Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
  • G05D1/02—Control of position or course in two dimensions
  • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
  • G05D1/0259—Control of position or course in two dimensions specially adapted to land vehicles using magnetic or electromagnetic means
  • G05D1/0265—Control of position or course in two dimensions specially adapted to land vehicles using magnetic or electromagnetic means using buried wires

Definitions

• the present invention relates to a method and a device for determining the orientation of a vehicle according to the preamble to patent claims 1 and 15 respectively.
• Unmanned vehicle are used in many different types of manufacturing plants and warehouses. They are for example used to move automobile chassis to different welding and assembly stations and for retrieving objects from a warehouse in order to fill the orders of a customer quickly. Loop-guided vehicles are especially common in such contexts.
• the antenna arrangement consists of a single antenna, and guidance and drive circuits for the motors of the vehicle strive to keep the antenna as close lXE to the guidance loop as possible. Nearness is in this case determined by the sensed strength of the magnetic field around the guidance conductor.
• Another known antenna arrangement utilizes two small coils 15 which are mounted on the vehicle in such a way, that they are mainly parallel to each other and perpendicular to the floor, and thereby also perpendicular to the guidance loops.
• the guidance and driving circuits of the vehicle thereby try to keep the coils on either side of the 20 guidance loop. This is for example done by comparing the strength of the current which is induced in each coil.
• 35 directions, and their driving motors and transmissions are arranged for direct driving in both directions, that is, without the vehicle needing to rotate 180° when switching. What constitutes the forward direction and the reverse direction is determined for each loop installation. The choice can usually be made arbitrarily since the vehicles are as a role electrically symmetrical.
• the electrical symmetry of the vehicle leads to significant difficulty, which is best explained by means of an example. Assume for example that the vehicle is at rest and that it receives a start signal via the guidance loop. Assume further that this start signal also contains information to the effect that the vehicle is to move "forwards" or “backwards”. The problem is then apparent: since the vehicle is electrically symmetrical, this signal does not provide unambiguous information about which driving direction is. forward or backwards.
• the object of the present invention is therefore to eliminate these problems.
• the stated object is achieved by means of a method and a device whereby directional information is included in a single guidance signal, this signal being sensed and, in an unambiguous manner, decoded by a detector provided for accomplishing the method, which detector is also able to serve as or be included in an existing antenna arrangement in a loop-guided vehicle.
• Fig. 1 is a block diagram of an arrangement according to the invention for determining the orientation of a vehicle in relation to a guidance loop?
• Fig. 2 illustrates the preferred shape of a relationship between certain signals which are generated in the arrangement according to Fig. 1;
• Fig. 3 illustrates the shape of the signals illustrated in Fig. 2 when the orientation of the vehicle is the opposite of its orientation in Fig. 1;
• Fig. 4 illustrates an alternative composition of two of the signals which are senses by the arrangement; and
• Figs. 5 and 6 illustrate yet another alternative composition of certain ones of the signals which are used by the arrangement when the orientation of the vehicle is reversed. Best mode of carrying out the invention:
• the arrangement includes a guidance loop L which includes at least one electrical conductor.
• the guidance loop L may be of a known type and may even be an already existing guidance loop in the plant, within which the loop-guided vehicles are to work.
• the guidance loop L is shown as a simple electrical loop but existing guidance loops may equally include branches and may follow an arbitrary path.
• a first signal generator SIG1 generates a first electrical guidance signal SI and a second signal generator SIG2 generates a second electrical guidance signal S2.
• the guidance signal SI and S2 are preferably sinusoidal, but are at least periodic.
• the frequency of the guidance signal S2 is preferably at least twice the frequency of the guidance signal SI.
• the signal generator SIG1 is connected with the signal generator SIG2 via a polarity detector POL. POL generates and issues to the second signal generator SIG2 a first electrical polarity signal when the first guidance signal SI is positive in relation to an electrical zero level, and a second electrical polarity signal when SI is negative in relation to the zero level.
• the guidance signals SI and S2 are added in a summing element SUM. If the signal generators SIG1 and SIG2, as well as the summing element SUM, are made in analog technology, this addition becomes equivalent to a superpositioning of S2 on SI.
• the output signal S c from the summing element SUM that is to say, the composite signal which consists of the result of the addition of SI and S2, is applied to an output stage AMP.
• AMP amplifies and carries out other processing of the composite signal S c which is necessary for adapting S c to the loop as a loop signal S L .
• S L is thus substantially identical to the composite guidance signal S c , apart from any necessary amplification.
• Such output stages are well known when using guidance loops and will therefore not be described in further detail.
