Abstract:
A bias-field device for a magneto-optical system having a magneto-optical recording element which includes a conductive substrate and which moves through a magnetic field created by the bias-field device so that information is selectively recorded on or erased from the recording element, the device comprises: a rotatable magnet that rotates so that when the recording element rotates the conductive substrate creates a magnetic coupling with the magnet for causing the magnet to rotate; and an escapement mechanism that releases and latches the magnet for permitting the magnet to be selectively rotated.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to the field of magneto-optic recording and erasing and, more particularly, to such recording and erasing utilizing a motorless bias-field device for selectively inverting a bias field for permitting such recording and erasure. 
     BACKGROUND OF THE INVENTION 
     In the magneto-optic recording process, a vertically magnetizable recording layer is initially sensitized by simultaneously subjecting it to a uniform magnetic field and a temperature which exceeds its Curie temperature. The magnetic field, being directed perpendicular to the recording layer, serves to uniformly align all of the magnetic domains therewith. Once all the magnetic domains are facing in the same direction, the recording layer is ready to record information. Such recording is effected by subjecting the recording layer to a magnetic field of reverse polarity while scanning the layer with an intensity-modulated laser beam. 
     During the recording process, a laser beam intensity is switched between high and low levels, representing the digital (binary) information being recorded. Only the high level is sufficiently intense to raise the temperature of the irradiated portion of the recording layer to above its Curie temperature; thus, digital information is recorded at the point of incidence of the laser as the more intensely irradiated magnetic domains flip in orientation to align themselves with the magnetic bias field. Playback of the recorded information is commonly achieved by scanning the information tracks with a plane-polarized beam of radiation and monitoring the reflected beam for shifts in the plane of polarization, as produced by the well known Kerr effect. To erase the recorded information, the polarity of the applied external magnetic field is reversed, and the recording layer is scanned with a beam of sufficient intensity to again heat the recording layer to above its Curie temperature. After this erasure step, all of the irradiated magnetic domains will again face in the same direction. 
     Various schemes have been proposed to achieve the magnetic field inversions required in switching between the record and erase modes of the magneto-optic recording process. In the disclosures of U.S. Pat. Nos. 5,020,042 and 5,291,345, for example, the field inversion apparatus consists of a magnetic field producing coil surrounding a cylindrical bipolar magnet. One pole of the magnet is placed adjacent the recording medium for inducing its particular magnetization to the recording medium, and when the coil is energized, the field that the coil creates imparts a torque to the magnet forcing it to rotate for causing the other pole of the magnet to be adjacent the recording medium. 
     Although the presently known and utilized device is satisfactory, it is not without drawbacks. The coils are not energy efficient because they consume a substantial amount of energy. 
     Consequently, a need exists in the construction and mode of operating the bias-field device. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, the invention resides in a bias-field device for a magneto-optical system having a magneto-optical recording element which includes a conductive substrate and which moves through a magnetic field created by the bias-field device so that information is selectively recorded on or erased from the recording element, the device comprising: (a) a rotatable magnet that rotates so that when the recording element rotates the conductive substrate creates a magnetic coupling with the magnet for causing said magnet to rotate; and (b) an escapement mechanism that releases and latches said magnet for permitting said magnet to be selectively rotated. 
     It is an object of the present invention to provide a bias-field device for overcoming the above-described drawbacks. 
     It is also an object of the present invention to provide an energy efficient and motorless bias field device. 
     It is an advantage of the present invention to provide a cost efficient bias-field device. 
     It is a further advantage of the present invention to provide a bi-directional bias-field device for selectively inverting the magnetic bias field. 
