Abstract:
Apparatus for attaching a disk to a spindle of a spinstand includes a spindle having a fluid pressure port therethrough for delivery of fluid pressure. A spindle adapter is adapted to be attached to the spindle and for holding a disk. The spindle adapter has a piston movable therein to clamp a disk between the piston and an opposing surface in response to fluid pressure applied through the spindle fluid pressure port. A disk can be attached to the spindle by offering the disk up to the spindle adapter, and applying fluid pressure to the spindle fluid pressure port to cause the piston to clamp the disk against the opposing surface. The disk can then be spun up on the spindle.

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus and a method for attaching a disk to a spindle of a spinstand. 
     BACKGROUND 
     It is well known to use a spinstand to test various components of a hard disk assembly, such as in particular the read/write heads and the disk media. Such tests can be carried out in a manufacturing production environment, where typically every head and a proportion of disks are tested prior to being assembled into a hard disk assembly to ensure that they perform to the required standard. Testing using a spinstand can also be carried out in a research and development setting. 
     A spinstand typically comprises a deck, for example of granite, which is generally isolated from external sources of vibration in some way to avoid these affecting the accuracy of the test results. A spindle is attached to the deck for holding and rotating the disk. This will typically be an air bearing spindle with an integrated DC brushless motor. The spinstand has a puck for receiving the read/write head. The puck is positionable so as to move the head to a desired location under the surface of the disk. The puck will typically be positionable by a highly accurate x-y positional stage, having air bearings and linear encoders. It may also be possible to lock the puck down to the granite by application of a vacuum in order to prevent movement of the puck when in a desired position. The puck generally has some arrangement for loading/unloading the head to/from the test surface of the disk, such that the head can read and/or write a track of test data from the test surface of the disk. The puck also generally has some arrangement, such as a nanopositioner, for making very fine positional changes of the head relative to the test track. 
     When testing disks with a spinstand, particularly in a manufacturing environment, it is desirable to be able to swap the disk under test for a new disk as quickly and dependably as possible. It is also desirable to accelerate and decelerate the disk under test as fast as possible in order to increase throughput of disks tested. High accuracy in positioning the disk is also required. However prior art arrangements for attaching the disk to the spindle present many disadvantages in achieving these aims. 
     Another important consideration in attaching the disk to the spindle is accurately and dependably setting the so-called z-height of the test surface of the disk, i.e. the vertical height of the test surface relative to a datum or reference position. This is because, when loading a read/write head to a disk, the head must be vertically positioned with great accuracy relative to the test surface of the disk and so it is important that the z-height of the test surface is closely controlled when loading the disk to the apparatus. The maximum variation in the vertical positioning of the head relative to the head surface that is acceptable for the operation of the system is known as the “z-height budget”. 
     SUMMARY 
     According to a first aspect of the present invention, there is provided apparatus for attaching a disk to a spindle of a spinstand, the apparatus comprising: a spindle having a fluid pressure port therethrough for delivery of fluid pressure; and, a spindle adapter adapted to be attached to the spindle and for holding a said disk, the spindle adapter having a piston movable therein to clamp a said disk between the piston and an opposing surface in response to fluid pressure applied through the spindle fluid pressure port. 
     The clamping force on the disk can be varied by varying the fluid pressure applied to the fluid pressure port. This allows a high clamping force to be used when the disk is accelerated to test speed to avoid slipping of the disk. When the test speed has been reached, the clamping force can then be reduced to a test clamping force, which reduces the possibility of the disk being distorted due to excess clamping force. The clamping force can also be reduced even further to allow the disk to be jogged and centred in the spindle adapter when attached to the spindle. 
     The clamping force on the disk an also be independent upon the thickness of the disk. This has the advantage that the tolerance of the disk thickness between successively tested disks does not affect the clamping force. This also has the advantage that the same spindle adapter can be used with different classes of media. 
     In an embodiment, the opposing surface is a datum surface and the surface of a said disk that registers with the datum surface is the surface of a said disk that is to be tested. This arrangement provides that the disk surface that is to be tested is registered against a datum surface of the spindle adapter by being urged against it by the clamp piston. This removes the tolerance in the thickness of successively tested disks from the z-height budget. 
