A conveyor-mounted weighing apparatus is designed to eliminate any possible influence brought about by a rotational load, generated as a result of eccentric motion of at least one roller forming a part of a conveyor unit, on a weight measurement. The conveyor-mounted weighing apparatus includes a first load detector for detecting the weight of an article to be weighed then being transported by the conveyor unit and for outputting a first load signal, a second load detector for detecting a horizontally acting load imposed on the conveyor means and for outputting a second load signal, and a calculating unit for shifting a phase of the second load signal outputted from the second load detector and subtracting the phase-shifted second load signal from the first load signal outputted from the first load detector to thereby eliminate a noise component brought about by the conveyor unit.

BACKGROUND OF THE INVENTION 
1. (Field of the Invention) 
The present invention generally relates to a conveyor-mounted weighing 
apparatus of a type incorporated in a conveyor for weighing a load being 
transported by the conveyor. 
2. (Description of the Prior Art) 
A conveyor-mounted weighing apparatus is well known in the art. An example 
of the prior art conveyor-mounted weighing apparatus is shown in FIGS. 4 
and 5 which illustrate the conveyor-mounted weighing apparatus in a 
schematic side representation and a signal processing circuit used 
therein, respectively. Referring first to FIG. 4, the prior art 
conveyor-mounted weighing apparatus includes a conveyor means 8 for 
transporting an article 11 to be weighed and a load cell 10 for detecting 
the weight of the article 11 being transported by the conveyor means 8. 
The conveyor means 8 includes a generally horizontally extending frame 1 
mounted on a base structure 5 and having driven and drive rollers 2 and 3 
rotatably mounted respective opposite ends of the frame 1, a generally 
endless transport belt 4 trained around the rollers 2 and 3 so as to 
extend therebetween, and a drive motor 6 fixedly mounted on the base 
structure 5 and drivingly coupled with the drive roller 3 by means of a 
generally endless drive belt 7 for driving the endless transport belt 4 in 
one direction shown by the arrow A. The load cell 10 of a generally 
rectangular configuration having a longitudinal axis and including a fixed 
rigid body and a load bearing body (movable rigid body) opposite to each 
other along the longitudinal axis thereof is mounted on an upright support 
leg structure 9 with the fixed rigid body thereof secured to the support 
leg structure 9 and with the load bearing body secured to the base 
structure 5 of the conveyor means 8 while the longitudinal axis of the 
load cell 10 is laid substantially horizontally, i.e., transverse to the 
support leg structure 9. 
The prior art conveyor-mounted weighing apparatus of the structure 
described above operates in the following manner. The article 11 to be 
weighed having been delivered onto the transport belt 4 at a location 
adjacent the driven roller 2 is, during travel of the transport belt 4, 
transported in the direction shown by the arrow A, then weighed by the 
load cell 10 and finally ejected from the transport belt 4 at a location 
adjacent the drive roller 3. 
The load cell 10 employed in the prior art conveyor-mounted weighing 
apparatus is of a type comprising a strain inducing element incorporating 
the Roberval's parallel motion mechanism and having a plurality of strain 
gauges 12 disposed on a surface thereof. As shown in FIG. 5, this load 
cell 10 detects the weight of the articles 11 to provide a load signal 
which is subsequently amplified by a pre-amplifier 13. The amplified load 
signal emerging from the pre-amplifier 13 is converted by an 
analog-to-digital (A/D) converter 14 into a digital load signal which is 
subsequently supplied to a low-pass filter 15 employed in the form of a 
digital low-pass filter operable to remove a high frequency noise 
component from the digital load signal. The digital load signal outputted 
from the low-pass filter 15 is then supplied to a zero-point adjusting 
means 16 where zero-point adjustment is effected to the digital load 
signal. The zero-point adjusting means 16 finally outputs a weight signal 
indicative of the weight of the article 11. 
The prior art conveyor-mounted weighing apparatus of the structure 
described above has some problems. Specifically, since the drive and 
driven rollers and the drive motor are being driven to transport the 
article to be weighed, occurrence of an eccentric motion in one or both of 
the drive and driven rollers is accompanied by a rotational load which is 
transmitted to the load cell 10. Once this occurs, the load cell 10 
outputs the load signal containing a noise component attributable to the 
rotational load resulting from such eccentric motion and, therefore, the 
weighing accuracy of the weighing apparatus as a whole tends to be 
reduced. 
To lessen the rotational load brought about in the conveyor means, a 
balance adjustment for the purpose of eliminating the eccentric motion of 
the rollers which is considered an influential cause is carded out in the 
prior art conveyor-mounted weighing apparatus, but a complete balancing is 
difficult to achieve. 
