JPH0660488A - Magnetic type torque limiter - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a magnetic torque limiter that is easy to assemble. [Structure] A yoke plate 2 is fitted on a tape reel shaft 1, and a magnet plate 3 is attracted to one surface of the yoke plate 2. The hysteresis plate 27 is fitted inside the drive gear 28, the bearing member 26 is fitted inside the hysteresis plate 27, and the bearing member 26 is rotatably fitted onto the tape reel shaft 1.
The magnet 3 and the hysteresis plate 27 are opposed to each other with a gap. With this structure, the yoke plate 2 is made of a hardened material of martensitic stainless steel, and the coercive force is 1/2 or less of the coercive force of the hysteresis plate 27 and 10 [Oe] or more. [Effect] Positioning and bonding are unnecessary, and assembly is easy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic torque limiter, and more specifically, it is used in a reel stand device such as an 8 mm video tape recorder (8 mm VTR), a digital audio tape recorder (DAT), a cassette tape recorder and the like. The present invention relates to a magnetic torque limiter.

[0002]

2. Description of the Related Art FIG. 2 is a cross-sectional view of an essential part of an example of a conventional magnetic torque limiter. This magnetic torque limiter 2
00, a disc-shaped hysteresis plate 27 is fixedly provided inside the ring-shaped drive gear 28, and the bearing member 26 is provided inside the hysteresis plate 27.
Is fitted. The bearing member 26 is rotatably fitted on the tape reel shaft 21. 25 is a washer for height adjustment. The hysteresis plate 27 is made of a Mn steel-based magnetic material or a Cr—Co steel-based magnetic material,
The coercive force Hc = 140 Oe.

A yoke plate 22 is fixedly mounted on the tape reel shaft 21, and a disk-shaped magnet plate 23 having a plurality of poles alternately magnetized in the circumferential direction is provided on the upper surface of the yoke plate 22. It is attracted by magnetic force. The magnet board 2
The washer 25 adjusts the gap between the hysteresis plate 27 and the hysteresis plate 27. Reference numeral 24 is a rotation stopper that prevents the magnet plate 23 from slipping on the yoke plate 22. The yoke plate 22 is made of magnetic stainless steel,
Although it has a high magnetic permeability, the coercive force Hc is much smaller than 10 [Oe].

Reference numeral 29 is a magnetic sensor for measuring the number of rotations of the tape reel shaft 21. The diameter of the yoke plate 22 is made smaller than that of the magnet plate 23 to expose the magnet plate 23 to the lower surface, and the magnetic flux leaking from the exposed portion is detected by the magnetic sensor 29.

The magnetic torque limiter 200 as described above
When the hysteresis plate 27 is rotated from the outside via the drive gear 28, the hysteresis torque causes the magnet 23 to rotate, which causes the tape reel shaft 2 to rotate.
1 rotates. At the tape winding end, the tape reel shaft 21 is stopped with a force larger than the hysteresis torque, so that the drive gear 28 slips and rotates.
The magnetic sensor 29 measures the number of rotations of the tape reel shaft 21. Further, the stop of the tape reel shaft 21 is detected.

Incidentally, although different from the system according to the present invention, a prior art of a system in which magnetic flux leaking from a hysteresis plate is detected by a magnetic sensor is disclosed in JP-A-63-175245.

[0007]

In the above-mentioned conventional magnetic torque limiter 200, since the yoke plate 22 has a high magnetic permeability, leakage flux through the yoke plate 22 cannot be expected. The diameter is made smaller and the magnet plate 23 is exposed on the lower surface to secure a leakage magnetic flux for rotation detection. As a result, the yoke plate 22
Since the attraction area of the magnet plate 23 becomes smaller and the attraction force also becomes smaller, the rotation stopper 24 is provided to prevent the slip. However, when the rotation stopper 24 is provided, there is a problem that the alignment becomes necessary during the assembly and the work becomes complicated. If the yoke plate 22 and the magnet plate 23 are bonded, it is not necessary to provide the rotation stopper 24, but a bonding step is required, and there is a problem that the work is complicated. Therefore, an object of the present invention is to provide a magnetic torque limiter that does not require alignment or adhesion and is easy to assemble.

[0008]

A magnetic torque limiter of the present invention comprises a first rotary shaft, a hysteresis plate fixed to the first rotary shaft, a second rotary shaft, and a second rotary shaft. A fixed yoke plate; and a magnet plate that is attracted to one surface of the yoke plate and faces the hysteresis plate with a gap therebetween. In the magnetic torque limiter for transmitting the rotation from the to the second rotating shaft, the yoke plate is made of a material having a coercive force smaller than 1/2 of the coercive force of the hysteresis plate and 10 [Oe] or more. It is characterized by that. In the above structure, it is preferable that the yoke plate is made of a hardened martensitic stainless steel from the viewpoint of easy availability and cost.

