Damper for constant load arm

A head mount faithfully follows flexible media perturbations. The head mount consists of a pivoted rigid head support arm controlled by an offset spring having an offset damping and yieldably urging relationship to the rigid arm. The rigid arm acts as a free beam. The arm is pivoted to a record support radially movable with respect to a record disk.

DESCRIPTION 
TECHNICAL FIELD 
This invention relates to head support assemblies for use with flexible 
disk files and the like and pertains more particularly to a head-arm 
assembly with particular damping means for providing enhanced response to 
media motion perturbations. 
A prime object of the present invention is to provide an enhanced head-arm 
assembly which faithfully follows perturbations of media motions for 
maintaining enhanced transducer to record medium relationships. 
Another object of the present invention is to provide a low cost head-arm 
assembly that still provides faithful following of record medium motion 
perturbations. 
BACKGROUND ART 
Prior art head-arm assemblies have included resilient spring support 
members which were biased to force a transducer into recording contact or 
to a recording proximity to a record storage medium. The resiliency of the 
support arm could result in vibrations of the arm that are transmitted to 
the transducer resulting in erratic motion of the transducer with respect 
to the record medium. In other support assemblies, damping material was 
pressed against an urging spring in a head support assembly. The spring 
would urge the head or transducer into a recording relationship with a 
record storage medium. In other head-arm assemblies, bifurcated springs 
were used to urge the head support arm assembly toward a record storage 
medium. Some of the assemblies did provide a sliding motion between a 
spring and another member for achieving diverse purposes. None of the 
prior art assemblies provided extremely high resonant frequency such that 
vibrations induced by a head-arm positioner or vibrations caused by the 
record medium did not result in undesired vibratory motions of the 
head-arm assembly. 
Apparatus incorporating the present invention includes a head arm assembly 
having a free elongated rigid beam pivoted to a support and that is 
yieldably urged and its pivoting damped by a laterally offset yieldable 
force. In a preferred construction the yieldable bore is from a leaf 
spring rubbing on an upstanding boss. The rubbing contact is preferably 
adjacent the pivot.

