Apparatus for the operation of a plant for producing deinked pulp with state analysers constructed in the form of neural networks for the waste paper suspension

Apparatus for the operation of a plant for producing deinked pulp with state analysers constructed in the form of neural networks for the waste paper suspension. At least one measuring device (ME) records spectral and/or physical characteristic values (IMf, Mp) of a waste paper suspension (PS). Furthermore, there are closed-loop or open-loop control devices (RS1 . . . RS8) for operating means of a waste paper preparation (AAA) in the plant. According to the invention, there is at least one state analyser (ZA), configured in the form of a neural network (NNg) or a plurality of parallel neural networks (NN1 . . . NN4), for the waste paper suspension (PS). This analyser forms from the characteristic values (IMf, Mp) controlled variables (ST: AB, AZ, FL, AA, AS, AT) for process control of the closed-loop or open-loop control devices (RS1 . . . RS8) of operating means at least of the waste paper preparation (AAA). As controlled variables, the ratio of white to coloured papers (AB), the ratio of illustrated-magazine paper to newsprint paper (AZ), the average fibre length (FL), the ash content (AA), the content of dirt (AS) and/or the content of adhesive contaminants (AT) in the waste paper suspension (PS) are suitable with preference.

Apparatus for the operation of a plant for producing deinked pulp with 
state analysers constructed in the form of neural networks for the waste 
paper suspension. 
BACKGROUND OF THE INVENTION 
In the production of deinked pulp using as great a proportion as possible 
of waste paper, one problem is that the quality of the waste paper 
introduced into an apparatus for waste paper preparation in the plant for 
producing deinked pulp, i.e. pulp intended for producing recycled paper, 
varies greatly. Depending on the respective mixture of the waste paper, it 
may contain greatly varying proportions of, for example, coloured 
illustrated-magazine papers, grey newsprint papers, white papers, soiled 
papers, old books, for example with glued spines, such as, telephone 
directories, cardboard articles, packaging, coated papers, contaminants of 
all kinds and much more besides. At least the operating means of the 
apparatus for waste paper preparation must consequently be suitably 
controlled by a closed-loop or open-loop system in a way dependent on the 
state of a respectively introduced charge of waste papers in order to 
obtain a waste paper suspension suitable for the production of deinked 
pulp and having approximately constant characteristic quality values. 
For process control of the waste paper preparation, which is located at the 
beginning of the plant for producing deinked pulp, one important 
requirement is to meter as accurately as possible the addition of deinking 
chemicals and, if appropriate, dispersing chemicals in a way dependent on 
the current state of the waste paper fed in. Furthermore, the operating 
means of the waste paper preparation plant serving for homogenizing and 
sorting the cellulose fibres in the suspension should also be optimally 
controlled by an open-loop or closed-loop system. However, a prerequisite 
for exact process control of the waste paper preparation plant is the most 
accurate and fastest possible instrumentational recording at the intake of 
the waste paper preparation plant of selected characteristic values of the 
waste paper suspension obtained by disintegrating waste paper of extremely 
varied quality and type. 
Until now, the state of the waste paper suspension was determined by the 
measurement of physical characteristic values only. These variables have 
the disadvantage, however, that they allow the state of the waste paper 
suspension to be represented only inaccurately with regard to the possible 
grades of waste paper fed to the preparation plant and their quality 
characteristics. Consequently, controlling operating means of the waste 
paper preparation plant with the aid of these variables is possible only 
inaccurately. 
SUMMARY OF THE INVENTION 
Against this background, the invention is based on the object of specifying 
an operating apparatus which permits the best possible process control of 
a plant for producing deinked pulp. 
The object is achieved by the apparatus specified in claim 11. Advantageous 
further embodiments of the invention are specified in the subclaims. 
The apparatus according to the invention includes at least one measuring 
device for recording spectral and/or physical characteristic values of a 
waste paper suspension fed in for waste paper preparation. Furthermore, 
there are selected closed-loop or open-loop control devices for 
influencing at least operating means of the waste paper preparation plant. 
