EP0482324A1 - Data transmission for sliding contactlines - Google Patents

Abstract

A circuit arrangement for data transmission in base band or by means of a modulated carrier contains two sliding contact lines (12, 13). Two sliding contact pieces (14...17), which are connected in pairs to in each case one terminal of a data circuit (31), run on each sliding contact line. Each pair of sliding contact pieces (14, 15, 16, 17) has allocated to it in each case one voltage source (21, 26) which allows a current to flow via the associated pair of sliding contact pieces (14, 15 and 16, 17 respectively) and the corresponding sliding contact line (12, 13), which current burns through any existing insulating oxide skins and the like in order to produce a low-resistance connection between at least one of the sliding contact pieces (14...17) and the sliding contact line (12, 13). The two voltage sources (21, 26) are decoupled from one another with respect to the frequency to be transmitted. <IMAGE>

Description

The invention relates to a circuit arrangement for data transmission in the baseband or by means of a modulated carrier via conductor lines, according to the preamble of claim 1.

In rail-bound vehicles, such as those used in the area of shelf warehouses or in production, in order to transport goods or workpieces back and forth between different locations, there is an increasing need to transmit information to the vehicles. This information comes from a central computer system and is used to control the running of the vehicles. In particular, this makes it possible to simultaneously run several vehicles simultaneously and stop them at the correct points without operating block stations.

To control the vehicles, additional contact lines are laid in the travel rail, which serve for the transmission of information and on which slide pieces fitted in the vehicles slide, which are electrically connected to corresponding electronic circuits of the individual vehicles. The greater the number of vehicles moving at the same time, the greater the amount of information that must be exchanged between the central unit and the individual vehicles. It is therefore necessary to move to ever higher data rates, which in turn increases the data frequency and thus makes the data transmission more sensitive to electrical interference. A major cause of electrical interference that leads to transmission errors is the contact resistance that occurs between the contact strips and the contact lines. The conductor rails are unprotected and are therefore exposed to the atmosphere in the storage room or the factory building. This in turn results in contamination of the conductor rail surface with dust or other precipitation, as well as corrosion of the conductor rail surface due to aggressive components in the atmosphere. The air oxygen alone is sufficient to quickly produce an oxide skin on the surface of the conductor lines, which is usually a very good insulator and hinders the transmission of current from the conductor line to the contact strip.

The contact resistance that occurs between the contact strip and the contact line as a result of contamination and oxidation has a non-linear characteristic and is the more disturbing the lower the signal voltage that is to be transmitted via the contact lines and contact strips. As a result of the nonlinear resistance characteristic of the oxide layer on the conductor lines, there is a lower voltage below which the oxide layer cannot be removed by the flowing electrical current. At higher voltages, however, there is a voltage flashover through the oxide layer, which then disappears locally at this point, whereby the contact resistance at this point is reduced from a very high value in the range of megohms to values of mOhm.

The voltages that occur in modern digital circuits are below the voltage that allows the oxide layer of conductor rails made of base metal to break through.

For this reason, attempts have already been made in practice to transmit the data with impressed current at high voltage. This requires a corresponding power output stage on the data transmitter side, which is capable, for example, of supplying an open circuit voltage of 100 V and a short circuit current of 500 mA. The effort that must be driven in the output stage of such a circuit is enormous, apart from the fact that the voltage at the output of such a transmitter is already life-threatening and requires special safety precautions.

Data transmission systems are also known in practice, in which the information is supplied via a network line, similar to the in-house telephones, whose carrier frequency systems communicate with one another via the mains sockets. Although this has the advantage that the high voltage of approx. 220 V eliminates the oxide layer between the conductor line and the contact piece, on the other hand, precautions must be taken so that the signal is limited to the desired system and does not stray. In addition, the effort on the transmitter side is also not insignificant.

Proceeding from this, it is an object of the invention to provide data transmission via conductor lines which does not require any great expenditure on the device side and in which neither the transmitter nor the receiver has to be designed for large signal voltages.

This object is achieved by the circuit arrangement with the features of claim 1.

By using a further contact strip per contact line in connection with the voltage source, a current can be generated via the contact line and the two contact pieces, which current eliminates the oxide skin between the contact pieces and the contact line. Since this is otherwise galvanically isolated for the conductor lines, the data signal can be fed in and taken off with low electrical power and at low voltage. It is only necessary with regard to the frequency of the data signal, the voltage sources for the individual conductor lines to largely decouple gene from each other, which results overall in a very simple circuit arrangement.