The use of a band-pass filter may be contemplated to eliminate the noise 
component contained in the load signal outputted from the load cell. 
However, since the noise component to be eliminated is a low frequency 
component, the response of the band-pass filter is apt to be delayed and, 
in addition, when the transport speed at which the article is transported 
by the conveyor means is modified, a filter characteristics must also be 
changed, resulting in complicated and time-consuming handling. 
SUMMARY OF THE INVENTION 
Therefore, the present invention has been devised with a view to 
substantially eliminating the above discussed problems and is intended to 
provide an improved conveyor-mounted weighing apparatus which is easy to 
handle and, also, which is effective to secure a high weighing accuracy by 
assuredly eliminating an influence brought about on the weight measurement 
by the rotational load occurring in the conveyor means. 
In order to accomplish this object, the present invention provides a 
conveyor-mounted weighing apparatus which comprises a conveyor means 
including a plurality of rotating rollers for transporting an article to 
be weighed; a first load detector for detecting a weight of the article 
then being transported by the conveyor means and for outputting a first 
load signal; a second load detector for detecting a horizontally acting 
load imposed on the conveyor means and for outputting a second load 
signal; and a calculating means for shifting a phase of the second load 
signal from the second load detector and subtracting the phase-shifted 
second load signal from the first load signal from the first load detector 
to thereby eliminate a noise component brought about by the conveyor 
means. Preferably, the phase of the second load signal is shifted 
90.degree. relative to that of the first load signal. 
According to the present invention, the horizontally acting load imposed on 
the conveyor means is detected by the second load detector which provides 
the second load signal. This second load signal is shifted, for example, 
90.degree. in phase relative to the phase of the first load signal 
outputted from the first load detector and is then subtracted from the 
first load signal. By so doing, the noise component incident to drive of 
the conveyor means, particularly the noise component attributable to the 
rotational load brought about by eccentric motion of at least one roller 
forming a part of the conveyor means, can be eliminated effectively. For 
this reason, any possible error in weight measurement is advantageously 
avoided to attain a highly accurate weight measurement. In addition, even 
though the transport speed exhibited by the conveyor means is changed, no 
adjustment work including adjustment of filters is needed which would 
otherwise be required, rendering the weighing apparatus as a whole to be 
easy to handle. 
Each of said first and second load detectors has a fixed rigid body and a 
load bearing body. The fixed rigid body of the second load detector is 
preferably supported on the load bearing body of the first load detector 
and the conveyor means is preferably supported on the load bearing body of 
the second load detector. This arrangement is particularly advantageous in 
that a load detector unit of the conveyor-mounted weighing apparatus, 
including the first and second load detectors, can be assembled compact. 
Again, a cell sensitivity adjusting means is preferably disposed in a stage 
preceding the calculating means for compensating for a difference in 
sensitivity between the first and second load signals. The use of the cell 
sensitivity adjusting means is advantageous in that, since the difference 
between the cell sensitivity of the first load signal and the cell 
sensitivity of the second load signal can be compensated for, elimination 
of the noise component can be achieved effectively and precisely.

DETAILED DESCRIPTION OF THE EMBODIMENT 
A conveyor-mounted weighing apparatus embodying the present invention is 
generally similar to the prior art conveyor-mounted weighing apparatus so 
long as like reference numerals used in FIG. 4 in connection with the 
prior art conveyor-mounted weighing apparatus are also employed in FIG. 1 
in connection with the conveyor-mounted weighing apparatus of the present 
invention. However, the conveyor-mounted weighing apparatus of the present 
invention makes use of two load cells (load detectors) 10 and 19 which are 
interposed between the base structure 5 and the support leg structure 9 in 
a manner which will now be described. 
Referring now to FIG. 1, the first load cell 10 is comprised of a first 
strain inducing element of a generally rectangular configuration including 
a fixed rigid body 10a and a load bearing body (movable rigid body) 10b 
spaced from each other along a first longitudinal axis C1 of the first 
strain inducing element, but connected together by means of beams 10c 
extending parallel to the longitudinal axis C1. Similarly, the second load 
cell 19 is comprised of a second strain inducing element of a generally 
rectangular configuration including a fixed rigid body 19a and a load 
bearing body (movable rigid body) 19b spaced from each other along a 
second longitudinal axis C2 of the second strain inducing element, but 
connected together by means of beams 19c extending parallel to the 
longitudinal axis C2. 
