Stainless steel balancer having recess formed at a side surface, and head stack assembly with the same

A balancer installed on an overmold of an head stack assembly to adjust balance of the head stack assembly is formed of stainless steel and demagnetized through a thermal treatment after the stainless steel is processed to have a balancer shape. The balancer has a recess formed at a side surface of the balancer to prevent separation of the balancer from the overmold. The stainless steel is austenite based stainless steel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2006-0012880, filed on Feb. 10, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hard disk drive, and more particularly, to a balancer for controlling the balance of a head stack assembly (HSA), the HSA having the balance, a method for manufacturing the balancer, and a method for manufacturing an overmold of the HSA.

2. Description of the Related Art

Hard disk drives (HDDs) are auxiliary memory devices used for computers, MP3 players, or mobile phones. The HDD reads or writes data with respect to a disk that is a data storage medium, using a head slider that is a data read/write medium. During the operation of the HDD, the head slider maintains a floating state rising a predetermined distance from the disk and a magnetic head mounted on the head slider reads or writes data with respect to the disk. A device to support the head slider attached on an end portion thereof and moving the same to a predetermined position on the disk is referred to as a head stack assembly (HSA).

The HSA has unbalance due to factors such as allowance in parts or in assembly. The head slider mounted on an end portion of the HSA moves to a particular track as the HSA pivots, and performs reading and writing of data. Unexpected external interference applied to the HDD causes vibrations to the HSA. When a degree of the unbalance of the HSA is great, the vibration of the HSA due to the external interference increases so that a position error signal (PES) characteristic is deteriorated and data processing is delayed or prevented. Thus, a balancing work to reduce the unbalance of the HSA is needed.

SUMMARY OF THE INVENTION

To solve the above and/or other problems, the present invention provides a balancer for controlling the balance of a head stack assembly (HSA), the HSA having the balance, a method for manufacturing the balancer, and a method for manufacturing an overmold of the HSA.

According to an aspect of the present invention, a balancer installed on an overmold of an head stack assembly to adjust balance of the head stack assembly is formed of stainless steel and demagnetized through a thermal treatment after the stainless steel is processed to have a balancer shape.

The demagnetization thermal treatment may include a step to place the stainless steel having a balancer shape at a temperature between 950-1,150° C. for 30-120 minutes.

A hole may be formed in an upper or lower surface of the balancer to set a position where the balancer is placed when the balancer is placed inside a mold to form the overmold.

A recess may be formed at a side surface of the balancer to prevent separation of the balancer from the overmold.

The height of the balancer may not be more than the thickness of the overmold.

The stainless steel may be austenite based stainless steel.

According to another aspect of the present invention, a head stack assembly comprises a swing arm, a suspension coupled to an end portion of the swing arm, a head slider which is a data read/write medium and mounted on an end portion of the suspension, and an overmold having a voice coil wound therearound and at least one balancer installed to adjust balance and provided at a position opposite to the head slider with respect to the center of rotation of the swing arm, wherein the balancer is formed of stainless steel and demagnetized through a thermal treatment after the stainless steel is processed to have a balancer shape.

The demagnetization thermal treatment may include a step to place the stainless steel having a balancer shape at a temperature between 950-1,150° C. for 30-120 minutes.

The overmold may be formed by resin mold in which the inside of a mold is filled with liquid resin and the resin is solidified, and a hole is formed in an upper or lower surface of the balancer to set a position where the balancer is placed when the balancer is placed inside the mold to form the overmold.

A recess may be formed at a side surface of the balancer to prevent separation of the balancer from the overmold.

The height of the balancer may not be more than the thickness of the overmold, and the balancer may be installed not to protrude from an upper or lower side of the overmold.

The stainless steel may be austenite based stainless steel.

The center of gravity of the balancer and the center of gravity of the overmold except for the balancer may be located in different sides with respect to an imaginary line passing the center of rotation of the head slider and the center of rotation of the swing arm.

A distance from the center of rotation of the swing arm to the balancer may not be more than 4.5 mm.

A plurality of arm blades may be stacked and each of the arm blades may include a single swing arm, a single suspension, and a single head slider.

According to another aspect of the present invention, a method for manufacturing a balancer comprises processing stainless steel to have a balancer shape, and demagnetizing the stainless steel having the balancer shape through a thermal treatment.

The demagnetization thermal treatment may include a step to place the stainless steel having a balancer shape at a temperature between 950-1,150° C. for 30-120 minutes.

The stainless steel may be austenite based stainless steel.

According to another aspect of the present invention, a method for manufacturing an overmold of a head stack assembly comprises processing stainless steel to have a balancer shape and demagnetizing the stainless steel having the balancer shape through a thermal treatment, placing the balancer inside a mold, and filling the inside of the mold with liquid resin and solidifying the liquid resin to form the overmold.