The decoupling is very simple if the frequency of the data signal is significantly higher than the frequency of the output voltage of each voltage source, because then no steep-sided filters are required for the separation, but simple capacitors and inductors are sufficient.

The voltage source itself does not need to have a high output either, because it is sufficient if it outputs a current of a few mA in the event of a short circuit and a voltage of approximately 100 V in the event of an open circuit. Such a tension is otherwise not dangerous for humans, since it collapses at the slightest load, but on the other hand is sufficient to penetrate the oxide skin.

The high internal resistance on the one hand and the decoupling on the other hand can be achieved in a very simple manner by using inductors which are located in the circuit between the voltage source and the contact strips. On the other hand, the use of inductors reduces the power losses because essentially only reactive power is converted in the inductor.

In the simplest case, the voltage source consists of a secondary winding of a transformer, which is otherwise galvanically isolated from all other windings.

The data circuit is advantageously connected to the contact strips via a filter circuit, the filter circuit suppressing the frequency of the output voltage of the voltage source, i.e. prevents it from being forwarded to the input or output of the data circuit.

In order to simplify the filter circuit, the data signal itself is advantageously a DC-free signal, namely either a DC-free baseband signal or a data signal modulated on a carrier, which is anyway DC-free due to the modulation.

In order to prevent the propagation of line waves on the conductor lines at higher frequencies as far as possible, it is expedient if two conductor lines are terminated in each case via an ohmic resistor which has the magnitude of the wave resistance of the two conductor lines.

• Fig. 1 einen Ausschnitt aus einer Einschienen-Hängebahn-Anlage mit einem auf der Schiene laufenden Fahrzeug,
• Fig. 2 das teilweise schematisierte Schaltbild der Schaltungsanordnung zur Datenübertragung,
• Fig. 3 einen Ausschnitt des Schaltbildes aus Fig. 2,
• Fig. 4 die Stromspannungskennlinie der Spannungsquellen nach den Fig. 2 und 3, und
• Fig. 5 ein gleichstromfreies Binärsignal zur Signalübertragung bei der Schaltungsanordnung nach den Fig. 2 und 3.

In the drawing, an embodiment of the object of the invention is shown. Show it:

• 1 shows a section of a monorail overhead conveyor system with a vehicle running on the rail,
• 2 shows the partially schematic circuit diagram of the circuit arrangement for data transmission,
• 3 shows a detail of the circuit diagram from FIG. 2,
• 4 shows the current-voltage characteristic of the voltage sources according to FIGS. 2 and 3, and
• 5 shows a direct current-free binary signal for signal transmission in the circuit arrangement according to FIGS. 2 and 3.

In Fig. 1 a section 1 of a monorail overhead conveyor is illustrated in the detail, along which a vehicle 2 can travel back and forth. The running rail 1 has the shape of an I-profile and consists of an upper and a lower flange 3, 4, both of which are connected to one another by a vertical web. The vehicle 2 runs, as can be seen in the figure, with its wheels 6 on the upper side of the lower flange 4. In order to raise and lower a load 7 transported by the vehicle, the vehicle is provided in the known manner with a lifting device 8, on the traction means 9 of which the load 7 is attached.

The vehicle 2 is moved by a drive motor (not shown in the drawing) which drives at least one of the wheels 6 so that the vehicle 2 can move along the rail 1. For the transmission of current for the drive motor, conductor lines are provided on the web 5 on the side facing away from the viewer, which conduct current constantly and bring the current to the vehicle 2.

In order to set the drive motor to a corresponding standstill or in motion so that the vehicle 2 stops at the correct point or continues to run, a control circuit 11 is provided which also starts or stops the lifting device 8 at the same time. The data signals for the control circuit 11 are transmitted to the vehicle 2 via two conductor lines 12 and 13 which are mounted on the web 5.

The vehicle 2 picks up the data signals present on the conductor lines 12, 13 via contact strips 14... 17, which are shown in FIG. 2 and are movably mounted, for example, in a receptacle 18 of the vehicle 2.

As can be seen in FIG. 2, the vehicle 2 has two contact strips 14 and 15 or 16 and 17 per contact line 12, 13. Between the contact pieces 14 and 15 and the contact pieces 16 and 17, a voltage is applied in each case.

