Abstract:
A unitary cartridge, or module, provides a self-contained, high accuracy, ready-to-use assembly for controlling fine positioning of a head gimbal assembly (HGA) disposed on a head mounting unit mounted on the cartridge, with respect to a spinstand or other device associated with a head tester. In a form, the head-mounting unit and a counterweight element are configured to be moveable relative to the base in opposite directions along a displacement axis in response to actuators in the cartridge, and are operative in concert with a damping assembly configured to interact with the counterweight element and the heads mounting unit to mitigate vibrational movement of the cartridge.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 62/138,205, filed Mar. 25, 2015, incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to magnetic head and disk testers and in particular to head fine positioning mechanisms with improved dynamic characteristics. 
       BACKGROUND OF THE INVENTION 
       [0003]    A head/disk tester is an instrument that is used for testing the characteristics of magnetic heads and disks, such as a signal-to-noise ratio, track profile, etc. The tester should simulate those motions of the head with respect to the disk that occur in an actual hard disk drive during operation. A tester comprises a mechanical component, commonly referred to as a spinstand, that performs movements of the head with respect to the disk, and an electronic component that is responsible for measurement, calculation, and analysis of the measured signal. 
         [0004]    Examples of prior art spinstands for a head and disk tester include the Guzik V2002 XY-positioning spinstand and the Guzik 5-1701B Micro Positioning spinstand, both of which are available from the assignee of the present disclosure, Guzik Technical Enterprises, 2443 Wyandotte Street, Mountain View, Calif. 94043, USA (www.guzik.com). 
         [0005]    For testing, a magnetic read/write head is usually incorporated into a structure known as a head gimbal assembly (HGA). An exemplary HGA  1  is shown in  FIG. 1 . The basic components of an HGA  1  are a head  2 , an elongated load beam  4  bearing the head at a distal end, a tooling hole  6 , a base plate  8  having a planar mounting surface, a boss hole  10  with an angled surface  10   a , and an elongated flex circuit support sheet element  12  with an array of electrically conductive pads  18  at its distal end. The boss hole  10  passes through base plate  8  and is characterized by a radius R about an HGA mounting axis perpendicular to the planar mounting surface of base plate  8 . The head  2  is disposed along an “axis of symmetry” extending along the load beam  4  from the center point CP of the boss hole  10  to head  2 . The array of electrical contacts  18  is disposed along a “flex axis” extending from the center point CP of the boss hole  10  to array  18 . The tooling hole  6  is on load beam  4 , between the boss hole  10  and head  2 . The boss hole  10  and the tooling hole  6  (sometimes) are used, in the prior art, for orientation of the HGA in a plane transverse to an HGA mounting axis. The angled surface  10   a  of the boss hole  10  is used for clamping the HGA to an HGA support assembly associated with a spinstand. The flex circuit sheet element  12  is used to support electrical connections of the head of the HGA, by way of pads  18 , to an external head preamplifier (not shown). Generally, the base plate  8  and load beam  4  are relatively stiff compared to the flex circuit sheet element  12 . 
         [0006]    In order to test a head with a spinstand, an HGA is loaded to an HGA support assembly associated with the tester. The HGA is mechanically coupled to a corresponding component of the spinstand, and electrically connected to spinstand preamplifiers which provide test signals and receive back response signals from the head under test. To make these operations possible, an alignment of the HGA relative to the spinstand is carried out. In  FIGS. 2-5 , and the text below, HGAs  1  are illustrated only by their load beam (which is identified with the HGA&#39;s reference numeral  1 ); the other elements of the HGAs, and portions of a tester for applying test signals to and analyzing responses from the HGAs, although present in the illustrated and described HGAs, are not shown in the figures. 
         [0007]    A major step forward in improvement of the qualitative parameters of spinstands was made in the U.S. Pat. No. 8,169,750. In that patent, a spinstand is described that includes a base, a Y coarse positioning stage that moves in a Y direction and a X coarse positioning stage that is movable in a X direction, where the X and Y directions are defined with respect to an x-y-z Cartesian coordinate system. The X coarse positioning stage is coupled to the Y coarse positioning stage by a linear bearing. An X precision (or fine motion) positioning stage, movable in an X direction, is mounted on the X coarse positioning stage. The X precision positioning stage comprises a piezo-electric actuator and a parallelogram flexure assembly (or parallelogram) having a base element rigidly mounted to the X coarse positioning stage, and a movable (with respect to the X coarse positioning stage) element maintained parallel to the base element by a pair of equal length end elements flexure-coupled to the base element and the movable element. These components make possible movement of the X precision positioning stage in the X direction. Position feedback for X precision positioning stage is provided by a displacement sensor that comprises a linear glass scale mounted to the moving element of the parallelogram disposed opposite to an optical reader mounted to the X coarse positioning stage. The sensor carries out measurement of the displacement of the moving element of the parallelogram relative to the X coarse positioning stage, and produces in that way information of the read/write head position. 
