ELECTROSURGICAL GENERATOR WITH A LEAKAGE CURRENT DETECTION

Abstract

An electrosurgical generator which outputs high-frequency AC voltage for an electrosurgical instrument includes a leakage current detecting device for the connected electrosurgical instrument. The leakage current detecting device is embodied as a voltage measuring device, the inputs of which are connected in each case via a capacitive coupling to an active and a neutral line of the output line and which has a bipolar voltage divider having a predetermined fixed ratio. An asymmetry detector connected via a capacitive coupling compares upper and lower voltage at the voltage divider, and outputs a fault signal for leakage current in the case of deviation of the ratio of upper to lower voltage from the predetermined fixed ratio.

Claims

1. An electrosurgical generator configured to output a high-frequency AC voltage to an electrosurgical instrument, comprising an inverter for high voltage, which generates the high-frequency AC voltage that is passed via an output line to an output for connection of the electrosurgical instrument, and a leakage current detecting device for the electrosurgical instrument connected to the output. wherein the leakage current detecting comprises a voltage measuring device, which is connected by its inputs in each case via a capacitive coupling to an active and a neutral line of the output line and has a bipolar voltage divider having a predetermined fixed ratio, which has an upper connection and a lower connection, to which the capacitive coupling is applied, and also a center tap, and an asymmetry detector configured to compare an upper voltage between upper connection and center tap with a lower voltage between lower connection and center tap, and to output a fault signal for leakage current in the case of deviation of the ratio of upper voltage to lower voltage from the predetermined fixed ratio.

2. The electrosurgical generator as claimed in claim 1, wherein the asymmetry detector has a minimum threshold, below which a fault signal is not yet output.

3. The electrosurgical generator as claimed in claim 2, wherein the minimum threshold is adjustable.

4. The electrosurgical generator as claimed in claim 2, wherein different minimum thresholds are provided for the active electrode and the neutral electrode.

5. The electrosurgical generator as claimed in claim 3, wherein the minimum threshold is defined in an instrument-dependent manner.

6. The electrosurgical generator as claimed in claim 1, wherein the asymmetry detector is provided with a polarity detector for the leakage current.

7. The electrosurgical generator as claimed in claim 6, wherein the polarity detector interacts with a display device, which signals whether a leakage current occurs at the active electrode or the neutral electrode.

8. The electrosurgical generator as claimed in claim 1, wherein the asymmetry detector has a comparator having two inputs, the upper connection being connected to one of the inputs and the lower connection being connected to the other input.

9. The electrosurgical generator as claimed in claim 8, wherein the comparator is embodied using analog technology.

10. The electrosurgical generator as claimed in claim 1, wherein the asymmetry detector is embodied as a difference calculating unit with a threshold value switch connected downstream.

11. The electrosurgical generator as claimed in claim 1, wherein the asymmetry detector has an analog/digital converter.

12. The electrosurgical generator as claimed in claim 11, wherein the analog/digital converter is arranged on the input side of the asymmetry detector.

13. The electrosurgical generator as claimed in claim 1, wherein coupling is at high impedance relative to the voltage divider.

14. The electrosurgical generator as claimed in claim 1, wherein the voltage divider is capacitive.

15. The electrosurgical generator as claimed in claim 1, wherein the center tap is connected to a fixed potential.

16. The electrosurgical generator as claimed in claim 1, wherein the leakage current detector interacts with a device for determining a magnitude of the current.

17. The electrosurgical generator as claimed in claim 1, wherein the voltage divider is a symmetrical voltage divider.

Description

[0032] The invention is explained in greater detail below on the basis of an advantageous exemplary embodiment with reference to the accompanying drawing, in which:

[0033] FIG. 1 shows a schematic illustration of an electrosurgical generator in accordance with one exemplary embodiment with a connected electrosurgical instrument;

[0034] FIG. 2 shows a block diagram concerning the electrosurgical generator in accordance with FIG. 1;

[0035] FIG. 3 shows an exemplary circuit diagram for a measurement sensor with a leakage current detecting device;

[0036] FIG. 4a, b show embodiment variants for an asymmetry detector with respect to FIG. 3;

[0037] FIG. 5 shows a diagram concerning measured voltages without leakage current; and

[0038] FIG. 6 shows a diagram concerning measured voltages with leakage current.

