JPS62202310A - Scan unit for magnetic tape unit and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a magnetic tape device having a scanning unit mounted on a frame, comprising: at least one magnetic head mounted on a rotatable head support; - an upper drum in a fixed position on the frame; and a lower drum, the head support is rotatably mounted between these drums, and the outer peripheral surfaces of both drums are both located near the circular path of the magnetic head and have a curved surface along which the magnetic tape is guided. a magnetic drum-shaped guiding device forming a guiding surface; - a fixing device interconnecting the upper drum and the lower drum; and - a positioning device for relative positioning of the upper drum and the lower drum. The present invention relates to a scanning unit of a tape device.

This type of magnetic tape device is described in U.S. Pat.
No. 35154. In such devices, the tape is guided along a helical path in guide surfaces formed on the outer periphery of a stationary upper and lower drum, against a track that during operation is inclined with respect to the longitudinal axis of the magnetic tape. Writing or reading is performed using a magnetic head.

In order to interconnect the upper and lower drums, the known device uses a bridge member on the side facing away from the guide surfaces of the upper and lower drums, which bridge member connects the upper and lower drums by means of bolts. Interconnect the drums. Considering the accuracy of reading or writing to the inclined track during operation, the connection between the upper and lower drums is
Accurate relative positioning of the two drums is desirable.

For this purpose, the bridge member uses two locating pins, which are oriented axially with respect to the axis of rotation of the head support, so that the upper and lower drums can be slid against the locating pins during assembly. Move it and then fix it. Therefore, it is necessary to manufacture the bridge member and the two positioning pins with high precision. However, despite this accuracy, the relative positioning of the upper and lower drums is subject to variation for at least two reasons. The first cause is the diameter tolerance of the upper and lower drums due to the fact that the diameters of the upper and lower drums are not exactly the same.

Such tolerances result in a step in the guide surface formed by the outer peripheral edge of the drum after the scanning unit is assembled. The second cause lies in the bridge member used. That is, it is almost impossible to form each hole for the positioning pin in the bridge member so that its center axis is exactly perpendicular to the axial end walls of the upper drum and the lower drum. be. In fact, this results in each locating pin fitted in the bridge member being no longer perpendicular to the axial end wall. If the scanning unit is disassembled, for example to replace the head support, after reassembly these variations will cause the upper and lower drums to be positioned differently than before.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a scanning unit for a magnetic tape device capable of accurately positioning the guide surfaces of the upper and lower drums and maintaining this accurate positioning even after disassembly and reassembly, without using bridge members. is to obtain.

To achieve this objective, the scanning unit according to the invention comprises: wall portions which, in the vicinity of the axially opposite end walls of the upper drum and the lower drum, are provided with three positioning elements facing each other; , and the positioning elements on one wall part and the positioning elements on the other wall part are paired and engaged with each other directly or indirectly with an intervening intermediate element for interlocking operation, and the upper drum and the lower drum are connected to each other. and a uniquely defined connection between the positioning elements, and the fixing means press-bonds each pair of positioning elements to each other or to an intermediate element.

With this configuration, the invention provides a completely unambiguously defined three-point connection of the upper and lower drums by means of positioning elements, which allows the interconnection of the upper and lower drums without the use of bridge members. Produces accurate relative positioning.

Furthermore, accurate positioning of the two drums can be maintained even after the two drums are disassembled and reassembled, for example after the head support and the magnetic head attached thereto are replaced. The only remaining tolerance in the scanning unit is simply the amount of head protrusion of the magnetic head on the head support.

Due to the accurate relative positioning of the upper and lower drums, the outer peripheral surfaces of the two drums are aligned, and there is no step difference due to the difference in diameter on the guide surface formed by these outer peripheral surfaces. The thickness of the thin air film formed between the guide surface and the magnetic tape can be made constant at different positions. This results in a very good air film tape feed at the position of the guide surface of the drum, which is advantageous for accurate and uniform tape feed.

German Patent No. 1,474,433 describes a magnetic tape device C having upper and lower drums, each drum having a scanning unit carrying four elements for positioning the drums relative to each other. . The positioning and fixing elements are arranged in four pairs. These pairs of elements are associated with adjustment screws to position the height of the upper drum relative to the lower drum for proper resting. However, height adjustment using an adjustment screw causes the drum to rotate about the rotation axis, changing the positioning of the drum. This German publication shows four sets of elements instead of three,
There is also no mention of a repeatable specific relationship between the two drums based on integral, non-adjustable positioning elements that can be disassembled and reassembled while maintaining the original alignment.

