Magnetic disc apparatus for maintaining an optimum humidity in a head disc assembly

#The present invention relates to magnetic disc apparatuses used for information memory, and particularly relates to a specific type of magnetic disc apparatus designed to maintain an optimum humidity in a head disc assembly.

#Conventionally, this type of magnetic disc apparatus generally utilizes a contact-start-stop (C.S.S.) drive. This drive is carried out such that a head for recording and reproducing information contacts a disc medium when it is stationary, and the head floats over the medium through an air film (air bearing) due to an air flow being generated during the rotation of the disc medium so as to effect recording and reproducing. In this drive, the head surface and the medium surface must be maintained flat precisely in order to improve the floating performance of the head and to avoid head clash.

#However, when the head disc assembly (hereinafter, H.D.A.) contains air having relatively high humidity, the head tends to cling (i.e., adhere) to the medium when the head surface is placed in contact with the medium surface. This phenomenon has been reported in Japan Lubrication Society, the 33rd Spring Research Conference Brief, 1989, Andou and Miyamoto, "Affect of humidity to frictional characteristic of magnetic disc and slider." For this reason, conventionally desiccant is disposed inside the H.D.A. to remove moisture within the H.D.A. to prevent clinging.

#FIG. 1 is a partial front sectional view showing one embodiment of the inventive H.D.A.;

#FIGS. 2A and 2B are graphs showing changes in temperature and humidity inside the H.D.A. during the course of operation thereof in terms of time;

#FIG. 3 is a graph showing the relation between the static friction coefficient and the relative humidity, measured when a disc medium comes in contact with a head;

#Hereinafter, an embodiment of the invention will be described in conjunction with the drawings. Referring to FIG. 1, a base plate 1 has a box shape provided with a breathing filter 7 having an orifice. The breathing filter effects exchange of air between the interior and the exterior of the base plate. An H.D.A. is disposed inside the base plate 1. A spindle 2 is provided to support a plurality of superposed magnetic discs 3 to rotate the same. An arm 4 is provided to hold a magnetic head 5 which is driven by a carriage 6 through the arm 4 to move over the magnetic discs 3 to effect recording and reproducing of information. A humidity adjustor case 8 is disposed in the common spacing which also contains the H.D.A., and contains a humidity adjustor 9. This humidity adjustor 9 operates to effect humidity control through an orifice 10 provided through the humidity adjustor case 8 and a filter 11.

#In this embodiment, the humidity adjustor 9 is composed of silica gel, which is provisionally treated to retain a given amount of water. This water-containing silica gel is utilized to maintain a constant relative humidity around the H.D.A. Namely, this water-containing silica gel works to establish equilibrium at a given relative humidity. Accordingly, this water-containing silica gel functions to absorb moisture to establish the equilibrium condition when the humidity rises over a certain degree, and functions to release the moisture when the ambient humidity falls down. This equilibrium condition is determined by the water content of the silica gel and the interior relative humidity. This water content of silica gel is determined by the ratio of a weight of water contained in silica gel and a weight of dried silica gel. Generally, in view of the relatively small volume of the H.D.A. interior and the water content of silica gel, the water amount contained in the silica gel is significantly greater than the water amount contained in the space of the H.D.A so as normally to maintain a constant humidity ambience.

#However, this ideal regulation is realized by the quick absorbing and releasing performance of the water-containing silica gel. Namely, this function must be effected instantly to substantially maintain a given relative humidity while abrupt temperature change occurs. Hereinafter, the term "response" is defined to refer to a time needed to absorb or release a differential amount of water to reach the equilibrium condition. Actually, the response depends on the inherent or specific feature of silica gel and the arrangement of the silica gel.