Polishing apparatus with abrasive tape, polishing method using abrasive tape and manufacturing method for magnetic disk

An abrasive tape is supplied to a tape head by a tape supply unit and taken up from the tape head by a tape take-up unit. The tape head presses the abrasive tape against a surface of an object under polish, which is rotated by a rotating unit. A tape head pressuring unit utilizes a voice coil motor, for example. Since the tape head pressuring unit generates a pressuring force for pressuring the tape head using the electromagnetic force, it is able to set a minute pressuring force by controlling a drive signal, and to obtain the fine adjustment of the pressuring force easily by controlling the electric signal. Therefore, it becomes possible to press the abrasive tape against the surface of the object under polish with a desired low pressure.

FIELD OF THE INVENTION

The present invention relates to a polishing apparatus and a method for polishing an object under polish, which has a very thin surface to be polished, using an abrasive tape, and a manufacturing method for a magnetic disk utilizing them.

BACKGROUND OF THE INVENTION

For a magnetic disk, which is used as an information record medium in a computer, etc., a requirement of the high recording density is becoming greater in recent years; accordingly films formed on surfaces of the magnetic disk, such as magnetic layers and protective films, are becoming thinner.

In a manufacturing process of the magnetic disk, undercoating layers with non-magnetic metal, undercoating layers with metal, the magnetic layers, the protective films, etc. are formed on surfaces of a disk substrate. Then, in order to remove small protrusions generated during these membrane forming processes and in order to clean up the surfaces of the magnetic disk, the tape cleaning is carried out on the surfaces of the magnetic disk by a polishing apparatus. The tape cleaning is to polish the surfaces of the magnetic disk by pressing tape like abrasives against the surfaces of the magnetic disk while the disk is rotating.

In this tape cleaning process, an air pressure or the spring force as described in the Japanese Patent Laid-Open 1990-106264, for example, was conventionally employed for pressing abrasive tapes against the surfaces of the magnetic disk. In an apparatus employing the spring force as described in the Japanese Patent Laid-Open 1990-106264, for example, a pressure for pressing the abrasive tape against the surface of the magnetic disk was approximately 50-75 g. With regard to the polishing apparatus carrying out the tape cleaning, there are also the Japanese Patent Laid-Open 2001-67655 and the Japanese Patent Laid-Open 2001-71249. The Japanese Patent Laid-Open 2001-67655 has a description of “the pressing force is usually 30-200 g, preferably 50-150 g, more preferably 50-100 g”. The Japanese Patent Laid-Open 2001-71249 has a description of “10 g, for example”.

The thinner the protective film, etc. becomes due to the high recording density, the lower the pressure for pressing the abrasive tape against the surface of the magnetic disk needs to be in order to prevent the damage on the polished protective film, etc. Moreover, a surface position of the magnetic disk moves during a polish due to many factors, such as deformations or waves on the surface of the magnetic disk, a deflection of the surface when the magnetic disk is rotating, assembly alignment errors of the polishing apparatus and a vibration of a spindle that rotates the magnetic disk. In the conventional polishing apparatus employing the air pressure or the spring force, when the surface position of the magnetic disk moves, the pressure for pressing the abrasive tape against the surface of the magnetic disk fluctuates, so that it becomes difficult to polish the surface of the magnetic disk uniformly.

Furthermore, the damage occurs due to the shock when the abrasive tape touches the surface of the magnetic disk, even if the pressure for pressing the abrasive tape against the surface of the magnetic disk is made small in order to prevent the damage on the polished protective film, etc. This is also becoming a problem.

SUMMARY OF THE INVENTION

The present invention is made in view of above-mentioned issues. The purpose of the present invention is to press the abrasive tape against the surface of an object under polish with a desired low pressure.

Another purpose of the present invention is to make a fluctuation of the pressure for pressing the abrasive tape against the surface of the object under polish small, and to polish the surface of the object under polish uniformly.

Another purpose of the present invention is to polish the surface of the object under polish uniformly, even if the surface of the object under polish deflects while polishing with a low pressure for pressing the abrasive tape against the surface of the object under polish.

Another purpose of the present invention is to prevent the damage generated when the abrasive tape touches the surface of the object under polish.

