Patent Publication Number: US-6912102-B2

Title: Magnetic head with IC thereon with recording frequency controlled according to IC position

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This is a continuation of U.S. application Ser. No. 09/859,531, filed May 18, 2001 now U.S. Pat. No. 6,754,023, the subject matter of which is incorporated by reference herein. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a magnetic disk device, and in particular to a magnetic disk device having a magnetic head supporting mechanism including at least an IC for amplifying information on a magnetic head unit. 
   Conventionally, an IC is arranged in opposed relation with a disk surface in order to cool the IC while maintaining the distance of not more than 1 mm between the disk and the IC as disclosed in JP-A-11-195215. 
   Also, JP-A-11-296803 discloses a magnetic disk device in which a control circuit connected to an IC, after supplying a write current to the magnetic head unit for a predetermined length of time, prevents the write current from flowing to the magnetic head unit for a suspension time not shorter than the particular predetermined length of time. 
   SUMMARY OF THE INVENTION 
   In arranging an IC in opposed relation to the disk surface, various problems are liable to occur. For example, the length of the wiring (flexible print circuit: FPC) laid between the IC and the magnetic head unit is restricted, the disk may be damaged by the IC and the disk coming into contact with each other under an external shock, and the IC junction facing down makes the pattern inspection (electrical inspection) difficult. 
   Also, the cooling effect (ability) of the air flow with the disk rotation is varied with the radial position of the IC. Thus, the time during which the continuous write operation can be performed on the magnetic head unit is different depending on the radial position of the IC. If the continuous write time and the suspension time are determined without taking the cooling ability depending on the radial position of the IC into account, therefore, the continuous write time may be limited to a time length which is provided when the IC is located at the inner peripheral position which is low in cooling ability. As a result, the otherwise available continuous write time (ability) based on the high cooling ability with the IC located on the outer peripheral position may fail to be used, resulting in a reduced utilization rate. 
   In order to solve the problems described above, the object of the present invention is to provide means for maintaining the temperature rise of the IC not higher than a tolerable temperature without arranging the IC chip in opposed relation to the disk surface. 
   According to one aspect of the invention, there is provided a magnetic disk device comprising an IC mounted on a magnetic head supporting mechanism, for amplifying the information write/read signal on the magnetic head unit, and a control circuit connected with the IC, wherein the power consumption for the write/read operation is controlled in accordance with the head position on the magnetic disk by the control circuit thereby to maintain the IC temperature at a level not higher than a predetermined temperature. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a magnetic head supporting mechanism according to a first embodiment of the invention. 
       FIG. 2  is a block diagram showing the control circuit according to the first embodiment of the invention. 
       FIG. 3  is a diagram showing the relative positions of the head IC and the magnetic disk. 
       FIG. 4  is a diagram showing the relation between the thermal resistance and the Reynolds number of rotation. 
       FIGS. 5A ,  5 B and  5 C are diagrams for explaining the concept of the duty factor of the conduction time of the IC. 
       FIG. 6  is a block diagram showing the control circuit according to a second embodiment of the invention. 
       FIG. 7  is a diagram showing the relation between the calorific value and the response time according to a third embodiment of the invention. 
       FIG. 8  is a diagram showing the relation between the response time and the temperature change according to the third embodiment of the invention. 
       FIG. 9  shows a magnetic head supporting mechanism according to a fourth embodiment of the invention. 
       FIG. 10  is a block diagram showing the control circuit according to the fourth embodiment of the invention. 
       FIGS. 11A and 11B  each show a different magnetic head supporting mechanism according to other embodiments of the invention. 
       FIGS. 12A and 12B  are diagrams showing a general configuration of a magnetic disk device with the cover attached and removed, respectively. 
   

