Patent Description:
From <CIT> a moveable holder for cultivation of plants is known, the holder comprising a rectangular frame with one or more panels forming a support surface for supporting a plurality of plants thereon, each plant growing in a medium, typically earth, from which the plants can obtain at least some of their water requirement. At its longitudinal edges the frame of the known holder is provided with side walls and a number of crossbeams connect to both sidewalls to provide structural rigidity to the frame. Pairs of roller devices, each comprising one or two roller elements, are mounted on two of the crossbeams, allowing the holder to be rolled across a pair of rails or tubes. Generally, such a pairs of rails or tubes extends over tens or even hundreds of meters in a greenhouse.

Cultivation of plants on such a holder typically includes moving the holder over the rails or tubes at least a times a day, and monitoring a rate of water evaporation by the plants. A common way of estimating the amount of water evaporated by the plants is to place a sample of a number of the plants together with their medium on top of a scale, which scale in turn is placed on the support surface of the holder. A change in measured weight of the sample is then extrapolated to provide an indication of the amount of water that is evaporated by the all plants of the plurality of plants. The sample plants and their growth medium are generally held in a pot or the like, so that they can easily be placed on the scale.

A drawback of this known system is that during measuring of the weight of the sample, the sample is at a greater distance to the support surface of the frame than the other plants of the plurality of plants are. The climate conditions for the plants in the sample and the remaining plants of the plurality of plants are therefore likely to be different, e.g. with respect to average air temperature and/or air humidity. It is also possible that water in the growth medium of the sample partially flows out of the sample and to a location away from the scale. Estimates of evaporation of water by the plurality of plants based on change in weight in sample as measured using the known system are therefore likely to be inaccurate.

It is an object of the invention to provide a holder and method for more accurately determining water evaporation by plants supported on the holder.

To this end, the invention according to claim <NUM> provides a moveable holder for the cultivation of a plurality of plants, the moveable holder comprising: a frame, wherein said frame is provided with a support surface having an area of at least <NUM><NUM> for supporting thereon the plurality of plants; said support surface having two oppositely facing edges; the frame further comprising a plurality of crossbeams arranged below the support surface and substantially bridging a distance between the two oppositely facing edges; wherein the holder further comprises:
two or more support beams, each extending between two adjacent crossbeams and parallel to said crossbeams; a number of load cells for measuring a force exerted on the support beams by the frame; wherein each of the support beams is mounted to its two adjacent crossbeams via one or more of said load cells, and wherein on each of the support beams with roller devices are provided for allowing rolling movement of the holder across a pair of rails or tubes; and one or more transmitters connected to the load cells and adapted for wirelessly transmitting a message containing data on the force exerted on the support beams by the frame as measured by the load cells. The one or more transmitters are connected to the one or more load cells via, circuitry that is adapted for converting signals from the load cells into a message containing data on the force exerted on the support beams by the frame as measured by the load cells.

Each of the support beams is thus connected to the frame via one or more the load cells, and the support surface is completely supported on the support beams via the load cells, so that change in weight carried by the frame can be detected by the load cells. The roller devices on the two support beams allow the holder to be supported in a stable manner on a pair of rails or tubes below the support surface of the holder. At least two roller devices are mounted to each support beam, and each support beam spans a length between the two roller devices mounted thereon along the longitudinal direction of the support beam, and when one of the roller devices hits a slight bump or dimple in a tube or rail, the force thereof will be distributed over the entire support beam. Preferably, the axes of rotation of the roller elements of the roller devices on a same single support beam are substantially fixed with respect to each other.

In case only one transmitter is provided, it is connected to all of the load cells. In case two or more transmitters are provided, preferably each transmitter is connected to the load cells of one of the support beams and adapted for transmitting a message containing data on the force exerted on that support beam by the frame as measured by the corresponding load cells.

Generally, the support surface will be fixed with respect to the crossbeams, e.g. with the lower side of the support surface fixed to upper sides of the crossbeams, for instance by welded these together. The support beams typically are shorter than their adjacent crossbeams.

In an embodiment, the support beams are spaced apart from the frame and from the support surface. This allows slight movement between the support beams and the frame, and in turn allows slight compression of the load cells so that these can be used to measure a force that is exerted by the frame and any plants thereon, on the support beams.

In an embodiment the frame comprises sidewalls at the oppositely facing edges, and the crossbeams connect to both said side walls. The sidewalls provide structural rigidity to the holder and may also help preventing plants from falling off the upper side of the support surface.

In an embodiment, one or more reinforcement structures are provided between cross-beams of each pair of cross-beams that are adjacent to a same support beam, preferably wherein the one or more reinforcement structures spans between said pair of cross-beams on a side of the support beams opposite to the support surface of the holder. The reinforcement structures, which are spaced apart from the support beams, help prevent deformation of the cross-beams. When seen in projection onto the support surface and along the support beam, each reinforcement structure is arranged between the load cells which connect the corresponding support beam to the frame.

Preferably, at least two spaced apart reinforcement structures are connected to the pair of cross-beams, wherein more preferably the distance between the two reinforcement structures is less than a distance between the roller devices that are mounted on the corresponding support beam.

Each reinforcement structure may partially overlap a load cell when seen in top view. In this way, the reinforcement structures are arranged close to the locations where the support beams can exert a horizontally directed force on their adjacent crossbeams.

In an embodiment the support surface is a substantially closed surface. In this embodiment, if the sidewalls project upward from the support surface, the sidewalls and support surface form an open ended container. In an alternative embodiment the support surface is provided with plurality of through openings for allowing air and/or liquid to pass through. This embodiment is suitable for instance when the plants that are to be placed on the support surface are held in pots or other kinds of containers.

In an embodiment the support beams each have a length of at least <NUM>% of the maximum length of its two adjacent crossbeams. Generally, the length of each support beam will be less than the minimum length of its two adjacent cross beams, so that, in case the holder is provided with sidewalls to which the cross beams are connected, the support beams remain spaced apart from the sidewalls.

In an embodiment the support beams each have a lower surface that is substantially flush with the lower surface of one or more crossbeams that are not adjacent to the support beams. The support beams thus do not stand preferably wherein the crossbeams that are adjacent to the support beams each have a lower surface that is arranged vertically above the lower surface of the adjacent support beam, when in use.

In an embodiment, wherein the roller devices are each provided with one or more rollers adapted for rolling contact with a rail or tube of the pair of rails or tubes, wherein when the holder is in an orientation of use in which the support surface extends horizontally, no part of the holder projects further away from the support surface at the lower side of the holder than rollers.

In an embodiment the support surface and/or the holder, when seen in top view, has a substantially rectangular outline. A series of such rectangular holders can be moved over a pair of rails or tubes, in a manner in which the horizontal space for plants on the holders is nearly optimal.

In an embodiment the signal indicative of the force exerted on the support beams by the frame is indicative of a sum of signals provided by the load cells.

The invention provides an assembly for the cultivation of plants, the assembly comprising one or more holders according to any one of the preceding claims, and two parallel tubes or rails in contact with rollers of the roller devices of said one or more holders. The tubes or rails may for instance be mounted on uprights that are supported or the floor, or may be mounted directly on the floor. Preferably the assembly comprises a plurality of holders according to the invention, and a greater number of other holders that are adapted for rolling over the tubes or rails but which are not provided with load cells. Any change in weight derived from the messages transmitted by the holders of the invention will typically also be indicative of a change in weight of the other holders that are not equipped with load cells.

In an embodiment the assembly further comprises: a receiver adapted for receiving from a holder of the one or more holders, a message containing current data on the force exerted on the support beams by the frame of said holder as measured by the load cells thereof; a memory; and a processor connected to the memory and in communication with the receiver, configured for storing in the memory an array of at least six historical data elements derived from messages received earlier from the same holder, wherein the processor is further configured to:.

Preferably at least <NUM> or <NUM> historical data elements are stored in the memory.