According to the invention, there is at least one state analyser, which is 
configured in the form of a single neural network or a plurality of 
parallel neural networks. This analyser is fed the characteristic values 
of the waste paper suspension, recorded by the measuring device, as input 
variables. The at least one state analyser determines from these input 
variables controlled variables which are output at least for process 
control to closed-loop or open-loop control devices for operating means of 
the waste paper preparation plant, and if appropriate additionally to 
closed-loop or open-loop control devices of a following dewatering machine 
for producing deinked pulp or to closed-loop or open-loop control devices 
of at least one following paper machine in a plant for producing recycled 
paper, which processes the deinked pulp. 
For the construction of the state analyser, known neural networks, 
available for example as software modules for process computing systems, 
can be used. The setting of the neural network takes place in a known way 
by so-called "training" with the assistance of as large a number as 
possible of measured values which are obtained by manual laboratory 
analysis of the waste paper suspension. 
According to a preferred configuration of the invention, either the ratio 
of coloured papers to white papers and/or the ratio of 
illustrated-magazine papers to newsprint papers in the amount of waste 
paper processed to form the waste paper suspension are determined by the 
at least one state analyser as controlled variables. It has been found 
that these ratios are particularly suitable for describing the current 
state of the waste paper suspension, and, according to the invention, are 
used alternatively or else jointly as preferred controlled variables for 
the process control. They are used inter alia for the process control of 
apparatuses for metering so-called deinking chemicals into the waste paper 
suspension. This is a means of dissolving out printing inks which have 
been introduced into the waste paper suspension via the waste paper and 
would result in an inadmissibly strong grey haze in recycled paper. These 
can be subsequently washed out. 
In a further embodiment of the invention, values for the average fibre 
length and/or the ash content in the waste paper suspension are made 
available by the common neural network or by the plurality of parallel 
neural networks in the state analyser. These can serve as further 
controlled variables, in particular for controlling the operating means of 
the preparation plant serving for fibre sorting and for extracting 
unusable constituents to be rejected from the waste paper suspension. 
In a further configuration of the invention, count values for the content 
of dirt and/or for the content of adhesive contaminants in the waste paper 
suspension can be additionally provided by the common neural network or 
the plurality of parallel neural networks. These values also can be used 
advantageously as controlled variables, inter alia for the operating means 
of the preparation plant serving for homogenizing the cellulose fibres in 
the waste paper suspension and for the operating means of the preparation 
plant serving for metering in dispersing chemicals. 
Advantageously, the intensities of the respective wavelength ranges 
reflected and/or transmitted by the waste paper suspension under 
irradiation at selected wavelength ranges of visible and/or infrared light 
are recorded as spectral characteristic values, and are fed to the at 
least one state analyser as input variables. In a further embodiment of 
the invention, wavelength ranges which belong to the blue, red and/or 
green component of light are selected for the visible light, and the 
intensities reflected and/or transmitted by the waste paper suspension 
under irradiation with light from these wavelength ranges are measured as 
spectral characteristic values. Advantageously, the intensities in the 
near range and/or in the far range reflected and/or transmitted by the 
waste paper suspension under irradiation with light from the infrared 
wavelength range may also be instrumentation-ally recorded additionally as 
spectral characteristic values. 
For this type of measurement, the stream of waste paper suspension is 
illuminated with selected wavelengths of visible and, if appropriate, 
additionally of infrared light by the so-called incident light or 
transmitted light technique. Suitable for this purpose are, for example, 
so-called "white measuring instruments". These are equipped with 
light-emitting diodes, which emit light at different wavelengths. In this 
case there may be light-emitting diodes for visible light in the blue, red 
and green wavelength range, and light-emitting diodes for invisible light 
in the infrared wavelength range. The intensities of these characteristic 
spectral colours occurring after reflection at the pulp stream of the 
waste paper suspension or after passing through the pulp stream can be 
recorded, for example with the aid of a photospectrometer, as 
characteristic values. Advantageously, the consistency and/or the 
temperature of the waste paper suspension may be additionally measured 
with preference as physical characteristic values and fed to the at least 
one state analyser as input variables. 
The controlled variables formed by the at least one neural network in the 
state analyser may be used individually, in groups or in their entirety 
also for the process control of operating means of the at least one paper 
machine in a following recycled paper plant. For this purpose, they are 
output to corresponding closed-loop or open-loop control devices of the 
paper machine. 