[0039] An electrosurgical generator in accordance with one exemplary embodiment of the invention is illustrated in FIG. 1. The electrosurgical generator, designated in its entirety by the reference number 1, comprises a housing 11 provided with a connection 14 for an electrosurgical instrument 16. In the exemplary embodiment illustrated, the instrument is an electric scalpel. It is connected to the connection 14 of the electrosurgical generator 1 via a high-voltage connecting cable 15. A further connecting cable 15′ is led to an operating table 98 and connected there to a counter electrode 16′. The latter is configured to be arranged over a large area on the patient 99 to be operated on. The power output to the electrosurgical instrument 16 can be changed by way of a power controller 12.

[0040] For the following explanation of the construction of the electrosurgical generator 1, reference is made in particular to FIG. 2. For supplying the electrosurgical generator 1 with power, a DC voltage supply 2 is provided. It can be connected to the public electricity supply system via a supply system connection cable 13 and can be fed via a high-voltage power supply unit (High Voltage Power Supply—HVPS). The power supply unit 22 comprises a rectifier and feeds a DC voltage link circuit 24 in the exemplary embodiment illustrated. It should be noted that the supply from a power supply unit 22 is not mandatory, rather that other types of DC voltage supply 2 are also conceivable, for example a direct supply with DC voltage, particularly in the case of electrosurgical generators installed in vehicles or in the case of those provided in mobile or temporary hospitals.

[0041] The magnitude of the DC voltage is typically between 10 and approximately 500 volts, often 48 volts in the case of modern electrosurgical generators. It can be fixed or variable, which is dependent in particular on the design of the inverter that generates the high voltages. The absolute magnitude of the DC voltage may depend in particular on the power set, the type of electrosurgical instrument 16 and/or the load impedance thereof, which in turn depends on the type of tissue treated.

[0042] An inverter 3 is fed by the DC voltage supply 2 and generates from the DC voltage fed to it high-frequency AC voltage in the high-voltage range of a few kilovolts with frequencies in the range of between 200 kHz and 4 MHz. The inverter 3 provided can be a so-called single-ended converter, for example, which is driven by an oscillator in a free-running manner; these are generally supplied by a DC voltage supply 2 with variable voltage. This embodiment can afford the advantage of conceptional simplicity and generally directly passes the high voltage generated by it via an equipment-internal output line 4 to the output connection 14 for the electrosurgical instrument 16. Alternatively, however, provision can also be made for the inverter 3 to be embodied as an inverter. In the case of the latter, the setting of the power and also of the voltage to be output is effected by way of the inverter itself, such that a variable DC voltage supply 2 is not required, rather one with a fixed voltage (for example 48 V) is sufficient. The inverter has power semiconductor switches as so-called current valves, which are driven by an inverter controller 31 in a manner known per se, for example by means of known pulse width modulation as PWM control, for the purpose of generating a high-frequency high voltage. The high-frequency high voltage generated by the inverter is thus virtually freely adjustable with regard to frequency and waveform. The high-frequency voltage generated by the inverter is typically output via a low-pass filter and an output transformer (not illustrated) for voltage boosting to the generator-internal output line 4 to the connection 14 for the electrosurgical instrument 16.

[0043] Furthermore, voltage and current of the high voltage generated by the inverter 3 are measured by means of a voltage sensor 17 and a current sensor 18, and the measurement signals are fed to a processing unit 19, which applies the corresponding data about the output voltage, current and power to an operational controller 10 of the electrosurgical generator 1. The power controller 12 is also connected to the operational controller 10. The operational controller 10 is furthermore configured to set various modes, as they are called, which typically involve stored voltage/time profiles; however, they can also involve predefinitions containing the waveform of the high-frequency high voltage to be output.

[0044] The high-frequency high voltage generated is passed to the output connection 14 via the output line 4 with its lines 41 for an active electrode and line 42 for a neutral electrode. Owing to the high frequency of the voltage output by the electrosurgical generator, parasitic capacitances act on the lines 41, 42. They are represented by the capacitive elements 48, 49 in FIG. 3.

[0045] The electrosurgical instrument 16 is connected to the output connection 14. In the exemplary embodiment illustrated, this is a monopolar instrument connected to the line 41 with the active electrode; however, the use of bipolar instruments (not illustrated) can also be provided. In order to close the electric circuit, a counter electrode 16′ is connected to the line 42 via the connecting cable 15′. The counter electrode 16′ is situated on the operating table 98, the patient 99 to be operated on lying said table. There the counter electrode 16′ is connected to the patient 99 over a large area at a suitable location (this is illustrated merely symbolically in FIG. 1). Once the surgeon then places the electrosurgical instrument 16 on the patient 99, the electric circuit is closed via the body tissue of the patient 99. The body tissue situated directly at the instrument tip 16 is heated as a consequence of the contact resistance prevailing there and it is cut, cauterized, coagulated, etc., depending on the electrosurgical instrument 16 used.

