Abstract:
An electronic component mounting apparatus includes a plurality of pickup nozzles ( 1 ) which are attached to the periphery of a rotary table, that intermittently rotates. The apparatus also includes a cylindrical cam ( 105 ) having a cam groove ( 106, 107   a,    107   b ) which allows the pickup nozzles ( 1 ) to move up and down. A first roller ( 5 ) is attached to a first slide portion ( 4   a ), which is equipped with the pickup nozzles  1 . The first roller runs within the cam grooves ( 106, 107   a,    107   b ) to make the pickup nozzles  1  move up and down. A second roller ( 6 ) is attached to a second slide portion  4   b,  which is attached to the pickup nozzles ( 1 ). The second roller runs within the cam grooves ( 106, 107   a,    107   b ) to make the pickup nozzles move up and down together with the first roller. Also, springs ( 9 ) are provided for biasing the first and second rollers ( 5, 6 ) into contact with the two side surfaces, respectively, of the cam grooves ( 106, 107   a,    107   b ).

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to an electronic component mounting apparatus for mounting electronic components onto a circuit board and, more particularly, to an electronic component mounting apparatus in which a pickup nozzle (suction nozzle) is moved up and down by using a cylindrical cam. 
     2. Description of Related Art 
     As a prior art example of the electronic component mounting apparatus in which a pickup (suction) nozzle unit is moved up and down by using a cylindrical cam, one as described in Unexamined Japanese Patent Publication No. 3-8398, which is provided with a cylindrical cam having a fixed-portion and up/down-movable-portion composite cam groove over the entire circumference, is described with reference to FIGS. 8 to  12 . It is noted that some cylindrical cams have only fixed cam grooves. In such a case, in the following description of the prior art, the fixed-portion and up/down-movable-portion composite cam groove is replaced by a fixed cam groove, where the fixed cam groove moves a pickup nozzle unit to a specified working position, so that the pickup nozzle unit is positioned at the specified working position, and thereafter a pickup nozzle of the pickup nozzle unit is moved up and down by a rotating cam and a lever mechanism. 
     Referring to FIG. 8, on a support base  116  are fixed an index unit  101 , a cylindrical cam  105 , plate cams  109   a ,  109   b , levers  108   a ,  108   b  which are actuated by the plate cams  109   a ,  109   b , and springs  110   a ,  110   b  which bias the levers  108   a ,  108   b  into press contact with the plate cams  109   a ,  109   b , respectively. 
     The index unit  101  drives a rotating shaft  102  into intermittent rotational motion. A rotary table  103  is attached to a lower end of the rotating shaft  102 . Up/down guides  117  which guide the up and down sliding movement of a plurality of pickup nozzle units  104  are fixed at equal intervals on the periphery of the rotary table  103 . 
     Each of the plurality of pickup nozzle units  104  comprises: a block  111  which is inserted in the up/down guide  117  so as to slide up and down; a pickup nozzle  113  inserted in the block  111  in the up/down direction and biased upward toward the block  111  by a spring  118 ; and a cam follower  112  placed in a fixed-portion cam groove  106  and up/down-movable-portion cam grooves  107   a ,  107   b  which are provided in an up-and-down wavy shape over the entire circumference of the cylindrical cam  105  fixed to the support base  116 . The cam follower  112  is a roller as shown in FIG.  12 . 
     Next, detailed structure of the fixed-portion cam groove  106  and the up/down-movable-portion cam grooves  107   a ,  107   b  of the cylindrical cam  105  as well as operation of the cam follower  112  are described with reference to FIGS. 8 to  11 . 
     Referring to FIGS. 8 to  11 , the cylindrical cam  105  is fixed to outside of the rotating shaft  102  in a coaxial state with the rotating shaft  102  that performs intermittent rotational motion, as shown in FIGS. 8 and 9. 