Each of the holders is adapted for transmitting one or more messages, e.g. periodically once every <NUM> minutes or less, which contain with data on the force exerted on load cells of that holder. A holder may for example transmit separate messages with data indicative of the load exerted on one, a pair, or all of its load cells. Typically, a pair of load cells is connected to a single support beam, in which case the sum force of each pair of load cells is transmitted in the one or more messages.

This allows the total force exerted on the load cells of a holder to be estimated By collecting data on this force over time, a change in force over time can be determined, from which a trend in the evaporation of water by the plants can be derived while the plants remain held on the holder, for example for hours or days or even weeks. A holde periodically transmits one or more messages regarding the force exerted on its load cells by the frame e.g. once every <NUM> minutes or less, for instance once every <NUM> minutes, over a time period of at least <NUM> hours, for instance for a time period of <NUM> hours or more.

The assembly thus allows evaporation of water by the plants to be easily and accurately monitored. Preferably the receiver, memory, processor and display are integrated in trend monitoring device.

In an embodiment the historical data elements are stored in the memory in a queue, and updating the historical data elements based on the current data comprises discarding an oldest of the data elements from the queue and storing a new element that is based on the current data in the queue as a newest historical data element. In this manner a moving window average of historical data elements can be determined. The queue is preferably a fixed size queue, e.g. a circular queue, adapted for storing at least <NUM>, preferably at least <NUM> historical data elements.

In an embodiment the historical data elements comprise differences over time between measurements indicative of the total force measured by the load cells, and wherein the processor is configured for determining a difference value between the current data and the data from a most recent previously received message which contained data based upon which the historical data elements were updated, and wherein the current data differs by more than a predetermined degree from the historical data elements if the difference value differs by more than a predetermined percentage from an average value of the historical data elements, preferably wherein said predetermined percentage is <NUM>% or greater. For instance, if the one or more current received messages indicate that a total force of about <NUM> N is exerted on load cells, and a immediately preceding received message indicated a total force of about <NUM> was exerted earlier on the load cells, then the difference is <NUM> N. If this difference deviates by no more than <NUM> % from the average of the historical data elements stored in the memory, then the historical data elements are updated to include this difference of <NUM> N, which will likely change the average of the historical data elements. If the difference deviates by more than <NUM>%, e.g. due to a change in measured force on the load cells when the holder bumps into another holder or the like, then the historical data elements are not updated, and the average value of the historical data elements will remain the same.

In an embodiment said updating the historical data with the current data comprises discarding the oldest historical data and including a difference between the current data and a data on the local force exerted on the support beams by the frame of said holder as measured by the load cells thereof from directly previously received measurement.

In an embodiment the assembly further comprises an evaporation trend logging system comprising: a receiver adapted for receiving from a holder of the one or more holders, a message containing current data on the force exerted on the support beams by the frame of said holder as measured by the load cells thereof; a memory for storing said current data together with earlier data on the force exerted on the support beams by the frame of the same holder that was contained in messages that were received earlier from said holder; a processor adapted for determining from the current data and the earlier data, a trend of change in measured force exerted on the support beams by the frame of the holder over time; and a display adapted for displaying said trend.

By displaying the trend of change in the measured force as measured by the load cells of the holder, also a trend in evaporation of water by the plants on the holder is provided. Instead of, or in addition to, displaying the trend, the trend can be used to control climate in a greenhouse in which the holder is located, and in particular may be used to control supply of water to plants on said holder, e.g. by activating an irrigation system of the greenhouse.

The present invention provides a method of providing a weight change measuring capability to a moveable holder for the cultivation of a plurality of plants, wherein the moveable holder comprises a frame, wherein said frame comprises a support surface having an area of at least <NUM><NUM> for supporting thereon the plurality of plants, said support surface having two oppositely facing edges; the frame comprising a plurality of crossbeams arranged below the support surface and substantially bridging a distance between the two oppositely facing edges, wherein on a first and a second of the crossbeams roller devices are provided for allowing rolling movement of the holder across a pair of rails or tubes; the method comprising:.

