A ROTARY MAGNETIC HEAD DEVICE FOR A MAGNETIC RECORDING AND REPRODUCING APPARATUS.

Abstract: A rotary magnetic head device for a helical scanning magnetic recording and reproducing apparatus comprises a rotary drum, a thin-film magnetic head (6) protruding from said rotary drum in a diametrical direction for coming into contact with a magnetic tape (7), obliquely woundable around part of the outer peripheral surface of said rotary drum, and head control means for adjusting the protrusion of the magnetic head (6) in the diametrical direction. The head control means comprises a feed-forward control arrangement (9) to bring and hold the magnetic head into a protruded position in which it exerts a constant normal force on a tape (7) wound around the drum.

Description: A rotary magnetic head device for a magnetic recording and reproducing apparatus. The present invention relates to a rotary magnetic head device for a helical scanning magnetic recording and reproducing apparatus, comprising a rotary drum, a thin- film magnetic head protruding from said rotary drum in a diametrical direction for coming into contact with a magnetic tape, obliquely woundable around part of the outer peripheral surface of said rotary drum, head control means for adjusting the protrusion of the magnetic head in the diametrical direction. Such a rotary magnetic head device is known from US-A-5,223,992. The device in this document is provided with an envelope detector for detecting an envelope of an reproduced signal from said magnetic head, search means, coupled to the envelope detector, for obtaining a minimum amount of projection of said magnetic head in a projection range in which a detected envelope level is saturated, by sequentially driving the magnetic head to vary the projection of the magnetic head, and control means for controlling said magnetic head to position the magnetic head at a projection which coincides with the minimum amount of projection obtained by the search means. In other words the head control means comprises a feed-back control arrangement to bring and hold the magnetic head into a desired protruded position. An object of the invention is to simplify this magnetic head device while maintaining a good contact between the magnetic head and the tape, together with a relatively low thin-film head wear. To achieve this object the rotary magnetic head device in accordance with the invention is characterized in that the head control means comprises a feed-forward control arrangement to bring and hold the magnetic head into a protruded position in which it exerts a constant normal force on a tape wounded around the drum. This normal force is preferably about 3-4 mN, which values correspond more or less with about 10% of the normal force exerted by an ordinary inductive head. The omission of a specific feed-back arrangement implies a simplification with respect to the above mentioned prior art, while still the desired accuracy is obtained. In a particular embodiment the feed-forward control arrangement comprises a voice-coil-actuator which is energized with a constant electric current, the strength of which determining the magnitude of the normal force. This current will preferably be adjusted in such a manner that a normal force of about 3-4 mN is exerted on a tape wounded around the drum. The wear of the magnetic head is small compared with the voice-coil-actuator dimensions. The force exerted by means of the voice-coil-actuator varies linearly over such small length changes. Although a certain protection of the magnetic head caused by sudden mechanical shocks is obtained by the forced contact of the magnetic head against the tape, it may be desirable to provide the voice-coil-actuator with a voice-coil and a magnetic rod movable therethrough, of which magnetic rod one end is coupled with the magnetic head and the other end with a damping device. Over long time scales, such as those associated with wear, the damping will have no impact. Further, in this respect elastomer connection means may be provided to couple the magnetic head with the magnetic rod. In a specific embodiment the device comprises a house-like element for said magnetic head and said voice-coil-actuator. This house-like element comprises a first hole to accommodate the magnetic head, which first hole debauches into a second hole, the second hole accommodating the voice-coil-actuator and being in line with and wider than the first hole. A tape which, without contact with a magnetic head as in the case of an inductive head, is stretched over the first hole, will act like a drum membrane and will vibrate. These vibrations tend to modify the head-to-tape distance, giving rise to fluctuations and noise in the magnetic head signal. By the above mentioned low normal force of 3-4 mN such fluctuations and noise are strongly reduced. Further, the width of the first hole in at least the tape track direction must be matched to the dimensions of the magnetic head. On the one hand side motions of the magnetic head in the tape track direction must be strongly limited, while on the other hand the friction between the inner wall of the first hole and the magnetic head must be kept small with respect to the above mentioned constant normal force. To prevent the magnetic head from being launched out of the first hole, in the house-like element there is provided a stop for the movement of the magnetic head in the diametrical direction out of the house-like element. The invention also relates to a helical scanning magnetic recording and reproducing apparatus provided with a rotary magnetic head device in accordance with the invention as described here before. The invention will now be described in more detail, by way of example, with reference to the drawings, in which Fig. 1 is a diagrammatic side view of a rotary magnetic head device for a helical scanning magnetic recording and reproducing apparatus, and Fig. 2 a diagrammatic view of an embodiment of the magnetic head in accordance with the invention. The rotary magnetic head device for a helical scanning magnetic recording and reproducing apparatus as illustrated in fig. 1 comprises a rotary drum 1 and a fixed drum 2 situated below the rotary drum. The fixed drum 2 is rigidly connected in an oblique position to the house 3 of the helical scanning magnetic recording and reproducing apparatus and is provided with a motor for driving the rotary drum 1 with respect to the fixed drum 2. The rotary drum 1 is provided with two recesses 4, only one of which being visible in fig. 1, in each of which a house-like element 5 with a magnetic head 6 is mounted (fig. 2). When a magnetic tape 7 is wounded around part of the outer peripheral surface of the rotary drum 1 and moved along the magnetic head device, as a consequence of the oblique position thereof with respect to the house 3 and therefore to the tape 7, information is recorded or reproduced according oblique magnetic tracks 8. The magnetic head 6 is of the thin-film type and protrudes from the rotary drum 1 in the diametrical direction for coming into contact with the magnetic tape 7. In order to avoid fluctuations in the signal strength and to minimize noise, the rotary magnetic head device is provided with head control means for adjusting the protrusion of the magnetic head 6 and therewith the normal force exerted by the magnetic head 6 on the tape 7. The head control means comprises a feed-forward control arrangement, in the embodiment shown in fig. 2 formed by a voice-coil-actuator 9 which is energized with a constant electric current to bring and hold the magnetic head into a protruded position in which it exerts a constant normal force on the tape 7. In the present embodiment this normal force is about 3-4 mN and can be obtained by means of voice-coil-actuators which, as required, are small enough, viz. with a cross-section of about 1 x 1,5 mm 2 . The voice-coil-actuator 9 comprises a voice- coil 10 and a magnetic rod 11 movable therethrough, of which magnetic rod 11 one end is coupled with the magnetic head 6 and the other end with a damping device 12. Elastomer connections means 13 are provided to couple the magnetic head 6 with the magnetic rod 11. The house-like element 5 comprises a first hole 14 to accommodate the magnetic head 6. This first hole 14 debauches into a second hole 15, the second hole 15 accommodating the voice-coil-actuator 9. The second hole 15 is in line with and wider than the first hole 14. The first hole 14, having a width W in the direction parallel to the tape tracks 8 in the order of 25 μm, is matched in the tape track direction to the dimensions of the magnetic head 6, viz. in such a way that side motions of the magnetic head 6 in the tape track direction are strongly limited, while the friction between the inner wall of the first hole 14 and the magnetic head 6 is kept small with respect to the normal force exerted by the magnetic head 6 on the tape 7. Further, in the house-like element 5, and in the embodiment of fig. 2 in the second hole 15 thereof, there is provided a stop 16 for the movement of the magnetic head 6 in the diametrical direction out of the house-like element 5. It is to be noted that the invention is not limited to the described embodiment and that many modifications thereof are possible. In the rotary magnetic head device one or more magnetic heads, each in a corresponding house-like element, can be brought, depending on the rotational speed of the rotary drum and the required tape track distance. Instead of a voice-coil-actuator other types of feed-forward control arrangements can be applied, such as a mechanical feed-forward control arrangement in the form of controllable spring-like elements. It is noted that the feed-forward control arrangement (servo filter) may also be implemented as the cascade of a synchronous demodulator and a 5th order anolog filter. This measure has a favourable effect on the performance.

