LINEAR ACTUATOR FOR ADJUSTING READING/WRITING HEADS OF TAPE STREAMERS

Abstract: The present invention resolves the problem of micropositioning reading/writing heads quickly and precisely in relation to tape on a tape streamers, at the same time as the reading/writing head can be displaced across the complete width of the tape. At the same time it will have small stray field of magnetism which potentially can destroy tape and reading/writing heads.

Description: LINEAR ACTUATOR FOR ADJUSTING READING/WRITING HEADS OF TAPE STREAMERS Field of the invention The object of the present invention is to provide an actuator solution for adjusting reading/writing heads of tape streamers. Such an actuator will position the active elements of the reading/writing head, so that they take the correct position when reading and writing. With an increasing track density there is a need for bringing forth an accurate servo track tailing since the distance between the tracks becomes smaller and smaller with in¬ creasing number of tracks. Due to economic reasons it is at the same time desired to have as few active elements as possible in the reading/writing head. An actuator for head positioning must therefore be able to fine position the reading/writing head controlled by servo signals from for example the tape, said actuator at the same time being able to displace the reading/writing head over the total width of the tape, so that all tracks can be read and written. Up till today these two requirements for displacing the reading/writing head of a tape drive have appropriately been attended to by using a plurality of actuators in combination, or a plurality of channels on the reading/writing head. The present invention succeeds in both fine adjustment of the head (track tailing) and displacement of the read- ing/writing head across the complete width of the tape with the same motor. An additional objective has been to reduce the radiation of magnetic field from the electro¬ magnetic motor, so that the tape or the reading/writing head should not be damaged or disturbed by the motor. Prior Art Linear motors or "voice coil motor" constitute a known principle and is used in connection with both actuators and loudspeakers. There are also known various variants including displaceable magnet. In the present application the motor proper of the actuator is in the form of draw¬ ings realized as a "voice coil motor". However, other types of electromagnetic motors can also be used, refer- ence being had to Norwegian Patent Application No. 95.3646, which is regarded as a part of the known tech¬ nology. Tape drives represent prior art technology. The read- ing/writing head belongs to known technology, and paral¬ lel guiding is per se a known principle for controlling a movement. Servo control of linear motor is regarded as prior art technology - and has been disclosed in a series of text books for tape drives and loudspeakers. There exist a plurality of various manners for making such servo systems. When a concrete variant has not been included in this patent application, this is due to the fact that it is not important for the invention as regards which one is chosen. Materials which are used in connection with the invention are per se prior art materials, i.e. iron, copper, neodym magnets, ceramics, Liquid Crystaline polymer-plastics and ruby bearings. The publications which were presented in a pre-examination in the Norwegian Patent Office in connection with NO 94.4103 are well known and regarded as not barring the present invention. This relates to EP 0 477 030 A1 to Iwamatsu/- Okuda from Sharp. It clearly appears from the drawing and schedule of the publication that the second order dynamic system is based on suspension of leaf springs. Even if these have been made very long, they will not be able to carry out the long and at the same time precise movement as in accordance with the present invention. Neither is GB 2034956 to Billy Richard Baker to be regarded as barring the present invention, since it the¬ refrom clearly appears that this is a drum head adjust¬ ment for video tape recorder. US 5 182 683 to Yasuo Misu- hashi from Mitsubishi Denki also relates to a drum ad¬ justment actuator based on leaf spring for suspending voice coil. This actuator has not the necessary flexi¬ bility to carry out the movement which is necessary, and is neither regarded as a bar. US 5 247 404 to Munehisa Takeda from Mitsubishi Denki is, due to the same reasons as above, regarded as representing a bar even if the arrangement of the magnets of the motor is of the same type as in the present invention. Features of the present invention differing from known technology The specific features of the present invention, which differ from similar and prior art actuators being used within the same or associated applications, are as fol¬ lows: The combination of an electromagnetic linear motor com¬ prising: * Parallel guiding rendering a specifically long and free movement, providing for both fast and accurate micro positioning on the individual track of the tape