Floppy disc drive apparatus for preventing absorption between a head and a floppy disc

The present invention relates to a system (FDD) for driving such a magnetic disc as a floppy disc, in which, in a stand-by mode where recording or reproducing operation is not carried out, a magnetic head is moved to a track position in the vicinity of the innermost peripheral part of the disc or the disc is intermittently rotably driven so that an adsorbent phenomenon can be prevented from taking place between the magnetic head and the disc and even in the case of occurrence of such a adsorbent phenomenon, the magnetic head or disc can be easily released from such adsorbent binding, thus preventing any destruction of information recorded on the disc.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a magnetic disc drive system which 
prevents the damage of data recorded on such a magnetic disc as a floppy 
disc by an adsorbent phenomenon of a magnetic head when the recording and 
reproducing operations of the head are stopped. 
2. Description of the Prior Art 
Recently, a floppy disc drive system (hereinafter, which is referred to 
merely as the FDD) has been widely employed in a backup memory of a 
telephone exchange system, a word processor and so on. In the conventional 
FDD, a magnetic head is stopped at its initial stage at the outermost 
periphery of a floppy disc (hereinafter, which will be referred to merely 
as the disc) and during stoppage of the recording or reproducing 
operation, the magnetic head remains on a track on the disc at the 
corresponding position. For this reason, the conventional FDD has had such 
a problem that when the magnetic head and the disc are left under high 
temperature and high humidity conditions for a certain period of time, the 
magnetic head tends to adhere to the disc, that is, a so-called adsorbent 
or adhesive phenomenon tends to take place, which results undesirably in 
that information stored on the disc is destroyed or a rotary drive device 
cannot rotate the disc. 
Most FDDs, which use a disc having a diameter of, for example, 3.5 inches, 
are not equipped with such a head loading mechanism as loads and unloads 
the disc with the magnetic head (connects and disconnect the magnetic head 
to and from the disc) for the purpose of miniaturization of the FDD. For 
this reason, in the 3.5-inch FDD, when the recording or reproducing 
operation has been ended, the magnetic head remains stopped at the then 
track position in a contact relation with the disc to ready for the next 
operation, which further increases the possibility of occurrence of the 
adsorbent phenomenon. 
Especially in a PBX (private branch exchange) or a key telephone system 
which uses the aforementioned FDD as a memory backup device in case of 
power failure, the FDD is used to store exchange programs and customer 
data (abbreviated dialling numbers, ID codes and so on to be registered by 
users). In this respect, the FDD is driven only when it is necessary to 
rewrite the customer data and the disc is usually left in its loaded 
condition, i.e., loaded in the FDD for a long period of time, which leads 
to a much increased danger of occurrence of the disc adsorbent phenomenon. 
The mechanism of the adsorbent phenomenon is not clear yet, but it is 
generally considered that under high temperature and high humidity 
conditions, surface active agent coated on the surface of a disc increases 
its fluidity and starts to flow into a contact area between the disc and a 
magnetic head by the capillary action, whereby the magnetic head adheres 
to the disc. And when the adsorbent or adhesive force exceeds a starting 
torque of a disc driving motor, the disc motor cannot rotably drive the 
disc or the disc is subjected to an unreasonable force on its surface on 
which data are recorded, leading to the destruction of the data. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a floppy 
disc drive system which prevents an adsorbent phenomenon between a disc 
and a magnetic head to reliably avoid the destruction of data recorded on 
the disc and the erroneous operation of a disc motor. 
In accordance with an aspect of the present invention, there is provided a 
magnetic disc drive system which comprises a recording medium for storing 
therein data, a magnetic head through which data are written in and read 
out from the recording medium, first means for rotably driving the 
recording medium, second means for drivingly moving the magnetic head in a 
radial direction of the recording medium, and control means for, in a 
stand-by mode in which the data is not written nor read, stopping the 
driving operation of the first driving means and also for controllably 
driving the second driving means to move the magnetic head to a 
predetermined track in the vicinity of the innermost peripheral track of 
the recording medium. 