In a preferred embodiment of the invention, the wall portions are extensions of the axial end walls of the upper and lower drums.

With this configuration, the positioning elements of the axial end walls can uniquely determine the relative positioning of the upper and lower drums.

U.S. Pat. No. 3,435,154 describes a scanning unit H which is provided with a circular cylindrical guide surface whose cylindrical axis coincides at least approximately with the axis of rotation of the head support. In a preferred embodiment of the present invention, the guide surface has the shape of a part of the surface of an imaginary circular cylinder whose axis corresponds at least approximately to the axis of rotation of the rad support, and preferably in a direction parallel to the axis of rotation. extending the drum radially outwardly beyond the circular path drawn by the free end of the magnetic head in the outer region of the guide surface as seen in FIG. . With this configuration, the positioning elements in each of the two wall sections extend outside the area of the guide surface and outside the circular path of the magnetic head, since the wall sections located in the vicinity of the mutually opposing axial end walls of the drum extend outside the area of the guide surface and outside the circular path of the magnetic head. are arranged outside the circular path so that, after assembly, the positioning element does not interfere with the rotation of the head support and the magnetic head supported thereon.

Furthermore, in a preferred embodiment of the invention, the positioning element is formed integrally with the upper drum and the lower drum, respectively. By integrally forming the positioning elements on the upper and lower drums, the positioning elements can be manufactured simultaneously with the manufacture of the drums. This is cheaper and faster to form than forming these positioning elements separately after the drum has been manufactured.

In this embodiment, the positioning elements can also be formed as depressions and projections in the axial end walls of the upper and lower drums, respectively.

According to this, there is a completely unique 3 between the upper and lower drums.
Point connections are easily obtained.

In a further preferred embodiment of the invention, the fastening device is arranged in the vicinity of a wall portion of the outer region of the circular path. This allows the fixing device to connect the wall portions to each other without interfering with the rotation of the head support and the magnetic head carried thereon.

In a further preferred embodiment in this regard, the securing device comprises a single unit securing the upper drum and the lower drum to each other.
The bolt connection is located approximately on the line bisecting the guide surface when viewed parallel to the axis of rotation, and within the range of a triangle with the position of the positioning element as the apex. Place it in With this configuration, the interconnection of the upper and lower drums can be achieved by just one bolted connection, which is located inside the triangular area so that the positioning elements engage each other precisely, and The upper and lower drums are accurately positioned relative to each other.

The present invention further relates to a method for manufacturing the above-mentioned scanning unit, in which an upper drum and a lower drum are manufactured separately, and at the same time as these drums are manufactured, each drum is attached. forming corresponding positioning elements, combining the upper drum and the lower drum, positioning them relative to each other by means of the positioning element, and clamping them on a lathe; processing to at least partially form a guiding surface, separating the upper drum and the lower drum from each other, attaching a head support and associated drive to the head support, and - the upper drum and the lower drum; It is characterized in that it is assembled again with the drum, relatively positioned by a positioning element, and interconnected by a fixing device.

According to the method of the invention, therefore, after the production of the upper and lower drums, each drum has a different radius with relatively large tolerances. After the circumferential surfaces have been assembled by the two drums, they are suitably machined, at least partially, while rotating on a lathe, so that guide surfaces of exactly the same radius are produced on the upper and lower drums.

The positioning elements also allow the upper and lower drums to be separated even after the two drums have been separated, the head support and associated drive have been installed, the two drums have been reassembled and interconnected by the anchoring device. The guide surfaces on each of the drums can be precisely positioned relative to each other. Furthermore, according to the method of the invention, no special precision requirements are imposed on the positioning elements themselves during the manufacture of the upper and lower drums. What is important is to obtain a scanning unit assembly that is uniquely defined in the assembled state of the lower and upper drums. According to the method of the invention, therefore, accurate positioning of the guide surfaces on both drums can be produced inexpensively and quickly.

In this regard, in a preferred embodiment of the method of the invention:
During machining of the combined upper and lower drums, the tools used are controlled in both radial and axial directions. Other parts of the drum can also be formed as the drum rotates by controlling the tool, preferably a cutting tool, in both radial and axial directions during rotation.

In this respect, the wall portions carrying the positioning element and the fastening device in mutually opposite axial end walls of the upper and lower drums can effectively avoid cutting tools in the position of the positioning element and the fastening device. In this way, in the area where the positioning elements and the fastening device are located, these wall parts can retain their original shape immediately after manufacture.