[0046] It is critical if the electric circuit is (also) closed via other locations, in particular body parts of the patient 99. Uncontrolled leakage currents arise there. That is a considerable risk for the safety of the patient, possibly also of the medical personnel. In order to detect this, a leakage current detecting device 6 is provided.

[0047] For further explanation, reference is now made to FIG. 3, where the inverter 3 is symbolically illustrated as a source of the AC voltage in the left-hand part of the figure. Said voltage is output to the connecting cable 15 for the electrosurgical instrument 16 via the output line 4 with its lines 41, 42 for the active and neutral electrodes, respectively. The electric circuit is closed via the further connecting cable 15′. The electrosurgical instrument 16 and also the counter electrode 16′ are symbolically represented by a load resistor in FIG. 3.

[0048] The leakage current detecting device 6 comprises a bipolar voltage measuring device 7 having a bipolar voltage divider 73, and also an asymmetry detector 8. The voltage measuring device 7 is configured to carry out a voltage measurement on the lines 41, 42 of the output line 14 for the active and neutral electrodes. In the exemplary embodiment, the bipolar voltage divider of the voltage measuring device 7 is configured by way of example as a symmetrical voltage divider 73 having a division ratio of 1:1, which is embodied as a capacitive voltage divider having an upper measurement capacitance 74 and a lower measurement capacitor 77, which are connected to one another at a center tap 77. The respective other connection of the measurement capacitance 74, 77 is arranged at an upper connection 78 and a lower connection 79, respectively, of the voltage divider 73. The magnitude of the measurement capacitance is in the nanofarad range, for example approximately 10 nF.

[0049] For a measurement of the voltage in the lines 41, 42 that is as free of perturbations as possible, the symmetrical voltage divider 73 is connected to the lines 41, 42 via a high-impedance coupling. The high-impedance coupling is implemented by means of two capacitors having low capacitances, a capacitor 71 as connection between the line 41 and the upper connection 78 of the voltage divider 73 and also a second capacitor 72 as connection between the line 42 and the lower connection 79 of the voltage divider 73. The two capacitors 71, 72 have a capacitance in the Picofarad range, for example approximately 3 pF.

[0050] The upper connection 78 and the lower connection 79 are led out of the voltage divider 7 as output connections. They are applied to inputs 81, 82 of the asymmetry detector 8 connected downstream. The latter is configured to compare with one another the two voltages coming from the voltage divider 73 at the upper connection 78 and lower connection 79, respectively, and to check whether they have the predetermined fixed ratio (in the example, this is 1:1, since the voltage divider is symmetrical), i.e. have amplitudes (or root-mean-square values) of identical magnitudes. It should be noted that for the embodiment of the voltage measuring device 7 and of the asymmetry detector 8, it is not mandatory for both voltages to have exactly identical magnitudes, rather that this could also be implemented such that both voltages have a previously defined fixed ratio. Only of the case where both voltages are intended to be equal in magnitude is explained below, for the sake of simplification; the explanations apply, mutatis, mutandis, to other predefined fixed ratios. Inputs 81 and 82 of the asymmetry detector 8 are connected to the positive and negative inputs, respectively, of a comparator 83. The latter is configured to compare the two applied voltages with regard to their magnitude and to output a corresponding output signal which signals whether or not one voltage is higher than the other. Depending on the embodiment of the comparator 83, this output signal can be proportional to the deviation or digital, that is to say that it only provides information about whether or not there is equality.

[0051] In the last-mentioned case, the output of the comparator 83 can function directly as a fault signal and be applied to a signaling device, for example to an acoustic signal generator in the form of a warning horn 9.

[0052] During regulation operation, the voltages output by the symmetrical voltage divider 73 at the upper connection 78 and lower connection 79 are equal in magnitude, as is also illustrated in FIG. 5, where the curve designated by I shows the profile of the voltage U.sub.H present at the upper connection 78 and the curve II shows the profile of the voltage U.sub.L present at the lower connection 79. In the example illustrated, the two voltages are equal in magnitude and correspond to half of the voltage V1 output by the inverter 3, provided that no fault situation is present and, in particular, there is no ground fault in the region of the lines 15, 15′ of the electrosurgical instrument 16 or on the patent 99 with the latter's support 98. The comparator 83 ascertains that the voltages are equal in magnitude and does not output a fault signal.