A feature of the present invention is rotating the object under polish, supplying and taking-up the abrasive tape to/from a tape head, and pressing the abrasive tape against the surface of the object under polish by pressuring the tape head using the electromagnetic force. For example, a voice coil motor is utilized in a tape head pressuring unit, which pressures the tape head. Since the tape head pressuring unit generates a pressuring force for pressuring the tape head using the electromagnetic force, it is able to set a minute pressuring force by controlling a drive signal, and to obtain the fine adjustment of the pressuring force easily by controlling the electric signal. Therefore, it becomes possible to press the abrasive tape against the surface of the object under polish with a desired low pressure.

Moreover, the pressuring force generated by the electromagnetic force is constant when the drive signal is fixed, and it does not depend on a position of the tape head or a surface position of the object under polish. The tape head stops at a point where the pressuring force for pressuring the tape head, the reactive force from the surface of the object under polish and the reactive force due to the elasticity of the tape head are balanced. When the surface position of the object under polish will move, the tape head will follow it and stop at a newly balanced point. Therefore, a movement of the surface position of the object under polish will be absorbed, so that it becomes possible to make the fluctuation of the pressure, with which the tape head presses the abrasive tape against the surface of the object under polish, small, and to polish the surface of the object under polish uniformly.

Another feature of the present invention is rotating the object under polish, supplying the abrasive tape to a tape head, driving a voice coil motor by generating a signal indicating a target pressuring force so as to pressure the tape head by the voice coil motor, detecting a pressuring force of the voice coil motor, and pressing the abrasive tape against the surface of the object under polish by controlling the voice coil motor with a pressure detection signal fed back to the signal indicating the target pressuring force. For example, a load cell is mounted between the voice coil motor and the tape head for detecting the pressuring force of the voice coil motor. Since the voice coil motor is controlled by feeding the pressure detection signal back to the signal indicating the target pressure, even if the surface of the object under polish deflects, the pressuring force of the voice coil motor is finely adjusted in response to a deflection by the feedback control. Therefore, it becomes possible to polish the surface of the object under polish uniformly.

Another feature of the present invention is rotating the object under polish, supplying the abrasive tape to a tape head, driving a voice coil motor by generating a signal indicating the first target position so as to move the tape head by the voice coil motor, detecting a position of the tape head, moving the tape head toward the surface of the object under polish and stopping it at a point, which is close to the surface of the object under polish, by controlling the voice coil motor with a position detection signal fed back to the signal indicating the first target position, driving the voice coil motor by generating a signal indicating the second target position so as to move the tape head by the voice coil motor, detecting the position of the tape head, making the abrasive tape to touch the surface of the object under polish by controlling the voice coil motor with the position detection signal fed back to the signal indicating the second target position, driving the voice coil motor by generating a signal indicating a target pressuring force so as to pressure the tape head by the voice coil motor, detecting a pressuring force of the voice coil motor, and pressing the abrasive tape against the surface of the object under polish by controlling the voice coil motor with a pressure detection signal fed back to the signal indicating the target pressuring force. Since the tape head is once stopped at the point, which is close to the surface of the object under polish, and the contact of the abrasive tape and the magnetic disk is carried out softly, it becomes possible to prevent the damage generated when the abrasive tape touches the surface of the object under polish.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Further details are explained below with the help of examples illustrated in the attached drawings.FIG. 1is a schematic view showing a first embodiment of a polishing apparatus according to the present invention.FIG. 2is a part of the polishing apparatus shown in FIG.1. The polishing apparatus of this example comprises a magnetic disk rotating unit, abrasive tapes3, tape supply units, tape heads5, tape head pressuring units, tape take-up units and a VCM (Voice Coil Motor) drive circuit90. The magnetic disk rotating unit has a motor21and a spindle22. The tape head pressuring units have a swing arm61, a voice coil motor62, an arm63and a bearing65. The tape supply units have a supply reel4and guide rollers. The tape take-up units have guide rollers and a take-up reel7.

InFIG. 1, the magnetic disk rotating unit is not seen but located behind the equipment that polishes a right-side surface of a magnetic disk2. InFIG. 2, on the other hand, illustrations of the equipment that polishes the right-side surface of the magnetic disk2is omitted, and the magnetic disk rotating unit located behind it is shown.

InFIG. 2, the magnetic disk2, which is an object under polish, is attached at an end of the spindle22. The spindle22supports the magnetic disk2such that its surfaces to be polished are arranged vertically, and is rotated by the motor21.

