Abstract:
A vacuum assisted disc clamping device provides a number of fixture rings preferably concentrically stacked on a fixture body that is moveable in fixture ring stacking direction and actuated by a wedge drive to compensate for varying fixture levels associated with the individual fixture rings and disc standards. Each fixture ring includes a planar flange with a vacuum groove and a central conical portion that rises above the planar flange. The conical portion is defined with a diameter and cone angle such that a disc of corresponding dimensional standard may be readily placed on the fitting fixture ring with the disc bottom being sucked onto the planar flange while the disc hole centers on the conical portion.

Description:
FIELD OF INVENTION 
     The present invention relates to disc chucks. Particularly, the present invention relates to disc clamping devices adapted for centrally holding discs of varying disc standards. 
     BACKGROUND OF INVENTION 
     In the field of information technologies disc like structures are utilized in data storage applications, in which the discs are fixed at a central hole and spun to read and/or write information on one or both of its top and bottom planar surfaces. Such discs are fabricated in ever increasing dimensional standards. For example, at the time the present invention was made there exist in the field of hard disc drives dimensional standards ranging at least between 25.4 and 130 mm for the outer diameter, with central hole diameters of at least between 7 and 40 mm and disc thicknesses between at least 0.381 and 1.9 mm. During disc fabrication and inspection, the discs need to be repeatedly precisely positioned and fixed. For example in an optical measurement apparatus such as a well known spectrometer, fixtures need to be available to accommodate for the widely spanning dimensional ranges of the discs to be inspected. In the prior art, replaceable chucks are commonly mounted prior to fixing a disc of corresponding standard. 
     In fabrication or inspection environments where a number of different disc standards are fabricated simultaneously, exchanging the chuck prior to disc fixture may impose significant delay in the fabrication or inspection process. At the same time as disc standards increase, fabrication equipment is demanded that is more flexible and efficiently operated eliminating repetitive tasks as much as possible. Therefore, there exists a need for a disc chuck, capable of fixedly holding discs of varying dimensional standards. The present invention addresses this need. 
     SUMMARY OF INVENTION 
     A vacuum assisted disc clamping device provides a number of fixture rings preferably concentrically stacked on a fixture body that is combined with an actuation mechanism driving the fixture body in ring stacking direction to compensate for varying fixture levels associated with the individual fixture rings and disc standards. Each fixture ring includes a planar flange with a vacuum groove and a central conical portion that rises above the planar flange. The conical portion is defined with a diameter and cone angle such that a disc of corresponding dimensional standard may be readily placed on the fitting fixture ring with the disc bottom being sucked onto the planar flange while the discs hole centers on the conical portion. The actuation mechanism lifts the disc via the fixture body and the fixture ring such that the disc&#39;s top is within a reference level regardless of the disc&#39;s height and the associated one of the stacked fixture rings. The actuation mechanism preferably includes a linear actuator actuating a driving wedge that pushes against a corresponding actuation face of the precision guided fixture body. 
     In an alternate embodiment of the invention, vacuum may be provided by a selection valve that is integrated in the fixture body and concurrently switched by the fixture body&#39;s adjustment movement. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of an exemplary simplified clamping device. 
         FIG. 2  is a perspective exploded view of the clamping device of  FIG. 1 . 
         FIG. 3  is a frontal cut view of the clamping device of  FIG. 1 . 
         FIG. 4  illustrates an optical measurement apparatus including the clamping device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     According to  FIGS. 1-3 , a disc clamping device  1  includes a base  10 , a fixture body  20  and an actuation mechanism  30 . The fixture body  20  is guided movable along a stacking axis SA. The fixture body  20  has two or more fixture rings accessible from the top. At least one of the fixture rings has a planar flange  211 / 212 / 213  and a centering cone  221 / 222 / 223 . Each centering cone  221 / 222 / 223  has a distinct lateral dimension LD 1 /LD 2 /LD 3  along an interference contour between the planar flanges  211 / 212 / 213  and their respective centering cone  221 / 222 / 223 . In case, the planar flanges  211 / 212 / 213  are inward extending up to their respective centering cone  221 / 222 / 223 , the interference contour may in fact be an interference edge. For ease of fabrication, the planar flanges  211 / 212 / 213  may terminate in a slight offset from their respective centering cone  221 / 222 / 223  with a small recess in between, such that the centering cone  221 / 222 / 223  may extend slightly below their respective planar flanges  211 / 212 / 213 . 
