CA2068395A1 - Load sensor and pallet truck incorporating the same - Google Patents
Load sensor and pallet truck incorporating the sameInfo
- Publication number
- CA2068395A1 CA2068395A1 CA 2068395 CA2068395A CA2068395A1 CA 2068395 A1 CA2068395 A1 CA 2068395A1 CA 2068395 CA2068395 CA 2068395 CA 2068395 A CA2068395 A CA 2068395A CA 2068395 A1 CA2068395 A1 CA 2068395A1
- Authority
- CA
- Canada
- Prior art keywords
- load
- gauges
- load sensing
- tongue
- strain gauges
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01G—WEIGHING
- G01G19/00—Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups
- G01G19/08—Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups for incorporation in vehicles
- G01G19/083—Weighing apparatus or methods adapted for special purposes not provided for in the preceding groups for incorporation in vehicles lift truck scale
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01G—WEIGHING
- G01G3/00—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances
- G01G3/12—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing
- G01G3/14—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing measuring variations of electrical resistance
- G01G3/1402—Special supports with preselected places to mount the resistance strain gauges; Mounting of supports
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62B—HAND-PROPELLED VEHICLES, e.g. HAND CARTS OR PERAMBULATORS; SLEDGES
- B62B2203/00—Grasping, holding, supporting the objects
- B62B2203/50—Grasping, holding, supporting the objects comprising weighing means
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Forklifts And Lifting Vehicles (AREA)
- Measurement Of Force In General (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A load sensing unit having a plate member which can be secured in position in a load supporting machine, and having a tongue connected to the plate, a plurality of load sensing gauges secured to the tongue, at least two of the gauges being placed in tension by a load on the tongue, and at least two of the gauges being placed in compression by a load on the tongue, electrical connection means connecting the gauges, whereby the gauges in tension, are connected in series with the gauges in compression on opposite sides of a bridge circuit, a load bearing device on the tongue, on which a load may be applied to the tongue, to cause deflection, deflection of the tongue in turn placing at least two of the strain gauges in tension, and at least two of the strain gauges in compression, and electrical circuit means connected to bridge circuit to receive signals from the strain gauges, and signal device responsive to signals from the strain gauges to detect signals from the strain gauges in tension, and to detect signals from strain gauges in compression, and to generate load signals.
A load sensing unit having a plate member which can be secured in position in a load supporting machine, and having a tongue connected to the plate, a plurality of load sensing gauges secured to the tongue, at least two of the gauges being placed in tension by a load on the tongue, and at least two of the gauges being placed in compression by a load on the tongue, electrical connection means connecting the gauges, whereby the gauges in tension, are connected in series with the gauges in compression on opposite sides of a bridge circuit, a load bearing device on the tongue, on which a load may be applied to the tongue, to cause deflection, deflection of the tongue in turn placing at least two of the strain gauges in tension, and at least two of the strain gauges in compression, and electrical circuit means connected to bridge circuit to receive signals from the strain gauges, and signal device responsive to signals from the strain gauges to detect signals from the strain gauges in tension, and to detect signals from strain gauges in compression, and to generate load signals.
Description
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FIELD OF THE INVENTION
- The invention relates to load sensors, and in particular to load sensors adapted to be incorporated in a pallet lift truck of the type used for moving pallets loaded with goods.
BACKGROUND OF THE INVENTION
Load sensors of various kinds are well-known.
Typically, they incorporate a so-called "load sensing gaugel', which is essentially a length of resistive wire having a predetermined resistance. The gauge is placed in such a manner that it may be stressed either in tension or in compression. When stressed in kension, khe resistivity of the wire increases. ~en placed in compression the resistivity of the wire decreases.
The principles of such load sensors have been well-known for many years. Such load s~nsors are used in many applications.
The load sensing gauges themselv~s may be relatively small, typically having dimensions of perhaps one centimetre square, However, the incorporation of such load sensing gauges in a piece of equipment, which is capable o~ being stressed by a weight or mass, and the electrical connection o~ such load sensor sensing gauges, so that they produce meaning~ul information presents certain proklemsO In many cases, the entire load sensor comprising the gauges themselves, and khe mounting upon which they are mounted must be so arranged that it can be placed in a position where it is subjected to the stress ;
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Preferably, such a load sensor should be provided with a large excess capac.ity in terms of stress or mass, so that the likelihood of failure is extremely low. This in turn imposes certain limitations on the design of such a load sensor, since the objective is to permit the load sensor mounting to move in response to the stress or mass, in proportion to the actual intensity of the ~tress I or the weight of the mass, and thus provide a progressive measurement of the actual stress or mass. Consequently, ' the design o~ such a load sensor unit becomes a matter of ; in the first place designing a unit which is strong enough to resist stresses or masses substantially in excess of the rated or normal duty cycle, and which will yet yield, in response to stresses or masses within the normal duty cycle, so as to produce an e~fect on the load senæing gauges themselves, which can be detected and read out on measuring e~uipment.
These various problems become intensified, when it is necessary to incorporate such a load sensing unit in a restricted ~pace, and in a piece oE equipment with a predetermined existing design which substantially cannot be changed.
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:, For example, in the case of a pallet lift truck such as is typically used in industry for moving pallets loaded with goods from place to place, the two forks of the pallet trllck are required to be inserted into a space underneath a pallet. Typically, this space is no more than about 8.5 to 9 centimetres (about 3.5 inches). The forks must be adapted to be inserted beneath such a pallet, and must at the same time be strong enough to lift the pallet and its load of goods, and transport it to wherever it i5 required.
Pallet trucks of this type are designed to take a ~ prsdetermined maximum load on the forks. If that l.oad is - exceeded, either the truck may be damaged, or the load may simply fall offO
In extreme cases personal injury may result.
