Magnetic-tape apparatus with pivotably mounted magnetic head

A magnetic-tape apparatus has a magnetic-head unit with a magnetic head having a head face for guiding a magnetic tape. The magnetic head has transducing gaps for writing and/or reading information onto/from the magnetic tape. The magnetic-head unit further comprises two height limiters having tape-guide surfaces for guiding an edge of the magnetic tape. A tangent line, which is tangent to both tape-guide surfaces, extends perpendicularly to an imaginary line in the head face and passing through the transducing gaps. If an edge of the magnetic tape is in contact with the two height limiters, the position of the magnetic tape relative to the magnetic head is always the same, so that no azimuth errors can arise. In order to bring this edge of the magnetic tape into contact with the height limiters, the magnetic-head unit is mounted so as to be pivotable about an axis perpendicular to a tangent plane to the head face at the location of the transducing gaps. This axis extends through the center of gravity of the magnetic-head unit.

BACKGROUND OF THE INVENTION 
This invention relates to a magnetic-tape apparatus comprising a 
magnetic-head unit including a magnetic head having a head face and at 
least one transducing gap, which extends in the head face, for writing 
and/or reading information onto/from a magnetic tape. The magnetic-head 
unit further comprises two height limiters each having a tape-guide 
surface for guiding an edge of the magnetic tape, a tangent line, which is 
tangent to both tape-guide surfaces, extending perpendicularly to an 
imaginary line in the head face parallel to the transducing gap. The 
imaginary line and the tangent line, which are perpendicular to one 
another, may intersect one another or cross one another. Such a 
construction of the magnetic-head unit ensures that in operation the 
longitudinal axis of the magnetic tape extends perpendicularly to the 
transducing gap, so that the magnetic tape always occupies the same 
position relative to the transducing gap during writing and reading of 
information on the magnetic tape and no azimuth error can occur. 
The invention further relates to a magnetic-head unit suitable for use in 
the magnetic-tape apparatus, which unit comprises a magnetic head having a 
head face and a transducing gap adjacent the head face, and two height 
guides, which each have a tape-guide surface. 
A magnetic-tape apparatus and a magnetic-head unit of the types defined 
above are known from U.S. Pat. No. 4,485,420 (herewith incorporated by 
reference). In order to ensure that an edge of a magnetic tape remains in 
contact with height limiters control elements arranged opposite said 
height limiters press against the other edge of the magnetic tape. In the 
known magnetic-tape apparatus these control elements are formed by 
resilient means. A magnetic-head unit of the known apparatus is fixedly 
mounted in the magnetic-tape apparatus and is provided with a magnetic 
head. The magnetic head has two transducing gaps for reading and writing a 
left-channel and right-channel stereo/audio signal. If, in operation, the 
longitudinal axis of the magnetic tape is not oriented perpendicularly to 
the transducing gap the height limiters in conjunction with the resilient 
means, will correct the position of the magnetic tape at the location of 
the magnetic-head unit. The magnetic tape is then urged into the correct 
position. This gives rise to stresses in the magnetic tape, as a result of 
which the magnetic tape is not pressed against the head face with the same 
force over its entire width and may even come off the head face near one 
of the edges. In analog audio recording in accordance with the generally 
known standard Compact Cassette system this does not lead to any 
significant problems because the transducing gaps extend across a 
substantial part of the width of the magnetic tape and the signals have a 
large wavelength, so that during recording a small clearance between the 
magnetic head and the magnetic tape may exist without immediately giving 
rise to any appreciable signal loss. 
In digital audio recording in accordance with the generally known standard 
Digital Compact Cassette system the magnetic head of the magnetic-tape 
apparatus has a comparatively large number of transducing gaps and the 
wavelength of the audio signals is substantially smaller than with analog 
audio recording. Should the magnetic tape come off the head face near one 
of the edges of the magnetic tape this would result in one or more 
transducing gaps being no longer in contact with the magnetic tape, 
leading to signal loss. 
SUMMARY OF THE INVENTION 
It is one of the objects of the invention to provide a magnetic-tape 
apparatus of the type defined in the opening sentence, having an improved 
contact between the magnetic tape and the magnetic head in comparison with 
the known magnetic-tape apparatus. To this end the magnetic-tape apparatus 
in accordance with the invention is characterized in that the 
magnetic-head unit is pivotably mounted in the magnetic-tape apparatus and 
under the influence of the magnetic tape is pivotable about a pivotal axis 
perpendicular to a tangent plane to the head face near the transducing 
gap. If now the longitudinal axis of the magnetic tape is not 
perpendicular to the transducing gap the control elements will again press 
an edge of the magnetic tape against the height limiters but instead the 
magnetic tape being urged into the correct position the magnetic-head unit 
will be pivoted to align itself relative to the magnetic tape. The 
magnetic tape is then hardly or not deformed, so that the magnetic tape is 
pressed against the head face with substantially the same force over its 
entire width. 
