Electrical resistors – Resistance value responsive to a condition – Magnetic field or compass
Patent
1991-10-31
1993-07-13
Lateef, Marvin M.
Electrical resistors
Resistance value responsive to a condition
Magnetic field or compass
338306, 324249, H01L 4300
Patent
active
052277615
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a magnetoresistive sensor having a ferromagnetic thin film and for use in, for instance, a capstan motor for video cassette recorders (VCR) and a magnetic encoder.
BACKGROUND ART
Recently, a magnetoresistive sensor having a ferromagnetic thin film has been used for an accurate control of a magnetic encoder or an accurate control of a capstan motor for VCR and it has been necessary to use such a sensor for controlling a motor with high accuracy. FIG. 1 is a schematic cross sectional view of a capstan motor for VCR in which a conventional magnetoresistive sensor is incorporated. In this capstan motor shown in FIG. 1, reference numerals 16, 17 and 10' respectively represent a rotor yoke, a rotor magnet and a frequency-generating magnet (FG magnet) in which N poles and S poles are alternatively magnetized at small pitches and these elements constitute a rotor part. Reference numeral 18 stands for a stator coil for driving the motor and reference numeral 19 represents a case. Reference numeral 15 represents a magnetoresistive sensor which is fixed to a holder 15H made of a resin. The magnetic field detecting portion 15S is arranged facing the FG magnet 10' normally at a distance of about 100 .mu.m, and thus, the rotation control of the motor is performed by the output signal from the magnetoresistive sensor. Reference numeral 7 stands for a lead portion of the magnetoresistive sensor for electrically connecting the magnetoresistive sensor 15 and a printed circuit board 20.
The FG magnet is in general magnetized at small pitches, and correspondingly, the intensity of the generated magnetic field is small. For this reason, a desired output cannot be obtained if the gap between the magnetoresistive sensor 15 and the FG magnet 10' is large.
FIG. 2A shows a plan view of a conventional magnetoresistive sensor before it is attached to the holder made of resin, and FIG. 2B shows a sectional view thereof taken along the line A--A of FIG. 2A. Reference numerals 15S, 15M and 7 represent a magnetic field detecting portion of the magnetoresistive sensor 15, a molded portion for reinforcing lead-bonding portion and a lead, respectively. In the structure as shown in FIGS. 2A and 2B, the electrical connection between the lead and the sensor pellet is usually performed through the bonding with a solder. Moreover, an electrical short often arises and the lead is sometimes peeled off from the lead-bonding portions when they are in the exposed state. Thus, the bonding portions are reinforced by molding for the purpose of eliminating such inconvenience. The reinforcement of the bonding portions are in general performed with the aid of a resin such as epoxy resin and the thickness of the resin must be more than the thickness of the lead, and more specifically, it must be 200 .mu.m or thicker.
This sensor is arranged facing the FG magnet 10, which produces the magnetic field signals, as shown in FIG. 3A. Then, the minimum gap between the magnetic field detecting portion 15S and the surface of the FG magnet 10 becomes greater than 200 .mu.m even if the molded portion with a resin approaches the magnet to such an extent that the portion almost comes in contact with the latter. Recently, motors have been miniaturized and made highly precise, and correspondingly, the pitch of magnetization of the FG magnet has become smaller, hence, the intensity of the magnetic field produced by such a magnet has a very small value. Therefore, the desired output signal from the sensor cannot be obtained, as has been described above, if the gap between the magnetic field detecting portion 15S and the FG magnet 10 is as much as 200 .mu.m. As has been discussed above, a desired value of output signal from the sensor cannot be obtained unless the gap is in the order of 100 .mu.m or smaller.
For this reason, in the conventional technology as shown in FIG. 3B, an element is arranged so that a molded portion 15'M is kept away from the FG magnet 10. However, if the element is arranged in such a manner, a larg
REFERENCES:
patent: 4477794 (1984-10-01), Nomura et al.
Shibasaki Ichiro
Sugimoto Yoshiyasu
Asahi Kasei Kogyo Kabushiki Kaisha
Lateef Marvin M.
LandOfFree
Magnetoresistive sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetoresistive sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetoresistive sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2315117