Abstract:
A conveyor system able to safety convey a workpiece having a thickness of less than 100 μm and easily position the workpiece, provided with a plate-shaped member provided movably and swivelably and a moving and swiveling means moving and swiveling the plate-shaped member, the plate-shaped member being provided together with a lifting means for uniformly lifting in its entirety a workpiece carried at the carrying location and a holding means for holding a workpiece lifted by the lifting means by chucking its entirety on a workpiece chucking surface of the plate-shaped member, and a plurality of Verneuil nozzles serving as the lifting means and a plurality of vacuum chucking nozzles serving as the holding means being formed in the workpiece chucking surface near an outer periphery of the plate-shaped member along the outer periphery.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a conveyor system, more particularly relates to a conveyor system for conveying a wafer or other thin workpiece having a thickness of not more than 100 μm from a carrying location to another location. 
   2. Description of the Related Art 
   When conveying a wafer or other thin workpiece from a carrying location to another location, use can be made of a conveyor system as disclosed in for example U.S. Pat. No. 4,566,726, in particular  FIG. 2A  and  FIG. 2B . 
   The conveyor system disclosed in this is shown in  FIGS. 9A and 9B . The conveyor system is a conveyor system for conveying a wafer or other workpiece  100  provided with a plate-shaped member  102  at the center of one surface  102   a  where a Bernoulli nozzle  104  is formed. This Bernoulli nozzle  104  has a baffle plate  104   a  at its nozzle part and a pressurized air blowing port  104   b  formed in a crescent shape. Therefore, the pressurized air from the Bernoulli nozzle  104  is strongly blown out in the direction of a stopper  106  provided at the outer periphery of the plate-shaped member  102  as shown in  FIG. 9B . According to this Bernoulli nozzle  104 , the suction force based on the Bernoulli principle, that is, the lift, acts on the workpiece  100  and the workpiece  100  is lifted without abutting against the surface  102   a  of the plate-shaped member  102 . However, the Bernoulli nozzle  104  blows the air out strongly in the direction of the stopper  106 , so the workpiece  100  lifted by suction by the Bernoulli nozzle  104  moves in the direction of the stopper  106  and the side surface of the workpiece  100  contacts the stopper  106 . 
   The surface  102   a  of the plate-shaped member  102  is provided with three vacuum chucking nozzles  108 , 108 , and  108  near the outer periphery of the plate-shaped member  102  along the outer periphery. These vacuum chucking nozzles  108 , 108 , and  108 , as shown in  FIG. 9A , are connected with a vacuum pump or other vacuum generator (not shown) through a tube  112  and conduit  110  formed in the plate-shaped member  102 . The front ends of the vacuum chucking nozzles  108 , 108 , and  108 , as shown in  FIG. 9A , are provided projecting out from the surface  102   a  of the plate-shaped member  102 . Therefore, the workpiece  100  lifted by the Bernoulli nozzle  104  and abutting against the stopper  106  is chucked to the front ends of the vacuum chucking nozzles  108 , 108 , and  108  without abutting against the surface  102   a  of the plate-shaped member  102 . 
   According to the conveyor system shown in  FIGS. 9A and 9B , the workpiece  100  lifted in a noncontact state with the surface  102   a  of the plate-shaped member  102  by the Bernoulli nozzle  104  is chucked near the periphery to the front ends of the vacuum chucking nozzles  108 , 108 , and  108 , so it is possible to convey the workpiece  100  in a substantially noncontact state with the plate-shaped member  102 . Further, the workpiece  100  chucked to the front ends of the vacuum chucking nozzles  108 , 108 , and  108  are in a fixed state with the plate-shaped member  102 ,  50  by swiveling the plate-shaped member  102 , it is possible to easily position the work  100 . In recent years, however, the wafers used for semiconductor chips have been made thinner. Wafers of thicknesses of less than 100 μm are being provided to the market. If conveying such thin wafers using the conveyor system shown in  FIGS. 9A and 98 , it is learned that the wafers will easily fracture or other problems will occur during conveyance. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a conveyor system enabling safe conveyance and easy positioning of a workpiece without damaging a thin workpiece of a thickness of less than 100 μm. 