An embodiment of the magnetic-tape apparatus in accordance with the 
invention is characterized in that the pivotal axis extends through the 
centre of gravity of the magnetic-head unit. Thus, the magnetic-head unit 
will not subject the magnetic tape to any forces resulting from the 
pivotable arrangement and leading to deformation, so that an optimum 
contact can be obtained between the magnetic tape and the magnetic head. 
An embodiment of the magnetic-tape apparatus in accordance with the 
invention is characterized by the presence of a capstan and a pressure 
roller, the pressure roller having an at least substantially conical 
shape. Thus, the magnetic-tape apparatus has means for pressing the 
magnetic tape against the height limiters, thereby ensuring a correct 
positioning of the magnetic tape relative to the magnetic head. Since the 
magnetic-tape apparatus generally comprises a capstan and a pressure 
roller for the tape transport, the means for pressing the magnetic tape 
against the height limiters require hardly any additional adaptations of 
the magnetic-tape apparatus. The pressure which presses the magnetic tape 
against the height limiters is now produced as follows. In operation the 
pressure roller presses the magnetic tape against the capstan for the tape 
transport. Owing to the conical shape of the pressure roller the pressure 
roller exerts a moment on the magnetic tape, which at the location of the 
magnetic-head unit results in the magnetic tape being subjected to forces 
which press the magnetic tape with an edge against the height limiters. 
For this purpose the shape of the pressure roller need not be exactly 
conical but should be such that the magnetic tape is subjected to a moment 
resulting in a force which presses the magnetic tape against the height 
limiters. 
The magnetic-head unit in accordance with the invention is characterized in 
that the magnetic-head unit comprises pivoting means with a pivotal axis 
which extends perpendicularly to a tangent plane to the head face near the 
transducing gap. The pivotal axis preferably extends through the mass 
centre of the magnetic-head unit. 
These and other aspects of the invention will be apparent from and 
illustrated by means of the embodiments described hereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a magnetic-tape apparatus 1 in accordance with the invention, 
which apparatus is adapted to cooperate with a magnetic-tape cassette 3. 
The magnetic-tape apparatus 1 has two reel-drive spindles 5, 7 for the 
take-up and supply of magnetic tape on reels, two capstans 9, 11 
cooperating with two pressure rollers 13, 15 for the transport of magnetic 
tape in a longitudinal direction, and a magnetic-head unit 17 for reading 
and/or writing information from/onto magnetic tape. The magnetic-head unit 
17 is connected to a spindle 19, which is rotatable in a beating 21. 
FIG. 2 shows the magnetic-head unit 17. The magnetic-head unit 17 has a 
housing 23, which accommodates a magnetic head 25 having a head face 27. 
The housing 23 carries two tape guides 29, 31 having at their ends two 
height limiters 33, 35 and two tape-pressure walls 37, 39, which are 
inclined relative to the tape guides 29, 31 and which form control 
elements for pressing the magnetic tape against the height limiters 33, 
35. The height limiters 33, 35 have tape-guide surfaces 41, 43 for guiding 
an edge of the magnetic tape in operation. The magnetic-head unit 17 is 
pivotable about a pivotal axis 45 which is perpendicular to a plane 47 
tangent to the head face 27 at the location of transducing gaps 49 in the 
head face 27. The magnetic head 25 is accurately positioned in the housing 
23, an imaginary line 51 through the transducing gaps 49 and situated in 
the head face 27 being perpendicular to a tangent line 53 to the two 
tape-guide surfaces 41, 43 of the height limiters 33, 35. 
FIG. 3 illustrates the cooperation between the magnetic-head unit 17 and a 
magnetic tape 55 of a magnetic-tape cassette in operation. In operation 
the magnetic-head unit 17 extends partly into the magnetic-tape cassette 
via an opening in the housing of the cassette, the magnetic head 25 being 
in contact with the magnetic tape 55. Of the magnetic-tape cassette only 
the magnetic tape 55, tape guides 57, 59 provided in the magnetic-tape 
cassette and a tape-pressure felt 61 are shown. In operation the 
tape-pressure felt 61 presses the magnetic tape 55 against the head face 
of the magnetic head 25 at the location of the transducing gaps. For this 
purpose the tape-pressure felt 61 is arranged on a blade spring 63. The 
tape guides 57, 59 provided in the magnetic-tape cassette guide the 
magnetic tape 55 at both sides of the magnetic head 25 and thereby enlarge 
the wrapping angle of the magnetic tape around the magnetic head, which 
improves the head-to-tape contact. These tape guides 57, 59 are aim 
disposed on a blade spring 65. An edge 67 of the magnetic tape 55 is 
guided by the height limiters 33, 35. The other edge 69 of the magnetic 
tape 55 is guided by the tape-pressure walls 37, 39. Since these 
tape-pressure walls 37, 39 are inclined relative to the magnetic tape 55, 
the magnetic tape 55 is subjected to a force in a direction 71 towards the 
height limiters 33, 35. This construction of the magnetic-head unit 
ensures that an edge of the magnetic tape is always in contact with the 
height limiters, so that the magnetic tape always occupies the same 
position relative to the magnetic head and azimuth errors are consequently 
avoided. 