     These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a portion of the bias field device of the present invention in the presence of a conductive media substrate; 
     FIG. 2 is an exploded view of the bias-field device of the present invention illustrating its assembly; 
     FIG. 3 is a perspective view of the bias-field device of the present invention; and 
     FIG. 4 is a side view of the escapement mechanism of the bias-field device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, there is illustrated a magneto-optic recording element as shown in the form of a disk 10 which is adapted to be rotated about its central axis x. The essential features of the recording element are a vertically magnetizable recording layer 20 and a supporting substrate 30. The supporting substrate is made of a conductive material, preferably aluminum. During the recording step, the recording layer 20 is selectively heated by a beam of radiation, as provided by a laser source 35. The beam intensity is modulated by an information source (not shown) representing certain digital information which is to be recorded. The information source functions to switch the beam intensity of the laser source 35 between high and low levels, only the high level being sufficient to heat the recording layer 20 to at least its Curie temperature. A bias field device (only the magnet of which is shown in FIG. 1) includes a magnet 50 both having north and south poles oriented along their cross-sectional dimension, and is radially disposed with respect to the rotating disk 10 for providing a magnetic bias-field at recording layer 20. Although the preferred embodiment illustrates a magnet with one north and one south pole, the magnet may include a plurality of north and south poles. The magnet 50 is mounted for rotational movement, as will be described in detail below, so that the direction of the field under the desired location on the recording medium 10 may be switched from the downward direction in which one pole of magnet 50 (for example the north pole) is beneath the write/erase spot on recording layer 20 to an upward direction in which the magnet 50 is rotated so that south pole of magnet 50 is beneath the write/erase spot on recording layer 20. The reversal of poles of magnet 50 will cause magnetic domains in the recording element to flip orientations, e.g., from upward to downward, whenever the laser beam intensity is at its high level. In this manner, the digital information provided by the laser source 35 is magnetically recorded in the recording layer 20. 
     To erase the previously recorded information in the recording layer 20, the direction of the magnetic bias field is inverted. After such field inversion, the laser source 35 scans the recording element while its intensity is maintained at its high level. While so radiated, all of the magnetic domains align themselves with the bias field thereby providing a uniformly sensitized disk or track which is again ready to record information. 
     Referring to FIGS. 2 and 3, there are illustrated two views of the bias field device 60 of the present invention. The bias field device 60 includes a housing 70 having two retaining members 80 each having a hollowed-out interior portion 90 for partially enclosing the magnet 50. Each retaining member 80 includes two semi circular-shaped, hollowed out portions 100 that each respectively align with a corresponding hollowed out portion 100 on the other retaining member 80 which, when aligned together, form a bore through which two necks 110 of the magnet 50 respectively extend. The neck 110b includes a disk 120 having two lip portions 130 extending therefrom, which lip portions 130 interact with a escapement plate 140, as will be described in detail hereinbelow. The other neck 110a includes a ring 150 which matingly fits against the exterior portion of an end of the housing 70. 
     An escapement mechanism 160 includes the plate 140 having three prongs 170 positioned on its interior portion against which the lip portions 130 rest for inhibiting rotation of the magnet 50, as will be discussed in detail below. A solenoid 180 is attached to the plate 140 and includes a movable shaft 190 which is retracted when it is energized with direct current by a current source (not shown). A bracket 200 is attached to the shaft 190 at one of its ends and to the plate 140 at its other for providing structural attachment between the solenoid 180 and plate 140. Two deformable springs 210 are respectively attached to a side of the housing 70 at one of their ends and to the plate 140 at their other end. 
     The springs 210 are respectively attached to the housing 70 via two attachments devices 220. One attachment device 220a includes two support members 230 which are placed abutting each other, and each support member 230 includes two holes 240 therethrough which are respectively in alignment with the holes (240a and 240d; 240b and 240c) in the other support member and in alignment with two holes 250 in the spring. The spring 210a is placed against the housing 70, and with the two support members 230a and 230b disposed on the other side of the spring 210a, a screw 260 is inserted into each triplicate set of aligned holes (240a, 240d, 250b aligned together; 240b, 240c, and 250a aligned together) for attaching the spring 210a to the housing 70. The spring 210a further includes two holes 270 at its other end into which two screws are inserted therethrough and eventually into a pair of holes (not shown) in the plate 140 for attaching the bracket 200 to the plate 140. The bracket 200 also includes a hole 290 which is in registry with a pair of holes 300 (only one of which is shown) in the shaft 190, and a pin 305 is placed into the aligned holes 300 and 290 for attaching the bracket 200 to the shaft 190. 
