Abstract:
Clamp devices configured such that dust does not enter insides of casings. The clamp devices each include the casing, and a clamp-side end section of a clamp arm is exposed from an opening of the casing. The clamp arm includes: a first circular arc section which is exposed from the casing when a workpiece is clamped by the clamp arm and is contained within the casing when the workpiece is not clamped by the clamp arm; and a second circular arc section which is exposed from the casing when the workpiece is not clamped by the clamp arm and is contained within the casing when the workpiece is clamped by the clamp arm. A first scraper and a second scraper are in sliding contact with the first circular arc section and the second circular arc section, respectively. The clamp device can also include a side surface cleaning scraper for making sliding contact with a side surface of the first circular section.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a clamp apparatus (clamp device), and more specifically, to a clamp apparatus equipped with a swingable clamp arm for clamping a workpiece. 
       BACKGROUND ART 
       [0002]    For example, in a process for manufacturing an automobile, various constituent elements are welded with respect to the automotive vehicle body. When such welding is performed, clamping of the constituent elements using a clamp apparatus is widely practiced for positioning and fixing the constituent elements in place. 
         [0003]    As one type of clamp apparatus, the device disclosed in the specification of German Utility Model Registration No. 29504267 may be cited as an example. More specifically, such a clamp apparatus includes a casing, a cylinder disposed inwardly of the casing, and a clamp arm, which is connected to a rod of the cylinder through a toggle link mechanism. Linear translatory movement of the rod is converted into rotational movement by the toggle link mechanism, and as a result, the clamp arm undergoes swinging movement. 
         [0004]    In the clamp apparatus of German Utility Model Registration No. 29504267, as shown in FIGS. 1 and 2 of this publication, a main body of the toggle link mechanism is accommodated in the casing, such that only a connecting shaft is exposed from a side wall of the casing, with a structure being provided in which one end of the clamp arm is connected to a distal end of the exposed connecting shaft. In this case, adhering of so-called spatter (debris), which is generated during welding, onto the main body of the toggle link mechanism can be avoided. 
         [0005]    However, in the aforementioned structure in which the connecting shaft of the toggle link mechanism projects from a side surface of the casing, it is difficult for the casing, and hence the widthwise dimension of the clamp apparatus, to be made narrower in width, due to the fact that it is necessary for the connecting shaft to extend along a width direction of the casing. 
         [0006]    For this reason, for example, the clamp apparatus cannot be inserted into a narrow clearance. Stated otherwise, a problem occurs in that the locations in which the clamp apparatus can be installed are limited. 
         [0007]    For narrowing the widthwise dimension of the casing, as disclosed in German Utility Model Registration No. 9104532, a casing is constituted from a first casing member and a second casing member, in which it is thought to be effective for the clamp arm to project from an opening, which is formed by mating surfaces of the first casing member and the second casing member. In this case, as can be understood from FIG. 1 of this publication, it is not required for a connecting shaft of the toggle link mechanism to extend along the width direction of the casing. 
       SUMMARY OF INVENTION 
       [0008]    With the clamp apparatus disclosed in German Utility Model Registration No. 9104532, it is necessary for the opening to be disposed partially in the range within which the clamp arm swings. For this reason, because the opening extends over a long distance, it is easy for debris to enter and penetrate into the interior of the casing from the opening. Stated otherwise, it becomes difficult for the toggle link mechanism to be protected from such debris. 
         [0009]    In the invention of German Utility Model Registration No. 9104532, it is attempted to avoid penetration of debris into the casing interior by covering the clamp arm with a cover member. However, it is difficult to provide blockage over the entirety of the opening by means of such a cover member. 
         [0010]    A general object of the present invention is to provide a clamp apparatus in which the widthwise dimension of the clamp apparatus can be made narrower. 
         [0011]    A principal object of the present invention is to provide a clamp apparatus in which penetration of debris into the interior of the casing can be prevented. 
         [0012]    According to an embodiment of the present invention, a clamp apparatus is provided including a clamp arm, one end portion of which is exposed from an opening of a casing, and another end portion of which is accommodated inside the casing, a support shaft that pivotally supports the other end portion of the clamp arm at the interior of the casing, and a cylinder having a rod that is connected to the clamp arm through a toggle link mechanism arranged in the interior of the casing, and which causes the clamp arm to swing about the support shaft by converting linear movement of the rod into rotational movement through the toggle link mechanism. Further, an arcuate portion is formed on the clamp arm and is curved about the support shaft, and the arcuate portion is exposed to the exterior of the casing when the clamp arm swings so as to clamp a workpiece, whereas the arcuate portion is accommodated inside the casing when the clamp arm swings so as to release the workpiece. Also, a scraper, which is in sliding contact against an arcuate surface of the arcuate portion when the clamp arm swings, is provided on the casing. 
         [0013]    There is a concern that foreign matter could become adhered with respect to an exposed location (arcuate portion) of the clamp arm, which is exposed from the casing when the clamp arm clamps a workpiece. Further, in the event that welding is carried out with respect to the workpiece, spatter (debris) may also become adhered to such a location. When the arcuate portion, in a state of having such matter adhered thereto, is accommodated inside the casing upon the clamp arm releasing the workpiece, such foreign matter and debris enter and penetrate into the casing. 