   DESCRIPTION OF THE EMBODIMENTS 
   A first embodiment of the invention will be explained with reference to the accompanying drawings.  FIGS. 12A ,  12 B show a general configuration of a magnetic disk device according to the invention. 
   As shown in  FIG. 12A , the magnetic disk device is made up of a base  1  in the shape of a box having a magnetic disk and a magnetic head unit accommodated therein and hermetically sealed with a cover  2 . As shown in  FIG. 12B , the base  1  is configured to accommodate therein a magnetic disk  4  stacked on a spindle  3 , and a positioning mechanism  9  including a magnetic head supporting mechanism  5  for supporting the magnetic head unit (not shown), a guide arm  6  coupled to the magnetic head supporting mechanism  5 , a pivot bearing  7  and a voice coil motor  8 . 
   The configuration of the magnetic head supporting mechanism  5  is shown in detail in FIG.  1 .  FIG. 2  is a block diagram of a signal processing circuit for the magnetic head unit. A slider  10  on which the magnetic head unit (not shown) is mounted is supported on a flexure  11 . The flexure  11  is coupled to a load beam  18  including a flat portion  12 , a flange portion  13  and a spring portion  14 . The magnetic head unit is adapted to write or read information by flying over or contacting the magnetic disk  4  rotating in the direction of arrow  17 . The other end of the load beam  18  includes a guide arm coupler  16  for coupling to the guide arm  6  and an IC mount  19  for mounting a signal amplifier (hereinafter referred to as the IC)  30 . The magnetic head supporting mechanism  5  is mounted in such a manner that a cylindrical mounter (not shown) arranged on the guide arm coupler  16  is caulked in the mounting hole  61  of the guide arm  6 . 
   According to this embodiment, the load beam  18 , the guide arm coupler  16  and the IC mount  17  are formed of a single thin plate. The spring portion  14  is formed with a window  15  for optimizing the spring rigidity. The IC  30  is connected to a wiring  31  extending from the magnetic head unit. The wiring  31  reaches the IC  30  from the magnetic head unit through the flexure  11 . Also, the wiring from the IC  30  is connected to a read/write controller  51  as shown in FIG.  2 . The read/write signal is transmitted and received through a HDD controller  50  between the magnetic disk device and an external computer not shown. The controllers  50  and  51  are usually incorporated in a circuit inside the magnetic disk device, but are not limited thereto and can be disposed anywhere. 
   As shown in  FIG. 3 , the slider  10  moves between the inner periphery and the outer periphery of the magnetic disk  4 . As a result, the radial position of the IC  30  moves from the inner periphery to the outer periphery. Let r be the distance from the center of rotation of the magnetic disk and the IC  30 . The relation between the distance r and the power consumption (calorific value) of the IC, and the temperature rise of the IC with the change in the revolution speed N of the magnetic disk experimentally determined are shown in FIG.  4 . 
   An explanation will be given in more detail with reference to FIG.  3 . The magnetic disk device used in the experiment is 3.5 inch type. The IC used in the experiment has a heater and a temperature sensor built therein. The revolution speed is changed between 6000 r/min and 12000 r/min to study the relation between the power consumption and the temperature rise of the IC. As a result, as shown in  FIG. 4 , it has been found that all the measurements, organized using the relation between the Reynolds number of rotation Rew and the thermal resistance Rh (calorific value w/temperature rise k), can be expressed by the calculation formula of equation (1).
 
 Rh=a ×10 −8   ×Rew +1.8×10 −3   (1)
 
where Rew=ωr 2 /v, ω is the angular velocity, v is the kinematic viscosity coefficient, and a is an arbitrary numerical value between 1 and 2, or typically 1.6.
 
   In  FIG. 4 , the thermal resistance Rh at Rew=0 represents the thermal resistance Rh at the disk rotational speed of 0 (that is, when the disk is stationary). In other words, it indicates the thermal resistance due to the two effects including the heat conduction to the structure and the heat transmission by the natural convection. Also,  FIG. 4  shows the thermal resistance Rh of the IC at the inner peripheral position and the outer peripheral position of the magnetic head unit. From  FIG. 4 , it is seen that as long as the IC power consumption (calorific value) is the same, Rh is larger and therefore the temperature rise is smaller on the outer periphery than on the inner periphery. 
   Table 1 shows the Reynolds number Rew of rotation, the thermal resistance Rh and the temperature rise for the power consumption of 400 mW on the middle and outer peripheries. 
   
     
       
         
             
             
             
             
             
             
           
             
               TABLE 1 
             
             
                 
             
             
                 
                 
               Thermal 
               Temp. rise (K) 
               Calorific value 
               Duty factor (%) 
             
             
                 
               Reynolds 
               resistance 
               at power 
               (mW) at temp. 
               at temp. 
             
