DE1272363B - Electronic proximity switch - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN 4Ü07VW PATENT OFFICE Int. Cl .:

H03k

EDITORIAL

German class: 21 al - 36/18

Number: 1272 363

File number: P 12 72 363.6-31 (B 88958)

Filing date: September 17, 1966

Opening day: July 11, 1968

The invention relates to an electronic proximity switch with a with a first feedback loop provided oscillator, whose oscillation behavior by introducing a conductive object can be influenced.

From the French magazine "Electricite", January 1957, p. 21, the principle is already known, To influence an oscillator in its vibration behavior by bringing a piece of sheet metal towards it: If the sheet metal is brought close to the oscillator coils, the oscillator is heavily damped and stop vibrating. If, on the other hand, the sheet metal is removed, the oscillator oscillates, with the amplitude its output voltage depends on the size and distance of the sheet. This can Amplitude take arbitrary intermediate values, which are passed through continuously.

Such a known oscillator is not very suitable as a switching element, because a switching element, z. B. a limit switch, a bistable behavior (off-on) is required, and this must first the output voltage of the known oscillator is rectified and then an electronic one Switch, e.g. B. a Schmitt trigger, which shows a bistable behavior. Such However, equipment is expensive and prone to failure due to the large number of components required. In addition, this known oscillator must have a fairly strong feedback in order to ensure that it starts to oscillate to ensure. This in turn means that a fairly strong damping is necessary to it to block. Both make the design and the practical function of the oscillator more difficult.

It is therefore an object of the invention to provide an electronic proximity switch that is used in a small number of components has a bistable switching behavior. In particular, this proximity switch switch very quickly, so that he z. B. in electronic ignition systems for high speeds can be used.

According to the invention, this is the case with one mentioned at the beginning electronic proximity switch achieved in that the output voltage of the oscillator an AC voltage amplifier is supplied, which only at a predetermined size of this output voltage begins to amplify and that the alternating voltage component of the output voltage of this AC voltage amplifier is fed to the oscillator in the sense of positive feedback. Through this one achieves in a very simple way that the oscillator has at least two stable switching states, namely a first switching state with high Schwin-Electronic proximity switch

Applicant:

Robert Bosch G. m. B. H.,

7000 Stuttgart, Breitscheidstr. 4th

Named as inventor:

Dipl.-Ing. Richard Schleupen, 7000 Stuttgart - -

amplitude (current-conducting object far away) at which the AC voltage amplifier is effective, and a second switching state in which the oscillation amplitude is either smaller or equals zero. In this second switching state, the output voltage of the oscillator is so small that the AC amplifier is not amplifying. If the output voltage increases by removing the electrically conductive object, the oscillator voltage suddenly jumps within a very short time to a higher value corresponding to the first switching state, because the AC voltage amplifier takes effect.

According to a further feature of the invention, the proximity switch is designed so that the as Transistor oscillator designed oscillator to stabilize the current gain a negative feedback resistor has in its emitter circuit.

As a result, the switching device is largely independent of temperature and switches when it approaches of a certain electrically conductive object every time that object defines one Distance from the switching device. Such a switching device is particularly suitable for precise non-contact position controls, e.g. B. machine tools.

Furthermore, the proximity switch is advantageously designed so that in the AC voltage amplifier a transistor is provided whose conductivity type is complementary to that of the oscillator transistor is. This gives a particularly simple construction of the switching device with only two Transistors, with an additional power transistor optionally provided for controlling a relay can be.

A particularly simple structure of the proximity switch is obtained according to a further feature of the invention in that the AC voltage amplifier is switched as an audion, so that when a certain amplitude of the output voltage is reached of the oscillator as a rectifier

809 569/510

takes effect. This eliminates the need for a special rectifier.

Further details and advantageous developments emerge from what is described below and in the drawing illustrated embodiment of the invention. It shows

F i g. 1 the circuit of a proximity switch according to the invention,

F i g. 2 diagrams to explain how the circuit works and Fig. 3 according to Fig. 1,

F i g. 4 an additional device for an ignition distributor, with which the switching state of the proximity switch according to FIG. 1 can be controlled periodically can.

The proximity switch according to FIG. 1 has three transistors, namely an npn transistor 10, which forms an oscillator together with two coils 11, 12, also a pnp transistor 13, which as AC voltage amplifier with response threshold is used, and an npn power transistor 14 for Control of a relay 15, to which a quenching diode 16 is connected in parallel in the usual way.

