Rotary magnetic head drum assembly

Abstract: In a rotary magnetic head drum assembly (1) lands (15) connected to signal lines of a rotary magnetic head drum (1) are, upon assembly of the unit, brought into contact respectively with the upper ends of upwardly extending spring pins (20 a ) of a plurality of spring pin connectors (20) mounted on a connector base plate (18) secured to the underside of a drum base (11) which supports a stationary magnetic head drum (3). In this way the spring pins (20 a ) which are connected to external amplifiers are electrically connected to the rotary magnetic head drum (1) when the stationary magnetic head drum (3) is mounted on the drum base (11).

Description: The invention relates to a rotary magnetic head drum assembly. Such an assembly may, for example, be suitable for application to a digital video tape recorder. Usually, the signal system of the rotary magnetic head drum of a video tape recorder is connected electrically to external amplifiers by a wiring harness or a flexible printed wiring board. The rotary magnetic head drum of a digital video tape recorder, ie a video tape recorder capable of high-density magnetic recording, is provided with as many as ten-odd revolving magnetic heads, and the number of signal lines of the driving system for driving the rotary magnetic head drum has increased with the enhancement of performance, entailing an increase in the number of signal lines connected to the rotary magnetic head drum. Progressive reduction in size and weight of digital video tape recorders, as well as those of other video tape recorders, has however required reduction in diameter of the digital rotary magnetic head drum of digital video tape recorders and the rotary magnetic head drum is required to be constructed in the least necessary mechanical strength. In a digital video tape recorder, in particular, the small rotary magnetic head drum has many signal lines and the electrical connection of the signal lines by a wiring harness or a flexible printed wiring board to external amplifiers requires troublesome work in assembling or disassembling the rotary magnetic head drum and the drum base of the digital video tape recorder. A previously proposed method of electrically connecting the signal lines of the rotary magnetic head drum to external amplifiers puts plug-in connectors in a plurality of connector pockets formed in the lower drum of a rotary magnetic head drum, fixes the plug-in connectors to the lower drum, and plugs plug-in connectors connected to external amplifiers from below a drum base in the plug-in connectors fixed to the lower drum. However, the plurality of connector pockets formed in the lower drum of the rotary magnetic head drum having a small diameter reduces the mechanical strength of the lower drum greatly, and the work of plugging the plug-in connectors connected to the external amplifiers one by one from below the drum base into the plug-in connectors connected to the signal lines of the rotary magnetic head drum is very troublesome. European patent specification 0 349 430 discloses a rotary head drum apparatus wherein a rotary transformer has its cooperating members axially spaced and the coils of rotor thereof are electrically connected to magnetic heads of a rotary drum by contactors in the form of leaf springs which, when the rotor and rotary drum are coupled together, make electrical contact with contact portions on bases of the magnetic heads of the rotary drum. According to the invention there is provided a rotary magnetic head drum assembly comprising: a rotary magnetic head drum provided with a plurality of revolving magnetic heads; a stationary magnetic head drum rotatably supporting the rotary magnetic head drum; and a drum base fixedly supporting the stationary magnetic head drum thereon and provided with external signal lines; wherein a plurality of input and output terminals provided on the lower surface of the stationary magnetic head drum are connected to the external signal lines of the drum base by a connector assembly comprising a connector base plate attached to the lower surface of the drum base and pin connectors having a plurality of pins and attached to the upper surface of the connector base plate with the pins thereof extending upwardly so that the pins are in contact with the input and output terminals when the stationary magnetic head drum is mounted on the drum base; characterised in that the pin connectors are spring pin connectors having a plurality of spring pins which are in elastic contact with the input and output terminals. Thus upon mounting the rotary magnetic head drum assembly the electrical connection of signals of the rotary magnetic head drum to external amplifiers is effected automatically by seating the stationary drum of the rotary magnetic head drum assembly on the drum base. A rotary magnetic head drum assembly in a first aspect of the invention has input and output terminals connected to the