Conveyor belt with combined belt guide and belt drive rollingly engaging belt on horizontal carrying run, between loading station and weighing station

A metering belt feeder for gravimetrically measuring a flow of material with the aid of an endless belt which includes a loading zone (10), a weighing zone (10) and a belt drive which is located between these two zones. The belt is caused to move in a plane above both the loading zone and the weighing zone. The belt drive means is constructed so as to draw the belt from the loading zone in the absence of belt-slipping and to project the belt over the weighing zone, and also so as to guide the belt against sideways movement.

BACKGROUND OF THE INVENTION 
The present invention relates to apparatus for producing a specific flow of 
bulk material from a storage container. By bulk material is meant 
particulate materials having particle sizes which range from powder 
granules to lump goods. The apparatus falls in the category of metering 
belt feeders. Such belt feeders comprise a conveyor belt and a funnel, or 
hopper, from which the material is drawn or from which the material runs 
onto an endless belt, and on which the material is weighed on a given part 
of the belt, prior to leaving the belt. 
The flow of material leaving the belt is controlled by adjusting the supply 
of material thereto or by adjusting belt speed. 
The most difficult problem associated with belt feeders is one of guiding 
the side-edges of the belt. This is primarily because the length of the 
belt conveyor generally is provided to be as short as possible, for 
process reasons of a technical nature. The material transported on initial 
parts of the belt causes changes in the geometry which provides stable 
belt movement in the starting position, due to which, after a time, the 
belt tends to wander sideways until it comes into contact with an 
obstruction of some kind or another. Lateral displacement of the belt, and 
particularly lateral displacement to such extreme positions, results in 
weighing errors. The problem is accentuated by the fact that a low belt 
tension is desired, so that the material can be weighed effectively. 
It is known that this problem can be alleviated by cambering the drive 
roller and by providing the roller with a high friction surface. Soiling 
of the belt and changes in belt properties due to changes in temperature 
and also to wear, necessitate constant monitoring of the conveyor belt. 
Also known to the art are mechanisms which influence lateral distribution 
of belt tension in an attempt to compensate for wandering of the belt. 
Such mechanisms are complicated and become soiled or dirty and therefore 
require constant inspection. 
With the intention of reducing belt tension over that part of the belt 
which moves over the weighing path, it is known from FR-A-2 145 366 to 
position the belt drive means between that part of the belt onto which the 
material is drawn or runs out onto the belt and that section of the belt 
on which the material is weighed. 
The position of the belt drive means presumes that the belt is caused to 
move over a longer, substantially horizontal plane in the weighing path 
than the remainder of the belt onto which the material is deposited. The 
belt is caused to form a loop between those planes with the aid of at 
least three guide rollers, the loop being so configured as to be able to 
draw tire material supplied to the belt down to the lower belt plane. A 
guide roller located at the lowest hang of the belt loop has the form of a 
belt-tensioning roller and one of these rollers functions to drive the 
belt. The tension roller imparts to the belt sufficient tension for the 
friction generated by the drive roller against the belt to drive the belt 
around the loop, and also determines the tension in that part of the belt 
which is located above the weighing path. These two forces produced by the 
tensioning roller are equally as large, and in order to prevent the belt 
from slipping on the drive roller, a significant degree of tension is 
induced in the belt, and even in the belt-section that is located over the 
weighing path, even though this tension is lower than the tension in that 
part of the belt which runs on the higher level. The fact that the 
transported material is caused to fall freely between the height levels 
means that collections of the material, and therewith coatings of material 
on the rollers and on the belt, will render positive function impossible 
with regard to belt movement and to weighing accuracy, a drawback which is 
particularly manifest in the case of small material flows which a low belt 
speed must be maintained in order to achieve weighing accuracy. The drive 
arrangement does not therefore provide a solution to the problem of belt 
control. 
SUMMARY OF THE INVENTION 
An object of the present invention is to eliminate the possibility of the 
belt of a belt feeder from wandering sideways and to reduce belt tension 
to almost zero over the weighing path. 
