Geometrical instruments – Distance measuring – Opposed contacts
Reissue Patent
2000-03-16
2002-01-01
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Distance measuring
Opposed contacts
C033S784000, C033S708000, C324S207240
Reissue Patent
active
RE037490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to an electronic caliper. More particularly this invention is directed to electronic calipers using a reduced offset induced current position transducer.
2. Description of Related Art
U.S. patent application Ser. No. 08/645,483 filed May 13, 1996, and incorporated herein in its entirety, discloses an electronic caliper using an inductive position transducer.
The operation of the electronic caliper using the inductive position transducer described in the application Ser. No. '483 is generally shown in
FIGS. 1
,
2
, and
3
. As shown in
FIG. 1
, an inductive caliper
100
includes an elongated beam
102
. The elongated beam
102
is a rigid or semi-rigid bar having a generally rectangular cross section. A groove
106
is formed in an upper surface of the elongated beam
102
. An elongated measuring scale
104
is rigidly bonded to the elongated beam
102
in the groove
106
. The groove
106
is formed in the beam
102
at a depth about equal to the thickness of the scale
104
. Thus, the top surface of the scale
104
is very nearly coplanar with the top edges of beam
102
.
A pair of laterally projecting, fixed jaws
108
and
110
are integrally formed near a first end
112
of the beam
102
. A corresponding pair of laterally projecting movable jaws
116
and
118
are formed on a slider assembly
120
. The outside dimensions of an object are measured by placing the object between a pair of engagement surfaces
114
on the jaws
108
and
116
. Similarly, the inside dimensions of an object are measured by placing the jaws
110
and
118
within an object. The engagement surfaces
122
of the jaws
110
and
118
are positioned to contact the surfaces on the object to be measured.
The engagement surfaces
122
and
114
are positioned so that when the engagement surfaces
114
of the jaws
108
and
116
are contacting each other, the engagement surfaces
122
of the jaws
110
and
118
are aligned with each other. In this position, the zero position (not shown), both the outside and inside dimensions measured by the caliper
100
should be zero.
The caliper
100
also includes a depth bar
124
which is attached to the slider assembly
120
. The depth bar
124
projects longitudinally from the beam
102
and terminates at an engagement end
126
. The length of the depth bar
124
is such that the engagement end
126
is flush with a second end
128
of the beam
102
when the caliper
100
is at the zero position. By resting the second end
128
of the beam
102
on a surface in which a hole is formed and extending the depth bar
124
into the hole until the end
126
touches the bottom of the hole, the caliper
100
is able to measure the depth of the hole.
Whether a measurement is made using the outside measuring jaws
108
and
116
, the inside measuring jaws
110
and
118
, or the depth bar
124
, the measured dimension is displayed on a conventional digital display
134
, which is mounted in a cover
136
of the caliper
100
. A pair of push button switches
130
and
132
are also mounted in the cover
136
. The switch
130
turns on and off a signal processing and display electronic circuit
160
of the slider assembly
120
. The switch
132
is used to reset the display
134
to zero.
As shown in
FIG. 1
, the slider assembly
120
includes a base
138
with a guiding edge
140
. The guiding edge
140
contacts a side edge
146
of the elongated beam
102
when the slider assembly
120
straddles the elongated beam
102
. This ensures accurate operation of the caliper
100
. A pair of screws
144
bias a resilient pressure bar
146
against a mating edge of the beam
102
to eliminate free play between the slider assembly
120
and the elongated beam
102
.
The depth bar
124
is inserted into a depth bar groove
148
formed on an underside of the elongated beam
102
. The depth bar groove
148
extends along the underside of the elongated beam
102
to provide clearance for the depth bar
124
. The depth bar
124
is held in the depth bar groove
148
by an end stop
150
. The end stop
150
is attached to the underside of the beam
102
at the second end
128
. The end stop
150
also prevents the slider assembly
120
from inadvertently disengaging from the elongated beam
102
at the second end
128
during operation.
The slider assembly
120
also includes a read head assembly
152
mounted on the base
138
above the elongated beam
102
. Thus, the base
138
and read head assembly
152
move as a unit. The read head assembly
152
includes a substrate
154
such as a conventional printed circuit board. The substrate
154
bears an inductive read head
158
on its lower surface. A signal processing and display electronic circuit
160
is mounted on an upper surface of the substrate
154
. A resilient seal
156
is compressed between the cover
136
and the substrate
154
to prevent contamination of the signal processing and display electronic circuit
160
.
As shown in
FIG. 2
, the read head
158
is covered by a thin, durable, insulative coating
162
, which is preferably approximately 50 microns thick.
The scale
104
is preferably an elongated printed circuit board (PCB)
164
. As shown in
FIG. 1
, a set of magnetic flux modulators
166
are spaced apart along the PCB
164
in a periodic pattern. The flux modulators
166
are preferably formed of copper. The flux modulators
166
are preferably formed according to conventional printed circuit board manufacturing techniques, although many other methods of fabrication may be used. As shown in
FIG. 2
, a protective insulating layer
168
(preferably being at most 100 microns thick) covers the flux modulators
166
. The protective layer
168
can include printed markings, as shown in FIG.
1
.
The slider assembly
120
carries the read head
158
so that it is slightly separated from the beam
102
by an air gap
170
formed between the insulative coatings
162
and
168
. The air gap
170
is preferably on the order of 0.5 mm. Together, the read head
158
and the flux modulators
166
form an inductive transducer.
As shown in
FIG. 3
, the magnetic flux modulators
166
are distributed along a measuring axis
174
of the elongated beam
102
at a pitch equal to a wavelength &lgr;, which is described in more detail below. The flux modulators
166
have a nominal width along the measuring axis
174
of &lgr;/2. The flux modulators
166
have a width d in a direction perpendicular to the measuring axis
174
.
The read head
158
includes a generally square transmitter winding
176
that is connected to a drive signal generator
178
. The drive signal generator
178
provides a time varying drive signal to the transmitter winding
176
. The time varying drive signal preferably results in a sinusoidal signal in the transmitter winding
176
, and more preferably an exponentially decaying sinusoidal signal. When the time varying drive signal is applied to the transmitter winding
176
, the time varying current flowing in the transmitter winding
176
generates a time varying, or changing, magnetic field. Because the transmitter winding
176
is generally rectangularly shaped, the generated magnetic field is generally constant within a flux region inside the transmitter winding
176
.
The read head
158
further includes a first receiver winding
180
and a second receiver winding
182
positioned on the read head
158
within the flux region inside the transmitter winding
176
. Each of the first receiver winding
180
and the second receiver winding
182
is formed by a plurality of first loop segments
184
and second loop segments
186
. The first loop segments
184
are formed on a first surface of a layer of the printed circuit board
154
. The second loop segments
186
are formed on another surface of the layer of the printed circuit board
154
. The layer of the printed circuit board
154
acts as an electrical insulation layer between the first loop segments
184
and the second loop segments
186
. Each end of the first
Andermo Nils I.
Masreliez Karl G.
Bennett G. Bradley
Mitutoyo Corporation
Oliff & Berridg,e PLC
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