In this regard, in a preferred embodiment of the method of the invention:
Controlled axial movement of the tool forms one guide surface on the drum that guides the edge of the magnetic tape. Such a guide surface supports an edge of the magnetic tape in a direction perpendicular to the longitudinal axis of the tape while the tape runs on the guide surface.

This guide surface is thus precisely formed in the scanning unit, making it possible to precisely define the height of the magnetic tape in the scanning unit during the movement of the tape on the guide surface.

In this regard, in a preferred embodiment of the method of the invention:
At least one tape guide is formed simultaneously by controlled axial and radial movement of the tool. Forming the tape guide simultaneously eliminates the need to form it separately and also provides accurate positioning for both drums. In this way, all guiding devices for the magnetic tape to be accurately positioned in the device can be integrated into the scanning unit. If this additional tape guide is arranged close to the ends of the guide surface with respect to the direction of tape feed through the guide surface, the tape leaves the scanning unit at a level relative to the reference surface, e.g. the upper side of the deck plate, and passes this level. It can correspond to the level at which the tape enters the scanning unit.

This allows the parts that guide the lower edge of the tape of the other tape guides in the magnetic tape device to be placed at the same level with respect to the reference plane, making it easier to install other tape guides. This is extremely advantageous.

In this way, when the magnetic tape is wound around a reel that is equidistant from the reference plane, the magnetic tape device according to the present invention allows the tape to be easily fed from the cassette that stores the reel.

The invention will now be described in detail with reference to the drawings.

The magnetic tape device comprises a scanning unit 1 mounted on a frame 2 consisting of a flat deck plate (see FIG. 1). This scanning unit 1 is shown enlarged in FIGS. 2 to 4. The scanning unit has a drum-shaped guide device consisting of two fixed drums 3.4, which are mounted on the frame 2, and which thus form a lower drum, which will be described below. Attach the upper drum 4 in this manner.

A head support 5 carrying a plurality of magnetic heads 6, for example four heads, is rotatably mounted between a lower drum and an upper drum. The lower drum and the upper drum together form a curved guide surface 7 having the shape of a portion of the surface of an imaginary cylinder, the axis of which is at least approximately coincident with the axis of rotation of the head support 5. do. During operation of the device, the guide surface 7 guides a magnetic tape 8 which, as shown diagrammatically in FIG. 1, is attached to a tape reel 8a.

8b, and reel 8 from reel 8a during normal operation.
b in the direction shown by arrow A. For this purpose, the device is equipped with a winding spindle 9. These take-up spindles are driven from the underside of the frame in a manner not shown to feed the tape. The drive is provided by an electric motor 11 located on the right side of the scanning unit 1 in FIG. The head support 5 is driven by an electric motor 12 on the left side of the scanning unit. However, as an alternative, the drive of the head support 5 can be integrated into the scanning unit 1 in a manner not shown, in which case the drive is arranged close to the underside of the lower drum 3. A sliding plate 13 is arranged on the -[ side of the frame 2, and the sliding plate 13 is made slidable in a direction perpendicular to a line connecting the rotation axes of the winding spindles 9 and 10.Furthermore, a pressing roller lever is provided. 14 is disposed on the upper surface of the frame 2 so as to be rotatable around a spindle 14a.A pressure roller lever carries a pressure roller 15, and in the operating position shown in FIG. The capstan is also driven by the electric motor 11 in a manner not shown in the drawings.
The capstan 16 which operates in conjunction with the magnetic tape 8
can reliably move at a constant speed along the guide surface 7.

The sliding plate 13 controls two levers 17.18, which levers 17 and 18 respectively control the guide bins 19 and 2.
It carries 0. The magnetic tape is wound around these pins and guided from reel 8a to reel 8b. The sliding plate 13 carries two pairs of tape guides 21.22 and 23.24. The tape guides in each pair can be formed in part from a material such as plastic as a unit. The tape guides 21.23 are upright relative to the frame 2, and the tape guides 22.24 are tilted. The axis of rotation 5a is inclined with respect to the frame 2 and the tape guide 22.24 is also inclined so that during operation the tape is deposited along a helical path over the guide surface 7 of the drum; The tape is guided so as to come into contact with most of the width of the upper drum 4, and on the side of the tape guide 24, so as to come into contact with most of the width of the lower drum 3. In order to properly guide the tape in the width direction of the lower drum 3, a guide surface 25 as a shelf-like projection is provided on the outer peripheral surface of the lower drum 3. Thus, during its travel along the guide surface 7, the tape undergoes a precisely predetermined movement, and during the rotation of the head the head 6 reads and writes to the truts on the magnetic tape B, which are inclined with respect to the longitudinal axis of the tape. . The movement of the sliding plate 130 to various operating positions is described in Japanese Patent Application No. 1986-7 by the applicant.
Please refer to No. 8421 (Japanese Unexamined Patent Publication No. 61-233456).

