JPH10228742A - Flexure rigidity measuring device for suspension for hard disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply and correctly measure the roll rigidity and the pitch rigidity of a flexure by providing loading rods applying loads to a flexure at positions separated from a dimple, a load cell for detecting forces in an axial line direction acting on the rods and a means for detecting displacements in the axial line direction of the loading rods. SOLUTION: Loading rids 18 are driven in a flexure 2 direction until they are abbuted on a fixture 17 and the moment of the contact is detected with the sudden change of detection values of a load cell 20. Moreover, the loading rods of the left and the right are driven. A load setting to the flexure 2 is performed by adjusting the resultant of both loading rods 18 to be applied to the flexure 2 with both loading rods 18. Furthermore, the roll rigidity of the flexure 2 is calculated from increases and decreases of the loads and the sum of displacement of load points of left and right sides of the flexure 2 at that time. Especially, when points which apply loads with respect to the flexure 2 are set symmetrically in the left and the right or in the forward and the backward around the dimple, the simplifying of the measurement is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring apparatus for measuring roll and pitch stiffness of a flexure used for a suspension for a hard disk drive or the like.

[0002]

2. Description of the Related Art In the technique of suspension of a hard disk drive, as the capacity of a hard disk increases, an FH that defines a clearance between a slider and a disk is increased.
It has become necessary to keep (FlyHeight) a constant low value. For this purpose, the use of the negative pressure slider and the improvement of the assembling work have been improved. However, the precision of the flexure is required to be further improved. For example, Japanese Patent Application Laid-Open
Japanese Patent Publication No. -22296 discloses a configuration in which dimples to be brought into contact with a load beam are provided on a flexure and an access head is held so as to be displaceable in a roll and a pitch direction. Is desired. In particular, 1 (W) × which is recently called a pico slider
When a small slider of the order of 1.25 (L) × 0.3 (D) (mm) is used, the obtained lift is small, and it becomes more difficult to stabilize the FH. ing.

In such a hard disk suspension, it is necessary to accurately control the rigidity of the flexure, particularly the rigidity in the roll direction and the pitch direction, in order to suitably control the fly height of the read / write head.
Therefore, FEN analysis of roll and pitch stiffness,
Although measurement and the like have been performed, since it is difficult to perform measurement in a state close to the state of use, the measurement is usually performed by an indirect method, and the accuracy is often not always sufficient.

For example, a method is known in which a weight having a known second moment of inertia is attached to the tip of a flexure, and the roll and pitch stiffness of the flexure is calculated by measuring the frequency of the roll and pitch motions. I have. However, in this method, it is difficult to accurately grasp the magnitude of the inertial mass, that is, the magnitude of the second moment of inertia, and furthermore, a large variation occurs in the measurement of the frequency, so that it is difficult to obtain sufficiently high precision. Was. Also, it was difficult to measure in a state close to the use state, especially in a load state.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and a main object of the present invention is to provide an access head in a hard disk drive suspension or the like. An apparatus for simply and accurately measuring the roll and pitch stiffness of a flexure in order to be able to hold stably close to a moving target surface and displaceable in the roll and pitch directions. To provide.

A second object of the present invention is to provide an apparatus for measuring the roll and pitch stiffness of a flexure in a use state, particularly in a load state, in a suspension of a hard disk drive or the like.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided, in accordance with the present invention, a flexure mounted on a leading end of a load beam, the flexure being mounted via dimples provided on either of the two portions. An apparatus for measuring the rigidity of a flexure in a hard disk suspension supported on the load beam, comprising: a clamp for holding a base end of the load beam; First and second load rods for applying a load to the flexure at points spaced apart from each other, first and second drive means for individually displacing the rods in the axial direction, and the rods First and second load cells for detecting the axial force acting on each of the rods, and first and second load cells for detecting the respective axial displacements of the two rods. It is achieved by providing a device characterized by having a position detecting means.

According to such a structure, a load in the roll or pitch direction can be applied to the flexure as a pure couple while accurately controlling the load applied to the flexure as a resultant force applied to both rods. The roll and pitch stiffness of the flexure in a state close to the state can be accurately and easily obtained. In particular, the measurement can be simplified by setting the point at which the load is applied to the flexure symmetrically left or right or back and forth with the dimple as the center.