             
                 
               number of 
               (calorific value 
               consumption 
               increase of 
               rise of 
             
             
               IC position 
               rotation 
               W/temp rise K) 
               of 400 mW 
               50 K 
               50 K 
             
             
                 
             
           
          
             
               Inner 
                5.3 × 10 4   
               0.0026 
               160 
               125 
               31 
             
             
               periphery 
             
             
               Middle 
                8.1 × 10 4   
               0.0031 
               129 
               155 
               38 
             
             
               periphery 
             
             
               Outer 
               12.1 × 10 4   
               0.0037 
               108 
               185 
               46 
             
             
               periphery 
             
             
               Remarks 
                 
                 
                 
               Carried out in 
               Carried out in 
             
             
                 
                 
                 
                 
               first 
               second 
             
             
                 
                 
                 
                 
               embodiment 
               embodiment 
             
             
                 
             
             
               Note:  
             
             
               Duty factor is the value for 400 mW  
             
          
         
       
     
   
   Table 1 shows that the continuous heating with the power consumption of 400 mW causes the IC temperature rise of 160 K on the inner peripheral position, which exceeds the IC junction temperature of 120□C. Normally, the temperature in the disk device is expected to increase up to 70□C, and therefore the tolerable temperature rise of the IC is required to be considered as 50 K in maximum. For suppressing the temperature rise of the IC chip to not more than 50 K, therefore, the power consumption at each radial position is set to 125, 155 and 185 mW or less for the inner periphery, the middle periphery and the outer periphery, respectively, as shown in Table 1. 
   Further, the results shown in Table 1, organized by making the power consumption at the inner peripheral position  1  is shown in Table 2. This table indicates that the power consumption on the outer peripheral position is tolerable up to 1.5 times higher. 
   
     
       
         
             
             
             
             
             
             
           
             
               TABLE 1 
             
             
                 
             
             
                 
               Reynolds 
                 
               Temp. rise at 
               Calorific value 
               Duty factor 
             
             
                 
               number 
                 
               400 mW of power 
               at temp. 
               at temp. 
             
             
                 
               Rew of 
               Thermal 
               consumption 
               rise of 
               rise of 
             
             
               IC position 
               rotation 
               resistance 
               5.3 × 10 4   
               50 K 
               50 K 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
             
             
          
             
               Inner 
                5.3 × 10 4   
               1 
               1 
               1 
               1 
             
             
               periphery 
             
             
               Middle 
                8.1 × 10 4   
               1.2 
               0.81 
               1.2 
               1.2 
             
             
               periphery 
             
             
               Outer 
               12.1 × 10 4   
               1.5 
               0.68 
               1.5 
               1.5 
             
             
               periphery 
             
             
               Remarks 
                 
                 
                 
               Carried out in 
               Carried out in 
             
             
                 
                 
                 
                 
               first 
               second 
             
             
                 
                 
                 
                 
               embodiment 
               embodiment 
             
             
                 
             
             
               Note:  
             
             
               Made dimensionless by the value at inner peripheral position  
             
          
         
       
     
   
   This result shows that according to the first embodiment, the IC power consumption may be made larger when the IC is located on the outer periphery than when it is located on the inner periphery of the magnetic disk  4 . The difference ΔW in power consumption therebetween may be the one which satisfies the following relation determined by multiplying equation (1) by the tolerable temperature rise ΔT of the IC.
 
Δ W≈a ×10 −8 ×( Ro   2   −Ri   2 )ω/ v×ΔT   (2)
 
where ω is the angular velocity, v the kinematic viscosity coefficient of air (2×10 −5  m 2 /s), ΔW the power consumption difference (W), ΔT the tolerable temperature rise, a an arbitrary value between 1 and 2, or typically 1.6 and Ro and Ri outer and inner periphery positions of the IC, respectively.
 