   The inventors studied how to achieve this object and as a result discovered that by using a movable plate-shaped member formed with a plurality of Bernoulli nozzles and a plurality of vacuum chucking nozzles alternately at the workpiece chucking surface near the outer periphery of the plate-shaped member along the outer periphery, it is possible to safely convey a thin workpiece having a thickness of less than 100 μm and easily position the workpiece without damaging it and thereby perfected the present invention. 
   According to a first aspect of the present invention, there is provided a conveyor system for conveying a wafer or other thin workpiece having a thickness of not more than 100 μm from a carrying location to another location, wherein the conveyor system is provided with a plate-shaped member provided movably and swivelably and a moving and swiveling means moving and swiveling the plate-shaped member, the plate-shaped member is provided together with a lifting means for uniformly lifting in its entirety a workpiece carried at the carrying location and a holding means for holding a workpiece lifted by the lifting means by uniformly chucking its entirety on a workpiece chucking surface of the plate-shaped member, and a plurality of Bernoulli nozzles serving as the lifting means are formed in the workpiece chucking surface near an outer periphery of the plate-shaped member along the outer periphery. 
   By comprising the holding means by a plurality of vacuum chucking nozzles and by alternately forming the plurality of Bernoulli nozzles forming the lifting means and the plurality of vacuum chucking nozzles on the workpiece chucking surface near the outer periphery of the plate-shaped member along the outer periphery, it is possible to simplify the structure of the plate-shaped member. By using a porous member for a chucking pad of a vacuum chucking nozzle, it is possible to eliminate the danger of making chucking marks on the workpiece. Further, by comprising the holding means by at least one electrostatic chucking plate and providing the electrostatic chucking plate at the workpiece chucking surface of the plate-shaped member, it is possible to further simplify the structure of the plate-shaped member for an electrostatically chuckable workpiece. In the present invention, since a lifting means and a holding means are both used, by providing a controller for controlling a drive timing of the two, it is possible to accurately drive and stop the two means at predetermined timings and possible to reliably convey the workpieces. Further, by providing a detachment prevention member for preventing part of the workpiece lifted by the plurality of Bernoulli nozzles from being detached from the plate-shaped member at the outer periphery of the plate-shaped member, it is possible to reliably position the workpiece at one surface of the plate-shaped member. By biasing the detachment prevention member by an elastic member in a direction where its front end projects out from the workpiece chucking surface of the plate-shaped member, it is possible to easily change the length of the detachment prevention member projecting out from the workpiece chucking surface of the plate-shaped member by adjusting the biasing force of the elastic member etc. Further, by providing a switching station provided with a plurality of pressurized air blowing nozzles blowing pressurized air from below the workpiece so as to prevent the workpiece from dropping off when switching a workpiece lifted by the lifting means comprised of a plurality of Bernoulli nozzles to holding by the holding means, it is possible to reliably prevent a situation where the workpiece drops off and is damaged when switching from the lifting means to the holding means. 
   According to the present invention, it is possible to equally lift a workpiece having a thickness of less than 100 μm carried at the carrying location without the workpiece as a whole abutting against the workpiece chucking surface of the plate-shaped member by a plurality of Bernoulli nozzles formed in the workpiece chucking surface near the outer periphery of the plate-shaped member along the outer periphery. Further, the lifted workpiece is held by chucking to the workpiece chucking surface of the plate-shaped member equally as a whole by a holding means provided at the plate-shaped member. In this way, it is possible to easily recognize the position of a workpiece chucked to the workpiece chucking surface of the plate-shaped member and possible to position the workpiece by moving and/or swiveling the plate-shaped member by a moving and swiveling means based on this recognition. 