The method of the invention provides an easy manner of retrofitting a prior art holder to a holder capable of measuring a change in weight of plants supported thereby. The method in particular allows a conventional holder to be converted to a holder according to the the invention. Generally, a battery for powering the load cells and the transmitter is also mounted on the frame and connected for powering the load cells and the transmitter.

In an embodiment the first and second support beams are attached to their adjacent further crossbeams in such a manner that the vertical distance between the roller devices and the support surface when the first and second cross bars were mounted to the frame, is substantially equal to the distance between the roller devices and the support surface when the first and support beams are attached to their adjacent further crossbeams. In this manner, a plurality of prior art holders can be used in a greenhouse together with such holders that have been converted according to the method, with the upper sides of the support surfaces of all of these holders (i.e. both the converted and non-converted holders), at substantially a same height.

<FIG> shows an isometric bottom side view of a prior art moveable holder <NUM> for a plurality of plants. The moveable holder comprises a frame <NUM> which comprises a number of sidewalls <NUM>,<NUM>,<NUM>,<NUM> arranged to form a rectangle. The frame further comprises a plurality of crossbeams <NUM>, <NUM>, <NUM> which connect between the longitudinal sides of the sidewalls and provide structural strength to the holder. A substantially planar support surface for supporting thereon a plurality of plants is mounted on the crossbeams <NUM>,<NUM>,<NUM>, in such a manner that during use, a first side <NUM> of the support surface faces downward and an opposite second side <NUM> of the support surface faces upwards. The sidewalls <NUM>,<NUM> have a length of about <NUM>, and the sidewalls <NUM>,<NUM> have a length of about <NUM>. The support surface <NUM> covers substantially the entire surface area on the inner side of the sidewalls, i.e. when seen in top view the support surface has an area slightly less than <NUM><NUM>.

Two of the crossbeams, <NUM> and <NUM>, are each provided with a pair of roller devices 5a,5b, 7a,7b provided with which allow the moveable holder <NUM> to be rolled across a pair of tracks or tubes that are in contact with the roller devices. During normal use, in which the roller devices are arranged on rails or tubes, the roller elements of the roller devices typically form the lowest portions of the holder <NUM>.

<FIG> shows an isometric bottom side view of a holder <NUM> according to the present invention. The holder <NUM> comprises a frame <NUM> comprising sidewalls <NUM>, <NUM>,<NUM>,<NUM> and crossbeams <NUM>. However, instead of being mounted on crossbeams, pairs of roller devices 5a,5b and 7a,7b are provided on support beams <NUM>, <NUM>, which support beams in turn are mounted on directly adjacent crossbeams <NUM>,<NUM> and <NUM>,<NUM> via load cells. The support beams are spaced apart from the sidewalls and from the support surface. The load cells are shown in <FIG> and <FIG> which also show in greater detail how the support beams are connected to the frame. As the support surface is connected to the roller devices 5a,5b, 7a,7b via the load cells, the load cells can be used to provide measure of a change in weight that is supported on the support surface, and thus also can provide an indication of the amount of water evaporated by the plants. For powering the load cells, a module <NUM> is provided. The module <NUM> comprises a battery, which is connected via leads <NUM> to the load cells, and comprises circuitry for converting the signals from the load cells to a message suitable for transmission. The module <NUM> is also connected via leads to a transmitter <NUM>, which is adapted for wirelessly transmitting a message containing data on the force exerted on the support beams by the frame as measured by the load cells.

<FIG> respectively show an isometric view of the support beam <NUM>, and a front view thereof, together with attachment brackets for mounting the support beam <NUM> on crossbeams <NUM>,<NUM> of <FIG>. The entire support beam assembly of <FIG> is referred to using reference numeral <NUM>.

The support beam <NUM> of <FIG> is shorter than the crossbeams <NUM>,<NUM> so that the distal ends of the support beam remains spaced apart from the sidewalls of the frame. Each of the roller devices 5a,5b is provided with a respective cylindrical roller elements 6a,6b, which can roll over an upper surface of a tube, shown in <FIG>. The roller elements 6a,6b have axes of rotation that are substantially parallel the support surface and to each other, and which are fixed with respect to each other and the support beam <NUM>. The beam is provided with reinforced seats 302a,302b which are welded to the beam, and in which respective transverse arms 303a,303b, which extend transversely on either side of the beam, are fixed using bolts. Each arm 303a,303b is fixed, by means of a bolt connection, to an associated respective load cell 304a,304b. Each load cell in turn is fixed to an associated mounting bracket 305a, 305b, for attaching to adjacent crossbeams <NUM> and <NUM> respectively, again using bolts 306a,306b.