         [0008]    The spinstand also includes a removable HGA-bearing-only cartridge that enables magnetic head and disk testing using different magnetic heads with the possibility of quick installation of a head and quick dismount of the head from the cartridge without special tools or alignment procedures. The cartridge is rigidly coupled to the moving element of the parallelogram, which is located on the X precision positioning stage. A head gimbal assembly HGA mounts on the cartridge. A read/write head is a part of HGA. To move the read/write head, a piezo-electric actuator mounted on the X precision stage drives the parallelogram to move the cartridge, which typically has a mass that exceeds 500 grams. These large mass results in relatively slow movement and a relatively low mechanical bandwidth compared to generally desired movements and bandwidths. 
         [0009]    A substantial improvement of spinstand parameters was achieved in the cited &#39;750 patent by introducing an additional piezo-electric actuator that acts on the head-mounting unit. Such an actuator is mounted on the base of the cartridge and moves the relatively low mass head-mounting unit (compared to the above described head-mounting unit) together with the read/write head directly. The reduction of the mass of the head-mounting unit leads to corresponding widening of the mechanical bandwidth and an increase in movement speed. As a result, the accuracy of the read back process is improved, since the wider bandwidth extends the ability of the head to follow applied servo commands. 
         [0010]    Along with the noted positive properties applicable to operation in a servo read mode, a cartridge and spinstand according to the U.S. Pat. No. 8,169,750 has a serious drawback that limits positioning accuracy in a servo write mode. In an embodiment described in the &#39;750 patent, the position of read/write head in the servo write mode is changed by a piezo actuator acting on the parallelogram of the X precision positioning stage, and the change in position is measured by a glass scale on that stage. The piezo actuator on the cartridge is not used in that measurement of position change. For this reason, the movement is slow and servo writing takes a relatively long time. Moreover, the distance between the HGA and glass scale is relatively large and variations of that distance due to temperature changes, vibrations etc. create positioning errors during servo writing. For these reasons, the systems of U.S. Pat. No. 8,169,750 did not improve spinstand performance in a servo write mode. 
         [0011]    Another disadvantage of prior art spinstands, is connected to vibrational movement of the components that support the HGA. To move the head-mounting unit, the piezo-electric actuator acts on that unit with a force F directed along a displacement axis. According to a law of physics, the force F evokes a counteractive force R that is applied to the actuator and through the actuator to the cartridge itself. At each positioning operation, the counteractive force R causes oscillations of the cartridge base together with the adjacent components. For this reason, measurement of the HGA position cannot be initiated until the system has settled down to a substantially stable condition. Thus occurrence of the counteractive force R brings about degradation of the positioning accuracy and increase of the settling time. 
         [0012]    To reduce vibration of the cartridge base it was proposed in U.S. Pat. No. 6,006,614, issued on Dec. 28, 1999, assigned to the assignee of this disclosure, to complement the head-mounting unit by a counterweight. According to that proposal, two piezo-electric actuators are mounted on a precision positioner. During positioning of an HGA, the two actuators act simultaneously on the head-mounting unit and on the counterweight, with equal magnitude forces in opposing directions along the displacement axis. In this case, two counteraction forces appear where the forces are of equal magnitude and are oppositely directed. As a result, the composite force applied to the positioner turns out to be of negligible magnitude, so that the cause of vibrations is eliminated or reduced significantly. 
         [0013]    However, there is a necessary condition for effective suppression of system vibrations by counterweight introduction: the product of the mass of the head-mounting unit by the expansion coefficient of the actuator that advances the head-mounting unit, should equal the product of the mass of the counterweight by the expansion coefficient of the actuator that advances the counterweight. The practice of using a positioner with an added counterweight showed that it is was difficult to achieve sufficiently accurate fulfillment of this condition, especially for the case of high frequency vibration. 