For all of these reasons, it is desirable to provide such a pallet truck with a load sensing system, which is c~pable o~ measuring the load on the forks, so that the operator will not exceed the rated load for that 2a particular type of pallet truck.
Some pallet trucks are ~anually operated to movP
relatively small loads, and other pallet trucks are operated by prime movers, and move much heavier loads.
In all these cases however some orm o~ load sensing is highly desirable to ensure that the operator does not ~ exceed the rated load for that particular pallet truck.
: As explained above however such forks must fit within the space provided ~eneath a pallet. The design .~
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of load sensing units to fit into such forks, without increasing the vertical height of the forks, presents substantial problems. The forks themselves must be designed and structured to have sufficient strength to lift a predetermined load. In order to provide such strength, the forks must have certain dimensions. For example in typical cases the forks will have dimensions equal to about 7.5 to 7.75 centimetres in heightO
Bearing in mind that the clearance beneath a typical pallet is between 8 and ~.5 centimetres, it will be appreciated that there is only a restrir.ted space to incorporate additional equipment such as load sensors in the forks.
It is thus apparent that in order to provide load sensors, particularly load sensors designed for use in such low clearance equipment, the design of the load ,'1 sensor must be highly refined so that it may be fitted within the existing equipment without increasing its dimensions~
;. 20 BRIEF SUMMARY OF THE INVENTION
With a view to overcoming the various problems described above, the invention comprises a load sensing unit which in turn comprises a plate member adapted to be secured in position, in a load supporting apparatus, a tongue portion connected to said plate portion, a plurality o~ load sensing gauges secured to said tongue portion, at least two of said gauges being adapted to be placed in tension by a load on said tongue portion, and ~4--:
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at least two of said gauges being adapted to be placed in compression by a said load on said tongue portion, electrical connection means connecting said gauges, whereby said gauges in tension, are connected in series with said gauges in compression on opposite sides o~ a bridge circuit, load bearing means on said tongue means, whereby a load may be appli.ed to said tongue means, to cause deflection thereof, de~lection of said tongue means in turn placing at least two of said strain gauges in tension, and at least two of said strain gauges in compression, and electrical circuit means connected to said bridge circuit, whereby to receive signals ~rom said strain gaugesl and signal responsi~e means responsive to signals ~rom said strain gauges, whereby to detect signals from said strain gauges in tension, and whereby . to detect signals from said strain gauges in compression, : and to generate load signals responsive thereto.
.1 The invention further comprises the provision of a load sensing assembly comprising an elongated bar of metal, said elongated bar of metal having a load sensing unit as aforesaid located at each end thereof.
The inven~ion further comprises such a load sensing unit and incorporating groove means formed in said tongue means transversely thereoE, and electrical connection means extending between said strain gauges, running in said groove means, and further incorporating connection groove means in a portion of said plate means, for containing electrical connections ~rom said strain . '', ~' gauges, to said signal responsive means.
The invent.;.on further comprises such a load sensin~
unit and wherein there are two said groove means extending transversely vf said tongue means, and wherein there are four said load sensing gauges, a first pair of said load sensing gauges being located in a first one G~
said groove means and a second pair of said load sensing gaug~.s being located in a second one of said groove means, and connection channel means extending between said first and second groove means, for connecting said first and second pairs of strain gauges.
The invention further comprises such a load sensing unit and ~urther including an abutment device connected to said tongue means, and adapted to extend upwardly of said tongue means, for engagement by a load or mass.
The invention further comprises such a load sensing unit and wherein said tongue means, when subjected to a load, is adapted to place said first pair of strain gauges in tension, and is adapted to place said second pair of skrain gauges in compression, when subjected to a load on said tongue means.
The invention further comprises a pallet truck~
adapted to lift a pallet, and wherein said pallet truck incorporates at least two forks adapted to be inserted under a pallet, and in~luding load sensing units as a~oresaid incorporated in said forks.
The invention further comprises such a pallet truck and wherein said ~orks are formed of generally channel-::
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shaped construction, having webs with upper and under sides, and side walls extending downwardly from said webs, and wherein said load sensing units are secured to said under sides of said webs between said channel walls, and including opening means in said webs, and said abutment devices on said load sensing units extending upwardly through said webs, whereby to receive a load on said forks.
The invention further comprises such a pallet truck, and wherein said forks have a predetermined length, and including load sensing ~ssemblies extending for a substantial portion of said length, and having said load sensing units and abutment devices on each end of each of said load sensing assemblies, whereby there are four said load sensing units, and four said abutment devices extending upwardly through said webs, thereby engagi.ng a said pallet at four points.
The invention ~urther comprises such a pallet truck and wherein said ~orks are made o~ sheet metal, and wherein said load sensing assemblies are formed o~ rigid elongated bars of metal, said rigid elongated bars of metal being bolted to the underside o~ respective said webs, whereby substantially reinforcing the same, and eliminating flexing of said fork~ due to loads placed thereon n The invention further comprises such a pallet truck, and including instrument panel means supported at one end thereof, and electrical connection means connected ' - , ~ '. ~ '.
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between said load sensing units and said instrument panel means, whereby said instrument panel means is adapted to provide a visual indication of the load on said forks, when a pallet is supported thereon.
The various features of novelty which characterize the invention are pointed out with more particularity in : the claims annexed to and formi.ng a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are ., illustrated and described preferred embodiments of the ~ invention.
.i, IN THE ~RAWINGS
Figure 1 is a top plan view of a load sensing ~1 ~ssembly~ having two load sensing units in accordance with the invention;
Figure 2 i~ an upper perspective illustration of the load sensing unit of Figure 1;
~igure 3 is an electrical circuit diagram ; illustrating the circuits of the load sensing gauges of the load sensing unit of Figures 2;
Figure 4 is a schematic ill~stration of the operation of the load sensing unit of Figure 2 when . subjected to a load;
:, Figure 5 is a perspective illustration of a hand i operate~ pallet truck inoorporating the load sensing ; assemblies of Figure 1, and~
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Figure 6 is a section along the lines 6-6 of Figure 5.
