Abstract:
A spring has a fixed end and a free end. A specific portion of the free end is elevated from the fixed end, and a load measuring device that measures the load on the spring is arranged so as to make a physical contact with the free end. An elevation is measured from the fixed end of a specific portion of the load measuring device where the free end and the load measuring device make the physical contact with each other. It is determined whether the elevation measured is equal to a specific elevation and the load on the spring is measured with the load measuring device when the elevation measured is equal to a specific elevation.

Description:
BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The present invention relates to a technology for measuring load on a spring. More specifically, the present invention relates to technology for measuring the load on a leaf spring (suspension) that supports the magnetic head in a hard disk drive (HDD). 
   2) Description of the Related Art 
   In many cases it is necessary to measure the load on a spring. For example, it is necessary to measure the load on a suspension, which supports the magnetic head in the HDD. 
   In accordance with dramatic improvement in a recording density of the HDD, it has become necessary to accurately manufacture the suspension. An amount levitation of the magnetic head at the time of recording and reproduction is depends on how much load is there on the suspension in a stationary state. Consequently, a head load of the suspension significantly affects a levitation posture and a levitation characteristic of the magnetic head. Therefore, head load of each suspension is measured when manufacturing the suspension. 
     FIG. 7  is a schematic for explaining a relation between a suspension  200  a magnetic disk  21 . It is assumed here that the magnetic disk  21  is not rotating. The suspension  200  includes a support  24  that supports a base plate  201 , a load beam  203  that is attached to the base plate  201  via a leaf spring section  202 . A flexure  209  is attached to the load beam  203 . 
   A slider  210  is attached to an upper surface of the flexure  209 . The slider  210  slides with respect to a surface of the magnetic disk  21 . A magnetic read/write head (not shown) is housed inside the slider  210 . A sliding surface of the magnetic head opposed to the magnetic disk  21  is the slider  210 . A dimple  28   a  is provided at a tip of the load beam  203  and it is in contact with the flexure  209 . The dimple  208   a  serves as a rotation fulcrum for the slider  210 . 
   The load beam  203  is elastically supported by the leaf sprint section  202 . Therefore, when the magnetic disk  21  is not rotating, the slider  210  is pressed against the magnetic disk  21  due to the force of the leaf spring  202 . The contact load, when the magnetic disk  21  is not rotating, with which the slider  210  is pressed against the magnetic disk  21  will be called as the head load. 
   When the magnetic disk  21  rotates, the slider  210  is pushed away from the magnetic disk  21  because of an airflow that is generated because of the rotation of the magnetic disk  21 . In other words, the slider  210  levitates below (or above) the magnetic disk  21 . Recording and/or reproduction of information from/in the magnetic disk  21  is performed in this manner. The amount of levitation depends on the buoyant force and a force caused by the bending of the suspension. In general, this amount of levitation is several nanometers to several tens nanometers. 
   The head load has been conventionally measured by a method as described below. This method is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. H6-44760. 
   Note that, in an example described below, an object of measurement of the heat load is the suspension  200  not yet mounted with the slider  210 . When the suspension  200  mounted with the slider  210  is an object of measurement, it is possible to measure the head load with the same method except that only a thickness (Z 210  in  FIG. 8 ) of the slider  210  has to be taken into account. 
   In  FIG. 8 , reference numeral  200   a  denotes the suspension  200  at the time when it is free (no load state). Reference numeral  200   b  denotes the suspension  200  at the time when the slider  210  is in contact with the magnetic disk  21  at the time of rotation stop (the same state as  FIG. 7 ). A load given to the magnetic disk  21  by the suspension  200   b  via the slider  210  is the head load. 
   Reference sign Zf denotes a height of a flexure  209   a  of the suspension  200   a  at the time when it is free from a reference plane  25   a  of the fixed support  24 . Reference sign Z 21  denotes a height of a lower surface of the magnetic disk  21  (a surface in contact with the magnetic disk  21 ) from the reference plane  25   a . Reference sign Zh denotes a height of a flexure  209   b  of the suspension  200   b , which presses the slider  210  against the magnetic disk  21  at the time of rotation stop, from the reference plane  25   a . The height Z 21  of the lower surface of the magnetic disk  21  is (Zh+Z 210 ). 
