Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Mechanical measurement system
Reexamination Certificate
1999-04-13
2002-03-19
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Mechanical measurement system
C702S033000, C702S113000, C702S150000, C702S183000
Reexamination Certificate
active
06360176
ABSTRACT:
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates to a touch signal probe suitable for being a coordinate-measuring machine or a machine tool for measuring configuration of a workpiece. More specifically, it relates to a highly sensitive vibrating touch signal probe requiring low measurement power.
2. DESCRIPTION OF RELATED ART
A height gauge (linear measuring machine), a coordinate measuring machine and a contour measuring machine are known as a measuring machine for measuring configuration and dimension of a workpiece. For measuring coordinate and position, a touch signal probe is used to the measuring machine for detecting contact of the workpiece.
One detection mechanism uses a substantially cylindrical stylus having a contact portion to be abutted to the workpiece at the pointed end thereof, and a vibrating/detecting means for vibrating the stylus and detecting change of the vibration accompanied by the contact of the contact portion to the workpiece. In this arrangement, a touch trigger signal is transmitted when the vibration is damped to a detection trigger level and a coordinate value thereat is read.
In the vibrating touch signal probe, a radial arrangement (forming a plurality of stylus to a probe in a ramifying manner) is desirable for broadening the applicable range, and arranging the stylus crosswise is effective, for example.
One example of the probe having crosswise-arranged stylus is shown in FIG.
12
. In the Figure, the vibrating touch signal probe has a pair of stylus support
3
fixed to a pointed end of the probe body
5
as a probe axis. The pair of the stylus support
3
is joined to orient in X and Y axis direction respectively, and a stylus
2
is protruded on both sides thereof. An upper portion of respective stylus support
3
has a piezoelectric element
4
as a vibrating/detecting means provided along the respective styluses
2
. Each of the stylus
2
is vibrated by the piezoelectric element
4
and the contact ball
2
a
on the pointed end thereof is abutted to a workpiece, thereby detecting a change in restraining condition of the vibration (conventional art
1
).
According to the conventional art
1
, since two pairs of linear stylus support
3
are combined and the stylus is not disposed coplanarly, it is inconvenient in practical use and size reduction thereof is difficult.
On the other hand, a touch signal probe having a block-shaped stylus support, a piezoelectric element as vibrating/detecting means disposed to locating projection projectingly provided to four corners of respective upper and lower surfaces of the stylus support, and a symmetric first and second stylus respectively oriented in X and Y axis direction at a center of each side of the stylus support, thereby arranging radially, has been developed (Japanese Patent Laid-Open No. Hei 10-176902: conventional art
2
).
According to the conventional art
2
, since the symmetric first and second styluses oriented respectively in X and Y axis are disposed at the center of respective sides of the stylus support, there is no inconvenience as in the conventional art
1
. However, since a reciprocating vibration is caused to both of the X and Y axis by a single piezoelectric element, a total of four vibration system is combined, resulting in difficulty in raising Q value of a resonant vibration as compared to the conventional art
1
.
FIGS.
13
(A) and
13
(B) are graphs showing a relationship between a frequency and amplitude in the aforesaid conventional art
1
and
2
. FIG.
13
(A) shows small Q value case and FIG.
13
(B) shows large Q value case. Amplitude difference D (amplitude change by contact) between amplitude at a resonant point in a non-contact state and amplitude at the resonant point after contact is larger when the Q value is large than when the Q value is small. Accordingly, it can be observed that the Q value of the vibration at the resonant state is a significant factor which directly controls sensitivity of a vibrating touch signal probe, in which the change in resonance by contact is used as detection principle of detection.
As described above, the touch signal probe having radial arrangement as in the conventional art
2
is inferior in sensitivity to the conventional art
1
having the same stylus length, and the detection response time can be widely varied.
Furthermore, when the stylus contacts at a high speed (more than 10mm/sec, at present), the touch signal prove is vibrated by an impact in contact, resulting in unpredictable disorder of detected amplitude change.
When the stylus touches the workpiece at a high-speed, detected vibration displacement is regularly decreased from initiation of contact as shown in FIG.
14
(A). On the other hand, newly generated vibration waveform can be detected by the impact as shown in FIG.
14
(B). These signals are combined to be the detection signal of the stylus.
FIG.
14
(C) is a graph showing relationship between amplitude and time, the amplitude representing the signal detected by the stylus and converted to DC level. In FIG.
14
(C), the time before reaching detection level of the touch trigger signal differs between a case in which the vibration by the impact is applied in equal phase (shown in solid line) and a case in which the vibration by the impact is applied in inverse phase (shown in dotted line). The time difference becomes dispersion error C of detection response time, which causes detection error.
Accordingly, the dispersion of the detection response time increases in accordance with the increase of the contact speed. Incidentally, the phenomenon inevitably occurs in common to all of the conventional vibrating touch signal probes. Since the frequency of the vibration caused by the contact is intrinsic frequency of the vibrator composed of the stylus and the stylus support, it is difficult to separate the signal component on account of the principle in which the resonant frequency is used for vibration and detection.
A touch signal probe of a modification of the conventional art
2
is shown in
FIG. 15. A
probe support
50
supports a block-shaped stylus support
51
. Locating projections
52
are projectingly disposed on four comers of upper and lower side of the stylus support
51
. Piezoelectric elements
53
as vibrating means and detecting means are disposed on the respective locating projections
52
and symmetric first and second styluses
54
respectively oriented in X and Y-axis directions are disposed to a center of respective sides of the stylus support. Since the entire body including the stylus support
51
and the plurality of the styluses
54
is a vibrator forming one vibration system, the above-structured touch signal probe can be simply and easily assembled and stable resonance characteristic can be obtained.
The piezoelectric element
53
uses conventional linear wiring pattern for ultrasonic touch sensor. Specifically, a part of one piezoelectric element
3
is used as a vibrating electrode
53
A and the other part of the piezoelectric element
53
is used as a detecting electrode
53
B. The electrode
53
A and
53
B are disposed aligning a longitudinal direction of the styluses
54
opposed with each other. A vibrating circuit and a control circuit shown in
FIG. 16
is connected to the piezoelectric
53
. In the Figure, the vibrating circuit is composed of a driving circuit
55
for applying vibrating electric current to the vibrating electrode
53
A and a power supply
56
connected to the driving circuit
55
. The control circuit is composed of an amplitude-DC level converting circuit
57
for converting amplitude of the detected signal detected by the detecting electrode
53
B into DC (direct current) level and a touch trigger signal generating circuit
58
for generating a touch trigger signal in accordance with the signal outputted from the amplitude-DC level converting circuit
57
(conventional art
3
).
In the conventional art
3
, the vibration detecting direction of the vibrator of the piezoelectric element
53
is basically monoaxial. However
Ishikawa Nobuhiro
Nishioki Nobuhisa
Hoff Marc S.
Lowe Hauptman & Gilman & Berner LLP
Mitutoyo Corporation
Tsai Carol S
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