• An antenna arrangement ANT for example, one of the above- mentioned known antenna arrangements, is mounted on the vehicle.
• an induced signal S j is created in the antenna arrangement, with the induced signal corresponding to the loop signal S L .
• the antenna arrangement ANT is electrically connected to an amplification and signal processing stage COND, which generates an electrical output signal S R with the same shape as that of the induced signal S j .
• S R constitutes a received guidance signal and it is thus obtained mainly by amplification of S, .
• the received guidance signal S R is applied to a first and a second filter FLT1 and FLT2.
• the filters FLT1 and FLT2 are preferably band-pass filters tuned respectively to the frequency of the first guidance signal SI and the frequency of the second guidance signal S2.
• the output signal from the first filter FLT1 is applied to a first threshold or trigger circuit TR1, which generates a first trigger signal Dl only when the output signal from FLT1 meets certain trigger conditions, which will be described below.
• the output signal from the second filter FLT2 is applied to the second threshold trigger circuit TR2, which generates a second trigger signal D2 in accordance with certain conditions which are described below.
• the output signals from the filters FLT1 and FLT2 constitute filtered guidance signals SI' and S2' respectively.
• the antenna arrangement is preferably of the type mentioned above having at least two coils which, when the vehicle follows the path correctly, are located on either side of the loop.
• the present invention does not relate to a guidance device which ensures that the vehicle moves along the loop path — this may be accomplished using known guidance arrangements — but rather a method and an arrangement for determining the orientation of the vehicle in relation to the loop. In the description which follows it will therefore be assumed that if it is intended for the vehicle to move along the loop path in such a way that one coil is always kept for example outside of the loop, the guidance system of the vehicle is provided to ensure this.
• the direction of a current, which is induced in a conductor, for example a coil or a simple straight conductor, by an adjacent primary current flow is dependent upon the orientation of the conductor relative to the primary current flow.
• a straight antenna is located parallel to a main conductor through which is flowing direct current.
• the antenna is connected to sensing circuitry, which senses voltage induced in the antenna. If the antenna is rotated 180° relative to the main conductor, the polarity of the voltage which is induced in the antenna will be perceived as reversed by the sensing circuitry. The antenna is thus electrically anti-symmetrical relative to the main conductor.
• the trigger signals Dl and D2 are applied as input signals to a directional decoder DEC, whose output signal is an orientation signal D .
• the first guidance signal SI consists of a sine wave with the frequency f t .
• the polarity detector POL generates and applies to the signal detector SIG2 a first and a second polarity signal when the guidance signal SI is positive and negative, respectively, relative to an electrical zero level.
• the second signal generator SIG2 is arranged in such a way, that the second guidance signal S2 is sinusoidal with a frequency f 2 , which is preferably at least two times higher than f 1 and with a lower amplitude, when the second signal generator receives the first polarity signal, and such that S2 is held at the zero level when the second signal generator receives the second polarity signal.
• the frequency and amplitudes of SI and S2 are chosen for each installation considering the band width and other electrical characteristics of the various electrical components, and especially of the loop.
• the polarity detector POL can instead be connected to a switch between the second signal generator SIG2 and the summing element SUM.
• SIG2 can generate the sinusoidal signal continuously while the switch allows the sine wave to pass to the summing element SUM only when the polarity detector is generating the first polarity signal.
• the composite guidance signal S c is thereafter processed in the final stage AMP and is transmitted to the loop in a conventional manner as the loop signal S L , which is picked up by the antenna arrangement ANT, is processed by COND and is filtered by FLT1 and FLT2, so that the received guidance signal S R is separated into SI' and S2' .
• the orientation of the vehicle relative to the loop is such that the received guidance signal S R is in phase with S L , so that SI and SI', as well as S2 and S2' , are also in phase with each other, except for possible negligible phase shift in the filters FLT1 and FLT2.
• the trigger circuit TR1 is arranged so that the first trigger signal Dl assumes a logically “high” value ("1") when SI 1 is positive, and assumes a logically “low” value ("0") when SI 1 is negative' .
• the second trigger circuit TR2 is arranged so that D2 assumes a logically high value ("1") when S2* exhibits a sensed frequency component f 2 , and a logically low value ("0") otherwise.
• the direction decoder DEC is in this example arranged so that the orientation signal D * is set to its logically high value ("1") when Dl is equal to D2 and to its logically low value ("0") when Dl and D2 are not equal.
• Fig. 4 shows an alternative shape for the second guidance signal S2.
• the second signal generator SIG2 is arranged to form S2 in such a way that it has one frequency when SI is positive, and a different frequency when SI is negative. This may for example be accomplished by including two subordinate signal generators in SIG2 — one for each frequency — whereby the polarity detector POL determines which of them is to be coupled with the summing element SUM.
