Method and device for measuring forces

Details Method and device for measuring forces Method and device for measuring forces

2000-07-24

2002-04-02

Fuller, Benjamin R. (Department: 2855)

Measuring and testing

Dynamometers

Responsive to force

C073S862381, C073S862632, C073S862633

Reexamination Certificate

active

06363798

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to force measurement technique, in particular to a method and apparatus for measuring friction forces on a friction tester.
BACKGROUND OF THE INVENTION
Tribology is a science of friction, wear, and lubrication on friction surfaces. Many different types of friction testers, tribometers, and other devices for measuring various parameters of friction are known. One such friction tester is disclosed in U.S. Pat. No. 5,795,990 issued to Norm Gitis, et al in 1998. This tester has a lower disk-like test material specimen and an upper rod-like test material specimen or probe which performs orbital motions while being in contact with a stationary lower specimen. A disadvantage of this device is that the upper specimen has a leverage with respect to the point of attachment of the lower specimen, i.e., with respect to its center. As a result, the loading force applied to the lower specimen via the upper probe, as well as the reaction force applied to the probe from the lower specimen create an unbalanced momentum and deformations in the force measurement system. Similar problem occurs in a mechanism for attachment of a bi-directional force sensor in a friction tester, as disclosed in our pending patent application Ser. No. 09/588,054 filed by the same applicants on Jul. 24, 2000.
As shown in
FIG. 1
, which is a three-dimensional view of a sensor installed in a friction tester for measuring a friction force and other tribological parameters of various materials and lubricants, the device has a sensor
10
formed by a beam
12
flexible in two mutually perpendicular directions for measuring a loading force F
1
and a friction force F
FR
. Both ends of the beam are connected or integrally made with rigid end blocks
14
and
16
. The end block
16
is rigidly attached to a loading unit
18
of the tester (not shown), while the end block
14
supports an upper specimen or probe
20
which is maintained in contact with a disk-like lower specimen D. The solid end block
14
has a limited freedom of movement to ensure deformation within the range of measurements. Flexibility of the beam
12
in the X-Z plane, i.e., deformations caused by the loading force F
1
are allowed due to the provision of a through slot
21
with notches
22
and
24
. The notches have a width wider than the width of the slot
21
thus weakening the beam and making it deformable in the area of the notches
22
and
24
. Similarly, flexibility of the beam
12
in the Y-Z plane, i.e., deformations caused by the friction force F
FR
are allowed due to the provision of a through slot
26
with notches
28
and
30
. The notches
28
and
30
have a width wider than the width of the slot
26
thus weakening the beam and making it deformable in the area of the notches
28
and
30
. The slots
26
and
21
are partially overlapped within the body of the beam
12
so that the beam can be considered as two deformable parallelograms that arranged in two mutually perpendicular planes. Deformations of the beam
12
caused by the loading force F
1
in the X-Z plane are measured by two strain gauges
32
and
34
. Reference numeral
34
designates the strain gauge located on the other side of the beam. However, the strain gauge
34
itself is not seen in FIG.
1
. Similarly, deformations of the beam
12
caused by the friction force F
FR
in the Y-Z plane are measured by two strain gauges
36
and
38
located on both sides of the beam near the weakened portion on the other end of the beam (only one of these strain gauges
36
is seen in FIG.
1
). In more detail the construction of the beam
12
and principle of its operation during friction testing is described in pending U.S. patent application Ser. No. 09/588,054 filed by the same applicants on Jul. 24, 2000.
In the course of testing, the lower specimen D is brought into rotation, e.g., in the direction shown by an arrow R, and then a loading force F
1
is applied to the solid end block
16
whereby the upper specimen
20
comes into contact with the lower specimen D. Application of force F
1
causes interaction between the upper specimen
20
and the lower specimen D. The aforementioned interaction generates friction force F
FR
and reaction force F
R
. Due to flexibility of the beam
12
, these forces cause deformations of the beam
12
which are registered by the aforementioned pairs of strain gauges.
However, the friction force F
FR
generates unbalanced momentum and torsion deformations in the force measurement system. Such asymmetry results in a number of undesired phenomena, such as occurrence of parasitic vibrations generated during rotation of the lower specimen D, tilting of the upper specimen
20
, and as a result, limitation in the frequency of rotation, narrowing of test ranges, and inaccuracy of measurements.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a method and a force measurement apparatus which eliminate an unbalanced momentum and deformation in the force measurement system of the tester, improve accuracy of measurements, broaden the range of test conditions, and prevents such phenomena as parasitic vibrations.


REFERENCES:
patent: 3577779 (1971-05-01), Laimins
patent: 5795990 (1998-08-01), Gitis et al.
patent: 6038933 (2000-03-01), Meyer

Affiliated with

Also associated with

Rating

Method and device for measuring forces does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method and device for measuring forces, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for measuring forces will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2884075