Magnetic-tape apparatus comprising a threading mechanism for the displacement of a magnetic tape and a belt so as to form tape buffers

A magnetic-tape apparatus is disclosed which includes a drive mechanism for driving a magnetic tape and tape reels, a magnetic-head mechanism buffer mechanism comprising a belt (8), guide elements for guiding the belt in an operational position, a tape-threading mechanism which during the thread-out phase threads the tape out of the cassette and wraps it around the magnetic-head mechanism and during the thread-in phase threads the tape into the cassette. A belt-threading mechanism threads the belt between the guide elements into the tape path during said thread-out phase and brings the belt back into its initial position during the thread-in phase. The apparatus (1) also includes a mechanism for moving the belt-threading mechanism in such a way that the belt can be brought into the desired operational position and into said initial position.

BACKGROUND OF THE INVENTION 
The invention relates to a magnetic-tape apparatus, having a frame and 
reel-drive means for two rotatable reels on which a magnetic tape is wound 
for the purpose of tape transport from one reel to the other, a length of 
said magnetic tape extending between the two reels. The apparatus has at 
least one magnetic head for recording and/or reproducing information 
on/from the magnetic tape, and movable tape-threading means constructed to 
bring the magnetic tape, which is movable between an initial position, in 
which the magnetic tape is not in contact with the magnetic-head means, 
and an operational position, in which the magnetic tape is in contact with 
the magnetic-head means, into said initial position or said operational 
position. Buffer means in the apparatus capable of buffering parts of the 
length of the magnetic tape comprise an endless flexible belt having two 
guide sections which constitute tape guides for the magnetic tape. The 
magnetic tape is guided over the outer sides of the guide sections, the 
buffer means, in said operational position, forms two tape buffers which 
in relation to the tape transport are situated upstream and downstream of 
the magnetic-head means. Movable belt-threading means bring the flexible 
belt, which is movable between an initial position, in which the belt is 
not in contact with the magnetic tape and is positioned at that side of 
the magnetic tape which is remote from the magnetic-head means and in 
which the belt-threading means are situated within the circumference of 
the belt, and an operational position, in which the belt is in contact 
with the magnetic tape in such a way that the belt can act as a buffer, 
into said initial position or said operational position of the belt. 
Tape-drive means drive the magnetic tape past the magnetic-head means at a 
location in that part of the tape path which is situated between the first 
and the last tape buffer. The apparatus also has two pairs of guide 
elements between which the belt is guided in its operational position, the 
two guide elements of each pair, viewed in the tape-transport direction, 
respectively define the beginning and the end of the guide sections of the 
belt in the operational position and guide the magnetic tape in the 
operational position towards and away from the guide sections, the paths 
of movement of the tape-threading means extending between said pairs of 
guide elements. 
A tape-transport device for such a magnetic-tape apparatus has been 
proposed in U.S. application Ser. No. 496,060, filed 3/16/90, which is a 
continuation of Ser. No. 311,438 filed Feb. 15, 1989, now abandoned, which 
is a continuation of Ser. No. 024,731 filed Mar. 11, 1987, now abandoned, 
(herewith incorporated by reference), which aims at providing a 
tape-transport device in which the reel movement and the movement of the 
tape past the magnetic-head means are dynamically isolated from one 
another in such a way that strongly varying speeds of the tape past the 
magnetic head means can be realized with a minimal delay. This 
tape-transport device comprises magnetic head means and reel-drive means 
comprising two rotatable reels on which a magnetic tape is wound, which 
tape, as it is unwound, is moved in its longitudinal direction away from 
one of the reels with a first speed, which tape is moved passed the 
magnetic-head means with a second speed which is variable in magnitude 
relative to the first speed. The buffer means comprises an endless belt, 
with two tape guides which are formed by guide sections of the running 
belt and which control tape buffers disposed in the tape path between said 
reels and the magnetic-head means. The positions of the guide sections 
relative to the axis of rotation of the reels and the magnetic head means 
can be changed in order to change the length of the tape of the tape 
buffers, which results the reel rotations being isolated from the movement 
of the tape past the magnetic-head means. 
