Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1146~Sl
The invention relates to a method and apparatus for
feeding pieces of timber into a timber processing machine. The
expression pieces of timber as used here means elongated lengths
of timber which have a centre line and which possess in the lon-
gitudinal direction either only outside contours, such as logs,
or both outside contours and measurable inside contours such as
blocks, planks, and boards. A timber processing machine, which
also has a centre line, as referred to herein means a sawing
machine, a reducer, a reducing and sawing machine or some other
such machine. To achieve the optimum yield from a piece of timber,
the piece of timber should be fed into the processing machine
in a particular feed attitude, which can be defined, for example,
in terms of the position relationship between the centre lines
of the piece oftimber and the processing machine.
Methods are known in which thelongitudinal ccntours
of a piece of timber are sensed or measured b~ an optical or
mechanical measuring system which feeds the measurement results
in the form of electrical signals to a computer system in which
the optimum yield and the feed attitude required to achieve it
is determined, and in which control signals are produced, on the
basis of which the piece of timber is lined up in the necessary
feed attitude by special alignment devices. An arrangement of
this kind is described for example in the applicant's US Patent
No. 4,139~035 issued February 13, 1979.
Methods are likewise known in which, for planks and
other pieces of timber which, in the longitudinal direction, have
inside contours as well as outside contours, the inside contours
are used in the computer as a basis for determining the optimum
yield, since it is these, and not the outside contours, that
determine thevolume of sound wood.
Both optical and mechanical measuring devices for re-
cording the outside contours and/or the inside contours are known
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an~ are described, for example, in Swedish patent specification
~81,334 published December 1, 1975 and in German Offenlegungsshrift
2,706,149 published August 18, 1977.
The weakest link in all hitherto known arrangements
for feeding pieces of timber into a timber processing machine
is the mechanical holding or location of the piece of
timber when, during the feed sequence, it has already been engaged
by the processing tools of the machine, and is thus subjected
to the effect of by no means insignificant lateral forces.
However sophisticated the measurement of the geometry of the
of the pieces of timber and its relative position may be, the
results cannot be more accurate than the performance of the con-
trol equipment, and with optical measuring systems in particular,
the alignment stage is often a basic weakness.
The present invention overcomes the above-mentioned
disadvantage and develops the general concept that the
longitudinal contours of the piece of timber (outside contours or,
where applicable, outside and inside contours) are to be measured
during the longitudinal forward feeding of the piece of timber,
i.e. during a forward feeding motion of the same kind as the motion
with which the piece of timber is fed into the processing machine,
and with measuring devices which do not exert any significant
lateral force on the piece of timber (or no force at all).
Alignment is achieved during feeding-in at the same time as
guiding, and is performed by devices which apply lateral force to
the piece of timber and which ~ointly "re-create" the longitudinal
contour form of the piece of timber, calculated in the measuring
system, but generally in a corrected position (relative to the
centre line of the processing machine). The sawing technique in
which a piece of timber with a curved centre line is continuously
xotated during feeding about an axis perpendicular to the feed
centre line, is also to be possible.