     The fixture rings are positioned on the fixture body  20  along the stacking axis SA such that the one fixture ring with the least lateral dimension LD 3  is on top of one other of the fixture rings having the next larger lateral dimension LD 2 . The fixture body further includes a rest face  26  for receiving a moving impulse. The fixture rings are preferably concentrically stacked on top of each other. 
     The base  10  has body guides  11  structurally communicating with the fixture body  20 . The body guides  11  are preferably well known linear precision guides such as cylindrical columns in combination with ball bearing sleeves. The base  10  further features a base face  16  for opposing the moving impulse. The actuation mechanism  30  is configured for inducing the moving impulse in between the rest face  26  and the base face  16 . 
     At least one of the planar flanges  211 / 212 / 213  further includes an externally accessible vacuum groove  231 / 232 / 233 . As illustrated in  FIG. 3 , the vacuum grooves  231 / 232 / 233  may communicate via respective groove access channels  241 / 242 / 243  at a number of predetermined positions alternating with a valve opening  141 , which extends into a vacuum connect  13  of base  10 . The vacuum connect  13  may be sealed and sliding in direction of the stacking axis SA within a sealing guide  27  of the fixture body  20  such that a movement of the fixture body  20  along the stacking axis SA results in a relative motion of the groove access channels  241 / 242 / 243  with respect to the valve opening  141 . 
     As shown by example in  FIG. 3 , the centering cone  223  may comply to a center hole  51  of a disc  50  of a particular dimensional disc standard such that a hole bottom edge  54  may snugly contact the centering cone  223  when the disc  50  is placed on the fixture body  20 . Particularly, the lateral dimension LD 3  is defined that the snug contact between the hole bottom edge  54  and the centering cone  223  occurs at or would occur slightly below planar flange  213  such that a snug contact between disc bottom  53  and planar flange  214  is warranted. 
     During placement of a disc  50  on its corresponding fixture ring, the snug contact of the disc bottom  53  with its corresponding planar flange  213  seals the vacuum groove  233  against ambient pressure and a downward force is induced by the ambient pressure on the disc  50  while the vacuum groove  233  is evacuated. The vacuum causing disc  50  acts consequently also as a valve, which may be utilized by a device control  2  in combination with a vacuum sensor  3  to derive information about which fixture ring is populated by a disc  50 . This is explained in more detail further below. 
     The predetermined positions are selected with respect to a reference level RL and a disc height DH of the disc  50  of a particular dimensional disc standard to which one of the corresponding fixture rings is adapted. From the reference level RL and the disc height DH is the valve distance DV derived. The valve distance DV is constant for each fixture ring, its correspondingly dimensioned disc and corresponding reference level RL. As a result, vacuum is automatically and selectively applied to one of the vacuum grooves  231 / 232 / 233  the fixture ring of which is holding a disc with its top  52  at the reference level RL. In simplified embodiment of the invention, the groove access channels  241 / 242 / 243  may be independently supplied with vacuum without a valve mechanism as described above. 
     The actuation mechanism  30  is preferably a wedge drive actuating a wedge  35  along the drive axis DA preferably via a thread spindle  32  and a hollow shaft stepper motor  31 . The drive axis DA is oriented in an actuation angle AA of preferably 90 degrees with respect to the preferable vertical stacking axis DA. The wedge  35  has a wedge face  36  pushing against the rest face  26  either in a snug contact or by means of a roller bearing. The wedge  35  has further a bottom face  37  pushing against the base face  16  either in a snug contact or by means of a roller bearing. The roller bearing(s) may be utilized in a well known fashion to reduce friction between the opposite faces  26 ,  36  and  16 ,  37 . In a more general embodiment of the invention, the rest face  26  may be any well known low friction contacting feature. More specifically, the rest face  26  may be substituted by a roller in rolling contact with said wedge face  36 . 