         [0014]    However, according to the present invention, when the clamp arm is swung, the scraper is placed in sliding contact with the arcuate surface of the arcuate portion. Accordingly, since foreign matter and debris are scraped off from the arcuate surface, the arcuate surface is cleaned. Further, since the arcuate portion is accommodated inside the casing in this state, foreign matter and debris can be effectively prevented from penetrating into the casing interior. 
         [0015]    As a result, the adverse influence of foreign matter and debris on operations of the toggle link mechanism can be avoided. Owing thereto, appropriate swinging movement of the clamp arm can be maintained over a long time. Stated otherwise, the frequency at which maintenance is carried out is significantly reduced. 
         [0016]    More specifically, according to the present invention, when the clamp arm swings, the scraper is brought into sliding contact with respect to the arcuate portion as the arcuate portion becomes accommodated inside the casing, and therefore, penetration of foreign matter or debris into the casing interior can effectively be prevented. Consequently, because the adverse influence of foreign matter and debris on operations of the toggle link mechanism can be avoided, appropriate swinging movement of the clamp arm can be maintained over a long time. 
         [0017]    Further, because the clamp arm is exposed from the opening of the casing, there is no need for a connecting shaft of the toggle link mechanism to project outwardly from a side surface of the casing. Owing thereto, the casing, and hence the widthwise dimension of the clamp apparatus, can be made narrower in width. 
         [0018]    The scraper can be disposed while being exposed on the exterior of the casing. 
         [0019]    Further, preferably, the scraper functions as a seal for blocking a clearance between the casing and the arcuate portion. As a result, penetration of foreign matter or debris into the casing interior through the clearance can be prevented. 
         [0020]    Further, another arcuate portion may be formed on the clamp arm and may be curved about the support shaft, and the other arcuate portion is accommodated inside the casing when the clamp arm swings so as to clamp a workpiece, whereas the other arcuate portion is exposed to the exterior of the casing when the clamp arm swings so as to release the workpiece. In this case, another scraper, which is in sliding contact against an arcuate surface of the other arcuate portion when the clamp arm swings, may be provided on the casing. 
         [0021]    The other scraper, for example, can be disposed while being accommodated inside the casing. 
         [0022]    In addition, the other scraper preferably functions as a seal for blocking a clearance between the casing and the other arcuate portion. 
         [0023]    In the foregoing manner, the opening for enabling swinging movement of the clamp arm can be blocked substantially over the entirety thereof. Therefore, penetration of foreign matter or debris into the casing interior can be more effectively avoided. 
         [0024]    In the above configuration, side surface cleaning scrapers may be provided on the casing, which are in sliding contact against side surfaces of the arcuate portion when the clamp arm swings. In this case, when the clamp arm is swingably operated in the foregoing manner, since the side surface cleaning scrapers are in sliding contact with respect to side surfaces of the arcuate portion, side surfaces of the arcuate portion also are cleaned. Owing thereto, penetration of foreign matter or debris into the casing interior can be prevented more effectively, and the adverse influence on operations of the toggle link mechanism can be further avoided, so that the clamp arm can undergo suitable swinging movement over a longer time. 
         [0025]    Furthermore, a clamp unit may be constructed by connecting together a plurality of clamp apparatus. In this case, the clamp apparatus are connected in parallel such that respective clamp arms thereof are swingable in the same direction. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0026]      FIG. 1  is an overall outline perspective view of a clamp unit including a clamp apparatus according to an embodiment of the present invention; 
           [0027]      FIG. 2  is an exploded perspective view of the clamp unit; 
           [0028]      FIG. 3  is an overall outline perspective view of the clamp unit as seen from a different angle; 
           [0029]      FIG. 4  is an exploded perspective view of the clamp apparatus; 
           [0030]      FIG. 5  is a cross sectional view as observed in the direction of arrows V-V of  FIG. 2 ; 
           [0031]      FIG. 6  is an outline vertical cross sectional view showing a state in which the clamp arm constituting the clamp apparatus is swung from the state shown in  FIG. 5 ; 
           [0032]      FIG. 7  is an overall outline perspective view of a clamp apparatus according to another embodiment; and 
           [0033]      FIG. 8  is an overall outline perspective view of a clamp unit according to another embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0034]    Below, preferred embodiments of a clamp apparatus according to the present invention will be presented and described in detail with reference to the accompanying drawings. 
         [0035]      FIGS. 1 through 3 , respectively, show an overall outline perspective view, an exploded perspective view, and an overall outline perspective view as seen from a different angle, of a clamp unit  12  including clamp apparatus  10   a  to  10   c  according to an embodiment of the present invention. The clamp unit  12  is constituted by respective clamp apparatus  10   a  to  10   c  having the same structure mutually, and which are connected together through tie rods  16  and connecting brackets  14 ,  14 ,  14  (see  FIGS. 2 and 3 ), which are disposed on principal surfaces of the clamp apparatus  10   a  to  10   c.  In  FIG. 2 , claw members  20  (see  FIGS. 1 and 3 ) are not shown. 
         [0036]    The structure of the clamp apparatus  10   a  will now be described in detail. 
         [0037]      FIGS. 4 and 5 , respectively, are an exploded perspective view, and a cross sectional view as observed in the direction of arrows V-V in  FIG. 2 , of the clamp apparatus  10   a.  The clamp apparatus  10   a  includes a cylinder tube  24  that constitutes a cylinder  22 , and a casing  32  that is constructed by assembling together a first casing member  26 , a second casing member  28 , and a back surface cover  30 . One end portion (clamp side end portion  36 ) of a clamp arm  34  is exposed from an opening  33 , which is formed by mating surfaces of the first casing member  26  and the second casing member  28 . 