• the filter FLT2 then includes a band-pass filter for each partial frequency of S2.
• the trigger circuit TR2 is arranged so that D2 assumes for example its logically high value when S2' exhibits the one frequency component, and its logically low value when S2 exhibits the other frequency component.
• S2 is always an "active" signal, i.e., the decision of the system need never be based on possibly false zero values of S2• , for example when a conductor is broken. Test experience has however shown that the risk of this is none the less so insignificant, that the signal shapes shown in Figs. 1 and 2 are fully sufficient.
• Fig. 5 illustrates yet another composition of SI and S2 which may be used according to the invention, where S2 is an uninterrupted sine signal with a constant frequency which is an even multiple of the frequency of SI.
• Sensing of the loop signal S L and filtering in FLT1 and FLT2 may be the same as for the signal composition shown in Fig. 2.
• the trigger circuits TR1 and TR2 are arranged so that Dl and D2 are set to their logically high values when SI* and S2* , respectively, are positive, and to their logically low values when SI 1 and S2' , respectively, are negative.
• Dl and D2 could just as well be “low” when SI 1 and S2 • , respectively, are positive, and "high” when they are negative.
• Other alterna ⁇ tives are also possible as long as there is a one-to-one relationship between the values of the trigger signals and the polarity of the filtered guidance signals.
• the direction decoder DEC determines the orientation of the vehicle along the loop by determining the change of state of D2 at common zero crossings for SI' and S2• , that is to say, by sensing whether SI 1 and S2' both change from being positive to being negative, or vice versa. This will be understood best by considering both Fig. 5 and Fig. 6.
• Fig. 6 shows SI' and S2' with reversed polarity compared to Fig. 5. As has been explained above Fig. 6 therefore shows the signals which would result upon a reversed orientation of the vehicle. As Fig. 5 shows, D2 always changes from 0 to 1 at the zero crossings of SI', that is, every time Dl changes it value. This orientation may for example be defined as "forwards orientation".
• Fig. 6 shows, when SI' and S2' have reversed polarity, that is, when the vehicle is oriented in a reverse manner, D2 always changes from 1 to 0 at the zero crossings of SI', that is, every time Dl changes its value.
• the orientation of the vehicle may be unambiguously determined in this manner as well.
• TR1 and TR2 may furthermore also be simplified. This is however accomplished at the cost of the directional decoder DEC becoming more complicated, since it must consider changes in Dl and D2 and not simply to their instantaneous values.
• the guidance signal SI may be the "usual" guidance signal for the loop, that is, the signal which is used in existing loop guidance systems for keeping the vehicle on right course when it moves along the loop. This is so for all of the signal coding and decoding methods.
• Generalized signal coding and decoding method
• the loop signal S L is generated with at least two principal electrical states. According to the above described methods these principal states consist of the polarity of the first guidance signal SI.
• the second guidance signal S2 is then used to "mark" the first in an unambiguously distinguishable way with reference to the polarity, i.e., the loop signal is marked in such a way that its principal state may be decoded in order to provide unambiguous orientation information.
• the trigger circuits work together with the decoding unit to form a controlled rectifier, whereby, because S2 "marks" SI, D2 constitutes the guidance signal of the rectifier. Reversed orientation of the vehicle is sensed as a time shift of D2 relative to Dl.
• the guidance signals SI and S2 do not need to be sinusoidal or even to have varying polarity, as long as the loop signal is generated with two principal electrical states which are distinguishable by the antenna arrangement.
• the loop signal could for example consist of pulsating direct current. It could even consist of pulses of direct current, in which case the principal state of the loop signal would be the presence or absence of a pulse; by determining the direction of current relative to the antenna device, the orientation of the vehicle could also be determined.
• a micro-processor to implement all or certain ones of the components SIG1, SIG2, POL and SUM.
• the micro-processor would thus constitute a single signal generating device. It is of course also possible to implement this signal generating device completely or partially using analogue technology and even for example to include the adapter stage AMP therein.
• micro-processor which is provided in each vehicle in order to implement the filters FLT1 and FLT2 digitally as well as TR1, TR2 and DEC.
• This micro-processor may even be the same one which provides for control and driving of the motors of the vehicle and possibly its remaining functions.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Electromagnetism (AREA)
• Aviation & Aerospace Engineering (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• General Physics & Mathematics (AREA)
• Automation & Control Theory (AREA)
• Control Of Position, Course, Altitude, Or Attitude Of Moving Bodies (AREA)
• Variable-Direction Aerials And Aerial Arrays (AREA)
• Steering Controls (AREA)

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Cited By (5)

Citations (5)

• 1988
  • 1988-07-04 SE SE8802491A patent/SE463949B/sv not_active IP Right Cessation
• 1989
  • 1989-07-04 WO PCT/SE1989/000385 patent/WO1990000274A1/en unknown

Patent Citations (5)

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