     The wedge face  36  is in a first wedge angle WA 1  of preferably 30 degrees with respect to the drive axis DA. For the preferred 90 degree actuation angle AA, the second wedge angle WA 2  of the rest face with respect to the stacking axis SA is 60 degrees. The transmission ratio between wedge  35  movement and fixture body  20  movement is a trigonometric tangent function of WA 1  and WA 2 , which is for the exemplary angles of 30 and 60 degrees consequently 2:1. The transmission ratio may be well adjusted in accordance with the teachings above as may be appreciated by anyone skilled in the art. 
     As the wedge  35  is moved along the driving axis DA, it wedges in between the rest face  26  and the base face  16  causing a moving impulse onto the fixture body  20 . The body guides  11  provide sufficient stiffness to oppose the wedge&#39;s  35  force along the driving axis DA. The use of the described actuation mechanism provides for a smooth and highly precise actuation of the fixture body  20 . Position tolerance in direction of the stacking axis SA of about 0.012 mm with 0.005 mm repeatability with an overall movement range of about 7 mm of the fixture body  20  were achieved in an exemplary disc clamping device  1  providing fixture for discs  50  of following dimensional standards (outside diameter×hole diameter×thickness): 25.4×7×0.381 mm, 65×20×0.8 mm, and 85×25×0.8 mm. The footprint of that exemplary disc clamping device  1  was 110×180 mm with an overall height at maximum raised fixture body  20  of about 84 mm. 
     The disc clamping device  1  may further include a device control  2  controlling the actuation mechanism  30  by combining well known motion signals, which are processed in conjunction with predetermined parameters and a predetermined actuation algorithm to provide a driving current to the stepper motor  31 . A vacuum sensor  3  may also be part of the disc clamping device  1 . The vacuum sensor  3  may provide a signal to the device control  2  in response to a sensed vacuum in one of the vacuum grooves  231 / 232 / 233 , the groove access channels  241 / 242 / 243  and the vacuum access  14 . In  FIG. 3 , the vacuum sensor  3  is exemplarily illustrated as being placed in communication with the vacuum access  14 . 
     The actuation algorithm may be executed by the device control  2  such that the actuation mechanism  30  is brought to a controlled halt in response to the vacuum sensor&#39;s  3  signal and such that the fixture body  20  is positioned along the stacking axis SA at a predetermined position where the top  51  of a vacuum causing disc  50  coincides with the reference level RL. In that fashion, the placement of a disc  50  at any of the fixture rings seals one of the vacuum grooves  231 / 232 / 233  and the device control  2  may recognize the populated fixture ring by correlating a sensed vacuum to an associated position of the fixture body  20  along the stacking axis SA. The associated position of the fixture body  20  may be recognized by the device control  2  via a position signal or other position information of the actuation mechanism  30  as may be well appreciated by anyone skilled in the art. After recognizing the populated fixture ring, the device control  2  may fine adjust the fixture body  20  such that the disc top  52  may coincide with the reference level RL. 
     The disc clamping device  1  may further include tension springs  12  hinged between the fixture body  20  and the base  10 . The tension springs  12  force the fixture body towards the base  10  and warrant contact between the faces  26 ,  36  and  16 ,  37 . The tension springs  12  are preferably symmetrically placed with respect to the actuation mechanism  30  for an even force distribution onto the faces  16 , 26 , 36 , 37 . 
     The disc clamping device  1  may be integral part of a linear stage and/or integral part of a rotary stage. Moreover, the disc clamping device  1  may be part of an inspection apparatus  100  as illustrated in  FIG. 4 . Such inspection apparatus  100  may be a well known spectrometer having an inspection head  104  where an inspection beam  105  emerges from and focuses at the reference level RL. The disc clamping device  1  may be mounted on or integral part of a linear X stage  101  and/or and linear Y stage  102 . The highly compact disc clamping device  1  may in that fashion be moved with a disc  50  beneath the focused inspection beam  105 . The small footprint of the disc clamping device  1  requires minimal additional space and contributes to a minimal overall space requirement of the disc inspection apparatus  100 . The vacuum access  14  may be connected to a vacuum supply  109  via a vacuum line  108 . The device control  2  may be part of an apparatus control  103 . 
     Accordingly, the scope of the invention described in the specification above is set forth by the following claims and their legal equivalent: