GB2149955A

GB2149955A - Magnetic-tape guiding drum

Info

Publication number: GB2149955A
Application number: GB08428495A
Authority: GB
Inventors: Toshihide Irisa; Tatsumaro Yamashita
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1983-11-18
Filing date: 1984-11-12
Publication date: 1985-06-19
Also published as: KR850009671U; JPS6085715U; GB8428495D0; DE3441986A1; KR890005695Y1; GB2149955B

Abstract

In a helical-scan video tape recorder the head drum (8) has a rotatable portion (20) having a central shah (100) extending axially outwardly, a stationary portion (19) for rotatably supporting the rotatable portion together with the central shaft (100), and a magnetic recording and reproducing head (30) extending radially outwardly between the two portions. Electrostatic charge tending to be collected on the rotatable portion (20) is discharged through a grounding arrangement in which a planar contact (101) supported by a grounding strip (34) having a resilient nature and secured to the stationary portion (19) is brought into sliding contact with a projection (100a) provided at the centre of an end of the central shaft (100). <IMAGE>

Description

SPECIFICATION Magnetic tape guiding drum This invention relates to a magnetic image recording and reproducing device, and more particularly to a magnetic tape guiding drum used in the image recording and reproducing device for guiding magnetic tape to be wound around one part of the circumference of the drum.

Fig. 1 shows a tape feeding system of a conventional magnetic image recording and reproducing device wherein a magnetic tape 2 pulled out of a tape feeding reel 1 is passed through a guide post 3A, tension post 4, loading posts 5A, 5B and 5C, voice erasing head 7, and another guide post 3B to a magnetic tape guiding drum 8, around which the magnetic tape 2 is helically wound approximately one half of the circumference of the drum.

On the magnetic tape guiding drum 8 are provided one or more magnetic heads to be used for recording and reproducing an image on or out of the magnetic tape 2.

The magnetic tape 2 extending from the tape guiding drum 8 is passed through a guide post 9A, voice recording head 10, guide post 9B, a gap between a capstan 11 and a pinch roller 12, a loading post 13 and still another guide post 14 to a tape winding reel 15, so that the tape is wound around the tape winding reel 15. Numeral 16 designates a half part of the cassette, and numerals 17 and 18 designate loading grooves.

During the fast feed and rewinding operations, the magnetic tape 2 is fed through the tape feeding system following the above described path, while the tape guiding drum 8 is held to be rotating.

One example of the conventional construction of the tape guiding drum 8 is shown in Fig. 2. The guide drum comprises a stationary drum 19 and a rotating drum 20, both having an equal outer diameter, and the latter being supported by the former coaxially. A gap 21 is maintained between the two drums 19 and 20. A central shaft 23 is secured to the rotating drum 20 through a sleeve 22. A lower part of the shaft 23 is in turn secured through another sleeve 24 to a housing 25 on which permanent magnets 26 are arranged in a circular manner. To the stationary drum 19 are secured bearings 27 and 28 which support the rotating drum 20 rotatably, and also a driving coil 29 which in combination with the permanent magnets 26 forms a driving motor for driving the rotating drum 20.On the rotating drum 20 are further provided magnetic heads 30 that extend outwardly through the gap 21 formed between the two drums 19 and 20 for recording and reproducing image signals on or out of the magnetic tape 2. The image signals are supplied or received through rotary transformer windings 31 and 32 secured respectively to the rotating drum 20 and the stationary drum 19 and one of the windings is connected to a signal system provided outside of the magnetic tape guiding drum.

With the above described construction of the tape guiding drum 8, an electrostatic charge is created when the magnetic tape 2 slidingly contacts the rotating drum 20. The electrostatic charge may be affected defectively by weak signals at the time of the recording and reproducing operations. Furthermore, the electrostatic charge collected on the rotating drum 20 is conducted outside through bearings 27 and 28 which support the central shaft 23 secured to the rotating drum 20 in an irregularly contacting manner.

For obviating the difficulty and ensuring conductivity, a spring member 34 provided with a contact 33 is secured to a fixed member 35, and the fixed member 35 is secured to a chassis or other part (not shown) for grounding the same, while the contact 33 is brought into contact with the central shaft 23. Such an arrangement, however, is found to be disadvantageous because no stable contact between the contact 33 and the shaft 23 can be assured unless the contact 33 is arranged exactly at the centre of the shaft 23. Furthermore, wear of the contact 33 tends to deteriorate the ground connection, and the long and narrow construction of the spring member 34 and the fixed member 35 make it difficult to adjust the position of the contact 33 to the centre of the shaft 23.

An object of the present invention is to provide a magnetic tape guiding drum wherein the above described difficulties of the conventional construction can be substantially eliminated.

Another object of the invention is to provide a magnetic tape guiding drum wherein stable contact for grounding the drum can be realised regardless of the displacement of the contacting member from the centre of the rotating shaft, and also the possibility of creating sound from the contacting portion can be substantially eliminated.

