Abstract:
A device for transferring signals between itself and a record carrier tape, the device including a rotating head wheel disk, at least one head disposed on the rotating head wheel disk, a sensor and a signal emitter to indicate the position of the head wheel disk, the improvement wherein the signal emitter comprises two juxtaposed electrical conductors.

Description:
This application is a continuation of application Ser. No. 07/019,019, filed Feb. 26, 1987, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a device, particularly a video recorder, for playing back and/or recording signals on or from a record carrier tape, and particularly for a digital signal on a magnetic tape, wherein the device includes a rotating head wheel disk carrying at least one head thereon, a sensor and a signal emitter to indicate the angular position of the head wheel disk. 
     German Offenlegungsscrift [laid-open patent application] No. 3,115,670 discloses a method of determining the angular position of magnetic heads with respect to a tape. In addition to the two rotating magnetic heads, the head wheel disk includes two rotating permanent magnets which produce pulses of alternating polarity during rotation in a stationary head or in a stationary coil outside the head, fixed in the vicinity of the head wheel. The pulses serve as a criterion for the respective position and velocity of the head wheel disk (see page 6, first paragraph of the above cited German Offenlegungsschrift). 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an arrangement which improves the indication of the angular position of the head wheel disk. 
     The above and other objects are accomplished according to the invention in the context of a device as first described above, wherein the signal emitter is comprised of two juxtaposed electrical conductors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, embodiments thereof will be described below with reference to drawing figures, wherein: 
     FIG. 1 is a schematic showing a signal emitter at a head wheel disk according to one embodiment of the invention. 
     FIG. 2 is a schematic showing a signal emitter on a head wheel disk according to another embodiment of the invention. 
     FIG. 3 is a schematic representation of two signal emitters at a head wheel disk according to a further embodiment of the invention. 
     FIG. 4 is a diagram which shows the magnetic field of a signal emitter. 
     FIG. 5 is a diagram which shows a voltage induced by a signal emitter in a magnetic head. 
     FIG. 6 is a schematic showing a signal emitter in the vicinity of a head wheel according to the invention. 
     FIG. 7 is a schematic which shows a V-shaped arrangement including two conductor loops which can be used in FIG. 6. 
     FIG. 8 is a schematic which shows a V-shaped arrangement including one conductor loop which can be used in FIG. 6. 
     FIG. 9 is a diagram which shows a further arrangement of conductors according to the invention. 
     FIG. 10 is a diagram showing dimensional relationships of the conductor used for the pickup according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a head wheel disk or a head drum 1, hereinafter called head wheel, equipped with two magnetic heads 2 and 3. A magnetic tape 4 is placed around head wheel 1. Head wheel 1 rotates in the direction of arrow 5. Fields in magnetic tape 4 induce voltages in magnetic heads 2 and 3. These voltages are fed through lines to a demodulator 6. Demodulator 6 demodulates the signals coming from magnetic tape 4 and feeds demodulated signals to an output 7 at which a video signal can be picked up. In a synchronization separation stage 8, synchronizing words, hereinafter called sync words, are filtered out. These sync words are fed to a control 9 which regulates a head wheel control 11 via an amplifier 10. 
     Two conductors 12 and 13 are arranged parallel to the axis of rotation of head wheel 1. Conductors 12 and 13 are fixed in the chassis of the video recorder, in the vicinity of the head wheel. Via a limiting resistor 14, an alternating voltage source 15 supplies conductors 12 and 13 with an alternating current I1. Conductors 12 and 13 have an elongate shape. The direction of arrow 25 indicates the direction of the current. Current I1 flows through conductor 12 in the direction leading into the plane of the drawing and then through conductor 13 in the direction leading out of the plane of the drawing. Current Il flows through the two conductors 12, 13 in opposite directions, i.e. in opposite polarity, so that a magnetic field of a minimum field intensity builds up around the two conductors. A head position circuit 16 separates pulses from the signals coming from magnetic heads 2 and 3. These pulses are induced by conductors 12 and 13. The pulses are forwarded by head position circuit 16 through line 17 to control 9. Control 9 compares the sync words coming from sync separation stage 8 with the head position pulses and regulates head wheel control 11 based on the sync words and the pulses in a known manner. 