Moreover, the tape transport device proposed in said Patent Application 
enables the magnetic head and the belt to be moved between their 
respective initial positions and their operational positions with the aid 
of movable tape and belt-threading means. In said tape-transport device 
the belt comprises two end portions bent through 180.degree. between which 
straight connecting portions are situated and in the operational position 
the belt is guided between two pairs of guide elements. In the operational 
position such a belt offers resistance to the motion movement between the 
guide elements because this requires some degree of elastic deformation of 
the belt. Moreover, owing to its shape such a belt cannot readily be 
positioned between the guide elements but must be inserted between the 
guide elements in a specific orientation. 
SUMMARY OF THE INVENTION 
It is the object of the invention to construct a magnetic-tape apparatus 
whose buffer system comprises a belt that offers less resistance to 
deformation and, consequently, offers less resistance to motion and to 
deformation during the displacement between the initial position and the 
operational position. To this end, the invention is characterized in that 
in the non-constrained situation, i.e. the situation in which the belt is 
not subject to any external forces, the flexible belt has at least 
substantially the shape of a circle, and the mutual arrangement of the 
guide elements and the properties of the belt are such that, if the center 
of the figure bounded by the belt circumference is situated between the 
four guide elements, the belt is in a stable situation in which, as a 
result of the balance between the internal forces caused by elastic 
deformation of the belt and the forces exerted on the belt by the guide 
elements, the belt adopts a shape characterized by two end portions which 
are bent through 180.degree. and which adjoin two substantially parallel 
straight portions. This yields a magnetic-tape apparatus in which, owing 
to its originally circular shape, the belt offers less resistance to 
motion because the elastic deformation is smaller and is the same for 
every part of the belt during a revolution, enabling the belt to be 
brought more simply into the operational position because the shape of the 
belt does not impose any preferred orientation. 
A preferred embodiment of the magnetic-tape apparatus in accordance with 
the invention is characterized in that in said initial position the belt 
is clamped between at least one stationarily arranged element and the 
tape-threading means and in said initial position the belt is situated in 
the space between the two reels and the magnetic tape. This is an 
advantage if instead of separate reels the reels are accommodated in a 
cassette, for which it is necessary that after loading of the cassette the 
belt is situated in a recess in the cassette and that the belt is situated 
at that side of the magnetic tape which faces the reels. 
Another preferred embodiment of the magnetic-tape apparatus is 
characterized in that the guide elements are arranged stationarily and the 
belt is deformed elastically as the it is brought into said operational 
position with the aid of the belt-threading means. 
As a result of this the guide elements need not be movable to bring the 
belt into the operational position. 
A further preferred embodiment of the magnetic-tape apparatus is 
characterized in that the belt-threading means comprise a belt-threading 
pin, and the path of movement of the belt-threading pin extends between 
those two guide elements, one of each pair, which are situated at the side 
of the reels and between both guide elements of one of the pairs, and as 
the belt is brought into said operational position the belt-threading pin 
brings the entire belt into one of the tape-path branches between the 
magnetic-head means and the reels, after which by take-up onto at least 
one of the reels the magnetic tape is moved partly from one tape-path 
branch into the other tape-path branch to assume its operational position. 
As a result of this only one belt-threading pin is required for bringing 
the belt into its operational position. The known tape-transport device 
does not comprise any means with which the threading means can be 
displaced. To this end a further preferred embodiment of the magnetic tape 
apparatus is characterized in that the belt-threading means comprise a 
belt-threading pin, in that each threading means is secured to an arm at 
one end of said arm, which arm near its other end is secured to a 
rotatable spindle having substantially the same orientation as the 
threading means, in that during threading-in the two tape-threading means 
are moved first and subsequently the belt-threading pin, and during 
threading-out the belt-threading pin is moved first and subsequently the 
tape-threading means, in that the movement of the arm of the 
belt-threading pin is performed in another plane than the movement of the 
nearest arm of one of the tape-threading means, and in that the arms to 
which the tape-threading means are secured are curved in such a way that 
the movement of the arms is not restrained by the presence of the guide 
elements or by the presence of the spindles to which the arms are secured. 