According to a further configuration of the invention, at least one 
additional measuring device may be arranged inside the waste paper 
preparation plant for recording spectral and/or physical characteristic 
values of the waste paper suspension. Arranged downstream of this device 
is at least one further state analyser, according to the invention again 
configured in the form of a neural network or a plurality of parallel 
neural networks. The controlled variables provided by this are output for 
process control to closed-loop or open-loop control devices, which belong 
to operating means of the waste paper preparation plant or the paper 
machine which are arranged downstream of the additional measuring device 
and the further state analyser in the direction of the process sequence. 
This additional measuring device consequently evaluates a waste paper 
suspension which has already passed through one or more upstream operating 
means of the waste paper preparation plant. The waste paper suspension has 
consequently already experienced a number of "cleanings", so that its 
quality has approached the state necessary for producing deinked pulp. The 
process control of downstream operating means can take place much more 
accurately with the aid of such updated spectral and/or physical 
characteristic values and the controlled variables derived from them by 
the at least one state analyser, than if only characteristic values of the 
waste paper suspension in the initial state are recorded at the intake of 
the waste paper preparation with a single measuring device and a following 
state analyser.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows the example of a state analyser for the waste paper 
suspension, which is constructed in the form of a single, global neural 
network NNg. This is fed, for example, the spectral characteristic values 
IMf, recorded by at least one measuring device, and the physical 
characteristic values Mp as input variables. In the example represented in 
FIG. 1, the intensities occurring under irradiation of the waste paper 
suspension at selected wavelength ranges of visible and infrared light are 
envisaged as spectral characteristic values IMf. Thus, by way of example, 
the neural network NNg is fed as characteristic values the intensity 
WL-blue in the wavelength range for blue visible light, the intensity 
WL-red in the wavelength range for red visible light and the intensity 
WL-green for visible light from the green wavelength range. Further 
spectral characteristic values are the intensity WL-IR near for invisible 
infrared light in the near range and the intensity WL-IR far for invisible 
infrared light in the far range. As physical characteristic values Mp, the 
neural network NNg is fed the consistency K and the temperature T of the 
waste paper suspension. 
According to the invention, from these input variables the neural network 
NNg in the state analyser determines controlled variables, which are 
output for process control to the closed-loop or open-loop control devices 
of operating means of the waste paper preparation plant and, if 
appropriate, to a paper machine in a recycled paper plant. In the case of 
the example represented in FIG. 1, the global neural network NNg makes the 
following controlled variables ST available with preference at the output 
neurons: 
AB: ratio of coloured papers to white papers in the amount of waste paper 
introduced, 
AZ: ratio of illustrated-magazine papers to newsprint papers in the amount 
of waste paper introduced, 
FL: average length of the pulp fibres in the waste paper suspension (for 
example in micrometers), 
AA: content of ash (for example kaolin, colour pigments and the like) in 
the waste paper suspension (in per cent), 
AS: density of dirt spots in the waste paper suspension or count value of 
dirt or dirt spots, for example per square metre of recycled paper, and 
AT: content of adhesive contaminants in the waste paper suspension 
(so-called "stickies", i.e. thermoplastic constituents which originate, 
for example, from coatings and book bindings). 
In other embodiments of the invention, the variables AB and AZ, i.e. the 
ratios of coloured papers to white papers and illustrated-magazine papers 
to newsprint papers in the amount of waste paper introduced, may also be 
made available separately by a plurality of neural networks. Thus, in 
FIGS. 2a-2d the example of a state analyser which comprises four parallel 
neural networks NN1 . . . NN4 is represented. All the networks are fed the 
spectral characteristic values IMf, already described for the example of 
FIG. 1, at the input neurons. Of the physical characteristics Mp, all the 
sub-neural networks NN1 . . . NN4 are fed the consistency K, while the 
temperature T of the waste paper suspension is additionally fed only to 
the sub-neural network NN4. 