     In an embodiment, the apparatus comprises a cap, the cap being fittable to and removable from the spindle adapter to allow a said disk to be positioned on or removed from the spindle adapter, the cap having a first surface portion for registering with a surface portion of the spindle adapter and a second surface portion providing the datum surface. This arrangement allows simple removal or insertion of the disk from the spindle adapter. The cap provides the datum surface for registering against the test surface of the disk. The cap also registers against the spindle adapter. This allows the bottom surface of the disk to register against the spindle adapter in an inverted spindle configuration. This allows the bottom surface of the disk to be tested whilst removing the tolerance of the thickness of successively tested disks from the z-height budget. (An inverted spindle is a spindle that is mounted in an inverted position, i.e. the end of the spindle to which the disk is mounted is positioned below the body of the spindle.) 
     In an embodiment, the apparatus comprises a cap, the cap being fittable to and removable from the spindle adapter to allow a said disk to be positioned on or removed from the spindle adapter, the cap providing the opposing surface. This arrangement allows the disk to be attached to the spindle easily and quickly. 
     The piston may be annular. This allows an even clamping force to be applied circumferentially to the disk. 
     The spindle may be an inverted spindle. An inverted spindle has the advantage that the spindle can be relatively short. 
     According to a second aspect of the present invention, there is provided a method of attaching a disk to a spindle of a spinstand, the spindle having a fluid pressure port therethrough for delivery of fluid pressure and having a spindle adapter attached thereto adapted for holding the disk, the spindle adapter having a piston movable therein to clamp the disk between the piston and an opposing surface in response to fluid pressure applied through the spindle fluid pressure port, the method comprising: offering the disk up to the spindle adapter; applying a fluid pressure to the spindle fluid pressure port to cause the piston to clamp the disk against the opposing surface; and, spinning up said disk with the spindle. 
     The method may comprise reducing the fluid pressure to a test fluid pressure when the disk has been spun up to a predetermined test speed; and, reading from or writing to the disk with a read/write head when the disk is at the predetermined test speed. 
     The opposing surface may be a datum surface, the method comprising: reading from or writing to the surface of the disk that registers with the datum surface with a read/write head. 
     In an embodiment, there is provided a cap having a first surface portion for registering with a surface portion of the spindle adapter and a second surface portion providing the datum surface, the step of offering the disk up to the spindle adapter comprising: positioning the disk on the cap; moving the cap and disk to be in position opposing the spindle adapter; offering the disk on the cap up to the spindle adapter; and, fitting the cap to the spindle adapter so that the first surface portion registers with the surface portion of the spindle adapter and the second surface portion registers with the surface of the disk that is read from or written to. 
     The method may comprise reducing the fluid pressure so as to allow the disk to move transversely relative to the opposing surface in response to an impulse force. 
     The piston may be annular. The spindle may be an inverted spindle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: 
         FIG. 1  shows a plan view of an example of a spinstand in accordance with an embodiment of the present invention; 
         FIG. 2  shows a partially sectioned side view of the apparatus of  FIG. 1 ; 
         FIG. 3  shows a more detailed view of the spindle, spindle adapter and cap of  FIG. 1 ; 
         FIG. 4  shows a plan view of the disk exchanger of  FIG. 1 ; 
         FIG. 5  shows a side view of the disk exchanger of  FIG. 1 ; 
         FIG. 6  shows a sectioned side view of the disk exchanger of  FIG. 1 ; and, 
         FIG. 7  shows the disk exchanger of  FIG. 1  with a disk in place. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a spinstand  1  comprises a deck  2 . The deck  2  may be made from granite and may be mounted on isolation mounts (not shown) to isolate the spinstand  1  from external vibrations. 