This results in a compact construction, which can perform the required 
displacements for the tape and belt-threading means, which comprises a 
small number of parts and in which the displacement is attended with 
minimal friction. 
A further preferred embodiment of the magnetic-tape apparatus is 
characterized in that the arm of the belt-threading pin is arcuate, and 
the arms of the tape-threading means each comprise two portions which 
extend at an angle of approximately 90.degree. relative to one another. 
This is necessary in order to ensure that the movement of the threading 
means is not obstructed by the drive spindle of the arm of the 
belt-threading pin and by the guide elements. 
A further preferred embodiment of the magnetic-tape apparatus is 
characterized in that the guide elements are constructed as guide rollers, 
in that the tape-drive means comprise a capstan and a pressure roller, in 
that the belt-threading means comprise a belt-threading pin, in that the 
tape-threading means are constructed as tape-threading rollers, of which 
at least one of the two rollers functions as a pressure roller for the 
capstan, in that the magnetic-head means comprise a rotatable and a 
stationary magnetic-head unit, which rotatable magnetic-head unit 
comprises at least one rotatable magnetic head and which stationary 
magnetic-head unit comprises at least one stationary magnetic head, in 
that the frame comprises a supporting plate formed with openings through 
which the tape-threading rollers can move, and in that the drive means for 
the reels comprise drive spindles. 
This results in a construction which exhibits minimal friction between the 
tape and the guide and tape-threading rollers during tape transport. 
Moreover, on account of the rotatable magnetic-head unit the apparatus can 
now be constructed as a helical-scan apparatus. 
Yet another preferred embodiment of the magnetic-tape apparatus is 
characterized in that the two reels are accommodated in a magnetic-tape 
cassette whose housing is provided with two tape guides near the front 
corners, between which tape guides a taut part of the tape extends when 
the cassette is not in operation, which housing has a recess behind said 
part of the tape, which recess has such a shape that the endless belt can 
be positioned in said recess, and in that the threading means are adapted 
to withdraw the magnetic tape and the belt from the magnetic-tape cassette 
towards the magnetic-head means to bring the magnetic tape and the belt 
into their respective operational positions. This has the advantage that 
during loading of the cassette the cassette housing can be placed with its 
recess over the belt, so that during threading-in of the magnetic tape the 
belt does not obstruct the tape and during the threading-in movement 
towards the operational position the belt is readily movable into a 
position between the guide elements. 
A further preferred embodiment of the magnetic-tape apparatus is 
characterized in that the plane of movement of the arm of the 
belt-threading pin is situated above the planes of movement of the arms of 
the tape-threading means. This is necessary because if the plane of 
movement of the belt-threading pin should coincide with the planes of 
movement of the arms of the tape-threading means the arms would restrain 
each other's motions. 
A further preferred embodiment of the magnetic-tape apparatus is 
characterized in that during threading-in of the belt and the magnetic 
tape, when they are both brought from an operational position into an 
initial position, after the movement of the belt-threading pin the 
right-hand tape-threading means begins to move first, followed by the 
left-hand tape-threading means. 
This has the advantage that the belt resumes the same position as in the 
initial situation. As a result of this no additional operations are 
required to attain the required initial position of the belt, in which a 
cassette can be placed over the belt. 