The contact piece 14 is connected via a line 19 to one end of a secondary winding 21, the other end of which is connected to the contact piece 15 via an inductor 22 in the form of a choke and via a line 23 leading away therefrom. The contact strip 16 is connected to another via a line 24 and a throttle 25 Secondary winding 26 connected, the other end of which lies on the contact piece 17 via a line 27. The two secondary windings 21 and 26 are part of a transformer 28, the primary winding 29 of which is supplied with a mains voltage, which is brought in via the travel rail 1 in order to supply the drive motor or the hoist 8 with current when required. The two secondary windings 21 and 26 , which are galvanically isolated from each other and from the primary winding 29, form voltage sources, one of which is connected to a pair of contact strips 14, 15 and 16, 17, respectively.

The schematically indicated control circuit 11 also contains a schematic data circuit 31 with a transmission device 32 in order to process the data signals received via the lines 12, 13 and to forward them to other modules of the control circuit 11 via outputs 33. An isolating transformer 35 with two electrically isolated windings 36 and 37 is connected to an input 34 of the transmission circuit, the winding 37 being connected directly to the transmission circuit 32. The other winding 36 is connected to the contact strips 14 .. 17. One end of winding 36 is AC connected to lines 19 and 23 via two capacitors 38, 39, i.e. the two contact strips 14 and 15, which both run on the contact line 12. The other end of the winding 36, however, is also connected to the other two contact strips 16 and 17 in terms of alternating current via two capacitors 41 and 42. These two contact strips run, as the figure shows, on the contact line 13, i.e. the data circuit 31 receives, as an input signal, the signal which is present between the conductor lines 12 and 13.

Since the rails 1 can reach considerable length, it is expedient if the two conductor lines 12 and 13 are terminated at both ends by ohmic resistors 43, the impedance of which corresponds to the characteristic impedance of the two conductor lines 12, 13 in order to excite standing waves to prevent on the conductor lines 12, 13.

The data signals are fed in at one end of the two conductor lines 12, 13 from a data transmitter 44, which on the output side also contains an isolating transformer 45, the secondary winding 46 of which is connected to the two conductor lines 12, 13.

Because not only one, but several vehicles 2 are running on the running rail 1, the part of a second vehicle 2 ′ that is essential for data transmission is also shown in FIG. 2. This electrical part of the vehicle 2 'is constructed in the same way as for the vehicle 2.

To explain the mode of operation of the circuit arrangement described so far, reference is also made to FIGS. 3 and 4. FIG. 3 is simplified and shows an extract from FIG. 2, namely the conductor line 13 with the two contact pieces 16 and 17 running thereon and the transformer 28, including the secondary winding 26 connected to the two contact pieces 16 and 17.

As soon as a driving voltage is applied to the corresponding conductor lines of the running rail 1 in order to supply the vehicles 2 with the necessary voltages, the transformer 28 on its primary winding 29 is also supplied with the driving voltage, for example. 220 V AC voltage, applied. The voltage is transformed down in the transformer 28, for example to an open circuit voltage of approximately 100 V on each of the two secondary windings 26 and 21. The voltage of the secondary winding 26 is across the inductor 25 on the two contact strips 16 and 17, which are on the same contact line , namely the conductor line 13, run. Characterized a current is generated via the conductor line 13 between the contact strips 16 and 17, which is only a few mA, because from the point of view of the two contact pieces 16 and 17, the internal resistance of the voltage source feeding them from the secondary winding 26 and the choke 25 has a relatively high internal resistance Has.

The relationship between the no-load output voltage, which can be measured on the two contact strips 16 and 17 when they are lifted from the contact line 13, and the short-circuit current which flows when the two contact strips 16 and 17 are connected to one another with virtually no resistance, is shown in FIG. 4 shown. The relationship is essentially linear if the internal resistance has an active component that is approximately equal to the reactive component. If the reactive component predominates, the curve approximates an elliptical arc as shown in broken lines in FIG. In any case, the lower the resistance between the contact strips 16 and 17, the smaller the tension between the two contact strips 16 and 17. Under certain circumstances, it may also be expedient to install a non-linear element in one of the lines 24, 27 or 19, 23 in order to achieve a faster voltage drop.

