GB2115953A - Industrial truck comprising a travel drive and a steering drive - Google Patents

Abstract

An industrial truck comprising a travel drive and a steering drive and sensors for scanning a trail laid in the ground and for guiding the vehicle along that trail includes a microprocessor for delivering steering commands to the steering drive. At least two pairs of sensors consisting of coils are connected to a multiplexer. Only a single processing channel is provided between the multiplexer and the microprocessor and is connected to a data memory of the microprocessor.

Description

SPECIFICATION Industrial truck comprising a travel drive and a steering drive This invention relates to an industrial truck comprising a travel drive and a steering drive, sensors for scanning a trail laid in the ground and for guiding the vehicles along said trail, and a microprocessor for delivering steering commands to the steering drive.

Such a control involves a certain expenditure for each sensor array, which is usually axially spaced from the vehicle. A separate processing channel is required and may be arranged at the forward and rear ends of the vehicle. It is known to provide a plurality of channels and a computer. But this involves also a substantial expenditure, particularly if filters are used in conjunction with the alternating fields established by a guide wire, which filters may be variable if desired, and serve to select different results. A selection of destination addresses may be provided for.

It is also known to operate different guide wires at different frequencies used for a travel control.

When a vehicle is guided along a guide wire it is difficult to determine the direction of any lateral deviation. For this purpose it is known from Laidopen German Application 2328863 to effect a phase comparison in conjunction with a system of crossing coils. In case of an in-phase rectification, a phase opposition will remain on one side of the guide wire so that a direction can be detected. In accordance with Laid-open German Application 28 10 664, a time difference is used to represent a phase displacement so that lateral deviations can be detected. Laid-open German Application 19 02 037 discloses the use of lateral sensors, which generate signals from which the vertical and horizontal field strengths can be ascertained so that different signs can be detected.

Laid-open German Application 1902037 discloses a special control effected in response to the crossovers for a distinction of the phase angle by means of a logic circuit. Special attention is directed to Laidopen German Application 27 52 027, which teaches to utilize an interval of time in that the pulse duration is counted by a microprocessor. This practice involves certain disadvantages in connection with sign determination.

Laid-open German Application 29 46 559 discloses also a phase shift for defining an interval of time, which is used to control an arithmetic stage so that the sign of a lateral deviation is detected. Owing to the comparison which is effected, a plurality of channels are always used and each of said channels is associated with a pair of sensors.

It is an object of the invention to provide an industrial truck which is of the kind described first hereinbefore and is so designed that the control can be effected by simpler and less expensive means and with a higher reliability.

This object is accomplished according to the invention in that at least two pairs of sensors are connected to a multiplexer and a processing channel is provided between the multiplexer and the microprocessor and is connected to a data memory of the microprocessor. This affords a substantial advantage and requires the vehicle to be provided with only one processing channel, which is used in alternation and may comprise known, reliable components. If a sensor array comprising two crossing coils is used, the processing channel has two input branches. The provision of these two input branches affords the advantage that each signal can be subjected to a frequency selection and to a demodulation individually before a division is effected to ascertain the distance.The provision of two input branches involves a branching at the beginning whereas the channel has only one terminal at the other end. The main aspect resides in the provision of a single processing channel for a plurality of pairs of sensors.

In a particularly preferred arrangement, a filter for one frequency is provided in the processing channel or in each input branch and said filter is adapted to be tuned to a frequency which is determined by a position address. In the control of an industrial truck it is known to use a frequency selection, either to cause a response of a specific vehicle or to define a specific path. The invention contemplates also the use of such a control system but this is primarily provided on the vehicle because the control is effected in dependence on the sensors, which are mounted on the vehicle. The adjustable filters for different frequencies may be used for a selection in dependence on specific destination addresses.A frequency selection register for the at least one filter may be associated with the microprocessor and a control register for controlling the multiplexer may be connected to the frequency control register in an arrangement in which a digital-to-analog converter is provided at the output end of the processing channel and is operable in dependence on the frequency selection and frequency control effected by the multiplexer. This results in a compact design.