With such an arrangement, when the FDD is in a stand-by mode in which the 
recording or reproducing operation is stopped, the control means drives 
the second driving means which in turn drivingly moves the magnetic head 
in the radial direction (usually, in the centripetal direction) of the 
recording medium and positions the magnetic head, for example, at the 
innermost peripheral track of the medium. 
Since the innermost peripheral part of the recording medium has a low 
possibility that information is recorded in the innermost part, the 
destruction of the information can be minimized. In addition, even when an 
adsorbent phenomenon takes place between the magnetic head and the 
recording medium, the magnetic head can be released with a small torque 
from the adsorbent bound condition because the magnetic head is located at 
the nearest distance from a rotary shaft of the first driving means. 
Further, in accordance with another aspect of the present invention, there 
is provided a magnetic disc drive system which comprises a disc-shaped 
recording medium for storing therein data, a magnetic head through which 
data are written in and read out from the recording medium, first driving 
means for rotably driving recording medium, second driving means for 
drivingly move said magnetic head in a radial direction of the recording 
medium, and control means for, in a stand-by mode in which the data is not 
written nor read out, causing the second driving means to stop its driving 
operation and the first driving means to rotably drive intermittently at 
intervals of a predetermined time. 
With the aforementioned arrangement, the disc is rotated intermittently 
during stoppage of recording or reproducing operation of the FDD so that 
the magnetic head can be prevented from coming into a long and continuous 
contact with the disc at its identical part, thus preventing the 
destruction of information recorded on the recording medium by an 
adsorbent phenomenon between the magnetic head and the disc.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 shows an inside perspective arrangement of an FDD 7 using a 3.5 
-inch disc, while FIG. 3 is a cross-sectional view thereof. 
In FIGS. 2 and 3, a magnetic head 4 is mounted on a carriage 3 so that the 
movement of the carriage 3 in a radial direction of a disc 2 through a 
worm gear (not shown) by a motor 5 causes the radial movement of the 
magnetic head 4. Provided in the center of the disc 2 is a disc motor 1 
which rotably drives the disc 2. These constituent elements are housed in 
a body casing 6. This 3.5inch FDD is not equipped with a head loading 
mechanism which functions to connect and disconnect the magnetic head 4 to 
and from the disc 2 as mentioned above. 
There is shown in FIG. 1 an arrangement of a first embodiment of the 
present invention which comprises the FDD 7 and a central control unit 
(CCU) 10 which transfers signals to and from the FDD 7. The FDD 7 includes 
not only the disc motor 1, step motor 5 and magnetic head 4 mentioned 
above but also a control device 20 which controls these elements. The 
control device 20 includes a rotation control unit 21 for controlling the 
rotation and stoppage of the disc motor 1, a rotational speed detecting 
unit 22 for detecting the rotational speed of the disc motor 1, a 
forward/backward rotation control unit 23 for controlling the forward and 
backward rotation of the stepping motor 5, a rotation control unit 24 for 
controlling the rotation and stoppage of the stepping motor 5, and a 
head-position detecting unit 25 for detecting the track position of the 
magnetic head 4. Note that a track indicates a radial position on the disc 
2 and the outermost track is referred to as a track 00 and the innermost 
track is referred to as a track 76 herein (refer to FIG. 3). 
On the other hand, the CCU 10 includes a floppy disc controller (FDC) 11 
for transferring signals to and from the control device 20 of the FDD 7, a 
data separator 12 for separating a data signal from a clock pulse and 
modulating it, a RAM 14, a direct memory access (DMA) 13 for transferring 
read/write (R/W) data to the RAM 14 and a CPU 15. 
Many sorts of signals are transferred between the FDC 11 and the control 
device 20 but among them only signals concerning the present invention are 
explained in the following. 