and displacement of the reading/writing head across the complete width of the tape, and all of this within one actuator. The present actuator is aimed for a 1/4" - 1/2" taper. * Double servo possibility by receiving the servo signals from pre-formatted tracks on the tape together with servo signals from positioning coil, so that these signals individually and in combina- tion can be used for controlling the actuator. * The application of novel and specifically stiff materials for avoiding undesired deflection in the suspension (Liquid Crystaline polymer and ceramics). * The solution including a linear motor which gene¬ rates very small stray field values for the magnetic field in the direction wherein the sensitive read- ing/writing head and the tape are present. * It is included in a first order regulating system. Disclosure of the invention Point by point. The present invention is a first order actuator system. In Fig. 1 the invention is characteristic in comprising a base iron serving as a carrier of the magnet system of the motor and anchoring to the tape drive. The arrange¬ ment comprises adjustment points in order to align Azi¬ muth and Zenith in relation to the tape. On the base iron according to Fig. 1 the magnet according to Fig. 2 will be arranged, thereafter the pole shoe, and thereafter the magnet, so that said magnets will have N-N or S-S against each other. Thereby the magnetic field will in all essen¬ tials be concentrated in the motor. In order to close the iron path for the magnetic field, the magnet housing according to Fig. 3 and the housing top will be placed on the Fig. 2 magnet. The coils illustrated in Fig. 5 com¬ prise motor coil(s) and in Fig. 13 there are illustrated positioning coil(s) which are assembled in the Fig. 4 arrangement and attached in coil holder/head mount with glue. The supply wires can pass through the gap illus¬ trated in Fig. 3, through the magnet housing, and attach¬ ment to coil holder/head mount is by means of glue. According to the present invention, the magnet system renders an embodiment including two symmetrically arranged magnets in a closed magnet system. The magnets are so arranged that 100% of the flux from the magnets is concentrated in the circular air gap in which the coil is to be displaced. This is done by mounting the magnets N-N or S-S. The closed design of the magnet system including a narrow gap opening facing away from the reading/writing head, see Fig. 6, will be to the fact that the distribution of the magnetic field to the reading/writing head will be very small, in the range of 2-5 Gauss which is illustrat- ed by the field lines in a simulated graph. When alter¬ nating current is supplied to the coil of Fig. 5, the latter will move in accordance with the direction of the current. The position can therefore be decided with the applied signal. The displaceable coil, see Fig. 5, or the plurality of coils as illustrated by the design, is or are attached to the coil carrier which at the same time is a support for the head, see Fig. 6. The coil is in its air gap guided, between Fig. 3 and Fig. 2, by a parallel guiding comprising linker arms as illustrated in Fig. 7. The linker arms are suspended in the iron base as illustrated in Fig. 1, and in the coil holder as illustrated in Fig. 4, by means of needles in each end, see Fig. 8 needles. These needles traverse the linker arms and are pressed into their bearings as illus¬ trated in Fig. 9. The needles must have a small diameter in order to provide a large friction force ratio. They are in the drawings designed as ruby clock bearings (pin bearings) , wherein the pins are kept in by means of leaf springs, see Fig. 10, plate springs. The stress on this leaf spring will determine the power which can be effected sideways on the head, see Fig. 6, without ob- taining "Azimuth" error, or an angular displacement in relation to the direction of movement on the tape. The ruby bearings, see Fig. 9, are attached by means of glue and are adjusted to the correct position by mounting linker arms, see Fig. 7. Thereby said elements will be self-adjusting during the mounting. Alternatively, this parallel guiding (Fig. 7, linker arms) could be designed as a blade bearing, see Fig. 11 or Fig. 12, with linker arms in ceramics and a spring, see Fig. 11, in between to keep the same together. This will also provide a very stable guiding including small friction. The linker arms must in all embodiments (Fig. 7, Fig. 11, Fig. 12) be sturdy and light (Fig. 11 and Fig. 12 illus¬ trating principles for blade bearing linker arm) . The linker arms can be manufactured from bent steel, ceramics or press moulded light metal. Possibly, also a very sturdy reinforced plastics, for example PPS or Liquid Crystaline polymer including carbon, may be used. The manner in which the parallel guiding is designed will render thereto a small offset perpendicularly to the tape surface. With a 23 mm bearing spacing this will in the present design render approximately 0,2 mm offset includ¬ ing 8 mm total displacement length. This is allowed for