Disc balancing device

A disc balancing device and a method thereof. The disc balancing device includes a disc assembly having a driving source, and a disc rotatably disposed at the driving source, a displacement measurement unit measuring vibration in the rotation of the disc assembly, a phase angle measurement unit measuring a phase angle from a reference point of the disc assembly in the rotation of the disc assembly, an operation/control unit calculating an eccentric mass and an eccentric position of the disc assembly, by using the biased vibration measured in the displacement measurement unit and the phase angle measured in the phase angle measurement unit, and a laser cutter tracking and laser-cutting the side portion of the disc corresponding to the eccentric position according to the information from the operation/control unit, whereby the eccentric mass of the disc assembly is balanced to reduce vibration in the rotation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 00-59309 filed on Oct. 9, 2000 in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disc balancing device and a method thereof, and in particular to an improved disc balancing device which can balance an eccentric mass of a disc rotatably disposed at a driving source, and a method thereof.

2. Description of the Related Art

In general, a disc drive such as the HDD includes a housing consisting of a base and a cover, a disc positioned in the housing and rotated by a spindle motor at a high speed, and a head suspension assembly for storing data in the disc or reproducing the stored data. The head suspension assembly is positioned adjacent to the disc and controlled by a linear motor. Here, one end portion of the head suspension assembly supports a head. The movement of the head suspension assembly is precisely controlled.

On the other hand, the head suspension assembly is very sensitive to vibration or impact. When the head suspension assembly is considerably impacted, the head damages the disc surface. Especially, the precise control of the head suspension assembly is much influenced by vibration generated due to an eccentric mass of the disc in driving of the spindle motor. That is, when the vibrations are generated due to the eccentric mass of the disc, the head cannot precisely sense a track of the disc. Accordingly, when displacement of the rotated disc is varied due to the eccentric mass, it is impossible to precisely store and reproduce the data through the head.

This eccentric mass of the disc may be generated during the fabrication process of the disc. As shown inFIG. 1, the eccentric mass may also be generated due to an assembly tolerance when discs5and6are connected to a rotor3. An exemplary method for balancing the eccentric mass will now be explained. Referring toFIG. 1, a plurality of discs5and6are positioned at the upper and lower portions of the rotor3of a spindle motor1. Force F is applied to the outsides of the discs5and6in the symmetrical direction from the rotor3. Therefore, the discs5and6are respectively adhered to the rotor3facing in the opposite direction. In this state, a clamping member7is connected to the rotor3to fix the discs5and6in place. This method is called a biasing method. As a result, the biasing method adjusts the eccentric mass of the disc resulting from an assembly tolerance. However, in the biasing method, the eccentric mass due to an assembly error can be corrected only when a plurality of discs are assembled. Conversely, it is impossible to correct the eccentric mass of a single disc itself. In addition, in the case that only one disc is installed, the biasing method cannot balance the disc.

Another exemplary disc balancing method will now be described with reference toFIG. 2. A clamp7having a plurality of holes7aand the disc6are installed at the rotor3. Thereafter, a sensing unit senses an eccentric position of the disc6. A mass member9is inserted into the hole7acorresponding to the eccentric position. The mass member9fixed to the hole7acompensates for the eccentric mass of the disc6. However, a few tens of mass members are required to be inserted into the holes7a. Furthermore, the plurality of mass members require having different mass. Also, it is inconvenient for the operator to insert each mass member9into the hole7a. Moreover, although various mass members are provided, there is a limit to the preciseness of control of the eccentric ass of the disc.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a disc balancing device which can precisely control an eccentric mass of a disc disposed at a spindle motor.

Another object of the present invention is to provide a disc balancing method which can precisely control an eccentric mass of a disc disposed at a spindle motor.

The foregoing objects of the present invention are achieved by providing a disc balancing device including a disc assembly having a driving source, and a disc rotatably disposed at the driving source; a displacement measurement unit measuring vibration in the rotation of the disc assembly; a phase angle measurement unit measuring a phase angle from a reference point of the disc assembly in the rotation of the disc assembly; an operation/control unit calculating an eccentric mass and the eccentric mass position of the disc assembly, by using the biased vibration measured in the displacement measurement unit and the phase angle measured in the phase angle measurement unit; and a laser cutter tracking and laser-cutting the side portion of the disc corresponding to the eccentric mass position according to the information from the operation/control unit, whereby the eccentric mass of the disc assembly is balanced to reduce vibration in its rotation.

The disc balancing device further includes a dust inhaler inhaling dust generated when the side portion of the disc is cut by the laser cutter. Here, the dust inhaler and the laser cutter are moved by a robot unit controlled by the operation/control unit, tracking the eccentric mass position.