The demagnetization thermal treatment may include a step to place the stainless steel having a balancer shape at a temperature between 950-1,150° C. for 30-120 minutes.

The stainless steel may be austenite based stainless steel.

A protrusion to set a position where the balancer is placed may be formed on an inner surface of the mold and a hole is formed in an upper or lower surface of the balancer so that, when the balancer is placed inside the mold, the protrusion of the mold is inserted in the hole of the balancer.

A recess may be formed at a side surface of the balancer to prevent separation of the balancer from the overmold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, a hard disk drive (HDD)100having a head stack assembly (HSA)130according to an exemplary embodiment of the present invention includes a housing (not shown) consisting of a base member101and a cover member (not shown) coupled to the base member101. In the housing, a spindle motor105, a disk107that is a data storage medium, an HSA130, and a voice coil motor (VCM) block115. The spindle motor105to rotate the disk107at high speed is fixed to the base member101. The disk107is coupled to the spindle motor105and rotates at high speed in a direction indicated by an arrow. The high speed rotation of the disk107causes air flow moving in the same direction indicated by the arrow on the surface of the disk107.

The HSA130includes a head slider140where a magnetic head (not shown) to read/write data is formed. The head slider140moves to a particular position on the disk107, in particular, a particular track, to write data on the disk107or read data from the disk107. The HSA130includes a swing arm135pivoting around the center C of a pivot bearing131on a base member101, a suspension137coupled to an end portion of the swing arm135and extending therefrom, and a head slider140mounted on an end portion of the suspension137. The HSA130also includes an overmold145extending from a pivot bearing131in the opposite direction to the direction in which the swing arm135extends, and having a voice coil147wound therearound.

While the air flow generated by the high speed rotation of the disk107passes between the surface of the disk107and the surface of the head slider140facing the disk107, a lift force acts on the head slider140. The head slider140maintains a floating state at a height where the lift force and an elastic pressing force of the suspension137pressing the head slider140toward the disk107are balanced. In such a state, a magnetic head (not shown) formed on the head slider140performs a data read/write function with respect to the disk107.

When the operation of the HDD100is stopped, the head slider140is out of the disk107and parked on a ramp125provided at the outer side of the disk107. The suspension137includes an end-tap139at an end portion thereof. As the end-tap139contacts the ramp125and slides upward, the HSA130and the head slider140are parked.

The HDD100includes a latch120which locks the HSA130by interfering with a hook148formed on the overmold145when the HSA130is parked on the ramp125. The latch120prevents damage to the head slider140and the disk107due to the external interference when the operation of the HDD100is stopped.

The VCM block115is fixed to the base member101and the overmold145is inserted in the VCM block115. The VCM block115includes a magnet116arranged at each of the upper and lower sides of the overmold145, and a yoke117supporting the magnet116. The voice coil147of the overmold145generates an electromagnetic force by the interaction with the magnet116. The electromagnetic force is used as a force rotating the HSA130. The rotation of the HSA130is controlled by a servo control system.

The HSA130is electrically connected to a flexible printed circuit110that is connected to a main circuit board (not shown) arranged under the base member101, through a connector112coupled to the flexible printed circuit110. The flexible printed circuit110functions as a medium exchanging electric signals between the HSA130and the main circuit board.

A crash stopper119to restrict a range of counterclockwise pivot of the HSA130is provided on the HDD100. When the HSA130pivots counterclockwise, as a collision portion150formed on the overmold145collides against the crash stopper119, the rotation of the HSA130is mechanically stopped. Accordingly, in spite of the external interference, the collision between the HSA130and the spindle motor105is prevented.

FIG. 2is a perspective view of the HSA ofFIG. 1.FIG. 3is a perspective view of an overmold shown inFIG. 2. Referring toFIGS. 2 and 3, the HSA130is a so-called unmounted type HSA in which the swing arm135, the suspension137, and the head slider140constitute an arm blade134and a pair of the arm blades134are stacked with respect to the overmold145interposed therebetween. The unmounted type HSA130is mainly employed in a compact HDD having the disk107ofFIG. 1whose diameter is less than 2.5 inches.

A pair of balancers155is installed on the overmold145of the HSA130to adjust balance of the HSA130. To install the balancer155, a balancer installation portion152is provided between a pivot bearing through hole146and the collision portion150of the overmold145. Referring back toFIG. 1, the overmold145is positioned to be inclined to one side with respect to an imaginary line L passing the head slider140and the center C of the pivot bearing131that is the center of rotation of the swing arm135. This can be confirmed by the voice coil147being positioned to be inclined to one side with respect to the imaginary line L. This inclination is to make the HSA130and the VCM block115arranged compacter. The overmold145inclined to one side with respect to the imaginary line L causes eccentricity of the HSA130. To compensate for the eccentricity, the balancers155are located in the opposite area to an area where the overmold145is inclined with respect to the imaginary line L. In other words, the center of gravity of the pair of balancers155and the center of gravity of the overmold145except for the balancers155are located in different areas (in different sides and/or on different sides) with respect to the imaginary line L. A protrusion149inFIGS. 2 and 3is to set a relative position of the overmold145with respect to the arm blade134.