The proximity switch according to FIG. 1 is from a voltage source, not shown, with a DC voltage of, for example, 12 V supplied. To this voltage source are one of the following Line 17 designated as a plus line and a line 18 designated below as a minus line connected.

The emitter of the transistor 10 is connected to the negative line 18 via a resistor 21, to which the emitter of transistor 14 is also connected.

The coil 12 serves as the feedback coil of the oscillator and is connected at one end to the base of the oscillator transistor 10 and at its other end on the one hand via a resistor 22 with a point 23 of constant potential, on the other hand via a capacitor 24 with the tap 25 of a potentiometer 26 connected, which is at the output of the AC voltage threshold amplifier 13. During operation, a voltage is applied to this potentiometer 26 which is shown in FIGS. 1 and ₂ is denoted by U 2. At an oscillator frequency of 500 kHz, the capacitor 24 has a value of about 100 pF.

Between the positive line 17 and the point 23 there is a resistor 27, between the point 23 and the negative line 18 a resistor 28, and parallel to this a capacitor 29.

The collector of the oscillator transistor 10 is connected via a collector resistor 32 to the base of the transistor 13 and to one terminal of a parallel oscillation circuit which consists of the coil 11 and a capacitor 33 and the other terminal of which is connected to the positive line 17. During operation, this oscillating circuit 11, 33 produces a voltage which is shown in FIGS. 1 to 3 is denoted _{by M 1.} The capacitor 33 has a dielectric made of mica or Styroflex so that its loss angle tg <5 is independent of temperature; As has been shown, this temperature independence of the loss angle is important for stable functioning of the switching device.

The coils 11 and 12 are coupled to one another. By approaching an electrically conductive object, As indicated schematically at 34 in the form of a piece of sheet metal, this coupling can be reduced and - with appropriate spatial design of switching device and object 34 - so far be reduced so that the oscillator stops oscillating. In the sense of the invention, however, it is in the In most cases it is more advantageous to reduce the coupling only so far that the oscillator still oscillates, but with a lower amplitude, as will be described in the following. By suitable electrical and spatial dimensioning, this can easily be achieved.

The emitter of the threshold amplifier transistor 13 is connected to the connection point of two resistors 35, 36 serving as voltage dividers, which are connected between the plus line 17 and minus line 18, that is to say at a fixed voltage. One connection of the potentiometer 26 is connected to the collector of the transistor 13 and the other connection to a connection A, which in turn is connected to the positive line 17 via a filter capacitor 37 and to the negative line 18 via two resistors 38, 39 connected in series. The base of the power transistor 14 is connected to the connection point of these resistors. The collector of this transistor is connected via a terminal A ' to the anode of the quenching diode 16 and one terminal of the relay 15 and is connected via a collector resistor 42 to the positive line 17, on which the cathode of the quenching diode 16 and the other terminal of the relay 15 lie.

The proximity switch according to FIG. 1 works as follows: It is initially assumed that the current-conducting object 34 is in such a position between the Spulenil and 12 that the feedback is still sufficient to meet the oscillation condition of the oscillator 10, so that it operates at a frequency of for example 50OkHz oscillates. In the diagram according to FIG. 3, in which the distance between the object 34 and the coils 11, 12 is denoted by s and the voltage at the resonant circuit 11, 33 is denoted by U ₁ , this corresponds to a distance between S ₁ and λ . The oscillator 10 then oscillates with a voltage which is denoted by M ₁₀ in FIGS. 2, α and 3. Since the amplitude of this voltage is greater than the fixed potential set at the emitter of transistor 13, it is not amplified by transistor 13, ie this transistor remains blocked because voltage M _{10 is} below its threshold value (so-called audio circuit). Correspondingly, there is a negative potential at the output ^ and a positive potential at the output A ' which is complementary thereto (the transistor 14 is blocked in this case because its emitter-base voltage is equal to zero).

If the conductive object 34 is now removed from the coil parts 12 and 12, the feedback becomes stronger and the voltage U ₁ rises somewhat. At a distance s ₃ , this voltage becomes so great ( _{voltage M 11} in Fig. 2, b) that the threshold amplifier transistor 13 begins to conduct at each of the negative voltage maxima, so that voltage pulses M ₂ arise at the potentiometer 26, as they are in the lower row from F i g. 2 are shown.