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1146~51
According to the present invention there is provided
a method for feeding pieces of timber into a timber processing
machine, in which a measuring system longitudinally measures the
contours of the piece of timber, and the measurment ~esults
are input in the form of electrical measurement signals to a
computer system in which, on the basis of these signals and a
stored optimisation program, are calculated both the optimum
yield that can be obtained from the piece of timber, and the
attitude in which the piece of timber must be fed into the pro-
cessing maching to achieve this yield, the electrical order sig-
nals are generated for aligning the piece of timber with the
above-mentioned necessary attitude, in which method the piece
of timber is advanced longitudinally on a conveyor arrangement
relative to which it is positionally fixed, through the measuring
system a~ong the centre line of the conveyor system, and is
further conveyed from the measuring system to a control
system situated closely adjacent to the processing machine, the
piece of timber is advanced longitudinally through the control
system along the centre line of the control system, which
coincides with the centre line of the processing machine, at a
rate defined relative to the feed rate through the measuring sys-
tem, the measurement results from the measuring system, containing
information on the longitudinal contours of the piece of
timber, including the outside contours, and
on the position of the said contours
relative to the centre line of the measuring system,
`. are input to the computer system in the form of at least one
continuous sequence of longitudinal contour signals, the control
signals are output from the computer in the form of at least one
continuous sequence and are fed to the above-mentioned control
system for operating its control devices with a delay corresponding
to the time taken by a reference point on the piece of timber to
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~146Q51
travel from a reference point in the measuring system to the
corresponding reference point in the control system so that when
the piece of timber passes through the control system the
external longitudinal contour shape determined in the measuring
system is re-created in the control system, but, relative to the
centre line of the control system, in a position corrected by
calculation on the computer system to the above-mentioned necessary
feed attitude, and the piece of timber is fed into the
processing machine under forced control by the thus-operated con-
trol devices, which are each subjected by an actuating devicewith sufficient force for lateral guiding of the piece of timber.
The present invention also provides an apparatus for
feeding pieces of timber into a timber processing machine by the
method comprising at least one measuring arrangement to measure
the contours of each piece of timber in the longitudinal direction,
an alignment arrangement to align the piece of timber to a
feed attitude necessary for optimum yield, a computer system to
which the measuring and alignment stations are connected and
which is arranged to receive measurement signals from the
measuring system or systems and to process the measurement signals
with the aid of a stored optimisation program into control signals
to operate aiignment devices in.the alignment arrangement so that
the piece of timber is aligned to the said necessary feed attitude
and at least one conveyor arrangement to advance the pieces of
timber, in which apparatus the measuring system comprises a conveyor
arrangement to advance the piece of timber longitudinally and in
a state in which its position is fixed, through the measuring
system along the centre line of the measuring system, and at
least one measuring device to measure the contours of the piece of
timber in the longitudinal direction and to send the measurement
results to the computer system in the form of at least one con-
tinuous sequence of measurement signals, closely adjacent to the
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1146Q51
processing machine there is arranged a control system which
comprises a conveyor arrangement to advance the piece of timber
lonc3itudinally through the control system along the centre line
whic:h coincides with the centre line of the processing machine
and for feeding the piece of timber into the processing machine,
and at least one control device which is powered by an actuating
device that can be operated by control signals from the computer
system, with a force sufficient to displace the piece of timber
laterally on the conveyor arrangement and to hold the piece of
timber firmly under the action of lateral force acting upon it
in the processing machine during processing, the computer system
is arranged to output the control signals in the form of at
least one continuous sequence of control signals and comprises
a delay unit to delay the said output of control signals to the
control system by a time corresponding to the time required
for a reference point on the piece of timber to travel from a
reference point in the measuring system to a corresponding re-
ference point in the control system.
The invention will be explained in detail with
reference to the accompanying drawings in which:-
Fig. 1 is a schematic plan view of a first embodiment
of an apparatus according to the invention,
Fig. 2 is a schematic plan view of a second, and
Fig. 3 of a third embodiment of the present invention,
Figs. 4a and 4b show a board with waney edges in two
different positions,
Fig. 5 shows measurement of the inside and outside
contours of a board according to Fig. 4a, and
Fig. 6 shows in a diagram examples of the behaviour
of the signal obtained in a measuring system.
According to Fig. 1, a log lOA is moved on a longitu-
dinal conveyor tchain conveyor) 20 which is driven in the direction
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1146~51
of the arrow Pl in a conventional manner, (not shown in the
drawing). The log is pressed against the conveyor by one or
more retaining rollers 21 above the log with such a force
that the log is fixed in position relative to the conveyor.