"MOTOR ON" (hereinafter, which will be abbreviated as MO) 
This is a signal for stopping and rotating the disc motor 1 when it has a 
value of "1" and a value of "0" respectively. 
"DIRECTION SELECT" (hereinafter, which will be abbreviated as DS) 
This is a signal for rotating the stepping motor 5 forwardly and 
backwardly, that is, for determining whether or not the magnetic head 4 is 
moved in a radially inward or outward direction of the disc. When the 
signal has a value of "1", the magnetic head 4 is moved in the radially 
inward direction, while when the signal has a value of "0", the magnetic 
head is moved in the radially outward direction respectively. 
"STEP" (hereinafter, which will be abbreviated as SP) 
This signal determines the amount of movement of the magnetic head 4 in 
the disc radial direction. When this signal has one pulse, the magnetic 
head is shifted by one track and when the signal has three pulses, the 
magnetic head is shifted by three tracks. 
"WRITE GATE" (hereinafter, which will be abbreviated as WG) 
When this signal has a value of "1", a write circuit (not shown) in the 
control device 20 is put in its operative condition, whereas when the 
signal has a value of "0", the drive is put in a write inhibit mode. 
"READY" (hereinafter, which will be abbreviated as RY) 
This is a signal which is applied from the rotational speed detecting unit 
25 to the FDC 11. When the signal has a value of "1", this indicates that 
the disc 2 has been inserted and the rotational speed of the disc motor 1 
has reached at a constant level. 
"TRACK NO" (hereinafter, which will be abbreviated as TN) 
This is a signal which is applied from the head position detecting unit 25 
to the FDC 11. The head position detecting unit 25 detects a position or 
track position of the magnetic head 4 in the disc radial direction and 
outputs a signal TN indicative of the detected track number. This head 
position detecting unit 25 has been newly added in the present embodiment 
to form an essential part of the present invention. 
The operation of the arrangement shown in FIG. 1 will be explained by 
referring to a flowchart of FIG. 4. This flowchart comprises usual 
read/write operation routine (steps 100 to 180) added with an 
anti-adsorption routine (steps 200 to 220). 
In the read/write operation, the FDC 11 of the CCU 10 first outputs a 
signal MO (step 100). The control device 20 of the FDD 7 confirms that the 
disc 2 has been loaded and then controls to cause the rotation control 
unit 21 therein to rotably drive the disc motor 1 (step 120). When the 
rotational speed detecting unit 22, which is detecting the rotational 
speed of the disc motor 1, detects a predetermined rotational speed, the 
control device 20 outputs a signal RY (steps 130 and 140). 
The FDC 11, when receiving this signal RY, outputs signals DS and SP to 
move the magnetic head 4 to a predetermined track. And in the read 
operation, the CPU 15 writes into the RAM 14 through the DMA 13 the read 
data applied to the data separator 12. In the write operation, data stored 
in the RAM 14 is transferred to the magnetic head 4 through the DMA 13 and 
the data separator 12 to be written into the disc 2 (step 160). 
Thereafter, the CPU 15 checks the data and confirms that there is no 
abnormality (step 170). 
At this stage, the magnetic head 4 is located at a track position where 
aforementioned access (read/write) has been carried out, and comes into 
contact with the disc 2 at that position. In the conventional read/write 
operation, after this, the CPU 15 sets the signal MO to be 0 and stops the 
disc motor 1, after which the magnetic head 4 is put in its stand-by state 
with the head brought into contact with the disc at the above track 
position during the accessing operation. In the present embodiment, 
however, the following anti-adsorption routine are executed. 
More specifically, the CPU 15 confirms the completion of the accessing 
operation (read/write operation) to the FDD (step 180) and then first 
judges or determines the current track position of the magnetic head 4 on 
the basis of the output TN of the head position detecting unit 25. And on 
the basis of the determined head position, the CPU 15 calculates the 
number of pulses in the signal SP necessary to move the magnetic head 4 to 
the innermost peripheral track (refer to track 76 in FIG. 3). As has been 
already mentioned above, the number of pulses in the signal SP corresponds 
to the number of tracks crossed. 