DESCRIPTION OF_A SPECIFIC EMBODIMENT
~ eferring first of all to Figure 1, a load sensing assembly is indicated generally as 10. It will he seen to comprise an elongated rigid bar of metal 12.
Preferably the metal is of high tensile steel at least one half inch in thickness, in the case of the present : application, and having a plurality of securement holes 14 therealong whereby it may be secured in position where desired.
At each end of the bar 12 there is located a load sensing unit 16-16. This form of construction is particularly suited to incorporation in the forks of a typical pallet truck (Figure 6) as will be described later. It will o~ course be appreciated however that the load sensing units 16-16 may be provided in other forms of equipment, other than pallet trucks. In some forms of equipment, the load sensing units 16-16 may be separate from one another and need not necessarily be at opposite ends of a rigid bar 12.
Referring now to Figure 2, a load sensing unit 16 ~ will be seen to comprise two side mounting plates 20-22, ; and a central tongue 24. The side mounting plates 20 and 22 and the tongue 24 in khis embodiment are formed out of a single piece of bar stock joined as at 25, and are partially separated from one another by two severance slots 26-26, terminating in gen~rally cylindrical _g_ .. . . : ~
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recesses 28-28.
In this way, the tongue 24 is rendered movable relative to th~ mounting plate 20-22 and bar 25.
Ref~rring now to Figure 2, the tongue 24 will be seen to be provided with two generally transverse recesses or grooves 30-32. The grooves extend into the mounting plates 20-22 merely for the sake of convenience in machining.
An axial cross-groove 34 extends between transverse grooves 30-32.
A load bearing stud 35 is secured at the end of tongue 24.
An electrical connection groove 36 in plate 2~
communicates with one end of groove 30 for reasons to be des~ribed below.
Within the groove 30 of the tongue 24, thera are located two load sensing gauges 38-40.
Within the groove 32 in ~he tongue 24 there are located a further two load sensing gauges 42-44.
The two gauges 38-40 are adapted to be placed in tension, and the two gauges 4~-44 are adapted to be placed in compression as will be described below.
These four gauges are connected, substantially as shown in Figure 3, so as to provide what is known as a wheatstone bridge".
This type of electrical circuit has been well-known for many years. It consists of four resistances, arranged in pairs in series with one another, and at the .
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connections between one pair of resistance an electrical ~urrent is supplied, and at the connection between the opposite pair of resistances the negative side of the same electrical circuit is connected.
- Between the two pairs of xesistances in each case, connections are made to some form of signal reading device. Such a signal reading device may be a digital read out, or for example maybe a moving coil device, having a swinging needle.
When all of the resistances are equal, on all four sides of the circuit, ~hen current will flow from one side to the other, but there will be no signal supplied to the signalling device which will then read zero.
:, However, when the resistances change, then current ; will flow to one side of the signalling circuit, andcurrent will return from the other side of the signalling circuit. This will then cause the signalling device to ~,~` deliver a reading.
Such circuits have been known ~or very many years and are fully described in text books of electrical engineering, and require no special un~erstanding for the purposes of the invention.
In the present case, electrical current is supplied, ~; in the bridge circuit of Figure 3, through the wires 46 and 48.
The signal device i5 connected to the wires 50 and 52.
Th~ load sensing gauge 38 is connected in series --11~
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with the load sensing gauge 44, and the load sensing yauge 42 is connected in series with the load sensing gauge 40.
The respective bridge circuits for the respective units 16 are connected in parallel to a signal readout instrument described below.
Referring now to Figure 4, this is a schematic illustration of the tongue, when subjected to a load~
It will be seen that the two grooves 30-32 are spaced apart from one another and extend transversely ~rom side to side of the tongue 24.
It will be seen that the two strain gauges 38-40 in the groove 30, when subjected to a load are placed in tension. It will also be seen that the two strain gauges 42-42 located in the groove 42 when subjected to a load are placed in compression.
From the explanation already given in the Figure 3, and from an understanding of Figure 4, it will now be seen that when a load is applied to the tongue 24, the two strain gauges 38 and 4~ on the one side of the bridge, will be place respectively in tension and in compression. At the same time the two strain gauges 42 and 40 on the other side of the bridge will be pla~ed respectively in compression and in tension.
It will thus be understood that the resistance o~
the strain gauge 38 increases whereas the resistance o~
the strain gauge 44 decreases. It will also be understood that the resistance o~ the strain gauge 42 ' ~ . " : ' , ~$~3~
decreases while the resistance of the strain gauge 40 increases.
Since the current through the strain gauge connects from 46 to 48, it will thus be seen that current will flow through the strain gauge 42, and will be resisted by the strain gauge 38, since the resistance of the strain gauge 38 is higher and thP resistance of the strain gauge 42 is lower.
Similarly, it will be seen that the return current through the wire 48, will flow through the strain gauge 44, having a lower resistance and will be resisted by the strain gauge 40 having a higher resistanceO
Thus the signals in the signal connection wire 50 ~ will be high and the signal in the connection wire 52 will be low, and current will flow~
It will of course be appreciated that the nominal resistances of the strain gauges themselves may be in the ;i xegion of this type of case, for example 350 ohms. Achange of one or two ohms upwardly and one or two ohms downwardly, ~etween respective gauges 38 and 42, and between respective gauges 40 and 44, will be proportional to the degree of deflection of the tongue 24 in response to the for¢e.
However, in the design of such strain gauges, even j these relatively minor changes in resistance, will provide a direct read out of the actual load applied to the tongue.
