DE2031715C - Device for monitoring a magnetic tape - Google Patents

Description

to a superimposed DC voltage component

to be led. Circuit I removes the DC component. The remaining AC voltage component is rectified in circuit II. The DC output signal actuates a load (for example a Relay).

If the roller 2 is stationary, the contact brush 4 (depending on whether it is currently standing on a conductive part la or on an insulating part la ' ) emits only a DC voltage signal or no signal at all. In the absence of an alternating voltage component, the circuit II therefore does not provide an output signal.

With reference to the following figures, it will now be explained how a signal is additionally provided in the device for the presence or absence of the magnetic tape is obtained.

In the case of the FIG. 2 a, 2 b, 3 a and 3 b illustrated embodiment, the roller 2 is provided on its periphery with a> Nem electrically conductive rubber part Ib , which tapers towards the outer periphery of the roller and has a width on the outer periphery that is smaller than that Width W of the magnetic tape T is. The axis 3 of the roller 2, the inner part la of the roller, a bushing 2 c and the tape drive shaft 8 are made of electrically conductive material. In the electrically conductive portion of the insulating parts la la 'in the region of an end side are arranged.

2a shows the electrical equivalent circuit diagram of the device. The internal resistance of the roller is denoted by r , the transition resistance between the belt drive shaft 8 and the rubber part Ib with r '. Resistors R, R ₁ and R _{2 are also} provided in the circuit. K is the voltage applied between the axis 3 and the tape drive shaft 8. . There can now be various cases during operation. If the magnetic tape T is present between the tape drive shaft 8 and the roller 2, but if the magnetic tape is still, the brush 4 is either in contact with an insulating part la ' or with the conductive part la. A constant voltage V ₁ or V ₁ then prevails across the resistor R. If there is no magnetic tape T between the tape drive shaft 8 and the roller 2, then these two parts are electrically connected to one another.

a) If the brush 4 is in contact with an insulating part la ', the resistors R and (r + r') are connected in parallel, with R ₁ in series with this parallel connection. The voltage is then obtained at the resistor R.

V ₃ =

b) If, on the other hand, the brush 4 touches the conductive part la, the resistors R, R ₂ and (r + r ') are connected in parallel, the resistance R _{1 being} in series with this parallel connection. The voltage is then obtained at the resistor R.

K ₄ = V

+ 1

Assuming the following resistance values:

to step:

R ₁ = 200 k, r - r '= 10 k, Ri = 200 k, R = 100 k,

The magnetic tape T runs between the roller 2 and the tape drive shaft 8. The managerial ^ ⁰ tends connection between the axle 3 and the capstan 8 is consequently interrupted by the magnetic tape T.

a) If under these circumstances the contact brush 4 touches an insulating part 2a '. the voltage K is only present at the resistors R ₁ and R. The voltage K ₁ at the resistor R then results from the following relationship:

the following relationships result:

Ik

23 '
1 .,

'■ ~' R ₁ + R-

b) If the brush 4 is in contact with the electrically conductive part 2a, the resistors R ₂ and R are connected in parallel, the resistor R _{1 being} in series with this parallel connection. A voltage then occurs at resistor R:

If K = 10 volts, the result is

55

i + l-k-

K ₂ = V \

If the magnetic tape T runs between the tape drive shaft 8 and the roller 2, voltages V ₁ and K _{2 occur alternately across the resistor R.}

K ₁ = 3.3VoIt,

K ₂ = 2.5VoIt,

K ₃ = 0.435VoIt,

K ₄ = 0.416 Volts.

60 In case 1 (i.e. when a magnetic tape T runs between the tape drive shaft 8 and the roller 2) a square-wave voltage appears at the resistor R, which fluctuates between 3.3 and 2.5 volts (curve a

in Fig. 2 b). In Fill 2 (when a magnetic tape T present between the tape drive shaft 8 and the roller 2 is stationary), a constant DC voltage of 3.3 or 2.5 volts appears at the resistor R.

In case 3 (when there is no magnetic tape T between the tape drive shaft 8 and the roller 2), a square-wave voltage occurs across the resistor R. which fluctuates between the values 0.435 and 0.416 volts (curve b in Fig. 2b).

In the case of the square wave α, the difference between the maximum value and the minimum value is 0.8 volts; in case 3, however, the difference is only 0.019 volts. The distinction between the two cases can thus be made very simply by applying the voltage prevailing at the resistor R to an AC amplifier and thereby determining the amplitude difference.

In the embodiment of FIG. 4 a and 4 b, the electrically conductive rubber part Ib _{x is arranged in the form of a} disk between two electrically non-conductive rubber parts Ib ₁ , 2 // J and has a width W ″ which is smaller than the width W of the magnetic tape T, while that of the three Rubber parts 2b, Ib ₁ and 2b ₃ , the total contact width W 'formed is greater than the width W of the magnetic tape T. This results in a particularly stable guidance of the magnetic tape T on the tape drive shaft 8. The function is otherwise the same as that of the previous one explained exemplary embodiment.