     In FIG. 2 the two elongate conductors 12 and 13 are fixed in head wheel 1 parallel to the axis of rotation thereof. Conductors 12 and 13 are supplied with a current I2 from alternating voltage source 15 via a limiting resistor 14. Conductors 12 and 13 are connected with voltage source 15 and limiting resistor 14 by way of slip rings 19 and 20 and contact brushes. Advantageously, magnetic heads 2 and 3 and conductors 12 and 13 are arranged in two planes on head wheel 1 so that conductors 12 and 13 do not influence magnetic tape 4. During rotation of head wheel 1, conductors 12 and 13 induce a voltage in a magnetic head 18. This voltage is fed via line 17 to control 9 and compared with the synch words as in FIG. 1 for regulating head wheel control 11. 
     FIG. 3 shows a magnetic head 2 on a head wheel path 21. Magnetic head 2 rotates on head wheel path 21 and is displaceable in the direction of the axis of rotation 25. Two conductor loops 22 and 23 are disposed at head wheel path 21. Each one of the two conductor loops 22, 23 is composed of two current carrying conductors 12 and 13. Conductor loop 23 is disposed parallel to axis of rotation 25. Conductor loop 22 extends over the lifting range of head wheel path 21. Conductor loop 22 forms an acute angle, or better a V-shaped arrangement, with conductor loop 23. Conductor loop 22 is arranged so that it is able to induce a voltage in magnetic head 2 over the entire lifting range of head wheel path 21. The precise position of head 2 can be determined by way of conductor loop 23. The frequency of the induced pulses can be used to determine the velocity of magnetic head 2. Due to the oblique position of conductor loop 22 with respect to conductor loop 23, different distances are given between conductor loops 22 and 23 depending on the displacement of head 2 in the direction of axis 25. Thus, these different distances between conductor loops 22, 23, correspond to the displacement in height of the head wheel path in the direction of axis of rotation 25 which can be calculated over the lifting range. The lifting range serves the purpose of sequentially scanning a plurality of parallel longitudinal tracks arranged in blocks on a magnetic tape as will be appreciated by those skilled in the art. This scanning takes place over a defined height, i.e. the width of the magnetic tape. 
     FIG. 4 shows two current carrying conductors 12 and 13 which build up an magnetic field having field lines 24. The two electrical conductors 12 and 13 are disposed at a head wheel path 21. After mathematically forming the quadrature or the sum, which corresponds to electrical rectification, this electrical field is a minimum at location X0. See in this connection G. Joos, Lehrbuch der theoretischen Physik [Textbook of Theoretical Physics], Eighth Edition, Leipzig 1954, published by Akademische Verlagsgesellschaft Geest &amp; Portig K.-G, at page 280, Equation (4). 
     FIG. 5 shows an induced voltage U after rectification. This voltage was induced in a magnetic head on head wheel path 21 at point X0 in the magnetic head. It is also possible to observe this with a time abscissa and a point in time t0. The difference in voltage between U1 and U0 in the vicinity of location X0 permits a precise determination of the phase, or better the angular position of heads 2, 3 or of the head position on a head wheel path 21. In the vicinity of X0, the magnetic field has a strong gradient. The induced voltage changes its sign at point X0. For good transmission, the frequency of the change in polarity of currents I1 to I4 should be selected to be approximately the resonant frequency of a head/transmission system. That means, that frequency should be selected at which the system composed of head, equalizer and amplifier reacts with the greatest sensitivity. 
     FIG. 6 shows a head wheel 1 with two magnetic heads 2 and 3, mounted in the direction of axis of rotation 25 so as to be movable in both directions 26 and 27. To characterize the respective positions of head wheel 1 relative to its environment, the two conductor loops 22 and 23 are fixed to the chassis 28 of a video recorder in the vicinity of head wheel 1. 
     FIG. 7 shows a side view of a chassis 28 in the vicinity of head wheel 1 and two conductor loops 22 and 23. Each conductor loop 22 and 23 is provided with conductors 12 and 13. Conductor loop 22 carries current I1, conductor loop 23 carries current I2. 
     FIG. 8 shows a V-shaped arrangement including a single conductor loop 22. Each conductor 12 and 13 of loop 22 forms a V-shaped arrangement. Only a single conductor loop 22 through which flows a current I1 is required for this V-shaped arrangement. 
     FIG. 9 shows a plurality of conductors 12 and 13 in a coil-shaped arrangement. 
     FIG. 10 shows conductors 12 and 13 wherein a distance s between the two conductors is on the order of magnitude of a distance d between each one of conductors 12 and 13 and heads 2, 3. Distances s and d are small compared to the length of the circumference of the head wheel path. In the ideal case, distance s between the two conductors equals zero. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.