Signal reading equipment such as digital read out .
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devices or moving coil devices, at the present time, are entirely adequate to detect such changes, and will provide an accurate read out of the actual load, over all reasonable working ranges of a particular device.
Referring again to Figure 4, it will be seen that the tongue 24 when subjected to a load, is deflected in an S-shape in sections. The tonyue ~4 behaves in this way due to the characteristics of the metal, and the formation of the grooves 30 and 32.
~eferring now to Figures 5 and Z, it will be seen that the load sensing assembly as illustrated in Figure 1, may be applied to the forXs of a pallet truck - indicated generally as 60. Typically such a pallet truck will have a pair of forks 62-62, connected to a cross-frame 64. The cross-frame 64 may be connected to a heavy duty pallet truck and prime mover (not shown). Howe~er, in the present case the cross member 64 is conn~cted simply to an operating handle 66. Wheels 68-68 are locat~d underneath the forks 62-62, and further wheels 72 are located underneath the cross members 6~. By use of suitable controls on the handle 66 (not shown) the forks may be first of all inserted underneath the clearance beneath a typical pallet (not shown) and the forks may then be raised, so that they lift the pallet off the floor. The pallet is then rendered mobile, and can be dragged by operation of a handle 66, while being supported on the fork 62.
All of this is well-known in the art, and requires - ~
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no special description.
For the purposes of the present invention however load lifting assemblies 10, as illustrated in Figure 1, are incorporated in each of the forks 62.
Reference may be made to Figure 7, showing the cross-section Qf one of the forks 62. It will be seen to comprise a first channel portion, comprising side walls 72-72, and a cross-member 74, and a second channel comprising side walls 76-76 and a cross-member 78.
The side walls 72 72 will be seen to support the wheels 68.
Located beneath the cross wall 74, extending between the side walls 72, there is located the load sensing assembly 10. The load sensing assembly 10 is secured by bolts (not shown) or other suitable attachment devices, and extends the length of the cxoss member 74.
Cross wall 76, is formed with an opening 84, registering with stud 35 on tongue 24~
The top of stud 34 is generally dome-shaped, and ~0 engages the underside of cross wall 80.
Thus when a load is applied to the forks 62 of the pallet truck~ the load first of all sits on the cross walls 80. Since there are four load sensing units 16, one at each end of each bar 10, the load is thus shared i between the four load sensiny units.
At the same time, it will be appreciated that the load sensing assemblies 10, extend substantially the full length of the cross walls 76, and substantially reinforce ~15--' -. ~
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the same rendering them rigid from end to end. This is an important feature of the invent.ion, since if any flexing takes place, when a load is applied to the forks, the load sensing units will not provide an accurate read out.
For the sake of the convenience of the operator, a pedestal 86 is secured on cross member 64 of the pallet truck 60. On top of the pedestal 86, there is an instrument panel 88. The instrument panel 88 will contain any suitable signal responsive equipment : indicated generally as 90. The operator when loading the pallet truck will thus immediately be given an accurate reading o the load.
The operation of the devices is believed to be self-evident from the foregoing description.
The foregoing is a description of a preferred embodiment of the invention which is given here by way of I example only. The invention is not to be taken as limited to any of the specific features as described, but comprehends all such variations thereof as come within the scope of the ap~ended claims.
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FIELD OF THE INVENTION
- The invention relates to load sensors, and in particular to load sensors adapted to be incorporated in a pallet lift truck of the type used for moving pallets loaded with goods.
BACKGROUND OF THE INVENTION
Load sensors of various kinds are well-known.
Typically, they incorporate a so-called "load sensing gaugel', which is essentially a length of resistive wire having a predetermined resistance. The gauge is placed in such a manner that it may be stressed either in tension or in compression. When stressed in kension, khe resistivity of the wire increases. ~en placed in compression the resistivity of the wire decreases.
The principles of such load sensors have been well-known for many years. Such load s~nsors are used in many applications.
The load sensing gauges themselv~s may be relatively small, typically having dimensions of perhaps one centimetre square, However, the incorporation of such load sensing gauges in a piece of equipment, which is capable o~ being stressed by a weight or mass, and the electrical connection o~ such load sensor sensing gauges, so that they produce meaning~ul information presents certain proklemsO In many cases, the entire load sensor comprising the gauges themselves, and khe mounting upon which they are mounted must be so arranged that it can be placed in a position where it is subjected to the stress ;
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, , 2~ J3~a or weight of the mass, without interfering with the operation of the equipment for which it is designed. In addition, Eor example, if such load sensor should fail, it is essential that it be so designed that the equipment itself can function even though the load sensor itself is no longer operating.
Preferably, such a load sensor should be provided with a large excess capac.ity in terms of stress or mass, so that the likelihood of failure is extremely low. This in turn imposes certain limitations on the design of such a load sensor, since the objective is to permit the load sensor mounting to move in response to the stress or mass, in proportion to the actual intensity of the ~tress I or the weight of the mass, and thus provide a progressive measurement of the actual stress or mass. Consequently, ' the design o~ such a load sensor unit becomes a matter of ; in the first place designing a unit which is strong enough to resist stresses or masses substantially in excess of the rated or normal duty cycle, and which will yet yield, in response to stresses or masses within the normal duty cycle, so as to produce an e~fect on the load senæing gauges themselves, which can be detected and read out on measuring e~uipment.
These various problems become intensified, when it is necessary to incorporate such a load sensing unit in a restricted ~pace, and in a piece oE equipment with a predetermined existing design which substantially cannot be changed.
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:, For example, in the case of a pallet lift truck such as is typically used in industry for moving pallets loaded with goods from place to place, the two forks of the pallet trllck are required to be inserted into a space underneath a pallet. Typically, this space is no more than about 8.5 to 9 centimetres (about 3.5 inches). The forks must be adapted to be inserted beneath such a pallet, and must at the same time be strong enough to lift the pallet and its load of goods, and transport it to wherever it i5 required.