     The spinstand  1  has a bridge  3  mounted to the deck  2 . The bridge  3  supports a spindle assembly  4  for holding a disk  5  to be tested in an inverted configuration, i.e. such that the end of the spindle assembly  4  to which the disk  5  is fixed is lowermost. As can best be seen in  FIG. 2 , the spinstand  1  also has a disk exchanger  6 . The spindle assembly  4  and the disk exchanger  6  will be described further below. 
     The deck  2  also has a movable stage for holding a read/write head  8  to be tested. The read/write head  8  is incorporated in a head gimbal assembly (HGA). In the embodiment as shown in the drawings, the movable stage includes or is a puck  7  for holding the head  8 , the puck  7  being supported on the surface of the deck  2 , and is movable by a highly accurate x-y positional stage  9 . The puck  7  is positionable by the x-y positional stage  9 , for example being supported on air bearings (not shown) and having linear encoders (not shown) to allow its position to be accurately determined. The puck  7  is positionable so as to move the head  8  to a desired location under the surface of the disk  5  when the disk  5  is mounted on the spindle assembly  4 . It may also be possible to lock down the puck  7  and/or the elements of the x-y positional stage  9  to the granite deck  2  by application of a vacuum in order to prevent movement of the puck  7  when in a desired position. Other arrangements of the movable stage are possible. For example, the head  8  may be held on and supported by a different arrangement provided on the x-y positional stage  9 , rather than being held on and supported by a puck  7  that is in turn supported by the deck  2  and positioned by the x-y positional stage  9 . 
     As is conventional in the art, the terms x and y directions as used herein refer to orthogonal directions parallel to the surface of the deck  2  and disk  5  (i.e. the horizontal), whereas the term z-direction refers to the direction perpendicular to the deck  2  and parallel to the spindle  4  (i.e. the vertical). The terms downward or lowered are used to refer to moving perpendicularly toward the deck  2 , whereas the terms upward or raised are used to refer to moving perpendicularly away from the deck  2 . The terms axial and radial are to be taken to be relative to the spindle shaft  22  of the spindle assembly  4  unless the context demands otherwise. 
     The puck  7  also has an arrangement for loading the head  8  to the test surface of the disk  5 , such that the head  8  can read from and/or write to a track of test data on the test surface of the disk  5 . The puck  7  also has an arrangement, such as a nanopositioner on which the head  8  is mounted, for making very fine positional changes of the head  8  relative to the test track. 
     Thus the spinstand  1  allows a head  8  to be loaded to the disk  5  and very fine positioning of the head  8  across the test surface of the disk  5  whilst test data is written to and read from the disk  5 . The test data can then be analysed as appropriate to the test being conducted. 
       FIG. 2  shows a sectional view of the spindle assembly  4 . The spindle assembly  4  comprises an air bearing spindle having a fixed outer part  21  for attachment to the bridge  3 , and a rotatable spindle shaft  22  to which the disk  5  is attached in use. The spindle assembly  4  is “inverted” in that it is mounted so that the end of the spindle shaft  22  to which attachment is made extends below the body of the spindle assembly  4 . The spindle assembly  4  has an integral DC brushless motor (not shown) for rotating the spindle shaft  22 . The spindle assembly  4  also has a plurality of ports  23 , 24  running axially therethrough, one port  23  being central and the other ports  24  being circumferentially spaced at a given outer radial position. These ports  23 , 24  allow fluid communication through the rotating part of the spindle  22  of for example a vacuum (negative air pressure) or positive air pressure. Inlets  25 , 26  in the top of the spindle assembly  4  allow fluid communication with the respective ports  23 , 24 . 
     Referring to  FIG. 3 , a spindle adapter  40  (also known as a media adapter) is connected to the spindle shaft  22 . A cap  60  is releasably connectable to the spindle adapter  40 . The disk  5  is held between the spindle adapter  40  and the cap  60  as will be described in the following. 
     The spindle adapter  40  has a cavity  45  in which a drawbar  41  is movably disposed. The drawbar  41  has generally an extended cylindrical shape, the axis of which is co-linear with the rotational axis of the spindle adapter  40  and spindle shaft  22 . The end portion  42  of the drawbar  41  extends beyond the bottom surface  43  of the spindle adapter  40 . The drawbar  41  also has a piston  44  in the form of a radially extending flange along the body of the drawbar  41  attached to it or integrally formed with it. 