InFIG. 1, the tape head5is provided near the surface of the magnetic disk2in both sides respectively. The abrasive tapes3, wherein a base film is coated with abrasive particles, are wound on the supply reels4. The abrasive tapes3are fed from the supply reels4to the tape heads5, which are provided near the surfaces of the magnetic disk2, through the guide rollers. The tape heads5consist of a roller, and axes5aof the rollers are attached on the swing arms61that are arranged vertically. The swing arms61balance the tape heads5by means of gravity, so that the tape heads5are supported parallel to the surfaces of the magnetic disk2. When the swing arms61rotate around axes61a, the tape heads5move and the abrasive tapes3are pressed against the surfaces of the magnetic disk2. While pressing the abrasive tapes3against the both surfaces of the magnetic disk2by the tape heads5in the both sides, the magnetic disk2is rotated by the motor21and the abrasive tapes3are run by the supply reels4and the guide rollers, so that the tape heads5rotate and the abrasive tapes3polish the both surfaces of the magnetic disk2simultaneously. The abrasive tapes3are recovered from the tape head5by the take-up reels7through the other guide rollers, and wound on the take-up reels7.

The arms63are connected to movable portions62aof the voice coil motors62. The arms63are supported movably by the bearings65, and ends of the arms63contact the axes5aof the tape heads5. When the VCM drive circuit90supplies drive currents to the voice coil motors62, the movable portions62amove due to the electromagnetic force and the arms63push the tape heads5, so that the tape heads5press the abrasive tapes3against the surfaces of the magnetic disk2.

Since the voice coil motors62generate pressuring forces for pressuring the tape heads5using the electromagnetic force, they are able to set minute pressuring forces by controlling the drive currents, and to obtain the fine adjustment of the pressuring forces easily by controlling the electric signals. Therefore, it becomes possible to press the abrasive tapes3against the surfaces of the magnetic disk2with desired low pressures.

InFIG. 2, a surface position of the magnetic disk2moves in the direction indicated by an arrow A due to many factors, such as deformations or waves on the surface of the magnetic disk2, a deflection of the surface when the magnetic disk2is rotating, assembly alignment errors of the polishing apparatus and a vibration of the spindle22. The pressuring force generated by the electromagnetic force in the voice coil motor62is constant when the drive current is fixed, and it does not depend on a position of the tape head5or the surface position of the magnetic disk2. The tape head5stops at a point where the pressuring force from the voice coil motor62, the reactive force from the surface of the magnetic disk2and the reactive force due to the elasticity of the tape head5are balanced. When the surface position of the magnetic disk2will move, the tape head5will follow it and stop at a newly balanced point. Therefore, a movement of the surface position of the magnetic disk2will be absorbed, so that it becomes possible to make a fluctuation of a pressure, with which the tape head5presses the abrasive tape3against the surface of the magnetic disk2, small, and to polish the surface of the magnetic disk2uniformly.

Moreover, inFIG. 2, the tension is applied to the running abrasive tape3in the direction indicated by an arrow B. In this example, the pressuring force is applied to the tape head5in the direction indicated by an arrow C as shown inFIG. 2, so that the direction of the tension applied to the abrasive tape3and the direction of the pressuring force are almost right-angled. Therefore, according to this example, the pressuring force applied to the tape head5has no influence from the tension applied to the abrasive tape3, and it becomes possible to stabilize the pressure, with which the tape head5presses the abrasive tape3against the surface of the magnetic disk2.

Furthermore, according to this example, since the abrasive tape3is pressed against the surface of the magnetic disk2by the tape head5that consists of a roller, the tape head5helps the abrasive tape3to run, and it becomes easy to supply the abrasive tape3.

Furthermore, according to this example, since the magnetic disk2is supported by the spindle22such that the surface to be polished are arranged vertically, polish wastes generated from the surface to be polished drop from there, and it becomes possible to prevent the deposition of the polish wastes on the surface to be polished.

Furthermore, according to this example, since the swing arm61balances the tape head5by means of gravity such that the tape head5is supported parallel to the surface of the magnetic disk2, and the tape head5is moved in the direction of pressing the abrasive tape3against the surface of the magnetic disk2when the swing arm61rotates, it becomes possible to support the tape head5movably by a simple component as the swing arm61. Although, the arm63pushes the axis5aof the tape head5in this example, other portions of the tape head5or the swing arm61may be pushed.