Pallet trucks of this type are designed to take a ~ prsdetermined maximum load on the forks. If that l.oad is - exceeded, either the truck may be damaged, or the load may simply fall offO
In extreme cases personal injury may result.
For all of these reasons, it is desirable to provide such a pallet truck with a load sensing system, which is c~pable o~ measuring the load on the forks, so that the operator will not exceed the rated load for that 2a particular type of pallet truck.
Some pallet trucks are ~anually operated to movP
relatively small loads, and other pallet trucks are operated by prime movers, and move much heavier loads.
In all these cases however some orm o~ load sensing is highly desirable to ensure that the operator does not ~ exceed the rated load for that particular pallet truck.
: As explained above however such forks must fit within the space provided ~eneath a pallet. The design .~
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of load sensing units to fit into such forks, without increasing the vertical height of the forks, presents substantial problems. The forks themselves must be designed and structured to have sufficient strength to lift a predetermined load. In order to provide such strength, the forks must have certain dimensions. For example in typical cases the forks will have dimensions equal to about 7.5 to 7.75 centimetres in heightO
Bearing in mind that the clearance beneath a typical pallet is between 8 and ~.5 centimetres, it will be appreciated that there is only a restrir.ted space to incorporate additional equipment such as load sensors in the forks.
It is thus apparent that in order to provide load sensors, particularly load sensors designed for use in such low clearance equipment, the design of the load ,'1 sensor must be highly refined so that it may be fitted within the existing equipment without increasing its dimensions~
;. 20 BRIEF SUMMARY OF THE INVENTION
With a view to overcoming the various problems described above, the invention comprises a load sensing unit which in turn comprises a plate member adapted to be secured in position, in a load supporting apparatus, a tongue portion connected to said plate portion, a plurality o~ load sensing gauges secured to said tongue portion, at least two of said gauges being adapted to be placed in tension by a load on said tongue portion, and ~4--:
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at least two of said gauges being adapted to be placed in compression by a said load on said tongue portion, electrical connection means connecting said gauges, whereby said gauges in tension, are connected in series with said gauges in compression on opposite sides o~ a bridge circuit, load bearing means on said tongue means, whereby a load may be appli.ed to said tongue means, to cause deflection thereof, de~lection of said tongue means in turn placing at least two of said strain gauges in tension, and at least two of said strain gauges in compression, and electrical circuit means connected to said bridge circuit, whereby to receive signals ~rom said strain gaugesl and signal responsi~e means responsive to signals ~rom said strain gauges, whereby to detect signals from said strain gauges in tension, and whereby . to detect signals from said strain gauges in compression, : and to generate load signals responsive thereto.
.1 The invention further comprises the provision of a load sensing assembly comprising an elongated bar of metal, said elongated bar of metal having a load sensing unit as aforesaid located at each end thereof.
The inven~ion further comprises such a load sensing unit and incorporating groove means formed in said tongue means transversely thereoE, and electrical connection means extending between said strain gauges, running in said groove means, and further incorporating connection groove means in a portion of said plate means, for containing electrical connections ~rom said strain . '', ~' gauges, to said signal responsive means.
The invent.;.on further comprises such a load sensin~
unit and wherein there are two said groove means extending transversely vf said tongue means, and wherein there are four said load sensing gauges, a first pair of said load sensing gauges being located in a first one G~
said groove means and a second pair of said load sensing gaug~.s being located in a second one of said groove means, and connection channel means extending between said first and second groove means, for connecting said first and second pairs of strain gauges.
The invention further comprises such a load sensing unit and ~urther including an abutment device connected to said tongue means, and adapted to extend upwardly of said tongue means, for engagement by a load or mass.
The invention further comprises such a load sensing unit and wherein said tongue means, when subjected to a load, is adapted to place said first pair of strain gauges in tension, and is adapted to place said second pair of skrain gauges in compression, when subjected to a load on said tongue means.
The invention further comprises a pallet truck~
adapted to lift a pallet, and wherein said pallet truck incorporates at least two forks adapted to be inserted under a pallet, and in~luding load sensing units as a~oresaid incorporated in said forks.
The invention further comprises such a pallet truck and wherein said ~orks are formed of generally channel-::
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shaped construction, having webs with upper and under sides, and side walls extending downwardly from said webs, and wherein said load sensing units are secured to said under sides of said webs between said channel walls, and including opening means in said webs, and said abutment devices on said load sensing units extending upwardly through said webs, whereby to receive a load on said forks.
The invention further comprises such a pallet truck, and wherein said forks have a predetermined length, and including load sensing ~ssemblies extending for a substantial portion of said length, and having said load sensing units and abutment devices on each end of each of said load sensing assemblies, whereby there are four said load sensing units, and four said abutment devices extending upwardly through said webs, thereby engagi.ng a said pallet at four points.
The invention ~urther comprises such a pallet truck and wherein said ~orks are made o~ sheet metal, and wherein said load sensing assemblies are formed o~ rigid elongated bars of metal, said rigid elongated bars of metal being bolted to the underside o~ respective said webs, whereby substantially reinforcing the same, and eliminating flexing of said fork~ due to loads placed thereon n The invention further comprises such a pallet truck, and including instrument panel means supported at one end thereof, and electrical connection means connected ' - , ~ '. ~ '.
:
~. .
$ ~
between said load sensing units and said instrument panel means, whereby said instrument panel means is adapted to provide a visual indication of the load on said forks, when a pallet is supported thereon.
The various features of novelty which characterize the invention are pointed out with more particularity in : the claims annexed to and formi.ng a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are ., illustrated and described preferred embodiments of the ~ invention.