     FIG. 2  is a block diagram of the control system. As shown in the block diagram of  FIG. 2 , a microprocessor  58  calculates the increment of the power consumption allowed by the use at the outer peripheral position Ro with respect to the inner peripheral position Ri, from equation (4) and the radial position of the head unit IC  52  determined by an IC position converter  56  in response to a signal from the magnetic head unit  53  (made up of two heads including a write head  54  and a read head  55 ), and thereby controls the power supplied to the head IC  52  through a read/write controller  51 . As a result, even in the case where the power supplied to the IC (power consumption) is increased, the temperature rise of the IC can be suppressed to not higher than the tolerable temperature. 
   In  FIG. 2 , the positioning controller  59  is for setting the magnetic head unit  53  at a predetermined radial position. A spindle controller, though not shown, for controlling the rotational speed of the magnetic disk is also included in the actual magnetic disk device. Also, the IC has therein a temperature sensor  57  making up a temperature detector to cut off the power to the IC in the case where the IC is heated abnormally. Specifically, in the case where the IC has reached the junction temperature of 120□ or higher, for example, the data write/read operation by the magnetic head unit is suspended. As a result, the damage to the IC can be prevented. Also, the power consumption can also be controlled using the information from this temperature sensor. 
   In the case where the write operation of the magnetic head unit is suspended, the (write) data is stored in the memory of the magnetic disk device (HDD). Thus, the performance of the magnetic disk device as viewed from the personal computer PC can be prevented from decreasing. 
   The aforementioned configuration makes it possible to supply the IC with the power commensurate with the cooling ability at the radial position of the IC. As a result, the power supplied to the IC can be increased progressively from inner to outer periphery while suppressing the temperature rise of the IC to a predetermined level. Thus, the IC capacity can be utilized to maximum. As a specific example, the write (read) frequency (capacity) of the IC, i.e. the read/write speed can be increased progressively from inner to outer periphery. In this way, the read/write performance of the magnetic head unit can be improved while keeping the IC temperature rise within a tolerable range. 
   A second embodiment of the invention will be explained with reference to  FIGS. 5A ,  5 B,  5 C,  6  and Tables 1, 2. According to the first embodiment, the optimization of the power consumption of the IC at each radial position was considered on the assumption that the power (power consumption) corresponding to the radial position is supplied continuously to the IC. In the case where the IC is operating normally, on the other hand, a specified power (power consumption) may be required. According to the second embodiment, therefore, a system is employed in which the specified operation power is supplied for a short length of time to assure normal IC operation, after which a suspension time is provided. The ratio between the heating time and the suspension time (duty factor) is optimized, so that like in the first embodiment, the rated power is supplied to the IC while suppressing the IC temperature rise within a predetermined value. As a result, the operation efficiency of the IC can be maximized.  FIGS. 5A ,  5 B and  5 C show the concept of the duty factor. In the case where the rated power consumption W is required, assume that the conduction time T is reduced to one half so that the suspension time is the same as the conduction time (i.e. 50% in duty factor). Then, it is thermally (i.e. from the viewpoint of the IC temperature rise) equivalent to the case where the continuous heating is carried out with one half of the power consumption (W/2).
 
Duty factor  D=Tw /( Tw+Tk )  (3)
 
where Tw is the continuous conduction time, and Tk the suspension time.
 
   In the case where the rated power consumption of the IC is 400 mW, therefore, the duty factor thereof may be set to 31%, 38% and 46% for the inner periphery, middle periphery and the outer periphery, respectively, as shown in Table 1. In the case where the duty factor for the inner periphery is set to unity, on the other hand, the value for the outer periphery can be set to 1.5 times larger as shown in Table 2. It is thus see that the duty factor for the outer periphery can be increased beyond the value for the inner periphery and the ratio can be set to about 1.5. As a result, the predetermined rated power can be supplied to the IC while suppressing the IC temperature within the tolerable temperature rise. 
     FIG. 6  shows a block diagram for explaining the operation. The present embodiment is different from the first embodiment shown in  FIG. 2  in that a duty factor calculator  60  corresponding to the radial position of the IC is provided. A duty factor table can be provided in place of the duty factor calculator  60 . Based on the result of the calculation result of the duty factor calculator  60 , the microprocessor  58  controls the read/write controller  51  to secure a predetermined value of the duty factor corresponding to the radial position of the IC, thereby supplying the predetermined power to the head IC  52  for a predetermined length of time (corresponding to the duty factor). Thus, like in the first embodiment, the temperature rise of the IC is suppressed within the tolerable value, while at the same time making it possible to maximize the IC efficiency, i.e. the read/write performance of the head unit. 
   The third embodiment of the invention will be explained with reference to  FIGS. 7 ,  8  and Table 3.  FIG. 7  shows the relation between the response time and the thermal resistance Rh (calorific value W/temperature rise K) determined by the Reynolds number Rew of rotation, and  FIG. 8  the relation between the dimensionless time and the temperature change. These diagrams are based on the formulae determined by the experiments conducted by the inventors. Assume that the tolerable temperature rise of the IC is 50 K and the rated power of the IC is 400 mW. The time required before reaching 50 K assumes the values shown in Table 3. 
   