FIG. 3is a part of another embodiment of the polishing apparatus according to the present invention. In this example, a feature different from the example shown inFIG. 1is that the tape head pressuring unit does not utilize the swing arm61but utilizes a linear-type voice coil motor66for supporting the tape head5. Other elements are the same as those of the example shown in FIG.1. The axis5aof the tape head5is directly connected to a movable portion66aof the linear-type voice coil motors66whose movable portion66amoves straight. The tape head5moves in the direction indicated by an arrow D when the linear-type voice coil motor66is driven.

According to this embodiment, since the tape head5is connected to the movable portion66aof the linear-type voice coil motor66, the swing arm and the like is unnecessary, so that the structure becomes simple.

FIG. 4is a part of another embodiment of the polishing apparatus according to the present invention. In this example, a feature different from the embodiment shown inFIG. 1is that the tape head pressuring unit does not utilize the swing arm61but utilizes a rotary-type voice coil motor67for supporting the tape head5. Other elements are the same as those of the embodiment shown in FIG.1. The axis5aof the tape head5is directly connected to a movable portion67aof the rotary-type voice coil motors67whose movable portion67arotates. The tape head5moves in the direction indicated by an arrow E when the rotary-type voice coil motor67is driven.

According to this embodiment, since the tape head5is connected to the movable portion67aof the rotary-type voice coil motor67, the swing arm and the like is unnecessary, so that the structure becomes simple, and the equipment becomes small comparing with the equipment utilizing the linear-type voice coil motor.

FIG. 5is a schematic view showing another embodiment of the polishing apparatus according to the present invention. In this embodiment, a feature different from the embodiment shown inFIG. 1is that the tape supply units, which have the supply reel4and the guide rollers, and the tape take-up units, which have the guide rollers and the take-up reel7, are located below a rotation axis of the magnetic disc2.

The polish wastes adhere to the abrasive tapes3after polish. If the abrasive tapes3are recovered above the magnetic disk2, the polish wastes removed from the abrasive tapes3will float in the air near the surfaces to be polished. However, according to this embodiment, since the abrasive tapes3are recovered below the magnetic disk2by the recovery reels7, it becomes possible to prevent the flotation of the polish wastes removed from the abrasive tapes3in the air near the surfaces to be polished. Although both the tape supply units and the tape take-up units are located below the magnetic disk2in this example, the tape supply units may be located above the magnetic disk2and only the tape take-up units may be located below the magnetic disk2.

In the polishing apparatuses according to the embodiments explained above, it is required to rotate the magnetic disk2at high speed in order to improve the throughput. However, when a high-speed rotation of the magnetic disk2will be carried out to some extent, the voice coil motors will resonate to vibrations caused by many factors, such as deflections of the surfaces of the magnetic disk2, etc., and mechanical vibrations will occur in the voice coil motors. Once the mechanical vibrations occur in the voice coil motors, the pressures, with which the tape heads5press the abrasive tapes3against the surfaces of the magnetic disk2, will fluctuate.

FIG. 6is a block diagram showing an operation inside the voice coil motor of the polishing apparatus according to the present invention when the voice coil motor is driven with a certain voltage. In this case, the voice coil motors62shown inFIG. 1are driven by supplying certain voltages to them from the VCM drive circuit90.

Inside the voice coil motor62, as shown inFIG. 6, an input voltage is first transformed into a current by an inductance L and a resistance R of a coil inside the voice coil motor62. Then, the pressuring force is generated by multiplying the current by the torque constant Kt. Dividing the pressuring force by the total mass of the movable portion and a load of the voice coil motor62gives the acceleration, the acceleration is integrated into a speed, and the speed is further integrated into a displacement. When the vibration caused by the resonance is added to this displacement, the counterelectromotive force arises at the coil inside the voice coil motor62, which is driven with a certain voltage. Differentiating the displacement gives a speed, then an oscillation voltage is generated by multiplying the speed by the power generation constant Ke, as shown inFIG. 6, and the oscillation energy is consumed as the heat.

According to this embodiment, the oscillation energy of the voice coil motor62can be consumed as the heat, and the mechanical vibration can be attenuated. Therefore, it becomes possible to stabilize the pressure, with which the tape head5presses the abrasive tape3against the surface of the magnetic disk2, and to polish the magnetic disk2while rotating it at high speed.