.i, IN THE ~RAWINGS
Figure 1 is a top plan view of a load sensing ~1 ~ssembly~ having two load sensing units in accordance with the invention;
Figure 2 i~ an upper perspective illustration of the load sensing unit of Figure 1;
~igure 3 is an electrical circuit diagram ; illustrating the circuits of the load sensing gauges of the load sensing unit of Figures 2;
Figure 4 is a schematic ill~stration of the operation of the load sensing unit of Figure 2 when . subjected to a load;
:, Figure 5 is a perspective illustration of a hand i operate~ pallet truck inoorporating the load sensing ; assemblies of Figure 1, and~
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.
.
.~
-3 ~ ~
Figure 6 is a section along the lines 6-6 of Figure 5.
DESCRIPTION OF_A SPECIFIC EMBODIMENT
~ eferring first of all to Figure 1, a load sensing assembly is indicated generally as 10. It will he seen to comprise an elongated rigid bar of metal 12.
Preferably the metal is of high tensile steel at least one half inch in thickness, in the case of the present : application, and having a plurality of securement holes 14 therealong whereby it may be secured in position where desired.
At each end of the bar 12 there is located a load sensing unit 16-16. This form of construction is particularly suited to incorporation in the forks of a typical pallet truck (Figure 6) as will be described later. It will o~ course be appreciated however that the load sensing units 16-16 may be provided in other forms of equipment, other than pallet trucks. In some forms of equipment, the load sensing units 16-16 may be separate from one another and need not necessarily be at opposite ends of a rigid bar 12.
Referring now to Figure 2, a load sensing unit 16 ~ will be seen to comprise two side mounting plates 20-22, ; and a central tongue 24. The side mounting plates 20 and 22 and the tongue 24 in khis embodiment are formed out of a single piece of bar stock joined as at 25, and are partially separated from one another by two severance slots 26-26, terminating in gen~rally cylindrical _g_ .. . . : ~
' . . .
. ~.
2~3~
recesses 28-28.
In this way, the tongue 24 is rendered movable relative to th~ mounting plate 20-22 and bar 25.
Ref~rring now to Figure 2, the tongue 24 will be seen to be provided with two generally transverse recesses or grooves 30-32. The grooves extend into the mounting plates 20-22 merely for the sake of convenience in machining.
An axial cross-groove 34 extends between transverse grooves 30-32.
A load bearing stud 35 is secured at the end of tongue 24.
An electrical connection groove 36 in plate 2~
communicates with one end of groove 30 for reasons to be des~ribed below.
Within the groove 30 of the tongue 24, thera are located two load sensing gauges 38-40.
Within the groove 32 in ~he tongue 24 there are located a further two load sensing gauges 42-44.
The two gauges 38-40 are adapted to be placed in tension, and the two gauges 4~-44 are adapted to be placed in compression as will be described below.
These four gauges are connected, substantially as shown in Figure 3, so as to provide what is known as a wheatstone bridge".
This type of electrical circuit has been well-known for many years. It consists of four resistances, arranged in pairs in series with one another, and at the .
`~
2~$~
connections between one pair of resistance an electrical ~urrent is supplied, and at the connection between the opposite pair of resistances the negative side of the same electrical circuit is connected.
- Between the two pairs of xesistances in each case, connections are made to some form of signal reading device. Such a signal reading device may be a digital read out, or for example maybe a moving coil device, having a swinging needle.
When all of the resistances are equal, on all four sides of the circuit, ~hen current will flow from one side to the other, but there will be no signal supplied to the signalling device which will then read zero.
:, However, when the resistances change, then current ; will flow to one side of the signalling circuit, andcurrent will return from the other side of the signalling circuit. This will then cause the signalling device to ~,~` deliver a reading.
Such circuits have been known ~or very many years and are fully described in text books of electrical engineering, and require no special un~erstanding for the purposes of the invention.
In the present case, electrical current is supplied, ~; in the bridge circuit of Figure 3, through the wires 46 and 48.
The signal device i5 connected to the wires 50 and 52.
Th~ load sensing gauge 38 is connected in series --11~
''' ~' , .
:.
'~$~3g~
with the load sensing gauge 44, and the load sensing yauge 42 is connected in series with the load sensing gauge 40.
The respective bridge circuits for the respective units 16 are connected in parallel to a signal readout instrument described below.
Referring now to Figure 4, this is a schematic illustration of the tongue, when subjected to a load~
It will be seen that the two grooves 30-32 are spaced apart from one another and extend transversely ~rom side to side of the tongue 24.
It will be seen that the two strain gauges 38-40 in the groove 30, when subjected to a load are placed in tension. It will also be seen that the two strain gauges 42-42 located in the groove 42 when subjected to a load are placed in compression.
From the explanation already given in the Figure 3, and from an understanding of Figure 4, it will now be seen that when a load is applied to the tongue 24, the two strain gauges 38 and 4~ on the one side of the bridge, will be place respectively in tension and in compression. At the same time the two strain gauges 42 and 40 on the other side of the bridge will be pla~ed respectively in compression and in tension.
It will thus be understood that the resistance o~
the strain gauge 38 increases whereas the resistance o~
the strain gauge 44 decreases. It will also be understood that the resistance o~ the strain gauge 42 ' ~ . " : ' , ~$~3~
decreases while the resistance of the strain gauge 40 increases.
Since the current through the strain gauge connects from 46 to 48, it will thus be seen that current will flow through the strain gauge 42, and will be resisted by the strain gauge 38, since the resistance of the strain gauge 38 is higher and thP resistance of the strain gauge 42 is lower.