Advantageously, the phase angle measurement unit is a photo sensor measuring the phase angle by irradiating light to the reference point and receiving a reflected light from the disc assembly.

It is a further object of the present invention to provide a method of balancing a disc to reduce vibration due to an eccentric mass of the disc in the rotation of the disc rotatably disposed at a driving source, the disc balancing method includes the operations of: preparing a disc assembly having the driving source and the disc; rotating the disc assembly, and simultaneously measuring an initial vibration due to the eccentric mass of the disc assembly by using a displacement measurement unit; measuring a phase angle from a reference point of the rotated disc assembly by using a phase angle measurement unit; calculating the eccentric mass and position of the disc assembly according to the initial vibration and phase angle from an operation/control unit; and cutting the side portion of the disc corresponding to the eccentric position calculated in the operation/control unit according to the calculated eccentric mass with the aid of a laser cutter.

The disc balancing method further includes inhaling dust generated when the side portion of the disc is cut with the aid of a dust inhaler.

In addition, the disc balancing method further includes the operations of: re-measuring vibration of the disc assembly after the cutting of the side portion of the disc; and comparing the measured vibration with a predetermined reference value. If the measured vibration is greater than the reference value, operations of the rotating, measuring, calculating and cutting are repeated until the measured vibration is smaller than the reference value. Here, the laser cutter is moved by a robot unit controlled by the operation/control unit. The dust inhaler may also be moved by a robot unit that may be controlled by the operation/control unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 3, a disc balancing device in accordance with the present invention includes a disc assembly10, a displacement measurement unit20measuring vibration in the rotation of the disc assembly10, a phase angle measurement unit21, an operation/control unit23, and a laser cutter25.

The disc assembly10includes a spindle motor12which is a driving source disposed at a base11, and discs14connected to a rotation unit13of the spindle motor12. In this embodiment, the rotation unit13incorporates a rotation shaft12aof the spindle motor12and a hub connected to the rotation shaft12a. The discs14are formed in a multi-layer structure. A single disc14may also be used. Spacers15are provided between the discs14. The discs14are fixed to the rotation unit13by a clamp16disposed at the rotation unit13. The clamp16is fixed to the rotation unit13by a screw. Accordingly, the clamp16is rotated with the rotation unit13and the discs14. As illustrated inFIG. 4, a reference point P is marked on the clamp16.

The displacement measurement unit20measures vibration in the rotation of the disc assembly10. That is, in the rotation, the disc assembly10is repeatedly and/or non-repeatedly biased due to the eccentric mass of the discs14, thereby causing vibration. The displacement measurement unit20measures the biased vibration due to the eccentric mass of the discs14. More particularly, the displacement measurement unit20measures displacement of the rotated disc assembly10, and thus calculates the vibration thereof. The displacement measurement unit20is connected to the operation/control unit23, transmitting the vibration information to the operation/control unit23. An amplifier22may be provided between the displacement measurement unit20and the operation/control unit23. The amplifier22improves, for example, accuracy and reliability of the vibration information transmitted to the operation/control unit23. The displacement measurement unit20is positioned at a predetermined path of a contact or non-contact type assembly and production line of the disc assembly10. In general, a Gep sensor, acceleration sensor, laser sensor, strain gage, or any other appropriate type of sensor may be used as the displacement measurement unit20. The phase angle measurement unit21simultaneously measures a phase angle of the clamp16, from the reference point P, when the discs14are rotating on the production line of the disc assembly10.

As depicted inFIG. 4, the phase angle measurement unit21is preferably a photo sensor measuring the phase angle by irradiating light toward the reference point P and receiving a reflected light from the clamp16. However, an appropriate alternative type sensor may be used. In the assembly process of the disc assembly10, the phase angle measurement unit21may be positioned adjacent to the displacement measurement unit20so that the vibration and the phase angle can be measured at the same time. In addition, the phase angle measurement unit21is connected to the operation/control unit23, thus transmitting the phase angle information to the operation/control unit23.

The operation/control unit23may be a computer which can operate data and control a mechanical device such as a robot. The operation/control unit23calculates the eccentric mass and position of the disc assembly10by using the biased vibration information from the displacement measurement unit20and the phase angle information from the phase angle measurement unit21. The eccentric mass and position information of the disc assembly10calculated in the operation/control unit23are used as reference data for controlling the laser cutter25and the dust inhaler27.

