Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
2000-07-24
2002-11-26
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
C033S503000, C033S504000, C033S551000, C033S553000, C033S554000, C033S556000, C033S558000, C033S559000, C033S561000
Reexamination Certificate
active
06484571
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for measuring the surface configuration of a workpiece by a contact-type probe attached to a coordinates measuring machine, etc. More specifically, the present invention relates to improvement in measurement efficiency and accuracy with use of contact detection probe vibrated by ultrasonic wave.
2. Description of Related Art
A height gauge (one-dimensional measuring machine), a coordinates measuring machine, and a profile measuring machine are known for measuring the configuration and/or dimension of a workpiece. Various probes are used by these measuring machines in order to detect the positional relation between the measuring machine and the workpiece. The probes are classified into non-contact type probes and contact type probes, continuously measuring probes, and contact detection probes (touch trigger probes), etc.
A touch signal probe vibrated by ultrasonic waves disclosed in Japanese Patent Laid-Open Publication No. Hei 6-221806 is known as a contact detection probe used for a coordinates measuring machine. The contact type vibrating probe disclosed in this publication has a stylus having a contact portion to be in contact with a workpiece at a tip end thereof, 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's vibration by the vibrator.
According to the touch signal probe, since the vibration status of the stylus changes when the tip end of the stylus touches a surface of the workpiece, the surface position of the workpiece can be detected by the detector.
Such a touch signal probe vibrated by an ultrasonic wave is sometimes used for measuring the diameter of a small hole etc. For measuring small holes, another touch signal probe shown in U.S. patent application Ser. No. 09/366,774 has been proposed as a small size touch signal probe vibrated by ultrasonic wave.
As shown in
FIG. 12
, the touch signal probe
100
has 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 counter balance
102
B is provided at a base end of the stylus
102
. When the stylus
102
vibrates in an axial direction thereof, the centroid position becomes a node of vibration.
In the touch signal probe
100
, the stylus
102
is composed of a thin stick member and the contact portion
102
A composed of a small sphere in line with the stylus
102
to enable small hole measurement. Further, since the thin stylus
102
is difficulty 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
resonates along the axial direction by the vibrator
103
A, the node of vibration is caused at the centroid position of the stylus
102
. The supporting portions of the stylus
102
of the stylus holder
101
sandwich the node of vibration.
According to the touch signal probe
100
, since the stylus holder
101
supports the stylus
102
at the two portions sandwiching the node of vibration, the stylus
102
can be supported by the stylus holder
101
even when the stylus
102
is made from an extremely thin stick member, thus enabling the inner surface measurement of a small hole having a large aspect ratio.
On the other hand, another method for touching the surface of the workpiece by vibration movement (“tapping method”) has been proposed (e.g. U.S. patent application Ser. No. 09/540,051).
According to the above method, a second vibrator is provided to, for instance, the above-described stylus holder
101
and the stylus
102
is vibrated by the second vibrator, so that the contact portion
102
A at the tip end vibrates toward and away from the workpiece.
According to this tapping method, even when the stylus
102
moves along the surface of the workpiece to measure the surface configuration continuously, since the contact portion
102
A moves toward and away from the workpiece, dragging (adhesion phenomenon) by the workpiece can be avoided even with the stylus
102
having less rigidity. Therefore, the method is advantageous in that work efficiency can be improved by the continuous measurement while maintaining high accuracy.
However, measurement accuracy is largely influenced by a timing for outputting trigger of contact detection in the above-described touch signal probe vibrated by ultrasonic wave.
Specifically, when the stylus vibrated by the vibrator moves toward the workpiece and the contact portion touches the surface of the workpiece, vibration starts to be restrained when contact is initiated. When the contact portion further moves toward the workpiece and the contact portion touches the surface of the workpiece with a certain pressing force, the vibration of the stylus is further restrained. At this time, since the pressing condition toward the workpiece surface and restraint of the vibration are interrelated, the force of the stylus toward the workpiece can be made constant by sensing that the restraint of the vibration reaches a predetermined level by monitoring the output signal of the detector, so that accurate position detection is possible.
However, for measuring a position of one point on the surface of the workpiece, it is necessary to repeatedly move the stylus toward and away from the workpiece detecting when the vibration of the stylus is settled at the position. An enormous total amount of work time may be required for checking numerous points when, for instance, continuously measuring the surface of the workpiece.
On the other hand, the work time can be shortened for measuring respective positions of the workpiece if the vibration of the stylus is not strictly settled at the position but, settled only to a predetermined level. However, in this case, measurement accuracy naturally deteriorates.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a surface configuration measuring method for avoiding the influence of convergence time at each contact point on the workpiece while detecting contact by vibration, thereby improving work efficiency while maintaining high measurement accuracy.
The present invention focuses on the fact that, in the conventional contact detection by vibration, the stylus is moved to a position where the vibration of the stylus reaches a predetermined level, and position information of the stylus at the position is read to obtain contact position. The time to take the troublesome steps for minutely moving the stylus toward and away from the workpiece is known as the convergence time. In the present invention, the stylus is not settled to a predetermined position, but a coordinate of the predetermined position conventionally to be settled is calculated by the detected value of the detector obtained adjacent to the predetermined position and the detected position of the stylus, thus measuring the position of the surface of the workpiece with high accuracy and efficiency.
More specifically, the present invention is a surface configuration measuring method for measuring a surface configuration of a workpiece using a contact detection probe comprising: a support body for moving in a three-dimensional space by a predetermined command velocity vector based on an outside command; a stylus being supported by the support body and having a contact portion to be in contact with the workpiece; a vibrator for resonating the stylus at a first frequency f
1
in an axial direction; and a detecting circuit for detecting change in vibration of the stylus by the vibrator, the surface configuration of the workpiece being measured by a position of the support body when the contact portion touches the surface of the work
Hidaka Kazuhiko
Okamoto Kiyokazu
Saito Akinori
Larkin Daniel S.
Mitutoyo Corporation
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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