Log lOA is in the process of passing through a measuring station
M in which there is arranged a measuring system that includes
two measuring devices, each comprising a pair of contact rollers
22, 23 with vertical spindles 22a, 23a. The pairs of rollers
are arranged a distance e apart, where e is preferably 2 m
(for the measurement of pieces of timber at least 4 m long).
The contact rollers can move freely transversely to conveyor 20,
and pressure devices, for example a helical spring 22b, which
for clarity is shown only on contact roller 22, press the contact
rollers against log lOA, but with such a small force that the
position of the log on conveyor 20, held by retaining roller
21, is not affected. The distance apart of each pair of
contact rollers ("the opening width"), and their position
relative to the centre line CM of the measuring station is
continuously sensed and is fed to a computer D as a continuous
sequence of signals from each measuring device. For clarity
only the connection between the left-hand contact rollers and
the computer have been drawn in Fig. 1, although obviously
the positions of the right-hand rollers are fed to the computer.
The forward motion of log lOA
f 30
4 1146~)51
through measuring station M is also sensed and fed to the
computer D; this can be done either by means of a separate
motion detector such as pulse transmitter 16, or by means of
retaining roller 21.
In principle only one measuring device is sufficient to
measure the longitudinal contours of the piece of timber,
but the piece of timber, which may for example be up to 6 m
long, must then first pass completely through the measuring
device before control can begin. However, this distance is
reduced by using several measuring devices in the measuring
system, for example two 3 m apart, as shown, or three 2 m
apart. A piece of timber 6 m long then has only to be
conveyed 3 m or 2 m respectively through the measuring
station to be fully measured.
In the rest position contact rollers 22, 23 may be either at
a minimum distance apart, smaller than the smallest log
diameter, or at a maximum distance apart, greater than the
largest log diameter In the first case the measuring
process is initiated by the piece of timber forcing the
contact rollers apart; in the second it is initiated by a
signalling device such as a photocell arrangement 29
signalling that the top end of the piece of timber has
arrived at the last measuring device in the direction of
feed, after which all the contact rollers in the measuring
system are pressed against the piece of timber.
The same conveyor 20 moves log 1OA from measuring station M
to and through a control station I in which the log has the
position 1OD, and is then fed into a reducer 11 with two
reducing discs 15. The centre line CI of control station I
coincides with the centre line Cg of reducer 11, and in the
example shown also with the centre line CM of measuring
station M. Since log 1OA, 1OD is being carried all the way
on a conveyor 20, the speed of its forward motion through
control station I is equal to its speed in measuring station
M, and no additional sensors are required. As a general
principle, the speed in control station I must be unambigu-
ously defined relative to the speed through measuring
section M.
5 1146051
Control statlon I is adjacent to reducer 11, and is equipped
with a control system consisting of two control devices,
each comprising a pair of guide rollers 32, 33, which have
vertical spindles such as 33a and which, at least in the
parts that come into contact with log 1OD, resemble the
corresponding parts of contact rollers 22, 23 in measuring
station M.
In this description, control device, control system etc
means the arrangements etc that act upon the piece of timber
with the combined effect of positioning it in the required
feed attitude and keeping it in that attitude during
feeding.
Unlike the contact rollers in the measuring station, the
guide rollers in the control stàtion are therefore actuated
with such a great force that they are able, despite
retaining roller 21', to change the position of log 10D
relative to conveyor 20. In the example shown this is
achieved by each guide roller or guide roller spindle being
carried by the piston rod of double-acting hydraulic
cylinder-pi8ton assemblies 34, 35, which are the actuating
devices of the control devices. For alignment a device is
needed to position the top end of piece of timber 1OD (this
is the alignment that is often performed in known arrange-
ments). At least one aditional control device is required
for possible parallel displacement and/or rotation (around
an axis perpendicular to its centre line) of the piece of
timber. For alignment of short pieces of timber the
distance e' between two adjacent control devices must be
less than the shortest length of a piece of timber, which on
the other hand leads to problems with the alignment of
pieces of timber of maximum length (6 m). It therefore
proves particularly advantageous to use at least three
control devices 2 m apart, as shown in ~ig. 3.