The sub-networks NN1 and NN2 of the state analyser represented in FIGS. 2a 
and 2b, respectively, form the ratio AB of coloured papers to white papers 
and the ratio AZ of illustrated-magazine papers to newsprint papers, 
respectively, in the amount of waste paper processed to form the waste 
paper suspension. Both variables serve as controlled variables for process 
control for the closed-loop or open-loop control devices of the operating 
means of the plant for producing deinked pulp. The third sub-neural 
network NN3 of the state analyser, in FIG. 2c, is designed such that the 
values of the average fibre-length FL and of the ash content AA in the 
waste paper suspension output as are controlled variables for the process 
control. Finally, the fourth sub-neural network NN4, in FIG. 2d, 
determines from the abovementioned input variables a count value AS for 
the content of dirt or dirt spots and a count value AT for the content of 
adhesive contaminants in the waste paper suspension. The sub-networks NN3 
and NN4 are consequently advantageously designed such that in each case a 
pair of mutually associated controlled variables FL, AA and AS, AT is 
respectively formed. In this way, the so-called training of the neural 
networks NN3, NN4 with the aid of measured values obtained analytically in 
the laboratory is also facilitated. Thus, for example in a determination 
of the count value AS for the dirt with the aid of a laboratory analysis, 
the related count value AT for the content of adhesive contaminants can 
also be determined in an easy way. 
In contrast, the sub-neural networks NN1 and NN2 respectively form with 
preference only a single controlled variable AB and AZ respectively. These 
values can consequently be determined very accurately independently of 
each other. This is advantageous, since the ratio values AB, AZ are 
important main controlled variables for the process control of the 
recycling plant, which are often not used simultaneously but only 
alternatively. By virtue of the separate determination of the ratio values 
with the aid of a dedicated sub-network in each case, there is for example 
the possibility of using for process control in an individual case the 
measured value which appears more plausible in that particular case. 
In the related FIGS. 3 and 4 there is represented in the form of a block 
diagram an example of an overall plant for generating recycled paper RP, 
comprising an upstream waste paper preparation AAA and a downstream paper 
machine PAM, the latter directly processing the deinked pulp formed. 
At the intake of the plant there is a disintegrator AU, in which waste 
paper AP introduced is converted with the aid of an agitator R1 and the 
appropriate addition of fresh water into a waste paper suspension PS. This 
is fed to a first operating means of the preparation plant, which, in the 
form of a defibrator DS with agitator R2, effects a first homogenization 
of the fibres in the waste paper suspension. Furthermore, dispersing 
chemicals DC may be added into the defibrator or into the pulp stream in 
order to speed up the disintegration of lumps of fibre. 
The waste paper suspension PS treated in such a way is fed, if appropriate 
with the addition of further fresh water FW1, to a presorter VS as a 
further operating means of the plant. By means of a wire S1, unusable 
constituents of the waste paper suspension are eliminated in the form of a 
so-called reject RJ1, while usable fibre constituents pass through the 
wire S1 and go on to further operating means of the plant. 
In the case of the example represented in FIG. 3, the presorted waste paper 
suspension PS is fed to a concentrator ED, for the purpose of adjusting 
the consistency. Excess water WA occurring during concentrating is drained 
off. There follows as an important operating means of the waste paper 
preparation a so-called deinker DI. This is fed deinking chemicals IC for 
chemically neutralizing dyes in the waste paper suspension. The suspension 
PS prepared in this way is then fed to a washer WS as a further operating 
means of the plant. This washer is represented on the left-hand side of 
the following FIG. 4. The washer has a fresh water feed FW2 and a 
wastewater or chemical discharge CA. As a further operating means, there 
may follow a post-sorter NS. In the latter, further unusable constituents 
of the waste paper suspension PS are eliminated with the aid of a rotating 
cylinder or a battery of cyclones Z (not shown) and discharged as reject 
RJ2. 
At this point of the plant AAA, the waste paper suspension is already 
prepared for high grade. As one of the last operating means there follows 
in the example of FIG. 4 a fibre sorter FS. In the latter, a separation of 
the waste paper suspension PS into two pulp streams is effected with the 
aid of a wire S2. The one stream KF substantially contains short pulp 
fibres, which are suitable directly for the production of recycled paper. 
The second pulp stream LF has substantially long pulp fibres, which are 
fed for comminution to a grinder MW. Subsequently, the pulp streams are 
reunited. The waste paper suspension PS has at this end D of the waste 
paper preparation AAA attained such a quality that deinked pulp can be 
produced from it by means of a dewatering machine (not shown). In the 
example represented, the waste paper suspension AP is fed directly to a 
following paper machine PAM for the production of recycled paper RP. If 
appropriate, a small content of fresh pulp FZ is added beforehand. 
