FR2546014A1 - Multitrack magnetic head, method of manufacturing the said head and system using the latter - Google Patents

Abstract

The invention relates to a multitrack magnetic head for recording point-wise on a magnetic medium. According to the invention, it includes a first 31 and a second 32 row of air gaps, the air gaps E1, E3 ... E2n+1 in one row 31 being aligned but laterally offset with respect to those E2 ... E2n of the other row 32, so that in the direction of travel of the recording medium, each recording track corresponding to an air gap E5 of the first row 31 is arranged between two tracks corresponding to two successive air gaps E4, E6 of the second row 32 and vice versa, the distance between the first 31 and the second 32 rows being equal to n times the distance between two successive rows of points recorded on the magnetic medium with n an integer greater than or equal to 1.

Description

MULTI-PISTON MAGNETIC HEAD, PROCESS
MANUFACTURING OF SAID HEAD AND SYSTEM
USING THE SAME
The present invention relates to a multitrack magnetic head for spot recording on a magnetic medium.

 It is known to perform a reproduction of information by recording point by point on a magnetic drum using a suitable magnetic head which successively records each point of a line by translation parallel to the generatrix drum. Such systems can be used for example in the transmission of documents by facsimile, or facsimile. The magnetic image thus created is then developed using a magnetic development powder called "toner", the image thus developed being then transferred by pressure or under the action of an external field on the copy medium prior to fixation in a furnace.I Such a recording system is particularly slow to implement and requires a precise mechanical system of translation of the head parallel to the generatrices of the drum and tangentially thereto.

 To solve this problem, the Applicant proposes to use a multi-track magnetic head, that is to say having as many magnetic heads as tracks to be recorded on a line of the magnetic recording medium. Since the size of the points randomly recorded in facsimile is of the order of 100 microns per 100 microns, it is conceivable that it is particularly difficult to produce magnetic heads having air gaps of this length and arranged side by side. In practice, however, it is found that the technology usually used to produce magnetic heads is not applicable in this case, given the small size of the points on the one hand and their short distance, on the other hand, the order of 100 microns as well.

 The magnetic head according to the invention provides a simple solution to this problem. For this purpose, it is characterized in that it comprises first and second rows of air gaps, the air gaps in a row being aligned, but laterally offset from those of the other row, so that, in the direction of travel of the recording medium, each recording track corresponding to a gap of the first row is arranged between two tracks corresponding to two successive gaps of the second row and vice versa, the distance between the first and second rows being equal to n times the distance between two successive rows of points recorded on the magnetic medium, with n integer greater than or equal to 1.

 Preferably, the distance between said rows of air gaps will be equal to n times the distance between the axes of the gaps of two successive recording lines.

The invention also relates to a method for manufacturing a magnetic head, in which process:
a) vertically grooving a parallelepiped block of non-magnetic material, said grooves of width 1 being arranged in two rows on either side of an axis parallel to one of the sides of the parallelepiped, each groove being spaced from each groove neighbor in the same row by a distance P, while the two rows are shifted relative to each other along said axis by a distance P / 2,
b) vertically grooving two parallelepipedal blocks of magnetic material on one of their opposite faces, grooves spaced apart by a pitch P, of width 1 and of identical depth, with the clearance, to that of the grooves of the non-magnetic block,
c) assembling the non-magnetic block and the magnetic blocks so as to mesh the grooves and obtain a new parallelepiped block which is rectified on its two opposite faces parallel to the plane of the grooves 1 to obtain a block of dimensions substantially identical to those of the non-block; magnetic before grooving, but having grooves filled with magnetic material,
d) forming a U-shaped groove on each face of said block parallel to the plane of the vertical grooves, so as to obtain a block whose section in a vertical plane perpendicular to the plane of the vertical grooves has the shape of an I,
e) rectify parallel to the plane of said grooves the upper branch of I, on both sides, to a thickness corresponding to that of the desired air gap of the head,
f) forming two side pieces, symmetrical to each other, comprising a parallelepiped plate of non-magnetic material, U-grooved on one of its faces, a groove in which a ferrite plate is introduced so as to form a parallelepipedal block of height and length substantially identical to those of the block obtained at the end of step d, then vertical grooves are made on one side of each side piece, on the side of the ferrite plate, perpendicular to the groove in U, each groove being of width 1, and of sufficient depth to eliminate the ferrite, the distribution pitch of said grooves being equal to P,
g) is assembled, groove against groove, the block from step e above and the blocks from step f above, the grooves of I and those of the two side pieces being substantially the same height and put face to face, so as to form a succession of magnetic circuits parallel to each other, arranged in two rows, in line with the non-magnetic central edge, the air gaps of the elementary magnetic heads thus formed being aligned in the same row ,
h) the reading face of the head is read in a manner known per se so as to reveal the ferrite on either side of each air gap.

