Dosing or feeding apparatus for precisely feeding loose bulk material

A dosing or metering feeding apparatus for precisely feeding a stream of powdered or fine grained loose bulk material includes a cylindrical container (1) for storing the loose material (3). A rotating turntable (4) essentially closing the bottom of the container (1). A discharge groove (6) is located in the turntable around the circumference of the turntable (4), whereby the discharge groove (6) opens radially outwardly. A stripper is arranged to reach into the discharge groove (6) for stripping the dosed material (3) from the discharge groove (6) and for discharging the dosed or metered material. This arrangement provides a clearly defined discharge rate of the loose material. The discharge rate may be simply adjusted to different desired feed rates by varying the rotational speed of the turntable (4). A high dosing or metering precision is achieved. The dosing apparatus may be used together with a weighing scale for carrying out a gravimetric feeding by controlling the turntable drive in closed loop fashion by a control signal derived from the weighing scale.

FIELD OF THE INVENTION 
The invention relates to a dosing apparatus for precisely feeding loose 
bulk material, especially in the form of powdered or fine grained 
material. Such a dosing apparatus includes a container or housing for the 
loose bulk material, a driven turntable, and a stripper. The loose bulk 
material is deposited on the turntable from the container and is then 
stripped off the turntable for discharging a metered quantity from the 
container by means of the stripper. 
BACKGROUND INFORMATION 
German Patent Publication (DE-PS) 2,636,521 discloses a known conveyor 
apparatus for powdered material. The known conveyor includes a turntable, 
a storage container arranged above the turntable, and several strippers of 
which a primary or coarse stripper produces a uniform layer thickness of 
powder on the turntable, and at least one further stripper strips or 
strikes the uniform layer of powdered material off the turntable. Such an 
arrangement has the disadvantage that it requires a coarse stripper and 
that the surplus material stripped off by the coarse stripper must somehow 
again be returned into the container. Further, the loose powder material 
could possibly flow from a pouring feed cone on the turntable directly to 
the final dosing stripper without having been stripped to the appropriate 
layer thickness by the first course stripper. Such a direct flow leads to 
non-uniformly dosed streams of loose powdered material. 
European Patent Publication (EP-BL) 0,112,398 discloses another known 
apparatus for precisely dosing or feeding loose bulk materials by using 
dosing rollers having grooves machined in their surfaces and which rotate 
on a horizontally arranged shaft. In apparatus of the above type there is 
a danger or disadvantage that the loose bulk material may become too 
greatly compacted in the grooves of the dosing rollers or that the loose 
bulk material falls out of the grooves too early due to gravity. Such 
failures lead to a non-uniform discharge or feed stream of the material. 
The known apparatus volumetrically dose or feed precisely the loose bulk 
material. However, known devices generally only operate with a relatively 
low output or conveying volumes which may, for example, only amount to a 
few grams per hour. turntable or rollers are driven at a constant 
rotational speed, whereby a single, non-adjustable output rate is 
provided. 
OBJECTS OF THE INVENTION 
In view of the foregoing it is the aim of the invention to achieve the 
following objects singly or in combination: 
to construct a dosing or feed apparatus for precisely feeding exact 
quantities of loose bulk materials in such a manner that stripper means 
can strip a precise quantity of loose material from a rotating turntable; 
to construct such a dosing apparatus in a manner so that there is no stream 
of surplus material which must be returned to the material storage 
container; 
to ensure that no spill over of material or other failures can occur in 
such a dosing apparatus so that a uniform and precisely dosed output 
stream of loose output material is achieved; 
to avoid excessive compaction of the discharged loose material in such a 
dosing apparatus and thereby to avoid fluctuations of the output stream of 
material; 
to allow the rotational speed of the rotating turntable of such a dosing 
apparatus to be adjusted so that the discharge rate of loose bulk material 
can be adjusted to a desired dosing or output feed rate; and 
to achieve, after adjustment, a dosing or feeding accuracy and constancy so 
that the output rate is consistently repeatable. 
SUMMARY OF THE INVENTION 
The dosing apparatus according to the invention includes a cylindrical 
container for storing the loose bulk material to be fed or dosed. A 
rotatable turntable substantially closes the bottom of the cylindrical 
container. A discharge groove is arranged around the circumference of the 
rotating turntable. The discharge groove opens radially outwardly for 
delivering exact quantities of bulk material out of the container. A 
stripper reaches into the discharge groove to strip loose bulk material 
from the groove to thereby discharge the material from the container. The 
arrangement of the discharge groove along the circumference of the 
rotating turntable assures an output rate of the discharge stream of the 
bulk material which is clearly defined by the rotational speed of the 
rotating turntable. Therefore, the discharge rate may be simply yet 
precisely adjusted by adjusting the rotational speed of the drive means of 
the turntable. 
Further, according to the invention the discharge groove may be partially 
covered on top. In this embodiment openings are provided in the top cover 
of the discharge groove so that the loose material may enter the discharge 
groove from above. A cover plate is arranged above the immediate area of 
the stripper and the discharge opening of the container to prevent 
uncontrolled flowing of the loose material out of the container. 
