Geometrical instruments – Gauge – Having a movable contact probe
Reexamination Certificate
2002-05-30
2003-11-11
Fulton, Christopher W. (Department: 2859)
Geometrical instruments
Gauge
Having a movable contact probe
C033S561000
Reexamination Certificate
active
06643944
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a touch signal probe and a signal processing apparatus and a signal processing method of the touch signal probe, the touch signal probe being attached to a surface texture measuring machine such as a form measuring instrument or a CMM (Coordinate Measuring Machine). More particularly, the present invention relates to a touch signal probe, and a signal processing apparatus and a signal processing method of the touch signal probe which comprises a fixed member, a movable member, a reseat position system for allowing displacement of the movable member relative to the fixed member when an external force acts on the movable member and precisely restoring the movable member to a still position when the force acting on the movable member disappears, and deformation detection elements attached to a stylus.
2. Description of the Related Art
With the CMM, a touch signal probe is widely used for measuring a surface texture of a work by detecting contact between the probe and the work. With the CMM using such a touch signal probe, a contact element of the probe that can make a relative move in a three-dimensional direction is brought into contact with a work placed on a stage. The coordinate values of axes (axes in the three-dimensional direction) of the contact element are read with the instant at which the contact element comes in contact with the work as an electric trigger. Then, the dimensions and the shape of the work are found based on the coordinate values. Thus, the contact state between the probe and the work can be used as an electric touch signal to detect the position.
FIG. 8
shows a touch signal probe in a related art. In
FIG. 8
, the touch signal probe in the related art comprises a stylus
1
, a movable member
2
, posts
3
, a housing
4
, a fixed member
5
, hardballs (steel balls)
6
, bias means
7
, and a contact element
8
. The stylus
1
is fixed to the movable member
2
. The stylus
1
is provided at the tip with the spherical contact element
8
. In an outer circumference face of the movable member
2
, three posts
3
are provided radially with a 120-degree spacing within a plane at the right angle to the axis of the stylus
1
and with the axis of the stylus
1
as the center. On the other hand, three pairs of hard balls
6
are fixed to the fixed member
5
at the positions corresponding to the posts
3
of the movable member
2
. The posts
3
and the hard balls
6
form reseat position elements for uniquely defining the relative position between the fixed member
5
and the movable member
2
.
In such a configuration, the movable member
2
is pressed against the fixed member
5
by the action of a bias force F of a bias means
7
and is forcibly brought into contact with the fixed member
5
through reseat position members. The movable member
2
is standing still at six contact points with the fixed member
5
in the state that the press force from the work is applied to the contact element
8
provided at the tip of the stylus
1
. This means that each post
3
of the movable member
2
is standing still at two contact points with two hard balls
6
(at six contact points as a whole). Therefore, this is called a six-point contact type reseat position system. The six contact points are connected in series electrically as switch. The contact element
8
comes in contact with the work W and the movable member
2
performs relief operation, so that an out-of-contact condition occurs at any of the six contact points and thus a touch signal can be produced.
In such a six-point contact type reseat position system, the restoration position after the movable member
2
performs relief operation is defined uniquely. That is, assuming that the stylus
1
is displaced in each contact point direction in parallel with the axial direction of the still position of the stylus
1
while the stylus
1
is held in contact with a movable member side reseat position member (posts
3
) and a fixed member side reseat position member (hard balls
6
), each locus drawn by the tip of the stylus
1
crosses the axis at the still position of the stylus
1
. According to such a configuration, at the restoration operation time after the movable member
2
performs relief operation by the press force from the work W, the contact with each contact point is only recovered by the bias force F and the stylus
1
is restored to the unique still position and the still position of the stylus
1
can be held constant.
With the six-point contact type reseat position system, the position of the movable member relative to the fixed member is determined uniquely by contact at six points and thus vibration-resistant rigidity in a reseat position state is high. If press force is applied from any direction, the six-point contact type reseat position system has high restoration accuracy when viewed in comparatively rough order in 10-&mgr;m units, for example.
The touch signal probe uses an out-of-contact condition of each contact point in the reseat position system as a touch signal. A touch signal is not output at the instant at which the contact element
8
actually comes in contact with the work W. Signal output is delayed as much as deformation (or distortion) of the stylus
1
. If the stylus
1
is long, the tendency becomes noticeable, leading to a bottleneck in high accuracy of measurement.
To deal with this problem, a touch signal probe for detecting deformation of a stylus and producing a touch signal, as shown in
FIGS. 9A and 9B
is proposed (Japanese Patent Unexamined Publication No. Hei. 10-288502).
In
FIG. 9A
, a stylus
22
has, at one end, a contact element
24
for coming in contact with a work. Four piezoelectric elements
121
to
124
are attached to a roughly columnar part at an opposite end of the stylus
22
.
Each of piezoelectric element support parts
101
C and
101
D is a flange-like rectangular parallelepiped which is square in cross section orthogonal to the stylus axis. The piezoelectric elements
121
to
124
are fixedly secured to full sides of both rectangular parallelepipeds with an adhesive, etc., so as straddle both rectangular parallelepipeds. According to such a structure, the piezoelectric elements are used as deformation detection elements of the stylus to detect deformation (distortion) of the stylus
22
when the contact element
24
comes in contact with a work W for producing a touch signal.
The detection accuracy of the touch signal probe comprising such a deformation detection type stylus can be 1 &mgr;m or higher performance.
Then, if an attempt is made to attach the deformation detection type stylus
22
to the movable member
2
in place of the stylus
1
and use the above-described six-point contact type reseat position system in combination, the reseat position accuracy of the reseat position system becomes insufficient. That is, when the movable member performs relief operation, the contact element of the movable member is pushed into the work and causes relative displacement to the fixed member.
With the six-point contact type reseat position system, from the viewpoint of higher accuracy, for example, 1 &mgr;m or less, at the time of the restoration operation after contact, the relative displacement between the movable member and the fixed member causes an error in restoration position (reseat position shift error) to occur.
That is, if the contact element
8
comes in contact with the work W in the orthogonal direction to the axis of the stylus
1
and is pushed into the work W, the stylus
1
and the movable member
2
are inclined and the hard balls
6
and the post
3
are brought out of contact. At this time, drag almost in opposite directions occurs between the movable member
2
and the fixed member and a slight shift in the orthogonal direction to the axis of the stylus occurs in the movable member
2
. After this, if the work W and the contact element
8
are brought out of contact with each other, the movable member
2
performs restoration operation
Akagi Keiji
Kobayashi Yoshikazu
Miyazaki Tomoyuki
Nishitsuji Yutaka
Yoda Yukiji
Fulton Christopher W.
Mitutoyo Corporation
Rankin, Hill Porter & Clark LLP
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