Flexible band positioning device for a read/write head

A flexible band positioning device arranged to convert rotaty motion of an outout drum of a stepper motor to linear motion of a carriage supporting a read/write head. A flexible band is attached to the drum and is at least partially wrapped around it. The end portions of the band are each guided around a different idler roller and are attached to a support frame. The idler rollers are rotatably mounted on the carriage and upon wrapping and unwrapping of the band around the drum, caused by rotary movement of the drum, move the carriage linearly.

DESCRIPTION 
TECHNICAL FIELD 
This invention relates to mechanisms for converting rotary motion into 
linear motion and more particularly, to a flexible band device for 
converting rotary motion of a drum driven by a stepper motor into linear 
motion of a read/write head. 
BACKGROUND ART 
Flexible band devices for converting rotary motion of a drum or a roller 
into linear motion are well known and are disclosed, for example, in U.S. 
Pat. No. 3,167,962 issued to D. P. Scotto and U.S. Pat. No. 3,488,098 
issued to B. J. Sobczak. 
Furthermore, a flexible band device has been incorporated into a magnetic 
head positioning mechanism as disclosed in U.S. Pat. No. 4,170,146 issued 
to W. M. Owens. Therein, angular movement of a stepper motor output drum 
is converted to linear motion of a carriage which carries a magnetic head 
along a diameter of a flexible record disk known in the trade as a "floppy 
disk". The disclosed mechanism has a stainless steel flexible band wrapped 
around the output drum of the stepper motor with the ends of the band 
coming off the drum tangentially and aligned with each other. One end of 
the band has a slot in it through which the other end passes. The ends of 
the band are attached to the carriage carrying the magnetic head and 
thereby angular movements of the drum are transmitted to the carriage as 
linear motion. 
The standard floppy disk, which may be a disk of plastic coated with 
iron-oxide, has a track density of 48 tracks per inch on a recording area 
approximately 0.729 inches wide. The flexible band-drum connection, 
because of its construction, limits the drum to one partial revolution of 
approximately 320 degrees. Within this partial revolution, the drum must 
move the read/write head across the width of the recording area. 
Commercially available floppy disk drives utilizing flexible band position 
devices for positioning of read/write heads over a recording area usually 
employ a stepper motor having a step angle of 3.6 degrees and an output 
drum having a circumference of approximately 2 inches and a diameter of 
0.66 inches. While such a positioning device provides positioning of the 
head with the required accuracy, one of its drawbacks is that it is costly 
because the stepper motor with a 3.6 degree step angle is a relatively 
expensive item. 
Attempts have been made to reduce the cost of flexible band positioning 
devices by incorporating a less expensive stepper motor. For example, a 
sheet metal stepper motor which costs approximately two and a half times 
less than a conventional stepper motor is commercially available and has 
been considered for use in the flexible band positioning device. The 
problem however, with the use of a sheet metal stepper motor is that it is 
not available with a step angle of less than 7.5 degrees. Thus, use of a 
stepper motor with a 7.5 degree step angle requires an output drum with a 
circumference of approximately 1 inch and a diameter of 0.33 inches. 
Wrapping and unwrapping of the metal band around the drum with such a 
small diameter will introduce stresses in the material which could cause 
fatigue failure and thus destroy the positioning device. 
DISCLOSURE OF THE INVENTION 
In accordance with the present invention, I provide a flexible band 
positioning device wherein each end of the flexible band wrapped around an 
output drum of a stepper motor passes around a different idler roller, 
rotatably mounted on a carriage for moving a read/write head. The two 
idler rollers permit a two to one reduction in the linear step of the 
carriage.

DETAILED DESCRIPTION 
FIG. 1 shows a partial view of a disk drive unit 10 incorporating a 
flexible band positioning device 11. The positioning device 11 converts 
angular motion of an output drum 16 of a stepper motor 12 into linear 
motion of a carriage 13 which supports a read/write head 14. The stepper 
motor 12 is securely fastened to a disk drive support frame 15 and has an 
output shaft 30 upon which the drum 16 is mounted. The carriage 13 is 
movably mounted on guide rods 17 and 18 which are fastened to frame 15. 
The carriage 13 and its guide rods 17 and 18 are positioned in such a way 
that the carriage 13 moves in a line along the diameter of a recording 
disk (not shown) which may be a plastic disk covered with iron-oxide. The 
movement of the read/write head 14, which may be magnetic, allows it to 
selectively access the areas of the recording disk which are designated 
for storage of information. 
The carriage 13 is positioned in response to signals supplied to the 
stepper motor 12 by a control unit (not shown) of the disk drive unit 10. 
The control unit may be in a form of a digital computer. The stepper motor 
12 in response to the received signals from the control unit rotates the 
output shaft 30 and thus the drum 16 through a predetermined angular 
displacement. The angular displacement of the drum 16 is converted into a 
linear displacement of the carriage 13 by the flexible band device 11 
which includes a thin flexible band 19 which may be made of stainless 
steel and with a typical thickness of 0.002 inches. The flexible band 19 
may be attached to drum 16 by a bar 23 and two flat head screws 24. The 
drum 16 may also be made of stainless steel and, for example, could have a 
diameter of 0.66 inches with a circumference of 2 inches. 
FIG. 2 illustrates construction of flexible band 19 and its attachment to 
drum 16. One end 20 of the flexible band 19 has a slot 21 through which 
the other end 22 of the flexible band 19, which end is narrower than the 
width of the slot 21, passes. The flexible band 19 is wrapped, at least 
partially, around the drum 16 and the two ends of the bands 20 and 22 are 
brought off the drum tangentially so that they lie substantially in the 
same plane parallel to the path of travel of the carriage 13 and are 180 
degrees apart. After coming off the drum 16, the end 20 of the flexible 
band 19 is then passed around an idler roller 25. The idler roller 25 is 
rotatably mounted on a shaft 26 affixed to the carriage 13 and has an axis 
of rotation parallel to the axis of rotation of the drum 16. The end 22 of 
the flexible band 19 is passed around an idler roller 27. The idler roller 
27 is rotatably mounted on a shaft 28 affixed to carriage 13 and has an 
axis of rotation parallel to the axis of rotation of the drum 16. Idler 
rollers 25 and 27 may be made of stainless steel and may have diameters 
less than, equal to, or greater than the diameter of the drum 16. Each end 
20 and 22 of the band 19, after passing around idler rollers 25 and 27 
respectively, is attached to support frame 15 so that each end lies in a 
plane which is substantially parallel to the plane containing the portions 
of the flexible band 19 coming off the drum 16. The ends 20 and 22 of band 
19 may be attached to frame 15 with flat head screws 21. 
As pointed out before, control signals received by the stepper motor 12 are 
converted into angular displacement of the drum 16 which causes one end of 
the band 19 to unwrap from the drum 16 while the other end wraps around 
the drum 16 with corresponding linear movement being imparted to the 
carriage 13. FIGS. 3a and 3b illustrate angular movements of drum 16 and 
corresponding linear movements of the carriage 13.