signal lines of the rotary magnetic head drum and arranged on the lower end of the rotary magnetic head drum so as to be brought into contact respectively with the spring pins of spring pin connectors connected to external amplifiers and attached to the drum base with the spring pins thereof extending upward when the rotary magnetic head drum is mounted on the drum base. When the rotary magnetic head drum of the rotary magnetic head drum assembly is mounted on the drum base, the input and output terminals connected to the signal lines of the rotary magnetic head drum come into contact with the upper ends of the spring pins of the spring pin connectors attached to the drum base from above the spring pins to connect the signal lines of the rotary magnetic head drum automatically and electrically to the external amplifiers. Accordingly, very troublesome connecting work using wiring harnesses or flexible printed wiring boards is not necessary at all in assembling the rotary magnetic head drum assembly, which facilitates work for assembling and disassembling the rotary magnetic head drum assembly greatly. Since the lower drum of the rotary magnetic head drum need not be provided with any large holes for receiving connectors and hence the mechanical strength of the lower drum is not reduced, which enables further reduction in size and weight of the rotary magnetic head drum. A rotary magnetic head drum assembly in a second aspect of the invention positions a connector base plate to which the spring pin connectors are attached relative to the rotary magnetic head drum. In mounting the rotary magnetic head drum of the rotary magnetic head drum assembly, since the connector base plate attached to the drum base is positioned relative to the rotary magnetic head drum, the spring pins of the spring pin connectors attached to the connector base are not dislocated from correct positions respectively corresponding to the input and output terminals connected to the signal lines of the rotary magnetic head drum and the input and output terminals can be correctly connected to the corresponding spring pins. A rotary magnetic head drum assembly in a third aspect of the invention enables the connector base plate to move on the drum base at least in directions perpendicular to the direction of the thickness thereof. In mounting the rotary magnetic head drum of the rotary magnetic head drum assembly on the drum base, the positioning of the connector base plate relative to the rotary magnetic head drum can be easily achieved because the connector base plate is able to move at least in directions perpendicular to the direction of the thickness thereof, which facilitates assembling work for assembling the rotary magnetic head drum assembly and prevents subjecting the connector base plate, the drum base and the rotary magnetic head drum to excessively large force and deforming the same. A rotary magnetic head drum assembly stated in a fourth aspect of the invention positions the spring pin connectors on the connector base plate by positioning pins. Since the spring pin connectors on the connector base plate by the positioning pins, the dislocation of the spring pins of the spring pin connectors from correct positions corresponding to the input and output terminals connected to the signal lines of the rotary magnetic head drum due to the accumulation of positional tolerances for the spring pins can be eliminated, so that the input and output terminals can be correctly connected to the corresponding spring pins. A rotary magnetic head drum assembly in a fifth aspect of the invention uses the positioning pins for positioning the spring pin connectors on the connector base plate also for positioning the connector base plate relative to the rotary magnetic head drum. The rotary magnetic head drum assembly uses the positioning pins for positioning the spring pin connectors on the connector base plate also for positioning the connector base plate relative to the rotary magnetic head drum, which reduces the number of component parts and enables the input and output terminals connected to the signal lines of the rotary magnetic head drum to be brought into contact with the corresponding spring pins in a high accuracy with the least dislocation. The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 is a longitudinal sectional view through a rotary magnetic head drum assembly of a preferred embodiment according to the invention; Figures 2A and 2B are partly sectional side elevations, respectively, of assistance in explaining a spring pin connector; Figure 3 is a plan view of assistance in explaining a spring pin connector; Figure 4 is a perspective view of assistance in explaining a connector base plate; Figure 5 is a plan view of assistance in explaining a manner of positioning spring pin connectors on a connector base plate; Figures 6A and 6B are side elevations, respectively, of assistance in explaining a manner of positioning a spring pin