         [0038]    A cylinder chamber  38 , which is elliptically shaped and having a large diameter, is formed along an axial direction in the cylinder tube  24 . The cylinder chamber  38  is blocked by a head cover  42  and a rod cover  44 , which are connected via elongate connecting rods  40  on respective lower and upper ends of the cylinder tube  24 , as shown in  FIGS. 4 and 5 . 
         [0039]    As shown in  FIG. 5 , at a region corresponding to the back surface of the head cover  42 , a first port  48  is formed that communicates with the cylinder chamber  38  through a communication passage  46 . Further, a damper  50  is attached to an end surface on the head cover  42  on a side facing toward the cylinder chamber  38 , with a recess  52  being formed as a depression in a substantially central portion of the damper  50 . 
         [0040]    Similar to the head cover  42 , at a region corresponding to the back surface of the rod cover  44 , a second port  56  is formed that communicates with the cylinder chamber  38  through a communication passage  54 . The first port  48  and the second port  56  make up intake and exhaust openings for introducing or discharging compressed air with respect to the cylinder chamber  38 . Moreover, as shown in  FIG. 3 , intake and exhaust pipes  58  are connected respectively to the first port  48  and the second port  56  through non-illustrated pipe fittings. 
         [0041]    An elliptically shaped piston  62  having a seal member  60  externally fitted thereon is accommodated in the cylinder chamber  38  (see  FIGS. 4 and 5 ). Naturally, the seal member  60  is held in contact slidably with respect to the inner wall of the cylinder chamber  38 , and therefore, compressed air that is introduced into the cylinder chamber  38  from the first port  48  does not flow past the piston  62  and is not discharged from the second port  56 , and similarly, compressed air that is introduced into the cylinder chamber  38  from the second port  56  does not flow past the piston  62  and is not discharged from the first port  48 . 
         [0042]    A circular insertion hole  64  is formed in the piston  62 , and a rod  66  is fitted into the circular insertion hole  64 . By crimping or swaging the end portion on the rod  66  that is inserted into the piston  62 , the piston  62  is prevented from being pulled off from the rod  66 . 
         [0043]    On the other hand, another end portion (connection side end portion  72 ) of the clamp arm  34  is connected through a toggle link mechanism  70  to the distal end of the rod  66 . 
         [0044]    More specifically, the toggle link mechanism  70  includes in this order a knuckle joint  74 , a first link member  76 , and a second link member  78 , which extend from the side of the rod  66  to the clamp arm  34 , and is constructed such that the knuckle joint  74  and the first link member  76  are connected together via a first rod pin  80 , and the first link member  76  and the second link member  78  are connected together via a second rod pin  81 . Guide rollers  82 ,  83  are externally fitted, respectively, onto the first rod pin  80  and the second rod pin  81 . 
         [0045]    A small diameter fitting portion  84 , which is reduced in diameter, is formed to project integrally on the distal end of the rod  66 . On the other hand, a fitting groove is formed in the knuckle joint  74 , such that the rod  66  and the knuckle joint  74  are connected together by fitting the small diameter fitting portion  84  into the fitting groove  86 . 
         [0046]    Further, the clamp arm  34  includes a wide connection side end portion  72  that is connected to the toggle link mechanism  70 , and an elongate substantially rectangular parallelepiped shaped clamp side end portion  36 , which projects outwardly and extends from the casing  32 . The connection side end portion  72  is formed as a hollow body, and link pin engagement holes  88  are formed respectively therein to penetrate through end surfaces on sides facing toward respective end surfaces of the first casing member  26  and the second casing member  28 . 
         [0047]    An end of the second link member  78  is inserted into the hollow connection side end portion  72 . Link pins  90  are formed, respectively, to project on respective side surfaces of the second link member  78 , such that the two link pins  90  are made to engage respectively with the two link pin engagement holes  88 . 
         [0048]    As a result of the first link member  76  bridging the knuckle joint  74 , which is connected to the rod  66  as described above, and the second link member  78 , which is connected to the connection side end portion  72  of the clamp arm  34 , as described later, linear translatory movement of the rod  66  is converted into rotational (swinging) movement of the clamp arm  34 . Further, in a state in which the clamp arm  34  clamps a workpiece, a curved end surface of the second link member  78  abuts against a later-described fixed roller  124 . 
         [0049]    On the connection side end portion  72  of the clamp arm  34 , a pivot pin  92  (support shaft), which is oriented toward respective end surfaces of the first casing member  26  and the second casing member  28 , is formed so as to project outwardly at a location further downward from, i.e., below, the link pins  90 . As discussed later, the clamp arm  34  swings about the pivot pin  92 . 
         [0050]    A first arcuate portion  94 , which curves toward the clamp side end portion  36  from the second link member  78 , is formed on the connection side end portion  72 . The first arcuate portion  94  forms an arc about the pivot pin  92  and with an arclength which is roughly ¼ the circumferential length of a circle centered about the pivot pin  92 . 
         [0051]    In the vicinity of the pivot pin  92  on the connection side end portion  72 , a second arcuate portion  96  is formed so as to bend centrally about the same pivot pin  92 . The arclength of the second arcuate portion  96  is roughly ¼ the circumferential length of a circle centered about the pivot pin  92 . 