After assembly of the scanning unit 1, it is important that the lower drum 3 and the upper drum 4 are positioned accurately relative to each other. For this purpose, the axially opposite end walls of the lower and upper drums are provided with arcuate or crescent-shaped extensions (forming wall sections 3a, 4a, respectively), each of these extensions or wall sections Three positioning elements, namely positioning elements 26, 27 and 2 in wall section 3a.
It carries positioning elements 29, 30 and 31 in the wall section 4a. In the combined state of the scanning unit 1, the positioning elements 26 and 29, 27 and 30, and 28 and 31 engage each other in pairs. Positioning element 29,3
0.31 is hemispherical, and the positioning element 27 is formed with a wall that exists on a plane perpendicular to the rotation axis 5a. The positioning element 26 is formed as a depression surrounded by three walls, which depression has the shape of a tetrahedron. The positioning element 28 has two walls forming a V-shape. The three pairs of positioning elements 26 and 29, 28 and 31 and 27 and 30 engage each other when the upper and lower drums are assembled, so that the drums are in completely unambiguous defined positions relative to each other. Take. Preferably, the positioning elements are formed integrally with the respective lower or upper drum.

As clearly shown in FIG.
a and 4a are arranged outside the trajectory (circular path) 6a drawn by the head 6. For this purpose, the axially opposite end walls of the drum extend from the area adjacent to the guide surface 7 to a point outside the circular path or trajectory 6a traced by the free end of the magnetic head 6. The lower and upper drums are simply one bolt 3
interconnected by an anchoring device with 2. This bolt 3
2 is passed through the smooth box in the upper drum 4 and screwed into the threaded box 33 in the lower drum 3.

It is assumed that these boxes have a common axis parallel to the rotation axis 5a. A spring 34 is disposed between the upper axial end surface of the upper drum 4 and the head of the bolt 32,
When tightened, the spring applies pressure to the upper and lower drums at the location of the positioning element. In this respect, viewed parallel to the axis of the axis of rotation 5a, the bolt 32 is located approximately on a line (not shown) bisecting the guide surface 7, within the confines of a triangle with an apex defined by the positioning element. . In this way, a proper and uniform pressure is applied to the pair of positioning elements.

Due to the unique relative positioning of the lower drum and the upper drum by means of the three positioning element pairs according to the invention, the scanning unit can be manufactured with high precision and with ease. First, the lower drum 3 and the upper drum 4 are manufactured separately, and at the same time the positioning elements 26 to 28 and 29 to 31 are manufactured separately.
are formed on the corresponding wall portions 3a, 4a, respectively. The positioning elements on the drums are then interlocked to assemble the lower and upper drums, after which the lower and upper drum assembly is clamped on the lathe. The lathe is preferably of the numerically controlled hydrostatic type. During machining using such a lathe, preferably during rotation using a cutting tool, this tool can be controlled both radially and axially with respect to the axis of rotation 5a.

By stopping the controlled movement of the cutting tool on the side of the guide surface 7, both the guide surface 7 and the guide surface 25 can be formed. After being taken out from the lathe, the upper drum and the lower drum are separated, and a head support 5 provided with a head 6 is installed between the lower drum and the upper drum. Next, the lower drum and the upper drum are repositioned by the positioning elements and reassembled by fixing with the bolts 32 to complete the assembly of the scanning unit 1. By arranging the positioning element outside the circular path 6a drawn by the head 6, the guide surface 7 is aligned with the tape 8.
The angle through which it can be guided is limited to approximately 200°. In the illustrated embodiment, the scanning unit 1 is intended for reading or writing tracks with digitally encoded audio signals, so that the angle at which the tape 8 wraps around the guide surface 7 is at least approximately 90°. Therefore, the structure of the magnetic tape device having the scanning unit according to the present invention is suitable for a magnetic tape device in which the tape winding angle is 90° or more.