   Therefore, in measuring the head load of the suspension  200 , as shown in  FIGS. 8 and 9 , in a state in which a load probe  310  of a load cell  300  is in contact with the flexure  209 , the load cell  300  only has to be lowered to depress the flexure  209  to a position of the height Zh and measure a load (reaction) from the flexure  209  in that state with the load cell  300 . In the following description, a more specific method of measuring a head load will be explained with reference to  FIG. 10 :
     (1) first, prepare a suspension  200 M (master workpiece), a load of which is known in advance;   (2) nip the master workpiece  200 M with a workpiece clamp  400  and press the master workpiece  200 M upward to fix it on a reference plane  401 ;   (3) move a load cell  420  upward with a vertical movement unit  410  such as an air cylinder to bring a load probe  425  of the load cell  420  into contact with the master workpiece  200 M;   (4) move up and down an ascending-end stopper  430  to adjust a height of the load cell  420  while monitoring a load outputted by the load cell  420 , and fix the ascending-end stopper  430  at a position where the load outputted by the load cell  420  coincides with the known load of the master workpiece  200 M (completion of the adjustment of a height of the load cell  420 );   (5) lower the load cell  420  and also lower the workpiece clamp  400  to release the master workpiece  200 M;   (6) fix the suspension  200 , which is the object of measurement, on the reference plane  401  with the workpiece clamp  400 ;   (7) lift the load cell  420  to bring it into abutment against the ascending-end stopper  430  which has been adjusted in (4) above; and   (8) obtain a load outputted by the load cell  420  in the state of (7) as a head load of the suspension  200 .   

   However, the conventional technique does not give accurate results. In particular, in a suspension that supports a magnetic head, accuracy required in measurement of a head load is extremely high. Whereas a load required of the suspension was about 3±1.5 grams-force (gf) or 2.5±0.4 gf in the past, the load is measured at accuracy of as high as, for example, 0.4±0.04 gf recently. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to increase the accuracy of measurement of the load on the spring. 
   A method according to an aspect of the present invention is a method of measuring load on a spring, the spring having a fixed end and a free end, a specific portion of the free end is elevated from the fixed end, and a load measuring device that measures the load on the spring is arranged so as to make a physical contact with the free end. The method includes measuring an elevation from the fixed end of a specific portion of the load measuring device where the free end and the load measuring device make the physical contact with each other; determining whether the elevation measured is equal to a specific elevation; and measuring the load on the spring with the load measuring device when it is determined at the determining that the elevation measured is equal to a specific elevation. 
   A method according to another aspect of the present invention is a method of measuring load on a spring, the spring having a fixed end and a free end, a specific portion of the free end is elevated from the fixed end, and a load measuring device that measures the load on the spring is arranged so as to make a physical contact with the free end. The method includes measuring an elevation from the fixed end of a specific portion of the free end where the free end and the load measuring device make the physical contact with each other; determining whether the elevation measured is equal to a specific elevation; and measuring the load on the spring with the load measuring device when it is determined at the determining that the elevation measured is equal to a specific elevation. 
   A method according to still another aspect of the present invention is a method of measuring load on a spring, the spring having a fixed end and a free end, the free end is elevated from the fixed end, and a load measuring device that measures the load on the spring is arranged so as to make a physical contact with the free end. The method includes calculating a spring constant of the spring; determining whether the free end is elevated from the fixed end to a specific elevation; and measuring the load on the spring with the load measuring device when it is determined at the determining that the free end is elevated from the fixed end to the specific elevation. 
   A device according to still another aspect of the present invention is a device for measuring load on a spring, the spring having a fixed end and a free end, a specific portion of the free end is elevated from the fixed end, and a load measuring device that measures the load on the spring is arranged so as to make a physical contact with the free end. The device includes a measuring/determining unit that measures an elevation from the fixed end of a specific portion of the load measuring device where the free end and the load measuring device make the physical contact with each other, and determines whether the elevation measured is equal to a specific elevation. The load measuring device is caused to measure the load on the spring when it is determined by the measuring/determining unit that the elevation measured is equal to a specific elevation. 
   A system according to still another aspect of the present invention is a system for measuring load on a spring, the spring having a fixed end and a free end, a specific portion of the free end is elevated from the fixed end. The system includes a load measuring device that measures the load on the spring is arranged so as to directly or indirectly make a physical contact with the free end; and a measuring/determining unit that measures an elevation from the fixed end of a specific portion of the load measuring device where the free end and the load measuring device make the physical contact with each other, and determines whether the elevation measured is equal to a specific elevation. The load measuring device is caused to measure the load on the spring when it is determined by the measuring/determining unit that the elevation measured is equal to a specific elevation. 