         [0052]    In  FIGS. 1 through 5 , a state is shown in which the clamp side end portion  36  of the clamp arm  34  is in a recumbent posture for clamping a non-illustrated workpiece, and at this time, the first arcuate portion  94  is exposed from the casing  32 , whereas the second arcuate portion  96  is accommodated inside the casing  32  (see  FIGS. 1 to 3  and  5 ). On the other hand, as shown in  FIG. 6 , in the case that the clamp side end portion  36  is placed upright to release the workpiece, the first arcuate portion  94  is accommodated inside the casing  32 , whereas the second arcuate portion  96  is exposed from the casing  32 . As will be discussed later, during both processes, when the clamp arm  34  is swung and the clamp side end portion  36  is moved from the recumbent posture into an upstanding condition, or is moved from the upstanding condition into a recumbent posture, a first scraper  98  is in sliding contact against the arcuate surface of the first arcuate portion  94 , and a second scraper  100  is in sliding contact against the arcuate surface of the second arcuate portion  96 . 
         [0053]    In the clamp side end portion  36 , which is joined to the connection side end portion  72  that is constructed in the foregoing manner, a plurality of claw connecting screw insertion holes  104  are formed to penetrate therethrough (see  FIG. 4 ), for insertion of claw connecting screws  102 , which serve to connect claw member  20  (see  FIG. 1 ) to the clamp side end portion  36 . Stated otherwise, the claw member  20  is connected securely to the clamp arm  34  through the claw connecting screws  102 . 
         [0054]    A recessed part  106  is formed as a depression at the border between the first arcuate portion  94  and the clamp side end portion  36 . An end of the first scraper  98  is inserted into the recessed part  106  when the clamp side end portion  36  is placed in an upstanding posture (see  FIG. 6 ). 
         [0055]    Further, a regulating screw  107  is provided on the clamp arm  34 , on a surface opposite from the recessed part  106 , at a position corresponding roughly to the position of the recessed part  106 . 
         [0056]    Support shaft holes  108 ,  110  are formed to penetrate respectively through the first casing member  26  and the second casing member  28  (see  FIG. 4 ). The pivot pin  92  is inserted rotatably via bushes  112 ,  114  into each of the support shaft holes  108 ,  110 . 
         [0057]    In the first casing member  26  and the second casing member  28 , at principal side surfaces of end faces on the inner wall side of the casing  32 , and at positions proximate to the clamp side end portion  36  in a recumbent posture, two bracket positioning holes  116 ,  118  are formed as recesses parallel with the vertical direction in  FIG. 4 . Furthermore, between the bracket positioning holes  116 ,  118 , support screw through holes  122 ,  123  are formed through which support screws  120  are passed for connection to and supporting of the connecting bracket  14 . 
         [0058]    As can be understood from  FIG. 4 , the connecting bracket  14  is substantially T-shaped as viewed in plan, on which there are integrally provided a narrow elongate end portion  134 , which extends along the axial direction of the casing  32 , and a wide short end portion  136 , which extends in a direction perpendicular to the direction of extension of the elongate end portion  134 . Additionally, two bracket positioning holes  138  are formed to penetrate through the narrow elongate end portion  134 . Between the bracket positioning holes  138 , a support screw hole  140  is formed for screw-engagement therein of the support screws  120 . 
         [0059]    Positioning pins  142  are inserted respectively through the bracket positioning holes  138 , and respective end surfaces of the positioning pins  142  are seated on bottom surfaces of the bracket positioning holes  116 ,  118 , which are formed as recesses in the first casing member  26  and the second casing member  28 . Owing thereto, the positioning pins  142 , and thus the connecting bracket  14 , are positioned with respect to the casing  32 . 
         [0060]    In such a condition, the support screws  120  are inserted through each of the support screw through holes  122 ,  123  of the first casing member  26  and the second casing member  28 , and further, together with screw-engagement thereof in the support screw hole  140  formed in the elongate end portion  134  of the connecting bracket  14 , the connecting bracket  14  is connected securely to the casing  32 . Moreover, the entirety of the exposed regions of the positioning pins  142 , which are exposed from the bracket positioning holes  138 , are inserted into the bracket positioning holes  116 ,  118 . Accordingly, no clearances are formed between the elongate end portion  134  of the connecting bracket  14  and the first casing member  26  and the second casing member  28 . 
         [0061]    The second scraper  100  is fixed in position on the elongate end portion  134  by a first set screw  144 . Further, a stopper member  146  for restricting swinging movement of the clamp arm  34  (clamp side end portion  36 ) by abutment and stoppage of the regulating screw  107  thereagainst is connected to the short end portion  136  through a second set screw  148 . Two tie rod insertion holes  150  are formed to penetrate through in the axial direction of the short end portion  136 . 
         [0062]    Two projection pin engagement holes  152  are formed as recesses, which are sandwiched between the two tie rod insertion holes  150  on one side surface of the short end portion  136 . Further, on the other side surface thereof, projection pins  154  are formed, which engage with the projection pin engagement holes  152  of the connecting bracket  14  of another clamp apparatus  10   b  adjacent to the clamp apparatus  10   a  (see  FIG. 2 ). 
         [0063]    Further, roller shaft holes  126 ,  128 , into which a roller shaft of the fixed roller  124  is inserted, are formed in the first casing member  26  and the second casing member  28  so as to penetrate at positions proximate to the toggle link mechanism  70  on rear surface sides in the end surfaces on the inner wall sides of the casing  32 . In addition, two spacer connection screw insertion holes  130 ,  132  are provided, which sandwich the roller shaft holes  126 ,  128  therebetween. 
