Mass flow measurement in forage harvesters

A forage harvester is equipped with a device for measuring the mass flow rate of the crop material processed by the machine. The device comprises a sensor member having a curved surface which is mounted for pivotment in an aperture in the spout of the harvester. The moment resulting from the mass flow is measured by a transducer. A resilient sealing is provided between the sensor member and the spout.

FIELD OF INVENTION 
This invention relates to a device for measuring the mass flow of bulk 
material, such as the flow of comminuted crop material in the spout of a 
forage harvester. More particularly it relates to apparatus comprising a 
sensor surface installed in a channel in which a streamline flow of the 
crop material is established. 
BACKGROUND OF INVENTION 
It is already known in the art to equip agricultural harvesters with 
apparatus for establishing the mass flow rate of crop material in order to 
gather data on the amount of harvested material over a time period and on 
the local yield rate in distinct areas of a field. Such apparatus has 
already been described with respect to combine harvesters in U.S. Pat. No. 
5,343,761 and European Pat. No. EP-A-0 501 099. In U.S. Pat. No. 5,343,761 
the mass flow rate is derived from the measurement of the forces resulting 
from the impact of grain kernels on a vertical plate which is installed in 
a clean grain elevator. The left and right edges of the impact plate are 
spaced from the elevator walls to prevent lodging of material other than 
grain between these edges and the walls. Consequently small particles may 
reach the area behind the impact plate and accumulate on the rear of the 
plate, thereby affecting the zero load of the apparatus and distorting the 
mass flow readings. Such apparatus requires cleaning at regular intervals. 
The apparatus disclosed in European EP-A-0 501 099 uses variations in 
capacitance caused by a flow of grain to establish the momentary flow 
rate. This device comprises no movable sensor portions whereof the 
displacement under action of the mass flow is measured. 
Another type of measuring device is shown in European Pat. No. EP-A-0 753 
720. Herein the flow of crop material is guided along a curved surface 
which is mounted for pivotment about a transverse axis. A gap is provided 
between the curved surface and the housing of the grain elevator to enable 
free oscillation of the surface in its normal measurement range. The inlet 
section of the surface has to be dimensioned slightly larger than the 
dimension of the outlet of the grain elevator to preclude false readings, 
caused by impact on the edge, and loss of conveyed crop material. In the 
forage harvester illustrated in the same publication a sensor member for 
monitoring the mass flow rate has been installed in an aperture in the 
spout. The inlet portion of the sensor member is installed over the front 
edge of the aperture and its outlet portion extends over the rear edge of 
the same aperture in order to maintain all material within the spout. The 
gap between the body of the spout and the sensor member is a critical area 
for pollution by stray material, as a plugging thereof will result in 
false readings of the measuring apparatus. 
SUMMARY OF THE INVENTION 
Hence, it is an object of the present invention to provide a mass flow 
measuring apparatus which on the one hand provides reliable mass flow rate 
readings and on the other hand is not susceptible to disturbances caused 
by stray material hampering the displacement of movable parts of the 
apparatus. 
According to the invention, an apparatus for measuring a mass flow rate of 
bulk material is provided, the apparatus comprising channel means, means 
for establishing a streamline flow of the bulk material along at least one 
guide surface of the channel means, a sensor surface installed in an 
aperture in the channel means, and at least one transducer for measuring a 
measurable quantity resulting from forces acting on the sensor surface, 
the forces comprising the force resulting from the flow of the processing 
crop material on the sensor surface. More particularly, it is contemplated 
that the sensor surface is installed in substantial alignment with the 
guide surface, and sealing means are provided between the outer rim of the 
sensor surface and the inner rim of the aperture in the channel means.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a typical forage harvester 101 comprising a main frame 102 to 
which are mounted ground engaging traction wheels 104 and steering wheels 
105. The forage harvester is shown equipped with a row crop attachment 
109, suitable for the harvesting of corn, but which can be replaced with 
another type of attachment, depending on the type of crop to be harvested. 
The row crop attachment delivers the crop material to crop comminuting 
means installed in a front unit 110 of the forage harvester 101. The 
processed crop material is delivered to a blower rotor 111 which is 
installed within a blower housing, attached to the main frame 102. The 
blower rotor 111 throws said material upwardly into a discharge means 112, 
comprising a straight tube 113 and a curved discharge spout 114, which can 
be positioned by an operator to direct the cut crop material as required, 
normally into a wagon which is moving alongside or behind the forage 
harvester. The outlet direction of the spout is controlled by rotation of 
the tube 113 and extension or retraction of a hydraulic cylinder 116. 
Inside the spout 114 the crop is guided along channel means comprising a 
lower wear plate 118 and an upper wear plate 119. The wear plates 118, 119 
are U-shaped in cross section and are mounted by bolts to the back of the 
spout 114 for easy replacement when they are worn out. 