The first load cell 10 is mounted on the support leg structure 9 with the 
fixed rigid body 10a secured fixedly to the support leg structure 9 so as 
to be oriented substantially horizontally with the first longitudinal axis 
C1 thereof lying perpendicular to the support leg structure 9. The second 
load cell 19 is supported by the first load cell 10 by means of an angled 
coupling piece 20 having right-angled side faces coupled respectively to 
the load bearing body 10b of the first load cell 10 and the fixed rigid 
body 19a of the second load cell 19. With the second load cell 19 so 
supported, the second load cell 19 is oriented substantially vertically 
with the second longitudinal axis C2 thereof lying perpendicular to the 
first longitudinal axis C1 of the first load cell 10 while the load 
bearing body 19b thereof is coupled with the base structure 5. Thus, the 
load cell assembly represents a generally L-shaped configuration with the 
first and second load cells 10 and 19 occupying respective positions of 
transverse and upright arms of the shape of a figure "L". 
Each of the first and second load cells 10 and 19 comprises a so-called 
Roberval's parallel motion mechanism which is effective to generate a 
strain of a magnitude proportional to a load acting thereon in a direction 
transverse to the first or second longitudinal axis C1 or C2 and in which 
generation of a strain resulting from the bending moment is suppressed. It 
is to be noted that the strain inducing element constituting the 
respective load cell may not be of the shape as shown, but may be of any 
suitable shape so long as each of the load cells which can be employed in 
the practice of the present invention comprises the Roberval's parallel 
motion mechanism. 
Each of the first and second load cells 10 and 19 is so designed and so 
structured that the strain induced in the strain inducing element thereof 
can be detected by the strain gauges 12 and a load signal proportional to 
the magnitude of the strain so detected is outputted from a respective 
bridge circuit (not shown) including the strain gauges 12. 
Of them, the first load cell 10 is operable to measure the total weight of 
the conveyor means 8, the second load cell 19, the angled connecting piece 
20 and the article 11 to be weighed which is being transported by the 
endless transport belt 4. On the other hand, the second load cell 19 is 
operable to detect a horizontal component of the rotational load acting on 
the conveyor means 8. 
The principle of counterbalancing the rotational load imposed by the 
eccentric motion of the driven and drive rollers 2 and 3, that is 
accomplished in accordance with the present invention, will now be 
discussed. Referring to FIG. 2A, assuming that the center of gravity of 
each of the driven and drive rollers 2 and 3 is displaced a quantity r 
from the respective longitudinal axis O thereof, a centrifugal force f, 
expressed by the following formula, acts on the conveyor means 8 as a 
rotational load: 
EQU f=m.multidot.r.multidot..omega..sup.2 
wherein m represents the mass of the respective roller 2 or 3 and .omega. 
represents the angular velocity of rotation of the respective roller 2 or 
3. A component of the rotational load f acting in a vertical direction, 
that is, a vertical component fV of the rotational load f, is represented 
by a signal having such a phase as shown in FIG. 2B and which is detected 
by the first load cell 10. 
On the other hand, a component of the rotational load f acting in a 
horizontal direction, that is, a horizontal component fH of the rotational 
load f, is represented by a signal having such a phase as shown in FIG. 2C 
and which is detected by the second load cell 19. This horizontal 
component fH is a signal having a phase advanced 90.degree. relative to 
that of the signal representative of the vertical component fV detected by 
the first load cell 10. Accordingly, if a signal delayed 90.degree. in 
phase from that of the vertical component fV detected by the first load 
cell 10 is subtracted from a first load signal w1 outputted from the first 
load cell 10, a noise component brought about by the rotational load of 
the driven and drive rollers 2 and 3 can be eliminated effectively. 
It is to be noted that the difference in phase between the signal 
representative of the horizontal component fH and the signal 
representative of the vertical component fV may not be always limited to 
90.degree. such as described above, but may be of a value smaller than 
90.degree. and, even in this case, the noise component can be eliminated 
to some extent. 
Referring now to FIG. 3, there is shown a block circuit diagram of a signal 
processing circuit designed to utilize the above discussed 
counterbalancing principle in accordance with the present invention. The 
first load signal w1 outputted from the first load cell 10 is, after 
having been amplified by a first pre-amplifier 13, converted by a first 
analog-to-digital (A/D) converter 14 into a first digital load signal 
which is subsequently filtered through a first low-pass filter 15, 
employed in the form of a digital low-pass filter, to remove a high 
frequency noise component resulting from a mechanical vibration taking 
place predominantly in the conveyor means 8. 
On the other hand, a second load signal w2 outputted from the second load 
cell 19 is, after having been amplified by a second pre-amplifier 21, 
converted by a second analog-to-digital (A/D) converter 22 into a second 
digital load signal which is subsequently supplied to a second low-pass 
filter 23 where a low frequency component mainly associated with the cycle 
of rotation of the driven and drive rollers 2 and 3 is filtered out. 