Furthermore, stirring means may be arranged in the material storage 
container to cooperate with deflector or guide elements arranged around 
the inner surface of the container above the discharge groove for assuring 
that the discharge groove is uniformly filled with loose material without 
excessive compaction or compressing of the loose material into the 
discharge groove. 
For gravimetrically dosing or feeding a discharge stream of loose bulk 
material the dosing apparatus as described above may be arranged on a 
scale or weighing means. The weighing comprise a control apparatus which 
generates a signal for controlling the rotational speed of the drive for 
the rotating turntable. In this manner it is assured that a discharge 
stream may be precisely gravimetrically dosed or fed and may be simply 
adjusted to a desired discharge rate.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE 
OF THE INVENTION 
As shown in FIG. 1, the dosing or feeding apparatus according the invention 
includes a cylindrical container 1 mounted on a base plate 2. The loose 
bulk material 3 which is to be dosed feed is placed into the container 1. 
A rotating turntable 4 is arranged near the bottom of the container 1, 
that is near the base plate 2 so that the rotating turntable 4 effectively 
closes the bottom of the container 1 to prevent uncontrolled escape of the 
loose material 3. The turntable 4 is mounted on a hollow shaft 5 which is 
rotatably supported in the base plate 2 by bearings 2a. The hollow shaft 5 
and thus the turntable 4 is driven by a schematically indicated drive 9 at 
a relatively low rotational speed which is generally only a few 
revolutions per minute. 
A discharge groove 6 runs around and along next to the circumference of the 
turntable 4 and opens radially outwardly. A discharge opening 15 is 
provided in the wall of the container 1 near the discharge groove 6. A 
stripper 7 reaches into the discharge groove 6 in the area of the 
discharge opening 15. The stripper 7 is, for example, attached to the wall 
of the container 1 so that it is stationary relative to the rotation of 
the turntable 4, whereby the material is removed when the turntable groove 
6 moves past the stripper 7 because the stripper 7 strips the dosed loose 
material out of the discharge groove 6 and out through the discharge 
opening 15 to drop, e.g., into a receiving receptacle 8 outside the 
storage container 1. The receiving receptacle 8 may be transported by 
conveying means of conventional construction. Metered bulk material 3a 
falls into the receptacle 8. 
Stirring means 10 are arranged within the container 1 on a drive shaft 10a 
which is rotationally supported in the hollow shaft 5 by bearings 5a. The 
drive shaft 10a extends through the hollow shaft 5 of the turntable 4. 
Drive means 11 which are only schematically indicated, drive the shaft 10a 
and thus the stirring means 10. The stirring means 10 are driven in the 
same rotational direction, but at a higher rotational speed than the 
turntable 4. However, in an alternative embodiment the mixing means 10 may 
be driven in an opposite rotational direction than the turntable 4. The 
stirring means 10 comprise several stirring paddles 12 which are 
preferably arranged directly above the turntable 4. A plurality of 
wedge-shaped deflecting and guiding elements 13 are arranged around the 
inside wall of the container 1 and extend radially inwardly substantially 
across the radial width of the discharge groove 6. The deflecting and 
guiding elements 13 cooperate with the stirring paddles 12 for achieving a 
uniform filling of loose material 3 into the guide channel 6. 
FIG. 2a shows a partial horizontal sectional detailed view of the discharge 
area of the apparatus according to the invention. The stripper 7 has a leg 
7a slanting against the direction R of rotation of the turntable 4 and 
reaching through a discharge slot 15 in the wall of the container 1 into 
the discharge groove 6. The edges of the slanted stripper leg 7a rest 
against the horizontal and vertical walls of the groove 6, thereby guiding 
bulk material 3 out of the groove 6. A thin cover plate 16 covers the 
stripper 7 and the stripper area above the discharge slot 15. The cover 
plate 16 reaches radially inwardly at least to the radially inner edge of 
the discharge groove 6 for preventing loose bulk material 3 from escaping 
the container 1 in an uncontrolled manner. The stripper 7 and the cover 
plate 16 are attached to the container 1 by means of a bracket 17. 
While the embodiment shown in FIG. 2a has a straight or angular stripper 7, 
the portion of the stripper which reaches into the discharge groove 6 may 
alternatively be curved or plow shaped. Furthermore, the stripper 7 may be 
rigid or may be elastic. As the turntable 4 rotates in the direction R, 
the loose material carried in the discharge groove 6 is smoothly and 
effectively removed from the groove 6 by the stripper 7 and discharged 
through the opening 15. 
FIG. 2b is a view similar to that of FIG. 2a, but for clarity does not show 
the stripper arrangement 7. FIG. 2b shows a cover 19 of the groove 6a in 
the turntable 4. As shown in FIG. 2b, the groove 6a is partially covered 
from above by the cover 19 which comprises semicircular openings 18 near 
its circumference for admitting material into the discharge groove 6a. The 
cover 19 partially covering the discharge groove 6a may, for example be a 
thin sheet metal member which rotates with the turntable 4. Alternatively, 
the discharge groove 6a may be machined into the circumferential edge of 
the turntable 4, whereby the top cover 19 remains as a piece or extension 
of the turntable 4 with upwardly open holes therein for the bulk material 
to enter the groove 6a. The cover 19 prevents the loose material 3 from 
being compressed or compacted into the discharge groove 6a, whereby the 
precision or accuracy of the dosing is improved. 