   According to a second aspect of the present invention, there is provided a conveyance method using any of the above conveyor systems including the steps of moving the plate-shaped member to a first position on which a workpiece is placed, lowering the plate-shaped member down to the workpiece, starting the blowing of air from the Bernoulli nozzles, chucking the workpiece by the Bernoulli nozzles, lifting up the plate-shaped member, starting suction by vacuum chucking nozzles to chuck the workpiece by both of the vacuum chucking nozzles and Bernoulli nozzles, stopping the blowing of air from the Bernoulli nozzles and chucking the workpiece by only the vacuum chucking nozzles, and moving the plate-shaped member to a second position for processing of the next workpiece. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, wherein: 
       FIG. 1  is a schematic view for explaining an example of a conveyor system according to the present invention; 
       FIGS. 2A and 2B  are a front view and a bottom view for explaining a plate-shaped member used in  FIG. 1 ;  FIG. 3  is a partial sectional view for explaining a Bernoulli nozzle provided at the plate-shaped member of  FIGS. 2A and 2B ; 
       FIG. 4  is a partial sectional view for explaining a vacuum chucking nozzle provided at the plate-shaped member of  FIGS. 2A and 2B ; 
       FIG. 5  is a front view for explaining the structure of a switching station shown in  FIG. 1 ; 
       FIG. 6  is a partial front view for explaining another example of a detachment prevention member; 
       FIG. 7  is a bottom view for explaining another example of the plate-shaped member; 
       FIG. 8  is a flow chart of an example of a process for conveying a wafer using the conveyor system of  FIG. 1 ; and 
       FIGS. 9A and 9B  are a partial sectional front view and partial bottom view for explaining a plate-shaped member of the related art. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described in detail below while referring to the attached figures. 
     FIG. 1  shows a conveyor system taking out from a cassette  12  placed at a carrying position of a base  10  a silicon wafer  14  having a thickness of less than 100 μm as one of a plurality of workpieces stacked via interlayer paper (hereinafter referred to simply as a “wafer  14 ” in some cases) in the cassette  12 , positioning it, and adhering it to an adhesive ring  16 . In the conveyor system shown in  FIG. 1 , a multiarticulated robot  18  is placed on the base  10 . Around this, a position measurement area  22  on which a camera  22   a  is provided, an adhesion area  24  for adhering a wafer  14  positioned by the tape adhered to the adhesive ring  16 , and rails  26 ,  26  for sending to the next step the adhesive ring  16  on which a wafer  14  is attached by the tape. 
   The front end head of the multiarticulated robot  18  has the plate-shaped member  20  attached swivelably to it. This plate-shaped member  20  takes out one wafer  14  among the plurality of wafers  14 ,  14  . . . stacked in the cassette  12 . The wafer  14  taken out by the plate-shaped member  20  is moved to the position measurement area  22  by movement of the plate-shaped member  20  by the multiarticulated robot  18 . In this position measurement area  22 , the position of the taken out wafer  14  is recognized. Next, the plate-shaped member  20  is moved on the adhesion area  24  by the multiarticulated robot  18 , the plate-shaped member  20  is swiveled to position the wafer  14  based on the positional data of the wafer  14  recognized by the position measurement area  22 , then the wafer  14  is placed on and adhered to the tape of the adhesive ring  16 . Next, the adhesive ring  16  comprised of the tape with the wafer  14  adhered to it is turned upside down, placed on the reels  26 ,  26 , and conveyed to the next step. In this conveyor system, the interlayer paper sandwiched between the wafers  14 ,  14  . . . in the cassette  12  is conveyed to a container  28  placed on the base  10  adjoining the cassette  12 . 
   The plate-shaped member  20  mounted to a shaft  19  at the front end of the multiarticulated robot  18  and taking out and conveying the wafer  14  from the cassette  12  is provided with both a lifting means for lifting a wafer stacked in the cassette  12  and a holding means for chucking and holding the wafer  14  lifted by the lifting means at the workpiece chucking surface of the plate-shaped member  20 . The plate-shaped member  20  is shown in  FIGS. 2A and 2B . This plate-shaped member  20  is formed with openings  30   a  of the plurality of Bernoulli nozzles  30 ,  30  . . . serving as the lifting means and chucks  32   a  of the plurality of vacuum chucking nozzles  32 ,  32  . . . serving as the holding means at the wafer chucking surface  20   a  near the outer periphery of the plate-shaped member along the outer periphery of the plate-shaped member  20 . 