Similarly, it will be seen that the return current through the wire 48, will flow through the strain gauge 44, having a lower resistance and will be resisted by the strain gauge 40 having a higher resistanceO
Thus the signals in the signal connection wire 50 ~ will be high and the signal in the connection wire 52 will be low, and current will flow~
It will of course be appreciated that the nominal resistances of the strain gauges themselves may be in the ;i xegion of this type of case, for example 350 ohms. Achange of one or two ohms upwardly and one or two ohms downwardly, ~etween respective gauges 38 and 42, and between respective gauges 40 and 44, will be proportional to the degree of deflection of the tongue 24 in response to the for¢e.
However, in the design of such strain gauges, even j these relatively minor changes in resistance, will provide a direct read out of the actual load applied to the tongue.
Signal reading equipment such as digital read out .
2~3~
devices or moving coil devices, at the present time, are entirely adequate to detect such changes, and will provide an accurate read out of the actual load, over all reasonable working ranges of a particular device.
Referring again to Figure 4, it will be seen that the tongue 24 when subjected to a load, is deflected in an S-shape in sections. The tonyue ~4 behaves in this way due to the characteristics of the metal, and the formation of the grooves 30 and 32.
~eferring now to Figures 5 and Z, it will be seen that the load sensing assembly as illustrated in Figure 1, may be applied to the forXs of a pallet truck - indicated generally as 60. Typically such a pallet truck will have a pair of forks 62-62, connected to a cross-frame 64. The cross-frame 64 may be connected to a heavy duty pallet truck and prime mover (not shown). Howe~er, in the present case the cross member 64 is conn~cted simply to an operating handle 66. Wheels 68-68 are locat~d underneath the forks 62-62, and further wheels 72 are located underneath the cross members 6~. By use of suitable controls on the handle 66 (not shown) the forks may be first of all inserted underneath the clearance beneath a typical pallet (not shown) and the forks may then be raised, so that they lift the pallet off the floor. The pallet is then rendered mobile, and can be dragged by operation of a handle 66, while being supported on the fork 62.
All of this is well-known in the art, and requires - ~
..
3 ~ ~
no special description.
For the purposes of the present invention however load lifting assemblies 10, as illustrated in Figure 1, are incorporated in each of the forks 62.
Reference may be made to Figure 7, showing the cross-section Qf one of the forks 62. It will be seen to comprise a first channel portion, comprising side walls 72-72, and a cross-member 74, and a second channel comprising side walls 76-76 and a cross-member 78.
The side walls 72 72 will be seen to support the wheels 68.
Located beneath the cross wall 74, extending between the side walls 72, there is located the load sensing assembly 10. The load sensing assembly 10 is secured by bolts (not shown) or other suitable attachment devices, and extends the length of the cxoss member 74.
Cross wall 76, is formed with an opening 84, registering with stud 35 on tongue 24~
The top of stud 34 is generally dome-shaped, and ~0 engages the underside of cross wall 80.
Thus when a load is applied to the forks 62 of the pallet truck~ the load first of all sits on the cross walls 80. Since there are four load sensing units 16, one at each end of each bar 10, the load is thus shared i between the four load sensiny units.
At the same time, it will be appreciated that the load sensing assemblies 10, extend substantially the full length of the cross walls 76, and substantially reinforce ~15--' -. ~
. . ~ , .
2 ~ ~ ~ 3 ~ ~
the same rendering them rigid from end to end. This is an important feature of the invent.ion, since if any flexing takes place, when a load is applied to the forks, the load sensing units will not provide an accurate read out.
For the sake of the convenience of the operator, a pedestal 86 is secured on cross member 64 of the pallet truck 60. On top of the pedestal 86, there is an instrument panel 88. The instrument panel 88 will contain any suitable signal responsive equipment : indicated generally as 90. The operator when loading the pallet truck will thus immediately be given an accurate reading o the load.
The operation of the devices is believed to be self-evident from the foregoing description.
The foregoing is a description of a preferred embodiment of the invention which is given here by way of I example only. The invention is not to be taken as limited to any of the specific features as described, but comprehends all such variations thereof as come within the scope of the ap~ended claims.
' .- ~ , :
Claims (11)
1. A load sensing unit which in turn comprises;
a plate member adapted to be secured in position, in a load supporting apparatus;
a tongue portion connected to said plate portion;
a plurality of load sensing gauges secured to said tongue portion, at least two of said gauges being adapted to be placed in tension by a load on said tongue portion, and at least two of said gauges being adapted to be placed in compression by a said load on said tongue portion;
electrical connection means connecting said gauges, whereby said gauges in tension, are connected in series with said gauges in compression on opposite sides of a bridge circuit;
load bearing means on said tongue means, whereby a load may be applied to said tongue means, to cause deflection thereof, deflection of said tongue means in turn placing at least two of said strain gauges in tension, and at least two of said strain gauges in compression;
electrical circuit means connected to said bridge circuit, whereby to receive signals from said strain gauges, and, signal responsive means responsive to signals from said strain gauges, whereby to detect signals from said strain gauges in tension, and whereby to detect signals from said strain gauges in compression, and to generate load signals responsive thereto.
a plate member adapted to be secured in position, in a load supporting apparatus;
a tongue portion connected to said plate portion;
a plurality of load sensing gauges secured to said tongue portion, at least two of said gauges being adapted to be placed in tension by a load on said tongue portion, and at least two of said gauges being adapted to be placed in compression by a said load on said tongue portion;
electrical connection means connecting said gauges, whereby said gauges in tension, are connected in series with said gauges in compression on opposite sides of a bridge circuit;
load bearing means on said tongue means, whereby a load may be applied to said tongue means, to cause deflection thereof, deflection of said tongue means in turn placing at least two of said strain gauges in tension, and at least two of said strain gauges in compression;
electrical circuit means connected to said bridge circuit, whereby to receive signals from said strain gauges, and, signal responsive means responsive to signals from said strain gauges, whereby to detect signals from said strain gauges in tension, and whereby to detect signals from said strain gauges in compression, and to generate load signals responsive thereto.