   The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view for explaining the method of measuring the load on a spring according to an embodiment of the present invention; 
       FIG. 2  is another side view for explaining the method of measuring the load on a spring according to an embodiment of the present invention; 
       FIG. 3  is a side view showing a step of a spring load measurement method according to an embodiment of the present invention; 
       FIG. 4  is a side view showing another step of the spring load measurement method according to the embodiment; 
       FIG. 5  is a side view showing yet another step of the spring load measurement method according to the embodiment; 
       FIG. 6  is a graph showing a load-height diagram used in the spring load measurement method according to the embodiment; 
       FIG. 7  is a side view showing a state of use of a conventional general suspension; 
       FIG. 8  is a side view showing a height at the time when the conventional general suspension is free; 
       FIG. 9  is a side view showing a conventional method of measuring a head load of a suspension; and 
       FIG. 10  is a side view showing another conventional method of measuring a head load of a suspension. 
   

   DETAILED DESCRIPTION 
   Exemplary embodiments of the present invention will be hereinafter explained in detail with reference to the accompanying drawings. Note that the present invention is not limited by the embodiments. 
   First, a premise leading to the embodiments will be explained. 
   Accurate measurement cannot be performed with a conventional spring load measurement method shown in  FIG. 9 . This will be explained with reference to  FIG. 1 . 
   Conventionally, as shown in  FIG. 9 , in measuring a head load of a suspension  200 , in a state in which a load probe  310  of a load cell  300  is in contact with a flexure  209 , the load cell  300  is lowered to depress the flexure  209  to a position of a height Zh and measure a load from the flexure  209  in that state with the load cell  300 . 
   However, in actual measurement, as shown in  FIG. 1 , a tip of the load cell  300  (the part of the load probe  310 ) is subject to a load from the flexure  209  and bends, and the flexure further separates from a reference plane  25   a  by α equivalent to an amount of the bending. In the above description, when the flexure  209  is depressed to the position of the height Zh, conventionally, an amount of depression of the flexure  209  (height of the load cell  300 ) is determined based on a height of a housing  320  of the load cell. 
   Since the amount of depression is determined based on the height of the housing  320  of the load cell  300  in this way, the bending of the tip of the load cell  300  is not taken into account. Consequently, the load cell  300  actually measures a load at a height of (Zh+α) from the reference plane  25   a , and a load smaller than an actual load at the height Zh, at which it is truly desired to measure a load, is outputted. 
   In addition, the suspension  200  has a tolerance of the height Zf at the time when it is free, a tolerance of a length in a longitudinal direction, and the like. The amount of bending α at the tip of the load cell  300  varies depending on the suspension  200  and affects the height of the flexure  209  differently. 
   Therefore, accurate measurement cannot be performed with the conventional method. 
   This will be hereinafter verified using specific numerical values. 
   A suspension with 2.5 grams-force is measured using a load cell with a rated capacity of 10 grams-force and a rated displacement amount of ±0.4 millimeters (mm). Note that a spring constant of the suspension is assumed to be 2.3 gf/mm. When a suspension with 2.7 grams-force is measured in this setting, the following relation is obtained:
 
0.4:10= X :(2.7−2.5)
 
where X is 0.008 (a tip of the load cell bends away from the suspension by 0.008 mm).
 
   This is converted into a load as follows:
 
 P =0.008×2.3=0.018 gf
 
   A load to be outputted by the load cell is smaller than an actual load by about 0.02 gf. 
   Some suspensions have a load tolerance of ±0.04 gf. In this case, practical measurement cannot be performed. 
   The tip of the load cell  300  is subjected to the load of the spring and bends as described above, whereby accurate measurement for the spring is prevented. Thus, it is conceivable to measure a load of the spring accurately using a load cell having a tip that does not easily bend (with less bending). 
   However, when the same suspension  200  is measured using a load cell with a characteristic of small bending and a load cell with a characteristic of large bending, an output level of the load cell with the characteristic of small bending is smaller than an output level of the load cell with the characteristic of large bending. Since the output level is small in the load cell with the characteristic of small bending, there is only a small difference between an output level at the time when no load is applied to the load cell and an output level at the time when a load is applied to the load cell. When the difference in the output level is small, the load cell is easily affected by noise (has a low SN ratio) and cannot measure a load accurately. 