In the case of the belt feeder of the invention, the belt drive location is 
positioned between the feed funnel and the weighing path and is 
constructed to guide the belt uniformly and positively. This can be 
achieved, for example, by perforating the edges of the belt and by using a 
toothed drive wheel provided with corresponding teeth and placed between 
the belt parts, i.e. the top and bottom runs of the belt. The teeth can 
also be caused to engage the perforations in the bottom run of the belt. 
This arrangement will therefore lock the belt against sideways movement. 
The belt is drawn forwards beneath the feed funnel and is moved over the 
weighing path. During its movement beneath the funnel, the belt will 
entrain the material, from the funnel and the belt will not be tensioned 
or made taut as it passes along the weighing path. Alternatively, the 
drive means may include of a drive wheel which is placed between the belt 
parts and which is provided with a lateral shoulder or abutment which 
guides the edges of the belt. The arrangement may also include a pressure 
means in the form of a spring-loaded wheel which functions to urge the 
belt against the drive wheel, the drive wheel having a high friction 
surface around the circumference thereof. 
The material is preferably weighed by successively taking-up the load over 
the weighing path by a load measuring sensor or transducer along the 
weighing path, with maximum load-sensing being effected at the center of 
the weighing path and decreasing belt support from that center to the 
other end of the weighing path. This can be effected in a known manner 
with the aid of a load plate which is pivotally mounted at the load onfeed 
end and which extends along half the load measuring path and is supported 
by the load measuring sensor or transducer. Such an arrangement is found 
described, for instance, in SU-A-480 913. 
Alternatively, the load measuring sensor may be supported by a transversely 
extending cam or freely-rotating roller mounted in the center of the 
weighing path, the belt hanging freely between this support and the ends 
of the weighing path. The material may also be weighed in a known manner 
with the aid of a weighing plate which extends from the center of the 
weighing path towards the ends thereof, such that the belt will hang 
freely over a shorter distance of the weighing path at each end thereof, 
said plate being supported by the load measuring sensor in the center of 
the plate. An example of one such arrangement is found described in U.S. 
Pat. No. 3,363,585. Because the belt tension is very low, the conveyor 
frame can be made relatively weak. In order to eliminate the disadvantages 
of a relatively weak frame, the frame can be mounted on three support 
points, thereby eliminating intrinsic mechanical deformation. The 
arrangement may also be such as to enable the whole of the frame to be 
withdrawn laterally, so as to simplify cleaning of the belt feeder and 
belt-changing operations.

The invention will now be described with reference to FIGS. 1-10. 
FIG. 1 illustrates the principle construction of the arrangement. The 
conveyor belt 1 of the illustrated metering feeder is positioned between 
the rollers 2 and 3. A feed funnel 4 is mounted at one end of the feeder. 
The illustrated funnel is constructed for metering material 5 whose 
properties enable it to run gravitationally onto the belt. In other cases, 
the funnel is constructed so that a column of material will form on the 
belt and be drawn from the funnel over the belt. The rollers 2 and 3 are 
journalled at the ends of the frame 6. Also connected to the frame is a 
belt support plate 7. In the illustrated arrangement, a belt drive means 8 
is mounted on the right of the funnel. In the illustrated case, the drive 
means has the form of a wheel, but is constructed in a manner to drive the 
belt in a uniform direction in the absence of belt sliding and in a manner 
to hold the belt against sideways movement. Alternative embodiments are 
illustrated in remaining figures of the drawings. 
The support plate 7 extends slightly beyond the drive means in the belt 
parts direction, so as to leave the belt hanging freely up to the location 
of a cam 9 which extends transversely across the belt and which is the 
sole belt support up to the roller 3. The cam is instrumental in the 
measuring of the weight of the material on the belt and the weight of the 
belt along the weighing path 10. These weights are measured by a 
load-measuring sensor or transducer 11, which is preferably a resistive or 
magnetic type sensor. 
The frame 6 is placed on a supporting surface (not shown). The drive means 
8 is rotated via the drive belt 12 driven by a motor provided with a 
suitable gearbox 13. The rotational speed of the motor constitutes a 
measurement of belt speed and is measured by a tachometer 14. A control 
signal for the rotational speed of the motor is produced electronically 
with the aid of the weight signal produced by the load measuring sensor 
and also the belt speed. This enables the flow 15 of material from the 
belt feeder to be measured and controlled in a known manner, for example 
so as to achieve constant flow with time or to control the flow to a given 
magnitude with the aid of an external control signal. 