These voltage pulses are generated via the capacitor 24 in the sense of a positive feedback fed back to the oscillator transistor 10, namely at the junction of resistor 22 and coil 12 is added to the potential at point 23

(The resistor 22 serves as an addition resistor). As a result, the amplitude of the voltage M ₁ is increased further and swings to a stable value M ₁ within two to three periods, as shown in FIG. 2, b . The voltage pulses U ₂ have then - due to the saturation of the transistor 13 - reached their highest value, so that larger voltage values can no longer be transmitted via the second feedback circuit, which consists of the threshold amplifier transistor 13, the potentiometer 26 and the capacitor 24.

At the capacitor 37, the voltage pulses U ₂ produce a wavy DC voltage which controls the transistor 14 to be conductive, so that the relay 15 picks up. The resistors 38, 39 are provided for the case that the transistor 13 should already carry a small collector current before the higher voltage U _{1n is reached.}

The voltage drop across resistor 39 caused by such a small collector current is not sufficient to make the transistor 14 conductive. So this transistor only changes at Reaching a certain voltage level at the output of the threshold amplifier transistor 13 is his Conductivity state.

As can be seen, the transistor 13 fulfills a multiple function in the circuit, namely once as an amplifier with a response threshold in the second feedback circuit and then as a rectifier with a response threshold for transistor 14. This is achieved in that it is connected as an audion. Man This saves a special diode. However, it is also possible - e.g. B. when using built-in Circuits, amplifiers and rectifiers to be carried out separately.

As is particularly evident from FIG. 2, b clearly shows, an essential advantage of the present circuit is its short response time, which is achieved by the fact that the oscillator of the switching device always oscillates during operation, so that the additional time otherwise required for the oscillator to oscillate is eliminated. However, the switching device also works completely satisfactorily when the coupling of the coil parts 12 and 12 is reduced so far that the oscillation condition of the oscillator is no longer fulfilled by the object 34 being brought closer. This state is reached in FIG. 3 for paths smaller than 5 * ₀ . The voltage U ₁ drops to zero. With a suitable dimensioning of the switching device, depending on the approach of the object 34, three stable switching states are obtained, namely a first switching state in which the oscillator voltage U _{1 is} equal to zero, a second in which it has the value M ₁₀ and a third switching state with the Tension value M ₁₂ . In this way you can z. B. realize two switching operations in a machine tool with a single switching device, z. B. Slow speed from a certain position and stopping at a second position of the moving part. In such a case, of course, a second threshold voltage amplifier must also be provided for actuating a second relay or other switching element.

The switching curve shown in Fig. 3 is shown somewhat exaggerated for the sake of clarity. As can be seen, the jump to the larger amplitude occurs when the object 34 is moved away and at a distance ^, whereas the jump to the lower amplitude occurs when the object 34 approaches and at the distance designated by s _2. In practice, the difference between S ₃ and S _{2 is} extremely small and is on the order of 1 mm. It can be set with the tap 25 of the potentiometer 26. - In the lower diagram of FIG. 3, the current la through the relay 15 is indicated, which jumps to its maximum value when the object 34 moves away at the path s ₃ and jumps back to zero when it approaches the path s _2.

F i g. 4 shows the design of the coils 11 and 12 when used to control the ignition of a four-cylinder internal combustion engine. (In this case, the relay 15 is omitted in FIG. 1 and an arrangement for generating ignition sparks, e.g. a transistor ignition system, is used in its place.)
The coils 11 and 12 each sit on one of the two free ends of an iron core 46, which has approximately the shape of a C. Between these free ends is the edge of a bell-shaped bronze part 47 in which four slots 48 are milled, each offset by 90 °.

The bronze part 47 is fastened by a nut 49 on a shaft 50 on which the distributor arm is also 51 seated. The shaft 50 is driven by the internal combustion engine in the manner customary in ignition distributors Way driven.

The arrangement according to FIG. 4 works as follows: As long as there is a slot 48 between the coils 11 and 12, the oscillator 10 oscillates with the maximum amplitude M ₁₂ , and the ignition system emits an ignition spark. If, on the other hand, the solid bronze edge of the bronze part 47 lies between the coils 11, 12, the coupling is reduced to such an extent that the oscillator 10 only oscillates with the amplitude M ₁₀ and the ignition system is in its retirement. The edge of the bronze part 47 is dimensioned in such a way that it does not completely fill the space between the two coils 11 and 12 and that sufficient coupling is still present at all times to enable the oscillator 10 to oscillate. This is important because it is particularly important in ignition systems that the maximum oscillation of the oscillator 10 begins without delay, which is achieved particularly reliably with the invention due to its short switching time of only two to three periods of the oscillator frequency.

