, it need not be replaced frequently and will commonly not require replacement until after about 50 uses (or 50 patient treatments). 
     A back-up emergency filter is coupled between the annular filter volume and vacuum pump to prevent the flow of abrasion particles to the pump in the event of a failure or accidental bypass of the main filter. 
     The novel cylindrical filter may be mounted between top and bottom flexible disks or flanges which have a larger diameter than the cylindrical filter to permit the easy and rapid replacement of a new filter assembly after a given time or number of operations. The used sand and removed tissue will be trapped within the filter and between the gaskets during this operation. Note that the gaskets may have connection nipples or simple connection openings for input and output conduits which enter the filter interior and annular chamber respectively. 
     As an alternative to the above cylindrical filter which is rigid, it is also possible to employ a removable paper bag type of filter which is clamped around the inlet conduit, providing similar benefits to those described above at lower cost. 
     A novel hand-held head or handpiece is also provided with a novel modified design from that of the prior art. 
     As a first feature of the novel handpiece, a screw-on tip of clear plastic is used which makes threaded engagement with the body of the tool. Thus the tip is easily removed from and replaced on the handpiece body after a single use. The tip is hemispherical in shape and has a sand-blast opening on its central axis. Sand input and output channels in the body extend parallel to the central axis and the axis of the tip and are displaced toward opposite sides of the central axis. Thus, the opening in the tip is on the central axis of the tool body but is displaced from the input and output channels. The sand will then sweep past the opening (and skin adjacent thereto) in its travel within the tip to abrade the skin. Moreover, the diameter of the sand input channel to the tip interior is relatively smaller than the output vacuum channel (for example, {fraction (1/16)} inch versus ⅛ inch respectively). This enables the quicker and easier withdrawal of used sand and skin particles from the interior vacuum chamber formed between the end of the body and the tip and aids in prevention of leakage of sand from the skin area being treated if the tip is removed from the area having treated. Note that in use, the hole in the tip is sealed against the skin area to preserve the vacuum and sand flow within the tip. 
     As a further feature of the novel handpiece, the entire body is shortened to a length less than about 3 inches. This makes it much easier to manipulate the tip over the surface being treated. 
     As a still further feature of the new handpiece, a small opening is provided in the side of the tip which can be easily covered by the finger of the operator. Thus, the vacuum pressure within the tip can be immediately changed by the operator without having to reach for the main pressure control at the main housing to which the handpiece is attached. It should be noted that this opening can also be placed in the handpiece body and can communicate with either the inlet or the outlet channel and still accomplish the stated function. 
     As a still further feature of the handpiece, the end of the channel carrying sand to the tip is not restricted by a nozzle, but is of the same diameter as the input channel or even flared out to a larger diameter to prevent clogging of the input channel. The flare may also be used at the end of the output channel adjacent the tip. It has been found that the elimination of the nozzle does not adversely affect the operation of the system. 
     As a further feature of the present invention, a novel large volume particle supply reservoir is provided in which, for example, a five pound supply of an abrasive, such as, irregularly shaped aluminum oxide particles of a maximum dimension less than about 120 microns and with sharp irregular edges is stored. A nipple at the bottom of the container is connected to an outlet tube, which in turn is coupled to a particle flow control valve which permits air flow into the conduit to carry the sand around the system with a controlled mass flow. The container can be easily replaced or replenished. 
     In accordance with an improvement of the present application, the screw-on tip has a central elongated barrier or separator extending along the axis of the tip to its opening to define sand input and outlet chambers along the length of the tip to increase the volume of sand which reaches and abrades the area being treated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S) 
     FIG. 1 is a schematic diagram of the novel system of the invention. 
     FIG. 2 is a schematic cross-sectional view of the novel filter structure of FIG.  1 . 
     FIG. 3 is a top view of FIG.  2 . 
     FIG. 4 is a cross-sectional view of a prior art handpiece. 