In a particularly preferred arrangement, the control register is provided with a command-generating circuit for enabling the units which precede the microprocessor and comprise the digital-to-analog converter, a status register, a frequency selection register and the control register, and the control register is adapted to be shifted in dependence on frequency. This design permits a simple circuit, which affords a higher safety.

In a particularly preferred arrangement, the units or registers of the control circuit which precede the microprocessor are periodically activated. Terminals for receiving signals indicating the selected measuring range, the presence of the required field strength of the wire trail, and the direction of the deviation, are suitably associated with the status register.

The sign determination and the signal magnitudes can be improved in that a D flip-flop is used as a latch for determining the sign of a signal and generates a sign signal during a rising edge of the signal the sign of which is to be determined. In that connection an important feature resides in that a special clock input is detected at each rising edge. In conjunction therewith, two zero voltage comparators are suitably provided, the outputs of which are delivered as logic signals to an EXCLUSIVE OR gate, the output of which is delivered to the flip-flop as well as a signal which is formed in that an input signal is passed through an integrator and a zero voltage comparator and after the zero voltage comparator is at phase quadrature to the input and is then delivered to the corresponding input terminal of the D flip-flop.

The invention will be described hereinafter with reference to illustrative embodiments, which are shown in the drawings, in which Figure 1 is a block circuit diagram of an embodiment of the invention, Figure 2 a circuit diagram which is coordinated with the block circuit diagram and illustrates the intended embodiment, inclusive of the control system, Figure 3 is a block circuit diagram of a processing circuit which is specially designed for a correct sign determination, and Figures 4 and 5 are fu nctional representations of parameter signals used in the explanation of the invention.

It is assumed that a vehicle comprises at least two coil arrays 1,2 or a larger number of coil arrays. One of said arrays is designated 3. Each oil array receives two signals, which are related to directionsx and y so that a coordinate system can be imagined in which the x coordinates represent the lateral distance measured in a horizontal plane of reference and the ycoordinates represent the distance measured in the direction that is normal to the horizontal plane of reference, then it is apparent that each of the coil arrays 1 to 3 generates voltages Uvi, Uxl Uyn, Uxn so that two voltages are delivered, which are derived in known manner from the constantfrequency alternating field which surrounds the guide wire.The processing of such voltge signals in accordance with angle functions and a dividing circuit for generating a distance signal are known in the art.

In the embodiment described, the outputs 4 to 6 of the coil arrays 1 to 3 are connected to a multiplexer circuit 7, which is enabled by a separate control channel 8 and delivers output signals to only one processing channel 9 with an interchange of the pairs of signals. The processing channel 9 has two input branches 10, 11, to which signals and x signals are delivered, respectively. Each of the input branches for Uy and Ux includes a filter 12 or 13, which has a variable pass frequency. These filters can be controlled by a frequency selector 14, which is enabled in response to an address.

The input branches 10, 11 also include demodulators 15, 16, the outputs of which are delivered to an arithmetic circuit 17. The latter effects a division of the voltages Uy and Ux and delivers its output via a lead 18to an analog-to-digital converter 19. The latter delivers digital data representing the distance from the trail via a channel 20 to the data bus 21 of a microcomputer.

As is apparent from Figure 1, signals are delivered from the lead 18, which succeeds the input lead 11 and the demodulator 16 via links 22,23 to a status detector unit 24, which from its output terminal 25 delivers measuring range information to a status register 26, which via an output channel 27 delivers status data to the data bus 21 of the microcomputer.

A special circuit for this purpose will be explained with reference to Figure 3, from which the cooperation effected in this part of the circuit arrangement shown in Figure 1 is apparent.

The data bus feeds via a channel 28 also the frequency selection register 14 and via a channel 52 a so-called control register 53, which operates the multiplexer switch 7 via the control channel 8.

Figure 1 shows enabling or control lids 29, which come from an enabling coding circuit 30, which is fed via a channel 31 from the address bus 32 of the microcomputer.

The frequency signals derived from the voltage signals which are associated with the parameters y and x are delivered via functional links 34, 35 to the phase comparator 33, which delivers a sign signal via the lead 36 to the status register 26. This arrangement affords numerous advantages, which ensure a reliable operation particularly owing to the use of the status register. Sign determination is an important feature and is effected in dependence on the phase angle detected in connection with the deviation from the guide wire to the right or left.

