Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2000-03-10
2004-02-03
Kwok, Helen (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S625000, C073S628000, C073S633000, C073S641000, C073S598000, C073S600000
Reexamination Certificate
active
06684705
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the use of ultrasound testing to detect anomalies in wooden members. More specifically, the present invention relates to the use of a roller device housing an ultrasonic transducer element array for the ultrasound testing of wooden members.
BACKGROUND OF THE INVENTION
The grading of wooden members is important to the entire lumber and construction industry. Accurate grading allows a builder to match the strength of the wooden member to the type of construction project. In addition, proper grading permits a sawmill to charge a premium for stronger members, while dedicating weaker members for more appropriate tasks. Grading techniques have been developed that nondestructively measure certain physical properties of wooden members. One such technique uses ultrasonic waves to measure physical properties.
Ultrasound measurement systems often use rolling transducers to detect anomalies in, and thus the strength of, the wooden member. By passing an ultrasonic wave of known characteristics through the wooden member, the system is able to detect anomalies by analyzing a modification of the wave after it passes through the member. Specifically, a transducer located on one side of the wooden member directs an ultrasonic wave through the member to another transducer located on the opposite side of the wooden member. When part of the ultrasonic wave passes through the anomaly, it is modified and collected by a receiving transducer. A computer connected to the receiving transducer compares the transmitted wave with the wave that was passed through the wooden member, or with some “standard” or “ideal” wave. Based on the distorted difference between the two waves, the computer displays the anomalies on a monitor. Moreover, the system may be able to determine the type of anomaly (e.g., knots, checks, or split), its location, and its effect on the strength of the wooden member.
The demanding production line requirements of today's sawmill require that multiple characteristics of the wooden member be determined simultaneously. For structural softwood lumber and hardwood pallet stock, for example, the ultrasound measurement system must determine the location and severity of a knot at the same time it searches for other anomalies, like splits or checks (i.e., internal voids). In order to map out defects, multiple transducer systems have been used to produce rough maps of defect locations. In order to expand the coverage of the wooden members in such multiple transducer systems, the multiple transducers are staggered along the direction of movement of the wooden member (z direction), as illustrated in prior art FIG.
1
A. Due to mechanical mounting clearance requirements, the transducers are staggered in the z direction and not aligned along the y axis, thereby preventing any benefits from redundancy in geometry.
Those skilled in the art will appreciate that the presence of multiple transducers creates certain operational problems. Obviously, the use of multiple individual transducers increases the mechanical complexity of the ultrasound measurement system. Also, the transmitting transducers must be separated physically from each other to allow for mechanical mounting clearance. However, this required separation of the transmitting transducers and their dedication to one receiving transducer means that certain smaller anomalies, like splits, may fall between the ultrasound waves, thus foiling detection.
FIGS. 1A and 1B
provide an example of such a prior art multiple-transducer ultrasound measurement device
100
for grading a wooden member
107
. As will be understood from the following description, the term wooden member includes logs, cants, lumber, boards (like structural softwood lumber and hardwood pallet stock), and wood composites in various stages of processing.
FIG. 1A
is a perspective view of prior art multiple-transducer ultrasound measurement device
100
. As shown in
FIG. 1A
, multiple-transducer ultrasound device
100
includes three transmitting transducers
101
-
103
, located adjacent to each other. Multiple-transducer ultrasound device
100
also includes three receiving transducers
104
-
106
. Although
FIG. 1A
shows three transmitting transducers
101
-
103
and three receiving transducers
104
-
106
, it should be appreciated that multiple-transducer ultrasound device
100
may include any number of receiving and transmitting transducers. Wooden member
107
is located between transmitting transducers
101
-
103
and receiving transducers
104
-
106
.
Transmitting transducers
101
-
103
are separated from each other by some distance d along the z-axis. Distance d provides the necessary physical separation so that transducers do not physically interfere with each other. Receiving transducers
104
-
106
also are separated from each other by a distance d equal to distance d for the same reason. Separating receiving transducers
104
-
106
by distance d, equal to d, places receiving transducers
104
-
106
in the same x-axis plane as transmitting transducers
101
-
103
. Because of this, transmitting transducer
101
communicates exclusively with receiving transducer
104
, transmitting transducer
102
communicates exclusively with receiving transducer
105
, and transmitting transducer
103
communicates exclusively with receiving transducer
106
.
FIG. 1B
is a front-view of prior art multiple-transducer ultrasound measurement device
100
, further detailing communication between transmitting transducers
101
-
103
and receiving transducers
104
-
106
. In operation, as wooden member
107
moves along the z-axis, transmitting transducers
101
-
103
roll along one side of wooden member
107
, and receiving transducers
104
-
106
roil along the opposite side. Transmitting transducers
101
-
103
transmit ultrasonic waves through wooden member
107
to receiving transducers
104
-
106
. Anomalies within wooden member
107
affect the transmitted waves as they pass through wooden member
107
(as discussed further with reference to FIG.
3
). By analyzing the anomaly-affected waves received by receiving transducers
104
-
106
, as compared to the transmitted waves or a “standard” wave (as discussed further with reference to FIG.
6
), multiple-transducer ultrasound device
100
is able to provide an output that characterizes the various anomalies.
As shown in
FIG. 1B
, each of transmitting transducers
101
-
103
communicate exclusively with receiving transducers
104
-
106
, respectively. In particular, transmitting transducers
101
sends an ultrasonic wave
110
to receiving transducer
104
, transmitting transducers
102
sends an ultrasonic wave
111
to receiving transducer
105
, and transmitting transducers
103
sends an ultrasonic wave
112
to receiving transducer
106
. Notably, each of waves
110
-
112
travel in the x-direction, perpendicular to transmitting transducers
101
-
103
, receiving transducers
104
-
106
, and wooden member
107
. Because each receiving transducer
104
-
106
captures wave
110
-
112
, respectively, exclusively from one transmitting transducer
101
-
103
, respectively, portions of waves
110
-
112
that stray beyond their assigned receiving transducer
104
-
106
are ignored. As a result, small anomalies
108
and
109
that lie on the periphery of each transducer transmitter/receiver pair
101
/
104
,
102
/
105
, and
103
/
106
may go undetected.
The solution of
FIGS. 1A and 1B
is depicted by Fry et al. in U.S. Pat. No. 5,237,870, where Fry et al. describe multiple, independent ultrasound transducers (Fry—FIGS.
11
and
12
). Each transducer collects ultrasound information from a single aspect along the wooden member. Specifically, the information is collected along a linear arrangement of measurement points on a face of the member. Similarly, the publication “Ultrasonic defect detection in wooden pallet parts for quality sorting” (Schmoldt, D. L, R. M. Nelson, and R. J. Ross 1996. In S. Doctor, C. A. Lebowitz, and G. Y. Baaklini (eds.) Nondestructive Evaluation
Knauer Michael K.
McIntyre Raymond W.
Schafer Mark E.
Kwok Helen
U.S. Natural Resources, Inc.
Woodcock & Washburn LLP
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