Measuring and testing – Dynamometers – Responsive to torque
Patent
1995-06-26
1998-12-15
Oen, William L.
Measuring and testing
Dynamometers
Responsive to torque
73779, G01L 302, G01L 100, G01B 716
Patent
active
058500456
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relate to a magnetostrictive stress sensor (typically a torque sensor of magnetic head type) and an apparatus to which the sensor is applied.
BACKGROUND ART
A magnetostrictive stress (torque) sensor utilizes one of the magnetostriction phenomena, namely a phenomenon in which the permeability of a ferromagnetic material varies when a mechanical strain is produced in the ferromagnetic material.
An example of a conventional magnetostrictive stress sensor is illustrated in FIG. 29. Two U-shaped cores 161, 162 are used. Excitation coils 163 are wound on the ends of one U-shaped core 161 and an excitation current flows through the coils. Detection coils 164 are wound on the ends of the other U-shaped coil 162 and are connected to a detector (a rectifier, for example). The ends of these U-shaped cores 161, 162 are arranged in close proximity to a ferromagnetic material that is to be sensed or in contact with the material while electrical insulation is maintained between the cores and the material. Here the member in which strain is to be sensed is a rotary shaft 160, a plate-shaped body, etc.
FIG. 30 illustrates a magnetic equivalent circuit of the magnetostrictive sensor shown in FIG. 29. The ends of the core 161 for excitation are indicated at E1, E2, and the ends of the core 162 for detection are indicated at D1, D2.
Four magnetic resistors constructing a bridge in the magnetic equivalent circuit are equal (the bridge circuit is in a state of equilibrium) when a state prevails in which the rotary shaft 160 is not being subjected to a torsional torque. Since a magnetic flux passing through the interior of the detection core 162 does not exist, an induced electromotive force is not produced in the detection coils 162.
When the rotary shaft 160 is twisted in the direction of the arrows, tensile stress and compressive stress are produced in directions at angles of .+-.45.degree. with respect to the central axis of the rotary shaft 160. The result is a change in the permeability of the rotary shaft. The magnetic resistances of one pair of magnetic resistors in the bridge circuit decrease while the magnetic resistances of the other pair increase. This upsets the equilibrium of the bridge circuit so that a magnetic flux passes through the interior of the detection core 162. As a result, an induced electromotive force V is generated in the detection coils 164.
Such a magnetostrictive stress sensor is described in the following literature:
Yamada, et al., "Non-Contact Stress Measuring by Magnetic Anisotropy Sensor", Denki Gakkai Kenkyukai Shiryo, Magnetics Research Society, MAG-86-139, Denki Gakkai; and
Orvar, "The Ring Torductor--A Torque-Gauge, Without Slip Rings, For Industrial Measurement And Control", ASEA JOURNAL 1960, Volume 33, Number 3, pp. 23-32.
A magnetostrictive stress sensor of this kind requires the two U-shaped cores and further requires two types of coils, namely the excitation coils and the detection coils. Consequently, it is difficult to simplify and reduce the size of the arrangement. In addition, as will be understood also from FIG. 30, a further condition is that the four magnetic resistors constructing the bridge circuit be equal. In general, the member in which strain is to be sensed is formed to have properties (strength, material quality) commensurate with the use of the member and is not made to have properties (four magnetic resistors that are equal) suited to the magnetostrictive stress sensor. Accordingly, the permeability of the member often is so non-uniform as to be an impediment to measurement of strain by the magnetostrictive sensor. The fact that the permeability differs depending upon the location leads to a fluctuation in the zero point of the sensor.
DISCLOSURE OF THE INVENTION
An object of the present invention is to simplify the arrangement and reduce the size of a magnetostrictive stress sensor.
A further object of the present invention is to provide a magnetostrictive stress sensor which is not readily susceptible to the influence of a no
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Nonomura et al., "Measurements of Engine Torque with the Intra-Bearing Torque Sensor", SAE Technical Paper, 870472, 1988, pp. 2.329-2.339.
Yamada et al., "Non-Contact Stress Measuring By Magnetic Anisotropy Sensor", Magnetics Research Society, MAG-86-139, pp. 19-27.
Orvar Dahle, "The Ring Torductor--A Torque-Gauge, Without Slip Rings, For industrial Measurement And Control", ASEA Journal, vol. 33, No. 3, pp. 23-32, (1960).
I. Sasada et al., "Magnetic-Head Type Torque Sensor without Using Core", Record of 1992 Joint Conference of Electrical and Electronics Engineers in Kyushu, p. 324 (1992).
F. Koga et al., "Optimization of Sense Resistance and Rectification Phase for Magnetic Head Type Torque Sensors using a Phase-Sensitive-Detector", 11th SICE Kyushu Branch Annual Conference, pp. 257-258 (1992).
Harada Koosuke
Koga Fumitaka
Matsunaga Nobutomo
Misumi Shuichi
Sasada Ichiro
Oen William L.
Omron Corporation
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