   As described above, an amount of bending and the SN ratio are in a relation of tradeoff. Therefore, a method of measuring a spring load, with which a load can be measured accurately, is required even if a load cell has a large amount of bending. 
     FIG. 2  is a side for explaining a spring load measurement method according to a first embodiment of the present invention. 
   As shown in  FIG. 2 , a workpiece clamp unit  10 , which clamps a suspension  200  that is an object of measurement, a load cell  300 , which is capable of moving up and down along a column  22 , and a measurement unit  30 , which measures a height of a tip of the load cell  300  (the part of a load probe  310 ), are provided. Note that, in this embodiment, the load cell  300  is used as an example of a load measurement device. However, a load measurement device of the present invention is not limited to the load cell  300 . 
   This measurement unit  30  is preferably a non-contact type displacement gauge such as a laser that can perform the measurement even if the height or the load of the object changes. A position of this measurement unit  30  is fixed. When the height of the tip of the load cell  300  changes, for example, a laser beam is irradiated from the laser displacement gauge  30 , and a position where reflection of the laser beam (a return position, a return angle, etc.) changes. The measurement unit  30  detects the height of the tip of the load cell  300  according to the change in the position. 
   In this embodiment, a height of a flexure  209  including an amount of bending (α) (Zh+α) is calculated. In this case, a measurement position is a pressurization point F where the flexure  209  pressurizes the load cell  300 . 
   Thicknesses of the load probe  310  and a load cell body  300   a  are fixed. Thus, when a laser beam is irradiated on an upper surface of the load cell body  300   a  (right above the pressurization point F where the flexure  209  pressurizes the load cell  300 ), the height (Zh+α) of the flexure  209  can be calculated based on a position where reflection of the laser beam is received. 
   Next, a height of the load cell  300  is adjusted (in this case, the load cell  300  is lowered) based on the height of the tip of the load cell  300  detected by the laser displacement gauge  30  to set a height of the flexure  209  (the pressurizing point F where the flexure  209  pressurizes the load cell  300 ) to Zh. If an output (load) of the load cell  300  is calculated at that point, a head load of the suspension  200  can be calculated. 
   Note that a portion, where a height is detected by the laser displacement gauges  30 , may be a portion of a suspension  200  instead of the tip of the load cell  300 . In this case, a height near a portion, with which the load probe  310  of the flexure  209  is in contact, can be calculated by the laser displacement gauge  30 . The height of the load cell  300  is adjusted (in this case, lowered) based on the height of the flexure  209  detected by the laser displacement gauge  30  to set the height of the flexure  209  (the pressurizing point F where the flexure  209  pressurizes the load cell  300 ) to Zh. If an output (load) of the load cell  300  at that point is calculated, a head load of the suspension  200  can be calculated. 
   With the conventional measurement method, since it is necessary to reduce bending (an amount of clearance) of the tip of the load cell  300  to control a measurement error, it is necessary to use a load cell with a characteristic of minimum bending. Thus, the load cell has a low output voltage and is susceptible to noise in measurement of a very small load. 
   On the other hand, in this embodiment, the height of the pressurizing point F, where the flexure  209  pressurizes the load cell  300  (the height Zh+α at F at the time when the tip of the load cell  300  bends) is measured. This makes it possible to use a load cell with a characteristic of large bending and increases a degree of freedom of design or selection of a load cell. As a result, accurate measurement resistant to noise can be performed. 
   A second embodiment of the present invention will be explained with reference to  FIGS. 3 to 6 . 
   Loads (PH and PL) are measured at heights (δH and δL) at two points above and below a target height (δT) in product design corresponding to a height at which a head load should be measured. In that case, since a tip of a load cell  300  bends away from a suspension  200  due to a reaction of a load, a height of the tip is measured. A load-height (bending) diagram of the suspension  200 , which is an object of measurement, is prepared from the measured heights at two points ( FIG. 6 ). The target height (δT) is inputted in this diagram to calculate a load (PA) at that height (δT) and set the load as a measurement value. Consequently, displacement of a portion to be deformed is measured directly such that an error due to the bending (deformation) of the tip of the load cell  300  does not occur, whereby the deformation does not affect the measurement of the height. This will be hereinafter explained more specifically. 
   In the second embodiment, a height of the tip of the load cell  300  is measured using a laser displacement gauge  30  as in the first embodiment. 
