EP0818241A1 - Document shredder - Google Patents

Abstract

The document shredder has a cutting mechanism (12) driven by an electric motor (21), with a light beam switch (18,20) for the electric motor operated by the shredded material (15). The switch is coupled to a variable delay circuit (27) containing a phase detector (26), for operation of an electronic switch element (23) in the electric motor current supply circuit in synchronism with the mains voltage zero transition, for automatic cut-out of the motor.

Description

APPLICATION AREA AND PRIOR ART

The invention relates to a document shredder with a by an electric motor driven cutting unit and one if necessary, the switch for the electric motor operated by the material to be cut.

Such document shredders, including shredders for all kinds of flat material, waste or the like are understood either by mechanical switches or of light barriers, touch switches or the like set and switched off again. The especially with smaller ones Electric motors used in units are mostly single-phase AC motors or universal motors, i.e. Commutator motors. Their activation generates a current spike that affects the supply network and on the other hand also Caused radio interference. Certain such disorders will occur mostly accepted when they have a certain number in one do not exceed the specified time unit. If those "Click rate" but due to the high performance and the possibility successive numerous single sheets in one Entering document shredders that rise too high must be here be remedied.

Interference suppression devices that eliminate these interference or their Eliminating effects is very complex and often economical for small devices that are particularly high Cause crack rate, hardly portable.

TASK AND SOLUTION

The object of the invention is therefore a document shredder of the type mentioned at the beginning, in which the Problem of network interference and radio interference on possible simple or inexpensive way eliminated or at least is improved.

This object is achieved in that the Switch for the electric motor and a phase detector containing variable delay circuit activated, the an electronic switching element provided in the motor circuit for switching in the zero crossing of the mains voltage controls.

The switch that triggers the operation, i.e. either on mechanical, manually operated switch, one of the Micro-operated switch or an output switch a light barrier control does not switch the motor directly. Rather, the circuit is used to activate a Phase detector used, e.g. the next zero crossing the mains voltage and then switches on the motor. The motor voltage therefore runs together with the mains shaft high and causing radio interference or network interference No voltage peak. It will not, as with a normal interference suppression that eliminates the interference that arises, but it becomes the cause of a disturbance, namely the Voltage spike, avoided. Special suppressors can So if the engine does not malfunction even when running caused.

This type of malfunction avoidance is particularly important for document shredders advantageous because they are natural for you very strong surge operation must be designed and also operated like this. You need a high starting torque often have and will reach the limits of their performance Electric motors and beyond.

With many triggers, for example with light barrier control, it is advisable to provide a wake, thus the one provided for example at the document inlet Light barrier cuts the incoming sheet to the end, after the end has already passed the light barrier. In in this case the delay circuit would be of one corresponding follower of the light barrier control for delayed switching off can be activated.

It is useful to have one with the electronic switching element mechanical switch to combine so that the switching time is determined by the electronic switching element, e.g. through series connection. This avoids rare, but possible accidents, e.g. the case that a semiconductor of electronic switching element e.g. due to an overvoltage alloyed and is therefore no longer controllable. This mechanical switches would then, however, before or after the on or Switch off take effect and thus switch off.

The electronic switching element can, for example, by a Bridge rectifier can be realized by one in the Bridge diagonal lying transistor is controlled. As Phase detector can be a comparator responsive to "zero volts" be used.

These and other features go beyond the claims also from the description and the drawings, wherein the individual features individually or separately several in the form of sub-combinations in one embodiment of the invention and in other fields be and advantageous as well as protective designs can represent, for which protection is claimed here.

The division of the application into individual sections as well Inter-headings limit those made under them Statements are not generally applicable.

BRIEF DESCRIPTION OF THE DRAWING

ein schematisches Schaltbild der Steuerung eines Aktenvernichters.

An embodiment of the invention is shown in the drawing and is explained in more detail below. The only description figure shows:

a schematic diagram of the control of a shredder.

DESCRIPTION OF THE EMBODIMENT

A shredder 11 includes a cutter 12 Cutting rollers 13, whose toothed cutting disks 14 intermesh and thus a material to be cut 15 in strips or can cut particles 16. To turn on on the one hand a mechanical, manually operable pre and Reverse switch 17 provided and on the other hand a light barrier circuit, the sensors 18 on a feed chute 19 of the document shredder and a corresponding light barrier control 20 has. This gives an output signal that starts the motor 21 driving the cutting rollers and, possibly via a delay element after a lag phase of for example 2 seconds, switches off again after the end of the material to be cut 15 has passed the light sensor 18.

In the exemplary embodiment, the motor is a Single-phase AC motor (asynchronous motor) with one Capacitor enabling start-up 22. It could also be a Universal motor, i.e. a collector series motor is provided be.

After the switch 17 is actuated and the direction of rotation via it the motor is determined, the activation of an electronic switching element 23 determines that in series with the motor branch of the mechanical switch 17 in the Power supply to the motor is. It is about a bridge rectifier 24 containing four diodes, in whose bridge diagonal a transistor 25 is arranged. He is driven by a phase detector 26, which is part of a variable delay circuit 27, which is controlled by the light barrier 20 is activated.

FUNCTION

The function is as follows:

With the switch 17, the machine is ready for operation switched. The switch 17 closes the circuit to the motor M. If a cutting material 15 is now fed to the machine, there are the light barrier control 20 ON signal to the variable Delay circuit 27. The phase detector 26 now determines the next zero crossing of the mains voltage and switches in the transistor 25 at this moment. The rectifier 24 is activated and the engine 21 starts to work. The voltage and current rise in the motor is corresponding the sinusoidal rise of the mains wave gently and generates no voltage peaks due to the in the motor and other parts of the device containing inductors or Capacities.

As soon as the material to be cut 15 has passed the light barrier, a follow-up time of for example started two seconds. If this is finished, so gives the light barrier control 20 of the variable delay circuit the OFF signal. The phase detector determines again the next zero crossing of the mains voltage and turns off transistor 25 at this time. Of the Rectifier 25 is deactivated and the document shredder is switched off. The one from the variable delay circuit The on and off delay caused is therefore from the time of the signal triggering the process (e.g. addressing the Light barrier) in relation to the mains frequency cycle and is usually between zero and one hundredth Second.

Other switching elements are also electronic switching elements such as thyristors, TRIAC, IGBT's etc. possible. It should be an electronic switching element that is at zero crossing is switchable or if it is a different structure Relay is acting, should the delay circuit Proper time of the relay are taken into account.

The invention therefore does not normally need to be minimized RC filters or LC filters used by interference and nevertheless avoids EMC interference.

Claims (5)

Document shredder with one from an electric motor (21) driven cutting unit (12) and one if necessary the material to be cut (15) actuated switch (18, 20) for the Electric motor (21), characterized in that the Switches (18, 20) containing a phase detector (26) variable delay circuit (27) activated, the an electronic one provided in the motor circuit Switching element (23) for switching at the zero crossing of the Controls mains voltage. Document shredder according to claim 1, characterized in that the variable delay circuit (27) by a light barrier control (20), possibly with a Follower for delayed switching off, activated becomes. Document shredder according to claim 1 or 2, characterized characterized in that with the electronic switching element (23) a mechanical switch (17) is assigned so that the switching point is determined by the switching element, is preferably connected in series. Document shredder according to one of the preceding Claims, characterized in that the electronic Switching element (23) with a bridge rectifier (24) one of the variable delay circuit (27) controllable electrical switches, for example contains a transistor (25). Document shredder according to one of the preceding Claims, characterized in that the electronic Switching element (23) instead of motor suppressors is provided.

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