SE464270B - Fail-safe safety device - Google Patents

Abstract

In a fail-safe safety device for supplying electrical energy to a load K the energy is transferred from a voltage source to the load by two connection elements Q1,Q2 alternately conducting and being cut off dependent upon two control signals S1,S2 generated in antiphase. A first condenser C1 acts as a transmission component for transmitting energy from the connection point C of the connection element to the connection point D of two series-connected diodes D1,D2. The load is connected across the diodes. The first condenser is charged via the first diode D1 and alternately is discharged via the second diode D2 to generate the voltage across the load. The supply of energy to the load is broken off when any one or more of the following conditions arises: a) absence of either or both of the control signals; b) both connection elements conducting or being cut off at the same time; c) short-circuiting of the first connection element and/or the second connection element and/or the first diode and/or the second diode and/or the first condenser; d) interruption in the first connection element and/or the first diode and/or the second diode and/or the first condenser. <IMAGE>

Description

464 270 å 8107568-1. In the described emergency stop device, the systems alternating with square signals generated in opposite phase. IN the simplest embodiment with two transistors is connected one emitter of the first transistor to the collector of a second transistor as well as to the negative electrical line via the primary winding of a transformer and a capacitor. A load is connected 'to the secondary winding of the transformer. The downside with this device is that the load is powered and driven even if the capacitor would be shorted. Other described embodiments forms omit the capacitor and use instead one or two more pairs of transistors, or the center socket at the primary winding of the transformer. Even in these alternatives embodiments, however, the load can be driven on individual components become short-circuited or interrupted.

Both JP 60-229102 and JP 60-229103 describe others load control circuits, which interrupt the operation of a load when errors occur in a parent microprocessor. Firstly these solutions are unnecessarily complicated, with several active components, incl. two NAND gates and, in one case, an operational amplifier, between the microprocessor and the load.

Secondly, they do not take into account any errors in the intermediate components themselves; if the microprocessor is whole and functioning, the load can thus be driven on others as well components have broken.

Technical problem: The object of the present invention is therefore to provide a safety device built up of a few components, by means of which supply voltage is supplied safely forward. to a load under the active control of a superior system, but which quickly interrupts the voltage supply when someone component breaks down, or when the correct control signals does not exist. 464 270 lw Solution: Said object is achieved by means of a device according to the finding, which is characterized by: the first input is connected to an electrical voltage supply source with a supply voltage; the first output is connected to the second input; the second output is connected to an electrical ground; the first output year is connected to the electrical ground it over a first capacitor and a first diode; a first load connection point is connected to it electric earth; a second load connection point is connected to it electric earth over a second diode and the first diode; the first diode is connected in series with the second diode; the first control signal and the second control signal are in opposite phase to alternately attach the first coupling element. the element and the second coupling element in the conductive the state of alternating charge via the first diode of it first capacitor and discharge via the second diode that of the first capacitor with the generation of an electric potential over the load; a fuse is connected between said voltage source and said first input whereby energy supply to the load by means of the safety device is interrupted if any or some of the following conditions occur: a) absence of one or both of the control signals; b) both coupling elements simultaneously occupy the conductive the permit or at the same time the non-conductive permit the; c) short circuit of the first coupling element and / or the second coupling element and / or the first the diode and / or the second diode and / or the first con- densator; d) interruption of the first coupling element and / or the first diode and / or the second diode and / or the first capacitor. 464 270 bh Figure description: Fig. 1 is a circuit diagram of an advantageous embodiment form of the invention; and Fig. 2 illustrates representative signals that occur at selected points in the load control circuit according to the invention.

Description of preferred embodiments: An embodiment of the safety device according to the invention will now be described with reference to the figures. One voltage source (not shown) supplies the circuit with the supply voltage and + Us volt. In the current path between the voltage source and it electric earth there is a first and a second controllable coupling element Q1 resp. Q2. Each coupling element can take a leading state and a non-leading state.

A first control signal S1 is connected to a control input thereof the first coupling element Q1, so that Q1 takes the lead the state when the amplitude of S1 exceeds a threshold de, and the non-conductive state when the amplitude of S1 below the threshold. In an analogous way, one decides second control signal S2 the state of the second switching element meant Q2. Maximum amplitude of control signals S1 and S2 selected with regard to the electrical properties of the coupling elements. and of course need not be equal to the supply voltage ningen + Us.