Though the crossbeams <NUM>, <NUM> are not shown in <FIG>, they are shown in the front view of <FIG>, which also shows a tube <NUM> with which the cylindrical roller elements 6a,6b are in rolling contact. As can be seen, the upper surfaces of the crossbeams <NUM>,<NUM> are spaced apart by a distance h from an upper surface of the support beam <NUM>, so that the support beam will not directly contact the support surface of the frame, and any weight borne by the support beam is carried via the load cells 304a,304b.

<FIG> respectively show a similar isometric view and front view of the support beam <NUM>. The beam <NUM>, reinforced seats 402a,403b, transverse arms 403am,403b, load cells 404a,404b, mounting brackets 405a,405b and bolts 406a,406b are of same construction as beam <NUM>, reinforced seats 302a, 303b, transverse arms 303am,303b, load cells 304a,304b, mounting brackets 305a,305b and bolts <NUM>,306b of <FIG>. The beam support assembly <NUM> differs from beam support assembly <NUM> in that different roller devices are provides. In <FIG> roller devices 7a,7b each comprise two wheels 8a, the wheels of each roller device having axes of rotation that are at an angle of about <NUM> degrees to each other. The two wheels 8a of each roller 7a,7b device can thus rest on a tube <NUM>, shown in <FIG>, and help to keep the holder aligned with respect to tube <NUM>, whereas the cylindrical rollers of <FIG> contribute to supporting the weight of the holder, but do not contribute to aligning the holder with respect to tube <NUM>.

<FIG> schematically show a top view and a side view of an assembly <NUM> of the invention. <FIG> shows that the assembly comprises parallel tubes <NUM>, <NUM> on which two holders <NUM> according to the invention are arranged. Additionally, a greater number of prior art holders <NUM> is arranged on the tubes <NUM>,<NUM>, the prior art holders having substantially the same height and width dimensions as the holders <NUM>. As can be seen from <FIG>, the top surfaces of the holders <NUM> and <NUM> are substantially at a same level, so that measurements of change in weight supported by the holders <NUM> are likely to be representative of evaporation of water by the plants on all holders <NUM>, <NUM>, assuming these holders are all loaded with a similar number of plants under similar conditions.

The holders <NUM>, <NUM> are moveable across the tubes <NUM>,<NUM> along a transport direction T, during which the holders are likely to bump in to each other and be subjected to other kinds of impact that may influence the signal measured by the load cells of holders <NUM>. Each of the holders <NUM> according to the invention wirelessly transmits messages with weight measurements as measured using its load cells, via transmitters 242a, 242b to a wireless receiver <NUM> that is connected to an evaporation trend logging device <NUM>, e.g. a computer. The transmitter 242a of each holder <NUM> is connected to the load cells 304a,304b and transmits messages with data on the force exerted thereon by the frame, and transmitter 242b of each holder is connected to the load cells 404a,404b and transmits messages with data on the force exerted thereon by the frame.

Typically, each holder <NUM> transmits one or more such messages at least once every <NUM> minutes to the receiver <NUM>, and the messages include a unique identifier for the holder. Thus, a trend logging device <NUM>, which is connected to the receiver and comprises a memory <NUM> and a processor <NUM> can keep track of the holder from which a message has been received. The trend logging device <NUM> is further equipped with display <NUM>, though this display is optional.

The processor <NUM> is configured to carry out method steps for filtering out that data that has been received from a holder <NUM> which deviates from more than a predetermined amount from a trend of change in weight over time for the same holder. Plants generally evaporate water in a gradual manner, so that sudden changes in measured weight, especially sudden increases in measured weight, are more likely to be due to impact on the holders <NUM>, than due to sudden evaporation by the plants on the holders <NUM>. By filtering out such sudden measured changes in weight, a more reliable estimate of the evaporation by the plants on each individual holder <NUM> of the invention can be obtained.