Referring toFIG. 1, the crash stopper119must not interfere with the balancers155. Thus, in the compact HDD100, the distance D from the center C of the pivot bearing131to the balancers155is limited to be within 4.5 mm and the weight of a material for the balancers155needs to be relatively great. Brass, bronze, and stainless steel are metallic materials having a relatively greater weight and a superior processing characteristic. Since the brass and bronze easily corrode, the stainless steel is preferably used as a material for the balancers155. The stainless steel is largely divided into a ferrite based stainless steel and austenite based stainless steel. Since the ferrite based stainless steel that is ferromagnetic is likely to interfere with the magnet116ofFIG. 1, the austenite based stainless steel that is paramagnetic is preferably used.

FIG. 4is a perspective view of the balancer155according to an exemplary embodiment of the present invention.FIG. 5is a cross-sectional view of the balancer155ofFIG. 4placed in a mold for forming the overmold145. Referring toFIGS. 4 and 5, the balancer155is a cylindrical member having a weight of about 1.5 mg, a diameter W1of about 0.7 mm, and a height H1of about 0.6 mm. The height H1of the balancer155is set to be the same as or not more than the thickness of the balancer installation portion152of the overmold145ofFIG. 2, so that the balancer155does not protrude from the upper or lower side of the balancer installation portion152. This is to minimize a possibility of the balancer155interfering with the magnet116ofFIG. 1.

A recess158having a height H2of about 0.25 mm and a depth W2of about 0.05 mm is formed on the side surface of the balancer155. The recess158has a function to hold the balancer155in the balancer installation portion152ofFIG. 2not to be separated therefrom. A hole156having a depth H3of about 0.15 mm is formed in the lower surface of the balancer155. The hole156is used to set the position of the balancer155when the balancer155is placed inside a mold160ofFIG. 5to form the overmold145ofFIG. 3. The hole156can be formed in the upper surface of the balancer155unlike the present exemplary embodiment.

The shape of the balancer155is formed by a mechanical processing method such as stamping processing. Even when austenite based stainless steel is used as a material for the balancer155, as strong stress is applied to the material during the process of forming the shape of the balancer155, the internal structure of the austenite based stainless steel is changed to martensite phase so that the balancer155becomes ferromagnetic.

Thus, to remove the magnetism generated by the shape processing, a demagnetization thermal treatment is performed to the stainless steel having the shape of the balancer155. The demagnetization thermal treatment includes a step of placing the stainless steel having the shape of the balancer155having ferromagnetism at a temperature between 950° C.-1,150° C. for 30 minutes-120 minutes. After the demagnetization thermal treatment, the balancer155is reduced to be paramagnetic so that interference with the magnet116ofFIG. 1is prevented.

Referring toFIGS. 3 and 5, the balancer155manufactured (made) by the above-described method can be forcibly installed in the balancer installation portion152of the overmold145. However, since the balancer installation portion152having a small thickness can be deformed, the balancer155can be installed on the balancer installation portion152of the overmold145by insert molding like a method of installing the voice coil147on the overmold145.

The overmold145is formed by injecting liquid resin R to fill the inside of a mold160, which includes a mold base161and a mold cover164and solidifying the resin R. The voice coil147and the balancer155are placed inside the mold160before the mold160is filled with the liquid resin R. A protrusion162is formed on an inner surface of the mold base161to set a position where the balancer155is placed and not to disturb the position. The size of the protrusion162corresponds to the size of the hole156of the balancer155. The balancer155is placed on the mold base161such that the protrusion162is inserted in the hole156of the balancer155. The inside of the mold160is sealed by covering the mold cover164and the liquid resin R is injected into the mold160. After the resin R is solidified, the mold base161and the mold cover164are separated to obtain the overmold145. Since the resin R fills the recess158having a height H2of about 0.25 mm and a depth W2of about 0.05 mm without a gap and then solidified, the balancer155is not separated from the overmold145.

Since the balancer according to the present invention is formed of stainless steel, a manufacturing cost is low. Since the balance is reduced to paramagnetism by the demagnetization thermal treatment, there is no possibility of interfering with the magnet. Also, since the balancer is relatively small and light, the balance of the HSA can be easily adjusted without much change in the shape of the HSA. Thus, the balancer is useful for the adjustment of the balance of an HSA for a compact HDD which has a limitation in its shape due to a limited space.