And the CPU 15 orders the FDC 11 to transfer the signal of "1" to the 
forward/backward rotation control unit 23 and also to transfer the signal 
SP having said calculated number of pulses to the rotation control unit 24 
(step 200). This causes the control unit 23 and the rotation control unit 
24 to drive the stepping motor 5, which results in that the magnetic head 
is moved in the radially inward direction of the disc and finally 
positioned at the innermost peripheral track (track 76). The CPU 15 
confirms on the basis of the output TN of the head position detector 25 
that the magnetic head 4 has been located at the innermost peripheral 
track position (step 210). After this confirmation, the CPU 15 controls to 
cause the FDC 11 to set the signal MO to be "0", thus stopping the disc 
motor 1 (step 220) and subsequently putting the system in the stand-by 
mode. 
In accordance with the presnt embodiment, when the FDD does not perform 
information recording and reproducing operations over the disc 2, the 
magnetic head 4 is located at the innermost peripheral part of the disc 2 
where there is a low possibility that information is recorded. As a 
result, even if the magnetic head 4 is stopped at that position for a long 
period of time and adsorbent phenomenon takes place between the magnetic 
head 4 and the disc 2, the destruction of the information can be reduced 
to the minimum extent. In particular, such important data as formats 
recorded in the outermost peripheral part of the disc can be completely 
prevented from being destroyed. 
In addition, even if the occurrence of such an adsorbent phenomenon between 
the magnetic head 4 and the disc 2 leads to the fact that the magnetic 
head 4 adheres to the disc 2, the magnetic head can be released from the 
adsorbent binding with the minimum torque, because such an adhesive 
position is located nearest to the rotary shaft of the disc motor 1. A 
moment J of inertia at a given point on the disc 2 is expressed by the 
following equation. 
EQU J=mr.sup.2 /2 
where, m is mass and r is radius. It will be appreciated from the above 
equation that a torque proportional to the second power of radius is 
necessary to release the magnetic head 4 from the adsorbent binding force 
and thus it is less advantageous to locate the magnetic head farther from 
the rotary shaft of the motor 1. 
Although the magnetic head has been retreated to the innermost peripheral 
track in the foregoing embodiment, the present invention is not limited to 
the particular one and the magnetic head may be retreated to an arbitrary 
track in the vicinity of the innermost peripheral track. 
Referring now to FIG. 5, there is shown a second embodiment of the present 
invention, in which the same constituent elements as those in FIG. 1 are 
denoted by the same reference numerals. 
In the arrangement of FIG. 5, the head postion detecting unit 25 in FIG. 1 
is omitted and a timer 30 is newly added in the CCU 10. 
The timer 30 is provided to measure a predetermined time period (for 
example, one hour) and functions to apply an interrupt signal IR to the 
CPU 15 each time the above predetermined time elapses. 
Explanation will be made as to the operation of the second embodiment with 
reference to a flowchart of FIG. 6. 
There is no accessing operations to the FDD in such occasions that, for 
example, when the disc 2 is in its initial state where the disc 2 is set 
in the casing 6 and no recording or reproducing operation has taken place 
yet, or when the magnetic head 4 is standing by at a track on the disc 2 
after the completion of a recording or reproducing operation. When it is 
judged at the step 300 that there is no accessing operations to the FDD, 
the CPU 15 executes the following anti-adsorption routine. 
That is, the timer 30, when measuring the predetermined time (step 310), 
applies the interrupt signal IR to the CPU 15 (step 320). 