connector; Figure 7 is a sectional side elevation of assistance in explaining a manner of positioning a rotary magnetic head drum; Figures 8A and 8B are plan views, respectively, of assistance in explaining a manner of positioning spring pins relative to lands formed on a terminal board; and Figures 9A and 9B are fragmentary sectional views, respectively, of assistance in explaining a manner of positioning a connector base plate on a rotary magnetic head drum. Referring to Figure 1, a rotary magnetic head assembly applied to a digital video tape recorder has a rotary magnetic head drum 1 constructed by coaxially combining an upper drum 2, ie a rotary drum, and a lower drum 3, ie a stationary drum. A plurality of revolving magnetic heads 4, (ten-odd revolving magnetic heads) are attached to the outer circumference of the upper drum 2 so as to be disposed between the upper drum 2 and the lower drum 3. The lower drum 3 is provided integrally, internally and coaxially with an inner boss 3 a , and a spindle 6 is supported for rotation in a pair of ball bearings 5 fitted in the inner boss 3 a . A disc 7 combined with the upper drum 2 is fixed to the upper end of the spindle 6. A spindle motor 8 is connected to the lower end of the spindle 6 to rotate the upper drum 2 together with the revolving magnetic heads 4. The disc 7 is provided integrally and coaxially with a cylinder 7 a extending downward from the lower surface of the disc 7. When the disc 7 is fixed to the upper end of the spindle 6, the cylinder 7 a of the disc 7, and the inner boss 3 a of the lower drum 3 are coaxial and an annular space is formed between the cylinder 7 a and the inner boss 3 a . A plurality of rotary transformers 9 having stationary components 9 a and rotary components 9 b , respectively, are stacked in the annular space between the cylinder 7 a and the inner boss 3 a . The lower drum 3 of the rotary magnetic head drum 1 is seated on the upper surface of a drum base 11 and fastened to the drum base 11 with a plurality of screws 12 to fix the rotary magnetic head drum 1 to the drum base 11. An annular terminal board 13 is fastened to the lower surface of the lower drum 3 with a plurality of screws 14 so as to surround the spindle motor 8. As shown in Figure 8A, a plurality of lands 15, ie input and output terminals connected to signal lines of the rotary magnetic head drum 1, are formed on the lower surface of the terminal board 13, and lead wires extending from the rotary transformers 9 and connected to signal lines of the recording system and reproducing system of the revolving magnetic heads 4, and a plurality of signal lines of a wiring harness 16 (or a flexible printed wiring board) connected to a driving system for driving the spindle motor 8 are soldered, respectively to the lands 15. An annular connector base plate 18 is attached to the lower surface of the drum base 11 with a plurality of shoulder bolts 19 so as to surround the spindle motor 8. As shown in Figure 8B, a plurality of spring pin connectors 20 attached to the upper surface of the connector base plate 18 have spring pins 20 a extending upward and are inserted from below in openings 21 formed around the spindle motor 8 in the base drum 11. As shown in Figure 2A the lands 15 come into contact with the upper ends of the spring pins 20 a of the spring pin connectors 20 when the rotary magnetic head drum 1 is mounted on the drum base 11. The spring pins 20 a are connected respectively to external amplifiers, not shown, by a wiring harness 20 e . When the lower drum 3 of the rotary magnetic head drum of the rotary magnetic head drum assembly is fastened to the upper surface of the drum base 11, the lands 15 serving as input and output terminals connected to the signal lines of the rotary magnetic head drum 1 come into contact with the upper ends of the spring pins 20 a of the spring pin connectors 20 to achieve automatically electrical connection of the signal lines of the rotary magnetic head drum 1 to the external amplifiers. The components of the rotary magnetic head drum assembly will be described in detail hereinafter. First, the spring pin connectors 20 will be described with reference to Figures 2A, 2B and 3. Each spring pin connector 20 is provided with the plurality of spring pins 20 a , for example, several or several tens of spring pins. As shown in Figure 2A, each spring pin 20 a is biased upward in the direction of the arrow a by a compression coil spring 20 b and connected to a terminal 20 c projecting downward from the lower surface of the connector base plate 18 and held in place by a bump 20 d of solder. As shown in Figure 2B when the rotary magnetic head drum 1 is mounted on the drum base 11, the land 15 of the terminal board 13 depresses the corresponding spring pin 20 a against the resilience of the compression coil spring 20 b in the direction of the arrow b by a distance Δ x. The compression coil spring 20 a maintains a contact pressure between the land 15 and