FIG. 7is a block diagram showing an embodiment of a control circuit of the polishing apparatus according to the present invention. In this example, a current sensor81, which measures a current in the voice coil motor62, is further provided to the example shown inFIG. 1, and a control circuit91, which controls the voice coil motor62, is provided instead of the VCM drive circuit.

The control circuit91sets the pressuring force of the voice coil motor62with a gain G1of a setting circuit93and supplies an electric signal101to the voice coil motor62through a drive amplifier94. The electric signal101causes the voice coil motor62to generate a certain pressuring force, and it is a current in this example. On the other hand, the current sensor81measures the current that flows into the coil of the voice coil motor62. When the mechanical vibration occurs in the voice coil motor62, a detection signal102from the current sensor81includes the information showing the amplitude, frequency, etc. of the vibration. Therefore, the current sensor81detects the vibration of the voice coil motor62by measuring the current that flows into the coil of the voice coil motor62.

The detection signal102from the current sensor81is fed back to the control circuit91, and the electric signal101supplied to the voice coil motor62is adjusted depending on the detection signal102. In this example, the detection signal102fed back to the control circuit91is integrated and amplified with a gain G2in an adjustment circuit95, and a speed element103is obtained. This speed element103plays a role of attenuating the mechanical vibration of the voice coil motor62by negating a part of the output from the setting circuit93.

According to this embodiment, it becomes possible to attenuate the mechanical vibration of the voice coil motor62by detecting the vibration of the voice coil motor62and feeding them back to the electric signal101that causes the pressuring force. Therefore, it becomes possible to stabilize the pressure, with which the tape head5presses the abrasive tape3against the surface of the magnetic disk2, and to polish the magnetic disk2while rotating it at high speed. Moreover, comparing with the example shown inFIG. 6, the attenuation effect of the mechanical vibration can be improved by adjusting the gain G2of the adjustment circuit95or the like.

FIG. 8is a block diagram showing another embodiment of the control circuit of the polishing apparatus according to the present invention. In this example, a feature different from the example shown inFIG. 7is that a control circuit92has a high frequency signal generator96. A high frequency signal generated by the high frequency signal generator96is added to the output of the setting circuit93, so that a high frequency signal is included in the electric signal101supplied to the voice coil motor62from the drive amplifier94.

According to this embodiment, since the high frequency signal is included in the electric signal101, the pressuring force generated by the voice coil motor62includes a high frequency element, and the pressure, with which the tape head5presses the abrasive tape3against the surface of the magnetic disk2, changes at high frequency, so that the polish performance improves.

FIG. 9is a schematic view showing another embodiment of the polishing apparatus according to the present invention. The polishing apparatus of this embodiment comprises a magnetic disk rotating unit, abrasive tapes3, tape supply units, tape heads5, tape head pressuring units, tape take-up units, load cells64, linear displacement sensors66and a control circuit110. The magnetic disk rotating unit, which has a motor and a spindle, is not seen just like FIG.1. The tape head pressuring units have a swing arm61, a voice coil motor62, an arm63and a bearing65. The tape supply units have a supply reel4and guide rollers. The tape take-up units have guide rollers and a take-up reel7. Operations of the magnetic disk rotating unit, the abrasive tapes3, the tape supply units, the tape heads5, the tape head pressuring units and the tape take-up units are the same as those of the emdodiment shown in FIG.1.

InFIG. 9, the load cells64are mounted between movable portions62aof the voice coil motors62and the arms63. The load cells64are pressure sensors detecting pressuring forces, with which the voice coil motors62pressure the tape heads5. Moreover, the linear displacement sensors66are connected to the movable portions62aof the voice coil motors62. The linear displacement sensors66, which generate two signals of different frequencies using magnets and coils inside and detect minute displacements by a phase difference between them, here act as poison sensors detecting positions of the tape heads5.

When the control circuit110supplies drive currents to the voice coil motors62, the movable portions62amove due to the electromagnetic force and the arms63push the tape heads5, so that the tape heads5bring the abrasive tapes3close to the surfaces of the magnetic disk2. At this time, the linear displacement sensors66detect the positions of the tape heads5, and position detection signals from the linear displacement sensors66are input to the control circuit110. The control circuit110carries out the feedback control depending on the position detection signals from the linear displacement sensors66and adjusts the drive currents supplied to the voice coil motors62, so that the voice coil motors62make the abrasive tapes3to touch the surfaces of the magnetic disk2.