The laser cutter25tracks the side portion of the disc14corresponding to the eccentric mass position calculated in the operation/control unit23, and laser-cuts the side portion of the disc14corresponding to the calculated eccentric mass. The laser cutter25may be installed with the aid of arms of an industrial robot (not shown) controlled by the operation/control unit23. As an example, the side portion of the disc14is cut, but another portion of the disc14may be cut to remove the eccentric mass in the alternative.

The dust inhaler27, illustrated inFIG. 3, may be provided to remove dust generated when, for example, the side portion of the disc14, namely the rim of the disc14, is laser-cut. Similarly to the laser cutter25, the dust inhaler27may be installed with the aid of a robot arm and controlled by the operation/control unit23. Accordingly, the dust inhaler27tracks the eccentric position calculated in the operation/control unit23, namely the cutting position, and inhales dust created during the cutting process. As with the other measurement units20and21, the laser cutter25and the dust inhaler27are disposed at the production line of the disc assembly10. Therefore, the eccentric mass of the disc assembly10can be balanced to reduce vibration before finishing production of a disc drive using the disc assembly10, which results in high quality products.

According to an aspect of the present invention, a disc balancing method, using the disc balancing device in accordance with the present invention is provided, and will now be described.

Referring toFIGS. 3 to 5, the disc assembly10is prepared by connecting the discs14and the spindle motor12in a disc driver assembly process (S10). Here, the discs14are fixed to the rotation unit13by the clamp16. Thereafter, the disc assembly10is positioned on the production line where the measurement units20and21, the laser cutter25, and dust inhaler27are provided. The disc assembly10is rotated at a predetermined speed by driving the spindle motor12(S11). When the disc assembly10is rotated, the displacement measurement unit20and the phase angle measurement unit21measure an initial vibration and a phase angle (S12). As illustrated inFIG. 6, the displacement measurement unit20measures the repeated biased vibration A due to the eccentric mass of the disc assembly10in the rotation of the disc assembly10. In addition, the phase angle measurement unit21measures the phase angle from the reference point P on the clamp16in a repeated cycle type. Accordingly, the displacement measurement unit20measures the phase angle φ between the reference point P and the biased vibration A. The information with respect to the initial vibration, namely the biased vibration A and the information of the phase angle φ, are transmitted to the operation/control unit23. The operation/control unit23calculates the eccentric mass and position of the disc assembly10according to the biased vibration A and the phase angle φ (S13). When the eccentric mass and position of the disc assembly10are calculated, rotation of the disc14is interrupted (S14). Thereafter, the operation/control unit23controls driving of the robot (not shown) to move the laser cutter25so that the laser light, irradiated from the laser cutter25, can be focused on the side portion of the disc14corresponding to its eccentric position. The operation/control unit23also controls the on/off driving of the laser cutter25to irradiate the laser light, thereby laser-cutting the side portion of the disc14corresponding to the calculated eccentric mass (S15).

When the side portion of the disc14is cut as discussed above, dust is generated. In response to the dust created, the operation/control unit23also controls positioning and driving of the dust inhaler27to inhale the dust (S15). The position tracking and on/off control of the dust inhaler27are performed in the same manner as is the laser cutter25.

As discussed earlier, the eccentric mass of the disc assembly10is precisely removed by laser-cutting the side portion of the disc14, and thus the eccentric vibration is efficiently prevented. As compared with the conventional methods, the discs14used in the present invention need not be re-assembled due to removing the eccentric mass of the completely-assembled disc assembly10. In addition, with the present invention as described, contamination of the production line of the disc assembly10and the discs14is prevented by inhaling dust with the aid of the dust inhaler27in the cutting process.

After laser-cutting the side portion of the disc14, the disc assembly10is re-rotated, and vibration is re-measured by the displacement measurement unit20(S17). The operation/control unit23receives the vibration information, and compares the vibration with a predetermined reference value (S18). If the measured vibration is greater than the predetermined reference value, the above steps S11to S17are repeated until the vibration is smaller than the predetermined reference value. When the measured vibration is smaller than the predetermined reference value, the eccentric mass balancing process of the disc, namely the disc assembly10, is finished. As described above, the vibration of the disc assembly10may be measured and laser-cut several times, thereby improving precision of the balancing process. Accordingly, inferiority of the products is reduced, and recording density of the disc14is increased by reducing vibration in the rotation of the disc assembly10.

In accordance with the present invention, the disc balancing process is easily performed without dissembling or re-assembling the disc assembly. Moreover, since vibration measurement and laser cutting process may be repeated several times, inferiority of the disc drive using the disc assembly such as the HDD is reduced, and recording density of the disc is increased.

Although preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principle and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.