Method and apparatus for releasing a magnetic head

Releasing adhesion between a magnetic head and a magnetic disk by radially moving the head before the disk begins to rotate. The head movement is accomplished by compressing an elastic stopper means by driving a head actuator motor with drive current so that unwanted vibration of bounce back of the head is prevented.

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetic disk file unit; and more 
particularly, relates to a method and apparatus for releasing a magnetic 
head from a magnetic disk when starting up the magnetic disk file unit. 
When a magnetic disk file unit is operated, the magnetic head floats on a 
thin layer of air which is caused by rotation of the disk. Precisely 
speaking, the magnetic head is part of a slider. In this specification, 
however, the term "head" refers to the entire slider including the actual 
magnetic head. 
In these days, most magnetic disk file units employ a so-called CSS or 
"Contact Start Stop" system, in which the head contacts the disk surface 
when the disk is not rotating. This system is practical because 
miniaturization of the head has reduced the amount of pressure on the disk 
due to the head. The use of much cleaner air in the disk housing and the 
use of a lubricant also aid in making the system practical. The lubricant 
reduces dynamic friction between the head and the disk when starting and 
stopping the rotation of the disk and reduces damage if the head either 
crashs onto the disk due to mechanical shock or the head forces dust into 
the disk. 
However, because heads continue to be further-miniaturized, and because the 
finish of both the head and disk surfaces are continuingly being made 
smoother, the head tends to adhere to the disk surface when the disk is 
not rotated. This adhesion is caused by a kind of attraction force which 
can occur between two mirror smooth surfaces. This attraction force 
becomes stronger with presence of the lubricant, and would cause serious 
damage to the head, its suspension structure or the disk if not released 
properly. 
To ensure the release of the adhesion before starting to rotate the disk, 
conventional magnetic disk file units employ a specific release mechanism. 
This mechanism includes moving a head actuator along a radius direction of 
the disk before the disk starts to rotate. Since the suspension structure 
gimbals have enough stiffness in the radial direction, the head can be 
released from the adhesion without causing any damage to the gimbals. 
Several ways of moving the head have been proposed. In U.S. Pat. Nos. 
4,530,021 and 4,589,036, the head is supplied with an alternating current 
to cause "micromotion" when starting rotation of the disk. Further, in 
4,589,036, actual movement of the head is sensed and the "micromotion" is 
controlled thereby. However, these methods require a precisely controlled 
alternating current generator and sophisticated sensing circuits. 
Another method, which uses a much simpler circuit, is disclosed in Japanese 
laid open patent Tokkaisho 61-198480 (published Sept. 9, 1986). In this 
method, when the unit is stopped, the head actuator is positioned, close 
to a stopper means. The stopper means restricts the actuator movement and 
comprises an elastic material. Upon starting up the disk unit, the 
actuator is moved towards the stopper and compresses the elastic material. 
This causes the head to be slightly offset in the radial direction before 
the disk actually begins to rotate. This method requires only an actuator 
drive current large enough to compress the elastic material. A square 
waveform is used as the drive current, because the movement of the 
actuator is safely restricted by the stopper. 
However, the inventor of present invention has discovered that use of such 
a simple waveform, with steep rise and fall characteristics can cause 
serious impact to the head and its gimbals, and in some cases, causes 
damage to the disk. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of this invention to provide an improved method 
and apparatus for a magnetic disk file unit to release the adhesion 
between the head and the disk with a simple circuit. 
Another object of this invention is to provide an improved method and 
apparatus which releases the adhered head softly and without severe impact 
to the head. 
Yet another object of this invention is to provide an improved method and 
apparatus which drives a head actuator with a gradually increasing and 
gradually decreasing acceleration. 
To accomplish these and other objects of the present invention, a head 
actuator motor is driven by a current having gradual rise and fall 
characteristics. 
Yet still other objects and precise solutions thereof will be understood by 
refering to the attached drawings and explanations thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a partial plane view of a conventional magnetic disk memory unit 
in which a magnetic disk 1 rotates around a spindle la, and a magnetic 
head 2 is actuated by a so-called swing-arm type actuator 3. This actuator 
3 includes: a swing arm 30; a rotation axis 31; a voice-coil motor 32 
comprising a coil winding 32a fixed at the one end of the swing arm 30 and 
a magnetic circuit 32b fixed on a frame (not shown); a recess 34 on the 
swing arm 30; stoppers 33a and 33b positioned at the both ends of the 
recess 34, the stoppers comprise an elastic material such as rubber; a 
stop pin 35 secured to the frame (not shown) and positioned between the 
stoppers 33a and 33b; and gimbals 2a fixed at the other end of the swing 
arm 30, the head 2 is suspended from gimbals 2a. 
When a drive current is applied to the coil winding 32a, one end of the 
swing arm 30 is driven in the direction indicated by the arrow A-B, the 
direction depending on the polarity of the drive current. The other end of 
the swing arm 30, and thus the head 2, is driven in the direction 
indicated by the arrow C-D. The stop pin 35, together with the stoppers 
33a and 33b, restrict the movement of the swing arm 30 within a specific 
region so that the head 2 does not exceed a specific region on the disk 
surface. 
FIG. 2 illustrates a conventional drive circuit used with the FIG. 1 unit. 