the spring pin 20 a . The positioning of the spring pin connectors 20 on the connector base plate 18 and the positional accuracy of the spring pin connectors 20 will be described hereinafter with reference to Figures 4, 5, 6A and 6B. Four spring pin connectors 20A, 20B, 20C and 20D are attached to the upper surface of the connector base plate 18 in a substantially square arrangement around a central hole 18 a of the connector base plate 18. The spring pin connector 20A, which is to transmit the signals of the recording system of the revolving magnetic heads 4 of the rotary magnetic head drum 1, and the spring pin connector 20B, which is to transmit the signals of the recording system of the revolving magnetic heads 4 of the rotary magnetic head drum 1, are disposed opposite to each other with respect to the centre of the connector base plate 18 at a substantially large interval to prevent cross talk between the signals of the recording system and those of the reproducing system. Signals of a driving system to drive the spindle motor 8 are transmitted by the spring pin connectors 20C and 20D. In positioning the spring pin connector 20 by inserting the terminals 20 a of the spring pin connector 20 shown in Figure 6B in through holes 22 (Figure 5) formed in the connector base plate 18, the dislocation of the opposite spring pin connectors 20A and 20B relative to each other is, at a maximum, ±0.2 mm if the accuracy in the pitch of the through holes 22 of the connector base plate 18 is ±0.1 mm. If the diameter of the terminals 20 c is D, the diameter of the through holes 22 is about D+0.2 mm and hence the play of the spring pin connectors 20A, 20B, 20C and 20D is ±0.1 mm at a maximum. Since the accuracy of the diameter of the through holes 22 is about ±0.1 mm, the accumulated dimensional tolerance is ±0.2 + 2 x ±0.1 mm + ±0.1 mm = ±0.5 mm at a maximum, which is relatively large. To allow the accumulated dimensional tolerance as large as ±0.5 mm, the size of the lands 15 must be 1 x 1 mm 2 or greater. As shown in Figure 6A, a pair of positioning pins 23 are attached to the spring pin connector 20 respectively in the longitudinally opposite ends of the same so as to project from the lower surface of the same, and positioning holes 24, ie a around hole and a slot, are formed respectively at the opposite ends of each row of the through holes 22. The positioning pins 23 are inserted in the positioning holes 24 to position the spring pin connectors 20A, 20B, 20C and 20D on the connector base plate 18. When the spring pin connectors 20A, 20B, 20C and 20D are positioned in such a manner, the tolerance for the diameter of the through holes 22 is negligible. Consequently, the cumulative dimensional tolerance can be limited to a value not greater than ±0.2 mm and hence the lands 15 need not be very large. Accordingly, it is possible to arrange the lands 15 and the spring pins 20 a at reduced pitches and the signal lines can be accurately connected in a small area. The positioning of the rotary magnetic head drum 1 and the connector base plate 18 will be described hereinafter with reference to Figures 7, 8A, 8B, 9A and 9B. As shown in Figure 7, a plurality of positioning pins 25, ie drum positioning means, projecting from the upper surface of the drum base 11 fit in a plurality of positioning holes 26 formed in the lower surface of the lower drum 3 to position the rotary magnetic head drum 1 on the drum base 11 when the rotary magnetic head drum 1 is mounted on the drum base 11. The lower drum 3 is fastened to the drum base 11 with the plurality of screws 12 screwed into the lower drum 3 from below the drum base 11. As shown in Figures 8A and 9A, positioning holes 27, ie a round hole and a slot, serving as connector positioning means, are formed in the lower surface of the lower drum 3 of the rotary magnetic head drum 1 at positions corresponding to positions near the opposite ends of a diameter p of the terminal board 13, respectively. As shown in Figure B, a pair of positioning pins 28, ie connector positioning means, are attached to the upper surface of the terminal board 13 at positions near the opposite ends of a diameter p of the connector base plate 18, respectively. The positioning pins 28 are the upper ends of two of the four positioning pins 23 for positioning the spring pin connectors 20 on the connector base plate 18. The terminal board 13 is positioned by using the positioning holes 27 and fastened to the lower surface of the lower drum 3 with the screws 14 inserted through through holes 31. In mounting the rotary magnetic head drum 1 on the drum base 11, the pair of positioning pins 28 are fitted in the positioning holes 27, respectively to position the connector base plate 18 on the rotary magnetic head drum 1 so that the lands 15 are in accurate contact with the spring pins 20 a respectively. As shown in Figure 9A, the connector base plate 18 is attached to the lower surface of the drum base 11 with the shoulder