     FIG. 5 is an end view of the handpiece of FIG. 4 as seen from line  5 — 5  in FIG.  4 . 
     FIG. 6 is a sectional view of the handpiece of FIG. 4 as seen from line  6 — 6  in FIG.  4 . 
     FIG. 7 is a cross-sectional view of a novel handpiece containing many of the features of the present invention. 
     FIG. 8 is a sectional view of the handpiece of FIG. 7 as seen from line  8 — 8  in FIG.  7 . 
     FIG. 9 is an end view of FIG. 7 as seen from the line  9 — 9  in FIG.  7 . 
     FIG. 10 schematically shows a novel handpiece which contains a sand velocity control aperture in the tool tip. 
     FIG. 11 schematically shows a handpiece which contains a sand input channel which extends into the tip interior. 
     FIG. 12 schematically shows flares at the ends of the input and output channels in the handpiece to prevent clogging. 
     FIG. 13 is a perspective view of a preferred embodiment of the tip portion 32/90/110 of the preceding figures. 
     FIG. 14 is a side view of the tip portion of FIG.  13 . 
     FIG. 15 is a cross-sectional view of FIG. 14 taken across section line  15 — 15  in FIG.  14 . 
     FIG. 16 is an end view of FIG.  14 . 
     FIG. 17 is a perspective view of a preferred handpiece for the replaceable tip of FIGS. 13 to  16 . 
     FIG. 18 is a side view of the handpiece of FIG.  17 . 
     FIG. 19 is an end view of the handpiece of FIG.  18 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIG. 1, there is shown a supply container  20 , which can, for example, contain about 5 pounds of a suitable abrasive sand  21 , for example, aluminum oxide particles with very sharp edges and a non-critical maximum dimension of about 120 microns. An output particle supply line  22  which may be a plastic conduit of about ¼ inch O.D. is connected to a suitable connection nipple (not shown) on the bottom of can  20 . A particle flow control valve  23  is provided to control the air flow from the atmosphere into supply line  22  to move abrasive particles in the input conduit  30  of handpiece  31 ; moving sand faster when the valve is closed. 
     Handpiece  31  further includes a hemispherical shaped tip  32  which is removably connected to body  33 . The body  33  contains input channel  30  and output channel  34  which will be later described in detail. Channel  30  conventionally has a diameter of about ⅛ inch and channel  34  is conventionally about 1 inch in diameter. 
     Removable tip  32  is a hollow hemispheric structure having a diameter of about 1 inch, a length of about 1½ inch, and has a central aperture  35  on its axis. Typically, aperture  35  has a non-critical diameter of ¼ to ⅜ inch. In use, the aperture  35  is sealed against the surface to be treated and particles from conduit  30  pass by and abrade the skin exposed through aperture  35 . The used sand particles and abraded tissue are then removed through channel  34  and are directed to a novel filter  40 . 
     Filter  40  consists of a cylindrical metal container  41  (FIGS. 2 and 3) which may have a 6 inch diameter and contains a cylindrical pleated filter  42  which may be over-wrapped with a flat filter paper. A standard 3 pound coffee container has been used for can  41 . The filters are sized to ensure trapping of the 120 micron sized particles and the abraded tissue. The cylindrical filter  42  is fixed as by cementing at top and bottom to rubber flange disks  43  and  44  respectively best shown in FIGS. 2 and 3. These may be formed of a silicone rubber about ¼ inch thick. The top disk  43  has openings  45  and  46  which receive air outlet conduit  47  and an air-plus-particle inlet conduit  48 . Conduits  47  and  48  are fused or otherwise sealably connected to openings in disk  43 . Conduits  47  and  48  may be flexible plastic tubes with O.D.&#39;s of ⅜ and ¼ inch respectively. 
     The disks  43  and  44  are press-fitted into the inner diameter of container  41  and can be glued to the container interior. They form a sealed annular chamber  50  which surrounds filter  42  and communicates with conduit  47 . 
