Abstract:
A device for holding a part comprises a retainer member provided for applying and holding the part and having a convexly spherical surface section which is received in a concavely spherical surface section of a receptacle member. To enable movement of the spherical surface sections relative to one another, the device includes an arrangement for forming a temporary friction-free air bearing between the two surface sections, which can be removed once the surfaces of the two parts have been brought into the desired alignment and engagement to fix the receptacle and retainer members in position.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to a device for holding a part, which has a retainer member received in a receptacle member. The retainer member is provided for applying and holding the part and has a convexly spherical surface section and a surface section for the application of the part to be held, while the receptacle member provides a rotatable seating for the retainer member and comprises a concavely spherical surface forming al sliding seating surface for the convexly spherical surface section of the retainer member. 
     A device of this type is disclosed in German 196 02 636. The problem of plane-parallel alignment and adjustment of the two parts respectively comprising a planar surface section can be solved with such a device. This problem particularly occurs when the parts are to be permanently connected to one another after the adjustment, for example with laser welding, soldering or gluing. 
     For laser welding given the device disclosed by the German document, a laser beam serving this purpose can be supplied to the weld location for attachment of the part to be held unimpeded by the receptacle, the retainer member and the surface section as a result of a recess fashioned in the retainer member and the receptacle member. 
     When the surface sections of the parts to be connected to one another that face toward one another are aligned plane-parallel, a wedge-shaped gap, for example between these surface sections, leads to a warping when a weld or a solder hardens or when an adhesive cures. This warping generally modifies the relative position of the parts connected to one another in an unfavorable way. 
     An automatic, plane-parallel alignment is achieved with a device of this type in that one part is held on a rotatably seated retainer member of the device while the other part is firmly held outside the device. 
     For automatic alignment of the parts, the planar surface section of the part held on the retainer member and the planar surface section of the part firmly held outside the device are placed into contact with one another under a slight pressure. 
     Given proper dimensioning of the device, the two parts are aligned such that their planar surface sections facing toward one another are aligned plane-parallel relative to one another. 
     According to the above-mentioned German document, it is necessary for this purpose that the tilting or alignment moment generated by the pressing power is greater than the frictional moment of the convexly spherical surface section of the retainer member on the concavely spherical surface section of the receptacle member of the device forming the glide surface. With a given geometry of the device, the automatic alignment can only occur up to a maximum coefficient of friction and, thus, frictional moment as well. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of offering a device for holding a part for an automatic alignment of this part that produces an automatic alignment largely independently of the dimensioning and/or geometry of the device, even given slight pressing power. 
     According to the solution of the present invention, the inventive device comprises the features of an improvement in a device having a retainer member received in a receptacle member with the retainer member having a convexly spherical surface section and a surface section for applying the part to be held and the receptacle member providing a rotatable bearing for the retainer member, said rotatable bearing being a concavely spherical surface forming a glide seat surface for the convexly spherical surface section of the retainer member. The improvement comprises a glide means for arrangement between the concavely spherical surface section of the receptacle member and the convexly spherical surface section of the retainer member of the device, which accepts this section, the glide means being in the form of a glide layer. 
     As a result of the glide layer arranged between the concavely spherical surface section of the receptacle member and the convexly spherical surface section of the retainer member accepted in this section, the coefficient of friction between these two sections can be advantageously kept so slight that the dimensions and geometry of the device no longer have any influence on the pressing power or pressure needed for the alignment, and this pressing power can be extremely low. 
     A preferred and advantageous development of the inventive device comprises a means for at least temporarily producing the glide layer composed of the glide means between the concavely spherical surface section of the receptacle member and the convexly spherical surface section of the retainer member accepted therein. 
     In this case, one can advantageously proceed so that the glide layer is produced during the alignment event in order to keep the friction between the retainer member and the receptacle member as low as possible. After self-alignment has occurred, the glide layer can be eliminated for a secure fixing of the alignment and, thus, this friction can be, in turn, increased. 
     This can be especially simply implemented when the glide means is a gas, for example air. 
     In this case, it is advantageous in view of a simple structure when the means for producing the glide layer of the gas comprises at least one inflow opening fashioned in one of the two spherical surface sections, preferably an inflow opening fashioned in the surface section of the receptacle member for allowing a gas to flow in under pressure into the interspace between the two spherical surface sections. 
     The means for producing the glide layer of the gas can thereby comprise an optionally actuatable means for producing a gas under pressure, preferably arranged outside the retainer member and the receptacle member. This means is connected to the inflow opening, preferably by a channel fashioned in the receptacle member and leading to the inflow opening and a pressure conduit, which connects the channel to the means. 