Yet another preferred embodiment of the magnetic-tape apparatus in 
accordance with the invention is characterized in that the belt is made of 
polyethylene terephthalate. This material is already elastically 
deformable under a very small external force and resumes its original 
shape if said external force is removed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The magnetic-tape apparatus 1 is constructed to cooperate with a magnetic 
tape 7 accommodated in a cassette 29. The magnetic tape 7 is wound on 
reels 5, 6 accommodated in the housing of the cassette 29. After the 
cassette 29 has been loaded into the magnetic-tape apparatus 1 the reels 
5, 6 can be driven by electric motors 41, 42 by means of spindles 3, 4 
which form part of the reel-drive means. The magnetic-tape apparatus 1 
comprises magnetic-head means which in the present embodiment comprise a 
rotatable magnetic-head unit, which comprises a rotatable drum 9 carrying 
two rotatable magnetic heads 11a, and a stationary magnetic-head unit 10, 
not shown in FIG. 1 and comprising a stationary magnetic head 11b. A 
shutter, not shown, is arranged at the front of the cassette 29 in its 
open position it exposes a length of tape 31. In the initial position of 
the magnetic-tape apparatus 1, in which the magnetic tape 7 is not in 
contact with the magnetic-head means, said length of tape 31 is stretched 
over two tape guides 32, 33 disposed near the two front corners of the 
cassette 29. Behind this length of tape 31 the cassette 29 has a recess 30 
in which a flexible endless belt 8 is situated in an initial position, 
which initial position is characterized by the fact that the belt 8 is not 
in contact with the magnetic tape 7. A belt-threading means constructed as 
a belt-threading pin 14 is arranged within the circumference of the belt 
8. This belt 8 is clamped between, on the one hand, four pins 28 arranged 
on a supporting plate 2 and, on the other hand, two tape-threading means 
constructed as tape-threading rollers 12, 13. In the initial position of 
the belt 8 the pins 28 and the tape-threading rollers 12, 13 are also 
situated in the recess 30 formed in the cassette 29. The supporting plate 
2 forms part of the frame of the apparatus 1. The tape-threading rollers 
12, 13 and the belt-threading pin 14 are secured to arms 15, 16, 17 
connected to spindles 18, 19, 20 which, in a manner not shown, can be 
driven by one or more electric motors. 
In the operational position of the magnetic tape 7, in which the magnetic 
tape 7 is in contact with the magnetic-head means (FIG. 6), buffer means 
are situated between the magnetic-head means and the cassette 29. The 
buffer means comprise the endless belt 8, which in its operational 
position, in which the belt 8 is in contact with the magnetic tape 7, is 
guided at its outer circumference between guide elements 21, 22, 23, 24 
constructed as rollers arranged on the supporting plate 2. These guide 
rollers 21, 22, 23, 24 guide the magnetic tape 7 near the entry and exit 
locations of the magnetic tape 7 in tape buffers 34, 35 formed by the belt 
8, which locations also constitute the beginning and the end respectively 
of the guide sections 36, 37 of the belt 8 which function as tape guides. 
The arm 17 on which the belt-threading pin 14 is arranged, is arcuate in 
order to enable the rotation required for threading the belt 8 to be 
realised without being obstructed by one of the guide rollers 21, 22, 23, 
24. The arms 15, 16 of the tape-threading rollers 12, 13 each comprise two 
portions which extend at an angle of substantially 90.degree. relative to 
each other in order not to be obstructed by the spindle 20 of the arm 17 
of the belt-threading pin 14. The arm 17 of the belt-threading pin 14 
extends above the supporting plate 2 and the arms 15, 16 of the 
tape-threading rollers 12, 13 are situated underneath the supporting plate 
2. Openings 25, 26 formed in the supporting plate 2 allow movement of the 
tape-threading rollers 12, 13 and define the paths of movement of the 
tape-threading rollers 12, 13. 
In the operational position the magnetic tape 7 is driven by tape-drive 
means comprising a pressure-roller/capstan 27 combination driven by an 
electric motor 43. Driving is effected at the location of the left-hand 
tape-threading roller 12, which functions as the pressure roller for the 
capstan 27 on the supporting plate 2. In the operational position of the 
belt 8 the position of the right-hand guide section 37 is dictated by 
position-detection means comprising a position-detection unit 38 provided 
with a combination of a light source 39 and a light-sensitive cell 40. In 
the left-hand tape-path branch, between the tape-drive means and the 
left-hand tape buffer 34, tape-tension detection means 44 are arranged. 
These means 44 comprise a pressure roller 46 which presses against the 
magnetic tape 7 with a substantially constant pressure. The tension in the 
magnetic tape 7 is derived from the position of the pressure roller 46. 