     While filter  42  is shown as a rigid filter fixed between rubber disks  43  and  44 , it can be replaced by a simple filter bag suitably clamped to input conduit  48 . 
     In operation, waste particles and tissue flow from the handpiece and into filter  42  and are collected therein. Filtered air passes through the filter  42 , into the low pressure annular volume  50  and out through conduit  47  toward vacuum pump  60 . This filtered air also flows through an secondary back-up filter  55  which prevents flow of abrasive particles into vacuum pump  60  (a ⅓ horse power pump) if filter  40  is accidentally bypassed. A ⅜ inch conduit  61  connects filter  55  to pump  60 . 
     A pressure gauge  62  monitors the pressure at the input to pump  60  (reading from 0 to 100 KPA vacuum). The exhaust air from pump  60  is exhausted to the exterior atmosphere through muffler  65 . A valve  66  controls the vacuum in line  61 . 
     It will be noted that valves  23  and  66  along with selected other elements of the system may be housed in a control box (not shown). The filters  40  and  55  and reservoir  20  are suitably mounted for greatest convenience. The handpiece  31  is connected to the particle supply by the elongated and flexible supply line  22 , and to the filter  40  by a similar elongated flexible line  70 . Lines  22  and  70  ensure that an operator can manipulate the handpiece  31  as necessary for its use. 
     FIG. 4,  5  and  6  show a prior art type of handpiece  80  which can be used with the novel filter and system of FIGS. 1,  2  and  3 . The handpiece  80  consists of a solid plastic body  81  having a large diameter channel  82  which is coaxial with the axis of body  81  and a smaller diameter outflow channel  83 . A restrictive nozzle is commonly placed at the end of channel  82 . Body  80  has a length of about 5 inches and a reduced diameter end section  84 , about 1 inch long. An O-ring gasket  85  is fixed around the diameter of section  84 , at a point removed from the shoulder  86 . A rigid transparent plastic tip is fitted over gasket  85  to form a chamber  91  leading to a central hole or aperture  92 . 
     In use, the hole  92  is pressed (or sealed) against the skin area to be treated. Abrading particles flowing along channel  82  and in line and coaxial with hole  92  impinge on the skin exposed through hole  92  and the used particles and abraded skin are reflected from the skin and are withdrawn through channel  83 . 
     FIGS. 7,  8  and  9  show a handpiece in accordance with several of the features of the invention. A body  100  of rigid plastic, for example Teflon, has a central axis  101  (FIGS. 8 and 9) and off-center inlet and outlet channels  102  and  103  respectively. Note that these channels are reversed in relative sizes from those of FIG.  4  and are ⅛ inch and ¼ inch respectively. 
     The body  100  has a very short length, less than about 3 inch and has a reduced diameter threaded end section  105 . A sealing O-ring  106  is placed against shoulder  107  between the large diameter and small diameter sections of body  100 . A transparent plastic tip  110  is then threaded onto the threaded portion of body extension  105  and compresses O-ring  106  against shoulder  107  to create a seal. The tip  110  forms a vacuum chamber  111  interior spaced from the end of body  100  and has a central aperture  112  (FIGS. 7 and 9) which is about {fraction (5/16)} inch in diameter and is laterally off-set from the axis of channels  102  and  103 . 
     The novel shortened length of handpiece  100  makes it easier for an operator to manipulate the opening  112  over the skin of a patient. Further, the large output diameter of channel  103  improves the operation of the device and makes it easier to quickly evacuate particles from chamber  111  to ensure against loss of particles to atmosphere if the handpiece is removed from the skin of a subject, breaking the vacuum in chamber  111 . 
     As a further advantage over prior handpieces, the tip  110  can be easily detached and replaced by a new tip after use on a given patient by simply unscrewing the tip and screwing on a new one for the next patient. In the prior art structure of FIGS. 4,  5  and  6 , the press fit of tip  90  over seal  85  formed a tight fit making it difficult to remove the used tip and replace it with a new one. 