[0009]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a typical flexure support structure to which the present invention is applied, in which a free end of a relatively rigid load beam 1 is attached to one end of a flexible flexure 2. And an access head 4 such as a magnetic head is fixed to the tongue piece 3 cut out by the flexure 2. The load beam 1 and the flexure 2 may be made of any metal material having appropriate properties,
It is generally made of stainless steel (SUS). As shown in FIG. 2, the load beam 1 has dimples 5
And a spherical protrusion having a radius of about 0.25 mm, which is generally referred to as a movement of the head 4 in a pitch direction (FIG. 2) and a roll direction when the head 4 accesses the disk surface. The rear surface of the flexure 3 is supported so as to allow the movement (FIG. 3). However, the access head 4 read / write position 6 is arranged on one side of the head 4, and the attitude of the access head 4 when flying has a great effect on the FH. In particular, the movement of the access head 4 in the roll direction is FH
Is known to have a significant effect on

FIG. 4 shows a model in the case where the head 4 with dimple displacement and static roll is stationary in a horizontal state (disk surface). The balance of the force at this time is as follows.

[0012]

F = F ₀ + F _i (Equation 1) F _i · (X / 2 + ΔX) −F ₀ · (X / 2−ΔX) ± S ₀ · θ _s = 0 (Equation 2)

Here, F _i and F ₀ are reaction forces applied to both sides of the head, ie, the rail, from the disk surface, S ₀ is the roll rigidity of the flexure, and θ _s is the static roll angle of the flexure. The following equation is derived from these two equations.

[0014]

(Equation 2)

Equations (3) and (4) show F · ΔX when the load is F / 2.
/ X ± S ₀ · (θs / X) indicates that a load acts on both ends of the span X in the opposite direction, that is, the force is a couple. Therefore, the torque around the dimple is given by the following equation.

T _s = F · ΔX ± S ₀ · θ _S (Equation 5)

Hereinafter, this torque is called a static torque, and F _i and F ₀ are called static loads. From the above, it can be seen that in the case where there is a dimple deviation and a static roll, a difference always occurs in the static load of each rail, and a static torque acts.

When the disk starts to rotate in the above-described state, the head flies, but when the static load is F _i ≠ F ₀ , FIG.
As shown in FIG. The balance of the force at this time is as follows.

F = P ₀ · A ₀ + P _i · A _i (Equation 6) P _i · A _i · (X / 2 + ΔX) -P ₀ · A ₀ · (X / 2−ΔX) ± S ₀ · θ _S− S _L · θ = 0 (Equation 7) where P ₀ and _Pi are the dynamic pressures of the air applied to each rail of the slider, and A _o and A _i are the area of each rail.

Here, if the pressure is inversely proportional to the square of the flying height, the following relational expression holds.

P _i = C / H _i ² (Equation 8) P ₀ = C / H _O ² (Equation 9) Here, C is a constant obtained experimentally, and _Hi , H
₀ is the flying height of each slider. The following equation holds from the geometric relationship.

Sin (θ) = (H _i −H ₀ ) / X (Equation 10)

When θ ≒ 0, the following equation holds.

Θ = (H _i −H ₀ ) / X (Equation 11)

Equations 6 to 10 represent five unknowns (P _o , P _i , θ,
H _i , H ₀ ), and the equation becomes five equations, which can be solved.

Equations 6 and 7 can be rearranged into the following equations.

(Equation 8)

Equation (1) is obtained using Equations (3), (4), (8) and (9).
2. The following equation is obtained by rearranging equation 13.

Equation 9] ^{_{C · A i / H i 2}} = F i + S L · θ / X ( Equation _{14) C · A 0 / H} 0 2 = F 0 -S L · θ / X ( Equation 15)

Therefore, F _i , H _i , H ₀ and the attitude angle θ
It can be seen that is governed by the static loads F _i , F _{0, the} load state roll stiffness (stiffness) S _L , and the rail areas A _i , A ₀ . Then, if there is dynamic attitude angle theta and static attitude angle theta _S, it can be seen a load condition and no load roll stiffness S _L affects the FH. Therefore, it is important to measure the stiffness using the load as a parameter. In the FEM analysis, the roll stiffness in a no-load state can be calculated relatively easily, but the calculation of the roll stiffness in a loaded state is considerably difficult.

FIG. 6 shows the principle of measurement of roll stiffness under a flexure load condition according to the present invention. FIGS. 6A and 6B show the case where the flexure angle is 0 deg and the case where it is not.

The load beam load and torque when the flexure angle is 0 deg are given by the following equations.