     In the cylindrical cam  105 , as shown in FIGS. 9 to  11 , the fixed-portion cam groove  106  as well as the up/down-movable-portion cam grooves  107   a ,  107   b  which intervene partly across the fixed-portion cam groove  106  are provided in an up-and-down wavy state over the entire circumference of the cylindrical cam  105 . The up/down-movable-portion cam grooves  107   a ,  107   b  are provided at specified positions on the circumference of the cylindrical cam  105 , i.e., at the locations of a component pickup station and a component mounting station where the pickup nozzle units  104  work. In FIG. 8, the up/down-movable-portion cam groove  107   a  is positioned at the location of the component mounting station where an electronic component is mounted onto a circuit board  115 , while the up/down-movable-portion cam groove  107   b  is positioned at the location of the component pickup station where a component is picked up from a component feed unit  114 . 
     Then, as shown in FIG. 8, upper ends of the up/down-movable-portion cam grooves  107   a ,  107   b  are connected to the levers  108   a ,  108   b , respectively, and the up/down-movable-portion cam grooves  107   a ,  107   b  will be slid up and down by the levers  108   a ,  108   b  which are actuated up and down by the rotation of the plate cams  109   a ,  109   b , respectively. 
     Within the fixed-portion cam groove  106  and the up/down-movable-portion cam grooves  107   a ,  107   b , as shown in FIGS. 8 to  11 , is placed the cam follower  112 . The cam follower  112  is integrally combined with the block  111  that is inserted in the up/down guide  117  so as to slide up and clown as described above. Therefore, when the rotation of the rotary table  103  causes the block  111  to go into intermittent rotational motion around the cylindrical cam  105 , the cam follower  112  moves up and down along the fixed-portion cam groove  106  and the up/down-movable-portion cam grooves  107   a ,  107   b  while rotating. 
     In this case, the plate cams  109   a ,  109   b  will rotate in synchronization with the intermittent rotational motion of the rotating shaft  102  and the rotary table  103  driven by the index unit  101 . However, the plate cams  109   a ,  109   b  have such a shape that the levers  108   a ,  108   b  will not be actuated during time durations when the cam follower  112  is within the fixed-portion cam groove  106  of the cylindrical cam  105 , and as shown in FIG. 11, the up/down-movable-portion cam grooves  107   a ,  107   b  will not be moved down until the cam follower  112  reaches the up/down-movable-portion cam grooves  107   a ,  107   b  of the cylindrical cam  105 . As the up/down-movable-portion cam grooves  107   a ,  107   b  move down, the cam follower  112  moves as shown by a cam follower track  119  indicated by two-dot chain line in FIG.  11 . While the rotating shaft  102  and the rotary table  103  are at an intermittent rest, the cam follower  112  reaches a lowermost position  119   a  as shown by the cam follower track  119 , at which lowermost position  119   a  the pickup nozzle  113  is made to perform an electronic component pickup operation or mounting operation. With this operation completed, as the rotating shaft  102  and the rotary table  103  start rotating, the plate cams  109   a ,  109   b  make the up/down-movable-portion cam grooves  107   a ,  107   b  move upward again, thereby rising them until the up/down-movable-portion cam grooves  107   a ,  107   b  coincide with the fixed-portion cam groove  106  of the cylindrical cam  105 . 
     With the above constitution, the operation time of component mounting operation can be reduced in the following way. 
     By the drive of the index unit  101 , the rotating shaft  102  and the rotary table  103  are caused to go into intermittent rotational motion, and the plurality of pickup nozzle units  104  attached to the periphery of the rotary table  103  are caused to start rotating. While the cam follower  112  is within the fixed-portion cam groove  106  of the cylindrical cam  105 , the plate cams  109   a ,  109   b  are equal in the diameter of operative portion to each other so that the levers  108   a ,  108   b  will not be actuated. However, as shown in FIG. 11, when the cam follower  112  has reached the portions of the cylindrical cam  105  corresponding to the up/down-movable-portion cam grooves  107   a ,  107   b , the plate cams  109   a ,  109   b  have operative portions in troughs so that the levers  108   a ,  108   b  will be actuated, and the up/down-movable-portion cam grooves  107   a ,  107   b  will be lowered. During the rest time of the intermittent rotational motion of the index unit  101 , the up/down-movable-portion cam grooves  107   a ,  107   b  reach the lowermost position  119   a , causing the pickup nozzle  113  to perform the electronic-component pickup or mounting operation. With this operation completed, as the rotating shaft  102  and the rotary table  103  start rotating, the up/down-movable-portion cam grooves  107   a ,  107   b  move upward again, rising until the up/down-movable-portion cam grooves  107   a ,  107   b  coincide with the fixed-portion cam groove  106 . 