Claims: CLAIMS: 1. A rotary magnetic head device for a helical scanning magnetic recording and reproducing apparatus, comprising a rotary drum, a thin-film magnetic head protruding from said rotary drum in a diametrical direction for coming into contact with a magnetic tape, obliquely woundable around part of the outer peripheral surface of said rotary drum, head control means for adjusting the protrusion of the magnetic head in the diametrical direction, characterized in that the head control means comprises a feed-forward control arrangement to bring and hold the magnetic head into a protruded position in which it exerts a constant normal force on a tape wounded around the drum. 2. A rotary magnetic head device according to claim 1, characterized in that the normal force is about 3-4 mN. 3. A rotary magnetic head device according to claim 1 or 2, characterized in that the feed-forward control arrangement comprises a voice-coil-actuator which is energized with a constant electric current, the strength of which determining the magnitude of the normal force. 4. A rotary magnetic head device according to claim 3, characterized in that the voice-coil-actuator comprises a voice-coil and a magnetic rod movable therethrough, of which magnetic rod one end is coupled with the magnetic head and the other end with a damping device. 5. A rotary magnetic head device according to claim 4, characterized in that elastomer connection means are provided to couple the magnetic head with the magnetic rod. 6. A rotary magnetic head device according to any one of the claims 3-5, characterized in that the device comprises a house-like element for said magnetic head and said voice-coil-actuator. 7. A rotary magnetic head device according to claim 6, characterized in that the house-like element comprises a first hole to accommodate the magnetic head, which first hole debauches into a second hole, the second hole accommodating the voice-coil-actuator and being in line with and wider than the first hole. 8. A rotary magnetic head device according to claim 7, characterized in that at least in the tape track direction the width of the first hole must be matched to the dimensions of the magnetic head, such that side motions of the magnetic head in the tape track direction are limited, while friction between the inner wall of the first hole and the magnetic head is kept small with respect to the said constant normal force. 9. A rotary magnetic head device according to claim 7 or 8, characterized in that in the house-like element there is provided a stop for the movement of the magnetic head in the diametrical direction out of the house-like element. 10. Helical scanning magnetic recording and reproducing apparatus provided with a rotary magnetic head device according to any one of the preceding claims.

Inventors: MAKINWA KOFI A A, STUPP STEVEN E, VAN DE VEN MARTINUS L J M, MAKINWA, KOFI, A., A., STUPP, STEVEN E., VAN DE VEN, MARTINUS, L., J., M.
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SVENSKA AB, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS AB
Application year: 1999
Main classification: G11B5
IPC codes: G11B5