In the lower half of the block diagram of FIGS. 3 and 4, exemplary 
closed-loop or open-loop control devices RS1 . . . RS9 for the process 
control of operating means of the waste paper preparation AAA, and 
exemplary closed-loop or open-loop control devices for the process control 
of the following paper machine PAM are represented. One possible 
embodiment for the forming of controlled variables by at least one state 
analyser ZA, and their possible assignments to the closed-loop or 
open-loop control devices of the individual operating means, are explained 
in more detail furthermore with reference to FIGS. 3, 4. 
Thus, on the left-hand edge of the block diagram of FIG. 3 there is a 
measuring device ME, which records spectral characteristic values IMf and 
physical characteristic values Mp of the waste paper suspension PS formed 
in the disintegrator AU. The characteristic values are fed as input 
variables to a state analyser ZA, configured with preference according to 
the exemplary embodiment of FIG. 1 in the form of a single global neural 
network NNg. The said analyser forms from these input variables a set of 
controlled variables ST, which preferably comprises the values already 
explained above AB, AZ, FL, AA, AS and AT. The state analyser ZA may also 
be configured in the form of a plurality of parallel sub-neural networks, 
for example according to the example represented in FIGS. 2a-2d. 
The controlled variables ST are fed to the individual closed-loop or 
open-loop control devices RS1 . . . RS8, RS9 individually or in selected 
sub-groups for the purpose of process control of the connected operating 
means. Thus, the value of the average fibre length FL or the ratio AB of 
coloured papers to white papers or the ratio AZ of illustrated-magazine 
papers to newsprint papers may serve with preference as the controlled 
variable for the closed-loop or open-loop control device RS1, which drives 
the rotor R2 in the defibrator DS, serving as the operating means. 
The further closed-loop or open-loop control device RS2 influences that 
operating means of the waste paper preparation plant AAA which meters 
dispersing chemicals DC into the defibrator DS or into the pulp streams. 
The pair of values from the average fibre length FL and the content AT of 
adhesive contaminants of the waste paper suspension are suitable with 
preference as controlled variables ST for RS2. 
The closed-loop or open-loop control device RS3 which follows in the block 
diagram of FIG. 3 influences on the one hand the consistency of the waste 
paper suspension PS by controlling the fresh water feed FW1, and on the 
other hand the wire S1 in the following presorter VS. Suitable with 
preference as controlled variables ST for RS3 is the group of values 
comprising the ash content AA, the content AS of dirt and the content AT 
of adhesive contaminants in the waste paper suspension. As an alternative 
to this, however, either the ratio AB of coloured papers to white papers 
or the ratio AZ of illustrated-magazine paper to newsprint paper in the 
waste paper suspension may also serve as the controlled variable for RS3. 
In the block diagram of FIG. 3 there follows the closed-loop or open-loop 
control device RS4, which influences the concentrator ED and the means 
serving for the addition of deinking chemicals IC into the deinker DI. 
Particularly suitable as the controlled variable is the ratio AB of 
coloured papers to white papers or the ratio AZ of illustrated-magazine 
paper to newsprint paper in the waste paper suspension. As an alternative 
to this, groups of controlled variables may also serve for process 
control. Thus, RS4 may also be fed as controlled variables the pair of 
values from the ratio AB of coloured papers to white papers and the 
content AT of adhesive contaminants or the pair of values from the ratio 
AZ of illustrated-magazine paper to newsprint paper and the content AS of 
dirt in the waste paper suspension. Finally, the group of controlled 
variables comprising the ratio AB of coloured papers to white papers, the 
ratio AZ of illustrated-magazine papers to newsprint papers and the 
content AS of dirt is also suitable for the process control of RS4. 
There follows on the left-hand side of FIG. 4 the closed-loop or open-loop 
control device RS5, which influences a fresh water feed FW2 and a chemical 
discharge CA at the washer WS for the waste paper suspension PS. 
Particularly suitable as the controlled variable for RS5 is the ratio AB 
of coloured papers to white papers, or the ratio AZ of 
illustrated-magazine papers to newsprint papers, or the content AS of 
dirt, or content AT of adhesive contaminants in the waste paper 
suspension. Alternatively, the group of controlled variables comprising 
the content AS of dirt and the content AT of adhesive contaminants may 
also be used for the process control of RS5. 