According to the invention, it is therefore possible to use a drum 3.4 for manufacturing the scanning unit 1, which does not have to be precisely manufactured from the beginning. That is, after turning on a lathe and installing the head support 5, the drums 3 and 4 are positioned in a uniquely defined relative relationship to each other, and there is a tolerance between the radii of the lower drum and the upper drum at the position of the guide surface 7. This is because it can be made to have no or almost no occurrence. Only the difference in the amount of radial protrusion of the head 6 on the head support or head disk 5 constitutes a residual tolerance. During the rotation of the drum a thin air layer is created between the magnetic tape 8 and the guide surface 7. The structure according to the invention has the advantage that the thin air layer has a uniform thickness on the lower and upper drums in the width direction of the tape. As a result, thin air layer guidance of the tape at the position of the guide surface is performed very efficiently, which is convenient for proper and uniform tape feeding. Since this thin air layer is uniform across the width of the tape, the tolerance of the radial distance of each head 6 from the axis of rotation 5a is slightly larger than that of the conventional structure, but is not large enough to cause problems. Furthermore, by optimizing the shape of the guide surface 7, the tape 8 of the guide surface
A magnetic head 6 is arranged near the part where the magnetic head meets the guide surface,
The amount of radial protrusion of the magnetic head 6 relative to the guide surface can be made slightly larger than the amount of radial protrusion at the position where the tape leaves the guide surface. As a result, the thickness of the thin air layer is greater at the starting point of the guide surface than at the end point of the guide surface.

Proper positioning of the drums of the construction according to the invention requires tolerances in the distance between the axially opposite end walls of the drums 3, 4 and in the height of the gap between these end walls around which the head support 5 rotates. can be reduced. As a result, the discontinuity of the guide surface 7 at the position of the gap becomes extremely small. Furthermore, when the head support 5 is replaced due to wear of the head 6, for example, there is an advantage that reassembly after removal and replacement is simple. This simplifies and speeds up such replacements and is advantageous for repairs.

Furthermore, by using a lathe that controls cutting tools in both the axial and radial directions while the assembled drums 3 and 4 are rotating, the guide surface 25 can be precisely formed on the lower side of the guide surface 7. . It is advantageous if the cutting tool only rests on the circumferential surface of the drum at the location of the guide surface 7. This is achieved by radial control of the cutting tool, so that machining takes place only at the location of the guide surface 7, leaving the cutting tool free to pass over the rest of the circumference of the drum.

As shown in FIG. 5, the structure according to the invention allows the tape guides 35, 36 to be formed simultaneously with the manufacture of the lower and upper drums.

These tape guides 35, 36 replace the inclined tape guides 22, 24 of FIG. The formation of such a tape guide at the circumferential end points of the guide surface 7 is made possible by controlling the rotating cutting tool in the lathe in the axial and radial directions.

Using such a tape guide, the tape can exit the scanning unit via the tape guide 36 at the same level that the tape enters the scanning unit at the position of the tape guide 35 relative to the frame 2. In this way, all guide devices that must be precisely positioned can be concentrated in the scanning unit 1. All other tape guides of the magnetic tape device can be arranged with their lower end faces at the same level with respect to the frame 2, which simplifies the installation of these tape guides.

It is also possible for the drums 3, 4 to be made of metal and for the positioning elements 26 to 31 to be attached to the end walls of the drums. As an alternative, the drum can also be made of plastic, in which case it is advantageous because the positioning elements 26 to 31 can be formed at the same time by injection molding. This provides accurate relative positioning of the parts of the drums 3.4 that interact with the tape. Alternatively, the drum can be made of die-cast aluminum.

As shown in FIG. 6, the lower drum 3 and the upper drum 4
The magnetic head 6 can also be positioned by an intermediate member constituted by an arcuate plate 37, and in the assembled state, the magnetic head 6 can be positioned between the drum wall portions 3a and 4a.
It is placed outside the circular path 6a drawn by. wall parts 3a, 4
In a, each of the positioning elements is configured to have a prismatic depression, and depressions 38a, 38c and 39a
.

The longitudinal axes of 39c coincide with the recess 38b.

39b is recessed along the longitudinal axis of 38a, 38c and 39.
a, perpendicular to the longitudinal axis of 39c. The plate 37 has balls 40a and 40b.

40c, these balls are fixed in holes in plate 37, and plate 3
protrude from the upper and lower surfaces of 7.

In the assembled state, the bolt 32 has a ball 40a.

40b, 40c are pressed against the walls of the recesses of the wall portions 3a, 4a. This results in a three-point connection that completely unambiguously defines the relative positioning of the two drums. Intermediate member 37
The advantage of using this is that the height of the gap between the drums 3, 4 on which the head 6 rotates can be adjusted by appropriate selection of the diameter of the ball 40.