The activating devices operate in accordance with order
signals received from computer system D, which produces the
order signals on the basis of a stored program and of the
signals rscsivsd from msasuring station ~ and pu1ss
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6051
transmitter 16. For clarity Fig. 1 shows connections only
from computer D to the left-hand actuating devices, bu-t
obviously there are the corresponding connections to the
right-hand actuating devices.
Such signals from the measuring station are shown in the
diagram in Fig. 6, where the abscissa represents -the travel
distance of the piece of timber, and the ordinate the
measurement signals. The curve A is the midpoint curve of
the piece of timber, corresponding to the expression Y(x),
whilst the curve ~1 represents one longitudinal outside
contour of the piece of timber and F2 the other outside
contour.
(y(x) + ( ) ) . . . . . . . . . . . . . . . . . . . (~ )
(y(x) _ (x)) . . . . . . . . . . . . . . . . . . . . (2),
where b(x) represents the width curve of the piece of
timber.
In principle, measurement can be performed in two ways of
equal value, either by recording the outside contours and
calculating the midpoint and width, or by recording the
midpoint and width and calculating the outside contours.
In computer system D there is stored in a known manner a
program for calculation of optimum yield (which need not
always be the greatest yield in volume terms) from a piece
of timber for which the measurement signals have been
received, and of the feed attitude required to obtain the
optimum yield. On the basis of the calculation results, the
computer D generates order signals to position the piece of
timber in control station I to the required feed attitude.
According to the present invention, the computer D is
equipped with a delay unit R to which the generated order
signals are first fed, and in which their output from
computer D is delayed by such an amount that when, for
example, a point S' on log 1OD passes through control device
32, ~2, actuating device ~4, ~4 of this control device
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7 114605~
is controlled by an order signal that was generated on the
basis of tne measurement signal that was produced when the
point S on log 1OA passed through measuring device 22, 22.
It can thus be said that the control devices "re-create" the
longitudinal contour form of the log that was sensed by the
rneasuring devices, but with the important difference that it
is re-created in a corrected, i.e. changed, position rel-
ative to the centre line CI of the control system, compared
with the position of the centre line Cv of log 10 relative
to the centre line CM of tl1e measuring station. This change
of position is the result ^f the optimisation calculation
performed in computer D, so that the basically random
position of log 10 in measuring station M relative to centre
line CM is now corrected to a calculated optimum position
relative to centre line CI of control section I, and
therefore also relative to centre line Cg of processing
machine 11, which is to say that the required feed attitude
has been achieved.
The measurement signals can be used in different ways,
depending on the design of the processing machine and the
type o~ control required. Various control possibilities are
stated in more detail at the end of this description. They
also include the case of zero correction, in which the
computer D determines that the log 10 was already by chance
in a position in measuring station M corresponding to the
required feed attitude in control station I.
Fig. 1 shows the log 1OD after the position correction has
been carried out and the centre line Cv of the log coincides
with centre line CI of the control section, which was not
the case relative to the centre line CM of the measuring
station.
In principle the length of the delay in delay unit R can be
determined in two ways. Either a signalling device, for
example a photocell arrangement 39, generates a signal which
indicates that the top end of log 1OD has arrived at control
device 32, 32, this signal is fed to delay unit R and causes
the order signals to be issued, or the sequence of signals
from pulse transmitter 16 is fed to delay unit R and is used
8 ~4~
there, when the program contains the distance between the
measuring station and the control station to determine the
instant at which the order signals are issued. It should be
noted that in the example according to ~ig. 1, provided that
the speed of conveyor 20 is constant, the log moves at the
same speed in positions 1OA and 1OD. This means that the
order signal sequence must ~e issued at the same rate as the
measurement signal sequence was fed in.