If the voice coil motors62are driven with linear ramp currents (or linear ramp voltages) when making the abrasive tapes3to touch the surfaces of the magnetic disk2, there will be a high risk of damaging the magnetic disk2due to the inertia of the tape heads5since fixed pressures are applied to the tape heads5. Moreover, since the tape heads5and the magnetic disk2have the inertia, it is difficult to adjust shock pressures when the abrasive tapes3touch the rotating magnetic disk2only by adjusting waveforms of the drive signals. For this reason, in this example, the tape heads5are stopped once just before the magnetic disk2, then the tape heads5are positioned such that the abrasive tapes3touch the surfaces of the magnetic disk2.

When the control circuit110further supplies the drive currents to the voice coil motors62, the movable portions62amove due to the electromagnetic force and the arms63push the tape heads5, so that the tape heads5press the abrasive tapes3against the surfaces of the magnetic disk2. At this time, the load cells64detect pressuring forces of the voice coil motors64, and pressure detection signals from the load cells64are input to the control circuit110. The control circuit110carries out the feedback control depending on the pressure detection signals from the load cells64and adjusts the drive currents supplied to the voice coil motors62, so that the voice coil motors62gradually raise the pressuring forces and keep them after they become target pressures. Therefore, it becomes possible to stably carry out the fine adjustment of the pressuring forces of the voice coil motors62, in other words, the load control for the magnetic disk2.

FIG. 10is a block diagram showing the control circuit of the polishing apparatus shown in FIG.9. AndFIG. 11shows an operation sequence of the control circuit shown in FIG.10. InFIG. 10, only the control circuit for the equipment, which polishes one surface of the magnetic disk2, is shown in order to simplify the explanation.

The control circuit110comprises a logic control circuit111, a load control circuit120, a head position control circuit130and a detection circuit140. The load control circuit120has a D/A converter121, a differential amplifier122, a phase compensation circuit123, a selector124and a VCM drive circuit125. The head position control circuit130has a D/A converter131, a differential amplifier132, a phase compensation circuit133, the selector124and the VCM drive circuit125. The selector124and the VCM drive circuit125are shared in the load control circuit120and the position control circuit130. The detection circuit140has a selector141, which receives detection signals from the load cell64and the linear displacement sensor66, and an A/D converter142, which converts the detection signal selected by the selector141into the digital data.

The logic control circuit111consists of a so-called gate array or a programmable logic device having a microprocessor unit. The logic control circuit111switches the load control circuit120and the head position control circuit130alternatively by generating selection signals, inputs the detection signal detected by each sensor and converted into the digital data from the detection circuit140, and makes the VCM drive circuit125to supply a certain drive current according to the sequence shown inFIG. 11by generating a target position signal or a target load signal.

An operation of the control circuit110will be hereafter explained according to the sequence shown in FIG.11. First, the control circuit110carries out the bias control, in which the tape head5is moved from a starting point0and positioned at a point HP. Next, the control circuit110carries out the positioning control, in which the tape head5is moved from the point HP and stopped at a point NP, which is close to the surface of the magnetic disk2. Then, the control circuit110carries out the soft contact control. In the soft contact control, the tape head5is moved to a point CP first, so that the abrasive tape3touches the surface of the magnetic disk2. Then, the control circuit110turns into the load feedback control when the tape head5reaches the point CP, and gradually raises a load up to a final target load. When the load becomes the final target load, the control circuit110carries out the target load control and keeps the load. At last, after finishing a polish, the control circuit carries out the shunting control, in which the tape head5is positioned at the starting point O and shunted.

In the soft contact control, there are two methods in making the abrasive tape3to touch the surface of the magnetic disk2. One is to position the tape head5at a predetermined position, so that the abrasive tape3is considered to contact the surface of the magnetic disk2. Another one is to check a contact of the abrasive tape3and the magnetic disk2by actually detecting a contact pressure of approximately 50 mN using the load cell64. The former is taken here for an example and each control will be explained hereafter.

First, in the bias control, the logic control circuit111generates selection signals S1, S2for positioning. The selection signal S1is a signal that switches the selector124from the load control circuit120to the head position control circuit130. The selector124selects a signal in the load control circuit120when the selection signal S1is not supplied, and it selects a signal in the head position control circuit130when the selection signal S1is supplied. The selection signal S2is a signal that switches the selector141from the load cell64to the linear displacement sensor66. The selector141selects a signal from the load cell64when the selection signal S2is not supplied, and it selects a signal from the linear displacement sensor66when the selection signal S2is supplied.