In the illustrated embodiment, the coupling element elements Q1 and Q2 of MOS-FET transistors. This choice is to minimize the voltage drop across each element. ment, but is not necessary. Common PNP and NPN transis- relays, relays, thyristors, and other controllable switching ment can also be used. Only for the purpose of simplifying it further description, the coupling elements below shall be called "transistors" Ql resp. Q2, each transistor being passage, output, and control input shall be called collector, emitter, respective bass. That a transistor occupies the conductive supply the state means that it bottoms out, and that it does not take it leading condition means that it is strangled. These terms and concepts are well known in digital technology and are therefore described not closer. 464 270 ä As illustrated in Fig. 2, each control signal has S1 and S2 a logic high value and a logic low value, whereby the high. the value. corresponds to a signal amplitude over the trans- the threshold value of the meters and the low value corresponds to a lamp height less than the threshold value, preferably at or close to the ground potential. The control signals S1 and S2 are generated on known method as pulse train in opposite phase of a parent (not shown) unit. Under normal conditions, the other is thus generated the control signal S2 is simplest as the logical inverse of the sta control signal S1: however, this is not necessary, and short periods during which no control signal is "high" may also occur occur, under conditions which will be apparent from it continued description. It is also beneficial though not necessary for the control signals to have a constant frequency vens. In a practical application of the invention was generated both control signals, for example with a frequency of the order of 1 kHz.

The parent unit preferably consists of a micro- processor to achieve the highest degree of adaptability and monitoring ability. However, it can also consist of examples bistable flip-flops or other known circuits.

In a basic embodiment, the voltage source is connected to it the collector of the first transistor Q1. The emitter of Q1 is connected to the collector of the second transistor Q2 (at point C in FIG. 1), and the emitter of Q2 is connected to the electrical ground.

However, a first fuse F1 is preferably arranged between the source and the first transistor Q1. About the control signals S1 and S2 would inadvertently assume the logically high value simultaneously, for example due to simultaneous short circuit, so that both transistors are grounded, the fuse F1 will be broken. is taken, whereby the supply voltage to the entire rest of the circuit quickly fails.

A signal path from the emitter of the first transistor Q1 also goes via a first capacitor C1 to a first diode D1 (at point D) and over D1 to ground.

A load K has two connection points P1 and P2. In it illustrated embodiment, the load K is inductive, closer definitely a relay, but it can also be a non-inductive one 464 270 á load such as a light bulb, an alarm system, etc. The load K can also include more than one power consumer, such as two or more relays, lamps, etc. In the example shown, in which the load K consists of a single relay, the load relay controls in a manner a break contact, which connects a second non shown voltage source, with voltage U1, with a connection point F. The load K is via its second connection point P2 connected across a second fuse F2 to a second diode D2, and thence across the first diode D1 to ground. The other one fuse F2 can be omitted, but is included with advantage to further protect the load against any incorrect coupling.

In a practical application of the invention, it worked the present safety circuit with the supply voltage Us i range 20 - 35 VDC. However, the invention is, of course equally useful at other supply voltage levels.

Diodes D1 and D2 are preferably of the Schottky type to reduce the voltage drop across them.

From its first connection point P1, the load K is connected to ground, preferably via a third diode D3. The the third diode D3 can be omitted but, as described in more detail below, by including it increases the system's failsafe.

In the preferred embodiment, the security features include the device according to the invention also a second capacitor C2, which is connected in parallel with the series-connected diodes D1 and D2. In the embodiment shown, one end of C2 connected to a point E between the second connection of the load point P2 and the other diode D2, and the other end grounded.

As shown below, the second capacitor C2 smooths the voltage signal to the load K.

Due to the large amount of energy provided by the capacitors C1 and C2 will normally need to be stored when the invention used to protect loads with such a large power consumption such as gear motors, they are preferably electrolytic. In a practical application was the first the capacitor C1, for example, electrolytic with a capacitance in of the order of 1000 uF. This capacitance may be less, but was chosen to reduce the internal resistance of Cl. IN this practical application 'was the second capacitor C2 -x 464 270 Z electrolytic with a capacitance of approximately 220 uF. The other one the capacitor C2 was chosen with less capacitance than C1 because the average current through C2 is smaller, and because one is too large value had given too long a cut-off time for the selected load, which consumed current of 0.3 to 1.0 A. In other applications C1 and C2 are selected with regard to the current load power consumption.

If the supply voltage + Us is positive, it is connected positive line of the first capacitor C1 to the point A between lan the transistors, and the positive of the second capacitor C2 wire is connected to ground. The first and the second diode D1 and D2, respectively, are prestressed in the direction of the earth, and if the If the diode D3 is included, it is biased in the direction of the load K.

With reference to both Fig. 1 and Fig. 2, the operation of the invention during normal operation and in the event of faults is now described. VaS.