At rest, the guide rollers in each pair of guide rollers are
the maximum distance apart. At the instant when the top end
of log 1OD enters the control device 32, 32, closest to the
processing machine 11, the issue of order signals from com-
puter D starts, and both guide rollers 32, 32, and guide
rollers 33, 33, grip log 10D and hold it firmly under the
influence of the order signal sequences that are now being
supplied to actuating devices 34, 35 during the entire
process of feeding into reducer 11. This effectively pre-
vents the unwanted lateral forces occurring in this reducer
from laterally deflecting the piece of timber.
~ig. 2 shows an alternative execution in which the meas-
uring station and the control station are arranged alongside
each other. The connections to and from computer D are
indicated only schematically, but are essentially the same
as in ~ig. 1. Here the measurement and control stations
each have their own longitudinal conveyor 20 and 30 res-
pectively. The speed of each conveyor is sensed by pulse
transmitters 16' and 16". These speeds need not be identi-
cal, since the relationship betwen them can be determined in
computer D on the basis of the signals from the two pulse
transmitters 16', 16", and thus also the correct rate at
which the order signals must be issued, for instance in
order that, when a reference point T' passes through control
device 33, 33, the control device is subjected to an order
signal that was generated on the basis of a measurement
signal obtained when the reference point T passed through
measuring device 23, 23, regardless of whether conveyors 20
and 30 are moving at equal or different speeds.
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In principle conveyors 20 and 30 can be mechanically syn-
chronised or coupled together and pulse transmitters 16',
16" can be omitted. But there must then be no sliding or
slipping, and this can hardly be guaranteed in practice.
As a consequence of the transverse motion between the
mea~urement and control stations, a signalling device such
as a photocell arrangement 39 is essential here to determine
when the output of the order signals is to begin.
The above-mentioned transverse motion is achieved in the
following manner. Conveyor 20 feeds piece of timber 10A
into measuring station M in the direction of arrow P1, with
the root end forward. After discharge from the discharge
end Mu of the measuring station, the piece of timber arrives
in a position 10~ on a roller convey~r 37a-37c which extends
in the same direction as conveyor 20, and which is crossed
by a transverse conveyor which includes three conveyor
chains 36a-36c with driver elements. Transverse conveyor
36a-36c may possibly equipped be in a known manner with buf-
fer arrangements to regulate the flow at the required rate.
The transverse conveyor move~ the piece of timber in the
direction of the arrows P2 to another conveyor 38a-38c
which, driven in the direction of arrows P3, runs in the
same direction as conveyor 30 of control station I. The
drawing shows the piece of timber in a position 10C just
before it has reached the above-mentioned second roller
conveyor 38a-38c, by which it is then fed top end first into
control station I via input end Ii Of the control section.
The piece of timber moves to position 1OD on conveyor 30 and
is advanced by conveyor 30 in the direction of arrow P4, as
well as being aligned and guided by control devices 32, 33
in the same manner as described in connection with ~ig. 1.
Any rotation of the pieces of timber about a vertical axis
during travel between conveyor 20 and conveyor 30 is im-
material since it cannot influence the result. On the other
hand, the pieces of timber must not rotate about their
centre line during this travel, and for this reason the
arrangement according to Fig. 2 is best suited for pieces of
timber such as boards, planks and blocks, which have a fl!at
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surface resting on the conveyor arrangement.
In view of the fact that the piece of timber can be fed
through the measurement and control stations at different
speeds, it is evident from ~ig. 2 that one control station
can be combined with or can interact with several measuring
stations, or that one measuring station can be combined with
or can interact with several control stations. As a general
rule, timber can be fed faster through a measuring station
than through a control station, since the control station
also acts as a feed station, and must maintain a working
rate that is determined by the feed rate possible in the
processing machine.