     In comparison with the olc type in which the up/down-movable-portion cam grooves  107   a ,  107   b  are not provided and the plate cams  109   a ,  109   b  will not start operating, neither will the pickup nozzle of the pickup nozzle unit start lowering, before the pickup nozzle unit reaches the location of the next working station, the above-described prior art example accomplishes a reduction in the cycle time of the pickup nozzle by virtue of the arrangement that the pickup nozzle  113  starts its lowering operation midway of the move from one working position to the next working position, so that the pickup nozzle  113  has substantially completed the lowering operation at the time point when it reaches the next working position, in the aforementioned manner. 
     However, with the construction of the prior art example of the electronic component mounting apparatus in which the pickup-nozzle unit is moved up and down by using the cylindrical cam, both old and new types described above, as shown in FIG. 12, would be required to make the diameter of the roller of the cam follower  112  smaller than the groove widths of the cam grooves  106 ,  107   a ,  107   b  (FIG. 12 shows the cam groove  106  representatively), such that there would necessarily exist a gap G between the roller of the cam follower  112  and each of the cam groove surfaces of the cam grooves  106 ,  107   a ,  107   b . Accordingly, each time the cam follower  112  changes in the moving direction between up and down, the roller of the cam follower  112  would collide with the cam groove, for example, cam groove surfaces c, e of the cam groove  106  in FIG.  12 . Upon this collision, vibrations caused by the collision would transfer from the cam follower  112  to the pickup nozzle  113 , thereby causing a shift in the mounting position of the electronic component picked up by the pickup nozzle  113 . 
     Also, because the contacting cam groove surfaces c, e will be changed over between upward movement and downward movement of the roller of the cam follower  112 , rotational directions d, f of the roller, which is a rotating member of the cam follower  112 , will be changed over upon each changeover of the cam groove surfaces c, e. A change in the rotational directions d, f of the roller of the cam follower  112  would adversely affect the service life of the cam follower  112  such that, particularly when the apparatus is driven at high speed, its service life would be shortened as an issue. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is therefore to provide an electronic component mounting apparatus which produces less vibration and is long in service life. 
     In order to achieve the above object, the electronic component mounting apparatus according to a first aspect of the present invention comprises: 
     a rotary table which is intermittently driven into rotation; 
     a plurality of pickup nozzles which are attached movable up and down on periphery of the rotary table; 
     a cylindrical cam which is provided inside the rotary table and coaxial with the rotary table and which has, over its entire circumference, a cam groove for allowing the pickup nozzles to move up and down with intermittent rotation of the rotary table; 
     a first roller which is attached to the pickup nozzle and which runs within the cam groove to make the pickup nozzles move up and down; and 
     a first spring for biasing the first roller into press contact with one side surface of the cam groove. 
     According to a second aspect of the present invention, in the first aspect, the apparatus may further comprise: 
     a second roller which is attached to the pickup nozzle and which runs within the cam groove to make the pickup nozzles move up and down together with the first roller; and 
     a second spring for biasing the second roller into press contact with a side surface of the cam groove. 
     According to a third aspect of the present invention, in the second aspect, it is also possible that at least either one of the first roller or the second roller is attached to the pickup nozzle so as to be movable in a biasing direction of the spring. 
     According to a fourth aspect of the present invention, in any one of the first to third aspects, the cam groove may comprise one groove. 
     According to a fifth aspect of the present invention, in the second or third aspect, it is also possible that the cam groove is provided as two grooves comprising a first cam groove and a second cam groove, and that the first roller is pressed against one side surface of the first cam groove by the first spring while the second roller is pressed against one side surface of the second cam groove by the second spring. 
     In a sixth aspect of the present invention, in any one of the first to fifth aspects, it is also possible that a center line of lines of force of the spring is substantially coincident with a contact point of the roller and the cam groove. 