[0009]

In the magnetic torque limiter of the present invention, since the coercive force Hc of the yoke plate is set to 10 [Oe] or more, the magnetic permeability becomes small and the leakage magnetic flux comes out through the yoke plate. Therefore, the rotation can be detected without exposing the magnet plate by making the yoke plate smaller than the magnet plate. Therefore, it is possible to increase the attraction area between the yoke plate and the magnet plate to obtain a sufficient attraction force that does not cause slip, so that rotation stop is not required and therefore alignment is not required. On the other hand, the coercive force Hc of the yoke plate is 1 / the coercive force of the hysteresis plate.
Since the magnet plate is made smaller than 2, it is also prevented that the magnet plate is transferred to the hysteresis plate and attracted due to vibration, etc., and therefore, adhesion for preventing this is not necessary. Therefore, there is no need for alignment and adhesion, and the assembly is easy.

[0010]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 is a sectional view of a main part of a magnetic torque limiter according to an embodiment of the present invention. In this magnetic torque limiter 100, a disk-shaped hysteresis plate 27 is fixedly provided inside the ring-shaped drive gear 28 that is the first rotation shaft, and the bearing member 26 is provided inside the hysteresis plate 27. Is fitted. The bearing member 26 is the tape reel shaft 1 which is the second rotating shaft.
It is fitted rotatably. 25 is a washer for height adjustment. Drive gear 28 and bearing member 26
Is made of engineering plastic such as polyacetal resin. The hysteresis plate 27 is made of a Mn steel-based magnetic material or a Cr—Co steel-based magnetic material, and has a coercive force H.
c = 140 [Oe] and Br = 9000 [Gaus
s]. The washer 25 is made of 66-nylon.

A yoke plate 2 is fixedly mounted on the tape reel shaft 1. On the upper surface of the yoke plate 2, there are provided disc-shaped magnet plates 3 which are magnetized to have a plurality of poles alternately in the circumferential direction. It is attracted by magnetic force. The gap between the magnet plate 3 and the hysteresis plate 27 is adjusted by the washer 25. The tape reel shaft 1 is not provided with a rotation stopper that prevents the magnet plate 3 from slipping on the yoke plate 2.

The tape reel shaft 1 is made of a high sliding grade polyacetal (POM) resin. In addition to these, polyacetal resin containing carbon fiber, polycarbonate resin, unsaturated polyester resin and the like can be used. The yoke plate 2 is made of martensitic stainless steel (SUS42
0J2) hardened material, coercive force Hc = 70 [Oe],
Br = 9000 [Gauss]. Martensitic stainless steel is easily available, inexpensive, and easy to process. In addition to the above, precipitation hardening stainless steel can also be used. The magnet plate 23 is an Nd-Fe-B system magnet. In addition to this, a ferrite plastic magnet can be used.

The magnetic sensor 29 detects the magnetic flux leaking through the yoke plate 2 and measures the number of rotations of the tape reel shaft 1.

In the above magnetic torque limiter 100, when the hysteresis plate 27 is rotated from the outside through the drive gear 28, the hysteresis torque causes the magnet 3 to rotate, which causes the tape reel shaft 1 to rotate. At the tape winding end, the tape reel shaft 1 is stopped with a force larger than the hysteresis torque, so that the drive gear 28 slips and rotates. The magnetic sensor 29 measures the number of rotations of the tape reel shaft 1. Also,
The stop of the tape reel shaft 1 is detected.

Since the magnetic torque limiter 100 can measure the rotation by detecting the leakage magnetic flux emitted through the yoke plate 2, the attracting area of the yoke plate 2 and the magnet plate 3 is increased to prevent slippage. Sufficient suction power can be obtained. Therefore, there is no rotation stopper, and alignment during assembly is unnecessary. Further, since the magnet plate 3 is more easily attracted to the yoke plate 2 than the hysteresis plate 27, even if it is subjected to vibrations or the like due to external factors,
There is no transfer to the hysteresis plate 27 and adsorption. Therefore, no adhesive is required. After all, the magnetic torque limiter 100 does not require alignment or adhesion and is easy to assemble.

[0016]

According to the magnetic torque limiter of the present invention, since the magnetic torque limiter has the above-mentioned structure, the step of aligning and the step of adhering are not necessary, so that the assembly is easy.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a magnetic torque limiter according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of essential parts of an example of a conventional magnetic torque limiter.

[Explanation of symbols]

 100 magnetic torque limiter 1 tape reel shaft 2 yoke plate 3 magnet plate 27 hysteresis plate 28 drive gear 29 magnetic sensor

Claims (2)

[Claims] 1. A first rotary shaft, a hysteresis plate fixed to the first rotary shaft, a second rotary shaft, a yoke plate fixed to the second rotary shaft, and one surface of the yoke plate. A magnetic plate that is attracted to and is opposed to the hysteresis plate with a gap therebetween, and that transmits the rotation from the first rotating shaft to the second rotating shaft by the hysteresis torque between the hysteresis plate and the magnet plate. In the torque limiter, a magnetic torque limiter characterized in that the yoke plate is made of a material having a holding force of less than 1/2 of the holding force of the hysteresis plate and 10 [Oe] or more. 2. The magnetic torque limiter according to claim 1, wherein the yoke plate is made of a hardened material of martensitic stainless steel.