Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-03-27
2003-04-15
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
Reexamination Certificate
active
06549003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a position transducer which detects an amount of travel and moved position of a moving part which is a linearly moving part of a machine tool, industrial robot or the like.
2. Description of the Related Art
Various types of position transducer has been proposed to detect an amount of travel and moved position of a moving part which is a linearly moving part of the machine tool, industrial robot or the like. An example of such position transducers is known from the disclosure in the Japanese Published Unexamined Application No. 10-531835 for example. The position transducer disclosed in this publication includes a scale which develops a magnetic field whose strength and direction change linearly correspondingly to a position of such a moving part, and a magnetic sensor which moves in relation to the scale and detects a magnetic field from the scale at a position to which has moved.
The position transducer proposed in the Japanese Published Unexamined Application No. 10-531835 is constructed as schematically illustrated in FIG.
1
.
The position transducer is generally indicated with a reference
100
. The position transducer
100
includes a scale
101
and a magnetic sensor
102
. The scale
101
consists of a pair of members
101
a
and
101
b
formed from a ferrite plastic magnet plate or the like and each having an end face which is oblique at a predetermined angle &thgr; in relation to a direction of movement thereof relative to the magnetic sensor
102
. The members
101
a
and
101
b
in pair are joined integrally to each other with their respective oblique end faces placed to abut each other. The pair of members
101
a
and
101
b
is magnetized to be opposite in polarity to each other in a direction perpendicular to main sides thereof.
The magnetic sensor
102
includes a magnetic core
103
formed from a square ring of a high permeability material such as NI—Fe alloy or amorphous alloy and which forms a closed magnetic circuit, and a pair of detection coils
104
and
105
wound on two longitudinal core pieces, opposite to each other, of the magnetic core
103
, respectively. The detection coils
104
and
105
in pair are driven in opposite phases to each other with a high frequency pulsed current to develop magnetic fields in opposite directions.
When the magnetic sensor
102
is at a predetermined distance from the scale
101
, the two longitudinal core pieces of the core
103
, on which the detection coils
104
and
105
in pair are wound, respectively, are perpendicular to the main sides of the scale
101
, a line connecting these two core pieces is perpendicular to a longitudinal center line n of the scale
101
and the mid point between the two core pieces is right above the longitudinal center line n of the scale
101
.
In the above geometric relation, the scale
101
and magnetic sensor
102
are installed to a stationary part and a moving part, respectively, of a machine tool, industrial robot or the like, and moved relatively to each other along the longitudinal center line n of the scale
101
as the moving part moves linearly. At each position the magnetic sensor
102
will take along the length of the scale
101
, the magnetic sensor
102
will detect a magnetic field developed by the scale
101
and perpendicular to the main sides of the scale
101
.
On the assumption that the longitudinal direction of the scale
101
, that is, the direction in which the magnetic sensor
102
is moved in relation to the scale
101
, is taken as X-direction while a lateral (short-side) direction of the scale
101
, perpendicular to the X-direction is taken as Y-direction, and a direction perpendicular to the main sides of the scale
101
is taken as Z-direction, the principle of detection of the position transducer
100
will be described below with reference to
FIGS. 2 and 3
.
FIG. 2
is a Y-directional sectional view of the scale
101
located at a position where the longitudinal center line n of the scale
101
intersects with a boundary line of the pair of members
101
a
and
101
b
forming together the scale
101
. As seen from
FIG. 3
, in the Y-directional section of the scale
101
, a magnetic flux &PHgr;z produced in the Z-direction changes linearly in a range of ±W/4 (where W is a Y-directional length of the scale
101
) from a Y-directional center of the scale
101
, that is to say, the boundary line of the pair of members
101
a
and
101
b
forming together the scale
101
. Therefore, with a position transducer construction in which when the magnetic sensor
102
is moved in X-directionally in relation to the scale
101
, it will have moved substantially in the Y-direction of the scale
101
within a range of ±W/4 from the boundary line of the pair of members
101
a
and
101
b
forming together the scale
101
, it is possible to detect an X-directionally moved position of the magnetic sensor
102
relative to the scale
101
from the strength of the magnetic flux &PHgr;z produced in the Z-direction.
In the position transducer
100
, the X-directional length L
1
of the scale
101
is larger than the effective length for detection L
2
, and an angle &thgr; formed between the moving direction of the magnetic sensor
102
relative to the scale
101
and boundary line of the pair of members
101
a
and
101
b
forming together the scale
101
is &thgr;=tan −1(d/L
2
)(where d is W/2 or less), so that the magnetic sensor
102
will be moved relatively moved in the X-direction along the longitudinal center line n of the scale
101
. Therefore, the Z-directional magnetic flux &PHgr;z at each position the magnetic sensor
102
will take when the latter is moved relatively to the scale
101
will change linearly as in the Y-directional movement of the magnetic sensor
102
.
In the position transducer
100
, a Z-directional magnetic flux &PHgr;z at each position the magnetic sensor
102
will take when the latter is moved relatively to the scale
101
is detected by the pair of detection coils
104
and
105
driven in opposite phases to each other with a high frequency pulsed current to develop magnetic fields in opposite directions, impedances of these detection coils
104
and
105
, which will change correspondingly to an external magnetic field, are converted to voltages, respectively, and a difference between the voltages is determined, to thereby detect a moved position of the magnetic sensor
102
relative to the scale
101
.
With the position transducer
100
, since a moved position of the magnetic sensor
102
relative to the scale
101
is detected by determining a difference between outputs of the pair of detection coils
104
and
105
driven in opposite phases to each other, it is possible to provide a large output while canceling the influence of electric noises and detect, with an extremely high accuracy, a moved position of the magnetic sensor
102
relative to the scale
101
, namely, an amount of travel and moved position of the moving part relative to the stationary part of the machine tool, industrial robot or the like.
The position transducer disclosed in the aforementioned Japanese Published Unexamined Application No. 10-531835 is an excellent one capable of detecting, with an extremely high accuracy of an amount of travel and moved position of a moving part relative to a stationary part of a machine tool, industrial robot or the like. However, the results of experiments conducted on this position transducer proved that if the position transducer is used in an environment where a disturbing magnetic field such as geomagnetism acts strongly, such a disturbing magnetic field and a magnetic field indicative of positional data, developed by the scale
101
, cannot be differentiated between them and a change of DC output due to a disturbing magnetic field is superposed on the output from the magnetic sensor
102
and thus no accurate positional data can be provided by the position transducer.
OBJECT AND SUMMARY OF THE INVENTION
It is
Lefkowitz Edward
Maioli Jay H.
Sony Precision Technology Inc.
Zaveri Subhash
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