     In the electronic component mounting apparatus according to the above aspects of the invention, because the cam follower comprises the first roller which is attached to the pickup nozzle and which runs within the cam groove, and the spring for biasing the first roller into press contact with the one side surface of the cam groove, the first roller runs while being normally pressed against the one side surface of the cam groove. Therefore, it becomes possible to solve the issue that the roller of the cam follower would collide with the side surface of the cam groove upon each changeover of the up-and-down moving direction of the cam follower, causing vibrations, as would inevitably be involved in the prior art example having a gap between the roller of the cam follower and the side surface of the cam groove. As a result, the precision at which the electronic component is mounted onto the circuit board can be improved. Further, because the first roller will contact with an unchanged side surface of the cam groove, thus rotating constantly in one direction, the roller is prolonged in service life while higher-speed operation is facilitated. 
     In the electronic component mounting apparatus according to the above aspects of the invention, provided that the cam follower further comprises the second roller which is attached to the pickup nozzle and which runs within the cam groove, and the spring for biasing the second roller into press contact with the other side surface of the cam groove, then the first roller is normally pressed against the one side surface of the cam groove as described above and moreover the second roller runs while being normally pressed against the other side surface of the cam groove. Therefore, it becomes possible to solve the issue that the roller of the cam follower would collide with the side surface of the cam groove upon each changeover of the up-and-down moving direction of the cam follower, causing vibrations, as would inevitably be involved in the prior art example having a gap between the roller of the cam follower and the side surface of the cam groove. As a result, the precision at which the electronic component is mounted onto the circuit board can be improved. Further, because both the first roller and the second roller will contact with unchanged side surfaces of the cam groove, respectively, thus each rotating constantly in one direction, the rollers are prolonged in service life while higher-speed operation is facilitated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the present invention will become apparent from the following description taken in conjunction with preferred embodiments thereof with reference to the accompanying drawings, in which: 
     FIG. 1 is a partial side view in cross section showing part of an electronic component mounting apparatus according to a first embodiment of the present invention; 
     FIG. 2 is a front view showing part of the first embodiment; 
     FIG. 3 is a plan view showing part of the first embodiment; 
     FIGS. 4A and 4B are a plan view and a side view, respectively, showing part of the first embodiment, 
     FIG. 5 is a schematic diagram showing part of the first embodiment; 
     FIG. 6 is a partial side view in cross section showing part of an electronic component mounting apparatus according to a second embodiment of the present invention; 
     FIGS. 7A and 7B are a partial side view in cross section and a plan view, respectively, showing part of an electronic component mounting apparatus according to a third embodiment of the present invention; 
     FIG. 8 is a sectional view of a prior art electronic component mounting apparatus having a cylindrical cam; 
     FIG. 9 is a sectional view of a prior art electronic component mounting apparatus having a cylindrical cam; 
     FIG. 10 is a side view showing a main part of a prior art electronic component mounting apparatus having a cylindrical cam; 
     FIG. 11 is a side view showing a main part of a prior art electronic component mounting apparatus having a cylindrical cam; 
     FIG. 12 is a schematic diagram showing main part of a prior art electronic component mounting apparatus having a cylindrical cam. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. 
     An electronic component mounting apparatus according to a first embodiment of the invention will now be described with reference to FIGS. 1 to  5 . 
     The difference between the electronic component mounting apparatus according to the first embodiment and the electronic component mounting apparatus according to the prior art lies in the cam follower portion. Whereas the cam follower of the prior art example comprises one roller  112  as shown in FIG. 12, the cam follower of the electronic component mounting apparatus according to the first embodiment comprises two rollers  5 ,  6  as shown in FIGS. 1 to  5 . More specifically, the cam follower comprises: a first roller  5  which is fixed to a first block  4   a  of a pickup nozzle unit  204  and which runs within a cam groove  106 ; a second roller  6  which is supported by the pickup nozzle unit so as to be slightly movable upward and downward and which runs within the cam groove  106 ; and a compression spring  9  for biasing the first roller  5  and the second roller  6  into press contact with upper and lower side surfaces of the cam groove  106 . The rest of the electronic component mounting apparatus is the same as the one described in the prior art example in which the pickup nozzle unit  204  (corresponding to the pickup nozzle unit  104  in the prior art example) is moved up and down by using the cylindrical cam  105 , and so its description is omitted. 