As indicated in European Pat. No. EP-A-0 753 720, the operator may want to 
assess the actual mass flow rate of the forage crop during normal 
harvesting operations. To this end a flow measurement device 121 is 
installed on the spout 114. A substantially rectangular aperture is 
provided in the curved top plate of the spout 114, between the wear plates 
118, 119. This aperture is closed by a sensor assembly, comprising a 
curved sensor member 151 having a U-shaped cross section generally equal 
to the cross section of the wear plates 118, 119. The sensor member 151 is 
held in alignment with the channel means by a pair of support arms 160, 
attached via an extension 187 to the middle portion of the sensor member 
151 and mounted for pivotment to a pair of upright brackets 162 extending 
from the lower half of the spout 114. The inlet portion of this sensor 
member 151 registers with the outlet portion of the lower wear plate 118 
and the inlet portion of the upper wear plate 119 registers with the 
outlet portion of the sensor member 151. Preferably, the curvatures of 
both wear plates 118, 119 are equal in the areas adjacent the aperture and 
the curvature of the sensor member 151 is equal thereto. In this manner 
the flow of forage material in the spout 114 is not hampered by the 
transitions from the lower wear plate 118 to the sensor member 151 and 
from the sensor member 151 to the upper wear plate 119. 
The sensor assembly further comprises a counterweight 165 provided at the 
front end of the support arms 160, for bringing the center of gravity of 
the sensor assembly to its pivot axis P. Because of this arrangement the 
zero load on the sensor member 151 will not be affected by changes in 
inclination of the spout 114. 
As shown in FIG. 4, L-shaped profiles 169 are welded to both sides of the 
sensor member 151. These profiles are put to rest on a pair of 
longitudinal strips 170, which are held in reardwardly extending profiles 
172 welded to the sides of the spout 114. The strips 170 are made of 
resilient, preferably impermeable material, such as rubber or closed-cell 
polyvinylchloride or polyurethane foam. The strips 170 seal the 
longitudinal gap between the sides of the sensor member 151 and the spout 
114. 
The transverse gaps between the rear and front edges of the sensor member 
151 and the lower and upper wear plates 118, 119 are sealed by a pair of 
transverse strips 174, made out of the same material (FIG. 5). The strips 
174 are held in place by inverted U-profiles 175 extending transversely 
over the transitions from the wear plates 118, 119 to the curved sensor 
member 151. A pair of bolts 177 extending through holes in the outer 
portions of the profiles 175 connect these profiles to mounting lugs 178 
welded to the rear and front ends of the longitudinal profiles 169. 
The resilient strips 170, 174 permit a small pivotal movement of the sensor 
member 151 about its pivot P, while sealing the gaps between the outer rim 
of the sensor member and the edges of the aperture in the spout 114. 
A flow of crop material along the curved sensor member 151 forces the same 
upwardly. This upward force is sensed by a transducer, which may be a load 
cell 181 as illustrated in FIGS. 2 and 6. The load cell is attached at its 
top to a bracket 183 which is mounted over the sensor member 151 and to 
the side walls of the spout 114. An adjustment screw 184 extends 
downwardly from the load cell 181 against the extension 187 of the support 
arms 160. The screw 184 is adjusted to provide a small pre-load on the 
load cell 181 and then is secured in place by a lock nut 185. 
The total force acting on the sensor member 151 is the resultant of 
centrifugal, friction and gravity forces from the crop material as it 
flows along the curved surface of the sensor. By proper design of the 
sensor assembly as described in European Pat. No. EP-A-0 753 720, it is 
possible to balance the effects of friction on these forces, such that the 
resultant is substantially independent of changes in friction coefficient. 
This is particularly important in forage harvesters, which have to process 
a wide range of products, such as grass, alfalfa or corn, under a wide 
range of weather conditions. For instance, it is not uncommon to continue 
harvesting operations while it has started raining. 
A satisfactory embodiment comprised a sensor member 151 having a curvature 
radius of 2550 mm and a length D2 of 490 mm (FIG. 3). The pivot P is 
located at a radius 2652 as seen from the center of curvature of the 
sensor member and at an angle .alpha.=-4.824.degree. from its inlet edge. 
The distance D1 from this inlet edge to the pivot P is 240 mm. In the 
intermediate position of the spout 114, the inlet is at an angle of 
51.50.degree. to the horizontal. The force readings generated by this 
configuration are not dependent on the friction coefficient of the forage 
material on the wear plate 118 and the sensor member 151. The 
counterweight 165 is mounted at a distance D3 of 450 mm from the pivot P. 
The front edge of the sensor member 151 is at about 1 m from the inlet of 
the spout, such that the material flow has time to adapt to the form of 
the lower wear plate 118. No further guide plate is needed for 
conditioning the material flow into a streamline flow before the 
measurement can take place. 
It may be assumed that the velocity of the forage material in the spout 114 
does not vary much. However it may be advantageous to combine the reading 
of the transducer with the reading of a velocity sensor directed to the 
material flow adjacent or on the sensor member 151 in order to adjust the 
mass flow result for variations of the velocity. The velocity sensor may 
be directed to the lower side of the flow, but it has been found 
advantageous to direct it to the upper side of the flow, e.g. through an 
aperture in the spout 114 and a transparent section in the wear plate 118. 
Although the present invention has been described with respect to a forage 
harvester, it will be understood that other embodiments can be thought of 
without departing however from the original idea of the invention. For 
example, a similar mounting and sealing may be used for measuring the mass 
flow rate in a combine harvester or other types of agricultural machinery. 
The load cell may also be replaced with another type of transducer, such 
as a proximity sensor or by a torque sensor on the pivot shaft of the 
sensor assembly. 
While preferred structure in which the principles of the present invention 
are shown and described above, it is to be understood that the invention 
is not limited to such structure, but that, in fact, widely different 
means of varying scope and configuration may be employed in the practice 
of the invention.