6A - 6C illustrate steps of converting a prior art holder <NUM> as shown in <FIG> to a holder <NUM> according to the present invention. Starting from the holder <NUM> of <FIG>, first the crossbeams <NUM> and <NUM> which carry roller devices 5a,5b and 7a,7b, are removed from the frame, resulting in the holder <NUM>' shown in Fig. 6A. Next, at locations adjacent to where the crossbeams <NUM> and <NUM> were mounted, pairs of crossbeams <NUM>, <NUM> and <NUM>,<NUM> are mounted to the frame in such a manner that the width between the crossbeams of each pair <NUM>,<NUM> and <NUM>,<NUM> of crossbeams is greater than the respective widths of the crossbeams <NUM>,<NUM> that were removed. This results in the holder <NUM>" shown in Fig. 6B. The distance between crossbeams <NUM> and <NUM> may for instance be between <NUM>,<NUM> times and <NUM> times the width of the support beam of the crossbeam <NUM> that was removed.

Next, a module <NUM>, which comprises a battery and circuitry for converting the signals from the cells to a message suitable for transmission, is attached to the frame, and a transmitter <NUM> is mounted on top of the holder. The circuitry is connected to the transmitter <NUM>, so that messages of signals that are received from load cells via leads <NUM> can be transmitted. This results in the holder <NUM>" shown in Fig. 6C.

As a final step, between each pair <NUM>,<NUM> and <NUM>,<NUM> of crossbeams, a support beam is mounted, via one or more load cells, to the two crossbeams of the pair, and the load cells are connected to the circuitry of module <NUM> The support beams may comprise crossbeams <NUM> and <NUM> that were previously removed and have been shortened on both sides to ensure each support beam remains spaced apart from sidewalls <NUM> and <NUM> of the frame. This results in the holder <NUM> of the invention as shown in <FIG>.

<FIG> shows a flowchart of a method <NUM> for filtering out such measured sudden changes in measured force, or weight, exerted by the frame on the load cells, as may be executed by processor <NUM> of the embodiment of <FIG>. In step <NUM> the device receives, from one of the holders <NUM>, one or more messages with data indicative of force exerted on the load cells of the holder, as well as data identifying the holder which transmitted the message(s), and stores the indication in the memory. The data indicative of force exerted on the load cells may simply correspond to an addition of the measured signals of all load cells of the holder. For instance, the message received may indicate that the load cells of one of the holders <NUM> shown in <FIG>, together measure a weight of <NUM> N, which corresponds to a mass of <NUM>.

In step <NUM>, a current difference is calculated between the received data indicative of the force, and same data in most recently received previously stored data in the memory <NUM>, wherein the previously stored data is associated with the same holder and is indicative of the force exerted on the same holder at an earlier point in time. For instance, a directly previously received message for the same holder received earlier may have indicated a load of about <NUM>,<NUM> N (or a mass of <NUM>,<NUM>) on the load cells. In that case, the calculated difference is <NUM>,<NUM> N, which corresponds to a change in mass of <NUM>,<NUM>.

The memory also contains a queue with data of a plurality of earlier differences calculated by the processor for data received from the same holder. In the present example, the memory stores <NUM> such differences that are based on earlier measurements which were not filtered out. Assuming that the holder transmits a message once every <NUM> minutes, and if no data is filtered out, the memory queue thus olds historical data elements on the change in weight over the last <NUM> minutes.

In step <NUM> the current difference is compared with an average of the <NUM> historical data elements that were calculated based on data received earlier from the same holder. In step <NUM> it is checked whether the current difference deviates more by than a predetermined degree from this average. In the present example this predetermined degree is <NUM>%, i.e. if the average of the historical differences is <NUM>,<NUM> N, and the newly received data indicates a difference in the measured force that would correspond to <NUM>,<NUM> N (i.e. a change in mass of <NUM>,<NUM>), then the newly received data would fall within the expected trend. In such a case, in step <NUM> the current difference is used to update the historical elements, remaining historical elements in the queue are all moved back one element and the current difference data is stored in the memory at the head of the queue.

