Specifications

Figure 1 Arrangement of MR element and magnetic media
H
X
I
SN
MR element
（X）
Figure 2 Structure of high-precision Magnescale
Metal base
Magnetic media
MR element
1ch
MR element pattern
Ch+
Ch-
V
G
（m+1/2）P
（n+1/2）P
P
6
1
2
3
4
5
7
8
MR element
Magnetic media
Base
P
12 34 56 78
λ
Scale
P/6
e3 =E 3sin(3(2πx / λ+π / 3))
=E
3sin(6πx / λ+π)
=-E
3sin(6πx / λ)
A
Signal detection sensor
(MR sensor)
The MR sensor is a thin-film
sensor patterned on a PWB. It
obtains the signal output
through the change in the
resistance value according to
the size of magnetic field
leakage from the scale when it
moves keeping a certain
distance from the magnetic
media (scale) to which
magnetic signals have been
recorded as shown in Figure 1.
In this case, however, the signal
obtained from the resistance
change characteristics of the
sensor and the status of
magnetic field leakage from the
scale also contains distortion
components (such as harmonic
components) in addition to the
sine wave components of the
signal pitch. Therefore, the
sensor is positioned by shifting
it in the operating direction by
the distance of 1/6 of another
signal pitch λ (Figure 2). In this
case, when third-order
harmonic components are
observed, the following
Equation “A” is established for
three-fold periodic signal
components because 1/6 of the
signal pitch λ is π/3 in the
periodic phase, and the phase
is shifted by 180° with respect
to the three-fold periodic signal
components of the first sensor,
resulting in a reverse signal.
The addition of this signal
enables the third-order
harmonic components to be
cancelled out. That is, the
combination of these sensors
enables harmonic components
of the 3n-th orders to be
canceled out. In the same way,
the combination of multiple
units of the sensors also
enables the harmonic
components of other orders
such as 5th and 7th orders to
be cancelled out simultaneously.
In detection sensors, the circuit
is generally formed in a bridge
structure for stability of the
temperature characteristics, etc.
as well. In that case, distortion
of odd numbered orders are
cancelled out by the
arrangement of sensors
configuring a bridge. Therefore,
the use of the bridge structure
and the arrangement of the
sensor configuration that
cancels out harmonic
components of the extent of
the 3rd, 5th, and 7th orders
enable a signal close to sine
waves to be obtained. In this
way, the scale achieves high
precision and high resolution by
digitization of electrical
interpolation based on a
distortion-less signal,
coinciding with various
electrical signal compensation.
Measurement Principle
Scale material
The magnetic recording media,
or the raw material for scales,
was developed as the scale
material that realizes
high-density recording at high
precision, based on
Magnescale’s magnetic
technology that has been
cultivated for magnetic tapes
and magnetic discs.
The scales adopt magnetic
metal powder that is used for
data storage systems because
of its high density and reliability.
Its magnetic characteristics are
that Br: 0.2 to 0.25T and Hc:
approximately 120 kA/m. The
magnetic media form a strong
coated surface resistant to
cutting fluids and strong
alkaline solutions through a
hardening process after
coating.
Magnetic powder
Magnetic metal powder used for
data storage systems because
of its high density and reliability
Br: 0.2 to 0.25T, Hc: Approx.
120 kA/m
Coating
Resistant to cutting fluids and
strong alkaline solutions
Die head
Scale manufacturing
equipment
Magnetic media’s B - H curve
H（x80A/m）
B（T）
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-6000
-4000
-2000 0 2000 4000
6000
* Magnetic material is coated from the
tip of the die head onto a scale.
8 9