in the motor and the efficiency will be effected only insignificantly. Here, one can enjoy the symmetrical design including two magnets, see Fig. 2 , rendering in its outspring a stronger motor than conventional voice coil motors. This offset can be reduced with longer linker arms. By design- ing the system with two motor coils, see Fig. 5, this will render the possibility of driving the motors longer or control each coil so as to divide the current between said two coils. Aside from the motor coils, see Fig. 5, the system com¬ prises one or more sensor coils, see Fig. 13, which reg¬ ister position. Said coils move in and out of a ferrite, see Fig. 14, which is attached to a plastics rod, still see Fig. 14, in the iron base according to Fig. 1. There¬ by the variation in inductance can be utilized as a posi¬ tion indicator and render the possibility for servo oper¬ ation. This combination including its own positioning system on the motor opens up for the possibility of driv¬ ing double servo. Both servo including feedback informa¬ tion from the tape (medium) and feedback information from said two sensor coils, see Fig. 13, on the actuator. Depending on the track width of the tape, it will then be possible to go from micropositioning (track tailing) on one track at the lower edge of the tape, to a new track at the upper edge of the tape, directly, by utilizing the actuator sensor as an absolute indicator. This sensor system must then firstly be calibrated, which can be put in as a routine in each individual tape drive. The accuracy needs not to be built into the mechanical construction of the sensor system of the actuator. The actuator sensor (Fig. 13 and Fig. 14) can also be utiliz¬ ed as a lock for the actuator when the current to the coils, see Fig. 5, is on. The complete actuator must be set with its correct angles in relation to the tape (Azi- muth - longitudinally of the tape, and Zenith - transversely of the tape). This can be done by having an affixing screw at the bottom of the actuator (into the iron base, see Fig. 1 ) which is spring loaded, and having three supporting points including adjustment screws going up towards defined points on the bottom side of the iron base, see Fig. 1. Figures 15, 16 and 17 illustrate the assembled actuator in an isoview, top view and side view, respectively. Fig. 18 illustrates a section through the assembled actuator taken in the longitudinal direction. Figures 19 and 20 illustrate the simulation of the stray field from the 8 motor comprising double magnets. Specific description of the actuator The present actuator meets the requirements for following pre-formatted tracks on the tape combined with movement in transverse direction of the complete tape, by the present embodiment of the invention. With small varia¬ tions the same concept may be realized by using small variants of material or arrangements of linker arms, or in motor type selection. This specific variant is specifically characteristic in the design of the parallel guiding (linker arms) compris- ing ruby bearings, and by the motor selection including two magnets and two coils. Variations Within the same structural design the following different variations can be contemplated in a first order system. a) Comprising movable coil(s) as illustrated in the drawings. b) Comprising movable magnet, round with radial magnet¬ izing or flat magnet with axial magnetizing. c) Comprising a) or b) and parallel guiding comprising ruby pin bearing. d) Comprising a) or b) and parallel guiding comprising blade bearing of ceramics or some other specifically stiff and wear resistant material.

Claims: P a t e n t c l a i m s 1. Arrangement in a linear motor for reading/writing heads, c h a r a c t e r i z e d i n both micropositioning and long displacement transversely of the tape with one and same motor. 2. Arrangement as claimed in claim 1 , c h a r a c t e r i z e d i n positioning coils on ferrite for reading the position of the motor and thereby enabling driving of double servo based on information both from positioning coil and from pre-formatted track on the tape. 3. Arrangement as claimed in claim 1 or 2, c h a r a c t e r i z e d i n specifically precise parallel guiding of displaceable coil or displaceable magnet provided as ruby bearing needle pin or blade bear- ing. 4. Arrangement as claimed in claims 1-3, c h a r a c t e r i z e d i n that the motor is com¬ pletely closed with only a narrow gap for taking out the displacement. Thereby the arrangement renders a specifi¬ cally favourable screening of the magnetic tape and heads when this gap is facing away from the latters. The gap does not introduce a mentionable reduction of the motor power (short circuiting of the magnetic field or simi- lar).

Inventors: LIAN RAGNAR, RUDI GUTTORM, SIMONSEN LARS, LIAN, RAGNAR, RUDI, GUTTORM, SIMONSEN, LARS
Applicants: LIAN RAGNAR, RUDI GUTTORM, SIMONSEN LARS, TANDBERG DATA STORAGE AS, LIAN, RAGNAR, RUDI, GUTTORM, SIMONSEN, LARS, TANDBERG DATA STORAGE A/S
Application year: 1995
Main classification: G11B5
IPC codes: G11B5, G11B15