     The other attachment device 220b also includes two support plates 310 between which the spring 210b rests and the plates 310 and spring 210 also include a triplicate set of aligned holes (320b, 340a, 320c; 320a, 340b and 320d)as in the other attachment device. With plate 310b resting against the housing 70, a screw 350 is inserted into each triplicate set of aligned holes for attaching the spring 210b on the housing 70. The spring 210b also includes two holes 360 which are respectively in alignment with two holes 370 in a support structure 380, and a screw 390 is inserted into each pair of aligned holes (360a and 370a; 360b and 370b) for permitting each screw 390 to be respectively placed in a pair of holes 400 in the plate 140 for attaching the spring 210b to the plate 140. 
     Referring to FIGS. 3 and 4, there is illustrated the operation of the escapement mechanism 160. For purposes of illustration, the disk 10 is rotating in the direction illustrated by the arrow which causes the conductive substrate 30 to induce a force on the magnet 50 as illustrated by the arrows. When rotation of the magnet 50 is not desired, the shaft 190 of the solenoid 180 is fully extended outwardly so that the prong 170a contacts the lip portion 130a thereby prohibiting rotation, as illustrated by the lip portion 130a in solid lines. When rotation of the magnet 50 is desired, the solenoid 180 is energized so that the shaft 190 is retracted for permitting the lip portion 130a to rotate, as illustrated by the dashed lines. The opposite lip portion 130b rotates until it contacts the prong 170b, as also illustrated by the dashed lines. This permits control of rotation of the magnet 50 so that approximately one hundred eighty degree rotation of the magnet 50 is permitted and so that multiple rotations of the magnet 50 are eliminated. The solenoid 180 is then de-energized so that the prongs 170 return to their original position. This permits the lip portion 130b to rotate until it contacts the prong 170a so that it is disposed in the original position of lip portion 130a, and lip portion 130a rotates to the original position of lip portion 130b. The hereinabove described process permits the opposite polarity pole of the magnet 50 to be adjacent the disk. This process is repeated when the original polarity of the magnet 50 pole is desired to be adjacent the disk 10. 
     It is instructive to note that, when the disk 10 rotates in the opposite direction, the induced rotation on the magnet 50 is in the opposite direction from that illustrated by the arrows. In this case, the lip portion 130b is prohibited from rotation by the prong 170a, and the one hundred eighty degree rotation of the magnet is permitted by retracting the shaft 180, as discussed hereinabove. It is readily apparent to those skilled in the art that the interaction of the prongs 170 and lip portions 130 are in a different configuration from rotation in the opposite direction for prohibiting, permitting and controlling rotation of the magnet 50. It is instructive to note that the disk 120 may be divided into two distinct disks for the purposes of achieving precisely one hundred eighty degree rotation. 
     The preferred embodiment has been illustrated utilizing a two pole magnet. As those skilled in the art will recognize, if a plurality of poles are utilized, the quantity of lip portions 130 would be correspondingly increased according to the number of poles, and the rotation between positions would be correspondingly less than one hundred eighty degrees. 
     The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. 
     Parts List 
     10 disk 
     20 recording layer 
     30 substrate 
     35 laser source 
     50 magnet 
     60 bias field device 
     70 housing 
     80 retaining members 
     90 interior portion 
     100 hollowed out portions 
     110 two necks 
     110a neck 
     110b neck 
     120 disk 
     130 lip portions 
     130a lip portion 
     130b lip portion 
     140 escapement plate 
     150 ring 
     160 escapement mechanism 
     170 prongs 
     170a prong 
     170b prong 
     180 solenoid 
     190 shaft 
     200 bracket 
     210 springs 
     210a spring 
     210b spring 
     220 attachment devices 
     220a attachment device 
     220b attachment device 
     230 support members 
     230a support members 
     Parts List (cont&#39;d) 
     230b support members 
     240 two holes 
     240a hole 
     240b holes 
     240c hole 
     240d hole 
     250 two holes 
     250a hole 
     250b hole 
     260 pin 
     270 two holes 
     280 screws 
     290 hole 
     300 pair of holes 
     305 pin 
     310 support plates 
     310b plate 
     320a hole 
     320b hole 
     320c hole 
     320d hole 
     340a hole 
     340b hole 
     350 screw 
     360 two holes 
     360a hole 
     36b hole 
     370 two holes 
     370a hole 
     370b hole 
     380 support structure 
     390 screw 
     400 pair of holes