FIGS. 2 and 3 illustrate an embodiment of the drive means 8 shown in FIG. 
1. FIG. 2 is a side view of the arrangement and FIG. 3 shows the belt from 
above, solely at the right-hand belt edge. The drive wheel 16 is provided 
with a number of teeth 17 which engage in perforations or holes 23 (shown 
in FIG. 3), and the circumference of the wheel is positioned so as to be 
level with the underside of the belt 18, which is also supported by the 
support plate 19. The wheel 21 is mounted on the shaft 20 and is driven by 
the drive belt 22. 
The FIG. 3 embodiment includes a bearing housing 24 for the drive shaft 20 
and a number of holes 23, which conform to the teeth 17 with respect to 
size and hole spacing. Guiding of the belt can be improved by also 
mounting a drive wheel 16 on the shaft at the other edge of the belt, on 
the other side of the symmetry line 25-26, this edge also being provided 
with corresponding perforations or holes. With the intention of further 
improving guiding of the belt, the return side or bottom run 18' of the 
belt can be raised by means of a transversal arm 27 attached to the frame 
28 such that the teeth 17 on the drive wheel are also caused to engage in 
the holes or perforations 23. 
FIGS. 4 and 5 illustrate an alternative embodiment of the drive means 8 
shown in FIG. 1. FIG. 4 is a side view of the arrangement and FIG. 4 shows 
the belt from above and solely at the right-hand belt edge. The drive 
wheel 29 is provided with a flange 30 (shown in FIG. 5), and the wheel 
periphery is positioned so as to be level with the underside of the belt 
31, which is also supported by the support plate 32. The wheel 34 is 
mounted on the shaft 33 and driven by the drive belt 35. Mounted on the 
upper side of the belt 31 is a freely-rotating wheel 36, which is 
journalled on an arm 37, the other end of which is journalled to the frame 
38. The wheel 36 functions to press the belt against the drive wheel 29, 
with the aid of the spring 39. The flange 30 on the drive wheel 29 
prevents the belt from wandering in a sideways direction. The drive wheel 
29 is suitably provided with a surface which provides a high degree of 
friction with the belt surface. 
Also shown in FIG. 5 is a bearing housing for the shaft 33. The mechanism 
can be improved by mounting a drive wheel 29 on the other edge of the 
belt, on the other side of the symmetry line 41-42, and a wheel 36 which 
functions to press against the upper side of the belt can also be provided 
on this other edge of the belt. In the case of the illustrated embodiment, 
the flanges 30 prevent the belt from wandering to one side or the other. 
This belt guide can be further improved by providing a freely-rotating 
wheel 43 which functions to press the return side or bottom run 31' of the 
belt against the underside of the drive wheel 29, the wheel 33 being 
journalled on an arm 44 whose other end is journalled to the frame 38 and 
also connected to the spring 39. 
A drive means 8, shown in FIG. 1, constructed in accordance with FIGS. 6 
and 7, may be suitable for certain feeder constructions. FIG. 6 is a side 
view of the belt and FIG. 7 illustrates the belt from above and at the 
right-hand edge of the belt. The wheel 45 mounted between the top and 
bottom runs of the belt is positioned level with the underside of the belt 
46 and runs freely on the shaft 47. The belt 46 is also supported by the 
support plate 48. Mounted above the wheel 45 is a drive wheel 49 having a 
flange 50 (shown in FIG. 7), this drive wheel being mounted on the drive 
shaft 51, which extends transversely to the longitudinal axis of the belt. 
The drive shaft is, in turn, driven by the wheel 52 and the drive belt 53. 
The shaft 51 is journalled on the arm 54 which, with the aid of the spring 
55, presses the wheel 49 against the upper side of the belt. 