     
       
         
             
             
             
             
             
           
             
                 
               TABLE 3 
             
             
                 
                 
             
             
                 
                 
               Reynolds 
               Tolerable 
               Tolerable 
             
             
                 
                 
               number Rew of 
               time(s) at 
               time(s) at 
             
             
                 
               IC position 
               rotation 
               400 mW 
               500 mW 
             
             
                 
                 
             
           
          
             
                 
               Inner periphery 
               5.3 × 10 4   
               0.17 
               0.13 
             
             
                 
               Middle 
               8.1 × 10 4   
               0.19 
               0.13 
             
             
                 
               periphery 
             
             
                 
               Outer 
               12.1 × 10 4   
               0.20 
               0.13 
             
             
                 
               periphery 
             
             
                 
                 
             
          
         
       
     
   
   As shown in Table 3, the values are substantially the same for the inner and outer peripheries, although the value for the outer periphery is somewhat longer than the value for the inner periphery. These values are 0.17 s, 0.19 s and 0.2 s for the inner periphery, the middle periphery and the outer periphery, respectively. This indicates that by reducing the continuous conduction time to 0.17 s or less, the IC temperature rise can be reduced to lower than the tolerable temperature even when the rated power of 400 mW is supplied, thereby producing the same effect as the first embodiment. Also, in the case where the rated power of the IC is 500 mW, the continuous conduction time may be set to 0.13 s or less. 
   A fourth embodiment of the invention will be explained with reference to  FIGS. 9 and 10 . The difference between this embodiment and the first embodiment lies in that as shown in  FIG. 9 , the present embodiment has two head ICs  30   a  and  30   b  mounted. Also, as shown in  FIG. 10 , each head IC has a temperature sensor. The use of two ICs makes it possible to switch to the IC  52   b  when the other IC  52   a  approaches the tolerable temperature rise as detected by the temperature sensor. As a result, the same effect as the second embodiment is achieved. Specifically, as viewed from the magnetic head unit, power is continuously supplied from the IC to the magnetic head unit, and therefore the continuous read/write operation is possible. Also, from the viewpoint of the IC temperature rise, the alternate use of the two ICs is equivalent to the fact that one of the ICs is suspended in operation and can be cooled during the suspension time. Therefore, in the case where the two ICs are switched for every 0.17 s for the inner periphery, for example, as shown in the third embodiment, the same effect is obtained as if the IC is apparently continuously used at the rated power. 
   The experiments conducted by the inventors show that the temperature rise due to heating and the cooling due to the heat radiation last for substantially the same length of time. The use of two ICs alternately as described above, therefore, can prevent the faulty operation which otherwise might be caused by the temperature rise due to the heating of the IC itself. The effect of the present embodiment is especially significant for a magnetic disk device having a single magnetic head mounted thereon. Specifically, with the magnetic disk unit device having a plurality of magnet heads mounted thereon, in the case where the temperature of the IC of one of the magnetic heads increases beyond the tolerable value, the operation is switched to the other magnetic head unit to record the data with the particular other magnetic head unit (other IC). 
   In the case where only one magnetic head is provided and the other magnet head is unavailable for use, on the other hand, the available magnetic head is used with a lower duty factor as in the second embodiment, or the suspension time is inserted as in the third embodiment, resulting in the deteriorated performance of the read/write operation. On the other hand, the present embodiment using two ICs exhibits an especially high effect for the magnetic disk device having only one head. Also, the present embodiment is effective especially in the case where the two magnetic heads, if any, of the magnetic head unit cannot be switched, i.e. in the case where the continuous read/write operation is required with a single head. 
   In the aforementioned embodiments, the IC is arranged on the outer peripheral side at the forward end of the guide arm. As shown in  FIGS. 11A ,  11 B, however, the IC can be mounted on the suspension means or on the inner peripheral side at the forward end of the guide arm with equal effect. In the case where the IC is mounted on the suspension means as shown in  FIG. 11A , the heat conduction to the suspension means increases and the cooling performance is improved. In the case where the IC is mounted on the inner peripheral side of the magnetic disk  4  as shown in  FIG. 11B , on the other hand, the advantage is that the cooling performance (heat conduction) by the air flow is improved. 
   According to the embodiments described above, the temperature of the signal amplifier (IC) mounted on the magnetic head supporting mechanism can be controlled to not higher than a predetermined temperature without any special cooling means. Therefore, a large volume of information can be recorded/reproduced at high speed while securing reliability.