GB2153583A

GB2153583A - Arrangement for producing control pulses for the operation of a video recording and reproduction device

Info

Publication number: GB2153583A
Application number: GB08502345A
Authority: GB
Inventors: Horst Zimmermann; Sandor Gyarmati
Original assignee: Deutsche Thomson Brandt GmbH
Current assignee: Deutsche Thomson Brandt GmbH
Priority date: 1984-01-31
Filing date: 1985-01-30
Publication date: 1985-08-21
Also published as: GB8502345D0; GB2153583B; FR2561425A1; DE3403150C1; NL8500227A; JPS60205850A

Abstract

An arrangement in video recording equipment for producing commutation pulses for a brushless electronically commutated head-drum motor (10) as well as for producing head actuating pulses for the magnetic heads (11, 12) and for measuring the speed of rotation of the head drum (13) consists of an optical pattern (2,2' - 7,7') (Figure 2) which cooperates with an optical sensor (8). The optical markings may be on a transparent or reflective disc (1) or etched on the circumference of the head drum (13). Markings (2-7) of the pattern are equi-angularly spaced and the marking (7) serving to produce the head actuating pulse occupies a larger angular range than the others. A processing circuit is detailed (Figure 2). <IMAGE>

Description

SPECIFICATION Arrangement for producing control pulses for the operation of a video recording and reproduction device This invention concerns an arrangement for producing control pulses for the operation of video recording and reproduction equipment having a brushless electrically commutated head-drum motor.

Such arrangements are known, for which hitherto a plurality of receivers have been needed from which the commutating pulses and the head actuating pulses are derived. For commutation of the brushless head-drum motor, Hall elements are used which supply the commutating pulses in co operation with the multipolar magnetized rotor of the motor. Via another receiver, a separate magnet on the head drum produces the head actuating pulse which switches on the correct head at the correct moment, that is to say as soon as it comes into contact with the magnetic tape. This requires heavy material expense and the adjustment of the magnetic tape equipment with regard to the cor rect phase position of the pulses is also time-consuming.

It is known (DE-PS 24 07 748) to effect the production of the commutating pulses for an electronically commutated head-drum motor in video recorders as well as its speed and phase control by means of a single signal transmitter. No concrete solution is, however, given in the said Patent Specification.

It is an object of the invention to provide a simplified signal transmitter for producing commutating and head actuating pulses in an arrangement of the type mentioned above.

The invention accordingly provides an arrangement for a video tape recorder comprising a head drum which can be partially enwrapped by a magnetic tape and is secured to the driving shaft of a brushless electronically commutated direct-current motor and means for controlling the phase position and speed of rotation of the head drum depending on reference signals, said means including a signal transmitter rotating with the head drum for the electronic commutation of the direct-current motor and to control the phase position and speed of rotation of the head drum, wherein the signal transmitter consists of optical markings which are distributed with equal angular spacing and, in use, produce the commutating pulses in cooperation with an optical sensor, one of said markings occupying a larger angular range than the rest and being so arranged with respect to video magnetic heads of the drum that it serves to produce headactuating pulses, and the regions situated between the said markings serving to provide a measure of the speed of rotation of the head drum.

The invention brings the advantage that calibration of the heads with respect to the marking generating the head actuating pulse no longer has to be carried out. The production of the control pulses is very accurate because the marking is ef fected by etching the surface. The arrangement of the invention is particularly advantageous if the marking is integrated in the head drum. Since the commutating pulse does not have to be nearly so accurate as the head actuating pulse, an adjust ment is greatly simplified because the marking does not have to be adjusted to the position of the rotor magnets but the magnets of the rotor are aligned with respect to the marking. As a result, the precise position of the head actuating pulses is guaranteed by the fixed positional relationship between marking and magnetic heads.The electronic expense of the drive system described above is re duced considerably and there is also a saving in adjustment work. The actuating pulses are pro duced with the greatest accuracy.

The invention is illustrated by way of example in the accompanying drawings, in which: Figure 1 shows one embodiment of arrangement according to the invention, Figure 2 shows a circuit arrangement for processing the pulses derived from the arrangement shown in Figure 1, and Figure 3 shows pulse diagrams to explain the mode of operation of the circuit shown in Figure 2.

