DE4319508A1 - Protection circuit - Google Patents

Abstract

A protection circuit is used for switching off and temporarily blocking the load section of a machine circuit in the event of an action or the operation of a safety switch (2) by an operator. The circuit has a radio-frequency transformer (T1) which converts the mains voltage (UN) on the primary side into the output voltage (UA) which is required on the secondary side for operation of the machine circuit, and a control loop which acts on the transformation ratio of the radio-frequency transformer (T1) and has a safety switch (2). In order to create a protection circuit in which it is possible to dispense with the use of expensive safety relays, at least one power circuit breaker (3, 4) is connected upstream of the radio-frequency transformer (T1) on the primary side, the drive (5) to said power circuit breaker being supplied via a safety circuit (6) which is DC-isolated from the mains voltage (UN) and the load section (1) and can be activated by operating the safety switch (2). <IMAGE>

Description

The invention relates to a protective circuit for switching off and preliminary blocking of the load part of a machine circuit in the event of an intervention or the operation of a protective scarf ters by an operator, with a high frequency transmitter, the mains voltage available on the primary side into the seconds required to operate the machine circuit converts output side voltage, and with one on the over wearing behavior of the high-frequency transformer Control circuit with a safety switch.

To protect operators, it is often necessary to elec trical machines, e.g. B. moving parts or a laser when Switch off intervention in these machines quickly and safely. This is usually done using safety switches established circuit, which has special security relays the corresponding supply voltages of the machine switches. The disadvantage here is that the security used safety relays have to switch large powers, and therefore are very expensive.

The invention is based, protection circuit for switching off and temporarily blocking the load to create part of a machine circuit in which on the Use of expensive safety relays can be dispensed with.  

To solve this problem it is proposed that the High-frequency transformer at least one power on the primary side is connected upstream, its control via a Safety circuit is supplied, the opposite mains voltage and load part is galvanically isolated and by pressing the Safety switch can be activated.

In this way, special expensive safety relays can be used be waived, and there are only a few in the safety circuit Process voltages and currents.

The circuit breakers are preferably actuated by means of a control transformer whose input voltage is off the voltage in the safety circuit is obtained.

With the invention it is further proposed that in series with the Safety switch a fuse is arranged.

To increase the security of the protective circuit is also suggested that the safety circuit through the network voltage fed and this by a converter gal is vanically separated. The galvanic isolation of the security circuit can also use a 50 Hz transformer respectively.

With an embodiment it is finally proposed that the Converter has its own regulation. This allows stabilization of the voltage in the safety circuit pass.

Further details and advantages of the subject of the invention result from the following description of the drawing. This is based on an exemplary embodiment, a possible Auf Construction of the protective circuit according to the invention shown.

The protective circuit shown serves the load part 1 of a machine circuit shown in the drawing at the top right with the output voltages U _A1 , U _A2 . . . _An ERS U turn and block temporarily if a safety switch 2 is operated by an operator in an emergency. Switching off and temporarily blocking the load part 1 can also be provided if, in the event of an intervention, such a safety switch 2 is actuated automatically, ie internally in the machine. This can e.g. B. depending on sensor signals he follow, for example a light barrier.

The mains voltage U _{N provided} is converted in a main converter in the form of a high-frequency transformer T 1 into the output voltage U _A required for operating the machine or system. The high frequency transformer T₁ can work as a clock, single-ended or flyback converter. The control of the high-frequency transformer T 1 takes place via circuit breakers 3 , 4 , which are connected upstream of the high-frequency transformer T 1 on the primary side. By appropriate control of the circuit breaker 3 , 4 , the load part 1 can thus be completely decoupled from the mains, and thus switch off and block the machine in question in an emergency.

The switching pulses for the circuit breakers 3 , 4 are generated in a control 5 , which is part of a safety circuit 6 that is completely galvanically isolated from the load part 1 . The control pulses are transmitted from the control 5 to the circuit breakers 3 , 4 by means of a control transformer T₂.

The safety circuit 6 , in order to be able to work completely independently of the load part 1 , has its own supply voltage, which is provided to the safety circuit 6 via a converter T 3 serving as a galvanic separation, the converter T 3 being connected to the network on the primary side . Therefore, the transducers T₃ provides galvanically isolated power supply voltage for the safety circuit 6, wherein the primary side of the transformer T₃ is connected a control 7, which is designed so that the voltage is stabilized in the safety circuit. 6 A 50 Hz transformer can also be used for the converter T₃.

The supply voltage of the safety circuit 6 is guided to the control 5 for the circuit breakers 3 , 4 via a fuse 8 and the safety switch 2 , which is preferably clearly visible on the respective machine.

By actuating the safety switch 2 , the safety circuit 6 is first opened. The control 5 now has no supply voltage and the circuit breakers 3 , 4 are blocked ge, so that the machine circuit is switched off and is blocked before. A subsequent start-up of the machine takes place in such a way that the supply voltage of the control 5 is switched on by closing the safety switch 2 and this now switches the circuit breakers 3 , 4 by means of controlled pulses via the control transformer T 2 .

The protective circuit shown offers the additional possibility of precisely regulating the output voltages U _A by means of a suitable control circuit, in that the output voltage U _{A is} detected and the pulses of the control 5 are modulated as a function of the measured voltage. Through this feedback, the output voltage U _{A can be} effectively regulated.

Reference list

1 load section
2 safety switches
3 circuit breakers
4 circuit breakers
5 control
6 safety circuit
7 regulation
8 fuse
U _A1 output voltage
U _A2 output voltage
U _On output voltage
U _N mains voltage
T₁ high frequency transformer
T₂ level transmitter
T₃ converter.

Claims (6)

1. Protection circuit for switching off and temporarily blocking the load part of a machine circuit in the event of an intervention or the actuation of a safety switch by an operator, with a high-frequency transformer (T₁), the primary side available network voltage (U _N ) in the for the operation of Machine current circuit required secondary-side output voltage (U _A ), and with a control circuit acting on the transmission behavior of the high-frequency transmitter (T₁) with a safety switch ( 2 ), characterized in that the high-frequency transmitter (T₁) upstream of at least one circuit breaker ( 3 , 4 ) is whose control ( 5 ) is supplied via a safety circuit ( 6 ) which is galvanically isolated from the mains voltage (U _N ) and load section ( 1 ) and can be activated by actuating the safety switch ( 2 ). 2. Protection circuit according to claim 1, characterized in that the operation of the circuit breaker by means of a control transformer (T₂), whose input voltage is obtained from the voltage in the safety circuit ( 6 ). 3. Protection circuit according to claim 1 or claim 2, characterized in that a fuse ( 8 ) is arranged in series with the safety switch ( 2 ). 4. Protection circuit according to one of claims 1 to 3, characterized in that the safety circuit ( 6 ) fed via the mains voltage (U _N ) and this is galvanically isolated from it by a converter (T₃). 5. Protection circuit according to claim 4, characterized in that the electrical isolation of the safety circuit ( 6 ) is carried out by a 50 Hz transformer. 6. Protection circuit according to claim 4 or claim 5, characterized in that the converter (T₃) has its own regulation ( 7 ).