In the exemplary embodiment of Fi g. 5a and 5b are provided between the conductive rubber part Ib _x and the non-conductive rubber parts Ib ₁ and 2b, annular grooves 2 (, Ic ₁ , in order to improve the insulation between the tape drive shaft 8 and the electrically conductive rubber part Ib _x in the presence of the magnetic tape T. .

In the embodiment of FIG. 6a and 6b, the electrically conductive rubber part Ib _{x is arranged} next to an electrically non-conductive rubber part Ib _1. The contact width W between the roller 2 and the tape drive shaft 8 is greater than the width IV of the magnetic tape T. The tape drive shaft 8 has in its the electrically conductive rubber part Ib _x opposite zone, but not covered by the magnetic tape T , has an insulating coating 8 a.

In this way, too, a relatively large total contact width W can be selected for a stable, calm!, Desired, relatively large.

In the embodiment of FIG. 7a and 7b, the contact width W is greater than the width W of the magnetic tape. The tape drive shaft 8 is provided on two villi not covered by the magnetic tape, each with an insulating coating 8a or 86; the distance W " between these two coatings 8a. 8fr is somewhat smaller than the width W of the magnetic tape.

F i g. 8 shows a comparison with FIG. 2a modified exemplary embodiment of a circuit for the device according to the invention. In addition to the elements already mentioned, the arrangement contains alternating current amplifiers I, or I, ', rectifier circuits If ₁ or H,', a signal converter III, or III, 'arranged downstream of the rectifier circuit II, or 11 /. also to a signalraiscber IV and an output circuit V.

Dk mode of action is as follows:

1. If the magnetic tape T moves between the tape drive shaft 8 and the roller 2 and the conductive part 2a of the roller has a bias

. with respect to a reference potential from the brush 4 to the AC amplifier 1, an alternating voltage signal with a superimposed direct current component is supplied. Latter is removed while the AC component in circuit II, is rectified, so that a DC voltage output signal is given.

2. If the magnetic tape T is present between the tape drive shaft 8 and the roller 2, but if it is at a standstill, either no signal or only a DC voltage signal is emitted by the brush 4. As a result, the output of the rectifier circuit II does not deliver a signal.

3. In the presence of a magnetic tape T between the tape drive shaft 8 and the reel 2 (i.e. in the above cases 1 and 2) there is no signal _{at the input of the amplifier I 1 ';} As a result, there is also no signal at the output of the rectifier circuit U _{1 '.}

4. If there is no belt T between the belt drive shaft 8 and the roller 2, the roller 2 and the belt drive shaft 8 (depending on the design) are in continuous or intermittent contact with one another. A direct current or an alternating current signal is fed to the amplifier I _{1 '.} In both cases, a direct voltage output signal is obtained at the output of the rectifier circuit Μ, '.

In the two above-mentioned cases 2 and 4, the same control of the magnetic tape device is required; For this purpose, the output signals must be of the same type in both cases. This is why the signal converter III, provided, and it is the control circuit via the signal mixer IV or an OR gate is operated in such a way that the same effect is triggered in both cases.

While the first current path intermittently interrupting insulating parts are provided on a scanned by the contact brush end face of the roller in the previously described embodiments, FIGS. 13 and 14, a Ausrührungsbeispiel, wherein the first current path intermittently producing contact portions 2e on which the tape drive shaft S in contact circumference of the roller 2 are provided. The role also contains an insulating part la. in which the contact parts Ie are embedded, furthermore an electrically conductive rubber part 2 /. This rubber part 2 / is arranged (see FIG. 10) in such a way that it is not in contact with the tape drive shaft 8 when the magnetic tape T is present. In this embodiment, as in FIG. 9 reveals - the contact parts Ie formed in one piece with the electrically conductive rubber part 2 /, which in turn is in electrical connection with the roller wheel 3

In the embodiment of FIG. 11, an insulating material part 2a is provided between the electrically conductive rubber part 2 / and the element forming the electrically conductive contact parts Ie.

The mode of operation of the exemplary embodiments in FIG. 9 to 11 is as follows:

1. If the magnetic tape T is located between the tape drive shaft 8 and the roller 2. the electrically conductive rubber part 2 / is isolated from the tape drive shaft 8

On the other hand roller 2 there are the contact parts 2i> intermittently in contact with the Banduntricbswcllc 8. The Wecliselstromverstärkcr 16 supplies as a result a signal C (Fig. 12), which is rectified by the Gleichrichtcrschaltung 17 and actuates a contact 19 via a Rclaisspule 18th

If the magnetic tape T is present between the reel 2 and the tape drive shaft 8, but it is stationary (e.g. because it is being held by the supply reel), either the insulating material part 2 (1 or a contact part le) is in contact with the idling tape drive shaft 8. As a result, the reverse signal C illustrated in FIG. 12 is not generated.

as a result, no out-of-contact 19 is open

judges 17 delivers
output signal so that
will.