   In this way, by forming the openings  30   a  of the Bernoulli nozzles  30 ,  30  . . . at the wafer chucking surface  20   a  near the outer periphery of the plate-shaped member  20 , it is possible to evenly lift up the entirety of the wafer  14  by the Bernoulli nozzles  30 ,  30  . . . Therefore, warping occurring at the wafer  14  lifted can be reduced as much as possible as in the case of lifting the wafer  14  by a Bernoulli nozzle  104  with an opening  104   b  formed at the center of the plate-shaped member  102  shown in  FIGS. 9A and 9B . Therefore, when driving the Bernoulli nozzles  30 ,  30  . . . to lift a thin wafer of a thickness of less than 100 μm from the cassette  12 , it is possible to prevent fracture etc. due to warping of the wafer  14 . 
   A Bernoulli nozzle  30 , as shown in  FIG. 3 , is formed with a tapered opening  30   a  at the wafer chucking surface  20   a  of the plate-shaped member  20 . A lift based on the so-called “Bernoulli principle” acts on the wafer  14 . That is, a conical air flow is blown out from the tapered opening  30   a  shown in  FIG. 3 . The outer peripheral air flow blown out along the inclined surface of the opening  30   a  in the conical air flow becomes higher in speed than the internal air flow blown out from the center of the opening  30   a . The internal air flow is pulled to the high speed outer peripheral air flow side, so the conical space (part directly before the opening  30   a ) becomes a negative pressure and the wafer  14  is lifted. On the other hand, if the wafer  14  is lifted up to block the air flow blown out along the inclined surface of the opening  30   a , the negative pressure occurring near the center of the conical air flow is eliminated and the lifted up wafer  14  is lowered. However, if the wafer  14  is lowered, the air flow blown out along the inclined surface of the opening  30   a  is reproduced, negative pressure is reproduced near the center of the conical air flow, and the wafer  14  is lifted up again. These two contradictory actions balance out, whereby the wafer  14  is lifted up to a predetermined height without abutting against the wafer chucking surface  20   a  of the plate-shaped member. The wafer  14  lifted up by the Bernoulli nozzles  30 ,  30  . . . is moved by the air flow along the wafer chucking surface  20   a  of the plate-shaped member  20  without being affixed to the wafer chucking surface  20   a . Therefore, the wafer  14  is kept from detaching from part of the wafer chucking surface  20   a  of the plate-shaped member  20  by providing plates  34 ,  34  . . . serving as detachment prevention members at the side wall surfaces of the plate-shaped member  20 . Further, according to the Bernoulli nozzles  30 ,  30  . . . , it is possible to also lift up the interlayer paper between the wafers  14  stacked in the cassette  12  and possible to convey it from the cassette  12  to the container  28 . 
   However, with just the Bernoulli nozzles  30 ,  30  . . . , the wafer  14  moves without being fixed to the wafer chucking surface  20   a  of the plate-shaped member  20 , so the position of the wafer  14  cannot be recognized at the position measurement area  22  and the wafer  14  cannot be positioned. Therefore, with the plate-shaped member  20  shown in  FIGS. 2A and 2B , the chucks  32   a  of the vacuum chucking nozzles  32 ,  32  . . . are opened at the wafer chucking surface  20   a  near the outer periphery of the plate-shaped member  20  along the outer periphery of the plate-shaped member  20 . Therefore, a wafer  14  lifted up by the Bernoulli nozzles  30 ,  30  . . . can be fixed to the wafer chucking surface  20   a  of the plate-shaped member  10  by the vacuum chucking nozzles  32 ,  32  . . . , the plate-shaped member  20  can be swiveled based on the positional data of the wafer  14  recognized by the position measurement area  22 , and the wafer  13  can be positioned. 
   The chuck  32   a  of the vacuum chucking nozzle  32  of the plate-shaped member shown in  FIGS. 2A and 2B  is given a porous member  32   b  serving as a chucking pad as shown in  FIG. 4 . By using this porous member  32   b  for the chucking pad, it is possible to chuck the wafer  14  without causing chucking marks. As this porous member  32   b , it is possible to use a porous member made for example of a ceramic. Further, the chuck  32   a  of the vacuum chucking nozzle  32  is formed in the wafer chucking surface  20   a  of the plate-shaped member  20 . The end surfaces of the porous member  32   b  are attached to the chuck  32   a  in the same plane as the wafer chucking surface  20   a . Therefore, the wafer  14  is brought into close contact with and chucked to the wafer chucking surface  20   a  of the plate-shaped member  20 . In this way, in the plate-shaped member  20  shown in  FIGS. 2A and 2B , as in the plate-shaped member  102  shown in  FIGS. 9A and 9B  having the front ends of the vacuum chucking nozzles  108  projecting out from the surface  102   a  of the plate-shaped member  102 , there is no gap between the workpiece  100  chucked to the front ends of the vacuum chucking nozzles  108  and the surface  102   a  of the plate-shaped member  102 . Therefore, it is possible to reduce to a minimum the warping occurring in the wafer  14  chucked to the wafer chucking surface  20   a  of the plate-shaped member by the vacuum chucking nozzles  32 ,  32  . . . and possible to eliminate fracture or other damage occurring due to warping of the wafer  14 . 