However, if in operation the longitudinal axis of the magnetic tape 
initially does not extend perpendicularly to the transducing gap the 
tape-pressure walls will urge the magnetic tape into the correct position. 
This gives rise to stresses in the magnetic tape, so that the magnetic 
tape is not pressed against the head face with the same force over its 
entire width and may even come off the head face near one of its edges. 
FIG. 4 shows the deformation of the magnetic tape 55 in the known 
magnetic-tape apparatus in operation. The magnetic tape 55 is deformed in 
the shaded areas 73 and 75 and may come off the tape guides 29, 31 and the 
magnetic head 25, which is undesirable. 
FIG. 5 illustrates the cooperation between a magnetic tape 77 and a 
magnetic-head unit 79 of the known magnetic-tape apparatus. In this 
apparatus the magnetic-head unit 79 is secured to a mounting surface 81 of 
the magnetic-tape apparatus, the imaginary line 83 through the transducing 
gaps of the magnetic head extending perpendicularly to the mounting 
surface 81 of the magnetic-tape apparatus. Moreover, the imaginary line 83 
extends perpendicularly to the tangent line 85 to the two tape-guide 
surfaces 87, 89. Since the inclined tape-pressure walls 97, 99 press the 
magnetic tape 77 against the tape-guide surfaces 87, 89 of the height 
limiters 93, 95 with an edge 91, the longitudinal axis 101 of the magnetic 
tape 77 extends perpendicularly to the imaginary line 83 through the 
transducing gaps. If initially the longitudinal axis of the magnetic tape 
does not extend perpendicularly to the imaginary line, represented as a 
broken line 103, the magnetic tape is urged into the correct position. As 
already stated, this gives rise to stresses in the magnetic tape. This may 
result in the magnetic tape coming off the head face of the magnetic head 
and, as a consequence, a break occurs in the signal transmission between 
the magnetic tape and the magnetic head. 
FIG. 6 illustrates the cooperation between a magnetic tape 55 and the 
magnetic-head unit 17 of the magnetic-tape apparatus in accordance with 
the invention. The magnetic-head unit 17 is connected to a spindle 19, 
which is rotatable in a beating 21. If the magnetic tape 55 is inclined 
relative to the mounting surface 105 of the magnetic-tape apparatus, the 
magnetic-head unit 17 is pivoted in that an edge 67 of the magnetic tape 
55 is pressed against the tape-guide surfaces 41, 43 of the height 
limiters 33, 35. In other words, the height limiters 33, 35 are pressed 
against the edge 67 of the magnetic tape 55 in that the tape-guide 
surfaces 37, 39 push off against the magnetic tape 55, causing the 
magnetic-head unit 17 to be pivoted in a manner such that the imaginary 
line 51 through the transducing gaps is oriented perpendicularly to the 
longitudinal axis 107 of the magnetic tape 55. In order to achieve a 
smooth pivotal movement the construction is such that the pivotal axis 
extends through the centre of gravity 109 of the magnetic-head unit 17. 
FIG. 7 shows a second embodiment of the magnetic-tape apparatus in 
accordance with the invention. Also in this embodiment a magnetic-head 
unit 111 is pivotable about an axis 113 and the magnetic-head unit has 
height limiters 115, 117 for guiding an edge 119 of a magnetic tape 121. 
However, the present magnetic-head unit 111 does not comprise any control 
elements in the form of, for example, tape-pressure walls to press an edge 
of the magnetic tape against the height limiters. For this purpose the 
magnetic-tape apparatus has a conical pressure roller 123. The pressure 
roller 123 presses the magnetic tape 121 against a capstan 125 in order to 
obtain proper contact between the magnetic tape and the capstan for the 
purpose of tape transport. Owing to the conical shape of the pressure 
roller 123 the pressure roller subjects the magnetic tape 121 to a moment 
127, which results in forces 129, 131 being exerted on the magnetic tape 
12 1 at the location of the magnetic-head unit 111, which causes the 
magnetic tape to be pressed against the height limiters 115, 117 with an 
edge 119. The shape of the pressure roller 123 need not be conical for 
this purpose but should be of a form such that the magnetic tape is 
subjected to a moment resulting in a force which presses the magnetic tape 
against the height limiters. 
Although the invention has been described with reference to the drawings 
this does not imply that the invention is limited to the embodiment shown 
in the drawings. The invention likewise relates to all embodiments which 
deviate from those shown in the drawings but fall within the inventive 
scope defined by the Claims. For example, for pressing the magnetic tape 
against the height limiters it is also possible to provide the 
magnetic-tape apparatus with other means than the means, such as the 
tape-pressure walls and the conical pressure roller, shown herein.