     An air bearing of the retainer member, which advantageously enables a practically friction-free and, thus, resistance-free turning of the retainer member in all directions around a center of a sphere of the convexly spherical surface section, is realized by the glide layer of the pressurized gas formed between the convexly spherical surface section of the retainer member and the concavely spherical surface section of the receptacle member. 
     A better fixing of the alignment following the alignment event can be advantageously achieved by means of a temporary producing of an under-pressure between the two spherical surface sections for mutually pressing these two surface sections against one another. The retainer member and the receptacle member can thereby be advantageously firmly fixed relative to one another so that a modification of the alignment of the retainer member and, thus, of the part held on this member is practically only possible with the application of a force. 
     The means for temporarily producing an under-pressure between the two spherical surface sections can be constructed similar to a means for generating the pressure when the means for generating the under-pressure comprises at least one extraction opening formed in one of these two surface sections, preferably, the section of the receptacle member for removal of the gas in the interspace between the two spherical surface sections. 
     Similar to the means for generating the pressure, it is also advantageous here when the means for generating the under-pressure between the two spherical surface sections comprises an optionally actuatable means for generating the under-pressure, preferably arranged outside the retainer member and the receptacle member. The means is connected to an extraction opening, preferably by a channel fashioned in the receptacle member and leading to the extraction opening and an under-pressure conduit that connects the channel to this under-pressure generating means. 
     Advantageously, recesses are formed in the retainer member and the receptacle member, and the recesses allow at least two light beams directed onto the convexly spherical surface section in directions that are oblique relative to one another to emerge unimpeded through the receptacle and retainer member and from the surface section for application on the part to be held. When, in this case, laser beams for welding are employed as the light beams, two or more weld locations separate from one another can be simultaneously achieved. In this way, two parts to be aligned plane-parallel relative to one another and to be joined to one another can be simultaneously welded to one another at two or more separate points. 
     For holding a part on the device, a fastening tool for optionally releasable fastening of the part to be held on the retainer member is preferably secured on the retainer member. 
     Often, the part to be held is cylindrical, at least in sections thereof, and comprises a planar end face to be aligned plane-parallel with respect to another planar surface. In this case, the fastening tool is preferably a clamp tool having clamping jaws grouped around an axis and perpendicularly adjustable, for example adjustable radially relative to this axis, between which the part can be held with its cylindrical axis coaxially to the axis of the tool. The clamp tool is preferably secured on the retainer member so that the axis of the clamp tool coincides with an axis proceeding through the spherical center of the convexly spherical surface section of the retainer member. 
     For example, housings for holding optical lenses or fiber ends that are to be connected to optical transmitter modules via a planar end face of these modules are cylindrical, at least in sections. Given a housing for holding a fiber end, the fiber forming this end usually hangs from the housing in the form of a long fiber tail that, for example, can have a length of a few decimeters or more. This fiber tail can be a disturbing factor when fastening the housing to the retainer member. 
     This problem can be entirely or at least partially eliminated when a slot for the acceptance of the fiber is fashioned in the retainer member. The slot expediently extends in the direction of the cylindrical axis of the housing held on the retainer member, extending entirely through the retainer member in the direction perpendicular to this axis, but only partly, so that the retainer member remains together and does not fall apart. Since the retainer is arranged on the receptacle member and hardly any interspace is located between these members, it is expedient when a slot for the acceptance of the fiber is also fashioned in the receptacle member, and this slot is aligned with the slot of the retainer member. 
     An optional fastening and re-release of a part to be held in the fastening tool fastened on the retainer member can be advantageously achieved by a pneumatic means for an optional opening and closing of the fastening tool. Preferably and advantageously, such a means for optionally opening and closing the fastening tool is fashioned in the retainer member and is externally actuatable. 
     When, for example, the fastening tool is composed of a clamp tool having two or more adjustable clamping or clamp jaws, then the means arranged in the inside of the retainer member for optionally opening and closing the clamp tool can, per clamp jaw, comprise a respective hydraulic or, preferably, pneumatic cylinder and a force transmission means for the transmission of a piston force of the cylinder onto the clamp jaw for optionally opening said clamp jaw in the direction of a closing or opening of the clamp tool. 
