Log testing apparatus

Details Log testing apparatus Log testing apparatus

2002-03-20

2004-11-09

Williams, Hezron (Department: 2856)

Measuring and testing

Testing by impact or shock

Specimen impactor detail

C073S012090, C073S579000

Reexamination Certificate

active

06813927

ABSTRACT:

This is a nationalization of PCT/NZ00/00139 filed Jul. 27, 2000 and published in English.
TECHNICAL BACKGROUND
The invention relates to apparatus useful in a method of assessing pulp, paper or wood from the stem of a felled tree (e.g., so as to be determinate of possible destinies of logs to be cut from the stem), such as stiffness of sections of wood cut from the stem, or wood fibre characteristics such as fibre length or the strength of pulp produced from the wood.
BACKGROUND ART
The timber industry faces a need to efficiently utilise its rather variable forest resource. Timber classification, for example machine stress grading, is currently done at the end of the production chain. This process results in wastage from processing which ultimately proves to have been inappropriate. Clearly, it would be more efficient to measure log properties early in the chain and process the logs accordingly.
In our New Zealand Patent Specification Nos. 331527 (filed Aug. 1998) and NZ333434 filed Dec. 17, 1998 there are disclosed procedures in respect of the testing of felled tree stems or logs with a view to determining a destiny for that tree stem or log or logs to be cut from the tree stem.
New Zealand Patent Specification 331527 is directed to the selection of wood according to fibre characteristics so as to determine materials appropriate for the pulp and paper industry whilst, New Zealand Patent Application 333434 is directed to timber or lumber cutting determinations but with the prospects of directing inappropriate tree stems or logs to the pulp and paper industry.
DISCLOSURE OF THE INVENTION
The present invention is directed to apparatus sufficiently portable and effective in usage which will allow the adoption of such aforementioned methods in the field.
It is therefore an object of the present invention to provide such apparatus and the use of such apparatus in the field for such tree stem or log assessment purposes. As used herein MOE is the dynamic modulus of elasticity derived by the product of (A) the square of the velocity of an appropriate wave propagation between the ends of a felled tree stem or a log (V
2
) and (B) the specimen density &rgr;.
In one aspect the invention consists in an apparatus for providing an indicator of or from which stiffness can be estimated for elongate timber, logs or felled tree stems (hereafter “logs”) of known length L or measurable length L, said apparatus comprising or including
sensing means capable of being placed in contact with or in close proximity to a log end to detect the impulse and echoes thereof resulting from a striking of the other or that same log end,
processing means to derive using an echo or echoes sensed by said sensing means a said indicator, and
display means to display said indicator or any derivative thereof received from said processing means,
wherein said processing means tests algorithmically frequency transformed data derived from time based echo data with a view to deriving a measure or good estimate of fundamental frequency f
0
,
and wherein L is or can be entered into said processing means,
and wherein said processing means derives said indicator by reference to both f
0
and L.
Preferably said processing means tests all spectral peaks of the echo data for membership of a series from which a best value of fundamental frequency f
0
can be derived and related to the plane wave speed V and specimen length L by V=2L/f
0
rather than by reliance on the identification of any single resonance peak.
Preferably said processing means recognises that the characteristic frequencies may be shifted significantly from a harmonic series f
0
, 2f
0
, 3f
0
. . . . . set and recognises that a better indication of the fundamental frequency f
0
, from which the speed V can be found is obtained from higher harmonics.
Preferably said processing means recognises that a better indication of the fundamental frequency f
0
than an attempted direct measure of f
0
itself is from at least the second harmonic.
Preferably said processing means recognises that whilst the natural resonance frequencies of stems and logs may be far from harmonic (principally on account of the asymmetry introduced by their taper or loading eg; when stacked) they may be transformed to a harmonic series by applying a correction which decreases as the harmonic number increases.
Preferably said processing means can transform observed resonant frequencies f
n
into multiples of a “true” fundamental frequency f
0
from which a plane wave velocity can be derived by reliance upon the relationship (f
n
=n f
0
)/f
n
=kc
−n
.
Preferably said the fractional deviation falls in geometric progression with ratio approximately 2.7.
Preferably the relationship is f
n

f
0
−1=k

2
.
Preferably said processing means discriminates against noise spikes in the spectra, peaks from unwanted modes inadvertently excited, or any other signals which differ from the spectral peaks sought and which have the desired relationship by using a comb filter comprising a number of frequencies (“centre” frequencies) which match the sought relationship, which can themselves be harmonic or have some other relationship, the comb filter having passbands wide enough to allow small derivations about each centre frequency.
forming the sum of the products of the actual spectral peaks and the comb filter, and
identifying as the sequence or filter which accounts for most spectral power, and, where necessary.
deciding between two filters which produce equal power sums on the basis of the comb which produces the least frequency offset between the actual spectral peaks and the filter centre frequencies.
Preferably said processing means uses such transforms to convert a harmonic series with a defined base frequency f
0
to a non-harmonic series, thereby defining the centre frequencies of a comb filter with which the actual series may be compared, without the need for all members of the actual series to be present.
Preferably said processing means can calculate a confidence number to be displayed by said display means to indicate the likelihood that the indicated velocity is correct or whether a re-measure is advisable based on the amount of power in the spectral peak series identified with a base value off
0
, compared with spectral power not accounted for, e.g. that assumed to be in spurious noise spikes or non-longitudinal resonances inadvertently excited.
Preferably said indicator is V or V
2
or a function of V or a function of V
2
.
Preferably said indicator is V
2
or a function of V
2
derived from a value or function of V, V having been determined by V=2L f
n
.
Preferably said display means displays V
2
or an indicator or indicators of the one or more properties being assessed, such as MOE or an approximation of MOE derived from MOE=&rgr;V
2
where &rgr; has been approximated (e.g. as near 1000 kg/m
3
for green felled logs).
Preferably said sensing means and/or processing means includes amplification means to ensure a sufficient gain to ensuing echoes in use.
Preferably said sensing means is adapted to be placed in contact with said log end.
Preferably said sensing means carries a switch for said processing means conducive, when activated, of good log/sensing means contact.
Preferably said sensing means is compliantly mounted by a sensing head to be physically pressed by a user against the log surface to be tested.
Preferably the compliant mounting of said sensing means within the means to be handled by a user i.e. the sensing head, is compliantly mounted by use of silicone rubber.
Preferably said sensing means is in a sensing head connected by flexible means to apparatus carrying said processing means and said display means.
Preferably said sensing means is or includes a piezo-style accelerometer.
Preferably said processing means has analog signal acquisition means, means for digitization and processing into a characteristic spectrum of the acquired analog signal data of the echoes and further software algorithms to interpret the data.
Preferably, wi

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