 Preferably, the write windings of the head will be introduced into the grooves of the blocks obtained in step f above before assembly of the head.

 According to a preferred embodiment, the groove made in step d will be of depth (g) equal to that of the air gap, but of such height that the upper part of the non-grooved face comes to rest, as well as its lower part, against the upper parts, respectively lower, teeth located between the grooves of the side pieces, so as to create a depth spacing e between the corresponding magnetic portions of the piece from step e and that resulting from the step f, thereby creating an air gap of predetermined thickness.

 Also preferably, a curable resin will be injected into the openings of the head resulting from the juxtaposition of the grooves as well as in the air gap zones, this resin injection being performed more advantageously before rectification of the active face of the head. .

 The invention also relates to a magnetic reprographic system using a head as described above, in which system magnetic information is recorded using said head on a mobile magnetic medium, said system comprising means for advancing said support step by step, the distance between the rows of air gaps of the head being equal to n not, with n integer greater than or equal to 1, said system further comprising a memory provided with at least n + 1 memory lines, each memory line comprising at least as many cells as the total number of air gaps of said head, and a clock controlling the advance of one step of the magnetic medium, the advance of a memory line in the next line and allowing recording a new first line, said clock further allowing reading, for example even rank memory cells of the first memory line and odd rank of the last memory line which are transmitted to corresponding gaps of said head.

The invention will be better understood with the aid of the following exemplary embodiments, given in a non-limiting manner, together with the figures which represent:
- Figures 1 to 11: the various steps of producing a head according to the invention;
- Figure 12: a preferred embodiment of the head according to the invention;
- Figure 13, a partial record obtained with the head according to the invention;
- Figure 14, a block diagram of a magnetic reprographic system using a head according to the invention.

 On a ceramic substrate 1 of parallelepiped shape (Figure 1) previously rectified and set to the sides, are made a series of grooves 2 on. the two opposite parallel faces of this substrate. These grooves are arranged vertically in the figure. The pitch, that is to say the distance between two successive grooves in the same row is equal to P, identical on both sides but offset by a half step. Each groove with a width 1 equal, with the clearance, to P / 2, the depth of each groove is equal to hl while the central portion of the blocks is of width hz, the central portion on either side of which are distributed , on the other hand, the teeth of ceramic material remaining between the grooves, teeth such as D1, D3, etc.

D2n + 1 on the right of the central part and D2, etc ... D2n + 2 on the left.

 In a ferrite material, preferably in an iron-manganese-zinc or iron-nickel-zinc composition well known to those skilled in the art for the production of magnetic heads, two parallelepipedal plates 3 (FIG. 2) are produced in which are performed grooves of pitch P, the width L of the teeth thus obtained being less than the width 1 of the grooves made in the ceramic substrate 2 to allow insertion into each other: L and I are of the same value, with the clearance. These two parallelepipedic plates 3 are symmetrical rune of the other and their grooves are offset by P / 2 with respect to each other.

 The parts thus prepared are assembled by gluing on the ceramic substrate shown in FIG. 1b, so that the rite teeth 4 are engaged in the grooves 2. An epoxy type glue, mono or bi-component or a cyan acrylate type glue is perfect for this assembly.

 The block thus obtained is then subjected to plane grinding on each of its large lateral faces in order to eliminate the ferrite soles and leave only the small bars 5 placed at the bottom of the grooves 2 (FIGS. ). FIG. 4 thus gives a block of ceramic (more generally of non-magnetic material having pointed grooves as shown in FIG. 1b, each groove being filled with a magnetic material, said block having a width d2 identical to that from the initial block of Figure 1.