Figure 2 is related to Figure 1 and shows the three coil arrays 1 to 3 of the sensors, which are connected to the processing circuit 37, which contains substantally the components shown in Figure 1 and as a whole precedes the so-called data bus 21 and the so-called control leads 29 ofthe microcomputer. In Figure 2, the circuit arrangement shown in more detail in Figure 1 is supplemented in that the delivery by the control signals is shown too, and is simplified with respect to Figure 1 as regards details.

Figure 2 shows entirely the processing circuit 37 and a unit 69, which is connected to the steering drive unit 40.

The processing circuit 37 comprises an enabling coding circuit 70, which corresponds to the unit 30 in Figure 1 and is connected by function lead 71 to the unit 72, which comprises the frequency selector 14, the analog-to-digital converter 19, the status register 26 and the status register 53, which are shown in Figure 1. The channels 31 and 38 are the same as those shown in Figure 1.

The unit 69 comprises an address decoder 73, a data register74with a digital memory for the desired steering angle and a digital-to-analog converter 75, which are shown in a simplified arrangement and are enabled via the channels 31 and 42. As a result, the steering control means 39 comprising in known manner a reversible motor may be used to control the steering of the vehicle by means of the steering drive 40. The digital-to-analog converter 75 delivers via a lead 41 a set point signal. Figure 2 shows the use of the address bus 32 and the connection to and dependence on the microprocessor 43, a read-write memory 44 and a memory circuit 45, which contain fixed data, such as constants for the control, and the program. These units are connected by functional links 46 to 48 to the data bus 21 and by functional links 49 to 51 to and from the address bus 32.

The circuit arrangement described hereinbefore is particularly desirable and permits of a variable selection for the performance of numerous opera tions and with a selection of various paths of travel and various vehicles and ensures a high reliability in operation.

Special advantages are afforded by the circuit arrangement which is shown in Figure 3 and the operation of which will be explained also with reference to Figures 4 and 5.

Figure 3 shows the two input leads 10 and 11 with reference to Figure 4 whereas the variable filters for selecting special responsive units have not been shown. The special circuit shown in Figure 3 is an advantageous embodiment of the phase comparator 33 shown in Figure 1. Forthis reason the functional links 34,35 and the link 36 are indicated in brackets at the proper positions so that the association is more easily apparent.

In accordance with Figure 3, the input leads 10, 11 lead to zero voltage comparators 54, 55, which deliver outputs Q1 and Q2 as shown in Figures 4 and 5 via leads 56, 57 to an EXCLUSIVE OR gate 58.

In such circuits, phase shifts may occur, particularly owing to component tolerances in the filter stage shown in Figure 1,and may adversely affect the generation of the output Q3 of the gate 58. For this reason a branch lead 59 extends from one of the input leads 10, 11 in Figure 3, particularly from the input lead 11 carrying the input Ux. In accordance with Figure 3 the lead 59 is connected to lead 11 before the zero voltage comparator 55, which effectively corresponds to the demodulator 16 in Figure 1.

Also in accordance with Figure 3, a phase shift is effected by an integrator 60, which comprises the resistor and capacitor shown in the drawing.

The output of the EXCLUSIVE OR gate 58 is on a first level when theinputs Qs and Q2 are different and is on a second level when the inputs are equal, either on a high or a low level. To permit a distinction in this respect, a branch circuit 59 is provided, which contains an integrator 60 and a zero voltage comparator 61. In the integrator 60, the signal Ux is shifted 90" in phase by means of the capacitor and the resistor which are shown. In the zero voltage comparator 61, the phase-shifted signal is transformed to a signal Q4, which has been shifted 90 in phase and is delivered from the output terminal of the zero voltage comparator 61 via lead 62 to the input of a D flip-flop 63. The flip-flop 63 receives also the signal Q3 from the OR gate 58 via a functional link.As a result, the flip-flop 63, which corresponds to the junction 36 in Figure 1, delivers on its output lead 64 a definite sign signal V2, which is also shown in Figures 4 and 5 for various combinations of Ux and Uy.