The comparatively high open circuit voltage now ensures that there is always good galvanic contact between the contact strip 16 and the contact line 13 on the one hand and the contact piece 17 and the contact line 13 on the other hand. If an oxide skin has formed on the conductor line 13, onto which the contact strips 16 and 17 run when the vehicle 2 is moving, As can be seen from the relationship in FIG. 4, the voltage between the two contact strips 16 and 17 automatically increases in the direction of the open circuit voltage and thereby achieves values which are large enough to break through the oxide skin between the contact line 13 and the contact strips 16, 17 , so that the contact resistance at the contact point between the conductor line 13 and the relevant contact piece 16 or 17 practically disappears. The high internal resistance, on the other hand, prevents intolerably large values in the event of a "short circuit", ie when the oxide skin and thus the contact resistance between the conductor line 13 and the two contact pieces 16, 17 has disappeared. As soon as the contact resistance has disappeared, there is no need for any current to flow at all.

The use of the choke 25 in connection with, for example, a transformer 28 produced with high leakage inductance allows the large internal resistance to be generated, which on top of that has practically only a reactive component, so that almost no active power is converted.

The relationships explained in connection with FIG. 3 for the contact strips 16 and 17 also apply to the two contact pieces 14 and 15 on the conductor line 12. These two contact pieces 14 and 15 are provided with their own voltage source in the form of the secondary winding 21 and the choke 22 Voltage or current is applied so that the oxide skin between the contact strips 14 and 15 and the contact line 12, which increases the contact resistance, is constantly removed.

Due to the high internal resistance from the point of view of the contact strips 14, 15 or 16, 17, there is practically no AC coupling between the contact strips 14 and 16, i.e. the existing alternating current and direct current separation between the conductor lines 12 and 13 is not impaired by the transformer 28, which feeds the contact strips 14... 17. The contact strips 14 and 15 on the one hand and the contact pieces 16, 17 on the other hand are practically separated from one another in terms of direct and alternating current. No current therefore flows from the contact piece 14 to the contact piece 16 or the contact piece 17 as a result of the voltage supply to the contact pieces 14... 17 through the transformer 28.

From the point of view of the transformer 28, the contact strips 16 and 17 or the contact pieces 14 and 15 are in series, the connection being made via the contact line 13 or 12. From the point of view of the data circuit 31, on the other hand, the contact strips 14... 17 running on one and the same contact line 13 or 12 are connected in parallel, since the contact pieces 36 running on a contact line have one end of the isolating transformer 36 via the capacitors 38, 39 and the other Conductor line, for example 12, running contact strips 14, 15 are connected to the other end of the isolating transformer 36 via the capacitors 41 and 42. With regard to the data signal to be transmitted, the grinding pieces 14 and 15 on the one hand and the grinding pieces 16 and 17 on the other hand are connected in parallel, i.e. the data circuit 31 is connected to a pair of contact strips 14, 15 and 16, 17, respectively. The data circuit 31 thus receives as a signal the voltage that is present between the two conductor lines 12, 13.

If it is assumed that the data signals are only transmitted to the vehicle 2, the data circuit 31 consists of a receiving unit which receives data signals which are fed in at the end of the conductor line 12, 13 via the data transmission device 44, as a voltage signal between the two Contact lines 12, 13. Since the internal resistance, measured between the contact pieces 14 and 16, for example, is high - it lies in the several kOhm range - the data transmission device 44 is practically not loaded at its output and can transmit the data signals with low power. The data circuit 31 is also not affected at its input 34 by the circuit fed by the transformer 28, in particular the 50 Hz signal does not lead to an input signal at the data circuit 31 or at the data transmission device 44 due to the use of the mains voltage, since this 50 Hz voltages on the contact strips 14 .. 17 are symmetrical and potential-free with respect to the data circuit 31 or the data transmission device 44.

In the new circuit arrangement shown, the voltage present between each pair of contact strips 14, 15 or 16, 17 ensures that the contact resistance between each pair of contact pieces 14, 15 or 16, 17 and the associated contact line 12, 13 is eliminated. so that the data signals can also be transmitted with very low voltages, for example 12 V or less. Without the use of the additional voltage generated by transformer 28, the voltage of the data signals would be too low to be able to place an oxide skin between the conductor lines 12, 13 and the contact pieces 14. 17 running on them to eliminate. In this way, however, the data signals always hit a low-resistance contact point, which is eliminated with the aid of the high voltage supplied by the transformer 28.