         [0064]    As shown in  FIG. 4 , spacer connection screws  160  are inserted respectively into the spacer connection screw insertion holes  130 ,  132 . Each of the spacer connection screws  160  are screw-engaged with spacer connection screw holes  164 ,  166 , which are bored into bottom surfaces of substantially cylindrical shaped spacers  162 . The height dimension from one bottom surface to the other bottom surface of each of the spacers  162  corresponds to the widthwise dimension of the elongate end portion  134  of the connection bracket  14 . Therefore, the first casing member  26  and the second casing member  28  extend mutually in parallel from principal surface side end portions thereof proximate to the clamp side end portion  36  of the clamp arm  34 , to the back surface side end portions thereof proximate to the fixed roller  124 . 
         [0065]    At the back surface side end portions proximate to the fixed roller  124 , a clearance is formed between the first casing member  26  and the second casing member  28 . The back surface cover  30 , which constitutes part of the casing  32 , blocks this clearance. The back surface cover  30  is made up from a downwardly hanging portion  168  that extends along the vertical direction in  FIGS. 1 through 5 , and a scraper fixing part  170 , which is bent and extends substantially perpendicularly with respect to the downwardly hanging portion  168 . The downwardly hanging portion  168  is connected securely to the first casing member  26  and the second casing member  28  through cover connecting screws  172 . More specifically, non-illustrated cover connecting screw holes are formed in the first casing member  26  and the second casing member  28 , and the cover connecting screws  172  are screw-engaged with the cover connecting screw holes. 
         [0066]    A proximity switch  176  that detects when the knuckle joint  74  is positioned at a bottom dead center or a top dead center position is fitted into an opening  174  formed in the downwardly hanging portion  168  of the back surface cover  30 . The proximity switch  176  is connected securely to the first casing member  26  and the second casing member  28  through switch connecting screws  178 . Switch connecting screw insertion holes  180  are formed to penetrate through the downwardly hanging portion  168 , such that after the switch connecting screws  178  have passed through each of the switch connecting screw insertion holes  180 , the switch connecting screws  178  are screw-engaged with non-illustrated switch connecting screw holes that are formed in the first casing member  26  and the second casing member  28 . 
         [0067]    The first scraper  98 , which is substantially T-shaped, is positioned and fixed securely in place through a scraper connecting screw  182  to the scraper fixing part  170  of the back surface cover  30 . Of course, a scraper connecting screw hole  184  is provided in the scraper fixing part  170 , and the scraper connecting screw  182  is screw-engaged with the scraper connecting screw hole  184 . 
         [0068]    In the aforementioned structure, the first scraper  98  and the second scraper  100  are formed from thin metallic plates, which exhibit elasticity and further exhibit a suitable elastic force. The material of the first scraper  98  and the second scraper  100  may also be rubber. 
         [0069]    The first scraper  98  blocks a clearance formed between the arcuate surface of the first arcuate portion  94  of the clamp arm  34  and the casing  32 , whereas the second scraper  100  blocks a clearance between the arcuate surface of the second arcuate portion  96  and the casing  32 . As can be understood from this fact, the first scraper  98  and the second scraper  100  function as seals. 
         [0070]    Claw connecting screw holes  186  are provided in plurality on the claw member  20  for screw-engagement therein of the claw connecting screws  102 . When the claw member  20  is attached with respect to the clamp arm  34 , the claw connecting screw insertion holes  104  through which the claw connecting screws  102  are inserted, and the claw connecting screw holes  186  with which the claw connecting screws  102  are screw-engaged are selected corresponding to a required projecting length (reach length) of the claw member  20 . 
         [0071]    The remaining clamp apparatus  10   b,    10   c  are of the same structure as the clamp apparatus  10   a.  Therefore, the same constituent elements thereof are designated by the same reference numerals, and detailed descriptions of such features are omitted. 
         [0072]    The clamp apparatus  10   a,    10   b  are provisionally connected and positioned by engagement of the projection pins  154  of the connecting bracket  14  of the clamp apparatus  10   a  with the projection pin engagement holes  152  of the connecting bracket  14  of the clamp apparatus  10   b.  The clamp apparatus  10   b,    10   c  are provisionally connected and positioned in a similar manner. In addition, by tightening the tie rods  16 , which are inserted through the tie rod insertion holes  150  of the three connecting brackets  14 ,  14 ,  14 , the clamp apparatus  10   a  through  10   c  are mutually and firmly connected to each other. 
         [0073]    Additionally, a non-illustrated directional control valve and a non-illustrated pressure control valve are connected to the intake and exhaust pipes  58  (see  FIG. 3 ), to thereby constitute the clamp unit  12  shown in  FIGS. 1 and 3 . 
         [0074]    The clamp unit  12 , including the clamp apparatus  10   a  to  10   c  according to the present embodiment, is constructed basically as described above. Next, operations and advantages of the clamp unit  12  and the clamp apparatus  10   a  to  10   c  will be described. 