In Figure 1, a disc 1 is illustrated which carries markings 2 to 7 with equal angular spacing. The markings represent zones with less light reflection, while the intervening zones 2' to 7' reflect the light well. This disc cooperates with an optical sensor 8 responsive to reflected light. The disc may, however, also consist of transparent material with the corresponding markings 2 to 7 at which the disc is non-transparent. Such a disc may appropriately cooperate with an optical sensor responsive to transmitted illumination. Narrow markings 2 to 6 will be seen and a wide marking 7 which differs from the rest. This disc is disposed on the motor shaft 9 of a head-drum motor 10 in a precisely fixed spatial relationship to rotating magnetic heads 11 and 12 in such a manner that head actuating pulses derived from the light sensor 8 switch on the heads 11 and 12 in the correct time interval.It is a particular advantage if the low-reflecting markings 2 to 7 are etched directly on the edge 14 of the head drum 13 so that the assignment of the markings 2 to 7 to the magnetic heads 11 and 12 is firmly preset from the beginning.

By means of Figure 2 in conjunction with Figure 3, a possible circuit arrangement will be described whereby the signals derived from the disc 1 can be converted into the desired control pulses. The pulses produced by the disc 1 or by the edge 14 of the magnetic drum 13 by means of the light sensor 8 (Figure 3a) reach a decimal counter which has outputs "0", "1", "2", "3", "4", "5" and "6" which are switched up cyclically on the arrival of a negative signal jump as shown in Figure 3a. The output "6" is applied to the reset input R of the counter 15 so as to reset this to the state 0 when the counter state 6 is reached. The outputs 0, 3, 1, 4 and 2, 5 are each combined through Or-gates 17, 18, 19 at the outputs 20, 21 and 22 of which, the pulses for the commutation of the coils of the motor 10 are taken off.The pulses are illustrated in Figure 3b, c and d. The outputs 3, 4 and 5 of the counter 15 are combined through the Or-gate 24 at the output 25 of which, the head actuating pulse K1 and, via an inverting stage 25, the head actuating pulse K2 can be taken off in the correct phase position in the manner described hereinafter. The wider marking 7 on the disc 1 serves for this. It will be seen that as a result of this, according to Figure 3a, a low level of longer duration results. This period of time is so great that a monostable trigger stage 16, triggered by the negative edge of a pulse, can come into action and delivers a pulse R which, via the Or-gate 23, reaches the reset input R of the counter 15 and sets this to the "0" output regardless of its instantaneous output state.

This is illustrated in Figure 3b, c and d. As a result of this, the counter counts beginning from zero from the marking "7" on. In this manner, the outputs 3, 4 and 5 of the counter 15 come into a position necessary for the precise switching over of the heads, at the correct moment (Figure 3e, f). In the lines g, h, i of Figure 3 it is assumed that the disc 1 was in such a position, with respect to the light sensor 8, that the marking 5 delivered the first pulse at the beginning of the counting. Thus the correct correlation of the head actuating pulses K1 and K2 again results in Figure 3k and I.

For the speed control of the head-drum motor 10, the pulses shown in Figure 3a can be used which open a gate circuit, which measure oscillations of an oscillator 29. A control signal for the motor 10 can be derived from the result of the measurement which can be taken off at the output 30.

Claims

1. An arrangement for a video tape recorder comprising a head drum which can be partially enwrapped by a magnetic tape and is secured to the driving shaft of a brushless electronically commutated direct-current motor and having means for controlling the phase position and speed of rotation of the head drum depending on reference signals, said means including a signal transmitter rotating with the head drum for the electronic commutation of the direct-current motor and to control the phase position and speed of rotation of the head drum, wherein the signal transmitter consists of optical markings which are distributed with equal angular spacing and, in use, produce the commutating pulses in cooperation with an optical sensor, one of said markings occupying a larger angular range than the rest and being so arranged with respect to video magnetic heads of the head drum that it serves to produce head-actuating pulses, and the regions situated between said markings serving to provide a measure of the speed of rotation of the head drum.

2. An arrangement as claimed in Claim 1, wherein the optical markings are applied to the edge of the head drum in the form of an etched pattern which cooperates with an optical sensor responsive to reflected light.

3. An arrangement as claimed in Claim 1, wherein the markings are disposed on a transparent disc and cooperate with an optical sensor arranged to receive transmitted light, the disc being rigidly connected to the spindle of the head drum and the said one marking being so positioned that it produces the head actuating pulse in the correct phase position.

4. An arrangement for a video tape recorder, substantially as described herein with reference to the accompanying drawings.