If a delay were to occur here, the ignition point would be referred to as the speed increases on the distance between two ignitions, lagging more and more in percentage terms, which is very desirable. In addition, the invention allows a high ignition frequency, so it is particularly suitable for high-performance engines suitable for high speeds.

As can be seen, thanks to its simple structure, the invention can also be used with advantage in the inductive Train protection can be used, as well as for non-contact position indication in measuring instruments.

Claims (16)

Patent claims: 1. Electronic proximity switch with one provided with a first feedback circuit Oscillator, whose vibration behavior is caused by the introduction of an electrically conductive object can be influenced, thus characterized shows that the output voltage (M ₁ ) of the oscillator (10, 11, 12) is fed to an AC voltage amplifier which only begins to amplify this output voltage (M _{1 ) at a predetermined value (M 11} ) and that the AC voltage component of the output voltage (m ₂ ) this AC voltage amplifier (13) is fed to the oscillator in the sense of positive feedback. 2. Proximity switch according to claim 1, characterized in that the transistor oscillator (10, 11, 12) designed oscillator to stabilize the current gain a negative feedback resistor (21) in its emitter circuit. 3. Proximity switch according to claim 2, characterized in that the AC voltage amplifier a transistor (13) is provided, the conductivity type (pnp) of which is complementary to that of the oscillator transistor (10; npn type) is. 4. Proximity switch according to at least one of claims 1 to 3, characterized in that that at the output of the oscillator (10, 11, 12) via a threshold rectifier (13) a consumer (14, 15) is connected. 5. Proximity switch according to claim 4, characterized in that the AC voltage amplifier (13) is connected as an audion so that it _{becomes effective as a rectifier when a certain amplitude of the output voltage (M 1} ) of the oscillator (10, 11, 12) is reached. 6. Proximity switch according to at least one of the preceding claims, characterized in that that the emitter of the transistor (13) serving as an AC voltage amplifier a voltage divider (33, 36) connected to a fixed voltage is connected. 7. Proximity switch according to claim 6, characterized in that a partial resistance (35) of the voltage divider (35, 36) as an emitter resistor as an AC voltage amplifier serving transistor (13) is formed. 8. Proximity switch according to at least one of the preceding claims, characterized in that that the oscillator (10, 11, 12) fed in the sense of a positive feedback output voltage of the transistor (13) serving as an AC voltage amplifier is adjustable to the To be able to set the switching hysteresis of the switching device. 9. Proximity switch according to at least one of the preceding claims, characterized in that that a feedback coil (12) is connected to the base of the oscillator transistor (10) and that one terminal of this feedback coil not connected to the base on the one hand via a resistor (22) with a point (23) of constant potential, on the other hand Connected via a capacitor (24) to the output of the AC voltage amplifier (13) is. 10. Proximity switch according to at least one of the preceding claims, characterized characterized in that the oscillator (10, 11, 12) in a manner known per se is a frequency-determining Inductance (11) and a frequency-determining capacitance (33) and that the loss angle tg <5 of the frequency-determining capacitance (33) at least almost independent of temperature is. 11. Proximity switch according to claim 5, characterized in that the output connected to the AC amplifier (13) connected as an audion, a transistor (14) which only becomes conductive when a certain voltage is reached at the output of the audio changes. 12. Proximity switch according to at least one of the preceding claims, characterized by an oscillator (11, 10, 12) with two stable oscillation _{states, namely a stable oscillation state with a small amplitude (M 10} ) and a stable switching state with a large amplitude (m ₁₂ ), wherein these oscillation states are dependent on the position of the electrically conductive object (34), that is to say on the damping of the oscillator. 13. Proximity switch according to claim 12, characterized by a third stable state, in which the oscillator (10, 11, 12) does not oscillate. 14. Use of a proximity switch according to at least one of the preceding claims for controlling the ignition system of an internal combustion engine. 15. Use of the proximity switch according to at least one of claims 1 to 13 in a non-contact limit switch. 16. Use of the proximity switch according to at least one of claims 1 to 13 for inductive train protection. 1 sheet of drawings 809 569/510 7.68 © Bundesdruckerei Berlin