         [0075]    In each of the clamp apparatus  10   a  to  10   c,  the clamp side end portion  36  of the clamp arm  34  projects from the opening of the casing  32 . Accordingly, there is no need for a connecting shaft of the toggle link mechanism to extend and be exposed to the exterior of the casing  32 , as disclosed in the specification of the aforementioned German Utility Model Registration No. 29504267. Therefore, the widthwise dimension of the clamp apparatus  10   a  to  10   c  can be made narrow, thereby enlarging the degree of freedom of locations in which the clamp unit  12  can be installed. 
         [0076]    The clamp unit  12  is attached to a non-illustrated fixing means or the like, and in this state, is installed, for example, in a welding station of an automobile production line. At this time, as shown in  FIG. 6 , the clamp side end portion  36  of each of the clamp arms  34  is in an upstanding condition, whereby a constituent element that makes up the workpiece is not clamped thereby. Stated otherwise, the clamp arm  34  is in an unclamped state. At this point in time, the piston  62  is in a bottom dead center position, and the rod  66  is retracted to a rearward end. 
         [0077]    Further, the bottom dead center positioned piston  62  is seated on the damper  50 . Moreover, the first arcuate portion  94  of the clamp arm  34  is accommodated inside the casing  32 , whereas the second arcuate portion  96  is exposed from the casing  32 . 
         [0078]    Upon clamping a workpiece, compressed air is supplied from a non-illustrated compressed air supply source. The compressed air, after passing through the aforementioned directional control valve, the pressure control valve, and the intake and exhaust pipes  58  (see  FIG. 3 ), is introduced into the first port  48  (see  FIG. 6 ) of the head cover  42 , and then passes through the communication passage  46  and arrives at the cylinder chamber  38 . Of course, compressed air that is already accommodated inside the cylinder chamber  38  passes through the communication passage  54  and the second port  56  of the rod cover  44 , and the intake and exhaust pipes  58 , and then is directed out to an intake and exhaust manifold. 
         [0079]    As a result, an upwardly directed pressure acts on the bottom dead center positioned piston  62 , and consequently, the piston  62  begins to be displaced upwardly (in the direction of arrow A) in  FIG. 6 , and following thereon, the rod  66  also begins to advance in an upward direction (in the direction of arrow A). 
         [0080]    Accompanying advancement of the piston  62 , the knuckle joint  74  and the first link member  76  rise. As a result, the end of the second link member  78  is pressed upward, and the clamp arm  34  that is connected to the second link member  78  by the link pin  90  is swung and oriented in the direction of the arrow X about the pivot pin  92 . 
         [0081]    Accompanying such swinging movement, the first arcuate portion  94  gradually becomes exposed from the casing  32 , whereas the second arcuate portion  96  gradually is accommodated inside the casing  32 . During this process, the second scraper  100  is in sliding contact with the arcuate surface of the second arcuate portion  96 . Accordingly, even if foreign matter or debris floating within the assembly station comes into contact with and adheres to the arcuate surface of the second arcuate portion  96 , such foreign matter is scraped off under the action of the second scraper  100 . 
         [0082]    At the same time, the first scraper  98  is in sliding contact with the arcuate surface of the first arcuate portion  94 , and thus, the cleaned first arcuate portion  94  is exposed from the casing  32 . Accordingly, adherence of foreign matter to the arcuate surface of the first arcuate portion  94 , and mixing of such foreign matter in welding locations can be prevented. 
         [0083]    The first scraper  98  is in sliding contact over the entire arcuate surface of the first arcuate portion  94 , and similarly, the second scraper  100  is in sliding contact over the entire arcuate surface of the second arcuate portion  96 . That is because, as described above, the first arcuate portion  94  and the second arcuate portion  96  are formed to curve about the pivot pin  92 , and the center of swinging motion of the first arcuate portion  94  and the second arcuate portion  96  is defined by the pivot pin  92 . 
         [0084]    Lastly, as shown in  FIG. 5 , the regulating screw  107  abuts against and is stopped by the stopper member  146 , and swinging movement of the clamp side end portion  36  of the clamp arm  34  is restricted, together with the knuckle joint  74  and the piston  62  reaching the top dead center position, whereby the advancing operation of the rod  66  to the forward end is completed. At this time, as shown in  FIGS. 1 through 5 , the clamp side end portion  36  of the clamp arm  34  is placed in a recumbent posture, and the claw member  20  (see  FIG. 1 ) clamps the workpiece. Further, the entirety of the first arcuate portion  94  is exposed from the casing  32 , whereas the entirety of the second arcuate portion  96  is accommodated inside the casing  32 . 
         [0085]    While the workpiece is being clamped, a reactive force is generated responsive to the clamping force. Such a reactive force is transmitted to the second link member  78  through the clamp arm  34 , and furthermore, is transmitted to the fixed roller  124  that is in contact with the curved end face of the second link member  78 . More specifically, the reactive force is received and absorbed by the fixed roller  124 . 
         [0086]    In this condition, arrival of the knuckle joint  74  at the top dead center position is detected by the upper part of the proximity switch  176 . The proximity switch  176  transmits a detection signal to a non-illustrated control circuit. The control circuit, having received the detection signal, judges that “workpiece clamping is completed,” and issues a command with respect to a non-illustrated welding robot to carry out a welding operation. 
         [0087]    Thereafter, welding is carried out on the workpiece and the automotive vehicle body. At this time, so-called spatter is scattered as debris from the welding location. However, because the first scraper  98  and the second scraper  100  function as seals, which block clearances between the casing  32  and the clamp arm  34 , such debris does not enter and penetrate into the interior of the casing  32 . Accordingly, the toggle link mechanism  70  is prevented from becoming contaminated. 