     The drawbar piston  44  has a pressure chamber  45   a  beneath it. O-ring seals  46  seal the pressure chamber  45   a  to the drawbar  41  and piston  44 . The pressure chamber  45   a  is in fluid communication with ports  47  in the spindle adapter  40 . When the spindle adapter  40  is connected to the spindle shaft  22 , these ports  47  are aligned with and in fluid communication with the outer ports  24  in the spindle shaft  22 . Thus fluid pressure can be supplied to inlet  26  of the spindle  4 , via ports  24 , 47  to the pressure chamber  45   a  and thereby to the piston  44 . Thus by applying positive fluid pressure, such as pneumatic pressure to inlet  24 , the piston  44  and drawbar  41  are forced upwards, and by applying negative fluid pressure (i.e. a vacuum) to inlet  24 , the piston and drawbar  41  assembly are forced downwards. 
     The end portion  42  of the drawbar  41  incorporates a ball-latch connector  50  for connecting the cap  60  to the drawbar  41 . The connector  50  comprises a plurality of ball bearings  54  housed in the drawbar  41 . The ball bearings  54  are arranged such that they can move between a radially extended position where they project beyond the sides of the drawbar  41  through holes in the wall of the drawbar  41 , and a radially retracted position where they retract into the body of the drawbar  41  so as not to project from the drawbar  41 . 
     The connector  50  also comprises a latch release button  51  which is disposed in a recess in the end of the end portion  42  of the drawbar  41 . The button  51  is biased axially downward by a spring  52 . The button  51  has an upper conical portion  51   a , and a lower shaft portion  51   b  of reduced diameter. When the latch release button  51  is in its lowermost position, the conical portion  51   a  cams the ball bearings  54  to their extended position. When the latch release button  51  is depressed against the action of the biasing spring  52  by pressing on the shaft portion  51   b , the ball bearings  54  can fall inward to their retracted position within the drawbar  41 . 
     The cap  60  has a hollow collet  61  at its centre. The interior of the collet  61  has a smaller diameter portion at one end forming a detent edge  62  or shoulder. 
     In order to connect the cap  60  to the spindle adapter  40 , the latch release button  51  is first depressed so that the ball bearings  54  fall inward to their retracted position. The drawbar  41  is in its relaxed position during this process. Next, the cap  60  with a disk supported thereon is offered up to the spindle adapter  40 , with the connector part  50  of the drawbar  41  being accepted into the hollow collet  61 . The cap  60  is advanced until a mating surface  63  of the cap  60  registers or abuts with a mating surface  43  of the spindle adapter  40 , whereupon the cap  60  is fully advanced. This mating of surfaces  43 , 63  takes place through the centre hole in the disk  5 . At this position, the upwardly facing end of the collet  61  engages with a cooperating recess  43   a  in the mating surface  43  of the spindle adapter  40  so as to keep the cap  60  centred on the spindle adapter  40 . Also at this position, the ball bearings  54  below the detent edge  62  of the collet  61 . The latch release button  51  is then released so that the ball bearings  54  are cammed outward to their extended position by the conical portion  51   a . At this point, the ball bearings  54  prevent the cap  60  from detaching from the drawbar  41 , thus holding the cap  60  in position on the drawbar  41 . 
     Once the cap  60  is connected to the drawbar  41  in this way, fluid pressure is applied to the inlet  26  of the spindle assembly  4  in order to draw up the drawbar  41 . This has the effect of first engaging and then urging the ball bearings  54  against the detent edge  62  of the collet  61  and then in turn, engaging and urging the mating surface  63  of the cap  60  against the mating surface  43  of the spindle adapter  40 . Once all of the play between components has been taken up, this provides a tightly registered connection between the cap  60  and spindle adapter  40 . 