For controlling the tape tension and the position of the belt 8 and for 
locating information on the tape 7 the drive means are controlled by a 
control unit comprising a microprocessor 45. This microprocessor 45 
receives measurement signals (a) from the tape-tension detection means 44, 
from the position-detection unit 38, and from the magnetic-head units 9, 
10, which together with signals (c) corresponding to the desired situation 
are processed to derive control signals (b) supplied by the microprocessor 
45 for controlling the electric motors 41, 42, 43 for the drive systems. 
The signals (c) corresponding to the desired situation are obtained from 
input means, not shown, which may be external to or arranged in the 
apparatus 1. Said input means may be constituted by a computer. 
In order to make the apparatus 1 described above suitable for the storage 
of large amounts of information, in such a way that random access to the 
information on a specific length of tape is possible, the microprocessor 
45 should be capable of performing a plurality of additional operations to 
be described hereinafter. Moreover, the information on the magnetic tape 7 
should meet some requirements to enable the system comprising the 
magnetic-tape apparatus 1 and the magnetic tape 7 to be used for the above 
purpose. To this end the information on the magnetic tape 7 is divided 
into sections 47 (FIG. 10) having a length which is smaller than or equal 
to the total length of the tape buffered by the two tape buffers 34, 35 
and constituting the buffer capacity. In each section 47 the information 
is recorded in individual discrete tracks 48. Each section 47 has a 
magnetically recorded address 49 to locate a section 47 during fast 
winding. Reading and writing the address 49 from/onto the magnetic tape 7 
is possible by means of the rotary magnetic heads 11a or by means of the 
stationary magnetic head 11b. In the latter case the magnetic tape 7 has a 
separate longitudinal track 50 (FIG. 11). 
For controlling the tape drive in order to wind the magnetic tape 7 within 
the section 47 rapidly in either direction and hence bring the individual 
discrete tracks 48 before the magnetic-head means the system comprises 
control means, which include said microprocessor 45. For the rapid 
location of a selected address the system comprises a selection device, 
which also includes said microprocessor 45. 
The operation of the apparatus 1 described in the foregoing will now be 
explained with reference to the figures. The magnetic-tape cassette 29 is 
loaded into the apparatus 1 and brought into an initial position (FIG. 1). 
In this position the shutter at the front of the cassette 29 is open to 
expose a length of tape 31 stretched between two tape guides 32, 33 
arranged in the front part of the cassette 29. In this position the two 
reels 5, 6 in the cassette 29, on which the magnetic tape 7 is wound, 
engage with drive spindles 3, 4 of the apparatus 1. 
In the initial position the flexible belt 8 is situated in the recess 30 in 
the cassette 29 behind said length of tape 31. The belt 8 is clamped 
between, on the one hand, the four pins 28 on the supporting plate 2 and, 
on the other hand, the two tape-threading rollers 12, 13. The 
belt-threading pin 14 is situated within the periphery of the belt 8. 
During the tape thread-out phase the magnetic tape 7 is brought from said 
initial position into the operational position, in which the magnetic tape 
7 is in contact with the magnetic head means 9, 10 (FIG. 3). The magnetic 
tape 7 is then withdrawn from the cassette 29 by means of the two tape 
threading rollers 12, 13 and is moved between the two pairs of guide 
rollers 21, 22 and 23, 24 (FIG. 2) to the magnetic-head means 9, 10, where 
the magnetic tape 7 is wrapped around the drum 9 through an angle of 
90.degree. (FIG. 3). The movement of the tape-threading rollers 12, 13 is 
passed by rotating the spindles 18, 19 of the arms 15, 16 to which the 
tape-threading rollers 12, 13 are secured. If the left-hand tape-threading 
roller 12 had been secured to a straight arm this arm would intersect the 
spindle 20. In order to solve this problem the arm 15 is constructed in 
such a way that it does not intersect said spindle 20 during threading-in 
and threading-out of the tape 7. 