         [0014]    More importantly, it has been determined that the introduction of counterweight suppresses vibration in the cartridge base only, and it does not affect the vibration of a head-mounting unit itself and of the counterweight. Therefore, the introduction of a counterweight does not solve the problem of vibration completely. 
         [0015]    The goal of the current invention is to effect an HGA positioning cartridge that eliminates the above-outlined disadvantages and thereby improves the head positioning accuracy with simultaneous reduction of the settling time. 
       SUMMARY 
       [0016]    According to the present invention, a unitary cartridge, or module, provides a self-contained, high accuracy, ready-to-use assembly for controlling fine positioning of an HGA-bearing head mounting unit mounted on the cartridge, with respect to a spinstand or other device associated with a head tester. 
         [0017]    In a form, a head gimbal assembly (HGA) support cartridge, or module, for a magnetic head tester is provided for a head tester which includes (i) a base having a support surface for receiving on, and securing, an HGA support cartridge, and (ii) a spinstand for supporting a magnetic disk and spinning the disk about a spin axis SA. 
         [0018]    The head gimbal assembly (HGA) support cartridge, or module, having a parallelogram support assembly including (i) an HGA support parallelogram element extending a distance D 1  about and along a displacement axis DA from an HGA support (HGAS) end to a displacement force receiving (DFR) end, (ii) a base parallelogram element extending a distance D 1  in a direction parallel to the displacement axis DA from an HGA support (HGAS) end to a displacement force receiving (DFR) end, (iii) a first parallelogram end element extending a distance D 2  between the HGA support (HGAS) end of the HGA support parallelogram element and the HGA support (HGAS) end of the base parallelogram element, and (iv) a second parallelogram end element extending a distance D 2  between the displacement force receiving (DFR) end of the HGA support parallelogram element and the displacement force receiving (DFR) end of the base parallelogram element. 
         [0019]    The base parallelogram element has a cartridge coupling surface shaped to be selectively received by and secured to the cartridge support surface of the head tester whereby the displacement axis DA is perpendicular to spin axis SA of the spinstand. The base parallelogram element also has a parallelogram base surface facing away from the cartridge coupling surface and on a side of the base parallelogram element opposite to the cartridge coupling surface of the base parallelogram element, and extending between the HGA support (HGAS) end to a displacement force receiving (DFR) end of the base parallelogram element in a direction parallel to the displacement axis DA. 
         [0020]    The HGA support parallelogram element has an HGA coupling surface adapted to selectively receive thereon at or near the HGA support (HGAS) end, an HGA support element bearing an HGA. The HGA support parallelogram element also has an undersurface on a side of the HGA support parallelogram element opposite to the HGA coupling surface and facing the base surface of the base parallelogram element, and extending in a direction parallel to the displacement axis DA. 
         [0021]    A first end of the first parallelogram end element is coupled to the HGA support (HGAS) end of the HGA support parallelogram element by a flexure. A second end, opposite the first end, of the first parallelogram end element is coupled to the HGA support (HGAS) end of the base parallelogram element by a flexure. 
         [0022]    A first end of the second parallelogram end element is coupled to the displacement force receiving (DFR) end of the HGA support parallelogram element by a flexure, and a second end, opposite the first end, of the second parallelogram end element is coupled to the displacement force receiving (DFR) end of the base parallelogram element by a flexure. 
         [0023]    A counter force assembly is disposed along the DA axis and opposite the parallelogram support assembly. The counter force assembly includes a counterweight disposed along the axis DA and an associated structure to limit motion of the counterweight to be along the axis DA. 
         [0024]    A rigid actuator housing rigidly is coupled to the parallelogram support assembly along the axis DA between the parallelogram support assembly and the counter force assembly, and is rigidly coupled to the base parallelogram element. The actuator housing includes a rigid plate extending transverse to the axis DA defining a first open-faced void region extending from a first side of the plate and extending toward the displacement force receiving (DFR) end of the HGA support parallelogram element. A first piezo actuator is disposed in the first open-faced void region and an associated coupling rod for applying a force relative to the plate to the displacement force receiving (DFR) end of the HGA support parallelogram element in the direction of the axis DA. 
         [0025]    The rigid plate of the actuator housing also defines a second open-faced void region extending from a second side opposite the first side of the plate and extending toward the counterweight assembly. A second piezo actuator is disposed in the second open-faced void region and an associated coupling rod for applying a force relative to the plate to the counterweight in the direction of the axis DA. 