It is apparent that a definite sign signal is generated by the circuit arrangement shown in Figure 3.

The inputs to the status register are such that the detection in the unit 24 is taken into account too.

To facilitate the understanding of the circuit arrangement shown in Figure 3, the abovementioned signals Qr to Q4 and V2 plotted each in a coordinate system 65,66 in which voltage is plotted along the axis of ordinates 67 and time is plotted along the axis of abscissae 68. The voltages Ux and Uy are sinusoidal. The circuit combinations shown in Figure 3 will then result in the generation of the signals Q1 to Q4 and V2, which are shown underneath in alignment with the coordinate system. It is apparent that the output of the D flip-flop 63 assumes the state Q3 only during the rising edge of the output of 58 (Figure 5).

When the arrangement which has been described is used for multiplexer operation at a normal speed of travel of 3 metres per second, the transient time of the change-over to another sensor amounts only to 1 millisecond and can be neglected because the vehicle travels only 3 mm in that time. If during such a control operation the vehicle has an inclination of up to 20 from a predetermined trail defined for instance, by a guide wire, then the deviation will be of an order of 0.1 mm so that the signals from the coil arrays can be received and processed in succession with virtually the same results as with a simultaneous measurement, which is advantageously omitted according to the invention.

Claims (2)

1. An industrial truck comprising a travel drive and a sterring drive, sensors for scanning a trail laid in the ground and for guiding the vehicles along said trail, and a microprocessor for delivering steering commands to the steering drive, characterized in that the at least two pairs of sensors consisting of coils are connected to a multiplexer and a processing channel is provided between the multiplexer and the microprocessor and is connected to a data memory of the microprocessor.

2. A vehicle according to claim 1, characterized by having at least two pairs of the said sensors.

2. A vehicle according to claim 1, comprising a sensor array comprising two crossing coils, characterized in that the processing channel has two input terminals.

3. A vehicle according to claims 1 and 2, characterized in that a filter for one frequency is provided in the processing channel and said filter is adapted to be tuned to a frequency which is determined by a position address.

4. A vehicle according to claim 3, characterized in that a frequency selection register for the at least one filter is associated with the microprocessor and a control register for controlling the multiplexer is connected to the frequency selection register in an arrangement in which a digital-to-analog converter is provided at the output end of the processing channel and is operable in dependence on the frequency selection and frequency control effected by the multiplexer.

5. A vehicle according to claim 4, characterized in that the control register is provided with a command-generating circuit for enabling the units which precede the microprocessor and comprise the digital-to-analog converter, a status register, a frequency selection register and the control register, and the control register is adapted to be shifted in dependence on frequency.

6. A vehicle according to any of claims 1 to 5, characterized in that the control circuit is adapted to periodically enable the units or registers which precede the microprocessor.

7. A vehicle according to claim 6, characterized in that terminals for receiving signals indicating the selected measuring range, the presennce of the required field strength of the wire trail, and the direction of the deviation, are associated with the status register.

8. A vehicle according to any of claims 1 to 7, characterized in that a latch consisting of a flip-flop is used to determine the sign of a signal by a sign signal generated during a rising edge of the signal the sign of which is to be determined.

9. Vehicle according to claim 8, characterized in that two zero voltage comparators are provided, the outputs of which are delivered as logic signals to an EXCLUSIVE OR gate, the output of which is delivered to the flip-flop as well as a signal which is formed in that an input signal is passed through an integrator and a zero voltage comparator and after the zero voltage comparator is at phase quadrature to the input and is then delivered to the flip-flop.

10. A vehicle according to claim 1, substantially as described hereinbefore with reference to the accompanying drawings.

New claims or amendments to claims filed on 7 June 1983 Superseded claims 1 New or amended claims:

1. An industrial truck having a travel drive, a steering drive, at least two sensors for scanning a track laid in the ground in order to guide the truck along the track, a processing channel arrangement, a microprocessor, and a multiplexor arrangement, characterized in that the multiplexor arrangement is connected to the sensors, which comprise coils, and that there is provided between the multiplexor arrangement and the microprocessor the processing channel arrangement which consists of only one processing channel which is connected to a data memory of the microprocessor.