FIG. 5 shows the block of FIG. 4 which has been grooved in a horizontal plane, on each of the large faces, grooving having a C-shaped section, of height h3 and depth h7, of such so that the block thus formed has an I-shaped section. On the upper part 20, 21 of the part shown in FIG. 5, above each C-shaped groove, a flat grinding is carried out so as to eliminate of the material on the end of the upper branch of the I, this elimination of material being done on a depth g with respect to the corresponding lower face of the I, this difference in thickness
ffi defining the width of the gap as will be seen later. The dimension of the upper branch of I is d2 - 2 6 (Figure 6).

 Then, in FIGS. 7 to 9, two symmetrical lateral pieces are produced (only the left piece in the figures is shown, the right piece being symmetrical and with grooves offset by half a step with respect to that # i). Each side piece is composed of a ceramic substrate 7 of the same external dimensions as those of the part of FIG. 1, except the width d5, which may be different. In this ceramic substrate, is produced a groove 8 of depth e and height d4, in which is placed a parallelepipedal ferrite plate 9 of the same dimensions with play.

 After the establishment of this plate 9, a grooving 10 is performed along the entire length of the composite part, grooving of C section of height d7 less than d4 and dc depth d6 less than e. The piece thus obtained comprises a top portion of thickness d8 of non-magnetic ceramic material. A groove of pitch P is then identical to the pitch of the preceding grooves so as to produce in the piece teeth of width 1 identical to that made on the pieces 3. The groove depth d is greater than the thickness e of the groove. plate 9, so as to define again small magnetic circuits C-shaped, substantially symmetrical with those previously made on the part 1, and magnetically independent of each other.However, in practice, the depth d6 is greater than the depth h7 of the corresponding groove of the center piece.

The length of the parts 12 is made in such a way that the teeth of these coincide perfectly with those of the part 13 (FIG. 6), taking into account the fact that there is a shift of half a step between the two faces. On the parts 12, left and right, are put in place the windings such as 14 of each of the elementary heads. This is usually composed of a few turns of insulated wire and these are immobilized by gluing. After placing parts 12 with their coil on the central portion 1, the assembly is secured by introducing a resin, such as an epoxy resin, into the two openings 15. This resin also fills the areas of air gap 16 (Figure 10). Then proceeds to a final cylindrical grinding operation according to the curve 17, to remove the nonmagnetic ceramic parts 18 existing at the top of the side pieces 12. This cylindrical grinding also allows to obtain the form and the quality of the surface condition necessary to ensure that the magnetic head has excellent contact with the magnetic strip to be treated. The obtained head is shown schematically in Figure 11, figure on which we see the two rows 31 and 32 of air gaps, each gap being surrounded by magnetic ferrite parts. In the figure, the even-numbered gaps, such as E2,
E4, e6, etc ... E2n are located on the row 32, while the gaps of odd rank E1, E3, etc ... E2n + 1 are located on the row 31. Each elementary magnetic head has a gap of width I and is separated from the next head by a non-magnetic ceramic portion of width 1 also, the distance between the axes of the two gaps being equal to the pitch P. The distance between the two rows 31 and 32 is equal to n times 1 .

 With such an embodiment method, it has been possible to make multi-track magnetic heads whose distribution density was 8 tracks per millimeter, that is to say 4 heads or air gaps per millimeter in a row.

 In Figure 12, there is shown a preferred embodiment of itinvention. In this variant, the depth h7 of the U-shaped groove formed on the central block (FIG. 5) is equal to E, the value of the desired gap. The height h3 of this groove (FIG. 12a) is, unlike that of the groove of FIG. 5, of such height that the upper part 20 or 21 of the central piece 13 of I-shaped section comes to bear against the part 22 of height d8 (Figure 8), ceramic part located above the magnetic part. It is thus found that ron created simply by application of the two corresponding parts Pune against the other, an air gap 23 of width e perfectly calibrated. This method offers the advantage of providing a very stable support, thus an excellent closure of the magnetic circuits between the elements of parts 12 and 13. The cylindrical grinding operation along the line 17 here also serves to simultaneously ensure a good surface and clearance of the air gap areas.