         [0026]    With this structure, the base parallelogram element, the HGA support parallelogram element, the first parallelogram end element and the second parallelogram end element, with the flexures, define a parallelogram structure wherein the HGA support parallelogram element is movable in the direction of the axis DA in response to a force applied thereto by the first piezo actuator to the displacement force receiving (DFR) end of the HGA support parallelogram element and the counterweight is movable in the direction of the axis DA in response to a force applied thereto by the second piezo actuator to the counterweight. 
         [0027]    With the disclosed structure, positional errors are highly reduced, or eliminated, by measuring the position of an HGA relative to a cartridge itself, from the perspective of the cartridge. For this purpose, a displacement sensor is made a part of the cartridge: for example, a glass scale is coupled to the head-mounting unit and an optical reader is mounted on the cartridge base. That structure provides highly accurate positional information for the HGA. 
         [0028]    Moreover, high suppression of vibration during positioning of the head-mounting unit is established by a novel construction that combines use of a counterweight with a damping mechanism. A combination of the counterweight with a damping mechanism suppresses vibration not only in the cartridge base, but also in the head-mounting unit itself, and in the counterweight as well. That configuration is considerably less sensitive to an imbalance between mechanical properties of the head-mounting unit and the counterweight, compared to systems of the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a perspective view of an exemplary prior art head gimbal assembly. 
           [0030]      FIGS. 2 and 3  are side cross-section schematic representations of a cartridge according to an embodiment of the present disclosure mounted to a head tester, including a spinstand of the head tester and a disk to be tested, with an HGA support element/module bearing an HGA about to be mounted and tested ( FIG. 2 ) and mounted in position to be tested ( FIG. 3 ). 
           [0031]      FIG. 4  and  FIG. 5  are perspective, exploded views, from opposite ends, of an exemplary cartridge according to an embodiment of the present disclosure. 
           [0032]      FIG. 6  is a partial cross-sectional view of the exemplary cartridge of  FIG. 4 . 
           [0033]      FIG. 7  is a side cross-sectional view of the exemplary cartridge of  FIG. 4 . 
           [0034]      FIG. 8  shows a preassembled stage of an actuator assembly of the exemplary cartridge of  FIG. 4 . 
           [0035]      FIG. 9  shows amplitude and phase frequency responses of an exemplary cartridge according to the present disclosure (with an optical scale and actuator on the cartridge), and amplitude and phase frequency responses of a cartridge according to the prior art (with an optical scale and actuator on the parallelogram). 
       
    
    
     DETAILED DESCRIPTION 
       [0036]      FIGS. 2 and 3  show a schematic cross-section representation of an exemplary cartridge  100  according to an embodiment of the present disclosure, mounted to an upward facing surface  90 A of a head tester  90 . Head tester  90  includes a spinstand  92  of the head tester and is shown with a disk  94  mounted for testing. Spinstand  92  includes a rotary actuator  96  mounted on top surface  90 A for spinning the disk  94  about a spin axis SA.  FIG. 2  shows an HGA support element/module  102  bearing an HGA  1  overlying and about to be mounted to cartridge  100  and tested.  FIG. 3  shows the configuration of  FIG. 2 , with HGA support element/module  102  bearing the HGA  1  mounted in position to be tested. 
         [0037]      FIGS. 4-8  show detailed diagrams of an exemplary form of a cartridge  100  of the present disclosure from different points of view. Perspective, exploded front and rear views of cartridge  100  are shown in  FIGS. 4 and 5 , respectively, with an HGA  1  mounted to a head-mounting unit  102 , which in turn is mounted on an upward-facing receiving surface of a mounting platform  160 . 
         [0038]      FIG. 6  shows a partial cut-away perspective view of the cartridge  100  of  FIG. 4 , particularly showing actuators  240  and  242  and their surrounding structures.  FIG. 7  shows a side cross-sectional view of cartridge  100 .  FIG. 8  shows a perspective, exploded view of the interconnected components of the actuator assembly of the cartridge  100  of  FIG. 4 . 
         [0039]    As seen in the drawings, a cartridge  100  includes a cartridge base  108  that carries a head-mounting unit  102 . The head-mounting unit  102  includes a HGA mounting block  104  and an upward-facing surface of element  160 , forming a mounting platform  160 . A head gimbal assembly HGA  1  is mounted on the mounting block  104  of the head-mounting unit  102 . The mounting platform  160  of the head-mounting unit  102  extends along, and is adapted for translation along, a displacement axis (DA)  270 , as described below. 