While generating the selection signals S1, S2, the logic control circuit111generates the position data of the point HP as the target position signal. The control circuit110becomes a feedback control circuit and generates the drive current that makes a position of the tape head5equal to a target position. The target position signal from the logic control circuit111is supplied to the VCM drive circuit125through the D/A converter131, the differential amplifier132, the phase compensation circuit133and the selector124, and the drive current is supplied to the voice coil motor62from the VCM drive circuit125. At this time, the differential amplifier132generates a differential signal depending on the difference between the position detection signal from the linear displacement sensor66and the target position signal converted by the D/A converter131. The position detection signal from the linear displacement sensor66is input to the logic control circuit111through the selector141and the A/D converter142, and monitored. The tape head5stops when reaching the point HP.

In the positioning control, the logic control circuit111generates the drive signal data of a trapezoid wave as the target position signal while generating the selection signals S1, S2. This target position signal is supplied to the VCM drive circuit125through the D/A converter131, the differential amplifier132, the phase compensation circuit133and the selector124, and the drive current is supplied to the voice coil motor62from the VCM drive circuit125. At this time, the differential amplifier132generates the large differential signal, and the tape head5is moved toward the point NP, which is close to the surface of the magnetic disk2, at high speed. The position detection signal from the linear displacement sensor66is input to the logic control circuit111through the selector141and the A/D converter142, and monitored. The logic control circuit111carries out the stopping control when the tape head5reaches the point NP and makes the tape head5to once stop at the point NP or a close point beyond it.

In the soft contact control, the logic control circuit111first generates the position data of the point CP as the target position signal while generating the selection signals S1, S2. This target position signal is supplied to the VCM drive circuit125through the D/A converter131, the differential amplifier132, the phase compensation circuit133and the selector124, and the drive current is supplied to the voice coil motor62from the VCM drive circuit125. At this time, the differential amplifier132generates the differential signal depending on the difference between the position detection signal from the linear displacement sensor66and the target position signal converted by the D/A converter131. The position detection signal from the linear displacement sensor66is input to the logic control circuit111through the selector141and the A/D converter142, and monitored.

Here, when the logic control circuit111generates the position data of points, which gradually approach the point CP, by many steps instead of the position data of the point CP, the contact becomes softer. However, even if the logic control circuit111generates the position data of the point CP and moves the tape head5directly to the point CP, the contact can be soft since the distance from the point NP to the point CP is short and the tape head5has been once stopped.

Next, the logic control circuit111stops generating the selection signals S1, S2when the tape head5reaches the point CP. By this, the selector124is switched from the head position control circuit130to the load control circuit120, and the selector141is switched from the linear displacement sensor66to the load cell64. A load detection signal from the load cell64is input to the logic control circuit111through the selector141and the A/D converter142.

The logic control circuit111generates the load data, which rises gradually up to the final target load, as the target load signal depending on the load detection signal from the load cell64. The control circuit110becomes a feedback control circuit and generates the drive current that makes the pressuring force of the voice coil motor62equal to a target load. The target load signal from the logic control circuit111is supplied to the VCM drive circuit125through the D/A converter121, the differential amplifier122, the phase compensation circuit123and a selector124, and the drive current is supplied to the voice coil motor62from the VCM drive circuit125. At this time, the differential amplifier122generates a differential signal depending on the difference between the load detection signal from the load cell64and the target load signal converted by the D/A converter121. And when the pressuring force reaches the target load, the control circuit110carries out the target load control and keeps the pressuring force equal to the target load while polishing the magnetic disk2.

In order to check the contact of the abrasive tape3and the magnetic disk2by actually detecting the contact pressure using the load cell64, as mentioned above, the selector141should be time division controlled and both the position detection signal from the linear displacement sensor66and the load detection signal from the load cell64should be input to the logic control circuit111. Then, the head position control circuit130and the load control circuit120should operate in parallel, so that the soft contact control and the load control are carried out simultaneously.

Even if such time division control is not carried out, the contact of the abrasive tape3and the magnetic disk can be checked by actually detecting the contact pressure using the load cell64, and the load control can be carried out by monitoring the detection signal from each sensor independently, without employing the selectors141,124, and integrating the phase compensation circuits123,133. In this case, the contact pressure to be detected will be approximately dozens to ten dozens mN.