[0053] The situation is different if a fault situation is present, i.e. if for example one of the body parts of the patient 99 touches a grounded component (grounded metal part). A parasitic impedance 97 to ground is thus formed, via which a leakage current flows. The voltages at the upper connection 78 and lower connection 79 that are ascertained by the voltage measuring device 73 are thus no longer equal in magnitude. As illustrated in FIG. 6, the voltage in the line 41 and thus at the upper connection dips owing to the leakage current. The resulting voltage profile for U.sub.H is represented by the curve I progressing close to the zero line. By contrast, the voltage U.sub.L at the lower connection 79, represented by the curve II, is maintained. As is clearly evident in FIG. 6, when a leakage current occurs, the voltages are not equal in magnitude, but rather have considerable differences. This is ascertained by the comparator 83 of the asymmetry detector 8. It outputs a corresponding fault signal which is passed to the warning horn 9 and thus provides the surgeon with a readily perceptible warning signal for the presence of the leakage current. At the same time, the signal can be connected to the operational controller 10 of the electrosurgical generator 1, such that the latter can react to the detected fault situation, for example by means of a rapid shut down of the inverter 3.

[0054] If the intention is for a fault signal not already to be triggered in the case of tiny deviations, then it is possible to provide the Schmitt trigger 85 as a threshold value switch. The latter has an adjustable threshold value 85′. In this way, it is possible to set what magnitude is permitted for the difference between the voltages at the upper connection 8 and at the lower connection 79 before the fault signal is triggered.

[0055] Expediently, a polarity detector 87 is furthermore provided. The input thereof is connected to the comparator 83. The sign from the result of the comparator 83 can thus be used to ascertain whether the leakage current flows away from the upper line 41 with the active electrode or from the connection line 15 (so-called “AE” fault), or whether the leakage current flows away from the lower line 42 with the neutral electrode or the connection line 15′ (so-called “NE” fault). Depending on that the polarity detector 87 drives a signal luminaire 89, 89′, which correspondingly signals the presence of an AE or NE fault, respectively.

[0056] Alternative embodiment variants for the asymmetry detector 8 are indicated in FIGS. 4a) and b). In the case of the variant in accordance with FIG. 4a), two analog/digital converters 84, 84′ are provided. The upper connection 78 is connected to the analog/digital converter 84, such that this converter converts a voltage signal for the voltage of the active electrode in the connecting line 15 into a corresponding first digital signal. The lower connection 79 is connected to the analog/digital converter 84′, such that this converter converts a voltage signal for the voltage of the neutral electrode, such as is present in the line 15′, into a corresponding digital signal. These two digital signals are applied to the inputs of a difference element 86. The latter is embodied using digital technology, for example using microprocessor technology. A check is made to establish the magnitude of the difference between the two digitally converted voltage signals. If it exceeds a likewise digitally adjustable threshold value (not illustrated in FIG. 4a), then the outputs of the difference elements 86 are activated. The latter has an output for connection to the, preferably acoustic, signal device 9 and also two further outputs, to which displays 89, 89′ are connected, which are indicative of whether the leakage current is to be assigned to the active electrode “AE” or to the neutral electrode “NE”.

[0057] FIG. 4b) illustrates a simplified variant. In the case of the latter, the signals coming from the voltage divider 73 for the voltage at the upper connection 78 and the voltage at the lower connection 79 are applied to a Schmitt trigger 85 with an integrated difference forming unit 88, for example a comparator circuit. Here, too, as in the case of the Schmitt trigger 85 in FIG. 3, the switching threshold of the Schmitt trigger can be adjusted by way of an adjustable threshold value signal 85′.

[0058] In this way, with little additional outlay, the invention enables a reliable detection of whether a leakage current occurs. Furthermore, with little outlay, the invention can ascertain the polarity, i.e. whether said leakage current occurs at the active electrode “AE” or the neutral electrode “NE”.

[0059] In addition to the warning horn 9, the fault signal output by the asymmetry detector 8 can be applied to a separate device 80 that interacts with the operational controller 10. The device 80 is expediently configured, in the case where the asymmetry detector 8 detects the occurrence of leakage current, to ascertain the magnitude of the leakage current. This can be done for example by a procedure in which, by means of the operational controller 10, on the basis of measurement values for the current in the output line such as are present there anyway and originate from the measuring sensor 18, said device compares with one another current measurement values of the current output overall directly before and after detection of a leakage current by the asymmetry detector 8 and optionally outputs them via a display device.