Electricity: motive power systems – Positional servo systems – Vehicular guidance systems with single axis control
Reexamination Certificate
2000-03-17
2001-10-09
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Positional servo systems
Vehicular guidance systems with single axis control
C318S587000, C180S167000
Reexamination Certificate
active
06300737
ABSTRACT:
TECHNICAL FIELD
The subject invention refers to an electronic bordering system for a working tool, in which system a border cable, i.e. an electric cable, is placed above, under or on ground or floor, so that it separates an inner area within the border cable from an outer area, which working tool is preferably intended for attendance of ground or floor, such as grass cutting, moss-scratching, watering, vacuum-cleaning, polishing, transportation etc., and a signal generator feeds the border cable with current, whose magnetic field affects at least one sensing unit located on the working tool, so that the sensing unit emits signals to a control unit, which in cooperation with an engine control, or a signal system for a driver, and at least one driving source directs the tool's movement in order to prevent it from remoting from the inner area.
BACKGROUND OF THE INVENTION
The idea to create a working tool, which manage completely by itself, such as a robot lawn mover or a robot vacuum-cleaner, is old. However, it has taken a long time before such kind of tool has reach the market The solar cell driven lawn mover, called Solar Mower, is an example of that kind of product. It cuts the grass within a border cable, which has been placed in order to fence off the cutting area. Preferably the border cable is excavated into the ground. A signal generator feeds the border cable with current, whose magnetic field affects a sensing unit on the working tool. The sensing unit detects the intensity of the magnetic field and this intensity will increase when the working tool is coming closer and closer to the border cable. The microcomputer in the lawn mover is so programmed that the lawn mover reverses when a certain signal intensity has been achieved during the increasing of the signal intensity that occurs when the sensing unit is approaching the border cable. The lawn mover will as said move backwards from the border cable and then turn and begin to cut in a direction away from the border cable. Consequently, the lawn mover turns when the powerful magnetic field at the border cable has caused a signal intensity of a certain degree. On the other hand, the microcomputer cannot in any way separate the magnetic field on the outside from that on the inside of the border cable. It means that if the lawn mover should slide outside the border cable, or be pushed outside the border cable, the lawn mover will remote from the border cable in the wrong direction, i.e. out from the cutting area. However it stops after approximately 4 metres since the picked up signals then have dropped so much that the machine stops and sends out an alarm signal. Considering the great disadvantage it means to come outside the border cable the lawn mover must therefore change direction already before the sensing unit reaches the border cable. The strength of the signals going from the lawn mover's sensing unit and further into its microcomputer depends on a number of factors, such as spreading of components, sling geometry, excavation depth, iron materials in the ground etc. etc. All this contributes to that a relatively large margin must be given as to how close the sensing unit may come to the border cable, or rather more correctly, at which signal intensity the lawn mover should turn. At cutting work the result will be an uncut edge, which can be several decimetres broad. The problem will be especially large when the cable cannot be placed outside the lawn, for instance at a house ground, an asphalt walk or a flower bed. In case the tool should be pushed outside the border cable by a child or a domestic animal, this will inevitably lead to that the tool stops and sends out an alarm signal, and then it must be lifted in or pushed back inside the border cable.
PURPOSE OF THE INVENTION
The purpose of the subject invention is to substantially reduce the above outlined problems.
SUMMARY OF THE INVENTION
The above purpose is achieved in an electronic bordering system in accordance with the invention having the characteristics appearing from the appended claims.
The electronic bordering system in accordance with the invention is thus essentially characterized in that the signal generator feeds the border cable with current containing at least two components of alternating-current with different frequency, and the components are lying in a known relation of time to each other, e.g. a regularly varying time relation, and hereby the control unit can evaluate the difference in the signals caused by the magnetic field's different directions in the inner area and the outer area, and the control unit can therefore emit an area signal, which mainly takes up one of two states depending on the position of the sensing unit in relation to the border cable, i.e. an outer area state or an inner area state. Accordingly, this means that the tool's microcomputer all the time knows if the tool is on the inside or the outside of the border cable. Hereby the tool can drive past the border cable a bit before it turns. This means, on the one hand that the uncut edge can be eliminated or reduced, and on the other hand that the border cable can be placed at a distance from flower beds, house grounds and asphalt walks. Obviously, this is a very big advantage. The possibility for the control unit to evaluate if the sensing unit is located inside or outside the border cable is created in that the signal generator feeds the border cable with current containing at least two alternating-current components of different frequency, and in that the components are lying in a known relation of time to each other. Furthermore the frequences can preferably consist of multiples of each other, and preferably the alternating-current components should stay in an essentially permanent time relation to each other. In order to increase the safety of the bordering system preferably an analogue signal is used, a so called quality signal, whose signal intensity is a measure of the intensity of the incoming signals of the control unit. Owing to this the tool can be shut off when the signal intensity is riskfully low. These and other characteristics and advantages of the invention will become more apparent from the detailed description of various embodiments with the support of the annexed drawing.
REFERENCES:
patent: 3698523 (1972-10-01), Bellinger
patent: 3893536 (1975-07-01), Marshall et al.
patent: 3924389 (1975-12-01), Kita
patent: 4180964 (1980-01-01), Pansire
patent: 4855656 (1989-08-01), Saitoh et al.
patent: WO 90/00274-A1 (1990-01-01), None
Bergvall Bengt Allan
Petersson Ulf
Aktiebolaget Electrolux
Martin Edgardo San
Nappi Robert E.
Pearne & Gordon LLP
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