In the block diagram of FIGS. 3, 4 there then follows the closed-loop or 
open-loop control device RS6, which influences the rotational speed of a 
centrifugal sorter Z in the post-sorting apparatus NS and the discharge of 
reject RJ2 from the latter. The group of controlled variables comprising 
the ash content AA, the content AS of dirt and the content AT of adhesive 
contaminants of the waste paper suspension is particularly suitable. 
Alternatively to this, the group of controlled variables ST comprising the 
ratio AB of coloured papers to white papers, the content AS of dirt and 
the content AT of adhesive contaminants may also serve for the process 
control of RS6. In this group, the ratio AZ of illustrated-magazine paper 
to newsprint paper may also be used instead of AP. 
The following closed-loop or open-loop control device RS7 preferably 
influences the action of the wire S2 in the fibre sorter FS by setting a 
differential pressure. The value of the average fibre length FL or the 
ratio AB of coloured papers to white papers or the ratio AZ of 
illustrated-magazine papers to newsprint papers is suitable as controlled 
variables for RS7. 
The grinder MW for the long-fibre suspension LF, serving as the last 
operating means of the waste paper preparation plant AAA, is influenced by 
the closed-loop or open-loop control device RS8. The value FL of the 
average fibre length in the waste paper suspension PS is suitable in 
particular as the controlled variable for RS8. 
In the example of FIG. 4, there follows a further closed-loop or open-loop 
control device RS9, which influences selected operating means in the paper 
machine PAM with the aid of controlled variables ST, which are derived 
from the waste paper suspension PS by the state analyser ZA with the 
neural network NNg. 
RS9 can be used to control, for example, the ratio SB of wire speed to jet 
speed, i.e. the degree of charging of suspension onto the wire of the 
paper machine. Furthermore, the speed Vm of the paper machine PAM and 
consequently the rate of production for recycled paper RP can be 
influenced. As a further process variable in the paper machine, the paper 
drying can be controlled by controlling the heating temperature T of the 
drying cylinders. For this purpose, the closed-loop or open-loop control 
device RS9 is in turn fed controlled variables ST individually or in 
groups. Particularly suitable are the ratio AB of coloured papers to white 
papers, or the ratio AZ of illustrated-magazine papers to newsprint 
papers, or the content AA of ash in the waste paper suspension, or the 
group of controlled variables ST comprising the average fibre length FL 
and the content AT of adhesive contaminants. 
In a further embodiment of the invention, further measuring devices are 
arranged inside the waste paper preparation plant AAA. Thus, in the block 
diagram of FIGS. 3, 4, further measuring devices ME1 following the 
defibrator DS, ME2 following the presorter VS, ME3 following the deinker 
DI, ME4 following the washer WS and ME5 following the post-sorter NS are 
shown by way of example. All the measuring devices form as far as possible 
the same group of spectral and physical characteristic values IMf, Mp from 
the waste paper suspension PS. Since the measuring devices ME1 . . . ME5 
are arranged at different points in the waste paper preparation plant, the 
characteristic values recorded by them deviate on account of the 
increasing purity of the waste paper suspension PS. 
The characteristic values recorded in this way are advantageously used for 
the forming of controlled variables by which the operating means 
downstream in the process sequence are influenced at least in the waste 
paper preparation. Thus, the characteristic values IMf, Mp recorded by the 
measuring device ME1 are fed to a further state analyser ZA1, again 
constructed in the form of at least one neural network. This analyser 
again forms from these values controlled variables ST with the values AB, 
AZ, FL, AA, AS, AT. Since these values represent more accurately the 
actual state of the waste paper suspension PS at the outlet of the 
defibrator DS, they are advantageously passed on as controlled variables 
for process control to downstream open-loop and closed-loop control 
devices, in the example of FIGS. 3, 4 to the closed-loop and open-loop 
control devices RS3 . . . RS9. 
In the same way, the spectral and physical characteristic values IMf, Mp 
recorded by possibly existing further measuring devices ME2 . . . ME5 can 
be fed to further state analysers ZA2 . . . ZA5, again constructed in the 
form of neural networks. Each of these analysers makes available a 
dedicated set of controlled variables ST, which is passed on for process 
control to the closed-loop or open-loop control devices RS4 . . . RS9 of 
downstream operating means in the waste paper preparation AAA and, if 
appropriate, to a paper machine PAM in a recycling paper plant.