3. If there is no magnetic tape T between the roller 2 and the tape drive shaft 8, the electrically conductive rubber part 2 / is in constant contact with the tape drive shaft 8. In this case too, the contact 19 is thus opened.

In the embodiment of FIG

the contact parts 2c formed by an elastic, electrically conductive element. Between this Elcmcnl and the electrically conductive rubber part 2 / is cir Isolicrstoffteil ld arranged.

For this purpose 2 sheets of drawings

Claims (6)

Patent claims: 1. Device for monitoring a magnetic building, with a roller carried along by the movement of the magnetic tape and a circuit arrangement which, when the roller rotates, generates an intermittently controlled voltage and provides a voltage signal for the movement or the standstill of the roller, thereby j ₀ indicates that the roller (2) provided on its circumference with an electrically conductive rubber part (2fc, 2f> ,, 2 /) presses the magnetic tape (T) against an element, in particular a tape drive shaft (8) or a sensing pin that between the roller axis (3) and the element a voltage is applied which, when the magnetic tape is present and moving, intermittently interrupts one of the roller by insulating parts (2a '). Ren or generated by contact parts (2 e) intermittently produced first current path and which, in the absence of the magnetic tape, creates a further current path through direct contact of the electrically conductive rubber part of the roller with the element. 2. Apparatus according to claim 1, characterized in that the electrically conductive rubber part (Ib) tapers towards the outer circumference of the roller (2) and has a width on the circumference which is smaller than the width (W) of the magnetic tape (T) . 3. Device according to \ nspruch 1, characterized in that Her electrically conductive rubber part (Ib ₁ ) is disc-shaped; between two electrically non-conductive rubber parts (Ib ₂ -, 2b ₃ ) and has a width which is smaller than the width (W) of the magnetic tape (T), while the total contact width (W) formed by the three rubber parts is greater than that Width (W) of the magnetic tape ( T) . 4. Apparatus according to claim 1, characterized in that the electrically conductive rubber part (2fc,) is arranged next to an electrically non-conductive rubber part (Ib ₂ ) that the contact width (W) between the roller (2) and the element (8) is greater than the width (W) of the magnetic tape (T) and that the element (8) has an insulating coating (8 a) in its zone opposite the electrically conductive rubber part (2 £,) but not covered by the magnetic tape (T) 5. The device according to claim 1, characterized in that the first current path is intermittent interrupting insulating parts (2a ') on a scanned by a contact brush (4) End face of the roller (2) are provided. 6. The device according to claim 1, characterized in that the first current path is intermittent producing contact parts (2e) on the one with the element (8) in contact Scope of the role (2) are provided. The invention relates to a device for monitoring of a magnetic tape, with a roll taken along by the movement of the Maenet tape and a "? circuitry that when rotated the roller generates an intermittently controlled voltage and from this a voltage signal for the Movement or the standstill of the role supplies. In a known device of the type mentioned is that of the movement of the magnetic tape The entrained roll is designed as a conventional tape-guide roll, which is basically made of insulating material. The circuit arrangement controlled by the roller delivers different signals, depending on whether the roller is turning or whether it is stationary. However, a stoppage of the roller may have a different cause: can the tape be prevented at a different location of the device from moving either, or it can be the magnetic tape - for example, because it is torn - ^ in the role at all lacking. The invention is now based on the object of providing a monitoring device of the type mentioned at the beginning Kind to train in such a way that besides the voltage signals for the movement and the standstill of the Roll an additional signal for the lack of the magnetic tape is supplied. This object is achieved according to the invention in that the on its periphery with an electrical Conductive rubber part provided roll the magnetic tape against an element, in particular a tape drive shaft or a guide pin, and that between the roller axis and the element a Voltage is applied, which is caused by insulating parts in the presence and movement of the magnetic tape the role intermittently interrupted or intermittently produced by contact parts first Generated current path and in the absence of the magnetic tape a further current path through immediate Creates contact of the electrically conductive rubber part of the roller with the element Some embodiments of the invention are illustrated in the drawing. It shows F i g. 1 is a schematic representation of a first embodiment of the device according to the invention, 2a shows a basic circuit diagram of the inventive Contraption, F i g. FIG. 2 b shows a diagram to explain the function of the circuit according to FIG. 2 a, F i g. 3 a and 3 b to F i g. 7a and 7b sections through various embodiments of the role and the element interacting with it, Fig. 8 is a basic circuit diagram (similar to Fig. 2 a) another embodiment, F i g. 9 to 11 schematic representations of further embodiments, 12 is a diagram for explaining the function of the embodiment of Fig. 10, 13 shows a schematic view of a further embodiment. F i g. 1 schematically shows a device for monitoring a magnetic tape. A roller 2 is entrained by the movement of the magnetic tape and has conductive parts la and insulating parts la ' on its circumference in alternating succession. The roller 2 is supplied by a direct current connection (+ B) and scanned by a contact brush 4. When the roller 2 rotates, an intermittently controlled voltage is drawn from the contact brush 4, so that the circuit I has a square-wave voltage