         [0088]    In the foregoing manner, penetration of foreign matter or debris into the interior of the casing  32  is prevented. Consequently, the adverse influence of foreign matter and debris on operations of the toggle link mechanism  70  can effectively be avoided. 
         [0089]    Moreover, from time to time, debris may come into contact with and adhere to the first arcuate portion  94 . 
         [0090]    After completion of welding, compressed air is supplied from the non-illustrated compressed air supply source, so that a state is brought about in which the clamp side end portion  36  of the clamp arm  34  is placed in an upstanding posture and the clamp arm  34  is in unclamped state again. In this case, compressed air passes through the intake and exhaust manifold, the intake and exhaust pipes  58  (see  FIG. 3 ), the second port  56  of the rod cover  44  (see  FIG. 5 ), and the communication passage  54 , and is introduced into the cylinder chamber  38 . Simultaneously therewith, compressed air that is already accommodated inside the cylinder chamber  38  passes through the communication passage  46  of the head cover  42 , the first port  48 , and the intake and exhaust pipes  58 , and then is directed out to the intake and exhaust manifold. 
         [0091]    As a result, a downwardly directed pressure acts on the top dead center positioned piston  62 , and consequently, the piston  62  begins to be displaced downwardly in  FIG. 5  (in the direction of arrow B), and following thereon, the rod  66  also begins to retract in an downward direction (in the direction of arrow B). 
         [0092]    Accompanying retraction of the piston  62 , the knuckle joint  74  and the first link member  76  are lowered. Following thereon, the end of the second link member  78  is pulled downward, and the clamp arm  34  that is connected to the second link member  78  by the link pin  90  is swung and oriented in the direction of the arrow Y about the pivot pin  92 . 
         [0093]    Accompanying such swinging movement, the first arcuate portion  94  gradually becomes accommodated inside the casing  32 , whereas the second arcuate portion  96  gradually is exposed from the casing  32 . During this process, the first scraper  98  is in sliding contact with the arcuate surface of the first arcuate portion  94 . Accordingly, even if debris comes into contact with and adheres to the arcuate surface of the first arcuate portion  94 , such debris is scraped off under the action of the first scraper  98 . Foreign matter that may be adhered to the arcuate surface of the first arcuate portion  94  is handled in a similar manner. Owing thereto, the arcuate surface of the first arcuate portion  94  can always be maintained in a clean condition. 
         [0094]    Consequently, entry and penetration of debris or foreign matter that is adhered to the arcuate surface of the first arcuate portion  94  into the interior of the casing  32  can be prevented. From this standpoint as well, the toggle link mechanism  70  can be protected from debris or foreign matter, and as a result, suitable operations of the toggle link mechanism  70 , and hence suitable swinging movement of the clamp arm  34 , can be maintained over a long period. 
         [0095]    At the same time, the second scraper  100  remains in sliding contact with respect to the arcuate surface of the second arcuate portion  96 . 
         [0096]    Ultimately, the piston  62  arrives at the bottom dead center position shown in  FIG. 6 . Along therewith, the retracting operation to the rear end of the rod  66  is brought to an end, and as shown in  FIG. 6 , the clamp side end portion  36  of the clamp arm  34  is placed in an upstanding condition, and the claw member  20  (see  FIG. 1 ) is separated away from the workpiece. More specifically, an unclamped condition is brought about, whereby the workpiece is released. 
         [0097]    At this time, the entirety of the first arcuate portion  94  is accommodated in the interior of the casing  32 , whereas the entirety of the second arcuate portion  96  is exposed from the casing  32 . Naturally, during the process of becoming exposed from the casing  32 , the second arcuate portion  96  is subjected to cleaning by the second scraper  100 . 
         [0098]    In the foregoing manner, entry and penetration of debris into the interior of the casing  32  is prevented. More specifically, according to the present embodiment, clamp apparatus  10   a  to  10   c  can be constructed in which the widthwise dimension thereof can be made narrower, and penetration of debris into the interior of the casing  32  can easily be prevented. 
         [0099]    In the above condition, arrival of the knuckle joint  74  at the bottom dead center position is detected by the lower part of the proximity switch  176 . The proximity switch  176  transmits a detection signal to the non-illustrated control circuit. The control circuit, having received the detection signal, judges that “workpiece releasing is completed,” and issues a command to send out the automotive vehicle body on which the workpiece has been welded, and to transport a next automotive vehicle body on which the workpiece is to be welded. In this manner, continuous welding of workpieces is carried out on the automotive vehicle bodies. 
         [0100]    Naturally, in subsequent operations as well, similar to the aforementioned processes, entry and penetration of debris or foreign matter into the interior of the casing  32  can effectively be avoided. 
         [0101]    Next, explanations will be made concerning an embodiment in which side surface cleaning scrapers are provided for cleaning side surfaces of the first arcuate portion  94 . Constituent elements that are the same as those shown in  FIGS. 1 through 6  are designated by like reference characters, and detailed descriptions of such features are omitted. 
         [0102]      FIG. 7  is an overall outline perspective view of a clamp apparatus  202  in which two third scrapers  200   a,    200   b  (side surface cleaning scrapers) are provided, in addition to the first scraper  98  and the second scraper  100 . Similar to the first scraper  98  and the second scraper  100 , the third scrapers  200   a,    200   b  are formed from thin metal plates, which exhibit elasticity and further exhibit a suitable elastic force. 