F = f ₁ + f ₂ (Equation 15) T ₀ = L ₁ · f ₁ −L ₂ · f ₂ (Equation 16)

Here, f is the load beam load (gf),
f ₁ is the left side load cell load at the time of the flexure angle 0deg (g
f), f ₂ is the right load cell load in flexure angle 0deg (gf), T ₀ is the torque at the time of flexure angle 0 deg (g
f · mm), L ₁ is the distance (mm) between the dimple and the left load point, and L ₂ is the distance (m) between the dimple and the right load point.
m).

In this case, given the torque fluctuation,

Equation 11] _{f = f 1 + Δf + f} 2 -Δf = f 1 + f 2 ( Formula _{17) T a = L 1 ·} (f 1 + Δf) -L 2 · (f 2 -Δf) ( Formula 18)

[0028] Here, Delta] f is the load variation to provide a variation in torque (gf), T _a torque during flexure angle θdeg (gf · mm).

Therefore, the fluctuation of the torque is given by the following equation.

ΔT = T _a −T ₀ = Δf · (L ₁ + L ₂ ) = Δf · L ₃ (Equation 19)

Here, ΔT is the torque fluctuation (gf · m
m), L ₃ (= L ₁ + L ₂ ) is the distance (m
m). Therefore, when giving the variation of the torque left and right load variation equal to (couple) As described above, the load beam load does not vary, L ₁ and L ₂ are not necessarily equal.

On the other hand, the flexure angle at this time is as follows.

Tan (θ) = (h ₁ + h ₂ ) / (L ₁ + L ₂ ) = h ₃ / L ₃ (Equation 20)

Here, θ is the flexure angle (deg), h ₁
The displacement of the left loading point (mm), h ₂ is the displacement of the right loading point _{(mm), h 3 = h1} + h2 (mm).

Therefore, the torsional spring constant (rigidity) is given by the following equation.

K _t = ΔT / θ = Δf · L ₃ / tan ⁻¹ (h ₃ / L ₃ ) (Equation 21) where K _t is a torsion spring constant (gf · mm / deg).

FIG. 7 shows an example of an apparatus for performing such a measuring method. A rotating stage 12 is mounted on a fixed base 11 so as to be rotatable about a vertical axis. In the X-axis direction and the Y-axis direction, a knob or an actuator 13a,
An X-axis stage 13 and a Y-axis stage 14 that can be displaced by 14a are provided, respectively, and a tilt stage 15 that can be displaced in the front-back tilt direction with respect to the Y-axis stage 14 is provided.

On the tilt stage 15, a clamp 16 for holding the base end of the load beam 1 is provided. A fixture 17 composed of a rod member extending in the left-right direction is fixed to the free end of the flexure 2 provided at the tip of the load beam 1 held by the clamp 16. The left and right ends of the fixture 17 are in contact with the tip of a load rod 18, and the load rod 18 is fixed to a Z-axis stage 21 via a load cell 20.

The Z-axis stage 21 is supported on the fixed frame 19 so as to be displaceable in the Z-axis direction, that is, in the vertical direction. The vertical displacement of the Z-axis stage 21 is measured by a displacement meter 22.
Is detected by In the drawing, one load rod 1 is shown.
Although only the structure for 8 is shown, two sets of structures, each including a Z-axis stage, are provided to be symmetrical with respect to both load rods 18 as will be readily understood.

In front of the above-mentioned structure, a fixed base 2 is provided.
An X-axis stage 24 is provided so as to be displaceable in the X-axis direction with respect to 3, and a lens barrel 26 is fixed to a column 25 erected on the X-axis stage 24, and the tip of the flexure 2 is enlarged. So that it can be observed. Thereby, the dimple is aimed at by the lens barrel 26, and then the lens barrel 26 is displaced in the X-axis direction until the position where the left and right load rods 18 come into contact with the fixture 17 is aimed, and from the displacement amount, h ₁ , it is possible to find the h _2.

The displacement and load values obtained for the left and right load rods 18 are sent to the control unit 28, where
It can be calculated immediately by the calculation formula of 1). In the measurement, first, the load rod 18 is fixed to the fixture 17.
, The load rod 18 is driven in the flexure direction. The moment of contact can be detected as a point in time when the detection value of the load cell 20 changes suddenly. Next, the left and right load rods 18 are further driven in the axial direction, and when the desired amount of deflection (load value) is reached, each load rod 18 is driven in the opposite direction, and Δf and h ₃ at that time are used. The roll rigidity of the flexure 2 can be calculated from (Equation 21).