Figure 13 shows a schematic view of a record obtained with a head according to the invention. We have successively represented the points recorded by the magnetic heads Ii + #, I # and li 1 1 of the first row and the heads Ji and I 1 of the
I. i ii second row. On the ordinate, the corresponding lines 1j, 12, 13, 14, 15 have been identified. In the present case, a distance between the two rows of heads equal to 4 times the width of the gap has been chosen. By means of the head li + for example, the points (circled in the figure) corresponding to the lines 11, 12, 13, 14 are successively recorded in advance by one step. + 1 records the point corresponding to the line 15 (surrounded by a rectangle), the head Ji records the point corresponding to the line 11 located between the recordings, on this line2 of the heads li + 1 and
Figure 14 schematically shows a view of a magnetic recording system according to the invention. In the case of a recording as shown in Figure 13, there is schematized a system for synchronizing and rewriting information on the magnetic medium (not shown in the figure). The 2m + 1 information of a line to be recorded on the magnetic medium are entered in series in the memory M1. Under the action of the clock signal, the information of the even memory cells are read and sent in parallel on the air gaps E2, E4, etc. E 2n of the row T2m via lines L2m. The next clock pulse enables the information of the memory M1 to be shifted into the memory M2, then the introduction of a new line of information in the memory M1 as well as a displacement of a magnetic support pitch (or possibly the magnetic head TM) under the action of the moving means MD synchronized by the clock. The preceding cycle is repeated with each set of clock pulses, until the information initially present in the memory M1 arrive by successive shift in the memory M5, in which only the information of odd rank is taken and sent via the line L2m + i to the gaps E1, E3, etc ... E2n + 1, of odd rank, of the row
T2m + 1 of the magnetic head TM.This information is sent, for example, by the same clock pulse that commanding the sending of the information of M1 in T2m airframe The unfolding operations are thus carried out until the end of the reception of an information line in the memory M1, prolonged by a number of clock pulses sufficient to obtain the transfer of said information in the memory M5. corresponding advance of the magnetic medium and the writing of odd-rank information on the medium. After registration, the information thus recorded by dot, line by line, will be developed in a manner known per se using a single-component magnetic toner. The order in which the different operations are executed is given here only as an indication. Other ways of proceeding can be exploited to obtain the same final configuration. Another embodiment consists in serially inserting the information of a line in a buffer memory, this information being recorded upon receipt. They are then transmitted line by line in a "write" memory whose even address cells are connected to the individual heads of even addresses (T2m), and the odd address cells to the individual address heads. odd (T2m + 1) - The organization of the information in each line to print then takes into account the shifts between the rows. In the writing memory, to use the example given above, we will have, for example, in the even cells, the even information of a line to be written, and in the odd cells, the odd information corresponding to five preceding lines (if the distance between the two rows of air gaps is equal to four times the pitch between two adjacent tracks ). This simplifies the control electronics of the head. Of course, the information from the "write" memory is transferred to the head, either in parallel or in serial or serial parallel with multiplexing. Other variants will be imagined without difficulty by the skilled person.

 By way of example, an assembly of the type described above of 1728 elementary magnetic heads has been realized for an A4 format printing equipment.

Claims (9)