     In order to release the cap  60  from the spindle adapter, the fluid pressure to the inlet  26  is removed. The latch release button  51  is then depressed to allow the ball bearings  54  to move inward to their retracted position and the cap  60  is allowed to separate from the spindle adapter  40 . 
     Thus this arrangement allows the cap  60  to be easily and quickly secured to and released from the spindle adapter  40  without using bolts or tools and the disadvantages associated therewith. 
     In spinstands in general, the read/write head is usually tested in an inverted position, i.e. the head is held so as to be pointing upwards. This means that it is the bottom surface of the disk under test that is written to and read from by the head. This makes controlling the z-height of the test surface of the disk relatively straightforward when a non-inverted spindle configuration is used. The bottom surface of the disk is clamped against the spindle (via the spindle adapter), which provides the known z-height reference or datum. Thus the bottom surface, i.e. the test surface, is directly referenced against the datum. 
     However, controlling the z-height is more challenging in an inverted spindle configuration. This is because in this configuration it is the top surface  10   a  of the disk  5  that is connected against the spindle  4 , the spindle  4  giving the known reference point or datum in the z-direction. However, it is the bottom surface  10   b  of the disk  5  that is tested, i.e. the opposite surface to the one referenced against the datum. This creates a problem in that the tolerance in the thickness of the successive disks  5  being tested greatly affects the z-height of the test surface  10   b  of the disk  5  under test. In fact, currently the tolerance in disk thicknesses is several times the acceptable z-height budget. 
     To address this potential problem, the spindle adapter  40  is provided with an annular piston  55  being movable in a recess  56  within the spindle adapter  40 . The piston  55  is sealed with the walls of the recess  56  by O-rings  57  thereby creating a pressure chamber  56   a  behind the piston  55 . The pressure chamber  56   a  is in fluid communication with a port  58  running through the centre of the drawbar  41  and exiting through the side wall of the drawbar  41 . The port  58  in the body of the drawbar  40  is in fluid communication with the central port  23  of the spindle shaft  22  which in turn is in fluid communication with the inlet  25  in the spindle assembly  4 . O-rings  59  are used to seal the port  58  to the pressure chamber  56   a . Thus, by supplying positive fluid pressure to the inlet  25 , fluid pressure is applied via the ports  23 , 58  to pressure chamber  56   a . This pressure causes the piston  55  to be lowered to engage the top surface of the disk  5  close to its inner diameter and to urge or clamp the disk  5  against a datum surface  64  of the cap  60 . In this example the datum surface  64  is the same as the mating surface  63  of the cap  60 . 
     Thus the test surface (i.e. the lowermost surface) of the disk  5  is made to register against the top surface  63 , 64  of the cap  60 , which in turn is made to register against the spindle adapter  40 . In effect then, the test surface of the disk  5  is made to register against the spindle adapter  40  (via the cap  60 ), which spindle adapter  40  provides a known z-height datum. Thus, the tolerance of the thickness of the disk  5  is removed in determining the z-height of the test surface of the disk  5  relative to the head  7 . 
     Another advantage of this clamping arrangement is that the clamping force delivered to the disk  5  is independent of the thickness of the disk  5 . Thus, the tolerance of the thickness of the disk  5  does not affect the clamping force. Also, this allows the same spindle adapter  40  to be used for different classes of disk  5 . 
     Another advantage of this clamping arrangement is that, by varying the fluid pressure supplied to piston  55 , the clamping force applied to the disk  5  between the piston  55  of the spindle adapter  40  and the datum surface  64  of the cap  60  can be controlled as required. Again, the clamping force achieved is independent of the thickness of the disk  5 . In all cases, whatever the clamping force applied, the test surface  10   b  of the disk  5  will be registered against the datum surface  64  of the cap  60 . 
     This allows a testing technique where greater clamping force can be applied to the disk  5  during acceleration of the disk  5  to test speed. This helps prevent slippage of the disk  5  in the adapter  40  due to the high torques required during acceleration. This in turn prevents the damage to the disk  5  that typically occurs when the disk  5  slips. Examples of minimum clamping pressures/axial loads for various disk accelerations are as follows: 
     12 krpm/s—26 N axial load or 1.4 Bar (approx. 145 kPa) clamp pressure 
     15 krpm/s—33 N axial load or 1.8 Bar (approx. 185 kPa) clamp pressure 
     18 krpm/s—44 N axial load or 2.3 Bar (approx. 235 kPa) clamp pressure. 