         [0103]    In this case, the third scraper  200   a  includes a long side portion, and a short side portion, which is shorter compared to the long side portion, and which is bent at substantially 90° with respect to the long side portion forming an L-shape. The long side portion thereof is attached by screws  204   a  in the vicinity of the vertical mouth of the opening  33  in the first casing member  26 . Further, one end surface of the short side portion is placed in sliding contact against the side surface on the first arcuate portion  94  of the clamp arm  34  that faces the first casing member  26 . 
         [0104]    The other third scraper  200   b  is constructed in the same manner as the aforementioned third scraper  200   a.  The long side portion thereof is attached by screws  204   b  in the vicinity of the vertical mouth of the opening  33  in the second casing member  28 , and together therewith, one end surface of the short side portion is placed in sliding contact against the side surface on the first arcuate portion  94  of the clamp arm  34  that faces the second casing member  28 . 
         [0105]    Accordingly, in this case, during the process in which the clamp arm  34  is swung and oriented along the direction of the arrow X about the pivot pin  92  in order to clamp the workpiece together with the first arcuate portion  94  gradually being exposed from the casing  32 , at the same time that the second scraper  100  is in sliding contact with the arcuate surface of the second arcuate portion  96 , the first scraper  98  is in sliding contact with the arcuate surface of the first arcuate portion  94 , and furthermore, the first scraper  98  and the third scrapers  200   a,    200   b  are placed in sliding contact respectively against side surfaces of the first arcuate portion  94 . As a result, the first arcuate portion  94 , both the arcuate surface and the side surfaces of which have been subjected to cleaning, is exposed from the casing  32 . Accordingly, adherence of foreign matter to the arcuate surface and side surfaces of the first arcuate portion  94 , and mixing of such foreign matter at welding locations can more reliably be avoided. 
         [0106]    Further, during the process in which the clamp arm  34  is swung and oriented in the direction of the arrow Y about the pivot pin  92  in order to place the workpiece in an unclamped state, together with the first arcuate portion  94  being accommodated gradually inside the casing  32 , the first scraper  98  is in sliding contact with the arcuate surface of the first arcuate portion  94 , along with the third scrapers  200   a,    200   b  being placed in sliding contact against the side surfaces. Moreover, at the same time, naturally, the second scraper  100  is kept in sliding contact with respect to the arcuate surface of the second arcuate portion  96 . 
         [0107]    Accordingly, when welding is carried out with respect to the workpiece, even if debris or foreign matter become adhered to the arcuate surface or the side surfaces of the first arcuate portion  94 , such debris or foreign matter is scraped off by the first scraper  98  and the third scrapers  200   a,    200   b.  Owing thereto, the arcuate surface and side surfaces of the first arcuate portion  94  can always be maintained in a clean condition. 
         [0108]    Consequently, entry and penetration of debris or foreign matter that is adhered to the arcuate surface or the side surfaces of the first arcuate portion  94  into the interior of the casing  32  can be prevented. From this standpoint as well, the toggle link mechanism  70  can be protected from debris or foreign matter, and as a result, suitable operations of the toggle link mechanism  70 , and hence suitable swinging movement of the clamp arm  34 , can be maintained over a long period. 
         [0109]    In addition, the third scrapers  200   a,    200   b,  similar to the first scraper  98  and the second scraper  100 , function as seals for blocking clearances between the casing  32  and the clamp arm  34 . Owing thereto, since debris does not enter and penetrate into the interior of the casing  32 , the toggle link mechanism  70  is prevented more easily from becoming contaminated. 
         [0110]    In this manner, by additionally providing the third scrapers  200   a,    200   b  that act to clean the side surfaces of the first arcuate portion  94 , penetration of debris or foreign matter into the interior of the casing  32  can be avoided more easily. 
         [0111]    The clamp apparatus according to the present invention is not limited by the aforementioned embodiments. It is a matter of course that various structures could be adopted therein without deviating from the essence and gist of the present invention. 
         [0112]    For example, the first scraper  98  may be disposed on the inside of the casing  32 , and the second scraper  100  may be disposed on the outside of the casing  32 . Similarly, the third scrapers  200   a,    200   b,  for example, may be made from rectangular shaped thin rubber sheets, and may be arranged at positions facing toward the side surfaces of the clamp arm  34  on inner walls of vertical mouth of the opening  33 . In this case, the dimensions of the third scrapers  200   a,    200   b  may be of a degree that does not interfere with swinging operations of the clamp arm  34 . 
         [0113]    Further, the first casing member  26  and the second casing member  28  can constitute the casing without being divided or separated from each other. 
         [0114]    Furthermore, the means for connecting the clamp apparatus  10   a  to  10   c  is not limited in particular to the connecting brackets  14  and the tie rods  16 . As shown in  FIG. 8 , a single connecting plate  210  may be employed, which bridges over the clamp apparatus  10   a  to  10   c.  The clamp apparatus  202  shown in  FIG. 7  may also be connected together as a plurality in a similar manner. 
         [0115]    Still further, although in the embodiments shown in  FIGS. 1 and 8 , the clamp unit  12  is constituted by three individual clamp apparatus  10   a  to  10   c,  it goes without saying that the number of clamp apparatus is not limited to three. Naturally, the same is true also in the case of connecting together the clamp apparatus  202  shown in  FIG. 7 .