bolts 19 screwed through through holes 29 into the drum base 11. The diameter of the through holes 29 of the connector base plate 18 is greater than the diameter of the shoulder bolts 19. A gap 30 is formed between the lower surface of the drum base 11 and the upper surface of the connector base plate 18. Accordingly, the terminal base plate 18 is able to move in both the directions indicated by the arrow c , ie directions in the direction of the thickness of the terminal base plate 18, and both of the directions indicated by the arrow d , ie directions perpendicular to the direction of the thickness of the terminal base plate 18. If the connector base plate 18 were to be rigidly fixed without tolerance to the drum base with screws 32 as shown in Figure 9B, in some cases, the positioning pins 28 would be unable to be fitted in the positioning holes 27 or the positioning pins 28 would be forcibly fitted in the positioning holes 27 and the positioning pin 28 would be deformed, which might possibly strain the connector base plate 18, the drum base 11 and the lower drum 3. However, when the connector base plate 18 is able to move in all directions (the directions indicated by the arrows c and d ) relative to the drum base 11 as shown in Figure 9A, the positioning pins 28 are able to drop smoothly into the positioning holes 27 when the rotary magnetic head drum 1 is mounted on the drum base 11, and the connector base plate 18, the drum base 11 and the lower drum 3 will not be strained by the positioning pins 28. The movement of the connector base plate 18 in the directions of the arrow c obviates subjecting the lands 15 and the spring pins 20 a to an excessively large force. The rotary magnetic head drum assembly thus assembled need not be provided with any large holes in the lower drum 3 to receive connectors therein, and hence the mechanical strength of the lower drum 3 will not be unduly reduced.

Claims: A rotary magnetic head drum assembly comprising: a rotary magnetic head drum (2) provided with a plurality of revolving magnetic heads (4); a stationary magnetic head drum (3) rotatably supporting the rotary magnetic head drum; and a drum base (11) fixedly supporting the stationary magnetic head drum (3) thereon and provided with external signal lines; wherein a plurality of input and output terminals (15) provided on the lower surface of the stationary magnetic head drum (3) are connected to the external signal lines of the drum base by a connector assembly comprising a connector base plate (18) attached to the lower surface of the drum base (11) and pin connectors (20) having a plurality of pins (20 a ) and attached to the upper surface of the connector base plate (18) with the pins (20a) thereof extending upwardly so that the pins (20 a ) are in elastic contact with the input and output terminals (15) when the stationary magnetic head drum (3) is mounted on the drum base (11); characterised in that the pin connectors (20) are spring pin connectors having a plurality of spring pins (20 a ) which are in elastic contact with the input and output terminals (15). A rotary magnetic head drum assembly according to claim 1, wherein the spring pin connectors (20) are positioned on the connector base plate (18) by positioning pins (23). A rotary magnetic head drum assembly according to claim 1, wherein the connector base plate (18) is positioned relative to the stationary magnetic head drum (3) by connector positioning means (27, 28) so that the spring pins (20 a ) of the spring pin connectors (20) are aligned respectively with the input and output terminals (15). A rotary magnetic head drum assembly according to claim 3, wherein the connector positioning means includes at least two positioning pins (28) fitted in positioning holes (27) formed in the lower surface of the stationary drum (3). A rotary magnetic head drum assembly according to claim 3, wherein the connector base plate (18) of the connector assembly is provided with clearance holes, and the connector base plate (18) is fastened to the lower surface of the drum base (11) by screws (19) screwed through the clearance holes into threaded holes formed in the lower surface of the drum base. A rotary magnetic head drum assembly according to claim 1, wherein each of at least two positioning pins (23) among those positioning the spring pin connectors (20) on the connector base plate (18) has an upper end projecting upwardly from the spring pin connector (20) and fitted in a positioning hole (27) of the drum base to position the connector base plate (18) on the drum base and a lower end projecting downward from the spring pin connector and fitted in a positioning hole (24) of the connector base plate (18) to position the spring pin connector (20) on the connector base plate (18).

Inventors: SAKAI SEIICHI, SAKAI, SEIICHI, Sakai, Seiichi, c/o Patents Division
Applicants: SONY CORP, SONY CORPORATION
Application year: 1992
Main classification: G11B5
IPC codes: G11B33, G11B5