Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2000-03-31
2002-10-01
Moller, Richard A. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
Reexamination Certificate
active
06457366
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a movement control mechanism for a contact-type vibrating probe for controlling the movement of a contact-type vibrating probe, the contact-type vibrating probe having a stylus with a contact portion at a tip end thereof to be abutted to a workpiece, a stylus holder for supporting the stylus, a vibrator for resonating the stylus in an axial direction at frequency fl, and a detector for detecting change in vibration of the stylus by the vibrator.
2.Description of the Related Art
A height gauge (one-dimensional measuring machine), a coordinates measuring machine, and a profile measuring machine are known as measuring machines for measuring the configuration and/or dimensions of a workpiece. Various probes are used by the measuring machines in order to detect positional relation between the measuring machine and the workpiece. The probes are classified into non-contact-type probes and contact-type probes, and continuously measuring probes and trigger transmission probes.
A contact-type vibrating probe disclosed in Japanese Patent Laid-Open Publication No. Hei6-221806 is known as a contact-type trigger transmission probe (touch trigger probe) used for a coordinates measuring machine.
The contact-type vibrating probe disclosed in the publication includes a stylus having a contact portion to be in contact at a tip end thereof with a workpiece, a stylus holder for supporting the stylus, a vibrator for resonating the stylus in an axial direction thereof by applying ultrasonic vibration, and a detector for detecting a change in the stylus' vibration caused by the vibrator.
With the contact-type vibrating probe, since the vibration status of the stylus changes by touching the tip end, the end surface position of the workpiece can be detected by detecting the change in vibration status.
On the other hand, a contact-type vibrating probe is sometimes used for measuring the diameter of a small hole.
For measuring small holes, another contact-type probe shown in Japanese Patent Application No. Hei10-22047 has been proposed as a small size contact-type vibrating probe.
As shown in
FIG. 24
, the contact-type vibrating probe
100
includes a stylus holder
101
, a stylus
102
, a vibrator
103
A and a detector
103
B. A contact portion
102
A to be in contact with the workpiece is provided at an end of the stylus
102
and a counterbalance
102
B is provided at a base end of the stylus
102
, so that the axially central position of the stylus
102
becomes the centroid position. When the stylus
102
vibrates in an axial direction, the centroid position becomes a node of vibration.
In the contact-type vibrating probe
100
, the stylus
102
is composed of a thin stick member and the contact portion
102
A is composed of a small sphere for adaptation to the small hole measurement. Further, since the thin stylus
102
is difficult to support at one point, the stylus holder
101
supports the stylus
102
at two points sandwiching the centroid position of the stylus
102
.
The vibrator
103
A and the detector
103
B are made by dividing a piezoelectric element
103
stretching over the two supporting portions of the stylus holder
101
. When the stylus
102
is resonated along the axial direction by the vibrator
103
A, the nodes of vibration are generated at the centroid position of the stylus
102
and the supporting portions of the stylus
102
of the stylus holder
101
.
According to the contact-type vibrating probe
100
, since the stylus holder
101
supports the stylus
102
at the two portions sandwiching the nodes of vibration, the stylus
102
can be supported by the stylus holder
101
even when the stylus
102
is made by an extremely thin stick member, thus enabling the inner face measurement of a small hole having a large aspect ratio.
However, the following disadvantage occurs in continuous measurement along an inside wall of a small hole by the above-described contact-type vibrating probe
100
.
Since the stylus
102
of the contact-type vibrating probe
100
has only a small axis diameter, the axis rigidity of the stylus
102
is lessened, so that the stylus
102
bends when the contact portion
102
A is in contact with the workpiece, thus causing the so-called “adhesion phenomenon”.
The adhesion phenomenon causes little problem in detecting contact between the contact portion
102
A and the workpiece. However, when continuous contact measurement is conducted along an end surface of the workpiece, a mechanical phase delay can be generated, thus resulting in mechanical deformation by the adhesive force causing a position error.
Further, the following problem also occurs. The above-described contact-type vibrating probe can detect contact with the workpiece with high accuracy since the detection signal sensitively changes by applying an extremely small contact force. On the other hand, it is impossible for the contact-type vibrating probe to discriminate which longitudinal position (a point on the contact portion surface defined as an angle on a plane orthogonal with the axis of the stylus) of the spherical contact portion touches the end surface of the workpiece. Accordingly, the contact-type vibrating probe has no sensitivity difference with regard to longitudinal direction of the spherical contact portion, so that it is impossible to know in which direction the contact portion touches the end surface of the workpiece. Accordingly, the contact-type vibrating probe is not suitably used as a probe for profiling measurement and continuous measurement.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a movement control mechanism for a contact-type vibrating probe capable of preventing the adhesion phenomenon of the stylus caused by the contact with the workpiece and for conducting continuous measurement along the surface of the workpiece.
For attaining the above object, a movement control mechanism for controlling movement of a contact-type vibrating probe according to the present invention comprises a contact-type vibrating probe having a stylus provided with a contact portion at a tip end thereof to be in contact with a workpiece, a stylus holder for supporting the stylus, a vibrator for resonating the stylus at frequency f
1
in an axial direction, and a detector for detecting a change in vibration of the stylus by the vibrator. The movement control mechanism is characterized in having:
a support body mechanically connected to the stylus holder to move in three-dimensional space at a predetermined velocity in accordance with an external command;
a second vibrator for vibrating the stylus relative to the workpiece at a frequency f
2
in a direction orthogonal to the axial direction of the stylus and also in a normal direction to a surface of the workpiece; and
a controller for controlling movement of the support body so that the state of a detection signal detected by the detector at contact of the contact portion with the surface of the workpiece remains constant when the contact portion touches the surface of the workpiece while vibrating the stylus by the second vibrator.
According to the above movement control mechanism of the contact-type vibrating probe, the contact-type vibrating probe can be used for continuous measurement of a surface of the workpiece while avoiding the adhesion phenomenon. As shown in FIG.
1
(
b
), when the contact portion
102
A of the stylus
102
is disposed adjacent to the surface of the workpiece W and is vibrated at a frequency f
2
in a normal line direction to the surface of the workpiece by the second vibrator, the contact portion
102
A touches and separates from the end surface of the workpiece W, thus conducting a tapping action.
At this time, since the vibration of the stylus
102
is either free in a non-contact state or is restricted by contact force F in a contact state, the vibration of the stylus
102
in the axial direction at the frequency f
1
decreases amplitude A of the vibration in the axial direction of the stylus
Hidaka Kazuhiko
Matsuki Kaoru
Okamoto Kiyokazu
Mitutoyo Corporation
Moller Richard A.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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