Geometrical instruments – Distance measuring – Opposed contacts
Reexamination Certificate
2000-02-11
2001-02-13
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Distance measuring
Opposed contacts
C033S787000, C033SDIG001, C073S073000
Reexamination Certificate
active
06185833
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the sensing of leaf thickness and in particular to the sensing of changes in leaf thickness, particularly for use in irrigation systems.
BACKGROUND OF THE INVENTION
Conventional irrigation systems are intended to periodically replenish accumulated soil water deficits which are associated inter alia with the water retention capacity of the soil, the type of the plants and environmental conditions.
Various proposals have been made and, in some cases implemented, to provide an irrigation system designed to be responsive to the water status of the soil. Thus, for example, it is known to monitor the relative humidity in the soil and to arrange for the irrigation system to be responsive to this relative humidity.
It is known that changes in the water status of a plant are reflected in dimensional changes in one or other of the plant's component elements such as leaves, stalks or stems, and fruits, etc. It has been proposed to monitor such changes and to arrange for periodic irrigation in response to such changes. Of these plant organs, it has been particularly proposed to utilize changes in a leaf's thickness for controlling an irrigation system seeing that it is believed that the instantaneous water status of a leaf of a plant as represented by its thickness provides an accurate indication of the instantaneous water status of the plant.
It is therefore clear that in order to provide for an efficiently operating irrigation system responsive to leaf thickness sensing, it is of prime importance to have available a reliable and efficient leaf thickness sensing device.
It is therefore an object of the present invention to provide a leaf thickness sensing device primarily for use in irrigation systems.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a leaf thickness sensing device comprising mounting means for flexibly mounting said device adjacent a leaf whose thickness is to be sensed, a leaf support element coupled to said mounting means, a displaceable leaf abutting element juxtaposed with respect to and biased towards said leaf support element so as to be in firm, non-destructive abutting contact with a leaf to be releasably retained on said support element; a displacement transducer element responsibly coupled to said leaf abutting element and serving to generate a signal corresponding to displacement of said second element relative to said first element.
Preferably, the displaceable leaf abutting element is constituted by a cantilever mounted resiliently flexible strip whose tip is adapted to bear on the leaf so that leaf thickness changes give rise to corresponding changes in flexing of the strip, said transducer preferably comprising a strain gauge responsive to changes in flexing of the strip.
It is known that a leaf's thickness typically expands and contracts over 20-50 microns during the course of a solar day, i.e. from sunrise to sunrise and, consequently, the displacement transducer element which is responsive to the separation between the abutting elements has a sensitivity to variations in thickness in the order of ±1 micron.
When the device is incorporated in an irrigation system, the output of the transducer when coupled to an irrigation controller is effective in actuating the system in response to the sensed cyclic diurnal variations in leaf thickness which are related to the water status of the plant bearing the leaf.
The irrigation controller is programmed so as to ensure that the required amount of irrigation is provided in accordance with needs of the particular plant, a leaf of which is having its thickness variations sensed.
The invention is preferably associated with a drip irrigation system as this has been found to be particularly effective in providing a rapid localized irrigation water supply as required.
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Sharon, et al., “Irrigation Control fo Citrus According to the Diurnal Cycling of Leaf Thickness”, Proceedings of International Conference on Water & Irrigation, Tel Aviv, Israel (1996).
Falk, et al., “On the Relation between Turgor Pressure and Tissue Rigidity”, Physiol.Plant., 11:802-817 (1958).
Syvertsen, et al., “Diurnal Changes in Citrus Leaf Thickness, Leaf Water Potential and Leaf to Air Temperature Difference”, J. Exp. Bot., 33 (135):783-789 (1982).
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Bravdo Ben-Ami
Seliemann Ron
Sharon Yehoshua
Bennett G. Bradley
Fish & Richardson P.C.
Yissum Research Development Company of the Hebrew University of
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