The CPU 15 is arranged to receive the interrupt signal IR from the timer 30 
under the control of the interrupt control unit only when there is no 
accessing operation to the FDD. The CUP 15, when detecting the interrupt 
signal IR (step 330), orders the FDC 11 to set the signal MO to be "1" for 
a short period of time. This causes the rotation control unit 21 to rotate 
the disc motor 1 for a time period during which the signal MO has a value 
of "1", thus turning the disc 2 for a predetermined time and then stopping 
the disc (step 340). The CPU 15 repetitively executes such control time 
the CPU receives the interrupt signal from the timer 30. As a result, the 
disc 2 is intermittently rotated as shown in FIG. 7 under such condition 
that the magnetic head 4 is positioned at a certain track. That is, in the 
case of the system not provided with a head loading mechanism, when access 
to the FDD is ended to enter the system in the stand-by mode, the magnetic 
head 4 stays at that track position where access has been completed, with 
the magnetic head being in contact with the disc. In the present 
invention, on the other hand, the disc motor 1 is intermittently rotated 
to intermittently run the magnetic head 4 on that track in such a stand-by 
mode 
In accordance with the present embodiment, in the initial state and in the 
stand-by mode in which the recording or reproducing operation has been 
ended, the disc 2 is intermittently rotably driven. As a result, it can be 
prevented that the magnetic disc 4 continues to come into contact with the 
same part of the disc 2 for a long period of time, that an adsorbent 
phenomenon takes place between the magnetic head 4 and the disc 2 and that 
information stored in the disc 2 is destroyed. 
The time set in the timer 30 is not restricted to the particular one and 
may be properly selected depending on the disc 2 and the ambient 
conditions. 
A third embodiment of the present invention will next be explained by 
referring to a flowchart of FIG. 8. 
The third embodiment corresponds to a combination of the first second 
embodiments. That is, the flowchart of FIG. 8 comprises a routine A (steps 
400 to 420) which corresponds to the first embodiment and a routine B 
(steps 430 to 460) which corresponds to the second embodiment. 
More specifically, when the third embodiment is in the stand-by or initial 
mode, the stepping motor 5 is first driven to move the magnetic head 4 to 
the innermost peripheral part of the disc 2 and then the disc motor 1 is 
driven to intermittently rotate the disc 2. 
In the third embodiment, since the magnetic head 4 is positioned at the 
innermost peripheral part where there is a low possibility that 
information is recorded and the disc 2 is intermittently driven along the 
innermost peripheral track, the adsorbent phenomenon occurs much less. 
Occurrence of such adsorbent phenomenon enables the disc to be released 
from the adsorbent force with a small torque, and the information 
destruction can be supressed to the minimum extent. 
Shown in FIG. 9 is an arrangement of a digital key telephone exchange 
system to which the present invention is applied and wherein the FDD 7 is 
used as a backup memory in case of power failure. 
This digital telephone exchange system comprises, in addition to such a 
central control unit (CCU) and an FDD 7 as mentioned above, a time switch 
40 which exchanges interconnections between inner line or extension 
highways IH and between an outer line highway OH and the extension highway 
IH, a trunk unit 41 as an outer line interface, telephone set units 42 as 
extension interfaces, terminals 43 comprising, for example, telephone 
sets, and a data highway DH. 
In this telephone exchange system, exchange programs and customer data 
(such as abbreviated telephone numbers) are rocorded on the disc of the 
FDD 7 and these recorded data are read out at the time of installing or 
starting the exchange system to be transferred to the RAM of the CCU 10. 
For this reason, in the exchange system, in other cases than when it 
becomes necessary to again transfer the recorded data due to power failure 
and when it becomes necessary to rewrite the customer data by users, the 
FDD is in the stand-by mode and thus there is a much high possibility of 
occurrence of the aforementioned adsorbent phenomenon. 
Therefore, the FDD 7 and CCU 10 of this exchange system are provided with 
such arrangement and function for preventing the adsorbent phenomenon as 
shown in FIGS. 1 and 5, thereby avoiding any destruction of the recorded 
data. 
The present invention is not limited to the foregoing digital telephone 
exchange system and may be applied to such an arbitrary electronic 
apparatus and equipment as a word processor, a PBX and so on.