         [0040]    The uppermost portion of mounting block  160  forms an HGA support parallelogram element extending a distance D 1  along a displacement axis DA from an HGA support (HGAS) end to a displacement force receiving (DFR), with the upward-facing surface of mounting block  160  forming a mounting surface for receiving head-mounting unit  102  and HGA mounting block  104 . 
         [0041]    A base parallelogram element extending a distance D 1  in a direction parallel to the displacement axis DA from an HGA support (HGAS) end to a displacement force receiving (DFR) end is integral with an uppermost region of the top portion of base  108 . 
         [0042]    A first parallelogram end element (flexures  170   a ) extends a distance D 2  between the HGA support (HGAS) end of the HGA support parallelogram element (mounting platform  160 ) and the HGA support (HGAS) end of the base parallelogram element(portion of base  108 ). The first parallelogram end element is in the form of a set of multi-leaf, parallel, equal length (and transverse to the displacement axis  270 ) elastic flexures  170   a.    
         [0043]    A second parallelogram end element (flexures  170   b ) similarly extends a distance D 2  between the displacement force receiving (DFR) end of the HGA support parallelogram element (mounting platform  160 ) and the displacement force receiving (DFR) end of the base parallelogram element (portion of base  108 ). The second parallelogram end element is in the form of a set of multi-leaf, parallel, equal length (and transverse to the displacement axis  270 ) elastic flexures  170   b.    
         [0044]    Thus, the opposite ends (along displacement axis  270 ) of the mounting platform  160  (the HGA support parallelogram element) having length D 1 , is connected to the underlying portion of cartridge base  108  (the base parallelogram element) having length D 1 , by multi-leaf, parallel, equal length D 2  (and transverse to the displacement axis  270 ) respective sets of elastic flexures  170   a  and  170   b , thereby forming a parallelogram structure 
         [0045]    The parallel elements of the elastic flexures  170  for the parallelogram end elements each include: (i) a relatively flexible flexure portion at the junction of the parallel elements of the first end elements and the HGA support (HGAS) end of the HGA support parallelogram element and the HGA support (HGAS) end of the base parallelogram element, and (ii) a relatively flexible flexure portion at the junction of the parallel elements of the respective end elements and the displacement force receiving (DFR) end of the HGA support parallelogram element and the displacement force receiving (DFR) end of the base parallelogram element, and (iii) relatively stiff planar core portions extending between the flexure portions of each of the parallel elements wherein the core portions are mutually parallel and nominally perpendicular to the displacement axis (DA)  270  (depending on the position along the displacement axis DA at any given time, of the (slightly) moveable HGA support parallelogram element, with respect to the stationary base parallelogram element of cartridge base  108   
         [0046]    The parallelogram structure enables (slight, or fine) movement of head-mounting unit  102  (and HGA  1 ) relative to the cartridge base  108  along the displacement axis (DA)  270 , while limiting movement of head-mounting unit  102  in directions transverse to the displacement axis  270 . As a result, that movement of mounting platform  160  is constrained to be substantially parallel to the displacement axis (DA)  270 . An actuator assembly  110  drives the head-mounting unit  102  relative to the cartridge base  108  in the direction of the displacement axis  270  by an elongated rod  250 . 
         [0047]    In the illustrated form of  FIGS. 4-8 , a displacement sensor assembly generates a signal representative of the displacement, or movement, of head-mounting unit  102  (and HGA  1 ) relative to the fixed cartridge base  108  along the displacement axis (DA)  270 . In the illustrated form, the displacement assembly includes a moving part of the sensor (affixed to the HGA support parallelogram element formed by the underside of mounting platform  160 ), and a stationary part (affixed to the upward-facing base parallelogram element formed on base  108 ). The moving part of the displacement sensor assembly, is in the form of a glass scale  302  which is coupled to the underside of the mounting platform  160 , facing downward, while the stationary part of the displacement sensor assembly, namely, an optical source and reader  300 , is mounted on the cartridge base  108 , facing glass scale  302 . 
         [0048]    To make efficient interaction between the optical source and reader  300  and glass scale  302 , optical source and reader  300  is disposed in a cavity  150  that is formed in the cartridge base  108  and extends through the cartridge base  108 . Such a construction enables passage of light from the optical source and reader  300  to glass scale  302  and for reflected light to pass from glass scale  302  back to optical source and reader  300 . The signal produced by optical source and reader  300  provides a highly accurate indication of movement of the head-mounting unit  102  and of the HGA  1  relative to the cartridge base  108 , along the displacement axis (DA)  270 . 