   In the second embodiment, sets of a load and a height at a pressurizing point, where the flexure  209  pressurizes the load cell  300 , are measured at two points of different heights to prepare a load-height (bending) diagram based on a result of the measurement. A load (heat load) at a predetermined height (height Zh for measuring a head load) is calculated based on this load-height diagram. This calculated load at the predetermined height is an accurate value with bending (clearance) of the tip of the load cell  300  cancelled. 
   A procedure for adjusting the origin will now be explained in detail. 
   As shown in  FIG. 3 , a zero adjustment gauge  50  is set on a support  24 . The zero adjustment gauge  50  is constituted to have a surface  51  that is at the same height as a reference surface  25   a  when the zero adjustment gauge  50  is set on the support  24 . 
   The height of the load cell  300  is adjusted to bring a load probe  310  of the load cell  300  into contact with the surface  51  of the zero adjustment gauge  50 . 
   Then, in a state in which the load probe  310  of the load cell  300  starts to come into contact with the surface  51  of the zero adjustment gauge  50 , a laser beam is irradiated on a laser irradiated section  330  of the load cell  300  from the laser displacement gauge  30 . A position of the laser irradiated section  330  obtained from reflection of the laser beam is recorded as a height zero point (reference point). 
   Here, the laser irradiated section  330  is a section that is provided at a position right above the load probe  310  of the load cell  300  and set as a target of laser irradiation to thereby measure a height of a pressurizing point F where the flexure  209  pressurizes the load cell  300  (load probe  310 ). Note that a thickness of the load probe  310 , a thickness of the load cell body  300   a , and a thickness of the laser irradiated section  330  are fixed. The height of the pressurizing point F where the flexure  209  pressurizes the load cell  300  can be calculated by deducting a total of the thickness of the load probe  310 , the thickness of the load cell body  300   a , and the thickness of the laser irradiated section  330  from the thickness of the laser irradiated section obtained by the laser displacement gauge  30 . 
   Next, as shown in  FIGS. 4 and 5 , heights of the laser irradiated section  330  and loads on the suspension  200  are measured at two points of different heights, respectively. The height of the laser irradiated section  330  is higher than that shown in  FIG. 5 . The height of the laser irradiated section  330  and the load of the suspension  200  in  FIG. 4  are assumed to be δH and PL, respectively. The height of the laser irradiated section  330  and the load of the suspension  200  in  FIG. 5  are assumed to be δL and PH, respectively. These heights and loads are plotted on a load-height diagram as shown in  FIG. 6 . 
   As shown in  FIG. 6 , a straight line La is obtained when a point P 2  that represents a result of measurement in  FIG. 4  and a point P 1  that represents a result of measurement in  FIG. 5  are joined. This line La corresponds to a spring constant of the suspension. Here, a graph corresponding to the spring constant is obtained by connecting the two plots with a straight line. 
   Next, when a load at a predetermined height of the suspension  200  is to be obtained, a load P corresponding to δ according to the predetermined height only has to be calculated on the graph La shown in  FIG. 6 . Conversely, when a height at a predetermined load of the suspension  200  is to be obtained, a height δ corresponding to P according to the predetermined load only has to be calculated on the graph La shown in  FIG. 6 . 
   In obtaining a head load of the suspension  200 , after setting the height δ to δT=(Zh+thickness of the load probe  310 +thickness of the load cell body  300   a +thickness of the laser irradiated section  330 ), a head load PA can be calculated from the graph La. 
   Next, when an object of measurement is changed to another suspension  200 , heights of the laser irradiated section  330  and loads on the suspension  200  are measured at two points of different heights for the suspension  200  in the same manner as described above. Results of the measurement at the two points are plotted on a load-height diagram in the same manner as  FIG. 6 . Both the plots are connected to obtain a graph corresponding to a spring constant. A load at a predetermined height or a height at a predetermined load for the suspension  200  can be calculated based on the graph. 
   Note that a portion where a height is detected by the laser displacement gauge  30  may be a portion of the suspension  200  itself instead of a portion of the laser irradiated section  330 . In this case, a height near a portion, with which the load probe  310  of the flexure  209  is in contact, can be calculated by the laser displacement gauge  30 . Heights of the suspension  200  itself and loads on the suspension  200  are measured at two points of different heights, respectively. The heights of the suspension  200  itself is assumed to be δH and δL to prepare a load-height diagram. A load at the time when the suspension  200  is at a predetermined height can be calculated based on the load-height diagram. 