     Referring to FIGS. 1 to  5 , which show the pickup nozzle unit  204  of the electronic component mounting apparatus according to the first embodiment, reference numeral  1  denotes a pickup nozzle and reference numeral  2  denotes a nozzle housing, where the nozzle housing  2  comprises the pickup nozzle  1 , and a first slide portion  4   a  and a second slide portion  4   b  both of which are inserted in a guide groove  117   a  of an up/down guide  117  attached to the periphery of the rotary table  103  as described in the prior art example to slide the pickup nozzle unit  204  up and down, and both of which are slidable up and down. A support shaft  15  that supports the first roller  5  rotatable is notably fixed to the first slide portion  4   a  and guided by the fixed-portion cam groove  106  and the up/down-movable-portion cam grooves  107   a ,  107   b  as described in the prior art example. The support shaft  15  is in contact with one side surface, for example the lower side surface in FIGS. 1 and 5, of each of the cam grooves  106 ,  107   a ,  107   b . The first slide portion  4   a  is fixed to a support plate  2   c  of the pickup nozzle unit  204  by bolts  602 ,  603 , and the first slide portion  4   a  will move up and down against the up/down guide  117  integrally with the pickup nozzle unit  2   c . On the other hand, the second slide portion  4   b  is enabled by a pair of ball guides  400  to smoothly move up and down against the support plate  2   c  as shown in FIGS. 4A and 4B. Each ball guide  400  is arranged so that a multiplicity of balls  401  are rotatably accommodated between a groove  403  of the support plate  2   c  of the pickup nozzle housing  2  and a groove  402  of the second slide portion  4   b . Accordingly, the second slide portion  4   b  will be moved up and down reliably and smoothly by the biasing force of the spring  9 , as described later, while being guided by the ball guides  400 . 
     The nozzle housing  2  has the second slide portion  4   b  up-and-down slidably attached to the guide groove  117   a of the up/down guide  117 , and the second roller  6  is fixed to the second slide portion  4   b . The second roller  6  is guided by the fixed-portion cam groove  106  and the up/down-movable-portion cam grooves  107   a ,  107   b  as described in the prior art example. The second roller  6  is in contact with one side surface opposite to the side surface with which the first roller  5  is in contact, for example the upper side surface in FIGS. 1 and 5, of each of the cam grooves  106 ,  107   a ,  107   b.    
     A spring holder  7  is fixed to the first slide portion  4   a  by a bolt  600 , and the support shaft  15  of the first roller  5  is fixed to the spring holder  7 . The support shaft  15  is fixed to the support plate  2   c  of the pickup nozzle housing  2 . A spring holder  8  is fixed to the second slide portion  4   b  by a bolt  601 , and a support shaft  16  of the second roller  6  is fixed to the spring holder  8 . The support shaft  16  is enabled by the support plate  2   c  of the pickup nozzle housing  2  to move up and down within a groove  2   a . Between the spring holders  7  and  8  are two springs  9 , which bias and press the first, and second rollers  5 ,  6  against the opposite-side surface of the cam groove  106  via the spring holders  7 ,  8 , respectively. That is, in FIG. 1, the first roller  5  is biased by the two springs  9  so as to be normally kept in contact with the lower side surface of the cam groove  106 , while the second roller  6  is biased by the two springs  9  so as to be normally kept in contact with the upper side surface of the cam groove  106 . Accordingly, the springs  9  have such a biasing force that the first roller  5  and the second roller  6  will be normally pressed into contact with the lower and upper side surfaces of the cam grooves  106 ,  107   a ,  107   b  even if the pickup nozzle moves up and down. In addition, with an arrangement that a center line  902  of the lines of force of the springs  9  is substantially coincident with a contact point  903  of the first, second rollers  5 ,  6  and the cam groove  106  as shown in FIG. 1, the biasing force of the springs  9  can be made to act on the rollers  5 ,  6  more efficiently. 
     With the above-described construction, as shown in FIG. 5, the first and second rollers  5 ,  6  will enter the fixed-portion cam groove  106  and the up/down-movable-portion cam grooves  107   a ,  107   b  and run along the directions of the arrows, thus determining the track along which the pickup nozzle unit moves. 