   Further, in the plate-shaped member  20  shown in  FIGS. 2A and 2B , the openings  30 a of the Bernoulli nozzles  30 ,  30  . . . and the chucks  32   a  of the vacuum chucking nozzles  32 ,  32  . . . are alternately formed at the wafer chucking surface  20   a  near the outer periphery of the plate-shaped member  20 . Therefore, it is possible to evenly disperse the openings  30   a  of the Bernoulli nozzles  30 ,  30  . . . near the outer periphery of the plate-shaped member  20  and possible to evenly disperse the chucks  32   a  of the vacuum chucking nozzles  32 ,  32  . . . As a result, it is possible to more evenly lift the wafer  14  by the Bernoulli nozzles  30 ,  30  . . . and chuck the entirety of the wafer  14  to the wafer chucking surface  20   a  by the vacuum chucking nozzles  32 ,  32  . . . and possible to further prevent fracture and other damage of the wafer  14 . 
   Next, an operational process for moving the wafer  14  by a plate-shaped member  20  attached to a front head of the robot  18  will be explained. As an example,  FIG. 8  shows an operational flow chart of the case of moving a wafer  14  from the cassette  12  to the position measurement area  22 . At step  1 , first the head to which the plate-shaped member  20  is attached is moved to the cassette  12  ( FIG. 1 ). At step  2 , next, the head is lowered to the wafer  14  in the cassette  12 . At step  3 , air starts to be blown out from the Bernoulli nozzles  30 . At step  4 , the wafer is chucked and the detection sensor is turned on. At step  5 , the head is raised. At step  6 , the suction by the vacuum chucking nozzles  32  is started. At step  7 , air stops being blown from the Bernoulli nozzles  30 . At step  8 , the vacuum pressure is confirmed. (If vacuum pressure is abnormal, an alarm is turned on.) At step  9 , the head is moved to the position measurement area  22 . At step  10 , the wafer position is measured. 
   The drive timings of the Bernoulli nozzles  30 ,  30  . . . and vacuum chucking nozzles  32 ,  32  . . . provided at the plate-shaped member  20  shown in  FIG. 2A  are controlled by the controller  36 . That is, when lifting the wafer  14  from the cassette  12 , the controller  36  emits signals for driving the Bernoulli nozzles  30 ,  30  . . . and emits signals for stopping the driving of the vacuum chucking nozzles  32 ,  32  . . . Next, when chucking the wafer  14  lifted by the Bernoulli nozzles  30 ,  30  . . . by the vacuum chucking nozzles  32 ,  32  . . . on the wafer chucking surface  20   a  of the plate-shaped member  20 , it emits signals for driving the vacuum chucking nozzles  32 ,  32  . . . and emits signals for stopping the drive of the Bernoulli nozzles  30 ,  30  . . . Regarding the timing for switching the operation of the Bernoulli nozzles  30 ,  30  . . . and vacuum chucking nozzles  32 ,  32  . . . , if the wafer  14  lifted by the Bernoulli nozzles  30 ,  30  . . . will not drop, it is possible to stop the operation of the Bernoulli nozzles  30 ,  30  . . . at the same time as operating the vacuum chucking nozzles  32 ,  32  . . . , but it is safer to provide a time for operation where the two overlap, then stop the operation of the Bernoulli nozzles  30 ,  30  . . . 