According to the present invention, there is provided a magnetic tape guiding drum adapted to be used in a magnetic image recording and reproducing device for guiding a magnetic tape such that the tape is obliquely in contact with the tape guiding drum, the drum including a rotatable portion having a central shaft extending outwardly and a magnetic recording and reproducing head extending radially outwardly, characterised in that a planar contact supported by a grounding strip secured to a stationary portion of the tape guiding drum is brought into sliding contact with a projection provided at the centre of an end of the central shaft extending axially outwardly.

A magnetic tape guiding drum embodying the invention will now be described, by way of example with reference to the accompanying diagrammatic drawings in which: Figure 1 is a diagram showing a tape feeding passage in a magnetic image recording and reproducing device; Figure 2 is a sectional view of a conventional magnetic tape guiding drum; Figure 3 is a sectional view showing an embodiment of the present invention; and Figure 4 is a sectional view showing another embodiment of the invention.

A preferred embodiment of the present invention will now be described with reference to Fig. 3 wherein similar members as those shown in Fig. 2 are designated by similar reference numerals.

The embodiment shown in Fig. 3 has a construction substantially similar to that of Fig. 2 except for the central shaft and the sliding contact.

More specifically, at the centre of an end of a central shaft 100 secured to the rotation drum 20 through the sleeve 22, a projection 100a having a predetermined radium is formed integral with the central shaft 100. On the other hand, a sliding contact piece 101 provided at an end of the spring member 34 secured to the fixed member 35 is made of an electrically conductive material such as carbon or other material, and is formed with a substantially planar contacting surface 101a which is urged by the spring member 34 to be brought into contact with the projection 100a.

As a consequence, the electric charge collected on the rotating drum 20 is discharged through the central shaft 100, projection 100a, contacting surface 101a of the contact piece 101, spring member 34 and the fixed member 35 fixed to the stationary drum 19 to be grounded to the frame or chassis (not shown) of the recording and reproducing device.

Since the projection 100a is formed at an end of the central shaft 100 supporting the rotating drum 20, and the projection is brought into contact with the planar contacting surface 101a of the sliding contact piece 101, freedom in positioning of the sliding contact piece 101 supported by the comparatively long spring member 34 and fixed member 35 is substantially increased and creation of the sliding sound at the time of the rotation of the central shaft 100 can be reduced.

Furthermore, the positional adjustment of the sliding contact piece 101 can be facilitated and the assembling cost of the tape guiding drum can be reduced.

Fig 4 illustrates another embodiment of the invention wherein a separate contacting piece 11 0a made of an electrically conductive material such as carbon is secured to the outwardly projecting end of the central shaft 110 in threaded engagement, bonding or a force fit manner so that the contacting piece 11 Oa further projects outwardly from the end surface of the central shaft 110. On the other hand, a planar contacting piece 111 made of phosphor-bronze or the like is secured to the fixed member 35 so as to be urged into contact with the contact piece 11 ova.

With the above described construction, electrostatic charge collected on the rotating drum 20 is discharged through the contact piece 11 0a on the central shaft 110 and the planar contacting piece 111 to be grounded to the chassis of the device as described in the previous embodiment shown in Fig. 3.

According to the present invention, since the planar contact supported by a grounding strip secured to the stationary portion of the tape guiding drum is brought into a sliding contact with a projection provided at an end of the central shaft extending axially outwardly, a slight displacement of the planar contact supported by the grounding strip such as the spring member and the fixed member against the projection on the central shaft does not adversely affect the stable contact between the two contacting members. The advantageous features of creating no abnormal second and eliminating wear of the contacting members and vibration of the rotating shaft at the time of a high speed rotation can thereby be obtained.

Claims

1. A magnetic tape guiding drum adapted to be used in a magnetic image recording and reproducing device for guiding a magnetic tape such that the tape is obliquely in contact with the tape guiding drum, the drum including a rotatable portion having a central shaft extending axially outwardly and a magnetic recording and reproducing head extending ra- dially outwardly, the improvement comprising: a projection provided at the centre of the axially outwardly extending end of said central shaft; and a planar contact member supported by a grounding resilient strap secured to a stationary portion of the tape guiding drum, so that said contact member is urged into contact with said projection provided on the central shaft.

2. A magnetic tape guiding drum as set forth in claim 1 wherein said projection is formed integrally with said central shaft, and said planar contact member is made of a sliding material such as carbon.

3. A magnetic tape guiding drum as set forth in claim 1 wherein said projection is constructed as a separate contacting piece made of an electrically conductive material such as carbon which is secured to the outwardly extending end of the central shaft by either of a threaded engagement, bonding, or a force fit, while said planar contact member is made of a phosphor-bronze strip which is also operable as said resilient grounding strip.

4. A magnetic tape guiding drum substantially as hereinbefore described, with reference to Figs. 3 and 4 of the accompanying drawings.