Fig. 3 shows another, space-saving execution. A log 1 OA,
which for clarity is shown in the lower part of the drawing,
is fed on a single longitudinal conveyor 20 through a
combined measuring and control station MI, arranged
immediately adjacent to processing machine 11 . The
following devices, in the order corresponding to the
direction of motion of conveyor 20, are arranged in the
combined station:
a measuring device 41 of essentially the
8ame kind as measuring devices 22, 23, two combined
measuring and control devices 42, 43, and a control device
of essentially the same kind as control devices 33, 34. The
combined measuring and control devices 42, 43 are essen-
tially identical to measuring devices 41, but they can also
be subjected to the effect of greater force by reason of the
fact that they are each subject to the action both of a weak
pressure device such as a spring 43d, and an actuating
device such as 43e. All devices in section MI are shown to
be of a basically known type in which the vertical spindles,
such as 41a, of the contact or guide rollers, are fixed to
arms such as 41b which in turn are pivoted on spindles such
as 41c, and are constantly pressed towards conveyor 20 by
weak pressure devices such as coil springs 41d. Control
; devices 44 are subject not to the action of the above-
mentioned weak pressure devices, but to the action of
actuating devices such as hydraulic-piston assemblies 34'.
These ectuating devices, :uch as actuating devices 43e,
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are fully comparable with actuating devices 33 and 34, also
with regard to control by order signals from computer D.
When the actuating device is not activated, the combined
devices work as measuring devices, and when the actuating
device is actuated they work as control devices. The com-
puter is informed of the forward feed rate of the piece of
timber either by a motion detector or a signalling device.
The arrangement operates in the following manner. ~og lOA
is inserted from the side with its top end at device 43, or
is fed to this position longitudinally in the direction of
arrow Pl, and measurement then starts. During measurement,
which is performed by measuring device 41 and by combined
devices 42, 43, all these devices operate as measuring
devices, and the actuating devices of combined devices 42,
43 and of control device 44 are deactivated. Log lOA is
advanced through the arrangement in the direction of arrow
Pl. When the top end of the log reaches control device 44,
the entire log has been measured and control can begin.
Combined devices 42, 43 change over to active control, and
control device 44 is al~o activated. When the rear end of
the log passes device 42 (position lOD), this device is
deactivated. When the rear end paase8 device 43, this
device is al~o deactivated, thus making the system ready to
receive the next log. When the rear end has passed device
44, this device is also deactivated.
Figs. 4a and 4b explain in more detail the process of
processing planks, boards, blocks etc which possess longi-
tudinally both outside contours H and inside contours G.
Between the outside and inside contours there are inferior
waney edge regions V. The usable volume is determined by
the clear area B between the inside contours G. The waney
edge regions V may be very irregular, so that the centre
line Cv of the whole piece of wood does not coincide with
the centre line Cg of the clear area B. Only clear area B
with delimiting contours G is of importance for calculating
the optimum yield, and the required feed attitude is that
shown in Fig. 4b, where the centre line CB Of the clear area
coincides with the centre line CR of the machine. However,
in the control arrangement board 10' can be gripped by
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12 ~460S~ ~
control devices 32, 33 only along its outside contours H.
Thus the optimum yield is calculated on the basis of inside
contours G, but the order signals for the control devices
are generated with respect to outside contours H.
Consequently both the outside and inside contours must be
measured in the measuring system and input to computer D.
Fig. 5 shows measurement of the inside contours in two
basically known manners. Either mechanical sensors in the
form of contact wheels 24 with bevelled surfaces, or a non-
contacting optical sensor 45 may be used. The vertical
spindles of the contact wheels are mounted on pivoted arms
in the same way as arms 41b in Fig. 3, and a known measuring
system of this kind is described for example in German
patent aplication 27 06 149. The optical sensor 45 is in
principle a camera with an objective 46 and an array 47 of
light-sensitive devices in the focal plane. A known measur-
ing system of this kind, which is described for example in
Swedish patent specification 381.334, can measure the inside
and outside contours at the same time, so that a measuring
section according to the present invention can be equipped
only with such mea8uring 8ystem8. The mechanical measurin~
system shown must be supplemented with a measuring system
for the outside contours, but mechanical measuring systems
that measure both the inside and the outside contours have
already been proposed.
