The invention relates to a control device for monitoring the proper use of an electrical apparatus, especially a copying machine.

The background of the invention is the heavily increasing volum of copies which are produced by means of copying machines at most offices. A major problem in this connection is that of unauthorized copying which often takes place to a relatively great extent. Moreover, for a given copying machine, there are difficulties in dividing the arising costs properly.

The object of the invention is to solve this problem and, thus, to effect an authority check and possibly even recordal of the respective operator's use of the apparatus by simple means which do not require any modification of the apparatus.

This object is achieved while using the electric power cable of the apparatus by means of a control device, which is characteri by

- a current sensor, e.g. an induction coil, adapted to sense the current through the electic cable and, when a current flows through the cable, to deliver a voltage signal to

- a voltage detector device adapted to detect a characteristi current variation occuring when the apparatus is used an thereupon deliver at least one operation indication puls to .

- a control unit which is connected, on the one hand, to an authority check unit, through which a user of the electr apparatus can feed an authorization signal into the con¬ trol unit, and, on the other hand, to a switch for incer rupting the supply current to the apparatus in the absence of said authorization signal.

Hereby, it is possible to effectively accomplish the desired authority check without any substantial modification of the electrical apparatus. Normally, it is sufficient to replace the electric supply cable of the apparatus or to insert a current sensor and switch unit therein. Thus, there- is no problem in using the invention in previously installed apparatus. For- example, in a previously installed copying machine, one can replace the old electric cable by a new cable provided with a current sensor and switch unit. If necessary, this cable can be provided with a strong protective shield, and the connection within the apparatus can be sealed.

Further embodiments of the invention are defined in the sub- claims and will be apparent from the detailed description below.

A preferred embodiment of the invention will now be described with reference to the appended drawing.

Fig. 1 shows a simplified block diagram illustrating the essential parts of a control device according to the invention;

Fig. 2 show a current diagramillustrating the operation of the d vice of Fig. 1.

Thus, Fig. 1 illustrates schematically an electrical apparatus 1 the authorized use of which is to be checked and possibly recor¬ ded, the apparatus being connected to the electrical network (not shown) by means of an electrical supply cable, the phase and neutral conduits 2a,2b of which are shown, whereas the earth conduit has been left out on the drawing.

For sensing a characteristic current variation in the conduits 2a,2b, occurring when the apparatus 1 is being used, an induc¬ tion coil 3 is disposed with its coils extending around one of t conduits, e.g. the neutral conduit 2b. The current variations in the neutral conduit 2b will cause an induced alternating voltage on the coil 3. This alternating voltage is rectified by means of a diod D and will charge a condensor C being connected in

parallel with a resistor R, and the voltage of the condensor C is applied to a voltage detecting device 5 via an amplifier 4.

In the illustrated example,the electrical apparatus 1 is assumed to be a copying machine which is preheated by thermostatic cont in a conventional manner in its stand-by state, wherein it oper with two predetermined current values between which switching takes place while being thermostatically controlled. When copyi an.additional current flows (light and motor power) which is superposed as a pulse onto the respective current level, as illustrated in Fig. 2, where 10 and 10' denote the two current leves in the stand-by state, whereas 11 and 12 denote the curre levels when copying takes place.

The voltage detector device 5 (fig. 1)is consequently provided with twovoltage level sensors 6 and 7, which are connected in parallel to each other for sensing of a respective voltage level (in practice a relatively narrow voltage interval) corresponding to the current levels 11 and 12. In case of copying, one of the voltage level sensors 6 or 7 delivers an operation indication pulse to a control unit constituted by a computer 8, which checks whether an authorization signal has been given from its peripheral equipment and which, in the absence of such an authorization signal, interrupts the supply current to the copyi machine 1 by means of a switch 9 that interrupts the phase and neutral conduits 2a, 2b but, of course, not the earth conduit of the cable.

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The computer 8 can be prgrammed for immediate interruption in which case not even the first copy will be delivered from the copying machine to an unauthorized user. In general, however, it is preferred to lat the working cycle for one copy be com¬ pleted and, thus, to interrupt the current after a corresponding time period, e.g. 5-10 seconds. Reconnection of the current shou not take place until an authorized user or operator has fed an authorization signal into the computer 8.

A display unit 10, a key-board 11, a card reader 12 and a printe 13 are preferably connected to the computer. Authorized users are given ordinary plastic cards provided with a magnetic strip which are inserted into the card reader 12 before copying. Hereby, the computer will receive the necessary authorization signal, and the copying process can proceed without current in¬ terruption. The display unit 10 indicates whether an authorized card has been inserted into the card reader 12 and, thereupon, the number of copies taken (or cost or e.g. the remaining part of a budgeted cost, etc).

- The key-board 11 can be used as a supplement to the card reader 12, e.g. for entering a personal code, as in cash delivery ma¬ chines, in order to prevent unauthorized use of the plastic cards. Alternatively, the card reader 12 can be omitted, in which case the authorization code is entered via the key-board 11 to provide authorization signals to the computer.

Without difficulties and while copying, the computer 8 can be programmed so as to count the number copies and to store the count results accumulated for each user or group of users. For example, a supervisor or head operator can effect a print¬ out by means of the printer 13 at desired times, the print-out listing the various user's accumulated number of copies for the preceding time period.

It is understood that the invention may be advantageously used at other electrical apparatuses than copying machines, .e.g.

_* other kinds of office equipment or apparatus in public environment.