     Once the disk  5  has reached the desired rotational speed for testing, less torque is required and the clamping force can accordingly be reduced whilst testing is carried out. This minimises the possibility of disk  5  distortion due to a high clamping force. This is desirable, since disk distortion will negatively affect the accuracy of the test results. Also, in a disk test apparatus  1  the disk  5  under test will be ultimately intended for incorporation into a head disk assembly and so distortion to the disk  5  is highly undesirable. 
     This arrangement of the clamping piston  55  also allows the disk  5  to be centred even when mounted to the spindle  4 . To do this, the clamping force is reduced still further, to nothing or substantially nothing, and the disk  5  is centred in the adapter  40 , for example by tapping an edge of the disk  5 . Thus for example the disk  5  can be centred relative to the spindle  4  without having to remove the spindle adapter  40  from the apparatus  1 , or without having to apply any tools for loosening bolts etc. 
     Turning to  FIGS. 4 ,  5  and  6 , detailed views of the automated disk exchanger  6  are shown. The disk exchanger  6  comprises a base  79  and a lift stage  80 . The lift stage  80  has a cap receiver  80   a  positioned on its uppermost surface for receiving a cap  60 . The base  79  has two pneumatic lifters  81   a , 81   b  by which the lift stage  80  can be raised. The disk exchanger  6  also has two gripper arms  82   a , 82   b  which are attached to the lift stage  80  and thus are also raised by the lifters  81   a , 81   b  with the lift stage  80 . 
     The ends of the gripper arms  82   a , 82   b  extend adjacent the cap receiver  80   a  on opposite sides. The gripper arms  82   a , 82   b  have inwardly protruding blades  83   a , 83   b  at their ends. The gripper arms  82   a , 82   b  are pivotably mounted to the lift stage  80  by a pivot  84  and can be actuated to pivot inwards by an actuator  85 . When actuated inwards, the protruding blades  83   a , 83   b  pass through respective holes  80   b  in the sides of the cap receiver  80   a  and, when a cap  60  is in the cap receiver  80   a , engage with respective recesses  65  in the sides of the cap  60 . In this position, the gripper blades  83   a , 83   b  securely hold the cap  60  in place within the cap receiver  80   a . To release the cap  60  so that it can be removed from the cap receiver  80   a , the gripper arms  82   a , 82   b  are actuated outwards so as to withdraw the gripper blades  83   a , 83   b  from the recesses  65  in the sides of the cap  60 . 
     As can best be seen in  FIG. 7 , the cap  60  has three cylindrical pins  66  projecting upward from its datum surface  64 . These pins  66  are spaced so that they pass through the centre of the disk  5  when the disk  5  is placed on the cap  60 , thereby centering the disk  5  on the cap  60  and retaining the disk  5  on the cap  60  when the disk exchanger  6  is being moved around as will be discussed below.  FIG. 7  shows the disk  5  in position on the cap  60 . 
     As can also be seen from  FIG. 7 , the disk exchanger  6  of this embodiment is connected to the puck  7 . Thus, the x-y positioner  9  of the puck  7  can be used to move the disk exchanger  6 . The disk exchanger  6  may be moved on an air bearing if desired and/or may be capable of being locked down to the deck  2 . The disk exchanger  6  can be moved by the x-y positioner  9  from a load position underneath the spindle assembly  4  to a receiving position away from the bridge  3 , where the lift stage  80  is more easily accessible by an operator for removing the disk  5  from the cap  60  and placing a new untested disk  5  in its place. 