DISCLOSURE OF THE INVENTION 
Referring now particularly to the drawing, like numerals indicate like 
parts of the structural features in the three views. Other objects and 
advantages of the invention can be obtained from a reading of this 
disclosure and to the appended claims in which the novel features of the 
invention are more particularly set forth. 
A record storage disk 10 of the flexible media type rotates in the 
direction of arrow 11. Transducer assembly support carriage 12 is mounted 
on a frame 13 for radial motions with respect to disk 10. Carriage 12 is 
suitably controlled by a track servoing control system 14, as is known in 
the art. Carriage 12 supports a head-arm assembly 15 having a mounting 
portion at its free end to carry a transducer or head 16 in a 
predetermined transducing relationship to the flexible disk record storage 
medium 10. Head-arm assembly 15 is constructed such that transducer or 
head 16 faithfully follows the axial perturbations of flexible disk 10 as 
it rotates along a nominal plane. Not shown are recording and readback 
circuits which are usually electrically connected to transducer 16 for 
exchanging signals with flexible record disk 10. The signals so exchanged 
are preferably of the digital data type, but can be video, audio or any 
other form of electrical signals. Flexible disk 10 is preferably of the 
type that carries a magnetic recording coating; however, it can also be an 
optical disk or other types of recording. 
FIGS. 2 and 3 illustrate the detail of the inventive head-arm assembly. 
Head-arm assembly 15 is preferably supported directly on carriage 12. Base 
20 includes an outwardly projecting flange 21 to which a leaf hinge 22 is 
suitably attached. At the free end of leaf hinge 22, a rigid or hinged 
free beam head support arm (also termed beam) 23 extends outwardly for 
supporting transducer or head 16, as shown. A pair of recessed bolts 24 
secure transducer 16 to the free end of beam 23. Beam 23 has a open 
interior for weight reduction, as best seen in FIG. 3. 
At the inner-end of hinged free beam 23, shoulder 25 extends upwardly, as 
seen in FIGS. 2, 3, to support a preformed leaf spring 26. In accordance 
with the present invention, leaf spring 26 is disposed in a laterally 
offset relationship (out of the plane of beam or arm 23) as seen in FIG. 3 
with respect to beam 23, as best seen in FIG. 3, and extends toward 
carriage 20 for engaging boss 27 in a predetermined rubbing contact. As 
hereinafter more fully described this contact damps vibrations of head-arm 
assembly 15. As shown, preformed leaf spring 26 extends from arm or beam 
23 to base 20, no limitation thereto intended. Also, preformed spring 26 
may take diverse shapes. 
Preformed spring 26 not only provides damping in coaction with boss 27, but 
also resiliently urges free beam or arm 23 for forcing transducer 16 into 
a recording relationship with flexible record disk 10. It has been found 
that a most advantageous employment of the illustrated head-arm assembly 
is in a flexible disk file having a plurality of co-rotating axially 
separable flexible record disks. Such storage apparatus, as is known in 
the art, imposes severe dynamic requirements on any head-arm assembly 
particularly as to faithful following of axial media perturbations. 
In a preferred constructed embodiment of the invention, spring 26 
preferably should be performed in a shallow arc such that spring 26 is 
substantially flat when arm 23 is loaded with a desired force with respect 
to storage medium 10, i.e., for most effective damping, spring 26 should 
move along boss 27 in a rubbing contact while simultaneously yieldably 
urging arm 23 toward record storage disk 10. The resultant flat leaf 
spring 26 reduces bending moments induced by the damping force to enhance 
its operation as small axial displacements of transducer 16 results in 
rubbing contact damping-type motions of spring 26 along boss 27. 
On the other hand, the design of leaf hinge 22 is non-critical. It could be 
a pin bearing or any other form of articulation. In any event, any motion 
of head 16 should result in some minor lengthwise motion to leaf spring 
26. 
Operation of the illustrated embodiment can be further adjusted by 
controlling the interaction of leaf spring 26 with boss 27. If such 
interface is not lubricated, then the coaction results in a Coulomb 
damper. On the other hand, if the interface is lubricated, then it behaves 
as a viscous damper. From all of the above described coactions it is seen 
that arm 23 should act as a hinged free beam between head 16 and leaf 
spring 26 and leaf hinge 22. The term "lubricated" is used in the usual 
preferred dictionary sense. 
Several tests were conducted on the constructed embodiment for relating 
acceleration at head 16; i.e., the responsiveness of the head-arm assembly 
to enable head 16 to track the axial perturbations of record disk 10. The 
tests were conducted first without the coaction of spring 26 with boss 27 
(i.e., undamped) and with the assemblage 26, 27. In the table below, the 
figure on the right side of the slash mark is the undamped test result, 
while the figure on the left side of the slash mark is the result with 
spring 26 coacting with boss 27. Various disk radii were employed, each 
radius being expressed in millimeters from the axis of rotation. As it 
turned out, a frequency of 320 Hz was a critical resonant frequency. 
______________________________________ 
AN EXEMPLARY TEST 
Acceleration 
Disk Radius 
Acceleration at 320 Hz 
______________________________________ 
140 3.6/6.6 1.0/5.6 
110 2.1/4.6 0.5/1.6 
80 2.0/3.0 0.4/1.1 
______________________________________ 
To illustrate differences between leaf spring mounts and rigid or free beam 
mounts one should consider that a leaf spring in an assemblage similar to 
that shown in FIGS. 2 and 3 has a first resonance of 80 Hz, that is, if 
spring 26 uses its spring motion, it does not move on boss 27; hence, no 
damping action. Only when spring 26 slides, however slight, does laterally 
offset damping occur between spring 26 and boss 27. This extremely low 
resonant frequency will result in vibratory condition occuring in the 
head-arm assembly which is detrimental to the recording process. In 
contrast, a rigid or free beam had a first bending mode above 600 Hz. Then 
relating stiffness or rigidity to the square of the natural frequency, it 
can be said that the FIGS. 2 and 3 illustrated head arm is at least 50 to 
60 times more rigid than a leaf spring mount which was tested. Ideally one 
would like to have beam 23 infinitely rigid; however, because of the 
constraints of weight, material availability and geometry of the arm, 
particularly as applied to multiple flexible disk files, this ideal is not 
achieveable in practice. In a practical sense, one needs rigidity to 
extend resonance to above 400 Hz. 
The damping between members 26 and 27 is offset from the main line of the 
beam 23 thereby providing leverage action for enhancing the damping effect 
providing a more responsive and more stable head-arm assembly. 
One alternative damping control at 26, 27 includes placing a pair of 
friction pads on opposite sides of member 26 and applying pressure 
thereto, such as by a constant force pressure block. This example, shows 
that diverse arrangements readily come within the scope of the present 
invention. 
While we have illustrated and described the preferred embodiment of our 
invention, it is to be understood that we do not limit ourselves to the 
precise constructions herein disclosed or otherwise eluded to and the 
right is reserved to all changes, modifications coming within the true 
scope of our invention as defined in the intended claims.