Positioning device for scanning means in a disk drive unit

A positioning device, comprising a cylindrical guide element and a guide surface, is so designed that an angle of less than 90.degree., especially of from 1.degree. to 80.degree., is formed between an axis at right angles to the direction of movement of the guide element over the guide surface and the axis of rotation of the guide element, in the plane containing these two axes. The peripheral surface of the guide element can be grooved or convex. The novel positioning device can be used with advantage in any type of recording/playback apparatus for disk records.

The present invention relates to a positioning device for at least one 
scanning means in a disk drive unit, in which the support for the scanning 
means is associated with a substantially cylindrical guide element mounted 
for rotation about one axis, the said guide element cooperating with at 
least one guide surface and travelling approximately horizontally along 
and in contact with said surface, as well as to a drive unit for disk 
records, especially floppy disks, which drive unit includes a positioning 
device according to the invention. 
A drive unit for floppy disks (e.g. FlexyDisk--Registered Trademark of BASF 
Aktiengesellschaft, 6700 Ludwigshafen, Germany), in which head positioning 
is effected by a wheel running in the spiral groove of a guide disk is 
known from U.S. Pat. No. 4,198,666. In this unit, the guide surface is 
vertical. 
We have found that particles of dust, abraded material and dirt on the 
guide wheel or on the guide surface lead to substantial positioning 
errors, for example track jumping during writing and reading. 
It is an object of the present invention to provide an improved positioning 
device which eliminates the said errors, and hence an improved drive unit 
for disk records, especially floppy disks. 
We have found that this object is achieved with a positioning device in 
which an angle of less than 90.degree. is formed between an axis at right 
angles to the direction of movement of the guide element and the axis of 
rotation of the guide element, in the plane containing these two axes. 
By arranging the guide element at an angle to its direction of movement in 
this manner, a cleaning action between the guide element and the guide 
surface is achieved, the width and location of the cleaned area depending 
on the effective width of the peripheral surface of the guide element and 
the angle of inclination of the guide element. 
This cleaning action is surprisingly effective and highly useful in 
precision guide means such as are used in all types of signal 
recording/reproducing apparatus. 
The particles of dirt, dust and abraded material are removed from the area 
of contact between the guide element and the guide surface and are pushed 
to the side, where they can no longer cause trouble. 
A drive unit for disk records, especially floppy disks for recording and/or 
reproducing digital or analog signals, is advantageously obtained if it is 
provided with a novel positioning device for one or more read/write heads 
where the guide element is arranged at an angle of less than 90.degree., 
and in particular at an angle of from 1.degree. to 80.degree., to the 
direction of motion. 
In practice, the angle of inclination is advantageously from about 
1.degree. to about 10.degree.. The peripheral surface of the guide element 
is advantageously grooved. In a particular embodiment, the grooves are 
arranged at an angle to the axis of rotation of the guide element, 
especially at an angle of 45.degree. thereto, whereby the cleaning action 
is intensified in a simple manner, without special matching of the 
materials of construction being necessary. 
In a further advantageous embodiment, the peripheral surface of the guide 
element is convex.