Obviously the measuring and control devices need not be of
the same typei an optical measuring device may be used
alongside a mechanical control device. The essential
requirement is that the measuring devices relative to each
other and the control devices relative to each other should
be equally spaced in the longitudinal direction of the piece
of timber. It is also essential that each measuring and
control device has a known position relative to the centre
lines of the sections in question, even if, as Fig. 2 shows,
the centre lines of the measuring and control sections need
not coincide. The opening width measured in the measuring
system (the distance between contact rollers 22, 2~, 41
within ~ pair) corresponde to the diameter of the piece of
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114~5~
1~
timber, and can be used to advantage for automatic setting
Of the tools in proces~ing machine 11, for example to set
the po~itions of reducing discs 15 relative to each other.
~he delay in computer D can also be achieved by delaying the
input measurement signals before calculation operations are
performed, and by then issuing the order signals
immediately.
In conclusion, with reference to Fig. 6 and to formulas (1)
and (2), seven typical cases will be described, in which ~k
represents the order signal to the control devices, rep-
resents the measurement signal from the measuring devices
and YN a polynomial of degree N: ~
1) yk = o No correction signal. The piece of timber i9 processed along the
midpoint curve corresponding to a fixed control device. During
processing it i8 subject to large lateral forces caused by irreg-
ularities in its outside contours. This is the conventional method, the
disadvantages of which it is the purpose of the present invention to
eliminate.
2) yk = y The correction signal is equal to the measurement signal. The piece
of timber is processed alone the centre line of the measurine section,
i.e. the lateral position of the piece of timber relative to the
processine machine is not changed. This corresponds to a feeding-in
arraneement desiBned in such a way that the piece of timber i9 fixed on
the feed conveyor, a method that leads to relatively complex arranee-
ments when known technology is used.
3) yk = y - yO (yO = constant) The difference between this and case 2) is that
a "best" lateral displacement is calculated, and the piece of timber is
processed in a position displaced parallel relative to the centre line
of the measuring station In the present description "best"
(adaptation) means an adaptation of a function expression to a given
curve such that the spread is as small as pos~ible. The dimension of
the spread can be defined in different ways, for example by the least
squares sum of all deviations or as the smallest maximum deviation, or
by means of a calculation based on the width information obtained at the
same time as the midpoint curve. It is also fully conceivable that
3 other measuring systsms msssurs othsr pmrsmeters of the plscs o~
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14 1~46Q5~
timber and a "best" processing curve i8 calculated, which is fed to the
feeding system according to the present invention.
) yk = y - Yl (Y1 = cO + clx~ .-. cO, c1 = constant) The difference between
this case and case 3) is that a "best" rotation is calculated and the
piece of timber is proces~ed in a parallel-displaced and rotated
position relative to the centre line of the measuring station.
~ yk = y - Y2 (Y2 = cO + clx + c2x2~ .-.-..-. cO, cl, C2 = constant) The
difference between this and case 4) is that a "best" parabola is
calculated and the piece of timber is now continuously turned while
beinB processed. This is a form of curve-sawing.
6) yk = y _ y3 (y~ = cO + clx + c2x2 + c3x3, ..... ---- cO, cl, c2, c3 = constant)
The difference between this and case 5) is that a "best" cubic arc is
calculated. The curved sawing follows the midpoint curve of the piece
of timber better, but this methGd can lead to larger and more abrupt
curves on the proce~sed piece.
) yk = y - YN (N > 3, high-degree polynomial) When N is increa~ed, the "best"curve is made to approximate increasingly to the measured midpoint
curve, i.e. Y ~ YN. which gives yk ~ o, which finally leads to yk = o,
which has already been dealt with in case 1). (A polynomial has been
u~ed here to descr-ibe the correction signal, even though this is not
necessary, but it is the commone~t and most effective form of function
expres~ion).