I. Normal operating conditions As mentioned above, during normal operation, control signals are generated. S1 and S2 as pulse trains in opposite phase, the transistors Q1 and Q2 alternately bottom and choke, but never take over their conducting or non-conducting state at the same time. When it the first transistor Q1 conducts, the first capacitor C1 is charged up to a voltage that is only slightly lower than the supply voltage + Us. The difference in voltages occurs due to of the voltage drop across the first fuse F1 (if this) included), across transistor Q1, and across the first diode D1. The difference is minimized by using MOS-FET and Schottky technology as mentioned above.

When the first transistor Q1 is throttled and the second the transistor Q2 conducts, the first capacitor C1 is discharged through the second diode D2. The second capacitor C2 is charged thereby to a voltage which is slightly smaller in amplitude than the supply voltage, but with reverse polarity. When it the second capacitor CZ has its maximum charge is thus the voltage at point E is approximately equal to -Uy Due to the voltage drop across different intermediate components comes 464 270 å however, the amplitude of the voltage at point E in practice that be approximately 2.0 V lower than that of the supply voltage. The excitement over the load K will then be equal to the voltage across it second capacitor C2, minus the voltage drop across it the second fuse F2 and the third diode D3, if these include their.

As long as the transistors Q1 and Q2 alternately conduct and all components of the circuit are therefore completely "pumped" energy through the load and up to point E. Fig. 2 illustrates the signal shapes at the points in the circuit indicated in Fig. 1.

Normal operating conditions are assumed to exist until a point tl.

Voltage variations in point C, i.e. in the first con- one electrode of the capacitor, the first control signal S1 follows, since the first transistor Q1 bottoms out when S1 takes its logically high value and thus connects the first satin Cl with the voltage source. When S1 is "low", so that Q1 throttled, on the other hand, Cl is discharged, the voltage: at point C also decreases. When the first capacitor C1 is discharged, increases the voltage at point D to approximately -Us. Due to tension the case of the first diode D1, when the first satator is charged, the voltage at point D rises to something above ground potential. In practice, the voltage varies in points D from about +0.7 V to about - (Us - 0.5) V.

As shown in Fig. 2, the second capacitor smooths C2 voltage to load K.

If the load K consists of a relay, it will be as long as the voltage at point E is higher than its stroke voltage. By selecting the second capacitor C2 with sufficiently high capacitance, and by selecting the vence of the transistors high enough, the charge will at C2 always to be large enough to hold the relay activated under normal, faultless operating conditions. Exciting the point in point F will therefore be kept constant at U1.

If the load itself has such a mechanical or electrical delay that wrapping can not take place during a single half period of the signal at point D does not require a smoothing capacitor at all, and the second capacitor C2 could then be omitted. One 464 270 2 advantage of including the second capacitor C2 is, however that the safety circuit according to the invention can also be applied for loads without self-delay. The smoothing does that too possible for both control signals to simultaneously assume the low value for short periods, which reduces the need for chronization of the control signals slightly.

It can be observed that the voltage at point E, i.e. it approximate voltage across the load, has reverse polarity compared to the supply voltage, and approximately the same amplitude.

II. Conditions in case of signal or component failure If the first control signal S1 ceases, the first will come the transistor Q1 to remain throttled, which effectively insulates the voltage source from the rest of the circuit, and in particular from lasten K.

If the second control signal S2 ceases, the first can not the capacitor C1 is discharged, so that no energy can be "pumped" to the second capacitor C2 and to the load K.

If both control signals are high at the same time, both will come transistors Q1 and Q2 to conduct simultaneously, the first the fuse F1 breaks and interrupts all voltage supply.

This also happens if both transistors Q1 and Q2 become shorted. closed. If only the first transistor Q1 is short-circuited F1 will also break as soon as the other transistor Q2 gets the next pulse.

If the first capacitor C1, which is a transfer component, is short-circuited, short-circuited to earth through the first diode D1, and no energy can be transferred to the second capacitor C2 and to the load K.

Interruptions in the first diode D1 also block energy from being fed to the second capacitor C2 and to the load K.

Energy transfer to the load is therefore interrupted when something or any of the following conditions occur: a) absence of one or both of the control signals; b) both transistors Q1, Q2 simultaneously occupy the lead the permit or at the same time the non-conductive permit the; 464 270 lQ c) short circuit of the first transistor Q1 and / or the second transistor Q2 and / or the first diode D1 and / - or the second diode D2 and / or the first capacitor Cl: d) interruption in the first transistor Q1 and / or it the first diode D1 and / or the second diode D2 and / or the first capacitor Cl.

Referring to Fig. 2, assume that energy transfer interrupt_ The negative charge on the other capacitor C2 will then decrease until at time tz no longer able to activate the load K. The load thus switches, and then the load consists of a relay also changes the state of its break contact.