In FIG. 2, reference numerals similar to those in FIG. 1 denotes the 
similar parts. In FIG. 2, an amplifying circuit 4 includes: an operational 
amplifier 41; an input resistor 40; a feed-back resistor 42; and a power 
amplifier 43. The amplifying circuit 4 is supplied with a servocontrol 
signal SV at one end of the input resistor 40 whose other end is connected 
to the negative input terminal of the operational amplifier 41. The 
positive input terminal of the operational amplifier 41 is grounded via a 
resistor 44. Thus the circuit 4 basically supplies drive current Iv which 
is proportional to the voltage of the signal SV. A control unit 6 
generates an appropriate voltage for the SV signal in accordance with 
commands and servo-signals read from servo-tracks on the disks and 
supplied on line 6a. 
The negative input terminal of operational amplifier 41 is also connected 
to a switch circuit 50 via another input resistor 51 for selectively 
applying a predetermined voltage Vee to the operational amplifier 41. The 
switch circuit 50 is closed in response to an adhesion release signal VC 
generated by the control circuit 6 upon starting of the unit. An analog 
switch IC, such as DG201 supplied by Siliconix Corp., can be used as the 
switch circuit 50. Numeral 7 identifies a motor for rotating the disk. 
The adhesion releasing operation is explained as follows. When the unit is 
turned off, the head is moved to an inner guard area of disk 1 by means of 
a spring (not shown). As the rotation of the disk stops, the head contacts 
the disk surface and stays there. At this stage, the stopper 33b is close 
to and is almost touching the stop pin 35. 
When the head is left at the same place on the disk surface, the lubricant 
gathers and fills all of the microscopic gaps between the head surface and 
the disk surface. As a result, the adhesion between the head surface and 
the disk becomes very tight. 
When the unit is turned on, the disk drive motor 6 and the release signal 
VC are activated at the same time. The inertia of the disk is relatively 
large and thus the rotation begins with a bit delay. However, the torque 
of the voice coil motor 32 (which is large enough to provide quick access 
times) moves the head further toward the inner side of the disk before the 
disk begins to rotate. Since, as noted above, the stopper 33b is almost 
touching the pin 35 already, the head movement compresses the stopper 33b 
against the pin 35 due to the torque of the voice coil motor 32. This 
compression must last until the disk actually begins to rotate, because if 
the head returns to the initial position while the disk is still not 
roating, then the head will again adhere tightly to the disk because of 
the lubricant that has gathered at that position. 
In this conventional system, the drive current Iv of the voice coil motor 
32 is a simple square waveform with steep rise and fall characteristics. 
The inventor of the present invention has discovered that, at the rising 
edge of the drive current waveform, the stopper 33b is driven with great 
acceleration against the pin 35. This causes an undesirable impact to or 
vibration of the head 2 and gimbals 2a. Furthermore, at the falling edge 
of the drive current waveform, the sudden release of the voice coil motor 
32 torque causes the compresses stopper 33b bounce back and the head to 
quickly move outerwards towards the disk area where data is recorded. If, 
when the head reaches the disk data recording area, the gimbals 2a are 
vibrating or the disk rotation speed is not yet high enough to cause the 
head to float, the head might damage (e.g., scratch) the data recording 
area. 
FIG. 3 illustrates an embodiment of the head actuator motor drive circuit 
of the present invention, wherein reference numerals that are the same as 
those in FIG. 2 denote the same or similar parts. FIG. 3 includes a time 
constant circuit 52 comprising a resistor 52R and a capacitor 52C. The 
time constant circuit 52 provides an improved drive current such as shown 
in FIG. 4 (c). FIG. 4 is a timing chart of various signals of the FIG. 3 
circuit when the disk file unit is started, wherein (a) is a unit start 
signal, (b) is the adhesion release signal VC, (c) is the drive current 
for the voice coil motor 32, (d) is a drive current for the disk rotating 
motor 7 and (e) is an actual rotating speed of the disk. In FIG. 4(c), the 
dotted line represents the conventional waveform. The duration T of signal 
VC is slected to be longer than the time necessary for the disk to 
actually begin to rotate, for example, approximately 200 to 300 
milliseconds. The time constant of the circuit 52 is empirially 
determined, an exemplary value is approximately 30 to 70 milliseconds. The 
total resistance of the resistors 52R and 53 corresponds to the resistance 
of the resistor 51 in FIG. 2. 
As the drive current Iv gradually increases, the stopper 33b is pressed 
against the pin 35 with only a small acceleration. This avoids any 
damaging inpact or vibration. More importantly, as the drive current Iv 
gradually decreases, the stopper 33b does not bounce back, and therefore, 
damage to the data recording area of the disk surface is prevented. 
The foregoing is considered illustrative of the principles of the present 
invention, and numerous modifications and changes are possible. For 
example, the time constant circuit 52 may be replaced by an integrated 
circuit utilizing an operational amplifier, or both the switch 50 and the 
circuit 52 may be replaced by a digital circuit which generates a 
pre-programed wave function. The swing-type actuator 3 also may be 
replaced by a linear voice coil motor. Many variations of the stopper 
means are also readily available. Therefore, it is not desired to limit 
the invention to the exact construction and operation of the embodiment of 
the present invention shown and described.