2. A load sensing unit as claimed in claim 1 comprising an elongated bar of metal, said elongated bar of metal having a said load sensing unit located at each end thereof.
3. A load sensing unit as claimed in claim 1 and incorporating groove means formed in said tongue means transversely thereof, and electrical connection means extending between said strain gauges, running in said groove means, and further incorporating connection groove means in a portion of said plate means, for containing electrical connections from said strain gauges, to said signal responsive means.
4. A load sensing unit as claimed in Claim 3 and wherein there are two said groove means extending transversely of said tongue means, and wherein there are four said load sensing gauges, a first pair of said load sensing gauges being located in a first one of said groove means and a second pair of said load sensing gauges being located in a second one of said groove means, and connection channel means extending between said first and second groove means, for connecting said first and second pairs of strain gauges.
5. A load sensing unit as claimed in Claim 3 and further including an abutment device connected to said tongue means, and adapted to extend upwardly of said tongue means, for engagement by a load or mass.
6. A load sensing unit as claimed in Claim 3 and wherein said tongue means, when subjected to a load, is adapted to place said first pair of strain gauges in tension, and is adapted to place said second pair of strain gauges in compression, when subjected to a load on said tongue means.
7. A pallet truck, adapted to lift a pallet, and wherein said pallet truck incorporates at least two forks adapted to be inserted under a pallet, and including a plurality of load sensing unit as claimed in Claim 1 incorporated in said forks.
8. A pallet truck as claimed in Claim 7 wherein said forks are formed of generally channel-shaped construction, having webs with upper and under sides, and side walls extending downwardly from said webs, and wherein said load sensing units are secured to said under sides of said webs between said channel walls, and including opening means in said webs, and said abutment devices on said load sensing units extending upwardly through said webs, whereby to receive a load on said forks.
9. A pallet truck, as claimed in Claim 8 wherein said forks have a predetermined length, and including load sensing assemblies extending for a substantial portion of said length, and having said load sensing units and abutment devices on each end of each of said load sensing assemblies, whereby there are four said load sensing units, and four said abutment devices extending upwardly through said webs, thereby engaging a said pallet at four points.
10. A pallet truck as claimed in Claim 9 wherein said forks are made of sheet metal, and wherein said load sensing assemblies are formed of rigid elongated bars of metal, said rigid elongated bars of metal being bolted to the underside of respective said webs, whereby substantially reinforcing the same, and eliminating flexing of said forks due to loads placed thereon.
11. A pallet truck, as claimed in Claim 10 including instrument panel means supported at one end thereof, and electrical connection means connected between said load sensing units and said instrument panel means, whereby said instrument panel means is adapted to provide a visual indication of the load on said forks, when a pallet is supported thereon.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2068395 CA2068395A1 (en) | 1992-05-11 | 1992-05-11 | Load sensor and pallet truck incorporating the same |
| PCT/CA1993/000196 WO1993023723A1 (en) | 1992-05-11 | 1993-05-10 | Load sensor and load carrying apparatus |
| AU40553/93A AU4055393A (en) | 1992-05-11 | 1993-05-10 | Load sensor and load carrying apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2068395 CA2068395A1 (en) | 1992-05-11 | 1992-05-11 | Load sensor and pallet truck incorporating the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2068395A1 true CA2068395A1 (en) | 1993-11-12 |
Family
ID=4149815
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2068395 Abandoned CA2068395A1 (en) | 1992-05-11 | 1992-05-11 | Load sensor and pallet truck incorporating the same |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU4055393A (en) |
| CA (1) | CA2068395A1 (en) |
| WO (1) | WO1993023723A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2304597A1 (en) * | 1998-07-28 | 2000-02-10 | Citizen Watch Co., Ltd. | Weighing scale |
| DE10227442A1 (en) | 2002-06-20 | 2004-01-08 | Mitsubishi Polyester Film Gmbh | Multi-layer, transparent, film made of polyethylene terephthalate (PET) and polyethylene naphthalate PEN) for the production of composite packaging with UV protection |
| DE10227440A1 (en) | 2002-06-20 | 2004-01-08 | Mitsubishi Polyester Film Gmbh | Multi-layer, transparent, film made of PET and PEN with at least one functional outer layer for the production of composite packaging with UV protection |
| DE10227439A1 (en) | 2002-06-20 | 2004-01-08 | Mitsubishi Polyester Film Gmbh | Transparent film made of PET and PEN with UV protection, process for their production and use in packaging with an extended service life |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4506746A (en) * | 1982-09-27 | 1985-03-26 | Hottinger Baldwin Measurements, Inc. | Gaged plate transducer weighing apparatus |
| DE3562110D1 (en) * | 1984-05-18 | 1988-05-11 | Pietzsch Ludwig Gmbh & Co | Wheel load measuring device |
| CA1249611A (en) * | 1984-10-05 | 1989-01-31 | Franz Balduin | Weighing device |
| US4848493A (en) * | 1988-10-20 | 1989-07-18 | Revere Corporation Of America | Load sensing structure for weighing apparatus |
| US4899840A (en) * | 1989-06-22 | 1990-02-13 | Boubille Jacques C | Apparatus for weighing a pallet with a load thereon for use with a vehicle having tines or the like |
-
1992
- 1992-05-11 CA CA 2068395 patent/CA2068395A1/en not_active Abandoned
-
1993
- 1993-05-10 WO PCT/CA1993/000196 patent/WO1993023723A1/en active Application Filing
- 1993-05-10 AU AU40553/93A patent/AU4055393A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO1993023723A1 (en) | 1993-11-25 |
| AU4055393A (en) | 1993-12-13 |
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| EEER | Examination request | ||
| FZDE | Dead |