If the control signals S1 and S2 are correct, energy can transferred to the load only if the following errors occur simultaneously igt: 1) short circuit in the first transistor Q1; 2) short circuit in the first capacitor C1; 3) interruption in the first diode D1; 4) short circuit in the second diode D2; and 5) short circuit in the third diode D3 (if D3 included).

Thus, by the invention, the probability of the load C unintentionally activated almost non-existent. The invention also enables this level of security through the use of a few common components, and with no other active components components other than transistors Q1 and Q2.

The third diode D3 is not necessary according to the invention. No. If it is included, however, security is increased slightly by it is another component that must break (short- end), ie an additional condition that must be met, so that energy could be inadvertently fed to the load.

However, this increased security is achieved at the cost of one most often negligible voltage drop of approximately 1.0 V across D3. About D3 included, some known monitoring circuit may also be included to detect any short circuit in D3. 'a of ' 464 270 ll As described above and indicated in Fig. 2 the voltage at point E (and D) is approximately equal to the supply voltage but with reverse polarity. If, for example, Us = +24 V the voltage at point E becomes approximately -24 V at full charge of C2. This thus means a voltage doubling (a change of 48 V). By arranging more diode / capacitor steps such as the one described above can further doubling, quadrupling, etc., is achieved. About quadrupling of the supply voltage is arranged so that the voltage across the load increased from, for example, -24 V to about -96 V, would the efficiency of the circuit is further increased, since not even the voltage, if it was inadvertently supplied, would be able to trigger the load.

Several alternatives to the design illustrated in the figures the leading example has been mentioned above. The invention is example is by no means limited to achieving an emergency stop feature. By a simple change of the coupling of a strelä could, for example, voltage loss of the load activate, instead of switching off, any connected system. Of course, all of these options are covered by patent claims.

Claims (8)

464 270 1% PATENT REQUIREMENTS A fail-safe safety device for supplying electrical energy to an electrical load (K) comprising a first controllable coupling element (Q1), which has a first control input, a first input and a first output and inlet and a conductive and a non-conductive conductive state in dependence on a first control signal (S1), which is connected to the first control input, and a second controllable switching element (Q2), f! which has a second control input, a second input and a second output and occupies a conductive and a non-conductive state depending on a second control signal (S2), which is connected to the second control input, characterized in that the first the input is connected to an electrical voltage source with a supply voltage (V); the first output is connected to the second input; the second output is connected to an electrical ground; the first output is connected to the electric ground via a first capacitor (C1) and a first diode (D1); a first load connection point (P1) is connected to the electrical earth; a second load connection point (P2) is connected to the electrical ground via a second diode (D2) and the first diode (D1); In the first diode (D1) is connected in series with the second diode (D2); the first control signal (S1) and the second control signal (S2) are in opposite phase to alternately place the first switching element (Q1) and the second switching element (Q2) in the conductive state for alternating charging via the first diode (D1). ) of the first capacitor (C1) and discharge via the second diode (D2) of the first capacitor with the generation of an electric potential across the load (K); a fuse (F1) is connected, between said voltage source and said first input whereby energy supply to the load (K) by the safety device is interrupted if one or some of the following conditions occur: a) absence of one or both of the control signals (S1, S2) : or 'g 464 279 b) both coupling elements (Q1, Q2) simultaneously assume the conductive state or simultaneously assume the non-conductive state; c) short circuit of the first coupling element and / or the second coupling element (Q2) and / or the first diode (D1) and / or the second diode (D2) and / or the first capacitor (C1); or d) interruption in the first switching element and / or the first diode (D1) and / or the second diode (D2) and / or the first capacitor (C1). Device according to claim 1, characterized in that the first switching element consists of a first transistor (Q1), and the second switching element consists of a second transistor (Q2). 3. A device according to claim 2, characterized in that the first transistor (Q1) and the second transistor (Q2) are MOS-FET transistors. Device according to claim 1, characterized in that it includes a second capacitor (C2) which is connected in parallel with the series-connected first and second diodes (D1, D2) for smoothing the voltage to the load (K) when charging it. the first capacitor (Cl) and for charging when discharging the first capacitor (Cl). Device according to claim 1, characterized in that it includes a first fuse (F1) between the voltage source and the first input of the first coupling element (Q1). Device according to claim 1, characterized in that the first load connection point (P1) is connected to the electrical earth via a load protection diode (ns). 464 270 ”f Device according to claim 1, characterized in that the voltage across the first and second diodes (D1 and D2) has the opposite polarity compared to the supply voltage. Device according to claim 1, characterized in that a second fuse (F2) is arranged between the second connection point (P2) of the load (K) and the second diode (D2). f!