[Brief explanation of drawings]

1 is a perspective view of a magnetic tape device comprising a scanning unit according to the invention; FIG. 2 is a side view of the scanning unit of the magnetic tape device of FIG. 1 on a different scale; FIG. FIG. 4 is an exploded perspective view of the lower drum and upper drum with positioning elements; FIG. 5 shows the present invention in which the scanning unit is provided with two tape guides. FIG. 6 is an exploded perspective view similar to FIG. 4 of the third embodiment of the scanning unit. 1...Scanning unit 2...Frame 3.4.
...Drum 5...Head support 6...Magnetic head 7...Guide surface 8...Magnetic tape
8a, 8b...Tape reel 9.10...Take-up spindle 11, 12...Electric motor 13...Sliding plate 14
...Press roller lever 14a...Spindle 15
...Press roller 16...Capstan 17
, 18... Lever'-19, 20... Guide pin 21,
22.23.24.35.36...Tape guide 25.
・Information surface

Claims (1)

[Claims] 1. A magnetic tape device having a scanning unit mounted on a frame, comprising: - at least one magnetic head mounted on a rotatable head support; - an upper drum and a lower drum in a fixed position on the frame; the head support is rotatably mounted between the side drums, the outer peripheral surfaces of both drums are both located near the circular path of the magnetic head, and have curved guide surfaces along which the magnetic tape is guided; - a fixing device for interconnecting an upper drum and a lower drum; and - a positioning device for relative positioning of the upper drum and the lower drum. - in the vicinity of the axially opposite end walls of the upper and lower drums, there are provided wall portions facing each other and each comprising three positioning elements, for positioning one of the wall portions; The element and the positioning element of the other wall portion are paired and engaged with each other directly or indirectly through an intermediate element to operate in conjunction with each other, and the element is uniquely defined between the upper drum and the lower drum. A scanning unit characterized in that: - the fixing means press each pair of positioning elements to each other or to an intermediate element. 2. The scanning unit according to claim 1, wherein the wall portions are extensions of the axial end walls of the upper and lower drums. 3. The positioning device is configured to include an intermediate member disposed between the axial end walls and supporting the intermediate element, and the intermediate member is configured to have two wall portions. A scanning unit according to claim 2. 4. The guide surface has the shape of a part of the surface of an imaginary circular cylinder whose axis line is at least approximately coincident with the rotation axis of the head support, and in an outer region of the guide surface when viewed in a direction parallel to the rotation axis. Claim 2, characterized in that the drum extends radially outward beyond a circular path drawn by the free end of the magnetic head, and the positioning element is arranged on a wall portion of an area outside the circular path. Scanning unit as described in Section. 5. The scanning unit according to claim 4, wherein the positioning element is formed integrally with the upper drum and the lower drum, respectively. 6. Scanning unit according to claim 5, characterized in that the positioning elements are formed as depressions and protrusions in the axial end walls of the upper and lower drums, respectively. 7. The scanning unit according to claim 4, wherein the fixing device is arranged near a wall portion of the outer region of the circular path. 8. The fixing device has one bolt that fixes the upper drum and the lower drum to each other, and this bolt connection is located on a line that bisects the guide surface when viewed parallel to the axis of rotation. 8. The scanning unit according to claim 7, wherein the scanning unit is located approximately at the position of the positioning element and is arranged within a triangular range having the position of the positioning element as the apex. 9. In a method for manufacturing a scanning unit of a magnetic tape device, - an upper drum and a lower drum are manufactured separately, and at the same time as these drums are manufactured, corresponding positioning elements are formed on each drum, - the upper drum and the lower drum. and a drum, relatively positioned by a positioning element, and clamped on a lathe, and machining the peripheral surfaces of both the upper drum and the lower drum of the combination to form a guide surface at least partially, - the upper and lower drums are separated from each other, the head support and the associated drive are mounted on this head support, and the upper and lower drums are recombined and positioned relative to each other by positioning elements and the fixing device is installed. 1. A method of manufacturing a scanning unit, comprising interconnecting the scanning unit with each other. 10. During machining of the combined upper and lower drums,
10. The scanning unit manufacturing method according to claim 9, wherein the tool used is controlled both in the radial direction and in the axial direction. 11. The scanning unit manufacturing method according to claim 10, wherein one guide surface of the drum for guiding the edge of the magnetic tape is formed by controlled movement of the tool in the axial direction. 12. A method for manufacturing a scanning unit according to claim 9, characterized in that at least one tape guide is formed simultaneously by controlled axial and radial movement of the tool.