The head positioning device P comprises the following principal components: 
a carriage 1, which at the same time serves as the support for the 
magnetic head 17, a spirally grooved disk 2 and a stepping motor, not 
shown in the drawing, which can be located above or below the spirally 
grooved disk 2. 
The stepping motor, spirally grooved disk 2 and carriage 1 are conveniently 
combined in a sub-unit, and are advantageously arranged one above the 
other. 
A frame 6 of the housing G or the disk drive unit is shown in 
cross-section. The spirally grooved disk 2 has a central hole 7, through 
which the shaft 8 of the stepping motor protrudes. The motor shaft 8 and 
spirally grooved disk 2 are rigidly connected together. 
The carriage 1 is slidably mounted on, for example, hardened steel shafts 
10 and 11, so that it can move longitudinally in the directions indicated 
by double arrow 5. The shafts 10 and 11 are fixed in the frame 6 of the 
housing, as shown in FIG. 1. The shaft 10 together with the bore 12 in the 
carriage 1, the shaft fitting in the bore with virtually no play, 
constitutes the actual carriage guide, whereas the second shaft 11 
prevents the carriage 1 and hence the magnetic head 17 from rotating. 
The disk 2 has a spiral groove 13 which is made by suitable machining, for 
example milling. The spiral groove 13 is advantageously of substantially 
constant pitch. In cross-section, the groove 13 shown in FIG. 1 is of 
rectangular shape and is hence easily produced. The groove 13 has a wall 
14 parallel to the axis of rotation of the disk 2. In a simple practical 
embodiment, a commercial ball bearing 15 is attached to the carriage 1 in 
an appropriate position with respect to the groove 13. On rotation of the 
spirally grooved disk 2, the ball bearing 15 travels along the spiral 
groove, so that, depending on the direction of rotation (double arrow 4) 
of the disk 2, the carriage 1 is shifted longitudinally in one of the 
directions indicated by double arrow 5, i.e. forward or backward. The 
carriage 1 is drawn toward the frame 6 by means of the tension spring 16 
attached thereto. As a result, the ball bearing 15 or, more precisely, the 
outer race thereof, bears against the wall 14 of the groove 13 and is thus 
essentially in rolling frictional contact with wall 14. 
Due to the direct contact between the wall 14 and the ball bearing 15, the 
carriage can be guided virtually without any backlash in both directions 
of rotation 4 of the disk 2. Advantageously, the pitch of the spiral 
groove 13 is such that, for every step of the stepping motor, the carriage 
1 is advanced by an amount corresponding to the track spacing. By means of 
the control current supplied to the stepping motor, the carriage 1 and 
hence the magnetic head 17 are held in position when the desired position 
on the disk record 20 has been reached, against the bias of the spring 16. 
While the disk 20, in particular a floppy disk, rotates on the drive shaft 
19, any desired track on the disk 20 can be reached for writing or reading 
data by displacing the carriage 1 and hence the head 17. The guide disk 2 
is shown in plan view. As can be seen, the spiral groove extends over an 
angle of more than 360.degree. and is preferably of such a length that the 
carriage 1 and hence the magnetic head 17 can move, in either of the 
directions indicated by double arrow 5, over their entire range of travel 
which corresponds to the sum of the track spacings and the number of 
tracks. 
FIG. 2 is a cross-sectional view of the guide disk 2 and clearly shows that 
the axis of rotation D of the ball bearing 15 is not arranged parallel to 
the axis of rotation S of the disk 2, but at angle .alpha. thereto, the 
angle .alpha. being formed between the axis V which is at right angles to 
the direction of movement B, B' of the guide element 15 (relative to the 
guide wall 14) and the axis of rotation D of the guide element 15. 
Owing to the fact that the guide roller 15 is arranged at an angle to the 
wall 14, i.e. is at an angle to the direction of movement, a sliding 
motion is superimposed on the rolling motion of the roller 15, as a result 
of which a strip on the wall 14 beneath the roller 15, the width of which 
strip depends on the size of the angle .alpha. and the effective width of 
the peripheral surface, is cleared of particles of dirt and other matter. 
The strip ST in FIG. 3 is cleaned in the direction of movement B and 
direction of rotation A of the roller 15 and the particles are pushed 
upward, as shown in the drawing, i.e. are removed from the track of the 
roller 15. If the direction of movement in FIG. 3 is reversed, the 
particles are pushed to the other side, namely downward. In the embodiment 
described above, the surface of wall 14 is curved, but of course the 
invention is also applicable if the guide surface is plane, as shown in 
FIG. 4. 
Referring to FIG. 4, a carriage 3 for at least one magnetic head 18 is 
slidably mounted on a bearing support 23 via an anti-friction bearing 9 
which cooperates with a guide surface on the upper face of the carriage 3, 
and an antifriction bearing 21 which cooperates with an inclined guide 
surface 22. Of course, a pair of anti-friction bearings 9, 21 is also 
arranged symmetrically on the other side of the carriage 3 but, for 
simplicity's sake, has been omitted. 
The two antifriction bearings 9 and 21 illustrated in FIG. 4 are at an 
angle to axis Q which is at right angles to the direction of movement C of 
the carriage 3, the axis Q lying in a horizontal plane. The axis of 
rotation is again marked D, and the angle of inclination is again marked 
.alpha.. A cleaned strip ST is also shown. 
The angle .alpha. should be smaller than 90.degree. and is generally from 
about 1.degree. to about 80.degree.. It is advantageously from about 
1.degree. to 40.degree. and preferably from about 1.degree. to 10.degree.. 
A soiling experiment with dirt particles applied to the wall 14 has shown 
that the maximum positioning error of 70 .mu.m after 100 positioning 
cycles, measured directly after soiling, can be reduced by the positioning 
device according to the invention to values of from 0 to 10 .mu.m. In 
another experiment using a guide element 15 which was not inclined, the 
positioning error after 100 positioning cycles was not reduced. 
To intensify the cleaning action, the peripheral surface of the guide 
roller 15 is advantageously profiled. For example, we have found it 
advantageous to provide the guide roller with a plurality of grooves which 
run round its peripheral surface. 
It is more advantageous to arrange the grooves at an angle, preferably of 
45.degree., to the axis of rotation D. An additional cleaning effect may 
also be achieved by appropriate matching of the materials of construction. 
It may also be advantageous for the peripheral surface of the guide element 
to be convex. 
The positioning device of the present invention can be used with advantage 
in any type of recording/reproducing apparatus where, for head positioning 
purposes, a guide roller runs along a guide surface.