As will be seen from FIG. 7, the flange 50 restrains the belt against 
sideways movement, and a corresponding mechanism is provided at the other 
edge of the belt, on the other side of the symmetry line 56-57, the 
flanges 50 preventing the belt from wandering to one side or the other. 
FIGS. 8-10 illustrate a complete belt feeder and frame. FIG. 8 is a side 
view and FIG. 9 a view taken from above. FIG. 10 illustrates a section 
taken transversely across the feeder on line 58-59 of FIG. 9. 
The belt 60 is shown positioned between the rollers 61 and 62. The roller 
shafts are mounted in recesses 63 so as to enable adjustments to be made 
to these shafts with the aid of setting screws 64 at the respective ends 
of the frame 65. The frame 65 comprises two elongated profiles 66 which 
are mutually connected by two transverse tubes 67 provided at respective 
ends of the profiles. The tubes 67 are fitted over two rods 68 which 
extend with clearances to the tubes 67. The contact surfaces between the 
components 67 and 68 include two knobs 69 on the one rod 68 and a knob 70 
on the right-hand rod as seen in the Figure. The frame 65 thus rests 
stably on three support points, thereby avoiding internal stresses 
resulting in warping of the frame. The rods 68 are affixed to the vertical 
posts 71 and the horizontal components 72 to form a frame. The feed funnel 
is not shown attached to the frame of the belt feeder, since the funnel 
often forms part of a larger storage container 74 positioned above the 
feeder. Drive wheels 75 are mounted on both sides of the belt, to the 
right of the funnel and between the belt parts. The drive wheels are 
provided with teeth 76 whose pitch is adapted to the pitch of the 
perforations or holes 77 in the belt. The return part, or bottom run, of 
the belt 60 is held raised by a transversal cam 78 attached to the frame 
65, and the teeth 76 are also caused to engage the bottom run of the belt. 
The left-hand part of the belt passing around the roller 61 can be made 
taut with the aid of the roller adjuster screws 64, so as to facilitate 
withdrawal of material from the feed funnel. The right-hand part of the 
belt can be caused to run with low belt tension at the same time, this 
being achieved by means of the adjuster screws for the roller 62. The 
shaft 79 is fixed to the drive wheels 75 and is journalled in the frame 
profile 66. The shaft is driven by the gearbox 81 and the motor 82, via a 
material entraining device 80. Mounted on the end of the motor is a 
tachometer 83 whose speed forms a measurement of belt speed. The support 
plate 84 extends from beneath the funnel outwardly on the right-hand side 
thereof, beyond the drive wheel 75, and the weighing plate 86 is pivotably 
mounted to the right-hand edge 85 of said plate. The weighing plate 
extends along about half the weighing path, i.e. along half of the 
distance from the end 85 of the support plate to the midway point of the 
roller 62. 
The weighing plate is supported by the load-measuring sensor 87 (shown in 
broken lines in FIG. 8) through the intermediary of the post 88. The other 
end of the sensor is attached to the frame 65 through the intermediary of 
a cross-beam 89 which extends between said profiles 66. The gearbox 81 
with motor 82 is attached to a bracket structure 90 on the left-hand post 
71. 
Depending on the type of bulk materials to be weighed, a complete belt 
feeder will include side-spill protectors and belt cleaning scrapers. 
These are not shown. If the feeder needs to be encased, the motor is 
preferably placed outside the casing, the extension of the casing walls 91 
being shown in broken lines in FIG. 10. When the funnel 73 is attached to 
the upper side of the casing and the vertical casing wall shown to the 
right in FIG. 10 can be removed, the whole of the feeder can be withdrawn 
from the right-hand end of the casing, wherewith engagement of the 
material entraining device 80 is released and the frame 65 slides against 
the knobs 69 and 70 on the rods 68. This greatly facilitates servicing of 
the feeder. 
When the belt feeder is intended for large flow capacitities or for 
material which has particular properties, the drive wheels 75 can be 
supplemented with pressure rollers 36 and 43 according to the embodiment 
illustrated in FIGS. 5 and 6. The frame bars 66 may also have the form of 
U-profiles and the attachment 89 attached to the bars 66 by means of 
adjuster screws, so as to enable the height of the weighing plate 86 to be 
adjusted.