     According to the above construction, between the first and second rollers  5 ,  6  and the upper and lower side surfaces of the fixed-portion cam groove  106  and the up/down-movable-portion cam grooves  107   a ,  107   b , there is no gap so that the first and second rollers  5 ,  6  are normally kept in contact with the upper and lower side surfaces of the cam grooves  106 ,  107   a ,  107   b  by the biasing force of the springs  9 . Therefore, when the pickup nozzle unit changes in the moving direction between up and down, the first and second rollers  5 ,  6  will never collide with the upper and lower side surfaces of the cam grooves  106 ,  107   a ,  107   b , so that occurrence of vibrations due to such collisions can be prevented. Also, that the precision at which the electronic component is mounted onto the circuit board can be enhanced. 
     Also, since the first and second rollers  5 ,  6  are normally kept in contact with the upper and lower side surfaces of the fixed-portion cam groove  106  and the up/down-movable-portion cam grooves  107   a ,  107   b  by the biasing force of the springs  9 , the rotational direction of each of the first and second rollers  5 ,  6  is limited to one direction (e.g., direction h for the first roller  5  and direction g for the second roller  6  in FIG.  5 ). Thus, the first and second rollers  5 ,  6  are prolonged in service life. 
     Next, FIG. 6 is a partial side view in cross section showing part of an electronic component mounting apparatus according to a second embodiment of the present invention. In this second embodiment, the cam groove  106  is replaced by two cam grooves, a first cam groove  406  on the lower side and a second cam groove  306  on the upper side. A first roller  5  is fitted to the first cam groove  406  and normally pressed against the lower side surface of the first cam groove  406  by the biasing force of the spring  9 , while a second roller  6  is fitted to the second cam groove  306  and normally pressed against the upper side surface of the second cam groove  306  by the biasing force of the spring  9 . This is the only point in which this second embodiment differs from the first embodiment, and the rest of the construction is the same as the first embodiment. In addition, for spatial reasons, one spring  9  is provided between the spring holders  7  and  8 . This second embodiment also can result in functional effects that are similar to those of the first embodiment. 
     FIGS. 7A and 7B are a partial side view in cross section and a plan view, respectively, showing part of an electronic component mounting apparatus according to a third embodiment of the present invention. In this third embodiment, one roller  5  is used in place of the two rollers  5 ,  6 , and this first roller  5  is normally kept in press contact with either the upper or lower side surface, for example the lower side surface in FIG. 7A, of the cam groove  206  by the biasing force of the spring  9 . A slide portion  204   a  is fixed to the pickup nozzle unit  2   c  by bolts  602  and  603  as in the first embodiment. A support shaft  210  of the first roller  5  is fixed to the pickup nozzle unit  2   c  and the slide portion  204   a . The slide portion  204   a  is slidable up and down against a fixed up/down guide  217  by the guide of a pair of ball guides  400  which are similar to those of the first embodiment, and the support shaft  210  of the first roller  5  is movable up and down within a guide groove  217   a  of the up/down guide  217 . An upper end of the up/down guide  217  is bent into an L shape, and a compression spring  209  is provided between the end and an upper portion of the slide portion  204   a  so that the slide portion  2   c  is normally biased downward against the up/down guide  207 . Accordingly, the first roller  5  is normally biased downward via the slide portion  204   a  and the support shaft  210  by the biasing force of the spring  209  so that the first roller  5  is pressed and biased against the lower side surface of the cam groove  206 . The spring  209  has such a biasing force that the first roller  5  will maintain normally in press contact with the lower side surface of the cam groove  206  even if the pickup nozzle  1  moves up and down. 
     This third embodiment also can result in functional effects similar to those of the first embodiment. 
     In the foregoing first and second embodiments, the first slide portion  4   a  is fixed to the support plate  2   c , while the second slide portion  4   b  is movable up and down against the support plate  2   c . However, without the limitation to such an arrangement, it may also be arranged that, conversely, the second slide portion  4   b  is fixed to the support plate  2   c  while the first slide portion  4   a  is movable up and down against the support plate  2   c . Moreover, both the first slide portion  4   a  and the second slide portion  4   b  may be movable up and down. 
     The present invention, without being limited to those in which the pickup nozzle moves up and down integrally with the pickup nozzle unit, may be applied to those in which the pickup nozzle alone moves up and down. 
     Although the present invention has been fully described in conjunction with preferred embodiments thereof with reference to the accompanying drawings, various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention as defined by the appended claims, they should be construed as included therein.