 I. Multi-track magnetic head for recording by points on a magnetic medium, characterized in that it comprises a first (31) and a second (32) row of gaps, the air gaps (E1, E3, .. E2m + 1) in a row (31) being aligned but laterally offset from those (E2, ... E2n) of the other row (32), so that in the running direction of the support of recording, each recording track corresponding to an air gap tE5) of the first row (31) is arranged between two tracks corresponding to two successive air gaps (E4, E6) of the second row (32) and vice Y.ersa, the distance between the first (31) and the second (32) rows being equal to n times the distance between two successive rows of points recorded on the magnetic medium with n integer greater than or equal to 1.  2. Magnetic head according to claim 1, characterized in that the distance between the rows (31, 32) is equal to n times the distance between the axes of the air gaps (E4, E5) of two successive recorded lines.  3. Magnetic head according to claim 1 or 2, characterized in that it comprises a central portion (13) non-magnetic axially having non-magnetic teeth distributed on either side thereof, each head elementary magnetic element of a row being secured to a tooth.  4. A method of manufacturing a multi-track magnetic head, characterized in that:  a) vertically grooving a parallelepiped block (1) of non-magnetic material, said grooves (2) of width I being arranged in two rows (D1, ... Dn + 1 and D2, ... D2n + 2) from and other an axis parallel to one of the sides of the parallelepiped (11), each groove (2) being spaced from each groove (2) neighbor in the same row by a distance P, while the two rows are offset relative to one another along said axis by one P / 2 ;;  b) vertically grooving two parallelepiped blocks (3)  magnetic materials on only one of their opposite faces, grooves (4) spaced apart by a pitch P, of width 1 and of identical depth, with the clearance, to that of the grooves (2) of the non-magnetic block;  c) assembling the non-magnetic block (1) and the magnetic blocks (3) so as to mesh the grooves (2, 4) and obtain a  a new parallelepipedal block which is ground on the two opposite faces parallel to the plane of the grooves (2, b) so as to obtain a block of dimensions (d1) d2, d31 which are identical to those of the non-magnetic block (1) before grooving, but having grooves (5) filled with magnetic material;  d) a groove (6) of U-section is formed on each face of said block, parallel to the plane defined by the vertical grooves (5), so as to obtain a block whose section in a vertical plane perpendicular to the plane of the vertical grooves <5) has the shape of an l;  e) rectify, parallel to the plane of said grooves (5) the upper branch of the I, on both sides, to a thickness (e> corresponding to that of the desired gap of the head ;;  f) forming two rune symmetrical side pieces of the other comprising a parallelepiped plate (7) of non  magnetic, U-grooved on one of its faces, in which a ferrite plate (9) is introduced so as to form a parallelepipedal block of height (dI) and length (d3) substantially identical to those of the block obtained at the end of step d, then the grooves are made on one side of each side piece, from the side  of the ferrite plate, perpendicular to the U-shaped groove, each groove being of width 1 and of sufficient depth to remove the ferrite, the pitch of the grooves being equal to P ;;  g) assembling, grooves against grooves, the block resulting from step e above and the blocks from step f above, the grooves  said blocks being of substantially the same height (d5) and facing each other  face to form a succession of magnetic circuits parallel to each other arranged in two rows on the cob with respect to the central non-magnetic edge, the air gaps of the magnetic heads thus formed being aligned in the same row;  h) rectify, in known manner, the reading face of the head so as to reveal ferrite on either side of each gap (E1, E2n +  5.Procédé according to claim 4, characterized in that the write coils (14) are introduced into the grooves of the blocks obtained in step f, before assembly of the head.  6. Method according to one of claims 4 or 5, characterized in that the groove (6) formed in step d is of depth () equal to that of the air gap but of such height that the upper part (20, 21 ) of said non-grooved face comes to bear, as well as its lower part, against the upper parts (22), respectively lower, teeth located between the grooves of the side pieces, so as to create a depth spacing  e between the corresponding magnetic parts of the part resulting from step e and those resulting from step f, thus making it possible to create an air gap with a determined thickness.  7. Method according to one of claims 4 to 6, characterized in that a curable resin is injected into the openings (15) of the head resulting from the juxtaposition of the grooves and in the air gap zones (23). .  8. Method according to claim 7, characterized in that this resin injection is carried out before rectification of the front face of the head.  9. Magnetic reprographic system, characterized in that it comprises means for recording (M1, ... M5) a plurality of lines of magnetic information, the first line of these means (M1) being connected to the first row (T2m) of a magnetic head (TM) according to one of claims 1 to 3, while the last line (M5) of said means is connected to the second row (T2m + 1) of said head (TM) ), control means (MD) and synchronization (clock) being provided to allow on the one hand the sending of the information located in the cells of the same parity of the first line (M1) to the first row (T2m) d of the magnetic head (TM), and secondly the information located in the cells of the second parity of the last line (hnj) at the second row tT2m + 1) of the gaps of said magnetic head (TM) , these control means (MD) and synchronization (clock) further allowing the shift l igneous by line (Mi, ... M5) of the information, as well as the advance of a step of the magnetic medium or of the magnetic head (TM), so as to allow the recording of a line of information on said medium magnetic, first using the air gaps of the first row (T2m) then using the air gaps of the second row (T 2m +