Now the belt-threading phase is started, in which the belt 8 is threaded 
into the tape path by means of the belt-threading pin 14. First of all the 
belt 8 is threaded into the left-hand tape-path branch, which branch 
extends from the cassette 29 to the magnetic-head means 9, 10. This is 
achieved by rotating the spindle 20 of the curved arm 17 carrying the 
belt-threading pin 14 in the counter-clockwise direction. The 
belt-threading pin 14 then moves the belt 8 and draws it between those two 
guide rollers 22, 24, one of each pair, which are situated at the side of 
the cassette 29 and between the guide rollers 21, 22 of the left-hand pair 
(FIG. 4) until the belt 8 is situated wholly within the left-hand 
tape-path branch (FIG. 5). The belt-threading pin 14 then performs an 
arcuate movement through an angle of approximately 270.degree. around the 
guide roller 22. Since the pivot of the arm 17 carrying the belt-threading 
pin 14 is situated at the location of the spindle 20 and since the plane 
in which the arm 17 moves is situated above the supporting plate 2, which 
also carries the guide roller 22, the arm 17 should be given an arcuate 
shape in order to move the belt-threading pin 14 around the guide roller 
22. During this phase the belt 8 is deformed elastically and the magnetic 
tape 7 is unwound from the left-hand reel 5. Subsequently the 
belt-threading pin 14 is moved back until it is situated between the guide 
rollers 21, 22, 23, 24. Finally, in order to reach the operational 
position of the belt 8, the belt 8 is moved partly out of the left-hand 
tape-path branch into the right-hand tape-path branch by winding a small 
length of tape onto the left-hand reel 5 (FIG. 6). 
In the operational situation the magnetic-tape apparatus 1 allows random 
access to any arbitrary section of the tape 7 of a specific length by 
moving the part of tape containing this section with a varying speed and 
in alternate directions past the magnetic-head means 9, 10, and for 
locating a specific section the magnetic tape 7 can be transported with a 
high speed during which transport the magnetic-head means 9, 10 scan the 
tape 7. 
Random access is particularly suitable in the case of 
high-information-density tape-recording, preferably helical-scan 
recording, so that tape transport can be minimal and short access times 
can be achieved. Moreover, in the case of helical-scan recording the 
information on the tape 7 is accommodated in the required individual 
discontinuous tracks 48 (FIGS. 10 and 11). When helical scanning is used 
in the apparatus 1 in accordance with the invention this means that the 
tape can leave the plane of the reels 5, 6 only in the part situated 
between the two buffers 34, 35. 
Locating a specific section 47 on the tape 7 at high speed is controlled by 
a selection device which comprises the microprocessor 45. Depending on the 
addresses 49 written by the magnetic heads 11a or 11b and the desired 
address entered via the input means said microprocessor 45 controls the 
drive of the reels 5, 6 in such a way that the tape 7 is moved at a higher 
speed until the desired address is found. 
As a result of this high relative tape/head speed the inclined information 
track 48 on the magnetic tape 7 (FIG. 10) cannot be scanned correctly 
because the path of the magnetic heads 11 over the tape 7 extends at a 
different angle when the speed of rotation of the magnetic head drum 9 is 
not changed. However, it is possible to read the beginning of such an 
inclined track 48. This beginning should then contain the address 49 of 
the section 48. Another method of reading the relevant information from 
the tape 7 at high tape-transport speeds is to use an additional 
longitudinal track 50 on the tape 7 (FIG. 11), which is scanned by a 
stationary magnetic head 11b. 
During this rapid-search mode the microprocessor 45 also controls the 
position of the belt 8 and the tape tension. In the operational position 
the belt 8 should remain guided between the four guide rollers 21, 22 or 
23, 24. The position-detection unit 38 supplies information about the 
position of the belt 8 to the microprocessor 45, which provides a position 
correction by making the left-hand reel 5 rotate more rapidly or slowly. 
If the speed with which the left-hand reel 5 takes up the tape 7 is higher 
or lower than the speed with which the capstan 27 drives the tape 7, the 
tape tension in the left-hand tape-path branch will increase or decrease 
respectively, causing the belt 8 to be moved to the right or the left 
respectively in order to restore the balance between the forces exerted on 
the belt 8 by the tape 7. 