     Each pneumatic cylinder is preferably connected, for example by a channel fashioned in the retainer member, to an inflow and outflow opening fashioned in the convexly spherical surface section of the retainer member. An inflow and outflow opening is arranged in the convexly spherical surface section of the receptacle member opposite the inflow and outflow opening, and the inflow and outflow opening is connected to a means preferably arranged outside the retainer and receptacle member for optionally generating a pressure and an under-pressure. Preferably, this means is connected by a channel formed in the receptacle member and leads to the inflow and outflow opening and by a pressure and under-pressure conduit connecting this channel to this means. The inflow and outflow opening fashioned in the concavely spherical surface section of the receptacle member preferably comprises a larger diameter than the inflow and outflow opening fashioned in the convexly spherical surface section of the retainer member. This has the advantage that a cylinder, even given a retainer member tilted relative to the receptacle member, can be actuated as long as the inflow and outflow openings of the tilted retainer member still lie in the region of the inflow and outflow openings of the receptacle member. 
     In any case, the means for an optional opening and closing of the fastening tool advantageously enables an actuation of the tool for fastening or releasing the part to be held, regardless of whether the retainer member happens to be movably seated on the receptacle member or happens to be fixed on the receptacle member. 
     Particularly given an employment of the inventive device for fastening a housing for holding an optical lens or a fiber end at an optical transmitter module, it is advantageous when an imaging optics and an optical detector are permanently arranged in the retainer member so that the imaging optics focuses light onto the detector. The light enters into this member through an opening fashioned in the surface section for applying the part of the retainer member to be held. As a result thereof, a pre-adjustment of the retainer member with respect to a light beam emitted by the module is enabled and the optical lens or fiber end in the housing can be adjusted thereto. 
     The imaging optics and the optical detector are preferably arranged on an axis of the retainer member proceeding through the spherical center of the convexly spherical surface section of the retainer member. In this case, the retainer member can be advantageously pre-adjusted relative to a light beam emitted by the module so that this axis of the retainer member coincides with an axis of the light beam. It is expedient to rigidly arrange the imaging optics and the optical detector in a preferably interchangeable fastening tool that is arranged coaxially relative to the axis of the retainer member and on which the housing with the lens or the fiber end is held coaxially relative to this axis. 
     The dimensions of the inventive device are largely arbitrary. In particular, a special advantage is to be seen wherein a radius of the surface sections of the retainer member cannot only lie in the millimeter range and below, but can also be larger than one centimeter, for example five centimeters. 
     An inventive device can be especially advantageously utilized for the parallel alignment of a planar surface section of the part relative to a planar surface section of another part facing toward this surface section. Thus, the one part is secured on the retainer member so that the planar surface section oft his part faces away from the retainer member and the receptacle member and wherein the planar surface section of the one part secured in this way and the planar surface of the other part are brought into planar contact with one another by moving the retainer member with the receptacle member and the other part relative to one another. 
     The planar surface sections of the one part secured on the retainer member and of the other part, that are brought into planar contact with one another, can be advantageously firmly joined to one another by laser welding. An optical lens and/or fiber mount can thereby be advantageously employed as the one part and an optical module, for example in the form of a laser module, to which the optical lens and/or the fiber mount is to be precisely coupled, can be employed as the other part. 
    
    
     Other advantages and features of the invention will be readily apparent from the following description of the preferred embodiments, the drawings and claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing the retainer member of an exemplary embodiment of the inventive device; 
     FIG. 1 a  is a plan view of the specific axes of the retainer member of FIG. 1 lying in a common plane; 
     FIG. 2 is a perspective view of a receptacle member of the exemplary embodiment of FIG. 1; 
     FIG. 3 is a side view with portions broken away of an exemplary embodiment wherein the retainer member is accepted in the receptacle member; 
     FIG. 4 is a perspective view of a fastening tool of the exemplary embodiment for holding a part; and 
     FIG. 5 is a partial cross sectional view along an axis A through the fastening tool of the exemplary embodiment that contains an imaging optics and an optical detector. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The principles of the present invention are particularly useful when incorporated in a holding device for a part, generally indicated at  1  in FIG. 3, which device has a retaining member, generally indicated at  2 , which is received in a receptacle member, generally indicated at  3 . The retainer member  2  has a fastening tool  8 , which is interchangeably arranged on the retainer member  2  for holding the part  1 . 
     As best illustrated in FIG. 1, the retainer member  2  has a convexly spherical surface section  20  and a preferably planar surface section  21  facing away from the section  20  to which the part  1  to be held is to be attached. 