         [0049]    The incorporation of the optical source and reader  300  and the scale  302  into the cartridge  100  itself provides various advantages that have been unavailable in prior art. The measurement of displacements at the intersection of the HGA  1  and the cartridge base  108  ensures a superior accuracy and reduces or eliminates errors caused by indirect measurements and errors attributable to deflection, expansion and/or other positional variations of intervening interfaces or intersections between different components. Accordingly, the described embodiment of the present disclosure localizes displacement measurements to the HGA  1  itself, an advantage and benefit that has not been achieved in prior systems. This advantageously increases mechanical bandwidth of the system during servo writing by reducing the weight of movable part (moving only the head-mounting unit  102  and the HGA  1  instead of an entire stage, as in prior systems). This permits high bandwidth feedback in the servo writing process (more specifically high bandwidth of the pass from optical reader to the actuator driver), therefore improving accuracy of the writing process. Moreover, such design solution essentially increases the speed of placing an HGA  1  into a required position (in other words reduces the settling time)—an advantage that is difficult to overestimate. The best position of the HGA mounting block  104  is on the centerline of the optical source and reader  300  to guarantee maximum accuracy of HGA  1  positioning. 
         [0050]    Along with an embodiment of the present disclosure that uses multi-element glass scale-based optical sensors, other embodiments are possible that use different positional measurement devices. The displacement-sensing assembly can include, for example, contact or non-contact sensors, for example, linear displacement sensors, capacitive displacement sensors, ultrasonic wave sensors, eddy current sensors, inductive sensors, magneto-inductive sensors, confocal sensors, laser sensors, LED sensors and ultrasonic sensors. 
         [0051]    To suppress vibration of the cartridge base  108 , a counterweight assembly  280  is incorporated in the cartridge  100 . The counterweight assembly  280 , shown most clearly in  FIGS. 5-8 , includes a housing  290  disposed about a cylindrical counterweight  289  disposed along the displacement axis (DA)  270 . The housing  290  is coupled to the cartridge base  108  by a flexible flange  288  through a platform  286  in a manner permitting movement of the counterweight assembly  280  substantially only along the displacement axis  270 . As described below, the counterweight assembly  280  is coupled to the actuator assembly  110 , containing piezo-electric actuators  240  and  242 , each for driving a respective one of head-mounting unit  102  and counterweight  289 . 
         [0052]    The actuator assembly  110  is mounted on the cartridge base  108 . The two piezo-electric actuators  240  and  242  of assembly  110  abut different sides of a rigid rest wall  248  extending transverse to displacement axis  270 , and shown as a part of actuator base  232  affixed to base  108 . 
         [0053]    The actuator base  232  is rigidly connected to the cartridge base  108 . The first actuator  240  drives the head-mounting unit  102  (and the HGA  1 ) via the rod  250  along displacement axis (DA)  270 . At the same time, the second actuator  242  drives the counterweight assembly  280  via a rod  252  in the opposite direction. The mass of the counterweight assembly  280  is adjusted to be approximately equal to the mass of the head-mounting unit  102 , and the elasticity of the flexible flange  286  is adjusted to be in accord with the elasticity of the flexures  170   a  and  170   b . The forces which actuators  240  and  242  apply to the head-mounting unit  102  and the counterweight assembly  280  evoke counteractive forces that are applied to the rest wall of actuator base  232 . Since these counteractive forces are of approximately the same magnitude and act in opposite directions, they cancel each other. The composite force that acts through the rest wall  232  on the cartridge base  108  equals the difference between the counteractive forces and is of a negligible value. 
         [0054]      FIG. 7  shows details, in a section view, of an exemplary actuator assembly  232 , mounting platform  160 , HGA mounting block  104 , stationary rest wall  248 , and counterweight assembly  280 . As noted above, the piezo-electric actuator  240  drives mounting platform  160  by elongated rod  250 . The rod  250  is preloaded to the piezo-electric actuator  240  by spring washes  294  and preload cap  293 . When a control voltage is applied to the piezo-electric actuator  240 , the actuator  240  expands and moves the mounting platform  160  in direction of expansion, away from the rest wall  248 . Movement in the opposite direction is forced by spring washers  294 . To provide movement in both directions, the elongated rod  250  is rigidly held in a circular cross-section hole inside of the mounting platform  160  (preferably by glue). 