FIG. 2c is a view similar to that of FIG. 2b, but showing an alternative 
embodiment of a partial cover 19a having openings 18a for the loose 
material 3 to flow from the container 1 into the discharge groove 6. These 
openings 18a are shown to have a substantially rectangular shape rather 
than the semicircular opening shape shown in FIG. 2b. However, these 
openings may have any suitable configuration. 
FIGS. 3a and 3b show vertical sections through two possible alternative 
embodiments of the discharge groove 6 in the turntable 4. 
FIG. 3a shows a turntable 4 with a discharge groove 6 which is essentially 
open radially outwardly and axially upwardly. The stripper 7 reaches with 
its leg 7a into the discharge groove 6 as described. The cover plate 16, 
e.g. of sheet metal, is arranged above the discharge groove 6 to cover the 
area of the stripper 7, specifically the stripper leg 7a. The discharge 
groove 6 has a rectangular cross-section but may have other appropriately 
cross-sectional shapes in alternative embodiments, e.g. a square 
cross-section or any other suitable cross-section. In any event, the 
stripper 7 has the same shape as the cross-section of the discharge groove 
6 so that all the loose material is effectively stripped out of the 
discharge groove 6. 
FIG. 3b is a vertical sectional detail through a rotating turntable 4 and 
discharge groove 6a covered by a cover resulting when the groove 6a is 
machined into the circumferential edge of the turntable 4 so that a top 
cover 19 remains, whereby, the discharge groove 6a is only completely open 
in a radially outward direction, while openings 18 in the top cover 19 
provide access into the discharge groove 6a for the bulk material passing 
from the container 1 through the openings 18 into the discharge groove 6a 
where it is then stripped out by the stripper 7 to be discharged from the 
opening 15 in the container wall 1. 
FIG. 4 shows an alternative embodiment of a stripper 7a in the form of a 
rotational stripper 7a rotating in the direction of the arrow S. The 
rotating stripper 7a comprises a plurality of stripper paddles 20 which 
reach through the discharge opening 15 into the discharge groove 6 or 6a. 
The paddles 20 strip the loose bulk material 3 from the discharge groove 
6, whereby an auxiliary stripper wall 7' prevents the loose material from 
spilling from the stripper paddles 20 back into the discharge groove 6 or 
6a. Drive means 7b for the rotating stripper 7a are shown in block form 
since any suitable conventional drive can be used. The rotational 
direction S of the rotating stripper 7 is shown to be opposite the 
rotational direction R of the rotating turntable 4. However, other 
rotational direction combinations are also possible. 
The dosing apparatus described herein may be used in combination with a 
weighing apparatus or scale for carrying out gravimetric dosing or feeding 
of a loose bulk material stream. To achieve this, the above described 
dosing or metering or feeding apparatus is arranged on the weighing 
apparatus. Then in a known manner the weighing apparatus comprises 
evaluating circuit means and a control arrangement for generating a signal 
to control the rotational speed of the turntable 4 in a closed loop 
manner, whereby the discharge rate of the dosed material may be adjusted. 
FIG. 5 shows the present apparatus supported with its container 1, 
turntable 4, and drive motor 9 on a platform scale 21 which weighs the 
instantaneous weight of the entire apparatus to produce a respective 
output signal. The scale 21 can, for example be of the type known as 
SIMPLEX loss-in-weight-system mode PHR, manufactured by Carl Schenck AG of 
Darmstadt, Federal Republic of Germany. A signal processing circuit 22, 
which may be part of the scale, deducts the instantaneous value from the 
initial filled value to produce a control value representing the actual 
feed rate of bulk material. The control signal is compared in the closed 
loop control cricuit 23 with a rated feed rate signal stored in the 
circuit 23 which may include, in addition to a memory and a comparator, an 
amplifier. The output 24 of the circuit 23 is supplied as a control signal 
to the drive motor 9 of the turntable 4. If the actual feed rate coincides 
with the rated feed rate no control is effected. If the actual feed rate 
exceeds the rated rate, the motor 9 is slowed down in the closed loop 
control until the rates coincide again. If the actual rate is lower than 
the rated rate, the motor 9 is accelerated until coincidence is 
established again. 
FIG. 6 is an embodiment similar to that of FIG. 5, whereby the 
volumetrically metered out quantity 3a in the receptacle 8 is weighed 
directly on a scale 21a. The circuit 22a compares the actual rate signal 
from the scale 21a with a rated rate signal which is stored in the circuit 
22a. The signal is then, for example, amplified at 23a and supplied at 24 
to the motor 9. Except for the formation of the difference signal in FIG. 
5, both circuits control the operation of the motor 9 in a closed loop 
manner for driving the turntable 4 at the desired feed rate. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.