The phase compensation circuit123mainly consists of a lead/lag filter circuit, which carries out the phase compensation when feeding the detection signal back during the load control. The phase compensation circuit133mainly consists of a lead/lag filter circuit, which carries out the phase compensation when feeding the detection signal back during the positioning control.

In the shunting control, the logic control circuit111generates the selection signals S1, S2again and generates the drive signal data of the trapezoid wave for returning to the starting point0as the target position signal. This target position signal is supplied to the VCM drive circuit125through the D/A converter131, the differential amplifier132, the phase compensation circuit133and the selector124, and the drive current is supplied to the voice coil motor62from the VCM drive circuit125. At this time, the differential amplifier132generates the large differential signal, and the tape head5is moved toward the starting point O at high speed. The position detection signal from the linear displacement sensor66is input to the logic control circuit111through the selector141and the A/D converter142, and monitored. The logic control circuit111carries out the stopping control when the tape head5reaches the starting point0, and makes the tape head5to stop at the starting point O or a close point beyond it.

According to this embodiment, since the voice coil motor62is driven by generating the target load signal and controlled by feeding the load detection signal from the load cell64back to the target load signal, even if the surface of the magnetic disk2deflects, the pressuring force of the voice coil motor62is finely adjusted in response to a deflection by the feedback control. Therefore, it becomes possible to polish the surface of the magnetic disk2uniformly.

Furthermore, according to this embodiment, since the voice coil motor62is driven by generating the target load signal, which rises gradually up to the final target load, depending on the load detection signal from the load cell64and controlled by generating the target load signal indicating the final target load after that, it becomes possible to prevent the damage generated when the abrasive tape3touches the surface of the magnetic disk2.

Furthermore, according to this embodiment, since the tape head5is once stopped at the point, which is close to the surface of the magnetic disk2, and the contact of the abrasive tape and the magnetic disk is carried out softly, it becomes possible to prevent the damage generated when the abrasive tape3touches the surface of the magnetic disk2.

The sensors for detecting the positions of the tape heads5in the present invention are not limited to the linear displacement sensor. Although the voice coil motor is driven forward and backward in this example, the feedback control can be carried out even if the voice coil motor is driven forward only since it receives the repulsion from the magnetic disk in practice. Moreover, although the D/A converter and the differential amplifier are provided in the load control circuit120and the head position control circuit130respectively in this example, the D/A converter and the differential amplifier may be used in common.

Although the voice coil motor is utilized in the tape head pressuring unit in the examples explained above, the present invention is not limited to this and what is necessary is to generate the pressuring force using the electromagnetic force.

FIG. 12is a flow chart showing an example of a manufacturing process, including the polishing apparatus and methods described herein, to manufacture a magnetic disk. First, a polishing process is carried out on both surfaces of a substrate, which consists of an aluminum alloy, etc., and its surfaces are mirror-polished so as to have the surface roughness of about 1 nanometer in average (Step210). Next, undercoating layers with non-magnetic metal, which consist of a nickel-phosphorus (Ni—P) alloy, etc. and whose thickness is about 5-20 micrometers, are formed on the surfaces of the substrate by electroless plating, etc. (Step220). Then, a mirror-polishing process is carried out and upper layers are polished out about 2-5 micrometers so as to have the surface roughness Ra of about 20-50 angstroms (Step230). Next, after carrying out a texturing process for making minute grooves (Step240), undercoating layers with metal, which consist of chromium, copper, NiAl, etc. and whose thickness is about 50-2000 angstroms, are formed by sputtering, etc. (Step250). Then, magnetic layers, which consist of a ferromagnetic cobalt alloy, etc. and whose thickness is about 100-1000 angstroms, are formed by sputtering, etc. (Step260). Then, protective films, which consist of a carbon film, a carbon hydride film, a carbon nitride film, etc. and whose thickness is about 10-150 angstroms, are formed (Step270). After forming the protective films in such a manufacturing process, in order to remove small protrusions generated during these membrane forming processes and in order to clean up the surfaces of the magnetic disk, the tape cleaning is carried out on the surfaces of the magnetic disk (Step280).

The polishing apparatus and the polishing method according to the present invention are applicable to the polishing process (Step220), the mirror-polishing process (Step230) and the tape cleaning (Step280). However, an object under polish is not limited to the magnetic disk, and the present invention is generally applicable to many things that tend to get the damage during a polish.