         [0055]    A similar assembly is used for the counterweight. The elongated rod  252  is preloaded by spring washers  294  and loading cap  293 . The rod  252  is rigidly held to counterweight plate  296 , preferably by glue. The counterweight includes counterweight cap  290  and selectable counterweights  289  and  291 . The weight of these two parts is selected to match the weight of the head mounting unit  102  and to compensate the force difference between piezo-electric actuators  240  and  242 . 
         [0056]    In the event of a necessary repair, elongated rod  250 , can be disassembled from mounting platform  160 , For this purpose, a threaded part  297  in mounting platform  160  ( FIG. 7 ) can be used. A proper size of screw can be used to apply disassembly force to elongated rod  250 . A similar disassembly can be performed from counterweight side, by a longer screw instead of screw  292 .  FIG. 8  shows preassembled stage of the piezo-electric actuator assembly. 
         [0057]    According to the present disclosure, the stabilizing effect of the counterweight assembly  280  is extended by using a damping assembly. The damping assembly comprises a pair of rigid arms  402  (preferably made of metal) that are coupled, by a set of screws, to the actuator base  232 . One distal end of the arm  402  is rigidly positioned along the lateral side of the head-mounting unit  102 , while a second distal end of the arm is rigidly positioned along the lateral side of the counterweight assembly  280 . A pad  410  made of a compliant, vibration absorbing material, under compression, is disposed between the ends of arms  402  and the adjacent ones of the lateral sides of the head-mounting unit  102 , and the lateral sides of the counterweight assembly  280 . The construction of the damping assembly ensures a match between forces applied by arms  402  to opposite sides of the head-mounting unit  102  and of the counterweight assembly  280 , so that the cumulative force directed transverse in relation to the displacement axis  270  is of a negligible magnitude. 
         [0058]    It should be clear for those experienced in the art that the number of arms in the damping assembly may be different from two. The important point is that (a) each of the arms is both rigid and rigidly coupled to the base of the actuators assembly, (b) each of the arms is in contact with a lateral side of the head-mounting unit and a lateral side of the counterweight assembly (via pads  410 ), so that (c) the damping assembly changes the frequency response of the system, producing a stabilizing effect and makes the movement of the head-mounting unit during positioning of the HGA more even, eliminating jerks and twitching. 
         [0059]    As noted above, the arms  402  of the damping assembly stabilize the movement of the head-mounting unit  102  and of the counterweight assembly  280 . The damping assembly referable (but not necessarily) contains resilient pads  410  that are interposed between the end of arm  402  and the lateral side of the head-mounting unit  102  and of the counterweight assembly  280 . By way of example, the resilient pads  410  may comprise an elastic material, such as rubber, or elastic polymer, such as Sorbothane. 
         [0060]    The resilient pads  410  may be adhesively coupled to the elongated arm  402  at its distal end. Again, as noted above, the resilient pads  410  are preferably compressed against the head-mounting unit  102  and against the counterweight assembly  280 , by tight attachment of the elongated, preferably high stiffness, arms  402  to the actuator base  232 . Typically the applied force compresses resilient pads  410  at about 10% their thickness. 
         [0061]    The joint action of the counterweight and the damping mechanism tends to eliminate or at least to reduce the vibration during HGA positioning in the cartridge base  108  and in the head-mounting unit  102  alike. Furthermore, the damping assembly limits movement of the head-mounting unit  102  in a direction transverse to the displacement axis  270 . 
         [0062]    The efficiency of described design was established by comparative test of a cartridge built in the form of the present disclosure, and prior art system with a parallelogram HGA support structure and optical scale with an actuator mounted in the parallelogram. In both cases, measurements are performed in a servo write mode where head position was monitored and controlled using an optical scale. It can be seen ( FIG. 9 ) that resonance on an amplitude response moved from 500 Hz in the case of a parallelogram HGA support structure-only prior art form, to 8 KHz in case of the cartridge built in accord with the present disclosure. That 500 Hz: 8K Hz (or 16:1) ratio of bandwidth improvement means that the bandwidth of the control loop is increased proportionally, and the speed of head movement from one position to another is proportionally higher (about 16 times). 
         [0063]    Although the foregoing description of the embodiment of the present disclosure contains some details for purposes of clarity of understanding, the disclosure is not limited to the detail provided. There are many alternative ways of implementing the invention. The disclosed embodiment is illustrative and not restrictive.