Electricity: measuring and testing – Magnetic – Displacement
Patent
1990-11-30
1992-12-15
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Displacement
32420722, 307309, 360113, 360121, 338 32R, G01R 3306, H01L 4308
Patent
active
051720574
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic encoder for performing positional detection by converting a change in magnetic field into an electric signal with respect to elements having a so-called magnetic resistant effect in which an electric resistance varies in accordance with an incident magnetic field, and more particularly, the invention relates to an improvement of the magnetic encoder in which the signal-detecting accuracy is enhanced.
2. Description of the Related Art
A highly accurate positional sensor or rotary sensor is necessary in a wide variety of technical fields, including the fields of NC machine tools, robots, OA instruments, VTRs, etc. In these industrial fields, various servo-motors and rotary encoders are utilized. With the development of OA and FA technologies, sensors having higher operating speeds and reliability are desired. Under these circumstances, for instance, conventional optical techniques are often used to realize a rotary sensor. However, such a sensor is composed of semiconductor elements such as photo-cells and LEDs, and is thus sensitive to dust and insufficiently stable in response to a change in temperature. Also, optical sensors suffer the additional drawbacks of numerous composing parts and complicated structures.
Accordingly, in recent years, magnetic type sensors using the magnetic resistance effect have been developed. Such sensors have a higher detecting accuracy and temperature stability, and are relatively insensitive to dust, and thus they are applied in many fields.
FIG. 5 shows a schematic oblique sectional view of the conventional magnetic rotary sensor. A rotary drum 51 rotates together with a rotary shaft 52, for instance, in the rotational direction identified by the arrow. A magnetic recording medium layer is provided on the peripheral surface of the rotary drum 51 in the form of NS-magnetic poles. The magnetic recording medium layer, for instance, may be magnetic coating films such as gamma-iron, etc., or may be formed of strontium ferrite, etc.
The detecting accuracy conforms to the number of magnetic poles selected. When there are several hundred to several thousand magnetic poles, the width of a single magnetic pole will be formed by a very narrow micro-magnet.
A magnetic sensor 53 is arranged to confront the magnetized surface of the rotary drum 51 and is provided with a magnetic resistant element unit 54 formed of plural magnetic sensing patterns (consisting of strongly magnetized thin film patterns having the magnetic resistant affect) formed on a glass board. The magnetic sensor 53 is spaced a specified interval G within the magnetizing range of the magnetic field of the micro-magnets of the rotary drum 51.
Upon rotation of the rotary drum 51, the magnetic field on the surface of drum 51 travels towards the confronting magnetic resistant element unit 54, whereby each magneto-sensitive pattern of the magnetic resistant element unit 54 undergoes electro-magnetic conversion in which the strength of the incident magnetic field changes the resistance value of the pattern. Thus, an electric signal is issued in response, and detection is effected of the rotary speed and position of the drum 51.
The conventional magnetic encoder as described above and as shown in FIG. 5 includes a magnetic drum for repeatedly generating a magnetic signal and a magnetic sensor confronting the magnetic drum in non-contact parallel form through the specified interval G. Also, the magnetic resistant element unit of the magnetic sensor is composed of plural magneto-resistive patterns coupled to electric components. According to such a magnetic encoder, for instance, it is possible to promptly and accurately detect the position of a moving object and/or the rotary speed of motors such as numerical control (NC)-machines or robots.
As the above mentioned control systems are desired to achieve various functions and higher accuracy, compact and high performance detecting instruments are desired as well. For instance, a magnetic en
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Murata Hideo
Sagara Takehiko
Yoshimura Kuniaki
Edmonds Warren S.
Hitachi Metals Ltd.
Strecker Gerard R.
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