     FIGS. 10,  11  and  12  schematically show several novel features for handpiece  31  of FIG. 1 which can be used with the handpieces of FIGS. 4 to  9 . In FIG. 10, the tip  32  is shown with a small control opening  119  therein which can be easily closed by the operator&#39;s finger to increase the vacuum to produce a more forceful stream of abrasive particles against the skin being abraded when such added force is required. This can be done directly at the handpiece, without requiring the operator to reach for the equipment housing valve  66  in FIG.  1 . 
     It should be further noted that the same result can be obtained by placing the control opening in the body of the handpiece and in communication with either the interior of the tip or the input channel or the output channel. 
     FIG. 11 shows a modification in which a tube  120  is added to channel  30  in body  33  to extend the point of exit of new abrading particles closer to opening  35  and the skin being treated. 
     FIG. 12 shows a variation in which the ends of channels  30  and  34  are flared outward at diffuser regions  122  and  123  respectively. It has been found that these diffuser flares tend to prevent clogging of the channels  30  and  34  at their ends entering vacuum chamber  130  formed by tip  31 . Note that in prior art handpieces a restriction nozzle has been used at the outlet of channel  30  which has been found to aggravate clogging of the handpiece after a short time. 
     FIGS. 13 to  16  show a preferred embodiment of a novel disposable plastic tip  200  which contains a central dividing barrier to define air/sand inlet and outlet chambers and FIGS. 17 to  19  describe a preferred handpiece  300  for holding the tip  200 . 
     Referring first to FIGS. 13 to  16 , the tip  200  is of clear molded plastic and comprises an outer cylindrical body  201  which extends from a knurled base  202  and having an opening  203  which is coaxial with the central axis of the tip  200 . A thread  204  is formed at the interior end of base  202 . In accordance with an important feature of the invention, a central barrier  210  extends from the end of chamber  211  (FIG. 15) which receives the handpiece to the apertured end  203  of the tip  200 . The end of barrier  210  has a cut-out  212  (FIG. 15) which defines a connection channel adjacent the end of the tip between the two air/sand chambers  213 ,  214  formed on opposite sides of the barrier  210  (FIG.  14 ). This novel barrier  210  has been found to substantially increase the volume of airborne sand to the tissue being treated, and the volume being withdrawn therefrom, to and from the handpiece. 
     FIGS. 17 to  18  show the preferred handpiece body  300  for the tip  200 . Handpiece body  300  is a unitary molded body and has an enlarged diameter base  301  from which a smaller diameter integral body portion  302  extends. The base of body portion  302  carries threads  303  which thread into the threads  204  of tip  200 , with body portion  302  entering and being fixed within volume  211  (FIG. 15) of tip  200 . A gasket can be compressed between the end of tip  200  and the shoulder  304  on base  301  when the tip  200  is threadably fixed to handpiece  300 . As in the prior embodiments, a small diameter inlet channel nozzle  310  (0.89 mm diameter) and a large diameter outlet channel nozzle  311  (1.9 mm diameter) are provided. These lead to connection nipples  312  and  313  respectively. Note that when the tip  200  is screwed onto hand piece  300 , the barrier  210  should bisect the openings of nozzles  310  and  311 . 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.
A novel handpiece and system for abrasion of skin is disclosed. A short handpiece with a threadably removable tip is used. The opening in the tip is centered on the handpiece axis and a small diameter particle inlet channel and larger diameter outlet channel are both offset from the handpiece axis. A central blade or barrier within the tip divides the tip into two volumes which each communicate with the opening and respective ones of the inlet and outlet passages. A vacuum control opening is formed in the tip for easy control by the operator. Abrasive particles and removed tissue are applied to the interior of a cylindrical filter supported within a supporting container. The annular area between the container and this filter is connected through a secondary emergency filter to a vacuum pump. The cylindrical filter can be a flexible filter bag. A large source of abrasive particles is coupled to the handpiece inlet and the filter is coupled to the handpiece outlet.