     When the disk exchanger  6  is in position below the spindle adapter  40 , by actuating the pneumatic lifters  81   a , 81   b  to raise the lift stage  80 , the cap  60  and disk  5  are offered up to the spindle adapter  40  so that connection can be made between them. The lift stage  80  has a further actuator  86  (shown in  FIG. 6 ) arranged to depress the latch release button  51  of the spindle adapter ball-latch connector  50  by pressing on the shaft portion  51   b  of the latch release button  51  which protrudes beneath the cap receiver  80   a  through a hole in the centre of the cap receiver  80   a.    
     Optionally the spinstand may have a disk flutter control device (DFCD) (not shown). The DFCD is a flat block of material of for example stainless steel or nickel-plated aluminium alloy which is positioned very close to the upper surface  10   a  of the disk  5  during testing, and helps to reduce vibrations of the disk  5  when it is spun. The DFCD can be raised and lowered by a pneumatic device (not shown). 
     Thus the following sequence of actions takes place for loading a disk to the spindle, some of which may be simultaneous or in a slightly different order:
     1. A disk  5  is placed on the cap  60  on the disk exchanger  6  and the puck  7  is moved by its x-y positioner  9  so that the cap  60  is under the spindle adapter  40 .   2. The DFCD is raised. This ensures that if the disk  5  has not been placed flat on the cap  60  and is sloping somewhat it will not contact the DFCD when the disk  5  is raised by the lift stage  80 .   3. The drawbar  41  is lowered and the lift stage  80  of the disk exchanger  6  is raised.   4. The connector assembly  50  of the drawbar  41  enters the collet  61 , and the latch button  51  is pressed upwards by the actuator  86  in the lift stage  80 . The ball bearings  54  of the connector assembly  50  fall inwards so that the ball bearings  54  can pass the detent edge  62  in the collet  61 .   5. The latch button  51  is released and is urged downwards by the biasing spring  52  so that the ball bearings  54  of the connector  50  engage with the detent edge  62 .   6. The gripper arms  82   a,b  are pivoted outwards to release the cap  60 .   7. The drawbar  41  is raised by pneumatic pressure on the piston  44 , which urges the cap  60  and the spindle adapter  40  together.   8. The DFCD is lowered.   9. The lift stage  80  is lowered.   10. High positive pressure is applied via piston  55  to clamp the disk  5  between the piston  55  and the datum surface  64  of the cap  60  so that no slipping occurs due to the high acceleration torque applied to the disk  5 .   11. The spindle motor starts and brings the disk  5  up to speed.   12. The clamping pressure is reduced to the level appropriate for testing.   13. The puck  7  is moved so that the head  8  is under the correct track of the disk  5 , and testing can take place.   

     To remove a disk  5  from the spindle adapter  40  the following sequence of actions takes place, some of which may be simultaneous or in a slightly different order: (It is assumed that that the spindle shaft  22  has stopped rotating, or that it stops during the first action.)
     1. The puck  7  is moved by its x-y positioner  9  so that the disk exchanger  6  is under the spindle adapter  40 .   2. The DFCD is raised.   3. The disk clamping pressure is removed.   4. The drawbar  41  is lowered and the lift stage  80  is raised.   5. The gripper arms  82   a , 82   b  engage with the cap  60 .   6. The latch button  51  is pressed upwards by the actuator  86  in the lift stage  80 . The ball bearings  54  of the connector  50  fall inwards so that the end of the drawbar  42  can be withdrawn past the shoulder  62  of the cap  60 .   7. The lift stage  80  is lowered, carrying the cap  60  and disk  5  with it.   8. The puck  7  is moved by its x-y positioner  9  to place the disk exchanger  6  at the receiving station.   

     Thus by supplying appropriate control signals to the various actuators and sources of fluid pressure hereinbefore described, for example co-ordinated by a computer or microcontroller, the exchange of disks  5  on the spindle  4  can be performed automatically except for an operator having to remove a tested disk  5  from the disk exchanger  6  and place a new disk  5  in its place when the disk exchanger  6  is in the receiver position. 
     Embodiments of the present invention have been described with particular reference to the example illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention. For example, the invention is not limited to the specific spindle types or arrangements, or puck positioning devices specifically described in the description.