     A central axis A of this section  20  proceeds through the spherical center ct of the convexly spherical surface section  20  and proceeds vertically in the plane of FIGS. 1-5. The convexly spherical surface section  20  has a radius R 1 . 
     The planar surface section  21  of the retainer member  2  is arranged, for example, so that the axis A is perpendicular to it. For example, three radial axes a 1 , a 2  and a 3 , offset by an angle of 120° relative to one another, pass through the axis A and the spherical center ct in the plane of the surface section  21 . These radial axes a 1 , a 2  and a 3  are shown again in FIG. 1 a in a perpendicular plan view onto the planar surface section  21 , so that the axis A in FIG. 1 a  is perpendicular to the plane of the drawing of this FIG. 1 a  and the radial axes a 1 , a 2  and a 3  lie in the plane of the drawing. The radial axis a 1  is only apparently parallel to the axis A in FIGS. 1 and 2. In reality, it is arranged perpendicular to the axis A like the other two axes a 2  and a 3 . 
     A recess or groove  25  is fashioned in the retainer member  2  under each radial axis a 1 , a 2  and a 3 . This recess  25  extends in the direction of the respective radial axis a 1 , a 2  or a 3  between the convexly spherical surface sections  20  and a bore  26  of the retainer member  2 , which bore is coaxial with the axis A for the acceptance of a fastening tool. 
     Each recess or groove  25  defines a circular sector-shaped opening  254  in the planar surface section  21 , an opening  255  adjoining this opening  254  at an acute angle in the convexly spherical surface section  20 , and an opening  263  in the inside wall  262  of the bore  26  of the retainer member  2 . The opening  263  in the inside wall  262  of the bore  26  adjoins the opening  254  fashioned in the planar surface  21  of the retainer member  2  at an angle thereto. 
     Each recess  25  comprises two planar side walls  251  and  253  converging in a radial direction to the axis A and respectively arranged at the angle relative to the planar surface section  21  of the retainer member and comprises a bottom surface  252  which, likewise, is preferably planar. The bottom surface  252  connects these two side walls to one another. 
     The bottom surface of each recess  25 , like the side walls  251  and  253 , extends between the openings  255  and  263 , and is arranged at an angle relative to each side wall  251  and  253 . The bottom surface  252  extends in the radial direction relative to the axis A obliquely relative to the planar surface  21  so that a vertical distance d with respect to this section of the bottom surface  252  from the planar surface  21  decreases with decreasing radial distance d 1  from the axis A. 
     As a result of the openings  254  in the planar surface section  21  of the retainer member  2  defined by the recesses or grooves  25 , this surface section  21  is divided into circular sector-shaped planar sections  210  separated from one another. Each of these planar sections  210  extends in the direction of one of the radial axes a 1 , a 2  and a 3  belonging to it. 
     A light beam or ray  7  (see FIG. 3) propagating in the direction r 1 , r 2  or r 3  obliquely relative to the planar surface section  21  can pass unimpeded through the retainer member  2  and emerge from the planar surface section  21  through each of these recesses or grooves  25 . For example, the light beam  7  can be a focused laser beam serving the purpose of a laser welding that is focused onto a point S lying in front of the planar surface section  21  of the retainer member  2 , so that welding will be carried out at this point S. In the present, specific instance of the three existing recesses or grooves  25 , three laser beams  7  can be simultaneously focused in directions r 1 , r 2  and r 3  obliquely relative to one another and focused onto the three points S lying in front of the planar surface section  21  of the retainer member  2  at which welding is to be respectively carried out. 
     The receptacle member  3  in the exemplary embodiment shown in FIG. 2 is fashioned essentially complementary relative to the retainer member  2 . For example, the receptacle member  3  has a concavely spherical surface section  30  forming a glide seat surface for the convexly spherical surface section  20  of the retainer member  2 . 
     The receptacle member  3  is arranged and shown so that the spherical center of the concavely spherical surface section  30  and a central axis of this section  30  which proceeds through the spherical center coincides with the spherical center ct and the central axis A of the convexly spherical surface section  20  of the retainer member  2 . 
     The receptacle member  3  comprises, for example, a planar surface section  31  surrounding the concavely spherical surface section  30 . This surface section  31  is parallel to the plane erected by the radial axes a 1 , a 2  and a 3  and, thus, extends perpendicular to the axis A. 
     In addition, a respective recess or groove  35  is fashioned in the receptacle member  3  under each of the radial axes a 1 , a 2  and a 3 . These recesses or grooves  35  extend in the direction of the respective radial axis a 1 , a 2  or a 3  between the concavely spherical surface  30  and an outside surface  310  of the receptacle member  2  facing away from this section  30 . 
     Each recess or groove  35  defines a respective opening  354  in the concavely spherical surface section  30  and a respective opening  355  in the outside surface  10 . These two openings are connected to one another by side walls  351  and  353  facing toward one another and by a bottom surface  352 . 
     Each recess or groove  35  is aligned with a respective groove or recess  25  of the retainer member  2  and is preferably fashioned so that the recess  35  is a continuation of the recess  25  in the direction of the radial axis a 1 , a 2  or a 3  of the two recesses  25  and  35  when this direction points away from the central axis A. 
     Each light beam  7  can propagate unimpeded both through the receptacle member  3  as well as through the retainer member  2  through the recesses or grooves  35 . 
     FIG. 3 shows an assembled exemplary embodiment with a vertical section that is conducted in the plane erected by the central axis A and the radial axis a 1 , whereby the sectional surface of the section half of the retainer member  2  and the receptacle member  3  lie to the right of this plane in FIGS. 1 and 2 is shown and the axis A now lies in the plane of the drawing of FIG.  3 . 
     A glide means  50 , which is preferably a gas under pressure that is at an excessive pressure relative to the ambient pressure, is located between the concavely spherical surface section  30  of the receptacle member  3  and the convexly spherical surface section  20  of the retainer member  2  accepted in this section  30 . The glide means  50  spreads between the two spherical surface sections  20  and  30  over the entire surface of the regions of these sections  20  and  30  lying opposite one another and forms a glide layer  5  of which only a fraction is shown in FIG.  3 . As a result of this glide layer, the retainer member  2  is seated practically friction-free on the receptacle member  3 . 
     The distance t between the two spherical surface sections  20  and  30  that defines the thickness of the gaseous glide layer  5  preferably lies in the micrometer range and, for example, can amount to 10 micrometers. 
     The gaseous glide layer  5  can be temporarily produced by a means  4 . The means  4  comprises an inflow opening  40  fashioned in a concavely spherical surface section  30  to allow the gas  50  to flow in under a pressure P into the interspace  23  between the two spherical surface sections  20  and  30 . The means  4  comprises an optionally actuatable means  43  connected to the inflow opening  40  for producing the gas  50  under the pressure P. The means  43  is connected by a channel  41  fashioned in the receptacle member  2  and leading to the inflow opening  40  and a pressure conduit  42  connecting the channel  41  to this means  43 . 
     As a result of a means  6 , an under-pressure −P can be generated between the two spherical surface sections  20  and  30  for pressing these two surface sections  20  and  30  against one another and for fixing the retainer member  2  and receptacle member  3  relative to one another. The means  6  comprises an extraction opening  60  fashioned in the concavely spherical surface section  30  for extracting the gas  50  in the interspace  23  between the two spherical sections  20  and  30 . An optionally actuatable means  63  is provided for generating the under-pressure −P that is connected to the extraction opening  60 . The means  63  is connected by a channel  61  fashioned in the receptacle member  3  and leading to an extraction opening  60  and an under-pressure or suction conduit  62  connecting the channel  61  to this means  63 . 
     The means  4  and the means  6  can be actuated independently of one another and, in particular, in alternation. 
     A fastening tool  8  for optional releasable fastening of the part  1  to be held on the retainer member  2  is secured on the retainer member  2 . The tool  8  is replaceably arranged in the central bore  26  of the retainer member  2 . For example, the fastening tool  8  is composed of a collet chuck that, in the condition of being installed in the retainer member  2 , comprises clamp jaws  81  grouped around the central axis A and radially adjustable relative to this axis A, between which, for example, the cylindrical part  1  can be held with its cylindrical axis coaxial to the axis A. 
     For example, the collet chuck  8  comprises three clamp jaws  81 , each of which is firmly connected by an oblong, individual spring  82  extending along the axis A to a solid base  83  that is shared by all springs  82 . In FIG. 3, this collet chuck  8  is shown partially and in section as well as built into the retainer member  2 , whereas the collet chuck  8  is shown uninstalled and in a perspective view in FIG.  4 . 
     In FIG. 3, for example, the built-in collet chuck  8  holds a part  1  in the form of a cylindrical housing for holding the end of a fiber  12 . This held housing  1  comprises a planar end face  11  facing away from the planar surface section  21  of the retainer member  2 . This end face  11  is arranged and aligned plane-parallel relative to a planar surface section  101  of another part  10 , for example a laser module, that faces toward this end face  11 . This alignment occurs, for example, automatically where the end face  11  is brought into contact with the rigidly arranged planar surface section  101  under a slight pressure and the retainer member  2  being air seated in the receptacle member  3 . As a result of a following fixing of the retainer member  2  relative to the receptacle member  3 , this alignment can be securely retained, for example for a multi-point laser welding wherein the parts  1  and  10  are firmly joined to one another. 
     A respective slot  200  or  300  for accepting the optical fiber  12  it formed in the retainer member  2  and receptacle member  3 . According to FIGS. 1-3, the slots  200  and  300  extend along the radial axis a 1  in the recess  25  or  35  located thereunder in the retainer member  2  and the receptacle member  3 . The slots extend following one another from the outside surface  310  over the spherical surface sections  30  and  20  up to the central bore  26 . The slot  300  is limited by planar side walls  301  and  302  facing toward one another, and the slot  200  is limited by planar side walls  201  and  202  facing toward one another. Each of the side walls  201 ,  202 ,  301  and  302  is parallel to a plane formed by the axis A in the radial axis a 1 . 
     A means  80  for optionally opening and closing the collet chuck  8  is fashioned on the inside of the retainer member  2 . This means includes a pneumatic cylinder  810  per clamp jaw  81  and a force transmission means  820  for transmitting a force of a piston  811  in the cylinder  810  onto the clamp jaw  81  for moving this clamp jaw  81  in the direction of a closing or opening of the collet chuck  8 , as desired. 
     Each pneumatic cylinder  810  is preferably connected to an inflow and an outflow opening  813  formed in the convexly spherical surface section  20  of the retainer member  2 , and this connection is made by a channel  812  fashioned in the retainer member  2 . An inflow and outflow opening  814  is arranged in the concavely spherical surface  30  of the receptacle member  3  opposite the inflow and outflow opening  813 . The inflow and outflow opening  814  is connected to a means  817  for optionally generating a pressure P 1  and an under-pressure −P 1 , which means  817  is arranged preferably outside the retainer member  2  and the receptacle member  3 . The connection to the means  817  is preferably by a channel  815  formed in the receptacle member  3  and leading to the inflow and outflow opening  814  and by a pressure and under-pressure conduit  816  connecting this channel  815  to the means  817 . 
     The inflow and outflow opening  814  is fashioned with a diameter d 2  in the concavely spherical surface section  30  of the receptacle member  3 , which diameter d 2  is preferably larger than the diameter of the inflow and outflow opening  813  fashioned in the convexly spherical surface section  20  of the retainer member  2 . This has the advantage that the cylinder  810  can also be actuated given a retainer member  2  that is tilted relative to the receptacle member  3 , as long as the inflow and outflow opening  813  of the tilted retainer member  2  still lies in the region and in communication with the inflow and outflow opening  814  of the receptacle member  3 . 
     The force transmission means  820  comprises a respective rotary lever  821  per clamp jaw  81  and is connected to the piston  811 . The lever  821  is rotatable about a rotational axis  822  perpendicular to the axis A and the respective radial axis a 1 , a 2  or a 3 . The means  820  has a lever section  823  located between the jaw  81  and this rotary axis  822 , and the section  823  actuates the clamp jaw  81  via, for example, an intermediate link  824 . On the side of the lever section  823  facing away from the clamp jaw  81 , a spring  825  firmly supported on a retainer member  2  presses against the section  823  and, thus, against the clamp jaw  81 . When the piston  811  is moved upward in the direction of the double arrow  826 , for example by generating an under-pressure −P 1  in the cylinder  810 , the spring  825  is compressed and the clamp jaw  81  is relieved, so that it opens. When the under-pressure is removed, the spring  825  again presses onto the clamp jaw  81  and closes it via the lever section  823  and the intermediate link  824 . 
     The means  80  for optionally opening and closing the collet chuck  8  enables an actuation of the clamp jaws  81  from the outside, regardless of whether the retainer member  2  happens to be movably seated on the retainer member  3  or is in a fixed position. 
     A collet chuck  8  illustrated in FIG. 5 in the longitudinal section differs from the chuck  8  according to FIG. 4 essentially only in that it has an imaging optics  91  and an optical detector  92  arranged so that the imaging optics  91  focuses light that propagates along the axis A onto the detector  92 . The imaging optics  91  and the optical detector  92  are rigidly arranged relative to the retainer member  2  as soon as the collet chuck  8  is rigidly built into the member  2 . 
     Although various minor modifications may be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent granted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.