It is understood that the circuit arrangement shown is not limited to establishing connections in simplex mode, in which the data only run towards the vehicle 2. It is also possible to use a half duplex or a To set up full duplex connection, in which case the data circuit 31 can also act as a transmitter at the same time, in order to in turn provide information to a central controller (not shown).

The new circuit arrangement can work both in the baseband when a DC-free binary signal is transmitted, or it can work with the aid of a carrier frequency in which the information is modulated onto an AC carrier. An example of an AC-free binary signal is shown in FIG. 5. The upper representation of FIG. 5 shows an exemplary binary signal to be transmitted, which oscillates back and forth between two voltage levels, depending on which of the two digital values 0 or 1 is to be transmitted. In the data circuit 31 or the transmitter 44, this signal is converted into the signal shown in FIG. 5 below, in such a way that the binary values 0 and 1 are formed by the signal edges and no longer by the signal levels. For example, a change in the voltage level from a positive to the negative value of equal magnitude means a binary 0, while the increase from the corresponding negative voltage value to the positive voltage value of equal magnitude is interpreted as binary 1. It is thereby achieved that the mean voltage value is practically always 0 and can be easily transmitted via the capacitors 38 .. 42.

Since the two secondary windings 21 and 26 are not only coupled magnetically but also capacitively to one another, it can be advantageous if the inductor 22 and 25 shown in each circuit is divided and one part in the line 23 and the other part in the Line 19 or a part in line 27 and the other in line 24. In this way, the decoupling of the two secondary windings 21 and 26 is improved from the point of view of the data signal, because capacitive coupling influences have less effect.

Claims (12)

1. Circuit arrangement for data transmission in the baseband or by means of a modulated carrier, with at least two contact lines (12, 13), at least one contact piece (14 .. 17) per contact line (12, 13), and one to the contact pieces (14 .. 17) Connected data circuit (31) either to receive electrical data signals transmitted via the conductor lines (12, 13), or to transmit data signals to be transmitted via the conductor lines (12, 13), or to record both data signals transmitted via the conductor lines (12, 13) , as well as to transmit data to be transmitted via the conductor lines (12, 13), characterized in that a second contact piece (14 .. 17) is present for each contact line (12, 13), which is separate from the associated first contact piece (14 .. 17th ) is kept isolated and forms a pair (14,15; 16,17) together with the slider running on the same conductor line (12,13), that each pair of sliders (14,15; 16,17) has its own sp voltage source (21, 26) is provided which outputs an output voltage and which generates a current which is passed through the two contact strips of each pair (14, 15; 16, 17) and a respective section of the conductor line (12, 13) which lies between the two contact pieces of each pair (14, 15; 16, 17), and that the voltage sources (21, 26) from one another at least with regard to the frequency of the electrical data signal to be transmitted are at least approximately decoupled. 2. Circuit arrangement according to claim 1, characterized in that the frequency of the data signal is above the frequency of the output voltage of each voltage source (21, 26). 3. Circuit arrangement according to claim 1, characterized in that the voltage source (21, 26) has a high internal resistance at least at the frequency of the output voltage of the voltage source (21, 26), the internal resistance having an inductive reactive component and / or a linear or non-linear active component having. 4. Circuit arrangement according to claim 1, characterized in that the voltage source (21, 26) has a high internal resistance at the frequency of the data signal. 5. A circuit arrangement according to claim 1, characterized in that an inductor (22, 25) is contained in each circuit leading over a pair of the contact strips (14, 15; 16, 17). 6. Circuit arrangement according to claim 1, characterized in that the output voltage of the voltage source (21, 26) has a mains frequency. 7. Circuit arrangement according to claim 1, characterized. characterized in that the voltage sources are each formed by a galvanically isolated secondary winding (21, 26) of a transformer (28). 8. Circuit arrangement according to claim 1, characterized in that the data circuit (31) is connected via a filter circuit (38 .. 42) to the contact strips (14 .. 17), which suppresses the frequency of the output voltage. 9. Circuit arrangement according to claim 8, characterized in that the filter circuit of coupling capacitors (38 .. 42) is formed. 10. Circuit arrangement according to claim 1, characterized in that the data signal is a DC-free baseband signal. 11. Circuit arrangement according to claim 10, characterized in that the data signal is a digital signal. 12. Circuit arrangement according to claim 1, characterized in that in each case two conductor lines (12, 13) are terminated via an ohmic resistor (43) which has the magnitude of the characteristic impedance of the two conductor lines.

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