   When switching the operation of the Bernoulli nozzles  30 ,  30  . . . and the vacuum chucking nozzles  32 ,  32  . . . , to reliably prevent dropping of the lifted wafer  14 , it is preferable to provide a switching station  38  between the cassette  12  shown in  FIG. 1  and the position measurement area  22 . This switching station  38  is provided with a plate-shaped station part  40  provided with a plurality of pressurized air blowing nozzles for blowing out pressurized air from below the wafer  14  lifted by the Bernoulli nozzles  30 ,  30  . . . of the plate-shaped member  20  as shown in  FIG. 5 . This station part  40  is connected with a feed pipe  42  for supplying pressurized air to the plurality of pressurized air blowing nozzles. By switching the operation between the Bernoulli nozzles  30 ,  30  . . . and the vacuum chucking nozzles  32   32  . . . on the switching station  38 , it is possible to reliably prevent dropping of the wafer  14  even with deviation in the timing of switching of operation between the two. 
   The plates  34 ,  34  . . . serving as the detachment prevention member provided at the plate-shaped member  20  shown in  FIG. 1  to  FIG. 5  are affixed to the side wall surfaces of the plate-shaped member  20 . Therefore, when stopping the operation of the vacuum chucking nozzles  32 ,  32  . . . at the adhesion area  24  shown in  FIG. 1  and taking out the wafer  14  chucked to the wafer chucking surface  20   a  by the vacuum chucking nozzles  32 ,  32  . . . of the plate-shaped member  20   d  and placing it on the carrying surface, the front ends of the plates  34 ,  34  . . . abut against the carrying surface of the adhesion area  24  and a predetermined gap is formed between the wafer chucking surface  20   a  of the plate-shaped member  20  and the carrying surface. Therefore, if stopping the operation of the vacuum chucking nozzles  32 ,  32  . . . , the wafer  14  descends by a predetermined distance and abuts against the carrying surface. To reduce as much as possible the gap between the wafer chucking surface  20   a  of the plate-shaped member  20  and the carrying surface of the adhesion area  24 , as shown in  FIG. 6 , it is preferable to use a detachment prevention member biasing the plate  34  by a spring  44  serving as an elastic member in a direction where the front end projects from the wafer chucking surface  20   a  of the plate-shaped member  20 . According to the detachment prevention member shown in  FIG. 6 , when the front end of the plate  34  abuts against the carrying surface of the adhesion area  24 , it is possible to bring the plate-shaped member  20  into proximity with the carrying surface against the biasing force of the spring  44  and possible to reduce as much as possible the gap between the wafer chucking surface  20   a  and the carrying surface of the adhesion area  24 . If it were possible to reduce as much as possible the gap between the wafer chucking surface  20   a  and the carrying surface of the adhesion area  24 , it would be possible to shorten the dropping distance of the wafer  14  and reduce the impact when the wafer  14  strikes the carrying surface of the adhesion area  24 . 
   Further, the plate-shaped member  20  shown in  FIG. 1  to  FIG. 5  uses the vacuum chucking nozzles  32 ,  32  . . . as the holding means, but when there is no problem with using electrostatic force for the wafer  14 , as shown in  FIG. 7 , it is possible to arrange an electrostatic chucking plate  46  as the holding means at the wafer chucking surface  20   a . The electrostatic chucking plate  46  has to evenly chuck the entirety of the wafer  14 , so, as shown in  FIG. 7 , it is also possible to arrange a single electrostatic chucking plate  46  so as to cover the part including the center of the plate-shaped member  20 . Instead of the plurality of chucks  32   a ,  32   a . . . shown in  FIG. 2B , it is also possible to arrange a plurality of electrostatic chucking plates. In this case as well, the openings  30   a  of the plurality of Bernoulli nozzles  30 ,  30  . . . and the plurality of electrostatic chucking plates are alternately provided at the wafer chucking surface  20   a  near the outer periphery of the plate-shaped member  20  along the outer periphery. In this way, by using the electrostatic chucking plate  46 , in the same way as the case of using the vacuum chucking nozzles  32 ,  32  . . . , it is possible to eliminate the vacuum pump etc. and possible to simplify the conveyor system. According to the present invention, it is possible to safely convey a thin wafer of a thickness of less than 100 μm without damage and possible to easily position the workpiece. Therefore, it is possible to deal with the increasing thinness of workpieces. 
   While the invention has been described with reference to specific embodiments chosen for purpose of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.