The second load signal w2 having passed through the second low-pass filter 
23 is supplied to a sensitivity adjusting means 25 so that a cell 
sensitivity can be corrected. In general, the relative magnitude of an 
output (a load signal) given by a load cell to a load imposed thereon, 
that is, the cell sensitivity, varies from one load cell to another. 
Accordingly, assuming that the cell sensitivities of the first and second 
load cells 10 and 19 are expressed by .alpha. and .beta., respectively, 
multiplication of the second load signal w2 by .beta./.alpha. compensates 
for a difference between the respective cell sensitivities of the first 
and second load cells 10 and 19, making it possible to equalize the level 
of the second load signal w2 to that of the first load signal w1 with 
respect to the same load. In this way, subtraction of the first and second 
load signals w1 and w2 as will be discussed later is accomplished 
accurately enough to bring about an improvement in weighing accuracy. 
The second load signal w2 to which the cell sensitivity adjustment has been 
effected by the sensitivity adjusting means 25 in the manner described 
above is then supplied to a calculating means 27. This calculating means 
27 includes a phase shifter 28 and a subtractor 29. The second load signal 
w2 supplied from the sensitivity adjusting means 25 to the phase shifter 
28 is delayed 90.degree. in phase relative to that of the first load 
signal w1 by the phase shifter 28 and is subsequently subtracted by the 
subtractor 29 from the first load signal w1. In this way, the noise 
component of the conveyor means 8 brought about by the rotational load of 
the driven and drive rollers 2 and 3 is eliminated effectively. It is to 
be noted that, where the orientation of a positive value of the horizontal 
component fH detected by the second load cell 19 is in a leftward 
direction which is counter to that shown in FIG. 2A (i.e., in a direction 
counter to the direction A of transport shown in FIG. 1), this horizontal 
component fH is delayed 90.degree. in phase relative to the vertical 
component fV and, therefore, the phase of the horizontal component fH must 
be advanced 90.degree. relative to that of the vertical component fV by 
the phase shifter. 
The first load signal cw1 which has been corrected in the manner described 
above to remove the noise component of the conveyor means 8 is supplied to 
a zero-point adjusting means 16 where a zero-point adjustment, that is, an 
adjustment of the level with respect to a zero-point represented by the 
level of the corrected first load signal obtained when no article 11 to be 
weighed is placed on the endless transport belt 4, is effected to the 
corrected first load signal cw1. After this zero-point adjustment, a 
weight signal indicative of the weight of the article 11 being transported 
is outputted from the zero-point adjusting means 16. 
As hereinbefore described, the noise component of the conveyor means 8 
brought about by the eccentric motion of the driven and drive rollers 2 
and 3 is effectively eliminated from the first load signal w1 
corresponding to the weight of the article 11 outputted from the first 
load cell 10 and, therefore, the weighing accuracy of the weighing 
apparatus can be increased. Moreover, even though the transport speed, 
that is, the speed of rotation of the driven and drive rollers 2 and 3, 
changes in accordance with the change of type of the article 11, no 
adjusting work is needed which would otherwise be required to adjust 
components of the weighing apparatus including adjustment of the filters 
15 and 23, rendering the weighing apparatus as a whole easy to handle. 
Furthermore, since the fixed rigid body 19a of the second load cell 19 is 
mounted on the load beating body 10b of the first load cell 10 and the 
conveyor means 8 is supported on the load bearing body 19b of the second 
load cell 19, the first and second load cells 10 and 19 are held in 
respective positions approaching each other and, therefore, the load cell 
assembly including the first and second load cells 10 and 19 can be 
assembled compact. 
Although the present invention has been fully described in connection with 
the preferred embodiments thereof with reference to the accompanying 
drawings which are used only for the purpose of illustration, those 
skilled in the art will readily conceive numerous changes and 
modifications within the framework of obviousness upon the reading of the 
specification herein presented of the present invention. For example, 
although in the illustrated embodiment of the present invention the 
conveyor means has been shown in which the endless transport belt is 
driven by the rollers for transporting the articles to be weighed, any 
other conveyor means such as, for example, a roller conveyor comprising a 
plurality of juxtaposed rollers adapted to be driven to transport the 
article to be weighed, may be equally employed in the practice of the 
present invention without substantially sacrificing the effects brought 
about by the present invention. 
Accordingly, such changes and modifications are, unless they depart from 
the scope of the present invention as delivered from the claims annexed 
hereto, to be construed as included therein.