In order to control the tape tension the microprocessor 45 controls the 
drive of the right-hand reel 6. If the speed with which the tape 7 is 
unwound from the right hand reel 6 is varied to be higher or lower than 
the speed with which the capstan 27 moves the tape 7, the tension in the 
right-hand tape-path branch is reduced or increased respectively. The 
balance between the forces acting on the belt 8 will cause the tape 
tension in the left-hand tape-path branch to change accordingly. The 
control system described above relates to tape transport from the 
right-hand reel 6 to the left-hand reel 5 but a similar line of reasoning 
can be applied to tape transport in the reverse direction. 
Once the desired section has been found the information within the section 
can be read or random access can be applied to the information within the 
section. Effective random access to an information carrier requires that 
the relevant location on the carrier must be formed rapidly. For this 
purpose the tape transport past the magnetic-head means is controlled by 
control means which also include the microprocessor 45. For locating an 
information track 48 within a section 47 the microprocessor 45 should have 
information about the position of the track 48 within the section 47. This 
can be achieved by assigning a separate track address to every track or by 
counting the number of tracks traversed, starting from a known position 
(for example the middle of the section). 
Since the masses of the two reels 5, 6 are too large to realise the 
required transport speeds via rotation of the reels with the aid of the 
electric motors 41, 42 in the apparatus 1, another solution should be 
adopted. The solution to this problem is that the reels 5, 6 should remain 
stationary and that the magnetic tape 7 is moved past the magnetic-head 
means 9, 10 by the tape-drive means 27, tape buffers 34, 35 being provided 
in the tape path at opposite sides of the magnetic-head means 9, 10. 
In order to enable all the tracks 48 within a section 47 to be moved 
towards the magnetic-head means the middle of the section 47 should be 
situated opposite the magnetic head 11a when the random access phase 
begins, and the belt 8 should be in its centre position in which the tape 
lengths in the two buffers 34, 35 are equal. Moreover, the length of the 
section 47 should not be larger than the length of each tape buffer 34, 
35. In addition, the tape tension at the location of the magnetic-head 
means 9, 10 should be sustained during acceleration, deceleration and 
reversal of the direction of transport of the magnetic tape 7. Said buffer 
system meets all the requirements. The mass of the elements to be 
accelerated (the mass of the length of tape plus half the mass of the belt 
8) is low, so that the tape-drive means 27 (the combination of the capstan 
27 and the pressure roller 12) in the apparatus 1 are capable of providing 
the required acceleration and deceleration. Since the use of the belt 8 
ensures that the changes in the lengths of the portions of the tape 
buffers 34, 35 guided over the belt 8 are complementary, i.e. the length 
reduction at one side of the belt 8 is equal to the length increase at the 
other side, the tension in the magnetic tape 7 will be maintained. 
The buffer system is also very suitable for use in, for example, video 
recorders in order to read the relevant information from the tape during 
winding at different speeds, for example in the "search mode" of the video 
recorder. 
The reel rotation then ensures that the tape 7 at the location of the guide 
rollers 22, 24 nearest the cassette 29 is moved with a first speed. The 
tape-drive means 27 ensure that at the location of the guide rollers 21, 
23 nearest the magnetic-head means 9, 10 and at the location of the 
magnetic-head means 9, the tape 7 is moved with a second speed. The first 
speed of the tape 7 is also the revolution speed of the belt 8. The 
difference between the first and the second speed of the tape 7 is the 
translational speed of the belt 8. This translational speed is directed 
perpendicularly to the connecting line between the drive rollers 23, 24 of 
a pair and is obtained automatically without an additional drive owing to 
the difference between said first and said second speed. This translation 
enables the length of the guide sections 36, 37 to be varied, which is 
accompanied by a change in length of the tape portions guided over the 
belt 8. 
In this way the guide sections 36, 37 constitute tape buffers 34, 35, 
enabling the speed of the tape 7 past the magnetic-head means 9, 10 to be 
varied considerably at a semi-stationary winding speed of the reels 5, 6. 