   According to the second embodiment, an accurate load with an amount of bending of the tip of the load cell  300  cancelled can be calculated. 
   In addition, since a spring constant of each spring (suspension  200 ) is measured, and then a load at a predetermined height is calculated, more accurate measurement can be performed. 
   For example, measurement of a load of the suspension for HDD (suspension)  200  will be described. In accordance with the improvement of a density of capacity in a HDD, load, which significantly affects reading and writing of signals, needs to be measured very accurately. A leaf spring section  202  (see  FIG. 7 ) of this suspension  200  is formed by rolling or half etching. A thickness of the leaf spring section  202  (see “t” in  FIG. 7 ) fluctuates by several percents in the rolling and several tens percents in the half etching. Thus, it is difficult to control the fluctuation within a load tolerance. On the other hand, in this embodiment, a spring constant is measured for each of the suspensions  200 , which are objects of measurement, and then a load at a predetermined height or a height at a predetermined load for each of the suspensions  200  is calculated. This is effective for solving the problem of the fluctuation in the thickness of the leaf spring  202 . 
   This embodiment is explained with the suspension  200  as an example. However, the present invention is not limited to this, and the above-mentioned effects can be realized for a spring in general. 
   Conventionally, as shown in  FIG. 10 , a tip of a load cell  420  is brought into abutment against a measured section of a workpiece  200 , and the workpiece  200  or the load cell  420  is moved to a predetermined height in a load generation direction to measure a load. In this case, the load cell  420  bends in a direction opposite to the workpiece  200  due to a reaction of the workpiece  200 . As an example, when a load is 30 grams-force, the load cell  420  bends by 0.012 millimeters. As explained with reference to  FIG. 10 , usually, the predetermined height is determined in anticipation of this bending. Therefore, accurate measurement cannot be performed when a spring constant is different or when a load is different. 
   Moreover, according to the second embodiment, a very small load can be measured in very little time. This effect will be hereinafter explained. In measuring a very small load of a spring, it takes several seconds until vertical vibration of a measurement system subsides. This is because, since the number of vibration peculiar to the measurement system is low, amplitude hardly attenuates. On the other hand, in this embodiment, vertical vibration may remain as long as a height and a load at a certain point in time can be measured. In addition, in this embodiment, since loads and heights are measured at two points of different heights, a graph indicating an accurate spring constant can be obtained, which is advantageous in that more accurate measurement can be performed. 
   Note that, when an electronic balance system is used, it takes several seconds until a spring comes into a balanced state. Thus, the electronic balance system is not suitable for high-speed measurement. 
   In each of the first and the second embodiments, a head load is measured with respect to the suspension  200  not yet mounted with the slider  210 . On the other hand, it is also possible to measure a head load with respect to the suspension  200  mounted with the slider  210  in each of the first and the second embodiments. As a measurement method in that case, all what should be performed is that, in the explanation of the first and the second embodiments, an object against which the load probe  310  of the load cell  300  is brought into abutment is changed from the flexure  209  to the slider  210  mounted on the flexure  209 , and in utilizing a result of measurement of the laser displacement gauge  30 , a thickness of the slider  210  is taken into account. 
   If a height of the tip of the load cell  300  is calculated in a state in which the slider  210  is attached, since a thickness involved in attachment of the slider  210  can be taken into account, a head load at the time when the slider  210  actually comes into contact with the magnetic disk  21  can be measured more accurately. 
   In the second embodiment in which heights and loads at two different points are calculated and a spring constant is fond from a height-load diagram, an object for which the heights are measured is the tip of the load cell  300 . However, the object may be the housing  320  of the load cell  300  as in the conventional technique. Even in this case, since heights and loads of the housing  320  are measured at plural points to prepare a height-load diagram, more accurate load measurement can be performed compared with the conventional technique. 
   In accordance with an increase in a capacity of a HDD, a load of the suspension  200  has become smaller, moreover, the load needs to measured more accurately. Conventionally, the load cell  300  is used to measure the load; however, there was a problem that the measurement was inaccurate due to clearance of the load cell  300 . On the contrary, according to the present invention, displacement of the load cell  300  is measured together with the load to prepare a load-bending diagram according to arithmetic operation processing and estimate a load at a predetermined height from the diagram. Therefore, the load on the spring can be measured more accurately so that the method can be used in manufacturing of improved springs. 
   Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.