According to such a configuration, both load rods 1
By controlling the resultant force (f = f ₁ + f ₂ ) of the forces applied by the load 8, the load applied to the flexure 2 can be set as described above, and the force applied by both load rods 18 is increased or decreased by the same amount (Δf). By doing so, it is possible to generate a couple that is weighted against this force. In this way, the roll stiffness under a constant load condition in which the value can be freely set can be measured continuously in both directions. In particular, if L ₁ = L ₂ is adjusted,
Since h ₁ = h ₂ can be satisfied, the measurement becomes easier.

Further, as shown in FIG.
7 is mounted in the pitch direction, that is, in the front-back direction, and by rotating the rotary stage 12 by 90 °, the pitch rigidity can be measured in the same manner as the roll rigidity. In addition,
If a cross-shaped fixture 29 as shown in FIG. 9 is used instead of the fixture 17, workability in measuring the rigidity in both the roll and pitch directions can be improved.

FIG. 10 shows an example of actual measurement results of the effective stiffness (stiffness) of the flexure under various load conditions obtained in this manner. According to the result, it is understood that the rigidity increases as the load related to the dimple increases, and the degree of nonlinearity with hysteresis increases. That is, when the load applied to the dimple is small, the rigidity is close to the calculated value and the hysteresis is small. Conversely, when the load is large, not only the rigidity is increased but also the hysteresis is increased. In particular, when the hysteresis increases, the stability of the FH tends to be impaired, and the ability to follow the disk surface tends to decrease. This is considered to be due to deformation of the flexure or the like due to the load on the dimple, or friction between the dimple and the flexure.

Although the calculated value and the actually measured value have not always been constant and the verification of the calculation has not been sufficient until now, the measurement with this apparatus has enabled verification in a wide range of 0.08 to 0.4 fgmm / degree. Was. In addition, for laminated flexures such as flexures with wiring, the physical properties of each layer are not accurately obtained. Therefore, it can be measured by the apparatus according to the present invention, and conversely, the physical property value (copper or polyimide) of the flexure can be estimated.

[0043]

As described above, the load, that is, f (= f ₁ + f ₂ )
It is possible to understand that the roll and pitch stiffness change greatly depending on the size of the hard disk. Based on these measurement results, the operating conditions of the flexure can be precisely optimized, It can greatly contribute to higher reliability and higher reliability.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a structure of a magnetic disk suspension to which the present invention is applied.

FIG. 2 is a longitudinal sectional view showing a main part of FIG.

FIG. 3 is a transverse sectional view showing a main part of FIG. 1;

FIG. 4 is an explanatory diagram showing the balance of forces when the head (slider) is stationary.

FIG. 5 is a view similar to FIG. 4, showing the balance of forces when the head is flying.

FIG. 6 is a diagram comprising (a) and (b) for explaining the measurement principle of the measuring device according to the present invention.

FIG. 7 is a schematic perspective view showing a partly broken state of measurement of roll stiffness by a measuring device according to the present invention.

FIG. 8 is a schematic perspective view similar to FIG. 7, showing a situation of measuring pitch stiffness by the measuring device shown in FIG. 7;

FIG. 9 is a perspective view showing a modification of the fixture.

FIG. 10 is a graph showing actual measurement results of effective stiffness (stiffness) of a flexure under various load conditions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Load beam 2 Flexure 3 Tongue piece 4 Head 5 Dimple 11 Fixed base 12 Rotary stage 13 X-axis stage 14 Y-axis stage 15 Inclined stage 16 Clamp part 17 Fixture 18 Load rod 19 Fixed frame 20 Load cell 21 Z-axis stage 22 Displacement meter 23 Fixed base 24 X-axis stage 25 pillar 26 lens barrel 28 control unit 29 fixture

Claims (3)

[Claims] 1. A hard disk suspension having a flexure attached to the distal end of a load beam and supporting the flexure with respect to the load beam via dimples provided at either of the two portions. A clamp for holding a base end of a load beam, and a load for applying a load to the flexure at a point which is separated from the dimple left, right, front and back. First and second
And a first rod for individually displacing the two rods in the axial direction.
And second driving means, first and second load cells for detecting an axial force acting on each of the rods, and a first for detecting an axial displacement of each of the rods.
And a second displacement detecting means. 2. The apparatus according to claim 1, further comprising means for measuring a distance from the dimple of a point of application of the first and second rods to the flexure. 3. The apparatus according to claim 2, wherein said distance measuring means comprises a lens barrel arranged to face said first and second rods.