This has the advantage that during fast winding the speed of the tape 7 
relative to the magnetic-head means 9, 10 can be reduced for brief periods 
to scan said tape with the normal speed, whereas during the other periods 
the tape 7 can be moved past the magnetic-head means 9, 10 at a higher 
speed (FIG. 7). The position-detection element 38 controls the speed of 
the drive spindles 5, 6 and the capstan 27 in such a way that the belt 8 
cannot exceed its permissible extreme position and in such a way that the 
tape tension is maintained constant. 
Before the cassette 29 can be removed from the apparatus 1 the tape 7 and 
the belt 8 should be returned into their initial positions. The 
belt-threading pin 14 is then first brought into its initial position by 
rotating the spindle 20 carrying the arm 17 to which the belt-threading 
pin 14 is secured. The belt-threading pin 14 then withdraws the belt 8 
from the tape-path branches and partly returns the belt 8 to its initial 
position (FIG. 8). Subsequently, the tape 7 is returned into its initial 
position by moving back the two tape-threading rollers 12, 13, which is 
effected by rotating the spindles 18, 19 of the arms 15, 16 carrying the 
tape-threading rollers 12, 13. The two tape-threading rollers 12, 13 then 
push the belt 8 back against the four pins 28 (FIG. 9) in the apparatus 1 
and the tape 7 is wound onto the reels 5, 6 by the drive spindles 3, 4. It 
is then necessary that the right-hand tape-threading roller 13 is returned 
first, because this roller pushes the belt 8 to the right whereas the belt 
8 at the left side is retained by the belt-threading pin 14. If the 
left-hand tape-threading roller 12 would be returned first the belt 8 will 
be situated at the extreme left inside the recess 30 in the cassette 29, 
because the belt 8 is not retained at the right. Now the cassette 29 can 
be removed from the apparatus 1. 
The threading mechanism, the buffer mechanism, the control system for the 
buffer mechanism and the control system for information storage and random 
access to the information can also be employed in systems in which the 
information is recorded in one or more longitudinal tracks on the magnetic 
tape. In that case the rotatable head unit may be replaced by a stationary 
head unit. In a system with individual discontinuous tracks the tracks may 
alternatively extend perpendicularly to or in the longitudinal direction 
of the tape. However, the rotary head unit should then be adapted 
accordingly. 
Moreover, the stationary head unit may be provided with a plurality of 
heads in the case of a plurality of address tracks. The stationary head 
unit may further comprise an erase head for erasing the information on the 
tape. Furthermore, the rotary head unit may be provided with a plurality 
of heads in order to achieve an even higher information density on the 
tape. The system is suitable both for analog and for digital information 
storage. 
The threading means need not necessarily be actuated by means of arms which 
are rotatable about spindles. Instead, the threading means may be actuated 
by linkage mechanisms or slotted-link mechanisms. Alternatively, the 
threading means may be secured to elements which are moved over rails or 
through guideways. Moreover, the belt can be threaded by two or more 
threading pins, during which threading operation the belt need not 
necessarily be threaded completely into one tape-path branch, but may be 
threaded into both tape-path branches at the same time, or the guide 
elements can be moved outwards during threading to engage them over the 
belt. 
The planes of movement of the arms of the belt-threading means need not 
necessarily be situated above those of the arms of the tape-threading 
means, but the two planes may also be interchanged. The supporting plate 
with the openings for the paths of movement of the tape-threading means 
may be dispensed with for reasons of constructional engineering. The four 
pins which are rigidly connected to the frame and against which the belt 
is clamped in the initial position may be replaced by one or more other 
elements such as, for example, a plate or a strip. 
Instead of defining the position of the belt at one end portion it is 
alternatively possible to arrange detection means in the proximity of the 
permissible extreme positions of the belt end portions, which detection 
means indicate when the belt has reached one of its extreme positions. 
Moreover, a separate pressure roller, which presses the tape against the 
capstan in the operational position, can be moved along with the 
tape-threading means during threading of the tape instead of one of the 
tape-threading rollers being used as a pressure roller. Alternatively, the 
belt can be made of other materials, provided that these have a 
satisfactory elasticity, another suitable material being for example 
phosphor bronze.