Otherwise, if in step <NUM> it is determined that the current difference does deviate by more than the predetermined margin from the average, step <NUM> is followed in which the current difference is not used to update the historical data, in this manner effectively ensuring that the values of the historical data are less likely to suddenly change significantly due to events that are not related to the evaporation of water by the plants held on the holder <NUM>.

In step <NUM> the currently received data is stored in the memory so that it may be used to calculate difference data when a next message with data regarding the force exerted on the load cells of the same holder is received. Thus, when the queue of historical data elements stored in the memory has at least <NUM> elements, a single measurement which deviates significantly from the average will not affect the average. However, two subsequent measurements which are close to each other but nonetheless deviate significantly from the average will result in the average being updated.

<FIG> show detailed upside down views of support beams <NUM> and <NUM>, e.g. as shown in <FIG>, wherein their adjacent crossbeams <NUM>,<NUM> and <NUM>,<NUM> are connected to reinforcement structures <NUM>. Due to the manner in which each support beam is connected to its crossbeams, a load that is exerted on a support beam can cause the support beam to exert a horizontally directed force on its adjacent cross-beams. Each reinforcement structure <NUM> comprises a reinforcement beam <NUM> that is mounted to a folded plate <NUM>, the beam <NUM> and <NUM> together spanning the distance between the two crossbeams to substantially prevent the crossbeams from bending due to such a horizontally directed force. The reinforcement structures <NUM> remain spaced apart from the support beams regardless of the force exerted on the support beams by the frame during normal use. The reinforcement structures <NUM> extend along a lower side of the cross-beams. Thus, the reinforcement structures <NUM> interconnect the crossbeams at the lower upper surfaces of the cross beams, and the crossbeams may be attached at their upper sides to a lower side of the support surface and/or at their distal ends to the sidewalls <NUM>, <NUM>. In summary, a moveable holder for a plurality plants is provided which comprises a frame with a support surface for supporting thereon the plurality of plants, wherein the frame is attached via load cells to support beams to which roller devices are attached for allowing rolling movement of the holder across a pair of rails or tubes, e.g. as may be present in a greenhouse. The holder is provided with one or more transmitters which are connected to corresponding load cells, and which can wirelessly transmit messages containing data on the force exerted on the support beams by the frame as measured by the load cells. In this manner, a change in weight of the plants that is indicative of evaporation of water by all of the plants held on the support surface can be obtained.

Claim 1:
Moveable holder (<NUM>) for the cultivation of a plurality of plants, comprising:
a frame (<NUM>), wherein said frame is provided with a support surface (<NUM>) having an area of at least <NUM><NUM> for supporting thereon the plurality of plants; said support surface having two oppositely facing edges; the frame (<NUM>) further comprising a plurality of crossbeams (<NUM>,<NUM>,<NUM>,<NUM>,<NUM>) arranged below the support surface and substantially bridging a distance between the two oppositely facing edges;
wherein the holder further comprises:
two or more support beams (<NUM>,<NUM>), each extending between two adjacent crossbeams (<NUM>,<NUM>; <NUM>,<NUM>) and parallel to said crossbeams; wherein on each of the support beams roller devices (5a,5b; 6a,6b) are provided for allowing rolling movement of the holder across a pair of rails or tubes (<NUM>,<NUM>), characterised in that the holder further comprises
a number of load cells (304a, 304b; 404a,404b) for measuring a force exerted on the support beams by the frame;
wherein each of the support beams (<NUM>,<NUM>) is mounted to its two adjacent crossbeams via one or more of said load cells, and
one or more transmitters (242a, 242b) connected to the load cells and adapted for periodically wirelessly transmitting a message containing data on the force exerted on the support beams by the frame as measured by the load cells,
wherein the support surface is completely supported on the support beams via the load cells, so that change in weight carried by the frame can be detected by the load cells.